All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
678.
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
Exploration Engineering (Rock &, Soil Drilling and Tunneling),
35
(12)
1-5
2008
677.
Lithospheric topography, tilted plumes, and the track of the Snake River-Yellowstone hot spot
Tectonics,
27
(5)
2008
ISSN: 02787407Keywords:▾
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
Abstract: ▾ 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.
676.
Lithospheric structure of the Bohemian Massif and adjacent Variscan belt in central Europe based on profile S01 from the SUDETES 2003 experiment
Journal of Geophysical Research: Solid Earth,
113
(10)
2008
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
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
Abstract: ▾ 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.
675.
Modeling of CO2-hydrate formation in geological reservoirs by injection of CO2 Gas
Journal of Energy Resources Technology, Transactions of the ASME,
130
(3)
0325021-03250211
2008
ISSN: 01950738Keywords:▾
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
Abstract: ▾ 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.
674.
Integrated interpretation of physical properties of rocks of the borehole Yaxcopoil-1 (Chicxulub impact structure)
Journal of Geophysical Research: Solid Earth,
113
(7)
2008
Abstract: ▾ 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.
673.
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
Marine and Petroleum Geology,
25
(9)
830-844
2008
ISSN: 02648172Keywords:▾
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
Abstract: ▾ 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.
672.
Environment: Carbon measures slow to emerge
Petroleum Economist,
75
(12)
2008
ISSN: 0306395X
Publisher: Petroleum Economist Ltd.
Abstract: ▾ 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.
671.
Impact ejecta and carbonate sequence in the eastern sector of the Chicxulub crater
Comptes Rendus - Geoscience,
340
(12)
801-810
2008
Abstract: ▾ 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 Académie des sciences.
670.
Establishment of floating astronomical time scale for the terrestrial Late Cretaceous Qingshankou Formation in the Songliao Basin of Northeast China
Earth Science Frontiers,
15
(4)
159-169
2008
669.
Estimating pore-space gas hydrate saturations from well log acoustic data
Geochemistry, Geophysics, Geosystems,
9
(7)
2008
ISSN: 15252027Abstract: ▾ 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.
668.
Estimation of hydraulic permeability considering the micro morphology of rocks of the borehole YAXCOPOIL-1 (Impact crater Chicxulub, Mexico)
International Journal of Earth Sciences,
97
(2)
385-399
2008
Abstract: ▾ 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.
667.
Experimental volcanology on eruptive products of Unzen volcano
Journal of Volcanology and Geothermal Research,
175
(1-2)
110-119
2008
ISSN: 03770273Keywords:▾
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
Abstract: ▾ 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.
666.
Fourier transform infrared spectroscopy, a new cost-effective tool for quantitative analysis of biogeochemical properties in long sediment records
Journal of Paleolimnology,
40
(2)
689 – 702
2008
ISSN: 09212728Keywords:▾
Chukchi; Elgygytgyn Lake; Eurasia; Europe; Lake Ohrid; Russian Federation; Southern Europe; biogenic deposit; biogeochemistry; cost-benefit analysis; FTIR spectroscopy; paleolimnology; quantitative analysis; sediment core
Abstract: ▾ 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.
665.
Fourier transform infrared spectroscopy, a new cost-effective tool for quantitative analysis of biogeochemical properties in long sediment records
Journal of Paleolimnology,
40
(2)
689-702
2008
ISSN: 09212728Keywords:▾
biogenic deposit; biogeochemistry; cost-benefit analysis; FTIR spectroscopy; paleolimnology; quantitative analysis; sediment core, Chukchi; Elgygytgyn Lake; Eurasia; Europe; Lake Ohrid; Russian Federation; Southern Europe
Abstract: ▾ 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.
664.
Groundmass crystallization in dacite dykes taken in Unzen Scientific Drilling Project (USDP-4)
Journal of Volcanology and Geothermal Research,
175
(1-2)
71-81
2008
ISSN: 03770273Keywords:▾
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
Abstract: ▾ 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.
663.
Impact effects and regional tectonic insights: Backstripping the Chesapeake Bay impact structure
Geology,
36
(4)
327-330
2008
ISSN: 00917613Keywords:▾
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
Abstract: ▾ 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.
662.
Sedimentary geochemistry of core PG1351 from Lake El'gygytgyn-a sensitive record of climate variability in the East Siberian Arctic during the past three glacial-interglacial cycles
Journal of Paleolimnology,
37
(1)
89-104
2007
ISSN: 09212728Keywords:▾
climate variation; geochemistry; glacial-interglacial cycle; Holocene; insolation; marine isotope stage; paleoclimate; paleolimnology; sediment core, Chukchi; Eurasia; Lake El'gygytgyn; Russian Federation
Abstract: ▾ The ca. 13 m long sediment core PG1351, recovered in 1998 from the central part of Lake El'gygytgyn, NE Siberia, was investigated for lithostratigraphy, water content, dry bulk density (DBD), total organic carbon (TOC), total nitrogen (TN), total sulphur (TS) and biogenic silica (opal) contents, and for TOC stable isotope ratios (δ13CTOC). The event stratigraphy recorded in major differences in sediment composition match variations in regional summer insolation, thus confirming a new age model for this core, which suggests that it spans the last 250 ka BP. Four depositional units of contrasting lithological and biogeochemical composition have been distinguished, reflecting past environmental conditions associated with relatively warm, peak warm, cold and dry, and cold but more moist climate modes. A relatively warm climate, resulting in complete summer melt of the lake ice cover and seasonal mixing of the water column, prevailed during the Holocene and Marine Isotope Stages (MIS) 3, 5.1, 5.3, 6.1, 6.3, 6.5, 7.1-7.3, 7.5, 8.1 and 8.3. MIS 5.5 (Eemian) was characterized by significantly enhanced aquatic primary production and organic matter supply from the catchment, indicating peak warm conditions. During MIS 2, 5.2, 5.4, 6.2 and 6.4 the climate was cold and dry, leading to perennial lake ice cover, little regional snowfall, and a stagnant water body. A cold but more moist climate during MIS 4, 6.6, 7.4, 8.2 and 8.4 is thought to have produced more snow cover on the perennial ice, strongly reducing light penetration and biogenic primary production in the lake. While the cold-warm pattern during the past three glacial-interglacial cycles is probably controlled by changes in regional summer insolation, differences in the intensity of the warm phases and in the degree of aridity (changing snowfall) during cold phases likely were due to changes in atmospheric circulation patterns. © 2006 Springer Science+Business Media B.V.
661.
Seismology inside the fault zone: Applications to fault-zone properties and rupture dynamics
Scientific Drilling
(1 SUPPL. 1)
84-87
2007
ISSN: 18168957660.
Sedimentology, clay mineralogy and grain-size as indicators of 65 ka of climate change from El'gygytgyn Crater Lake, Northeastern Siberia
Journal of Paleolimnology,
37
(1)
105-122
2007
ISSN: 09212728Keywords:▾
bioturbation; clay mineral; climate change; crater lake; grain size; lacustrine deposit; paleoclimate; proxy climate record; sedimentology, Chukchi; Eurasia; Lake El'gygytgyn; Russian Federation
Abstract: ▾ El'gygytgyn Crater Lake, NE Siberia was investigated for sedimentological proxies for regional climate change with a focus on the past 65 ka. Sedimentological parameters assessed relative to magnetic susceptibility include stratigraphy, grain size, clay mineralogy and crystallinity. Earlier work suggests that intervals of high susceptibility in these sediments are coincident with warmer (interglacial-like) conditions and well-mixed oxygenated bottom waters. In contrast, low susceptibility intervals correlate with cold (glacial-like) conditions when perennial ice-cover resulted in anoxia and the dissolution of magnetic carrier minerals. The core stratigraphy contains both well-laminated to non-laminated sequences. Reduced oxygen and lack of water column mixing preserved laminated sequences in the core. A bioturbation index based upon these laminated and non- laminated sequences co-varies with total organic carbon (TOC) and magnetic susceptibility. Clay mineral assemblages include illite, highly inter-stratified illite/smectite, and chlorite. Under warm or hydrolyzing conditions on the landscape around the lake, chlorite weathers easily and illite/smectite abundance increase, which produces an inverse relationship in the relative abundance of these clays. Trends in relative abundance show distinct down-core changes that correlate with shifts in susceptibility. The mean grain-size (6.92 μm) is in the silt-size fraction, with few grains larger than 65 μm. Terrigenous input to the lake comes from over 50 streams that are filtered through storm berms, which limits clastic deposition into the lake system. The sedimentation rate and terrigenous input grain-size is reduced during glacial intervals. Measurements of particle-size distribution indicate that the magnetic susceptibility fluctuations are not related to grain size. Lake El'gygytgyn's magnetic susceptibility and clay mineralogy preserves regional shifts in climate including many globally recognized events like the Younger Dryas and Bolling/Allerod. The sedimentary deposits reflect the climatic transitions starting with MIS4 through the Holocene transition. This work represents the first extensive sedimentological study of limnic sediment proxies of this age from Chukotka (Fig. 1). © 2006 Springer Science+Business Media B.V.
659.
Search for a meteoritic component in drill cores from the Bosumtwi impact structure, Ghana: Platinum group element contents and osmium isotopic characteristics
Meteoritics and Planetary Science,
42
(4-5)
743 – 753
2007
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ An attempt was made to detect a meteoritic component in both crater-fill (fallback) impact breccias and fallout suevites (outside the crater rim) at the Bosumtwi impact structure in Ghana. Thus far, the only clear indication for an extraterrestrial component related to this structure has been the discovery of a meteoritic signature in Ivory Coast tektites, which formed during the Bosumtwi impact event. Earlier work at Bosumtwi indicated unusually high levels of elements that are commonly used for the identification of meteoritic contamination (i.e., siderophile elements, including the platinum group elements [PGE]) in both target rocks and impact breccias from surface exposures around the crater structure, which does not allow unambiguous verification of an extraterrestrial signature. The present work, involving PGE abundance determinations and Os isotope measurements on drill core samples from inside and outside the crater rim, arrives at the same conclusion. Despite the potential of the Os isotope system to detect even small amounts of extraterrestrial contribution, the wide range in PGE concentrations and Os isotope composition observed in the target rocks makes the interpretation of unradiogenic, high-concentration samples as an impact signature ambiguous. © The Meteoritical Society, 2007. Printed in USA.
658.
Seismic investigation of the El'gygytgyn impact crater lake (Central Chukotka, NE Siberia): Preliminary results
Journal of Paleolimnology,
37
(1)
49-63
2007
ISSN: 09212728Keywords:▾
crater lake; impact structure; lacustrine deposit; paleoclimate; seismic data; seismic survey, Chukchi; Eurasia; Lake El'gygytgyn; Russian Federation
Abstract: ▾ The 12 km wide and about 175 m deep El'gygytgyn crater lake in Central Chukotka, NE Siberia, is of special interest for investigation as it could provide the first undisturbed 3.6 Ma terrestrial record from the Arctic realm, reaching back a million years before the first major glaciation of the Northern Hemisphere. A single-channel seismic survey was carried out on an expedition to the lake in 2000, in which both high resolution and deep penetration data were acquired. Seismic data suggest an impact crater structure in Cretaceous volcanic bedrock, indicated by velocities of >5000 m s-1, whose upper 500-600 m is brecciated. The lake is filled with two units of sediments, the upper one well stratified and the lower one massive. In the center of the lake, the combined thickness of the two sedimentary units is estimated to be 320-350 m. The upper unit is draped over the location of an interpreted central peak and is locally intercalated with debris flows, mainly in the western part of the lake and at the lake margins. Most of the lower unit is obscured by multiples as a result of high reflection coefficients in the upper unit. As at least the upper unit appears to be undisturbed by glaciation, the lake should yields unique information on the paleoclimatic development of the East Siberian Arctic. © 2006 Springer Science+Business Media B.V.
657.
Seismically induced changes of the fluid signature detected by a multi-isotope approach (He, CO2, CH4, N2) at the Wettinquelle, Bad Brambach (central Europe)
Journal of Geophysical Research: Solid Earth,
112
(4)
2007
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
Central Europe; Eger; Eurasia; Europe; Heves; Hungary; coseismic process; fluid composition; geodynamics; hydrothermal system; isotopic composition; thermal spring
Abstract: ▾ We present a study considering the systematics of gas and isotope compositions (3He/4He, δ13 CCO2, δ13 CCH4, δ 15N) of a permanent magmatic CO2 flux in the hydrothermal system of the spring "Wettinquelle" in Bad Brambach and their relation to the seismic activity beneath the western Eger rift. The gas and isotope compositions were monitored for more than 3 years. The time series includes periods before, during, and after a 4-month-long seismically active period from the end of August to the end of December 2000. Shifts due to admixture of crustal components were found for all monitored isotope ratios during and after the seismically active period. In case of helium and nitrogen, isotopic anomalies occurred already about 6 weeks before the beginning of the seismically active period, contemporaneous with a water level anomaly of the well VL4 near the Wettinquelle. On the one hand, preseismic deformations may be responsible for the observed isotope anomalies; on the other hand, coseismic fracturing processes in the surroundings of the hypocenters may play a role. Both effects produce greater permeability and result in the release of crustal fluids. The migration and admixture of these crustal components to the "permanent" upper mantle-derived fluid flux result in geochemical anomalies that persist for more than 2 years. The results of the detailed isotope monitoring have proven to be an important contribution to understand the geodynamic processes that may presently be going on in the region Vogtland/NW Bohemia. Copyright 2007 by the American Geophysical Union.
656.
Seismology inside the fault zone: Applications to fault-zone properties and rupture dynamics
Scientific Drilling
(1 SUPPL. 1)
84-87
2007
ISSN: 18168957655.
Stress orientations of Taiwan Chelungpu-Fault Drilling Project (TCDP) hole-A as observed from geophysical logs
Geophysical Research Letters,
34
(1)
2007
ISSN: 00948276Keywords:▾
Boreholes; Earthquakes; Image sensors; Mechanics; Structural geology; Tectonics, Dipole Sonic Imager (DSI); Formation Micro Imager (FMI); Geophysical logs, Geophysical prospecting, bedding plane; borehole; Chi-Chi earthquake 1999; earthquake rupture; Eurasian plate; Philippine Sea plate; shear zone; stress field; well logging, Asia; Eurasia; Far East; Taiwan
Abstract: ▾ The Taiwan Chelungpu-fault Drilling Project (TCDP) drilled a 2-km-deep research borehole to investigate the structure and mechanics of the Chelungpu Fault that ruptured in the 1999 Mw 7.6 Chi-Chi earthquake. Geophysical logs of the TCDP were carried out over depths of 500-1900 in, including Dipole Sonic Imager (DSI) logs and Formation Micro Imager (FMI) logs in order to identify bedding planes, fractures and shear zones. From the continuous core obtained from the borehole, a shear zone at a depth of 1110 meters is interpreted to be the Chelungpu fault, located within the Chinshui Shale, which extends from 1013 to 1300 meters depth. Stress-induced borehole breakouts were observed over nearly the entire length of the wellbore. These data show an overall stress direction (∼N115°E) that is essentially parallel to the regional stress field and parallel to the convergence direction of the Philippine Sea plate with respect to the Eurasian plate. Variability in the average stress direction is seen at various depths. In particular there is a major stress orientation anomaly in the vicinity of the Chelungpu fault. Abrupt stress rotations at depths of 1000 in and 1310 in are close to the Chinshui Shale's upper and lower boundaries, suggesting the possibility that bedding plane slip occurred during the Chi-Chi earthquake. Copyright 2007 by the American Geophysical Union.
654.
Shock-metamorphic petrography and microRaman spectroscopy of quartz in upper impactite interval, ICDP drill core LB-07A, Bosumtwi impact crater, Ghana
Meteoritics and Planetary Science,
42
(4-5)
591 – 609
2007
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ Standard and universal stage optical microscope and microRaman spectroscopic examination of quartz from the upper impactite interval of the International Continental Scientific Drilling Program (ICDP) Lake Bosumtwi crater drill core LB-07A demonstrates widespread but heterogeneous evidence of shock metamorphism. In the upper impactite, which comprises interbedded polymict lithic breccia and suevite from a drilling depth of 333.4-415.7 m, quartz occurs as a major component within metasedimentary lithic clasts and as abundant, isolated, single-crystal grains within matrix. The noted quartz shock-metamorphic features include phenomena related to a) deformation, such as abundant planar microstructures, grain mosaicism, and reduced birefringence; b) phase transformations, such as rare diaplectic quartz glass and very rare coesite; c) melting, such as isolated, colorless to dark, glassy and devitrified vesicular melt grains; and d) secondary, post-shock features such as abundant, variable decoration of planar microstructures and patchy grain toasting. Common to abundant planar deformation features (PDFs) in quartz are dominated by ω {1013}-equivalent crystallographic planes, although significant percentages of π{1012} and other higher index orientations also occur; notably, c(0001) planes are rare. Significantly, the quartz PDF orientations match most closely those reported elsewhere from strongly shocked, crystalline-target impactites. Barometry estimates based on quartz alteration in the upper impactite indicate that shock pressures in excess of 20 GPa were widely reached; pressures exceeding 40-45 GPa were more rare. The relatively high abundances of decorated planar microstructures and grain toasting in shocked quartz, together with the nature and distribution of melt within suevite, suggest a water- or volatile-rich target for the Bosumtwi impact event. © The Meteoritical Society, 2007. Printed in USA.