All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
844.
Contamination assessment in microbiological sampling of the Eyreville core, Chesapeake Bay impact structure
Special Paper of the Geological Society of America,
458951-964
2009
ISSN: 00721077
Publisher: Geological Society of America
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
Abstract: ▾ 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.
843.
Contemporary Arctic change: A paleoclimate déjà vu?
Proceedings of the National Academy of Sciences of the United States of America,
106
(44)
18431-18432
2009
ISSN: 00278424Keywords:▾
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
842.
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
Exploration Engineering (Rock &, Soil Drilling and Tunneling),
36
(S1)
388-392
2009
841.
Continuous gas monitoring in the West Bohemian earthquake area, Czech Republic: First results
Studia Geophysica et Geodaetica,
53
(3)
315 – 328
2009
ISSN: 00393169Keywords:▾
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
Abstract: ▾ Two stations monitoring concentrations of carbon dioxide and radon in soil gas (Oldřiášská and Nový 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 Oldŕliíǎská and Nový 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 Oldčíšská and Nový 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.
840.
Cretaceous phytoplankton assemblages from songke core-1, North and South (SK-1, N and S) of Songliao Basin, Northeast China
Acta Geologica Sinica (English Edition),
83
(5)
868-874
2009
ISSN: 10009515Keywords:▾
Acritarcha; Botryococcus; Chlorophyta; Dinophyceae; Pediastrum; Vesperopsis
Abstract: ▾ 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.
839.
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
Special Paper of the Geological Society of America,
458617-632
2009
ISSN: 00721077
Publisher: Geological Society of America
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
Abstract: ▾ 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.
838.
Deep drilling in the Chesapeake Bay impact structure - An overview
Special Paper of the Geological Society of America,
4581-20
2009
ISSN: 00721077
Publisher: Geological Society of America
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
Abstract: ▾ 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.
837.
Deep drilling into a mantle plume volcano: The Hawaii scientific drilling project
Scientific Drilling
(7)
4-14
2009
ISSN: 18168957Keywords:▾
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
Abstract: ▾ 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.
836.
Deep fault drilling project-alpine fault, New Zealand
Scientific Drilling
(8)
75-82
2009
ISSN: 18168957
Publisher: Integrated Ocean Drilling Program
835.
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
Tectonophysics,
475
(2)
204 – 219
2009
ISSN: 00401951Keywords:▾
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
Abstract: ▾ 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.
834.
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
Dixue Qianyuan/ Earth Science Frontiers,
16
(2)
314-323
2009
ISSN: 18725791Abstract: ▾ 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.
833.
Description of Cretaceous Sedimentary Sequence of the Quantou Formation Recovered by CCSD-SK-Is Borehole in Songliao Basin: Lithostratigraphy, Sedimentary Facies and Cyclic Stratigraphy
Dixue Qianyuan/ Earth Science Frontiers,
16
(2)
324 – 338
2009
ISSN: 18725791Abstract: ▾ 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.
832.
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
Dixue Qianyuan/ Earth Science Frontiers,
16
(2)
288 – 313
2009
ISSN: 18725791Abstract: ▾ 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.
831.
Complex drilling logistics for Lake El'gygytgyn, NE Russia
Scientific Drilling
(7)
38-39
2009
ISSN: 18168957830.
Clay mineral anomalies in the fault zone of the Chelungpu fault, Taiwan, and their implications
Geophysical Research Letters,
36
(18)
2009
ISSN: 00948276
Publisher: American Geophysical Union
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
Abstract: ▾ 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.
829.
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
Journal of Metamorphic Geology,
27
(9)
805 – 825
2009
ISSN: 15251314Keywords:▾
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
Abstract: ▾ 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.
828.
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
Special Paper of the Geological Society of America,
458543-557
2009
Abstract: ▾ 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.
827.
'PALEOVAN', International Continental Scientific Drilling Program (ICDP): site survey results and perspectives
Quaternary Science Reviews,
28
(15-16)
1555-1567
2009
ISSN: 02773791Keywords:▾
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)
Abstract: ▾ 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.
826.
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
Acta Petrologica Sinica,
25
(5)
1178 – 1190
2009
ISSN: 10000569
Publisher: Science Press
Abstract: ▾ 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.
825.
A 40,000-year record of environmental change from ancient Lake Ohrid (Albania and Macedonia)
Journal of Paleolimnology,
41
(3)
407 – 430
2009
ISSN: 09212728Keywords:▾
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
Abstract: ▾ 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.
824.
A dual-layer Chicxulub ejecta sequence with shocked carbonates from the Cretaceous-Paleogene (K-Pg) boundary, Demerara Rise, western Atlantic
Geochimica et Cosmochimica Acta,
73
(4)
1180-1204
2009
Abstract: ▾ 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.
823.
A model for the formation of the Chesapeake Bay impact crater as revealed by drilling and numerical simulation
Special Paper of the Geological Society of America,
458571-585
2009
Abstract: ▾ 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.
822.
A model for the formation of the Chesapeake Bay impact crater as revealed by drilling and numerical simulation
Special Paper of the Geological Society of America,
458571-585
2009
ISSN: 00721077
Publisher: Geological Society of America
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
Abstract: ▾ 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.
821.
A non-magmatic iron projectile for the Gardnos impact event
Chemical Geology,
258
(3-4)
145-156
2009
Abstract: ▾ 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.
820.
Acoustic impedance inversion and seismic reflection continuity analysis for delineating gas hydrate resources near the Mallik research sites, Mackenzie Delta, Northwest Territories, Canada
GEOPHYSICS,
74
(5)
B125-B137
2009
ISSN: 00168033
Publisher: Society of Exploration Geophysicists
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
Abstract: ▾ 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.