Sediment core fossils in ancient Lake Ohrid: Testing for faunal change since the Last Interglacial - Albrecht, C.; Vogel, H.; Hauffe, T.; Wilke, T. (Biogeosciences, 2010)
Ancient Lake Ohrid is probably of early Pleistocene or Pliocene origin and amongst the few lakes in the world harbouring an outstanding degree of endemic biodiversity. Although there is a long history of evolutionary research in Lake Ohrid, particularly on molluscs, a mollusc fossil record has been missing up to date. For the first time, gastropod and bivalve fossils are reported from the basal, calcareous part of a 2.6 m long sediment succession (core Co1200) from the north-eastern part of Lake Ohrid. Electron spin resonance (ESR) dating of mollusc shells from the same stratigraphic level yielded an age of 130 ± 28 ka. Lithofacies III sediments, i.e. a stratigraphic subdivision comprising the basal succession of core Co1200 between 181.5-263 cm, appeared solid, greyish-white, and consisted almost entirely of silt-sized endogenic calcite (CaCO3>70%) and intact and broken mollusc shells. Here we compare the faunal composition of the thanatocoenosis with recent mollusc associations in Lake Ohrid. A total of 13 mollusc species (9 gastropod and 4 bivalve species) could be identified within Lithofacies III sediments. The value of sediment core fossils for reconstructing palaeoenvironmental settings was evaluated and the agreement between sediment and palaeontological proxies was tested. The study also aims at investigating major faunal changes since the Last Interglacial and searching for signs of extinction events. The combined findings of the ecological study and the sediment characteristics suggest deposition in a shallow water environment during the Last Interglacial. The fossil fauna exclusively included species also found in the present fauna, i.e. no extinction events are evident for this site since the Last Interglacial. The thanatocoenosis showed the highest similarity with recent Intermediate Layer (5-25 m water depth) mollusc assemblages. The demonstrated existence of a mollusc fossil record in Lake Ohrid sediment cores also has great significance for future deep drilling projects. It can be hoped that a more far reaching mollusc fossil record will then be obtained, enabling insight into the early evolutionary history of Lake Ohrid. © Author(s) 2010.
Keywords: Lake Ohrid; Bivalvia; Gastropoda; Mollusca; biostratigraphy; deep drilling; fossil record; interglacial; mollusc; paleoenvironment; paleontology; sediment core

Sediment and particulate organic carbon fluxes in various lacustrine basins of tropical Africa and in the Gulf of Guinea - Giresse, P.; Makaya-Mvoubou (Global and Planetary Change, 2010)
This study presents a synthetic approach based on the combined use of sediment and C org accumulation rates of well studied lake systems and oceanic margins. Importance of latitude is expressed by the advected flux of terrestrial sediment and, especially, of particulate organic carbon. This most important factor varies throughout the Quaternary, particularly with the intensification of fluxes during Holocene. These changes are linked to the strengthening of monsoon circulation.In various lake systems from Cameroon (Barombi Mbo, Ossa, Assom and Bambili), Gabon (Kamalete) and Congo (Kitina and Sinnda), the global sedimentation and the C org accumulation were slow during dry period and increased during wet period. This relationship is verified to the scale of the Gabon and Congo oceanic margins where the accumulation rates increase during extent of ombrophilous forest. However, the greatest fluxes of organic carbon during wet periods would be balanced by higher concentrations values during the dry period resulting in a nearly homogenous carbon accumulation. These carbon concentrations are generally explained by the input of coarse debris by abrupt floods and by a less degraded organic matter as a result of the cooling of the climate. But, according to specific morphology features or vegetation cover, some lake systems exhibit distinct trends of the sedimentary and C org accumulation rates: (1) Highest accumulation rates coincided with a forest retreat when the slope is too steep (Kamalete in Gabon and Bosumtwi in Ghana) or when river flood overrun (Nguene in Gabon) (2) Increase of the accumulation rate are registered without change of the vegetal cover and express only rainfall growth (Bambili and Assom). © 2010 Elsevier B.V.
Keywords: Africa; Atlantic Ocean; Gulf of Guinea; Anoxic sediments; Debris; Drought; Lakes; Sedimentology; Accumulation rates; Cameroon; Carbon accumulation; Carbon concentrations; Gulf of Guinea; Holocene; Holocenes; Nearly homogenous; Organic matter; Particulate organic carbon; Particulate organic carbon fluxes; Synthetic approach; Terrestrial sediments; Vegetal cover; Vegetation cover; Wet period; accumulation rate; carbon flux; coastal sediment; Holocene; lacustrine environment; particulate organic carbon; sediment chemistry; sedimentation; terrestrial deposit; Organic carbon

Scientific drilling into the san andreas fault zone - Zoback, M.; Hickman, S.; Ellsworth, W. (Eos, 2010)
This year, the world has faced energetic and destructive earthquakes almost every month. In January, an M = 7.0 event rocked Haiti, killing an estimated 230,000 people. In February, an M = 8.8 earthquake and tsunami claimed over 500 lives and caused billions of dollars of damage in Chile. Fatal earthquakes also occurred in Turkey in March and in China and Mexico in April.
cited By 118
Keywords: earthquake damage; fault zone; hazard assessment; tsunami; California; Chile; China; Haiti; Mexico [North America]; San Andreas; Turkey; United States

Scale-invariant stress orientations and seismicity rates near the San Andreas Fault - Day-Lewis, A.; Zoback, M.; Hickman, S. (Geophysical Research Letters, 2010)
We analyzed measurements of the direction of maximum horizontal compressive stress as a function of depth in two scientific research wells near the San Andreas Fault in central and southern California. We found that the stress orientations exhibit scale-invariant fluctuations over intervals from tens of cm to several km. Similarity between the scaling of the stress orientation fluctuations and the scaling of earthquake frequency with fault size suggests that these fluctuations are controlled by stress perturbations caused by slip on faults of various sizes in the critically-stressed crust adjacent to the fault. The apparent difference in stress scaling parameters between the two studies wells seem to correspond to differences in the earthquake magnitude-frequency statistics for the creeping versus locked sections of the fault along which these two wells are located. This suggests that stress heterogeneity adjacent to active faults like the San Andreas may reflect variations in stresses and loading conditions along the fault. © 2010 by the American Geophysical Union.
cited By 28
Keywords: Compressive stress; Earthquakes; Horizontal wells; Wells; Active fault; Earthquake frequency; Earthquake magnitudes; Loading condition; San Andreas Fault; Scale-invariant; Scaling parameter; Scientific researches; Southern California; Stress orientations; Stress perturbations; Stress analysis; active fault; compression; creep; earthquake magnitude; earthquake recurrence; fault zone; seismicity; California; San Andreas; United States

Resource potential of gas hydrates: Recent contributions from international research and development projects - Collett, T.S. (Petroleum Geology Conference Proceedings, 2010)
It is generally accepted that the amount of gas in the world's gas hydrate accumulations exceeds the volume of known conventional gas resources. Researchers have long speculated that gas hydrates could eventually be a commercial producible energy resource yet technical and economic hurdles have historically made gas hydrate development a distant goal rather than a near-term possibility. This view began to change in recent years with the realization that this unconventional resource could possibly be developed with existing conventional oil and gas production technology. The most significant development has been gas hydrate production testing conducted at the Mallik site in Canada's Mackenzie Delta. The Mallik Gas Hydrate Production Research Well Program has yielded the first modern, fully integrated field study and production test of a natural gas hydrate accumulation. More recently, BP Exploration (Alaska) Inc. with the US Department of Energy and the US Geological Survey have successfully cored, logged and tested a gas hydrate accumulation on the North Slope of Alaska known as the Mount Elbert Prospect. The Mallik project along with the Mount Elbert effort has for the first time allowed the rational assessment of the production response of a gas hydrate accumulation. In addition to the gas hydrate production tests in Canada and the USA, marine gas hydrate research drilling, coring and logging expeditions launched by the national gas hydrate programmes in Japan, India, China and South Korea have also contributed significantly to our understanding of how gas hydrates occur in nature and have provided a much deeper appreciation of the geological controls on the occurrence of gas hydrates. With an increasing number of highly successful gas hydrate field studies, significant progress has been made in addressing some of the key issues on the formation, occurrence and stability of gas hydrates in nature. © Petroleum Geology Conferences Ltd. Published by the Geological Society, London.
cited By 3

Reply to Discussion by J. Zhang and J-C Roegiers on the paper Integrating borehole breakout dimensions, strength criteria, and leak-off test results, to constrain the state of stress across the Chelungpu Fault, Taiwan by Bezalel Haimson, Weiren Lin, Haruyuki Oku, Jih-Hao Hung, Sheng-Rong Song, published in Tectonophysics, vol. 482, p. 65-72, 2010 (Tectonophysics, 2010)
cited By 1

Seismic images of Chicxulub impact melt sheet and comparison with the Sudbury structure - Barton, P.J.; Grieve, R.A.F.; Morgan, J.V.; Surendra, A.T.; Vermeesch, P.M.; Christeson, G.L.; Gulick, S.P.S.; Warner, M.R. (Special Paper of the Geological Society of America, 2010)
Chicxulub is the only known impact structure on Earth with a fully preserved peak ring, and it forms an important natural laboratory for the study of large impact structures and understanding of large-scale cratering on Earth and other planets. Seismic data collected in 1996 and 2005 reveal detailed images of the uppermost crater in the central basin at Chicxulub. Seismic reflection profiles show a reflective layer ∼1 km beneath the apparent crater floor, topped by upwardly concave reflectors interpreted as saucer-shaped sills. The upper part of this reflective layer is coincident with a thin high-velocity layer identified by analyzing refractions on the 6 km seismic streamer data. The high-velocity layer is almost horizontal and appears to be contained within the peak ring structure. We argue that this reflective layer is the predicted coherent melt sheet formed during impact, and it may be comparable with the unit known as the Sudbury Igneous Complex at the Sudbury impact structure. The Sudbury Igneous Complex, interpreted as a differentiated impact melt sheet, appears to have a similar scale and geometry, and an uppermost lithological sequence consisting of a high velocity layer at the top and a velocity inversion beneath. This comparison suggests that the Chicxulub impact structure also contains a coherent differentiated melt sheet. © 2010 The Geological Society of America. All rights reserved.
cited By 20

Past atmospheric Pb deposition in Lake Qinghai, northeastern Tibetan Plateau - Jin, Zhangdong; Han, Yongming; Chen, Li (Journal of Paleolimnology, 2010)
Two short sediment cores were recovered from sub-basins of Lake Qinghai, China and were analyzed for concentrations of Pb and 16 other elements to determine historic, regional atmospheric Pb deposition on the Tibetan Plateau. Core chronologies, dating back to the eighteenth century, were established using activities of 210Pb and 137Cs. The 17 elements were divided into three principal components. Variations in concentrations of PC1 elements (Al, Cr, Cu, Fe, K, Mn, Ni, and Ti) demonstrate different patterns between the two cores, and are attributed to different sediment sources in the two subbasins. PC2 elements (Ba, Ca, Na, and Sr) may be associated with the degree of catchment weathering and/or water chemistry. Four elements (Pb, Zn, P, and Co) are related to both PC1 and PC2, and reflect a mixture of natural and anthropogenic sources. The PC3 element is Mg in the north sub-basin, and is perhaps related to aragonite precipitation and/or increased farming. Elevated Pb concentrations in uppermost sediments of both cores signify a recent regional/global increase in anthropogenic Pb release into the environment. After subtracting lithogenic Pb, derived from rock weathering and/or dust and normalized to the background immobile element Ti, results suggest that excess, anthropogenic Pb is transferred to the lake and its sediments predominantly via the atmosphere. This anthropogenic atmospheric Pb is comparable in magnitude and displays similar variation patterns in the two cores, reflecting regional atmospheric deposition and local erosion. The average anthropogenic Pb deposition rate in Lake Qinghai since the 1960s has been 12.2 ± 3.5 mg/ m2/a, comparable with atmospheric Pb fluxes reported for sites elsewhere in the northern hemisphere. © Springer Science+Business Media B.V. 2009.
Keywords: China; Qinghai; Qinghai Lake; Qinghai-Xizang Plateau; anthropogenic source; aragonite; atmospheric deposition; catchment; cesium isotope; chronology; concentration (composition); dust; eighteenth century; heavy metal; lacustrine deposit; lead isotope; magnitude; Northern Hemisphere; precipitation (chemistry); principal component analysis; sediment core; water chemistry; weathering

Productivity of Paleo-Songliao lake during the late Cretaceous in well Songke-1, Songliao Basin - Ning, WK; Fu, L; Huo, QL (Journal of Jilin University (Earth Science Edition), 2010)

Preferred orientation of phyllosilicates: Comparison of fault gouge, shale and schist - Wenk, H.-R.; Kanitpanyacharoen, W.; Voltolini, M. (Journal of Structural Geology, 2010)
Samples of fault gouge from the San Andreas Fault drill hole (SAFOD), a shale from the North Sea sedimentary basin and schists from metamorphic rocks in the Alps have been analyzed with high energy synchrotron X-rays to determine preferred orientation of mica and clay minerals. The method relies on obtaining 2D diffraction images which are then processed with the crystallographic Rietveld method, implemented in the software MAUD, allowing for deconvolution of phases and extraction of their orientation distributions. It is possible to distinguish between detrital illite/muscovite and authigenic illite/smectite, kaolinite and chlorite, and muscovite and biotite, with strongly overlapping peaks in the diffraction pattern. The results demonstrate that phyllosilicates show large texture variations in various environments, where different mechanisms produce the rock microfabrics: fault gouge fabrics are quite weak and asymmetric with maxima for (001) in the range of 1.5-2.5 multiples of random distribution (m.r.d.). This is attributed to heterogeneous deformation with randomization, as well as dissolution-precipitation reactions. Shale fabrics have maxima ranging from 3 to 9. m.r.d. and this is due to sedimentation and compaction. The strongest fabrics were observed in metamorphic schists (10-14. m.r.d.) and developed by deformation as well as recrystallization in a stress field. In the analyzed samples, fabrics of co-existing quartz are weak. All phyllosilicate textures can be explained by orientation of (001) platelets, with no additional constraints on a-axes. © 2010 Elsevier Ltd.
cited By 74
Keywords: Authigenic; Co-existing; Different mechanisms; Diffraction images; Drill hole; Fault gouge; Heterogeneous deformation; High energy synchrotron; Large textures; Micro fabric; North Sea; Orientation distributions; Overlapping peaks; Phyllosilicate; Phyllosilicate fabrics; Precipitation reaction; Preferred orientations; Random distribution; Recrystallizations; San Andreas Fault; Schist; Sedimentary basin; Stress field; Deformation; Dissolution; Holographic interferometry; Kaolinite; Metamorphic rocks; Mica; Oxide minerals; Quartz; Rietveld method; Shale; Silicate minerals; Textures; Fabrics; authigenic mineral; chemical composition; clay mineral; deconvolution; fault gouge; metamorphic rock; phyllosilicate; preferred orientation; recrystallization; Rietveld analysis; schist; sedimentary basin; shale; stress field; Atlantic Ocean; North Sea

Postglacial Faults in Fennoscandia: Targets for scientific drilling - Kukkonen, Ilmo T.; Olesen, Odleiv; Ask, Maria V.S.; PFDP WORKING GROUP (GFF, 2010)

Post-Columbian environmental history of Lago Pet'en Itz'a, Guatemala; [Historia ambiental postcolombina del Lago Pet'en Itz'a, Guatemala] - P'erez, Liseth; Bugja, Rita; Massaferro, Julieta; Steeb, Philip; Geldern, Robert; Frenzel, Peter; Brenner, Mark; Scharf, Burkhard; Schwalb, Antje (Revista Mexicana de Ciencias Geologicas, 2010)
Two 40-cm-long sediment cores, PI-SC-1-10m and PI-SC-2-40m, were recovered at 10 and 40 m water depth, respectively, from Lago Pet'en Itz'a, in the Department of Pet'en, northern Guatemala. The cores span the last 525 years of sediment accumulation in the basin. This study explores lake level and trophic state changes that Lago Pet'en Itz'a has experienced since European contact in the early 1500s. We inferred past environmental variability using changes in sediment geochemistry and fluctuations in relative species abundances of ostracode and chironomid fossil assemblages. Changes in concentrations of organic matter (OM), carbonate, total carbon (TC), total nitrogen (TN), C/N ratios, bromine (Br), and faunal relative abundances were used to infer changes in the trophic status of the lake. Cultural eutrophication began in the 1930s, and anthropogenic impact increased significantly after 1970. Higher linear sedimentation rates, up to 9.1 mm yr-1, began recently. They are attributed to increases in riparian settlement, deforestation and associated land use changes, which led to accelerated soil erosion. An ostracode-based transfer function was applied to assemblages in core PI-SC-1-10m, which enabled us to identify periods when lake level fluctuated. Such historical fluctuations in lake levels were driven primarily by changes in rainfall. Past lake levels can be summarized as follows: (1) fluctuating, high lake levels from 1550s to the 1730s and from the early 1940s to 2005, and (2) stable, lower lake levels from about 1750 to the early 1900s. Higher relative abundance of the ostracode Physocypria globula and higher rubidium (Rb) concentrations indicate higher lake levels than today. Chironomids also show sharp fluctuations along the cores that could be related to water level changes. The presence of chironomid assemblages Chironomus, Procladius, and Einfeldia from 1960-2000 AD shows high productivity levels. The Lago Pet'en Itz'a sediment record indicates a generally arid Little Ice Age (LIA), with exceptions around 1580 and 1650 when high lake levels similar to those of the 20th century, i.e. 5 m higher than today, indicate more humid conditions.

Plio-Pleistocene transition in the continental record from Lake Baikal: Diatom biostratigraphy and age model - Prokopenko, Alexander A.; Khursevich, Galina K. (Quaternary International, 2010)
Lake Baikal basin in the continental interior Asia preserved a unique continuous sedimentary archive of the late Cenozoic; large-scale regional environmental changes of the past were recorded in the composition of fossil diatom flora. Here, the Lake Baikal planktonic diatom biostratigraphy is extended over the Plio-Pleistocene transition, it includes 11 new local diatom assemblage zones (LDAZ) for the time interval 1.25-3.6. Ma. The comparison of the parallel BDP-96-1 and BDP-98 drill core records allows constructing the complete diatom biostratigraphic record at the time of the inception of the Northern Hemisphere glaciations; diatom biostratigraphic zones around Matuyama/Gauss paleomagnetic reversal are correlated with individual stages of marine oxygen isotope stratigraphy. Contrary to previous assumptions, the period 2.8-2.6. Ma in Lake Baikal record was characterized not by a prolonged minimum in diatom abundance but by a distinct maximum in the abundance of small-celled diatom taxa Tertiarius baicalensis and Stephanodiscus binderanus et var. hyalinus, which proliferated in the lake during the interval of relatively warm and humid climate.The Lake Baikal diatom biostratigraphic change at around 1.8. Ma occurs only at a species level of the genus Cyclotella. By contrast, around 2.8-2.5. Ma, spectacular appearances and extinctions occurred at a high taxonomic level of genera (including the genera of Tertiarius, Thalassiobeckia and Stepahanopsis) making the biostratigraphic changes around Matuyama/Gauss reversal more prominent. At least three distinct biostratigraphic boundaries are observed: at 2.69. Ma, 2.65. Ma and at 2.46. Ma. None of these boundaries, however, coincides with the paleomagnetic reversal at 2.58. Ma. Thus the new well-resolved Lake Baikal biostratigraphic record points to the difficulty of assigning a single 'golden spike' biostratigraphic boundary around Matuyama/Gauss paleomagnetic reversal in continental Asia. © 2009 Elsevier Ltd and INQUA.
Keywords: Lake Baikal; Russian Federation; Bacillariophyta; Cyclotella; Stephanodiscus binderanus; biostratigraphy; Cenozoic; continental interior; diatom; environmental change; glaciation; magnetic reversal; Northern Hemisphere; oxygen isotope; paleomagnetism; plankton; Pliocene-Pleistocene boundary

Petrography, mineralogy, and geochemistry of deep gravelly sands in the Eyreville B core, Chesapeake Bay impact structure - Bartosova, K.; Gier, S.; Horton Jr., J.W.; Koeberl, C.; Mader, D.; Dypvik, H. (Meteoritics and Planetary Science, 2010)
The ICDP-USGS Eyreville drill cores in the Chesapeake Bay impact structure reached a total depth of 1766 m and comprise (from the bottom upwards) basement-derived schists and granites/pegmatites, impact breccias, mostly poorly lithified gravelly sand and crystalline blocks, a granitic slab, sedimentary breccias, and postimpact sediments. The gravelly sand and crystalline block section forms an approximately 26 m thick interval that includes an amphibolite block and boulders of cataclastic gneiss and suevite. Three gravelly sands (basal, middle, and upper) are distinguished within this interval. The gravelly sands are poorly sorted, clast supported, and generally massive, but crude size-sorting and subtle, discontinuous layers occur locally. Quartz and K-feldspar are the main sand-size minerals and smectite and kaolinite are the principal clay minerals. Other mineral grains occur only in accessory amounts and lithic clasts are sparse (only a few vol%). The gravelly sands are silica rich (∼80 wt% SiO2). Trends with depth include a slight decrease in SiO2 and slight increase in Fe2O3. The basal gravelly sand (below the cataclasite boulder) has a lower SiO2 content, less K-feldspar, and more mica than the higher sands, and it contains more lithic clasts and melt particles that are probably reworked from the underlying suevite. The middle gravelly sand (below the amphibolite block) is finer-grained, contains more abundant clay minerals, and displays more variable chemical compositions than upper gravelly sand (above the block). Our mineralogical and geochemical results suggest that the gravelly sands are avalanche deposits derived probably from the nonmarine Potomac Formation in the lower part of the target sediment layer, in contrast to polymict diamictons higher in the core that have been interpreted as ocean-resurge debris flows, which is in agreement with previous interpretations. The mineralogy and geochemistry of the gravelly sands are typical for a passive continental margin source. There is no discernible mixing with marine sediments (no glauconite or Paleogene marine microfossils noted) during the impact remobilization and redeposition. The unshocked amphibolite block and cataclasite boulder might have originated from the outer parts of the transient crater. © 2010 The Meteoritical Society.
cited By 1

Passive seismic monitoring of natural and induced earthquakes: case studies, future directions and socio-economic relevance - Bohnhoff, Marco; Dresen, Georg; Ellsworth, William L; Ito, Hisao (New frontiers in integrated solid earth sciences, 2010)

Origin and tectonic implication of an UHP metamorphic mafic-ultramafic complex from the Sulu UHP terrane, eastern China: Evidence from petrological and geochemical studies of CCSD-Main Hole core samples - Zhang, R.Y.; Jahn, B.-M.; Liou, J.G.; Yang, J.S.; Chiu, H.-Y.; Chung, S.-L.; Li, T.-F.; Lo, C.-H. (Chemical Geology, 2010)
Study of the Maobei garnet peridotite and pyroxenite are significant, because these rocks were subjected to subduction-zone UHP metamorphism that is indicative of deep continental subduction. In order to better understand the origin of the Maobei peridotite and pyroxenite and the processes of continental subduction, we performed geochemical analyses on whole-rock and mineral samples. The studied samples were recovered in the main-hole of the Chinese Continental Scientific Drilling in the Sulu UHP terrane, east-central China. The garnet peridotites occur as lenses or layers in pyroxenite; they comprise garnet wehrlite and garnet dunite with minor interlayers of garnet websterite and garnet. Mini-bands, nodules or veins of eclogite and garnet clinopyroxenite (internal) also irregularly occur in garnet wehrlite. The peridotites are composed of olivine (Fo83-84), garnet (Prp51-56), ± diopside±enstatite (En86-87)±titanoclinochumite, and have lower Mg/(Mg+Fetotal) values of 0.79-0.83 and higher Al2O3 and CaO contents in comparison with the gneiss-hosted Sulu mantle peridotites. Garnet wehrlite displays variable REE patterns, from LREE-enriched to slightly LREE depleted relative to MREE and HREE; whereas, other ultramafic rocks show roughly flat REE patterns. In general, Rb, Ba and LREE increase, and compatible element (e.g. Cr, Co and Ni) abundances decrease from peridotite, pyroxenite to internal eclogite and internal Grt-clinopyroxenite. The calculated REE partition coefficients (DREE) between Cpx and Grt of the Maobei peridotite and pyroxenite decrease regularly from LREE (DCe=32-708) to HREE (DYb=0.01-0.10), which is comparable with natural mantle peridotite and eclogite crystallized at 800-1100°C. The geochemical data and occurrence of these rocks suggest that the protoliths of the Maobei peridotites are cumulates derived by differentiation of basaltic magma at the lower continental crust. Thus, the Internal eclogite and Grt-clinopyroxenite result from post-cumulus crystallization of the trapped melt. Ti-clinohumite orthopyroxenite may have formed by reaction between peridotitic olivine and indigenous melt or country rock-derived (exotic) TiO2-bearing fluids at high-P condition during continental subduction to mantle depths. The peak P-T estimates of 795-840°C and 5.3-6.8GPa of the Maobei peridotites and the available petrological data of country rocks indicate that the continental crust was subducted to a depth of 200km. © 2010 Elsevier B.V.
Keywords: China; Jiangsu; Maobei; Analytical geochemistry; Barium; Cerium; Chromium; Garnets; Geochronology; Levees; Metamorphic rocks; Minerals; Olivine; Petrology; Rocks; Rubidium; Ytterbium; Continental subduction; Differentiation of basic magma; Scientific drilling; Sulu garnet peridotite; UHP metamorphism; chemical analysis; Chinese Continental Scientific Drilling Project; continental crust; country rock; eclogite; garnet; P-T conditions; peridotite; petrology; pyroxenite; rare earth element; tectonic evolution; ultrahigh pressure metamorphism; ultramafic rock; wehrlite; Silicate minerals

Observations of rayleigh-wave phase velocity and coseismic deformation using an optical fiber, interferometric vertical strainmeter at the SAFOD borehole, California - Blum, J.; Igel, H.; Zumberge, M. (Bulletin of the Seismological Society of America, 2010)
We present observations from a vertical, optical fiber interferometric strainmeter in the San Andreas Fault Observatory at Depth borehole near Parkfield, California. The sensor detects both teleseismic earthquakes and local events, along with coseismic strain steps consistent with theoretical dislocation models. For tele-seismic events, we investigate the possibility of determining local Rayleigh-wave phase velocities beneath the borehole by comparing the ratio of vertical ground acceleration from a nearby seismometer to vertical strain. While similar studies have used horizontal components and rotations, this is the first such attempt utilizing vertical measurements. We show that at periods from around 16-40 seconds, we can recover general dispersion characteristics that are within a few percent of models of realistic local structure.
cited By 11
Keywords: California; Coseismic deformation; Dislocation models; Dispersion characteristics; Local structure; Rayleigh-wave phase velocity; San Andreas Fault; Seismic event; Strain-meter; Teleseismic earthquakes; Vertical ground accelerations; Vertical strain; Interferometry; Optical fibers; Phase velocity; Seismology; Strain measurement; coseismic process; deformation; interferometer; optical instrument; phase velocity; Rayleigh wave; seismograph; sensor; teleseismic wave; wave velocity; California; Parkfield; United States

Numerical study of gas evolution and transport behaviors in natural gas hydrate reservoirs - Uddin, M.; Wright, F.; Coombe, D. (Society of Petroleum Engineers - Canadian Unconventional Resources and International Petroleum Conference 2010, 2010)
Gas hydrates are a potentially vast untapped source of natural gas. Recent numerical and field studies suggest the Mallik gas hydrate field in Canada's Mackenzie Delta may represent a technically producible and potentially economically viable reservoir of natural gas. Our initial reservoir simulations using a kinetic reaction approach indicate that gas evolution and transport within porous geologic reservoirs have a significant effect on fluid production characteristics, while field and laboratory data suggest that significant amounts of evolved gas can be trapped for some time within the reservoir, depending on the field operation. In mis work, we invoke modeling concepts extensively employed in quantifying gas ex-solution from very viscous oils to further assess the kinetic behaviour of gas hydrate ex-solution via depressurization. Here the gas bubbles can be categorized into three groups with explicit transport behaviour: small bubbles (water phase), large bubbles (immobile) and connected bubbles (or free gas). These concepts allow the development of a new set of kinetic reactions for hydrate dissociation: one representing the (possibly delayed) conversion of hydrate into water and dispersed gas bubble phases, and one representing the evolution from dispersed bubbles to connected bubbles. These reactions can effectively capture the non-equilibrium fluid flow behaviour observed in field production tests. For modeling of the transport phenomenon, we assumed two explicit mobility formulations, 1) trapped bubbles (no mobility) and a flowing water phase, and 2) large connected gas bubbles and flowing water (with relative mobility). Relative mobility can be estimated by using traditional grid block relative permeability curves. We then develop a simple mechanistic gas bubbles trapping tool as a function of Capillary Number, which can easily be incorporated into our numerical simulator. This entrapment of me non-wetting gas phase results in higher values of critical gas saturation. Two case studies based on alternative representations of a Mallik-like gas hydrate reservoir demonstrate that significant errors can result in reservoir modeling if these fluid transport phenomena are not adequately represented in numerical simulations. Aspects of the model developed here have been applied to history matching and prediction of natural gas recovery from clastic, sand-dominated reservoir at the Mallik Site. Copyright 2010, Society of Petroleum Engineers.
cited By 0
Keywords: Bubbles (in fluids); Flow of fluids; Gas hydrates; Gas oils; Gases; Gasoline; Hydration; Kinetics; Natural gas; Natural gasoline plants; Petroleum reservoirs; Resource valuation; Transport properties; Wetting; Critical gas saturation; Gas hydrate reservoir; Hydrate dissociation; Natural gas hydrate reservoir; Natural gas recoveries; Numerical simulators; Relative permeability curves; Reservoir simulation; Natural gas fields

New integrated data analyses software components - Conze, R.; Krysiak, F.; Reed, J.; Chen, Y.-C.; Wallrabe-Adams, H.-J.; Graham, C.; Wennrich, V. (Scientific Drilling, 2010)
cited By 2

Native Dreissena freshwater mussels in the Balkans: In and out of ancient lakes - Wilke, T.; Schulthei{s, R.; Albrecht, C.; Bornmann, N.; Trajanovski, S.; Kevrekidis, T. (Biogeosciences, 2010)
The Balkans is a biogeographically highly diverse region and a worldwide hotspot of endemic freshwater diversity. A substantial part of this diversity is attributed to well recognized and potential ancient lakes in its southwestern part. However, despite considerable research efforts, faunal relationships among those lakes are not well understood. Therefore, genetic information from native representatives of the mussel genus Dreissena is here used to test the biogeographical zonation of the southwestern Balkans, to relate demographic changes to environmental changes, to assess the degree of eco-insularity, to reconstruct their evolutionary history, and to explore the potential of native taxa for becoming invasive. Phylogeographical and population genetic analyses indicate that most studied populations belong to two native species: D. presbensis (including the distinct genetic subgroup from Lake Ohrid, D. stankoviciquot;) and D. blanci. In addition, the first confirmed record of invasive D. polymorpha in the southwestern Balkan is presented. The distribution of native Dreissena spp. generally coincides with the biogeographical zonations previously suggested based on fish data. However, there is disagreement on the assignment of the ancient lakes in the area to respective biogeographical regions. The data for Lake Ohrid are not conclusive. A closer biogeographical connection to lakes of the Vardar region and possibly the northern Ionian region is, however, suggested for Lake Prespa. The reconstruction of the evolutionary history of Dreissena spp. suggests that populations underwent demographic and spatial expansions in the recent past. Expansions started around 320 000-300 000 years ago in D. stankovici, 160 000-140 000 years ago in D. blanci, and 110 000-70 000 years ago in D. presbensis. These time frames are discussed within the context of available paleogeological data for lakes Ohrid and Prespa. It is suggested that regional environmental changes may have had pronounced effects on the population histories of native Dreissena spp., though the high buffer capacity of Lake Ohrid may have lessened these effects in D. stankovici. In addition, local events influencing individual lakes had very likely considerable effects on the demographic histories of Dreissena spp. as well. The observed patterns of immigration and emigration in and out of ancient lakes may suggest that limited gene flow enabled the survival of few isolated subpopulations and that later on eco-insularity (selective advantages of locally adopted groups) may have prevented excessive hybridization and sympatry of closely related taxa. As for the potential invasiveness of native Dreissena spp., the inferred spatial expansions are not human-mediated and all taxa still appear to be restricted to their native ranges. A concern, however, is that today D. presbensis and D. blanci also occur in artificial water bodies, and that invasive D. polymorpha has reached the area. © Author(s) 2010.
Keywords: Balkans; Lake Mikri Prespa; Lake Ohrid; Dreissena; Dreissena polymorpha; Dreissena stankovici; bivalve; extinction; freshwater environment; genetic analysis; historical perspective; native species; paleoecology; reconstruction; species diversity; sympatry; zoogeography

Siderophile elements from the Eyreville drill cores of the Chesapeake Bay impact structure do not constrain the nature of the projectile - Goderis, S.; Hertogen, J.; Vanhaecke, F.; Claeys, Ph. (Special Paper of the Geological Society of America, 2010)
Fifteen impactites from various intervals within the Eyreville cores of the Chesapeake Bay impact structure were sampled to measure siderophile element concentrations. The sampled intervals include basement-derived rocks with veins, polymict impact breccias and associated rocks, and crater-fill sediments. The platinum group element (PGE) concentrations obtained are generally low (e.g., iridium concentrations less than 0.1 ng/g) and are fractionated relative to chondrites. There is no clear distinction in concentration between the different impactite units. So far in the Chesapeake Bay material, only the impact melt rocks from the 823-m-deep Cape Charles test hole, drilled over the central uplift of the structure, have generated a bulk chondritic signature of 0.01-0.1 wt% meteoritic contribution based on a mixing model of 187 Os/ 188 Os isotopic ratios and Os concentrations. However, none of the samples studied shows PGE abundances that enable identification of the type of projectile responsible for the formation of the structure. Hence, it is at present not possible to link the Chesapeake Bay impact to the proposed ordinary chondrite falls by projectiles recorded for other late Eocene craters, namely the 100-km-diameter Popigai impact structure in Siberia and 7.5-km-diameter Wanapitei structure in Canada. The absence of a clear projectile signature hinders further discussions on the existence and the nature of the late Eocene shower event (asteroid versus comet). © 2010 The Geological Society of America. All rights reserved.
cited By 10

Siderophile elements from the Eyreville drill cores of the Chesapeake Bay impact structure do not constrain the nature of the projectile - Goderis, S.; Hertogen, J.; Vanhaecke, F.; Claeys, Ph. (Special Paper of the Geological Society of America, 2010)
Fifteen impactites from various intervals within the Eyreville cores of the Chesapeake Bay impact structure were sampled to measure siderophile element concentrations. The sampled intervals include basement-derived rocks with veins, polymict impact breccias and associated rocks, and crater-fill sediments. The platinum group element (PGE) concentrations obtained are generally low (e.g., iridium concentrations less than 0.1 ng/g) and are fractionated relative to chondrites. There is no clear distinction in concentration between the different impactite units. So far in the Chesapeake Bay material, only the impact melt rocks from the 823-m-deep Cape Charles test hole, drilled over the central uplift of the structure, have generated a bulk chondritic signature of 0.01-0.1 wt% meteoritic contribution based on a mixing model of 187 Os/ 188 Os isotopic ratios and Os concentrations. However, none of the samples studied shows PGE abundances that enable identification of the type of projectile responsible for the formation of the structure. Hence, it is at present not possible to link the Chesapeake Bay impact to the proposed ordinary chondrite falls by projectiles recorded for other late Eocene craters, namely the 100-km-diameter Popigai impact structure in Siberia and 7.5-km-diameter Wanapitei structure in Canada. The absence of a clear projectile signature hinders further discussions on the existence and the nature of the late Eocene shower event (asteroid versus comet). © 2010 The Geological Society of America. All rights reserved.
cited By 10
Keywords: Infill drilling; Meteor impacts; Meteorites; Projectiles; Chesapeake Bay; Chesapeake bay impact structures; Impact structures; Isotopic ratios; Mixing models; Ordinary chondrites; Platinum group elements; Siderophile elements; Core drilling; chondrite; crater; impact structure; impactite; isotopic ratio; meteorite; platinum group element; siderophile element; Canada; Chesapeake Bay; Ontario [Canada]; United States; Wanapitei Lake

The chicxulub asteroid impact and mass extinction at the cretaceous-paleogene boundary - Schulte, P.; Alegret, L.; Arenillas, I.; Arz, J.A.; Barton, P.J.; Bown, P.R.; Bralower, T.J.; Christeson, G.L.; Claeys, P.; Cockell, C.S.; Collins, G.S.; Deutsch, A.; et al. (Science, 2010)
The Cretaceous-Paleogene boundary ∼65.5 million years ago marks one of the three largest mass extinctions in the past 500 million years. The extinction event coincided with a large asteroid impact at Chicxulub, Mexico, and occurred within the time of Deccan flood basalt volcanism in India. Here, we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction. Notably, a single ejecta-rich deposit compositionally linked to the Chicxulub impact is globally distributed at the Cretaceous-Paleogene boundary. The temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations (for example, darkness and cooling) lead us to conclude that the Chicxulub impact triggered the mass extinction.
cited By 947

Single crystal U-Pb zircon age and Sr-Nd isotopic composition of impactites from the Bosumtwi impact structure, Ghana: Comparison with country rocks and Ivory Coast tektites - Ferrière, Ludovic; Koeberl, Christian; Th{oni, Martin; Liang, Chen (Chemical Geology, 2010)
The 1.07. Myr old Bosumtwi impact structure (Ghana), excavated in 2.1-2.2. Gyr old supracrustal rocks of the Birimian Supergroup, was drilled in 2004. Here, we present single crystal U-Pb zircon ages from a suevite and two meta-graywacke samples recovered from the central uplift (drill core LB-08A), which yield an upper Concordia intercept age of ca 2145 ± 82 Ma, in very good agreement with previous geochronological data for the West African Craton rocks in Ghana. Whole rock Rb-Sr and Sm-Nd isotope data of six suevites (five from inside the crater and one from outside the northern crater rim), three meta-graywacke, and two phyllite samples from core LB-08A are also presented, providing further insights into the timing of the metamorphism and a possibly related isotopic redistribution of the Bosumtwi crater rocks. Our Rb-Sr and Sm-Nd data show also that the suevites are mixtures of meta-greywacke and phyllite (and possibly a very low amount of granite). A comparison of our new isotopic data with literature data for the Ivory Coast tektites allows to better constrain the parent material of the Ivory Coast tektites (i.e., distal impactites), which is thought to consist of a mixture of metasedimentary rocks (and possibly granite), but with a higher proportion of phyllite (and shale) than the suevites (i.e., proximal impactites). When plotted in a Rb/Sr isochron diagram, the sample data points (n=29, including literature data) scatter along a regression line, whose slope corresponds to an age of 1846 ± 160 Ma, with an initial Sr isotope ratio of 0.703 ± 0.002. However, due to the extensive alteration of some of the investigated samples and the lithological diversity of the source material, this age, which is in close agreement with a possible metamorphic age of . 1.8-1.9. Ga tentatively derived from our U-Pb dating of zircons, is difficult to consider as a reliable metamorphic age. It may perhaps reflect a common ancient source whose Rb-Sr isotope systematics has not basically been reset on the whole rock scale during the Bosumtwi impact event, or even reflect another unknown geologic event. © 2010 Elsevier B.V.
Keywords: Cote d' Ivoire; Ghana; comparative study; country rock; geochronology; graywacke; impact structure; impactite; isotopic composition; isotopic ratio; lithology; metamorphism; neodymium isotope; phyllite; strontium isotope; tektite; uranium-lead dating; zircon

The 2008 West Bohemia earthquake swarm in the light of the WEBNET network - Fischer, Tom'aš; Hor'alek, Josef; Mich'alek, Jan; Bouškov'a, Alena (Journal of Seismology, 2010)
A swarm of earthquakes of magnitudes up to ML = 3.8 stroke the region of West Bohemia/Vogtland (border area between Czechia and Germany) in October 2008. It occurred in the Nov'y Kostel focal zone, where also all recent earthquake swarms (1985/1986, 1997, and 2000) took place, and was striking by a fast sequence of macroseismically observed earthquakes. We present the basic characteristics of this swarm based on the observations of a local network WEBNET (West Bohemia seismic network), which has been operated in the epicentral area, on the Czech territory. The swarm was recorded by 13 to 23 permanent and mobile WEBNET stations surrounding the swarm epicenters. In addition, a part of the swarm was also recorded by strong-motion accelerometers, which represent the first true accelerograms of the swarm earthquakes in the region. The peak ground acceleration reached 0.65 m/s2. A comparison with previous earthquake swarms indicates that the total seismic moments released during the 1985/1986 and 2008 swarms are similar, of about 4E16 Nm, and that they represent the two largest swarms that occurred in the West Bohemia/ Vogtland region since the ML = 5.0 swarm of 1908. Characteristic features of the 2008 swarm are its short duration (4 weeks) and rapidity and, consequently, the fastest seismic moment release compared to previous swarms. Up to 25,000 events in the magnitude range of 0.5 < ML < 3.8 were detected using an automatic picker. A total of nine swarm phases can be distinguished in the swarm, five of them exceeding the magnitude level of 2.5. The magnitude-frequency distribution of the complete 2008 swarm activity shows a b value close to 1. The swarm hypocenters fall precisely on the same fault portion of the Nov'y Kostel focal zone that was activated by the 2000 swarm (ML ≤ 3. 2) in a depth interval from 6 to 11 km and also by the 1985/1986 swarm (ML ≤ 4.6). The steeply dipping fault planes of the 2000 and 2008 swarms seem to be identical considering the location error of about 100 m. Furthermore, focal mechanisms of the 2008 swarm are identical with those of the 2000 swarm, both matching an average strike of 170° and dip of 80° of the activated fault segment. An overall upward migration of activity is observed with first events at the bottom and last events at the top of the of the activated fault patch. Similarities in the activated fault area and in the seismic moments released during the three largest recent swarms enable to estimate the seismic potential of the focal zone. If the whole segment of the fault plane was activated simultaneously, it would represent an earthquake of ML 5. This is in good agreement with the estimates of the maximum magnitudes of earthquakes that occurred in the West Bohemia/Vogtland region in the past. © 2010 Springer Science+Business Media B.V.
Keywords: Bohemia; Czech Republic; Germany; Vogtland; earthquake epicenter; earthquake event; earthquake magnitude; earthquake mechanism; earthquake swarm; fault plane; focal mechanism; peak acceleration; seismic moment; seismicity; strong motion

Millennial-scale climate variability during the Last Glacial period in the tropical Andes - Fritz, S.C.; Baker, P.A.; Ekdahl, E.; Seltzer, G.O.; Stevens, L.R. (Quaternary Science Reviews, 2010)
Millennial-scale climate variation during the Last Glacial period is evident in many locations worldwide, but it is unclear if such variation occurred in the interior of tropical South America, and, if so, how the low-latitude variation was related to its high-latitude counterpart. A high-resolution record, derived from the deep drilling of sediments on the floor of Lake Titicaca in the southern tropical Andes, is presented that shows clear evidence of millennial-scale climate variation between ∼60 and 20 ka BP. This variation is manifested by alternations of two interbedded sedimentary units. The two units have distinctive sedimentary, geochemical, and paleobiotic properties that are controlled by the relative abundance of terrigenous or nearshore components versus pelagic components. The sediments of more terrigenous or nearshore nature likely were deposited during regionally wetter climates when river transport of water and sediment was higher, whereas the sediments of more pelagic character were deposited during somewhat drier climates regionally. The majority of the wet periods inferred from the Lake Titicaca sediment record are correlated with the cold events in the Greenland ice cores and North Atlantic sediment cores, indicating that increased intensity of the South American summer monsoon was part of near-global scale climate excursions. © 2010 Elsevier Ltd. All rights reserved.
Keywords: Andes; Lake Titicaca; Climatology; Glacial geology; Salinity measurement; Tropics; Climate variability; Climate variation; Deep drilling; Global scale; Greenland; High resolution; Ice core; Last glacial period; Nearshores; North Atlantic; Relative abundance; River transports; Sediment core; Sedimentary units; South America; Summer monsoon; Tropical Andes; Wet period; climate variation; deep drilling; lacustrine deposit; Last Glacial; paleoclimate; resolution; sedimentation; terrigenous deposit; Sedimentology

Zircon U-Pb ages, REE concentrations and Hf isotope compositions of granitic leucosome and pegmatite from the north Sulu UHP terrane in China: Constraints on the timing and nature of partial melting - Liu, Fulai; Robinson, Paul T.; Gerdes, Axel; Xue, Huaimin; Liu, Pinghua; Liou, Juhn G. (Lithos, 2010)
Granitic leucosome and pegmatite are widely distributed within biotite-bearing orthogneiss in the northern part of the Sulu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. A combined study of mineral inclusions, cathodoluminescence (CL) images, U-Pb SHRIMP dates, and in situ trace element and Lu-Hf isotope analyses of zircons provided insight into the nature and timing of partial melting in these rocks. Zircon grains separated from biotite-bearing orthogneiss typically have three distinct domains: (1) pre-metamorphic (magmatic) cores with Qtz. +. Kfs. +. Pl. +. Ap inclusions, which record a Neoproterozoic protolith age of 790. Ma, (2) mantles with Coe. +. Phe. +. Ap inclusions that record Triassic UHP age at 227 ± 3. Ma, and (3) narrow rims with quartz inclusions that record HP granulite-facies retrograde metamorphism at 210 ± 3. Ma. In contrast, zircons separated from granitic leucosome have only two distinct domains: (1) the central UHP areas with Coe. +. Phe. +. Ap inclusions record Triassic UHP age of 227 ± 3. Ma, and (2) outer magmatic areas with Qtz. +. Kfs. +. Ab. +. Ap inclusions that record partial melting time of 212 ± 2. Ma. Zircons separated from pegmatite contain mineral inclusions of Qtz. +. Kfs. +. Ap and show regular magmatic zoning from centre to edge. The centres record partial melting time of 212 ± 2. Ma in line with the outer domains of granitic leucosome, whereas the edges give a younger age of 201 ± 2. Ma related to Pb loss and partial recrystallization during late Triassic regional amphibolite-facies retrogression. These data indicate that partial melting in the north Sulu UHP gneissic rocks took place during post-UHP, retrograde HP granulite-facies metamorphism. Pre-metamorphic (magmatic) zircon cores from biotite-bearing orthogneiss give uniform 176Hf/177Hf of 0.28187±0.00003 (2SD; standard deviation) corresponding to εHf(790) and Hf model ages (TDM2) of about -16.3 and 2.41Ga, respectively. This is consistent with the generation of its protolith by reworking of Paleoproterozoic to late Archean crust. In contrast, UHP zircon domains from biotite-bearing orthogneiss and granitic leucosome are characterized by distinct trace element composition with low Lu/Hf (<0.006), low Th/U (<0.1) and considerably higher, 176Hf/177Hf (0.28233±0.00002; 2SD) than the pre-metamorphic cores. The uniform but significantly different Hf isotope composition between the UHP (εHf(227)=-14.6±0.8; 2SD) and pre-metamorphic (-Hf(227)=-27.7) domains indicates equilibration of the Lu-Hf isotope system only within the UHP metamorphic mineral assemblage. The disequilibrium between whole rock and UHP zircon suggests that about two thirds of the whole rock Hf retained in the pre-metamorphic zircon domains. Zircon domains crystallized during partial melting at 212Ma in granitic leucosome and pegmatites have a Hf isotope composition indistinguishable from that of the UHP zircon domains. This suggests that only Hf (and Zr) equilibrated during UHP metamorphism was remobilized during partial melting while pre-metamorphic zircon remained stable or was not accessible. In contrast, the magmatic zircon edges from pegmatite have somewhat lower 176Hf/177Hf ( 0.28216) and εHf(t) (-17.6±1.2; 2SD) indicating some release of less radiogenic Hf for instance by dissolution of pre-metamorphic zircon during late regional amphibolite-facies retrogression. © 2010 Elsevier B.V.
Keywords: China; Sulu Belt; biotite; granite; granulite facies; hafnium; inclusion; isotopic analysis; isotopic composition; partial melting; pegmatite; rare earth element; retrograde metamorphism; terrane; trace element; Triassic; uranium-lead dating; zircon

Weathering, Sr fluxes, and controls on water chemistry in the Lake Qinghai catchment, NE Tibetan Plateau - Jin, Zhangdong; Wang, Sumin; Zhang, Fei; Shi, Yuewei (Earth Surface Processes and Landforms, 2010)
Strontium (Sr) concentrations and isotopic ratios have been measured in a series of water and rock samples from most of the major tributaries of the Lake Qinghai basin on the north-eastern Tibetan Plateau. Dissolved Sr and 87Sr/86Sr show ranges of 488-12 240 nmol/l and 0·710497-0·716977, respectively. These data, together with measurements of major cations and anions in rivers and their tributaries and various lithologies of the catchment, were used to determine the contributions of Sr and its isotopic expense to rivers and lakes. Our results demonstrate that the chemical components and 87Sr/86Sr ratios of the alkaline waters are derived from mixing of carbonate and silicate sources, with the former contributing 72 ± 18% dissolved Sr to rivers. The difference in tributary compositions stems from the lithology of different river systems and low weathering intensity under a semi-arid condition. Variation in 87Sr/86Sr ratios places constraint on the Sr-isotopic compositions of the main tributaries surrounding Lake Qinghai. The water chemistry of the Buha River, the largest river within the catchment underlain by the late Paleozoic marine limestone and sandstones, dominates Sr isotopic composition of the lake water, being buffered by the waters from the other rivers and probably by groundwater. However, the characteristic chemical composition of the lake itself differs remarkably from the rivers, which can be attributed to precipitation of authigenic carbonates (low-magnesium calcite, aragonite, and dolomite), though this does not impact the Sr isotope signature, which may remain a faithful indicator in paleo-records. Regarding the potential role of groundwater input within the Lake Qinghai systems in the water budget and water chemistry, we have also determined the Sr concentration and 87Sr/S6Sr ratio of groundwater from diverse environments. This has allowed us to further constrain the Sr isotope systematic of this source. A steady-state calculation gives an estimate for the groundwater flux of 0·19 ± 0·03 x 108 m3/yr, accounting for about 8% of contemporary lake Sr budget. © 2010 John Wiley & Sons, Ltd.
Keywords: China; Qinghai; Qinghai Lake; Qinghai-Xizang Plateau; Budget control; Carbonate minerals; Catchments; Dissolution; Groundwater; Indicators (chemical); Isotopes; Lakes; Lithology; Magnesium; Precipitation (chemical); Rivers; Runoff; Silicates; Soil mechanics; Weathering; Alkaline water; Authigenic carbonates; Budget; Chemical component; Chemical compositions; Eastern Tibetan plateau; Groundwater fluxes; Isotope signatures; Isotopic composition; Isotopic ratios; Lake waters; Late Paleozoic; Magnesium calcite; River systems; Rivers and lakes; Rock sample; Semi-arid conditions; Sr fluxes; Tibetan Plateau; Water budget; Water chemistry; catchment; chemical weathering; concentration (composition); isotopic composition; isotopic ratio; strontium isotope; surface water; water budget; water chemistry; Strontium

Utilizing observations of borehole failure in deviated wellbores to constrain the full stress tensor in deep wells and mines: Application to two complex case studies - Zoback, M.D.; Paul, P.; Lucier, A. (Rock Stress and Earthquakes - Proceedings of the 5th International Symposium on In-Situ Rock Stress, 2010)
Over the past fifteen years,my colleagues and I have developed a suite of techniques for determination of the full stress tensor in arbitrarily- orientedwells and boreholes utilizing observations of non-catastrophic failures of the wellbore wall - compressive failures, drilling-induced tensile fractures and stress perturbations associated with slip on faults cutting through thewellbore. While these techniques have had extensive application in the petroleum industry, they have also been used in core holes drilled from excavations in mines to yield information about the state of stress within, and beyond, the area affected by the stress concentration surrounding the excavation. When possible, hydraulic fracturing is used to provide independent information about the magnitude of the least principal stress, but is not used to estimate the maximum horizontal principal stress. In this paper we review both the conceptual elements of this methodology and two challenging case studies. The first involves determination of the state of stress following the drilling of the first phase of the SAFOD project, a scientific borehole drilled through the San Andreas Fault in central California. The second involves determination of the state of stress in the crust surrounding a very deep mine is South Africa. These case studies document how observations of wellbore failure in deviated wells yield consistent stress orientations and magnitudes over appreciable depth ranges. © 2010 Taylor & Francis Group, London.
cited By 2
Keywords: California; Compressive failure; Conceptual elements; Core hole; Deep mines; Deep wells; Depth range; Deviated wells; Drilling-induced tensile fractures; Least principal stress; Maximum horizontal principal stress; San Andreas fault; South Africa; State of stress; Stress orientations; Stress perturbations; Stress tensors; Wellbore; Boring; Deflected boreholes; Hydraulic fracturing; Oil field equipment; Research; Stress concentration; Strike-slip faults; Tensors; Yield stress

Ultrasonic velocity of the upper gneiss series rocks from the Outokumpu deep drill hole, Fennoscandian shield - Comparing uniaxial to triaxial loading - Lassila, I.; Karlqvist, R.; Elbra, T.; Gates, F.K.; Pesonen, L.J.; Hæggstr{om, E. (Journal of Applied Geophysics, 2010)
P- and S-wave propagation velocities in dry mica schist samples obtained from the Outokumpu deep drill hole in Eastern Finland were measured under uniaxial compression in a custom built measurement device. At 300 MPa pressure the obtained velocities (5520 ± 130) m/s and (3270 ± 60) m/s, for P- and S-waves, respectively, agreed with those measured under triaxial compression, (5530 ± 200) m/s and (3300 ± 90) m/s. The increase in Vp with uniaxial pressure was steeper, whereas this was not the case with Vs. These results indicate that ultrasound velocity measurements can be performed under uniaxial compression without the need to alter the cylindrical geometry of a borehole sample. Results obtained with the device can improve the interpretation of seismic crustal structure maps by providing seismic velocity data of the Outokumpu drill core as well as seismic impedances and reflection coefficients measured under crustal conditions. © 2010 Elsevier B.V.
Keywords: Finland; Ita Suomen; Outokumpu; Core drilling; Cylinders (shapes); Mica; Rock drills; Seismology; Shear waves; Silicate minerals; Ultrasonic velocity; Ultrasonic velocity measurement; Ultrasonics; Wave propagation; Crustal structure; Cylindrical geometry; Drill core; Drill hole; Eastern Finland; Fennoscandian Shields; Measurement device; Mica schists; P- and S-waves; Reflection coefficients; Seismic impedance; Seismic velocities; Triaxial compression; Triaxial loading; Ultrasound; Uni-axial compression; Uniaxial pressures; Wave propagation velocities; compression; crustal structure; data interpretation; geometry; P-wave; S-wave; seismic reflection; seismic velocity; uniaxial strength; wave propagation; Velocity

Towards seismic detection and characterization of gas hydrate accumulations in permafrost environment: An example from the Mallik gas hydrate field, NWT, Canada - Bellefleur, G.; Riedel, M.; Huang, J.; Milkereit, B.; Brent, T. (Society of Petroleum Engineers - Canadian Unconventional Resources and International Petroleum Conference 2010, 2010)
Three internationally-partnered research well programs in 1998, 2002, and 2007-08 studied the Mallik gas hydrate accumulation in the Mackenzie Delta, Canada, and have allowed successful extraction of subpermafrost core samples with significant amount of hydrates. Gas hydrate bearing intervals were logged with a comprehensive suite of tools and their producibility was tested in 2002 using thermal stimulation and in 2007/08 using depressurization techniques. Thus, the Mallik gas hydrates are well-characterized and are ideal targets for testing geophysical imaging techniques. Here, we apply acoustic impedance inversion to 3D seismic data acquired over the Mallik area to characterize gas hydrate occurrences and to help define their spatial extent away from well control. The inversion method converts reflections into acoustic impedances from which velocity and hydrate saturation were estimated. The extent and geometry of the two lower hydrate zones were mapped with high confidence and show a distribution controlled by local geology. Correlation between the uppermost hydrate zone and the 3D seismic data could not be established with confidence, because of geological heterogeneity and/or inappropriate seismic imaging. The heterogeneity of the Mallik gas hydrates was parameterized following a method based on multivariate conditional stochastic simulation of well-logging data. Following this method, multi-dimensional heterogeneous models of petrophysical properties (Vp, Vs and density) of hydrate-bearing sediments were constructed and used to assess effects of heterogeneity on gas hydrate volume estimates. Models including small-scale heterogneities provide volume estimate nearly an order of magnitude lower than earlier estimates which did not include effect of heterogeneity. ©Her Majesty the Queen in Right of Canada 2010.
cited By 2
Keywords: Acoustic impedance; Gases; Gasoline; Geology; Geophysical prospecting; Hydration; Imaging techniques; Petrophysics; Resource valuation; Seismic response; Seismic waves; Stochastic control systems; Stochastic models; Stochastic systems; Well logging; Well testing; Acoustic impedance inversion; Geological heterogeneities; Heterogeneous models; Hydrate accumulations; Hydrate bearing sediments; Permafrost environment; Petrophysical properties; Stochastic simulations; Gas hydrates

The thermal regime in the resurgent dome of Long Valley Caldera, California: Inferences from precision temperature logs in deep wells - Hurwitz, S.; Farrar, C.D.; Williams, C.F. (Journal of Volcanology and Geothermal Research, 2010)
Long Valley Caldera in eastern California formed 0.76Ma ago in a cataclysmic eruption that resulted in the deposition of 600km3 of Bishop Tuff. The total current heat flow from the caldera floor is estimated to be 290MW, and a geothermal power plant in Casa Diablo on the flanks of the resurgent dome (RD) generates 40MWe. The RD in the center of the caldera was uplifted by 80cm between 1980 and 1999 and was explained by most models as a response to magma intrusion into the shallow crust. This unrest has led to extensive research on geothermal resources and volcanic hazards in the caldera. Here we present results from precise, high-resolution, temperature-depth profiles in five deep boreholes (327-1,158m) on the RD to assess its thermal state, and more specifically 1) to provide bounds on the advective heat transport as a guide for future geothermal exploration, 2) to provide constraints on the occurrence of magma at shallow crustal depths, and 3) to provide a baseline for future transient thermal phenomena in response to large earthquakes, volcanic activity, or geothermal production. The temperature profiles display substantial non-linearity within each profile and variability between the different profiles. All profiles display significant temperature reversals with depth and temperature gradients <50°C/km at their bottom. The maximum temperature in the individual boreholes ranges between 124.7°C and 129.5°C and bottom hole temperatures range between 99.4°C and 129.5°C. The high-temperature units in the three Fumarole Valley boreholes are at the approximate same elevation as the high-temperature unit in borehole M-1 in Casa Diablo indicating lateral or sub-lateral hydrothermal flow through the resurgent dome. Small differences in temperature between measurements in consecutive years in three of the wells suggest slow cooling of the shallow hydrothermal flow system. By matching theoretical curves to segments of the measured temperature profiles, we calculate horizontal groundwater velocities in the hydrothermal flow unit under the RD that range from 1.9 to 2.8m/yr, which corresponds to a maximum power flowing through the RD of 3-4MW. The relatively low temperatures and large isothermal segments at the bottom of the temperature profiles are inconsistent with the presence of magma at shallow crustal levels. © 2010.
cited By 12
Keywords: Caldera; Geothermal; Heat flows; Hydrothermal; Long Valley; Resurgent dome; Temperature log; Boreholes; Domes; Geothermal energy; Geothermal fields; Geothermal logging; Geothermal power plants; Geothermal prospecting; Groundwater; Heat transfer; Temperature control; Volcanoes; Wells; Thermal logging; caldera; crust; dome; geothermal power; groundwater flow; heat flow; hydrothermal system; igneous intrusion; temperature profile; thermal regime; uplift; California; Long Valley Caldera; United States; Calluna vulgaris

The precise naming and mineralogical characteristics of ferruginous lacustrine dolomite in Well CCSD-SK - 高翔; 王平康; 李秋英; 王成善; 高远 (Acta Petrologica Et Mineralogica, 2010)

The New Jersey margin scientific drilling project (IODP expedition 313): Untangling the record of global and local sea-level changes - Mountain, G.; Proust, J.-N. (Scientific Drilling, 2010)
cited By 15

The last glacial-interglacial cycle in Lake Ohrid (Macedonia/Albania): Testing diatom response to climate - Reed, J.M.; Cvetkoska, A.; Levkov, Z.; Vogel, H.; Wagner, B. (Biogeosciences, 2010)
Lake Ohrid is a site of global importance for palaeoclimate research. This study presents results of diatom analysis of a ca. 136 ka sequence, Co1202, from the northeast of the lake basin. It offers the opportunity to test diatom response across two glacial-interglacial transitions and within the Last Glacial, while setting up taxonomic protocols for future research. The results are outstanding in demonstrating the sensitivity of diatoms to climate change, providing proxy evidence for temperature change marked by glacial-interglacial shifts between the dominant planktonic taxa, Cyclotella fottii and C. ocellata, and exact correlation with geochemical proxies to mark the start of the Last Interglacial at ca. 130 ka. Importantly, diatoms show much stronger evidence in this site for warming during MIS3 than recorded in other productivity-related proxies, peaking at ca. 39 ka, prior to the extreme conditions of the Last Glacial maximum. In the light of the observed patterns, and from the results of analysis of early Holocene sediments from a second core, Lz1120, the lack of a response to Late Glacial and early Holocene warming from ca. 14.7-6.9 ka suggests the Co1202 sequence may be compromised during this phase. After ca. 7.4 ka, there is evidence for enhanced nutrient enrichment compared to the Last Interglacial, followed by a post-Medieval loss of diversity which is consistent with cooling, but not definitive. Taxonomically, morphological variability in C. fottii shows no clear trends linked to climate, but an intriguing change in central area morphology occurs after ca. 48.7 ka, coincident with a tephra layer. In contrast, C. ocellata shows morphological variation in the number of ocelli between interglacials, suggesting climatically-forced variation or evolutionary selection pressure. The application of a simple dissolution index does not track preservation quality very effectively, underlining the importance of diatom accumulation data in future studies. © 2010 Author(s).
Keywords: Albania; Lake Ohrid; Macedonia [Southern Europe]; Bacillariophyta; Cyclotella; Cyclotella ocellata; climate change; diatom; glacial-interglacial cycle; Holocene; Last Glacial; morphology; nutrient enrichment; paleoclimate; taxonomy; tephra

The great oxidation event recorded in Paleoproterozoic rocks from Fennoscandia - Melezhik, Victor A; Lepland, Aivo; Romashkin, Alexander E; Rychanchik, Dmitry V; Mesli, Melanie; Finne, RE; Conze, Ronald; et al. (Scientific Drilling, 2010)

The distribution of methylated-2-methyltrimethyltride-cylchromans and geochemical implication in Nenjiang Formation of the Late Cretaceous from Songliao Basin - Wang, L; Song, ZG (Geochimica, 2010)

The convincing identification of terrestrial meteorite impact structures: What works, what doesn't, and why - French, B.M.; Koeberl, C. (Earth-Science Reviews, 2010)
In the geological sciences it has only recently been recognized how important the process of impact cratering is on a planetary scale, where it is commonly the most important surface-modifying process. On the Moon and other planetary bodies that lack an appreciable atmosphere, meteorite impact craters are well preserved, and they can commonly be recognized from morphological characteristics, but on Earth complications arise as a consequence of the weathering, obliteration, deformation, or burial of impact craters and the projectiles that formed them. These problems made it necessary to develop diagnostic criteria for the identification and confirmation of impact structures on Earth. Diagnostic evidence for impact events is often present in the target rocks that were affected by the impact. The conditions of impact produce an unusual group of melted, shocked, and brecciated rocks, some of which fill the resulting crater, and others which are transported, in some cases to considerable distances from the source crater. Only the presence of diagnostic shock-metamorphic effects and, in some cases, the discovery of meteorites, or traces thereof, is generally accepted as unambiguous evidence for an impact origin. Shock deformation can be expressed in macroscopic form (shatter cones) or in microscopic forms (e.g., distinctive planar deformation features [PDFs] in quartz). In nature, shock-metamorphic effects are uniquely characteristic of shock levels associated with hypervelocity impact. The same two criteria (shock-metamorphic effects or traces of the impacting meteorite) apply to distal impact ejecta layers, and their presence confirms that materials found in such layers originated in an impact event at a possibly still unknown location. As of 2009 about 175 impact structures have been identified on Earth based on these criteria. A wide variety of shock-metamorphic effects has been identified, with the best diagnostic indicators for shock metamorphism being features that can be studied easily by using the polarizing microscope. These include specific planar microdeformation features (planar fractures [PFs], PDFs), isotropization (e.g., formation of diaplectic glasses), and phase changes (high pressure phases; melting). The present review provides a detailed discussion of shock effects and geochemical tracers that can be used for the unambiguous identification of impact structures, as well as an overview of doubtful criteria or ambiguous lines of evidence that have erroneously been applied in the past. © 2009 Elsevier B.V. All rights reserved.
cited By 369

Testing the spatial and temporal framework of speciation in an ancient lake species flock: The leech genus Dina (Hirudinea: Erpobdellidae) in Lake Ohrid - Trajanovski, S.; Albrecht, C.; Schreiber, K.; Schulthei{s, R.; Stadler, T.; Benke, M.; Wilke, T. (Biogeosciences, 2010)
Ancient Lake Ohrid on the Balkan Peninsula is considered to be the oldest ancient lake in Europe with a suggested Plio-/Pleistocene age. Its exact geological age, however, remains unknown. Therefore, molecular clock data of Lake Ohrid biota may serve as an independent constraint of available geological data, and may thus help to refine age estimates. Such evolutionary data may also help unravel potential biotic and abiotic factors that promote speciation events. Here, mitochondrial sequencing data of one of the largest groups of endemic taxa in the Ohrid watershed, the leech genus Dina, is used to test whether it represents an ancient lake species flock, to study the role of potential horizontal and vertical barriers in the watershed for evolutionary events, to estimate the onset of diversification in this group based on molecular clock analyses, and to compare this data with data from other endemic species for providing an approximate time frame for the origin of Lake Ohrid. Based on the criteria speciosity, monophyly and endemicity, it can be concluded that Dina spp. from the Ohrid watershed, indeed, represents an ancient lake species flock. Lineage sorting of its species, however, does not seem to be complete and/or hybridization may occur. Analyses of population structures of Dina spp. in the Ohrid watershed indicate a horizontal zonation of haplotypes from spring and lake populations, corroborating the role of lake-side springs, particularly the southern feeder springs, for evolutionary processes in endemic Ohrid taxa. Vertical differentiation of lake taxa, however, appears to be limited, though differences between populations from the littoral and the profundal are apparent. Molecular clock analyses indicate that the most recent common ancestor of extant species of this flock is approximately 1.99 ± 0.83 million years (Ma) old, whereas the split of the Ohrid Dina flock from a potential sister taxon outside the lake is estimated at 8.30 ± 3.60 Ma. Comparisons with other groups of endemic Ohrid species indicated that in all cases, diversification within the watershed started ≤2 Ma ago. Thus, this estimate may provide information on a minimum age for the origin of Lake Ohrid. Maximum ages are less consistent and generally less reliable. But cautiously, a maximum age of 3 Ma is suggested. Interestingly, this time frame of approximately 2-3 Ma ago for the origin of Lake Ohrid, generated based on genetic data, well fits the time frame most often used in the literature by geologists. © Author(s) 2010.
Keywords: Balkans; Lake Ohrid; Dina; Erpobdellidae; Hirudinea; Hirudinida; biotic factor; endemic species; geological record; hybridization; leech; molecular analysis; paleobiogeography; Pleistocene; Pliocene; population structure; spatial analysis; speciation (biology); watershed

Site selected for colorado plateau coring - Geissman, J.W.; Olsen, P.E.; Kent, D.V. (Eos, 2010)
cited By 0
Keywords: conference proceeding; plateau; site selection; Colorado; United States

Tephrostratigraphy and tephrochronology of lakes Ohrid and Prespa, Balkans - Sulpizio, R.; Zanchetta, G.; D'Orazio, M.; Vogel, H.; Wagner, B. (Biogeosciences, 2010)
Four cores from Balkans lakes Ohrid and Prespa were examined for recognition of tephra layers and cryptotephras, and the results presented along with the review of data from other two already published cores from Lake Ohrid. The six cores provide a previously unrealised tephrostratigraphic framework of the two lakes, and provide a new tephrostratigraphic profile (composite) for the Balkans, which spans from the end of the Middle Pleistocene to the AD 472. A total of 12 tephra layers and cryptotephras were recognised in the cores. One is of Middle Pleistocene age (131 ka) and correlated to the marine tephra layer P-11 from Pantelleria Island. Eight volcanic layers are Upper Pleistocene in age, and encompass the period between ca. 107 ka and ca. 31 ka. This interval contains some of the main regional volcanic markers of the central Mediterranean area, including X-6, X-5, Y-5 and Y-3 tephra layers. The other layers of this interval have been related to the marine tephra layers C20, Y-6 and C10, while one was for the first time recognised in distal areas and correlated to the Taurano eruption of probable Vesuvian origin. Three cryptotephras were of Holocene age. Two of which have been correlated to Mercato and AD 472 eruptions of Somma-Vesuvius, while the third has been correlated to the FL eruption from Mount Etna. These recognitions provide a link of the Ohrid and Prespa lacustrine successions to other archives of the central Mediterranean area, like south Adriatic, Ionian, and south Tyrrhenian seas, lakes of southern Italy (Lago Grande di Monticchio, Pantano di San Gregorio Magno and Lago di Pergusa) and Balkans (Lake Shkodra). © 2010 Author(s).
Keywords: Italy; Lake Mikri Prespa; Lake Ohrid; Pantelleria; Sicily; Trapani; data set; Holocene; Pleistocene; stratigraphy; succession; tephrochronology; volcanic eruption

Tectonostratigraphic units and stratigraphic sequences of the nonmarine Songliao basin, northeast China - Zhi-qiang, F.; Cheng-zao, J.; Xi-nong, X.; Shun, Z.; Zi-hui, F.; Cross, T.A. (Basin Research, 2010)
Through tectonostratigraphic analysis of the nonmarine, intracontinental Songliao basin in northeast China, four episodes of deformation are recognized: mantle upwelling, rift, postrift thermal subsidence and structural inversion. The episodes are related to regional geodynamics and plate motions. Each episode is associated with a specific stratigraphic signature. The first period of deformation occurred during the Middle and Late Jurassic when asthenospheric upwelling heated, thinned and stretched the lithosphere. These events may have been caused by the narrowing of the Okhotsk Sea through subduction. This deformation is characterized by doming, extension, widespread volcanism and intrusion, and erosion. Volcanics interfinger with alluvial fan and alluvial plain facies systems tracts. The second rifting episode began in the latest Jurassic and continued into the Early Cretaceous. It resulted in the formation of a large number of isolated, NNE-trending fault blocks of 'basin-and-range' style. Rifting may have been caused by the formation and subduction of the Izanagi and Pacific Plates. Coal-bearing fluvial, floodplain, lacustrine and fan-delta strata and widespread volcanic rocks filled the fault-block basins. Volcanic strata hundreds to several thousand meters thick in the Huoshiling and Yingcheng Formations record multiple intrusive events during the rifting stage in the basin. These events were concurrent with episodes of intrusion and volcanic eruption in northeast China. The third phase of regional postrift deformation and subsidence, which began with the Lower Cretaceous Denglouku Formation, was caused by lithospheric cooling and extension, modulated by multiple compressional events. Subsidence in the Songliao basin permitted accumulation of thick postrift deposits, in contrast with other Cretaceous basins in Mongolia and northeast Asia. Three compressional episodes, which episodically interrupted the long-term cooling subsidence, originated from development of the Okhotsk suture and subduction of the Pacific plate. In the Early Cretaceous, pronounced compression originated from closure of Okhotsk Sea, forming the mountain ranges of Daxinganling, which provided sediment to the northern part of the basin. In the Late Cretaceous, the intensity of compression from the Pacific margin increased through time, causing westward migration of depocentres and uplift in the east until the end of Cretaceous. Postrift strata, typically 3000-4000 m thick with a maximum thickness of 6000 m, extend beyond the rift blocks and onlap the basin margins to form a large uniform basin. Early thermal subsidence strata include alluvial fan, fluvial, floodplain, shallow lacustrine and delta facies tracts, overlain by large deltaic and lacustrine facies. Late postrift environments featured by large lakes in the basin centre rimmed by delta, fluvial and floodplain environments. Reflection seismic profiles show that strong structural inversion, including folding and uplift, began at the end of the Nenjiang Formation and culminated at the end of the Cretaceous. The main compressional stress field changed from NW to NWW at the end of the Cretaceous, which caused changes in the direction of folding. During the rifting stage, several sets of gas-bearing reservoirs formed in association with coal-bearing source rocks in fluvial and deltaic strata with reservoir-quality volcanics and fluvial and fan-delta sandstone. Thick, widespread mudstone deposited in deep lakes during the postrift stage contains abundant organic matter, and is an important source rock and regional cap rock. Good reservoirs occur in deltaic and fluvial strata. Because of the episodic compressional events that alternately caused subsidence and uplift, reservoirs are sandwiched between source rocks, providing direct fluid communication from source to reservoir. © 2009 The Authors. Journal Compilation © Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.
cited By 345
Keywords: alluvial fan; asthenosphere; Cretaceous; deformation mechanism; depocenter; extension; fan delta; floodplain; geodynamics; hydrocarbon reservoir; Jurassic; lacustrine deposit; lithostratigraphy; plate motion; rifting; sediment thickness; sedimentary sequence; seismic reflection; subduction; subsidence; systems tract; tectonostratigraphy; temperature effect; upwelling; volcanism; China; Pacific Ocean; Sea of Okhotsk; Songliao Basin

Target and impact deposits at Rochechouart impact structure, France - Lambert, P. (Special Paper of the Geological Society of America, 2010)
The 200 Ma, 24-km-diameter Rochechouart impact structure was formed in granitic intrusive and metamorphic rocks of Variscan age (400-300 Ma) close to the margin of the Mesozoic sea. Fractured basement and autochthonous breccias form a several-decameter-thick semicontinuous zone over an 18-20-km-diameter zone. Impact melt rocks, suevite, and polymict lithic breccia are spread over an ∼15 km inner zone, forming a centro-symmetric deposit inclined 0.6°N. No topographic expression of the central uplift exists. The crater floor is at the same elevation (∼±50 m) over a zone at least 20 km in diameter, corresponding to the central part of the original crater. The pre-erosional diameter of the crater is probably larger than previously thought and possibly reached 40-50 km. The structure appears much less eroded than previously thought, as the sequence of crater fill is complete as exposed near Chassenon. The suevite in Chassenon is capped by an ash-like horizontal deposit of very glass-poor, fine-grained, lithic debris derived from basement rocks. Material with similar grain size and composition is observed in centimeter-to meter-thick multilayered glassbearing intercalations (dikes) cutting through the suevite. The integrity of the Chassenon sequence strikingly contrasts with the age and morphology of the structure, implying that a rapid and thick sedimentary deposit has covered the crater to protect it from erosion. The impactoclastic top deposit also firmly constrains the thickness and volume of the initial crater fill, which appear extremely depleted (by a factor of 5 or more) compared with similar-sized impact structures and model-based calculations. This anomaly remains unexplained. All the impactites, including the glass-poor and glass-free impactites, are characterized by a prominent K-metasomatism signifying pronounced postimpact hydrothermal activity. Exposed in isolated occurrences from the center to the periphery of the inner 15-km-diameter zone, impact melt rocks are extremely unlikely to have formed a continuous sheet. They display a large variety of textures, grading from pure melt rock into basal suevite, which are distinct in composition, texture, and setting from the main suevite body forming the top of the impact deposit. Heterogeneity and relative inefficiency in mixing are characteristic of the whole impact deposit, resulting in heterogeneous melts at the scale of hand specimens, but also at the kilometer scale, as suggested by close ties between the composition of melt-bearing rocks and the subjacent target rocks.. © 2010 The Geological Society of America. All rights reserved.
cited By 21

Summary of physical properties measured at several boreholes penetrating through the Chelungpu fault in central Taiwan - Wang, J.-H. (Terrestrial, Atmospheric and Oceanic Sciences, 2010)
On 20 September 1999, the Ms 7.6 Chi-Chi earthquake ruptured the Chelungpu fault in central Taiwan. After the earthquake, several boreholes of different depths were drilled. Those boreholes penetrated the fault plane. The physical (mechanical, thermal, hydraulic, electric, and magnetic) parameters were measured either on the core samples or through well-loggings. Results are significant for studies of the Chelungpu fault. However, the measured results are published in different articles and reports. It is not convenient for the earth scientists to take advantage of those results. Hence, those results are compiled and described in this paper. In addition, the correlations among a few parameters are also reported.
cited By 4
Keywords: borehole; Chi-Chi earthquake 1999; earthquake magnitude; fault plane; physical property; rupture; well logging; Taiwan

Stress-dependence of the permeability and porosity of sandstone and shale from TCDP Hole-A - Dong, J.-J.; Hsu, J.-Y.; Wu, W.-J.; Shimamoto, T.; Hung, J.-H.; Yeh, E.-C.; Wu, Y.-H.; Sone, H. (International Journal of Rock Mechanics and Mining Sciences, 2010)
We utilize an integrated permeability and porosity measurement system to measure the stress dependent permeability and porosity of Pliocene to Pleistocene sedimentary rocks from a 2000m borehole. Experiments were conducted by first gradually increasing the confining pressure from 3 to 120MPa and then subsequently reducing it back to 3MPa. The permeability of the sandstone remained within a narrow range (10-14-10-13m2). The permeability of the shale was more sensitive to the effective confining pressure (varying by two to three orders of magnitude) than the sandstone, possibly due to the existence of microcracks in the shale. Meanwhile, the sandstone and shale showed a similar sensitivity of porosity to effective pressure, whereby porosity was reduced by about 10-20% when the confining pressure was increased from 3 to 120MPa. The experimental results indicate that the fit of the models to the data points can be improved by using a power law instead of an exponential relationship. To extrapolate the permeability or porosity under larger confining pressure (e.g. 300MPa) using a straight line in a log-log plot might induce unreasonable error, but might be adequate to predict the stress dependent permeability or porosity within the experimental stress range. Part of the permeability and porosity decrease observed during loading is irreversible during unloading. © 2010 Elsevier Ltd.
cited By 385
Keywords: Digital storage; Mechanical permeability; Microcracks; Porosity; Road construction; Rock pressure; Sandstone; Unloading; Confining pressures; Effective pressure; Log-log plots; Permeability and porosities; Stress dependence; Stress history; Stress-dependent; Three orders of magnitude; Shale

Stress field of the earth's crust - Zang, A.; Stephansson, O. (Stress Field of the Earth's Crust, 2010)
This book about rock stress is suitable for students in geosciences and rock engineering, who need to broaden their horizons about the Stress Field of the Earth?s Crust. The book covers the topic so that geosciences students will be able to grasp the Cauchy Stress Principle without fear of matrix transformations in an exercise. Students interested in mathematics, physics and engineering will learn how strain gauges are used to obtain in-situ stress by the overcoring method. Leading edge technology in determining rock stress like quadruple packer and the Kaiser effect are presented together with classical methods like hydraulic fracturing. Borehole techniques (breakouts) and core-based methods (anelastic strain recovery) are illustrated. With respect to stress data, we choose to present the scientific ultra-deep drilling project KTB (Germany), the excavation for nuclear waste disposal at Olkiluoto (Finland) and the drilling into a seismic active fault zone at SAFOD (USA). Stress compilations viewed by the World Stress Map project are presented and interpreted in terms of plate tectonics. © Springer Science+Business Media B.V. 2010.
cited By 343

Stratigraphic analysis of lake level fluctuations in Lake Ohrid: An integration of high resolution hydro-acoustic data and sediment cores - Lindhorst, K.; Vogel, H.; Krastel, S.; Wagner, B.; Hilgers, A.; Zander, A.; Schwenk, T.; Wessels, M.; Daut, G. (Biogeosciences, 2010)
Ancient Lake Ohrid is a steep-sided, oligotrophic, karst lake that was tectonically formed most likely within the Pliocene and often referred to as a hotspot of endemic biodiversity. This study aims on tracing significant lake level fluctuations at Lake Ohrid using high-resolution acoustic data in combination with lithological, geochemical, and chronological information from two sediment cores recovered from sub-aquatic terrace levels at ca. 32 and 60 m water depth. According to our data, significant lake level fluctuations with prominent lowstands of ca. 60 and 35 m below the present water level occurred during Marine Isotope Stage (MIS) 6 and MIS 5, respectively. The effect of these lowstands on biodiversity in most coastal parts of the lake is negligible, due to only small changes in lake surface area, coastline, and habitat. In contrast, biodiversity in shallower areas was more severely affected due to disconnection of today sub-lacustrine springs from the main water body. Multichannel seismic data from deeper parts of the lake clearly image several clinoform structures stacked on top of each other. These stacked clinoforms indicate significantly lower lake levels prior to MIS 6 and a stepwise rise of water level with intermittent stillstands since its existence as water-filled body, which might have caused enhanced expansion of endemic species within Lake Ohrid. © Author(s) 2010.
Keywords: Lake Ohrid; acoustic data; biodiversity; chronology; coastal zone; endemic species; geochemical method; habitat type; karst; lacustrine deposit; lithology; oligotrophic environment; paleoenvironment; Pliocene; resolution; sediment core; seismic data; stratigraphy; water depth; water level

Spatial variability of recent sedimentation in Lake Ohrid (Albania/Macedonia) - Vogel, H.; Wessels, M.; Albrecht, C.; Stich, H.-B.; Wagner, B. (Biogeosciences, 2010)
Lake Ohrid is likely of Pliocene age and thus commonly referred to as the oldest existing lake in Europe. In this study spatial variability of recent sediment composition is assessed using >50 basin wide distributed surface sediment samples. Analysis of biogeochemical bulk parameters, selected metals, pigment concentrations as well as grain size distributions revealed a significant spatial heterogeneity in surface sediment composition. It implies that sedimentation in Lake Ohrid is controlled by an interaction of multiple natural and anthropogenic factors and processes. Major factors controlling surface sediment composition are related to differences in geological catchment characteristics, anthropogenic land use, and a counterclockwise rotating surface water current. In some instances processes controlling sediment composition also seem to impact distribution patterns of biodiversity, which suggests a common interaction of processes responsible for both patterns.
Keywords: Lake Ohrid; anthropogenic source; assessment method; biodiversity; biogeochemistry; catchment; chemical composition; concentration (composition); grain size; heterogeneity; lacustrine deposit; land use; metal; pigment; Pliocene; sedimentation; spatial variation; surficial sediment

Spatial pattern of modern sedimentation rate of Qinghai Lake and a preliminary estimate of the sediment flux - Xu, Hai; Liu, Xiao Yan; An, Zhi Sheng; Hou, Zhao Hua; Dong, Ji Bao; Liu, Bin (Chinese Science Bulletin, 2010)
We investigated the spatiotemporal distribution of 137Cs radioactivity in surface sediment of Qinghai Lake, and developed the spatial pattern of sedimentation rate. The 137Cs inventory is higher near the estuary/bank area, but lower at the central lake. On the other hand, the average 137Cs activity is lower near the estuary/bank area, but higher at the central lake. The mass accumulation rate (MAR) and the fluxes and contents of the terrestrial detritus (e.g. SiO2, Fe2O3, and Ti) are higher near the estuary/bank area, but lower at the central lake. The chemical/biogenic deposits (e.g. the autogenic carbonates) take up higher fractions at the central lake. These suggest that the spatial pattern of recent sedimentation rate is dominated by the deposition of terrestrial detritus. The average MAR (0.0337g cm-2a-1) was estimated based on those of different cores of Qinghai Lake and was verified by a Ca mass-balance method. The fluxes of total lake sediments, terrestrial detritus, and direct atmospheric deposits were also estimated. © Science China Press and Springer-Verlag Berlin Heidelberg 2009.

Spatial and temporal variations of Rb/Sr ratios of the bulk surface sediments in Lake Qinghai - Xu, Hai; Liu, Bin; Wu, Feng (Geochemical Transactions, 2010)
The Rb/Sr ratios of lake sediments have been suggested as indicators of weathering intensity by increasing work. However, the geochemistry of Rb/Sr ratios of lake sediments is variable between different lakes. In this study, we investigated the spatial and temporal patterns of Rb/Sr ratios, as well as those of other major elements in surface sediments of Lake Qinghai. We find that the spatial pattern of Rb/Sr ratios of the bulk sediments correlates well with that of the mass accumulation rate, and those of the terrigenous fractions, e.g., SiO2, Ti, and Fe. The temporal variations of Rb/Sr ratios also synchronize with those of SiO2, Ti, and Fe of each individual core. These suggest that Rb/Sr ratios of the surface sediments are closely related to terrigenous input from the catchment. Two out of eight cores show similar trends between Rb/Sr ratios and precipitation indices on decadal scales; however, the other cores do not show such relationship. The result of this study suggests that physical weathering and chemical weathering in Lake Qinghai catchment have opposite influence on Rb/Sr ratios of the bulk sediments, and they compete in dominating the Rb/Sr ratios of lake sediments on different spatial and temporal scales. Therefore, it is necessary to study the geochemistry of Rb/Sr ratio of lake sediments (especially that on short term timescales) particularly before it is used as an indicator of weathering intensity of the catchment. © 2010 Xu et al; licensee BioMed Central Ltd.
Keywords: China; Qinghai; Qinghai Lake; accumulation rate; catchment; lacustrine deposit; rubidium; sediment chemistry; spatial variation; strontium; surficial sediment; temporal variation; terrigenous deposit; weathering

Southern hemispheric westerlies control the spatial distribution of modern sediments in Laguna Potrok Aike, Argentina - Kastner, Stephanie; Ohlendorf, Christian; Haberzettl, Torsten; L{ucke, Andreas; Mayr, Christoph; Maidana, Nora I.; Sch{abitz, Frank; Zolitschka, Bernd (Journal of Paleolimnology, 2010)
We studied the internal lake processes that control the spatial distribution and characteristics of modern sediments at the ICDP (International Continental Scientific Drilling Program) deep drilling site in Laguna Potrok Aike, southern Patagonia, Argentina. Sediment distribution patterns were investigated using a dense grid of 63 gravity cores taken throughout the lake basin and 40 additional shoreline samples. Analysis of the surficial sediment distribution points to distinct internal depositional dynamics induced by wind-driven lake internal currents. Distribution maps illustrate that the spatial characteristics of analysed variables are linked to high erosional wave activity. Persistent wave action and littoral erosion along all shores, especially the eastern shore, is caused by prevailing Southern Hemispheric Westerlies. Several sediment variables (grain size, benthic diatoms, total inorganic carbon and calcium) indicate re-suspension of littoral sediment followed by re-distribution to profundal accumulation areas near the eastern shore. Variations within the catchment influence sediment characteristics in the north-eastern bay. That area is characterized by different mineralogical and sedimentological conditions as well as greater accumulation of pollen, inorganic carbon and diatoms. These findings are related to the influence of episodic inflow into this bay. Spatial differences in stable isotope values throughout the lake suggest that ephemeral tributaries around the lake basin may also contribute to the detected spatial sediment variations. © 2010 Springer Science+Business Media B.V.
Keywords: Argentina; Laguna Potrok Aike; Patagonia; Santa Cruz [Argentina]; Bacillariophyta; bioaccumulation; calcium; catchment; deep drilling; diatom; grain size; gravity; inorganic carbon; intertidal environment; lacustrine deposit; microfossil; mineralogy; pollen; sediment; sediment chemistry; sedimentology; shoreline; Southern Hemisphere; spatial distribution; stable isotope; surficial sediment; wave action

Sources and flux of trace elements in river water collected from the Lake Qinghai catchment, NE Tibetan Plateau - Jin, Zhangdong; You, Chen-Feng; Yu, Tsai-Luen; Wang, Bo-Shian (Applied Geochemistry, 2010)
River waters play a significant role in supplying naturally- and anthropogenically-derived materials to Lake Qinghai, northeastern Tibetan Plateau. To define the sources and controlling processes for river water chemistry within the Lake Qinghai catchment, high precision ICP-MS trace element concentrations were measured in water samples collected from the Buha River weekly in 2007, and from other major rivers in the post-monsoon (late October 2006) and monsoon (late July 2007) seasons. The distributions of trace elements vary in time and space with distinct seasonal patterns. The primary flux in the Buha River is higher TDS and dissolved Al, B, Cr, Li, Mo, Rb, Sr and U during springtime than those during other seasons and is attributed to the inputs derived from both rock weathering and atmospheric processes. Among these elements, the fluxes of dissolved Cr, B and Rb are strongly influenced by eolian dust input. The fluxes of dissolved Li, Mo, Sr and U are also influenced by weathering processes, reflecting the sensitivity of chemical weathering to monsoon conditions. The anthropogenic sources appear to be the dominant contribution to potentially harmful metals (Ni, Cu, Co, Zn and Pb), with high fluxes at onset of the main discharge pulses due, at least partially, to a runoff washout effect. For other major rivers, except for Ba, concentrations of trace elements are higher in the monsoon than in the post-monsoon season. A total of 38.5 ± 3.1 tons of potentially harmful elements are transported into the lake annually, despite human activities within the catchment being limited. Nearly all river water samples contain dissolved trace elements below the World Health Organization guidelines for drinking water, with the exception of As and B in the Daotang River water samples collected in late July probably mobilized from underlying lacustrine sediments. © 2010 Elsevier Ltd.
Keywords: Buha River; China; Qinghai; Qinghai Lake; Agricultural chemicals; Atmospheric thermodynamics; Barium; Catchments; Chromium; Copper; Dissolution; Inductively coupled plasma mass spectrometry; Lakes; Lead; Molybdenum; Potable water; Rivers; Rubidium; Runoff; Sediments; Soil mechanics; Weathering; Zinc; Anthropogenic sources; Atmospheric process; Chemical weathering; Controlling process; Derived materials; Discharge pulse; Dominant contributions; Drinking water; Eolian dust; High flux; High precision; Human activities; Lacustrine sediments; Monsoon conditions; Post-monsoon; River water; River water samples; Rock weathering; Seasonal patterns; Tibetan Plateau; Time and space; Trace element concentrations; Water samples; Weathering process; World Health Organization; aluminum; anthropogenic source; catchment; chemical weathering; chromium; discharge; drinking water; human activity; lacustrine deposit; monsoon; plateau; pollutant source; river water; water chemistry; World Health Organization; zinc; Trace elements

Slip-rate variability and distributed deformation in the Marmara Sea fault system - Hergert, T.; Heidbach, O. (Nature Geoscience, 2010)
The slip rate along a fault controls the accumulation of strain that is eventually released during an earthquake. Along a 150-km-long stretch of the North Anatolian fault near Istanbul, Turkey, strain has been building up 2 since the last large earthquake in 1766. Estimates of the geodetic slip rates along the main Marmara fault vary widely, ranging between 17 and 27.9 mm yr-1 (refs 2-5). This slip rate is difficult to quantify because of the lack of satellite observations offshore and the complexity of the submarine fault system that includes the main Marmara fault2,6,7. Here we estimate the right-lateral slip rate on the main Marmara fault using a three-dimensional geomechanical model that incorporates these structural complexities. From our simulations we infer slip rates between 12.8 and 17.8 mm yr-1; our estimates are smaller and more variable than previous results, primarily because of slip partitioning and internal deformation. Our model results reconcile geodetic observations and geological fault slip rates8-10, which had been considered conflicting previously. We suggest that the inferred variability in slip rate on the main Marmara fault favours segmented release of seismic moment during consecutive events over the failure of the whole seismic gap in one large earthquake. © 2010 Macmillan Publishers Limited. All rights reserved.
cited By 72
Keywords: accumulation rate; analytical method; earthquake; fault displacement; satellite imagery; slip rate; three-dimensional modeling; Sea of Marmara; Turkey

Mudstone lithofacies in the Cretaceous Qingshankou Formation of Well Sk I, Songliao Basin, Northeastern China - Gu, J; Huang, YJ; Wang, C (China Mining Magazine, 2010)

Nanocoatings of clay and creep of the San Andreas fault at Parkfield, California - Schleicher, A.M.; Pluijm, B.A.; Warr, L.N. (Geology, 2010)
Mudrock samples were investigated from two fault zones at 3066 m and 3296 m measured depth (MD) located outside and within the main damage zone of the San Andreas Fault Observatory at Depth (SAFOD) drillhole at Parkfield, California. All studied fault rocks show features typical of those reported across creep zones with variably spaced and interconnected networks of polished displacement surfaces coated by abundant polished films and occasional striations. Electron microscopy and X-ray diffraction study of the surfaces reveal the occurrence of neocrystallized thin film clay coatings containing illite-smectite (I-S) and chlorite-smectite (C-S) minerals. 40Ar/39Ar dating of the illitic mix-layered coatings demonstrated Miocene to Pliocene crystallization and revealed an older fault strand (8 ± 1.3 Ma) at 3066 m MD, and a probably younger fault strand (4 ± 4.9 Ma) at 3296 m MD. Today, the younger strand is the site of active creep behavior, reflecting a possible (re)activation of these clay-weakened zones. We propose that the majority of slow fault creep is controlled by the high density of thin ( <100 nm thick) nanocoatings on fracture surfaces, which are sufficiently smectite-rich and interconnected at low angles to accommodate slip with minimal breakage of stronger matrix clasts. Displacements occur by frictional slip along particle surfaces and hydrated smectitic phases, in combination with intracrystalline deformation of the clay lattice, associated with extensive mineral dissolution, mass transfer, and residual precipitation of expandable layers. The localized concentration of smectite in both I-S and C-S minerals contributes to fault weakening, with fracturing and fluid infiltration creating new nucleation sites for neomineralization on displacement surfaces during continued faulting. The role of newly grown, ultrathin, hydrous clay coatings contrasts with previously proposed scenarios of reworked talc and/or serpentine phases as an explanation for weak fault and creep behavior at these depths. © 2010 Geological Society of America.
cited By 123
Keywords: California; Clay coating; Creep behaviors; Damage zones; Drill hole; Fault creep; Fault rock; Fault strands; Fault zone; Fracture surfaces; Frictional slip; High density; Illite-smectite; Interconnected network; Layered coatings; matrix; Measured depths; Mineral dissolution; Miocene; Nano-coatings; Nucleation sites; Older faults; Particle surface; Pliocene; San Andreas Fault; Smectites; Ultra-thin; X-ray diffraction studies; Coatings; Creep; Dissolution; Hydrates; Minerals; Precipitation (chemical); Serpentine; Silicate minerals; Structural geology; X ray diffraction; Clay minerals; argon isotope; clay mineral; creep; deformation; displacement; fault zone; illite; mudstone; San Andreas Fault; smectite; California; Parkfield; United States

Migration-based location of seismicity recorded with an array installed in the main hole of the San Andreas Fault Observatory at Depth (SAFOD) - Rentsch, S.; Buske, S.; Gutjahr, S.; Kummerow, J.; Shapiro, S.A. (Geophysical Journal International, 2010)
We present the principles of a recently developed event location procedure and its application to seismicity recorded in the main borehole of the San Andreas Fault Observatory at Depth (SAFOD). The basic idea of the location approach is the backpropagation of the recorded wavefield along rays using a Gaussian-beam-type weighting factor. In the case of a sufficient number of receivers, the intersection of these rays results in a distinct maximum at the corresponding hypocentre location. We have applied this technique to data recorded with an 80-level three-component (3C) receiver array in the SAFOD main hole and we have located a number of events in the vicinity of the fault system. A modification of the location algorithm also allowed the precise location of one of the so-called target events, which are the subject of recent drilling activities as well as ongoing research at SAFOD. We summarize the principles of the location method and the performed processing steps, provide estimates of the uncertainties for the target event location and test the robustness of the location using six different 3-D velocity models. Furthermore, we discuss the event locations in comparison with borehole logging data and coincident seismic reflection images and we also show identified events with highly correlated waveforms. © 2010 The Authors Journal compilation © 2010 RAS.
cited By 8
Keywords: back propagation; body wave; borehole; San Andreas Fault; seismic migration; seismic reflection; seismicity; seismotectonics; spatial analysis; time series analysis; wave propagation

Amorphous material in SAFOD core samples (San Andreas Fault): Evidence for crush-origin pseudotachylytes? - Janssen, C.; Wirth, R.; Rybacki, E.; Naumann, R.; Kemnitz, H.; Wenk, H.-R.; Dresen, G. (Geophysical Research Letters, 2010)
Several types of amorphous material in ultracataclastic core samples recovered from 3194 m and 3294 m depth of the main bore hole of the San Andreas Fault Observatory at Depth are identified and described with transmission electron microscopy and scanning electron microscopy. We observed (1) amorphous material on a slickenside surface, (2) glassy bands contained in an ultracataclastic matrix and (3) amorphous rims surrounding quartz or feldspar clasts. Chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix. We suggest that all amorphous material was formed by comminution of clasts (crush-origin pseudotachylytes) rather than by melting (melt-origin pseudotachylytes). The observed amorphous phases may act as lubricating layers that reduce friction in the San Andreas Fault. Copyright 2010 by the American Geophysical Union.
cited By 53
Keywords: Adjacent matrix; Amorphous phasis; matrix; Pseudotachylytes; San Andreas Fault; Silica content; Core samples; Grinding (comminution); Oxide minerals; Quartz; Scanning electron microscopy; Silica; Silicate minerals; Transmission electron microscopy; Amorphous materials; amorphous medium; borehole; chemical analysis; clast; feldspar; melting; San Andreas Fault; silica; slickenside; transmission electron microscopy

Distribution of seismicity across strike-slip faults in California - Powers, P.M.; Jordan, T.H. (Journal of Geophysical Research: Solid Earth, 2010)
The distribution of seismicity about strike-slip faults provides measurements of fault roughness and damage zone width. In California, seismicity decays with distance from strike-slip faults according to a power law -(1 + ×2/d2)-g/2. This scaling relation holds out to a fault-normal distance × of 3?6 km and is compatible with a ?rough fault loading? model in which the inner scale d measures the half width of a volumetric damage zone and the roll-off rate g is governed by stress variations due to fault roughness. According to Dieterich and Smith?s 2-D simulations, g approximates the fractal dimension of alongstrike roughness. Near-fault seismicity is more localized on faults in northern California (NoCal, d = 60 ± 20 m, g = 1.65 ± .05) than in southern California (SoCal, d = 220 ± 40 m, g = 1.16 ± .05). The Parkfield region has a damage zone half width (d = 120 ± 30 m) consistent with the SAFOD drilling estimate; its high roll-off rate (g = 2.30 ± .25) indicates a relatively flat roughness spectrum: k-1 versus k-2 for NoCal, k-3 for SoCal. Our damage zone widths (the first direct estimates averaged over the seismogenic layer) can be interpreted in terms of an across-strike ?fault core multiplicity? that is 1 in NoCal, 2 at Parkfield, and 3 in SoCal. The localization of seismicity near individual faults correlates with cumulative offset, seismic productivity, and aseismic slip, consistent with a model in which faults originate as branched networks with broad, multicore damage zones and evolve toward more localized, lineated features with low fault core multiplicity, thinner damage zones, and less seismic coupling. Our results suggest how earthquake triggering statistics might be modified by the presence of faults. Copyright 2010 by the American Geophysical Union.
cited By 69
Keywords: earthquake trigger; normal fault; roughness; seismicity; strike-slip fault; earthquake damage; power law; California; United States; Parkfield

Distribution of Recent ostracod species in the Lake Qinghai area in northwestern China and its ecological significance - Li, Xiangzhong; Liu, Weiguo; Zhang, Ling; Sun, Zhencheng (Ecological Indicators, 2010)
In order to interpret the climate-change data using the ecological characteristics of the ostracods from the drill cores in Lake Qinghai, the distribution of Recent ostracods was studied in Lake Qinghai area. A total of 34 species belonging to the Ostracoda class of Crustacea were collected from different bodies of water in the Lake Qinghai area, and the ecological information for Recent ostracod species was studied. Among these 34 species, Cypris pubera, Eucypris dulcifons, Ilyocypris sp. 1, Ilyocypris sp. 2, Fabaeformiscandona caudata, Fabaeformiscandona hyalina, Herpetocypris reptans, Prionocypris gansenensis, Potamocypris villosa, Potamocypris smaragdina, Paralimnocythere compressa and Subulacypris sp. were first reported by us in the Lake Qinghai area. Some of the species identified exhibited cosmopolitan distributions, at least in the Holarctic region, but P. gansenensis and Ilyocypris echinata appeared to be restricted to the cold regions in northwestern China. The ecological significance of the primary ostracod species in the Lake Qinghai area was described according to the observations made during our time in the field and according to data from a number of reports. Our results indicate that the species diversity and abundance of ostracods may be related to water salinity in the Lake Qinghai area. The ecological information for ostracods can be used to distinguish different water environments and types based on the characteristics of one species or of an assemblage of several species. © 2010 Elsevier Ltd. All rights reserved.
Keywords: China; Qinghai; Qinghai Lake; Caudata; Crustacea; Eucypris; Eurycypris pubera; Fabaeformiscandona; Herpetocypris reptans; Ilyocypris; Ostracoda; Paralimnocythere; Potamocypris smaragdina; Potamocypris villosa; Prionocypris; Animals; Climate change; Core drilling; Ecology; Salinity measurement; Stream flow; Associations; Cold regions; Crustacea; Drill core; Ecological characteristics; Ecological information; Northwestern China; Ostracoda; Paleolimnology; Species diversity; Water environments; Water salinity; abundance; climate change; community composition; Holarctic Region; lake water; ostracod; population distribution; salinity; species diversity; Lakes

Discussion on Integrating borehole-breakout dimensions, strength criteria, and leak-off test results, to constrain the state of stress across the Chelungpu Fault, Taiwan - Zhang, J.; Roegiers, J.-C. (Tectonophysics, 2010)
The in-situ stress computations presented by Haimson et al. (2010) overestimated the maximum horizontal stress in the vicinity of the Chelungpu Fault, Taiwan. Our analyses from extended leak-off tests, drilling-induced tensile fractures, and Anderson's faulting theory show considerable lower values for the maximum horizontal stress. Our results suggest that closer to the ruptured fault, more SH is released, implying a strong earth crest in the shallower section, which is far away from the ruptured fault. However, it would require more detailed and intensive work in order to achieve an accurate interpretation of the in-situ stress in this region. © 2010 Elsevier B.V.
cited By 26

Developments in gas hydrates - Birchwood, R.; Dai, J.; Shelander, D.; Boswell, R.; Collett, T.; Cook, A.; Dallimore, S.; Fujii, K.; Imasato, Y.; Fukuhara, M.; Kusaka, K.; Murray, D.; et al. (Oilfield Review, 2010)
International efforts and advanced techniques are being used to characterize properties and distributions of gas hydrates, which are crystalline solids that resemble ice. The Minerals Management Service (MMS) of the US Department of the Interior has used seismic data, along with wellbore, geologic, geochemical and paleontological information, to assess large areas of the Gulf of Mexico, where pressure and temperature conditions are suitable for hydrate-stability conditions. The team members acquired and analyzed seismic data, selected drilling locations and conducted a 35-day drilling, coring and logging expedition covering several sites. A new program was initiated in 2002 from the Mallik field to conduct production testing of gas hydrates. The USGS has studied gas hydrate accumulations in the Alaska North Slope and estimates that they contain between 25.2 and 157.8 Tcf of undiscovered recoverable natural gas.
cited By 44
Keywords: Crystalline solids; Gulf of Mexico; Hydrate accumulations; Minerals management services; Pressure and temperature; Production testing; Seismic datas; Team members; Wellbore; Exploratory geochemistry; Gases; Hydration; Natural gas well drilling; Offshore oil wells; Seismic response; Seismic waves; Software testing; Well drilling; Gas hydrates

Design, manufacture, and operation of a core barrel for the Iceland Deep Drilling Project (IDDP) - Skinner, A.C.; Bowers, P.; P'orhallsson, S.; Fridleifsson, G.Ó.; Gudmundsson, H. (Scientific Drilling, 2010)
The science program of the Iceland Deep Drilling Project (IDDP) requires as much core as possible in the transition zone to supercritical and inside the supercritical zone (>374°C), in the depth interval 2400-4500 m. The spot coring system selected has a 7 1/4″ (184.15 mm) OD at 10 m length and collects a 4″ (101.6 mm) diameter core using an 8 1/2″ (215.9 mm) OD core bit. It incorporates design characteristics, materials, clearances and bearings compatible with operation of the core barrel at temperatures as high as 600°C. Special attention was given to the volume of flushing which could be applied to the core barrel and through the bit while running in and out of the borehole and while coring. In November 2008 a successful spot coring test using the new core barrel was performed at 2800 m depth in the production well RN-17 B at Reykjanes, Iceland, where the formation temperature is 322°C. A 9.3-m hydrothermally altered hyaloclastite breccia was cored with 100% core recovery, in spite of it being highly fractured. A core tube data logger was also designed and placed inside the inner barrel to monitor the effectiveness of cooling. The temperature could be maintained at 100°C while coring, but it reached 170°C for a very short period while tripping in. The effective cooling is attributed to the high flush design and a top drive being employed, which allows circulation while tripping in or out, except for the very short time when a new drill pipe connection is being made.
cited By 3
Keywords: Core barrel; Core tube data logger; Deep drilling; Design characteristics; Drill pipe connection; Formation temperature; Hydrothermally; Icelands; Inner Barrel; Production wells; Running-in; Science programs; Short periods; Spot coring; Super-critical; Transition zones; Design; Drill pipe

Cretaceous calcareous paleosols, pedogenetic characteristics and paleoenvironmental implications (in Chinese with English abstract);[白垩纪钙质古土壤的发生学特征及古环境意义] - Huang, C.; Retallack, J.; Wang, C. (Acta Pedologica Sinca, 2010)

Coniacian seismites: Structure, sequence and volcanogenic origin of Qingshankou Formation in the Cretaceous Songliao Basin - Wang, G.; Cheng, R.; Wang, P.; Gao, Y. (Acta Petrologica Sinica, 2010)
Drilling core from Chinese Continental Scientific Drilling-SK-I(s) presents four sets of deep lake seismite from the lower part of the second member to the bottom of the third member of Qingshankou Formation. Typical structures of the seismites include step micro-fault, seismic fissure bed, autoclastic brecciated structure, load structure, ball-and-pillow structure (pseudonodule), vibration-induced liquefaction structure, enterolithic structure, liquefaction sand dyke and pseudo-mud crack. All of these synsedimentary-penecontemporaneous soft-sediment deformation and absence of seismo-turbidite indicate that the seismites in Qingshankou Formation are previous soft sediment reconstruction related to earthquake. Seismites of Qingshankou Formation exhibit typical developmental pattern and sedimentary sequence of seismite. This seismic sequence consists of the lower unit of liquefaction deformation corresponding to strong earthquake and the upper unit of plastic deformation corresponding to earthquake attenuation. Mudstone with few altered glass shards and volcanic ash interlayers simultaneously developed in Qingshankou Formation from SK-I(s). Mugearite and volcanic breccia developed in well Jin6 and Jin65 and basalt developed in well Qian124 and Qian 109 during corresponding geological time of volcanic ash in SK-I(s). These four wells containing volcanic rock in Qingshankou Formation distribute along the Sunwu-Shuangliao transcrustal fault, which indicates that tectonic-volcanic activities occurred during Qingshankou period in Songliao Basin and seismites recorded earthquake activities induced by tectonic-volcanic event in deep water. Existence of tectonic-volcanic event in Qingshankou Formation suggests that fault activities and volcano eruptions should be normal phenomena during the sag stage in Songliao Basin.
cited By 10
Keywords: Faulting; Geophysics; Liquefaction; Seismology; Tectonics; Volcanoes; Qingshankou formation; Seismic sequence; Seismite; SK-I(s); Songliao basin; Volcanic event; Earthquakes; Coniacian; deep water; deformation; geological time; mudstone; Ocean Drilling Program; sedimentary sequence; seismite; synsedimentary tectonics; turbidite; volcanic ash; volcanic eruption; volcanogenic deposit; China; Songliao Basin; Coniacian

Collisional Orogeny in the Scandinavian Caledonides (COSC) - Gee, D. G.; Juhlin, C.; Pascal, C.; Robinson, P. (GFF, 2010)
The COSC project is focused on the mid Paleozoic Caledonide Orogen in Scandinavia in order to better understand orogenic processes, both in the past and in today's active mountain belts. It relates to two of ICDP's main themes – the fundamental physics of plate tectonics and heat, mass and fluid transfer through Earth's crust, and on improving interpretation of geophysical data used to determine the structure and properties of the Earth's crust. Lateral transport of Caledonian allochthons over distances of several hundreds of kilometers in the Scandes, by a combination of thrusting and ductile extrusion, is comparable to that recognized in the Himalayas. The Caledonides in Scandinavia provide special opportunities for understanding Himalayan-type orogeny and the Himalayan Orogen itself, thanks to the deep level of erosion and the paucity of superimposed post-Paleozoic deformation. The surface geology in combination with the seismic, magnetotelluric, magnetic and gravity data provide control of the geometry of the Caledonian structure, both of the allochthon and the underlying parautochthon-autochthon, and define the locations for drilling. The latter will investigate both the high-grade, ductile Caledonian nappes and the underlying allochthons and basement, with two c. 2.5 km deep boreholes, located near Åre and J{arpen in western J{amtland. The two boreholes will also provide unique information about other important aspects of the Scandinavian bedrock, including the heat flow and potential for geothermal energy, mineralization in the Seve nappes and alum shales, the uplift history of the Scandes, the Holocene paleoclimatological changes and the deep biosphere.

Climate in continental interior Asia during the longest interglacial of the past 500 000 years: The new MIS 11 records from Lake Baikal, SE Siberia - Prokopenko, A.A.; Bezrukova, E.V.; Khursevich, G.K.; Solotchina, E.P.; Kuzmin, M.I.; Tarasov, P.E. (Climate of the Past, 2010)
A synthesis of paleoclimate responses from Lake Baikal during the MIS 11 interglacial is presented based on proxy records from two drill sites 245 km apart. BDP-99 is located in vicinity of the delta of the major Baikal tributary, whereas the BDP-96 site represents hemipelagic setting distant from riverine influence. The comparison of thicknesses of interglacial intervals in these contrasting depositional settings confirms the extended ca. 33-kyr duration of the MIS 11 interglacial. The new BDP-99 diatom biostratigraphic record matches that of the BDP-96-2 holostratotype and thus allows establishing establishes robust correlation between the records on the same orbitally-tuned timescale. The first detailed MIS 11 palynological record from the BDP-99 drill core indicates the dominance of boreal conifer (taiga) forest vegetation in the Baikal region throughout the MIS 11 interglacial, since at least 424 ka till ca. 396 ka. The interval ca. 420-405 ka stands out as a conifer optimum with abundant Abies sibirica, indicative of climate significantly warmer and less continental than today. The closest Baikal analog to this type of vegetation in the history of the current Holocene interglacial is at ca. 9-7 ka. The warm conifer phase lasted for ca. 15 kyr during MIS 11 interrupted by two millennial-scale cooling episodes at ca. 411-410 and 405-404 ka. Reconstructed annual precipitation of 450- 550 mm/yr during the MIS 11 interglacial is by ca. 100mm higher than during the Holocene; regional climate was less continental with warmer mean temperatures both in summer and in winter. © Author(s) 2010.
Keywords: Lake Baikal; Russian Federation; Siberia; Abies; Abies sibirica; Bacillariophyta; Coniferophyta; biostratigraphy; boreal forest; coniferous tree; correlation; diatom; dominance; interglacial; paleoclimate; palynology; proxy climate record; regional climate; timescale; vegetation history

Carbonate sedimentation and effects of eutrophication observed at the Kališta subaquatic springs in Lake Ohrid (Macedonia) - Matter, M.; Anselmetti, F.S.; Jordanoska, B.; Wagner, B.; Wessels, M.; W{uest, A. (Biogeosciences, 2010)
To date, little is known about the role of spring waters with respect to authigenic carbonate precipitation in a shallow lacustrine setting. Lake Ohrid, located in Southeastern Europe, is a large lake fed to over 50% by karstic springs of which half enter subaquatically and influence significantly its ecology and species distribution. In order to evaluate how sedimentological processes are influenced by such shallow-water springs, the Kališta subaquatic spring area in the north west of Lake Ohrid was investigated by a sidescan sonar survey and with sediment traps and three transects of gravity short cores. Results indicate that sedimentation in the spring area is dominated by authigenic carbonate precipitation. High sedimentation rates and evidences for bio-induced precipitation processes were observed in the water column and in the sediments. Two distinct stratigraphic units characterize the shallow subsurface, both composed of carbonate silts with high carbonate contents of up to 96%, but differing in color, carbonate content and diatom content. A chronological correlation of the cores by radiocarbon dates and 137Cs activities places the transition between the two stratigraphic units after ∼1955 AD. At that time, coastal sedimentation changed drastically to significantly darker sediments with higher contents of organic matter and more abundant diatoms. This change coincides with the recent human impact of littoral eutrophication. © 2010 Author(s).
Keywords: Lake Ohrid; Bacillariophyta; carbonate; chronology; diatom; eutrophication; lacustrine deposit; littoral environment; precipitation (chemistry); radiocarbon dating; sediment core; sediment trap; sedimentation; silt; sonar; stratigraphy; water column

Calibration of the Late Triassic time scale: U-Pb zircon ages from the Chinle Formation - Mundil, Roland; Irmis, Randall B; Olsen, Paul E; Kent, Dennis V (Geochimica et Cosmochimica Acta, 2010)

Astrochronology of the late Jurassic Kimmeridge Clay (Dorset, England) and implications for Earth system processes - Huang, Chunju; Hesselbo, Stephen P. (Earth and Planetary Science Letters, 2010)
The Late Jurassic Kimmeridge Clay Formation (KCF) is an economically important, organic-rich source rock of Kimmeridgian-Early Tithonian age. The main rock types of the KCF in Dorset, UK, include grey to black laminated shale, marl, coccolithic limestone, and dolostone, which occur with an obvious cyclicity at astronomical timescales. In this study, we examine two high-resolution borehole records (Swanworth Quarry 1 and Metherhills 1) obtained as part of a Rapid Global Geological Events (RGGE) sediment drilling project. Datasets examined were total organic carbon (TOC), and borehole wall microconductivity by Formation Microscanner (FMS). Our intent is to assess the rhythmicity of the KCF with respect to the astronomical timescale, and to discuss the results with respect to other key Late Jurassic geological processes. Power spectra of the untuned data reveal a hierarchy of cycles throughout the KCF with ∼ 167 m, ∼ 40 m, 9.1 m, 3.8 m and 1.6 m wavelengths. Tuning the ∼ 40 m cycles to the 405-kyr eccentricity cycle shows the presence of all the astronomical parameters: eccentricity, obliquity, and precession index. In particular, ∼ 100-kyr and 405-kyr eccentricity cycles are strongly expressed in both records. The 405-kyr eccentricity cycle corresponds to relative sea-level changes inferred from sequence stratigraphy. Intervals with elevated TOC are associated with strong obliquity forcing. The 405-kyr-tuned duration of the lower KCF (Kimmeridgian Stage) is 3.47 Myr, and the upper KCF (early part of the Tithonian Stage, elegans to fittoni ammonite zones) is 3.32 Myr. Two other chronologies test the consistency of this age model by tuning ∼ 8-10 m cycles to 100-kyr (short eccentricity), and ∼ 3-5 m cycles to 36-kyr (Jurassic obliquity). The 'obliquity-tuned' chronology resolves an accumulation history for the KCF with a variation that strongly resembles that of Earth's orbital eccentricity predicted for 147.2 Ma to 153.8 Ma. There is evidence for significant non-deposition (up to 1 million years) in the lowermost KCF (baylei-mutabilis zones), which would indicate a Kimmeridgian/Oxfordian boundary age of 154.8 Ma. This absolute calibration allows assignment of precise numerical ages to zonal boundaries, sequence surfaces, and polarity chrons of the lower M-sequence. © 2009 Elsevier B.V. All rights reserved.
Keywords: Dorset [England]; England; United Kingdom; Ammonoidea; Astrophysics; Boreholes; Clay minerals; Offshore oil wells; Organic carbon; Tuning; Absolute calibration; Accumulation history; Borehole records; Borehole wall; Cyclicity; Cyclostratigraphy; Data sets; Dolostones; Drilling projects; Earth systems; Eccentricity cycle; Elegans; England; Geological process; High resolution; Jurassic; Kimmeridge clay formation; M sequence; Microscanner; Orbital eccentricity; Organic-rich source rock; Power-spectra; Relative sea level; Rock types; Seafloor spreading; Sequence stratigraphy; Time-scales; Total organic carbon; accumulation; astrophysics; coccolith; cyclostratigraphy; data set; dolostone; drilling; eccentricity; geochronology; Jurassic; Kimmeridgian; lamination; limestone; marl; Oxfordian; parameterization; sea level change; seafloor spreading; sequence stratigraphy; shale; source rock; timescale; Tithonian; total organic carbon; wavelength; Stratigraphy

Analysis of production data for 2007/2008 mallik gas hydrate production tests in Canada - Kurihara, M.; Sato, A.; Funatsu, K.; Ouchi, H.; Yamamoto, K.; Numasawa, M.; Ebinuma, T.; Narita, H.; Masuda, Y.; Dallimore, S.R.; Wright, F.; Ashford, D. (Society of Petroleum Engineers - International Oil and Gas Conference and Exhibition in China 2010, IOGCEC, 2010)
The methane hydrate (MH) production tests were conducted using the depressurization method in the JOGMEC/NRCan/Aurora Mallik production program in April 2007 and in March 2008. In addition to attaining the first and the only successful methane gas production to the surface from a MH reservoir by depressurization in the world, various data such as wellhead/bottomhole pressure, temperature, gas and water flow rates and the temperature along the casing measured by Distributed Temperature Sensing (DTS) systems were acquired during these tests. The flow rates of gas and water from the reservoir sand face were then estimated by the comprehensive analysis of these data. This paper clarifies the details of the estimation of gas and water flow rates based on these data, for the first time after the 2008 winter test. In 2007, a certain amount of gas and water were produced from a 12 m perforation interval in one of the major MH reservoirs at the Mallik site in Canada, by reducing the bottomhole pressure down to about 7 MPa. However, because of the irregular (on-off) pumping operations due probably to the excessive sand production, the produced gas was not directly delivered to the surface via the tubing, but was accumulated at the top of the casing. Hence, the gas production rate was calculated based on the continuously monitored bottomhole and casing head pressure. Since the produced water was injected into the aquifer located below the MH reservoir, it was impossible to directly measure the water pumping rate. The pumping rate and water production rates were accurately estimated by matching the bottomhole temperature through the numerical simulation using a wellbore model. In 2008, much larger and longer gas production was accomplished with a stepwise reduction of the bottomhole pressure down to about 4.5 MPa, preventing sands from flowing into the wellbore by the screen. In this test, both the gas and water were delivered to the surface, which enables the estimation of the gas and water flow rates from the reservoir sand face as well as liquid level in casing based on the monitored parameters. Investigating the production performances thus estimated, it was inferred what really happened in the reservoir during the tests. These insights must be beneficial for future exploration and development planning for MH resources. Copyright 2010, Society of Petroleum Engineers.
cited By 79
Keywords: Aquifers; Boreholes; Bottom hole pressure; Flow of water; Flow rate; Gases; Hydration; Hydraulics; Methane; Oil field equipment; Oil wells; Petroleum prospecting; Pumps; Sand; Software testing; Surface testing; Wellheads; Bottom-hole temperatures; Comprehensive analysis; Depressurization methods; Distributed temperature sensing systems; Exploration and development; Gas-hydrate production; Production performance; Water production rate; Gas hydrates

Aeromagnetic anomaly modeling of central zone structure and magnetic sources in the Chicxulub crater - Ortiz-Aleman, C.; Urrutia-Fucugauchi, J. (Physics of the Earth and Planetary Interiors, 2010)
The analytic signal method and forward modeling in three dimensions are applied to magnetic field data over the Chicxulub crater in order to determine and document the main magnetic anomaly sources and crater structure in the central zone. Aeromagnetic data over the structure reveal three strong, well-defined concentric patterns, with a central 40-km diameter zone of high amplitude anomalies. Magnetic anomalies are interpreted to be associated with the melt sheet, upper breccias and central uplift, which present three to four orders of magnitude contrasts with the surrounding carbonate units. The limited number of magnetic property measurements, apparent wide range in the remanent intensity and susceptibility in the upper breccias and possible yet unconstrained zones of hydrothermal systems have restricted our ability to determine the characteristics and distribution of major structural elements of the Chicxulub crater. The amplitude of the analytic signal produces maxima over magnetization contrasts, independent of the direction of magnetization. Interpretation of maxima location and depth distribution is used, in a second stage, as a priori information in the construction of an input prism assemblage magnetic configuration and its properties for three-dimensional forward modeling. Results indicate that magnetic sources extend to a radial distance of ∼45. km from the center of the structure with average depths ranging between 2 and 4. km. The magnetic anomaly sources in the central structural uplift zone are located in the range from 3.5 to 8. km depth, with dominant contributions from an apparent large body forming the basement uplift. © 2010 Elsevier B.V.
cited By 27

Diversity of laboratory-reared prokaryotes in the bottom sediments of the Akademichesky Ridge, Lake Baikal - Khanaeva, T.A.; Zemskaya, T.I.; Bel'kova, N.L.; Khlystov, O.M.; Namsaraev, B.B. (Inland Water Biology, 2010)
Microbial communities in the bottom sediments of the Akademichesky Ridge, Lake Baikal, were studied. The samples were taken by deep drilling BDP-96 (a 100-m core). Vertical distribution of the prokaryotes with different physiological characteristics was studied for the core. The phylogenetic analysis of the organotrophic laboratory-reared microorganisms revealed the clusterization of Baikal strains and species which have not been identified yet. © Pleiades Publishing, Ltd., 2010.
Keywords: Akademichesky Ridge; Lake Baikal; Russian Federation; Prokaryota; deep drilling; lacustrine deposit; microbial community; phylogenetics; physiology; prokaryote; species diversity; vertical distribution

Advances of international continental scientific drilling program - Su, D.; Yang, J. (Acta Geologica Sinica (English Edition), 2010)
It has long been a dream for mankind to enter the deep Earth to sample and investigate the structures and inner geological progresses. Until now, scientific drilling has been the unique method in our understanding of the processes and structures of the Earth. This paper try to give a brief introduction of the history, the development, the mission, the structure and management, the membership, the project development scheme of International Continental Drilling Program (ICDP). Great advances have been brought about in many fields of earth sciences by continental scientific drilling in recent years. Based on the recent publications and website materials of ICDP, this paper summarize the main developments in Climate Dynamics and Global Environments, in the Study of Impact Craters, in the GeoBiospherc, in Active Volcanic Systems, in Active Faults, in Hotspot Volcanoes, in Convergent Plate Boundaries and Collision Zones, and in Natural Resources. Special introduction on the scientific results of ICDP drilling at Mt. Unzen, Japan and the Hawaii Scientific Drilling Project (HSDP) is introduced in this paper. Fascinating discoveries such as the gouge layer of San Andreas Fault and the finding of talc in cuttings of SAFOD project are also introduced in this paper. As one of the three founding members of ICDP, China has also gained a lot of developments in continental scientific drilling; typical examples are the achievements of Chinese Continental Scientific Drilling (CCSD) and the progress of Lake Qinghai Scientific Drilling Project. The preliminary progresses . of the third approved ICDP project of China -the Chinese Cretaceous Continental Scientific Drilling Project and the development of ICDP-China are also summarized in this paper.
cited By 9
Keywords: active fault; climate change; collision zone; crater; deep drilling; hot spot; mantle plume; natural resource; San Andreas Fault; talc; China; Hawaii [United States]; Japan; Kyushu; Nagasaki [Kyushu]; Qinghai; Qinghai Lake; United States; Unzen Volcano

Advances of international continental scientific drilling program (Acta Geologica Sinica (English Edition), 2010)
It has long been a dream for mankind to enter the deep Earth to sample and investigate the structures and inner geological progresses. Until now, scientific drilling has been the unique method in our understanding of the processes and structures of the Earth. This paper try to give a brief introduction of the history, the development, the mission, the structure and management, the membership, the project development scheme of International Continental Drilling Program (ICDP). Great advances have been brought about in many fields of earth sciences by continental scientific drilling in recent years. Based on the recent publications and website materials of ICDP, this paper summarize the main developments in Climate Dynamics and Global Environments, in the Study of Impact Craters, in the GeoBiospherc, in Active Volcanic Systems, in Active Faults, in Hotspot Volcanoes, in Convergent Plate Boundaries and Collision Zones, and in Natural Resources. Special introduction on the scientific results of ICDP drilling at Mt. Unzen, Japan and the Hawaii Scientific Drilling Project (HSDP) is introduced in this paper. Fascinating discoveries such as the gouge layer of San Andreas Fault and the finding of talc in cuttings of SAFOD project are also introduced in this paper. As one of the three founding members of ICDP, China has also gained a lot of developments in continental scientific drilling; typical examples are the achievements of Chinese Continental Scientific Drilling (CCSD) and the progress of Lake Qinghai Scientific Drilling Project. The preliminary progresses . of the third approved ICDP project of China -the Chinese Cretaceous Continental Scientific Drilling Project and the development of ICDP-China are also summarized in this paper.
Keywords: China; Hawaii [United States]; Japan; Kyushu; Nagasaki [Kyushu]; Qinghai; Qinghai Lake; United States; Unzen Volcano; active fault; climate change; collision zone; crater; deep drilling; hot spot; mantle plume; natural resource; San Andreas Fault; talc

A theoretical model of the explosive fragmentation of vesicular magma - Fowler, A.C.; Scheu, B.; Lee, W.T.; McGuinness, M.J. (Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2010)
Recent experimental work has shown that, when a vertical column of rock under large pressure is suddenly depressurized, the column can 'explode' in a structured and repeatable way. The observations show that a sequence of horizontal fractures forms from the top down, and the resulting blocks are lifted off and ejected. The blocks can suffer secondary internal fractures. This experiment provides a framework for understanding the way in which catastrophic explosion can occur, and is motivated by the corresponding phenomenon of magmatic explosion during Vulcanian eruptions. We build a theoretical model to describe these results, and show that it is capable of describing both the primary sequence of fracturing and the secondary intrablock fracturing. The model allows us to suggest a practical criterion for when such explosions occur: firstly, the initial confining pressure must exceed the yield stress of the rock, and, secondly, the diffusion of the gas by porous flow must be sufficiently slow that a large excess pore pressure is built up. This will be the case if the rock permeability is small enough. © 2010 The Royal Society.
cited By 35
Keywords: Brittle fracture; Explosions; Nitration; Submarine geophysics; Yield stress; Brittle fragmentation; Catastrophic explosion; Confining pressures; Excess pore pressure; Explosive fragmentation; Explosive volcanism; Horizontal fractures; Internal fracture; Magma fragmentation; Magmatic explosion; Porous flow; Primary sequences; Rock permeability; Silicic magmas; Theoretical models; Topdown; Vertical columns; Explosives

A theoretical exercise in the modeling of ground-level ozone resulting from the K-T asteroid impact: Its possible link with the extinction selectivity of terrestrial vertebrates - Kikuchi, R.; Vanneste, M. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2010)
The extinction pattern of the Maastrichtian indicates that long-term and short-term events contributed to the Cretaceous-Tertiary (K-T) mass extinction at 65 Ma. However, it is not clear how the impact events are linked with the extinction selectivity; e.g. non-avian dinosaurs became extinct, whereas birds survived. The post-impact air quality is discussed, and attention is focused on the then land vertebrates. Although ground-level (tropospheric) O3 is a powerful irritant on the order of 0.1 ppm toxicity, the presence of ground-level O3 has hardly been considered since the K-T impact theory was reported about 30 years ago. Under the post-impact conditions reconstructed by simulating the carbon cycle (including isotope balance) and impact chemistry, a trajectory model suggests that the then photochemical reactions formed ground-level O3 whose concentration was apparently low at ∼ 1.0 ppm, but it is much greater than the current level of ∼ 0.04 ppm: that is, an O3 concentration above the health-threatening level persisted on the ground after the K-T impact. All land vertebrates must have suffered from respiratory O3 irritation at the time. However, analysis suggests that variables of O3 characteristics - hourly variation, short half-life in water and decomposition due to catalytic effects in soil - were randomly combined with variables of lifestyle features such as habitat, torpor, etc. to form new variables (i.e. survival rates): a high survival probability for amphibians; middle/high probabilities for semi-aquatic reptiles, mammals and birds; low/middle probabilities for marsupials and terrestrial reptiles; and a zero probability for non-avian dinosaurs. © 2010 Elsevier B.V. All rights reserved.
cited By 6

A tephrostratigraphic record for the last glacial-interglacial cycle from Lake Ohrid, Albania and Macedonia - Vogel, Hendrik; Zanchetta, Giovanni; Sulpizio, Roberto; Wagner, Bernd; Nowaczyk, Norbert (Journal of Quaternary Science, 2010)
Here we present a tephrostratigraphic record (core Co1202) recovered from the northeastern part of Lake Ohrid (Republics of Macedonia and Albania) reaching back to Marine Isotope Stage (MIS) 6. Overall ten horizons (OT0702-1 to OT0702-10) containing volcanic tephra have been recognised throughout the 14.94m long sediment succession. Four tephra layers were visible at macroscopic inspection (OT0702-4, OT0702-6, OT0702-8 and OT0702-9), while the remaining six are cryptotephras (OT0702-1, OT0702-2, OT0702-3, OT0702-5, OT0702-7 and OT0702-10) identified from peaks in K, Zr and Sr intensities, magnetic susceptibility measurements, and washing and sieving of the sediments. Glass shards of tephra layers and cryptotephras were analysed with respect to their major element composition, and correlated to explosive eruptions of Italian volcanoes. The stratigraphy and the major element composition of tephra layers and cryptotephras allowed the correlation of OT0702-1 to AD 472 or AD 512 eruptions of Somma-Vesuvius, OT0702-2 to the FL eruption of Mount Etna, OT0702-3 to the Mercato from Somma-Vesuvius, OT0702-4 to SMP1-e/Y-3 eruption from the Campi Flegrei caldera, OT0702-5 to the Codola eruption (Somma-Vesuvius or Campi Flegrei), OT0702-6 to the Campanian Ignimbrite/Y-5 from the Campi Flegrei caldera, OT0702-7 to the Green Tuff/Y-6 eruption from Pantelleria Island, OT0702-8 to the X-5 eruption probably originating from the Campi Flegrei caldera, OT0702-9 to the X-6 eruption of generic Campanian origin, and OT0702-10 to the P-11 eruption from Pantelleria Island. The fairly well-known ages of these tephra layers and parent eruptions provide new data on the dispersal and deposition of these tephras and, furthermore, allow the establishment of a chronological framework for core Co1202 for a first interpretation of major sedimentological changes. © 2009 John Wiley & Sons, Ltd.
Keywords: Albania; Greece; Lake Ohrid; Macedonia [Greece]; caldera; Campanian; ignimbrite; Last Glacial-Interglacial; magnetic susceptibility; marine isotope stage; potassium; stratigraphy; strontium; tephra; tephrochronology; tuff; volcanic eruption; X-ray fluorescence; zircon

A paleoclimate record with tephrochronological age control for the last glacial-interglacial cycle from Lake Ohrid, Albania and Macedonia - Vogel, Hendrik; Wagner, Bernd; Zanchetta, Giovanni; Sulpizio, Roberto; Ros'en, Peter (Journal of Paleolimnology, 2010)
Lake Ohrid is probably of Pliocene age, and the oldest extant lake in Europe. In this study climatic and environmental changes during the last glacial-interglacial cycle are reconstructed using lithological, sedimentological, geochemical and physical proxy analysis of a 15-m-long sediment succession from Lake Ohrid. A chronological framework is derived from tephrochronology and radiocarbon dating, which yields a basal age of ca. 136 ka. The succession is not continuous, however, with a hiatus between ca. 97. 6 and 81. 7 ka. Sediment accumulation in course of the last climatic cycle is controlled by the complex interaction of a variety of climate-controlled parameters and their impact on catchment dynamics, limnology, and hydrology of the lake. Warm interglacial and cold glacial climate conditions can be clearly distinguished from organic matter, calcite, clastic detritus and lithostratigraphic data. During interglacial periods, short-term fluctuations are recorded by abrupt variations in organic matter and calcite content, indicating climatically-induced changes in lake productivity and hydrology. During glacial periods, high variability in the contents of coarse silt to fine sand sized clastic matter is probably a function of climatically-induced changes in catchment dynamics and wind activity. In some instances tephra layers provide potential stratigraphic markers for short-lived climate perturbations. Given their widespread distribution in sites across the region, tephra analysis has the potential to provide insight into variation in the impact of climate and environmental change across the Mediterranean. © 2010 Springer Science+Business Media B.V.
Keywords: Albania; Greece; Lake Ohrid; Macedonia [Greece]; accumulation rate; climate variation; geochemical method; Last Glacial-Interglacial; lithology; lithostratigraphy; paleoclimate; paleolimnology; Pliocene; proxy climate record; radiocarbon dating; sedimentology; tephrochronology

A high-performance, safer and semi-automated approach for the δ18O analysis of diatom silica and new methods for removing exchangeable oxygen - Chapligin, B.; Meyer, H.; Friedrichsen, H.; Marent, A.; Sohns, E.; Hubberten, H.-W. (Rapid Communications in Mass Spectrometry, 2010)
The determination of the oxygen isotope composition of diatom silica in sediment cores is important for paleoclimate reconstruction, especially in non-carbonate sediments, where no other bioindicators such as ostracods and foraminifera are available. Since most currently available analytical techniques are time-consuming and labour-intensive, we have developed a new, safer, faster and semi-automated online approach for measuring oxygen isotopes in biogenic silica. Improvements include software that controls the measurement procedures and a video camera that remotely records the reaction of the samples under BrF5 with a CO2 laser. Maximum safety is guaranteed as the laserfluorination unit is arranged under a fume hood in a separate room from the operator. A new routine has been developed for removing the exchangeable hydrous components within biogenic silica using ramp degassing. The sample plate is heated up to 1100°C and cooled down to 400°C in 7 h under a flow of He gas (the inert Gas Flow Dehydration method - iGFD) before isotope analysis. Two quartz and two biogenic silica samples ( 1.5 mg) of known isotope composition were tested. The isotopic compositions were reproducible within an acceptable error; quartz samples gave a mean standard deviation of <0.15%(1σ) and for biogenic silica <0.25%(1σ) for samples down to 0.3 mg. The semiautomated fluorination line is the fastest method available at present and enables a throughput of 74 samples/week. © 2010 John Wiley & Sons, Ltd.
cited By 38
Keywords: helium; oxygen; silicon dioxide; article; chemistry; desiccation; diatom; instrumentation; ion exchange; isolation and purification; laboratory automation; methodology; paleontology; reproducibility; sensitivity and specificity; Automation; Laboratory; Desiccation; Diatoms; Helium; Ion Exchange; Oxygen Isotopes; Paleontology; Quartz; Reproducibility of Results; Sensitivity and Specificity; Silicon Dioxide

A freshwater biodiversity hotspot under pressure - Assessing threats and identifying conservation needs for ancient Lake Ohrid - Kostoski, G.; Albrecht, C.; Trajanovski, S.; Wilke, T. (Biogeosciences, 2010)
Immediate conservation measures for world-wide freshwater resources are of eminent importance. This is particularly true for so-called ancient lakes. While these lakes are famous for being evolutionary theatres, often displaying an extraordinarily high degree of biodiversity and endemism, in many cases these biota are also experiencing extreme anthropogenic impact. Lake Ohrid, a major European biodiversity hotspot situated in a trans-frontier setting on the Balkans, is a prime example for a lake with a magnitude of narrow range endemic taxa that are under increasing anthropogenic pressure. Unfortunately, evidence for a creeping biodiversity crisis has accumulated over the last decades, and major socio-political changes have gone along with human-mediated environmental changes. Based on field surveys, monitoring data, published records, and expert interviews, we aimed to (1) assess threats to Lake Ohrids' (endemic) biodiversity, (2) summarize existing conservation activities and strategies, and (3) outline future conservation needs for Lake Ohrid. We compiled threats to both specific taxa (and in cases to particular species) as well as to the lake ecosystems itself. Major conservation concerns identified for Lake Ohrid are: (1) watershed impacts, (2) agriculture and forestry, (3) tourism and population growth, (4) non-indigenous species, (5) habitat alteration or loss, (6) unsustainable exploitation of fisheries, and (7) global climate change. Among the major (well-known) threats with high impact are nutrient input (particularly of phosphorus), habitat conversion and silt load. Other threats are potentially of high impact but less well known. Such threats include pollution with hazardous substances (from sources such as mines, former industries, agriculture) or climate change. We review and discuss institutional responsibilities, environmental monitoring and ecosystem management, existing parks and reserves, biodiversity and species measures, international conservation activities, and ongoing research on conservation and raising of public awareness. Following this summary, we evaluate the status quo and future of Lake Ohrid and its biota. A comprehensive conservation strategy should include measures that result in an immediate reduction of nutrient input, particularly with phosphorus, in order to slow down the ongoing eutrophication process. The existing watershed management should become more effective. Implementation and particularly with a view to the enforcement of national laws should be enhanced. Increased research on the lakes' limnology, biodiversity, and conservation management practices are necessary. The latter research should identify conservation priorities. Public awareness should be enhanced. Facing these parallel needs to protect the unique biodiversity of Lake Ohrid, we suggest urging (a) implementation and enforcement of the General Management Plan that would ensure long-term integrated and sustainable use of the lake and its watershed, (b) scientific studies on ecology, biodiversity and effects of human impact, (c) the establishment of Core Conservation areas (CCA), including underwater reserves, and (d) Coastal Zone Management (CZM) areas that would constitute buffer zones for the CCAs around the lake. Given the number of identified threats, it is clear that only concerted international action can stop or at least slow down further degradation of Lake Ohrid and the creeping biodiversity crisis already evident. All conservation activities should, among others, ultimately lead to a trans-boundary major conservation area of the Ohrid-Prespa region that would allow long-term integration of both humans and nature. © Author(s) 2010.
Keywords: Lake Ohrid; anthropogenic effect; biodiversity; buffer zone; coastal zone management; eutrophication; future prospect; habitat conservation; hot spot; lake ecosystem

A combined oxygen and silicon diatom isotope record of Late Quaternary change in Lake El'gygytgyn, North East Siberia - Swann, G.E.A.; Leng, M.J.; Juschus, O.; Melles, M.; Brigham-Grette, J.; Sloane, H.J. (Quaternary Science Reviews, 2010)
Determining the response of sites within the Arctic Circle to long-term climatic change remains an essential pre-requisite for assessing the susceptibility of these regions to future global warming and Arctic amplification. To date, existing records from North East Russia have demonstrated significant spatial variability across the region during the late Quaternary. Here we present diatom δ18O and δ30Si data from Lake El'gygytgyn, Russia, and suggest environmental changes that would have impacted across West Beringia from the Last Glacial Maximum to the modern day. In combination with other records, the results raise the potential for climatic teleconnections to exist between the region and sites in the North Atlantic. The presence of a series of 2-3‰ decreases in δ18Odiatom during both the Last Glacial and the Holocene indicates the sensitivity of the region to perturbations in the global climate system. Evidence of an unusually long Holocene thermal maximum from 11.4 ka BP to 7.6 ka BP is followed by a cooling trend through the remainder of the Holocene in response to changes in solar insolation. This is culminated over the last 900 years by a significant decrease in δ18Odiatom of 2.3‰, which may be related to a strengthening and easterly shift of the Aleutian Low in addition to possible changes in precipitation seasonality. © 2009 Elsevier Ltd. All rights reserved.
cited By 55
Keywords: Aleutian low; Arctic Circle; Climatic changes; Cooling trends; Environmental change; Global climate system; Holocenes; Isotope record; Last glacial; Last Glacial Maximum; Late quaternary; North Atlantic; North-East Siberia; Seasonality; Solar insolation; Spatial variability; Teleconnections; Thermal maxima; Amplification; Global warming; Isotopes; Oxygen; Glacial geology; climate variation; Holocene; isotopic analysis; oxygen isotope; perturbation; silicon; spatial variation; Atlantic Ocean; Atlantic Ocean (North); Chukchi; Elgygytgyn Lake; Russian Federation; Bacillariophyta

A chemostratigraphic method to determine the end of impact-related sedimentation at marine-target impact craters (Chesapeake Bay, Lockne, Tv{aren) - Orm{o, J.; Hill, A.C.; Self-Trail, J.M. (Meteoritics and Planetary Science, 2010)
To better understand the impact cratering process and its environmental consequences at the local to global scale, it is important to know when in the geological record of an impact crater the impact-related processes cease. In many instances, this occurs with the end of early crater modification, leaving an obvious sedimentological boundary between impactites and secular sediments. However, in marine-target craters the transition from early crater collapse (i.e., water resurge) to postimpact sedimentation can appear gradual. With the a priori assumption that the reworked target materials of the resurge deposits have a different chemical composition to the secular sediments we use chemostratigraphy (δ13Ccarb, %Corg, major elements) of sediments from the Chesapeake Bay, Lockne, and Tv{aren craters, to define this boundary. We show that the end of impact-related sedimentation in these cases is fairly rapid, and does not necessarily coincide with a visual boundary (e.g., grain size shift). Therefore, in some cases, the boundary is more precisely determined by chemostratigraphy, especially carbonate carbon isotope variations, rather than by visual inspection. It is also shown how chemostratigraphy can confirm the age of marine-target craters that were previously determined by biostratigraphy; by comparing postimpact carbon isotope trends with established regional trends. © The Meteoritical Society, 2010.
cited By 12

Melt-bearing impactites (suevite and impact melt rock) within the Gardnos structure, Norway - Kalleson, E.; Dypvik, H.; Nilsen, O. (Meteoritics and Planetary Science, 2010)
Melt-bearing impactites dominated by suevite, and with a minor content of clast-rich impact melt rock, are found within the central part of the Gardnos structure. They are preserved as the eroded remnants in the relatively small complex impact structure with a present diameter of 5 km. These rocks have been mapped in the field and in the Branden drill core, and described according to mineralogy/petrology, including matrix, litho clast, and melt content, as well as geochemistry. Based on our extensive field mapping, a simple 3-D model of the original crater was constructed to estimate tentative volumes for the melt-bearing impactites. The variations in lithic and melt fragment content and chemistry of suevite matrix can mostly be explained by incorporation of mafic rocks into a dominant mixture of granitic, gneissic, and quartzitic target rocks, reflecting mixing of material from different parts of the crater. Melt fragments within suevite occur with a variety of shapes and textures, probably related to different original target rock composition, to the various temperatures the individual fragments were subjected to during the impact event and deposition processes. This study discusses the impact-related deposits based on a sedimentological approach. Their overall composition and structures indicate dominating gravity flow processes in the final transportation and deposition of the suevite. © 2010 The Meteoritical Society.
cited By 14

Distribution, diversity and ecology of modern freshwater ostracodes (crustacea), and hydrochemical characteristics of Lago Pet'en Itz'a, Guatemala - P'erez, Liseth; Lorenschat, Julia; Bugja, Rita; Brenner, Mark; Scharf, Burkhard; Schwalb, Antje (Journal of Limnology, 2010)
We analyzed modern ostracode species assemblages and water column physico-chemical characteristics in Lago P'eten Itz'a, Guatemala. Lake waters are dominated by sulfate, bicarbonate, calcium and magnesium and display a total ion concentration of 11 meq L-1. Eleven extant ostracode species were identified. We found higher abundances of living ostracodes, as well as relatively higher species richness (eight species) and biodiversity (H of 1.6) between the littoral zone and a water depth of <20 m. At water depths >40 m, these variables all decreased. The thermocline is located at a water depth of 20-40 m. Cluster analysis revealed three water depth ranges in the lake of importance to ostracode distribution: 1) littoral zone (0.1-3 m), 2) water depths from the base of the littoral zone to the base of the thermocline (3-40 m), and 3) water depths below the thermocline (40-160 m). The assemblage Darwinula-Heterocypris-Pseudocandona-Strandesia is characteristic of waters <15 m. The Cypridopsis-Cytheridella-Limnocythere assemblage characterizes waters <40 m and Physocypria indicates waters >40 m. Ostracode taxa from Lago Pet'en Itz'a show specific ecological preferences related to water depth and associated physico-chemical characteristics, thus illustrating the potential of ostracodes as indicators of lake level changes and hydrodynamics.

Dynamics and internal structure of the Hawaiian plume - Farnetani, Cinzia G.; Hofmann, Albrecht W. (Earth and Planetary Science Letters, 2010)
A thorough understanding of the internal structure of the Hawaiian plume conduit requires to link geochemical observations of surface lavas to fluid dynamic simulations able to quantify the flow trajectories of upwelling geochemical heterogeneities and their sampling by volcanoes. With the present work we fill a gap between the numerous geochemical studies of Hawaiian lavas and the paucity of dynamical models that relate the observed geochemical record to the internal plume structure. Our three-dimensional numerical simulation of a vigorous plume sheared by a fast moving oceanic plate shows that the dominant deformation in the conduit is vertical stretching, while horizontal spreading and vertical shortening prevail in the sublithospheric part of the plume (hereafter referred to as plume head). Flow trajectories indicate that a young volcano like Loihi samples the 'upstream' side of the plume, not its center, whereas volcanoes in the post-shield phase sample deep melts from the 'downstream' side of the plume. To constrain the internal conduit structure we focus on two geochemical observations: old (>350 kyr) Mauna Kea lavas from the Hawaii Scientific Drilling Project are isotopically distinct from recent Mauna Kea lavas, but they are isotopically identical to present-day Kilauea lavas. By modelling a plume conduit with several long-lasting filaments of 10. km radius, we find that the isotopic record of a volcano (e.g., Mauna Kea) is expected to change over time-scales of 400. kyr. Furthermore, by requiring that two age progressive volcanoes (e.g., Mauna Kea and Kilauea) sample the same filament, we constrain the minimum filament length to be 600. km. In this paper we adopt a 'top-down' approach: from geochemical observations of surface lavas, to dynamical models of the conduit structure, and further down to the 'geochemical architecture' of the thermal boundary layer feeding the plume. A conduit structure with filaments maps back into heterogeneous volumes with azimuthal and radial extents of several hundred kilometers in the source region of plumes. © 2010 Elsevier B.V.
Keywords: Hawaii [United States]; United States; Computer simulation; Filaments (lamp); Conduit structure; Dynamical model; Fluid dynamic simulation; Geochemical heterogeneity; Internal structure; Isotopic record; Kilauea; Long lasting; Mantle heterogeneity; Oceanic plate; Phase samples; Plume dynamics; Plume structure; Scientific drilling; Source region; Thermal boundary layer; Three-dimensional numerical simulations; Time-scales; Topdown; fluid dynamics; igneous geochemistry; isotopic composition; lava; mantle plume; simulation; volcano; Volcanoes

Hydrothermal alteration in the Reykjanes geothermal system: Insights from Iceland deep drilling program well RN-17 - Marks, N.; Schiffman, P.; Zierenberg, R.A.; Franzson, H.; Fridleifsson, G.Ó. (Journal of Volcanology and Geothermal Research, 2010)
The Reykjanes geothermal system is a seawater-recharged hydrothermal system that appears to be analogous to seafloor hydrothermal systems in terms of host rock type and low water/rock alteration. The similarities make the Reykjanes system a useful proxy for seafloor vents. At some time during the Pleistocene, the system was dominated by meteoric water recharge, and fluid composition at Reykjanes has evolved through time as a result of changing proportions of meteoric water influx as well as differing pressure and temperature conditions. The purpose of this study is to characterize secondary mineralization, degree of metasomatic alteration, and bulk composition of cuttings from well RN-17 from the Reykjanes geothermal system. The basaltic host rock includes hyaloclastite, breccia, tuff, extrusive basalt, diabase, as well as a marine sedimentary sequence. The progressive hydrothermal alteration sequence observed with increasing depth results from reaction of geothermal fluids with the basaltic host rock. An assemblage of greenschist facies alteration minerals, including actinolite, prehnite, epidote and garnet, occurs at depths as shallow as 350 m; these minerals are commonly found in Icelandic geothermal systems at temperatures above 250 °C (Bird and Spieler, 2004). This requires hydrostatic pressures that exceed the present-day depth to boiling point curve, and therefore must record alteration at higher fluid pressures, perhaps as a result of Pleistocene glaciation. Major, minor, and trace element profiles of the cuttings indicate transitional MORB to OIB composition with limited metasomatic shifts in easily mobilized elements. Changes in MgO, K2O and loss on ignition indicate that metasomatism is strongly correlated with protolith properties. The textures of alteration minerals reveal alteration style to be strongly dependent on protolith as well. Hyaloclastites are intensely altered with calc-silicate alteration assemblages comprising calcic hydrothermal plagioclase, grandite garnet, prehnite, epidote, hydrothermal clinopyroxene, and titanite. In contrast, crystalline basalts and intrusive rocks display a range in alteration intensity from essentially unaltered to pervasive and nearly complete albitization of igneous feldspar and uralitization of clinopyroxene. Hydrothermal anorthite (An92-An98) occurs in veins in the most altered basalt cuttings and is significantly more calcic than igneous feldspar (An48-An79). Amphibole compositions change from actinolite to hornblende at depth. Hydrothermal clinopyroxene, which occurs in veins, has greater variation in Fe content and is systematically more calcic than igneous pyroxene and also lacks uralitic textures. Solid solutions of prehnite, epidote, and garnet indicate evolving equilibria with respect to aluminum and ferric iron. © 2009 Elsevier B.V. All rights reserved.
cited By 60
Keywords: Albitization; Amphibole compositions; Bulk compositions; Clinopyroxenes; Deep drilling; Fe content; Ferric iron; Fluid composition; Fluid pressures; Geothermal fluids; Geothermal systems; Greenschist; Host rocks; Hyaloclastites; Hydrothermal alterations; Hydrothermal system; Icelandics; Icelands; Intrusive rocks; Loss on ignition; Meteoric waters; Pleistocene; Prehnite; Pressure and temperature; Protoliths; Sea floor; Seafloor hydrothermal systems; Sedimentary sequence; Basalt; Boiling point; Crystalline rocks; Feldspar; Garnets; Geothermal fields; Geothermal prospecting; Glacial geology; Hydrostatic pressure; Mineralogy; Minerals; Seawater; Sedimentary rocks; Silicate minerals; Textures; Trace elements; Underwater mineral resources; Well drilling; Igneous rocks; amphibole; basalt; breccia; diabase; geothermal system; host rock; hyaloclastite; hydrothermal alteration; hydrothermal system; mid-ocean ridge basalt; mineralization; Pleistocene; seafloor; solid solution; tuff; water-rock interaction; Iceland; Reykjanes Peninsula; Aves

Melt particle characteristics of the within-and out-of-crater suevites from the Bosumtwi impact structure, Ghana: Implications for crater formation - Coney, L.; Reimold, W.U.; Gibson, R.L.; Koeberl, C.; Ogilvie, P. (Special Paper of the Geological Society of America, 2010)
A petrographic and geochemical comparison of suevites from the LB-07A and LB-08A cores recovered during 2004 by the International Continental Scientific Drilling Program with suevites from outside of the crater rim of the Bosumtwi impact structure indicates contrasting mechanisms of formation for these respective impact breccias. The within-crater suevites form only a small part of the lithic impact breccia-dominated impactite crater fill, in contrast to the impactites from outside of the crater, which consist solely of suevite. The clasts of suevites from within the crater display relatively low levels of shock (for most material <45 GPa). The numbers of shocked quartz grains, as well as fragments of diaplectic glass of quartz and feldspar in suevites decrease with depth through the LB-07A core (maximum three sets of planar deformation features [PDFs]). In contrast, the out-of-crater suevites sampled north and south of the crater contain up to four PDF sets in quartz clasts, ballen cristobalite, and higher proportions of diaplectic glass than the within-crater suevites. In addition, the suevites from outside of the crater contain significantly more melt particles (18-37 vol%) than the within-crater suevites (<5 vol%). Melt fragment sizes in suevites from outside the crater are much larger than those from suevites within the crater (maximum 40 cm versus 1 cm). The currently known distribution of impactites outside of the crater would be consistent with a low-angle impact from the east. We propose that the within-crater suevites and polymict lithic breccias were emplaced either via slumping off the crater walls or lateral movement of some melted and much displaced target rock within the crater. Limited admixture of fallback material from the ejecta plume is evident in the uppermost impactite deposit encountered in core LB-05B. In contrast, the out-of-crater suevites formed by fallout from a laterally differentiated ejecta plume, which resulted in different clast populations to the north and south of the crater. © 2010 The Geological Society of America. All rights reserved.
cited By 12

EarthScope - The latest advances of the united state's deep exploration program - Liu, G.; Dong, S.; Chen, X.; Zhou, Q.; Liu, Z. (Acta Geologica Sinica (English Edition), 2010)
The implementation of EarthScope, the deep exploration program in North American continent has become the focus of attention in the field of Earth Sciences. This paper gives a brief description of the background, scientific problems to be solved, observational approaches adopted,some research progresses of the EarthScope program in the fields such as seismic tomographic imaging, earth stress change, continental structure, topographic survey and so on.
cited By 4
Keywords: exploration; geological survey; imaging method; research program; tomography; topographic mapping; North America

Melt particle characteristics of the within-and out-of-crater suevites from the Bosumtwi impact structure, Ghana: Implications for crater formation - Coney, Louise; Reimold, Wolf Uwe; Gibson, Roger L.; Koeberl, Christian; Ogilvie, Paula (Special Paper of the Geological Society of America, 2010)
A petrographic and geochemical comparison of suevites from the LB-07A and LB-08A cores recovered during 2004 by the International Continental Scientific Drilling Program with suevites from outside of the crater rim of the Bosumtwi impact structure indicates contrasting mechanisms of formation for these respective impact breccias. The within-crater suevites form only a small part of the lithic impact breccia-dominated impactite crater fill, in contrast to the impactites from outside of the crater, which consist solely of suevite. The clasts of suevites from within the crater display relatively low levels of shock (for most material <45 GPa). The numbers of shocked quartz grains, as well as fragments of diaplectic glass of quartz and feldspar in suevites decrease with depth through the LB-07A core (maximum three sets of planar deformation features [PDFs]). In contrast, the out-of-crater suevites sampled north and south of the crater contain up to four PDF sets in quartz clasts, ballen cristobalite, and higher proportions of diaplectic glass than the within-crater suevites. In addition, the suevites from outside of the crater contain significantly more melt particles (18-37 vol%) than the within-crater suevites (<5 vol%). Melt fragment sizes in suevites from outside the crater are much larger than those from suevites within the crater (maximum 40 cm versus 1 cm). The currently known distribution of impactites outside of the crater would be consistent with a low-angle impact from the east. We propose that the within-crater suevites and polymict lithic breccias were emplaced either via slumping off the crater walls or lateral movement of some melted and much displaced target rock within the crater. Limited admixture of fallback material from the ejecta plume is evident in the uppermost impactite deposit encountered in core LB-05B. In contrast, the out-of-crater suevites formed by fallout from a laterally differentiated ejecta plume, which resulted in different clast populations to the north and south of the crater. © 2010 The Geological Society of America. All rights reserved.
Keywords: Ashanti; Ghana; Lake Bosumtwi; Feldspar; Glass; Quartz; Rocks; Silicate minerals; Continental scientific drillings; Crater formation; Impact structures; Lateral movement; Mechanisms of formation; Particle characteristics; Planar deformation; Shocked quartz; crater; geochemistry; impact structure; petrography; suevite; Meteor impacts

Major ion chemistry of waters in Lake Qinghai catchments, NE Qinghai-Tibet plateau, China - Xu, Hai; Hou, Zhaohua; An, ZhiSheng; Liu, Xiaoyan; Dong, Jibao (Quaternary International, 2010)
Major ion concentrations were measured in lake water, river water, ground water, and rainfall water around the Lake Qinghai catchment. The dissolution of carbonate particles in dust has a strong impact on the chemical composition of rainfall as inferred from the Gibbs model and the ternary plots of the major ions. The chemical composition of the ground water can be divided into two groups, one influenced by river water and the other dominated by deeper aquifers. The chemical composition of lake water can be mainly ascribed to evaporation and crystallization. Total dissolved solid (TDS) of river waters during the wet periods is higher than during the dry periods. Calcium and bicarbonate are the dominant cations and anions of the river waters, and they have higher fractions during the wet periods than during the dry periods. Comparisons between (Mg2+ + Ca2+)/TZ+, (Mg2+ + Ca2+)/(Na+ + K+), HCO3-/Na+, and Cl-/Na+ suggest that the chemical composition of the river waters is mainly controlled by carbonate weathering and that the carbonate weathering is much stronger during the wet periods than during the dry periods. Seasonal melting may be one of the important factors that influence the seasonal variations of water chemistry of the rivers. © 2008 Elsevier Ltd and INQUA.
Keywords: China; Qinghai; Qinghai Lake; Qinghai-Xizang Plateau; catchment; chemical composition; crystallization; evaporation; groundwater; lake water; rainwater; river water; water chemistry

Low energy deposition in the Chicxulub crater during the impact to post-impact transition - Bahlburg, H.; Weiss, R.; W{unnemann, K. (Earth and Planetary Science Letters, 2010)
The crater fill units that were deposited during the terminal stages of the formation of the shallow marine Chicxulub crater in northern Yucatan were interpreted by some authors as products of a catastrophic resurge of water. This interpretation contrasts markedly with the dominant sand grain size <300μm and the abundant small-scale current cross bedding structures indicative of low energy deposition. To solve this discrepancy we applied first principles of physical sedimentology in an analysis of grain size and sedimentary structures to determine current velocities and minimum water depths required to generate the observed sedimentary bedforms. We combine this approach with numerical modeling of crater formation in order to explore the dimensions of the ejecta ring wall being formed by a Chicxulub impactor in water depths of 1000m. We find that the ejecta wall reaches heights in the order of 1200m above sea floor and 200m above sea level. It thus prevented the resurge of water into the crater cavity and consequently also the subsequent formation of a collapse wave. The ring wall significantly retarded the refilling of the crater cavity with seawater, and refilling took place by permeation through and localized erosion of the ring wall. This resulted in low-energy currents with velocities between 1.5 and 0.18ms-1 slowly reentering the crater and depositing the cm-scale, low energy laminated and crossbedded sandy terminal impact deposits. © 2010 Elsevier B.V.
cited By 8

Localized rotation of principal stress around faults and fractures determined from borehole breakouts in hole B of the Taiwan Chelungpu-fault Drilling Project (TCDP) - Lin, W.; Yeh, E.-C.; Hung, J.-H.; Haimson, B.; Hirono, T. (Tectonophysics, 2010)
To reveal details of stress perturbations associated with faults and fractures, we investigated the faults and large fractures accompanied by stress-induced borehole breakouts or drilling-induced tensile fractures in hole B of the Taiwan Chelungpu-fault Drilling Project (TCDP). Then, we determined the relationship between the faults and fractures and stress orientation changes. We identified faults and fractures from electrical images of the borehole wall obtained by downhole logging but also from photographs and descriptions of retrieved core samples, and measured the variations in the principal horizontal stress orientation ascertained from borehole breakouts observed on the electrical images in the vicinity of the faults and fractures. Identification of geological structures (faults, fractures, and lithologic boundaries) by electrical images only is difficult and may sometimes yield incorrect results. In a novel approach, therefore, we used both the electrical images and core photographs to identify geological structures. We found four patterns of stress orientation change, or no change, in the vicinity of faults and fractures in TCDP hole B: (i) abrupt (discontinuous) rotation in the vicinity of faults or fractures; (ii) gradual rotation; (iii) suppression of breakouts at faults, fractures, or lithologic boundaries; and (iv) no change in the stress orientation. We recognized stress fluctuations, that is, heterogeneous mesoscale (≥ 10 cm) stress distributions with respect to both stress orientation and magnitude. In addition, we found that stress state changes occurred frequently in the vicinity of faults, fractures, and lithologic boundaries. © 2009 Elsevier B.V. All rights reserved.
cited By 67
Keywords: Borehole wall; Downholes; Drilling projects; Drilling-induced tensile fractures; Electrical images; Fracture stress; Geological structures; Horizontal stress; Mesoscale; Principal stress; Stress distribution; Stress fluctuations; Stress orientations; Stress perturbations; Stress state; Stress-induced; Drilling; Fracture; Photography; Rotation; Stress concentration; Boreholes; borehole breakout; core analysis; drilling; electrical method; fault; fracture; image analysis; spatial variation; stress analysis; stress field; tensile stress; Chelungpu Fault Zone; Taiwan

Lipid biomarkers in Holocene and glacial sediments from ancient Lake Ohrid (Macedonia, Albania) - Holtvoeth, J.; Vogel, H.; Wagner, B.; Wolff, G.A. (Biogeosciences, 2010)
Organic matter preserved in Lake Ohrid sediments originates from aquatic and terrestrial sources. Its variable composition reflects climate-controlled changes in the lake basin's hydrology and related organic matter export, i.e. changes in primary productivity, terrestrial plant matter input and soil erosion. Here, we present first results from lipid biomarker investigations of Lake Ohrid sediments from two near-shore settings: site Lz1120 near the southern shore, with low-lying lands nearby and probably influenced by river discharge, and site Co1202 which is close to the steep eastern slopes. Variable proportions of terrestrial n-alkanoic acids and n-alkanols as well as compositional changes of ‰-hydroxy acids document differences in soil organic matter supply between the sites and during different climate stages (glacial, Holocene, 8.2 ka cooling event). Changes in the vegetation cover are suggested by changes in the dominant chain length of terrestrial n-alkanols. Effective microbial degradation of labile organic matter and in situ contribution of organic matter derived from the microbes themselves are both evident in the sediments. We found evidence for anoxic conditions within the photic zone by detecting epicholestanol and tetrahymanol from sulphur-oxidising phototrophic bacteria and bacterivorous ciliates and for the influence of a settled human community from the occurrence of coprostanol, a biomarker for human and animal faeces (pigs, sheep, goats), in an early Holocene sample. This study illustrates the potential of lipid biomarkers for future environmental reconstructions using one of Europe's oldest continental climate archives, Lake Ohrid. © Author(s) 2010.
Keywords: Lake Ohrid; Animalia; Capra hircus; Ciliophora; Ovis aries; Photobacteria; Suidae; anoxic conditions; aquatic environment; bacterium; biodegradation; biomarker; climate change; glacial deposit; Holocene; hydrology; lacustrine deposit; lipid; organic acid; organic matter; paleoenvironment; primary production; river discharge; soil erosion; soil organic matter; terrestrial environment; vegetation cover

Late Quaternary palaeoenvironment of northern Guatemala: Evidence from deep drill cores and seismic stratigraphy of Lake Pet'en Itz'a - Mueller, Andreas D.; Anselmetti, Flavio S.; Ariztegui, Daniel; Brenner, Mark; Hodell, David A.; Curtis, Jason H.; Escobar, Jaime; Gilli, Adrian; Grzesik, Dustin A.; Guilderson, Thomas P.; Kutterolf, Steffen; Pl{otze, Michael (Sedimentology, 2010)
Long sediment cores were collected in spring 2006 from Lake Pet'en Itz'a, northern Guatemala, in water depths ranging from 30 to 150 m, as part of an International Continental Scientific Drilling Program project. The sediment records from deep water consist mainly of alternating clay, gypsum and carbonate units and, in at least two drill sites, extend back >200 kyr. Most of the lithostratigraphic units are traceable throughout the basin along seismic reflections that serve as seismic stratigraphic boundaries and suggest that the lithostratigraphy can be used to infer regional palaeoenvironmental changes. A revised seismic stratigraphy was established on the basis of integrated lithological and seismic reflection data from the basin. From ca 200 to ca 85 ka, sediments are dominated by carbonate-clay silt, often interbedded with sandy turbidites, indicating a sediment regime dominated by detrital sedimentation in a relatively humid climate. At ca 85 ka, an exposure horizon consisting of gravels, coarse sand and terrestrial gastropods marks a lake lowstand or partial basin desiccation, indicating dry climate conditions. From ca 85 to ca 48 ka, transgressive carbonate-clay sediments, overlain by deep-water clays, suggest a lake level rise and subsequent stabilization at high stage. From ca 48 ka to present, the lithology is characterized by alternating clay and gypsum units. Gypsum deposition correlates with Heinrich Events (i.e. dry climate), whereas clay units coincide with more humid interstadials. © 2010 The Authors. Journal compilation © 2010 International Association of Sedimentologists.
Keywords: Guatemala [Central America]; Lake Peten Itza; Peten; Gastropoda; Anoxic sediments; Carbonation; Climatology; Core drilling; Deepwater drilling; Drills; Gypsum; Lakes; Lithology; Offshore oil wells; Sedimentology; Seismic waves; Seismology; Guatemala; Lake level changes; Lake sediments; Palaeoclimatology; Seismic stratigraphy; climate conditions; deep drilling; deposition; environmental change; Heinrich event; lacustrine deposit; lake level; lithostratigraphy; paleoclimate; paleoenvironment; Quaternary; sediment core; sedimentation; seismic reflection; seismic stratigraphy; Stratigraphy

Laboratory-based maximum slip rates in earthquake rupture zones and radiated energy - McGarr, A.; Fletcher, J.B.; Boettcher, M.; Beeler, N.; Boatwright, J. (Bulletin of the Seismological Society of America, 2010)
Laboratory stick-slip friction experiments indicate that peak slip rates increase with the stresses loading the fault to cause rupture. If this applies also to earthquake fault zones, then the analysis of rupture processes is simplified inasmuch as the slip rates depend only on the local yield stress and are independent of factors specific to a particular event, including the distribution of slip in space and time. We test this hypothesis by first using it to develop an expression for radiated energy that depends primarily on the seismic moment and the maximum slip rate. From laboratory results, the maximum slip rate for any crustal earthquake, as well as various stress parameters including the yield stress, can be determined based on its seismic moment and the maximum slip within its rupture zone. After finding that our new equation for radiated energy works well for laboratory stick-slip friction experiments, we used it to estimate radiated energies for five earthquakes with magnitudes near 2 that were induced in a deep gold mine, an M 2.1 repeating earthquake near the San Andreas Fault Observatory at Depth (SAFOD) site and seven major earthquakes in California and found good agreement with energies estimated independently from spectra of local and regional ground-motion data. Estimates of yield stress for the earthquakes in our study range from 12 MPa to 122 MPa with a median of 64 MPa. The lowest value was estimated for the 2004 M 6 Parkfield, California, earthquake whereas the nearby M 2.1 repeating earthquake, as recorded in the SAFOD pilot hole, showed a more typical yield stress of 64 MPa.
cited By 13
Keywords: California; Crustal earthquakes; Deep gold mines; Earthquake fault; Earthquake rupture; Ground-motion; Maximum slip; Pilot holes; Radiated energies; Repeating earthquake; Rupture process; Rupture zone; San Andreas Fault; Seismic moment; Slip rates; Space and time; Stick-slip friction; Stress parameter; Earthquakes; Experiments; Friction; Gold mines; Gravitational effects; Laboratories; Slip forming; Tectonics; Yield stress; earthquake magnitude; earthquake rupture; fault zone; ground motion; seismic moment; slip rate

Introduction: Impact cratering and planetary studies - A fifty-year perspective - Gibson, R.L.; Reimold, W.U. (Special Paper of the Geological Society of America, 2010)
cited By 1
Keywords: cratering; impact structure; literature review; planetary evolution

Integrating borehole-breakout dimensions, strength criteria, and leak-off test results, to constrain the state of stress across the Chelungpu Fault, Taiwan - Haimson, B.; Lin, W.; Oku, H.; Hung, J.-H.; Song, S.-R. (Tectonophysics, 2010)
The paper describes the computation of the maximum horizontal stress (σH) magnitude in the vicinity of the Chelungpu Fault, Taiwan, host of the slip zone during the Chi-Chi earthquake (Mw 7.6; 1999). The scientific hole B intercepts the Chelungpu Fault at 1136 m. At the depths of logged breakouts (940-1310 m), the vertical stress (σv) as estimated from density logs increases linearly with depth from 22 to 31 MPa. A series of leak-off tests yielded two reliable shut-in pressures, 23.7 MPa at 1085 m and 29.8 MPa at 1279 m, which are lower than the estimated σv, albeit by only 2.1 and 0.6 MPa, respectively. In our analysis the shut-in pressures were considered to represent estimates of the least horizontal principal stresses (σh) at the respective depths, and consequently the test-induced fractures were assumed to have been vertical. Principal stress directions had been previously determined by others (105°-155° for the maximum horizontal stress, σH, except in the immediate vicinity of the Chelungpu Fault). The contribution of this paper is the estimation of the σH magnitude by considering that the state of stress at the points of intersection between breakout and borehole wall is in a state of limit equilibrium with the true triaxial strength criterion. The resulting σH in the range of logged breakouts increases with depth from 55 MPa at 940 m to 59 MPa at 1310 m. Thus, the estimated state of stress prevailing across the Chelungpu Fault is compatible with strike-slip, but marginally also with thrust faulting. However, the likelihood that the shut-in pressures actually represent σv magnitudes, and that the leak-off test-induced fractures were sub-horizontal, cannot be ignored. In that case the state of stress would clearly favor thrust faulting. © 2009 Elsevier B.V. All rights reserved.
cited By 41
Keywords: Borehole wall; ChiChi earthquake; Density log; Estimated state; Horizontal stress; Insitu stress; Leak-off tests; Limit equilibrium; Principal stress; Shut-in pressure; Slip zones; State of stress; Strength criteria; Thrust faulting; True triaxial strength; True triaxial strength criteria; Vertical stress; Asphalt pavements; Blowouts; Electromagnetic logging; Fracture; Instruments; Maximum likelihood estimation; Radioactivity logging; Stress measurement; Boreholes; borehole breakout; fault zone; in situ stress; integrated approach; pressure effect; stress analysis; strike-slip fault; thrust fault; triaxial test; well logging; Chelungpu Fault Zone; Taiwan

Inside the crater, outside the crater: Stratigraphic details of the margin of the Chesapeake Bay impact structure, Virginia, USA - Edwards, L.E.; Powars, D.S.; Horton Jr., J.W.; Gohn, G.S.; Self-Trail, J.M.; Litwin, R.J. (Special Paper of the Geological Society of America, 2010)
Two cores at the outer margin of the Chesapeake Bay impact structure show significant structural and depositional variations that illuminate its history. Detailed stratigraphy of the Watkins School core reveals that this site is outside the disruption boundary of the crater with respect to its lower part (nonmarine Cretaceous Potomac Formation), but just inside the boundary with respect to its upper part (Exmore Formation and a succession of upper Eocene to Pleistocene postimpact deposits). The site of the U.S. Geological Survey-National Aeronautics and Space Administration Langley core, 6.4 km to the east, lies wholly within the annular trough of the crater. The Potomac Formation in the Watkins School core is not noticeably impact disrupted. The lower part of crater unit A in the Langley core represents stratigraphically lower, but similarly undeformed material. The Exmore Formation is only 7.8 m thick in the Watkins School core, but it is over 200 m thick in the Langley core, where it contains blocks up to 24 m in intersected diameter. The upper part of the Exmore Formation in the two cores is a polymict diamicton with a stratified zone at the top. The postimpact sedimentary units in the two cores have similar late Eocene and late Miocene depositional histories and contrasting Oligocene, early Miocene, and middle Miocene histories. A paleochannel of the James River removed Pliocene deposits at the Watkins School site, to be filled later with thick Pleistocene deposits. At the Langley site, a thick Pliocene and thinner Pleistocene record is preserved. © 2010 The Geological Society of America. All rights reserved.
cited By 7
Keywords: Deposits; NASA; Stratigraphy; Chesapeake bay impact structures; Early Miocene; Middle Miocene; Pleistocene deposits; Pliocene deposits; Sedimentary units; U.s. geological surveys; Undeformed materials; Meteor impacts; crater; depositional sequence; impact structure; Miocene; paleochannel; Pleistocene; stratigraphy; Chesapeake Bay; United States

Impact of lake level change on deep-water renewal and oxic conditions in deep saline Lake Van, Turkey - Kaden, H.; Peeters, F.; Lorke, A.; Kipfer, R.; Tomonaga, Y.; Karabiyikoglu, M. (Water Resources Research, 2010)
Changes in the hydrological regime of the saline closed basin Lake Van, a large, deep lake in eastern Turkey, resulted in a lake level increase by about 2 m between 1988 and 1995, followed by a 1.5 m decrease until 2003 and a relatively constant lake level thereafter. Based on measurements of transient tracers (sulfur hexafluoride, CFC-12, 3H, 3He, 4He, Ne), dissolved oxygen, light transmission, conductivity- temperature-depth profiles, and thermistor data, we investigate the implications associated with lake level fluctuations for deep-water renewal and oxygenation. Our data suggest that deep-water renewal was significantly reduced in Lake Van between 1990 and 2005. This change in mixing conditions resulted in the formation of a more than 100 m thick anoxic deep-water body below 325 m depth. Apparently, the freshwater inflows responsible for the lake level rise between 1988 and 1995 decreased the salinity of the surface water sufficiently that the generation of density plumes during winter cooling was substantially reduced compared to that in the years before the lake level rise. Significant renewal and oxygenation of the deep water did not occur until at least 2005, although by 2003 the lake level was back to almost the same level as in 1988. This study suggests that short-term changes in the hydrological regime, resulting in lake level changes of a couple of meters, can lead to significant and long-lasting changes in deep-water renewal and oxic conditions in deep saline lakes. Copyright © 2010 by the American Geophysical Union.
cited By 48
Keywords: Conductivity temperature depths; Deep-water renewals; Deepwater; Eastern Turkey; Freshwater inflow; Hydrological regime; Lake level fluctuations; Lake levels; Long lasting; Mixing conditions; Oxic conditions; Saline lake; Transient tracers; Winter cooling; Biochemical oxygen demand; Dissolved oxygen; Light transmission; Neon; Oxygenation; Oxygenators; Pumps; Saline water; Sulfur; Sulfur hexafluoride; Lakes; deep water; dissolved oxygen; freshwater input; hydrological regime; inflow; lake level; oxic conditions; oxygenation; saline lake; salinity; surface water; tracer; Lake Van; Turkey

Late Quaternary palaeoenvironmental reconstruction from Lakes Ohrid and Prespa (Macedonia/Albania border) using stable isotopes - Leng, M.J.; Baneschi, I.; Zanchetta, G.; Jex, C.N.; Wagner, B.; Vogel, H. (Biogeosciences, 2010)
Here we present stable isotope data from three sediment records from lakes that lie along the Macedonian-Albanian border (Lake Prespa: 1 core, and Lake Ohrid: 2 cores). The records only overlap for the last 40 kyr, although the longest record contains the MIS 5/6 transition (Lake Ohrid). The sedimentary characteristics of both lakes differ significantly between the glacial and interglacial phases. At the end of MIS 6 Lake Ohrid's water level was low (high δ18Ocalcite) and, although productivity was increasing (high calcite content), the carbon supply was mainly from inorganic catchment rock sources (high δ13Ccarb). During the last interglacial, calcite and TOC production and preservation increased, progressively lower δ18Ocalcite suggest increase in humidity and lake levels until around 115 ka. During ca. 80 ka to 11 ka the lake records suggest cold conditions as indicated by negligible calcite precipitation and low organic matter content. In Lake Ohrid, δ13Corg are complacent; in contrast, Lake Prespa shows consistently higher δ13Corg suggesting a low oxidation of 13C-depleted organic matter in agreement with a general deterioration of climate conditions during the glacial. From 15 ka to the onset of the Holocene, calcite and TOC begin to increase, suggesting lake levels were probably low (high δ18Ocalcite). In the Holocene (11 ka to present) enhanced productivity is manifested by high calcite and organic matter content. All three cores show an early Holocene characterised by low δ18Ocalcite, apart from the very early Holocene phase in Prespa where the lowest δ18Ocalcite occurs at ca. 7.5 ka, suggesting a phase of higher lake level only in (the more sensitive) Lake Prespa. From 6 ka, δ18Ocalcite suggest progressive aridification, in agreement with many other records in the Mediterranean, although the uppermost sediments in one core records low δ18Ocalcite which we interpret as a result of human activity. Overall, the isotope data present here confirm that these two big lakes have captured the large scale, low frequency palaeoclimate variation that is seen in Mediterranean lakes, although in detail there is much palaeoclimate information that could be gained, especially small scale, high frequency differences between this region and the Mediterranean. © 2010 Author(s).
Keywords: Lake Mikri Prespa; Lake Ohrid; aridification; calcite; catchment; core analysis; geological record; Holocene; human activity; humidity; Mediterranean environment; paleoclimate; paleoenvironment; reconstruction; sediment core; stable isotope; total organic carbon; water level

Hydrological and solute budgets of Lake Qinghai, the largest lake on the Tibetan Plateau - Jin, Zhangdong; You, Chen-Feng; Wang, Yi; Shi, Yuewei (Quaternary International, 2010)
Water level and chemistry of Lake Qinghai are sensitive to climate changes and are important for paleoclimatic implications. An accurate understanding of hydrological and chemical budgets is crucial for quantifying geochemical proxies and carbon cycle. Published results of water budget are firstly reviewed in this paper. Chemical budget and residence time of major dissolved constituents in the lake are estimated using reliable water budget and newly obtained data for seasonal water chemistry. The results indicate that carbonate weathering is the most important riverine process, resulting in dominance of Ca2+ and DIC for river waters and groundwater. Groundwater contribution to major dissolved constituents is relatively small (4.2 ± 0.5%). Wet atmospheric deposition contributes annually 7.4-44.0% soluble flux to the lake, resulting from eolian dust throughout the seasons. Estimates of chemical budget further suggest that (1) the Buha-type water dominates the chemical components of the lake water, (2) Na+, Cl-, Mg2+, and K+ in lake water are enriched owing to their conservative behaviors, and (3) precipitation of authigenic carbonates (low-Mg calcite, aragonite, and dolomite) transits quickly dissolved Ca2+ into the bottom sediments of the lake, resulting in very low Ca2+ in the lake water. Therefore, authigenic carbonates in the sediments hold potential information on the relative contribution of different solute inputs to the lake and the lake chemistry in the past. © 2009 Elsevier Ltd and INQUA.
Keywords: China; Qinghai; Qinghai Lake; carbon cycle; carbonate; paleohydrology; residence time; solute; water budget; water chemistry; water level; weathering; wet deposition

Fourier transform infrared spectroscopy, a new method for rapid determination of total organic and inorganic carbon and biogenic silica concentration in lake sediments - Rosen, P.; Vogel, H.; Cunningham, L.; Reuss, N.; Conley, D.J.; Persson, P. (Journal of Paleolimnology, 2010)
We demonstrate the use of Fourier transform infrared spectroscopy (FTIRS) to make quantitative measures of total organic carbon (TOC), total inorganic carbon (TIC) and biogenic silica (BSi)concentrations in sediment. FTIRS is a fast and cost-effective technique and only small sediment samples are needed (0.01 g). Statistically significant models were developed using sediment samples from northern Sweden and were applied to sediment records from Sweden, northeast Siberia and Macedonia. The correlation between FTIRS-inferred values and amounts of biogeochemical constituents assessed conventionally varied between r = 0.84-0.99 for TOC, r = 0.85-0.99 for TIC, and r = 0.68-0.94 for BSi. Because FTIR spectra contain information on a large number of both inorganic and organic components, there is great potential for FTIRS to become an important tool in paleolimnology. © Springer Science+Business Media B.V. 2009.
cited By 73
Keywords: biogenic deposit; biogeochemistry; concentration (composition); correlation; FTIR spectroscopy; inorganic carbon; lacustrine deposit; paleolimnology; quantitative analysis; sediment chemistry; silica; total organic carbon; Greece; Macedonia [Greece]; Siberia; Sweden

Environmental change within the Balkan region during the past ca. 50 ka recorded in the sediments from lakes Prespa and Ohrid - Wagner, B.; Vogel, H.; Zanchetta, G.; Sulpizio, R. (Biogeosciences, 2010)
Lakes Prespa and Ohrid, in the Balkan region, are considered to be amongst the oldest lakes in Europe. Both lakes are hydraulically connected via karst aquifers. From Lake Ohrid, several sediment cores up to 15 m long have been studied over the last few years. Here, we document the first long sediment record from nearby Lake Prespa to clarify the influence of Lake Prespa on Lake Ohrid and the environmental history of the region. Radiocarbon dating and dated tephra layers provide robust age control and indicate that the 10.5 m long sediment record from Lake Prespa reaches back to 48 ka. Glacial sedimentation is characterized by low organic matter content and absence of carbonates in the sediments, which indicate oligotrophic conditions in both lakes. Holocene sedimentation is characterized by particularly high carbonate content in Lake Ohrid and by particularly high organic matter content in Lake Prespa, which indicates a shift towards more mesotrophic conditions in the latter. Long-term environmental change and short-term events, such as related to the Heinrich events during the Pleistocene or the 8.2 ka cooling event during the Holocene, are well recorded in both lakes, but are only evident in certain proxies. The comparison of the sediment cores from both lakes indicates that environmental change affects particularly the trophic state of Lake Prespa due to its lower volume and water depth. © Author(s) 2010.
Keywords: Balkan; Lake Mikri Prespa; Lake Ohrid; Turkmenistan; carbonate; core analysis; environmental change; glacial deposit; Heinrich event; Holocene; karst hydrology; lacustrine deposit; organic matter; paleoenvironment; paleolimnology; Pleistocene; radiocarbon dating; sedimentation rate; tephra; trophic status

Hydrogeology of the south-eastern Yucatan Peninsula: New insights from water level measurements, geochemistry, geophysics and remote sensing - Gondwe, B.R.N.; Lerer, S.; Stisen, S.; Mar'in, L.; Rebolledo-Vieyra, M.; Merediz-Alonso, G.; Bauer-Gottwein, P. (Journal of Hydrology, 2010)
The Yucatan Peninsula is one of the world's largest karstic aquifer systems. It is the sole freshwater source for human users and ecosystems. The region hosts internationally important groundwater-dependent ecosystems (GDEs) in the 5280km2 Sian Ka'an Biosphere Reserve. The GDEs are threatened by increasing groundwater abstractions and risks of pollution. Hydrogeological exploration work is needed as basis for sound groundwater management. A multidisciplinary approach was used to study this data-scarce region. Geochemical data and phreatic surface measurements showed distinct hydrogeological units in the groundwater catchment of Sian Ka'an. The hilly southwestern areas had a low hydraulic permeability, likely caused by a geology containing gypsum, whereas the transition zone and flat areas in the east and north had a high permeability. In the latter areas, the fresh groundwater could be described by a Dupuit-Ghyben-Herzberg lens. Geophysical borehole logging and time-domain electromagnetic soundings identified a shallow, low-resistive and high-gamma-radiation layer present throughout the hilly area and transition zone. Its thickness was 3-8m, apparent conductivity was 200-800mS/m and natural gamma-radiation about 80 counts pr. second. The layer is proposed to be ejecta from the Chicxulub impact (Cretaceous/Paleogene boundary). Spatial estimates of recharge were calculated from MODIS imagery using the 'triangle method'. Average recharge constituted 17% of mean annual precipitation in the study area. Recharge was greatest in the hilly area and towards Valladolid. Near the coast, average actual evapotranspiration exceeded annual precipitation. The multidisciplinary approach used in this study is applicable to other catchment-scale studies. © 2010 Elsevier B.V.
cited By 72

Erratum: Constraints on the stress state of the San Andreas Fault with analysis based on core and cuttings from San Andreas Fault Observatory at Depth (SAFOD) drilling phases 1 and 2 (Journal of Geophysical Research B: Solid Earth) - Tembe, S.; Lockner, D.; Wong, T.-F. (Journal of Geophysical Research: Solid Earth, 2010)
cited By 4

Evolution of ancient Lake Ohrid: A tectonic perspective - Hoffmann, N.; Reicherter, K.; Fern'andez-Steeger, T.; Gr{utzner, C. (Biogeosciences, 2010)
Lake Ohrid Basin is a graben structure situated in the Dinarides at the border of the Former Yugoslavian Republic of Macedonia (FYROM) and Albania. It hosts one of the oldest lakes in Europe and is characterized by a basin and range-like geological setting together with the halfgraben basins of Korca, Erseka and Debar. The basin is surrounded by Paleozoic metamorphics in the northeast and north and Mesozoic ultramafic, carbonatic and magmatic rocks in the east, northwest, west and south. Paleocene to Pliocene units are present in the southwest. With the basin development, Neogene sediments from Pliocene to recent deposited in the lows. There are three major deformation phases: (A) NWĝ€SE shortening from Late Cretaceous to Miocene; (B) uplift and diminishing compression during Messinian ĝ€ Pliocene; (C) vertical uplift and (N)Eĝ€(S)W extension from Pliocene to recent led to the basin formation. Neotectonic activity of the study area concentrates on Nĝ€S trending normal faults that bound the Ohrid Basin eastwards and westwards. Seismic activity with moderate to strong events is documented during the last 2000 yrs; the seismic hazard level is among the highest in Albania and Macedonia. Activity of the youngest faults is evidenced by earthquake data and field observations. Morphotectonic features like fault scarps, a stepped series of active normal faults, deformed paleosols, a wind gap and fault-related hydrothermal activity are preserved around Lake Ohrid and allow delineating the tectonic history. It is shown that the Lake Ohrid Basin can be characterized as a seismogenic landscape. This paper presents a tectonic history of the Lake Ohrid Basin and describes tectonic features that are preserved in the recent landscape. The analysis of morphotectonic features is used to derive the deformation history. The stratigraphy of the area is summarized and concentrates on the main units. © 2010 Author(s).
Keywords: Albania; Lake Ohrid; Macedonia [Southern Europe]; data set; hydrothermal activity; lake evolution; landscape; magmatism; metamorphism; Neogene; neotectonics; observational method; Paleozoic; seismic anisotropy; seismic hazard; stratigraphy; uplift

Extreme coring - Skinner, A.; Bowers, P.; P'orhallsson, S.; Frioleifsson, G.O.; Guomundsson, H. (Geodrilling International, 2010)
The science program of the Iceland Deep Drilling Project (IDDP) requested that as much coring as possible should be done in the transition zone to supercritical and inside the supercritical zone in the depth interval 2,400-4,500m. The coring system selected is of conventional design, non-wireline with a 184.15mm OD and capable of collection of a 101.6mm diameter core using a 215.9mm OD core bit. The effective cooling is attributed to a top drive being employed that allows circulation while tripping in or out, except for the very short time when a new drill pipe connection is being made. The core barrels were made by Rok-Max Drilling Tools Ltd and the core bits were made by GeoGem Ltd, both UK companies with a good track record in making specialist coring equipment. The cored section consisted of a hyaloclastite breccia, thoroughly altered to greenschist facies mineralogy.
cited By 3

Electromagnetic methods to monitor gas hydrate distribution and production in layered sediments - Enkin, R.J.; Hamilton, T.S.; Wright, J.F.; Kilduff, M.; Bild-Enkin, D.J.W. (Society of Petroleum Engineers - Canadian Unconventional Resources and International Petroleum Conference 2010, 2010)
Natural gas hydrate reservoirs are hosted in heterogeneous sediments having variable pore fluid salinity. Questions concerning GH formation, detection and production are being addressed and measured in real time with simple laboratory apparatus. Our vessel is pressurized with methane and monitored with individually calibrated pressure transducers and thermistors. The silt or sand pack is assembled using uniform grain size layers containing ∼20% by weight of pore fluids. This results in mixed wettability, with pendant water and initial partial gas saturation. Sand packs consisting of silica silts, sands, and charcoal were selected to emulate the dominant lithofacies observed in the Mallik gas hydrate reservoir. Fluids range from distilled-water to 37ppt salinity. A central needle probe permits the measurements of electromagnetic signals across the specimen. Formation of GH alters the bulk dielectric constant of the mixture, through the conversion of water to gas hydrate crystals and or ice. The infilling of primary porosity by gas hydrate or water ice tends to reduce permeability and increase electrical resistivity, while the expulsion of solutes by hydrate or ice formation decreases resistivity by building a salt bridge along alternate permeability paths. Four methods monitored GH formation and dissociation: 1) Deposition or evolution of gas derived from measurement of the ambient pressure and temperature; 2) Calorimetric measurements of latent heat production by exothermic crystallization and consumption by endothermic dissociation; 3) Time-Domain Reflectometry (TDR) measurement of the velocity of electromagnetic signal propagation and reflections at boundaries in the sand pack; 4) Electrical Impedance Spectroscopy (EIS), a frequency domain method permitting direct measurement of the resistance and capacitance spectra. Improvements in real time digital monitoring and data analysis have made possible the recognition of TDR reflections previously considered unattainable in the presence of conducting fluids. The independent monitoring methods, with their various temporal and spatial sensitivities, capture the intricate details of GH formation and dissociation as a time series. In more porous and permeable beds, GH formation as evidenced by a coherent pressure drop and thermal pulse precedes the increase in electrical conductivity and dielectric constant. These results are interpreted to be the result of a diffusive pulse of solute exclusion from the GH-bearing layer into neighbouring sediment. Measurable EM effects suggest that borehole EIS, with lower frequency and greater penetration than TDR, may be effective for monitoring the variable position of GH-Methane interfaces during GH production tests. ©Her Majesty the Queen in Right of Canada 2010.
cited By 1
Keywords: Charcoal; Dissociation; Electric conductivity; Frequency domain analysis; Gases; Gasoline; Heat resistance; Hydration; Ice; Methane; Natural gasoline plants; Resource valuation; Sand; Sediments; Silica; Silt; Time domain analysis; Calorimetric measurements; Electrical impedance spectroscopy; Exothermic crystallization; Frequency-domain methods; Heterogeneous sediments; Natural gas hydrate reservoir; Temporal and spatial sensitivity; Time domain reflectometry; Gas hydrates

Fault zone structure at depth from differential dispersion of seismic guided waves: Evidence for a deep waveguide on the San Andreas Fault - Wu, J.; Hole, J.A.; Snoke, J.A. (Geophysical Journal International, 2010)
Seismic guided wave dispersion can be used to image fault-zone structure at seismogenic depth. A two-station differential group velocity technique previously used for surface waves was adapted to solve for local fault-zone structure between two stations. This method was extended to solve for fault-zone structure between two earthquakes using differential group arrival times at a single station. The method was tested with finite-difference synthetic data for an inhomogeneous fault, as well as with a pair of shallow earthquakes recorded in the San Andreas Fault Observatory at Depth (SAFOD) borehole station. Results from a pair of deep earthquakes recorded in the SAFOD borehole station indicate that the low-velocity waveguide of the San Andreas Fault extends to >10 km depth. The waveguide at 10-12 km depth is 120-190 m wide and the velocity contrast is >20 per cent, similar to the values in the shallow subsurface. Multiple earthquakes and receivers could be used to map fault zone structure at seismogenic depth as a function of depth and strike. © 2010 The Authors Journal compilation © 2010 RAS.
cited By 25
Keywords: arrival time; fault zone; finite difference method; image analysis; San Andreas Fault; seismic data; seismic velocity; seismic wave; wave dispersion; wave propagation

Geochemistry of basement rocks and impact breccias from the central uplift of the Bosumtwi crater, Ghana - Comparison of proximal and distal impactites - Ferrière, Ludovic; Koeberl, Christian; Brandst{atter, Franz; Mader, Dieter (Special Paper of the Geological Society of America, 2010)
Crater-fill impact breccia and basement rock samples from the 1.07 Ma Bosumtwi impact structure (Ghana) were recovered for the first time in 2004 during an International Continental Scientific Drilling Program (ICDP)-sponsored drilling project. Here, we present detailed results of major-and trace-element analyses of 119 samples from drill core LB-08A, together with the chemical compositions of melt particles from suevite. The meta-graywacke and phyllite/slate crater basement rocks can be easily distinguished from each other on the basis of their bulk chemical compositions. A comparison of the chemical compositions of crater-fill and fallout suevites, as well as between proximal and distal impactites, reveals that LB-08A suevites have higher MgO, CaO, and Na 2 O contents than fallout suevites and, similarly, that the CaO and Na 2 O contents are higher by a factor of approximately two in LB-08A suevites than in Ivory Coast tektites. Noticeable differences occur in Cr, Co, and Ni contents between the different impactites; higher abundances are observed for these elements in distal impactites. The observed differences in composition in the various impactites mainly reflect mixing of different proportions of the original target lithologies, as can be seen in the differences in the clast populations between crater-fill and fallout suevites. However, the original impactite compositions may have also been modifi ed by postimpact alteration, particularly in the proximal impactites. Melt particles in suevite show signifi cant differences in major-element compositions between the different samples investigated, but also within a given sample, indicating that they represent melts derived from different lithologies.© 2010 The Geological Society of America. All rights reserved.
Keywords: Ashanti; Ghana; Lake Bosumtwi; Chemical analysis; Core drilling; Fallout; Infill drilling; Magnesia; Rocks; Sodium compounds; Trace elements; Bulk chemical composition; Chemical compositions; Continental scientific drillings; Different proportions; Drilling projects; Impact structures; In compositions; Major and trace elements; basement rock; breccia; chemical composition; crater; geochemistry; impact structure; impactite; suevite; trace element; Meteor impacts

Geoelectrical Investigations in the Cheb Basin/W-Bohemia: An Approach to Evaluate the Near-Surface Conductivity Structure - Flechsig, Christina; Fabig, Tobias; R{ucker, Carsten; Sch{utze, Claudia (Studia Geophysica et Geodaetica, 2010)
The Cheb Basin, located in the western Eger (Ohře) Rift, is part of the European Cenozoic Rift system. Although presently non-volcanic, it is the most active area within the European Rift with signs of recent geodynamic activity like emanations of mantle derived CO2, and the repeated occurrence of swarm earthquakes, which are common features in active volcanic regions. It is assumed that the fluids, uprising in permeable channels, play a key role for the genesis of these earthquake swarms. An image of the distribution of the electrical conductivity (resp. resistivity) in the upper crust can give information about the fluid distribution since the electrical patterns reflect pathways of fluids and fluid properties like ionic content. This was the motivation to start both a regional-scale direct current (DC) geoelectrical test covering the Cheb Basin area and several local-scale near surface investigations inside the basin at the seismically active faults Poč'atky-Plesn'a Zone (PPZ) and Mari'ansk'e L'azně Fault Zone (MLF) near Nov'y Kostel. It was the research idea to test electrical tomography's ability to detect faults and tectonic deformation in a complex geological environment and to identify characteristic features of these faults. The more methodically justified regional field test mainly aimed at clarifying the opportunity to trace DC electrical signals in an area with known high industrial noise in a sufficient quality. A field set-up with a range of 15-20 km is necessary for an investigation depth of 4-5 km in case of DC geoelectrics. A new developed inversion strategy for sparse electrical data sets allows for a first (coarse) model of resistivity distribution. The near surface investigations in prominent fault zones of the Cheb Basin give more detailed information about the structure of fault zones, divide the sedimentary units in different resistivity zones and detect vertical displacements in the quaternary formations. © 2010 Institute of Geophysics of the ASCR, v.v.i.
Keywords: Bohemia; Cheb Basin; Czech Republic; Karlovarsky; active fault; electrical conductivity; electrical resistivity; fault zone; geodynamics; geoelectric field; mantle source; numerical model; tomography; upper crust; vertical electrical sounding

Geology: A trip to dinosaur time - Qiu, J. (Nature, 2010)
cited By 1
Keywords: environmental temperature; geological time; geology; greenhouse; note; paleoclimatology; Paleogene; priority journal; science; sediment; volcano; Dinosauria

Geophysical properties within the San Andreas Fault Zone at the San Andreas Fault Observatory at Depth and their relationships to rock properties and fault zone structure - Jeppson, T.N.; Bradbury, K.K.; Evans, J.P. (Journal of Geophysical Research: Solid Earth, 2010)
We examine the relationships between borehole geophysical data and physical properties of fault-related rocks within the San Andreas Fault as determined from data from the San Andreas Fault Observatory at Depth borehole. Geophysical logs, cuttings data, and drilling data from the region 3-to 4-km measured depth of the borehole encompass the active part of the San Andreas Fault. The fault zone lies in a sequence of deformed sandstones, siltstone, shale, serpentinite-bearing block-in-matrix rocks, and sheared phyllitic siltstone. The borehole geophysical logs reveal the presence of a low-velocity zone from 3190 to 3410 m measured depth with Vp and Vs values 10-30% lower than the surrounding rocks and a 1-2 m thick zone of active shearing at 3301-3303 m measured depth. Seven low-velocity excursions with increased porosity, decreased density, and mud-gas kick signatures are present in the fault zone. Geologic data on grain-scale deformation and alteration are compared to borehole data and reveal weak correlations and inverse relationships to the geophysical data. In places, Vp and Vs increase with grain-scale deformation and alteration and decrease with porosity in the fault zone. The low-velocity zone is associated with a significant lithologic and structural transition to low-velocity rocks, dominated by phyllosilicates and penetratively foliated, sheared rocks. The zone of active shearing and the regions of low sonic velocity appear to be associated with clay-rich rocks that exhibit fine-scale foliation and higher porosities that may be a consequence of the fault-related shearing of foliated and fine-grained sedimentary rocks. Copyright 2010 by the American Geophysical Union.
cited By 35
Keywords: borehole logging; data inversion; deformation; fault zone; foliation; geophysical method; porosity; rock property; San Andreas Fault; sandstone; shale; siltstone

High-precision orientation of three-component magnetic downhole logs - Virgil, Christopher; H{ordt, Andreas; Klein, Torsten; K{uck, Jochem; Leven, Martin; Steveling, Erich (Scientific Drilling, 2010)

Palaeoenvironmental significance of carbon- and oxygen-isotope stratigraphy of marine Triassic-Jurassic boundary sections in SW Britain - Korte, Christoph; Hesselbo, Stephen P.; Jenkyns, Hugh C.; Rickaby, Rosalind E.M.; Sp{otl, Christoph (Journal of the Geological Society, 2009)
Carbon-isotope stratigraphy is a useful tool for stratigraphic correlation, especially for strata deposited during major perturbations of the carbon cycle that affected the marine, terrestrial and atmospheric reservoirs. For the Triassic-Jurassic boundary, effectively defined by a first-order mass extinction, major fluctuations in carbon-isotope values have been well documented, but these datasets have generally been derived from bulk-rock samples. Hence, the extent to which features of the isotopic curve reflect diagenetic alteration or changing proportions of constituent materials is unconstrained. Here, carbon- and oxygen-isotope data are presented from well-preserved oyster shells (Liostrea) comprising low-magnesium calcite, a mineral species relatively resistant to diagenetic alteration. Samples were obtained from Lavernock Point, Glamorgan, Wales, a coastal section close to a candidate stratotype for the base of the Jurassic at St Audrie's Bay, Somerset, England. The carbon-isotope signature from St Audrie's Bay, previously defined on the basis of analysis of bulk organic matter, is confirmed by our new data. Major features are (1) the upper part of an 'initial' negative isotope excursion in the lowest part of the section, followed by (2) a pronounced positive excursion, and (3) an extended 'main' negative isotope excursion in the highest part of the section. The data confirm that the carbon-isotope stratigraphy previously documented from bulk organic matter in SW England records the chemical composition of the contemporaneous seawater. Bulk carbonates sampled over the same interval near Lyme Regis, England, show similar trends to those from oyster calcite in the lower part of the study section, but there are more 13C-depleted values up-section. These lower values probably result from an admixture of primary and diagenetic carbonate. Palaeotemperatures calculated from oxygen-isotope values from Lavernock Point oyster shells are relatively cool at the beginning of the positive carbon-isotope excursion, and increased by up to 10 8C during the main negative carbon-isotope excursion. The new results are compatible with the view that positive carbon-isotope excursions correspond to times of low atmospheric carbon dioxide content, whereas negative carbon-isotope excursions correspond to times of high atmospheric carbon dioxide content, as is also found to be the case during the Early Jurassic (Toarcian) Oceanic Anoxic Event. The Mg/Ca and Sr/Ca ratios and 18O of investigated Liostrea hisingeri show no correlation,supporting data from modern bivalves that indicate that incorporation of Mg and Sr is controlled mainly by factors other than temperature. © 2009 Geological Society of London.
Keywords: England; Eurasia; Europe; Glamorgan; Saint Audrie' s Bay; Somerset; United Kingdom; Wales; Western Europe; Bivalvia; Ostreidae; carbon cycle; carbon dioxide; carbon isotope; chemical composition; Jurassic; oxygen isotope; paleoenvironment; paleotemperature; seawater; stratigraphic boundary; stratigraphic correlation; Triassic

Palaeolimnological evidence for environmental change over the past millennium from Lake Qinghai sediments: A review and future research prospective - Henderson, Andrew C.G.; Holmes, Jonathan A. (Quaternary International, 2009)
Lake Qinghai, on the NE Tibetan Plateau, is China's largest natural lake that lies at a triple junction of major climatic influences, making it sensitive to global climate change. As such, the sediments of Lake Qinghai have been the focus of numerous palaeoenvironmental studies spanning a range of timescales. However, as a result of uncertain age controls, uncertainties over interpretation of the proxies, the relative dearth of proxy calibration and lack of understanding of the modern lake system a coherent picture of climate over the NE Tibetan Plateau has yet to emerge from Lake Qinghai's sediment record. We review the state of knowledge for this important site, focusing on the last millennium. A comparison of the major proxy records show significant variability with a general pattern of change over the last 1000 years, notably those linked to the onset of the Little Ice Age, but due to poor chronological constraints a detailed picture of climate change cannot be established. Further, some of the proxy records produced from Lake Qinghai's sediments are open to alternative explanations. This compounds the sediment record as a palaeoenvironmental archive. To fully realise the potential of Lake Qinghai, future research must concentrate on defining a reliable old carbon effect for the lake, calibrating proxy records with climatic processes and understanding spatial variability of proxy records within this large lake. © 2008 Elsevier Ltd and INQUA.
Keywords: Asia; China; Eurasia; Far East; Qinghai; Qinghai Lake; climate change; Holocene; lacustrine deposit; paleoenvironment; paleolimnology; proxy climate record

Palaeoproterozoic petrified oil field (Shunga Event) - Medvedev, PV; Melezhik, VA; Filippov, MM (Paleontological Journal, 2009)

Paleoenvironmental recovery from the Chesapeake Bay bolide impact: The benthic foraminiferal record - Poag, C.W. (Special Paper of the Geological Society of America, 2009)
The late Eocene Chesapeake Bay bolide impact transformed its offshore target site from an outer neritic, midshelf seafl oor into a bathyal crater basin. To obtain a depositional record from one of the deepest parts of this basin, the U.S. Geological Survey (USGS) and the International Continental Scientifi c Drilling Program (ICDP) drilled a 1.76-km-deep core hole near Eyreville, Virginia. The Eyreville core and eight previously cored boreholes contain a rarely obtainable record of marine deposition and microfossil assemblages that characterize the transition from synimpact to postimpact paleoenvironments inside and near a submarine impact crater. I used depositional style and benthic foraminiferal assemblages to recognize a four-step transitional succession, with emphasis on the Eyreville core. Step 1 is represented by small-scale, silt-rich turbidites, devoid of indigenous microfossils, which lie directly above the crater-fi lling Exmore breccia. Step 2 is represented by very thin, parallel, silt and clay laminae, which accumulated on a relatively tranquil and stagnant seafl oor. This stagnation created a dead zone, which excluded seafl oor biota, and it lasted 3-5 ka. Step 3 is an interval of marine clay deposition, accompanied by a burst of microfaunal activity, as a species-rich pioneer community of benthic foraminifera repopulated the impact site. The presence of a diagnostic suite of agglutinated foraminifera during step 3 indicates that paleoenvironmental stress related to the impact lasted from 9 ka to 400 ka at different locations inside the crater. During step 4, the agglutinated assemblage disappeared, and an equilibrium foraminiferal community developed that contained nearly 100% calcareous species. In contrast to intracrater localities, core sites outside and near the crater rim show neither evidence of the agglutinated assemblage, nor other indications of long-term biotic disruption from the bolide impact. © 2009 The Geological Society of America.
cited By 7

Overview of energy-related studies of gas hydrates in Canada - Dallimore, S.R. (ACS National Meeting Book of Abstracts, 2009)
Canada has been involved in assessing the energy potential of gas hydrates since the 1970's when the Geological Survey of Canada (GSC) assisted industry in appraising problems encountered during exploratory drilling in the Arctic. This work led to the first regional studies of permafrost gas hydrates in the 1980s and preliminary resource estimates in the 1990s. On Canada's Pacific coast GSC researchers first discovered the widespread characteristic gas hydrate bottom-simulating reflector in multichannel seismic surveys in 1985. Since then there has been extensive multi-disciplinary surveys/studies by GSC, Canadian universities, and international scientists on Canada's west and east coasts. Two ODP/IOPD expeditions have been dedicated to sampling and measuring gas hydrates off Vancouver Island. Over the past decade Canada has played a leading role internationally in hydrate production technology, improving geophysical detection techniques, and undertaking laboratory investigations of geologic controls. In 1998, the GSC, in partnership with the Japan National Oil Corporation, recovered the world's first Arctic gas hydrate-bearing core samples from the Mallik site, Mackenzie Delta. This program defined a highly concentrated, reservoir-scale occurrence of gas hydrates within a potentially producible porous sand matrix. In 2002, a five-nation international research consortium (Canada, Japan, USA, Germany, India) conducted large- and small-scale production experiments at Mallik to evaluate the efficiency of pressure reduction vs. heat stimulation for initiating in situ dissociation of gas. These experiments, along with state-of-the-art well logging and extensive post-field laboratory studies, provided critical scientific and technical data supporting the design and engineering of a subsequent Canada-Japan extended production testing program conducted during the winters of 2007/2008. In March 2008, 6 days of continuous methane production were achieved by depressurization of a concentrated gas hydrate interval. The Mallik test results have been widely acknowledged as Proof of Concept for the production of methane from hydrates by the depressurization method.
cited By 0

Paleoenvironmental recovery from the Chesapeake Bay bolide impact: The benthic foraminiferal record - Poag, C.W. (Special Paper of the Geological Society of America, 2009)
The late Eocene Chesapeake Bay bolide impact transformed its offshore target site from an outer neritic, midshelf seafl oor into a bathyal crater basin. To obtain a depositional record from one of the deepest parts of this basin, the U.S. Geological Survey (USGS) and the International Continental Scientifi c Drilling Program (ICDP) drilled a 1.76-km-deep core hole near Eyreville, Virginia. The Eyreville core and eight previously cored boreholes contain a rarely obtainable record of marine deposition and microfossil assemblages that characterize the transition from synimpact to postimpact paleoenvironments inside and near a submarine impact crater. I used depositional style and benthic foraminiferal assemblages to recognize a four-step transitional succession, with emphasis on the Eyreville core. Step 1 is represented by small-scale, silt-rich turbidites, devoid of indigenous microfossils, which lie directly above the crater-fi lling Exmore breccia. Step 2 is represented by very thin, parallel, silt and clay laminae, which accumulated on a relatively tranquil and stagnant seafl oor. This stagnation created a dead zone, which excluded seafl oor biota, and it lasted 3-5 ka. Step 3 is an interval of marine clay deposition, accompanied by a burst of microfaunal activity, as a species-rich pioneer community of benthic foraminifera repopulated the impact site. The presence of a diagnostic suite of agglutinated foraminifera during step 3 indicates that paleoenvironmental stress related to the impact lasted from 9 ka to 400 ka at different locations inside the crater. During step 4, the agglutinated assemblage disappeared, and an equilibrium foraminiferal community developed that contained nearly 100% calcareous species. In contrast to intracrater localities, core sites outside and near the crater rim show neither evidence of the agglutinated assemblage, nor other indications of long-term biotic disruption from the bolide impact. © 2009 The Geological Society of America.
cited By 7
Keywords: C (programming language); Deposition; Infill drilling; Offshore oil well production; Silt; Agglutinated foraminifera; Benthic foraminifera; Foraminiferal assemblages; Impact craters; Microfossil assemblages; Offshore targets; Paleoenvironments; U.s. geological surveys; Boreholes; accumulation; benthic foraminifera; bolide; crater; deep drilling; deep-sea sediment; deposition; depositional environment; Eocene; fossil assemblage; geological survey; impact structure; paleoenvironment; turbidite; Chesapeake Bay; United States; Virginia; Foraminifera

Paleontological interpretations of crater processes and infilling of synimpact sediments from the Chesapeake Bay impact structure - Self-Trail, J.M.; Edwards, L.E.; Litwin, R.J. (Special Paper of the Geological Society of America, 2009)
Biostratigraphic analysis of sedimentary breccias and diamictons in the Chesapeake Bay impact structure provides information regarding the timing and processes of late-stage gravitational crater collapse and ocean resurge. Studies of calcareous nannofossil and palynomorph assemblages in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B cores show the mixed-age, mixed-preservation microfossil assemblages that are typical of deposits from the upper part of the Chesapeake Bay impact structure. Sparse, poorly preserved, possibly thermally altered pollen is present within a gravelly sand interval below the granite slab at 1392 m in Eyreville core B, an interval that is otherwise barren of calcareous nannofossils and dinocysts. Gravitational collapse of watersaturated sediments from the transient crater wall resulted in the deposition of sediment clasts primarily derived from the nonmarine Cretaceous Potomac Formation. Collapse occurred before the arrival of resurge. Low pollen Thermal Alteration Index (TAI) values suggest that these sediments were not thermally altered by contact with the melt sheet. The arrival of resurge sedimentation is identified based on the presence of diamicton zones and stringers rich in glauconite and marine microfossils at 866.7 m. This horizon can be traced across the crater and can be used to identify gravitational collapse versus ocean-resurge sedimentation. Glauconitic quartz sand diamicton dominates the sediments above 618.2 m. Calcareous nannofossil and dinoflagellate data from this interval suggest that the earliest arriving resurge from the west contained little or no Cretaceous marine input, but later resurge pulses mined Cretaceous sediments east of the Watkins core in the annular trough. Additionally, the increased distance traveled by resurge to the central crater in turbulent flow conditions resulted in the disaggregation of Paleogene unconsolidated sediments. As a result, intact Paleogene clasts in Eyreville cores are rare, but clasts of semilithified Potomac Formation silts and clays are common. © 2009 The Geological Society of America.
cited By 17
Keywords: Gravitational effects; Infill drilling; Mica; Stars; Biostratigraphic analysis; Calcareous nannofossil; Calcareous nannofossils; Chesapeake bay impact structures; Continental scientific drillings; Microfossil assemblages; U.s. geological surveys; Unconsolidated sediment; Sediments; biostratigraphy; breccia; crater; diamicton; dinoflagellate cyst; fossil assemblage; infill; microfossil; micropaleontology; Paleogene; palynomorph; pollen; research program; sedimentation; turbulent flow; Chesapeake Bay; United States; Dinophyceae

Petrology of impact melt rocks from the Chesapeake Bay crater, USA - Wittmann, A.; Schmitt, R.T.; Hecht, L.; Kring, D.A.; Reimold, W.U.; Povenmire, H. (Special Paper of the Geological Society of America, 2009)
The Eyreville B drill core in the inner annular moat of the 85-km-diameter Chesapeake Bay impact structure recovered the first coherent impact melt volumes from within the crater as two bodies, 1 and 5.5 m thick. This study focuses on the petrogenesis of these well-preserved rocks. Mixing calculations reveal that the chemical composition of these melts can be modeled as a hybrid of ̃40% sedimentary target and ̃60% crystalline basement component. The melt rocks contain abundant lithic and mineral clasts that display all stages of shock metamorphism. Zircon clasts record the cooling of the melt from temperatures above 1700 °C to below 1200 °C within the first minutes after formation. Glassy melt with a peraluminous, rhyolitic composition that contains ̃5 wt% water is preserved. This melt records a crystallization sequence of aluminum-rich orthopyroxene and hercynitic spinel, followed by plagioclase, titanomagnetite and cordierite, and late sanidine. Spherulitic aluminosilicate-SiO 2 -cordierite aggregates that are comparable to buchites at temperatures below ̃1465 °C complement this assemblage. Lack of hyaloclastic fragmentation suggests dry emplacement conditions. Complete cooling by conductive heat transfer took ̃7 weeks and ̃4 years for the 1-m- and the 5.5-m-thick melt bodies, respectively. Alteration stages below ̃100 °C produced smectite, phillipsite, chalcedony, and a rare zeolite phase that is tentatively identified as terranovaite. © 2009 The Geological Society of America.
cited By 40

Petrographic and geochemical comparisons between the lower crystalline basement-derived section and the granite megablock and amphibolite megablock of the Eyreville B core, Chesapeake Bay impact structure, USA - Townsend, G.N.; Gibson, R.L.; Horton Jr., J.W.; Reimold, W.U.; Schmitt, R.T.; Bartosova, K. (Special Paper of the Geological Society of America, 2009)
The Eyreville B core from the Chesapeake Bay impact structure, Virginia, USA, contains a lower basement-derived section (1551.19 m to 1766.32 m deep) and two megablocks of dominantly (1) amphibolite (1376.38 m to 1389.35 m deep) and (2) granite (1095.74 m to 1371.11 m deep), which are separated by an impactite succession. Metasedimentary rocks (muscovite-quartz-plagioclase-biotite-graphite ± fibrolite ± garnet ± tourmaline ± pyrite ± rutile ± pyrrhotite mica schist, hornblende-plagioclase-epidote-biotite- K-feldspar-quartz-titanite-calcite amphibolite, and vesuvianite-plagioclase- quartz-epidote calc-silicate rock) are dominant in the upper part of the lower basement-derived section, and they are intruded by pegmatitic to coarse-grained granite (K-feldspar-plagioclase-quartz-muscovite ± biotite ± garnet) that increases in volume proportion downward. The granite megablock contains both gneissic and weakly or nonfoliated biotite granite varieties (K-feldspar-quartz-plagioclase-biotite ± muscovite ± pyrite), with small schist xenoliths consisting of biotite-plagioclase-quartz ± epidote ± amphibole. The lower basement-derived section and both megablocks exhibit similar middleto upper-amphibolite-facies metamorphic grades that suggest they might represent parts of a single terrane. However, the mica schists in the lower basement-derived sequence and in the megablock xenoliths show differences in both mineralogy and whole-rock chemistry that suggest a more mafi c source for the xenoliths. Similarly, the mineralogy of the amphibolite in the lower basement-derived section and its association with calc-silicate rock suggest a sedimentary protolith, whereas the bulk-rock and mineral chemistry of the megablock amphibolite indicate an igneous protolith. The lower basement-derived granite also shows bulk chemical and mineralogical differences from the megablock gneissic and biotite granites. © 2009 The Geological Society of America.
cited By 18
Keywords: Biotite; Buildings; Calcite; Feldspar; Granite; Quartz; Sedimentary rocks; Silicate minerals; Amphibolite facies; Biotite granite; Chesapeake bay impact structures; Crystalline basement; Metamorphic grade; Metasedimentary rocks; Mineral chemistry; Silicate rocks; Mica; amphibolite; crater; geochemistry; granite; impact structure; impactite; metasedimentary rock; petrography; schist; Chesapeake Bay; United States

Petrographic and geochemical comparisons between the lower crystalline basement-derived section and the granite megablock and amphibolite megablock of the Eyreville B core, Chesapeake Bay impact structure, USA - Townsend, G.N.; Gibson, R.L.; Horton Jr., J.W.; Reimold, W.U.; Schmitt, R.T.; Bartosova, K. (Special Paper of the Geological Society of America, 2009)
The Eyreville B core from the Chesapeake Bay impact structure, Virginia, USA, contains a lower basement-derived section (1551.19 m to 1766.32 m deep) and two megablocks of dominantly (1) amphibolite (1376.38 m to 1389.35 m deep) and (2) granite (1095.74 m to 1371.11 m deep), which are separated by an impactite succession. Metasedimentary rocks (muscovite-quartz-plagioclase-biotite-graphite ± fibrolite ± garnet ± tourmaline ± pyrite ± rutile ± pyrrhotite mica schist, hornblende-plagioclase-epidote-biotite- K-feldspar-quartz-titanite-calcite amphibolite, and vesuvianite-plagioclase- quartz-epidote calc-silicate rock) are dominant in the upper part of the lower basement-derived section, and they are intruded by pegmatitic to coarse-grained granite (K-feldspar-plagioclase-quartz-muscovite ± biotite ± garnet) that increases in volume proportion downward. The granite megablock contains both gneissic and weakly or nonfoliated biotite granite varieties (K-feldspar-quartz-plagioclase-biotite ± muscovite ± pyrite), with small schist xenoliths consisting of biotite-plagioclase-quartz ± epidote ± amphibole. The lower basement-derived section and both megablocks exhibit similar middleto upper-amphibolite-facies metamorphic grades that suggest they might represent parts of a single terrane. However, the mica schists in the lower basement-derived sequence and in the megablock xenoliths show differences in both mineralogy and whole-rock chemistry that suggest a more mafi c source for the xenoliths. Similarly, the mineralogy of the amphibolite in the lower basement-derived section and its association with calc-silicate rock suggest a sedimentary protolith, whereas the bulk-rock and mineral chemistry of the megablock amphibolite indicate an igneous protolith. The lower basement-derived granite also shows bulk chemical and mineralogical differences from the megablock gneissic and biotite granites. © 2009 The Geological Society of America.
cited By 18

Petrographic and shock metamorphic studies of the impact breccia section (1397-1551 m depth) of the Eyreville drill core, Chesapeake Bay impact structure, USA - Bartosova, K.; Ferrière, L.; Koeberl, C.; Reimold, W.U.; Gier, S. (Special Paper of the Geological Society of America, 2009)
The moat of the 85-km-diameter and 35.3-Ma-old Chesapeake Bay impact structure (USA) was drilled at Eyreville Farm in 2005-2006 as part of an International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) drilling project. The Eyreville drilling penetrated postimpact sediments and impactites, as well as crystalline basement-derived material, to a total depth of 1766 m. We present petrographic observations on 43 samples of suevite, impact melt rock, polymict lithic impact breccia, cataclastic gneiss, and clasts in suevite, from the impact breccia section from 1397 to 1551 m depth in the Eyreville B drill core. Suevite samples have a fine-grained clastic matrix and contain a variety of mineral and rock clasts, including sedimentary, metamorphic, and igneous lithologies. Six subunits (U1-U6, from top to bottom) are distinguished in the impact breccia section based on abundance of different clasts, melt particles, and matrix; the boundaries between the subunits are generally gradational. Sedimentary clasts are dominant in most subunits (especially in U1, but also in U3, U4, and U6). There are two melt-rich subunits (U1 and U3), and there are two melt-poor subunits with predominantly crystalline clasts (U2 and U5). The lower part (subunits U5 and U6), which has large blocks of cataclastic gneiss and rare melt particles, probably represents ground-surge material. Subunit U1 possibly represents fallback material, since it contains shard-like melt particles that were solidified before incorporation into the breccia. The melt-poor, crystalline clast-rich subunit U2 could have been formed by slumping of material, probably from the central uplift or from the margin of the transient crater. Melt particles are most abundant near the top of the impact breccia section (above 1409 m) and around 1450 m, where the suevite grades into impact melt rock. Five different types of melt particles have been recognized: (1) clear colorless to brownish glass; (2) melt altered to fine-grained phyllosilicate minerals; (3) recrystallized silica melt; (4) melt with microlites; and (5) dark-brown melt. Proportions of matrix and melt in the suevite are highly variable (̃2-67 vol% and 1-67 vol%, respectively; the remainder consists of lithic clasts). Quartz grains in suevite commonly show planar fractures (PFs) and/or planar deformation features (PDFs; 1 or 2 sets, rarely more); some PDFs are decorated. On average, ̃16 rel% of quartz grains in suevite samples are shocked (i.e., show PFs and/or PDFs). Sedimentary clasts (e.g., graywacke or sandstone) and polycrystalline quartz clasts have relatively higher proportions of shocked quartz grains, whereas quartz grains in schist and gneiss clasts rarely show shock effects. Rare feldspar grains with PDFs and mica with kink banding were observed. Ballen quartz was noted in melt-rich samples. Evidence of hydrothermal alteration, namely, the presence of smectite and secondary carbonate veins, was found especially in the lower parts of the impact breccia section. © 2009 The Geological Society of America.
cited By 14
Keywords: Binary alloys; Clay alteration; Crystalline materials; Crystalline rocks; Drills; Feldspar; Igneous rocks; Infill drilling; Metamorphic rocks; Mica; Quartz; Sedimentary rocks; Sedimentology; Silicate minerals; Silicon alloys; Chesapeake bay impact structures; Continental scientific drillings; Crystalline basement; Derived materials; Hydrothermal alterations; Planar deformation; Polycrystalline quartz; U.s. geological surveys; Core drilling; breccia; crater; drilling; hydrothermal alteration; impact structure; impactite; petrography; shock metamorphism; suevite; Chesapeake Bay; United States

Petrographic observations on the Exmore breccia, ICDP-USGS drilling at Eyreville, Chesapeake Bay impact structure, USA - Reimold, W.U.; Bartosova, K.; Schmitt, R.T.; Hansen, B.; Crasselt, C.; Koeberl, C.; Wittmann, A.; Powars, D.S. (Special Paper of the Geological Society of America, 2009)
The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B drill cores sampled crater fill in the region of the crater moat, ̃9 km to the NE of the center of the Chesapeake Bay impact structure, Virginia, USA. They provide a 953 m section (444-1397 m depth) of sedimentary clast breccia and intercalated sedimentary and crystalline megablocks knownas Exmore beds, deposited on top of the impactite sequence between 1397 and 1551 m depth. We petrographically investigated the sandy-clayey groundmass-dominated breccia, which resembles a diamictite (Exmore breccia), and which, in its lower parts, carries sedimentary and crystalline blocks. The entire breccia interval is characterizedby the presence of glauconite and bioclastic carbonate, which distinguishes the Exmore breccia from other sandy facies above and below in the stratigraphy. The sediment-clast breccia exhibits strong heterogeneity from sample to sample with respect to groundmass nature, e.g., clay versus sand content, as well as clast content, in general, and shocked clast content, in particular. There is a consistently signifi cantly larger macroscopic sedimentary to crystalline clast content. On the microscopic scale, the intersample sediment to crystalline clast ratios are quite variable. A very small component of shocked material, in the form of shock-deformed quartz, and to an even lesser degree feldspar, and somewhat more abundant but still relatively scarce shardshaped,altered melt particles, is present throughout the section. However, between ̃458 and 469 m, and between 514 and 527 m depths, the abundance of such melt particlesis notably enhanced. These sections are also chemically distinct and relatively more mafic than the other parts of the Exmore breccia. It appears that from the time of deposition of the 527 m material, calming of the ocean occurred over the crater area as a result of abatement of resurge activity, so that ejecta from the plume abovethe crater could accumulate within the crater area to a larger degree. Deposition ofejecta fallout from the collapsing ejecta plume was terminated by the time of deposition of the 458 m material. This raises questions about the positioning of the exact upper contact of Exmore breccia to post-Exmore sediment (Chickahominy Formation), which is currently placed at 444 m depth and which possibly should be revisedto 458 m depth. Based on a signifi cant record of granite-derived material with shocked minerals, the shocked debris component seems to be largely derived from crystalline target rocks. This provides further evidence that the basement-derived material of the basal section of the Eyreville drill cores, which is essentially unshocked, is likely of an allochthonous nature and that the drilling did not intersect the actual crater floor. 76°W. © 2009 Geological Society of America.
cited By 27
Keywords: Crystalline materials; Crystalline rocks; Deposition; Drills; Feldspar; Infill drilling; Mica; Rocks; Sedimentology; Sediments; Stratigraphy; Bioclastic carbonates; Chesapeake bay impact structures; Continental scientific drillings; Crystalline target rocks; Derived materials; Microscopic scale; Strong heterogeneities; U.s. geological surveys; Core drilling; bedform; breccia; clast; crater; deposition; heterogeneity; impactite; particle size; petrography; research program; sedimentary petrology; shock metamorphism; Chesapeake Bay; United States; Virginia

Petroleum surface oil seeps from a Palaeoproterozoic petrified giant oilfield - Melezhik, Victor A; Fallick, Anthony E; Filippov, Michail M; Lepland, Aivo; Rychanchik, Dmitry V; Deines, Yuliya E; Medvedev, Pavel V; Romashkin, Alexander E; Strauss, Harald (Terra Nova, 2009)

Petrology of impact melt rocks from the Chesapeake Bay crater, USA - Wittmann, A.; Schmitt, R.T.; Hecht, L.; Kring, D.A.; Reimold, W.U.; Povenmire, H. (Special Paper of the Geological Society of America, 2009)
The Eyreville B drill core in the inner annular moat of the 85-km-diameter Chesapeake Bay impact structure recovered the first coherent impact melt volumes from within the crater as two bodies, 1 and 5.5 m thick. This study focuses on the petrogenesis of these well-preserved rocks. Mixing calculations reveal that the chemical composition of these melts can be modeled as a hybrid of ̃40% sedimentary target and ̃60% crystalline basement component. The melt rocks contain abundant lithic and mineral clasts that display all stages of shock metamorphism. Zircon clasts record the cooling of the melt from temperatures above 1700 °C to below 1200 °C within the first minutes after formation. Glassy melt with a peraluminous, rhyolitic composition that contains ̃5 wt% water is preserved. This melt records a crystallization sequence of aluminum-rich orthopyroxene and hercynitic spinel, followed by plagioclase, titanomagnetite and cordierite, and late sanidine. Spherulitic aluminosilicate-SiO 2 -cordierite aggregates that are comparable to buchites at temperatures below ̃1465 °C complement this assemblage. Lack of hyaloclastic fragmentation suggests dry emplacement conditions. Complete cooling by conductive heat transfer took ̃7 weeks and ̃4 years for the 1-m- and the 5.5-m-thick melt bodies, respectively. Alteration stages below ̃100 °C produced smectite, phillipsite, chalcedony, and a rare zeolite phase that is tentatively identified as terranovaite. © 2009 The Geological Society of America.
cited By 40
Keywords: Feldspar; Heat transfer; Infill drilling; Petrology; Silica; Silicate minerals; Structural geology; Zeolites; Zircon; Chemical compositions; Chesapeake Bay; Chesapeake bay impact structures; Conductive heat transfer; Crystalline basement; Emplacement conditions; Mixing calculations; Titanomagnetites; Core drilling; crater; crystallization; impact structure; marine sediment; petrogenesis; shock metamorphism; Chesapeake Bay; United States

Physical property data from the ICDP-USGS Eyreville cores A and B, Chesapeake Bay impact structure, Virginia, USA, acquired using a multisensor core logger - Pierce, H.A.; Murray, J.B. (Special Paper of the Geological Society of America, 2009)
The International Continental Scientific Drilling Program (ICDP) and the U.S. Geological Survey (USGS) drilled three core holes to a composite depth of 1766 m within the moat of the Chesapeake Bay impact structure. Core recovery rates from the drilling were high (̃90%), but problems with core hole collapse limited the geophysical downhole logging to natural-gamma and temperature logs. To supplement the downhole logs, ̃5% of the Chesapeake Bay impact structure cores was processed through the USGS GeoTek multisensor core logger (MSCL) located in Menlo Park, California. The measured physical properties included core thickness (cm), density (g cm -3 ), P-wave velocity (m s -1 ), P-wave amplitude (%), magnetic susceptibility (cgs), and resistivity (ohm-m). Fractional porosity was a secondary calculated property. The MSCL data-sampling interval for all core sections was 1 cm longitudinally. Photos of each MSCL sampled core section were imbedded with the physical property data for direct comparison. These data have been used in seismic, geologic, thermal history, magnetic, and gravity models of the Chesapeake Bay impact structure. Each physical property curve has a unique signature when viewed over the full depth of the Chesapeake Bay impact structure core holes. Variations in the measured properties reflect differences in pre-impact target-rock lithologies and spatial variations in impact-related deformation during late-stage crater collapse and ocean resurge. © 2009 The Geological Society of America.
cited By 7
Keywords: Boreholes; Infill drilling; Magnetic susceptibility; Seismic waves; Thermal logging; Wave propagation; Chesapeake bay impact structures; Continental scientific drillings; Measured properties; P-wave velocity; Spatial variations; Temperature log; Thermal history; U.s. geological surveys; Structural properties; crater; deformation; drilling; geophysical method; impact structure; magnetic susceptibility; P-wave; physical property; Chesapeake Bay; United States

On the origin of mixed-layered clay minerals from the San Andreas Fault at 2.5-3 km vertical depth (SAFOD drillhole at Parkfield, California) - Schleicher, A.M.; Warr, L.N.; Pluijm, B.A. (Contributions to Mineralogy and Petrology, 2009)
A detailed mineralogical study is presented of the matrix of mudrocks sampled from spot coring at three key locations along the San Andreas Fault Observatory at depth (SAFOD) drill hole. The characteristics of authigenic illite-smectite (I-S) and chlorite-smectite (C-S) mixed-layer mineral clays indicate a deep diagenetic origin. A randomly ordered I-S mineral with ca. 20-25% smectite layers is one of the dominant authigenic clay species across the San Andreas Fault zone (sampled at 3,066 and 3,436 m measured depths/MD), whereas an authigenic illite with ca. 2-5% smectite layers is the dominant phase beneath the fault (sampled at 3,992 m MD). The most smectite-rich mixed-layered assemblage with the highest water content occurs in the actively deforming creep zone at ca. 3,300-3,353 m (true vertical depth of ca. 2.7 km), with I-S (70:30) and C-S (50:50). The matrix of all mudrock samples show extensive quartz and feldspar (both plagioclase and K-feldspar) dissolution associated with the crystallization of pore-filling clay minerals. However, the effect of rock deformation in the matrix appears only minor, with weak flattening fabrics defined largely by kinked and fractured mica grains. Adopting available kinetic models for the crystallization of I-S in burial sedimentary environments and the current borehole depths and thermal structure, the conditions and timing of I-S growth can be evaluated. Assuming a typical K+ concentration of 100-200 ppm for sedimentary brines, a present-day geothermal gradient of 35°C/km and a borehole temperature of ca. 112°C for the sampled depths, most of the I-S minerals can be predicted to have formed over the last 4-11 Ma and are probably still in equilibrium with circulating fluids. The exception to this simple burial pattern is the occurrence of the mixed layered phases with higher smectite content than predicted by the burial model. These minerals, which characterize the actively creeping section of the fault and local thin film clay coating on polished brittle slip surfaces, can be explained by the influence of either cooler fluids circulating along this segment of the fault or the flow of K+-depleted brines. © Springer-Verlag 2008.
cited By 52
Keywords: chlorite; crystallization; deformation mechanism; diagenesis; illite; mudstone; San Andreas Fault; smectite; thermal structure; California; North America; Parkfield; United States

Physical rock properties of the Eyreville core, Chesapeake Bay impact structure - Mayr, S.I.; Burkhardt, H.; Popov, Y.; Romushkevich, R.; Miklashevskiy, D.; Gorobtsov, D.; Heidinger, P.; Wilhelm, H. (Special Paper of the Geological Society of America, 2009)
The physical properties of rocks in drill core from impact structures can be used to distinguish individual nonimpact and impact-generated lithologies, and to investigate the effect of the impact process on the target rocks. Here, we present the results of laboratory measurements of porosity, density, velocity, and thermal properties on the densely sampled cores from the Eyreville borehole in the Chesapeake Bay impact structure, USA. With increasing depth, the lithologies encountered (and porosities) are: postimpact sediments (40%-60%), Exmore breccia and sedimentary blocks (27%-44%), a large megablock of granitoids (<1%), suevite and polymict lithic impact breccia (1%-25%), and schist, granite, and pegmatite of the basementderived section (1%-13%). The low bulk densities and thermal properties of the postimpact sediments show a good correlation with the high porosity values. The physical properties within the Exmore bed sequence overall display relatively small variation but are heterogeneous on the core sample scale. Physical properties along the impact-breccia sequence are highly variable on all scales, and they are interpreted to be controlled by the structural arrangement of particles as well as by the highly variable mineral and clast compositions of the samples. The physical properties of the rocks of the lowermost basement-derived section are also heterogeneous and are interpreted as having been influenced by both lithology and overprinting as a result of the impact process. These results are important for further lithological and petrophysical interpretation and for calibrating future geophysical models of the Chesapeake Bay impact structure. © 2009 The Geological Society of America.
cited By 8
Keywords: Boreholes; Core drilling; Granite; Infill drilling; Lithology; Porosity; Structural geology; Thermodynamic properties; Chesapeake bay impact structures; Geophysical models; Good correlations; Impact structures; Laboratory measurements; Petrophysical interpretation; Small variations; Structural arrangement; Structural properties; breccia; bulk density; impact structure; physical property; porosity; rock property; sedimentary structure; Chesapeake Bay; United States

Organic geochemical characteristics of anoxic levels in the Cretaceous Qingshankou Formation of Songliao Basin. - Hui, KONG; Yong-Jian, HUANG; Qing-Hua, HUANG; Wen-Jing, ZHANG; Lei, XIE; Hua-Gong, LIU; Xiao-Yun, XIE (Earth Science Frontiers, 2009)

Interpretation and mathematical modeling of temporal changes of temperature observed in borehole Yaxcopoil-1 within the Chicxulub impact structure, Mexico - Šafanda, J.; Wilhelm, H.; Heidinger, P.; Čerm'ak, V. (Journal of Hydrology, 2009)
Geothermal research of the Chicxulub impact structure on the Yucatan Peninsula, Mexico, included repeated temperature logs following 0.3-0.8, 15, 24, 34 and 50 months after shut-in of drilling operations at the 1.5 km deep Yaxcopoil-1 borehole. A gradual distortion of the linear temperature profile by a cold wave propagating downward from 145 m to 317 m was detected within the observational period of 49 months (March 2002-April 2006). The amplitude of the cold wave was increasing with depth and time in the range of 0.8-1.6 °C. As an explanation of this unusual phenomenon, the hypothesis of downward migration of a large volume of drilling mud, reported lost during drilling within the overlying and cooler highly porous and permeable karstic rocks, has been proposed. The thermal effects of the migrating fluid have been evaluated by solving numerically the heat conduction-convection equation in appropriate geothermal models. The best coincidence between the observed data and the simulations was yielded by the model of the drilling mud migrating as a large body. Parameters of this model are constrained by the measured temperature logs relatively tightly: (i) the vertical extent of the downward migrating fluid body is about 5-10 m, possibly increasing within the observational period of 49 months by a factor of 2; (ii) the horizontal extent of the body must be at least 15-20 m, i.e. by order(s) of magnitude larger than the diameter of the borehole; (iii) the average speed of the migration is about 5 metres per month and (iv) the fluid must migrate through a highly porous rock (80% porosity or more). This high porosity, which is necessary for the model to fit the observed data, and the observed relatively stable velocity of the migration indicate the existence of a well-developed system of interconnected cavities down to more than 300 m about 150 m more than the deepest cave system known in Yucatan yet. © 2009 Elsevier B.V. All rights reserved.
cited By 3

Multi-dimensional, multi-variable, and multi-scale modeling of reservoir heterogeneities - Huang, J.W.; Bellefleur, G.; Milkereit, B. (71st European Association of Geoscientists and Engineers Conference and Exhibition 2009: Balancing Global Resources. Incorporating SPE EUROPEC 2009, 2009)
A new approach is developed to model 3D reservoirs that capture different scales of heterogeneities and simultaneously honor statistical features observed in the well logs. Our approach provides a platform to estimate rock physics properties at the well log scale and to study the behavior of waves in reservoirs with various scales of heterogeneities. The modeling algorithm is applied to the gas hydrate reservoir located in Mallik area, Northwestern Territory of Canada. We show that by using the Biot-Gassmann theory, the statistical parameters obtained from Mallik 5L-38 borehole logs, and the horizontal correlation length estimated from inverted acoustic impedance, the gas hydrate volume fraction is estimated to be 1.8% of a 500m by 500m by 226m rock volume. This represents approximately 167.5x10∧6 m∧3 of natural gas stored in hydrate bearing intervals under standard condition. We find that the degree of lateral heterogeneity play a significant role in assessing the amount of gas hydrates and thus more adequate lateral sampling is desired to constrain the resource assessment in the reservoir. Copyright 2009, European Association of Geoscientists and Engineers.
cited By 0
Keywords: Acoustic impedance; Engineering exhibitions; Hydration; Petroleum reservoir evaluation; Three dimensional; Well logging; Borehole logs; Correlation lengths; Different scale; Gas hydrate reservoir; Gassmann theory; Lateral heterogeneity; Multi-scale Modeling; New approaches; Reservoir heterogeneity; Resource assessments; Rock physics; Standard conditions; Statistical features; Statistical parameters; Well logs; Gas hydrates

Lake Van, Eastern Anatolia, hydrochemistry and history - Reimer, A.; Landmann, G.; Kempe, S. (Aquatic Geochemistry, 2009)
Saline, 450-m-deep Lake Van (Eastern Anatolia, Turkey) is, with 576 km3, the third largest closed lake on Earth and its largest soda lake. In 1989 and 1990, we investigated the hydrochemistry of the lake's water column and of the tributary rivers. We also cored the Postglacial sediment column at various water depths. The sediment is varved throughout, allowing precise dating back to ca. 15 ka BP. Furthermore, lake terrace sediments provided a 606-year-long floating chronology of the Glacial high-stand of the lake dating to 21 cal. ka BP. The sediments were investigated for their general mineralogical composition, important geochemical parameters, and pore water chemistry as well. These data allow reconstructing the history of the lake level that has seen several regressions and transgressions since the high-stand at the end of the Last Glacial Maximum. Today, the lake is very alkaline, highly supersaturated with Ca-carbonate and has a salt content of about 22 g kg-1. In summer, the warmer epilimnion is diluted with river water and forms a stable surface layer. Depth of winter mixing differs from year to year but during time of investigation the lake was oxygenated down to its bottom. In general, the lake is characterized by an Na-CO3-Cl-(SO4)-chemistry that evolved from the continuous loss of calcium as carbonate and magnesium in the form of Mg-silica-rich mineral phases. The Mg cycle is closely related to that of silica which in turn is governed by the production and dissolution of diatoms as the dominant phytoplankton species in Lake Van. In addition to Ca and Mg, a mass balance approach based on the recent lake chemistry and river influx suggests a fractional loss of potassium, sodium, sulfur, and carbon in comparison to chloride in the compositional history of Lake Van. Within the last 3 ka, minor lake level changes seem to control the frequency of deep water renewal, the depth of stratification, and the redox state of the hypolimnion. Former major regressions are marked by Mg-carbonate occurrences in the otherwise Ca-carbonate dominated sediment record. Pore water data suggest that, subsequent to the major regression culminating at 10.7 ka BP, a brine layer formed in the deep basin that existed for about 7 ka. Final overturn of the lake, triggered by the last major regression starting at about 3.5 ka BP, may partly account for the relative depletion in sulfur and carbon due to rapid loss of accumulated gases. An even stronger desiccation phase is proposed for the time span between about 20 and 15 ka BP following the LGM, during which major salts could have been lost by precipitation of Na-carbonates and Na-sulfates. © The Author(s) 2008.
cited By 106
Keywords: desiccation; dissolution; Holocene; hydrochemistry; hydrogeochemistry; lake level; paleolimnology; porewater; water column; water depth; Eurasia; Lake Van; Turkey; Bacillariophyta

Polar organic compounds in pore waters of the Chesapeake Bay impact structure, Eyreville core hole: Character of the dissolved organic carbon and comparison with drilling fluids - Rostad, C.E.; Sanford, W.E. (Special Paper of the Geological Society of America, 2009)
Pore waters from the Chesapeake Bay impact structure cores recovered at Eyreville Farm, Northampton County, Virginia, were analyzed to characterize the dissolved organic carbon. After squeezing or centrifuging, a small volume of pore water, 100 μL, was taken for analysis by electrospray ionization-mass spectrometry. Porewater samples were analyzed directly without filtration or fractionation, in positive and negative mode, for polar organic compounds. Spectra in both modes were dominated by low-molecular-weight ions. Negative mode had clusters of ions differing by -60 daltons, possibly due to increasing concentrations of inorganic salts. The numberaverage molecular weight and weight-average molecular weight values for the pore waters from the Chesapeake Bay impact structure are higher than those reported for other aquatic sources of natural dissolved organic carbon as determined by electrospray ionization-mass spectrometry. In order to address the question of whether drilling mud fluids may have contaminated the pore waters during sample collection, spectra from the pore waters were compared to spectra from drilling mud fluids. Ions indicative of drilling mud fluids were not found in spectra from the pore waters, indicating there was no detectable contamination, and highlighting the usefulness of this analytical technique for detecting potential contamination during sample collection. © 2009 The Geological Society of America.
cited By 5
Keywords: Boreholes; Dissolution; Electrospray ionization; Infill drilling; Ions; Mass spectrometry; Molecular weight; Mud logging; Organic carbon; Stream flow; Water; Chesapeake bay impact structures; Dissolved organic carbon; Electrospray ionization mass spectrometry; Inorganic salts; Low molecular weight; Polar organic compounds; Sample collection; Weight-average molecular weight; Drilling fluids; analytical method; detection method; dissolved organic carbon; drilling fluid; fractionation; impact structure; ionization; mass spectrometry; organic compound; porewater; Chesapeake Bay; United States; Virginia

Identification of the projectile component in the impact structures Rochechouart, France and S{a{aksj{arvi, Finland: Implications for the impactor population for the earth - Tagle, R.; Schmitt, R.T.; Erzinger, J. (Geochimica et Cosmochimica Acta, 2009)
A set of 11 impact melt rock samples from the Rochechouart impact structure, France and nine impact melt rock samples from S{a{aksj{arvi impact structure, Finland were studied for their major and trace element compositions, including the abundances of the platinum group elements. The main goal of this study was to identify the projectile type(s) responsible for the formation of these two impact structures. The results confirmed previous studies that suggested extraterrestrial contamination in both the Rochechouart and S{a{aksj{arvi impact melt rocks. The projectile types found for Rochechouart and S{a{aksj{arvi are quite similar, and compatible with the composition of non-magmatic iron meteorites (IA and IIIC). This interpretation is based on: identical platinum group element patterns as well as peculiar Ni/Cr, Ni/Ir and Cr/Ir ratios, which can be explained by mixing of the different components of non-magmatic iron meteorites. This result indicates that, besides ordinary chondrites, non-magmatic iron may be among the most common material impacting the Earth, as they also represent the majority of the projectiles for craters smaller that 1.5 km. The abundance of non-magmatic irons as projectiles as well as their composition (olivine, pyroxene and iron) supports the assumption that a fraction of the S-type asteroids could by related to this type of material. © 2009.
cited By 27

Impact cratering on volatile-rich targets: Some remarks related to the deep impact experiment - Claeys, P. (ESO Astrophysics Symposia, 2009)
The NASA Deep Impact experiment has important implications to better understand cratering processes on planetary bodies and the production and evolution of ejecta. This man-made impact of a solid Cu body on the nucleus of a comet fills the large gap existing between data derived from small-scale cratering experiments and large-scale field or remote sensing observations of craters. DI thus complements hydrocode modeling of cratering processes. The majority of cratering studies focus on solid silicate-rich targets rather than on porous, poorly consolidated and/or volatile-rich materials. However, volatile targets are common in the Solar System. The lessons learned from the DI collision with comet 9P/Tempel not only clarify the composition and physical properties of the cometary nucleus, but also can shed light on cratering mechanisms and evolution of plume and ejecta. © 2009 Springer-Verlag Berlin Heidelberg.
cited By 0

In situ LA-SF-ICP-MS U-Pb dating of metasomatic zircon growth during retrogression of UHP eclogites, Sulu deep drilling hole, China - Riemann, Astrid; Oberh{ansli, Roland; M{oller, Andreas; Gerdes, Axel; Xu, Zhigin (European Journal of Mineralogy, 2009)
Thermobarometry and in situ U-Pb dating of zircon in texturally and petrologically defined positions are used to assess exhumation accompanied by fluid-enhanced retrogression of ultra high pressure (UHP) eclogite core samples from the Chinese Continental Scientific Drilling (CCSD) project. Eclogites from the CCSD project show discrete retrograde zones that can be attributed to exhumation processes. The retrogression from UHP eclogite to HP eclogite, amphibolite and finally greenschist facies conditions is fluid-induced. The occurrence of significant barium concentrations in two mica generations points to an external fluid source during retrogression. This Ba and F-bearing fluid mobilized zirconium from the eclogitic host, which was preferentially precipitated as overgrowths on pre-existing grains in the retrograde zone. Thermodynamic modelling with progressive addition of H2O to the bulk composition simulates the petrological development of the fluid-influenced retrograde zone. Growth of zircon precipitated from the fluid occurred between 730°-740 °C at 3.46 GPa and 700 °C at 1.4 GPa. LA-SF-ICPMS analyses point to a local onset of metasomatic zircon growth at 233.1 ± 5.3 Ma ongoing to 207.4 ± 1.6 Ma that is spatially limited to the retrograde zone. © 2009 E. Schweizerbart'sche Verlagsbuchhandlung.
Keywords: Binary alloys; Gasoline; Geochronology; Inductively coupled plasma mass spectrometry; Infill drilling; Metamorphic rocks; Mica; Barium concentrations; Continental scientific drillings; Eclogites; Retrogression; Thermodynamic modelling; U-Pb dating; Ultra high pressure (UHP); Ultra-high pressure metamorphisms; amphibolite; Chinese Continental Scientific Drilling Project; eclogite; exhumation; inductively coupled plasma method; mass spectrometry; petrology; ultrahigh pressure metamorphism; uranium-lead dating; zircon; Zircon

Integrated sequence stratigraphy of the postimpact sediments from the Eyreville core holes, Chesapeake Bay impact structure inner basin - Browning, J.V.; Miller, K.G.; McLaughlin Jr., P.P.; Edwards, L.E.; Kulpecz, A.A.; Powars, D.S.; Wade, B.S.; Feigenson, M.D.; Wright, J.D. (Special Paper of the Geological Society of America, 2009)
The Eyreville core holes provide the first continuously cored record of postimpact sequences from within the deepest part of the central Chesapeake Bay impact crater. We analyzed the upper Eocene to Pliocene postimpact sediments from the Eyreville A and C core holes for lithology (semiquantitative measurements of grain size and composition), sequence stratigraphy, and chronostratigraphy. Age is based primarily on Sr isotope stratigraphy supplemented by biostratigraphy (dinocysts, nannofossils, and planktonic foraminifers); age resolution is approximately ±0.5 Ma for early Miocene sequences and approximately ±1.0 Ma for younger and older sequences. Eocene-lower Miocene sequences are subtle, upper middle to lower upper Miocene sequences are more clearly distinguished, and upper Miocene- Pliocene sequences display a distinct facies pattern within sequences. We recognize two upper Eocene, two Oligocene, nine Miocene, three Pliocene, and one Pleistocene sequence and correlate them with those in New Jersey and Delaware. The upper Eocene through Pleistocene strata at Eyreville record changes from: (1) rapidly deposited, extremely fi ne-grained Eocene strata that probably represent two sequences deposited in a deep (>200 m) basin; to (2) highly dissected Oligocene (two very thin sequences) to lower Miocene (three thin sequences) with a long hiatus; to (3) a thick, rapidly deposited (43-73 m/Ma), very fi ne-grained, biosiliceous middle Miocene (16.5-14 Ma) section divided into three sequences (V5-V3) deposited in middle neritic paleoenvironments; to (4) a 4.5-Ma-long hiatus (12.8-8.3 Ma); to (5) sandy, shelly upper Miocene to Pliocene strata (8.3-2.0 Ma) divided into six sequences deposited in shelf and shoreface environments; and, last, to (6) a sandy middle Pleistocene paralic sequence ( 400 ka). The Eyreville cores thus record the fi lling of a deep impact-generated basin where the timing of sequence boundaries is heavily infl uenced by eustasy. © 2009 The Geological Society of America.
cited By 27
Keywords: Lithology; Chesapeake bay impact structures; Chronostratigraphy; Measurements of; Middle Pleistocene; Paleoenvironments; Pleistocene strata; Sequence boundary; Sequence stratigraphy; Stratigraphy; biostratigraphy; chronostratigraphy; deposition; Eocene; impact structure; lithology; Miocene; paleoenvironment; Pleistocene; Pliocene; sequence boundary; sequence stratigraphy; strontium isotope; Chesapeake Bay; Delaware; New Jersey; United States; Foraminifera

Joint inversion for Vp, Vs, and Vp/Vs at SAFOD, Parkfield, California - Zhang, H.; Thurber, C.; Bedrosian, P. (Geochemistry, Geophysics, Geosystems, 2009)
We refined the three-dimensional (3-D) Vp, Vs and Vp/Vs models around the San Andreas Fault Observatory at Depth (SAFOD) site using a new double-difference (DD) seismic tomography code (tomoDDPS) that simultaneously solves for earthquake locations and all three velocity models using both absolute and differential P, S, and S-P times. This new method is able to provide a more robust Vp/Vs model than that from the original DD tomography code (tomoDD), obtained simply by dividing Vp by Vs. For the new inversion, waveform cross-correlation times for earthquakes from 2001 to 2002 were also used, in addition to arrival times from earthquakes and explosions in the region. The Vp values extracted from the model along the SAFOD trajectory match well with the borehole log data, providing in situ confirmation of our results. Similar to previous tomographic studies, the 3-D structure around Parkfield is dominated by the velocity contrast across the San Andreas Fault (SAF). In both the Vp and Vs models, there is a clear low-velocity zone as deep as 7 km along the SAF trace, compatible with the findings from fault zone guided waves. There is a high Vp/Vs anomaly zone on the southwest side of the SAF trace that is about 1-2 km wide and extends as deep as 4 km, which is interpreted to be due to fluids and fractures in the package of sedimentary rocks abutting the Salinian basement rock to the southwest. The relocated earthquakes align beneath the northeast edge of this high Vp/Vs zone. We carried out a 2-D correlation analysis for an existing resistivity model and the corresponding profiles through our model, yielding a classification that distinguishes several major lithologies. © 2009 by the American Geophysical Union.
cited By 115

Lake El'gygytgyn's emerging IPY record of Pliocene to recent Arctic change. - Brigham-Grette, J; Melles, M; Minyuk, P; Koeberl, C; et al. (PAGES (Past Global Changes) News, 2009)

Late quaternary mass movement events in lake el'gygytgyn, north-eastern Siberia - Juschus, O.; Melles, M.; Gebhardt, A.C.; Niessen, F. (Sedimentology, 2009)
Lake El'gygytgyn is situated in a 3·6 Myr old impact crater in North-eastern Siberia. Its sedimentary record probably represents the most complete archive of Pliocene and Quaternary climate change in the terrestrial Arctic. In order to investigate the influence of gravitational sediment transport on the pelagic sediment record in the lake centre, two sediment cores were recovered from the lower western lake slope. The cores penetrate a sub-recent mass movement deposit that was identified by 3·5 kHz echo sounding. In the proximal part of this deposit, deformed sediments reflect an initial debris flow characterized by limited sediment mixture. Above and in front of the debrite, a wide massive densite indicates a second stage with a liquefied dense flow. The mass movement event led to basal erosion of ca 1 m thick unconsolidated sediments along parts of its flow path. The event produced a suspension cloud, whose deposition led to the formation of a turbidite. The occurrence of the turbidite throughout the lake and the limited erosion at its base mainly suggest deposition by 'pelagic rain' following Stokes' Law. Very similar radiocarbon dates obtained in the sediments directly beneath and above the turbidite in the central lake confirm this interpretation. When applying the depositional model for the Late Quaternary sediment record of Lake El'gygytgyn, the recovered turbidites allow reconstruction of the frequency and temporal distribution of large mass movement events at the lake slopes. In total, 28 turbidites and related deposits were identified in two, 12·9 and 16·6 m long, sediment cores from the central lake area covering approximately 300 kyr. © 2009 The Authors. Journal compilation © 2009 International Association of Sedimentologists.
cited By 27
Keywords: Basal erosion; Debris flows; Depositional models; Eastern Siberia; Flow path; Impact craters; Lake areas; Late Quaternary; Mass movement; Pelagic sediments; Pliocene; Quaternary climate; Radiocarbon dates; Sediment core; Sedimentary records; Siberian Arctic; Stokes' law; Temporal distribution; Turbidite; Unconsolidated sediment; Anoxic sediments; Climate change; Debris; Deposits; Erosion; Petroleum geology; Sediment transport; Sedimentation; Sedimentology; Lakes; climate variation; debris flow; deposition velocity; echo sounding; erosion rate; formation mechanism; lacustrine deposit; mass movement; paleoclimate; Pliocene-Pleistocene boundary; Quaternary; sediment core; sediment transport; Stokes formula; turbidite; unconsolidated medium; Chukchi; Elgygytgyn Lake; Russian Federation

Mollusc biodiversity and endemism in the potential ancient Lake Trichonis, Greece - Albrecht, Christian; Hauffe, Torsten; Schreiber, Kirstin; Trajanovski, Sasho; Wilke, Thomas (Malacologia, 2009)
Ancient lakes are hotspots of biodiversity, often harboring a large number of endemic species that make them prime model systems for evolutionary biologists. Besides such well-recognized ancient or long-lived lakes as Baikal, Biwa, Ohrid, and Tanganyika, there are other potentially old and biodiverse lakes in the world with poorly specified ages and under-studied faunas. We here report on the mollusc fauna of one such lake, Lake Trichonis in continental Greece. This graben lake is situated in a highly tectonized area, characterized by karst features and probably of middle to late Pliocene origin. Lake Trichonis is deep, oligotrophic, and rich in such specific habitat types as macrophyte meadows, rocky shores and sublacustrine spring systems. Moreover, it is a hotspot of freshwater biodiversity in Greece, particularly in molluscs. After reviewing newly collected material and the published mollusc records, we found that at least 33 mollusc species occur in Lake Trichonis, with 24 gastropod and 9 bivalve species currently being recognized. This is 24% of the total freshwater mollusc diversity of Greece; 21% of the gastropods (five species) are endemic to Lake Trichonis. If the whole Trichonis Basin is considered, which also includes neighboring Lake Lysimachia, eight species (33%) of the total fauna appear to be endemic. Taking lake surface areas into account, the index of gastropod endemism of 0.442 (log Nendemic species/log Asurface area) for the Lake Trichonis Basin resembles on a world-wide scale values known for Lake Baikal, Russia, and Lake Biwa, Japan, and is only exceeded by Lake Ohrid, Macedonia/Albania, and ancient lakes of Sulawesi, Indonesia. Despite the limited knowledge about the lake's evolutionary history, the suggested age of origin, the palaeogeographical characteristics, and the potential timing of phylogenetic events reviewed here support the presumed status of Lake Trichonis as an ancient lake. From a conservational standpoint, more research, management and conservation efforts are necessary because ancient lakes are among the most vulnerable and threatened ecosystems on earth. Effects of human-induced environmental change are already noticeable in Lake Trichonis. Recognition of Lake Trichonis as a unique system with an unusually high biodiversity may help promoting conservation efforts.
Keywords: Bivalvia; Gastropoda; Lysimachia; Mollusca

Mantle deformation beneath the Chicxulub impact crater - Christeson, G.L.; Collins, G.S.; Morgan, J.V.; Gulick, S.P.S.; Barton, P.J.; Warner, M.R. (Earth and Planetary Science Letters, 2009)
The surface expression of impact craters is well-known from visual images of the Moon, Venus, and other planets and planetary bodies, but constraints on deep structure of these craters is largely limited to interpretations of gravity data. Although the gravity models are non-unique, they do suggest that large impact craters are associated with structure at the base of the crust. We use seismic data to map Moho (crust-mantle interface) topography beneath the Chicxulub crater, the youngest and best preserved of the three largest known terrestrial impact craters. The Moho is upwarped by 1.5-2 km near the center of the Chicxulub crater, and depressed by 0.5-1.0 km at a distance of 30-55 km from the crater center. A comparison with numerical modeling results reveal that immediately following impact a transient crater reached a maximum depth of at least 30 km prior to collapse, and that subsequent collapse of the transient crater uplifted target material from deep below the crater floor. These results demonstrate that deformation from large terrestrial impacts can extend to the base of the continental crust. A similar Moho topography is also modeled for some large lunar and Martian craters, which suggests that mantle deformation may play a prominent role in large crater formation. © 2009 Elsevier B.V. All rights reserved.
cited By 28

Measuring velocity dispersion and attenuation in the exploration seismic frequency band - Sun, L.F.; Milkereit, B. (Geophysics, 2009)
No perfectly elastic medium exists in the earth. In an anelastic medium, seismic waves are distorted by attenuation and velocity dispersion. Velocity dispersion depends on the petrophysical properties of reservoir rocks, such as porosity, fractures, fluid mobility, and the scale of heterogeneities. However, velocity dispersion usually is neglected in seismic data processing partly because of the insufficiency of observations in the exploration seismic frequency band (∼5 through 200 Hz). The feasibility of determining velocity dispersion in this band is investigated. Four methods are used in measuring velocity dispersion from uncorrelated vibrator vertical seismic profile (VSP) data: the moving window crosscorrelation (MWCC) method, instantaneous phase method, time-frequency spectral decomposition method, and cross-spectrum method. The MWCC method is a new method that is satisfactorily robust, accurate, and efficient in measuring the frequency-dependent traveltime in uncorrelated vibrator records. The MWCC method is applied to the uncorrelated vibrator VSP data acquired in the Mallik gas hydrate research well. For the first time, continuous velocity dispersion is observed in the exploration seismic frequency band using uncorrelated vibrator VSP data. The observed velocity dispersion is fitted to a straight line with respect to log frequency to calculate Q. This provides an alternative method for Q measurement. © 2009 Society of Exploration Geophysicists. All rights reserved.
cited By 36
Keywords: Data handling; Dispersion (waves); Gas hydrates; Petroleum prospecting; Petrophysics; Seismic waves; Seismology; Velocity; Vibrators; Frequency dependent; Instantaneous phase; Petrophysical properties; Seismic data processing; Seismic frequencies; Spectral decomposition methods; Velocity dispersion; Vertical seismic profiles; Seismic prospecting; accuracy assessment; conference proceeding; data processing; efficiency measurement; frequency analysis; frequency dependence; heterogeneity; observational method; seismic attenuation; seismic data; seismic velocity; seismic wave; wave dispersion

Megablocks and melt pockets in the Chesapeake Bay impact structure constrained by magnetic field measurements and properties of the Eyreville and Cape Charles cores - Shah, A.K.; Daniels, D.L.; Kontny, A.; Brozena, J. (Special Paper of the Geological Society of America, 2009)
We use magnetic susceptibility and remanent magnetization measurements of the Eyreville and Cape Charles cores in combination with new and previously collected magnetic field data in order to constrain structural features within the inner basin of the Chesapeake Bay impact structure. The Eyreville core shows the first evidence of several-hundred-meter-thick basement-derived megablocks that have been transported possibly kilometers from their pre-impact location. The magnetic anomaly map of the structure exhibits numerous short-wavelength (<2 km) variations that indicate the presence of magnetic sources within the crater fill. With core magnetic properties and seismic reflection and refraction results as constraints, forward models of the magnetic field show that these sources may represent basementderived megablocks that are a few hundred meters thick or melt bodies that are a few dozen meters thick. Larger-scale magnetic field properties suggest that these bodies overlie deeper, pre-impact basement contacts between materials with different magnetic properties such as gneiss and schist or gneiss and granite. The distribution of the short-wavelength magnetic anomalies in combination with observations of small-scale (1-2 mGal) gravity field variations suggest that basement-derived megablocks are preferentially distributed on the eastern side of the inner crater, not far from the Eyreville core, at depths of around 1-2 km. A scenario where additional basement-derived blocks between 2 and 3 km depth are distributed throughout the inner basin-and are composed of more magnetic materials, such as granite and schist, toward the east over a large-scale magnetic anomaly high and less magnetic materials, such as gneiss, toward the west where the magnetic anomaly is lower-provides a good model fi t to the observed magnetic anomalies in a manner that is consistent with both gravity and seismic-refraction data. © 2009 The Geological Society of America.
cited By 12
Keywords: Buildings; Electromagnetic field effects; Granite; Magnetic materials; Magnetic susceptibility; Magnetization; Refraction; Seismology; Chesapeake bay impact structures; Magnetic anomalies; Magnetic field data; Remanent magnetization; Seismic reflections; Seismic refraction data; Short wavelengths; Structural feature; Structural properties; crater; gravity anomaly; magnetic anomaly; magnetic field; magnetic property; magnetic susceptibility; remanent magnetization; seismic reflection; seismic refraction; Chesapeake Bay; United States

Microbial abundance in the deep subsurface of the Chesapeake Bay impact crater: Relationship to lithology and impact processes - Cockell, C.S.; Gronstal, A.L.; Voytek, M.A.; Kirshtein, J.D.; Finster, K.; Sanford, W.E.; Glamoclija, M.; Gohn, G.S.; Powars, D.S.; Horton Jr., J.W. (Special Paper of the Geological Society of America, 2009)
Asteroid and comet impact events are known to cause profound disruption to surface ecosystems. The aseptic collection of samples throughout a 1.76-km-deep set of cores recovered from the deep subsurface of the Chesapeake Bay impact structure has allowed the study of the subsurface biosphere in a region disrupted by an impactor. Microbiological enumerations suggest the presence of three major microbiological zones. The upper zone (127-867 m) is characterized by a logarithmic decline in microbial abundance from the surface through the postimpact section of Miocene to Upper Eocene marine sediments and across the transition into the upper layers of the impact tsunami resurge sediments and sediment megablocks. In the middle zone (867-1397 m) microbial abundances are below detection. This zone is predominantly quartz sand, primarily composed of boulders and blocks, and it may have been mostly sterilized by the thermal pulse delivered during impact. No samples were collected from the large granite block (1096-1371 m). The lowest zone (below 1397 m) of increasing microbial abundance coincides with a region of heavily impact-fractured, hydraulically conductive suevite and fractured schist. These zones correspond to lithologies infl uenced by impact processes. Our results yield insights into the infl uence of impacts on the deep subsurface biosphere. © 2009 The Geological Society of America.
cited By 12
Keywords: Biospherics; Lithology; Submarine geology; Chesapeake Bay; Chesapeake bay impact structures; Impact craters; Impact process; Marine sediments; Microbial abundances; Subsurface biosphere; Surface ecosystems; Sediments; abundance; asteroid; biosphere; comet; crater; Eocene; hydraulic conductivity; impact structure; lithology; marine sediment; microbial activity; microbial community; microbiology; Miocene; schist; suevite; Chesapeake Bay; United States

Microseismic activity and fluid fault interactions: Some results from the Corinth Rift Laboratory (CRL), Greece - Bourouis, S.; Cornet, Francois H. (Geophysical Journal International, 2009)
The Gulf of Corinth, in western-central Greece, is one of the fastest continental rifts in the world. In its western section near the city of Aigion, the previous work has outlined the existence of a shallow dipping seismogenic zone between 5 and 12 km. This seismic activity has been monitored with a network of 12 three-component stations for the period 2000-2007. Three, few months long, seismic swarms have been observed. They mobilize a complex structural fault system that associates both shallow dipping elements and subvertical structures with very different azimuths, some of which extend to depths greater than that of the shallow dipping zone. The swarm activity associates intensely active, short crises (a few days) with more quiescent periods. The long-term growth velocity of the seismically activated domains is compatible with a fluid diffusion process. Its characteristics are discussed in the context of the results from the 1000 m deep AIG10 well that intersects the Aigion Fault at 760 m. The vertical growth directions of the seismically activated volumes outline two different sources for the fluid and imply non-steady pressure conditions within the seismic domain. The diffusivity along the cataclastic zone of the faults is in the order of 1 m2 s-1, while faults act as hydraulic barrier in the direction perpendicular to their strike. If the vertical direction is a principal stress component, the high pore pressure values that must be reached to induce slip on the shallowly dipping planes can result only from transitory dynamic conditions. It is argued that the shallow dipping active seismic zone is only local and does not correspond to a 100 km scale decollement zone. We propose to associate the localization process with deep fluid fluxes that have progressively modified the local stress field and may be the cause for the quiescence of the West Heliki Fault presently observed. © 2009 The Authors, Journal compilation © 2009 RAS.
Keywords: Eurasia; Europe; Greece; Gulf of Corinth; Ionian Sea; Mediterranean Sea; Southern Europe; backarc basin; earthquake swarm; fault zone; fluid-structure interaction; permeability; porosity; rheology; seismicity; stress field

Microseismicity at the North Anatolian Fault in the Sea of Marmara offshore Istanbul, NW Turkey - Bulut, F.; Bohnhoff, M.; Ellsworth, W.L.; Aktar, M.; Dresen, G. (Journal of Geophysical Research: Solid Earth, 2009)
The North Anatolian Fault Zone (NAFZ) below the Sea of Marmara forms a seismic gap where a major earthquake is expected to occur in the near future. This segment of the fault lies between the 1912 Ganos and 1999 İzmit ruptures and is the only NAFZ segment that has not ruptured since 1766. To monitor the microseismic activity at the main fault branch offshore of Istanbul below the Çinarcik Basin, a permanent seismic array (PIRES) was installed on the two outermost Prince Islands, Yassiada and Sivriada, at a few kilometers distance to the fault. In addition, a temporary network of ocean bottom seismometers was deployed throughout the Çinarcik Basin. Slowness vectors are determined combining waveform cross correlation and P wave polarization. We jointly invert azimuth and traveltime observations for hypocenter determination and apply a bootstrap resampling technique to quantify the location precision. We observe seismicity rates of 20 events per month for M < 2.5 along the basin. The spatial distribution of hypocenters suggests that the two major fault branches bounding the depocenter below the Çinarcik Basin merge to one single master fault below ∼17 km depth. On the basis of a cross-correlation technique we group closely spaced earthquakes and determine composite focal mechanisms implementing recordings of surrounding permanent land stations. Fault plane solutions have a predominant right-lateral strike-slip mechanism, indicating that normal faulting along this part of the NAFZ plays a minor role. Toward the west we observe increasing components of thrust faulting. This supports the model of NW trending, dextral strike-slip motion along the northern and main branch of the NAFZ below the eastern Sea of Marmara. Copyright 2009 by the American Geophysical Union.
cited By 45
Keywords: azimuth; depocenter; earthquake hypocenter; earthquake mechanism; earthquake rupture; fault geometry; fault zone; focal mechanism; observational method; P-wave; seismic tomography; seismicity; seismograph; spatial distribution; strike-slip fault; tectonic setting; travel time; waveform analysis; Anatolia; Eurasia; Istanbul [Turkey]; Sea of Marmara; Turkey

Modeling on gas hydrate formation conditions in the Qinghai-Tibet plateau permafrost - Lu, Z.-Q.; Sultan, N.; Jin, C.-S.; Rao, Z.; Luo, X.-R.; Wu, B.-H.; Zhu, Y.-H. (Acta Geophysica Sinica, 2009)
Based on field-investigated gas geochemistry and predecessors data such as the permafrost ground temperature, thermal gradients within/below the frozen layer, the modeling on gas hydrate formation conditions is conducted in the Qinghai-Tibet plateau permafrost. The modeled results show that the permafrost characteristics generally meet gas hydrate formation conditions in the study area. Gas composition, temperature-related permafrost parameters (e. g. permafrost thickness or its ground temperature and thermal gradients within / below the frozen layer) are the most important factors affecting gas hydrate occurrences, whose variance may cause the heterogeneity of gas hydrate occurrences in the study area. The most probable gas hydrate is the kind of hybrid of methane and weight hydrocarbon gases (ethane and propane). In the predicted gas hydrate locations, the upper gas hydrate occurrence depth may be around several ten to more than one hundred meters and the lower depth may range from several hundred meters to about one thousand meters and the thickness may reach several hundred meters. Compared with Canadian Mallik permafrost, the Qinghai-Tibet plateau permafrost has similar thermal gradients within / below the frozen layer and gas composition, except for relatively thinner permafrost, still suggesting great gas hydrate potentials.
cited By 26
Keywords: frozen ground; gas hydrate; geochemistry; heterogeneity; permafrost; temperature gradient; Asia; China; Eurasia; Far East; Qinghai-Xizang Plateau

Modeling the formation of the K-Pg boundary layer - Artemieva, N.; Morgan, J. (Icarus, 2009)
In this paper we investigate the formation of the Cretaceous-Paleogene (K-Pg) boundary layer through numerical modeling. The K-Pg layer is widely agreed to be composed of meteoritic material and target rock from the Chicxulub impact site, that has been ejected around the globe and mixed with local material during final deposition. The observed composition and thickness of the K-Pg boundary layer changes with azimuth and distance from the impact site. We have run a suite of numerical simulations to investigate whether we can replicate the observational data, with a focus on the distal K-Pg layer and the impact glasses at proximal sites such as Beloc, Haiti. Previous models of the K-Pg ejecta have assumed an initial velocity distribution and tracked the ejecta to its final destination. Here, we attempt to model the entire process, from impact to the arrival of the ejecta around the globe. Our models replicate the observed ejecta thickness at proximal sites, and the modeled ejecta is composed of sediments and silicate basement rocks, in agreement with observational data. Models that use a 45° impact angle are able to replicate the total ejecta and iridium volume at distal sites, and the majority of the ejecta is composed of meteorite and target sediments. Sub-vertical impacts generate too little iridium, and oblique impacts of ≤30 degrees generate too much. However, in contrast to observations, models that involve ballistic transport of ejecta lead to ejecta thickness decreasing with increasing distance, and are unable to transport shocked minerals (quartz and zircon) from the Chicxulub basement rocks around the globe. We suggest that much of the K-Pg ejecta is transported non-ballistically, and that the most plausible mechanism is through re-distribution from a hot, expanding atmosphere. The results are important for future investigations of the environmental effects of the Chicxulub impact. © 2009 Elsevier Inc. All rights reserved.
cited By 74

Physical rock properties of the Eyreville core, Chesapeake Bay impact structure - Mayr, S.I.; Burkhardt, H.; Popov, Y.; Romushkevich, R.; Miklashevskiy, D.; Gorobtsov, D.; Heidinger, P.; Wilhelm, H. (Special Paper of the Geological Society of America, 2009)
The physical properties of rocks in drill core from impact structures can be used to distinguish individual nonimpact and impact-generated lithologies, and to investigate the effect of the impact process on the target rocks. Here, we present the results of laboratory measurements of porosity, density, velocity, and thermal properties on the densely sampled cores from the Eyreville borehole in the Chesapeake Bay impact structure, USA. With increasing depth, the lithologies encountered (and porosities) are: postimpact sediments (40%-60%), Exmore breccia and sedimentary blocks (27%-44%), a large megablock of granitoids (<1%), suevite and polymict lithic impact breccia (1%-25%), and schist, granite, and pegmatite of the basementderived section (1%-13%). The low bulk densities and thermal properties of the postimpact sediments show a good correlation with the high porosity values. The physical properties within the Exmore bed sequence overall display relatively small variation but are heterogeneous on the core sample scale. Physical properties along the impact-breccia sequence are highly variable on all scales, and they are interpreted to be controlled by the structural arrangement of particles as well as by the highly variable mineral and clast compositions of the samples. The physical properties of the rocks of the lowermost basement-derived section are also heterogeneous and are interpreted as having been influenced by both lithology and overprinting as a result of the impact process. These results are important for further lithological and petrophysical interpretation and for calibrating future geophysical models of the Chesapeake Bay impact structure. © 2009 The Geological Society of America.
cited By 8

Three-dimensional passive seismic waveform imaging around the SAFOD site, California, using the generalized Radon transform - Zhang, H.; Wang, P.; Van Der Hilst, R.D.; Toksoz, M.N.; Thurber, C.; Zhu, L. (Geophysical Research Letters, 2009)
We apply a three-dimensional (3D) generalized Radon transform (GRT) to scattered P-waves from 575 local earthquakes recorded at 68 temporary network stations for passive-source imaging of (near-vertical) structures close to the San Andreas Fault Observatory at Depth (SAFOD) site. The GRT image profiles through or close by the SAFOD site reveal near-vertical reflectors close to the fault zone as well as in the granite to the southwest and the Franciscan m'elange to the northeast of the main fault. Although slightly lower in resolution, these structures are generally similar to features in 2D images produced with steep-dip prestack seismic migration of data from active source seismic reflection and refraction surveys. Our GRT images, however, also reveal several vertical reflectors to the northeast of the SAF that do not appear in the migration images but which are consistent with local geology. These results suggest that in a seismically active area, inverse scattering of earthquake data (for instance with the GRT) can be a viable and, in 3D, economic alternative to an active source survey. Copyright 2009 by the American Geophysical Union.
cited By 20
Keywords: 2D images; Active area; California; Earthquake data; Fault zone; Generalized radon transform; Image profile; Inverse scattering; P-waves; Prestack; San Andreas Fault; Seismic migration; Seismic reflections; Seismic waveforms; Source imaging; Temporary networks; Three-dimensional (3D); Earthquakes; Radon; Reflection; Seismic waves; Surveys; Three dimensional; data inversion; earthquake event; fault zone; imaging method; P-wave; prestack migration; Radon transform; seismic migration; seismic reflection; three-dimensional modeling; wave scattering; waveform analysis; California; North America; United States

Pore-water chemistry from the ICDP-USGS core hole in the Chesapeake Bay impact structure-Implications for paleohydrology, microbial habitat, and water resources - Sanford, W.E.; Voytek, M.A.; Powars, D.S.; Jones, B.F.; Cozzarelli, I.M.; Cockell, C.S.; Eganhouse, R.P. (Special Paper of the Geological Society of America, 2009)
We investigated the groundwater system of the Chesapeake Bay impact structure by analyzing the pore-water chemistry in cores taken from a 1766-m-deep drill hole 10 km north of Cape Charles, Virginia. Pore water was extracted using high-speed centrifuges from over 100 cores sampled from a 1300 m section of the drill hole. The pore-water samples were analyzed for major cations and anions, stable isotopes of water and sulfate, dissolved and total carbon, and bioavailable iron. The results reveal a broad transition between freshwater and saline water from 100 to 500 m depth in the postimpact sediment section, and an underlying synimpact section that is almost entirely filled with brine. The presence of brine in the lowermost postimpact section and the trend in dissolved chloride with depth suggest a transport process dominated by molecular diffusion and slow, compaction-driven, upward flow. Major ion results indicate residual effects of diagenesis from heating, and a pre-impact origin for the brine. High levels of dissolved organic carbon (6-95 mg/L) and the distribution of electron acceptors indicate an environment that may be favorable for microbial activity throughout the drilled section. The concentration and extent of the brine is much greater than had previously been observed, suggesting that its occurrence may be common in the inner crater. However, groundwater-flow conditions in the structure may reduce the saltwater-intrusion hazard associated with the brine. © 2009 The Geological Society of America.
cited By 22
Keywords: Chemical analysis; Chlorine compounds; Dissolution; Groundwater; Groundwater flow; Hydrochemistry; Infill drilling; Organic carbon; Rock drills; Salt water intrusion; Sulfur compounds; Chesapeake bay impact structures; Dissolved organic carbon; Electron acceptor; Groundwater system; Microbial activities; Molecular diffusion; Pore-water chemistry; Stable isotopes of water; Saline water; cation; dissolved organic carbon; geological survey; groundwater flow; impact structure; microbial activity; microbial community; paleohydrology; porewater; saline intrusion; sediment core; stable isotope; sulfate; transport process; water chemistry; water resource; Chesapeake Bay; United States; Virginia

Tidal modulation of temperature oscillations monitored in borehole Yaxcopoil-1 (Yucat'an, Mexico) - Čerm'ak, V.; Bodri, L.; Šafanda, J. (Earth and Planetary Science Letters, 2009)
For better understanding of temperature state in the subsurface, temperature-depth logs can be suitably completed by high-resolution long-run temperature-time monitoring at selected depths. The results of temperature monitoring at three depth levels in borehole Yaxcopoil-1, Chicxulub impact structure, Mexico (April/May 2006) proved that even when a borehole is in fully stabilized conditions, temperature may exhibit certain unrest resembling irregular oscillations in the order of hundredths or (in the extreme case) even first tenths of degree. Two novel methods for detection of the weak fingerprints of stable periodic components in long noisy records, namely the RQI (Recurrence Quantification Interval) analysis and the HiCum (Histograms Cumulation) were used to isolate the constituents with tidal periodicities from temperature oscillations measured in borehole Yaxcopoil-1. Both analyses revealed that temperature series contain perceptible tidal component. The field data were correlated with the simulated synthetic tides. The comparison of staked HiCum records for the theoretical gravity tide and monitored temperature shows significant positive linear correlation between both variables. There is a small lag between two signals corresponding to 25 min phase difference. © 2009 Elsevier B.V. All rights reserved.
cited By 2

The crust-mantle transition and the Moho beneath the Vogtland/West Bohemian region in the light of different seismic methods - Hrubcov'a, Pavla; Geissler, Wolfram H. (Studia Geophysica et Geodaetica, 2009)
The structure of the crust and the crust-mantle boundary in the Vogtland/ West Bohemian region have been a target of several seismic measurements for the last 25 years, beginning with the steep-angle reflection seismic studies (DEKORP-4/KTB, MVE-90, 9HR), the refraction and wide-angle experiments (GRANU'95, CELEBRATION 2000, SUDETES 2003), and followed by passive seismic studies (receiver functions, teleseismic tomography). The steep-angle reflection studies imaged a highly reflective lower crust (4 to 6 km thick) with the Moho interpreted in a depth between 30 and 32 km and a thinner crust beneath the Eger Rift. The refraction and wide-angle reflection seismic studies (CELEBRATION 2000) revealed strong wide-angle reflections in a depth of 26-28 km interpreted as the top of the lower crust. Long coda of these reflections indicates strong reflectivity in the lower crustal layer, a phenomenon frequently observed in the Caledonian and Variscan areas. The receiver function studies detected one strong conversion from the base of the crust interpreted as the Moho discontinuity at a depth between 27 and 37 km (average at about 31 km). The discrepancies in the Moho depth determination could be partly attributed to different background of the methods and their resolution, but could not fully explain them. So that new receivers function modelling was provided. It revealed that, instead of a first-order Moho discontinuity, the observations can be explained with a lower crustal layer or a crust-mantle transition zone with a maximum thickness of 5 km. The consequent synthetic ray-tracing modelling resulted in the model with the top of the lower crust at 28 km, where highly reflective lower crustal layer can obscure the Moho reflection at a depth of 32-33 km. © Institute of Geophysics of the ASCR, v.v.i 2009.
Keywords: Bohemian Massif; Central Europe; Eurasia; Europe; Germany; Vogtland; coda; crust-mantle boundary; crustal structure; lower crust; Moho; ray tracing; seismic method; seismic reflection; seismic refraction; transition zone

The Eocene-Oligocene sedimentary record in the Chesapeake Bay impact structure: Implications for climate and sea-level changes on the western Atlantic margin - Schulte, P.; Wade, B.S.; Kontny, A.; Self-Trail, J.M. (Special Paper of the Geological Society of America, 2009)
A multidisciplinary investigation of the Eocene-Oligocene transition in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville core from the Chesapeake Bay impact basin was conducted in order to document environmental changes and sequence stratigraphic setting. Planktonic foraminifera and calcareous nannofossil biostratigraphy indicate that the Eyreville core includes an expanded upper Eocene (Biozones E15 to E16 and NP19/20 to NP21, respectively) and a condensed Oligocene-Miocene (NP24-NN1) sedimentary sequence. The Eocene-Oligocene contact corresponds to a =3-Ma-long hiatus. Eocene- Oligocene sedimentation is dominated by great diversity and varying amounts of detrital and authigenic minerals. Four sedimentary intervals are identified by lithology and mineral content: (1) A 30-m-thick, smectite- and illite-rich interval directly overlies the Exmore Formation, suggesting long-term reworking of impact debris within the Chesapeake Bay impact structure. (2) Subsequently, an increase in kaolinite content suggests erosion from soils developed during late Eocene warm and humid climate in agreement with data derived from other Atlantic sites. However, the kaolinite increase may also be explained by change to a predominant sediment input from outside the Chesapeake Bay impact structure caused by progradation of more proximal facies belts during the highstand systems tract of the late Eocene sequence E10.Spectral analysis based on gamma-ray and magnetic susceptibility logs suggests infl uence of 1.2 Ma low-amplitude oscillation of the obliquity period during the late Eocene. (3) During the latest Eocene (Biozones NP21 and E16), several lithological contacts (clay to clayey silt) occur concomitant with a prominent change in the mineralogical composition with illite as a major component: This lithological change starts close to the Biozone NP19/20-NP21 boundary and may correspond to sequence boundary E10-E11 as observed in other northwest Atlantic margin sections. It could result from a shift to more distal depositional environments and condensed sedimentation during maximum fl ooding, rather than refl ecting a climatic change in the hinterland. The distinct 1% increase of the oxygen isotopes may correspond to the short-term latest Eocene precursor isotope event. (4) The abrupt increase of sediment grainsize, carbonate content, and abundance of authigenic minerals (glauconite) across the major unconformity that separates Eocene from Oligocene sediments in the Eyreville core refl ects deposition in shallower settings associated with erosion, winnowing, and reworking. Sediments within the central crater were affected by the rapid eustatic sea-level changes associated with the greenhouse-icehouse transition, as well as by an abrupt major uplift event and possibly enhanced current activity on the northwestern Atlantic margin. © 2009 The Geological Society of America.
cited By 9
Keywords: Deposition; Erosion; Gamma rays; Infill drilling; Isotopes; Kaolinite; Lithology; Magnetic susceptibility; Mica; Sea level; Sedimentology; Stratigraphy; Chesapeake bay impact structures; Continental scientific drillings; Depositional environment; Highstand systems tract; Mineralogical compositions; Planktonic foraminifera; U.s. geological surveys; Warm and humid climates; Sediments; biostratigraphy; depositional environment; Eocene-Oligocene boundary; eustacy; geological survey; impact structure; lithology; paleoclimate; progradation; sea level change; sedimentary sequence; sedimentation; sequence boundary; sequence stratigraphy; systems tract; Atlantic Ocean; Atlantic Ocean (West); Chesapeake Bay; United States; Foraminifera

The floating astronomical time scale for the terrestrial Late Cretaceous Qingshankou Formation from the Songliao Basin of Northeast China and its stratigraphic and paleoclimate implications - Wu, H.; Zhang, S.; Jiang, G.; Huang, Q. (Earth and Planetary Science Letters, 2009)
The Upper Cretaceous Qingshankou Formation (K2qn) in the Songliao Basin (SLB) of Northeast China consists of up to 550 m thick, lacustrine mudstone and shale that constitute one of the most important source rocks of the Daqing oil field. A high-resolution cyclostratigraphic analysis of the natural gamma-ray logging from 10 wells of the Qingshankou Formation (K2qn) reveals orbital cycles of precession (20 ka), obliquity (40 ka) and eccentricity (100 ka and 405 ka), providing strong evidence for astronomically driven climate changes in the Late Cretaceous terrestrial environments. Floating astronomical time scales (ATS) are established for all sections, which demonstrate variable durations of K2qn across the basin (1.09 Ma-5.20 Ma) and strong diachroneity of the lacustrine strata. Four periods of high depositional rates can be identified in the central parts of the basin, possibly recording deposition during times of sustained wet climate and high chemical weathering. An ATS established from well M206 in the central depression zone of the basin, where the most complete and stable Milankovitch cycles are present, suggests that the maximum duration of the K2qn is 5.20 Ma (from 94.27 Ma to 89.07 Ma; Late Cenomanian to Early Coniacian). The lacustrine anoxic event 1 (LAE1) at the Cenomanian-Turonian boundary lasted 210-310 ka, during which the most prolific petroleum source rocks in SLB were deposited. The onset ( 94.21-94.18 Ma) and duration ( 210-310 Ka) of LAE1 in SLB are comparable to those of the oceanic anoxic event 2 (OAE2; onset at 94.21 Ma and duration of 320-900 ka), suggesting that the same trigger mechanism, such as increased atmospheric CO2 from large-scale igneous activity, may have initiated high primary productivity and organic carbon burial in both marine and terrestrial systems. © 2008 Elsevier B.V. All rights reserved.
cited By 107
Keywords: astronomical time scale (ATS); lacustrine anoxic event 1 (LAE1); Late Cretaceous; Milankovitch cycles; Songliao Basin; Astrophysics; Climate change; Fire hazards; Gamma rays; Oil fields; Oil shale; Organic carbon; Photosynthesis; Radioactivity logging; Shale oil; Stratigraphy; Weathering; Oil well logging; climate change; Cretaceous; cyclostratigraphy; Milankovitch cycle; mudstone; organic carbon; paleoclimate; source rock; Asia; China; Eurasia; Far East; Songliao Basin; Coniacian

The laguna potrok aike scientiic drilling project PASADO (ICDP expedition 5022) - Zolitschka, Bernd; Anselmetti, Flavio; Ariztegui, Daniel; Corbella, Hugo; Ohlendorf, Christian; Sch{abitz, Frank (Scientific Drilling, 2009)

The mineralogy of the Exmore beds- Chickahominy Formation boundary section of the Chesapeake Bay impact structure revealed in the Eyreville core - Ferrell Jr., R.E.; Dypvik, H. (Special Paper of the Geological Society of America, 2009)
Core descriptions, thin-section analyses, and X-ray powder diffraction analyses of whole-rock samples and clay-sized fractions were employed to interpret the sedimentology and mineralogy of synimpact Exmore beds and the overlying Chickahominy Formation. This study attempts to explain the origin and postdepositional alteration of materials in the Eyreville core from the central zone of the Chesapeake Bay impact crater. Samples were obtained from eight zones extending from core depths of 435 to 1471 m, with emphasis on the interval from 435 to 455 m, representing the upper Exmore beds and the lower Chickahominy Formation. Qualitative clay mineral determinations were aided by peak decomposition procedures to unravel overlapping diffraction bands, and quantifi cation was accomplished by least squares matching of actual and computed patterns. The major facies in approximate ascending order are suevite breccias, poorly sorted conglomerate and sandstone, and upward-fi ning glauconitic sandstone within the Exmore beds followed by parallel laminated sandy siltstone and claystone in the Chickahominy Formation. They all contain clay minerals (mica, smectites, and some serpentine, kaolinite, and chlorite) plus quartz and feldspar. Heulandite, pyrite, calcite, and disordered silica (partly representing nanofossils and microfossils) are present in the Chickahominy Formation. The boundary beds (upper 7 m) of the Exmore beds have higher clay contents but fewer varieties of expandable clay minerals than in the Chickahominy Formation. The Exmore beds are enriched in reworked glauconite, but there are no indications of heulandite, calcite, disordered silica, or pyrite, except in the very top of the 7-m-thick boundary bed interval. The clay fractions of the Eyreville materials are dominated by different species of expanding clay minerals (smectite, fi ne and coarsely crystalline nontronite, and fi ne and coarsely crystalline smectite-illite mixed-layered clay minerals), but dioctahedral mica and illite are also present. Amorphous material and minor amounts of quartz,chlorite, and mixed-layered smectite (0.95)/iron-rich illite (0.05) are common. The abundance of the clays in most intervals is highly variable due to the chaotic assemblage of sediments and crystalline materials from diverse sources. The boundary beds are dominated by a single smectitic mineral, nontronite, which is assumed to be the principal product of melt glass alteration. Amorphous material (melt glass) and nontronite are calculated to represent 13 vol% and 13-19 vol% of the sediments in this interval, respectively. Grain size, or clast size, has a major infl uence on mineralogical variability, i.e., when grain size (clast size) is large, the mineral content of adjacent samples is highly variable. © 2009 The Geological Society of America.
cited By 19
Keywords: Calcite; Crystalline materials; Diffraction; Feldspar; Glass; Grain size and shape; Kaolinite; Mica; Pyrites; Quartz; Sandstone; Sediments; Serpentine; Silicate minerals; X ray powder diffraction; Zeolites; Chesapeake bay impact structures; Clay-sized fractions; Diffraction bands; Disordered silicas; Glass alteration; Layered clay minerals; Least-squares matching; Quantifi cations; Core samples; clay mineral; depositional sequence; facies; glauconite; grain size; illite; impact structure; least squares method; mineral alteration; mineralogy; qualitative analysis; sedimentology; X-ray diffraction; Chesapeake Bay; United States

The record of ground zero in the Chesapeake Bay impact crater-Suevites and related rocks - Wittmann, A.; Reimold, W.U.; Schmitt, R.T.; Hecht, L.; Kenkmann, T. (Special Paper of the Geological Society of America, 2009)
The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville boreholes through the annular moat of the Chesapeake Bay crater recovered polymict impact breccias and associated rocks from the depth range of 1397-1551 m. These rocks record cratering processes before burial beneath resurge deposits. Quantitative analyses of clast sizes, matrix contents, and distribution of impact melt reveal a shock metamorphic gradient in these impactites. The reason for the low estimated quantity of impact melt in the crater (̃10 km3) remains elusive. Possible causes may relate to increased excavation efficiency due to a high ratio of water column and sedimentary target to depth of excavation, an oblique impact, or a buried melt sheet at depth. A plausible petrogenetic scenario consists of a lower blockrich section that slumped from an outer region of the transient cavity into the annular moat ̃1.5 min after impact. This blocky debris was mixed with the remains of the excavation fl ow, which contained a pod of melt entrained in ground-surge debris on top. Subsequently, melt-rich suevites were emplaced that record interaction of the expanding ejecta plume with fallback material related to the evolving central uplift. A clast-rich impact melt rock that likely shed off the central uplift covers these suevites. Incipient collapse of the ejecta plume is recorded in the uppermost subunit, but the arrival of resurge fl ow terminated its continuous deposition ̃6-8 min after impact. Limited thermal annealing allowed preservation of glassy melt and high-pressure polymorphs. Mild hydrothermal overprint in the central crater was likely driven by the structural uplift of ̃100 °C warmer basement rocks. © 2009 The Geological Society of America.
cited By 28
Keywords: Boreholes; Debris; Excavation; Infill drilling; Structural geology; Basement rocks; Continental scientific drillings; Continuous deposition; High-pressure polymorph; Oblique impact; Thermal-annealing; Transient cavities; U.s. geological surveys; Rocks; crater; drilling; impact structure; impactite; marine sediment; petrogenesis; suevite; Chesapeake Bay; United States

The record of ground zero in the Chesapeake Bay impact crater-Suevites and related rocks - Wittmann, A.; Reimold, W.U.; Schmitt, R.T.; Hecht, L.; Kenkmann, T. (Special Paper of the Geological Society of America, 2009)
The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville boreholes through the annular moat of the Chesapeake Bay crater recovered polymict impact breccias and associated rocks from the depth range of 1397-1551 m. These rocks record cratering processes before burial beneath resurge deposits. Quantitative analyses of clast sizes, matrix contents, and distribution of impact melt reveal a shock metamorphic gradient in these impactites. The reason for the low estimated quantity of impact melt in the crater (̃10 km3) remains elusive. Possible causes may relate to increased excavation efficiency due to a high ratio of water column and sedimentary target to depth of excavation, an oblique impact, or a buried melt sheet at depth. A plausible petrogenetic scenario consists of a lower blockrich section that slumped from an outer region of the transient cavity into the annular moat ̃1.5 min after impact. This blocky debris was mixed with the remains of the excavation fl ow, which contained a pod of melt entrained in ground-surge debris on top. Subsequently, melt-rich suevites were emplaced that record interaction of the expanding ejecta plume with fallback material related to the evolving central uplift. A clast-rich impact melt rock that likely shed off the central uplift covers these suevites. Incipient collapse of the ejecta plume is recorded in the uppermost subunit, but the arrival of resurge fl ow terminated its continuous deposition ̃6-8 min after impact. Limited thermal annealing allowed preservation of glassy melt and high-pressure polymorphs. Mild hydrothermal overprint in the central crater was likely driven by the structural uplift of ̃100 °C warmer basement rocks. © 2009 The Geological Society of America.
cited By 28

Toward a geochemical mass balance of major elements in Lake Qinghai, NE Tibetan Plateau: A significant role of atmospheric deposition - Jin, Zhangdong; You, Chen-Feng; Yu, Jimin (Applied Geochemistry, 2009)
Sediments in Lake Qinghai archive important information about past environmental changes. In order to faithfully interpret the sediment records and constrain the elemental cycles, it is critical to trace various sources of sediments in the lake. The results show that the elemental input-output budgets are imbalanced for most major elements between riverine fluxes and mass accumulation rate (MAR) of Lake Qinghai sediments. A realistic model must include contributions of dry/wet atmospheric deposition that allow the major element mass balance for the lake to be defined. The budget estimation is based on mass balances of Si and Al, which are relatively immobile and carried to the lake via particulate forms. Estimated annual budget of dry atmospheric deposition is ∼1.3 ± 0.3 × 103 kt/a (accounting for ∼65% of the total inputs) to the lake sediments, assuming local loess within the catchment as a candidate for dry atmospheric deposition to the lake. The resultant flux of 300 ± 45 g/m2/a falls within the flux average of the desert area (400 g/m2/a) and the loess plateau (250 g/m2/a), consistent with the geographical setting of Lake Qinghai. The role of atmospheric deposition would be more significant if wet deposition via rainfall and snow were taken into account. This highlights the potential importance of dust as a significant source for sediment preservation flux for other catchments worldwide. The results also indicate that nearly all Ca input was preserved in the lake sediments under modern conditions, consistent with Ca2+ supersaturation of the lake water. © 2009 Elsevier Ltd. All rights reserved.
Keywords: Asia; China; Eurasia; Far East; Qinghai; Qinghai Lake; Qinghai-Xizang Plateau; Atmospheric chemistry; Atmospherics; Budget control; Calcium; Catchments; Deposition; Meteorological problems; Patient monitoring; Runoff; Sedimentology; Annual budget; Atmospheric depositions; Desert area; Environmental change; Input-output; Lake sediments; Lake waters; Loess Plateau; Major elements; Mass accumulation rates; Mass balance; Realistic model; Riverine flux; Tibetan Plateau; Wet deposition; atmospheric deposition; environmental change; geochemistry; lacustrine deposit; mass balance; Lakes

Supplemental materials for the ICDP-USGS Eyreville A, B, and C core holes, Chesapeake Bay impact structure: Core-box photographs, coring-run tables, and depth-conversion files - Durand, C.T.; Edwards, L.E.; Malinconico, M.L.; Powars, D.S. (Special Paper of the Geological Society of America, 2009)
During 2005-2006, the International Continental Scientific Drilling Program and the U.S. Geological Survey drilled three continuous core holes into the Chesapeake Bay impact structure to a total depth of 1766.3 m. A collection of supplemental materials that presents a record of the core recovery and measurement data for the Eyreville cores is available on CD-ROM at the end of this volume and in the GSA Data Repository. The supplemental materials on the CD-ROM include digital photographs of each core box from the three core holes, tables of the three coring-run logs, as recorded on site, and a set of depth-conversion programs. In this chapter, the contents, purposes, and basic applications of the supplemental materials are briefly described. With this information, users can quickly decide if the materials will apply to their specific research needs. © 2009 The Geological Society of America.
cited By 8
Keywords: Boreholes; CD-ROM; Infill drilling; Photography; Basic application; Chesapeake bay impact structures; Continental scientific drillings; Conversion programs; Data repositories; Digital photographs; Measurement data; U.s. geological surveys; Electronic document exchange; borehole logging; impact structure; information technology; photograph; Chesapeake Bay; United States

Trends, rhythms and events in Plio-Pleistocene African climate - Trauth, Martin H.; Larrasoaña, Juan C.; Mudelsee, Manfred (Quaternary Science Reviews, 2009)
We analyzed published records of terrigenous dust flux from marine sediments off subtropical West Africa, the eastern Mediterranean Sea, and the Arabian Sea, and lake records from East Africa using statistical methods to detect trends, rhythms and events in Plio-Pleistocene African climate. The critical reassessment of the environmental significance of dust flux and lake records removes the apparent inconsistencies between marine vs. terrestrial records of African climate variability. Based on these results, major steps in mammalian and hominin evolution occurred during episodes of a wetter, but highly variable climate largely controlled by orbitally induced insolation changes in the low latitudes. © 2008 Elsevier Ltd. All rights reserved.
Keywords: Africa; Sub-Saharan Africa; West Africa; Mammalia; Climatology; Mammals; Salinity measurement; Submarine geology; climate variation; dust; marine sediment; Mediterranean Water; Pleistocene; statistical analysis; subtropical region; terrigenous deposit; trend analysis; Arabian seas; Climate variabilities; Dust fluxes; East africa; Eastern mediterraneans; Environmental significances; Marine sediments; West-Africa; Dust

Ultrahigh-pressure texture inheritance during retrogression: Evidence from magnetofabrics in eclogites and ultramafic rocks (Chinese Continental Scientific Drilling project) - Xuexiang, Qi; Grimmer, Jens C.; Zhiqin, Xu (Tectonophysics, 2009)
In order to contribute to a better understanding of exhumation related retrogression processes ultrahigh-pressure (UHP) mafic and ultramafic rocks from the Chinese Continental Scientific Drilling (CCSD) in the Maobei eclogite body of the Sulu ultrahigh-pressure metamorphic belt in eastern China were studied for their magnetofabrics. Variably retrogressed eclogites and serpentinized ultramafic rocks were retrieved from the depth interval of 100 to 1000 m of the borehole. A vein network of irregular shaped veins with a retrograde metamorphic assemblage cuts across the eclogite foliation at both low and high angles. SEM imaging of the eclogites documents that magnetite associated with retrograde pargasitic amphiboles developed around shape-preferred garnet. SEM imaging of the serpentinized ultramafic rocks documents that magnetite rims grew around shape-preferred garnet and that magnetite formed within a mesh texture related to serpentinization. Syn-serpentinization magnetite growth increased bulk susceptibilities, but reduced anisotropy. Maximum susceptibility axes from both eclogites and serpentinized garnet-peridotites trend N-S, i.e. parallel with the stretching lineation as defined by olivine and omphacite grains. This implies that the magnetic fabric mimics the UHP fabric and survived retrogression and that the fabric is inherited from the UHP stage. As a consequence, retrogression was not associated with substantial ductile deformation and the mafic-ultramafic Maobei body behaved as a rigid body within a ductile deforming quartzo-feldspathic matrix during exhumation. Internal strain is restricted to brittle fracturing, associated fluid circulation and vein formation facilitating retrograde reactions in the mafic-ultramafic rocks. © 2008 Elsevier B.V. All rights reserved.
Keywords: Asia; China; Eurasia; Far East; Sulu Belt; Deformation; Drilling; Fabrics; Garnets; Magnetite; Olivine; Oxide minerals; Rocks; Silicate minerals; Textures; CCSD; Exhumation; Magnetofabrics; Sulu; Ultrahigh-pressure; amphibole; Chinese Continental Scientific Drilling Project; eclogite; exhumation; magnetic fabric; magnetite; retrograde metamorphism; texture; ultrahigh pressure metamorphism; ultramafic rock; Metamorphic rocks

Understanding paleoclimate and human evolution through the hominin sites and paleolakes drilling project - Cohen, Andrew; Arrowsmith, Ramon; Behrensmeyer, Anna K.; Campisano, Christopher; Feibel, Craig; Fisseha, Shimeles; Johnson, Roy; Bedaso, Zelalem Kubsa; Lockwood, Charles; Mbua, Emma; Olago, Daniel; Potts, Richard; et al. (Scientific Drilling, 2009)

Unique coesite-bearing zircon from allanite-bearing gneisses: U-Pb, REE and Lu-Hf properties and implications for the evolution of the Sulu UHP terrane, China - Liu, Fulai; Gerdes, Axel; Liou, Jahnguang; Liu, Plnghua (European Journal of Mineralogy, 2009)
Zircon from allanite-bearing para- and ortho-gneisses provides a unique insight into the geologic evolution of the Sulu ultrahigh-pressure (UHP) terrane in eastern China. Laser Raman, cathodoluminescence (CL) imaging combined with trace-element, U-Pb, and Lu-Hf isotope data indicate that zircon grains consist of three distinct zones. Inherited magmatic core records a Neoproterozoic protolith age, the coesite-bearing mantle reveals a UHP metamorphic age of 230 ± 7 Ma, and the low-P mineralbearing rim retains an age of 210 ± 3 Ma for the amphibolite-facies retrogression. Positive εHf(t) values for the inherited cores reflect involvement of juvenile materials in the protolith. Low 176Lu/177Hf ratios of coesite-bearing mantles indicate their formation during / after gamet crystallization. Their 176Hf/177Hf ratios are homogenous and more radiogenic than those of the inherited cores, implying fractionation of the Lu-Hf system during isotope equilibration within the metamorphic mineral assemblage. Moreover, coesitebearing mantles show geochemical characteristics that are distinctly different from those of previous studies: (1) The chondritenormalized pattern shows a steep slope from HREE (heavy rare earth elements) to LREE (light rare earth elements) with a moderately negative Eu anomaly (mean Eu/Eu* = 0.53). Such a pattern requires that phases enriched in LREE (e.g., allanite) and europium (e.g., K-feldspar) were stable during UHP conditions. (2) The positive Ce anomaly is very pronounced (Ce/Ce* of 612-657), e.g., about seven to eight times higher than that of the inherited core; (3) The uranium content is very low (6-25 ppm) and the Th/U ratio elevated (0.52-2.83). These data for the coesite-bearing mantle are distinctly different from those of previous studies. We interpret the data to suggest high O fugacity during the UHP and retrograde metamorphic evolution, which also played a critical role in restraining diamond growth in Sulu-Dabie UHP rocks. © 2009 E. Schweizerbart'sehe Verlagsbuchhandlung.
Keywords: China; Dabie-Sulu Belt; Sulu Belt; Binary alloys; Exploratory geochemistry; Feldspar; Geochronology; Isotopes; Lead alloys; Levees; Metamorphic rocks; Rare earth elements; Rare earths; Silica; Trace elements; Zircon; Allanite; Coesite; Gneiss; Hf isotope; Sulu UHP terrane; U-Pb dating; allanite; cathodoluminescence; coesite; diamond; gneiss; hafnium; isotopic fractionation; lutetium; rare earth element; retrograde metamorphism; trace element; uranium-lead dating; zircon; Lutetium alloys

Unlocking a cretaceous geologic and geophysical puzzle: Scientific drilling of Songliao Basin in northeast China - Wang, C.; Huang, Y.; Zhao, X. (The Leading Edge, 2009)
Our Earth is a dynamic planet, changing on temporal scales ranging from millions of years required to complete a solid Earth cycle, or to form mountain ranges, to the few seconds required for a devastating earthquake or explosive volcanic eruptions. The Cretaceous was a period of great unrest in geologic history. It included a series of extraordinary global geological events - a significant increase of marine water temperature and the deposition of black shales; oceanic anoxia events (OAEs); biotic turnovers and mass extinctions; and the formation of many mountain ranges (California's Sierra Nevada and the Rockies in the western United States, the Andes in South America, and the Alps). Sea level rose during the mid-Cretaceous, covering about a third of the land area. Sea level was up to 250 m higher than at present. © 2009 Society of Exploration Geophysicists.
cited By 12
Keywords: Earth (planet); Volcanoes; Geologic history; Geological events; Mass extinction; Mountain ranges; Northeast China; Scientific drilling; Volcanic eruptions; Western United States; Sea level; anoxic conditions; Cretaceous; drilling; mass extinction; mountain region; sea level; seawater; volcanic eruption; water temperature; Alps; Andes; California; China; Rocky Mountains; Sierra Nevada [California]; Songliao Basin; South America; United States

Uppermost Cretaceous sediments: Sedimentary microfacies and sedimentary environment evolution of Sifangtai Formation and Mingshui Formation in SK-Ⅰ (n). - Ri-Hui, CHENG; Guo-Dong, WANG; Pu-Jun, WANG; Wei-Feng, GAO (Earth Science Frontiers, 2009)

Well site selecting, core section characteristics and distribution of the special lithological layers in CCSD-SK-In borehole, Songliao Basin. - Wei-Feng, GAO; Cheng-Shan, WANG; Pu-Jun, WANG; Xiao-Qiao, MO; Yan-An, LIN; Ri-Hui, CHENG; Guo-Dong, WANG (Earth Science Frontiers, 2009)

Tectonic evolution of the Ganos segment of the North Anatolian Fault (NW Turkey) - Janssen, C.; Bohnhoff, M.; Vapnik, Y.; G{org{un, E.; Bulut, F.; Plessen, B.; Pohl, D.; Aktar, M.; Okay, A.I.; Dresen, G. (Journal of Structural Geology, 2009)
We analyzed the paleostress field, ongoing deformation, meso- to micro-scale faulting, cataclasis, fault rock alteration and veining within turbidite and limestone sequences at the Ganos Fault which represent a major branch of the North Anatolian Fault Zone in NW Turkey. Fault damage was found to occur across a several kilometers wide zone. Effects of faulting are shown by localized subsidiary brittle faults and fault rock alteration in the turbidites as well as fault breccia formation in the limestone sequence. Microseismicity along the Ganos Fault cluster at two locations, the more pronounced being located offshore at a fault bend associated with a change from a transpressional to a transtensional regime. Kinematic analysis reveals a dextral strike-slip regime with components of normal and thrust faulting. Along strike paleostress orientation at the Ganos Fault is rather uniform. Deformation mechanisms and fluid inclusion data from quartz and calcite veins suggest that fault-related quartz veins were formed at temperatures between 170 and 250 °C and pressures between 40 and 120 MPa. Fault-related calcite vein growth occurred during a temperature decrease from 170 °C to 70 °C with pressures likely below 50 MPa. Fluid inclusion and stable isotope data show that the fluids are predominantly of meteoric origin and migrated upwards into the fault. Pure CH4 inclusions in quartz also suggest a biogenic or thermogenic methane origin. © 2008 Elsevier Ltd. All rights reserved.
cited By 23
Keywords: Fault architecture; Fluid inclusions; Ganos fault; Seismicity; Stable isotopes; Turkey; Calcite; Carbonate minerals; Deformation; Inclusions; Isotopes; Limestone; Methane; Mineralogy; Oxide minerals; Quartz; Structural geology; deformation mechanism; fault zone; faulting; kinematics; North Anatolian Fault; paleostress; strike-slip fault; tectonic evolution; Eurasia; Turkey

Subsurface structure, physical properties, fault-zone characteristics and stress state in scientific drill holes of Taiwan Chelungpu Fault Drilling Project - Hung, J.-H.; Ma, K.-F.; Wang, C.-Y.; Ito, H.; Lin, W.; Yeh, E.-C. (Tectonophysics, 2009)
Continuous cores and a suit of geophysical measurements were collected in two scientific drill holes to understand physical mechanisms involved in the large displacements during the 1999 Chi-Chi earthquake. Physical properties obtained from wire-line logs including P- and S-wave sonic velocity, gamma ray, electrical resistivity, density and temperature, are primarily dependent on parameters such as lithology, depth and fault zones. The average dip of bedding, identified from both cores and FMI (or FMS) logs, is about 30° towards SE. Nevertheless, local azimuthal variations and increasing or decreasing bedding dips appear across fault zones. A prominent increase of structural dip to 60°-80° below 1856 m could be due to deformation associated with propagation of the Sanyi fault. A total of 12 fault zones identified in hole-A are located in the Plio-Pleistocene Cholan Formation, Pliocene Chinshui Shale and Miocene Kueichulin Formation. The shallowest fault zone occurs at 1111 m depth (FZ1111). It is a 1 m gouge zone including 12 cm of thick indurate black material. We interpreted this zone as the slip zone during Chi-Chi earthquake. FZ1111 is characterized by: 1) bedding-parallel thrust fault with 30-degree dip; 2) the lowest resistivity; 3) low density, Vp and Vs, 4) high Vp/Vs ratio and Poisson's ratio; 5) low energy and velocity anisotropy, and low permeability within the homogeneous 1 m gouge zone; 6) increasing gas (CO2 and CH4) emissions, and 7) appearance of smectite within the primary slip zone. In situ stresses at the drill site were inferred from leak-off tests, borehole breakouts and drilling-induced tensile fractures from borehole FMS/FMI logs, and shear seismic wave anisotropy from DSI logs. The dominant fast shear-wave polarization direction is in good agreement with regional maximum horizontal stress axis, particularly within the strongly anisotropic Kueichulin Formation. A conjugate set of secondary directions are parallel to microcrack orientations. A drastic change of orientation of fast shear-wave polarization across the Sanyi thrust fault at the depth of 1712 m reflects the change of stratigraphy, physical properties and structural geometry. © 2007 Elsevier B.V. All rights reserved.
cited By 52
Keywords: Azimuthal variations; Black materials; Chi-Chi earthquake; Drill holes; Drill sites; Drilling-induced tensile fractures; Electrical resistivities; Fault zones; Fault-zone properties; Gamma-ray; Geophysical measurements; Horizontal stress; In-situ stress; Large displacements; Leak-off tests; Low densities; Low energies; Low permeabilities; Micro cracks; Miocene; Physical mechanisms; Plio-pleistocene; Pliocene; Poisson' s ratios; S-wave anisotropy; Slip zones; Smectite; Sonic velocities; Stress state; Structural geometries; Subsurface structures; Taiwan Chelungpu Fault Drilling Project; Thrust faults; Velocity anisotropies; Wave polarizations; Anisotropy; Clay minerals; Drilling; Earthquakes; Electric resistance; Gamma rays; Lithology; Poisson ratio; Polarization; Rock drills; Seismic waves; Shear waves; Stratigraphy; Structural geology; Thermal logging; Viscosity measurement; Waves; Boreholes; borehole breakout; Chi-Chi earthquake 1999; deformation; drilling; fault geometry; fault propagation; fault zone; in situ stress; lithology; Miocene; P-wave; physical property; Pleistocene; Pliocene; S-wave; seismic anisotropy; wave velocity

Postimpact alteration of sedimentary breccias in the ICDP-USGS Eyreville A and B cores with comparison to the Cape Charles core, Chesapeake Bay impact structure, Virginia, USA - Larsen, D.; Stephens, E.C.; Zivkovic, V.B. (Special Paper of the Geological Society of America, 2009)
In this study, we extend the knowledge of postimpact alteration processes through an investigation of mineralogy and petrology of 24 samples from the Exmore Formation and sedimentary megablock intervals in the Eyreville borehole within the Chesapeake Bay impact structure and comparisons to similar studies of cored intervals of the Cape Charles borehole. The bulk mineralogical studies reveal quartz, feldspars (microcline and albite), muscovite, smectite-vermiculite clays, and kaolinite with variable quantities of pyrite, zeolites, calcite, and chlorite. X-ray diffraction analysis of the clay (<2 μm) fraction of samples indicates that the clays are dominated by expandable clays with lesser quantities of illite, kaolinite, glauconite, and mixed- layered clays. The expandable clays include smectite, vermiculite, and smectite-vermiculite intergrade varieties; illite interlayering is minimal (generally, <10% illite layers). Thin section and scanning electron microscope petrography in the Exmore breccia show evidence for extensive authigenic expandable clay in the matrix and dispersed pyrite lepispheres and fine calcite rhombs. Grain alteration includes feldspar dissolution and albitization, glauconite recrystallization, and dissolution and expandable-clay replacement of micas. Taken together, the results indicate that low-temperature alteration (maximum temperatures 60-80 °C) is prevalent in the sedimentary clast-rich intervals in the Eyreville cores, and the maximum effects are observed between 600 and 970 m depth. In comparison, the Exmore Formation from the Cape Charles borehole, 8 km to the southwest and overlying the central peak of the inner crater, shows more advanced authigenesis with Fe-rich chlorite, common quartz overgrowths, and mixed-layered illite-smectite clay with as much as 20% interlayered illite. A low-temperature hydrothermal mineral assemblage is documented in suevite and crystalline-clast breccia at depths of 725-820 m in the Cape Charles borehole. The fine-grained clastic target material and contained seawater are argued to have limited initial target melting and initial crater-floor temperatures in the Chesapeake Bay impact structure to an even greater degree than that of other marine craters targeted in consolidated sedimentary substrates. Subsequent hydrothermal circulation was confined to the central uplift and neighboring fractured zones, whereas alteration in the overlying sedimentary breccias involved conductive heat flow, reaction with hypersaline pore fluids, and minor fluid flow into more porous, permeable sedimentary blocks adjacent to the central uplift. © 2009 The Geological Society of America.
cited By 7
Keywords: Boreholes; Calcite; Dissolution; Feldspar; Flow of fluids; Kaolinite; Mica; Pyrites; Quartz; Rocks; Scanning electron microscopy; Sedimentology; Silicate minerals; Temperature; X ray powder diffraction; Zeolites; Chesapeake bay impact structures; Feldspar dissolution; Hydrothermal circulation; Hydrothermal mineral assemblages; Low temperature alteration; Low temperatures; Maximum temperature; Sedimentary substrates; Clay alteration; albitization; breccia; dissolution; feldspar; hydrothermal activity; hydrothermal alteration; hydrothermal system; impact structure; kaolinite; mineralogy; muscovite; petrography; quartz; recrystallization; research program; sedimentary petrology; smectite; vermiculite; Chesapeake Bay; United States; Calluna vulgaris; Micas

Rheological properties of dome lavas: Case study of Unzen volcano - Cordonnier, B.; Hess, K.-U.; Lavall'ee, Y.; Dingwell, D.B. (Earth and Planetary Science Letters, 2009)
Transitions between effusive and explosive styles of lava dome eruptions are likely accompanied by changes in lava rheology. The common presence of crystals in dome lavas produces a complex non-Newtonian rheology. Thus models of such complex rheology are essential for volcanic eruption models. Here, we have measured the rheology of natural Unzen lavas with a compressive uniaxial press operating at stresses between 1 and 70 MPa and temperatures between 940 and 1010 °C. Crystal-rich Unzen lavas are characterised by two essential rheological features which produce non-Newtonian effects. The first is an instantaneous response of the apparent viscosity to applied stress which requires that the magma be described as a visco-elastic fluid that exhibits shear-thinning. The second effect takes the form of a time-dependence of the viscosity at moderate to high stress (≥ 10 MPa). In this regime, the apparent viscosity slowly decreases as increasing fracturing of the phenocrysts and the groundmass occurs. Fragmentation of crystals and alignment of crystal fragments are observed to produce flow banding-effects which in turn lower the apparent viscosity of natural dome lavas. Ultimately, deformation may lead to complete rupture of the lava if the stress is sufficient. Cracking thus stands as an important process in natural dome lava rheology. The ubiquitous non-Newtonian rheology of dome lavas, observed experimentally here, needs to be adequately treated in order to generate appropriate eruption models. © 2008 Elsevier B.V. All rights reserved.
cited By 91
Keywords: brittle; ductile; flow banding; lava; magma; non-Newtonian rheology; Unzen; visco-elastic; Cements; Crystals; Domes; Elasticity; Non Newtonian flow; Plasticity; Rheology; Volcanic rocks; Volcanoes; Viscosity; cracking; crystal structure; deformation; fragmentation; lava dome; magma; phenocryst; rheology; stress; viscoelasticity; volcanic eruption; volcanic rock; Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano

Postimpact alteration of sedimentary breccias in the ICDP-USGS Eyreville A and B cores with comparison to the Cape Charles core, Chesapeake Bay impact structure, Virginia, USA - Larsen, D.; Stephens, E.C.; Zivkovic, V.B. (Special Paper of the Geological Society of America, 2009)
In this study, we extend the knowledge of postimpact alteration processes through an investigation of mineralogy and petrology of 24 samples from the Exmore Formation and sedimentary megablock intervals in the Eyreville borehole within the Chesapeake Bay impact structure and comparisons to similar studies of cored intervals of the Cape Charles borehole. The bulk mineralogical studies reveal quartz, feldspars (microcline and albite), muscovite, smectite-vermiculite clays, and kaolinite with variable quantities of pyrite, zeolites, calcite, and chlorite. X-ray diffraction analysis of the clay (<2 μm) fraction of samples indicates that the clays are dominated by expandable clays with lesser quantities of illite, kaolinite, glauconite, and mixed- layered clays. The expandable clays include smectite, vermiculite, and smectite-vermiculite intergrade varieties; illite interlayering is minimal (generally, <10% illite layers). Thin section and scanning electron microscope petrography in the Exmore breccia show evidence for extensive authigenic expandable clay in the matrix and dispersed pyrite lepispheres and fine calcite rhombs. Grain alteration includes feldspar dissolution and albitization, glauconite recrystallization, and dissolution and expandable-clay replacement of micas. Taken together, the results indicate that low-temperature alteration (maximum temperatures 60-80 °C) is prevalent in the sedimentary clast-rich intervals in the Eyreville cores, and the maximum effects are observed between 600 and 970 m depth. In comparison, the Exmore Formation from the Cape Charles borehole, 8 km to the southwest and overlying the central peak of the inner crater, shows more advanced authigenesis with Fe-rich chlorite, common quartz overgrowths, and mixed-layered illite-smectite clay with as much as 20% interlayered illite. A low-temperature hydrothermal mineral assemblage is documented in suevite and crystalline-clast breccia at depths of 725-820 m in the Cape Charles borehole. The fine-grained clastic target material and contained seawater are argued to have limited initial target melting and initial crater-floor temperatures in the Chesapeake Bay impact structure to an even greater degree than that of other marine craters targeted in consolidated sedimentary substrates. Subsequent hydrothermal circulation was confined to the central uplift and neighboring fractured zones, whereas alteration in the overlying sedimentary breccias involved conductive heat flow, reaction with hypersaline pore fluids, and minor fluid flow into more porous, permeable sedimentary blocks adjacent to the central uplift. © 2009 The Geological Society of America.
cited By 7

Postimpact deposition in the Chesapeake Bay impact structure: Variations in eustasy, compaction, sediment supply, and passive-aggressive tectonism - Kulpecz, A.A.; Miller, K.G.; Browning, J.V.; Edwards, L.E.; Powars, D.S.; McLaughlin Jr., P.P.; Harris, A.D.; Feigenson, M.D. (Special Paper of the Geological Society of America, 2009)
The Eyreville and Exmore, Virginia, core holes were drilled in the inner basin and annular trough, respectively, of the Chesapeake Bay impact structure, and they allow us to evaluate sequence deposition in an impact crater. We provide new high-resolution geochronologic ( <1 Ma) and sequence-stratigraphic interpretations of the Exmore core, identify 12 definite (and four possible) postimpact depositional sequences, and present comparisons with similar results from Eyreville and other mid- Atlantic core holes. The concurrence of increases in δ 18 O with Chesapeake Bay impact structure sequence boundaries indicates a primary glacioeustatic control on deposition. However, regional comparisons show the differential preservation of sequences across the mid-Atlantic margin. We explain this distribution by the compaction of impactites, regional sediment-supply changes, and the differential movement of basement structures. Upper Eocene strata are thin or missing updip and around the crater, but they thicken into the inner basin (and offshore to the southeast) due to rapid crater infilling and concurrent impactite compaction. Oligocene sequences are generally thin and highly dissected throughout the mid-Atlantic region due to sediment starvation and tectonism, except in southeastern New Jersey. Regional tectonic uplift of the Norfolk Arch coupled with a southward decrease in sediment supply resulted in: (1) largely absent Lower Miocene sections around the Chesapeake Bay impact structure compared to thick sections in New Jersey and Delaware; (2) thick Middle Miocene sequences across the Delmarva Peninsula that thin south of the Chesapeake Bay impact structure; and (3) upper Middle Miocene sections that pinch out just north of the Chesapeake Bay impact structure. Conversely, the Upper Miocene-Pliocene section is thick across Virginia, but it is poorly represented in New Jersey because of regional variations in relative subsidence. © 2009 The Geological Society of America.
cited By 15
Keywords: Compaction; Concurrency control; Infill drilling; Offshore oil well production; Sediments; Stratigraphy; Basement structures; Chesapeake bay impact structures; Depositional sequences; Regional tectonics; Regional variation; Sediment starvation; Sequence boundary; Sequence-stratigraphic interpretation; Deposition; deposition; depositional sequence; Eocene; geochronology; glacioeustacy; impact structure; Miocene; Oligocene; Pliocene; sedimentation rate; sequence boundary; sequence stratigraphy; subsidence; Chesapeake Bay; Delmarva Peninsula; New Jersey; United States; Virginia

Postimpact heat conduction and compaction-driven fluid flow in the Chesapeake Bay impact structure based on downhole vitrinite reflectance data, ICDP-USGS Eyreville deep core holes and Cape Charles test holes - Malinconico, M.L.; Sanford, W.E.; Wright Horton Jr., W.J.J. (Special Paper of the Geological Society of America, 2009)
Vitrinite reflectance data from the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville deep cores in the centralcrater moat of the Chesapeake Bay impact structure and the Cape Charles test holes on the central uplift show patterns of postimpact maximum-temperature distribution that result from a combination of conductive and advective heat flow. Within the crater-fill sediment-clast breccia sequence at Eyreville, an isoreflectance (-0.44% Ro) section (525-1096 m depth) is higher than modeled background coastal-plain maturity and shows a pattern typical of advective fluid flow. Below an intervening granite slab, a short interval of sediment-clast breccia (1371-1397 m) shows a sharp increase in reflectance (0.47%-0.91% Ro) caused by conductive heat from the underlying suevite (1397-1474 m). Refl ectance data in the uppermost suevite range from 1.2% to 2.1% Ro. However, heat conduction alone is not sufficient to affect the temperature of sediments more than 100 m above the suevite. Thermal modeling of the Eyreville suevite as a 390 °C cooling sill-like hot rock layer supplemented by compaction- driven vertical fluid flow (0.046 m/a) of cooling suevitic fluids and deeper basement brines (120 °C) upward through the sediment breccias closely reproduces the measured reflectance data. This scenario would also replace any marine water trapped in the crater fill with more saline brine, similar to that currently in the crater, and it would produce temperatures sufficient to kill microbes in sediment breccias within 450 m above the synimsuevite. A similar downhole maturity pattern is present in the sediment-clast breccia over the central uplift. High-reflectance (5%-9%) black shale and siltstone clasts in the suevite and sediment-clast breccia record a pre-impact (Paleozoic?) metamorphic event. Previously published maturity data in the annular trough indicate no thermal effect there from impact-related processes. © 2009 The Geological Society of America.
cited By 17
Keywords: Boreholes; Compaction; Heat conduction; Infill drilling; Reflection; Rocks; Saline water; Sediments; Software testing; Chesapeake bay impact structures; Conductive heat; Continental scientific drillings; Metamorphic events; Reflectance data; U.s. geological surveys; Vertical fluid flow; Vitrinite reflectance; Flow of fluids; black shale; breccia; crater; fluid flow; geological survey; heat flow; impact structure; Ocean Drilling Program; temperature effect; thermal conductivity; thermal regime; uplift; vitrinite reflectance; Chesapeake Bay; United States; Calluna vulgaris

Pre-impact tectonothermal evolution of the crystalline basement-derived rocks in the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure - Gibson, R.L.; Townsend, G.N.; Horton Jr., J.W.; Reimold, W.U. (Special Paper of the Geological Society of America, 2009)
Pre-impact crystalline rocks of the lowermost 215 m of the Eyreville B drill core from the Chesapeake Bay impact structure consist of a sequence of pelitic mica schists with subsidiary metagraywackes or felsic metavolcanic rocks, amphibolite, and calc-silicate rock that is intruded by muscovite (±biotite, garnet) granite and granite pegmatite. The schists are commonly graphitic and pyritic and locally contain plagioclase porphyroblasts, fi brolitic sillimanite, and garnet that indicate middle- to upper-amphibolite-facies peak metamorphic conditions estimated at ̃0.4-0.5 GPa and 600-670 °C. The schists display an intense, shallowly dipping, S1 composite shear foliation with local micrometer- to decimeter-scale recumbent folds and S-C' shear band structures that formed at high temperatures. Zones of chaotically oriented foliation, resembling breccias but showing no signs of retrogression, are developed locally and are interpreted as shear-disrupted fold hinges. Mineral textural relations in the mica schists indicate that the metamorphic peak was attained during D1. Fabric analysis indicates, however, that subhorizontal shear deformation continued during retrograde cooling, forming mylonite zones in which high-temperature shear fabrics (S-C and S-C') are overprinted by progressively lower- temperature fabrics. Cataclasites and carbonate-cemented breccias in more competent lithologies such as the calc-silicate unit and in the felsic gneiss found as boulders in the overlying impactite succession may refl ect a fi nal pulse of low-temperature cataclastic deformation during D1. These breccias and the shear and mylonitic foliations are cut by smaller, steeply inclined anastomosing fractures with chlorite and calcite infill (interpreted as D2). This D2 event was accompanied by extensive chlorite-sericitecalcite ± epidote retrogression and appears to predate the impact event. Granite and granite pegmatite veins display local discordance to the S1 foliation, but elsewhere they are affected by high-temperature mylonitic shear deformation, suggesting a late-D1 intrusive timing close to the metamorphic peak. The D1 event is tentatively interpreted as a thrusting event associated with westward-verging collision between Gondwana and Laurentia before or during the Permian-Carboniferous Alleghanian orogeny. It is unclear whether subsequent brittle deformation, described here as D2, could be part of regional dextral Alleghanian strike-slip faulting or younger Mesozoic normal faulting. © 2009 The Geological Society of America.
cited By 14
Keywords: Calcite; Core drilling; Crystalline materials; Fault slips; Feldspar; Garnets; Granite; Infill drilling; Mica; Shear deformation; Silicate minerals; Strike-slip faults; Structural geology; Temperature; Amphibolite facies; Brittle deformation; Cataclastic deformation; Chesapeake bay impact structures; Crystalline basement; Metamorphic conditions; Metavolcanic rocks; Strike slip faulting; Crystalline rocks; amphibolite; brittle deformation; crystalline rock; faulting; impact structure; metagreywacke; metamorphism; metavolcanic rock; schist; tectonic evolution; thermal evolution; Chesapeake Bay; United States

Productivity cycles in Lake Hovsgol, NW Mongolia, during the last 1 Ma and the age model of the HDP-04 drill core record - Prokopenko, A.A.; Khursevich, G.K.; Kuzmin, M.I.; Kawai, T. (Quaternary International, 2009)
Repetitive patterns in the records of total organic carbon (TOC), total nitrogen (TN) and δ13Corg observed in the Lake Hovsgol sediment section from HDP-04 drill core reflect past changes in productivity of Lake Hovsgol and in the isotopic composition of the lake's carbon pool. Lake Hovsgol productivity proxy signals are interpreted to represent the response of the Hovsgol lacustrine system to glacial-interglacial cycles of the Pleistocene. This interpretation is supported by the apparent orbitally-forced pattern in the TOC, TN and δ13Corg records of the past 250 ka in the BDP-96-2 drill core from neighboring Lake Baikal. The intervals with independent age control, such as the radiocarbon-dated last glacial-interglacial transition and the paleomagnetic reversals, make it evident that productivity proxy signals are reliable indicators of past cold-to-warm and warm-to-cold climate transitions, as seen from the agreement with the pattern of global climate change in marine δ18O records. The Brunhes/Matuyama reversal during the MIS 19 interglacial coincides with a distinct peak of TOC and TN in the Hovsgol record, similar to the signal during the Holocene interglacial. By contrast, the upper Jaramillo reversal in the Lake Hovsgol record occurs in a diatom-free calcareous interval characterized by minima in TOC, TN and by a 'glacial'-type range of δ13Corg values. In both Lake Baikal and Lake Hovsgol records, peaks in TOC and TN contents help distinguishing past interglacials and interstadials, and isotopically-heaviest δ13Corg values help identify past glacial intervals. An age model for the HDP-04 drill core section is proposed based on recognizing the repetitive patterns in Lake Hovsgol productivity and lithologic records as regional paleoclimate cycles of middle to late Pleistocene. Absolute dates and diatom biostratigraphic correlation ties to the Lake Baikal record are used as key controls. In the proposed age model, the interval 81-24 m in the HDP-04 sediment section below the major unconformity is correlated to MIS 27 through late MIS 13, whereas the upper 24 m of the HDP-04 section is suggested to have recovered the sedimentary record of late MIS 7 to MIS 1.
Keywords: Asia; Eurasia; Far East; Hvsgol Aymag; Lake Baikal; Mongolia; Russian Federation; Bacillariophyta; biostratigraphy; climate change; diatom; Holocene; interglacial; isotopic composition; lacustrine deposit; nitrogen; paleoclimate; paleoenvironment; Pleistocene; sediment core; total organic carbon

Radiogenic heat production in the lithosphere of Sulu ultrahigh-pressure metamorphic belt - He, Lijuan; Hu, Shengbiao; Yang, Wencai; Wang, Jiyang (Earth and Planetary Science Letters, 2009)
The Chinese Continental Scientific Drilling (CCSD) project is located at the Sulu ultrahigh-pressure metamorphic (UHPM) belt. It offers a unique opportunity for studying the radiogenic heat production of both shallower and deeper rocks. Based on the concentrations of radiogenic elements U, Th and K on 349 samples from main hole of CCSD (CCSD MH), pilot holes and exposures, we determined radiogenic heat productions of all major rock types in the Sulu UHPM belt. Results show the mean values of orthogneiss and paragneiss are respectively 1.65 ± 0.81 and 1.24 ± 0.61 μW m- 3. Due to different composition and grade of retrogressive metamorphism, the eclogites display significant scatter in radiogenic heat production, ranging from 0.01 to 2.85 μW m- 3, with a mean of 0.44 ± 0.55 μW m- 3. The radiogenic heat production in ultramafic rocks also varies within a large range of 0.02 to 1.76 μW m- 3, and the average turns out to be 0.18 ± 0.31 μW m- 3. Based on the measurements and crustal petrologic model, the vertical distribution model of heat production in Sulu crust is established. The resulting mean heat production (0.76 μW m- 3) contributes 24 mW m- 2 to the surface heat flow. 1-D thermal model indicates that the temperature at the Moho reaches above 750 °C, and the thermal thickness of the lithosphere is 75 km, in good agreement with the geophysical results. The high teat flow ( 75 mW m- 2) together with thin lithosphere presents strong support for the extension events during the late Cretaceous and Cenozoic. © 2008 Elsevier B.V. All rights reserved.
Keywords: Asia; China; Eurasia; Far East; Sulu Belt; Calluna vulgaris; Structural geology; Uranium alloys; CCSD; CCSD-MH; Cenozoic; Chinese Continental Scientific drillings; Eclogites; Heat productions; Large ranges; Mean values; Metamorphic belts; Pilot holes; radiogenic heat production; Rock types; Sulu UHPM belt; Surface heat flows; Thermal models; thermal structure; Ultramafic rocks; Vertical distributions; Cenozoic; Chinese Continental Scientific Drilling Project; Cretaceous; eclogite; heat flow; heat production; lithosphere; metamorphism; Moho; petrology; retrogression; thermal structure; ultrahigh pressure metamorphism; ultramafic rock; vertical distribution; Production

Results of recent sediment drilling activities in deep crater lakes - Pienitz, R; Melles, M; Zolitschka, B (Pages News, 2009)

Rock-avalanche and ocean-resurge deposits in the late Eocene Chesapeake Bay impact structure: Evidence from the ICDP-USGS Eyreville cores, Virginia, USA - Gohn, G.S.; Powars, D.S.; Dypvik, H.; Edwards, L.E. (Special Paper of the Geological Society of America, 2009)
An unusually thick section of sedimentary breccias dominated by target-sediment clasts is a distinctive feature of the late Eocene Chesapeake Bay impact structure. A cored 1766-m-deep section recovered from the central part of this marine-target structure by the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) drilling project contains 678 m of these breccias and associated sediments and an intervening 275-m-thick granite slab. Two sedimentary breccia units consist almost entirely of Cretaceous nonmarine sediments derived from the lower part of the target sediment layer. These sediments are present as coherent clasts and as autoclastic matrix between the clasts. Primary (Cretaceous) sedimentary structures are well preserved in some clasts, and liquefaction and fluidization structures produced at the site of deposition occur in the clasts and matrix. These sedimentary breccias are interpreted as one or more rock avalanches from the upper part of the transient-cavity wall. The little-deformed, unshocked granite slab probably was transported as part of an extremely large slide or avalanche. Water-saturated Cretaceous quartz sand below the slab was transported into the seafloor crater prior to, or concurrently with, the granite slab. Two sedimentary breccia units consist of polymict diamictons that contain cobbles, boulders, and blocks of Cretaceous nonmarine target sediments and less common shocked-rock and melt ejecta in an unsorted, unstratified, muddy, fossiliferous, glauconitic quartz matrix. Much of the matrix material was derived from Upper Cretaceous and Paleogene marine target sediments. These units are interpreted as the deposits of debris flows initiated by the resurge of ocean water into the seafloor crater. Interlayering of avalanche and debris-flow units indicates a partial temporal overlap of the earlier avalanche and later resurge processes. A thin unit of stratified turbidite deposits and overlying laminated fine-grained deposits at the top of the section represents the transition to normal shelf sedimentation. © 2009 The Geological Society of America.
cited By 28
Keywords: Debris; Deposits; Fluidization; Granite; Infill drilling; Quartz; Sedimentology; Sediments; Chesapeake bay impact structures; Continental scientific drillings; Fluidization structures; Sedimentary structure; Shelf sedimentation; Transient cavities; Turbidite deposits; U.s. geological surveys; Sedimentary rocks; breccia; clast; debris flow; deposition; diamicton; Eocene; fluidization; impact structure; marine sediment; matrix; research program; rock avalanche; sediment transport; sedimentation; turbidite; Chesapeake Bay; United States; Virginia

Static stress drop associated with brittle slip events on exhumed faults - Griffith, W.A.; Toro, G.D.; Pennacchioni, G.; Pollard, D.D.; Nielsen, S. (Journal of Geophysical Research: Solid Earth, 2009)
We estimate the static stress drop on small exhumed strike-slip faults in the Lake Edison granodiorite of the central Sierra Nevada (California). The subvertical strike-slip faults were exhumed from 4 to 15 km depth and were chosen because they are exposed in outcrop along their entire tip-to-tip lengths of 8-12 m. Slip nucleated on joints and accumulated by crystal-plastic shearing (forming quartz mylonites from early quartz vein filling in joints) and successive brittle faulting (forming epidote-bearing cataclasites). The occurrence of thin, ≤300 fim wide, pseudotachylytes along some small faults throughout the study area suggests that some, if not all, of the brittle slip on the study area faults may have been seismic. We suggest that the contribution of brittle, cataclastic slip to the total slip along the studied cataclasite-bearing small faults may be estimated by the length of epidote-filled, rhombohedral dilatational jogs (rhombochasms) distributed quasi-periodically along the length of the faults. The interpretation that slip recorded by rhombochasms occurred in single events is based on evidence that (1) epidote crystals are randomly oriented and undeformed within the rhombochasm; (2) cataclasite in principal slip zones does not include clasts of previous cataclasite, and (3) rhombochasm lengths vary systematically along the length of the faults with slip maximum occurring near the fault center, tapering to the fault tips. We thereby constrain both the rupture length and slip. On the basis of these measurements, we calculate stress drops ranging over 90-250 MPa, i.e., one to two orders of magnitude larger than typical seismological estimates for earthquakes, but similar in magnitude to seismological estimates of small (<M2) earthquakes from the San Andreas Fault Observatory at Depth (SAFOD). The slip events described in the present study occurred along small, deep-seated faults, and, given the calculated stress drops and observations that brittle faults exploited joints sealed by quartz-bearing mylonite, we conclude that these were strong faults. © 2009 by the American Geophysical Union.
cited By 30
Keywords: earthquake; epidote; faulting; mylonite; quartz; seismology; shear stress; slip; strike-slip fault; California; North America; San Andreas; Sierra Nevada [California]; United States

Rock-magnetic properties of the ICDP-USGS Eyreville core, Chesapeake Bay impact structure, Virginia, USA - Elbra, T.; Kontny, A.; Pesonen, L.J. (Special Paper of the Geological Society of America, 2009)
Chesapeake is a 35-Ma-old shallow-marine, complex impact structure with a diameter of ̃85 km. The structure is completely buried beneath several hundreds of meters of postimpact sediments. Therefore, subsurface information can be obtained only from geophysical surveys and drill holes. Recently, deep drilling into the inner crater zone, at Eyreville near Cape Charles, was carried out in order to provide constraints on geophysical modeling and cratering processes in a multilayered marine target. We analyzed samples of the Eyreville core including postimpact, impactproduced, and basement-derived units in order to clarify the magneto-mineralogy, to provide physical parameters for better understanding the influence of the impact on the petrophysical and rock-magnetic properties, and to provide rock-magnetic data for magnetic modeling. Results show a complex behavior of physical properties of the lithologies in the Eyreville core due to different lithologies having been affected by shock-induced changes. Our data suggest that pyrrhotite and magnetite carry the magnetic properties in most of the core samples, whereas hematite is present in oxidized clays from the uppermost impact-generated unit (Exmore beds) and related sediment megablocks. The granitic megablock appears to be undeformed based on lack of brittle deformation in magnetite and petrophysically appears as a single block. In contrast, the impactite sequence below the megablock shows brittle deformation and magnetic fabric randomization, and the pyrrhotite in the associated schist fragments is strongly fractured. Thus, the Chesapeake Bay deep core provides an extraordinary opportunity to study the effect of impact on magnetite and pyrrhotite, the two main magnetic minerals creating crustal magnetic anomalies. © 2009 The Geological Society of America.
cited By 15
Keywords: Core samples; Deformation; Geomagnetism; Hematite; Infill drilling; Iron ores; Lithology; Magnetic properties; Magnetite; Petrophysics; Structural geology; Brittle deformation; Chesapeake bay impact structures; Crustal magnetic anomalies; Geophysical modeling; Geophysical surveys; Physical parameters; Rock magnetic properties; Subsurface information; Structural properties; brittle deformation; cratering; geophysical survey; hematite; impact structure; magnetic anomaly; magnetic method; magnetic mineral; magnetic property; magnetite; mineralogy; physical property; pyrrhotite; Chesapeake Bay; United States

Scientific collaboration on past speciation conditions in Lake Ohrid-SCOPSCO workshop report - Wagner, Bernd; Wilke, Thomas; Krastel-Gudegast, Sebastian; Grazhdani, Andon; Reicherter, Klaus; Trajanovski, Sasho; Zanchetta, Giovanni (Scientific Drilling, 2009)
In summary, the SCOPSCO workshop provided a reliable platflorm to discuss the present state of knowledge and future steps towards a deep drilling campaign. A full proposal for an ICDP drilling campaign will be submitted in 2009.
Keywords: Deep drillings; Lake ohrid; Scientific collaborations

Search for a meteoritic component in impact breccia from the Eyreville core, Chesapeake Bay impact structure: Considerations from platinum group element contents - Mcdonald, I.; Bartosova, K.; Koeberl, C. (Special Paper of the Geological Society of America, 2009)
This paper documents an attempt to detect a meteoritic component in both washback (resurge) crater-fill breccia (the so-called Exmore breccia) and in suevites from the Eyreville core hole, which was drilled several kilometers from the center of the 85-km-diameter Chesapeake Bay impact structure, Virginia, USA. Determining the presence of an extraterrestrial component and, in particular, the projectile type for this structure, which is the largest impact structure currently known in the United States, is of importance because it marks one of several large impact events in the late Eocene, during which time the presence of extraterrestrial 3He and multiple impact ejecta layers provide evidence for a comet or asteroid shower. Previous work has indicated an ordinary chondritic projectile for the largest of the late Eocene craters, the Popigai impact structure in Siberia. The exact relation between the Chesapeake Bay impact event and siderophile element anomalies documented in late Eocene ejecta layers from around the world is not clear. The only clear indication for an extraterrestrial component related to this structure has been the discovery of a meteoritic osmium isotopic signature in impact melt rocks recovered from a hydrogeologic test hole located on Cape Charles near the center of the structure, and confirmation of a similar signature in suevitic rocks would have been desirable in order to place constraints on the type of projectile involved in formation of the Chesapeake Bay crater. Unfortunately, the current data show no discernible differences in the contents of the platinum group elements (PGEs) among the suevite, the Exmore breccia, and several crystalline basement rocks, all from the Eyreville core hole. Abundances of PGEs are uniformly low (e.g., <0.1 ppb Ir), and chondrite-normalized abundance patterns are nonchondritic. These data do not allow unambiguous verification of an extraterrestrial signature. Thus, the nature of the Chesapeake Bay projectile remains ambiguous. © 2009 The Geological Society of America.
cited By 10
Keywords: Crystalline rocks; Hydrogeology; Infill drilling; Isotopes; Meteorites; Platinum; Projectiles; Rocks; Chesapeake bay impact structures; Crystalline basement; Extraterrestrial components; Impact structures; Isotopic signatures; Platinum group elements; Platinum group elements (PGEs); Siderophile elements; Economic geology; breccia; chondrite; coastal sediment; ejecta; Eocene; impact structure; isotopic composition; meteorite; osmium; platinum group element; research program; sediment chemistry; siderophile element; suevite; Chesapeake Bay; United States

Search for a meteoritic component in impact breccia from the Eyreville core, Chesapeake Bay impact structure: Considerations from platinum group element contents - Mcdonald, I.; Bartosova, K.; Koeberl, C. (Special Paper of the Geological Society of America, 2009)
This paper documents an attempt to detect a meteoritic component in both washback (resurge) crater-fill breccia (the so-called Exmore breccia) and in suevites from the Eyreville core hole, which was drilled several kilometers from the center of the 85-km-diameter Chesapeake Bay impact structure, Virginia, USA. Determining the presence of an extraterrestrial component and, in particular, the projectile type for this structure, which is the largest impact structure currently known in the United States, is of importance because it marks one of several large impact events in the late Eocene, during which time the presence of extraterrestrial 3He and multiple impact ejecta layers provide evidence for a comet or asteroid shower. Previous work has indicated an ordinary chondritic projectile for the largest of the late Eocene craters, the Popigai impact structure in Siberia. The exact relation between the Chesapeake Bay impact event and siderophile element anomalies documented in late Eocene ejecta layers from around the world is not clear. The only clear indication for an extraterrestrial component related to this structure has been the discovery of a meteoritic osmium isotopic signature in impact melt rocks recovered from a hydrogeologic test hole located on Cape Charles near the center of the structure, and confirmation of a similar signature in suevitic rocks would have been desirable in order to place constraints on the type of projectile involved in formation of the Chesapeake Bay crater. Unfortunately, the current data show no discernible differences in the contents of the platinum group elements (PGEs) among the suevite, the Exmore breccia, and several crystalline basement rocks, all from the Eyreville core hole. Abundances of PGEs are uniformly low (e.g., <0.1 ppb Ir), and chondrite-normalized abundance patterns are nonchondritic. These data do not allow unambiguous verification of an extraterrestrial signature. Thus, the nature of the Chesapeake Bay projectile remains ambiguous. © 2009 The Geological Society of America.
cited By 10

Seasonally chemical weathering and CO2 consumption flux of Lake Qinghai river system in the northeastern Tibetan Plateau - Zhang, Fei; Jin, Zhangdong; Hu, Guang; Li, Fuchun; Shi, Yuewei (Environmental Earth Sciences, 2009)
The major cation and anion compositions of waters from the Lake Qinghai river system (LQRS) in the northeastern Tibetan Plateau were measured. The waters were collected seasonally from five main rivers during premonsoon (late May), monsoon (late July), and post-monsoon (middle October). The LQRS waters are all very alkaline and have high concentrations of TDS (total dissolved solids) compared to rivers draining the Himalayas and the southeastern Tibetan Plateau. Seasonal variations in the water chemistry show that, except the Daotang River, the TDS concentration is high in October and low in July in the LQRS waters. The forward models were used to quantify the input of three main rivers (Buha River, Shaliu River, and Hargai River) from rain, halite, carbonates, and silicates. The results suggest that (1) atmospheric input is the first important source for the waters of the Buha River and the Shaliu River, contributing 36-57% of the total dissolved cations, (2) carbonate weathering input and atmospheric input have equal contribution to the Hargai River water, (3) carbonate weathering has higher contribution to these rivers than silicate weathering, and (4) halite is also important source for the Buha River. The Daotang River water is dominated by halite input owing to its underlying old lacustrine sediments. The water compositions of the Heima River are controlled by carbonate weathering and rainfall input in monsoon season, and groundwater input may be important in pre-monsoon and post-monsoon seasons. After being corrected the atmospheric input, average CO2 drawdown via silicate weathering in the LQRS is 35×103 mol/km2 per year, with highest in monsoon season, lower than Himalayas and periphery of Tibetan Plateau rivers but higher than some rivers draining shields. © Springer-Verlag 2009.
Keywords: China; Himalayas; Qinghai; Qinghai Lake; Qinghai-Xizang Plateau; Atmospheric chemistry; Atmospheric thermodynamics; Carbonation; Dissolution; Geochemistry; Groundwater; Lakes; Positive ions; Rain; Sediments; Silicates; Sodium chloride; Soil mechanics; Water levels; Weathering; Anion composition; Atmospheric inputs; Carbonate weathering; Chemical weathering; Forward models; High concentration; Himalayas; Lacustrine sediments; Monsoon season; Post-monsoon; Pre-monsoon; River systems; River water; Seasonal variation; Silicate weathering; Tibetan Plateau; Total dissolved solids; Water chemistry; Water composition; carbon dioxide; chemical weathering; ionic composition; lacustrine deposit; river system; river water; seasonal variation; water chemistry; Rivers

Sedimentary organic matter characteristics and hydrocarbon potential of Qingshankou Formation of SK-1 drilling from Songliao Basin - Zhong, YF; Guo, JT; Wang, L; Song, ZG (Geochimica, 2009)

Seismic modeling of multidimensional heterogeneity scales of mallik gas hydrate reservoirs, Northwest territories of Canada - Huang, J.-W.; Bellefleur, G.; Milkereit, B. (Journal of Geophysical Research: Solid Earth, 2009)
In hydrate-bearing sediments, the velocity and attenuation of compressional and shear waves depend primarily on the spatial distribution of hydrates in the pore space of the subsurface lithologies. Recent characterizations of gas hydrate accumulations based on seismic velocity and attenuation generally assume homogeneous sedimentary layers and neglect effects from large- and small-scale heterogeneities of hydrate-bearing sediments. We present an algorithm, based on stochastic medium theory, to construct heterogeneous multivariable models that mimic heterogeneities of hydrate-bearing sediments at the level of detail provided by borehole logging data. Using this algorithm, we model some key petrophysical properties of gas hydrates within heterogeneous sediments near the Mallik well site, Northwest Territories, Canada. The modeled density, and P and S wave velocities used in combination with a modified Biot-Gassmann theory provide a first-order estimate of the in situ volume of gas hydrat'e near the Mallik 5L-38 borehole. Our results suggest a range of 528 to 768 × 106 m3/km2 of natural gas trapped within hydrates, nearly an order of magnitude lower than earlier estimates which did not include effects of small-scale heterogeneities. Further, the petrophysical models are combined with a 3-D finite difference modeling algorithm to study seismic attenuation due to scattering and leaky mode propagation. Simulations of a near-offset vertical seismic profile and cross-borehole numerical surveys demonstrate that attenuation of seismic energy may not be directly related to the intrinsic attenuation of hydrate-bearing sediments but, instead, may be largely attributed to scattering from small-scale heterogeneities and highly attenuate leaky mode propagation of seismic waves through larger-scale heterogeneities in sediments. Copyright 2009 by the American Geophysical Union.
cited By 42
Keywords: borehole; fault propagation; finite difference method; gas hydrate; geoaccumulation; heterogeneity; natural gas; P-wave; reservoir; S-wave; seismic attenuation; seismic velocity; spatial distribution; stochasticity; three-dimensional modeling; Canada; North America

High-resolution sequence stratigraphic characteristic and favorable hydrocarbon accumulation prediction of Sifangtai to Mingshui formation in the north of Songliao Basin - Zhang, Lei; Wang, Ying-Min; Li, Shu-Qing; Han, Jian-Hui; Zhang, Xing-Tao; Zhu, Yan-He; Wang, Gai-Yun; Yang, Ting (Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology), 2009)
According to seismic, logging, core, outcrop palaeoclimate and palaeontologic data, synthetic seismogram was used to demarcate and analyze the area structure evolution characteristic, and using concept and method of sedimentology and sequence stratigraphy, four types of sequence boundaries were identified, including regional unconformity surface, exposure surface, channel scouring and eroding surface and formation stacking transformation surface, and a new supersequence boundary SB4 was also divided. The results show that Sifangtai to Mingshui formation in the north of Songliao Basin finally can be divided into one supersequence group, two supersequences(SSQ1 and SSQ2), six sequences(SQ1?SQ6) and seventy systems tracts and the high resolution sequence stratigraphic framework is also established. The rule of sediment fill and evolution in the sequence stratigraphic framework in the north of the basin is as follows: In the deposition period of sequence SQ1 to SQ3, the basin mainly develops fluvial and coastal-shallow lake facies where provenance's direction is in the direction of SN along the long axis of the basin, while in the deposition period of sequence SQ4 to SQ6, the basin mainly develops braid river delta and costal-shallow lake facies where provenance is in the direction of EW along the short axis of the basin. The basin's deposit center has also constantly migrated to the northwest from the beginning of the Sifangtai formation. Based on the comprehensive research on the reservoir-cap combination distribution of sequence stratigraphy framework and the conditions of the migration, accumulation of oil and gas show that sequence SQ1 of Sifangtai formation develops the most favorable reservoir-cap combination, and the thick bedded channel sand of the lowstand systems tract of sequence SQ1 in Da'an-Xinzhan area is the most favorable hydrocarbon accumulation area which probably develops structural-lithologic secondary hydrocarbon reservoir.
Keywords: Coastal zones; Hydrocarbons; Sedimentology; Seismology; Braid river; Channel sands; Comprehensive research; Favorable hydrocarbon accumulation; High resolution; High resolution sequence stratigraphy; Hydrocarbon accumulation; Hydrocarbon reservoir; Long axis; Oil and gas; Palaeoclimate; Sequence boundary; Sequence stratigraphic framework; Sequence stratigraphy; Shallow lakes; Songliao basin; Structure evolution; Supersequence; Synthetic seismogram; Systems tracts; Stratigraphy

Hydrothermal processes and mineral systems - Pirajno, F. (Hydrothermal Processes and Mineral Systems, 2009)
Hydrothermal processes on Earth have played an important role in the evolution of our planet. These processes link the lithosphere, hydrosphere and biosphere in continuously evolving dynamic systems. Terrestrial hydrothermal processes have been active since water condensed to form the hydrosphere, most probably from about 4.4 Ga. The circulation of hot aqueous solution (hydrothermal systems) at, and below, the Earth's surface is ultimately driven by magmatic heat. This book presents an in-depth review of hydrothermal proceses and systems that form beneath the oceans and in intracontinental rifts, continental margins and magmatic arcs. The interaction of hydrothermal fluids with rockwalls, the hydrophere and the biophere, together with changes in their composition through time and space, contribute to the formation of a wide range of mineral deposit types and associated wallrock alteration. On Earth, sites of hydrothermal activity support varied ecosystems based on a range of chemotrophic microorganisms both at surface and in the subsurface. This book also provides an overview of hydrothermal systems associated with meteorite impacts and explores the possibility that hydrothermal processes operate on other terrestrial planets, such as Mars, or satellites of the outer planets such as Titan and Europa. Possible analogues of extraterrestrial putative hydrothermal processes pose the intriguing question of whether primitive life, as we know it, may exist or existed in these planetary bodies. © Springer Science+Business Media B.V. 2009, 2010.
cited By 775

Silicate glasses and sulfide melts in the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure, Virginia, USA - Belkin, H.E.; Horton Jr., J.W. (Special Paper of the Geological Society of America, 2009)
Optical and electron-beam petrography of melt-rich suevite and melt-rock clasts from selected samples from the Eyreville B core, Chesapeake Bay impact structure, reveal a variety of silicate glasses and coexisting sulfur-rich melts, now quenched to various sulfi de minerals (±iron). The glasses show a wide variety of textures, fl ow banding, compositions, devitrifi cation, and hydration states. Electron-microprobe analyses yield a compositional range of glasses from high SiO 2 ( >90 wt%) through a range of lower SiO 2 (55-75 wt%) with no relationship to depth of sample. Some samples show spherical globules of different composition with sharp menisci, suggesting immiscibility at the time of quenching. Isotropic globules of higher interfacial tension glass (64 wt% SiO 2 ) are in sharp contact with lower-surface-tension, high-silica glass (95 wt% SiO 2 ). Immiscible glass-pair composition relationships show that the immiscibility is not stable and probably represents incomplete mixing. Devitrifi cation varies and some low-silica, high-iron glasses appear to have formed Fe-rich smectite; other glass compositions have formed rapid quench textures of corundum, orthopyroxene, clinopyroxene, magnetite, K-feldspar, plagioclase, chrome-spinel, and hercynite. Hydration (H 2 O by difference) varies from 10 wt% to essentially anhydrous; high-SiO 2 glasses tend to contain less H2O. Petrographic relationships show decomposition of pyrite and melting of pyrrhotite through the transformation series; pyrite? pyrrhotite? troilite→ iron. Spheres ( 1 to 50 μm) of quenched immiscible sulfi de melt in silicate glass show a range of compositions and include phases such as pentlandite, chalcopyrite, Ni-As, monosulfi de solid solution, troilite, and rare Ni-Fe. Other sulfi de spheres contain small blebs of pure iron and exhibit a continuum with increasing iron content to spheres that consist of pure iron with small, remnant blebs of Fe-sulfi de. The Ni-rich sulfi de phases can be explained by melting and/or concentrating targetderived Ni without requiring an asteroid impactor source component. The presence of locally unaltered glasses in these rocks suggests that in some rock volumes, isolation from postimpact hydrothermal systems was suffi cient for glass preservation. Pressure and temperature indicators suggest that, on a thin-section scale, the suevites record rapid mixing and accumulation of particles that sustained widely different peak temperatures, from clasts that never exceeded 300 ± 50 °C, to the bulk of the glasses where melted sulfi de and unmelted monazite suggest temperatures of 1500 ± 200 °C. The presence of coesite in some glass-bearing samples suggests that pressures exceeded 3 GPa. © 2009 Geological Society of America.
cited By 14
Keywords: Copper compounds; Corundum; Electron probe microanalysis; Feldspar; Hydration; Iron; Magnetite; Melting; Mixing; Phosphate minerals; Positive ions; Pyrites; Silica; Silicates; Spheres; Structure (composition); Sulfur compounds; Textures; Chesapeake bay impact structures; Compositional range; Glass compositions; High silica glass; Hydrothermal system; Peak temperatures; Pressure and temperature; Spherical globules; Glass; chemical composition; crater; impact structure; marine sediment; silicate; suevite; sulfide; Chesapeake Bay; United States

High-resolution seismic-reflection images across the ICDP-USGS Eyreville deep drilling site, Chesapeake Bay impact structure - Powars, D.S.; Catchings, R.D.; Goldman, M.R.; Gohn, G.S.; Horton Jr., J.W.; Edwards, L.E.; Rymer, M.J.; Gandhok, G. (Special Paper of the Geological Society of America, 2009)
The U.S. Geological Survey (USGS) acquired two 1.4-km-long, high-resolution (̃5 m vertical resolution) seismic-reflection lines in 2006 that cross near the International Continental Scientifi c Drilling Program (ICDP)-USGS Eyreville deep drilling site located above the late Eocene Chesapeake Bay impact structure in Virginia, USA. Five-meter spacing of seismic sources and geophones produced high-resolution images of the subsurface adjacent to the 1766-m-depth Eyreville core holes. Analysis of these lines, in the context of the core hole stratigraphy, shows that moderateamplitude, discontinuous, dipping reflections below ̃527 m correlate with a variety of Chesapeake Bay impact structure sediment and rock breccias recovered in the cores. High-amplitude, continuous, subhorizontal reflections above ̃527 m depth correlate with the uppermost part of the Chesapeake Bay impact structure crater-fi ll sediments and postimpact Eocene to Pleistocene sediments. Refl ections with ̃20-30 m of relief in the uppermost part of the crater-fi ll and lowermost part of the postimpact section suggest differential compaction of the crater-fi ll materials during early postimpact time. The top of the crater-fi ll section also shows ̃20 m of relief that appears to represent an original synimpact surface. Truncation surfaces, locally dipping reflections, and depth variations in reflection amplitudes generally correlate with the lithostratigraphic and sequence-stratigraphic units and contacts in the core. Seismic images show apparent postimpact paleochannels that include the fi rst possible Miocene paleochannels in the Mid-Atlantic Coastal Plain. Broad downwarping in the postimpact section unrelated to structures in the crater fi ll indicates postimpact sediment compaction. © 2009 The Geological Society of America.
cited By 18
Keywords: C (programming language); Compaction; Infill drilling; Seismic waves; Seismology; Stratigraphy; Chesapeake bay impact structures; Differential compaction; High resolution image; High resolution seismic; Pleistocene sediments; Reflection amplitude; Seismic reflections; U.s. geological surveys; Sediments; deep drilling; impact structure; lithostratigraphy; seismic reflection; seismic tomography; sequence stratigraphy; Chesapeake Bay; United States