Continental Cretaceous scientific drilling Songke-1 well (North well) drilling engineering technical support (in Chinese); 中国陆相白垩纪科学钻探松科一井(北井)钻探工程技术配套 - Zhu, Y.; Wang, W. (Exploration Engineering (Rock &, Soil Drilling and Tunneling), 2009)

Comparison of clast frequency and size in the resurge deposits at the Chesapeake Bay impact structure (Eyreville A and Langley cores): Clues to the resurge process - Orm{o, J.; Sturkell, E.; Horton Jr., J.W.; Powars, D.S.; Edwards, L.E. (Special Paper of the Geological Society of America, 2009)
Collapse and inward slumping of unconsolidated sedimentary strata expanded the Chesapeake Bay impact structure far beyond its central basement crater. During crater collapse, sediment-loaded water surged back to fill the crater. Here, we analyze clast frequency and granulometry of these resurge deposits in one core hole from the outermost part of the collapsed zone (i.e., Langley) as well as a core hole from the moat of the basement crater (i.e., Eyreville A). Comparisons of clast provenance and flow dynamics show that at both locations, there is a clear change in clast frequency and size between a lower unit, which we interpret to be dominated by slumped material, and an upper, water-transported unit, i.e., resurge deposit. The contribution of material to the resurge deposit was primarily controlled by stripping and erosion. This includes entrainment of fallback ejecta and sediments eroded from the surrounding seafloor, found to be dominant at Langley, and slumped material that covered the annular trough and basement crater, found to be dominant at Eyreville. Eyreville shows a higher content of crystalline clasts than Langley. There is equivocal evidence for an anti-resurge from a collapsing central water plume or, alternatively, a second resurge pulse, as well as a transition into oscillating resurge. The resurge material shows more of a debris-flow-like transport compared to resurge deposits at some other marine target craters, where the ratio of sediment to water has been relatively low. This result is likely a consequence of the combination of easily disaggregated host sediments and a relatively shallow target water depth. © 2009 The Geological Society of America.
cited By 25
Keywords: Buildings; Sediments; Chesapeake bay impact structures; Debris flows; Flow dynamics; Granulometries; Sea floor; Sedimentary strata; Shallow targets; Water depth; Deposits; clast; comparative study; crater; debris flow; entrainment; frequency-magnitude distribution; granulometry; provenance; sediment transport; sedimentary structure; unconsolidated medium; Chesapeake Bay; United States

Complex drilling logistics for Lake El'gygytgyn, NE Russia - Brigham-Grette, J.; Melles, M. (Scientific Drilling, 2009)
cited By 3

Constraints on mineralization, fluid-rock interaction, and mass transfer during faulting at 2-3 km depth from the SAFOD drill hole - Schleicher, A.M.; Tourscher, S.N.; Warr, L.N. (Journal of Geophysical Research: Solid Earth, 2009)
Mineralogical and geochemical changes in mudrock cuttings from two segments of the San Andreas Fault Observatory at Depth (SAFOD) drill hole (3066-3169 and 3292-3368 m measured depth) are analyzed in this study. Bulk rock samples and hand-picked fault-related grains characterized by polished surfaces and slickensides were investigated by X-ray diffraction, electron microscopy and geochemical analysis. The elemental changes in fault-related grains along the sampled San Andreas Fault are attributed to dissolution of detrital grains (particularly feldspar and quartz) and local precipitation of illite-smectite and/or chlorite-smectite mixed layers in fractures and veins. Assuming ZrO 2 and TiO2 to be immobile elements, systematic differences in element concentrations show that most of the elements are depleted in the fault-related grains compared to the wall rock lithology. Calculated mass loss between the bulk rock and picked fault rock ranges from 17 to 58% with a greater mass transport in the shallow trace of the sampled fault that marks the upper limit the fault core. The relatively large amount of element transport at temperatures of ∼110-114°C recorded throughout the core requires extensive fluid circulation during faulting. Whereas dissolution/precipitation may be partly induced by the disequilibrium between fluids and rocks during diagenetic processes, stress-induced dissolution at grain contacts is proposed as the main mechanism for extensive mineral transformation in the fault rocks and localization of neomineralization along grain interface slip surfaces. Copyright 2009 by the American Geophysical Union.
cited By 37
Keywords: diagenesis; disequilibrium; dissolution; electron microscopy; faulting; fluid-structure interaction; geochemistry; lithology; mass transfer; mineralization; mudstone; observatory; precipitation (chemistry); titanium; X-ray diffraction; zircon; California; North America; San Andreas; United States

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 - Tembe, S.; Lockner, D.; Wong, T.-F. (Journal of Geophysical Research: Solid Earth, 2009)
Analysis of field data has led different investigators to conclude that the San Andreas Fault (SAF) has either anomalously low frictional sliding strength (μ < 0.2) or strength consistent with standard laboratory tests (μ > 0.6). Arguments for the apparent weakness of the SAF generally hinge on conceptual models involving intrinsically weak gouge or elevated pore pressure within the fault zone. Some models assert that weak gouge and/or high pore pressure exist under static conditions while others consider strength loss or fluid pressure increase due to rapid coseismic fault slip. The present paper is composed of three parts. First, we develop generalized equations, based on and consistent with the Rice (1992) fault zone model to relate stress orientation and magnitude to depth-dependent coefficient of friction and pore pressure. Second, we present temperature-and pressure-dependent friction measurements from wet illite-rich fault gouge extracted from San Andreas Fault Observatory at Depth (SAFOD) phase 1 core samples and from weak minerals associated with the San Andreas Fault. Third, we reevaluate the state of stress on the San Andreas Fault in light of new constraints imposed by SAFOD borehole data. Pure talc (μ≈0.1) had the lowest strength considered and was sufficiently weak to satisfy weak fault heat flow and stress orientation constraints with hydrostatic pore pressure. Other fault gouges showed a systematic increase in strength with increasing temperature and pressure. In this case, heat flow and stress orientation constraints would require elevated pore pressure and, in some cases, fault zone pore pressure in excess of vertical stress. Copyright 2009 by the American Geophysical Union.
cited By 44
Keywords: drilling; fault gouge; fault zone; friction; pore pressure; San Andreas Fault; stress field; Calluna vulgaris

Constraints on water chemistry by chemical weathering in the Lake Qinghai catchment, northeastern Tibetan Plateau (China): Clues from Sr and its isotopic geochemistry - Jin, Zhangdong; Yu, Jimin; Wang, Sumin; Zhang, Fei; Shi, Yuewei; You, Chen-Feng (Hydrogeology Journal, 2009)
Lake water, river water, and groundwater from the Lake Qinghai catchment in the northeastern Tibetan Plateau, China have been analyzed and the results demonstrate that the chemical components and 87Sr/86Sr ratios of the waters are strictly constrained by the age and rock types of the tributaries, especially for groundwater. Dissolved ions in the Lake Qinghai catchment are derived from carbonate weathering and part from silicate sources. The chemistry of Buha River water, the largest tributary within the catchment, underlain by the late Paleozoic marine limestone and sandstones, constrains carbonate-dominated compositions of the lake water, being buffered by the waters from the other tributaries and probably by groundwater. The variation of 87Sr/86Sr ratios with cation concentrations places constraint on the Sr-isotopic compositions of the main subcatchments surrounding Lake Qinghai. The relative significance of river-water sources from different tributaries (possibly groundwater as well) in controlling the Sr distribution in Lake Qinghai provides the potential to link the influence of hydrological processes to past biological and physical parameters in the lake. The potential role of groundwater input in the water budget and chemistry of the lake emphasizes the need to further understand hydrogeological processes within the Lake Qinghai system. © 2009 Springer-Verlag.
Keywords: Asia; Buha River; China; Eurasia; Far East; Qinghai; Qinghai-Xizang Plateau; catchment; chemical weathering; geochemistry; groundwater flow; hydrochemistry; hydrogeology; isotopic composition; lake water; limestone; river water; sandstone; strontium isotope; tributary; water budget; water chemistry

Contamination assessment in microbiological sampling of the Eyreville core, Chesapeake Bay impact structure - Gronstal, A.L.; Voytek, M.A.; Kirshtein, J.D.; Heyde, N.M.; Lowit, M.D.; Cockell, C.S. (Special Paper of the Geological Society of America, 2009)
Knowledge of the deep subsurface biosphere is limited due to difficulties in recovering materials. Deep drilling projects provide access to the subsurface; however, contamination introduced during drilling poses a major obstacle in obtaining clean samples. To monitor contamination during the 2005 International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) deep drilling of the Chesapeake Bay impact structure, four methods were utilized. Fluorescent microspheres were used to mimic the ability of contaminant cells to enter samples through fractures in the core material during retrieval. Drilling mud was infused with a chemical tracer (Halon 1211) in order to monitor penetration of mud into cores. Pore water from samples was examined using excitation-emission matrix (EEM) fl uorescence spectroscopy to characterize dissolved organic carbon (DOC) present at various depths. DOC signatures at depth were compared to signatures from drilling mud in order to identify potential contamination. Finally, microbial contaminants present in drilling mud were identified through 16S ribosomal deoxyribonucleic acid (rDNA) clone libraries and compared to species cultured from core samples. Together, these methods allowed us to categorize the recovered core samples according to the likelihood of contamination. Twenty-two of the 47 subcores that were retrieved were free of contamination by all the methods used and were subsequently used for microbiological culture and culture-independent analysis. Our approach provides a comprehensive assessment of both particulate and dissolved contaminants that could be applied to any environment with low biomass. © 2009 The Geological Society of America.
cited By 15
Keywords: Contamination; Coremaking; Infill drilling; Mud logging; Organic carbon; Chesapeake bay impact structures; Comprehensive assessment; Contamination assessment; Continental scientific drillings; Dissolved organic carbon; Excitation emission matrices; Fluorescent micro spheres; Microbiological cultures; Core samples; assessment method; biomass; biosphere; deep drilling; dissolved organic carbon; fluorescence spectroscopy; geological survey; impact structure; microbiology; pollution monitoring; porewater; sediment core; sediment pollution; tracer; Chesapeake Bay; United States

Contemporary Arctic change: A paleoclimate d'ejà vu? - Brigham-Grette, J. (Proceedings of the National Academy of Sciences of the United States of America, 2009)
cited By 9
Keywords: arctic climate; deglaciation; global climate; greenhouse effect; lake ecosystem; note; paleoclimate; priority journal; temperature measurement; Arctic Regions; Fresh Water; Geography; Geologic Sediments; Global Warming; Paleontology; Time Factors

Continuous gas monitoring in the West Bohemian earthquake area, Czech Republic: First results - Faber, Eckhard; Hor'alek, Josef; Bouškov'a, Alena; Teschner, Manfred; Koch, Ulrich; Poggenburg, J{urgen (Studia Geophysica et Geodaetica, 2009)
Two stations monitoring concentrations of carbon dioxide and radon in soil gas (Oldři'ašsk'a and Nov'y Kostel) and one station monitoring flow of carbon dioxide at a mofette (Soos) have been operated in the area of the West Bohemian earthquake swarms. We present preliminary results obtained on the base of four-year observations. We found that data are not influenced considerably by barometric pressure. Although the CO2 concentration varies greatly, the long-term trends at stations Oldŕli'iǎsk'a and Nov'y Kostel are similar, which indicates that the CO2 flow is controlled by common geogenic processes. Also temporal trends of CO2 and Rn concentrations in soil gas at individual stations are analogous. We found diurnal variations of both CO2 concentration in soil gas and the CO2 flow at mofettes due to the earth tides. A response to tides of semi-diurnal period is insignificant in CO2 concentration and only weak in the CO2 flow. We also examined possible pre-seismic, co-seismic and post-seismic effects of the intensive 2008 earthquake swarm on the CO2 concentration at Oldč'išsk'a and Nov'y Kostel, and on the CO2 flow at Soos. However, all potential indications were insignificant and there has not been proven any influence of the swarm on the CO2 concentration as well as on the CO2 flow. Nevertheless, a gradual decrease of amplitudes of diurnal variations before the swarm and the lowest amplitudes during the swarm is a noteworthy phenomenon, which might indicate the strain changes of the rock associated with earthquake swarm. © Institute of Geophysics of the ASCR, v.v.i 2009.
Keywords: Bohemia; Central Europe; Czech Republic; Eurasia; Europe; amplitude; carbon dioxide; concentration (composition); diurnal variation; Earth tide; earthquake swarm; gas flow; radon; soil gas; time series analysis

Broadband records of earthquakes in deep gold mines and a comparison with results from SAFOD, California - McGarr, A.; Boettcher, M.; Fletcher, J.B.; Sell, R.; Johnston, M.J.S.; Durrheim, R.; Spottiswoode, S.; Milev, A. (Bulletin of the Seismological Society of America, 2009)
For one week during September 2007, we deployed a temporary network of field recorders and accelerometers at four sites within two deep, seismically active mines. The ground-motion data, recorded at 200 samples/sec, are well suited to determining source and ground-motion parameters for the mining-induced earthquakes within and adjacent to our network. Four earthquakes with magnitudes close to 2 were recorded with high signal/noise at all four sites. Analysis of seismic moments and peak velocities, in conjunction with the results of laboratory stick-slip friction experiments, were used to estimate source processes that are key to understanding source physics and to assessing underground seismic hazard. The maximum displacements on the rupture surfaces can be estimated from the parameter Rv, where v is the peak ground velocity at a given recording site, and R is the hypocentral distance. For each earthquake, the maximum slip and seismic moment can be combined with results from laboratory friction experiments to estimate the maximum slip rate within the rupture zone. Analysis of the four M 2 earthquakes recorded during our deployment and one of special interest recorded by the in-mine seismic network in 2004 revealed maximum slips ranging from 4 to 27 mm and maximum slip rates from 1.1 to 6:3 m=sec. Applying the same analyses to an M 2.1 earthquake within a cluster of repeating earthquakes near the San Andreas Fault Observatory at Depth site, California, yielded similar results for maximum slip and slip rate, 14 mm and 4:0 m=sec.
cited By 16
Keywords: Broadband records; California; Deep gold mines; Ground motion parameters; Ground-motion; Hypocentral distance; Maximum displacement; Maximum slip; Peak ground velocity; Peak velocities; Repeating earthquake; Rupture surface; Rupture zone; San Andreas Fault; Seismic hazards; Seismic moment; Seismic networks; Slip rates; Source process; Stick-slip friction; Temporary networks; Experiments; Friction; Gold mines; Mines; Mining; Parameter estimation; Risk assessment; Slip forming; Tectonics; Earthquakes; earthquake catalogue; earthquake hypocenter; earthquake magnitude; gold mine; ground motion; mining-induced seismicity; seismic hazard; seismic moment; slip rate; California; North America; United States

Cooling rates of basaltic hyaloclastites and pillow lava glasses from the HSDP2 drill core - Nichols, A.R.L.; Potuzak, M.; Dingwell, D.B. (Geochimica et Cosmochimica Acta, 2009)
Cooling rates have been determined for basaltic glasses from different depths of the submarine section of the drill core recovered in the 1999 phase of Hawaii Scientific Drilling Project (HSDP2). The glasses include degassed blocky hyaloclastite clasts and undegassed pillow rims. The degassed glassy clasts were generated in subaerial or shallow submarine environments, during explosive interactions between lava and seawater, before eventual deposition under water. The volatile contents of the glassy pillow rims are consistent with eruption and quenching in water several hundred metres deep. The cooling rates have been calculated from the calorimetric properties of the glass across the glass transition. The heat capacity (cp) of each sample was measured during several cycles of heating from room temperature to temperatures above their glass transition using a differential scanning calorimeter (DSC). Their compositions did not change during the thermal treatment, a prerequisite for successful cp measurements, although the glasses with higher H2O contents became more opaque and their mid-IR spectra changed. Each cp-T path exhibits the now classic features of the glass transition; glassy and liquid states separated by a hysteresis marking the transition. After experiencing the same experimental thermal history the glass transition occurs at lower temperatures in glasses with higher H2O contents. Except for one sample, the cp-T path measured on initial heating also releases energy stored during the natural quench, which is not recovered during subsequent experimental cooling. The energy stored in the HSDP2 glasses is much less than that observed in hyperquenched natural and synthetic glasses. Even so, the Tool-Narayanaswamy enthalpy relaxation geospeedometer, usually used to determine the cooling rates in volcanic glasses, is unable to deal with this energy release. For those samples that exhibit this feature an alternative method, developed for hyperquenched glasses, is applied. This uses the energy released to calculate Tf, from which the cooling rate is calculated. The degassed blocky hyaloclastite clasts exhibit cooling rates 0.1-72.2 K s-1, while the undegassed pillow rims span 0.2-46.4 K s-1. The fastest cooling rates are consistent with the cooling of lava bodies in seawater. The wide variation for both types of glass could reflect quenching at different distances from the basalt-seawater interface. However, for the degassed hyaloclastite clasts the range could indicate that the clasts were generated by different processes operating during the explosive interaction between lava and seawater in the littoral zone. In the undegassed pillow lavas, glassy rims may have been reheated, giving rise to more complex, slower, thermal histories, as a result of latent heat released during the crystallisation of pillow interiors, or flow replenishment. Both types of glass may also have experienced reheating from succeeding flows or deposits. Compared to deep-sea limu o Pele hyaloclastite fragments, whose hyperquench rates indicate simultaneous cooling and fragmentation, the shallow blocky hyaloclastite clasts may have formed during post-cooling brittle fragmentation. © 2008 Elsevier Ltd. All rights reserved.
Keywords: basalt; calorimetry; chemical composition; clastic rock; cooling; Deep Sea Drilling Project; deposition; differential thermal analysis; experimental study; fragmentation; hyaloclastite; phase transition; pillow lava; underwater environment; volatile substance

Cretaceous phytoplankton assemblages from songke core-1, North and South (SK-1, N and S) of Songliao Basin, Northeast China - Zhang, Y.; Bao, L. (Acta Geologica Sinica (English Edition), 2009)
Cretaceous phytoplankton from the newly completed core hole (SK-1, N &S) in the central Songliao Basin was studied. The target interval is from the upper Quantou Formation of Upper Cretaceous to Mingshui Formation. Twelve genera of dinoflagellates, six of acritarcha and three of chlorophyta were identified in 588 samples from the 2300-m deep core. Ten phytoplankton assemblages have been classified: Tetranguladinium-Subtilisphaera-Botryococcus, Botryococcus-Pediastrum, Pediastrum, Dinogymniopsis-ChlamydophreUa-Vesperopsis bifurcate, Dinogymniopsis minor-Balmula, Pediastrum-Botryococcus, Schizosporis-Campenia, Kiokansium-Dinogymniopsis-Botryococcus, Dinogymniopsis-Granodiscus-Filisphaeridium and Granodiscus. According to the findings mentioned above, the age of the upper Qantou Formation is Cenomanian, the Qingshankou Formation belongs to upper Cenomanian-Turonian, the Yaojia Formation to Coniancian-Santonian age, the Nenjiang Formation is of Campanian age, and Sifangtai-Mingshui formations are referred to Maastrichtian stage. The ecology of phytoplankton is closely related to water salinity. Each type of phytoplankton is within a certain living water mass whose evolution type reflects salinity change of the Songliao Lake. The assemblages from the SK-1 indicate that water salinity changes with the cycle of freshwater-alight brackish water-brackish water-slight brackish water-freshwater in the lake.
cited By 7
Keywords: Acritarcha; Botryococcus; Chlorophyta; Dinophyceae; Pediastrum; Vesperopsis

Deep drilling in the Chesapeake Bay impact structure - An overview - Gohn, G.S.; Koeberl, C.; Miller, K.G.; Reimold, W.U. (Special Paper of the Geological Society of America, 2009)
The late Eocene Chesapeake Bay impact structure lies buried at moderate depths below Chesapeake Bay and surrounding landmasses in southeastern Virginia, USA. Numerous characteristics made this impact structure an inviting target for scientific drilling, including the location of the impact on the Eocene continental shelf, its threelayer target structure, its large size (̃85 km diameter), its status as the source of the North American tektite strewn field, its temporal association with other late Eocene terrestrial impacts, its documented effects on the regional groundwater system, and its previously unstudied effects on the deep microbial biosphere. The Chesapeake Bay Impact Structure Deep Drilling Project was designed to drill a deep, continuously cored test hole into the central part of the structure. A project workshop, funding proposals, and the acceptance of those proposals occurred during 2003-2005. Initial drilling funds were provided by the International Continental Scientific Drilling Program (ICDP) and the U.S. Geological Survey (USGS). Supplementary funds were provided by the National Aeronautics and Space Administration (NASA) Science Mission Directorate, ICDP, and USGS. Field operations were conducted at Eyreville Farm, Northampton County, Virginia, by Drilling, Observation, and Sampling of the Earth's Continental Crust (DOSECC) and the project staff during September-December 2005, resulting in two continuously cored, deep holes. The USGS and Rutgers University cored a shallow hole to 140 m in April-May 2006 to complete the recovered section from land surface to 1766 m depth. The recovered section consists of 1322 m of crater materials and 444 m of overlying postimpact Eocene to Pleistocene sediments. The crater section consists of, from base to top: basement-derived blocks of crystalline rocks (215 m); a section of suevite, impact melt rock, lithic impact breccia, and cataclasites (154 m); a thin interval of quartz sand and lithic blocks (26 m); a granite megablock (275 m); and sediment blocks and boulders, polymict, sediment-clast-dominated sedimentary breccias, and a thin upper section of stratified sediments (652 m). The cored postimpact sediments provide insight into the effects of a large continental-margin impact on subsequent coastal-plain sedimentation. This volume contains the first results of multidisciplinary studies of the Eyreville cores and related topics. The volume is divided into these sections: geologic column; borehole geophysical studies; regional geophysical studies; crystalline rocks, impactites, and impact models; sedimentary breccias; postimpact sediments; hydrologic and geothermal studies; and microbiologic studies. © 2009 The Geological Society of America.
cited By 16
Keywords: Boreholes; Crystalline materials; Crystalline rocks; Geophysics; Groundwater; Infill drilling; NASA; Sedimentary rocks; Sedimentology; Structural geology; Chesapeake bay impact structures; Continental scientific drillings; Continental shelves; Pleistocene sediments; Regional groundwater; Scientific drilling; Temporal association; U.s. geological surveys; Sediments; continental margin; continental shelf; deep drilling; Eocene; impact structure; Pleistocene; sedimentation; Chesapeake Bay; United States; Virginia

Deep drilling into a mantle plume volcano: The Hawaii scientific drilling project - Stolper, E.W.; DePaolo, D.J.; Thomas, D.M. (Scientific Drilling, 2009)
The Hawaii Scientific Drilling Project drilled and cored two holes in Hilo, Hawaii, the deeper reaching a depth of 3508 mbsl, and it retrieved a total of 4600 meters of rock core (525 meters from the Mauna Loa volcano and the remainder from the Mauna Kea volcano). The Mauna Loa core extends the continuous lava stratigraphy of that volcano back to 100 ka and reveals major changes in lava geochemistry over that time period. The Mauna Kea core spans an age range from about 200 ka to perhaps 700 ka, and when combined with surface outcrops, it provides a 700-kyr record of the lava output from a single volcano. During the time covered by the lavas from the core, the volcano drifted some 60-80 km across the melting region of the Hawaiian mantle plume, and therefore the HSDP rock core provides the first systematic cross-sectional sampling of a deep mantle plume. The geochemical characterization of the core, which involved an international team of forty scientists over a period of fifteen years provides information about mantle plume structure and ultimately about the deepest parts of the Earth's mantle. The study of the lava core (which still continues) has provided unprecedented information about the internal structure of a large oceanic volcano and the time scale over which volcanoes grow. The hole also provides an intriguing glimpse of a complex subsurface hydrological regime that differs greatly from the generalized view of ocean island hydrology. Drilling conditions were favorable in the subaerial parts of the volcanic section, where coring was generally fast and efficient. The submarine part of the lava section, made up primarily of volcanogenic sediments and pillow lavas, proved considerably more difficult to drill. Some of the difficulties and considerable additional expense were due to pressurized aquifers at depth and a few critical mistakes made while setting casing. Even with the more difficult conditions, the project retrieved about 2400 meters of nearly continuous core from the submarine section of Mauna Kea. Overall, the HSDP project was highly successful even though the original target depth was about 20% deeper than the final hole depth. As expected, the project results answer several important questions about oceanic volcanoes, mantle plumes, and ocean island water resources, but they raise many more that might be addressed with further moderate-depth drilling in other Hawaiian volcanoes.
cited By 40
Keywords: Deep drillings; Earth' s mantles; Geochemical characterizations; Hole depths; Hydrological regimes; Internal structures; International teams; Mantle plumes; Mauna Loa; Oceanic volcanoes; Pillow lavas; Rock cores; Scientific drillings; Time periods; Time-scale; Volcanogenic sediments; Aquifers; Hydrogeology; Ocean engineering; Oceanography; Offshore oil wells; Rock drilling; Stratigraphy; Submarines; Thermal plumes; Water; Water resources; Volcanoes

Deep fault drilling project-alpine fault, New Zealand - Townend, J.; Sutherland, R.; Toy, V. (Scientific Drilling, 2009)
cited By 51

Deep root of a continent-continent collision belt: Evidence from the Chinese Continental Scientific Drilling (CCSD) deep borehole in the Sulu ultrahigh-pressure (HP-UHP) metamorphic terrane, China - Xu, Zhiqin; Yang, Wencai; Ji, Shaocheng; Zhang, Zeming; Yang, Jingsui; Wang, Qin; Tang, Zhemin (Tectonophysics, 2009)
The Chinese Continental Scientific Drilling (CCSD) deep borehole, which reached a depth of 5158 m in the Sulu ultrahigh-pressure (UHP) metamorphic terrane, provides a new window into the deep root of a continent-continent collision belt, and the tectonic processes by which supracrustal material is recycled into the mantle by subduction and then uplifted to the surface. Major research themes of the CCSD project were to: (1) determine the three-dimensional composition, structure and geophysical character of the deep root of this orogenic belt; (2) investigate the nature and timing of the UHP metamorphism; (3) investigate the processes of crust-mantle interaction involved in the formation and exhumation of the UHP rocks; (4) study the process of fluid circulation and mineralization during subduction and exhumation; (5) study the rheological properties of the various rocks during subduction and exhumation; (6) develop and refine dynamic models for deep subduction and exhumation of crustal rocks, and (7) establish a long-term, natural laboratory for the study of present-day crustal dynamics (e.g., stress, strain, fluid activity). The CCSD has developed precise oriented profiles of the main borehole in terms of lithology, geochemistry, oxygen isotopes, zircon SHRIMP U-Pb ages, 40Ar-39Ar ages, deformation, rheology, mineralization, physical properties of the rocks, petrophysical logs, seismic reflections and underground fluids. The present paper summarizes the integrated research results of this project, especially the new findings concerning the deep root of a continent-continent collision. © 2009 Elsevier B.V. All rights reserved.
Keywords: Asia; China; Eurasia; Far East; Sulu Belt; Isotopes; Lead; Lithology; Mineralogy; Oxygen; Rheology; Rocks; Silicate minerals; Tectonics; Zircon; Chinese Continental Scientific Drilling (CCSD); Continent collisions; Crustal rocks; Deep boreholes; Deep root of a continent-continent collision belt; Deep roots; Fluid circulation; Integrated research; Natural laboratories; Orogenic belts; Oxygen isotopes; Petrophysical; Rheological property; Scientific drilling; Seismic reflections; Sulu HP-UHP metamorphic terrane; Tectonic process; U-Pb ages; UHP metamorphism; Ultrahigh pressure; Ultrahigh-pressure metamorphic terranes; Chinese Continental Scientific Drilling Project; continental collision; exhumation; mineralization; orogenic belt; subduction; tectonic setting; ultrahigh pressure metamorphism; uplift; Drilling

Description of Cretaceous Sedimentary Sequence of the First Member of the Qingshankou Formation Recovered by CCSD-SK-Is Borehole in Songliao Basin: Lithostratigraphy, Sedimentary Facies, and Cyclic Stratigraphy - Gao, Y.; Wang, P.; Cheng, R.; Wang, G.; Wan, X.; Wu, H.; Wang, S.; LIANG, W. (Dixue Qianyuan/ Earth Science Frontiers, 2009)
The first member of the Qingshankou Formation recovered by CCSD-SK-Is borehole (China Cretaceous Continental Scientific Drilling-SongkeI-the south borehole) is 81.41 m long, and the recovery of cores is 100%. The age of the member is approximately Turonian. The sequence and process of lithology-lithofacies and cyclic stratigraphy were revealed by a detailed core description. 6 rock types (mudstone, dolomite, marl, limestone, ostracode limestone, and volcanic ash) comprise the sedimentary strata. Deposition occurred in a deep lake, including 6 sedimentary microfacies: mudstone, sandy turbidite, dolomite, marl, limestone, and volcanic ash microfacies. The first member of the Qingshankou Formation represents 81 meter-scale cycles (sixth-order cycle), 25 fifth-order cycles, 6 fourth-order cycles, and 2 third-order cycles. The occurrence and detailed description of mudstone, dolomite, and volcanic ash are of significance for the study of anoxic events, the source rock development, and the potential linkage between lake-marine depositional events. © 2009 China University of Geosciences (Beijing) and Peking University.
cited By 25

Clay mineral anomalies in the fault zone of the Chelungpu fault, Taiwan, and their implications - Kuo, L.-W.; Song, S.-R.; Yeh, E.-C.; Chen, H.-F. (Geophysical Research Letters, 2009)
The Taiwan Chelungpu-fault Drilling Project (TCDP) Hole-A recovered continuous core samples across the rupture zone of the 1999 Chi-Chi earthquake (Mw7.6). Studying in-situ chemical properties sequentially from fresh-fault-zone materials of the Chelungpu fault provides insight into possible faulting mechanisms. Distinct anomalies of mineral assemblages at the 1111-m fault zone of TCDP Hole-A are found to be: (1) A decrease in clay content within the primary slip zone (PSZ); and (2) A significant decline of illite, disappearance of chlorite and kaolinite, and spike in smectite within the PSZ. Meanwhile, features relating to melting or amorphous material in the PSZ have been observed by SEM and TEM. The results suggest that the PSZ might have experienced generation of glassy materials such as pseudotachylyte by the expense of clay minerals due to strong shear heating, then prompt alteration of pseudotachylyte into smectite. Characteristics of clay minerals and images obtained from electronic microscopes in the PSZ thus imply that pseudotachylyte possibly developed during the 1999 Chi-Chi earthquake, but quickly altered into smectite. This particular phenomenon may explain why pseudotachylyte is rarely found in exhumed hydrated fault zones. Copyright 2009 by the American Geophysical Union.
cited By 77
Keywords: Amorphous materials; Chemical properties; Clay alteration; Earthquakes; Hydrates; Kaolinite; Silicate minerals; ChiChi earthquake; Clay content; Drilling projects; Electronic microscopes; Fault zone; Glassy materials; In-situ; Mineral assemblage; Pseudotachylytes; Rupture zone; SEM and TEM; Shear heating; Slip zones; Smectites; Minerals; amorphous medium; chemical property; Chi-Chi earthquake 1999; clay mineral; earthquake magnitude; earthquake rupture; fault zone; faulting; pseudotachylite; seismic zone; smectite; Asia; Chelungpu Fault Zone; Eurasia; Far East; Taiwan

Description of Cretaceous Sedimentary Sequence of the Second and Third Member of the Qingshankou Formation Recovered by CCSD-SK-Is Borehole in Songliao Basin: Lithostratigraphy, Sedimentary Facies and Cyclic Stratigraphy - Wang, Pujun; Gao, Youfeng; Cheng, Rihui; Wang, Guodong; WU, Heyong; Wan, Xiaoqiao; Yang, Gansheng; WANG, Zhongxing (Dixue Qianyuan/ Earth Science Frontiers, 2009)
The second and third member of the Qingshankou Formation recovered by CCSD-SK-Is borehole (China Cretaceous Continental Scientific Drilling-SongkeI-the south borehole) is 415.61 m long and 100% of cores recovery. The age of the member corresponds approximately to the Coniacian. The sequence and process of lithology-lithofacies and cyclic stratigraphy were revealed by a detailed core description. 12 rock types and 2 kinds of sedimentary subfacies including semi-deep lake and shallow lake were recognized from the drilling core of the second and third member of the Qingshankou Formation. 10 sedimentary microfacies are present, including dolomite, marl, limestone, oil shale, semi-deep lake turbidite, volcanic ash, seismite, semi-deep lake mudstone, shallow lake mudstone, and shallow lake turbidite microfacies. The second and third member of the Qingshankou Formation represents 422 meter-scale cycles (sixth-order cycle), 130 fifth-order cycles, 21 fourth-order cycles, and one third-order cycles. The special lithologies, such as mudstone, seismite, dolomite, volcanic ash, and so on are important to researches on source rocks and lacustrine event sediments. © 2009 China University of Geosciences (Beijing) and Peking University.

A non-magmatic iron projectile for the Gardnos impact event - Goderis, S.; Kalleson, E.; Tagle, R.; Dypvik, H.; Schmitt, R.-T.; Erzinger, J.; Claeys, P. (Chemical Geology, 2009)
The goal of this study is to identify the type of projectile responsible for the formation of the late Precambrian Gardnos impact structure in Norway. Fifteen impactite samples, predominantly impact breccias and suevites from the central and northeastern part of the structure, were analyzed for platinum group elements (PGE) and Au using nickel-sulfide fire assay combined with inductively coupled plasma mass spectrometry (ICP-MS). Major and trace elements were measured in the same samples using X-ray fluorescence (XRF). In addition, the concentrations of siderophile elements Ni, Cr, and Co were determined by ICP-MS after acid digestion. The samples collected at the contact between suevite and the sedimentary infill yielded the highest PGE concentrations (Ir = 1.926 ng/g, Ru = 3.494 ng/g, Pt = 4.716 ng/g, Rh = 0.766 ng/g, Pd = 2.842 ng/g for GC6). The CI-normalized PGE patterns are characterized by Ru and Rh enrichments suggesting a non-chondritic impactor. Concentration plots of the different PGE display an excellent correlation (R > 0.99), indicative of a single source for the PGE enrichment. The Ni/Cr ratio of the Gardnos impactor (2.56 ± 0.20) agrees with that of chondrites (2 to 7), whereas Ir is depleted relative to Ni in this projectile (Ni/Ir ratio of 92 000 ± 8000 compared to an average Ni/Ir ratio of 23 150 ± 4250 for chondrites). There is no clear indication of selective post-depositional remobilization of the characteristic highly siderophile elements. The Ni/Ir and Cr/Ir data combined with the non-chondritic PGE ratios probably indicate a differentiated projectile. Based on (1) the similarity of the inter-element ratios of the impactor with the iron phase of non-magmatic iron meteorites and (2) the presence of characteristics of both chondrites and iron meteorites (Ni/Cr and Ni/Ir ratios), an IA or IIIC non-magmatic iron meteorite is a very plausible impactor. © 2008 Elsevier B.V. All rights reserved.
cited By 15

High-K alkali basalts of the Western Snake River Plain (Idaho): Abrupt transition from tholeiitic to mildly alkaline plume-derived basalts - Shervais, J.W.; Vetter, S.K. (Journal of Volcanology and Geothermal Research, 2009)
Basaltic volcanism in the western Snake River Plain underwent an abrupt change circa 700 ka to 900 ka, from low-K tholeiitic basalt and ferrobasalt to high-K transitional alkali basalt. The low-K tholeiitic basalts share major element, trace element, and isotopic characteristics with olivine tholeiites of the eastern Snake River Plain, and must have been derived by similar processes from similar sources. In contrast, the younger high-K alkali basalts share major element, trace element, and isotopic characteristics with plume-derived alkali basalts of ocean islands suites like Hawaii. We conclude that this abrupt transition reflects either or both the erosion of pre-existing mantle lithosphere in the wake of the Yellowstone-Snake River plume, or the depletion of this lithosphere in fusible components so that it no longer contributed to the overall mass flux of magma. The abruptness of the transition implies that it may have a catastrophic origin, such as lithospheric delamination caused by a Rayleigh-Taylor instability beneath the Idaho batholith. © 2009 Elsevier B.V. All rights reserved.
cited By 14
Keywords: Abrupt change; Abrupt transition; Alkali basalt; Alkaline plumes; Basaltic volcanism; Hotspots; Idaho Batholith; Isotopic characteristics; Lithospheric; Major elements; Mantle lithosphere; Mass flux; Rayleigh-Taylor instabilities; Snake River; Snake river plains; SRP; Tholeiitic basalts; Yellowstone plume; Yellowstones; Isotopes; Oceanography; Olivine; Rivers; Sedimentary rocks; Silicate minerals; Trace elements; Basalt; alkali basalt; alkaline rock; hot spot; mantle plume; ocean island basalt; tholeiite; trace element; volcanism; Idaho; North America; Snake River Plain; United States

'PALEOVAN', International Continental Scientific Drilling Program (ICDP): site survey results and perspectives - Litt, T.; Krastel, S.; Sturm, M.; Kipfer, R.; Orcen, S.; Heumann, G.; Franz, S.O.; {Ulgen, U.B. (Quaternary Science Reviews, 2009)
Lake Van is the fourth largest terminal lake in the world (volume 607 km3, area 3570 km2, maximum depth 460 m), extending for 130 km WSW-ENE on the Eastern Anatolian High Plateau, Turkey. The sedimentary record of Lake Van, partly laminated, has the potential to obtain a long and continuous continental sequence that covers several glacial-interglacial cycles (ca 500 kyr). Therefore, Lake Van is a key site within the International Continental Scientific Drilling Program (ICDP) for the investigation of the Quaternary climate evolution in the Near East ('PALEOVAN'). As preparation for an ICDP drilling campaign, a site survey was carried out during the past years. We collected 50 seismic profiles with a total length of ∼850 km to identify continuous undisturbed sedimentary sequences for potential ICDP locations. Based on the seismic results, we cored 10 different locations to water depths of up to 420 m. Multidisciplinary scientific work at positions of a proposed ICDP drill site included measurements of magnetic susceptibility, physical properties, stable isotopes, XRF scans, and pollen and spores. This core extends back to the Last Glacial Maximum (LGM), a more extended record than all the other Lake Van cores obtained to date. Both coring and seismic data do not show any indication that the deepest part of the lake (Tatvan Basin, Ahlat Ridge) was dry or almost dry during past times. These results show potential for obtaining a continuous undisturbed, long continental palaeoclimate record. In addition, this paper discusses the potential of 'PALEOVAN' to establish new results on the dynamics of lake level fluctuations, noble gas concentration in pore water of the lake sediment, history of volcanism and volcanic activities based on tephrostratigraphy, and paleoseismic and earthquake activities. © 2009 Elsevier Ltd. All rights reserved.
cited By 165
Keywords: Drill sites; Earthquake activity; Glacial-interglacial cycles; Lake level fluctuations; Lake sediments; Last Glacial Maximum; New results; Noble gas; Palaeoclimate; Pore waters; Quaternary climate; Scientific drilling; Sedimentary records; Sedimentary sequence; Seismic data; Seismic profiles; Site surveys; Stable isotopes; Tephrostratigraphy; Terminal lakes; Total length; Volcanic activities; Water depth; Arctic engineering; Drilling; Engineering geology; Glacial geology; Inert gases; Magnetic susceptibility; Sedimentology; Seismic waves; Seismology; Surveys; Water; Lakes; climate change; concentration (composition); drilling; geological record; glacial-interglacial cycle; Last Glacial Maximum; noble gas; paleoclimate; paleoseismicity; porewater; research program; seismic property; Eurasia; Lake Van; Turkey; Bacteria (microorganisms)

40 Ar /39Ar age and geochemical features of mugearite from the Qingshankou Formation; Significances for basin formation, hydrocarbon generation and petroleum accumulation of the Songliao Basin in Cretaceous - Wang, Pu Jun; Gao, You Feng; Ren, Yan Guang; Liu, Wan Zhu; Zhang, Jian Guang (Acta Petrologica Sinica, 2009)
Interlayers of mugearite are recognized within lacustrine mudstone of the Upper Cretaceous Qingshankou Formation (K2qn) in the Songliao basin (SB) of Northeast China. Precise 40 Ar/39Ar plateau age of 88. 0 ±0. 3 Ma is obtained for the mugearite, interpreted as a Late Cretaceous, Coniacian stage. The volcanic rocks are characterized by glassy matrix and porphyritic texture. Phenocrysts are olivine, augite and plagioclase. The rocks are rich in Na, Al, LREE ( σ LREE/ σHREE = g 0 ∼ 9. 7) and LILE (e. g. U, Th, Pb, Rb, Sr and Ba) , with high Rb/Sr ratios, low Sm/Nd ratios and the δEu value ranges from 0. 95 to 1. 36. The volcanics have also high Mg# values (0. 61 ∼ 0. 64) , high Ox° values (0. 62 ∼ 0. 68) , and low MDI values (3.4 ∼ 5.3). Standard mineral pressure plot coupled with MgO/Al2 03 ratios indicate a depth of ≥ 60km for the magma chamber. Hereby, the magma originates from enriched mantle, turns to be intraplate rift volcanism as a result of maximal transtension cutting through the crust. The volcanic activities have two effects on oil & gas, accelerating hydrocarbon generation owing to the rising regional heat flow, and resulting in biolithite sediments of important source rocks owing to the local reef-building environment. Three factors involved in the volcanism are favorable for petroleum accumulation, including drag structures beneath, topographic highs above and turbidites around the volcanic rocks.
Keywords: Asia; China; Eurasia; Far East; Songliao Basin; Calluna vulgaris; Coniacian; Geochemistry; Hydrocarbons; Lead; Rocks; Rubidium; Silicate minerals; Volcanoes; Building environment; Cretaceous qingshankou formation; Geochemical features; Hydrocarbon generation; Mugearite; Petroleum accumulations; Songliao basin; Volcanic activities; argon isotope; basin evolution; Cretaceous; geochemistry; geochronology; heat flow; hydrocarbon generation; magma chamber; mudstone; petroleum; volcanic rock; volcanism; Volcanic rocks

A 40,000-year record of environmental change from ancient Lake Ohrid (Albania and Macedonia) - Wagner, Bernd; Lotter, Andr'e F.; Nowaczyk, Norbert; Reed, Jane M.; Schwalb, Antje; Sulpizio, Roberto; Valsecchi, Verushka; Wessels, Martin; Zanchetta, Giovanni (Journal of Paleolimnology, 2009)
Lake Ohrid is considered to be of Pliocene origin and is the oldest extant lake in Europe. A 1,075-cm-long sediment core was recovered from the southeastern part of the lake, from a water depth of 105 m. The core was investigated using geophysical, granulometric, biogeochemical, diatom, ostracod, and pollen analyses. Tephrochronology and AMS radiocarbon dating of plant macrofossils reveals that the sediment sequence spans the past ca. 39,500 years and features a hiatus between ca. 14,600 and 9,400 cal. year BP. The Pleistocene sequence indicates relatively stable and cold conditions, with steppe vegetation in the catchment, at least partial winter ice-cover of the lake, and oxygenated bottom waters at the coring site. The Holocene sequence indicates that the catchment vegetation had changed to forest dominated by pine and summer-green oak. Several of the proxies suggest the impact of abrupt climate oscillations such as the 8.2 or 4.0 ka event. The observed changes, however, cannot be related clearly to a change in temperature or humidity. Human impact started about 5,000 cal. year BP and increased significantly during the past 2,400 years. Water column mixing conditions, inflow from subaquatic springs, and human impact are the most important parameters influencing internal lake processes, notably affecting the composition and characteristics of the sediments. © 2008 Springer Science+Business Media B.V.
Keywords: Eurasia; Europe; Lake Ohrid; Southern Europe; Bacillariophyta; Ostracoda; anthropogenic effect; diatom; environmental change; fossil; ostracod; paleolimnology; palynology; Quaternary; radiocarbon dating; sediment core; sedimentary sequence; steppe; tephrochronology

A dual-layer Chicxulub ejecta sequence with shocked carbonates from the Cretaceous-Paleogene (K-Pg) boundary, Demerara Rise, western Atlantic - Schulte, P.; Deutsch, A.; Salge, T.; Berndt, J.; Kontny, A.; MacLeod, K.G.; Neuser, R.D.; Krumm, S. (Geochimica et Cosmochimica Acta, 2009)
An up to ∼2-cm thick Chicxulub ejecta deposit marking the Cretaceous-Paleogene (K-Pg) boundary (the K-T boundary) was recovered in six holes drilled during ODP Leg 207 (Demerara Rise, tropical western Atlantic). Stunning features of this deposit are its uniformity over an area of 30 km2 and the total absence of bioturbation, allowing documentation of the original sedimentary sequence. High-resolution mineralogical, petrological, elemental, isotopic (Sr-Nd), and rock magnetic data reveal a distinct microstratigraphy and a range of ejecta components. The deposit is normally graded and composed predominantly of rounded, 0.1- to max. 1-mm sized spherules. Spherules are altered to dioctahedral aluminous smectite, though occasionally relict Si-Al-rich hydrated glass is also present, suggesting acidic precursor lithologies. Spherule textures vary from hollow to vesicle-rich to massive; some show in situ collapse, others include distinct Fe-Mg-Ca-Ti-rich melt globules and lath-shaped Al-rich quench crystals. Both altered glass spherules and the clay matrix (Site 1259B) display strongly negative εNdT = 65 Ma values (-17) indicating uptake of Nd from contemporaneous ocean water during alteration. Finally, Fe-Mg-rich spherules, shocked quartz and feldspar grains, few lithic clasts, as well as abundant accretionary and porous carbonate clasts are concentrated in the uppermost 0.5-0.7 mm of the deposit. The carbonate clasts display in part very unusual textures, which are interpreted to be of shock-metamorphic origin. The preservation of delicate spherule textures, normal grading with lack of evidence for traction transport, and sub-millimeter scale compositional trends provide evidence for this spherule deposit representing a primary air-fall deposit not affected by significant reworking. The ODP Leg 207 spherule deposit is the first known dual-layer K-Pg boundary in marine settings; it incorporates compositional and stratigraphic aspects of both proximal and distal marine sites. Its stratigraphy strongly resembles the dual-layer K-Pg boundary deposits in the terrestrial Western Interior of North America (although there carbonate phases are not preserved). The occurrence of a dual ejecta layer in these quite different sedimentary environments - separated by several thousands of kilometers - provides additional evidence for an original sedimentary sequence. Therefore, the layered nature of the deposit may document compositional differences between ballistic Chicxulub ejecta forming the majority of the spherule deposit, and material falling out from the vapor (ejecta) plume, which is concentrated in the uppermost part. © 2008 Elsevier Ltd. All rights reserved.
cited By 45

A model for the formation of the Chesapeake Bay impact crater as revealed by drilling and numerical simulation - Kenkmann, T.; Collins, G.S.; Wittmann, A.; W{unnemann, K.; Reimold, W.U.; Melosh, H.J. (Special Paper of the Geological Society of America, 2009)
The combination of petrographic analysis of drill core from the recent International Continental Scientific Drilling Program (ICDP)-U.S Geological Survey (USGS) drilling project and results from numerical simulations provides new constraints for reconstructing the kinematic history and duration of different stages of the Chesapeake Bay impact event. The numerical model, in good qualitative agreement with previous seismic data across the crater, is also roughly consistent with the stratigraphy of the new borehole. From drill core observations and modeling, the following conclusions can be drawn: (1) The lack of a shock metamorphic overprint of cored basement lithologies suggests that the drill core might not have reached the parautochthonous shocked crater floor but merely cored basement blocks that slumped off the rim of the original cavity into the crater during crater modification. (2) The sequence of polymict lithic breccia, suevite, and impact melt rock (1397-1551 m) must have been deposited prior to the arrival of the 950-m-thick resurge and avalanche-delivered beds and blocks within 5-7 min after impact. (3) This short period for transportation and deposition of impactites may suggest that the majority of the impactites of the Eyreville core never left the transient crater and was emplaced by ground surge. This is in accordance with observations of impact breccia fabrics. However, the uppermost part of the suevite section contains a pronounced component of airborne material. (4) Limited amounts of shock-deformed debris and melt fragments also occur throughout the Exmore beds. Shard-enriched intervals in the upper Exmore beds indicate that some material interpreted to be part of the hot ejecta plume was incorporated and dispersed into the upper resurge deposits. This suggests that collapse of the ejecta plume was contemporaneous with the major resurge event(s). Modeling indicates that the resurge flow should have been concluded some 20 min after impact; hence, this also likely marked the end of the major episode of deposition from the ejecta plume. © 2009 The Geological Society of America.
cited By 31

A model for the formation of the Chesapeake Bay impact crater as revealed by drilling and numerical simulation - Kenkmann, T.; Collins, G.S.; Wittmann, A.; W{unnemann, K.; Reimold, W.U.; Melosh, H.J. (Special Paper of the Geological Society of America, 2009)
The combination of petrographic analysis of drill core from the recent International Continental Scientific Drilling Program (ICDP)-U.S Geological Survey (USGS) drilling project and results from numerical simulations provides new constraints for reconstructing the kinematic history and duration of different stages of the Chesapeake Bay impact event. The numerical model, in good qualitative agreement with previous seismic data across the crater, is also roughly consistent with the stratigraphy of the new borehole. From drill core observations and modeling, the following conclusions can be drawn: (1) The lack of a shock metamorphic overprint of cored basement lithologies suggests that the drill core might not have reached the parautochthonous shocked crater floor but merely cored basement blocks that slumped off the rim of the original cavity into the crater during crater modification. (2) The sequence of polymict lithic breccia, suevite, and impact melt rock (1397-1551 m) must have been deposited prior to the arrival of the 950-m-thick resurge and avalanche-delivered beds and blocks within 5-7 min after impact. (3) This short period for transportation and deposition of impactites may suggest that the majority of the impactites of the Eyreville core never left the transient crater and was emplaced by ground surge. This is in accordance with observations of impact breccia fabrics. However, the uppermost part of the suevite section contains a pronounced component of airborne material. (4) Limited amounts of shock-deformed debris and melt fragments also occur throughout the Exmore beds. Shard-enriched intervals in the upper Exmore beds indicate that some material interpreted to be part of the hot ejecta plume was incorporated and dispersed into the upper resurge deposits. This suggests that collapse of the ejecta plume was contemporaneous with the major resurge event(s). Modeling indicates that the resurge flow should have been concluded some 20 min after impact; hence, this also likely marked the end of the major episode of deposition from the ejecta plume. © 2009 The Geological Society of America.
cited By 31
Keywords: Boreholes; Buildings; Deposition; Drills; Infill drilling; Numerical models; Rocks; Seismology; Stratigraphy; Structural geology; Chesapeake Bay; Continental scientific drillings; Different stages; Drilling projects; Impact craters; Melt fragments; Petrographic analysis; U.S geological surveys; Core drilling; basement rock; breccia; computer simulation; crater; deposition; ejecta; emplacement; impactite; kinematics; lithology; mantle plume; numerical model; petrography; pyroclastic flow; research program; shock metamorphism; Chesapeake Bay; United States

A petrographic and fluid inclusion assessment of hydrothermal alteration of some impactites and crystalline rocks in the Chesapeake Bay impact structure, ICDP-USGS Eyreville B core - Vanko, D.A. (Special Paper of the Geological Society of America, 2009)
Core samples from the International Continental Scientific Drilling Program (ICDP)-U.S Geological Survey (USGS) Eyreville B core, located in the central crater of the Chesapeake Bay impact structure, were studied to determine the degree to which postimpact hydrothermal activity is recorded in secondary minerals and fluid inclusions. The Chesapeake Bay impact event occurred ̃35 Ma ago on the siliciclastic continental shelf of eastern North America, in up to several hundred meters of water. The combination of hot materials, such as impact melts and suevite breccias, with overlying crater-fill material and seawater is hypothesized to have led to postimpact hydrothermal circulation. Secondary minerals are distinguished from pre-impact minerals by textural features such as the presence or absence of shock metamorphic effects. Minerals in veins and cavities that are shown to have formed after the impact include secondary calcite, chalcedony, phillipsite, clinoptilolite-heulandite, mordenite, and montmorillonite. Some secondary calcite contains liquid-only fluid inclusions with trapping temperatures constrained to be less than or equal to ̃50 °C. Salinities of the inclusion fluids are mostly around 4.3 ± 1 wt% NaCl equivalent, or ̃43 ± 10 g/L total dissolved solids. This salinity is similar to that of the anomalously saline groundwater that currently exists within the crater-fill material, and that could be relict brine that originated just after the impact. © 2009 The Geological Society of America.
cited By 4

Biotic effects of the Chicxulub impact, K-T catastrophe and sea level change in Texas - Keller, G.; Abramovich, S.; Berner, Z.; Adatte, T. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2009)
Biotic effects of the Chicxulub impact, the K-T event and sea level change upon planktic foraminifera were evaluated in a new core and outcrops along the Brazos River, Texas, about 1000 km from the Chicxulub impact crater on Yucatan, Mexico. Sediment deposition occurred in a middle neritic environment that shallowed to inner neritic depths near the end of the Maastrichtian. The sea level fall scoured submarine channels, which were infilled by a sandstone complex with reworked Chicxulub impact spherules and clasts with spherules near the base. The original Chicxulub impact ejecta layer was discovered 45-60 cm below the sandstone complex, and predates the K-T mass extinction by about 300,000 years. Results show that the Chicxulub impact caused no species extinctions or any other significant biotic effects. The subsequent sea level fall to inner neritic depth resulted in the disappearance of all larger ( > 150 μm) deeper dwelling species creating a pseudo-mass extinction and a survivor assemblage of small surface dwellers and low oxygen tolerant taxa. The K-T boundary and mass extinction was identified 40-80 cm above the sandstone complex where all but some heterohelicids, hedbergellids and the disaster opportunistic guembelitrids went extinct, coincident with the evolution of first Danian species and the global δ13C shift. These data reveal that sea level changes profoundly influenced marine assemblages in near shore environments, that the Chicxulub impact and K-T mass extinction are two separate and unrelated events, and that the biotic effects of this impact have been vastly overestimated. © 2008 Elsevier B.V.
cited By 42

A petrographic and fluid inclusion assessment of hydrothermal alteration of some impactites and crystalline rocks in the Chesapeake Bay impact structure, ICDP-USGS Eyreville B core - Vanko, D.A. (Special Paper of the Geological Society of America, 2009)
Core samples from the International Continental Scientific Drilling Program (ICDP)-U.S Geological Survey (USGS) Eyreville B core, located in the central crater of the Chesapeake Bay impact structure, were studied to determine the degree to which postimpact hydrothermal activity is recorded in secondary minerals and fluid inclusions. The Chesapeake Bay impact event occurred ̃35 Ma ago on the siliciclastic continental shelf of eastern North America, in up to several hundred meters of water. The combination of hot materials, such as impact melts and suevite breccias, with overlying crater-fill material and seawater is hypothesized to have led to postimpact hydrothermal circulation. Secondary minerals are distinguished from pre-impact minerals by textural features such as the presence or absence of shock metamorphic effects. Minerals in veins and cavities that are shown to have formed after the impact include secondary calcite, chalcedony, phillipsite, clinoptilolite-heulandite, mordenite, and montmorillonite. Some secondary calcite contains liquid-only fluid inclusions with trapping temperatures constrained to be less than or equal to ̃50 °C. Salinities of the inclusion fluids are mostly around 4.3 ± 1 wt% NaCl equivalent, or ̃43 ± 10 g/L total dissolved solids. This salinity is similar to that of the anomalously saline groundwater that currently exists within the crater-fill material, and that could be relict brine that originated just after the impact. © 2009 The Geological Society of America.
cited By 4
Keywords: Calcite; Clay alteration; Crystalline rocks; Groundwater; Infill drilling; Mineralogy; Sodium chloride; Zeolites; Chesapeake bay impact structures; Continental scientific drillings; Eastern north america; Hydrothermal activity; Hydrothermal alterations; Hydrothermal circulation; Total dissolved solids; U.S geological surveys; Nitrogen compounds; assessment method; breccia; crystalline rock; fluid inclusion; hydrothermal activity; hydrothermal alteration; hydrothermal circulation; hydrothermal deposit; hydrothermal system; impact structure; impactite; petrography; research program; secondary mineral; shock metamorphism; suevite; Chesapeake Bay; United States

Acoustic impedance inversion and seismic reflection continuity analysis for delineating gas hydrate resources near the Mallik research sites, Mackenzie Delta, Northwest Territories, Canada - Riedel, M.; Bellefleur, G.; Mair, S.; Brent, T.A.; Dallimore, S.R. (GEOPHYSICS, 2009)
We combine acoustic impedance inversion of 3D seismic data, log-to-seismic correlation, and seismic attribute analyses to delineate gas-hydrate zones at the Mallik site, Mackenzie Delta, Northwest Territories, Canada. Well-log data define three distinct hydrate zones over a depth range of 890-1100 m. Synthetic seismic modeling indicates the base of the two deeper hydrate zones are prominent reflectors. The uppermost gas-hydrate zone correlates to seismic data with a lower degree of confidence. The extent and geometry of the two lower hydrate zones suggest that local geology plays a significant role in the lateral and vertical distribution of gas hydrate at Mallik. The reliability of the hydrate concentrations calculated from the inverted impedances isqualified by the match between original and synthetic seismic data to produce confidence maps for the two lower gas-hydrate-bearing intervals. A total in-place volume estimate of solid gas hydrate for an area of 1.44 km2 around well 5L-38 yields a value of approximately 45 × 106m3 (equivalently, 6.6 × 109m3 of gas). We further qualify our mapping of gas hydrates by some amount of continuous resource, defined as lateral continuity measured by seismic attribute similarity and sand-dominated rock. Using these attributes, the continuous amount of hydrate at Mallik is about half the in-place volume (i.e., 25 × 106 m3). Elsewhere within the 3D seismic cube, the seismic impedance inversion yields evidence of potential gas-hydrate deposits near wells A-06 and P-59 at levels near the predicted base of the hydrate stability zone. © 2009 Society of Exploration Geophysicists. All rights reserved.
cited By 43
Keywords: Acoustic impedance; Gases; Geophysical prospecting; Hydration; Seismic response; Seismic waves; Well logging; Acoustic impedance inversion; Degree of confidence; Hydrate concentration; Hydrate stabilities; Seismic attribute analysis; Seismic attributes; Seismic reflections; Vertical distributions; Gas hydrates; acoustic data; conference proceeding; confidence interval; gas field; gas hydrate; gas well; hydrocarbon resource; seismic data; seismic reflection; spatial distribution; three-dimensional modeling; well logging; Canada; Mackenzie Delta; North America; Northwest Territories

Active seismic imaging using microseismic events - Reshetnikov, A.; Buske, S.; Shapiro, S. (71st European Association of Geoscientists and Engineers Conference and Exhibition 2009: Balancing Global Resources. Incorporating SPE EUROPEC 2009, 2009)
We have developed a passive seismic imaging approach which consists of two steps. Firstly, the hypocenter of the microseismic event is precisely located. Secondly, this event is treated as a pseudo-active seismic source and we process the reflections within the recorded wavefield using a directional migration algorithm in order to construct a high-resolution image in the close vicinity of the located hypo-center. In this paper we describe this approach and demonstrate the application to several microseismic events recorded by a borehole array in the SAFOD (San-Andreas-Fault-Observatory-at-Depth) main hole. The results are high-resolution images of different fault branches related to the San-Andreas-Fault (SAF) system in the close vicinity of the borehole. The comparison of these findings with existing surface seismic reflection images as well as additional borehole information demonstrate some interesting features. In summary our results allow a spatial characterization of the complex internal structure of the SAF and can certainly be helpful for other studies which rely on this knowledge. Copyright 2009, European Association of Geoscientists and Engineers.
cited By 0
Keywords: Boreholes; Strike-slip faults; Directional migration; High resolution image; Internal structure; Microseismic events; San Andreas fault; Seismic imaging; Seismic reflections; Spatial characterization; Seismology

Analyses of pseudotachylyte from Hole-B of Taiwan Chelungpu Fault Drilling Project (TCDP); their implications for seismic slip behaviors during the 1999 Chi-Chi earthquake - Otsuki, K.; Hirono, T.; Omori, M.; Sakaguchi, M.; Tanigawa, W.; Lin, W.; Soh, W.; Rong, S.-S. (Tectonophysics, 2009)
The seismic slip behavior during the 1999 Chi-Chi, Taiwan, earthquake (Mw 7.6) was contrastive between the northern and southern segments of the activated Chelungpu fault; large, fast and smooth slips with large stress drop in the north, while smaller, slower and irregular slips with smaller stress drop in the south. We analyzed the pseudotachylyte samples recovered from 1194 m, 1243 m and 1314 m depths of Hole-B of Taiwan Chelungpu fault Drilling Project (TCDP) to reveal the spatial difference in friction mechanism. All pseudotachylyte layers are thin (0.7-2.8 cm), the volume fraction of protoliths is very large (more than 63%), and the estimated temperature distribution is very heterogeneous from ca. 750-1750 °C. These observations suggest that these pseudotachylyte melts were in the partial melting regime of Montgomery [Montgomery, R.S., 1976. Friction and wear at high sliding speeds. Wear 36, 275-298] where friction coefficient is abnormally large. Similar pseudotachylyte was found already in the core sample from 175 m depth of the Nanto borehole penetrating the southern fault. Since both pseudotachylyte samples from the two boreholes are older than the 1999 Chi-Chi event and have been uplifted from depths farther down-dip of their current locations, it is likely that recent seismic ruptures also would have encountered these mechanical barriers of viscous melt patches at deeper parts in the north than in the south. Elastohydrodynamic lubrication of clayey gouge worked effectively at the shallower parts of the northern segment, however there is no evidence that it played an important role in the south. These differences are the plausible causes of the contrastive local slip behaviors during the Chi-Chi earthquake. © 2008 Elsevier B.V. All rights reserved.
cited By 21
Keywords: Chelungpu fault; Chi-Chi earthquake; Partial melting; Pseudotachylyte; Seismic slip; Boreholes; Drops; Elastohydrodynamic lubrication; Friction; Melting; Tribology; Earthquakes; active fault; Chi-Chi earthquake 1999; earthquake magnitude; earthquake rupture; fault gouge; fault slip; focal mechanism; partial melting; pseudotachylite; uplift

Analysis of Izmit aftershocks 25 days before the November 12th 1999 D{uzce earthquake, Turkey - G{org{un, E.; Zang, A.; Bohnhoff, M.; Milkereit, C.; Dresen, G. (Tectonophysics, 2009)
We investigate spatial clustering of 2414 aftershocks along the Izmit Mw = 7.4 August 17, 1999 earthquake rupture zone. 25 days prior to the D{uzce earthquake Mw = 7.2 (November 12, 1999), we analyze two spatial clusters, namely Sakarya (SC) and Karadere-D{uzce (KDC). We determine the earthquake frequency-magnitude distribution (b-value) for both clusters. We find two high b-value zones in SC and one high b-value zone in KDC which are in agreement with large coseismic surface displacements along the Izmit rupture. The b-values are significantly lower at the eastern end of the Izmit rupture where the D{uzce mainshock occurred. These low b-values at depth are correlated with low postseismic slip rate and positive Coloumb stress change along KDC. Since low b-values are hypothesized with high stress levels, we propose that at the depth of the D{uzce hypocenter (12.5 km), earthquakes are triggered at higher stresses compared to shallower crustal earthquake. The decrease in b-value from the Karadere segment towards the D{uzce Basin supports this low b-value high stress hypothesis at the eastern end of the Izmit rupture. Consequently, we detect three asperity regions which are correlated with high b-value zones along the Izmit rupture. According to aftershock distribution the half of the D{uzce fault segment was active before the 12 November 1999 D{uzce mainshock. This part is correlated with low b-values which mean high stress concentration in the D{uzce Basin. This high density aftershock activity presumably helped to trigger the D{uzce event (Mw = 7.2) after the Izmit Mw 7.4 mainshock. © 2009 Elsevier B.V. All rights reserved.
cited By 27
Keywords: Aftershock distributions; B value; Crustal earthquakes; Earthquake frequency; Earthquake rupture; Fault asperities; Gutenberg-Richter law; High density; High stress; High stress concentration; Izmit earthquake; Mainshock; North Anatolian Fault Zone; Postseismic slip; Spatial cluster; Spatial clustering; Stress changes; Surface displacement; Earthquake effects; Stress concentration; Laws and legislation; aftershock; coseismic process; displacement; earthquake magnitude; earthquake rupture; earthquake trigger; fault zone; Kocaeli earthquake 1999; low velocity zone; North Anatolian Fault; postseismic process; slip rate; stress change; Duzce; Eurasia; Turkey

Anti-sloughing drilling fluid technology for bare hole in CCSD-SK1 - Yuanliang, LIU; Xiaoming, Wu; Yongyi, ZHU; Xiaofen, LI (石油钻采工艺, 2009)

As time goes by: A simple fool's guide to molecular clock approaches in invertebrates - Wilke, Thomas; Schulthei{s, Roland; Albrecht, Christian (American Malacological Bulletin, 2009)
Biologists have used a wide range of organisms to study the origin of taxa and their subsequent evolutionary change in space and time. One commonly used tool is the molecular clock approach, relating substitution rates of nucleotide or amino acid sequences to divergence times. The accuracy of the molecular clock, however, has long been subject to controversy, and numerous papers have addressed problems associated with estimating divergence times. Some workers pointed out a striking imbalance between sophisticated software algorithms used for molecular clock analyses on the one hand, and the poor data on the other hand. Moreover, there is often unease among workers relative to molecular clocks because of the controversy surrounding the approach, the complex mathematical background of many molecular clock tools, the still limited number of available, user-friendly software packages, the often confusing terminology of molecular clock approaches, and the general lack of reliable calibration points and/or external clock rates. The current review therefore briefly provides an overview of analytical strategies, covering approaches based on calibration points and/or bounds, approaches based on external clock rates, and approaches that attempt to estimate relative divergence times in the absence of information that can be used for estimating substitution rates. It also deals with major problems and pitfalls associated with data and analyses, including potential errors of calibration points and bounds, the performance of the gene(s) used, estimation of confidence limits, and misinterpretation of the results of clock analyses due to problems with sampling design. A substantial part of the review addresses the question of universal molecular clock rates and summarizes important biological and life history variables that account for deviations from rate constancy both between lineages and at different times within lineages. The usefulness of these factors is discussed within the framework of trait-specific molecular clock rates. One such clock rate is introduced here for the cytochrome c oxidase subunit I (COI) gene in small dioecious, tropical and subtropical Protostomia with a generation time of approximately one year. A flow chart is provided as a simple fool's guide to molecular clock analyses, together with a glossary of widely used terms in molecular clock approaches. Finally, step-by-step examples are provided for calculating divergence times in the caenogastropod subfamily Pyrgulinae based on both an internal calibration point and a trait-specific molecular clock rate, and it is demonstrated how a relative clock approach can be used for testing evolutionary hypotheses. Our review encourages a judicious use of molecular clock analyses in evolutionary studies of invertebrates by demonstrating their great potential on the one hand and (often-manageable) problems and pitfalls on the other hand.
Keywords: Caenogastropoda; Invertebrata; Protostomia

Atlantic forcing of persistent drought in West Africa - Shanahan, T.M.; Overpeck, J.T.; Anchukaitis, K.J.; Beck, J.W.; Cole, J.E.; Dettman, D.L.; Peck, J.A.; Scholz, C.A.; King, J.W. (Science, 2009)
Although persistent drought in West Africa is well documented from the instrumental record and has been primarily attributed to changing Atlantic sea surface temperatures, little is known about the length, severity, and origin of drought before the 20th century. We combined geomorphic, isotopic, and geochemical evidence from the sediments of Lake Bosumtwi, Ghana, to reconstruct natural variability in the African monsoon over the past three millennia. We find that intervals of severe drought lasting for periods ranging from decades to centuries are characteristic of the monsoon and are linked to natural variations in Atlantic temperatures. Thus the severe drought of recent decades is not anomalous in the context of the past three millennia, indicating that the monsoon is capable of longer and more severe future droughts.
Keywords: Africa; Ashanti; Atlantic Ocean; Ghana; Lake Bosumtwi; Sub-Saharan Africa; West Africa; rain; atmospheric forcing; drought; monsoon; reconstruction; sea surface temperature; twentieth century; Africa; article; Atlantic Ocean; controlled study; drought; environmental temperature; Ghana; hydrology; lake sediment; precipitation; priority journal; seasonal variation; spectroscopy

Description of Cretaceous Sedimentary Sequence of the Quantou Formation Recovered by CCSD-SK-Is Borehole in Songliao Basin: Lithostratigraphy, Sedimentary Facies and Cyclic Stratigraphy - Wang, Guodong; Cheng, Rihui; Wang, Pujun; Gao, Youfeng; Wang, Chengshan; Ren, Yanguang; Huang, Qinghua (Dixue Qianyuan/ Earth Science Frontiers, 2009)
The Quantou Formation recovered by CCSD-SK-Is borehole (China Cretaceous Continental Scientific Drilling-SongkeI-the south borehole) is 132.07 m long and the recovery of cores is 100%. The sequence and process of lithology-lithofacies and cyclostratigraphy are revealed by a detailed core description. Nine rock types and three kinds of sedimentary facies including meandering river, shallow lake, and delta front are recognized from the drilling core, there are ten sedimentary microfacies, which are point bar, natural levee, crevasse splay, crevasse channel, floodplain, flood lake, distributary mouth bar, interdistributary bay, mudstone of still water, and turbidite. The Quantou Formation represents seventy-six meter-scale cycles (sixth-order cycle), twenty-five fifth-order cycles, eight fourth-order cycles, and two third-order cycles. Meticulously depicted (centimeter level) continental red beds of the third and the fourth members of Quantou Formation will be a potential formulation profile for the studies of Cretaceous global oxygen-enriched events. The reservoir sandstones of the third and the fourth members were developed basin-wide as an inevitable product before the Songliao Basin was depressed or sagged on a large scale. The period of the third and the fourth members of Quantou Formation is a stage between the development of the fault basin and the sag basin on a large scale. © 2009 China University of Geosciences (Beijing) and Peking University.

Arkosic rocks from the san andreas fault observatory at depth (SAFOD) borehole, central california: Implications for the structure and tectonics of the San Andrea fault zone - Springer, S.D.; Evans, J.P.; Garver, J.I.; Kirschner, D.; Janecke, S.U. (Lithosphere, 2009)
The San Andreas Fault Observatory at Depth (SAFOD) drill hole encountered indurated, high-seismic-velocity arkosic sedimentary rocks west of the active trace of the San Andreas fault in central California. The arkosic rocks are juxtaposed against granitic rocks of the Salinian block to the southwest and against fine-grained Great Valley Group and Jurassic Franciscan rocks to the northeast. We identify three distinct lithologic units using cuttings, core petrography, electrical resistivity image logs, zircon fission-track analyses, and borehole-based geophysical logs. The upper arkose occurs from 1920 to 2530 m measured depth (mmd) in the borehole and is composed of five structural blocks defined by bedding orientations, wireline log character, physical properties, and lithologic characteristics. A clay-rich zone between 2530 and 2680 mmd is characterized by low V p and an enlarged borehole. The lower arkose lies between 2680 and 3150 mmd. Fission-track detrital zircon cooling ages are between 64 and 70 Ma, appear to belong to a single population, and indicate a latest Cretaceous to Paleogene maximum depositional age. We interpret these Paleocene-Eocene strata to have been deposited in a proximal submarine fan setting shed from a Salinian source block, and they correlate with units to the southeast, along the western and southern edge of the San Joaquin Basin, and with arkosic conglomerates to the northwest. The arkosic section constitutes a deformed fault-bounded block between the modern strand of the San Andreas fault to the northeast and the Buzzard Canyon fault to the southwest. Significant amounts of slip appear to have been accommodated on both strands of the fault at this latitude. © 2009 Geological Society of America.
cited By 18
Keywords: Boreholes; Fission reactions; Observatories; Silicate minerals; Strike-slip faults; Well logging; Zircon; Bedding orientations; Detrital zircon; Geophysical logs; Measured depths; San Andreas fault; Seismic velocities; Submarine fans; Zircon fission tracks; Sedimentary rocks; borehole; electrical resistivity; fission track dating; petrography; San Andreas Fault; sedimentary rock; seismic velocity; California; United States

Description of Cretaceous Sedimentary Sequence of the Yaojia Formation Recovered by CCSD-SK-Is Borehole in Songliao Basin: Lithostratigraphy, Sedimentary Facies and Cyclic Stratigraphy - Cheng, R.; Wang, G.; Wang, P.; Gao, Y.; Ren, Y.; Wang, C.; Zhang, S.; Wang, Q. (Dixue Qianyuan/ Earth Science Frontiers, 2009)
The Yaojia Formation recovered by CCSD-SK-Is borehole (China Cretaceous Continental Scientific Drilling-SongkeI-the south borehole) is 157.67 m long and 99.96% of cores recovery. The age of the formation corresponds with a range from the Santonian to the early Campanian. The sequences and processes of lithology-lithofacies and cyclic stratigraphy are revealed by a detailed core description. Eleven rock types and three kinds of sedimentary subfacies, including shallow lake, deep lake, and delta front, are recognized from the drilling core. There are eleven sedimentary microfacies including dolostone, argillaceous limestone, shallow lake turbidite, deep lake turbidite, subaqueous mouth bar, distal bar, sheet sandstone, subaqueous distributary bay, slump deposits, shallow lake mudstone, and deep lake mudstone. The Yaojia Formation represents one hundred and fifty-one meter-scale cycles (sixth-order cycle), forty-five fifth-order cycles, nine fourth-order cycles, and three third-order cycles. Meticulous depiction (centimeter level) of the whole Formation provides an approach to study its sedimentary process with high precision. The red beds with a thickness of 43% in the Yaojia Formation, being one of fewer continental red beds depicted meticulously in the world, will become a standard of potential formulation section for the studies of Cretaceous global oxygen-enriched events. © 2009 China University of Geosciences (Beijing) and Peking University.
cited By 23

Geochemistry of the impact breccia section (1397-1551 m depth) of the Eyreville drill core, Chesapeake Bay impact structure, USA - Bartosova, K.; Mader, D.; Schmitt, R.T.; Ferrière, L.; Koeberl, C.; Reimold, W.U.; Brandst{atter, F. (Special Paper of the Geological Society of America, 2009)
The Chesapeake Bay impact structure, which is 85 km in diameter and 35.5 Ma old, was drilled and cored in a joint International Continental Scientific Drilling Program (ICDP) and U.S. Geological Survey (USGS) drilling project at Eyreville Farm, Virginia, U.S.A. In the Eyreville drill core, 154 m of impact breccia were recovered from the depth interval 1397-1551 m. Major- and trace-element concentrations were determined in 75 polymict impactite samples, 10 samples of cataclastic gneiss blocks, and 24 clasts from impactites. The chemical composition of the polymict impactites does not vary much in the upper part of the section (above ̃1450 m), whereas in the lower part, larger differences occur. Polymict impactites show a decrease of SiO 2 content, and slight increases of TiO 2 , Al 2 O 3 , and Fe 2 O 3 abundances, with depth. This is in agreement with an increase of the schist/gneiss component with depth. Concentrations of siderophile elements (Co, Ni) are lower in the polymict impactites than in the basement-derived schists and do not indicate the presence of an extraterrestrial component. The fi ve petrographically determined types of melt particles, i.e., clear glass, altered melt, recrystallized silica melt, melt with microlites, and dark-brown melt, have distinct chemical compositions. Mixing calculations of the proportions of rocks involved in the formation of various polymict impactites and melt particles were carried out using the Harmonic least-squares MiXing (HMX) calculation program. The calculations suggest that the metamorphic basement rocks (i.e., gneiss and schist) constitute the main component of the polymict impactites, together with significant sedimentary and possible minor pegmatite/granite and amphibolite components. The sedimentary component is derived mostly from a sediment characterized by a composition similar to that of the Cretaceous Potomac Formation. Compositions of the melt particles were modeled as mixtures of target rocks or major rock-forming minerals. However, the results of the mixing calculations for the melt particles are not satisfactory, and the composition of the particles could have been modified by hydrothermal alteration. Carbon isotope ratios were determined for 18 samples. The results imply a hydrothermal origin for the carbonate veins from the basement-derived core section; carbon-rich sedimentary clasts from the Exmore breccia and suevite have a δ 13 C range typical for organic matter in sediments. © 2009 The Geological Society of America.
cited By 13

Frictional behavior of materials in the 3D SAFOD volume - Carpenter, B.M.; Marone, C.; Saffer, D.M. (Geophysical Research Letters, 2009)
We report on frictional properties of rocks within the 3-D crustal volume surrounding the San Andreas Fault Observatory at Depth (SAFOD). Samples include lithologies adjacent to the San Andreas Fault (SAF) in the subsurface, SAFOD borehole rocks, and synthetic fault gouge composed of talc, serpentinite, and quartz. Granodiorite, arkosic sandstone, and siltstone samples from the SAFOD borehole are frictionally strong (μ = 0.56 - 0.66). Sand and clay-rich lithologies from outcrop exhibit friction in the range /x = 0.56 - 0.68. Natural serpentinite thought to abut the SAF at depth exhibits low friction (μ = 0.18 - 0.26). Our results indicate that 1) serpentinite exhibits low strength, but is not weak enough to completely satisfy weak fault models, 2) all other samples are consistent with a strong fault and crust and, 3) if the SAF is weak (μ ≤ 0.2) due to the presence of serpentinite or talc, these minerals would likely need to constitute over 50% by weight of the shear zone. Copyright 2009 by the American Geophysical Union.
cited By 77
Keywords: Fault gouge; Fault model; Frictional behavior; Frictional properties; Granodiorite; Low friction; San Andreas Fault; Serpentinite; Shear zone; Siltstone; Clay minerals; Friction; Oxide minerals; Petrology; Quartz; Silicate minerals; Talc; Three dimensional; borehole; fault gouge; fault zone; friction; granodiorite; lithology; outcrop; quartz; rock mechanics; sandstone; serpentinite; shear zone; siltstone; strength; talc; California; North America; San Andreas; United States

Geochemical characteristics of basement target rocks, suevitic glasses from the Eyreville B drill core, Chesapeake Bay impact structure, and three bediasites - Sk'ala, R.; Langenhorst, F.; Deutsch, A. (Special Paper of the Geological Society of America, 2009)
The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville B core hole, drilled into the 35.5-Ma-old Chesapeake Bay impact crater, Virginia, has recovered postimpact sediments, crater-fill breccias, megablocks of the crystalline basement, and suevites with fresh glass shards. Bulk rock analyses of 2 glass shards, 21 crystalline target rocks, and microchemical analyses of 7 glass shards and 3 bediasites (tektites of the North American strewn field) were performed in order to contribute to the understanding of formation processes and to better constrain the precursor materials of these glasses as well as of the bediasites. Statistical treatment (hierarchical cluster analyses) yielded an assignment of the data for the crystalline basement samples into four groups; two of those (various schists, meta-graywackes, and gneisses) display characteristics similar to the impact glasses in the suevites and the bediasites. However, the suevitic glasses show a broad range in composition at the micrometer scale. These data show the frequent presence of schlieren, and in particular, enhanced TiO2 contents that require admixture of an amphibolitic component to the melt. Evidence for such a process is provided by the occurrence of relict, in-part thermally corroded grains of rutile and ilmenite, and by formation of Ti-rich tiny mineral aggregates in the glass. The three studied bediasites show only minor inter- and intrasample heterogeneity, and their chemical composition agrees well with previously published data. The new data for the bediasites are compatible with heating of the tektite melt to extreme temperatures, followed by quenching. © 2009 The Geological Society of America.
cited By 3
Keywords: Boreholes; Buildings; Cluster analysis; Crystalline materials; Crystalline rocks; Glass; Hierarchical systems; Infill drilling; Oxide minerals; Titanium dioxide; Chesapeake bay impact structures; Continental scientific drillings; Crystalline target rocks; Display characteristics; Geochemical characteristic; Hierarchical cluster analysis; Microchemical analysis; U.s. geological surveys; Core drilling; breccia; chemical composition; crater; impact structure; marine sediment; sediment chemistry; suevite; Chesapeake Bay; United States

Geochemical differences of the Hawaiian shield lavas: Implications for melting process in the heterogeneous Hawaiian plume - Ren, Z.-Y.; Hanyu, T.; Miyazaki, T.; Chang, Q.; Kawabata, H.; Takahashi, T.; Hirahara, Y.; Nichols, A.R.L.; Tatsumi, Y. (Journal of Petrology, 2009)
Numerous geochemical studies have indicated that the Hawaiian mantle plume consists of several distinct components. However, their origin remains controversial, with a number of different interpretations having been proposed. We present new major element, trace element and high-precision Sr-Nd-Pb-He isotope data for a suite of fresh submarine lavas erupted by the Koolau, Kilauea and Loihi volcanoes, which are widely believed to have sampled three distinct Hawaiian plume components. The Sr and Nd isotope compositions of the Loihi lavas are similar to those of Kilauea lavas. However, our double-spike Pb isotopic data show that Loihi lavas have both Kilauea-like and Loihi-like compositions. This discovery implies that the Loihi source region contains a Kilauea-like ('Kea') mantle component. Our new data support the existence of three major types of intrinsic plume component: a Loihi component, an 'enriched' (Koolau) component and a 'depleted' (Kea) component. We propose that the Loihi component is a common component, forming the matrix in the Hawaiian mantle plume, and that the isotopic differences between the various shield lavas reflect different mixing proportions of the Loihi component and recycled oceanic crust components (EM-1-like and HIMU-like). The Koolau component contains a higher proportion of EM-1, whereas the Kea component contains a higher proportion of HIMU. EM-1- and HIMU-like recycled oceanic crust components are distributed on a fine scale throughout the peridotitic matrix within the Hawaiian plume. Both components are present in the sources beneath Kea- and Loa-trend volcanoes. We infer that the thermal structure and spatially distributed compositional heterogeneity of the plume are important in controlling the isotopic composition of lavas from a given Hawaiian volcano. © The Author 2009. Published by Oxford University Press. All rights reserved.
cited By 45
Keywords: helium isotope; heterogeneity; igneous geochemistry; isotopic composition; lava; lead isotope; mantle chemistry; mantle plume; neodymium isotope; oceanic crust; partial melting; precision; shield; source rock; spatial distribution; strontium isotope; Hawaii [United States]; North America; United States

Geochemical research on the Late Cretaceous strata of Well SK1 in Songliao Basin. - FANG Wei, WANG Xue (Earth Science Frontiers, 2009)
Keywords: Key words: Songliao Basin; Well SK1; organic geochemistry; deposition environment

Geochemistry of impactites and crystalline basement-derived lithologies from the ICDP-USGS Eyreville A and B drill cores, Chesapeake Bay impact structure, Virginia, USA - Schmitt, R.T.; Bartosova, K.; Reimold, W.U.; Mader, D.; Wittmann, A.; Koeberl, C.; Gibson, R.L. (Special Paper of the Geological Society of America, 2009)
We investigated whole-rock chemical compositions of 318 samples of Exmore breccia (diamicton), impactite (suevite, impact melt rock, polymict lithic impact breccia), and crystalline basement-derived rocks from 444 to 1766 m depth in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B drill cores (Chesapeake Bay impact structure, Virginia, USA). Here, we compare the average chemical compositions for the Exmore breccia (diamicton), the impactites and their subunits, sandstone, granite, granitic gneiss, and amphibolite of the lithic block section (1095.7-1397.2 m depth), cataclastic gneiss of the impact breccia section, and schist and pegmatite/granite of the basal crystalline section (1551.2-1766.3 m depth). The granite of the megablock (1097.7-1371.1 m depth) is of I-type and is seemingly related to a syncollisional setting. The amphibolite (1377.4-1387.5 m depth) of the lithic block section is of igneous origin and has a tholeiitic character. Based on chemical composition, the Exmore breccia (diamicton) can be subdivided into five units (444.9-450.7, 450.7-468, 468-518, 518-528, and 528-̃865 m depth). The units in the depth intervals of 450.7-468 and 518-528 m are enriched in TiO2, MgO, Sc, V, Cr, and Zn contents compared to the other Exmore breccia units. In some samples, especially at ̃451-455 m depth, the Exmore breccia contains significant amounts of P 2 O 5 . The Exmore breccia is recognized as a mixture of all sedimentary and crystalline target components, and, when compared to the impactites, it contains a significant amount of a SiO 2 -rich target component of sedimentary origin. The chemical composition of the impactites overlaps the compositional range for the Exmore breccia. The impactites generally display a negative correlation of SiO 2 and CaO, and a positive correlation of TiO 2 , Al 2 O 3 , Fe 2 O 3 , and MgO with depth. This is the result of an increasing basement schist component, and a decreasing sedimentary and/or granitic component with depth. Suevite units S2 and S3 display distinct enrichment of Na 2 O by a factor of ̃2 compared to all other impactite units, which is interpreted to reflect a higher granitic component in these units. © 2009 The Geological Society of America.
cited By 18

Geochemistry of impactites and crystalline basement-derived lithologies from the ICDP-USGS Eyreville A and B drill cores, Chesapeake Bay impact structure, Virginia, USA - Schmitt, R.T.; Bartosova, K.; Reimold, W.U.; Mader, D.; Wittmann, A.; Koeberl, C.; Gibson, R.L. (Special Paper of the Geological Society of America, 2009)
We investigated whole-rock chemical compositions of 318 samples of Exmore breccia (diamicton), impactite (suevite, impact melt rock, polymict lithic impact breccia), and crystalline basement-derived rocks from 444 to 1766 m depth in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B drill cores (Chesapeake Bay impact structure, Virginia, USA). Here, we compare the average chemical compositions for the Exmore breccia (diamicton), the impactites and their subunits, sandstone, granite, granitic gneiss, and amphibolite of the lithic block section (1095.7-1397.2 m depth), cataclastic gneiss of the impact breccia section, and schist and pegmatite/granite of the basal crystalline section (1551.2-1766.3 m depth). The granite of the megablock (1097.7-1371.1 m depth) is of I-type and is seemingly related to a syncollisional setting. The amphibolite (1377.4-1387.5 m depth) of the lithic block section is of igneous origin and has a tholeiitic character. Based on chemical composition, the Exmore breccia (diamicton) can be subdivided into five units (444.9-450.7, 450.7-468, 468-518, 518-528, and 528-̃865 m depth). The units in the depth intervals of 450.7-468 and 518-528 m are enriched in TiO2, MgO, Sc, V, Cr, and Zn contents compared to the other Exmore breccia units. In some samples, especially at ̃451-455 m depth, the Exmore breccia contains significant amounts of P 2 O 5 . The Exmore breccia is recognized as a mixture of all sedimentary and crystalline target components, and, when compared to the impactites, it contains a significant amount of a SiO 2 -rich target component of sedimentary origin. The chemical composition of the impactites overlaps the compositional range for the Exmore breccia. The impactites generally display a negative correlation of SiO 2 and CaO, and a positive correlation of TiO 2 , Al 2 O 3 , Fe 2 O 3 , and MgO with depth. This is the result of an increasing basement schist component, and a decreasing sedimentary and/or granitic component with depth. Suevite units S2 and S3 display distinct enrichment of Na 2 O by a factor of ̃2 compared to all other impactite units, which is interpreted to reflect a higher granitic component in these units. © 2009 The Geological Society of America.
cited By 18
Keywords: Alumina; Aluminum oxide; Buildings; Crystalline materials; Crystalline rocks; Drills; Granite; Hematite; Infill drilling; Magnesia; Sedimentology; Silica; Sodium compounds; Structure (composition); Titanium dioxide; Chemical compositions; Chesapeake bay impact structures; Continental scientific drillings; Crystalline basement; Crystalline targets; Negative correlation; Positive correlations; U.s. geological surveys; Core drilling; amphibolite; basement rock; breccia; chemical composition; coastal sediment; crystalline rock; enrichment; gneiss; I-type rock; impact structure; impactite; lithology; research program; sandstone; schist; sediment chemistry; Chesapeake Bay; United States; Virginia

Geochemistry of the impact breccia section (1397-1551 m depth) of the Eyreville drill core, Chesapeake Bay impact structure, USA - Bartosova, K.; Mader, D.; Schmitt, R.T.; Ferrière, L.; Koeberl, C.; Reimold, W.U.; Brandst{atter, F. (Special Paper of the Geological Society of America, 2009)
The Chesapeake Bay impact structure, which is 85 km in diameter and 35.5 Ma old, was drilled and cored in a joint International Continental Scientific Drilling Program (ICDP) and U.S. Geological Survey (USGS) drilling project at Eyreville Farm, Virginia, U.S.A. In the Eyreville drill core, 154 m of impact breccia were recovered from the depth interval 1397-1551 m. Major- and trace-element concentrations were determined in 75 polymict impactite samples, 10 samples of cataclastic gneiss blocks, and 24 clasts from impactites. The chemical composition of the polymict impactites does not vary much in the upper part of the section (above ̃1450 m), whereas in the lower part, larger differences occur. Polymict impactites show a decrease of SiO 2 content, and slight increases of TiO 2 , Al 2 O 3 , and Fe 2 O 3 abundances, with depth. This is in agreement with an increase of the schist/gneiss component with depth. Concentrations of siderophile elements (Co, Ni) are lower in the polymict impactites than in the basement-derived schists and do not indicate the presence of an extraterrestrial component. The fi ve petrographically determined types of melt particles, i.e., clear glass, altered melt, recrystallized silica melt, melt with microlites, and dark-brown melt, have distinct chemical compositions. Mixing calculations of the proportions of rocks involved in the formation of various polymict impactites and melt particles were carried out using the Harmonic least-squares MiXing (HMX) calculation program. The calculations suggest that the metamorphic basement rocks (i.e., gneiss and schist) constitute the main component of the polymict impactites, together with significant sedimentary and possible minor pegmatite/granite and amphibolite components. The sedimentary component is derived mostly from a sediment characterized by a composition similar to that of the Cretaceous Potomac Formation. Compositions of the melt particles were modeled as mixtures of target rocks or major rock-forming minerals. However, the results of the mixing calculations for the melt particles are not satisfactory, and the composition of the particles could have been modified by hydrothermal alteration. Carbon isotope ratios were determined for 18 samples. The results imply a hydrothermal origin for the carbonate veins from the basement-derived core section; carbon-rich sedimentary clasts from the Exmore breccia and suevite have a δ 13 C range typical for organic matter in sediments. © 2009 The Geological Society of America.
cited By 13
Keywords: Alumina; Aluminum oxide; Buildings; Carbon; Clay alteration; Drills; Hematite; Infill drilling; Metamorphic rocks; Mixer circuits; Mixing; Sedimentary rocks; Sedimentology; Silica; Structure (composition); Titanium dioxide; Trace elements; Chesapeake bay impact structures; Continental scientific drillings; Extraterrestrial components; Hydrothermal alterations; Major and trace elements; Metamorphic basements; Rock-forming minerals; U.s. geological surveys; Core drilling; breccia; chemical composition; drilling; geochemistry; impact structure; impactite; marine sediment; trace element; Chesapeake Bay; United States

Geologic columns for the ICDP-USGS Eyreville A and C cores, Chesapeake Bay impact structure: Postimpact sediments, 444 to 0 m depth - Edwards, L.E.; Powars, D.S.; Browning, J.V.; McLaughlin Jr., P.P.; Miller, K.G.; Self-Trail, J.M.; Kulpecz, A.A.; Elbra, T. (Special Paper of the Geological Society of America, 2009)
A 443.9-m-thick, virtually undisturbed section of postimpact deposits in the Chesapeake Bay impact structure was recovered in the Eyreville A and C cores, Northampton County, Virginia, within the moat of the structure's central crater. Recovered sediments are mainly fine-grained marine siliciclastics, with the exception of Pleistocene sand, clay, and gravel. The lowest postimpact unit is the upper Eocene Chickahominy Formation (443.9-350.1 m). At 93.8 m, this is the maximum thickness yet recovered for deposits that represent the return to normal marine sedimentation. The Drummonds Corner beds (informal) and the Old Church Formation are thin Oligocene units present between 350.1 and 344.7 m. Above the Oligocene, there is a more typical Virginia coastal plain succession. The Calvert Formation (344.7-225.4 m) includes a thin lower Miocene part overlain by a much thicker middle Miocene part. From 225.4 to 206.0 m, sediments of the middle Miocene Choptank Formation, rarely reported in the Virginia coastal plain, are present. The thick upper Miocene St. Marys and Eastover Formations (206.0-57.8 m) appear to represent a more complete succession than in the type localities. Correlation with the nearby Kiptopeke core indicates that two Pliocene units are present: Yorktown (57.8-32.2 m) and Chowan River Formations (32.2-18.3 m). Sediments at the top of the section represent an upper Pleistocene channel-fill and are assigned to the Butlers Bluff and Occohannock Members of the Nassawadox Formation (18.3-0.6 m). © 2009 The Geological Society of America.
cited By 28
Keywords: Deposits; Recovery; Channel fills; Chesapeake bay impact structures; Coastal plain; Lower Miocene; Maximum thickness; Middle Miocene; Pleistocene sands; Siliciclastics; Sediments; crater; Eocene; fine grained sediment; impact structure; Oligocene; Pleistocene; sedimentation; Chesapeake Bay; United States

Fission track analysis and thermotectonic history of the main borehole of the Chinese Continental Scientific Drilling project - Liu, S.S.; Weber, U.; Glasmacher, U.A.; Xu, Z.Q.; Wagner, G.A. (Tectonophysics, 2009)
The Chinese Continental Scientific Drilling (CCSD) project, part of the International Continental Drilling Program (ICDP), has completed drilling a 5158 m hole in the eastern part of the Dabie-Sulu ultrahigh-pressure metamorphic belt. This study reports on an apatite fission track analysis of core samples from 0 to 4000 m depth in the CCSD main hole (CCSD-MH). We determined the fission track ages of 38 apatite samples from different depths. The ages range between 98.6 ± 17.0 and 3.2 ± 1.3 Ma, showing a general decreasing trend with depth, from 87.1 ± 11.2 Ma at the surface to 3.2 ± 1.3 Ma at 3899 m depth. As a first approximation, an average uplift rate of 35 m/Ma is calculated for the period 90-30 Ma. The trend in ages within the borehole shows some fluctuations, and indicates movements along major faults. It is inferred that the highest-level major normal fault occurs at a depth of 350 m, recording a vertical displacement of 400 m. Movement along another prominent normal fault at a depth of 2150 m occurred subsequent to 25 Ma. Three major reverse faults occur at about 2450, 3050 and 3250 m depth. Testing geological constrains against the fission track data set indicated an agreement with a reheating of the area during the late Cretaceous and Eocene, followed by cooling to 80 °C during the Eocene and a low cooling until the samples reached their present-day position in the Donghai area. © 2009 Elsevier B.V. All rights reserved.
cited By 13
Keywords: CCSD; Donghai; Fission track dating; Thermochronology; Ultrahigh-pressure metamorphic belt; Apatite; Cooling; Drilling; Fission reactions; Metamorphic rocks; Phosphate minerals; Statistical tests; Boreholes; age determination; apatite; borehole geophysics; Chinese Continental Scientific Drilling Project; displacement; fission track dating; geochronology; normal fault; thermochronology; ultrahigh pressure metamorphism; uplift; Asia; China; Dabie-Sulu Belt; Donghai [Jiangsu]; Eurasia; Far East; Jiangsu

Geologic columns for the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure: Impactites and crystalline rocks, 1766 to 1096 m depth - Wright Horton Jr., J.; Gibson, R.L.; Reimold, W.U.; Wittmann, A.; Gohn, G.S.; Edwards, L.E. (Special Paper of the Geological Society of America, 2009)
The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville drill cores from the Chesapeake Bay impact structure provide one of the most complete geologic sections ever obtained from an impact structure. This paper presents a series of geologic columns and descriptive lithologic information for the lower impactite and crystalline-rock sections in the cores. The lowermost cored section (1766-1551 m depth) is a complex assemblage of mica schists that commonly contain graphite and fibrolitic sillimanite, intrusive granite pegmatites that grade into coarse granite, and local zones of mylonitic deformation. This basement-derived section is variably overprinted by brittle cataclastic fabrics and locally cut by dikes of polymict impact breccia, including several suevite dikes. An overlying succession of suevites and lithic impact breccias (1551-1397 m) includes a lower section dominated by polymict lithic impact breccia with blocks (up to 17 m) and boulders of cataclastic gneiss and an upper section (above 1474 m) of suevites and clast-rich impact melt rocks. The uppermost suevite is overlain by 26 m (1397-1371 m) of gravelly quartz sand that contains an amphibolite block and boulders of cataclasite and suevite. Above the sand, a 275-m-thick allochthonous granite slab (1371-1096 m) includes gneissic biotite granite, fine- and medium-to-coarse-grained biotite granites, and red altered granite near the base. The granite slab is overlain by more gravelly sand, and both are attributed to debris-avalanche and/or rockslide deposition that slightly preceded or accompanied seawater-resurge into the collapsing transient crater. © 2009 The Geological Society of America.
cited By 40
Keywords: Biotite; Crystalline materials; Crystalline rocks; Granite; Infill drilling; Levees; Mica; Silicate minerals; Biotite granite; Chesapeake bay impact structures; Coarse-grained; Continental scientific drillings; Debris avalanches; Impact structures; Mylonitic deformation; U.s. geological surveys; Core drilling; crater; crystalline rock; deformation; impact structure; impactite; lithology; pegmatite; Chesapeake Bay; United States

Geologic columns for the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure: Impactites and crystalline rocks, 1766 to 1096 m depth - Wright Horton Jr., J.; Gibson, R.L.; Reimold, W.U.; Wittmann, A.; Gohn, G.S.; Edwards, L.E. (Special Paper of the Geological Society of America, 2009)
The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville drill cores from the Chesapeake Bay impact structure provide one of the most complete geologic sections ever obtained from an impact structure. This paper presents a series of geologic columns and descriptive lithologic information for the lower impactite and crystalline-rock sections in the cores. The lowermost cored section (1766-1551 m depth) is a complex assemblage of mica schists that commonly contain graphite and fibrolitic sillimanite, intrusive granite pegmatites that grade into coarse granite, and local zones of mylonitic deformation. This basement-derived section is variably overprinted by brittle cataclastic fabrics and locally cut by dikes of polymict impact breccia, including several suevite dikes. An overlying succession of suevites and lithic impact breccias (1551-1397 m) includes a lower section dominated by polymict lithic impact breccia with blocks (up to 17 m) and boulders of cataclastic gneiss and an upper section (above 1474 m) of suevites and clast-rich impact melt rocks. The uppermost suevite is overlain by 26 m (1397-1371 m) of gravelly quartz sand that contains an amphibolite block and boulders of cataclasite and suevite. Above the sand, a 275-m-thick allochthonous granite slab (1371-1096 m) includes gneissic biotite granite, fine- and medium-to-coarse-grained biotite granites, and red altered granite near the base. The granite slab is overlain by more gravelly sand, and both are attributed to debris-avalanche and/or rockslide deposition that slightly preceded or accompanied seawater-resurge into the collapsing transient crater. © 2009 The Geological Society of America.
cited By 40

Geological and archaeological implications of strontium isotope analysis of exposed bedrock in the Chicxulub crater basin, northwestern Yucat'an, Mexico - Gilli, A.; Hodell, D.A.; Kamenov, G.D.; Brenner, M. (Geology, 2009)
The surface geology of the site of the Chicxulub impact crater in northwestern Yucat'an, Mexico, has not been studied extensively since the discovery of the crater almost two decades ago. Strontium isotope (87Sr/86Sr) measurements in carbonate rock outcrops reveal near-uniform strontium signatures of 0.70905 inside the ring of cenotes (water-filled sinkholes), which represents the rim of the crater basin. Measured strontium isotope ratios were used to infer rock ages, employing the marine Sr isotope curve. We estimate the age of the exposed limestone within the Chicxulub crater basin to be late Miocene to early Pliocene, representing the age of the youngest sediment fill. Discovery of a large terrain of near-uniform strontium isotope ratios in northwestern Yucat'an offers new geoarchaeological opportunities to track ancient Maya migration and determine sources of manufactured goods. Our results have implications for applying the Sr isotope method to Maya archaeological sites, such as Mayap'an, the last Maya capital, and Chich'en Itz'a. © 2009 Geological Society of America.
cited By 19

Geomechanical response of permafrost-associated hydrate deposits to depressurization-induced gas production - Rutqvist, J.; Moridis, G.J.; Grover, T.; Collett, T. (Journal of Petroleum Science and Engineering, 2009)
In this simulation study, we analyzed the geomechanical response during depressurization production from two known hydrate-bearing permafrost deposits: the Mallik (Northwest Territories, Canada) deposit and Mount Elbert (Alaska, USA) deposit. Gas was produced from these deposits at constant pressure using horizontal wells placed at the top of a hydrate layer (HL), located at a depth of about 900 m at the Mallik site and 600 m at the Mount Elbert site. The simulation results show that general thermodynamic and geomechanical responses are similar for the two sites, but with substantially higher production and more intensive geomechanical responses at the deeper Mallik deposit. The depressurization-induced dissociation begins at the well bore and then spreads laterally, mainly along the top of the HL. The depressurization results in an increased shear stress within the body of the receding hydrate and causes a vertical compaction of the reservoir. However, its effects are partially mitigated by the relatively stiff permafrost overburden, and compaction of the HL is limited to less than 0.4%. The increased shear stress may lead to shear failure in the hydrate-free zone bounded by the HL overburden and the downward-receding upper dissociation interface. This zone undergoes complete hydrate dissociation, and the cohesive strength of the sediment is low. We determined that the likelihood of shear failure depends on the initial stress state as well as on the geomechanical properties of the reservoir. The Poisson's ratio of the hydrate-bearing formation is a particularly important parameter that determines whether the evolution of the reservoir stresses will increase or decrease the likelihood of shear failure.
cited By 175
Keywords: Alaska; usa; Cohesive strengths; Constant pressures; depressurization; Gas productions; Geomechanical properties; geomechanics; hydrate dissociation; Induced dissociations; Initial stress state; Poisson' s ratios; Reservoir stress; Shear failures; Simulation results; Simulation studies; Well bores; Bearings (structural); Compaction; Dissociation; Gases; Horizontal wells; Hydration; International trade; Oil wells; Permafrost; Poisson ratio; Shear stress; Strength of materials; Gas hydrates; computer simulation; gas hydrate; permafrost; Poisson ratio; shear stress; soil mechanics; thermodynamics

Gravity investigations of the Chesapeake Bay impact structure - Plescia, J.B.; Daniels, D.L.; Shah, A.K. (Special Paper of the Geological Society of America, 2009)
The Chesapeake Bay impact structure is a complex impact crater, ̃85 km in diameter, buried beneath postimpact sediments. Its main structural elements include a central uplift of crystalline bedrock, a surrounding inner crater filled with impact debris, and an annular faulted margin composed of block-faulted sediments. The gravity anomaly is consistent with that of a complex impact consisting of a central positive anomaly over the central uplift and an annular negative anomaly over the inner crater. An anomaly is not recognized as being associated with the faulted margin or the outer edge of the structure. Densities from the Eyreville drill core and modeling indicate a density contrast of ̃0.3-0.6 g cm -3 between crystalline basement and the material that fills the inner crater (e.g., Exmore breccia and suevite). This density contrast is somewhat higher than for other impact structures, but it is a function of the manner in which the crater fill was deposited (as a marine resurge deposit). Modeling of the gravity data is consistent with a depth to basement of ̃1600 m at the site of Eyreville drill hole and 800 m at the central uplift. Both depths are greater than the depth at which crystalline rocks were encountered in the cores, suggesting that the cored material is highly fractured para-allochthonous rock. © 2009 The Geological Society of America.
cited By 6
Keywords: Buildings; Core drilling; Crystalline materials; Drills; Infill drilling; Allochthonous rocks; Chesapeake bay impact structures; Crystalline basement; Crystalline bedrocks; Depth to basements; Gravity anomalies; Impact structures; Structural elements; Crystalline rocks; basement rock; bedrock; crater; crystalline rock; gravity anomaly; impact structure; uplift; Chesapeake Bay; United States

Groundwater geochemistry of the Yucatan Peninsula, Mexico: Constraints on stratigraphy and hydrogeology - Perry, E.; Paytan, A.; Pedersen, B.; Velazquez-Oliman, G. (Journal of Hydrology, 2009)
We report 87Sr/86Sr and ion concentrations of sulfate, chloride, and strontium in the groundwater of the northern and central Yucatan Peninsula, Mexico. Correlation between these data indicates that ejecta from the 65.95 m.y. old Chicxulub impact crater have an important effect on hydrogeology, geomorphology, and soil development of the region. Ejecta are present at relatively shallow subsurface depths in north-central Yucatan and at the surface along the Rio Hondo escarpment in southeast Quintana Roo, where they are referred to as the Albion Formation. Anhydrite/gypsum (and by inference celestite) are common in impact ejecta clasts and in beds and cements of overlying Paleocene and Lower Eocene rocks cored around the margin of the crater. The sulfate-rich minerals that are found in rocks immediately overlying the impact ejecta blanket, may either be partially mobilized from the ejecta layer itself or may have been deposited after the K/T impact event in an extensive pre-Oligocene shallow sea. These deposits form a distinctive sedimentary package that can be easily traced by the Eocene-Cretaceous 87Sr/86Sr signal. A distinct Sr isotopic signature and high SO4/Cl ratios are observed in groundwater of northwestern and north-central Yucatan that interacts with these rocks. Moreover, the distribution of the gypsum-rich stratigraphic unit provides a solution-enhanced subsurface drainage pathway for a broad region characterized by dissolution features (poljes) extending from Chetumal, Quintana Roo to Campeche, Campeche. The presence of gypsum quarries in the area is also consistent with a sulfate-rich stratigraphic package that includes ejecta. The distinctive chemistry of groundwater that has been in contact with evaporite/ejecta can be used to trace flow directions and confirms a groundwater divide in the northern Peninsula. Information about groundwater flow directions and about deep subsurface zones of high permeability is useful for groundwater and liquid waste management in the area. Where it discharges at the coast, the unique chemistry of the groundwater that has interacted with the evaporite/ejecta strata may also have significant geomorphologic implications. While groundwater-seawater mixing at the coast has been shown to dissolve and erode limestone, PHREEQC modeling shows that mixing of water nearly saturated in CaSO4 with seawater has a less vigorous dissolution effect due to its high Ca content. © 2009 Elsevier B.V. All rights reserved.
cited By 96

High-impact reservoirs - Barton, R.; Bird, K.; Hern'andez, J.G.; Grajales-Nishimura, J.M.; Murillo-Muñet'on, G.; Herber, B.; Weimer, P.; Koeberl, C.; Neumaier, M.; Schenk, O.; Stark, J. (Oilfield Review, 2009)
The processes that accompany asteroid impact and the roles they play in creating or destroying petroleum source rocks, reservoirs and traps are discussed. Most asteroids orbit the Sun in the asteroid belt, which lies between Mars and Jupiter but some come closer to the Earth. Excavation produces a bowl-shaped transient crater. Craters larger than a few kilometers in diameter usually have complex morphologies characterized by an uplift central area. The central high consists of shocked target rock that has been structurally uplifted by rebound. The bottom of the crater filled with melt brecias, mixtures of granite, carbonate, and dolomite in a spherulitic matrix. The impact that has drawn the most attention is the collision of the Chicxulub impactor with what is now the Mexican Yucat'an Peninsula. A direct hit by an asteroid can also cause the demise of an hydrocarbon accumulation.
cited By 15

Differential subduction and exhumation of crustal slices in the Sulu HP-UHP metamorphic terrane: Insights from mineral inclusions, trace elements, U-Pb and Lu-Hf isotope analyses of zircon in orthogneiss - Liu, F.L.; Gerdes, A.; Xue, H.M. (Journal of Metamorphic Geology, 2009)
Based on new evidence the Sulu orogen is divided from south-east to north-west into high-pressure (HP) crustal slice I and ultrahigh-pressure (UHP) crustal slices II and III. A combined set of mineral inclusions, cathodoluminescence images, U-Pb SHRIMP dating and in situ trace element and Lu-Hf isotope analyses was obtained on zircon from orthogneisses of the different slices. Zircon grains typically have three distinct domains that formed during crystallization of the magmatic protolith, HP or UHP metamorphism and late-amphibolite facies retrogression, respectively: (i) oscillatory zoned cores, with low-pressure (LP) mineral inclusions and Th/U > 0.38; (ii) high-luminescent mantles (Th/U < 0.10), with HP mineral inclusions of Qtz + Grt + Arg + Phe + Ap for slice I zircon and Coe + Grt + Phe + Kfs + Ap for both slices II and III zircon; (iii) low-luminescent rims, with LP mineral inclusions and Th/U < 0.08. Zircon U-Pb SHRIMP analyses of inherited cores point to protolith ages of 785-770 Ma in all seven orthogneisses. The ages recorded for UHP metamorphism and subsequent retrogression in slice II zircon (c. 228 and c. 215 Ma, respectively) are significantly older than those of slice III zircon (c. 218 and c. 202 Ma, respectively), while slice I zircon recorded even older ages for HP metamorphism and subsequent retrogression (c. 245 and c. 231 Ma, respectively). Moreover, Ar-Ar biotite ages from six paragneisses, interpreted as dating amphibolite facies retrogression, gradually decrease from HP slice I (c. 232 Ma) to UHP slice II (c. 215 Ma) and UHP slice III (c. 203 Ma). The combined data set suggests decreasing ages for HP or UHP metamorphism and late retrogression in the Sulu orogen from south-east to north-west. Thus, the HP-UHP units are interpreted to represent three crustal slices, which underwent different subduction and exhumation histories. Slice I was detached from the continental lithosphere at ∼55-65 km depth and subsequently exhumed while subduction of the underlying slice II continued to ∼100-120 km depth (UHP) before detachment and exhumation. Slice III experienced a similar geodynamic evolution as slice II, however, both UHP metamorphism and subsequent exhumation took place c. 10 Myr later. Magmatic zircon cores from two types of orthogneiss in UHP slices II and III show similar mid-Neoproterozoic crystallization ages, but have contrasting Hf isotope compositions (εHf(∼785) = -2.7 to +2.2 and -17.3 to -11.1, respectively), suggesting their formation from distinct crustal units (Mesoproterozoic and Paleoproterozoic to Archean, respectively) during the breakup of Rodinia. The UHP and the retrograde zircon domains are characterized by lower Th/U and 176Lu/177Hf but higher 176Hf/177Hf(t) than the Neoproterozoic igneous cores. The similarity between UHP and retrograde domains indicates that late retrogression did not significantly modify chemical and isotopic composition of the UHP metamorphic system. © 2009 Blackwell Publishing Ltd.
Keywords: Asia; China; Eurasia; Far East; Sulu Belt; amphibolite facies; cathodoluminescence; continental lithosphere; crystallization; exhumation; hafnium; isotopic analysis; isotopic composition; lead isotope; lutetium; orthogneiss; Proterozoic; rare earth element; SHRIMP dating; subduction; trace element; ultrahigh pressure metamorphism; uranium-lead dating; zircon

Frictional and transport properties of the Chelungpu fault from shallow borehole data and their correlation with seismic behavior during the 1999 Chi-Chi earthquake - Tanikawa, W.; Shimamoto, T. (Journal of Geophysical Research: Solid Earth, 2009)
We carried out low- and high-velocity friction tests on fault rock samples from shallow boreholes on the Taiwan Chelungpu fault and measured their fluid transport properties under high pressure, with the objective of explaining the different seismic behaviors in the northern and southern sections of the fault during the 1999 Chi-Chi earthquake. Our results of low-velocity friction tests demonstrate that fault gouge from the southern section of the fault exhibits velocity-weakening frictional behavior, whereas gouge from the northern section exhibits velocity-strengthening friction. Friction in the northern gouge decreased strongly with increasing wetness, whereas friction in southern gouge samples was not affected by wetness. A rapid reduction of friction was observed immediately after the onset of slip in high-velocity friction tests. The results of high-velocity friction tests were similar for all fault gouge samples tested, although permeability in the northern fault zone was lower than that in the south. Numerical modeling indicated that thermal pressurization in the northern fault zone promoted stress reduction and fault instability during slip, whereas it did not in the south. This contrasting seismic behavior between north and south is caused mainly by differences in fluid transport properties of the slip zones. More efficient thermal pressurization in the north explains the large slip displacement there. The results of our low-velocity friction tests are consistent with nucleation of the Chi-Chi earthquake in the south and propagation of the rupture from south to north. Copyright 2009 by the American Geophysical Union.
cited By 60
Keywords: borehole; Chi-Chi earthquake 1999; earthquake rupture; fault zone; fluid flow; friction; high pressure; numerical model; seismicity; slip; Asia; Chelungpu Fault Zone; Eurasia; Far East; Taiwan

Geologic columns for the ICDP-USGS Eyreville A and B cores, Chesapeake Bay impact structure: Sediment-clast breccias, 1096 to 444 m depth - Edwards, L.E.; Powars, D.S.; Gohn, G.S.; Dypvik, H. (Special Paper of the Geological Society of America, 2009)
The Eyreville A and B cores, recovered from the moat of the Chesapeake Bay impact structure, provide a thick section of sediment-clast breccias and minor stratified sediments from 1095.74 to 443.90 m. This paper discusses the components of these breccias, presents a geologic column and descriptive lithologic framework for them, and formalizes the Exmore Formation. From 1095.74 to ̃867 m, the cores consist of nonmarine sediment boulders and sand (rare blocks up to 15.3 m intersected diameter). A sharp contact in both cores at ̃867 m marks the lowest clayey, silty, glauconitic quartz sand that constitutes the base of the Exmore Formation and its lower diamicton member. Here, material derived from the upper sediment target layers, as well as some impact ejecta, occurs. The block-dominated member of the Exmore Formation, from ̃855-618.23 m, consists of nonmarine sediment blocks and boulders (up to 45.5 m) that are juxtaposed complexly. Blocks of oxidized clay are an important component. Above 618.23 m, which is the base of the informal upper diamicton member of the Exmore Formation, the glauconitic matrix is a consistent component in diamicton layers between nonmarine sediment clasts that decrease in size upward in the section. Crystalline-rock clasts are not randomly distributed but rather form local concentrations. The upper part of the Exmore Formation consists of crudely fining-upward sandy packages capped by laminated silt and clay. The overlap interval of Eyreville A and B (940-̃760 m) allows recognition of local similarities and differences in the breccias. © 2009 The Geological Society of America.
cited By 38
Keywords: Crystalline rocks; Rocks; Chesapeake bay impact structures; Impact ejecta; Local similarity; Quartz sand; Randomly distributed; Sediments; breccia; diamicton; ejecta; impact structure; lithology; marine sediment; Chesapeake Bay; United States

First results of geothermal investigations, Chesapeake Bay impact structure, Eyreville core holes - Heidinger, P.; Wilhelm, H.; Popov, Y.; Šafanda, J.; Burkhardt, H.; Mayr, S. (Special Paper of the Geological Society of America, 2009)
The Chesapeake Bay impact structure is a late Eocene complex crater that was excavated -35 Ma ago in a continental shelf environment at the Atlantic margin, in Virginia. It is the largest impact structure in the United States and the seventh largest on Earth. It has an average diameter of -85 km and is centered near Cape Charles. The scientific well Eyreville B drilled within the framework of the International Continental Scientific Drilling Program (ICDP) penetrated the deep crater moat -9 km from the center of the structure. Core holes drilled in impact structures are especially suited for investigations of the infl uence of lithological heterogeneities on petrophysical properties and the thermal field. In the Eyreville B core hole, two high-resolution temperature-logging campaigns and a petrophysical profile measured on core samples spaced at -10 m intervals were recorded. The temperature values of the first campaign in December 2005 were heavily disturbed by outflow of artesian water and could only be used for an estimation of the depth where the fluid originated. For the second campaign in May 2006, a riser was constructed to enable measurements in standing (equilibrated) fluid of the well without opening the well head. This construction yielded a measurement of the undisturbed temperature profile as well as recognition of thermal relaxation after some outflow of artesian water, which wellheated the surrounding rock. The data allowed determination of (1) the origin of the artesian water, (2) equilibrium temperatures derived from the relaxation process, (3) microclimatic effects at the nearby test well STP2, (4) lateral heterogeneities in the core holes STP2 and Eyreville B, and (5) a profile of vertical heat-flow density in the Eyreville B core. From the calculated vertical component of the thermal gradient and the thermal conductivity measured on core samples, a mean heat-flow density of 65 ± 6 mW/m2 in the 440-1100 m depth interval was determined. These data and results are now available for application in numerical models of the local and regional geologic, hydrologic, and geothermal regimes. © 2009 The Geological Society of America.
cited By 8
Keywords: Heat transfer; Infill drilling; Lithology; Petrophysics; Thermal conductivity; Wellheads; Chesapeake bay impact structures; Continental scientific drillings; Continental shelves; Equilibrium temperatures; Lateral heterogeneity; Microclimatic effects; Petrophysical properties; Temperature profiles; Core samples; borehole; continental shelf; crater; Eocene; estimation method; geothermal system; heat flow; impact structure; lithology; numerical model; temperature profile; thermal conductivity; thermal regime; Chesapeake Bay; United States; Virginia; Calluna vulgaris

Effect of thermal refraction on heat flow near the San Andreas Fault, Parkfield, California - Fulton, P.M.; Saffer, D.M. (Journal of Geophysical Research: Solid Earth, 2009)
Heat flow data near the San Andreas Fault (SAF) do not reveal a near-fault anomaly as expected from frictional heat generation, an observation interpreted to indicate that the fault slips at a depth-averaged shear stress <20 MPa. The data also contain large unexplained scatter, which has been a separate major issue in the analysis of heat flow within the California Coast Ranges. Here we use numerical models of heat conduction to evaluate the hypothesis that thermal refraction, due to contrasts in thermal conductivity in the subsurface, both produces the observed scatter in heat flow and as a result obscures the thermal signature from frictional heating on a fault that supports large shear stress during slip. Our study focuses on the region around the San Andreas Fault Observatory at Depth (SAFOD) near Parkfield, California. Our results show that surface heat flow is most sensitive to the contrast between Tertiary sediments and basement rocks and to wavelengths of basement topography of ∼10 km. With realistic thermal conductivity contrasts and a reasonable interpretation of this geologic contact, we show that thermal refraction is a plausible explanation for the observed heat flow scatter. However, refraction effects are unable to mask frictional heat generation in a manner consistent with observations. We show that even with large refraction effects, low background heat flow, a regional NW-SE decrease in heat flow, or nonsteady state heat conduction, the data are most consistent with a fault that produces little to no frictional heat. Copyright 2009 by the American Geophysical Union.
cited By 14
Keywords: basement rock; coastal zone; data acquisition; fault slip; flow measurement; friction; heat flow; numerical model; shear stress; slip; subsurface flow; thermal conductivity; California; North America; San Andreas; United States; Calluna vulgaris

Direct measurements of chemical composition of shock-induced gases from calcite: an intense global warming after the Chicxulub impact due to the indirect greenhouse effect of carbon monoxide - Kawaragi, K.; Sekine, Y.; Kadono, T.; Sugita, S.; Ohno, S.; Ishibashi, K.; Kurosawa, K.; Matsui, T.; Ikeda, S. (Earth and Planetary Science Letters, 2009)
Shock-induced devolatilization in hypervelocity impacts has been considered to play important roles in the atmospheric evolution and mass extinctions in Earth's history. Although the chemical composition of shock-induced gas species from carbonate rocks has been considered as a key to understand the environmental change after the Chicxulub impact, it has not been investigated extensively before. Here, we conduct direct measurements of the chemical composition (CO/CO2) of shock-induced gas species from calcite (CaCO3) using both a laser gun system and an isotopic labeling technique. The CO/CO2 ratio of the shock-induced gas species from calcite is measured to be 2.02 ± 0.41, suggesting that gaseous CO has been dominant in the shock-induced gases in the Chicxulub impact. In order to evaluate the environmental effects of the injection of CO gas, we investigated the post-impact atmospheric chemistry by incorporating our experimental results into a tropospheric photochemical model. The results suggest that an intense (2-5 °C) global warming would have lasted for several years after a Chicxulub-size impact mainly due to the greenhouse effect of tropospheric O3, which is produced via photochemical reactions associated with CO gas. Such an intense global warming could have damaged the biosphere in the mass extinction at the Cretaceous-Paleogene (K-P) boundary. © 2009 Elsevier B.V. All rights reserved.
cited By 30

Fabric kinematics of the ultrahigh-pressure metamorphic rocks from the main borehole of the Chinese Continental Scientific Drilling Project: Implications for continental subduction and exhumation - Xu, Zhiqin; Wang, Qin; Tang, Zhemin; Chen, Fangyuan (Tectonophysics, 2009)
The 5158-m-deep main borehole of the Chinese Continental Scientific Drilling Project (CCSD-MH) penetrated granitic gneisses, paragneisses, eclogites, retrograde eclogites, amphibolites and ultramafic rocks in the Sulu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. The CCSD-MH consists of four petro-structural units separated by three SE-dipping ductile shear zones DFa (835-1280 m), DFb (2010-2280 m) and DFc (2920-3225 m), which are correspondent with the regional shear zones in the northern Sulu UHP supracrustal zone. Using the electron backscatter diffraction (EBSD) technique, we investigated the lattice-preferred orientations (LPOs) of omphacite, diopside and quartz in core samples from the CCSD-MH. Omphacite from eclogites and diopside from garnet pyroxenites display very strong LPOs, which are characterized by the maximum concentration of [001]-axes parallel to the lineation and (010)-poles normal to the foliation. Quartz in para- and granitic mylonites/gneisses from the shear zones DFa, DFb and DFc developed multiple slip systems. 40Ar/39Ar dating of biotite in para- and granitic gneisses from the CCSD-MH yields 223-202 Ma, which constrains the formation ages of the quartz high-temperature prism slip systems m and m[c]. The asymmetric LPOs of omphacite, diopside, olivine and quartz with respect to the structural frame reveal three deformation phases in the Sulu terrane. In the Middle Triassic, the northward subduction of the Yangtze plate to depths > 100 km produced a top-to-the-south shear sense in LPOs of omphacite, diopside and olivine, and a nearly N-S-striking foliation and a subhorizontal N-S-trending lineation in eclogites and ultramafic rocks. In the Late Triassic, the UHP rocks were exhumed to the lower crust and quartz developed high-temperature slip systems with a top-to-the-NW shear sense, which is consistent with the regional SE-dipping foliation and SE-plunging lineation in the ductile shear zones. In the Cretaceous the UHP rocks were exhumed to the middle crust when the migmatization and granitic intrusion formed a NE-striking antiform structure. As a result, the activation of quartz low-temperature basal slip (0001) is characterized by a top-to-the-SE shear sense in the south, but a top-to-the-NW shear sense in the north. © 2009 Elsevier B.V. All rights reserved.
Keywords: Asia; China; Eurasia; Far East; Sulu Belt; Yangtze Platform; Drilling; Electron diffraction; Garnets; Housing; Kinematics; Metal vapor lamps; Mica; Olivine; Oxide minerals; Quartz; Rocks; Shear deformation; Silicate minerals; Spontaneous emission; Structural design; Structural geology; Tectonics; X ray powder diffraction; Ar dating; Continental subduction; Exhumation; Lattice-preferred orientation; Sulu terrane; amphibolite; asymmetry; borehole geophysics; Chinese Continental Scientific Drilling Project; deformation; dip-slip fault; eclogite; exhumation; gneiss; kinematics; lineation; petrofabric; preferred orientation; regional metamorphism; retrograde metamorphism; shear zone; subduction; tectonic evolution; tectonic setting; ultrahigh pressure metamorphism; ultramafic rock; Metamorphic rocks

Discovery of the first Quaternary maar in the Bohemian Massif, Central Europe, based on combined geophysical and geological surveys - Mrlina, J.; K{ampf, H.; Kroner, C.; Mingram, J.; Stebich, M.; Brauer, A.; Geissler, W.H.; Kallmeyer, J.; Matthes, H.; Seidl, M. (Journal of Volcanology and Geothermal Research, 2009)
Based on results of previous investigations of tephra-tuff volcaniclastic deposits and a geophysical survey in the surroundings of the Železn'a hůrka Quaternary volcano, West Bohemia, we performed detailed geophysical surveys using gravimetry, magnetometry and electrical conductivity techniques. Striking anomalies were revealed in a morphological depression near M'ytina, West Bohemia, as a strong evidence of the assumed maar-diatreme structure. The sharp isometric gravity low of - 2.30 mGal, as well as the corresponding positive magnetic anomaly of 200 nT with a negative rim on its northern side indicate a steeply dipping geological body of low density and containing magnetic rocks/minerals. Magnetic survey also showed pronounced local anomalies outside the depression that can reflect relicts of the tephra rim of the maar. This geophysical evidence was then proven by an exploratory drilling near the centre of the gravity anomaly. Macroscopic on-site evaluation of the core, and more detailed sedimentological, petrochemical, palynological and microbiological laboratory analyses further confirmed the existence of a maar structure filled by 84 m of lake sediments reflecting a succession of several warm and cold climatic periods. Results of palynological analyses confirm the presence of a continuous palaeoclimate archive, with at least three successive warmer periods of most probably interstadial character from the upper Quaternary Saalian complex. Therefore, the recovered sediment sequence holds strong potential for in-depth paleoclimate reconstruction and deep biosphere studies. At the bottom of the M'ytina-1 (MY-1) borehole (84-85.5 m), country rock debris was found, containing also volcanic bombs and lapilli. The discovered volcanic structure is considered to be the first known Quaternary maar-diatreme volcano on the territory of the Bohemian Massif. Because of hidden active magmatic processes in combination with earthquake swarm seismicity ca. 20-30 km north of the M'ytina maar, reconstruction of the palaeovolcanological evolution is important for evaluation of hazard potential of the NE and E part of the Cheb Basin. © 2009 Elsevier B.V. All rights reserved.
Keywords: Bohemian Massif; Central Europe; Eurasia; Europe; Debris; Earthquakes; Electric conductivity; Geological surveys; Geophysics; Gravitational effects; Hazards; Lakes; Minerals; Restoration; Sedimentology; Structural geology; Volcanoes; Eger Rift; geophysical survey; Quaternary maar volcanism; Saalian lake sediments; volcanic hazard potential; diatreme; earthquake swarm; electrical conductivity; geophysical survey; gravimetry; gravity anomaly; maar; magnetic anomaly; magnetometer; paleoclimate; paleoseismicity; Quaternary; Saalian; tephra; tuff; volcaniclastic deposit; Core analysis

Distributions of branched GDGTs in a tropical lake system: Implications for lacustrine application of the MBT/CBT paleoproxy - Tierney, Jessica E.; Russell, James M. (Organic Geochemistry, 2009)
Branched glycerol dialkyl glycerol tetraether (GDGT) lipids are abundant and ubiquitous in lake sediments, potentially allowing for a paleolimnological application of the so-called MBT/CBT proxy (methylation index of branched tetraethers/cyclization ratio of branched tetraethers). To investigate the origin and characteristics of these compounds in lacustrine environments, we examined the distributions of GDGTs in soils, river sediments and lake sediments from Lake Towuti on the island of Sulawesi, Indonesia. We found significant differences in the degree of methylation and cyclization (expressed by way of the MBT and CBT indices) between the soil samples and the aquatic samples, suggesting that there may be in situ production of GDGTs in the aquatic environment. Based on these findings, we urge caution in the application of the MBT/CBT paleoproxy to lake sediments and encourage more rigorous study of these compounds in freshwater environments. © 2009 Elsevier Ltd. All rights reserved.
Keywords: Asia; Eurasia; Indonesia; Lake Towuti; Malili Lakes; South Sulawesi; Southeast Asia; Alkylation; Glycerol; Lakes; Methylation; Sedimentology; Soils; Aquatic environments; Degree of methylations; Freshwater environments; In-situ production; Indonesia; Lake sediments; River sediments; Soil sample; Tropical lakes; ether; fluvial deposit; lacustrine deposit; lacustrine environment; lipid; methylation; tropical environment; Sediments

Drilling deep into the ultrahigh pressure (UHP) metamorphic terrane - Ji, Shaocheng; Xu, Zhiqin (Tectonophysics, 2009)
The Chinese Continental Scientific Drilling

Drilling into the El'gygytgyn Impact Crater, Arctic Russia: The 2009 ICDP Project - Koeberl, Christian; Brigham-Grette, Julie; Melles, Martin; Minyuk, Pavel (Meteoritics and Planetary Science Supplement, 2009)

Dynamics and internal structure of a lower mantle plume conduit - Farnetani, Cinzia G.; Hofmann, Albrecht W. (Earth and Planetary Science Letters, 2009)
Geochemical studies, including those made possible by the Hawaiian Scientific Drilling Project, have revealed the chemically and isotopically heterogeneous nature of hotspot lavas, yet their interpretation is highly controversial and there is little agreement as to how geochemical heterogeneities might be spatially arranged within the plume conduit. To address this issue we conduct high resolution numerical simulations of an axisymmetric purely thermal plume, focusing on the lower mantle part of the conduit and on the thermal boundary layer (TBL) feeding the plume. We explore the relation between length-scales of heterogeneities across the source region and the length- and time-scales of geochemical variations in the plume conduit. The vertical velocity inside the conduit decreases exponentially with the square of radial distance generating high strain rates (order 10- 13-10- 14 s- 1) that modify the shape of upwelling heterogeneities into elongated and narrow filaments. Therefore, the preservation of 'blob-like' heterogeneities (i.e., with a 1:1 aspect ratio in a vertical section) is quite unlikely, even in the central part of the plume. For example, initial lenses of size 100 × 10 km in the TBL are stretched into filaments 500-1000 km long. These filaments constitute 'long-lived' structures in a rising plume, and their geochemical fingerprints may be registered at a given radial distance for several millions of years. We also consider an idealized heterogeneous architecture inside the TBL, consisting of 'trains' of small scale lenses. When such trains upwell in the conduit, they form high radial geochemical gradients. Their 'geochemical record', registered over time at a given depth and radial distance, will fluctuate over time, with shorter period and a larger amplitude at the conduit center than at its periphery. Finally, we demonstrate that material existing 'side by side' in the conduit originated from regions in the TBL that are separated by distances of several hundred kilometers. This implies that vigorous plumes are able to sample, and to bring side by side, very distant portions of their source region. Our results provide a fluid dynamically consistent framework to discuss the main aspects of the different (and to some extent mutually exclusive) models of conduit structure used to interpret the geochemical observations of the Hawaiian lavas. © 2009 Elsevier B.V. All rights reserved.
Keywords: Hawaii [United States]; North America; United States; Aspect ratio; Filaments (lamp); Lenses; Locomotives; Optical instruments; Railroad cars; Strain rate; Transport properties; Axi-symmetric; Conduit structures; Geochemical fingerprints; geochemical heterogeneity; Geochemical variations; Hawaiian plume; Heterogeneous architectures; High strain rates; High-resolution numerical simulations; Hot spots; Internal structures; Lower mantles; mantle plumes; Radial distances; Scientific drillings; Small scale; Source regions; Thermal boundary layers; Time-scales; Vertical sections; Vertical velocities; isotopic composition; lower mantle; mantle chemistry; mantle plume; numerical model; Thermal plumes

Earthquake swarms in non-volcanic regions: What fluids have to say - Br{auer, Karin; K{ampf, Horst; Strauch, Gerhard (Geophysical Research Letters, 2009)
The detailed processes generating earthquake swarms are complex and not fully understood. Most earthquake swarms occur in volcanic regions and mid-ocean rifts. Here, we report new 3HeZ4He data of free gases monitored at CO2rich degassing locations close to the Nov'y Kostel focal zone (NKFZ) located in the western Eger rift. The NKFZ is known for the recurrence of earthquake swarms at which the focal zone ranges between 6 and 12 km depth. At degassing locations neighboring to the NKFZ a progressive increase of mantle-derived helium has been observed during the last 15 years - actually the highest 3He/4He ratios (>6 Ra) in Central Europe. The 3HeZ4He anomalies indicate hidden magmatic activity. We assume that the latest strong earthquake swarm in October 2008 was initiated by a hidden magma intrusion process from the upper mantle into the lower crust that has been indicated by a three month lasting increase of the 3HeZ4He ratios in spring 2006 at all degassing locations near the NKFZ. Copyright 2009 by the American Geophysical Union.
Keywords: Central Europe; Eger; Eurasia; Europe; Heves; Hungary; Degassing; Helium; Oceanography; Volcanoes; Central Europe; Earthquake swarms; Focal zones; Free gas; Lower crust; Magma intrusion; Magmatic activity; Upper mantle; Volcanic region; carbon dioxide; degassing; earthquake swarm; helium; lower crust; magmatism; rift zone; upper mantle; Earthquakes

Dynamic fault weakening and the formation of large impact craters - Senft, L.E.; Stewart, S.T. (Earth and Planetary Science Letters, 2009)
Impact craters are the most common landform on planetary surfaces; however, the mechanics of the end stages of their formation are not fully understood. The final stage of crater formation involves the collapse of a hemispherical transient cavity. Around small craters, the limited amount of collapse preserves a bowl-shaped cavity. In contrast, the observed shallow depths and complex inner morphologies of large craters require very low shear strength in the collapsing material. Because the observed amount of collapse cannot be reproduced using quasi-static values for the frictional strength of fractured rock, a temporary weakening mechanism is necessary. Here, we investigate the hypothesis that craters collapse along a network of impact-generated faults that weaken during long displacements at high slip velocities via, for example, frictional melting. Using the CTH shock physics code, we simulate the formation of about 100-km diameter impact craters using a simple strain-rate weakening model with parameters constrained by fault friction experiments on crystalline rocks. The model reduces the coefficient of friction from a quasi-static value (0.6-0.85) to a weakened value (0.1-0.2) when a parcel of fractured material exceeds thresholds for cumulative plastic shear strain (a proxy for slip distance) and shear strain rate (a proxy for slip velocity). During crater formation, the strain-rate weakening model leads to strain localizations that are interpreted to be fault zones. Fault zones are spontaneously created and slip over discrete time intervals during collapse. The strain-rate weakening model reproduces the major geologic features observed around the largest terrestrial craters (Vredefort, Sudbury, and Chicxulub), including shallow depths, fault structures, frictional melt distributions, and deep-seated central uplifts. The good agreement between calculations and observations supports the hypothesis that small volumes of transiently weakened material in fault zones control the collapse of large impact craters. © 2009 Elsevier B.V. All rights reserved.
cited By 60

Extension of Gutenberg-Richter distribution to Mw -1.3, no lower limit in sight - Boettcher, M.S.; McGarr, A.; Johnston, M. (Geophysical Research Letters, 2009)
[1] With twelve years of seismic data from TauTona Gold Mine, South Africa, we show that mining-induced earthquakes follow the Gutenberg-Richter relation with no scale break down to the completeness level of the catalog, at moment magnitude Mw -1.3. Events recorded during relatively quiet hours in 2006 indicate that catalog detection limitations, not earthquake source physics, controlled the previously reported minimum magnitude in this mine. Within the Natural Earthquake Laboratory in South African Mines (NELSAM) experiment's dense seismic array, earthquakes that exhibit shear failure at magnitudes as small as Mw -3.9 are observed, but we find no evidence that Mw -3.9 represents the minimum magnitude. In contrast to previous work, our results imply small nucleation zones and that earthquake processes in the mine can readily be scaled to those in either laboratory experiments or natural faults.
cited By 47
Keywords: Break down; Earthquake process; Earthquake source; Laboratory experiments; Lower limits; Moment magnitudes; Natural earthquake; Nucleation zone; Seismic arrays; Seismic data; Shear failure; South Africa; Mines; Mining; Earthquakes; earthquake; gold mine; mining-induced seismicity; nucleation; seismic data; spatial distribution; Africa; South Africa; Southern Africa; Sub-Saharan Africa

Elastic wave velocities, chemistry and modal mineralogy of crustal rocks sampled by the Outokumpu scientific drill hole: Evidence from lab measurements and modeling - Kern, H.; Mengel, K.; Strauss, K.W.; Ivankina, T.I.; Nikitin, A.N.; Kukkonen, I.T. (Physics of the Earth and Planetary Interiors, 2009)
The Outokumpu scientific deep drill hole intersects a 2500 m deep Precambrian crustal section comprising a 1300 m thick biotite-gneiss series (mica schists) at top, followed by a 200 m thick meta-ophiolite sequence, underlain again by biotite gneisses (mica schists) (500 m thick) with intercalations of amphibolite and meta-pegmatoids (pegmatitic granite). From 2000 m downward the dominating rock types are meta-pegmatoids (pegmatitic granite). Average isotropic intrinsic P- and S-wave velocities and densities of rocks were calculated on the basis of the volume fraction of the constituent minerals and their single crystal properties for 29 core samples covering the depth range 198-2491 m. The modal composition of the rocks is obtained from bulk rock (XRF) and mineral chemistry (microprobe), using least squares fitting. Laboratory seismic measurements on 13 selected samples representing the main lithologies revealed strong anisotropy of P- and S-wave velocities and shear wave splitting. Seismic anisotropy is strongly related to foliation and is, in particular, an important property of the biotite gneisses, which dominate the upper and lower gneiss series. At in situ conditions, velocity anisotropy is largely caused by oriented microcracks, which are not completely closed at the pressures corresponding to the relatively shallow depth drilled by the borehole, in addition to crystallographic preferred orientation (CPO) of the phyllosilicates. The contribution of CPO to bulk anisotropy is confirmed by 3D velocity calculations based on neutron diffraction texture measurements. For vertical incidence of the wave train, the in situ velocities derived from the lab measurements are significantly lower than the measured and calculated intrinsic velocities. The experimental results give evidence that the strong reflective nature of the ophiolite-derived rock assemblages is largely affected by oriented microcracks and preferred crystallographic orientation of major minerals, in addition to the lithologic control. © 2009 Elsevier B.V. All rights reserved.
Keywords: Anisotropy; Crystallography; Curve fitting; Elasticity; Fatigue of materials; Granite; Intercalation; Lithology; Mica; Mineralogy; Mining; Rock drills; Rocks; Seismic waves; Seismology; Shear waves; Silica; Silicate minerals; Single crystals; Three dimensional; Velocity; 3d velocities; Biotite gneiss; Bulk rocks; Crustal rocks; Crystallographic orientations; Crystallographic preferred orientations; Depth ranges; Elastic wave velocities; In-situ; Intrinsic velocities; Least squares fittings; Lithologic controls; Measured and calculated elastic properties; Mica schists; Micro probes; Mineral chemistries; Modal composition; Nature of seismic reflections; Outokumpu deep drill hole; Precambrian; Rock types; S-wave velocities; Seismic anisotropies; Seismic measurements; Shallow depths; Shear-wave splitting; Single-crystal properties; Strong anisotropies; Texture measurements; Velocity anisotropies; Wave trains; crustal structure; crystallography; drilling; elastic wave; granite; laboratory method; least squares method; mica; neutron diffraction; numerical model; P-wave; S-wave; schist; seismic anisotropy; seismic reflection; wave velocity; Minerals

Evaluation of oxygen isotopes in carbonate as an indicator of lake evolution in arid areas: The modern Qinghai Lake, Qinghai-Tibet Plateau - Liu, Weiguo; Li, Xiangzhong; Zhang, Ling; An, ZhiSheng; Xu, Liming (Chemical Geology, 2009)
The oxygen isotopic composition of carbonate in lakes has been used as a useful indicator in Palaeolimnological research, and has made some important contributions to our understanding of lacustrine systems. For modern lakes in arid or cold areas, however, there are few data available to test the effect of lake salinity and temperature on the oxygen isotopic composition of various carbonate sources such as ostracod, bulk carbonate, and fine-grained carbonate (< 60 μm). Here we examined the oxygen isotopic composition of ostracods, bulk carbonate, and fine-grained carbonates, as well as that of coexisting water from Lake Qinghai and the smaller surrounding lakes and ponds on the Qinghai-Tibet Plateau. Our investigation highlights three key effects. First, the oxygen isotopic composition of ostracods, bulk carbonate, and fine-grained carbonate in the lakes and ponds shows a clear response to lake water δ18O values, and these vary with water salinity. The relationship between lake water δ18O and salinity is not only dominated by the evaporation/freshwater input ratios, but is also controlled by the distance to the mouth of the major rivers supplying to the lake. Second, the ostracod, bulk carbonate, and fine-grained carbonate show similar isotopic change trends in the study area, and oxygen isotopic differences between ostracods and authigenic carbonate may be explained by the different water temperatures and very small 'vital offsets' of ostracods. Finally, the effect of water depth on temperature leads to increasing δ18O values in carbonates as water depth increases, both in benthic ostracods living on the lake bottom, as well as in bulk carbonate precipitated at the water surface. For arid, high-altitude Lake Qinghai, our results suggest that variations in the δ18O values of carbonate in Lake Qinghai are mainly controlled by the oxygen-isotope ratio of the lake water changing with water salinity. As a secondary effect, increasing water depth leads to cooler bottom and surface water, which may result in more positive δ18O values of ostracod and bulk carbonate. © 2009 Elsevier B.V. All rights reserved.
Keywords: Asia; China; Eurasia; Far East; Qinghai; Qinghai Lake; Ostracoda; arid environment; carbonate sediment; fine grained sediment; isotopic composition; lacustrine deposit; lake evolution; ostracod; oxygen isotope; salinity; water depth; water temperature

Evolution of crystalline target rocks and impactites in the chesapeake bay impact structure, ICDP-USGS eyreville B core - Horton Jr., J.W.; Kunk, M.J.; Belkin, H.E.; Aleinikoff, J.N.; Jackson, J.C.; Chou, I.-M. (Special Paper of the Geological Society of America, 2009)
The 1766-m-deep Eyreville B core from the late Eocene Chesapeake Bay impact structure includes, in ascending order, a lower basement-derived section of schist and pegmatitic granite with impact breccia dikes, polymict impact breccias, and cataclas tic gneiss blocks overlain by suevites and clast-rich impact melt rocks, sand with an amphibolite block and lithic boulders, and a 275-m-thick granite slab overlain by crater-fill sediments and postimpact strata. Graphite-rich cataclasite marks a detachment fault atop the lower basement-derived section. Overlying impactites consist mainly of basement-derived clasts and impact melt particles, and coastalplain sediment clasts are underrepresented. Shocked quartz is common, and coesite and reidite are confirmed by Raman spectra. Silicate glasses have textures indicating immiscible melts at quench, and they are partly altered to smectite. Chrome spinel, baddeleyite, and corundum in silicate glass indicate high-temperature crystallization under silica undersaturation. Clast-rich impact melt rocks contain α- cristobalite and monoclinic tridymite. The impactites record an upward transition from slumped ground surge to melt-rich fallback from the ejecta plume. Basement-derived rocks include amphibolite-facies schists, greenschist(?)-facies quartz-feldspar gneiss blocks and subgreenschist-facies shale and siltstone clasts in polymict impact breccias, the amphibolite block, and the granite slab. The granite slab, underlying sand, and amphibolite block represent rock avalanches from inward collapse of unshocked bedrock around the transient crater rim. Gneissic and massive granites in the slab yield U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon dates of 615 ± 7 Ma and 254 ± 3 Ma, respectively. Postimpact heating was 7lt; 350 °C in the lower basementderived section based on undisturbed 40 Ar/ 39 Ar plateau ages of muscovite and < 150 <C in sand above the suevite based on 40 Ar/ 39 Ar age spectra of detrital microcline. © 2009 The Geological Society of America.
cited By 24
Keywords: Buildings; Corundum; Feldspar; Glass; Granite; Lead alloys; Mica; Quartz; Silicate minerals; Structural geology; Tectonics; Textures; Zircon; Amphibolite facies; Chesapeake bay impact structures; Crystalline target rocks; Detachment fault; High temperature crystallization; Sensitive high-resolution ion microprobe; Shocked quartz; Undersaturation; Crystalline rocks; breccia; crystalline rock; crystallization; Eocene; granite; impact structure; impactite; marine sediment; SHRIMP dating; Chesapeake Bay; United States

Evolution of crystalline target rocks and impactites in the chesapeake bay impact structure, ICDP-USGS eyreville B core - Horton Jr., J.W.; Kunk, M.J.; Belkin, H.E.; Aleinikoff, J.N.; Jackson, J.C.; Chou, I.-M. (Special Paper of the Geological Society of America, 2009)
The 1766-m-deep Eyreville B core from the late Eocene Chesapeake Bay impact structure includes, in ascending order, a lower basement-derived section of schist and pegmatitic granite with impact breccia dikes, polymict impact breccias, and cataclas tic gneiss blocks overlain by suevites and clast-rich impact melt rocks, sand with an amphibolite block and lithic boulders, and a 275-m-thick granite slab overlain by crater-fill sediments and postimpact strata. Graphite-rich cataclasite marks a detachment fault atop the lower basement-derived section. Overlying impactites consist mainly of basement-derived clasts and impact melt particles, and coastalplain sediment clasts are underrepresented. Shocked quartz is common, and coesite and reidite are confirmed by Raman spectra. Silicate glasses have textures indicating immiscible melts at quench, and they are partly altered to smectite. Chrome spinel, baddeleyite, and corundum in silicate glass indicate high-temperature crystallization under silica undersaturation. Clast-rich impact melt rocks contain α- cristobalite and monoclinic tridymite. The impactites record an upward transition from slumped ground surge to melt-rich fallback from the ejecta plume. Basement-derived rocks include amphibolite-facies schists, greenschist(?)-facies quartz-feldspar gneiss blocks and subgreenschist-facies shale and siltstone clasts in polymict impact breccias, the amphibolite block, and the granite slab. The granite slab, underlying sand, and amphibolite block represent rock avalanches from inward collapse of unshocked bedrock around the transient crater rim. Gneissic and massive granites in the slab yield U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon dates of 615 ± 7 Ma and 254 ± 3 Ma, respectively. Postimpact heating was 7lt; 350 °C in the lower basementderived section based on undisturbed 40 Ar/ 39 Ar plateau ages of muscovite and < 150 <C in sand above the suevite based on 40 Ar/ 39 Ar age spectra of detrital microcline. © 2009 The Geological Society of America.
cited By 24

Experimental alteration of artificial and natural impact melt rock from the Chesapeake Bay impact structure - Declercq, J.; Dypvik, H.; Aagaard, P.; Jahren, J.; Ferrell Jr., R.E.; Wright Horton Jr., J. (Special Paper of the Geological Society of America, 2009)
The alteration or transformation of impact melt rock to clay minerals, particularly smectite, has been recognized in several impact structures (e.g., Ries, Chicxulub, Mjølnir). We studied the experimental alteration of two natural impact melt rocks from suevite clasts that were recovered from drill cores into the Chesapeake Bay impact structure and two synthetic glasses. These experiments were conducted at hydrothermal temperature (265 °C) in order to reproduce conditions found in meltbearing deposits in the first thousand years after deposition. The experimental results were compared to geochemical modeling (PHREEQC) of the same alteration and to original mineral assemblages in the natural melt rock samples. In the alteration experiments, clay minerals formed on the surfaces of the melt particles and as fine-grained suspended material. Authigenic expanding clay minerals (saponite and Ca-smectite) and vermiculite/chlorite (clinochlore) were identified in addition to analcime. Ferripyrophyllite was formed in three of four experiments. Comparable minerals were predicted in the PHREEQC modeling. A comparison between the phases formed in our experiments and those in the cores suggests that the natural alteration occurred under hydrothermal conditions similar to those reproduced in the experiment. © 2009 The Geological Society of America.
cited By 7

Efficiency of individual CRL stations in seismic monitoring of the western gulf of corinth - Jansk'y, Jarom'ir; Zahradn'ik, Jiř'i; Plicka, Vladim'ir (Acta Geodynamica et Geomaterialia, 2009)
We study the efficiency of individual stations of the CRL seismic network in recording the seismic activity in the western Gulf of Corinth, Greece. The stations are located on both the northern and southern coast of the Gulf. The study is based on 5027 earthquakes recorded in 2001, separated into three groups, the southern, central and the northern one. The events were located using the HYPO71PC algorithm. It is shown that the stations significantly differ in their monitoring ability.

Experimental alteration of artificial and natural impact melt rock from the Chesapeake Bay impact structure - Declercq, J.; Dypvik, H.; Aagaard, P.; Jahren, J.; Ferrell Jr., R.E.; Wright Horton Jr., J. (Special Paper of the Geological Society of America, 2009)
The alteration or transformation of impact melt rock to clay minerals, particularly smectite, has been recognized in several impact structures (e.g., Ries, Chicxulub, Mjølnir). We studied the experimental alteration of two natural impact melt rocks from suevite clasts that were recovered from drill cores into the Chesapeake Bay impact structure and two synthetic glasses. These experiments were conducted at hydrothermal temperature (265 °C) in order to reproduce conditions found in meltbearing deposits in the first thousand years after deposition. The experimental results were compared to geochemical modeling (PHREEQC) of the same alteration and to original mineral assemblages in the natural melt rock samples. In the alteration experiments, clay minerals formed on the surfaces of the melt particles and as fine-grained suspended material. Authigenic expanding clay minerals (saponite and Ca-smectite) and vermiculite/chlorite (clinochlore) were identified in addition to analcime. Ferripyrophyllite was formed in three of four experiments. Comparable minerals were predicted in the PHREEQC modeling. A comparison between the phases formed in our experiments and those in the cores suggests that the natural alteration occurred under hydrothermal conditions similar to those reproduced in the experiment. © 2009 The Geological Society of America.
cited By 7
Keywords: Chlorite minerals; Clay alteration; Core drilling; Infill drilling; Rocks; Zeolites; Chesapeake bay impact structures; Geochemical modeling; Hydrothermal conditions; Hydrothermal temperature; Impact structures; Mineral assemblage; Suspended material; Synthetic glass; Clay minerals; authigenic mineral; experimental study; hydrothermal activity; hydrothermal alteration; hydrothermal deposit; hydrothermal system; impact structure; numerical model; smectite; suevite; Chesapeake Bay; United States

Sedimentary cycles of the Cretaceous Quantou - Nenjiang formations and Milankovitch cycles of the south hole of the SLCORE-I in the Songliao basin - Cheng, Rihui; Wang, Guodong; Wang, Pujun (Acta Geologica Sinica (English Edition), 2008)

Raw pollen data from piston core CON01-605-3 (Vydrino) - Demske, Dieter; Heumann, Georg; Granoszewski, Wojciech; Nita, Malgorzata; Mamakowa, Kazimiera; Tarasov, Pavel; Oberh{ansli, Hedi (GFZ Data Services, 2008)

Real-time drill mud gas logging at the USDP-4 drilling, Unzen volcano, Japan - Tretner, A.; Zimmer, M.; Erzinger, J.; Nakada, S.; Saito, M. (Journal of Volcanology and Geothermal Research, 2008)
During the Unzen conduit drilling project USDP-4, the gas phase dissolved in the drill mud was continuously analyzed. Starting from the volcano's north flank an almost complete gas profile was achieved to the final depth of 1995.75 m in July 2004. Limitations were given due to the extremely difficult drilling conditions. The highly fractured rock formation led to loss of drill mud circulation in the shallow parts of the drill hole. Significant fluid inflow horizons did not occur above 800 m (drill string length). Starting from that depth on, invading fluids were detected with the real-time gas monitoring system. Major variations in the mud gas composition occurred only below a depth of 1000 m. Of major importance are fluid inflow zones with high 3He/4He at depths of 1555 m (7.3 RA), 1755.5 m (7.48 RA) and 1977.4 m (6.21 RA). These values indicate a significant influence of fluids with mantle signature. Furthermore, enhanced methane, radon and helium concentrations were also detected at specific depth. These detected major fluid- and gas inflow horizons may be able to explain magmatic degassing processes, related to the Unzen's eruption mechanism. This is generally true for the main fluid inflow zones and especially for the detected inflows at 1555 m, 1755.5 m and 1977.4 m. Furthermore, a correlation between lithology and gas composition was observed. Higher H2S concentrations were detected while drilling in pyrite-rich rocks. Cracks and fissures as well as lithological changes are often correlated with increasing amounts of gas. Trends with depth, from a minor to a more magmatic influenced regime were observed together with a change in hydrothermal alteration of the surrounding rock. This corresponds with the magmatic conduit zone which was penetrated at a depth of 1600 m, and supports the model of a high influence of hydrothermal fluid, accelerating cooling and mineral alteration. © 2008 Elsevier B.V. All rights reserved.
cited By 14
Keywords: Dissolution; Drilling; Drills; Gas detectors; Gases; Landforms; Mud logging; Volcanoes; Well drilling; conduit drilling; continuous gas monitoring; Drill holes; Drill strings; Fractured rocks; Gas compositions; Gas monitoring; Gas-phase; He isotopes; Mud circulation; Unzen; USDP-4; Natural gas well drilling; cooling; degassing; drilling; helium isotope; hydrothermal alteration; hydrothermal fluid; mineral alteration; real time; volcanic eruption; well logging; Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano

Reply to 'Chicxulub impact predates K-T boundary: New evidence from Brazos, Texas' Comment by Schulte et al. - Keller, G.; Adatte, T.; Baum, G.; Berner, Z. (Earth and Planetary Science Letters, 2008)
cited By 13

Scientific drilling of the terrestrial Cretaceous Songliao Basin - Huang, Y.; Wang, C. (Scientific Drilling, 2008)
cited By 4

Response to comment on Determining chondritic impactor size from the marine osmium isotope record - Paquay, F.S.; Ravizza, G.E.; Dalai, T.K.; Peucker-Ehrenbrink, B. (Science, 2008)
Morgan argues that excursions in the marine Os record are of little value for estimating impactor size. This claim is based on computer simulations of the formation of the Chicxulub crater and distribution of the ejecta, which are difficult to validate. More important, by narrowly focusing on the Cretaceous-Tertiary event Morgan's comment misses the broader implications of our study.
cited By 1

Role of crustal fluids in triggering the West Bohemia/Vogtland earthquake swarms: Just what we know (a review) - Hor'alek, J.; Fischer, T. (Studia Geophysica et Geodaetica, 2008)
We summarise the results of seismological studies related to triggering mechanisms, driving forces and source processes of the West Bohemia/ Vogtland earthquake swarms with the aim to disclose the role of crustal fluids in the preparation, triggering and governing of the swarms. We present basic characteristics distinguishing earthquake swarms from tectonic mainshock-aftershock sequences and introduce existing earthquakes swarm models. From the statistical characteristics and time-space distribution of the foci we infer that self-organization is a peculiarity of West Bohemia/Vogtland swarms. We discuss possible causes of the foci migration in these swarms from the viewpoint of co-seismic and/or post-seismic stress changes and diffusion of the pressurized fluids, and we summarize hitherto published models of triggering the 2000-swarm. Attention is paid to the source mechanisms, particularly to their non-shear components. We consider possible causes of different source mechanisms of the 1997-and 2000-swarms and infer that pure shear processes controlled solely by the regional tectonic stress prevail in them, and that additional tensile forces may appear only at unfavourably oriented faults. On data from the fluid injection experiment at the HDR site Soultz (Alsace), we also show that earthquakes triggered by fluids can represent purely shear processes. Thus we conclude that increased pore pressure of crustal fluids in the region plays a key role in bringing the faults from the subcritical to critical state. The swarm activities are mainly driven by stress changes due to co-seismic and post-seismic slips, which considerably depend on the frictional conditions at the fault; crustal fluids keep the fault in a critical state. An open question still remains the cause of the repeatedly observed almost simultaneous occurrence of seismic activity in different focal zones in a wider area of West Bohemia/Vogtland. The analysis of the space-time relations of seismicity in the area between 1991 and 2007 revealed that during a significant part of this time span the seismicity was switching among distant focal zones. This indicates a common triggering force which might be the effect of an increase of crustal-fluid pore-pressure affecting a wider epicentral region. © Institute of Geophysics of the ASCR, v.v.i 2008.
Keywords: aftershock; crustal structure; earthquake epicenter; earthquake swarm; fluid; fluid injection; pore pressure; seismic source; seismicity; trigger mechanism

San Andreas Fault damage at SAFOD viewed with fault-guided waves - Li, Y.-G. (Geophysical Research Letters, 2008)
Highly damaged rocks within the San Andreas fault zone at Parkfield form a low-velocity waveguide for seismic waves, giving rise to fault-guided waves. Prominent fault-guided waves have been observed at the San Andreas Fault Observatory at Depth (SAFOD) site, including a surface array across the fault zone and a borehole seismograph placed in the SAFOD well at a depth of ∼2.7 km below ground. The resulting observations are modeled here using 3-D finite-difference methods. To fit the amplitude, frequency, and travel-time characteristics of the data, the models require a downward tapering, 30-40-m wide faultcore embedded in a 100-200-m wide jacket. Compared with the intact wall rocks, the core velocities are reduced by ∼40% and jacket velocities by ∼25%. Based on the depths of earthquakes generating guided waves, we estimate that the low-velocity waveguide along the fault at SAFOD extends at least to depths of ∼7 km, more than twice the depth reported in pervious studies. Copyright 2008 by the American Geophysical Union.
cited By 53
Keywords: Seismology; Waveguides; American Geophysical Union; Bore hole; Fault zones; Finite difference (FD); Guided waves; Low velocities; Parkfield; San Andreas Fault (SAF); Surface array; Travel time; Guided electromagnetic wave propagation; fault zone; finite difference method; San Andreas Fault; seismic data; seismic wave; seismograph; three-dimensional modeling; wave velocity; California; North America; Parkfield; United States

Seismicity and seismotectonics of West Saxony, Germany - New insights from recent seismicity observed with the Saxonian seismic network - Korn, M.; Funke, S.; Wendt, S. (Studia Geophysica et Geodaetica, 2008)
A new network of permanently recording seismic stations in West Saxony has considerably improved detection threshold, location accuracy and depth determination in this seismically active region. Between 2001 and 2007 more than 900 events have been located. Seismicity mainly occurred along a band stretching north-south between Leipzig and Vogtland/NW Bohemia area with local magnitudes ranging between 0.8 and 2.8. Seismicity clearly delineates the Leipzig-Regensburg (L-R) fault zone striking N-S, and the Gera-Jachymov (G-J) fault zone striking roughly NNW-SSE. The hypocentral depths can be divided into two depth ranges, one at depths below 10 km, and a second at less than 10 km depth that only extends S-N from the Vogtland until the crossing between L-R and G-J fault zones. A small earthquake sequence that occurred near Werdau/ Zwickau in August 2006 at almost the same epicenters as an earlier sequence 1997/98 seems to confirm this finding: a relative localization of 15 events with the double-difference technique clearly reveals two distinct subclusters at about 6 and 12-14 km depth. With the improved station coverage 33 new fault plane solutions from events along the L-R fault zone north of the swarmquake area could be determined from P-polarities and P/S ratios. They do not differ significantly from solutions in the Vogtland/NW-Bohemia area and are mostly compatible with a N-S oriented fault plane. Strike slip mechanisms with or without a dip slip component dominate. © Institute of Geophysics of the ASCR, v.v.i 2008.
Keywords: Central Europe; Eurasia; Europe; Germany; Saxony; earthquake epicenter; earthquake hypocenter; fault zone; seismicity; seismotectonics; source parameters; strike-slip fault

Raw pollen data from kasten core CON01-603-5 part1 (counts) - Demske, Dieter; Heumann, Georg; Granoszewski, Wojciech; Nita, Malgorzata; Mamakowa, Kazimiera; Tarasov, Pavel; Oberh{ansli, Hedi (GFZ Data Services, 2008)

Raw pollen data from kasten core CON01-605-5 (Vydrino) - Demske, Dieter; Heumann, Georg; Granoszewski, Wojciech; Nita, Malgorzata; Mamakowa, Kazimiera; Tarasov, Pavel; Oberh{ansli, Hedi (GFZ Data Services, 2008)

Phase relations and liquid lines of descent in hydrous ferrobasalt - Implications for the skaergaard intrusion and Columbia river flood basalts - Botcharnikov, R.E.; Almeev, R.R.; Koepke, J.; Holtz, F. (Journal of Petrology, 2008)
Crystallization experiments using a hydrous ferrobasalt as starting material, conducted at 200 MPa, 940-1200°C, at a wide range of water activities (0.1-1) and redox conditions (QFM - 3 to QFM + 4, where QFM is the quartz-fayalite-magnetite oxygen buffer), show that H2O influences significantly the differentiation history of ferrobasaltic magmas. A combination of our data with published experiments on dry ferrobasalt at 1 atm provides an extensive experimental database for modeling and quantifying crystallization and differentiation processes within a typical Fe-rich tholeiitic system under both dry and hydrous conditions. The addition of H2O decreases liquidus temperatures and changes significantly the proportions, temperature range and sequence of crystallizing mineral phases. The dry liquidus is at about 1170°C whereas the liquidus for H2O-saturated melts is at ∼1060°C. The main phases crystallizing from H2O-bearing ferrobasalt at the investigated conditions are olivine (OL), clinopyroxene (CPX), plagioclase (PL), magnetite (MT), hematite (HM), ilmenite (ILM) and amphibole (AM). The phase assemblage is similar to that of the dry system except for the presence of HM at extremely oxidizing conditions and AM at low temperatures ( < 950°C) and H2O-saturated conditions. The important observation made in this study is that the stability of Fe-Ti-oxides, and in particular MT, as well as the simultaneous coprecipitation of MT and ILM, are almost independent of the activity of H2O (a H2O) in the system, whereas the liquidus temperatures of the silicate minerals are dramatically depressed by increasing a H2O. The stabilities of oxides are controlled mainly by the redox conditions prevailing in the system. The most pronounced effect of a H2O on the liquidus temperatures of silicates is observed for PL, which shows a considerable delay in crystallization with progressive magma differentiation. Early crystallization of Fe-Ti-oxides in H2O-bearing ferrobasaltic compositions precludes any significant Fe enrichment during differentiation. As Fe enrichment is a characteristic feature of the Skaergaard intrusion, it implies that the Skaergaard parental magma did not contain considerable amounts of water. On the other hand, our experiments indicate that the differentiation of some ferrobasaltic series from the Columbia River flood basalt province might have occurred in magmatic systems containing significant amounts of volatiles (∼0.5-3 wt % H2O). © The Author 2008. Published by Oxford University Press. All rights reserved.
cited By 152
Keywords: crystallization; differentiation; experimental study; flood basalt; hydrothermal system; magma; modeling; precipitation (chemistry); redox conditions; silicate mineral; Arctic; Columbia River; Greenland; North America; Skaergaard Intrusion

Raw pollen data from kasten core CON01-603-5 part1 - Demske, Dieter; Heumann, Georg; Granoszewski, Wojciech; Nita, Malgorzata; Mamakowa, Kazimiera; Tarasov, Pavel; Oberh{ansli, Hedi (GFZ Data Services, 2008)

Rapid eclogitisation of the Dabie-Sulu UHP terrane: Constraints from Lu-Hf garnet geochronology - Schmidt, Alexander; Weyer, Stefan; Mezger, Klaus; Scherer, Erik E.; Xiao, Yilin; Hoefs, Jochen; Brey, Gerhard P. (Earth and Planetary Science Letters, 2008)
The Qinling-Dabie-Sulu orogenic belt in eastern China is one of the largest ultrahigh-pressure (UHP) terranes worldwide. Mineral Sm-Nd- and zircon U-Pb dating has been widely used to reveal the metamorphic history of this collisional orogen. However, the exact timing of the UHP metamorphic event(s) remains controversial and ages ranging from 245 Ma to 220 Ma have been suggested. We present high precision garnet-cpx Lu-Hf ages for six eclogites from the Dabie and Sulu areas. All ages fall in a narrow range between 219.6 and 224.4 Ma. Five samples define a mean age of 223.0 ± 0.9 Ma and one sample yields a slightly younger age of 219.6 ± 1.4 Ma. This very tight age range is particularly remarkable considering the large regional distribution of sample localities (on the order of 100 km at the time of UHP metamorphism) and the wide variety of garnet and eclogite chemical compositions represented. Two samples yield Sm-Nd ages that are indistinguishable from their Lu-Hf ages, albeit with larger uncertainties. The identical ages of eclogites from both the Dabie and the Sulu region emphasize their close genetic relationship and similar metamorphic histories. The Lu-Hf results appear to date a punctuated event of garnet growth. Alternatively, the Lu-Hf garnet ages may represent the onset of rapid, contemporaneous uplift and subsequent cooling. However, trace element zoning of Lu and Hf is still preserved in garnet porphyroblasts, even in those with a homogeneous major element distribution. Thus, complete re-equilibration of the Lu-Hf system during peak-temperature conditions probably did not occur. The garnet forming event can be placed toward the final stage of the UHP metamorphism, in agreement with some published U-Pb zircon ages. A possible trigger for this short-lived and widespread mineral growth episode may have been a fluid that became available at that stage of the metamorphic history. Although HREE-depleted patterns of older zircon grains may indicate the presence of an older generation of garnet, complete eclogitisation may have been inhibited during the major part of the prograde P-T path due to dry conditions during most of the UHP metamorphism. The uniform Lu-Hf (and Sm-Nd) ages of all investigated Dabie and Sulu eclogites suggest that garnet growth and thus possibly fluid availability were limited to a short time interval over a remarkably large regional scale. © 2008 Elsevier B.V. All rights reserved.
Keywords: Asia; China; Dabie-Sulu Belt; Eurasia; Far East; Chemical elements; Garnets; Geochronology; Hafnium; History; Land use; Lead alloys; Lutetium; Metamorphic rocks; Mineralogy; Minerals; Mining; Neodymium; Silica; Trace elements; Zircon; Chemical compositions; Dry conditions; Eastern China; eclogite; Eclogites; eclogitisation; Genetic relationships; HF systems; High-precision; Lu-Hf geochronology; Major elements; Mineral growth; Orogenic belts; Porphyroblasts; Re-equilibration; Regional distribution; Regional scales; Short time; Sm-Nd geochronology; Subsequent cooling; Temperature conditions; U-Pb dating; U-Pb zircon; UHP metamorphism; ultrahigh-pressure; chemical composition; eclogite; garnet; geochronology; hafnium; lutetium; orogenic belt; P-T-t path; terrane; ultrahigh pressure metamorphism; Silicate minerals

Preseismic velocity changes observed from active source monitoring at the Parkfield SAFOD drill site - Niu, F.; Silver, P.G.; Daley, T.M.; Cheng, X.; Majer, E.L. (Nature, 2008)
Measuring stress changes within seismically active fault zones has been a long-sought goal of seismology. One approach is to exploit the stress dependence of seismic wave velocity, and we have investigated this in an active source cross-well experiment at the San Andreas Fault Observatory at Depth (SAFOD) drill site. Here we show that stress changes are indeed measurable using this technique. Over a two-month period, we observed an excellent anti-correlation between changes in the time required for a shear wave to travel through the rock along a fixed pathway (a few microseconds) and variations in barometric pressure. We also observed two large excursions in the travel-time data that are coincident with two earthquakes that are among those predicted to produce the largest coseismic stress changes at SAFOD. The two excursions started approximately 10 and 2 hours before the events, respectively, suggesting that they may be related to pre-rupture stress induced changes in crack properties, as observed in early laboratory studies. ©2008 Macmillan Publishers Limited. All rights reserved.
cited By 219
Keywords: crack; earthquake; fault zone; measurement method; monitoring; rupture; seismic velocity; seismic wave; article; earthquake; environmental monitoring; measurement; pressure; priority journal; rock; stress; California; North America; San Andreas; San Andreas Fault Zone; United States

Preliminary achievement of the Chinese Cretaceous continental scientific drilling project-SK-I - Wang, C.; Feng, Z.; Wu, H.; Wang, P.; Kong, F.; Ren, Y.; Yang, G.; Wan, X.; Huang, Y.; Zhang, S. (Acta Geologica Sinica (English Edition), 2008)
To obtain the global environmental and climatic records is going to be the aim of the international scientific drilling projects. As a paradigm of greenhouse climate in the geological history, the Cretaceous provides significant records of the global climate changes under the condition of greenhouse climate. But currently, the international scientific drilling programs on the Cretaceous have been focusing on marine sediments; in contrast, no terrestrial records have been recovered by any scientific program. Newly completed SK I and SK II drilling located at the northern part of the Songliao Basin are supposed to be an important breakthrough in this domain. After more than one year effort, the drilling project has been finished, and 2485.89 in of the cores have been obtained, with a high recovery ratio of 96.46%, and that is the longest and continuous Cretaceous terrestrial core all over the world. A number of important investigations and achievement on the cores from SK I and SK II have been carried out. One of the most significant contributions of this program is to get records with a resolution of ten thousand year by the centimeter-grade sampling and analysis, instead of the traditional records on million years of timescale, and hopefully, its research can provide an important reference to solve currently global warming. Combined with raw data and upcoming results for the core, an integrated accomplishment of the scientific can be made in ten profiles such as biostratigraphy, chemostratigraphy, magnetostratigraphy and geomicrobiology and so on. The preliminary progress has been achieved on sedimentology, organic geochemistry, cyclostratigraphy, paleolimnology, geomicrobiology and reconstruction of Pco'2. All the cores will be preserved in professional storeroom after being cut for our researches, and scientists all over the world are highly welcome. The follow-up the SK II drilling program has also been selected as one of the candidate programs of ICDP (International Continental Drilling Project).
cited By 36
Keywords: biostratigraphy; chemostratigraphy; climate change; Cretaceous; cyclostratigraphy; Deep Sea Drilling Project; geomicrobiology; greenhouse gas; magnetostratigraphy; marine sediment; paleoclimate; paleoenvironment; reconstruction; sediment core; Asia; China; Eurasia; Far East; Songliao Basin

Post-impact carbonate deposition in the Chicxulub impact crater region, Yucatan Platform, Mexico - Urrutia-Fucugauchi, J.; P'erez-Cruz, L. (Current Science, 2008)
The Chicxulub crater has attracted considerable attention as one of the largest terrestrial impact structures and its association with the Cretaceous/Palaeogene boundary. Analyses of stable isotopes and magnetostratigraphic results for the Paleocene carbonate sequence in the Santa Elena borehole are used to investigate the post-impact sequence and estimate the age of basal sediments in the southern crater sector. Studies of impact ejecta and cover sediments and modelling of post-impact processes suggest erosion effects due to seawater back surge, block slumping and partial rim collapse of post-impact crater modification. Correlation of stable isotope patterns with the global pattern for marine carbonate sediments provides a stratigraphic framework for the basal Paleocene carbonates. Magnetic polarity constrains correlation of stable isotope variations with the reference Cenozoic isotopic data suggest that the first 17 m above the breccia-carbonate contact represents about 2.5 Ma. The stable isotope data suggest a gap of less than 0.1 Ma, whereas the magnetic polarity data (absence of reverse-polarity samples above impact breccia contact) suggest a gap up to 0.25 Ma.
cited By 12

Post 2000-swarm microearthquake activity in the principal focal zone of West Bohemia/Vogtland: Space-time distribution and waveform similarity analysis - Fischer, T.; Mich'alek, J. (Studia Geophysica et Geodaetica, 2008)
We present the pattern of seismic activity in the period between 2001 and 2007 for the Nov{a Kostel focal zone, which is recently the most active zone of the West-Bohemia/Vogtland earthquake swarm region. While the year 2001 was characterized by dying out of the 2000-swarm activity in the form of a few microswarms, almost no seismicity occurred in the period between 2002 and 2003. Since 2004 an elevated seismic activity occurs in the form of repeating microearthquake swarms. We used a relative location method to relate the hypocenter positions of the post-swarm activity to the geometry of the 2000-swarm cluster. We found that the activity has concentrated in several clusters, which have been repeatedly activated. Some clusters coincide with the position of the previous activity; the others have activated so far inactive deep segments at the southern edge of the Nov{a Kostel fault. Besides the shift of the hypocenters to the edges of the previously active area we observe a southward migration of the activity and an increase of maximum depths of earthquakes from 10 to 13 km. The waveform similarity analysis disclosed that some fault patches consist of only a single, repeatedly activated fault plane, while the others consist of multiple, differently oriented fault planes activated almost simultaneously. Most of the focal mechanisms are consistent with the geometry of hypocenters showing NNW-SSE trending steep fault planes with left-lateral strike-slip mechanisms and varying dip-slip component. © Institute of Geophysics of the ASCR, v.v.i 2008.
Keywords: earthquake hypocenter; earthquake swarm; microearthquake; seismic migration; seismicity; strike-slip fault; waveform analysis

Pliocaenicus seczkinae sp. nov., from lake el'gygytgyn in chukotka (Ne Russia) - Stachura-Suchoples, K.; Genkal, S.; Khursevich, G. (Diatom Research, 2008)
Pliocaenicus seczkinae Stachura-Suchoples, Genkal & Khursevich, sp. nov. was described from the phytoplankton samples and surface bottom deposits of Lake El'gygytgyn located in central Chukotka, NE Russia. The species is distinguished from the nominate variety of P. costatus mainly by the different structure of the valve face fultoportulae, which open externally with distinct short tubes and are flanked by two satellite pores. The tubes are located in small depressions within the radial rows of areolae. These observations have important implications for the entire genus, as up until now all known Pliocaenicus species had external fultoportulae openings lacking tubuli. Pliocaenicus seczkinae is the second known species of the genus Pliocaenicus to be found in modern populations. © 2008 Taylor & Francis Group, LLC.
cited By 10
Keywords: diatom; morphology; phytoplankton; taxonomy; Chukchi; Elgygytgyn Lake; Eurasia; Russian Federation; Pliocaenicus; Pliocaenicus costatus

Physical rock properties in and around a conduit zone by well-logging in the Unzen Scientific Drilling Project, Japan - Ikeda, R.; Kajiwara, T.; Omura, K.; Hickman, S. (Journal of Volcanology and Geothermal Research, 2008)
The objective of the Unzen Scientific Drilling Project (USDP) is not only to reveal the structure and eruption history of the Unzen volcano but also to clarify the ascent and degassing mechanisms of the magma conduit. Conduit drilling (USDP-4) was conducted in 2004, which targeted the magma conduit for the 1990-95 eruption. The total drilled length of USDP-4 was 1995.75 m. Geophysical well logging, including resistivity, gamma-ray, spontaneous potential, sonic-wave velocity, density, neutron porosity, and Fullbore Formation MicroImager (FMI), was conducted at each drilling stage. Variations in the physical properties of the rocks were revealed by the well-log data, which correlated with not only large-scale formation boundaries but also small-scale changes in lithology. Such variations were evident in the lava dike, pyroclastic rocks, and breccias over depth intervals ranging from 1 to 40 m. These data support previous models for structure of the lava conduit, in that they indicate the existence of alternating layers of high-resistivity and high P-wave velocity rocks corresponding to the lava dikes, in proximity to narrower zones exhibiting high porosity, low resistivity, and low P-wave velocity. These narrow, low-porosity zones are presumably higher in permeability than the adjacent rocks and may form preferential conduits for degassing during magma ascent. © 2008 Elsevier B.V.
cited By 18
Keywords: Acoustic logging; Acoustic wave velocity; Degassing; Drilling; Forestry; Gamma rays; Harvesting; Human computer interaction; Hydraulic structures; Levees; Lithology; Logging (forestry); Neutron logging; Oil well logging; Porosity; Rock drilling; Rocks; Scale (deposits); Spontaneous potential logging; Structural geology; Alternating layers; Conduit structure; Data support; High porosity; Log data; Low resistivity; Magma ascent; Neutron porosity; P-wave velocities; Physical Properties; Pyroclastic rocks; Rock properties; Scale formation; Scientific drilling; Spontaneous potential; Unzen volcano; Wave velocities; Well logging; Well drilling; degassing; drilling; lava; lithology; magma; permeability; rock property; volcanic eruption; wave velocity; well logging; Corrosion; Degassing; Deposits; Drilling; Hydraulic Structures; Logging; Porosity; Velocity; Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano

Permeability measurements on rock samples from Unzen Scientific Drilling Project Drill Hole 4 (USDP-4) - Watanabe, T.; Shimizu, Y.; Noguchi, S.; Nakada, S. (Journal of Volcanology and Geothermal Research, 2008)
Permeability measurement was made on five rock samples from USDP-4 cores. Rock samples were collected from the conduit zone and its country rock. One sample (C14-1-1) is considered as a part of the feeder dyke for the 1991-1995 eruption. The transient pulse method was employed under confining pressure up to 50 MPa. Compressional wave velocity was measured along with permeability. The measured permeability ranges from 10- 19 to 10- 17 m2 at the atmospheric pressure, and is as low as that reported for tight rocks such as granite. The permeability decreases with increasing confining pressure, while the compressional wave velocity increases. Assuming that pores are parallel elliptical tubes, the pressure dependence of permeability requires aspect ratio of 10- 4-10- 2 at the atmospheric pressure. The pore aperture is estimated to be less than 1 μm. The estimated aspect ratio and pore aperture suggest that connectivity of pores is maintained by narrow cracks. The existence of cracks is supported by the pressure dependence of compressional wave velocity. Narrow cracks ( < 1 μm) are observed in dyke samples, and they must have been created after solidification. Dyke samples do not provide us information of pore structures during degassing, since exsolved gas has mostly escaped and pores governing the gas permeable flow should have been lost. Both dyke and country rock samples provide us information of materials around ascending magma. Although the measured small-scale permeability cannot be directly applied to geological-scale processes, it gives constrains on studies of large-scale permeability. © 2008 Elsevier B.V. All rights reserved.
cited By 12
Keywords: Capillarity; Liquids; Rocks; Solids; Compressional wave velocities; Confining pressures; crack; Drill holes; drilled core; permeability; Permeability measurements; pore structure; Rock samples; Transient pulse; Unzen volcano; Rock drilling; atmospheric pressure; country rock; crack; degassing; dike; drilling; gas flow; granite; permeability; solidification; volcanic eruption; wave velocity; Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano

Periglacial sediment variations controlled by late Quaternary climate and lake level change at Elgygytgyn Crater, Arctic Siberia - Schwamborn, G.; Fedorov, G.; Schirrmeister, L.; Meyer, H.; Hubberten, H.-W. (Boreas, 2008)
Late Quaternary sediments in a permafrost environment recovered from the Elgygytgyn Impact Crater were studied to determine regional palaeoenvironmental variability and infer past water-level changes of the crater lake. Stratigraphic analysis of a 5m long permafrost core is based on various lithological (grain size, total organic carbon, magnetic susceptibility) and hydrochemical (oxygen isotope composition, major cation content) properties and pore ice content. The results show that alluvial sediments accumulated on top of cryogenically weathered volcanic rock. Changes in the hydrochemical properties reflect different stages of cryogenic weathering. The lithological characteristics mark the transition from an erosive site to a site with accumulation. This environmental change is linked to a relative lake level highstand at >13 000 yr BP, when a shoreline bar was formed leading to slope sedimentation. Lake level dropped by 4m during the Holocene. © 2007 The Authors, Journal compilation © 2007 The Boreas Collegium.
cited By 30
Keywords: climate change; glacial deposit; highstand; lake level; paleoenvironment; paleohydrology; Quaternary; sedimentation rate; weathering; Chukchi; Elgygytgyn Lake; Eurasia; Russian Federation; Siberia

Sequence stratigraphy and inferred relative sea-level change from the onshore British Jurassic - Hesselbo, Stephen P. (Proceedings of the Geologists' Association, 2008)
Sequence stratigraphy - the subdivision of successions into facies packages bounded by surfaces representing major shifts in depositional environment - has provided a systematic methodology for inference of relative sea-level change from vertical facies successions. In the present review, sequence stratigraphic work on exposures of British Jurassic successions is summarized. Resultant inferred relative sea-level curves for Early Jurassic and early Mid Jurassic successions show some strong similarities at the scale of ammonite zones between widely separated basins, implying sea-level change of at least regional extent or, alternatively, regionally co-ordinated changes in sediment supply. Also well developed are coeval stage-level influxes of sandy sediments into widely separated marine basins during the Late Pliensbachian, Late Toarcian-Aalenian and Oxfordian. Similarly, widespread synchronous shifts to more offshore facies are evident in the Early Pliensbachian, Early Toarcian, Early Callovian and Early Kimmeridgian. © 2008 Geologists' Association.
Keywords: Eurasia; Europe; United Kingdom; Western Europe; Ammonoidea; depositional sequence; facies; Jurassic; sea level change; sequence stratigraphy

PDF orientations in shocked quartz grains around the Chicxulub crater - Nakano, Y.; Goto, K.; Matsui, T.; Tada, R.; Tajika, E. (Meteoritics and Planetary Science, 2008)
We measured 852 sets of planar deformation features (PDFs) in shocked quartz grains in impactite samples of the Yaxcopoil (YAX-1) core and from 4 Cretaceous/Tertiary (K/T) boundary deposits: the Monaca, the Cacaraj'icara, and the Peñalver formations in Cuba, and DSDP site 536, within 800 km of the Chicxulub crater, in order to investigate variations of PDF orientations in the proximity of the crater. Orientations of PDFs show a broad distribution with peaks at ω 1013, π 1012, and ξ 1112, plus r, z 1011 orientations with minor c(0001), s1121, t2241 plus x5161, and m1010 plus a1120 orientations. Planar deformation features with c(0001) orientation are relatively more abundant in the proximity of the Chicxulub crater than in distal sites such as North America, the Pacific Ocean, and Europe. This feature indicates that in the proximity of the crater, part of the shocked quartz grains in the K/T boundary deposits were derived from the low shock pressure zones. Moreover, the orientations of PDFs with ξ 1122 plus r, z 1011 are high in our studied sites, and frequencies of these orientations decrease with increasing distance from the crater. On the other hand, absence of c(0001) and the rare occurrence of PDFs with ξ 1122 plus r, z 1011 orientations in the sample from the YAX-1 core that was taken at the top of the impactite layer of the Chicxulub crater suggests that the sampling horizon that reflects a certain cratering stage is also an important factor for variations in shocked quartz. © The Meteoritical Society, 2008.
cited By 5

Seismotectonic setting at the North Anatolian Fault Zone after the 1999 Mw=7.4 Izmit earthquake based on high-resolution aftershock locations - Bohnhoff, M.; Bulut, F.; G{org{un, E.; Milkereit, C.; Dresen, G. (Advances in Geosciences, 2008)
The most recent devastating earthquakes that occurred along the North Anatolian Fault Zone (NAFZ) in northwestern Turkey were the 1999 Izmit (Mw=7.4) and D{uzce (Mw=7.1) events. In this study we present a catalog of Izmit aftershock hypocenters that was deduced from a network covering the entire 140 km long rupture of the mainshock. 7348 events with a location accuracy better than 5 km are analysed. Aftershocks were observed along the entire ruptured segment along a 20 km wide band of activity. Events are clustered in distinct regions and dominantly occur at 5 to 15 km depth. The eastern termination of the Izmit rupture is characterized by a sharp and steeply dipping boundary exactly where the D{uzce mainshock initiated 87 days after the Izmit event. Relocation of the events using double-difference technology results in 4696 high-resolution hypocenters that allow resolving the internal structure of the seismically active areas with a resolution of 300 m (horizontal) and 400m (vertical). Below the Akyazi Plain, representing a small pull-apart structure at a triple junction of the NAFZ, we identify planes of activity that can be correlated with nodal planes of EW extensional normal faulting aftershocks. Along the easternmost Karadere-D{uzce segment we identify the down-dip extension of the Karadere fault that hosted about 1 m of right-lateral coseismic slip. At the easternmost rupture we correlate a cloud-type distribution of seismic activity with the largest aftershocks in this area, a subevent of the Izmit mainshock and the D{uzce mainshock that all have an almost identical focal mechanism. This part of the NAFZ is interpreted as a classical example of a seismic barrier along the fault.
cited By 4
Keywords: aftershock; coseismic process; earthquake event; fault zone; faulting; Kocaeli earthquake 1999; seismotectonics; tectonic setting; triple junction; Anatolia; Duzce; Eurasia; Kocaeli [Turkey]; Turkey

Viscosity of andesite melts and its implication for magma mixing prior to Unzen 1991-1995 eruption - Vetere, F.; Behrens, H.; Schuessler, J.A.; Holtz, F.; Misiti, V.; Borchers, L. (Journal of Volcanology and Geothermal Research, 2008)
The viscosity of an iron-bearing melt with composition similar to Unzen andesite was determined experimentally in the high (109-1010.5 Pa s) and low (5-1000 Pa s) viscosity range using a parallel plate viscometer and the falling sphere method, respectively. Falling sphere experiments were carried out in an internally heated argon pressure vessel and in a piston cylinder apparatus at 1323 to 1573 K and 200 to 2000 MPa. Creep experiments were performed in the temperature range of 747-845 K at 300 MPa. The water content of the melt varies from nominally dry to 6.2 wt.% H2O. The Fe2+/Fetot ratio was determined for each sample in the quenched glass using a colorimetric method. Pressure has minor influence on the viscosity compared with the effect of temperature, water content (main compositional parameter controlling the viscosity) or with the Fe2+/Fetot ratio (especially important at low water content of the melt). Based on our new viscosity data and literature data with measured Fe2+/Fetot ratio we propose a new empirical equation to estimate the viscosity η (in Pa s) of andesitic melts as a function of temperature T (in K), water content w (in wt.%) and Fe2+/Fetot ratio. The derived relationship reproduces the experimental data (87 in total) in the viscosity range from 100.5 to 1013 Pa s with a 1σ standard deviation of 0.17 log units. However, application of this calculation model is limited to Fe2+/Fetot Fetot > 0.3 and to temperatures above Tg. Moreover, in the high viscosity range the variation of viscosity with water content is constrained only by few experimental data and needs verification by additional measurements. The viscosity data are used to interpret mixing processes in the Unzen magma chamber prior to 1991-1995 eruption. We demonstrate that the viscosities of the rhyolite and andesite melts from the two end-member magmas are nearly identical prior and during mixing, enabling efficient magma mixing. © 2008 Elsevier B.V. All rights reserved.
cited By 37
Keywords: Igneous rocks; Iron; Mixing; Viscometers; Viscosity; andesite melt; dissolved water; magma mixing; redox state of iron; Unzen; Hydrodynamics; andesite; magma chamber; redox conditions; rhyolite; viscosity; volcanic eruption; water content; Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano

Session 15. The Evolution of the Biogeochemical Cycling of Phosphorus and Other Bioessential Elements - Pasek, Matthew; Papineau, Dominic; Harnmeijer, Jelte (Astrobiology, 2008)

The last 40 ka tephrostratigraphic record of Lake Ohrid, Albania and Macedonia: a very distal archive for ash dispersal from Italian volcanoes - Wagner, B.; Sulpizio, R.; Zanchetta, G.; Wulf, S.; Wessels, M.; Daut, G.; Nowaczyk, N. (Journal of Volcanology and Geothermal Research, 2008)
A 1075 cm long core (Lz1120) was recovered in the south-eastern part of the Lake Ohrid (Republics of Macedonia and Albania) and sampled for identification of tephra layers. Magnetic susceptibility investigations show rather high magnetic values throughout the core, with peaks unrelated to the occurrence of tephra layers but instead to the relative abundance of detrital magnetic minerals in the sediment. Naked-eye inspection of the core allowed us to identify of two tephra layers, at 896-897 cm and 1070-1075 cm. Laboratory inspection of the grain-size fraction > 125 μm allowed for the identification of a third cryptotephra at 310-315 cm. Major element analyses on glass shards of the tephra layers at 896-897 cm and 1070-1075 cm show a trachytic composition, and indicate a correlation with the regionally dispersed Y-3 and Y-5 tephra layers, dated at ca 30 and 39 cal ka BP. The cryptotephra at 310-315 cm has a mugearitic-benmoreitic composition, and was correlated with the FL eruption of Mt. Etna, dated at 3370 ± 70 cal yr BP. These ages are in agreement with five 14C AMS measurements carried out on plant remains and macrofossils from the lake sediments at different depths along the core. The recognition of distal tephra from Italian volcanoes allows us to link the Lake Ohrid succession to other archives located in the Mediterranean area and in eastern Europe. The benmoreitic-mugearitic tephra layer at 310-315 cm is the first recognition in the Balkan area of a distal ash deposit from a mid-intensity explosive eruption of Mt. Etna, as far as 600 km from the source. © 2007 Elsevier B.V. All rights reserved.
Keywords: Albania; Eurasia; Europe; Macedonia [Southern Europe]; Mediterranean Sea; Southern Europe; Backpropagation; Landforms; Magnetic materials; Magnetic properties; Magnetic susceptibility; Minerals; Sedimentation; Sedimentology; Volcanoes; biostratigraphy; dispersion; explosive volcanism; magnetic susceptibility; tephra; tephrochronology; trachyte; volcanic ash; volcanic eruption; volcanology; Albania/Macedonia; Italian volcanoes; Lake Ohrid; tephrochronology; tephrostratigraphy; Lakes

Origin and spatial distribution of gas at seismogenic depths of the San Andreas Fault from drill-mud gas analysis - Wiersberg, T.; Erzinger, J. (Applied Geochemistry, 2008)
Data are presented on the molecular composition of drill-mud gas from the lower sedimentary section (1800-3987 m) of the SAFOD (San Andreas Fault Observatory at Depth) Main Hole measured on-line during drilling, as well as C and H isotope data from off-line mud gas samples. Hydrocarbons, H2 and CO2 are the most abundant non-atmospheric gases in drill-mud when drilling seismogenic zones. Gas influx into the well at depth is related to the lithology and permeability of the drilled strata: larger formation gas influx was detected when drilling through organic-rich shales and permeable sandstones. The SAF (San Andreas Fault), encountered between approximately 3100 m and 3450 m borehole depth, is generally low in gas, but is encompassed by two gas-rich zones (2700-2900 m and below 3550 m) at the fault margins with enhanced 222Rn activities and distinct gas compositions. Within the fault, two interstratified gas-rich lenses (3150-3200 m and 3310-3340 m) consist of CO2 and hydrocarbons (upper zone), but almost exclusively of hydrocarbons (lower zone). The isotopic composition indicates an organic source of hydrocarbons and CO2 in the entire sedimentary section of the well. Hydrocarbons in sedimentary strata are partly of microbial origin down to ∼2500 m borehole depth. The contribution of thermogenic gas increases between ∼2500 m and 3200 m. Below ∼3200 m, hydrocarbons fully derive from thermal degradation of organic matter. The lack of H2 in the center of the fault and the high concentration of H2 in the fractured zones at the fault margins are consistent with H2 formation by interaction of water with fresh silica mineral surfaces generated by tectonic activities, however, this needs to be verified by laboratory experiments. Based on these studies, it is concluded that the fault zone margins consist of strata with enhanced permeability, separated by a low-permeability fault center. © 2008 Elsevier Ltd. All rights reserved.
cited By 64
Keywords: Boreholes; Drilling; Gas fuel analysis; Hydrocarbons; Sedimentation; Gas compositions; Seismogenic zones; Spatial distribution; Seismographs; analytical method; chemical composition; concentration (composition); gas; hydrocarbon; isotopic composition; measurement method; permeability; sandstone; seismic zone; spatial distribution; California; North America; San Andreas Fault Zone; United States

Yellowstone plume-continental lithosphere interaction beneath the Snake River Plain - Hanan, B.B.; Shervais, J.W.; Vetter, S.K. (Geology, 2008)
The Snake River Plain represents 17 m.y. of volcanic activity that took place as the North American continent migrated over a relatively fixed magma source, or hotspot. The identification of a clear seismic image of a plume beneath Yellowstone is compelling evidence that the Miocene to recent volcanism associated with the Columbia Plateau, Oregon High Lava Plains, Snake River Plain, Northern Nevada Rift and Yellowstone Plateau represents a single magmatic system related to a mantle plume. A remaining enigma is, why do radiogenic isotope signatures from basalts erupted over the Mesozoic-Paleozoic accreted terrains suggest a plume source while basalts erupted across the Proterozoic-Archean craton margin indicate an ancient subcontinental mantle lithosphere source? We show that ancient cratonic lithosphere like that of the Wyoming province superimposes its inherent isotopic composition on sublithospheric plume and/or asthenospheric melts. The results show that Yellowstone plume could have a radiogenic isotope composition similar to the mantle source of the early Columbia River Basalt Group and that the plume source composition has persisted to the present day. © 2008 The Geological Society of America.
cited By 71
Keywords: Lithosphere; Mantle plume; Volcanic activity; Basalt; Geochemistry; Isotopes; Tectonics; Volcanoes; Volcanic rocks; basalt; continental lithosphere; isotopic composition; lead isotope; mantle plume; mantle source; neodymium isotope; strontium isotope; Idaho; North America; Snake River Plain; United States

Wellbore-stability study for the SAFOD borehole through the San Andreas Fault - Paul, P.K.; Zoback, M. (SPE Drilling and Completion, 2008)
This paper presents a wellbore-stability study of the San Andreas Fault Observatory at Depth (SAFOD) research borehole located near Parkfield, California, USA. In the summer of 2005, the SAFOD borehole was drilled successfully through the active trace of the San Andreas Fault (SAF) in an area characterized by fault creep and frequent microearthquakes. In this study, we report how the analysis of wellbore failures in the upper part of the hole, geophysical logs, and a model for stress gradients in the vicinity of the fault were used to estimate the mud weights required to drill through the fault successfully. Because logging-while-drilling (LWD) acoustic caliper data and real-time hole-volume calculations both showed that relatively little failure occurred while drilling through the SAF, the predicted mud weight was successful in drilling a stable borehole. However, a six-arm caliper log, run after drilling was completed, indicates that there was deterioration of the borehole with time, which appears to be caused by fluid penetration around the borehole. The LWD-resistivity measurements show that essentially no fluid penetration occurred as the hole was being drilled. Because of this, the mud weight used was capable of maintaining a stable wellbore. However, the resistivity data obtained after drilling show appreciable fluid penetration with time, thus negating the effectiveness of the mud weight and leading to time-dependent wellbore failure. Using finite-element modeling (FEM), we show that mud penetration into the fractured medium around the borehole causes failure with time. Copyright © 2008 Society of Petroleum Engineers.
cited By 7
Keywords: Acoustic logging; Boring; Finite element method; Logging while drilling; Strike-slip faults; A-stable; California; Fault creep; Fluid penetration; Logging while drilling; Microearthquakes; Mud weights; San Andreas fault; Wellbore; Wellbore stability studies; Boreholes; borehole geophysics; borehole stability; creep; drilling; drilling fluid; finite element method; microearthquake; numerical model; San Andreas Fault; California; North America; Parkfield; United States

Well site selecting, core profile characteristics and distribution of the special lithology in CCSD-SK II - Gao, Youfeng; Wang, Pujun; Wang, Chengshan; Ren, Yanguang; Wang, Guodong; Liu, Wanzhu; Cheng, Rihui (Acta Geologica Sinica (English Edition), 2008)
CCSD-SK II is one of the two drilling wells of the Cretaceous Scientific Drilling Project in Songliao Basin. It is located at limb section of the nose-like structure in the Gulong sag of the central depression, north of Songliao Basin. Based on the detailed description on the cores from the second member bottom of Nenjiang Formation to the third member top of Quantou Formation in CCSD-SK II, the core profile was established, and five common lithology (mudstone, silty mudstone, mudy siltstone, siltstone and sandstone) and eight special lithology (dolomite, volcanic ash, oil shale, lime mudstone, marlite, recrystalline limestone, ostracode clastic limestone and ostracode limestone) were identified. 172 layers of special lithology in CCSD-SK II were recognized with a total thickness of 14. 516m. They are distributed mainly in the Qingshankou Formation, the second and third member of Yaojia Formation and Nenjiang Formation. The detailed description of the cores and identification on special lithology are the base for the next studies.
Keywords: Asia; China; Eurasia; Far East; Songliao Basin; Ostracoda; Chinese Continental Scientific Drilling Project; core logging; Cretaceous; drilling fluid; lithology; site selection

Water content and dry bulk density of piston core CON01-603-2 from CONTINENT Ridge - Oberh{ansli, Hedi (GFZ Data Services, 2008)

Water content and dry bulk density of pilot core to CON01-603-2, PANGAEA - Oberh{ansli, Hedi (GFZ Data Services, 2008)

Using open hole and cased-hole resistivity logs to monitor gas hydrate dissociation during a thermal test in the mallik 5L-38 research well, Mackenzie Delta, Canada - Anderson, B.I.; Collett, T.S.; Lewis, R.E.; Dubourg, I. (Petrophysics, 2008)
Gas hydrates, which are naturally occurring ice-like combinations of gas and water, have the potential to provide vast amounts of natural gas from the world's oceans and polar regions. However, producing gas economically from hydrates entails major technical challenges. Proposed recovery methods such as dissociating or melting gas hydrates by heating or depressurization are currently being tested. One such test was conducted in northern Canada by the partners in the Mallik 2002 Gas Hydrate Production Research Well Program. This paper describes how resistivity logs were used to determine the size of the annular region of gas hydrate dissociation that occurred around the wellbore during the thermal test in the Mallik 5L-38 well. An open-hole logging suite, run prior to the thermal test, included array induction, array laterolog, nuclear magnetic resonance and 1.1-GHz electromagnetic propagation logs. The reservoir saturation tool was run both before and after the thermal test to monitor formation changes. A cased-hole formation resistivity log was run after the test.Baseline resistivity values in each formation layer (Rt) were established from the deep laterolog data. The resistivity in the region of gas hydrate dissociation near the wellbore (Rxo) was determined from electromagnetic propagation and reservoir saturation tool measurements. The radius of hydrate dissociation as a function of depth was then determined by means of iterative forward modeling of cased-hole formation resistivity tool response. The solution was obtained by varying the modeled dissociation radius until the modeled log overlaid the field log. Pretest gas hydrate production computer simulations had predicted that dissociation would take place at a uniform radius over the 13-ft test interval. However, the post-test resistivity modeling showed that this was not the case. The resistivity-derived dissociation radius was greatest near the outlet of the pipe that circulated hot water in the wellbore, where the highest temperatures were recorded. The radius was smallest near the center of the test interval, where a conglomerate section with low values of porosity and permeability inhibited dissociation. The free gas volume calculated from the resistivity-derived dissociation radii yielded a value within 20 per cent of surface gauge measurements. These results show that the inversion of resistivity measurements holds promise for use in future gas hydrate monitoring. © 2008 Society of Petrophysicists and Well Log Analysts. All rights reserved.
cited By 11
Keywords: Cased-hole formation resistivity (CHFR); Depressurization; Electromagnetic propagation; Gas Hydrate production; Hydrate dissociation; logging suite; Magnetic (CE); Monitor (CO); Northern Canada; Openhole (OH); Polar Regions; Resistivity logs; Resistivity values; Technical challenges; Well bores; Density measurement (specific gravity); Dissociation; Electric logging; Electromagnetic logging; Gas industry; Gases; Hydrates; Hydration; Magnetic fields; Magnetic resonance; Magnetism; Monitoring; Nuclear magnetic logging; Nuclear magnetic resonance; Offshore oil well production; Oil well logging; Radioactivity logging; Resonance; Testing; Thermal logging; Well stimulation; Gas hydrates

Three-dimensional seismic attenuation structure around the SAFOD site, Parkfield, California - Bennington, N.; Thurber, C.; Roecker, S. (Bulletin of the Seismological Society of America, 2008)
We present models of the three-dimensional (3D) seismic attenuation structure, both Q p and Q s for a 16 km 2 area centered on the San Andreas Fault Observatory at Depth (SAFOD). The P- and S-wave t*-values used in the inversion were determined from local earthquake data recorded by seismic network and portable array stations within the Parkfield region by inverting arrival spectra for source parameters, t* and site response. Two techniques for determining the site response, the joint and alternating methods, were compared and it was found that the alternating method significantly underestimated site response variations. The t*-values were inverted to obtain 3D frequency-independent Q p and Q s models using 3D V p and V s models and associated event locations. A shallow low-Q area (Q p and Q s about 50-75) on the southwest edge of both models is attributed to the low-velocity Cenozoic sedimentary rocks that overlie the Salinian basement rock. A high-Q feature (Q p and Q s about 250 to 300) abuts this area and is interpreted as the Salinian basement. Adjacent to the San Andreas fault (SAF) trace, on its southwest side, there is a low-Q feature (Q p and Q s about 50-80) attributed to a wedge of sedimentary rocks; uniformly low Q p- and Q s-values suggest that the wedge is fluid rich. A low-Q basin feature (Q p and Q's about 50-75) on the northeast side of the SAF is interpreted as a fluid rich zone. Beneath this area there is a high-Q feature (Q p and Q s about 220-300), which may be caused by crack closure due to increased pressure with depth in the rocks of the Franciscan formation. Given these high Q-values, it seems unlikely that this area acts as a fluid pathway for fluids entering the fault zone from the east into the seismogenic zone of the SAF.
cited By 31
Keywords: Alternating methods; California; Cenozoic; Earthquake datum; Event locations; Fault zones; Fluid pathways; Low velocities; Portable arrays; Q-values; Salinian basements; San andreas faults; Seismic attenuations; Seismic networks; Seismogenic zones; Site response; Source parameters; Three-dimensional (3D); Buildings; Crack closure; Earthquakes; Fluids; Sedimentology; Tectonics; Three dimensional; Sedimentary rocks; data inversion; fault zone; P-wave; S-wave; San Andreas Fault; seismic attenuation; seismic data; seismic source; three-dimensional modeling; California; North America; Parkfield; United States

The potential of Lake Ohrid for long-term palaeoenvironmental reconstructions - Wagner, Bernd; Reicherter, Klaus; Daut, Gerhard; Wessels, Martin; Matzinger, Andreas; Schwalb, Antje; Spirkovski, Zoran; Sanxhaku, Mitat (Palaeogeography, Palaeoclimatology, Palaeoecology, 2008)
Lake Ohrid, at the Macedonian/Albanian border, was likely tectonically formed during the Tertiary and therefore is one of the oldest lakes in Europe. However, only a few studies exist concerning the potential of Lake Ohrid sediments for long-term palaeoenvironmental reconstructions within the scope of future potential deep-drilling campaigns. Therefore, as a first step, a transect of short surface sediment cores was investigated for chronology, physical properties, grain size, and biogeochemistry. The results were compared with information derived from a shallow hydro-acoustic seismic survey. The investigations indicate a rather uniform and bioturbated sedimentation in the central part of the lake basin with mean sedimentation rates of ca. 0.5-1 mm/year. The sediment composition is dominated by authigenetic carbonates. Diatom frustules or fragments form the major part of biogenic matter deposits, as indicated by the relatively high contents of biogenic opal and low contents of total organic carbon and total nitrogen. The shallow hydro-acoustic seismic survey indicates that horizons of sediment redeposition occur sporadically. Towards the shore of the lake, the sedimentation rate increases and sedimentation is increasingly influenced by local inflows or mass-movement processes triggered by tectonic activities. Thus Lake Ohrid has a high potential for palaeoenvironmental reconstructions on a multi-decadal scale and provides additional information concerning tectonic activity in the region. © 2007 Elsevier B.V. All rights reserved.
Keywords: Albania; Eurasia; Europe; Lake Ohrid; Macedonia [Southern Europe]; Southern Europe; Bacillariophyta; biogeochemistry; bioturbation; chronology; comparative study; core analysis; grain size; lacustrine deposit; mass movement; paleoenvironment; physical property; reconstruction; sedimentation rate; seismic survey; tectonics; Tertiary

The neglected side of speciation in ancient lakes: Phylogeography of an inconspicuous mollusc taxon in lakes Ohrid and Prespa - Schulthei{s, Roland; Albrecht, Christian; B{o{sneck, Ulrich; Wilke, Thomas (Hydrobiologia, 2008)
The morphologically remarkable endemic fauna within ancient lakes has received much attention in the literature. More inconspicuous taxa, however, often lack detailed molecular and morphometrical examination, although their proportion of the endemic fauna of an ancient lake must not be underestimated. Consequently, a better understanding of evolutionary patterns and processes within these lakes requires more knowledge about the often-neglected inconspicuous taxa. In the present study, we focus on the notoriously cryptic pea clam genus Pisidium (Bivalvia: Sphaeriidae). Though the genus is widely distributed, most endemic species are reported only from ancient lakes, including the European ancient sister lake system of Ohrid and Prespa on the Balkan Peninsula. Here we test for the first time hypotheses on the evolution of the endemic pea clams in this European biodiversity hotspot by molecular means. Combining a broad 16S phylogeny (comprising most European pea clam species), network analyses and morphometrical analyses, we found interesting biogeographical patterns and provide evidence for cryptic species in both lakes. Furthermore, we confirmed the proposed sister-species relationship of the endemics P. edlaueri in Lake Ohrid and P. maasseni in Lake Prespa, and we suggest scenarios of the endemic pea clam evolution within both lakes. The patterns of speciation found in the genus Pisidium are compared to patterns in morphologically distinct molluscan groups in lakes Ohrid und Prespa. © 2008 Springer Science+Business Media B.V.
Keywords: Eurasia; Europe; Lake Mikri Prespa; Lake Ohrid; Southern Europe; Bivalvia; Mollusca; Pisidium; Pisum sativum; Sphaeriidae (bivalves); Biodiversity; Electric network analysis; Graph theory; Network protocols; Sensor networks; endemic species; fauna; lake; mollusc; morphometry; phylogenetics; phylogeography; speciation (biology); taxonomy; Ancient lakes; Cryptic speciation; Morphometrics; Phylogenetics; Pisidium; Pisidium edlaueri; Pisidium maasseni; Lakes

The forming mechanism of Dolostone of Nengjiang Formation in Songliao Basin - Example from CCSD-SK II - Wang, Guodong; Cheng, Rihui; Wang, Pujun; Gao, Youfeng (Acta Geologica Sinica (English Edition), 2008)
The CCSD-SK is the first scientific drilling well of whole core Cretaceous rocks in the continent of China, which is composed of two drilling wells: CCSD-SK I in the north and CCSD-SK II in the south. Totally, 62 layers of bedded and ellipsoidal dolostone were identified in the Nenjiang Formation during the description of CCSD-SK II. Dolostone nodular occurs as lens in the vertical section, and interior of the nodular is characterized by foliation which converges at both lateral edges. Under microscopic observation, dolostone is grey in the core and bright at the rim, and marl has been replaced, locally forming leopard spot dolomite. All these features indicate that dolomite of the Nengjiang Formation was the product of lacustrine facies limestone during penecontemporaneous replacement. The forming mechanism of dolostone of the Nenjiang Formation was that under the setting of the marine transgression of Late Cretaceous in the Songliao Basin, marls brought by turbidity flow and extinction of ostracoda began to deposit during the replacement, thus forming the dolostone.
Keywords: Asia; China; Eurasia; Far East; Songliao Basin; Ostracoda; Panthera pardus; Cretaceous; dolomite; dolostone; drilling; formation mechanism; hydrocarbon reserve; marl; transgression; turbidity

Shock metamorphism of Bosumtwi impact crater rocks, shock attenuation, and uplift formation - Ferrière, Ludovic; Koeberl, Christian; Ivanov, Boris A.; Reimold, Wolf Uwe (Science, 2008)
Shock wave attenuation rate and formation of central uplifts are not precisely constrained for moderately sized complex impact structures. The distribution of shock metamorphism in drilled basement rocks from the 10.5-kilometer-diameter Bosumtwi crater, and results of numerical modeling of inelastic rock deformation and modification processes during uplift, constrained with petrographic data, allowed reconstruction of the pre-impact position of the drilled rocks and revealed a shock attenuation by ∼5 gigapascals in the uppermost 200 meters of the central uplift. The proportion of shocked quartz grains and the average number of planar deformation feature sets per grain provide a sensitive indication of minor changes in shock pressure. The results further imply that for moderately sized craters the rise of the central uplift is dominated by brittle failure.
Keywords: crater; deformation; numerical model; pressure; quartz; shock metamorphism; shock wave; uplift; article; calculation; Craterostigma; crystallography; priority journal; rock; scientific literature; shock wave

The formation of biogeochemical laminations in Lake Bosumtwi, Ghana, and their usefulness as indicators of past environmental changes - Shanahan, Timothy M.; Overpeck, Jonathan T.; Beck, J. Warren; Wheeler, C. Winston; Peck, John A.; King, John W.; Scholz, Christopher A. (Journal of Paleolimnology, 2008)
The sediments from Lake Bosumtwi, Ghana contain a unique record of fine-scale (mm to sub-mm) laminations, which will provide a valuable annual chronometer for reconstructing paleoenvironmental changes in West Africa covering much of the last 1 Ma. Comparisons of laminae counts to independent 210Pb dates and the rise in anthropogenic bomb radiocarbon support the interpretation of the laminations in the uppermost sediments as registering annual events. Radiocarbon dates on in-situ fish-bone collagen are in agreement with varve counts, further supporting the annual nature of our varve chronology. Over the instrumental period (1925-1999), dark-varve thickness measurements are correlated with local rainfall (r = 0.54) and appear able to resolve decadal-scale changes in precipitation. The relationship between varve thickness and rainfall provides support for our interpretation that dark-colored varve thickness records catchment runoff during the rainy season rather than dust flux during the dry season. Dark laminae alternate with organic and carbonate-rich light laminae formed during the fall period of enhanced productivity. Downcore, varves undergo significant microstratigraphic and geochemical variations, but retain the same pattern of alternating clastic and organic-rich laminae, providing support that the laminae may represent annual time markers for reconstructions of the deeper part of the record. © 2007 Springer Science+Business Media B.V.
Keywords: Africa; Ashanti; Ghana; Lake Bosumtwi; Sub-Saharan Africa; West Africa; biogeochemistry; collagen; comparative study; crater lake; environmental indicator; lacustrine deposit; lamination; lead isotope; paleoenvironment; precipitation assessment; radiocarbon dating; reconstruction; stratigraphy; varve

Testing two contrasting evolutionary patterns in ancient lakes: Species flock versus species scatter in valvatid gastropods of Lake Ohrid - Hauswald, Anne-Kathrin; Albrecht, Christian; Wilke, Thomas (Hydrobiologia, 2008)
Ancient lakes have long been recognized as hot spots of evolution and evolutionary theatres and they have significantly contributed to a better understanding of speciation and radiation processes in space and time. Yet, phylogenetic relationships of many ancient lake taxa, particularly invertebrate groups, are still unresolved. Also, the lack of robust morphological, anatomical, and phylogeographical data has largely prevented a rigorous testing of evolutionary hypotheses. For the freshwater gastropod genus Valvata-a group with a high degree of endemism in several ancient lakes-different evolutionary scenarios are suggested for different ancient lakes. Lake Baikal, for example, is inhabited by several endemic Valvata taxa that presumably do not form a monophyletic group. For such an evolutionary pattern, the term ancient lake species scatter is introduced here. In contrast, for the Balkan Lake Ohrid, workers previously suggested the presence of a monophyletic group of endemic Valvata species, that is, an ancient lake species flock. Sequence data of the mitochondrial cytochrome oxidase c subunit I gene (COI) from worldwide taxa, with a strong emphasis on Balkan species, are here used to test whether the putative Ohrid Valvata endemics represent an ancient lake species flock and to study patterns of speciation both on the Ohrid and the Balkan scale. The study reveals three distinct clades of endemic Valvata in Lake Ohrid. Monophyly of these taxa, however, is rejected, and they therefore do not represent an ancient lake species flock, but rather an ancient lake species scatter. Also, in contrast to many other gastropod groups in Lake Ohrid, the valvatids apparently did not radiate. Many Valvata taxa in ancient lakes are characterized by enhanced levels of shell complexity. However, it remains unclear whether these patterns are associated with ancient lake environments per se. It is here suggested that similarities in shell structure between North American and Balkan taxa might simply be due to convergent evolution. © 2008 Springer Science+Business Media B.V.
Keywords: Eurasia; Europe; Lake Mikri Prespa; Lake Ohrid; Southern Europe; Gastropoda; Invertebrata; Valvata; Valvatida; Digital signal processing; Shells (structures); evolutionary biology; freshwater ecosystem; gastropod; lake; phylogenetics; species flock; taxonomy; Ancient lake species flock; Ancient lake species scatter; Ancient lakes; Lake Ohrid; Lake Prespa; Valvata; Lakes

Temperature variations at Lake Qinghai on decadal scales and the possible relation to solar activities - Xu, Hai; Liu, Xiaoyan; Hou, Zhaohua (Journal of Atmospheric and Solar-Terrestrial Physics, 2008)
Temperature variations at Lake Qinghai, northeastern Qinghai-Tibet plateau, were reconstructed based on four high-resolution temperature indicators of the δ18O and the δ13C of the bulk carbonate, total carbonate content, and the detrended δ15N of the organic matter. There are four obvious cold intervals during the past 600 years at Lake Qinghai, namely 1430-1470, 1650-1715, 1770-1820, and 1920-1940, synchronous with those recorded in tree rings at the northeast Qinghai-Tibet plateau. The intervals of 1430-1470, 1650-1715, and 1770-1820 are consistent with the three coldest intervals of the Little Ice Age. These obvious cold intervals are also synchronous with the minimums of the sunspot numbers during the past 600 years, suggesting that solar activities may dominate temperature variations on decadal scales at the northeastern Qinghai-Tibet plateau. © 2007 Elsevier Ltd. All rights reserved.
Keywords: Atmospheric composition; Carbonates; Meteorology; Solar energy; Decadal scales; Solar activity; Sunspot; Temperature variation; Atmospheric temperature

Temperature memory gauge survey and estimation of formation temperature of the USDP-4 conduit hole at Unzen Volcano, Japan - Suto, Y.; Sakuma, S.; Takahashi, H.; Hatakeyama, N.; Henfling, J. (Journal of Volcanology and Geothermal Research, 2008)
The Unzen Scientific Drilling Project was initiated in 1999 to investigate a magma conduit that had recently fed a volcanic eruption. The conduit hole, USDP-4, was drilled to 810 m in 2003. In 2004, the hole was extended with intention of reaching the conduit at a drilled depth of about 2000 m. This objective was achieved, and the final measured depth of USDP-4 was 1995.75 m. A new temperature memory gauge for rotary drilling application was designed and developed for the project in order to measure borehole temperatures as often as possible in the expected high temperature environment near the conduit. Temperature ratings of the tool are up to 250 °C with dewar. A total of 10 surveys were conducted at depths of 1555-1995.75 m. This tool was used in six surveys, and borehole temperature data was successfully obtained from all surveys. Based on the measured temperatures, it is apparent that the thermal energy potential of the conduit regime (i.e. thermal supply from conduit) is not large compared to that of most known geothermal systems. Formation temperatures along the conduit hole were estimated from measured temperatures by using a borehole temperature simulator, which we developed and subsequently modified. According to the simulation, the maximum in the formation temperature profile is located at a depth of about 1970 m, and its temperature was about 170 °C before the drilling operation started. This maximum approximately coincides with the center of the conduit, but is surprisingly low for a system that ceased eruption only 9 years before the temperature survey. © 2008 Elsevier B.V.
cited By 8
Keywords: Drilling; Estimation; Gages; Geothermal energy; Geothermal fields; Surveys; Volcanoes; Bore hole; borehole temperature; Drilling operations; Energy potential; formation temperature; Geothermal systems; High-temperature environments; Measured depth; Rotary drilling; temperature memory gauge; temperature simulation; temperature survey; volcanic conduit; Volcanic eruptions; Boreholes; borehole logging; drilling; gauge; geothermal system; magma; temperature profile; volcanic eruption; Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano

Surge deposit misidentification at Spor Mountain, Utah and elsewhere: A cautionary message for Mars - Burt, D.M.; Knauth, L.P.; Wohletz, K.H.; Sheridan, M.F. (Journal of Volcanology and Geothermal Research, 2008)
Before base surges were described in association with nuclear blasts and explosive volcanic eruptions (especially, the 1980 eruption of Mount St. Helens, Washington), laminar and cross-bedded volcanogenic surge deposits were commonly misinterpreted as being of fluvial or aeolian origin. One well-documented example involves the water-laid tuffs in and near the Spor Mountain beryllium mine, Utah; other examples abound. In light of how frequently volcanogenic surge deposits have been misinterpreted on Earth, extreme caution is urged for Mars studies. Contrary to what has been claimed, the markedly cross-bedded, salty deposits at Meridiani Planum on Mars need not have been formed by a combination of aeolian and aqueous processes, and their contained hematitic spherules need not have formed as aqueous concretions. Given the lack of indications of volcanism in the vicinity, and the planet-wide abundance of impact craters, deposition by surges associated with distant impact targets consisting of brine-soaked, locally sulfidic regolith is a reasonable explanation for all features observed, especially if diagenesis and weathering are considered. The uniformly sized and shaped, Ni-enriched blue-gray hematitic spherules would then be some type of vapor condensation spherules (including accretionary lapilli). A similar interpretation is possible for deposits in the Home Plate area, Gusev Crater. Unlike on the dry and atmosphereless Moon, salty impact surge deposits containing spherules should be common, and well-preserved, on Mars. © 2008 Elsevier B.V.
cited By 3

Summary on China Cretaceous Scientific Drilling Engineering in Well-1 of Songliao Scientific Drilling (in Chinese with English abstract);中国白垩纪科学钻探松科一井(主井)钻探工程概要 - Zhu, Y.; Wang, W. (Exploration Engineering, 2008)

Studies of the working mechanism of cuttings suspension of drilling fluid in the main hole of well Songke-1 - Sun, Ping-he; Wu, Xiao-ming; Zhu, Yong-yi; Cai, Ji-hua (Drilling Fluid and Completion Fluid, 2008)

Storage conditions and evolution of andesitic magma prior to the 1991-95 eruption of Unzen volcano: Constraints from natural samples and phase equilibria experiments - Botcharnikov, R.E.; Holtz, F.; Almeev, R.R.; Sato, H.; Behrens, H. (Journal of Volcanology and Geothermal Research, 2008)
The compositions of homogenized melt inclusions trapped in plagioclase (Pl) microphenocrysts (40-200 μm length) from mafic enclaves within dacitic rocks erupted at Unzen volcano in 1991-95 were investigated. The SiO2 contents of the melt inclusions vary from 58 to 70 wt.% and Pl anorthite content is An50-70. The stability fields (in terms of temperature and water activity) of natural Pl and coexisting melts from the melt inclusions were estimated from data of phase equilibria experiments performed with a synthetic andesite composition at T = 900-1140 °C, P = 200 MPa, log fO2 = NNO-2-NNO, and water activity of about 0-1. This composition is representative of the average composition of mafic enclaves from the 1991-95 eruption and nearly identical to the composition of andesitic lavas from 1663 Unzen eruption. The temperatures and H2O melt concentrations, calculated using the compositions of coexisting Pl and melt inclusions, provide an estimation of the conditions of andesitic magma evolution within the mafic enclaves prior to eruption. The formation of melt inclusions in plagioclase microphenocrysts occurred at a maximum temperature of 1010 ± 35 °C for a melt containing 2 wt.% H2O and a minimum temperature of ∼ 945 °C ± 30 °C for a melt with ∼ 4 wt.% dissolved H2O. The compositional range of the melt inclusions indicates that the composition of the mafic enclave was not significantly contaminated by the host magma when inclusions were formed. The difference between concentrations of dissolved S (up to 0.06 wt.%) and Cl (up to 0.05 wt.%) in melt inclusions in Pl of mafic enclaves and concentrations of S ( < 0.005 wt.%) and Cl (0.05-0.11 wt.%) in melt inclusions in phenocrysts of the dacitic magma clearly implies that two distinct sources for S and Cl in the 1991-95 eruption of Unzen volcano need to be considered. Sulfur degassing was generated by a release of fluids from the high-temperature andesitic magma whereas Cl was degassed from the low-temperature silicic magma. The combination of data from melt inclusions and phase equilibria experiments indicates that the mafic end-member magma at Unzen was already partially crystallized and contained significant proportions (20 to 40 wt.%) of Pl and orthopyroxene (Opx) when melt inclusions started to form. Since clinopyroxene (Cpx) and magnetite (Mt) crystallize after Pl and Opx, the temperatures derived for the mafic end-member magma from coexisting Opx-Cpx and Ilm-Mt pairs do not represent temperatures near to the liquidus. Assuming that the injected mafic magma was nearly aphyric, its initial temperature might have been higher than estimated in previous studies. © 2008 Elsevier B.V. All rights reserved.
cited By 25
Keywords: Chemical engineering; Feldspar; Landforms; Silicate minerals; Silicon compounds; Volcanic rocks; Volcanoes; andesite; experiment; magma mixing; melt inclusions; storage conditions; Unzen volcano; volatiles; Phase equilibria; andesite; clinopyroxene; magma; magnetite; melt inclusion; phase equilibrium; volatile element; volcanic eruption; Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano

Stability analysis of Hawaiian Island flanks using insight gained from strength testing of the HSDP core - Thompson, N.; Watters, R.J.; Schiffman, P. (Journal of Volcanology and Geothermal Research, 2008)
Hawaiian Island flank failures are recognized as the largest landslide events on Earth, reaching volumes of several thousand cubic kilometers and lengths of over 200 km and occurring on an average of once every 100 000 years. The 3.1 km deep Hawaii Scientific Drilling Project (HSDP) enabled an investigation of the rock mass strength variations on the island of Hawaii [Schiffman, P., Watters, R.J., Thompson, N., Walton, A.W., 2006. Hyaloclastites and the slope stability of Hawaiian volcanoes: insights from the Hawaiian Scientific Drilling Project's 3-km drill core. Journal of Volcanology and Geothermal Research, 151 (1-3): 217-228]. This study builds on that of Schiffman et al. [Schiffman, P., Watters, R.J., Thompson, N., Walton, A.W., 2006. Hyaloclastites and the slope stability of Hawaiian volcanoes: Insights from the Hawaiian Scientific Drilling Project's 3-km drill core. Journal of Volcanology and Geothermal Research, 151 (1-3): 217-228] by considering more in-depth rock mass classification and strength testing methods of the HSDP core. Geotechnical core logging techniques combined with laboratory strength testing methods show that rock strength differences exist within the edifice. Comparing the rock strength parameters obtained from the various volcano lithologies identified weak zones, suggesting the possible location of future slip surfaces for large flank failures. Relatively weak rock layers were recognized within poorly consolidated hyaloclastite zones, with increases in strength based on degree of alteration. Subaerial and submarine basalt flows are found to be significantly stronger. With the aid of digital elevation models, cross-sections have been developed of key flank areas on the island of Hawaii. Limit equilibrium slope stability analyses are performed on each cross-section using various failure criteria for the rock mass strength calculations. Based on the stability analyses the majority of the slopes analyzed are considered stable. In cases where instability (i.e. failure) is predicted, decreased rock mass quality (strength) of the altered and highly poorly consolidated lithologies is found to have a significant influence. These lithologies are present throughout the Hawaiian Islands, representing potential failure surfaces for large flank collapses. Failure criterion input parameters are considered in sensitivity analyses as are the influences of certain external stability factors such as sea level variation and seismic loading. © 2007 Elsevier B.V. All rights reserved.
cited By 12
Keywords: Failure analysis; Landslides; Lithology; Sensitivity analysis; Volcanic rocks; Digital elevation models; Edifice stability; Hawaiian Island flank failures; Volcanic slope stability; Volcanoes; collapse; core logging; digital elevation model; failure analysis; limit analysis; rock mass classification; sensitivity analysis; slope stability; stability analysis; strength; testing method; Hawaiian Islands; Pacific islands; Pacific Ocean

Signature of long supercycles in the Pleistocene history of Asian limnic systems - Phedorin, Mikhail Albertovich; Fedotov, Andrey P.; Vorobieva, Svetlana S.; Ziborova, Galina A. (Journal of Paleolimnology, 2008)
The analysis of sediment chemistry and biota in drill cores from Lake Khubsugul in Mongolia (KDP-01) and Lake Baikal in Siberia (BDP-96/1), two great Eurasian freshwater lakes, detected prominent climate and biological events at 460-420 and 670 kyrs BP in addition to the orbital cycles of precession, tilt and eccentricity. The revealed long-term events were associated with notable changes in biodiversity and geography/landscapes, mainly in water budgets and weathering patterns. The span between 460-420 and 670 kyrs BP was the time when the climate and geographic conditions differed from those before and after these events. The corresponding 33-24 m (670-460 kyr) interval of the Khubsugul core lacked the usual signature of the Milankovitch glacial/interglacial cycles. Events of approximately these ages were found in some other continental ecosystems and in oceanic δ13C records. The two events may mark the phases of a 300-500-kyr long supercycle (or megastadial) in the evolution of continental ecosystems. Among other causes (e.g., regional tectonic events), this periodicity, being globally correlated, may be associated with the 400-kyr cycle of the Earth's orbital eccentricity. © 2007 Springer Science+Business Media B.V.
Keywords: Asia; Eurasia; Far East; Hvsgol Aymag; Lake Baikal; Lake Khubsugul; Mongolia; Russian Federation; biodiversity; biota; carbon isotope; eccentricity; glacial-interglacial cycle; paleolimnology; periodicity; Pleistocene; sediment chemistry; water budget

SHRIMP U –Pb dating, trace elements and the Lu –Hf isotope system of coesite-bearing zircon from amphibolite in the SW Sulu UHP terrane, eastern China - Liu, Fulai; Gerdes, Axel; Zeng, Lingsen; Xue, Huaimin (Geochimica et Cosmochimica Acta, 2008)
In this study, we link mineral inclusion data, trace element analyses, U –Pb age and Hf isotope composition obtained from distinct zircon domains of complex zircon to unravel the origin and multi-stage metamorphic evolution of amphibolites from the Sulu ultrahigh-pressure (UHP) terrane, eastern China. Zircon grains separated from amphibolites from the CCSD-MH drill hole (G12) and Niushan outcrop (G13) were subdivided into two main types based on cathodoluminescence (CL) and Laser Raman spectroscopy: big dusty zircons with inherited cores and UHP metamorphic rims and small clear zircons. Weakly zoned, grey-white luminescent inherited cores preserve mineral inclusions of Cpx+Pl+Ap±Qtz indicative of a mafic igneous protolith. Dark grey luminescent overgrowth rims contain the coesite eclogite-facies mineral inclusion assemblage Coe+Grt+Omp+Phe+Ap, and formed at T=732 –839°C and P=3.0 –4.0GPa. In contrast, white luminescent small clear zircons preserve mineral inclusions formed during retrograde HP quartz eclogite to LP amphibolite-facies metamorphism (T=612 –698°C and P=0.70 –1.05GPa). Inherited zircons from both samples yield SHRIMP 206Pb/238U ages of 695 –520Ma with an upper intercept age of 800±31Ma. The UHP rims yield consistent Triassic ages around 236 –225 and 239 –225Ma for G12 and G13 with weighted means of 229±3 and 231±3Ma, respectively. Small clear zircons from both samples give 206Pb/238U ages around 219 –210Ma with a weighted mean of 214±3Ma, interpreted as the age of retrograde quartz eclogite-facies metamorphism. Matrix amphibole from both samples indicate Ar –Ar ages of 209±0.7 and 207±0.7Ma, respectively, probably dating late amphibolite-facies retrogression. The data suggest subduction of Neoproterozoic mafic igneous rocks to UHP conditions in Middle Triassic (∼230Ma) times and subsequent exhumation to an early HP (∼214Ma) and a late LP stage (∼208Ma) over a period of ∼16 and 6Myr, respectively. Thus, early exhumation from a mantle depth of 120 –100km to about 60km occurred at an average rate of 0.3cm/y, while subsequent exhumation to a middle crustal level took place at approximately 0.54cm/y. These exhumation rates are considerably slower than those obtained for UHP rocks in the Dora Maira and Kokchetav massifs (2 –3cm/y). Based on similar P –T estimates and trace element and Hf isotope compositions, Sulu amphibolites can be identified as retrograde UHP eclogites. The εHf(800) of +8 implies a significant input from the depleted mantle to the Sulu –Dabie terrane during the middle Neoproterozoic. Overgrown rims are characterized by a distinct trace element composition with low Lu/Hf and Th/U and significantly higher 176Hf/177Hf ratios than inherited cores, consistent with formation during/after garnet (re-)crystallization and fractionation of the Lu –Hf system during UHP metamorphism. The combined dataset suggests homogenization of the 176Hf/177Hf ratio within the metamorphic mineral assemblage and during protolith formation. Observed variations are explained by mixing of material from both domains during laser ablation, e.g., due to partial recrystallization of inherited cores.

Paleomagnetic reorientation of San Andreas Fault Observatory at Depth (SAFOD) core - Par'es, J.M.; Schleicher, A.M.; Pluijm, B.A.; Hickman, S. (Geophysical Research Letters, 2008)
We present a protocol for using paleomagnetic analysis to determine the absolute orientation of core recovered from the SAFOD borehole. Our approach is based on determining the direction of the primary remanent magnetization of a spot core recovered from the Great Valley Sequence during SAFOD Phase 2 and comparing its direction to the expected reference field direction for the Late Cretaceous in North America. Both thermal and alternating field demagnetization provide equally resolved magnetization, possibly residing in magnetite, that allow reorientation. Because compositionally similar siltstones and fine-grained sandstones were encountered in the San Andreas Fault Zone during Stage 2 rotary drilling, we expect that paleomagnetic reorientation will yield reliable core orientations for continuous core acquired from directly within and adjacent to the San Andreas Fault during SAFOD Phase 3, which will be key to interpretation of spatial properties of these rocks. Copyright 2008 by the American Geophysical Union.
cited By 6
Keywords: Boreholes; Demagnetization; Magnetic fields; Magnetization; Sandstone; Tectonics; Fine-grained sandstones; Paleomagnetic analysis; Paleomagnetic reorientation; Geomagnetism; borehole; Cretaceous; demagnetization; paleomagnetism; remanent magnetization; San Andreas Fault; California; Central Valley [California]; North America; United States

Monte-Carlo simulation for estimating topographic disturbance to heat flow data - Ayunov, D.E.; Duchkov, A.D. (Russian Geology and Geophysics, 2008)
The Earth's surface topography disturbs the thermal field making measured superficial thermal gradients (heat flow) higher or lower than the deep value. Topographic disturbance can be removed from data by applying the respective correction. We estimated the effect of the rugged bottom of Lake Baikal on thermal gradients from the vicinity of boreholes BDP-93 and BDP-96 drilled in the lake sediments and deep borehole L-2 on the western shore of the South Baikal basin near Listvyanka Village. The corrections were computed using a Monte-Carlo simulation algorithm specially designed to quantify the effect of surface topography on the thermal field. The performance of the algorithm was checked by a test example. The corrections turned out to be vanishing in the area of underwater drilling but significant at L-2 where the thermal gradient in the upper 1 km of rocks was about 20% underestimated. The corrected heat flow in L-2 data increased from 50 to 60 mW/m2 and approached the values measured in the central South Baikal basin. © 2008.
Keywords: Eurasia; Lake Baikal; Russian Federation; Calluna vulgaris; algorithm; computer simulation; correction; digital elevation model; estimation method; heat flow; lacustrine deposit; Monte Carlo analysis; performance assessment; temperature gradient; topographic effect

Observations and interpretations at Vredefort, Sudbury, and Chicxulub: Towards an empirical model of terrestrial impact basin formation - Grieve, R.A.F.; Reimold, W.U.; Morgan, J.; Riller, U.; Pilkington, M. (Meteoritics and Planetary Science, 2008)
The structural, topographic and other characteristics of the Vredefort, Sudbury, and Chicxulub impact structures are described. Assuming that the structures originally had the same morphology, the observations/ interpretations for each structure are compared and extended to the other structures. This does not result in any major inconsistencies but requires that the observations be scaled spatially. In the case of Vredefort and Sudbury, this is accomplished by scaling the outer limit of particular shock metamorphic features. In the case of Chicxulub, scaling requires a reasoned assumption as to the formation mechanism of an interior peak ring. The observations/interpretations are then used to construct an integrated, empirical kinematic model for a terrestrial peak-ring basin. The major attributes of the model include: a set of outward-directed thrusts in the parautochthonous rocks of the outermost environs of the crater floor, some of which are pre-existing structures that have been reactivated during transient cavity formation; inward-directed motions along the same outermost structures and along a set of structures, at intermediate radial distances, during transient cavity collapse; structural uplift in the center followed by a final set of radially outward-directed thrusts at the outer edges of the structural uplift, during uplift collapse. The rock displacements on the intermediate, inward and innermost, outward sets of structures are consistent with the assumption that a peak ring will result from the convergence of the collapse of the transient cavity rim area and the collapse of the structural uplift. © The Meteoritical Society, 2008.
cited By 72

Concurrent evolution of ancient sister lakes and sister species: The freshwater gastropod genus Radix in lakes Ohrid and Prespa - Albrecht, Christian; Wolff, Christian; Gl{oer, Peter; Wilke, Thomas (Hydrobiologia, 2008)
Ancient sister lakes are considered to be ancient lakes lying in close geographic proximity, sharing a related origin and significant time of co-existence, usually having hydrological connection as well as a balanced degree of faunal overlap and distinctness. A paradigm for studying sister lake relationships are the ancient lakes Ohrid and Prespa in the Balkans, which are characterized by high degrees of endemicity. Three general patterns of endemic species can be distinguished for these lakes: (1) taxa that are endemic to either lake, with no close relatives in the respective sister lake, (2) closely related but distinct endemic taxa in both lakes (sister species) and (3) shared endemic taxa occurring in both lakes. In the present paper, two endemic freshwater pulmonate gastropod species, Radix relicta (Lake Ohrid) and R. pinteri (Lake Prespa), are used to study the evolution of presumed sister species based on biogeographical and comparative DNA data from world-wide Radix taxa. Phylogenetic, phylogeographical and parametric bootstrap analyses all suggest a sister group relationship of R. relicta and R. pinteri (pattern 2 of endemic diversity). Sister to these two taxa is the widespread R. ampla, which does not occur in the vicinity of lakes Ohrid and Prespa. The southern feeder spring complexes of Lake Ohrid are inhabited by another lineage (Radix sp. 1), which resembles Radix relicta in morphology/anatomy. For Lake Prespa, the widespread R. auricularia was reported in addition to the endemic R. pinteri. Comparative phylogenetic data favour a western Adriatic zoogeographical affinity of lakes Ohrid and Prespa over an Aegean-Anatolian faunal connection. The status of lakes Ohrid and Prespa as sister lakes is evaluated in the light of current knowledge on gastropod speciation and endemism in these hotspots of biodiversity. © 2008 Springer Science+Business Media B.V.
Keywords: Eurasia; Europe; Lake Mikri Prespa; Lake Ohrid; Southern Europe; Gastropoda; Radix (gastropod); Radix ampla; Radix auricularia; Radix sp.; Biodiversity; Nucleic acids; Organic acids; biodiversity; DNA; endemic species; evolution; freshwater ecosystem; gastropod; lake; phylogenetics; taxonomy; Ancient lake; Balkan; Lake Ohrid; Lake Prespa; Radix; Sister lakes; Lakes

Drilling fluid technology in the core drilling of SLCORE-I well (main well) (in Chinese with English abstract);[松科1井(主井)取心钻进钻井液技术] - Cai, J.; Gu, S.; Wu, X. (Coal Geology & Exploration, 2008)

Drilling and logging results of USDP-4 - Penetration into the volcanic conduit of Unzen Volcano, Japan - Sakuma, S.; Kajiwara, T.; Nakada, S.; Uto, K.; Shimizu, H. (Journal of Volcanology and Geothermal Research, 2008)
Borehole USDP-4 was drilled into the Unzen volcanic conduit 9 years after its last eruption. The sub-surface mechanism of eruption at Unzen Volcano was investigated by taking cores and by geophysical logging. The drilling operations were carried out in 2003-04, as a joint research program sponsored by the Japanese Government and the International Continental Scientific Drilling Program (ICDP). Borehole USDP-4 was a directional 6-1/4 in. (158.8 mm) borehole drilled from a site located on the northern slope of the volcano at 840 m above sea level, and was designed to penetrate into the conduit at sea level with a final deviation angle of over 70° from vertical and a borehole depth of 1800 m. An igneous dyke with a high likelihood of being the Unzen conduit was encountered at 1996 m depth and core samples were taken from that location. Chemical analysis of drill cores confirmed the identification of the conduit. Geophysical logging, including recording of gamma ray, resistivity, self-potential, density, neutron porosity, sonic velocity, and temperature suggested an alternation of dykes and flows in rock penetrated during the drilling, and in-hole pictures confirmed the lithologic identifications. Although borehole collapse and high temperature had been expected in the conduit, the actual drilling and logging into the conduit experienced no gas or fluid kick, and the measured temperatures within the dyke were below 200 °C. © 2008 Elsevier B.V. All rights reserved.
cited By 33
Keywords: Acoustic logging; Core drilling; Drilling; Forestry; Gamma rays; Geophysics; Harvesting; Ionizing radiation; Landforms; Logging (forestry); Neutron logging; Oceanography; Offshore oil wells; Rock drilling; Sea level; Volcanic rocks; Volcanoes; Water levels; Bore hole; Chemical-; Deviation angles; Drilling operations; extended reach borehole; Geophysical logging; High temperature; Neutron porosity; Research programs; scientific drilling; Self-potential; Sonic velocity; spot coring; Surface mechanism; tough logging; volcanic conduit; Volcanic conduits; Boreholes; borehole logging; chemical analysis; dike; geophysical survey; volcanic eruption; Drilling; Forestry; Gamma Rays; Harvesting; Ionizing Radiation; Logging; Oceanography; Volcanism; Water; Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano

Drill bit noise illuminates the san andreas fault - Vasconcelos, I.; Snieder, R.; Sava, P.; Taylor, T.; Maun, P.; Chavarria, A. (Eos, 2008)
cited By 6
Keywords: drill bit; fault; noise; San Andreas Fault; California; North America; San Andreas; United States

Deep drilling into the Chesapeake Bay impact structure - Gohn, G.S.; Koeberl, C.; Miller, K.G.; Reimold, W.U.; Browning, J.V.; Cockell, C.S.; Horton Jr., J.W.; Kenkmann, T.; Kulpecz, A.A.; Powars, D.S.; Sanford, W.E.; Voytek, M.A. (Science, 2008)
Samples from a 1.76-kilometer-deep corehole drilled near the center of the late Eocene Chesapeake Bay impact structure (Virginia, USA) reveal its geologic, hydrologic, and biologic history. We conducted stratigraphic and petrologic analyses of the cores to elucidate the timing and results of impact-melt creation and distribution, transient-cavity collapse, and ocean-water resurge. Comparison of post-impact sedimentary sequences inside and outside the structure indicates that compaction of the crater fill influenced long-term sedimentation patterns in the mid-Atlantic region. Salty connate water of the target remains in the crater fill today, where it poses a potential threat to the regional groundwater resource. Observed depth variations in microbial abundance indicate a complex history of impact-related thermal sterilization and habitat modification, and subsequent post-impact repopulation.
cited By 92

Deep drilling into the Chesapeake Bay impact structure - Gohn, G.S.; Koeberl, C.; Miller, K.G.; Reimold, W.U.; Browning, J.V.; Cockell, C.S.; Horton Jr., J.W.; Kenkmann, T.; Kulpecz, A.A.; Powars, D.S.; Sanford, W.E.; Voytek, M.A. (Science, 2008)
Samples from a 1.76-kilometer-deep corehole drilled near the center of the late Eocene Chesapeake Bay impact structure (Virginia, USA) reveal its geologic, hydrologic, and biologic history. We conducted stratigraphic and petrologic analyses of the cores to elucidate the timing and results of impact-melt creation and distribution, transient-cavity collapse, and ocean-water resurge. Comparison of post-impact sedimentary sequences inside and outside the structure indicates that compaction of the crater fill influenced long-term sedimentation patterns in the mid-Atlantic region. Salty connate water of the target remains in the crater fill today, where it poses a potential threat to the regional groundwater resource. Observed depth variations in microbial abundance indicate a complex history of impact-related thermal sterilization and habitat modification, and subsequent post-impact repopulation.
cited By 92
Keywords: sea water; abundance; deep drilling; Eocene; groundwater resource; impact structure; petrology; sedimentary sequence; sedimentation; stratigraphy; article; asthenospheric upwelling; biosphere; controlled study; Cretaceous; drill; hydrology; instrument sterilization; microbial growth; nonhuman; petrology; priority journal; sedimentation; stratigraphy; terrestrial surface waters; Bacteria; Ecosystem; Geologic Sediments; Heat; Salinity; Seawater; Time; Virginia; Chesapeake Bay; North America; United States; Virginia

CPCP: Colorado Plateau Coring Project - 100 million years of early Mesozoic climatic, tectonic, and biotic evolution of an epicontinental basin complex - Olsen, P.E.; Kent, D.V.; Geissman, J.W. (Scientific Drilling, 2008)
cited By 1

Coseismic fluid-rock interactions at high temperatures in the Chelungpu fault - Ishikawa, T.; Tanimizu, M.; Nagaishi, K.; Matsuoka, J.; Tadai, O.; Sakaguchi, M.; Hirono, T.; Mishima, T.; Tanikawa, W.; Lin, W.; Kikuta, H.; Soh, W.; et al. (Nature Geoscience, 2008)
Aqueous fluids are thought to have an essential role in faulting and the dynamic propagation of earthquake rupture. Fluid overpressure can affect earthquake nucleation and in a process termed thermal pressurization, pore fluid pressure produced by frictional heating can reduce the effective normal stress acting on the fault surface. This may lead to a marked reduction in fault strength during slip. However, the coseismic presence of fluids within slip zones and the role of fluids in dynamic fault weakening is still a matter of debate. Here we present compositions of major and trace elements as well as isotope ratios of core samples representing relatively undamaged as well as very fine-grained deformed material from three active zones of the Chelungpu fault, Taiwan. Depth profiles across the most intensely sheared bands that range in thickness from 2-15 cm exhibit sharp compositional peaks of fluid-mobile elements and of strontium isotopes. We suggest that high-temperature fluids (>350 C) derived from heating of sediment pore fluids during the earthquake interacted with material within the fault zone and mobilized the elements. The coseismic presence of high-temperature fluids under conditions of low hydraulic diffusivity within the fault zone is favourable for thermal pressurization. This effect may have caused a dynamic decrease of friction along the Chelungpu fault during the 1999 magnitude 7.6 Chi-Chi earthquake. © 2008 Macmillan Publishers Limited.
cited By 105

Corrigendum to Quaternary glaciation and hydrologic variation in the South American tropics as reconstructed from the Lake Titicaca drilling project [Quaternary Research 68 (2007) 410-420] (DOI:10.1016/j.yqres.2007.07.008) - Fritz, Sherilyn C.; Baker, Paul A.; Seltzer, Geoffrey O.; Ballantyne, Ashley; Tapia, Pedro; Cheng, Hai; Edwards, R. Lawrence (Quaternary Research, 2008)

Coring Drilling technology in Well-1 (main shaft) of Songliao scientific drilling - Yongyi, ZHU; Wenshi, Wang (Exploration Engineering (Rock & Soil Drilling and Tunneling), 2008)

Core-log integration studies in hole-A of Taiwan Chelungpu-fault Drilling Project - Wu, Y.-H.; Yeh, E.-C.; Dong, J.-J.; Kuo, L.-W.; Hsu, J.-Y.; Hung, J.-H. (Geophysical Journal International, 2008)
Taiwan Chelungpu-fault Drilling Project (TCDP) was initiated to understand the physical mechanisms involved in the large displacements of the 1999 Taiwan Chi-Chi earthquake. Continuous measurements of cores (including laboratory work) and a suite of geophysical downhole logs, including P- and S-wave sonic velocity, gamma ray, electrical resistivity, density, temperature, electrical borehole images and dipole-shear sonic imager, were acquired in Hole-A over the depth of 500-2003 m. Integrated studies of cores and logs facilitate qualitative and quantitative comparison of subsurface structures and physical properties of rocks. A total of 10 subunits were divided on the basis of geophysical characteristics. Generally, formation velocity and temperature increase with depth as a result of the overburden and thermal gradient, respectively. Gamma ray, resistivity, formation density, shear velocity anisotropy and density-derived porosity are primarily dependent on the lithology. Zones with changes of percentage of shear wave anisotropy and the fast shear polarization azimuth deduced from Dipole Shear-Imager (DSI) are associated with the appearance of fractures, steep bedding and shear zones. The fast shear wave azimuth is in good agreement with overall dip of the bedding (approximately 30° towards SE) and maximum horizontal compressional direction, particularly in the Kueichulin Formation showing strong shear wave velocity anisotropy. Bedding-parallel fractures are prevalent within cores, whereas minor sets of high-angle, NNW-SSE trending with N- and S-dipping fractures are sporadically distributed. The fault zone at depth 1111 m (FZA1111) is the Chi-Chi earthquake slip zone and could be a fluid conduit after the earthquake. The drastic change in fast shear wave polarization direction across the underlying, non-active Sanyi thrust at depth 1710 m reflects changes in stratigraphy, physical properties and structural geometry. © 2008 The Authors Journal compilation © 2008 RAS.
cited By 22
Keywords: azimuth; Chi-Chi earthquake 1999; displacement; earthquake mechanism; fault zone; S-wave; seismic anisotropy; seismicity; shear zone; Asia; Eurasia; Far East; Taiwan

Constraining the far-field in situ stress state near a deep south african gold mine - Lucier, A.M.; Zoback, M.D.; Heesakkers, V.; Reches, Z. (42nd U.S. Rock Mechanics - 2nd U.S.-Canada Rock Mechanics Symposium, 2008)
Researchers from The Natural Earthquake Laboratory in South African Mines (NELSAM) project are investigating the physics and mechanics of mining-induced earthquakes using the access to seismogenic depths provided by deep South African gold mines and the large number of seismic events that occur near these mines. To study these events, it is necessary to quantify the far-field stress field around the mine, determine how the presence of the mining excavation perturbs this stress field, and investigate how these mining-induced stress changes affect the pre-existing faults. In this paper, we develop and test a new technique for determining the far-field virgin state of stress near the TauTona gold mine. The technique we used to constrain the far-field stress state follows an iterative forward modeling approach that combines observations of drilling induced borehole failures in borehole images, boundary element modeling of the mining-induced stress perturbations, and forward modeling of borehole failures based on the results of the boundary element modeling. Following this approach, we determined that the state of stress is a normal faulting regime with principal stress orientations that are slightly deviated from vertical and. Modeling of breakout rotations and gaps in breakout occurrence associated with recent fault slip on critically stressed faults further confirmedthis stress state. ©2008, ARMA, American Rock Mechanics Association.
Keywords: African gold mine; Borehole images; Boundary elements; Far-field; Far-field stress; Fault slip; Forward modeling; Induced stress; Insitu stress; Mining excavation; Natural earthquake; Principal stress; Seismic event; State of stress; Stress field; Stress state; Virgin state; Earthquakes; Gold; Gold mines; Mines; Rock mechanics; Rocks; Stresses; Mining

Comparison of eruptive and intrusive samples from Unzen Volcano, Japan: Effects of contrasting pressure-temperature-time paths - Almberg, L.D.; Larsen, J.F.; Eichelberger, J.C.; Vogel, T.A.; Patino, L.C. (Journal of Volcanology and Geothermal Research, 2008)
Core samples from the conduit of Unzen Volcano, obtained only 9 years after cessation of the 1991-1995 eruption, exhibit important differences in physical characteristics and mineralogy, and subtle differences in bulk chemistry from erupted samples. These differences in the conduit samples reflect emplacement under a confining pressure where about half of the original magmatic water was retained in the melt phase, maintenance at hypersolidus temperature for some unknown but significant time span, and subsequent subsolidus hydrothermal alteration. In contrast, magma that extruded as lava underwent decompression to 1 atm with nearly complete loss of magmatic water and cooling at a sufficiently rapid rate to produce glass. The resulting hypabyssal texture of the conduit samples, while clearly distinct from eruptive rocks, is also distinct from plutonic suites. Given the already low temperature of the conduit (less than 200 °C, [Nakada, S., Uto, K., Yoshimoto, M., Eichelberger, J.C., Shimizu, H., 2005. Scientific Results of Conduit Drilling in the Unzen Scientific Drilling Project (USDP), Sci. Drill., 1, 18-22]) when it was sampled by drilling, this texture must have developed within a decade, and perhaps within a much shorter time, after emplacement. The fact that all trace-element concentrations of the conduit and the last-emplaced lava of the spine, 1300 m above it, are identical to within analytical uncertainty provides strong evidence that both were produced during the same eruption sequence. Changes in conduit magma that occurred between emplacement and cooling to the solidus were collapse of vesicles from less than or equal to the equilibrium value of about 50 vol.% to about 0.1 vol.%; continued resorption of quartz and reaction of biotite phenocrysts due to heating of magma prior to ascent by intruding mafic magma; breakdown of hornblende; and micro-crystallization of rhyolitic melt to feldspar and quartz. Subsolidus changes were deposition of calcite and pyrite, growth of sericite in anorthite-rich zones of plagioclase, and development of montmorillonite as an alteration product. Significant changes in bulk composition were depletion of Mg, Fe and Na and enrichment in C and S. These changes were due mainly to the breakdown of hornblende and plagioclase, and addition of carbonate and pyrite, respectively. The identical concentrations of REEs in the conduit and surface lava are consistent with low water to rock ratios during alteration. This suggests to us that despite convective hydrothermal removal of heat from the conduit, chemical open-system effects were limited to early loss of magmatic water and later addition of magmatic CO2 and SO2 and/or H2S streaming up the conduit from deeper levels. © 2008 Elsevier B.V.
cited By 8
Keywords: Calcite; Carbonate minerals; Clay minerals; Cooling; Crystallography; Dewatering; Drilling; Feldspar; Heating; Landforms; Lithology; Metallic glass; Mica; Mineralogy; Minerals; Ore deposit geology; Oxide minerals; Physical chemistry; Product development; Pyrites; Quartz; Rate constants; Silicate minerals; Sodium; Sulfate minerals; Textures; Trace elements; Volcanic rocks; Volcanoes; Analytical uncertainties; Bulk compositions; Chemical-; Confining pressures; crystallization texture; decompression experiments; Element concentrations; Equilibrium value; Hydrothermal alterations; Low temperature; Magmatic water; Melt phase; phase equilibria; Physical characteristics; Plutonic suites; Pressure-temperature-time paths; Rapid rate; Rhyolitic; Scientific results; Sericite; Subsolidus; System effects; Time span; Unzen; vesicularity; Cooling water; confining pressure; drilling; emplacement; hydrothermal alteration; igneous intrusion; lava; magmatic differentiation; phase equilibrium; trace element; volcanic eruption; Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano

Dry bulk density and water content of piston core CON01-605-3 from Vydrino - Oberh{ansli, Hedi (GFZ Data Services, 2008)

Comment on the paper Chicxulub impact predates K-T boundary: New evidence from Brazos, Texas by Keller et al. (2007) - Schulte, P.; Speijer, R.P.; Brinkhuis, H.; Kontny, A.; Claeys, P.; Galeotti, S.; Smit, J. (Earth and Planetary Science Letters, 2008)
cited By 13

Character and origin of lithofacies in the conduit of Unzen volcano, Japan - Goto, Yoshihiko; Nakada, Setsuya; Kurokawa, Masaru; Shimano, Taketo; Sugimoto, Takeshi; Sakuma, Sumio; Hoshizumi, Hideo; Yoshimoto, Mitsuhiro; Uto, Kozo (Journal of Volcanology and Geothermal Research, 2008)

Biot-type scattering effects in gas hydrate-bearing sediments - Rubino, J.G.; Ravazzoli, C.L.; Santos, J.E. (Journal of Geophysical Research: Solid Earth, 2008)
This paper studies the energy conversions that take place at discontinuities within gas hydrate-bearing sediments and their influence on the attenuation of waves traveling through these media. The analysis is based on a theory recently developed by some of the authors, to describe wave propagation in multiphasic porous media composed of two solids saturated by a single-phase fluid. Real data from the Mallik 5L-38 Gas Hydrate Research well are used to calibrate the physical model, allowing to obtain information about the characteristics of the cementation between the mineral grains and gas hydrates for this well. Numerical experiments show that, besides energy conversions to reflected and transmitted classical waves, significant fractions of the energy of propagating waves may be converted into slow-waves energy at plane heterogeneities within hydrated sediments. Moreover, numerical simulations of wave propagation show that very high levels of attenuation can take place in the presence of heterogeneous media composed of zones with low and high gas hydrate saturations with sizes smaller or on the order of the wavelengths of the fast waves at sonic frequencies. These attenuation levels are in very good agreement with those measured at the Mallik 5L-38 Gas Hydrate Research Well, suggesting that these scattering-type effects may be a key-parameter to understand the high sonic attenuation observed at gas hydrate-bearing sediments. Copyright 2008 by the American Geophysical Union.
cited By 5
Keywords: Biot theory; experimental study; gas hydrate; heterogeneous medium; numerical model; porous medium; single-phase flow; wave attenuation; wave propagation; wavelength

Assembly and concept of a web-based GIS within the paleolimnological project CONTINENT (Lake Baikal, Russia) - Heim, Birgit; Klump, Jens; Oberh{ansli, Hedi; Fagel, Nathalie (Journal of Paleolimnology, 2008)
Web-based Geographical Information Systems (GIS) are excellent tools within interdisciplinary and multi-national geoscience projects to exchange and visualize project data. The web-based GIS presented in this paper was designed for the paleolimnological project 'High-resolution CONTINENTal paleoclimate record in Lake Baikal' (CONTINENT) (Lake Baikal, Siberia, Russia) to allow the interactive handling of spatial data. The GIS database combines project data (core positions, sample positions, thematic maps) with auxiliary spatial data sets that were downloaded from freely available data sources on the world wide web. The reliability of the external data was evaluated and suitable new spatial datasets were processed according to the scientific questions of the project. GIS analysis of the data was used to assist studies on sediment provenance in Lake Baikal, or to help answer questions such as whether the visualization of present-day vegetation distribution and pollen distribution supports the conclusions derived from palynological analyses. The refined geodata are returned back to the scientific community by using online data publication portals. Data were made citeable by assigning persistent identifiers (DOI) and were published through the German National Library for Science and Technology (TIB Hannover, Hannover, Germany). © 2007 Springer Science+Business Media B.V.
Keywords: Eurasia; Lake Baikal; Russian Federation; catchment; data set; GIS; paleoclimate; paleolimnology; palynology; plant; population distribution

Archaeabacterial lipids in drill core samples from the Bosumtwi impact structure, Ghana - Escala, Marina; Rosell-Mel'e, Antoni; Fietz, Susanne; Koeberl, Christian (Meteoritics and Planetary Science, 2008)
Meteorite impacts are associated with locally profound effects for microorganisms living at the terrestrial surface and the subsurface of the impact zone. The Bosumtwi crater in Ghana (West Africa) is a relatively young (1.07 Myr) structure with a rim-to-rim diameter of about 10.5 km. In a preliminary study targeting the subsurface microbial life in the impact structure, seven samples of the impact breccia from the central uplift of the Bosumtwi crater were analyzed for the presence of typical archaeal membrane-lipids (GDGTs). These have been detected in four of the samples, at a maximum depth of 382 m below the lake surface, which is equivalent to 309 m below the surface sediment. The concentration of the GDGTs does not show a trend with depth, and their distribution is dominated by GDGT-O. Possible origins of these lipids could be related to the soils or rocks predating the impact event, the hydrothermal system generated after the impact, or due to more recent underground water transport. © The Meteoritical Society, 2008.

AntiSloughing Drilling Fluid in Main Well bore of SLCORE-I Well (in Chinese with English abstract); [松科1井(主井)防塌钻井液技术] - Cai, J.; Wu, X.; Zhu, Y.; Gu, S.; Li, X; Wang, W. (Petroleum Drilling Techniques, 2008)

Ancient Lake Ohrid: Biodiversity and evolution - Albrecht, Christian; Wilke, Thomas (Hydrobiologia, 2008)
Worldwide ancient lakes have been a major focal point of geological, biological, and ecological research, and key concepts in, for example, evolutionary biology are partly based on ancient lake studies. Ancient lakes can be found on most continents and climate zones with most actual or putative ancient lakes in Europe being restricted to the Balkan Region. The arguably most outstanding of them is the oligotrophic and karstic Lake Ohrid, a steep-sided graben of rift formation origin situated in the central Balkans. Here, an attempt is made to summarize current knowledge of the geological, limnological, and faunal history of Lake Ohrid. Additionally, existing data on biodiversity and endemism in Lake Ohrid are updated and evaluated, and patterns and processes of speciation are reviewed in the context of the Ohrid watershed, including its sister lake, Lake Prespa. Whereas the geological history of the Ohrid Graben is relatively well studied, there is little knowledge about the limnological and biotic history of the actual lake (e.g., the age of the extant lake or from where the lake first received its water, along with its first biota). Most workers agree on a time frame of origin for Lake Ohrid of 2-5 million years ago (Mya). However, until now, the exact limnological origin and the origin of faunal or floral elements of Lake Ohrid remain uncertain. Two largely contrasting opinions either favour the theory of de novo formation of Lake Ohrid in a dry polje with a spring or river hydrography or a palaeogeographical connection of Lake Ohrid to brackish waters on the Balkan Peninsula. Whereas neither theory can be rejected at this point, the data summarized in the current review support the de novo hypothesis. An assessment of the fauna and flora of Lake Ohrid confirms that the lake harbours an incredible endemic biodiversity. Despite the fact that some biotic groups are poorly studied or not studied at all, approximately 1,200 native species are known from the lake, including 586 animals, and at least 212 species are endemic, including 182 animals. The adjusted rate of endemicity is estimated at 36% for all taxa and 34% for Animalia. In terms of endemic biodiversity, Lake Ohrid is with these 212 known endemic species and a surface area of 358 km2 probably the most diverse lake in the world, taking surface area into account. Preliminary phylogeographical analyses of endemic Lake Ohrid taxa indicate that the vast majority of respective sister taxa occurs in the Balkans and that therefore the most recent common ancestors of Ohrid- and non-Ohrid species likely resided in the region when Lake Ohrid came into existence. These data also indicate that there is relatively little faunal exchange and overlap between Lake Ohrid and its sister lake, Lake Prespa, despite the fact that the latter lake is a major water supplier for Lake Ohrid. Studies on selected species flocks and scatters, mostly in molluscs, point towards the assumption that only few lineages originally colonized Lake Ohrid from the Balkans and that the majority of endemic species seen today probably started to evolve within the lake during the early Pleistocene. Within the Ohrid watershed, endemism occurs at different spatial and taxonomic scales, ranging from species endemic to certain parts of Lake Ohrid to species endemic to the whole watershed and from subspecies to genus level and possibly beyond. Modes of speciation in the Ohrid watershed are largely affected by its degree of isolation. Observational evidence points towards both allopatric (peripatric) and parapatric speciation. Though sympatric speciation within a habitat is conceivable, so far there are no known examples. Today, the lake suffers from increasing anthropogenic pressure and a creeping biodiversity crisis. Some endemic species presumably have already gone extinct, and there are also indications of invasive species penetrating Lake Ohrid. The comparatively small size of Lake Ohrid and the extremely small range of many endemic species, together with increasing human pressure make its fauna particularly vulnerable. It is thus hoped that this review will encourage future research on the ecology and evolutionary biology of the lake's taxa, the knowledge of which would ultimately help protecting this unique European biodiversity hot spot. © 2008 Springer Science+Business Media B.V.
Keywords: Animalia; Mollusca; Mya; Animals; Biodiversity; Offshore oil well production; Rivers; biodiversity; evolution; evolutionary biology; lake; limnology; native species; Pleistocene; speciation (biology); Ancient lake; Balkans; Endemism; Geology; Lake Ohrid; Lake Prespa; Limnology; Sister lakes; Speciation; Lakes

An 85-ka record of climate change in lowland Central America - Hodell, David A.; Anselmetti, Flavio S.; Ariztegui, Daniel; Brenner, Mark; Curtis, Jason H.; Gilli, Adrian; Grzesik, Dustin A.; Guilderson, Thomas J.; M{uller, Andreas D.; Bush, Mark B.; Correa-Metrio, Alexander; Escobar, Jaime; et al. (Quaternary Science Reviews, 2008)
Drill cores obtained from Lake Pet'en Itz'a, Pet'en, Guatemala, contain a ∼85-kyr record of terrestrial climate from lowland Central America that was used to reconstruct hydrologic changes in the northern Neotropics during the last glaciation. Sediments are composed of alternating clay and gypsum reflecting relatively wet and dry climate conditions, respectively. From ∼85 to 48 ka, sediments were dominated by carbonate clay indicating moist conditions during Marine Isotope Stages (MIS) 5a, 4, and early 3. The first gypsum layer was deposited at ∼48 ka, signifying a shift toward drier hydrologic conditions and the onset of wet-dry oscillations. During the latter part of MIS 3, Pet'en climate varied between wetter conditions during interstadials and drier states during stadials. The pattern of clay-gypsum (wet-dry) oscillations during the latter part of MIS 3 (∼48-23 ka) closely resembles the temperature records from Greenland ice cores and North Atlantic marine sediment cores and precipitation proxies from the Cariaco Basin. The most arid periods coincided with Heinrich Events when cold sea surface temperatures prevailed in the North Atlantic, meridional overturning circulation was reduced, and the Intertropical Convergence Zone (ITCZ) was displaced southward. A thick clay unit was deposited from 23 to 18 ka suggesting deposition in a deep lake, and pollen accumulated during the same period indicates vegetation consisted of a temperate pine-oak forest. This finding contradicts previous inferences that climate was arid during the Last Glacial Maximum (LGM) chronozone (21±2 ka). At ∼18 ka, Pet'en climate switched from moist to arid conditions and remained dry from 18 to 14.7 ka during the early deglaciation. Moister conditions prevailed during the warmer Bolling-Allerod (14.7-12.8 ka) with the exception of a brief return to dry conditions at ∼13.8 ka that coincides with the Older Dryas and meltwater pulse 1A. The onset of the Younger Dryas at 12.8 ka marked the return of gypsum and hence dry conditions. The lake continued to precipitate gypsum until ∼10.3 ka when rainfall increased markedly in the early Holocene. © 2008 Elsevier Ltd. All rights reserved.
Keywords: Arctic; Atlantic Ocean; Atlantic Ocean (North); Cariaco Basin; Caribbean Sea; Central America; Greenland; Guatemala [Central America]; Lake Peten Itza; Peten; Drilling; Glaciers; Gypsum; Isotopes; Sediments; Soil moisture; climate change; climate conditions; deglaciation; gypsum; Holocene; hydrodynamics; ice core; interstadial; intertropical convergence zone; Last Glacial Maximum; last glaciation; lowland environment; Neotropical region; oceanic circulation; precipitation (chemistry); precipitation intensity; proxy climate record; reconstruction; sediment core; stratigraphy; Younger Dryas; Central America; Drill cores; Terrestrial climate; Climate change

A layered model of the upper crust in the Aigion region of Greece, inferred from arrival times of the 2001 earthquake sequence - Novotn'y, O.; Jansk{u, J.; Plicka, V.; Lyon-Caen, H. (Studia Geophysica et Geodaetica, 2008)
The western part of the Gulf of Corinth attracts attention due to its seismically active fault system and considerable seismic hazard. Detailed studies of the seismic activity of the region have been carried out especially as part of the so-called Corinth Rift Laboratory (CRL) Project. For standard earthquake locations, the CRL uses the HYPO algorithm and a special structural model that is composed of homogeneous layers (Rigo et al., 1996). This model was derived from a passive seismic experiment in a broader area around the western part of the Gulf. A significant part of the seismic activity is concentrated close to the town of Aigion, which was damaged by a strong earthquake in 1995. A sequence of smaller earthquakes occurred to the south of this town in the year 2001. In the present paper, we have used this sequence to derive an improved structural model for the region in the vicinity of the town of Aigion. This new model is based on the minimization of travel-time residuals. In particular, we used arrival times from a subset of 88 events recorded by at least 5 stations of the southern part of the CRL network, had magnitudes of over 2.3, and were recorded at the nearest station (station code AIO). A variant of the method of conjugate gradients has been used for this purpose. In comparison with the model derived by Rigo et al. (1996), the new model is characterized by a higher νP/νS velocity ratio and by higher velocities to a depth of about 7 km. The new model was derived with the aim to get more accurate locations of future events in the vicinity of the town of Aigion. © Institute of Geophysics of the ASCR, v.v.i 2008.
Keywords: Eurasia; Europe; Greece; Gulf of Corinth; Ionian Sea; Mediterranean Sea; Southern Europe; active fault; algorithm; arrival time; crustal structure; earthquake event; gradient analysis; layered medium; modeling; seismic velocity; travel time; upper crust; urban area

A deep crustal fluid channel into the San Andreas Fault system near Parkfield, California - Becken, M.; Ritter, O.; Park, S.K.; Bedrosian, P.A.; Weckmann, U.; Weber, M. (Geophysical Journal International, 2008)
Magnetotelluric (MT) data from 66 sites along a 45-km-long profile across the San Andreas Fault (SAF) were inverted to obtain the 2-D electrical resistivity structure of the crust near the San Andreas Fault Observatory at Depth (SAFOD). The most intriguing feature of the resistivity model is a steeply dipping upper crustal high-conductivity zone flanking the seismically defined SAF to the NE, that widens into the lower crust and appears to be connected to a broad conductivity anomaly in the upper mantle. Hypothesis tests of the inversion model suggest that upper and lower crustal and upper-mantle anomalies may be interconnected. We speculate that the high conductivities are caused by fluids and may represent a deep-rooted channel for crustal and/or mantle fluid ascent. Based on the chemical analysis of well waters, it was previously suggested that fluids can enter the brittle regime of the SAF system from the lower crust and mantle. At high pressures, these fluids can contribute to fault-weakening at seismogenic depths. These geochemical studies predicted the existence of a deep fluid source and a permeable pathway through the crust. Our resistivity model images a conductive pathway, which penetrates the entire crust, in agreement with the geochemical interpretation. However, the resistivity model also shows that the upper crustal branch of the high-conductivity zone is located NE of the seismically defined SAF, suggesting that the SAF does not itself act as a major fluid pathway. This interpretation is supported by both, the location of the upper crustal high-conductivity zone and recent studies within the SAFOD main hole, which indicate that pore pressures within the core of the SAF zone are not anomalously high, that mantle-derived fluids are minor constituents to the fault-zone fluid composition and that both the volume of mantle fluids and the fluid pressure increase to the NE of the SAF. We further infer from the MT model that the resistive Salinian block basement to the SW of the SAFOD represents an isolated body, being 5-8km wide and reaching to depths >7km, in agreement with aeromagnetic data. This body is separated from a massive block of Salinian crust farther to the SW. The NE terminus of resistive Salinian crust has a spatial relationship with a near-vertical zone of increased seismic reflectivity ∼15km SW of the SAF and likely represents a deep-reaching fault zone. © 2008 The Authors Journal compilation © 2008 RAS.
cited By 74
Keywords: aeromagnetic survey; crustal structure; data interpretation; data inversion; electrical conductivity; electrical resistivity; lower crust; magnetotelluric method; San Andreas Fault; seismic reflection; transform fault; two-dimensional modeling; California; North America; Parkfield; United States

Numerical model of the hydrothermal system beneath Unzen Volcano, Japan - Fujimitsu, Y.; Ehara, S.; Oki, R.; Kanou, R. (Journal of Volcanology and Geothermal Research, 2008)
Drilling of the volcanic conduit in the Unzen Scientific Drilling Project (USDP) was completed in 2004. Some conduit materials of the 1990-95 eruption were encountered at the bottom of Well USDP-4 (150 m below sea level), and a bottom temperature of about 200 °C was estimated using logging data, although before drilling a temperature of about 700 °C had been inferred. Accordingly, conduit cooling from the initial temperature (850 °C) to the estimated temperature (about 200 °C) was evaluated by numerical simulation. The drilling provides constraints for the numerical model. The drilling indicates that the N-S width of the conduit of the latest eruption is 20 to 30 m and that it occupies a zone of about 300 m, which includes conduits of past eruptions. The process of cooling in the conduit, from an initial temperature of 850 °C in 1995 (the end of the eruption) to 200 °C in 2004 (completion of the conduit drilling), was replicated in models with permeabilities of 1 and 10 mdarcys. This result demonstrates that a highly permeable volcanic body surrounding a small conduit is required to explain the estimated bottom temperature. Our study also aimed to use a numerical simulation to construct a comprehensive hydrothermal model beneath Unzen Volcano. There are four large geothermal systems in the Shimabara Peninsula (Obama hot springs, Unzen fumarolic field, Shimabara hot springs and the West Unzen High Temperature Body [WUHTB]). Three pressure sources (Sources A, B and C from shallow to the deep) were determined by geodetic data during the 1990-95 eruption. Source C is located at about 8 km deep at WUHTB, and is considered to be a magma body. We attempted to explain the existence of the four geothermal systems from the large-scale structures (the topography of the Shimabara Peninsula and Unzen Graben) and the various heat sources. We first set a heat source around Source C and changed its position and size. This numerical model produced the upflow zones at the Obama and Shimabara hot springs and WUHTB; however, the Unzen fumarolic field became a recharge area. This result indicates that another heat source is required to explain the Unzen fumarolic field and that two heat sources beneath WUHTB and the Unzen fumarolic field are involved in the formation of the four hydrothermal systems in the Shimabara Peninsula. © 2008 Elsevier B.V. All rights reserved.
cited By 7
Keywords: Computer simulation; Cooling; Drilling; Estimation; Geothermal fields; Geothermal prospecting; Geothermal springs; Geothermal wells; Hot springs; Landforms; Numerical methods; Oceanography; Offshore oil well production; Offshore oil wells; Oil well logging; Sea level; Springs (components); Temperature; Volcanic rocks; Volcanoes; Water levels; Well logging; Bottom temperature; Fumarolic field; Geodetic data; geothermal fluid; Geothermal systems; heat source; Heat sourcing; High temperature; Hydro-thermal systems; hydrothermal system; Initial temperature; Large-scale structures; Logging data; numerical model; Numerical modelling; Numerical simulations; Recharge area; Shimabara Peninsula; Unzen Volcano; Volcanic conduits; Well drilling; heat source; hydrothermal fluid; hydrothermal system; magma; numerical model; thermal spring; volcanic eruption; Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Shimabara Peninsula; Unzen Volcano

Drilling the North Anatolian Fault - Dresen, Georg; Bohnhoff, Marco; Aktar, Mustafa; Eyidogan, Haluk (Scientific Drilling, 2008)
cited By 3

Climatic, Tectonic, and Biotic Evolution in Continental Cores: Colorado Plateau Coring Project Workshop; St. George, Utah, 13 –16 November 2007 - Olsen, Paul E.; Kent, Dennis V.; Geissman, John W. (Eos, Transactions American Geophysical Union, 2008)
A workshop was convened in St. George, Utah, to advance planning for the Colorado Plateau Coring Project (CPCP). The vast continental basins of the southwestern United States, particularly well exposed on the Colorado Plateau and its environs, contain one of the richest stratigraphic records of early Mesozoic age (between roughly 145 and 250 million years ago). This time period was punctuated by two of the major mass extinctions in the past 550 million years and witnessed the evolutionary appearance of the modern biota and dramatic climate changes on the continents. Since the mid-nineteenth century, classic studies of these basins, their strata, and their fossils have made this sequence instrumental in framing our context for the early Mesozoic world. Nonetheless, striking ambiguities in temporal resolution, uncertainties in global correlations with other early Mesozoic strata, and major doubts about latitudinal position still hamper testing of the major competing climatic, biotic, and tectonic hypotheses.

Dynamic modeling suggests terrace zone asymmetry in the Chicxulub crater is caused by target heterogeneity - Collins, G.S.; Morgan, J.; Barton, P.; Christeson, G.L.; Gulick, S.; Urrutia, J.; Warner, M.; W{unnemann, K. (Earth and Planetary Science Letters, 2008)
We investigate the cause of terrace zone asymmetry in the Chicxulub impact crater using dynamic models of crater formation. Marine seismic data acquired across the crater show that the geometry of the crater's terrace zone, a series of sedimentary megablocks that slumped into the crater from the crater rim, varies significantly around the offshore half of the crater. The seismic data also reveal that, at the time of impact, both the water depth and sediment thickness varied with azimuth around the impact site. To test whether the observed heterogeneity in the pre-impact target might have affected terrace zone geometry we constructed two end-member models of upper-target structure at Chicxulub, based on the seismic data at different azimuths. One model, representing the northwest sector, had no water layer and a 3-km thick sediment layer; the other model, representing the northeast sector, had a 2-km water layer above a 4-km sediment layer. Numerical models of vertical impacts into these two targets produced final craters that differ substantially in terrace zone geometry, suggesting that the initial water depth and sediment thickness variations affected the structure of the terrace zone at Chicxulub. Moreover, the differences in terrace zone geometry between the two numerical models are consistent with the observed differences in the geometry of the terrace zone at different azimuths around the Chicxulub crater. We conclude that asymmetry in the pre-impact target rocks at Chicxulub is likely to be the primary cause of asymmetry in the terrace zone. © 2008 Elsevier B.V. All rights reserved.
cited By 96

Impact ejecta and carbonate sequence in the eastern sector of the Chicxulub crater - Urrutia-Fucugauchi, J.; Chavez-Aguirre, J.M.; P'erez-Cruz, L.; Rosa, J.L. (Comptes Rendus - Geoscience, 2008)
The Chicxulub 200 km diameter crater located in the Yucatan platform of the Gulf of Mexico formed 65 Myr ago and has since been covered by Tertiary post-impact carbonates. The sediment cover and absence of significant volcanic and tectonic activity in the carbonate platform have protected the crater from erosion and deformation, making Chicxulub the only large multi-ring crater in which ejecta is well preserved. Ejecta deposits have been studied by drilling/coring in the southern crater sector and at outcrops in Belize, Quintana Roo and Campeche; little information is available from other sectors. Here, we report on the drilling/coring of a section of ∼34 m of carbonate breccias at 250 m depth in the Valladolid area (120 km away from crater center), which are interpreted as Chicxulub proximal ejecta deposits. The Valladolid breccias correlate with the carbonate breccias cored in the Peto and Tekax boreholes to the south and at similar radial distance. This constitutes the first report of breccias in the eastern sector close to the crater rim. Thickness of the Valladolid breccias is less than that at the other sites, which may indicate erosion of the ejecta deposits before reestablishment of carbonate deposition. The region east of the crater rim appears different from regions to the south and west, characterized by high density and scattered distribution of sinkholes. © 2008 Acad'emie des sciences.
cited By 30

Neural network analysis of crosshole tomographic images: The seismic signature of gas hydrate bearing sediments in the Mackenzie Delta (NW Canada) - Bauer, K.; Pratt, R.G.; Haberland, C.; Weber, M. (Geophysical Research Letters, 2008)
Crosshole seismic experiments were conducted to study the in-situ properties of gas hydrate bearing sediments (GHBS) in the Mackenzie Delta (NW Canada). Seismic tomography provided images of P velocity, anisotropy, and attenuation. Self-organizing maps (SOM) are powerful neural network techniques to classify and interpret multi-attribute data sets. The coincident tomographic images are translated to a set of data vectors in order to train a Kohonen layer. The total gradient of the model vectors is determined for the trained SOM and a watershed segmentation algorithm is used to visualize and map the lithological clusters with well-defined seismic signatures. Application to the Mallik data reveals four major litho-types: (1) GHBS, (2) sands, (3) shale/coal interlayering, and (4) silt. The signature of seismic P wave characteristics distinguished for the GHBS (high velocities, strong anisotropy and attenuation) is new and can be used for new exploration strategies to map and quantify gas hydrates. Copyright 2008 by the American Geophysical Union.
cited By 24
Keywords: Anisotropy; Bearings (structural); Conformal mapping; Diagnostic radiography; Earthquakes; Electric network analysis; Feature extraction; Graph theory; Hydration; Image enhancement; Lithology; Medical imaging; Neural networks; Petroleum engineering; Petroleum prospecting; Sedimentology; Seismic prospecting; Seismology; Self organizing maps; Strength of materials; Tomography; Vectors; Attribute datums; Crosshole; Data vectors; Exploration strategies; High velocities; In-situ; Interlayering; Kohonen layers; Model vectors; Neural network analyses; Neural Network techniques; P velocities; P waves; Seismic signatures; Seismic tomographies; Strong anisotropies; Tomographic images; Watershed segmentation algorithms; Gas hydrates; algorithm; artificial neural network; crosshole seismic method; data set; gas hydrate; lithology; lithotype; P-wave; seismic anisotropy; seismic attenuation; seismic tomography; seismic velocity; Canada; Mackenzie Delta; North America; Northwest Territories

Early response of continental Asia to Pleistocene climate cycles (retuned orbital chronologies for Baikal, marine, and ice core records) - Phedorin, M.A.; Goldberg, E.L. (Russian Geology and Geophysics, 2008)
Assuming orbital modulation of Pleistocene climate cycles, we have generated a new time scale for the Asian geochemical limnic record in the BDP-96-2 Baikal and the KDP-01 Hovsgol cores and updated the chronologies for the global marine δ18O and Vostok ice-gas records. The time scales were obtained by orbital tuning with the assumption of arbitrary but time invariable amplitudes and phase lags of the orbital parameters and responses. The retuned chronologies highlighted the cycles of eccentricity (100 kyr), obliquity (41 kyr), and precession (23 and 19 kyr), but the combined 70- and 30-kyr cycles became less prominent in the continental (Baikal) record though persisted in the global data (Vostok δD). The residual 70- and 30-kyr harmonics more likely result from errors in the untuned chronology for the Baikal record but are rather due to nonlinearity in the climate response. We investigated the leads and lags of orbital climate signals with a special focus on the 100-kyr cycle. The phases of precession, obliquity, and eccentricity cycles, compared among the records, showed the lead of the continent. The Baikal geochemical signal at the 100-kyr band led the global glacial and greenhouse CH4 responses and was almost synchronous with the earliest responding polar temperature signal. The reported results characterize the continent as a system highly responsive to eccentricity variations but do not contradict alternative hypotheses for the origin of the 100-kyr cycle in the Earth's climate history. © 2007.
Keywords: chronology; climate cycle; eccentricity; geochemistry; ice core; methane; paleoclimate; Pleistocene

Natural laboratory NW Bohemia: Comprehensive fluid studies between 1992 and 2005 used to trace geodynamic processes - Br{auer, Karin; K{ampf, Horst; Niedermann, Samuel; Strauch, Gerhard; Tesař, Jiř'i (Geochemistry, Geophysics, Geosystems, 2008)
Comprehensive studies of CO2-rich fluids close to the swarm earthquake region Nov'y Kostel at the Czech-German border have been started 15 years ago and have in particular included two extended chemical and isotope monitoring studies lasting for several years each. The regional surface distribution patterns of the fluid signatures including the identification of the origin of fluid components are the focus of the detailed studies. Three degassing centers (Cheb basin, Mari'ansk'e L'azně, and Karlovy Vary) with high CO2 flux and the same level of δ13C values, but different levels of 3He/ 4He ratios, have been identified. The studies have located the CO2 source and have investigated seismically induced changes in fluid characteristics on the basis of unique weekly sampling campaigns at selected locations. A seismically triggered release of crustal helium was confirmed by both monitoring campaigns. Finally, indications for a presently active magmatic process beneath the Cheb basin have been found. In contrast to volcanically active regions, magma accumulation in the study area takes place at the crust-mantle boundary and is not yet accompanied by heat transfer to the surface. Likewise, reactive magma-derived components are absent in the degassing fluids. The area of investigation has the potential to be a natural laboratory for fundamental studies of active geodynamic processes. The results of our fluid monitoring, including the stunning observation of mantle-derived free fluids marked by 3He/4He ratios within the subcontinental mantle range, are supported by geophysical findings from seismic studies and geologic indications. Copyright 2008 by the American Geophysical Union.

Modeling of CO2-hydrate formation in geological reservoirs by injection of CO2 Gas - Uddin, M.; Coombe, D.; Wright, F. (Journal of Energy Resources Technology, Transactions of the ASME, 2008)
Continuing concern about the impacts of atmospheric carbon dioxide (CO 2) on the global climate system provides an impetus for the development of methods for long-term disposal of CO2 produced by industrial and other activities. Investigations of the CO2-hydrate properties indicate the feasibility of geologic sequestration CO2 as gas hydrate and the possibility of coincident CO2 sequestration/CH4 production from natural gas hydrate reservoirs. Numerical studies can provide an integrated understanding of the process mechanisms in predicting the potential and economic viability of CO2 gas sequestration, especially when utilizing realistic geological reservoir characteristics in the models. This study numerically investigates possible sequestration of CO2 as a stable gas hydrate in various reservoir geological formations. As such, this paper extends the applicability of a previously developed model to more realistic and relevant reservoir scenarios. A unified gas hydrate model coupled with a thermal reservoir simulator (CMG STARS) was applied to simulate CO2-hydrate formation in four reservoir geological formations. These reservoirs can be described as follows. The first reservoir (Reservoir I) is similar to tight gas reservoir with mean porosity 0.25 and mean absolute permeability 10 mD. The second reservoir (Reservoir II) is similar to a conventional sandstone reservoir with mean porosity 0.25 and mean permeability 20 mD. The third reservoir (Reservoir III) is similar to hydrate-free Mallik silt with mean porosity 0.30 and mean permeability 100 mD. The fourth reservoir (Reservoir IV) is similar to hydrate-free Mallik sand with mean porosity 0.35 and mean permeability 1000 mD. The Mallik gas hydrate bearing formation itself can be described as several layers of variable thickness with permeability variations from 1 mD to 1000 mD, and is addressed as a separate part of this study. This paper describes numerical methodology, model input data selection, and reservoir simulation results, including an enhancement to model the effects of ice formation and decay. The numerical investigation shows that the gas hydrate model effectively captures the spatial and temporal dynamics of CO2-hydrate formation in geological reservoirs by injection of CO2 gas. Practical limitations to CO2-hydrate formation by gas injection are identified and potential improvements to the process are suggested. Copyright © 2008 by ASME.
cited By 40
Keywords: Atmospheric chemistry; Capillarity; Carbon dioxide; Data reduction; Gas hydrates; Gas industry; Gases; Hydration; Liquids; Numerical analysis; Petroleum reservoirs; Porosity; Solids; Water injection; CH4 hydrate; CO2 hydrate; CO2 sequestration; Geological reservoir; Hydrate decomposition; Hydrate formation; Numerical simulation; Petroleum reservoir engineering

Microtubules in basalt glass from Hawaii Scientific Driling Project #2 phase 1 core and Hilina slope, Hawaii: Evidence of the occurrence and behavior of endolithic microorganisms - Walton, A.W. (Geobiology, 2008)
Elongate, fine tubes, ∼1 μm wide and up to 200 μm long, extend from fractured surfaces, vesicle walls, and internal fractures into fragments of basalt glass in samples from the Hawaii Scientific Drilling Project #2 phase 1 (HSDP #21) core and the Hilina slope, Hawaii. Several features indicate that these tubes are microbial endolithic microborings: the tubes resemble many described microborings from oceanic basalt glass, their formation is postdepositional but restricted to certain but different ranges of time in the two sets of samples, and they are not uniformly distributed throughout glass fragments. Microtubules record several characteristic behaviors including boring into glass, mining, seeking olivine, and avoiding plagioclase. They also are highly associated with a particular form of glass-replacing smectite. Evidence of behavior should join morphological and geochemical criteria in indicating microbial alteration of basalt glass. In some samples, steeply conical tubes, ∼10-20 μm in diameter tapering to 1 μm and commonly filled with smectite, appear to be modifications or elaborations of the microtubules. These also curve toward olivine and are associated with replacement smectite. In HSDP #21 samples, microtubules initiated at margins of shards before palagonite replaced those margins and are preserved during palagonitization. In fact, microtubules appear to have provided routes that enhanced the efficiency of water's reaching of unaltered glass. In Hilina Slope samples, the microtubules appear to postdate palagonitization because they initiate at the boundary between palagonite and unaltered sideromelane. Preservation of microtubules during palagonitization in samples together with recognition of other associated characteristics representing behavior suggests that such features may be recognizable in more heavily altered ancient rocks. © 2008 The Author.
cited By 40
Keywords: silicate; silicon dioxide; basalt; endolithon; microorganism; olivine; palagonite; smectite; species occurrence; article; basalt; chemistry; microbiology; microscopy; microtubule; United States; Hawaii; Microscopy; Microtubules; Silicates; Soil Microbiology

Mechanical intrusion models and their implications for the possibility of magma-driven swarms in NW Bohemia Region - Dahm, Torsten; Fischer, Tom; Hainzl, S. (Studia Geophysica et Geodaetica, 2008)
Earthquake swarms are often assumed to be caused by magmatic or fluid intrusions, where the stress changes in the vicinity of the intrusion control the position, strength and rate of seismicity. Fracture mechanical models of natural intrusions or man-made hydrofractures pose constraints on orientation, magnitude, shape and growing rate of fractures and can be used to estimate stress changes in the vicinity of the intrusions. Although the idea of intrusion-induced seismicity is widely accepted, specific comparisons of seismicity patterns with fracture models of stress changes are rarely done. The goal of the study is to review patterns of intrusion-induced earthquake swarms in comparison to the observations of the swarm in NW Bohemia in 2000. We analyse and discuss the theoretical 3D shape of intrusions under mixed mode loading and apparent buoyancy. The aspect ratio and form of the intrusion is used to constrain parameters of the fluid, the surrounding rock and stress. We conclude that the 2000 NW Bohemia swarm could have been driven by a magmatic intrusion. The intrusion was, however, inclined to the maximal principal stress and caused shear displacement additional to opening. We estimate that the density diference between magma and rock was small. The feeding reservoir was possibly much larger than the area affected from earthquakes and may be a vertical dike beneath the swarm region. © Institute of Geophysics of the ASCR, v.v.i 2008.
Keywords: Bohemia; Central Europe; Czech Republic; Eurasia; Europe; earthquake swarm; fracture; igneous intrusion; magmatism; modeling; seismicity; stress

Lithospheric topography, tilted plumes, and the track of the Snake River-Yellowstone hot spot - Shervais, J.W.; Hanan, B.B. (Tectonics, 2008)
The trace of the Snake River-Yellowstone hot spot is the world's best example of a mantle plume that has been overridden by continental lithosphere. The standard model calls for the plume head to rise under northern Nevada and be forced northward to form basalts of the Columbia Plateau; subsequent movement of North America to the southwest over the plume tail created a hot spot trace on the surface. We present a new conceptual model for the origin of this feature that resolves inconsistencies in the current standard model and explains the recent documentation of a thermal anomaly in the mantle below Yellowstone today that plunges ∼ 65° WNW. Our model implies that the plume tail was forced beneath thinned cratonic lithosphere to the SE along with part of the plume head and has remained in this orientation for the last 12 Ma. We infer that almost all of the voicanism in SE Oregon and SW Idaho prior to 12 Ma results from overriding the southern extension of the plume head, not the plume tail, and that a distinct plume tail hot spot track was not established until formation of the Bruneau-Jarbidge eruptive center around 12 Ma. The plume tail track may also be controlled by a preexisting structural boundary in lithosphere that is thinner than adjacent lithosphere. This model demonstrates the potential importance of lithospheric topography on controlling the surface manifestation of plume volcanism and the complexity that may arise when lithospheric thickness is nonuniform. Copyright 2008 by the American Geophysical Union.
cited By 67
Keywords: basalt; continental lithosphere; craton; extensional tectonics; hot spot; mantle plume; structural control; topography; volcanic eruption; volcanism; Idaho; Nevada; North America; Oregon; Snake River; United States; Yellowstone River

Lithospheric structure of the Bohemian Massif and adjacent Variscan belt in central Europe based on profile S01 from the SUDETES 2003 experiment - Grad, Marek; Guterch, Aleksander; Mazur, Stanisław; Keller, G. Randy; Špič'ak, Aleš; Hrubcov'a, Pavla; Geissler, Wolfram H. (Journal of Geophysical Research: Solid Earth, 2008)
The SUDETES 2003 seismic experiment investigated the lithospheric structure of the eastern part of the Variscan belt of central Europe. The key profile of this experiment (S01) was 630 km long and extended southwestward from the margin of the East European craton, across the Trans-European suture zone (TESZ) and Sudetes, and across the Bohemian Massif that contains the active Eger (Ohře) rift, which is an element of the European Cenozoic rift system. Good quality first arrivals and later phases of refracted/reflected P and S waves were interpreted using 2-D ray-tracing techniques. The derived seismic model shows large variations in the internal structure of the crust, while the depth to the Moho varies in the relatively narrow depth interval of 28-35 km. Except for the Polish basin on the northeast end of the profile, the sedimentary cover is thin. The crystalline upper and middle crust with velocities of 5.9-6.4 km S-1 is about 20 km thick, and the 7-10 km thick lower crust can be divided into three regions based on P wave velocities: a low-velocity region (6.5-6.6 km s-1 beneath Eger rift and Sudetes) that is bounded on the southwest and northeast by regions of significantly higher velocity (6.8-7.1 km s-1 beneath the Saxothuringian and Moldanubian in the southwest and Fore-Sudetic Monocline and Polish Basin in the northeast). High-velocity bodies (Vp > 6.5 km s-1) were delineated in the upper crust of the Eger rift region. The seismic structure along the S01 profile images a Variscan orogenic wedge resting on the down warped margin of the plate margin containing the TESZ. This situation implies the northerly directed subduction of the Rheic Ocean that existed between the southern margin of the Old Red Continent and the Armorican terranes presently accreted into the Variscan belt. Closure of this ocean produced the Rheic suture between low-velocity crust of the Variscan orogenic wedge and higher-velocity crust of the TESZ. Copyright 2008 by the American Geophysical Union.
Keywords: Bohemian Massif; Central Europe; Eurasia; Europe; Cenozoic; craton; Hercynian orogeny; lithospheric structure; low velocity zone; Moho; orogenic belt; P-wave; ray tracing; S-wave; suture zone

Interferometry by deconvolution: Part 2 - Theory for elastic waves and application to drill-bit seismic imaging - Vasconcelos, I.; Snieder, R. (Geophysics, 2008)
Deconvolution interferometry successfully recovers the impulse response between two receivers without the need for an independent estimate of the source function. Here we extend the method of interferometry by deconvolution to multicomponent data in elastic media. As in the acoustic case, elastic deconvolution interferometry retrieves only causal scattered waves that propagate between two receivers as if one acts as a pseudosource of the point-force type. Interferometry by deconvolution in elastic media also generates artifacts because of a clamped-point boundary condition imposed by the deconvolution process. In seismic-while-drilling (SWD) practice, the goal is to determine the subsurface impulse response from drill-bit noise records. Most SWD technologies rely on pilot sensors and/or models to predict the drill-bit source function, whose imprint is then removed from the data. Interferometry by deconvolution is of most use to SWD applications in which pilot records are absent or provide unreliable estimates of bit excitation. With a numerical SWD subsalt example, we show that deconvolution interferometry provides an image of the subsurface that cannot be obtained by correlations without an estimate of the source autocorrelation. Finally, we test the use of deconvolution interferometry in processing SWD field data acquired at the San Andreas Fault Observatory at Depth (SAFOD). Because no pilot records were available for these data, deconvolution outperforms correlation in obtaining an interferometric image of the San Andreas fault zone at depth. © 2008 Society of Exploration Geophysicists. All rights reserved.
cited By 118
Keywords: Autocorrelation; Deconvolution; Drilling; Elastic waves; Imaging techniques; Impulse response; Interferometry; Seismic waves; Drill-bit seismic imaging; Elastic deconvolution interferometry; Multicomponent data; Seismic-while-drilling (SWD); Seismology; autocorrelation; boundary condition; deconvolution; drill bit; elastic wave; imaging method; interferometry; San Andreas Fault; seismic data; wave propagation; wave scattering

Integrated interpretation of physical properties of rocks of the borehole Yaxcopoil-1 (Chicxulub impact structure) - Mayr, S.I.; Wittmann, A.; Burkhardt, H.; Popov, Y.; Romushkevich, R.; Bayuk, I.; Heidinger, P.; Wilhelm, H. (Journal of Geophysical Research: Solid Earth, 2008)
The borehole Yaxcopoil-1, drilled within the Chicxulub meteoritic impact structure (Mexico), was completely cored from 404 to 1511 in through postimpact Tertiary limestones underlain by impactites. The impactites comprise impact melt-rich, suevitic breccia followed by megablocks of Cretaceous limestones, calcarenites, dolomites, and anhydrites. Measurements of porosity, density, and thermal parameters on 450 samples (equidistant sampling, complete depth range) and of ultrasonic velocities and electric resistivity on 80 representative samples are used to investigate the physical properties of carbonate rocks and to study the influence of the impact. Experiments under elevated pressure, calculations using frequency-dependent Biot-Gassmann theory, and cross-checking with borehole logs, where available, show that ultrasonic laboratory and sonic in situ data correspond. Sonic and electric quasi-continuous logs are obtained from empirical correlations with thermal conductivity, density, and porosity and consideration of mineralogical composition and microstructure. These data give constraints on interpretation and geophysical modeling of, e.g., seismic and gravity data. In the Tertiary postimpact limestone section, the rock fabric (porosity) influences the physical properties. The upper boundary of the impactites is distinctly determined by the high inhomogeneity factor and anisotropy coefficient of thermal conductivity and by the temperature gradient from high-resolution borehole temperature measurements. All physical properties indicate that the upper part of the suevitic breccia can be distinguished from the lower suevite unit. In the Cretaceous megablocks, a high variability of all properties (particularly, thermal conductivity, density of solid material, and temperature gradient) due to the high variability in the mineral composition (calcite, dolomite, anhydrite) is observed. Copyright 2008 by the American Geophysical Union.
cited By 23

Matching Technique for Drilling Engineering in Well-1of Songliao Scientific Drilling(in Chinese with English abstract); 松科一井(主井)钻探工程技术配套 - Zhang, Q.; Zhu, Y.; Li, X; Bi, J.; Wang, W. (Exploration Engineering (Rock &, Soil Drilling and Tunneling), 2008)

Impact effects and regional tectonic insights: Backstripping the Chesapeake Bay impact structure - Hayden, T.; Kominz, M.; Powars, D.S.; Edwards, L.E.; Miller, K.G.; Browning, J.V.; Kulpecz, A.A. (Geology, 2008)
The Chesapeake Bay impact structure is a ca. 35.4 Ma crater located on the eastern seaboard of North America. Deposition returned to normal shortly after impact, resulting in a unique record of both impact-related and subsequent passive margin sedimentation. We use backstripping to show that the impact strongly affected sedimentation for 7 m.y. through impact-derived crustal-scale tectonics, dominated by the effects of sediment compaction and the introduction and subsequent removal of a negative thermal anomaly instead of the expected positive thermal anomaly. After this, the area was dominated by passive margin thermal subsidence overprinted by periods of regional-scale vertical tectonic events, on the order of tens of meters. Loading due to prograding sediment bodies may have generated these events. © 2008 The Geological Society of America.
cited By 19
Keywords: Backstripping; Eocene; Impact processes; Passive margin; Sedimentology; Structural geology; Subsidence; Tectonics; deposition; Eocene; impact structure; passive margin; sedimentation; tectonic setting; temperature anomaly; Chesapeake Bay; North America; United States

Exploration for gas hydrates in the deepwater, northern Gulf of Mexico: Part I. A seismic approach based on geologic model, inversion, and rock physics principles - Dai, J.; Snyder, F.; Gillespie, D.; Koesoemadinata, A.; Dutta, N. (Marine and Petroleum Geology, 2008)
This article presents the results of applying a five-step process for using high-quality seismic data to locate marine gas hydrates. The process involved (1) reprocessing of seismic data for higher resolution, (2) detailed stratigraphic evaluation and interpretation to locate possible hydrate-bearing zones, (3) seismic attribute analysis to further delineate these zones, (4) seismic inversion to obtain appropriate elastic parameters of these zones in 3D, and (5) quantitative estimation of gas hydrate saturation from seismic data using inversion and rock physics principles. We used seismic data from Keathley Canyon 151 and Atwater Valley 14 in the northern Gulf of Mexico. Although careful analysis did indicate the presence of a bottom simulating reflector (BSR), our study mainly relied on a host of other seismic attributes (e.g., gas chimneys, seismically transparent zones, other features associated with the petroleum system) to characterize the occurrence of gas hydrates in these areas. We tested and verified a viable rock model for hydrate-bearing sediments using data from the Mallik (McKenzie Delta, Canada) and Blake Ridge (ODP Leg 164, southeast U.S. Atlantic margin) wells and modified it for application in the current area. We then used this model to estimate gas hydrate saturation in the host sediments of the northern Gulf of Mexico focus areas using estimates of P-wave and S-wave velocities from inversion of reflection seismic data. In this paper, we present the gas hydrate saturations predicted from the seismic processing methodology prior to 2005 drilling in the focus areas. In frontier areas where no well data are available and lithologic heterogeneities are poorly understood, implementing a seismic-based technique like the one described here to identify potential gas hydrates can provide valuable pre-drill information for site selection and for planning future characterization studies of gas hydrate-bearing sediments.
cited By 93
Keywords: Bottom simulating reflector (BSR); Gas hydrate; Gulf of Mexico; Rock physics models; Seismic inversion; Bearings (structural); Gases; Geologic models; Hydration; Modal analysis; Offshore oil well production; Offshore oil wells; Offshore petroleum prospecting; Parameter estimation; Petroleum engineering; Petroleum prospecting; Reflection; Sedimentation; Sedimentology; Seismic response; Seismic waves; Seismology; Site selection; Stratigraphy; Three dimensional; Gas hydrates; deep water; estimation method; gas hydrate; hydrocarbon exploration; hydrocarbon reservoir; inverse analysis; P-wave; S-wave; seismic data; seismic method; seismic reflection; seismic velocity; three-dimensional modeling; Atlantic Ocean; Gulf of Mexico

Environment: Carbon measures slow to emerge (Petroleum Economist, 2008)
The US Geological Survey (USGS) estimated that 85.4 tcf of methane could be trapped in these cage-like lattices of ice about 2000 ft below the permafrost. According to USGS Director Mark Myers, a growing body of evidence indicates that concentrated gas-hydrate accumulations in conventional hydrocarbons reservoirs, such as those in northern Alaska, can be produced with existing technology, particularly depressurization. This technique lowers the pressure in the well, which causes the hydrates to become unstable and dissociate into water and gas that can be pumped to the surface. The Mallik 2002 Gas Hydrate Production Research Well Program, conducted in the Mackenzie Delta, Northwest Territories, Canada, represented the first modern, fully integrated field study and production testing of a gas-hydrate accumulation. It demonstrated that methane could be produced from gas hydrates by using pressure stimulation and that combining depressurisation with heating increased gas production. Numerous technical problems must still be overcome before this potential resource can be considered economically producible. One, for example, is the risk of releasing methane into the atmosphere; this gas is about 20 times more potent than CO2 as a greenhouse gas, which contributes to global warming. However, the effort would be worthwhile. The North Slope's hydrate reserves could provide enough gas to heat 100 m homes for up to a decade. The opportunity to develop them would also provide another justification for the proposed 26 billion, 1700 mi pipeline to carry conventionally produced natural gas from the North Slope to markets in the lower 48 states.
cited By 0

Groundmass crystallization in dacite dykes taken in Unzen Scientific Drilling Project (USDP-4) - Noguchi, S.; Toramaru, A.; Nakada, S. (Journal of Volcanology and Geothermal Research, 2008)
Groundmass textural and compositional analyses of the drilled dacite dykes of the Unzen Scientific Drilling Project (USDP-4) identify the feeder dyke of the 1990-1995 eruption and elucidate the crystallization process of dykes at depth. In the drilling depth range of 1582-1996 m (conduit zone), four dacite dykes were recognized. The groundmasses of all but one of these dykes have textures ranging from cryptocrystalline to microcrystalline aggregate of crystals < 10 μm across forming an equigranular mosaic of plagioclase, alkali feldspar, quartz, and pyrite. The samples include a small number of coarser-grained plagioclase microlites (20 μm to 0.3 mm long). The compositions of groundmass consisting only of grains < 10 μm plotted at the lower pressure ( < 50 MPa) ternary minimum in the Qz'-Ab'-Or' system suggests that the crystallization of plagioclase, alkali feldspar, and quartz took place nearly simultaneously. The compositions of coarser plagioclase microlites and groundmass, the plagioclase microlite textures, and the phenocryst assemblages show significant differences from historical lavas exposed in the summit area. This implies the possibility that most of the dacite dykes are not feeder dykes for the lavas at the summit and remained beneath the surface, perhaps because of high viscosity associated with high SiO2. One sample C14-1-1 collected 1977 m, has a texture, composition, and phenocryst assemblage nearly identical to that of the dome lava of the 1990-1995 eruption, differing only in the presence of hydrothermal alternation. At this time we cannot definitely conclude that C14-1-1 was the feeder dyke for the 1990-1995 eruption until we can elucidate the time scale and the conditions governing hydrothermal alternation. © 2008 Elsevier B.V. All rights reserved.
cited By 20
Keywords: Crystallization; Crystallography; Drilling; Feeding; Feldspar; Metallic glass; Nanocrystalline alloys; Oxide minerals; Pyrites; Quartz; Silicon compounds; Textures; Alkali feldspar; annealing; Compositional analysis; conduit drilling; Crystallization processes; dacite dyke; Drilling depth; groundmass texture; hydrothermal alteration; Lower pressures; Microlite; Microlites; Unzen; Silicate minerals; crystallization; dacite; dike; drilling; hydrothermal alteration; lava dome; volcanic eruption; Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano

Estimating pore-space gas hydrate saturations from well log acoustic data - Lee, M.W.; Waite, W.F. (Geochemistry, Geophysics, Geosystems, 2008)
Relating pore-space gas hydrate saturation to sonic velocity data is important for remotely estimating gas hydrate concentration in sediment. In the present study, sonic velocities of gas hydrate-bearing sands are modeled using a three-phase Biot-type theory in which sand, gas hydrate, and pore fluid form threehomogeneous, interwoven frameworks. This theory is developed using well log compressional and shear wave velocity data from the Mallik 5L-38 permafrost gas hydrate research well in Canada and applied to well log data from hydrate-bearing sands in the Alaskan permafrost, Gulf of Mexico, and northern Cascadia margin. Velocity-based gas hydrate saturation estimates are in good agreement with Nuclear Magneto Resonance and resistivity log estimates over the complete range of observed gas hydrate saturations. Copyright 2008 by the American Geophysical Union.
cited By 142

Estimation of hydraulic permeability considering the micro morphology of rocks of the borehole YAXCOPOIL-1 (Impact crater Chicxulub, Mexico) - Mayr, S.I.; Burkhardt, H.; Popov, Yu.; Wittmann, A. (International Journal of Earth Sciences, 2008)
Internal surface, formation factor, Nuclear Magnetic Resonance (NMR)-T2 relaxation times and pore radius distributions were measured on representative core samples for the estimation of hydraulic permeability. Permeability is estimated using various versions of the classic Kozeny-Carman-equation (K-C) and a further development of K-C, the fractal PaRiS-model, taking into account the internal surface. In addition to grain and pore size distribution, directly connected to permeability, internal surface reflects the internal structure (micro morphology). Lithologies could be grouped with respect to differences in internal surface. Most melt rich impact breccia lithologies exhibit large internal surfaces, while Tertiary post-impact sediments and Cretaceous lithologies in displaced megablocks display smaller internal surfaces. Investigations with scanning electron microscopy confirm the correlation between internal surface and micro morphology. In addition to different versions of K-C, estimations by means of NMR, pore radius distributions and some gas permeability measurements serve for cross-checking and calibration. In general, the different estimations from the independent methods and the measurements are in satisfactory accordance. For Tertiary limestones and Suevites bulk with very high porosities (up to 35%) permeabilites between 10-14 and 10-16 m2 are found, whereas in lower Suevite, Cretaceous anhydrites and dolomites, bulk permeabilites are between 10-15 and 10-23m2. © Springer-Verlag 2007.
cited By 17

Experimental volcanology on eruptive products of Unzen volcano - Scheu, B.; Kueppers, U.; Mueller, S.; Spieler, O.; Dingwell, D.B. (Journal of Volcanology and Geothermal Research, 2008)
Protracted dome-building eruptions may be profitably investigated using laboratory-based experiments. Density distribution studies on the pyroclastic flow deposits of Unzen 1990-1995 allow us to apply the results of experimental investigations on Unzen samples to the interpretation of the last eruption of Unzen. Here, primary laboratory experiments have focused on several aspects of the degassing (permeability) and the fragmentation behavior (threshold, speed, and efficiency). Those investigations have been flanked by analyses of flexural strength, fracture toughness, and seismic velocities, to provide new insights into eruption related processes. Here we present a review of these results and their application to the eruption dynamics of Unzen Volcano. We propose that efforts be made to incorporate routinely such comprehensive experimental analyses into the response to emerging volcanic crises in future. © 2008 Elsevier B.V. All rights reserved.
cited By 36
Keywords: Degassing; Experiments; Fracture fixation; Landforms; Volcanic rocks; Volcanoes; block-and-ash flow; Density distributions; elastic wave velocities; Eruption dynamics; Experimental investigations; Flexural strength; fragmentation behavior; Laboratory experiments; permeability; porosity; Pyroclastic flow deposits; Seismic velocities; Unzen; volcanology; Fracture toughness; ash flow; degassing; fracture toughness; permeability; porosity; seismic velocity; volcanic eruption; volcanology; Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano

Formation evaluation of gas hydrate bearing sediments - Williams, F.; Lovell, M.; Brewer, T.; Buecker, C.; Jackson, P.; Camps, A. (49th Annual Logging Symposium 2008, 2008)
There is a growing interest in natural gas hydrate mainly due to the possibility that it may represent a large energy resource, potentially have an impact on global climate change and play a role in submarine slope failures. It is therefore of great importance to be able to identify the occurrence of in-situ gas hydrates and accurately assess their volume within the host sediments. The evaluation of gas hydrate volumes is dependent on a number of parameters, including the areal extent of the hydrate occurrence, reservoir thickness, porosity of reservoir and degree of hydrate saturation. Normally in hydrocarbon exploration of conventional oil and gas fields, the analysis of core samples, obtained while drilling, are used to evaluate this petrophysical data. However, because hydrate disassociates and loses gas as it is brought up to normal surface temperatures and pressure, it becomes problematical in obtaining meaningful porosity and saturation values from recovered cores. Therefore, downhole well logging techniques are used in order to obtain petrophysical data. These techniques have, in the main, been adapted from the standard hydrocarbon industry methods of determining porosity and saturations using resistivity and acoustic log data, together with the deterministic relationships such as the Archie (resistivity) and Wyllie (acoustic) time average equations. Deterministic formation evaluation methods follow a step-by-step approach to arrive at one solution for each depth step. In successive steps, the lithology, porosity, and saturations are determined. Thus the analytical parameters are fixed and the solutions unique. Another approach has been to use probabilistic statistical software such as the Mineral Solver module within the Interactive Petrophysics™ software package. Probabilistic evaluation, computes a solution from an assigned mineral model and all the available logs simultaneously, using statistical methods. This probabilistic method has been applied to log data acquired from the ODP/IODP (marine) and the Mallik (permafrost) exploration wells, successfully generating gas hydrate saturation estimates, with comparable results to Archie saturation estimates at high saturations. Further investigation is required to fully determine the potential of probabilistic methods for gas hydrate evaluation. © 2008 Society of Petrophysicists and Well-Log Analysts. All rights reserved.
cited By 0
Keywords: Climate change; Energy resources; Gas hydrates; Gas industry; Gases; Hydration; Hydrocarbons; Lithology; Natural gas deposits; Petroleum prospecting; Petroleum reservoir evaluation; Porosity; Well logging; Conventional oil and gas; Gas hydrate bearing sediments; Gas hydrate saturations; Global climate changes; Hydrocarbon exploration; Porosity and saturation; Probabilistic evaluation; Submarine slope failures; Oil well logging

Fourier transform infrared spectroscopy, a new cost-effective tool for quantitative analysis of biogeochemical properties in long sediment records - Vogel, H.; Rosen, P.; Wagner, B.; Melles, M.; Persson, P. (Journal of Paleolimnology, 2008)
Measurements of Fourier transform infrared spectroscopy (FTIRS) in the mid-infrared (MIR) region were conducted on sedimentary records from Lake El'gygytgyn, NE Siberia, and Lake Ohrid, Albania/Macedonia. Calibration models relating FTIR spectral information to biogeochemical property concentrations were established using partial least squares regression (PLSR). They showed good statistical performance for total organic carbon (TOC), total nitrogen (TN), and biogenic silica (opal) in the sediment record from Lake El'gygytgyn, and for TOC, total inorganic carbon (TIC), TN, and opal in sediments from Lake Ohrid. In both cases, the calibration models were successfully applied for down-core analysis. The results, in combination with the small amount of sample material needed, negligible sample pre-treatments, and low costs of analysis, demonstrate that FTIRS is a promising, cost-effective tool that allows high-resolution paleolimnological studies. © 2008 Springer Science+Business Media B.V.
cited By 69
Keywords: biogenic deposit; biogeochemistry; cost-benefit analysis; FTIR spectroscopy; paleolimnology; quantitative analysis; sediment core; Chukchi; Elgygytgyn Lake; Eurasia; Europe; Lake Ohrid; Russian Federation; Southern Europe

Fourier transform infrared spectroscopy, a new cost-effective tool for quantitative analysis of biogeochemical properties in long sediment records - Vogel, Hendrik; Ros'en, Peter; Wagner, Bernd; Melles, Martin; Persson, Per (Journal of Paleolimnology, 2008)
Measurements of Fourier transform infrared spectroscopy (FTIRS) in the mid-infrared (MIR) region were conducted on sedimentary records from Lake El'gygytgyn, NE Siberia, and Lake Ohrid, Albania/Macedonia. Calibration models relating FTIR spectral information to biogeochemical property concentrations were established using partial least squares regression (PLSR). They showed good statistical performance for total organic carbon (TOC), total nitrogen (TN), and biogenic silica (opal) in the sediment record from Lake El'gygytgyn, and for TOC, total inorganic carbon (TIC), TN, and opal in sediments from Lake Ohrid. In both cases, the calibration models were successfully applied for down-core analysis. The results, in combination with the small amount of sample material needed, negligible sample pre-treatments, and low costs of analysis, demonstrate that FTIRS is a promising, cost-effective tool that allows high-resolution paleolimnological studies. © 2008 Springer Science+Business Media B.V.
Keywords: Chukchi; Elgygytgyn Lake; Eurasia; Europe; Lake Ohrid; Russian Federation; Southern Europe; biogenic deposit; biogeochemistry; cost-benefit analysis; FTIR spectroscopy; paleolimnology; quantitative analysis; sediment core

Geologic effects of large terrestrial impact crater formation - Ivanov, B. (Catastrophic Events Caused by Cosmic Objects, 2008)
To date around 180 impact structures have been identified on Earth. The diameters of these structures are from ∼10 to ∼200-250 km. Knowledge about terrestrial impact structures accumulated during many decades includes a large amount of geological and geophysical data. These data are very useful in formulating important constraints for impact model parameters reaching a double goal: (1) to fit parameters in the available mechanical models of planetary crust reaction to the impact event, and (2) to use numerical modeling to make an insight into the possible original structure of partially eroded terrestrial impact structures. This chapter presents results of numerical modeling for selected terrestrial impact craters (Puchezh-Karunki, Popigai, Vredefort, Sudbury, and Chicxulub) and compares model results with available geologic and geophysical data, obtained in the field study of aforementioned structures. © 2008 Springer.
cited By 6

Establishment of floating astronomical time scale for the terrestrial Late Cretaceous Qingshankou Formation in the Songliao Basin of Northeast China - Huaichun, Wu; Zhang, Shihong; Huang, Qinghua (Earth Science Frontiers, 2008)

Preface to the special issue on Taiwan Chelungpu-Fault Drilling Project (TCDP): Site characteristics and on-site measurements - Song, S.-R.; Wang, C.-Y.; Hung, J.-H.; Ma, K.-F. (Terrestrial, Atmospheric and Oceanic Sciences, 2007)
cited By 12

Putting it all together: Exhumation histories from a formal combination of heat flow and a suite of thermochronometers - d'Alessio, M.A.; Williams, C.F. (Journal of Geophysical Research: Solid Earth, 2007)
A suite of new techniques in thermochronometry allow analysis of the thermal history of a sample over a broad range of temperature sensitivities. New analysis tools must be developed that fully and formally integrate these techniques, allowing a single geologic interpretation of the rate and timing of exhumation and burial events consistent with all data. We integrate a thermal model of burial and exhumation, (U-Th)/He age modeling, and fission track age and length modeling. We then use a genetic algorithm to efficiently explore possible time-exhumation histories of a vertical sample profile (such as a borehole), simultaneously solving for exhumation and burial rates as well as changes in background heat flow. We formally combine all data in a rigorous statistical fashion. By parameterizing the model in terms of exhumation rather than time-temperature paths (as traditionally done in fission track modeling), we can ensure that exhumation histories result in a sedimentary basin whose thickness is consistent with the observed basin, a physically based constraint that eliminates otherwise acceptable thermal histories. We apply the technique to heat flow and thermochronometry data from the 2.1 -km-deep San Andreas Fault Observatory at Depth pilot hole near the San Andreas fault, California. We find that the site experienced <1 km of exhumation or burial since the onset of San Andreas fault activity ∼30 Ma.
cited By 8
Keywords: burial (geology); exhumation; genetic algorithm; heat flow; numerical model; parameterization; thermochronology; California; North America; San Andreas; United States; Calluna vulgaris

Preliminary results of stress measurement using drill cores of TCDP Hole-A: An application of anelastic strain recovery method to three-dimensional in-situ stress determination - Lin, W.; Yeh, E.-C.; Ito, H.; Hirono, T.; Soh, W.; Wang, C.-Y.; Ma, K.-F.; Hung, J.-H.; Song, S.-R. (Terrestrial, Atmospheric and Oceanic Sciences, 2007)
In order to understand the feature of rock stress change at different depths above, within, and beneath the Chelungpu fault after the Chi-Chi earthquake, we employed a core-based stress measurement method, anelastic strain recovery (ASR) technique to determine both the orientations and magnitudes of present three-dimensional principal rock stresses using drill core samples retrieved from Taiwan Chelungpu-fault Drilling Project (TCDP) main Hole-A. The core samples used were taken from three depths; and their lithology were sandstone at depths of 592 and 1755 m and siltstone at 1112 m. The anelastic strains of the specimens in nine directions, including six independent directions, were measured after its in-situ stress was released. Acquired anelastic strains were of high quality and reached several hundred microstrains, which is sufficiently high for the accuracy of the measurement system used. Thus, the strain data could be used for three-dimensional analysis resulting in the determination of orientations and the estimation of magnitudes of the principal in-situ stresses. Preliminary stress measurement results showed that the orientations of principal stresses changed between the shallower depth above the fault and the deeper depth beneath it, that is, the present stress distribution in the TCDP hole might be influenced by the Chelungpu fault rupture. At the same time, anelastic strain recovery measurement is well suited for the task of directly determining the orientations of principal in-situ stresses and to estimate the magnitude of stresses at large/great depth.
cited By 37
Keywords: anelasticity; borehole; Chi-Chi earthquake 1999; core analysis; drilling; fault zone; in situ measurement; siltstone; strain; stress measurement; three-dimensional modeling

Progress in the Research on Major Geological Events in the Earth Surface System during the Cretaceous and Greenhouse Climate Change (in Chinese with English abstract);[白垩纪地球表层系统重大地质事件与温室气候变化研究进展] - Wang, C. (China Basic Science, 2007)

Preface - Koeberl, Christian; Milkereit, Bernd; Reimold, Wolf Uwe (Meteoritics and Planetary Science, 2007)

Progress report on the Iceland Deep Drilling Project (IDDP) - Fridleifsson, G.Ó.; Elders, W.A. (Scientific Drilling, 2007)
cited By 4

Results of pre-drilling potential field measurements at the Bosumtwi crater - Danour, S.K.; Menyeh, A. (Meteoritics and Planetary Science, 2007)
Gravity and magnetic measurements were carried out at the Bosumtwi crater to determine the geophysical signature of the crater. Land gravity data was acquired at 163 locations around the structure and on the shore of the lake. The separation between the gravity stations was 500 m for radial profiles, but 700-1000 m along roads and footpaths that ran parallel to the lake's shore. Additionally, a marine gravity survey was carried out along 14 north-south and 15 east-west profiles on the lake. Magnetic data was also acquired along 14 north-south profiles on the lake. In all marine surveys, the line spacing was 800 m, and navigation was provided by a Garmin 235 Echo Sounder/GPS. The gravity signature of the crater is characterized by a negative Bouguer anomaly with an amplitude of about -18 mgal. Using the seismic results as constraints, the gravity model obtained indicates the central uplift at a depth of 250 m. The negative anomaly is the contribution of the gravity deficiencies due to fractured and brecciated rocks in the rim area and below the crater floor, the impact breccias within the crater, and the sedimentary and water infilling of the lake. Magnetic modeling yielded a model for the causative body, which is located north of the central uplift: the model has a magnetic susceptibility of 0.03 S.I. and extends from a depth of 250 to 610 m. The causative bodies have been interpreted as impactites. © The Meteoritical Society, 2007. Printed in USA.

Quantification of soil erosion rates related to ancient Maya deforestation - Anselmetti, F.S.; Hodell, D.A.; Ariztequi, D.; Brenner, M.; Rosenmeier, M.F. (Geology, 2007)
We used seismic and sediment core data to quantify soil erosion rates for the past ∼6000 yr in the closed catchment of Lake Salpet'en, in the tropical lowlands of northern Guatemala. The region was affected by ancient Maya land use from before ca. 1000 B.C. to A.D. 900. This period of human impact coincided with deposition in the lake of a detrital unit (Maya Clay) as much as 7 m thick that contrasts sharply with the relatively organic-rich gyttja deposited both before and after Maya occupation of the watershed. The greatest soil loss, with mean sustained values of ∼1000 t/kM2 yr-1, occurred in the Middle and Late Preclassic Periods (700 B.C. to A.D. 250), associated with relatively low Maya population densities. Soil erosion slowed during the period of maximum population density in the Late Classic Period (A.D. 550-830), indicating a decoupling between human population density and soil erosion rate. The most rapid soil loss occurred early during initial land clearance, suggesting that even low numbers of people can have profound impacts on lowland tropical karst landscapes. © 2007 The Geological Society of America.
cited By 153
Keywords: Lake sediments; Seismic stratigraphy; Soil erosion rate; Erosion; Lakes; Sediments; Seismology; Stratigraphy; Structural geology; anthropogenic effect; Classic period; core analysis; deforestation; deposition; erosion rate; gyttja; lacustrine deposit; land use; seismic data; seismic stratigraphy; soil erosion; Central America; Guatemala [Central America]

Quaternary glaciation and hydrologic variation in the South American tropics as reconstructed from the Lake Titicaca drilling project - Fritz, Sherilyn C.; Baker, Paul A.; Seltzer, Geoffrey O.; Ballantyne, Ashley; Tapia, Pedro; Cheng, Hai; Edwards, R. Lawrence (Quaternary Research, 2007)
A 136-m-long drill core of sediments was recovered from tropical high-altitude Lake Titicaca, Bolivia-Peru, enabling a reconstruction of past climate that spans four cycles of regional glacial advance and retreat and that is estimated to extend continuously over the last 370,000 yr. Within the errors of the age model, the periods of regional glacial advance and retreat are concordant respectively with global glacial and interglacial stages. Periods of ice advance in the southern tropical Andes generally were periods of positive water balance, as evidenced by deeper and fresher conditions in Lake Titicaca. Conversely, reduced glaciation occurred during periods of negative water balance and shallow closed-basin conditions in the lake. The apparent coincidence of positive water balance of Lake Titicaca and glacial growth in the adjacent Andes with Northern Hemisphere ice sheet expansion implies that regional water balance and glacial mass balance are strongly influenced by global-scale temperature changes, as well as by precessional forcing of the South American summer monsoon. © 2007 University of Washington.
Keywords: Lake Titicaca; South America; Bacillariophyta; glaciation; ice sheet; interglacial; paleoclimate; paleohydrology; Quaternary; reconstruction; sediment core; tropical region; water budget

Reconstruction of the Chicxulub ejecta plume from its deposits in drill core Yaxcopoil-1 - Wittmann, A.; Kenkmann, T.; Hecht, L.; St{offler, D. (Bulletin of the Geological Society of America, 2007)
Formation conditions of suevite-like impactites from an ∼100 m thick drill core sequence through the Cretaceous-Tertiary Chicxulub crater were reconstructed from empirical data obtained by petrologic and image analytical methods. The temporal evolution of the cratering process from the initial stage of excavation to the collapse of the ejecta plume is evidenced by the petrographic characteristics and modal composition of the suevitic rocks, including the size distribution and shape parameters of melt particles. Emplacement of the lowermost suevitic deposits likely started in the first minute after the impact by the passing ejecta curtain that interacted with the expanding ejecta plume. These ejecta deposits were capped by a tongue of coherent impact melt that was transported outward from the crater center during the collapse of the central uplift ∼5 min after impact. On top of this brecciated impact melt rock, the collapsing ejecta plume deposited air-fall suevites. The basal air-fall unit, Middle Suevite, may have been deposited due to a density current-like clumping of hot debris. With progressive cooling, regions of the ejecta plume were entrained in its collapse that produced vapor condensates, accretionary rims, and different oxygen fugacities. After cooling progressed, atmospheric conditions began to reestablish over the crater and turbulence decreased, supposedly after the first 10 min of initial ejecta plume collapse. This led to a winnowing out of fine matrix material and distinct sorting. However, due to aquatic reworking, only material that was deposited until ∼1 h after cessation of turbulent atmospheric conditions was retained. © 2007 Geological Society of America.
cited By 27

Repeating earthquake finite source models: Strong asperities revealed on the San Andreas fault - Dreger, D.; Nadeau, R.M.; Chung, A. (Geophysical Research Letters, 2007)
We investigate the rupture process of a sequence of repeating Mw 2.1 earthquakes on the San Andreas Fault in Parkfield spanning the occurrence of the September 28, 2004 mainshock by inverting seismic moment rate functions obtained from empirical Green's function deconvolution. The results show that these events have extremely concentrated slip patches with radii on the order of 10-20 m, with peak slip between 8.4 and 11.4 cm. The rupture speed and rise time are consistent with values of larger earthquakes. The spatial distribution of stress drop for the events shows low average values 2.5-5.6 MPa and very large peak values of 66.7-93.9 MPa. The results show that strong asperities can exist at small scales on an otherwise weak fault, and helps reconcile differences between traditional spectra-based and tectonic loading methods for determining the stress drop of small repeating earthquakes. Copyright 2007 by the American Geophysical Union.
cited By 83
Keywords: Mathematical models; Seismic response; Seismographs; Seismology; Tectonics; Rupture process; Rupture speed; Seismic moment rate; Tectonic loading; Earthquakes; deconvolution; earthquake magnitude; earthquake rupture; Green function; San Andreas Fault; seismic moment; spatial distribution

San Andreas fault zone mineralogy, geochemistry, and physical properties from SAFOD cuttings and core - Solum, J.G.; Hickman, S.; Lockner, D.A.; Tembe, S.; Evans, J.P.; Draper, S.D.; Barton, D.C.; Kirschner, D.L.; Chester, J.S.; Chester, F.M.; Pluijm, B.A.; Schleicher, A.M.; et al. (Scientific Drilling, 2007)
cited By 11

Scientific drilling of active faults: Past and future - Reches, Z.; Ito, H. (Continental Scientific Drilling: A Decade of Progress, and Challenges for the Future, 2007)
Drilling into active faults has become a major scientific endeavor during the last decade and it appears as a most promising approach to resolve long-standing questions in earthquake and faulting processes. The first boreholes were drilled into the Nojima Fault following the 1995 Kobe earthquake. Since then, drilling into active faults has begun or been planned in a wide range of tectonic settings, such as a strike-slip plate boundary (San Andreas Fault, California), a thrust zone in an active orogenic belt (Chelungpu Fault, Taiwan), a normal fault in an active rift zone (Aigion Fault, Greece), a reactivated Archean fault (Pretorius Fault, South Africa), and a major subduction thrust (Nankai Thrust, Japan). These projects have already revealed many details on in-situ stresses, fault-zone structure, fault-rock composition, mechanical properties, heat flow, and near-field seismicity. Furthermore, most of these projects will continue to serve as observatories for monitoring fault deformation, fluid pressure and near-field earthquake source processes for a decade or two. Future drilling projects will focus on near-field observations and long-term monitoring of time-dependent processes and in-situ experimentation in active fault zones. Collaboration with industry and government will address practical issues pertaining to petroleum and geothermal energy, radioactive waste disposal, and urban seismic hazards. The outcome of these international efforts in drilling active faults will revolutionize our understanding of the processes controlling faulting and earthquakes and lead to a stronger scientific basis for earthquake hazard mitigation. © 2007 Springer-Verlag Berlin Heidelberg.
cited By 13

Post-impact structural crater modification due to sediment loading: An overlooked process - Tsikalas, F.; Faleide, J.I. (Meteoritics and Planetary Science, 2007)
Post-impact crater morphology and structure modifications due to sediment loading are analyzed in detail and exemplified in five well-preserved impact craters: Mjølnir, Chesapeake Bay, Chicxulub, Montagnais, and Bosumtwi. The analysis demonstrates that the geometry and the structural and stratigraphic relations of post-impact strata provide information about the amplitude, the spatial distribution, and the mode of post-impact deformation. Reconstruction of the original morphology and structure for the Mjølnir, Chicxulub, and Bosumtwi craters demonstrates the long-term subsidence and differential compaction that takes place between the crater and the outside platform region, and laterally within the crater structure. At Mjølnir, the central high developed as a prominent feature during post-impact burial, the height of the peak ring was enhanced, and the cumulative throw on the rim faults was increased. The original Chicxulub crater exhibited considerably less prominent peak-ring and inner-ring/crater-rim features than the present crater. The original relief of the peak ring was on the order of 420-570 m (currently 535-575 m); the relief on the inner ring/ crater rim was 300-450 m (currently ∼700 m). The original Bosumtwi crater exhibited a central uplift/high whose structural relief increased duringburial (current height 101-110 m, in contrast to the original height of 85-110 m), whereas the surrounding western part of the annular trough was subdued more that the eastern part, exhibiting original depths of 43-68 m (currently 46 m) and 49-55 m (currently 50 m), respectively. Furthermore, a quantitative model for the porosity change caused by the Chesapeake Bay impact was developed utilizing the modeled density distribution. The model shows that, compared with the surrounding platform, the porosity increased immediately after impact up to 8.5% in the collapsed and brecciated crater center (currently +6% due to post-impact compaction). In contrast, porosity decreased by 2-3% (currently -3 to -4.5% due to post-impact compaction) in the peak-ring region. The lateral variations in porosity at Chesapeake Bay crater are compatible with similar porosity variations at Mjølnir crater, and are considered to be responsible for the moderate Chesapeake Bay gravity signature (annular low of -8 mGal instead of -15 mGal). The analysis shows that the reconstructions and the long-term alterations due to post-impact burial are closely related to the impact-disturbed target-rock volume and a brecciated region of laterally varying thickness and depth-varying physical properties. The study further shows that several crater morphological and structural parameters are prone to post-impact burial modification and are either exaggerated or subdued during post-impact burial. Preliminary correction factors are established based on the integrated reconstruction and post-impact deformation analysis. The crater morphological and structural parameters, corrected from post-impact loading and modification effects, can be used to better constrain cratering scaling law estimates and impact-related consequences. © The Meteoritical Society, 2007.
cited By 11