All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1044.
Sediment and particulate organic carbon fluxes in various lacustrine basins of tropical Africa and in the Gulf of Guinea
Global and Planetary Change,
72
(4)
341 – 355
2010
ISSN: 09218181Keywords:▾
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
Abstract: ▾ 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.
1043.
Scientific drilling into the san andreas fault zone
Eos,
91
(22)
197-199
2010
ISSN: 00963941Keywords:▾
earthquake damage; fault zone; hazard assessment; tsunami, California; Chile; China; Haiti; Mexico [North America]; San Andreas; Turkey; United States
Abstract: ▾ 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.
1042.
Siderophile elements from the Eyreville drill cores of the Chesapeake Bay impact structure do not constrain the nature of the projectile
Special Paper of the Geological Society of America,
465395-409
2010
ISSN: 00721077
Publisher: Geological Society of America
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
Abstract: ▾ 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.
1041.
Plio-Pleistocene transition in the continental record from Lake Baikal: Diatom biostratigraphy and age model
Quaternary International,
219
(1-2)
26 – 36
2010
ISSN: 10406182Keywords:▾
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
Abstract: ▾ 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.
1040.
Resource potential of gas hydrates: Recent contributions from international research and development projects
Petroleum Geology Conference Proceedings,
71151-1154
2010
ISSN: 20479921DOI:10.1144/0071151
Abstract: ▾ 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.
1039.
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,
492
(1-4)
299-301
2010
ISSN: 004019511038.
Quantification of Microbial Communities in Forearc Sediment Basins off Sumatra
Geomicrobiology Journal,
27
(2)
170 – 182
2010
ISSN: 15210529Keywords:▾
Greater Sunda Islands; Indian Ocean; Sumatra; Sunda Isles; Archaea; Bacteria (microorganisms); Eukaryota; Geobacteraceae; Prokaryota; bacterium; marine sediment; methanogenesis; microbial community; polymerase chain reaction; prokaryote; quantitative analysis; seafloor
Abstract: ▾ Sediments in the Indian Ocean off the coast of the Indonesian island Sumatra were sampled at 25 stations in high resolution near the sediment surface and at three stations up to a maximum depth of 12 meter below seafloor (mbsf) for a quantitative microbial community analysis. Total cell counts were determined applying two different protocols including SYBR Green II as fluorescent staining dye. Total cell counts without detaching cells from sediment particles were 109 cells/ mL sediments at the sediment surface with little variation between all stations. They decreased to 108 cells/ mL at 0.2 to 0.4 mbsf and to 107 cells/ mL below 6 mbsf. The total cell counts after detaching cells from sediment particles were up to one order of magnitude lower above 6 mbsf and showed similar values below. This difference for the two protocols can be explained by a loss of cells during the detachment procedure and/or counting of unspecific signals without detaching cells from sediment particles. Particular phylogenetic and physiological prokaryotic groups were quantified by quantitative, real-time PCR (Q-PCR) targeting 16S rRNA and functional genes. Archaea and Bacteria were found overall in similar 16S rRNA gene copy numbers in the range of the total cell counts at all sediment depths, thus, neither Archaea nor Bacteria could be considered as dominant. The eukaryotic 18S rRNA gene occurred in two orders of magnitude lower numbers than prokaryotic 16S rRNA genes. Fe(III)- and Mn(IV)-reducing bacteria (16S rRNA gene of Geobacteraceae) and sulfate-reducing bacteria (functional gene dsrA) were detected in variable (up to 108 gene copies/ mL sediment) but in always significantly lower numbers than total Bacteria. The proportion of sulfate reducers on the prokaryotic community was between 0.2 and 19%. Calculated aereal sulfate reduction rates were overall low with values between 0.002 and 0.027 mmol m-2a-1, resulting in sulfate reduction rates per cell of 0.0007 and 0.81 fmol cell-1 a-1, similar to published data for other deeply buried marine sediments. Methanogenesis did not seem to play a big role since methane was detected only below 6.5 mbsf, and the functional gene of methanogens and anaerobic methanotrophs mcrA could not be detected in any sample.
1037.
Productivity of Paleo-Songliao lake during the late Cretaceous in well Songke-1, Songliao Basin
Journal of Jilin University (Earth Science Edition),
40
(5)
1020-1026
2010
1036.
Preferred orientation of phyllosilicates: Comparison of fault gouge, shale and schist
Journal of Structural Geology,
32
(4)
478-489
2010
ISSN: 01918141Keywords:▾
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
Abstract: ▾ 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.
1035.
Postglacial Faults in Fennoscandia: Targets for scientific drilling
GFF,
132
(1)
71-81
2010
1034.
Post-Columbian environmental history of Lago Petén Itzá, Guatemala; [Historia ambiental postcolombina del Lago Petén Itzá, Guatemala]
Revista Mexicana de Ciencias Geologicas,
27
(3)
490 – 507
2010
ISSN: 10268774Abstract: ▾ 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 Petén Itzá, in the Department of Petén, 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 Petén Itzá 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 Petén Itzá 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.
1033.
Petrography, mineralogy, and geochemistry of deep gravelly sands in the Eyreville B core, Chesapeake Bay impact structure
Meteoritics and Planetary Science,
45
(6)
1021-1052
2010
Abstract: ▾ 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.
1032.
Petrography, mineralogy, and geochemistry of deep gravelly sands in the Eyreville B core, Chesapeake Bay impact structure
Meteoritics and Planetary Science,
45
(6)
1021-1052
2010
ISSN: 10869379Abstract: ▾ 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.
1031.
Past atmospheric Pb deposition in Lake Qinghai, northeastern Tibetan Plateau
Journal of Paleolimnology,
43
(3)
551 – 563
2010
ISSN: 09212728Keywords:▾
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
Abstract: ▾ 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.
1030.
Passive seismic monitoring of natural and induced earthquakes: case studies, future directions and socio-economic relevance
New frontiers in integrated solid earth sciences
261--285
2010
1029.
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
Chemical Geology,
276
(1-2)
69 – 87
2010
ISSN: 00092541Keywords:▾
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
Abstract: ▾ 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.
1028.
Sources and flux of trace elements in river water collected from the Lake Qinghai catchment, NE Tibetan Plateau
Applied Geochemistry,
25
(10)
1536 – 1546
2010
ISSN: 08832927Keywords:▾
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
Abstract: ▾ 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.
1027.
Observations of rayleigh-wave phase velocity and coseismic deformation using an optical fiber, interferometric vertical strainmeter at the SAFOD borehole, California
Bulletin of the Seismological Society of America,
100
(5 A)
1879-1891
2010
ISSN: 00371106Keywords:▾
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
Abstract: ▾ 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.
1026.
Slip-rate variability and distributed deformation in the Marmara Sea fault system
Nature Geoscience,
3
(2)
132-135
2010
ISSN: 17520894DOI:10.1038/ngeo739
Keywords:▾
accumulation rate; analytical method; earthquake; fault displacement; satellite imagery; slip rate; three-dimensional modeling, Sea of Marmara; Turkey
Abstract: ▾ 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.
1025.
The precise naming and mineralogical characteristics of ferruginous lacustrine dolomite in Well CCSD-SK
Acta Petrologica Et Mineralogica,
29
(2)
213-218
2010
1024.
Southern hemispheric westerlies control the spatial distribution of modern sediments in Laguna Potrok Aike, Argentina
Journal of Paleolimnology,
44
(4)
887 – 902
2010
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
Abstract: ▾ 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.
1023.
The last glacial-interglacial cycle in Lake Ohrid (Macedonia/Albania): Testing diatom response to climate
Biogeosciences,
7
(10)
3083 – 3094
2010
ISSN: 17264189Keywords:▾
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
Abstract: ▾ 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).
1022.
Nanocoatings of clay and creep of the San Andreas fault at Parkfield, California
Geology,
38
(7)
667-670
2010
ISSN: 00917613DOI:10.1130/G31091.1
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
Abstract: ▾ 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.
1021.
[English]
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
Page 69-76
2010
Department of Geophysics, Stanford University, Stanford, CA, United States; Conoco-Phillips, Houston, TX, United States; Shell International Exploration and Production, Houston, TX, United StatesISBN:
9780415601658
1020.
[English]
Towards seismic detection and characterization of gas hydrate accumulations in permafrost environment: An example from the Mallik gas hydrate field, NWT, Canada
Volume 2
,
Page 1491-1499
Publisher
Society of Petroleum Engineers
2010
Geological Survey of Canada, Canada; University of Toronto, CanadaKeywords:▾
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
ISBN:
9781617820427