All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
819.
Broadband records of earthquakes in deep gold mines and a comparison with results from SAFOD, California
Bulletin of the Seismological Society of America,
99
(5)
2815-2824
2009
ISSN: 00371106Keywords:▾
Broadband records; California; Deep gold mines; Ground motion parameters; Ground-motion; Hypocentral distance; Maximum displacement; Maximum slip; Peak ground velocity; Peak velocities; Repeating earthquake; Rupture surface; Rupture zone; San Andreas Fault; Seismic hazards; Seismic moment; Seismic networks; Slip rates; Source process; Stick-slip friction; Temporary networks, Experiments; Friction; Gold mines; Mines; Mining; Parameter estimation; Risk assessment; Slip forming; Tectonics, Earthquakes, earthquake catalogue; earthquake hypocenter; earthquake magnitude; gold mine; ground motion; mining-induced seismicity; seismic hazard; seismic moment; slip rate, California; North America; United States
Abstract: ▾ For one week during September 2007, we deployed a temporary network of field recorders and accelerometers at four sites within two deep, seismically active mines. The ground-motion data, recorded at 200 samples/sec, are well suited to determining source and ground-motion parameters for the mining-induced earthquakes within and adjacent to our network. Four earthquakes with magnitudes close to 2 were recorded with high signal/noise at all four sites. Analysis of seismic moments and peak velocities, in conjunction with the results of laboratory stick-slip friction experiments, were used to estimate source processes that are key to understanding source physics and to assessing underground seismic hazard. The maximum displacements on the rupture surfaces can be estimated from the parameter Rv, where v is the peak ground velocity at a given recording site, and R is the hypocentral distance. For each earthquake, the maximum slip and seismic moment can be combined with results from laboratory friction experiments to estimate the maximum slip rate within the rupture zone. Analysis of the four M 2 earthquakes recorded during our deployment and one of special interest recorded by the in-mine seismic network in 2004 revealed maximum slips ranging from 4 to 27 mm and maximum slip rates from 1.1 to 6:3 m=sec. Applying the same analyses to an M 2.1 earthquake within a cluster of repeating earthquakes near the San Andreas Fault Observatory at Depth site, California, yielded similar results for maximum slip and slip rate, 14 mm and 4:0 m=sec.
818.
Analyses of pseudotachylyte from Hole-B of Taiwan Chelungpu Fault Drilling Project (TCDP); their implications for seismic slip behaviors during the 1999 Chi-Chi earthquake
Tectonophysics,
469
(1-4)
13-24
2009
ISSN: 00401951Keywords:▾
Chelungpu fault; Chi-Chi earthquake; Partial melting; Pseudotachylyte; Seismic slip, Boreholes; Drops; Elastohydrodynamic lubrication; Friction; Melting; Tribology, Earthquakes, active fault; Chi-Chi earthquake 1999; earthquake magnitude; earthquake rupture; fault gouge; fault slip; focal mechanism; partial melting; pseudotachylite; uplift
Abstract: ▾ The seismic slip behavior during the 1999 Chi-Chi, Taiwan, earthquake (Mw 7.6) was contrastive between the northern and southern segments of the activated Chelungpu fault; large, fast and smooth slips with large stress drop in the north, while smaller, slower and irregular slips with smaller stress drop in the south. We analyzed the pseudotachylyte samples recovered from 1194 m, 1243 m and 1314 m depths of Hole-B of Taiwan Chelungpu fault Drilling Project (TCDP) to reveal the spatial difference in friction mechanism. All pseudotachylyte layers are thin (0.7-2.8 cm), the volume fraction of protoliths is very large (more than 63%), and the estimated temperature distribution is very heterogeneous from ca. 750-1750 °C. These observations suggest that these pseudotachylyte melts were in the partial melting regime of Montgomery [Montgomery, R.S., 1976. Friction and wear at high sliding speeds. Wear 36, 275-298] where friction coefficient is abnormally large. Similar pseudotachylyte was found already in the core sample from 175 m depth of the Nanto borehole penetrating the southern fault. Since both pseudotachylyte samples from the two boreholes are older than the 1999 Chi-Chi event and have been uplifted from depths farther down-dip of their current locations, it is likely that recent seismic ruptures also would have encountered these mechanical barriers of viscous melt patches at deeper parts in the north than in the south. Elastohydrodynamic lubrication of clayey gouge worked effectively at the shallower parts of the northern segment, however there is no evidence that it played an important role in the south. These differences are the plausible causes of the contrastive local slip behaviors during the Chi-Chi earthquake. © 2008 Elsevier B.V. All rights reserved.
817.
Analysis of Izmit aftershocks 25 days before the November 12th 1999 Düzce earthquake, Turkey
Tectonophysics,
474
(3-4)
507-515
2009
ISSN: 00401951Keywords:▾
Aftershock distributions; B value; Crustal earthquakes; Earthquake frequency; Earthquake rupture; Fault asperities; Gutenberg-Richter law; High density; High stress; High stress concentration; Izmit earthquake; Mainshock; North Anatolian Fault Zone; Postseismic slip; Spatial cluster; Spatial clustering; Stress changes; Surface displacement, Earthquake effects; Stress concentration, Laws and legislation, aftershock; coseismic process; displacement; earthquake magnitude; earthquake rupture; earthquake trigger; fault zone; Kocaeli earthquake 1999; low velocity zone; North Anatolian Fault; postseismic process; slip rate; stress change, Duzce; Eurasia; Turkey
Abstract: ▾ We investigate spatial clustering of 2414 aftershocks along the Izmit Mw = 7.4 August 17, 1999 earthquake rupture zone. 25 days prior to the Düzce earthquake Mw = 7.2 (November 12, 1999), we analyze two spatial clusters, namely Sakarya (SC) and Karadere-Düzce (KDC). We determine the earthquake frequency-magnitude distribution (b-value) for both clusters. We find two high b-value zones in SC and one high b-value zone in KDC which are in agreement with large coseismic surface displacements along the Izmit rupture. The b-values are significantly lower at the eastern end of the Izmit rupture where the Düzce mainshock occurred. These low b-values at depth are correlated with low postseismic slip rate and positive Coloumb stress change along KDC. Since low b-values are hypothesized with high stress levels, we propose that at the depth of the Düzce hypocenter (12.5 km), earthquakes are triggered at higher stresses compared to shallower crustal earthquake. The decrease in b-value from the Karadere segment towards the Düzce Basin supports this low b-value high stress hypothesis at the eastern end of the Izmit rupture. Consequently, we detect three asperity regions which are correlated with high b-value zones along the Izmit rupture. According to aftershock distribution the half of the Düzce fault segment was active before the 12 November 1999 Düzce mainshock. This part is correlated with low b-values which mean high stress concentration in the Düzce Basin. This high density aftershock activity presumably helped to trigger the Düzce event (Mw = 7.2) after the Izmit Mw 7.4 mainshock. © 2009 Elsevier B.V. All rights reserved.
816.
Anti-sloughing drilling fluid technology for bare hole in CCSD-SK1
石油钻采工艺,
31
(4)
53-56
2009
815.
Arkosic rocks from the san andreas fault observatory at depth (SAFOD) borehole, central california: Implications for the structure and tectonics of the San Andrea fault zone
Lithosphere,
1
(4)
206-226
2009
ISSN: 19418264
Publisher: Geological Society of America
DOI:10.1130/L13.1
Keywords:▾
Boreholes; Fission reactions; Observatories; Silicate minerals; Strike-slip faults; Well logging; Zircon, Bedding orientations; Detrital zircon; Geophysical logs; Measured depths; San Andreas fault; Seismic velocities; Submarine fans; Zircon fission tracks, Sedimentary rocks, borehole; electrical resistivity; fission track dating; petrography; San Andreas Fault; sedimentary rock; seismic velocity, California; United States
Abstract: ▾ The San Andreas Fault Observatory at Depth (SAFOD) drill hole encountered indurated, high-seismic-velocity arkosic sedimentary rocks west of the active trace of the San Andreas fault in central California. The arkosic rocks are juxtaposed against granitic rocks of the Salinian block to the southwest and against fine-grained Great Valley Group and Jurassic Franciscan rocks to the northeast. We identify three distinct lithologic units using cuttings, core petrography, electrical resistivity image logs, zircon fission-track analyses, and borehole-based geophysical logs. The upper arkose occurs from 1920 to 2530 m measured depth (mmd) in the borehole and is composed of five structural blocks defined by bedding orientations, wireline log character, physical properties, and lithologic characteristics. A clay-rich zone between 2530 and 2680 mmd is characterized by low V p and an enlarged borehole. The lower arkose lies between 2680 and 3150 mmd. Fission-track detrital zircon cooling ages are between 64 and 70 Ma, appear to belong to a single population, and indicate a latest Cretaceous to Paleogene maximum depositional age. We interpret these Paleocene-Eocene strata to have been deposited in a proximal submarine fan setting shed from a Salinian source block, and they correlate with units to the southeast, along the western and southern edge of the San Joaquin Basin, and with arkosic conglomerates to the northwest. The arkosic section constitutes a deformed fault-bounded block between the modern strand of the San Andreas fault to the northeast and the Buzzard Canyon fault to the southwest. Significant amounts of slip appear to have been accommodated on both strands of the fault at this latitude. © 2009 Geological Society of America.
814.
As time goes by: A simple fool's guide to molecular clock approaches in invertebrates
American Malacological Bulletin,
27
(1-2)
25 – 45
2009
ISSN: 07402783
Publisher: American Malacological Society
Keywords:▾
Caenogastropoda; Invertebrata; Protostomia
Abstract: ▾ Biologists have used a wide range of organisms to study the origin of taxa and their subsequent evolutionary change in space and time. One commonly used tool is the molecular clock approach, relating substitution rates of nucleotide or amino acid sequences to divergence times. The accuracy of the molecular clock, however, has long been subject to controversy, and numerous papers have addressed problems associated with estimating divergence times. Some workers pointed out a striking imbalance between sophisticated software algorithms used for molecular clock analyses on the one hand, and the poor data on the other hand. Moreover, there is often unease among workers relative to molecular clocks because of the controversy surrounding the approach, the complex mathematical background of many molecular clock tools, the still limited number of available, user-friendly software packages, the often confusing terminology of molecular clock approaches, and the general lack of reliable calibration points and/or external clock rates. The current review therefore briefly provides an overview of analytical strategies, covering approaches based on calibration points and/or bounds, approaches based on external clock rates, and approaches that attempt to estimate relative divergence times in the absence of information that can be used for estimating substitution rates. It also deals with major problems and pitfalls associated with data and analyses, including potential errors of calibration points and bounds, the performance of the gene(s) used, estimation of confidence limits, and misinterpretation of the results of clock analyses due to problems with sampling design. A substantial part of the review addresses the question of "universal" molecular clock rates and summarizes important biological and life history variables that account for deviations from rate constancy both between lineages and at different times within lineages. The usefulness of these factors is discussed within the framework of "trait-specific" molecular clock rates. One such clock rate is introduced here for the cytochrome c oxidase subunit I (COI) gene in small dioecious, tropical and subtropical Protostomia with a generation time of approximately one year. A flow chart is provided as a "simple fool's guide" to molecular clock analyses, together with a glossary of widely used terms in molecular clock approaches. Finally, step-by-step examples are provided for calculating divergence times in the caenogastropod subfamily Pyrgulinae based on both an internal calibration point and a "trait-specific" molecular clock rate, and it is demonstrated how a relative clock approach can be used for testing evolutionary hypotheses. Our review encourages a judicious use of molecular clock analyses in evolutionary studies of invertebrates by demonstrating their great potential on the one hand and (often-manageable) problems and pitfalls on the other hand.
813.
High-resolution sequence stratigraphic characteristic and favorable hydrocarbon accumulation prediction of Sifangtai to Mingshui formation in the north of Songliao Basin
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology),
40
(6)
1679 – 1688
2009
ISSN: 16727207Abstract: ▾ According to seismic, logging, core, outcrop palaeoclimate and palaeontologic data, synthetic seismogram was used to demarcate and analyze the area structure evolution characteristic, and using concept and method of sedimentology and sequence stratigraphy, four types of sequence boundaries were identified, including regional unconformity surface, exposure surface, channel scouring and eroding surface and formation stacking transformation surface, and a new supersequence boundary SB4 was also divided. The results show that Sifangtai to Mingshui formation in the north of Songliao Basin finally can be divided into one supersequence group, two supersequences(SSQ1 and SSQ2), six sequences(SQ1?SQ6) and seventy systems tracts and the high resolution sequence stratigraphic framework is also established. The rule of sediment fill and evolution in the sequence stratigraphic framework in the north of the basin is as follows: In the deposition period of sequence SQ1 to SQ3, the basin mainly develops fluvial and coastal-shallow lake facies where provenance's direction is in the direction of SN along the long axis of the basin, while in the deposition period of sequence SQ4 to SQ6, the basin mainly develops braid river delta and costal-shallow lake facies where provenance is in the direction of EW along the short axis of the basin. The basin's deposit center has also constantly migrated to the northwest from the beginning of the Sifangtai formation. Based on the comprehensive research on the reservoir-cap combination distribution of sequence stratigraphy framework and the conditions of the migration, accumulation of oil and gas show that sequence SQ1 of Sifangtai formation develops the most favorable reservoir-cap combination, and the thick bedded channel sand of the lowstand systems tract of sequence SQ1 in Da'an-Xinzhan area is the most favorable hydrocarbon accumulation area which probably develops structural-lithologic secondary hydrocarbon reservoir.
812.
Biotic effects of the Chicxulub impact, K-T catastrophe and sea level change in Texas
Palaeogeography, Palaeoclimatology, Palaeoecology,
271
(1-2)
52-68
2009
Abstract: ▾ Biotic effects of the Chicxulub impact, the K-T event and sea level change upon planktic foraminifera were evaluated in a new core and outcrops along the Brazos River, Texas, about 1000 km from the Chicxulub impact crater on Yucatan, Mexico. Sediment deposition occurred in a middle neritic environment that shallowed to inner neritic depths near the end of the Maastrichtian. The sea level fall scoured submarine channels, which were infilled by a sandstone complex with reworked Chicxulub impact spherules and clasts with spherules near the base. The original Chicxulub impact ejecta layer was discovered 45-60 cm below the sandstone complex, and predates the K-T mass extinction by about 300,000 years. Results show that the Chicxulub impact caused no species extinctions or any other significant biotic effects. The subsequent sea level fall to inner neritic depth resulted in the disappearance of all larger (> 150 μm) deeper dwelling species creating a pseudo-mass extinction and a survivor assemblage of small surface dwellers and low oxygen tolerant taxa. The K-T boundary and mass extinction was identified 40-80 cm above the sandstone complex where all but some heterohelicids, hedbergellids and the disaster opportunistic guembelitrids went extinct, coincident with the evolution of first Danian species and the global δ13C shift. These data reveal that sea level changes profoundly influenced marine assemblages in near shore environments, that the Chicxulub impact and K-T mass extinction are two separate and unrelated events, and that the biotic effects of this impact have been vastly overestimated. © 2008 Elsevier B.V.
811.
Broadband records of earthquakes in deep gold mines and a comparison with results from SAFOD, California
Bulletin of the Seismological Society of America,
99
(5)
2815-2824
2009
ISSN: 00371106Keywords:▾
Broadband records; California; Deep gold mines; Ground motion parameters; Ground-motion; Hypocentral distance; Maximum displacement; Maximum slip; Peak ground velocity; Peak velocities; Repeating earthquake; Rupture surface; Rupture zone; San Andreas Fault; Seismic hazards; Seismic moment; Seismic networks; Slip rates; Source process; Stick-slip friction; Temporary networks, Experiments; Friction; Gold mines; Mines; Mining; Parameter estimation; Risk assessment; Slip forming; Tectonics, Earthquakes, earthquake catalogue; earthquake hypocenter; earthquake magnitude; gold mine; ground motion; mining-induced seismicity; seismic hazard; seismic moment; slip rate, California; North America; United States
Abstract: ▾ For one week during September 2007, we deployed a temporary network of field recorders and accelerometers at four sites within two deep, seismically active mines. The ground-motion data, recorded at 200 samples/sec, are well suited to determining source and ground-motion parameters for the mining-induced earthquakes within and adjacent to our network. Four earthquakes with magnitudes close to 2 were recorded with high signal/noise at all four sites. Analysis of seismic moments and peak velocities, in conjunction with the results of laboratory stick-slip friction experiments, were used to estimate source processes that are key to understanding source physics and to assessing underground seismic hazard. The maximum displacements on the rupture surfaces can be estimated from the parameter Rv, where v is the peak ground velocity at a given recording site, and R is the hypocentral distance. For each earthquake, the maximum slip and seismic moment can be combined with results from laboratory friction experiments to estimate the maximum slip rate within the rupture zone. Analysis of the four M 2 earthquakes recorded during our deployment and one of special interest recorded by the in-mine seismic network in 2004 revealed maximum slips ranging from 4 to 27 mm and maximum slip rates from 1.1 to 6:3 m=sec. Applying the same analyses to an M 2.1 earthquake within a cluster of repeating earthquakes near the San Andreas Fault Observatory at Depth site, California, yielded similar results for maximum slip and slip rate, 14 mm and 4:0 m=sec.
810.
Description of Cretaceous Sedimentary Sequence of the Yaojia Formation Recovered by CCSD-SK-Is Borehole in Songliao Basin: Lithostratigraphy, Sedimentary Facies and Cyclic Stratigraphy
Dixue Qianyuan/ Earth Science Frontiers,
16
(2)
140-151
2009
ISSN: 18725791Abstract: ▾ The Yaojia Formation recovered by CCSD-SK-Is borehole (China Cretaceous Continental Scientific Drilling-SongkeI-the south borehole) is 157.67 m long and 99.96% of cores recovery. The age of the formation corresponds with a range from the Santonian to the early Campanian. The sequences and processes of lithology-lithofacies and cyclic stratigraphy are revealed by a detailed core description. Eleven rock types and three kinds of sedimentary subfacies, including shallow lake, deep lake, and delta front, are recognized from the drilling core. There are eleven sedimentary microfacies including dolostone, argillaceous limestone, shallow lake turbidite, deep lake turbidite, subaqueous mouth bar, distal bar, sheet sandstone, subaqueous distributary bay, slump deposits, shallow lake mudstone, and deep lake mudstone. The Yaojia Formation represents one hundred and fifty-one meter-scale cycles (sixth-order cycle), forty-five fifth-order cycles, nine fourth-order cycles, and three third-order cycles. Meticulous depiction (centimeter level) of the whole Formation provides an approach to study its sedimentary process with high precision. The red beds with a thickness of 43% in the Yaojia Formation, being one of fewer continental red beds depicted meticulously in the world, will become a standard of potential formulation section for the studies of Cretaceous global oxygen-enriched events. © 2009 China University of Geosciences (Beijing) and Peking University.
809.
Atlantic forcing of persistent drought in West Africa
Science,
324
(5925)
377 – 380
2009
ISSN: 10959203Keywords:▾
Africa; Ashanti; Atlantic Ocean; Ghana; Lake Bosumtwi; Sub-Saharan Africa; West Africa; rain; atmospheric forcing; drought; monsoon; reconstruction; sea surface temperature; twentieth century; Africa; article; Atlantic Ocean; controlled study; drought; environmental temperature; Ghana; hydrology; lake sediment; precipitation; priority journal; seasonal variation; spectroscopy
Abstract: ▾ Although persistent drought in West Africa is well documented from the instrumental record and has been primarily attributed to changing Atlantic sea surface temperatures, little is known about the length, severity, and origin of drought before the 20th century. We combined geomorphic, isotopic, and geochemical evidence from the sediments of Lake Bosumtwi, Ghana, to reconstruct natural variability in the African monsoon over the past three millennia. We find that intervals of severe drought lasting for periods ranging from decades to centuries are characteristic of the monsoon and are linked to natural variations in Atlantic temperatures. Thus the severe drought of recent decades is not anomalous in the context of the past three millennia, indicating that the monsoon is capable of longer and more severe future droughts.
808.
Direct measurements of chemical composition of shock-induced gases from calcite: an intense global warming after the Chicxulub impact due to the indirect greenhouse effect of carbon monoxide
Earth and Planetary Science Letters,
282
(1-4)
56-64
2009
Abstract: ▾ Shock-induced devolatilization in hypervelocity impacts has been considered to play important roles in the atmospheric evolution and mass extinctions in Earth's history. Although the chemical composition of shock-induced gas species from carbonate rocks has been considered as a key to understand the environmental change after the Chicxulub impact, it has not been investigated extensively before. Here, we conduct direct measurements of the chemical composition (CO/CO2) of shock-induced gas species from calcite (CaCO3) using both a laser gun system and an isotopic labeling technique. The CO/CO2 ratio of the shock-induced gas species from calcite is measured to be 2.02 ± 0.41, suggesting that gaseous CO has been dominant in the shock-induced gases in the Chicxulub impact. In order to evaluate the environmental effects of the injection of CO gas, we investigated the post-impact atmospheric chemistry by incorporating our experimental results into a tropospheric photochemical model. The results suggest that an intense (2-5 °C) global warming would have lasted for several years after a Chicxulub-size impact mainly due to the greenhouse effect of tropospheric O3, which is produced via photochemical reactions associated with CO gas. Such an intense global warming could have damaged the biosphere in the mass extinction at the Cretaceous-Paleogene (K-P) boundary. © 2009 Elsevier B.V. All rights reserved.
807.
Geologic columns for the ICDP-USGS Eyreville A and C cores, Chesapeake Bay impact structure: Postimpact sediments, 444 to 0 m depth
Special Paper of the Geological Society of America,
45891-114
2009
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Deposits; Recovery, Channel fills; Chesapeake bay impact structures; Coastal plain; Lower Miocene; Maximum thickness; Middle Miocene; Pleistocene sands; Siliciclastics, Sediments, crater; Eocene; fine grained sediment; impact structure; Oligocene; Pleistocene; sedimentation, Chesapeake Bay; United States
Abstract: ▾ A 443.9-m-thick, virtually undisturbed section of postimpact deposits in the Chesapeake Bay impact structure was recovered in the Eyreville A and C cores, Northampton County, Virginia, within the "moat" of the structure's central crater. Recovered sediments are mainly fine-grained marine siliciclastics, with the exception of Pleistocene sand, clay, and gravel. The lowest postimpact unit is the upper Eocene Chickahominy Formation (443.9-350.1 m). At 93.8 m, this is the maximum thickness yet recovered for deposits that represent the return to "normal marine" sedimentation. The Drummonds Corner beds (informal) and the Old Church Formation are thin Oligocene units present between 350.1 and 344.7 m. Above the Oligocene, there is a more typical Virginia coastal plain succession. The Calvert Formation (344.7-225.4 m) includes a thin lower Miocene part overlain by a much thicker middle Miocene part. From 225.4 to 206.0 m, sediments of the middle Miocene Choptank Formation, rarely reported in the Virginia coastal plain, are present. The thick upper Miocene St. Marys and Eastover Formations (206.0-57.8 m) appear to represent a more complete succession than in the type localities. Correlation with the nearby Kiptopeke core indicates that two Pliocene units are present: Yorktown (57.8-32.2 m) and Chowan River Formations (32.2-18.3 m). Sediments at the top of the section represent an upper Pleistocene channel-fill and are assigned to the Butlers Bluff and Occohannock Members of the Nassawadox Formation (18.3-0.6 m). © 2009 The Geological Society of America.
806.
Geochemical differences of the Hawaiian shield lavas: Implications for melting process in the heterogeneous Hawaiian plume
Journal of Petrology,
50
(8)
1553-1573
2009
ISSN: 00223530Keywords:▾
helium isotope; heterogeneity; igneous geochemistry; isotopic composition; lava; lead isotope; mantle chemistry; mantle plume; neodymium isotope; oceanic crust; partial melting; precision; shield; source rock; spatial distribution; strontium isotope, Hawaii [United States]; North America; United States
Abstract: ▾ Numerous geochemical studies have indicated that the Hawaiian mantle plume consists of several distinct components. However, their origin remains controversial, with a number of different interpretations having been proposed. We present new major element, trace element and high-precision Sr-Nd-Pb-He isotope data for a suite of fresh submarine lavas erupted by the Koolau, Kilauea and Loihi volcanoes, which are widely believed to have sampled three distinct Hawaiian plume components. The Sr and Nd isotope compositions of the Loihi lavas are similar to those of Kilauea lavas. However, our double-spike Pb isotopic data show that Loihi lavas have both Kilauea-like and Loihi-like compositions. This discovery implies that the Loihi source region contains a Kilauea-like ('Kea') mantle component. Our new data support the existence of three major types of intrinsic plume component: a Loihi component, an 'enriched' (Koolau) component and a 'depleted' (Kea) component. We propose that the Loihi component is a common component, forming the matrix in the Hawaiian mantle plume, and that the isotopic differences between the various shield lavas reflect different mixing proportions of the Loihi component and recycled oceanic crust components (EM-1-like and HIMU-like). The Koolau component contains a higher proportion of EM-1, whereas the Kea component contains a higher proportion of HIMU. EM-1- and HIMU-like recycled oceanic crust components are distributed on a fine scale throughout the peridotitic matrix within the Hawaiian plume. Both components are present in the sources beneath Kea- and Loa-trend volcanoes. We infer that the thermal structure and spatially distributed compositional heterogeneity of the plume are important in controlling the isotopic composition of lavas from a given Hawaiian volcano. © The Author 2009. Published by Oxford University Press. All rights reserved.
805.
Geochemical research on the Late Cretaceous strata of Well SK1 in Songliao Basin.
Earth Science Frontiers,
16
(5)
181-191
2009
804.
Geochemistry of impactites and crystalline basement-derived lithologies from the ICDP-USGS Eyreville A and B drill cores, Chesapeake Bay impact structure, Virginia, USA
Special Paper of the Geological Society of America,
458481-541
2009
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Alumina; Aluminum oxide; Buildings; Crystalline materials; Crystalline rocks; Drills; Granite; Hematite; Infill drilling; Magnesia; Sedimentology; Silica; Sodium compounds; Structure (composition); Titanium dioxide, Chemical compositions; Chesapeake bay impact structures; Continental scientific drillings; Crystalline basement; Crystalline targets; Negative correlation; Positive correlations; U.s. geological surveys, Core drilling, amphibolite; basement rock; breccia; chemical composition; coastal sediment; crystalline rock; enrichment; gneiss; I-type rock; impact structure; impactite; lithology; research program; sandstone; schist; sediment chemistry, Chesapeake Bay; United States; Virginia
Abstract: ▾ We investigated whole-rock chemical compositions of 318 samples of Exmore breccia (diamicton), impactite (suevite, impact melt rock, polymict lithic impact breccia), and crystalline basement-derived rocks from 444 to 1766 m depth in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B drill cores (Chesapeake Bay impact structure, Virginia, USA). Here, we compare the average chemical compositions for the Exmore breccia (diamicton), the impactites and their subunits, sandstone, granite, granitic gneiss, and amphibolite of the lithic block section (1095.7-1397.2 m depth), cataclastic gneiss of the impact breccia section, and schist and pegmatite/granite of the basal crystalline section (1551.2-1766.3 m depth). The granite of the megablock (1097.7-1371.1 m depth) is of I-type and is seemingly related to a syncollisional setting. The amphibolite (1377.4-1387.5 m depth) of the lithic block section is of igneous origin and has a tholeiitic character. Based on chemical composition, the Exmore breccia (diamicton) can be subdivided into five units (444.9-450.7, 450.7-468, 468-518, 518-528, and 528-̃865 m depth). The units in the depth intervals of 450.7-468 and 518-528 m are enriched in TiO2, MgO, Sc, V, Cr, and Zn contents compared to the other Exmore breccia units. In some samples, especially at ̃451-455 m depth, the Exmore breccia contains significant amounts of P 2 O 5 . The Exmore breccia is recognized as a mixture of all sedimentary and crystalline target components, and, when compared to the impactites, it contains a significant amount of a SiO 2 -rich target component of sedimentary origin. The chemical composition of the impactites overlaps the compositional range for the Exmore breccia. The impactites generally display a negative correlation of SiO 2 and CaO, and a positive correlation of TiO 2 , Al 2 O 3 , Fe 2 O 3 , and MgO with depth. This is the result of an increasing basement schist component, and a decreasing sedimentary and/or granitic component with depth. Suevite units S2 and S3 display distinct enrichment of Na 2 O by a factor of ̃2 compared to all other impactite units, which is interpreted to reflect a higher granitic component in these units. © 2009 The Geological Society of America.
803.
Geochemistry of impactites and crystalline basement-derived lithologies from the ICDP-USGS Eyreville A and B drill cores, Chesapeake Bay impact structure, Virginia, USA
Special Paper of the Geological Society of America,
458481-541
2009
Abstract: ▾ We investigated whole-rock chemical compositions of 318 samples of Exmore breccia (diamicton), impactite (suevite, impact melt rock, polymict lithic impact breccia), and crystalline basement-derived rocks from 444 to 1766 m depth in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B drill cores (Chesapeake Bay impact structure, Virginia, USA). Here, we compare the average chemical compositions for the Exmore breccia (diamicton), the impactites and their subunits, sandstone, granite, granitic gneiss, and amphibolite of the lithic block section (1095.7-1397.2 m depth), cataclastic gneiss of the impact breccia section, and schist and pegmatite/granite of the basal crystalline section (1551.2-1766.3 m depth). The granite of the megablock (1097.7-1371.1 m depth) is of I-type and is seemingly related to a syncollisional setting. The amphibolite (1377.4-1387.5 m depth) of the lithic block section is of igneous origin and has a tholeiitic character. Based on chemical composition, the Exmore breccia (diamicton) can be subdivided into five units (444.9-450.7, 450.7-468, 468-518, 518-528, and 528-̃865 m depth). The units in the depth intervals of 450.7-468 and 518-528 m are enriched in TiO2, MgO, Sc, V, Cr, and Zn contents compared to the other Exmore breccia units. In some samples, especially at ̃451-455 m depth, the Exmore breccia contains significant amounts of P 2 O 5 . The Exmore breccia is recognized as a mixture of all sedimentary and crystalline target components, and, when compared to the impactites, it contains a significant amount of a SiO 2 -rich target component of sedimentary origin. The chemical composition of the impactites overlaps the compositional range for the Exmore breccia. The impactites generally display a negative correlation of SiO 2 and CaO, and a positive correlation of TiO 2 , Al 2 O 3 , Fe 2 O 3 , and MgO with depth. This is the result of an increasing basement schist component, and a decreasing sedimentary and/or granitic component with depth. Suevite units S2 and S3 display distinct enrichment of Na 2 O by a factor of ̃2 compared to all other impactite units, which is interpreted to reflect a higher granitic component in these units. © 2009 The Geological Society of America.
802.
Geochemistry of the impact breccia section (1397-1551 m depth) of the Eyreville drill core, Chesapeake Bay impact structure, USA
Special Paper of the Geological Society of America,
458397-433
2009
Abstract: ▾ The Chesapeake Bay impact structure, which is 85 km in diameter and 35.5 Ma old, was drilled and cored in a joint International Continental Scientific Drilling Program (ICDP) and U.S. Geological Survey (USGS) drilling project at Eyreville Farm, Virginia, U.S.A. In the Eyreville drill core, 154 m of impact breccia were recovered from the depth interval 1397-1551 m. Major- and trace-element concentrations were determined in 75 polymict impactite samples, 10 samples of cataclastic gneiss blocks, and 24 clasts from impactites. The chemical composition of the polymict impactites does not vary much in the upper part of the section (above ̃1450 m), whereas in the lower part, larger differences occur. Polymict impactites show a decrease of SiO 2 content, and slight increases of TiO 2 , Al 2 O 3 , and Fe 2 O 3 abundances, with depth. This is in agreement with an increase of the schist/gneiss component with depth. Concentrations of siderophile elements (Co, Ni) are lower in the polymict impactites than in the basement-derived schists and do not indicate the presence of an extraterrestrial component. The fi ve petrographically determined types of melt particles, i.e., clear glass, altered melt, recrystallized silica melt, melt with microlites, and dark-brown melt, have distinct chemical compositions. Mixing calculations of the proportions of rocks involved in the formation of various polymict impactites and melt particles were carried out using the Harmonic least-squares MiXing (HMX) calculation program. The calculations suggest that the metamorphic basement rocks (i.e., gneiss and schist) constitute the main component of the polymict impactites, together with significant sedimentary and possible minor pegmatite/granite and amphibolite components. The sedimentary component is derived mostly from a sediment characterized by a composition similar to that of the Cretaceous Potomac Formation. Compositions of the melt particles were modeled as mixtures of target rocks or major rock-forming minerals. However, the results of the mixing calculations for the melt particles are not satisfactory, and the composition of the particles could have been modified by hydrothermal alteration. Carbon isotope ratios were determined for 18 samples. The results imply a hydrothermal origin for the carbonate veins from the basement-derived core section; carbon-rich sedimentary clasts from the Exmore breccia and suevite have a δ 13 C range typical for organic matter in sediments. © 2009 The Geological Society of America.
801.
Geochemistry of the impact breccia section (1397-1551 m depth) of the Eyreville drill core, Chesapeake Bay impact structure, USA
Special Paper of the Geological Society of America,
458397-433
2009
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Alumina; Aluminum oxide; Buildings; Carbon; Clay alteration; Drills; Hematite; Infill drilling; Metamorphic rocks; Mixer circuits; Mixing; Sedimentary rocks; Sedimentology; Silica; Structure (composition); Titanium dioxide; Trace elements, Chesapeake bay impact structures; Continental scientific drillings; Extraterrestrial components; Hydrothermal alterations; Major and trace elements; Metamorphic basements; Rock-forming minerals; U.s. geological surveys, Core drilling, breccia; chemical composition; drilling; geochemistry; impact structure; impactite; marine sediment; trace element, Chesapeake Bay; United States
Abstract: ▾ The Chesapeake Bay impact structure, which is 85 km in diameter and 35.5 Ma old, was drilled and cored in a joint International Continental Scientific Drilling Program (ICDP) and U.S. Geological Survey (USGS) drilling project at Eyreville Farm, Virginia, U.S.A. In the Eyreville drill core, 154 m of impact breccia were recovered from the depth interval 1397-1551 m. Major- and trace-element concentrations were determined in 75 polymict impactite samples, 10 samples of cataclastic gneiss blocks, and 24 clasts from impactites. The chemical composition of the polymict impactites does not vary much in the upper part of the section (above ̃1450 m), whereas in the lower part, larger differences occur. Polymict impactites show a decrease of SiO 2 content, and slight increases of TiO 2 , Al 2 O 3 , and Fe 2 O 3 abundances, with depth. This is in agreement with an increase of the schist/gneiss component with depth. Concentrations of siderophile elements (Co, Ni) are lower in the polymict impactites than in the basement-derived schists and do not indicate the presence of an extraterrestrial component. The fi ve petrographically determined types of melt particles, i.e., clear glass, altered melt, recrystallized silica melt, melt with microlites, and dark-brown melt, have distinct chemical compositions. Mixing calculations of the proportions of rocks involved in the formation of various polymict impactites and melt particles were carried out using the Harmonic least-squares MiXing (HMX) calculation program. The calculations suggest that the metamorphic basement rocks (i.e., gneiss and schist) constitute the main component of the polymict impactites, together with significant sedimentary and possible minor pegmatite/granite and amphibolite components. The sedimentary component is derived mostly from a sediment characterized by a composition similar to that of the Cretaceous Potomac Formation. Compositions of the melt particles were modeled as mixtures of target rocks or major rock-forming minerals. However, the results of the mixing calculations for the melt particles are not satisfactory, and the composition of the particles could have been modified by hydrothermal alteration. Carbon isotope ratios were determined for 18 samples. The results imply a hydrothermal origin for the carbonate veins from the basement-derived core section; carbon-rich sedimentary clasts from the Exmore breccia and suevite have a δ 13 C range typical for organic matter in sediments. © 2009 The Geological Society of America.
800.
Geologic columns for the ICDP-USGS Eyreville A and B cores, Chesapeake Bay impact structure: Sediment-clast breccias, 1096 to 444 m depth
Special Paper of the Geological Society of America,
45851-89
2009
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Crystalline rocks; Rocks, Chesapeake bay impact structures; Impact ejecta; Local similarity; Quartz sand; Randomly distributed, Sediments, breccia; diamicton; ejecta; impact structure; lithology; marine sediment, Chesapeake Bay; United States
Abstract: ▾ The Eyreville A and B cores, recovered from the "moat" of the Chesapeake Bay impact structure, provide a thick section of sediment-clast breccias and minor stratified sediments from 1095.74 to 443.90 m. This paper discusses the components of these breccias, presents a geologic column and descriptive lithologic framework for them, and formalizes the Exmore Formation. From 1095.74 to ̃867 m, the cores consist of nonmarine sediment boulders and sand (rare blocks up to 15.3 m intersected diameter). A sharp contact in both cores at ̃867 m marks the lowest clayey, silty, glauconitic quartz sand that constitutes the base of the Exmore Formation and its lower diamicton member. Here, material derived from the upper sediment target layers, as well as some impact ejecta, occurs. The block-dominated member of the Exmore Formation, from ̃855-618.23 m, consists of nonmarine sediment blocks and boulders (up to 45.5 m) that are juxtaposed complexly. Blocks of oxidized clay are an important component. Above 618.23 m, which is the base of the informal upper diamicton member of the Exmore Formation, the glauconitic matrix is a consistent component in diamicton layers between nonmarine sediment clasts that decrease in size upward in the section. Crystalline-rock clasts are not randomly distributed but rather form local concentrations. The upper part of the Exmore Formation consists of crudely fining-upward sandy packages capped by laminated silt and clay. The overlap interval of Eyreville A and B (940-̃760 m) allows recognition of local similarities and differences in the breccias. © 2009 The Geological Society of America.
799.
Geologic columns for the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure: Impactites and crystalline rocks, 1766 to 1096 m depth
Special Paper of the Geological Society of America,
45821-49
2009
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Biotite; Crystalline materials; Crystalline rocks; Granite; Infill drilling; Levees; Mica; Silicate minerals, Biotite granite; Chesapeake bay impact structures; Coarse-grained; Continental scientific drillings; Debris avalanches; Impact structures; Mylonitic deformation; U.s. geological surveys, Core drilling, crater; crystalline rock; deformation; impact structure; impactite; lithology; pegmatite, Chesapeake Bay; United States
Abstract: ▾ The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville drill cores from the Chesapeake Bay impact structure provide one of the most complete geologic sections ever obtained from an impact structure. This paper presents a series of geologic columns and descriptive lithologic information for the lower impactite and crystalline-rock sections in the cores. The lowermost cored section (1766-1551 m depth) is a complex assemblage of mica schists that commonly contain graphite and fibrolitic sillimanite, intrusive granite pegmatites that grade into coarse granite, and local zones of mylonitic deformation. This basement-derived section is variably overprinted by brittle cataclastic fabrics and locally cut by dikes of polymict impact breccia, including several suevite dikes. An overlying succession of suevites and lithic impact breccias (1551-1397 m) includes a lower section dominated by polymict lithic impact breccia with blocks (up to 17 m) and boulders of cataclastic gneiss and an upper section (above 1474 m) of suevites and clast-rich impact melt rocks. The uppermost suevite is overlain by 26 m (1397-1371 m) of gravelly quartz sand that contains an amphibolite block and boulders of cataclasite and suevite. Above the sand, a 275-m-thick allochthonous granite slab (1371-1096 m) includes gneissic biotite granite, fine- and medium-to-coarse-grained biotite granites, and red altered granite near the base. The granite slab is overlain by more gravelly sand, and both are attributed to debris-avalanche and/or rockslide deposition that slightly preceded or accompanied seawater-resurge into the collapsing transient crater. © 2009 The Geological Society of America.
798.
Frictional behavior of materials in the 3D SAFOD volume
Geophysical Research Letters,
36
(5)
2009
ISSN: 00948276Keywords:▾
Fault gouge; Fault model; Frictional behavior; Frictional properties; Granodiorite; Low friction; San Andreas Fault; Serpentinite; Shear zone; Siltstone, Clay minerals; Friction; Oxide minerals; Petrology; Quartz; Silicate minerals; Talc, Three dimensional, borehole; fault gouge; fault zone; friction; granodiorite; lithology; outcrop; quartz; rock mechanics; sandstone; serpentinite; shear zone; siltstone; strength; talc, California; North America; San Andreas; United States
Abstract: ▾ We report on frictional properties of rocks within the 3-D crustal volume surrounding the San Andreas Fault Observatory at Depth (SAFOD). Samples include lithologies adjacent to the San Andreas Fault (SAF) in the subsurface, SAFOD borehole rocks, and synthetic fault gouge composed of talc, serpentinite, and quartz. Granodiorite, arkosic sandstone, and siltstone samples from the SAFOD borehole are frictionally strong (μ = 0.56 - 0.66). Sand and clay-rich lithologies from outcrop exhibit friction in the range /x = 0.56 - 0.68. Natural serpentinite thought to abut the SAF at depth exhibits low friction (μ = 0.18 - 0.26). Our results indicate that 1) serpentinite exhibits low strength, but is not weak enough to completely satisfy weak fault models, 2) all other samples are consistent with a strong fault and crust and, 3) if the SAF is weak (μ ≤ 0.2) due to the presence of serpentinite or talc, these minerals would likely need to constitute over 50% by weight of the shear zone. Copyright 2009 by the American Geophysical Union.
797.
Geological and archaeological implications of strontium isotope analysis of exposed bedrock in the Chicxulub crater basin, northwestern Yucatán, Mexico
Geology,
37
(8)
723-726
2009
Abstract: ▾ The surface geology of the site of the Chicxulub impact crater in northwestern Yucatán, Mexico, has not been studied extensively since the discovery of the crater almost two decades ago. Strontium isotope (87Sr/86Sr) measurements in carbonate rock outcrops reveal near-uniform strontium signatures of 0.70905 inside the ring of cenotes (water-filled sinkholes), which represents the rim of the crater basin. Measured strontium isotope ratios were used to infer rock ages, employing the marine Sr isotope curve. We estimate the age of the exposed limestone within the Chicxulub crater basin to be late Miocene to early Pliocene, representing the age of the youngest sediment fill. Discovery of a large terrain of near-uniform strontium isotope ratios in northwestern Yucatán offers new geoarchaeological opportunities to track ancient Maya migration and determine sources of manufactured goods. Our results have implications for applying the Sr isotope method to Maya archaeological sites, such as Mayapán, the last Maya capital, and Chichén Itzá. © 2009 Geological Society of America.
796.
Geomechanical response of permafrost-associated hydrate deposits to depressurization-induced gas production
Journal of Petroleum Science and Engineering,
67
(1-2)
1-12
2009
ISSN: 09204105Keywords:▾
Alaska , usa; Cohesive strengths; Constant pressures; depressurization; Gas productions; Geomechanical properties; geomechanics; hydrate dissociation; Induced dissociations; Initial stress state; Poisson's ratios; Reservoir stress; Shear failures; Simulation results; Simulation studies; Well bores, Bearings (structural); Compaction; Dissociation; Gases; Horizontal wells; Hydration; International trade; Oil wells; Permafrost; Poisson ratio; Shear stress; Strength of materials, Gas hydrates, computer simulation; gas hydrate; permafrost; Poisson ratio; shear stress; soil mechanics; thermodynamics
Abstract: ▾ In this simulation study, we analyzed the geomechanical response during depressurization production from two known hydrate-bearing permafrost deposits: the Mallik (Northwest Territories, Canada) deposit and Mount Elbert (Alaska, USA) deposit. Gas was produced from these deposits at constant pressure using horizontal wells placed at the top of a hydrate layer (HL), located at a depth of about 900 m at the Mallik site and 600 m at the Mount Elbert site. The simulation results show that general thermodynamic and geomechanical responses are similar for the two sites, but with substantially higher production and more intensive geomechanical responses at the deeper Mallik deposit. The depressurization-induced dissociation begins at the well bore and then spreads laterally, mainly along the top of the HL. The depressurization results in an increased shear stress within the body of the receding hydrate and causes a vertical compaction of the reservoir. However, its effects are partially mitigated by the relatively stiff permafrost overburden, and compaction of the HL is limited to less than 0.4%. The increased shear stress may lead to shear failure in the hydrate-free zone bounded by the HL overburden and the downward-receding upper dissociation interface. This zone undergoes complete hydrate dissociation, and the cohesive strength of the sediment is low. We determined that the likelihood of shear failure depends on the initial stress state as well as on the geomechanical properties of the reservoir. The Poisson's ratio of the hydrate-bearing formation is a particularly important parameter that determines whether the evolution of the reservoir stresses will increase or decrease the likelihood of shear failure.
795.
Gravity investigations of the Chesapeake Bay impact structure
Special Paper of the Geological Society of America,
458181-193
2009
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Buildings; Core drilling; Crystalline materials; Drills; Infill drilling, Allochthonous rocks; Chesapeake bay impact structures; Crystalline basement; Crystalline bedrocks; Depth to basements; Gravity anomalies; Impact structures; Structural elements, Crystalline rocks, basement rock; bedrock; crater; crystalline rock; gravity anomaly; impact structure; uplift, Chesapeake Bay; United States
Abstract: ▾ The Chesapeake Bay impact structure is a complex impact crater, ̃85 km in diameter, buried beneath postimpact sediments. Its main structural elements include a central uplift of crystalline bedrock, a surrounding inner crater filled with impact debris, and an annular faulted margin composed of block-faulted sediments. The gravity anomaly is consistent with that of a complex impact consisting of a central positive anomaly over the central uplift and an annular negative anomaly over the inner crater. An anomaly is not recognized as being associated with the faulted margin or the outer edge of the structure. Densities from the Eyreville drill core and modeling indicate a density contrast of ̃0.3-0.6 g cm -3 between crystalline basement and the material that fills the inner crater (e.g., Exmore breccia and suevite). This density contrast is somewhat higher than for other impact structures, but it is a function of the manner in which the crater fill was deposited (as a marine resurge deposit). Modeling of the gravity data is consistent with a depth to basement of ̃1600 m at the site of Eyreville drill hole and 800 m at the central uplift. Both depths are greater than the depth at which crystalline rocks were encountered in the cores, suggesting that the cored material is highly fractured para-allochthonous rock. © 2009 The Geological Society of America.