All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
353.
Characterization of the organic matter in lignites of the Kugmallit Formation (Oligocene) at the JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate production research well
Geological Survey of Canada, Bulletin,
585
2005
DOI:10.4095/220702
352.
Characterization of expandable clay minerals in Lake Baikal sediments by thermal dehydration and cation exchange
Clays and Clay Minerals,
53
(4)
389 – 400
2005
ISSN: 00098604Keywords:▾
Eastern Hemisphere; Eurasia; Lake Baikal; Russian Federation; World; Dehydration; High temperature effects; Magnetic susceptibility; Mineralogy; Positive ions; Sediments; X ray diffraction analysis; clay mineral; lacustrine deposit; physical property; Cation exchange capacity; Paleoclimate; Russia; Thermal dehydration; Clay minerals
Abstract: ▾ The sedimentary series from Academician Ridge, Lake Baikal, eastern Siberia, was examined using cation exchange capacity (CEC) to estimate the amount of expandable clay minerals (ECM) and high-temperature X-ray diffraction (HT-XRD) to determine their basic classification. The comparison of the magnetic susceptibility (MS) at sub-millennial resolution and the δ18O record of a reference Atlantic core (ODP 980) was used to create an age model. The most closely studied part of the series covered the major part of the last glacial cycle (120-20 ky BP). The HT-XRD analysis is based on monitoring the course of ECM dehydration with 5°C steps between 25 and 250°C and enabled us to improve the discrimination between ECM, chlorite and micas. The CEC obtained at millennial resolution showed that the neoformation of ECM in warmer periods of the last interglacial was either insignificant or fully compensated by their dissolution or dilution. The CEC record was correlated with the main climatic stages in the period studied. Both MS and CEC records reflected the environmental changes at about millennial resolution, including climatic instabilities between 117 and 73 ky BP (late MIS5). Copyright © 2005, The Clay Minerals Society.
351.
Can diagenetic processes influence the short term hydraulic behaviour evolution of a fault?
Oil and Gas Science and Technology,
60
(2)
213 – 230
2005
ISSN: 12944475
Publisher: Editions Technip
Keywords:▾
Calcite; Carbon dioxide; Carbonates; Cement additives; Computer software; Crystal growth; Crystals; Fracture; Groundwater; Hydrocarbons; Mechanical permeability; Porosity; Rocks; Seismology; Carbonate crystals; Carbonate rocks; Diagenetic processes; Hydraulic behaviour; fracture network; hydraulic property; permeability; Hydraulics
Abstract: ▾ The scope of this work is to quantify the impact of calcite cementation on the hydraulic behaviour of an active fault in carbonate rocks. In the studied context, the permeability mainly depends on the fracture network. Therefore the hydraulic regime depends on the way fractures become sealed by vein deposits. The work is based on the study of cores and groundwater recovered from an active normal fault in the Gulf of Corinth, the Aigion fault, in the framework of the Corinth Rift Laboratory Project. The data set includes cores, borehole images, pumping tests and in situ fluid samples. The cores show numerous recent fractures partially, or completely, sealed by recent carbonate crystals. We modelled the fluid-rock interaction to quantify the growth rate of calcite in the veins of this specific geological context. Modelling was carried out with Diaphore, a software designed to study the diagenetic evolution of porosity in hydrocarbon reservoirs. The required time to seal a 1 mm thick fracture in the case of the Aigion fault at 760 m depth was calculated to be within the range of a few hundred years, considering the composition of water sampled at this depth. As a conclusion, diagenetic processes are likely to have a key influence on the fault hydraulic behavior over the time scale of seismic cycles. However, the possibility of calcite growth strongly depends on the composition of the fluid. Tests were made with seawater and slightly higher values of pCO2, a fluid that could also be present around the Aigion fault. In this case dissolution, and therefore opening of the fractures, happens. Copyright © 2005, Institut français du pétrole.
350.
Bosumtwi impact structure, Ghana: Geochemistry of impactites and target rocks, and search for a meteoritic component
Meteoritics and Planetary Science,
40
(9-10)
1493 – 1511
2005
ISSN: 10869379
Publisher: University of Arkansas
Keywords:▾
crater; impact structure; impactite; meteorite; shock metamorphism
Abstract: ▾ Major and trace element data, including platinum group element abundances, of representative impactites and target rocks from the crater rim and environs of the Bosumtwi impact structure, Ghana, have been investigated for the possible presence of a meteoritic component in impact-related rocks. A comparison of chemical data for Bosumtwi target rocks and impactites with those for Ivory Coast tektites and microtektites supports the interpretation that the Bosumtwi structure and Ivory Coast tektites formed during the same impact event. High siderophile element contents (compared to average upper crustal abundances) were determined for target rocks as well as for impactites. Chondrite-normalized (and iron meteorite-normalized) abundances for target rocks and impactites are similar. They do not, however, allow the unambiguous detection of the presence, or identification of the type, of a meteoritic component in the impactites. The indigenous siderophile element contents are high and possibly related to regional gold mineralization, although mineralized samples from the general region show somewhat different platinum-group element abundance patterns compared to the rocks at Bosumtwi. The present data underline the necessity of extensive target rock analyses at Bosumtwi, and at impact structures in general, before making any conclusions regarding the presence of a meteoritic component in impactites. © The Meteoritical Society, 2005.
349.
Dielectric method of high-resolution gas hydrate estimation
Geophysical Research Letters,
32
(4)
1-4
2005
ISSN: 00948276Keywords:▾
Dielectric properties; Electric conductivity; Frequencies; Mathematical models; Natural gas; Dielectric properties; Dielectric properties of gases; Electric logging; Hydration; Induction logging, Dielectric tools; Hydrate saturation; Hydrate zones; Induction logs, Gas hydrates; Gas hydrates, clathrate; dielectric property; gas hydrate, Dielectric methods; Dielectric tools; Fine-scale structures; High resolution; Hydrate formation; Resistivity logs; Situ hydrates; Vertical resolution
Abstract: ▾ In-situ dielectric properties of natural gas hydrate are measured for the first time in the Mallik 5L-38 Well in the Mackenzie Delta, Canada. The average dielectric constant of the hydrate zones is 9, ranging from 5 to 20. The average resistivity is >5 ohm.m in the hydrate zones, ranging from 2 to 10 ohm.m at a 1.1 GHz dielectric tool frequency. The dielectric logs show similar trends with sonic and induction resistivity logs, but exhibits inherently higher vertical resolution (<5 cm). The average in-situ hydrate saturation in the well is about 70%, ranging from 20% to 95%. The dielectric estimates are overall in agreement with induction estimates but the induction log tends to overestimate hydrate content up to 15%. Dielectric estimates could be used as a better proxy of in-situ hydrate saturation in modeling hydrate dynamics. The fine-scale structure in hydrate zones could help reveal hydrate formation history. Copyright 2005 by the American Geophysical Union.
348.
Be isotopes with textural and mineralogical data of sediment from Lake Baikal (Siberia)
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen,
238
(3)
355 – 411
2005
ISSN: 00777749
Publisher: E. Schweizerbart'sche Verlagsbuchhandlung
Keywords:▾
Lake Baikal; Russian Federation; beryllium isotope; core analysis; detrital deposit; feldspar; isotopic analysis; mineralogy; sediment analysis
Abstract: ▾ In this study, results of Be isotopic analyses of sediments collected from the three longest cores drilled in Lake Baikal, i.e. BDP-98 (600 m long), BDP-96 (200 m long) and BDP-93 (102 m long), are presented in relation to their lithological variation. The sediment used in the study has a relatively uniform grain size distribution and mineral composition dominated by detrital feldspars and quartz. Biogenic silica is present in all samples, with amounts up to 40 %. The limited variability in textural and mineralogical (± biogenic silica) composition of the sediment resulted in a constrained 10Be concentration distribution that is mainly related to its production and radioactive decay. Normalization of 10Be to 9Be concentrations shows a trend similar to that of the 10Be distribution. The 10Be-based chronology for the BDP-98 and BDP-96 cores provides time spans of about 8 and 5.5 Myr respectively. Estimation of the 10Be flux indicates high values in the Late Miocene, which can be related to relatively low geomagnetic field intensity during that time. © 2005 E. Schweizerbart'sche Verlagsbuchhandlung.
347.
Basinward transport of Chicxulub ejecta by tsunami-induced backflow, La Popa basin, northeastern Mexico, and its implications for distribution of impact-related deposits flanking the Gulf of Mexico
Geology,
33
(2)
81-84
2005
DOI:10.1130/G21057.1
Abstract: ▾ Ejecta-bearing strata are present at the top of Cretaceous foreland-basin deposits throughout the La Popa basin in northeastern Mexico. In the southeast part of the basin, locally thick (as much as 4.6 m) ejecta-rich conglomeratic strata occupy valley-like features at a bathymetric break that separated Maastrichtian upper shoreface from lower shoreface and prodelta depositional settings. Clast-supported textures, normally graded planar conglomerate-sandstone couplets, upcurrent-dipping low-angle cross-laminae, sparse paleocurrent data, and transported fossils indicate deposition by south- to southeast-directed turbulent, supercritical flow. In the northwest part of the basin, ejecta grains are present but less common in correlative deposits. Sediment, ejecta, and organisms were eroded from shoreward environments and transported basinward by backflow of run-up surge(s) emplaced against the continent by one or several tsunami(s). High-discharge, supercritical offshore-directed flow provides a mechanism for transport of voluminous, ejecta-bearing sediment and late Maastrichtian marine organisms into deep-water Gulf of Mexico settings. © 2005 Geological Society of America.
346.
Basaltic volcanism of the central and western Snake River Plain: A guide to field relations between Twin Falls and Mountain Home, Idaho
GSA Field Guides,
627-52
2005
Keywords:▾
Granite; Rivers, Basalt geochemistry; Basaltic volcanism; First episodes; Lacustrine sediments; Mantle plume; Silicic volcanism; Snake river plains; Yellowstones, Basalt
Abstract: ▾ Basaltic volcanism in the Snake River Plain of southern Idaho has long been associated with the concept of a mantle plume that was overridden by North America during the Neogene and now resides beneath the Yellowstone plateau. This concept is consistent with the time-transgressive nature of rhyolite volcanism in the plain, but the history of basaltic volcanism is more complex. In the eastern Snake River Plain, basalts erupted after the end of major silicic volcanism. The basalts typically erupt from small shield volcanoes that cover up to 680 km 2 and may form elongate flows that extend 50-60 km from the central vent. The shields coalesce to form extensive plains of basalt that mantle the entire width of the plain, with the thickest accumulations of basalt forming an axial high along the length of the plain. In contrast, basaltic volcanism in the western Snake River Plain formed in two episodes: the first (ca. 7-9 Ma) immediately following the eruption of rhyolites lavas now exposed along the margins of the plain, and the second forming in the Pleistocene (δ2 Ma), long after active volcanism ceased in the adjacent eastern Snake River Plain. Pleistocene basalts of the western Snake River Plain are intercalated with, or overlie, lacustrine sediments of Pliocene-Pleistocene Lake Idaho, which filled the western Snake River Plain graben after the end of the first episode of basaltic volcanism. The contrast in occurrence and chemistry of basalt in the eastern and western plains suggest the interpretation of volcanism in the Snake River Plain is more nuanced than simple models proposed to date. © 2005 Geological Society of America.
345.
An ordinary chondrite impactor for the Popigai crater, Siberia
Geochimica et Cosmochimica Acta,
69
(11)
2877-2889
2005
Abstract: ▾ With a diameter of ∼100 km, Popigai in Northern Siberia is the largest crater known in the Cenozoic. The concentrations in platinum group elements (PGE) were analyzed in twenty samples of homogeneous impact melt collected in the northwestern flank of the crater to identify the composition of the projectile. The method selected was preconcentration by NiS fire assay followed by inductively coupled plasma-mass spectrometry (ICP-MS). This technique measures all the PGE (except Os) and by using aliquots >10g, the results are highly reproducible. The major and trace element composition of the impact melt resembles that of gneissic lithologies of the Anabar shield, which are representative of the target rock. The PGE are enriched in the melt by factors of 3 to 14 compared to the main target lithology, but the meteoritic contamination is only around 0.2 wt.%. Using plots of elemental ratios such as Ru/Rh vs. Pt/Pd or Ru/Rh vs. Pd/Ir, the Popigai impactor is clearly identified as an ordinary chondrite and most likely l-chondrite. This study indicates that PGE elemental ratios allow discrimination of the type of impactor, even in the case of low meteoritic contamination. This study confirms that a significant fraction of the crater-forming projectiles presently documented could have an ordinary chondrite composition. Their probable source, the S-type asteroids, appears to form the majority of the bodies in the main asteroid belt and among Near Earth Objects (NEOs). The ordinary chondrite origin of the Popigai projectile supports an asteroidal origin for the late Eocene impacts as a plausible alternative to the comet shower scenario proposed by Farley et al. (1998). Copyright © 2005 Elsevier Ltd.
344.
An olivine-free mantle source of Hawaiian shield basalts
Nature,
434
(7033)
590-597
2005
ISSN: 00280836Keywords:▾
Mathematical models; Minerals; Nickel; Seismology; Silicon; Volcanoes, Magmas; Mantle; Pyroxene; Recycled oceanic crusts, Basalt, mineral; nickel; silicon, basalt; mantle; petrogenesis; petrology, article; basalt; model; plume; priority journal; sea; United States; volcano, Hawaiian Islands; oceanic regions; Pacific islands; Pacific Ocean; World
Abstract: ▾ More than 50 per cent of the Earth's upper mantle consists of olivine and it is generally thought that mantle-derived melts are generated in equilibrium with this mineral. Here, however, we show that the unusually high nickel and silicon contents of most parental Hawaiian magmas are inconsistent with a deep olivine-bearing source, because this mineral together with pyroxene buffers both nickel and silicon at lower levels. This can be resolved if the olivine of the mantle peridotite is consumed by reaction with melts derived from recycled oceanic crust, to form a secondary pyroxenitic source. Our modelling shows that more than half of Hawaiian magmas formed during the past 1 Myr came from this source. In addition, we estimate that the proportion of recycled (oceanic) crust varies from 30 per cent near the plume centre to insignificant levels at the plume edge. These results are also consistent with volcano volumes, magma volume flux and seismological observations.
343.
Alteration of hyaloclastites in the HSDP 2 Phase 1 Drill core: 2. Mass balance of the conversion of sideromelane to palagonite and chabazite
Geochemistry, Geophysics, Geosystems,
6
(9)
2005
ISSN: 15252027Abstract: ▾ The Hawaii Scientific Drilling Project 2 Phase 1 core permits study of each stage of alteration of basalt glass during burial because stages of the process are separated vertically. Previous work has shown that alteration of hyaloclastite occurs progressively. The latest stage observed in the Phase 1 core involves marginal replacement of sideromelane in shards with palagonite while simultaneously forming chabazite in pores. The basic reaction at this stage is sideromelane + components from pore waters = palagonite + chabazite + components to pore waters. Mass balance calculations show that Fe was virtually immobile in this process, being retained in palagonite. Na, Ca, Ba, P, Al, and Si were lost during palagonitization and not fully consumed in making chabazite. Mg was lost during palagonitization but retained elsewhere in smectite. K, Rb, and Sr were extracted from pore waters and enriched in the sum of the alteration products. The amount of enrichment depended upon the amount of chabazite present, which depended upon the porosity when chabazite formed. Ti, Y, U, Zr, Nb, REE, and Th were enriched in palagonite, compared to sideromelane, but were absent in chabazite. Mass balance of all phases for the entire alteration process (including earlier stages) was not possible because poorly consolidated samples do not yield accurate modal values of phases, trace element analysis of smectite was not possible, and exchange with lavas and intrusions in the succession cannot be evaluated. Calculations indicate that too little of major oxides, except Na2O, was released during palagonitization to account for the amount of smectite observed in hyaloclastites. The results of this study, and several others published in the literature, indicate that under various circumstances palagonitization will consume particular elements from pore fluid or release them to it. Such mobility implies that the hydrology of the particular system and the composition of the dissolved solids in the pore water will control whether palagonitization is a source or sink of elements. The potential exists that palagonitization of basalt glass is an important source or sink of elements for seawater and fluids circulating in the ocean crust. Copyright 2005 by the American Geophysical Union.
342.
A tsunami deposit at the Cretaceous/Paleogene boundary in the Neuquén Basin of Argentina
Cretaceous Research,
26
(2)
283-297
2005
Abstract: ▾ A coarse-grained sandstone bed of Cretaceous/Paleogene (K/Pg) boundary age occurs in a homogeneous neritic shelf mudstone sequence (Jagüel Formation) in the Neuquén Basin of Argentina. This bed, 15 - 25 cm thick, contains abundant plagioclase, broken shells and sharks' teeth. Sedimentological features include an erosive base, abundant rip-up clasts, normal grading and hummocky cross-bedding. The K/Pg boundary age of the bed was confirmed by calcareous nannofossils. Similar to other sections in the Gulf Coast region and the Danish Basin, a "dead zone" significantly depleted in macrofossils is evident in the basal 1 m above the clastic layer. In combination, these features suggest that the clastic layer represents a tsunami deposit that was related to the Chicxulub impact event in Yucatan/Mexico. Mechanisms of tsunami wave amplification in this extremely distal and somewhat protected setting are poorly understood but the funnel-shape of the basin may have promoted the unusually strong sedimentological response. © 2005 Elsevier Ltd. All rights reserved.
341.
A simulation of the hydrothermal response to the Chesapeake Bay bolide impact
Geofluids,
5
(3)
185-201
2005
ISSN: 14688115Keywords:▾
bolide; hydrothermal circulation; impact structure, Chesapeake Bay; North America; United States; Western Hemisphere; World
Abstract: ▾ Groundwater more saline than seawater has been discovered in the tsunami breccia of the Chesapeake Bay impact Crater. One hypothesis for the origin of this brine is that it may be a liquid residual following steam separation in a hydrothermal system that evolved following the impact. Initial scoping calculations have demonstrated that it is feasible such a residual brine could have remained in the crater for the 35 million years since impact. Numerical simulations have been conducted using the code HYDROTHERM to test whether or not conditions were suitable in the millennia following the impact for the development of a steam phase in the hydrothermal system. Hydraulic and thermal parameters were estimated for the bedrock underlying the crater and the tsunami breccia that fills the crater. Simulations at three different breccia permeabilities suggest that the type of hydrothermal system that might have developed would have been very sensitive to the permeability. A relatively low breccia permeability (1 × 10-16 m2) results in a system partitioned into a shallow water phase and a deeper superheated steam phase. A moderate breccia permeability (1 × 10-15 m2 ) results in a system with regionally extensive multiphase conditions. A relatively high breccia permeability (1 × 10-14 m2 ) results in a system dominated by warm-water convection cells. The permeability of the crater breccia could have had any of these values at given depths and times during the hydrothermal system evolution as the sediments compacted. The simulations were not able to take into account transient permeability conditions, or equations of state that account for the salt content of seawater. Results suggest, however, that it is likely that steam conditions existed at some time in the system following impact, providing additional evidence that is consistent with a hydrothermal origin for the crater brine. © Blackwell Publishing Ltd.
340.
Influence of climate fluctuation on clay formation in the Baikal drainage basin
Journal of Paleolimnology,
33
(1)
105 – 121
2005
ISSN: 09212728Keywords:▾
Eastern Hemisphere; Eurasia; Lake Baikal; Russian Federation; World; biogenic deposit; clay mineral; climate change; Miocene; paleolimnology; sediment core; weathering
Abstract: ▾ Sedimentary cores BDP 96 and 98 and VER 96-2 St. 3 from Academician Ridge in Lake Baikal were investigated to investigate the effect of climatic fluctuations on rock weathering and clay formation in the Baikal drainage basin. Illite, smectite, vermiculite, and kaolinite were identified as the major clay minerals in the sediments by X-ray diffraction analysis. Biotite in gravels in alluvial soils of the Baikal drainage area weathers through illite to vermiculite, smectite, and finally to kaolinite. To investigate the relationship between weathering and climate, we measured the clay content and the concentration of biogenic silica in the sediments. High surface productivity (increased biogenic silica) and high chemical weathering (decreased clay content) occurred simultaneously, showing that crustal weathering and soil formation were enhanced under warm climatic conditions. Clay formation was enhanced in the watershed from the Late Miocene to the Middle Pliocene, and mechanical weathering of rocks increased during glacial intervals after the climate began to cool in Late Pliocene time. This change in the weathering mode in the watershed reduced the nutrient flux and aquatic productivity of Lake Baikal.
339.
Diatom biostratigraphy of Lake Baikal during the past 1.25 Ma: New results from BDP-96-2 and BDP-99 drill cores
Quaternary International,
136
(1 SPEC. ISS.)
95 – 104
2005
ISSN: 10406182
Publisher: Elsevier Ltd
Keywords:▾
Eastern Hemisphere; Eurasia; Lake Baikal; Russian Federation; World; biostratigraphy; community composition; diatom; marine isotope stage; sediment core
Abstract: ▾ Detailed diatom zonation in the Lake Baikal holostratotype section BDP-96-2 is extended over the interval 0.85-1.25 Ma and compared with diatom assemblage composition from the new BDP-99 drill core. Interglacial diatom assemblages at these two sites over 220 km apart are of similar composition, and the same complete and continuous succession of diatom zones is observed in both drill cores over the 0-800 ka interval. We propose a correlation of Baikal diatomaceous intervals with the marine oxygen isotope stratigraphy and with European climato-stratigraphic divisions of the early Pleistocene. We then use the diatom succession in BDP-96-2 to demonstrate evidence for disconformity in BDP-99 and to establish an approximate age model for this section. Diatom assemblages characteristic of the top of the Matuyama reversed polarity interval and the upper part of the Jaramillo normal polarity subchron are not found in the BDP-99 section below the disconformity boundary. The lack of diatom zones corresponding to the MIS 21-27 of the marine oxygen isotope stratigraphy in BDP-99 section suggests that the estimated age span of missing sediment interval in BDP-99 is ca 150-160 ka. The unusual diatom assemblage of cosmopolitan species during MIS 33 in both BDP-96-2 and BDP-99 drill core sections is indicative of abrupt ecological changes in the time interval 1.12-1.08 Ma. © 2004 Elsevier Ltd and INQUA. All rights reserved.
338.
A case study of impact-induced hydrothermal activity: The Haughton impact structure, Devon Island, Canadian High Arctic
Meteoritics and Planetary Science,
40
(12)
1859-1877
2005
Abstract: ▾ The well-preserved state and excellent exposure at the 39 Ma Haughton impact structure, 23 km in diameter, allows a clearer picture to be made of the nature and distribution of hydrothermal deposits within mid-size complex impact craters. A moderate- to low-temperature hydrothermal system was generated at Haughton by the interaction of groundwaters with the hot impact melt breccias that filled the interior of the crater. Four distinct settings and styles of hydrothermal mineralization are recognized at Haughton: a) vugs and veins within the impact melt breccias, with an increase in intensity of alteration towards the base; b) cementation of brecciated lithologies in the interior of the central uplift; c) intense veining around the heavily faulted and fractured outer margin of the central uplift; and d) hydrothermal pipe structures or gossans and mineralization along fault surfaces around the faulted crater rim. Each setting is associated with a different suite of hydrothermal minerals that were deposited at different stages in the development of the hydrothermal system. Minor, early quartz precipitation in the impact melt breccias was followed by the deposition of calcite and marcasite within cavities and fractures, plus minor celestite, barite, and fluorite. This occurred at temperatures of at least 200 °C and down to ∼100-120 °C. Hydrothermal circulation through the faulted crater rim with the deposition of calcite, quartz, marcasite, and pyrite, occurred at similar temperatures. Quartz mineralization within breccias of the interior of the central uplift occurred in two distinct episodes (∼250 down to ∼90 °C, and <60 °C). With continued cooling (<90 °C), calcite and quartz were precipitated in vugs and veins within the impact melt breccias. Calcite veining around the outer margin of the central uplift occurred at temperatures of ∼150 °C down to <60 °C. Mobilization of hydrocarbons from the country rocks occurred during formation of the higher temperature calcite veins (>80 °C). Appreciation of the structural features of impact craters has proven to be key to understanding the distribution of hydrothermal deposits at Haughton. © The Meteoritical Society, 2005.
337.
Drillbit seismic images fractures of San Andreas fault system
Oil and Gas Journal,
103
(41)
42-44+46-50
2005
ISSN: 00301388Abstract: ▾ Scientists recently used the drillbit seismic technique to image fractures and shear zones associated with the San Andreas fault near Parkfield, Calif. Low-level energy produced by the drillbit served as a downhole seismic source, and the wave response was measured by an array of geophones at the surface. In the complex structural environment underlying Parkfield, numerous faults that comprise a flower structure are interpreted to cut the Cenozoic sedimentary cover and the Salinian block at the San Andreas Fault Observatory at Depth (SAFOD) project drillsite. Based on updated surface geologic maps by Rymer, these fractures and faults appear to trend subparallel to the San Andreas fault (SAF) and have been mapped up to 3 km to the southwest of the main trace of the SAF. Our study included the interpretation of a surface seismic profile and the drillbit seismic data. These data indicate that faulting is more abundant and shearing more pervasive as one approaches the main trace of the San Andreas fault. In addition, our interpretation of the locations and dips of faults in the PSINE profile correlates very well with locations and dips of several linear features imaged in the migrated drillbit seismic data.
336.
Heterogeneity effects in thermal borehole measurements in the Chicxulub impact crater
Journal of Geophysics and Engineering,
2
(4)
357-363
2005
Abstract: ▾ Boreholes drilled in impact structures are especially suited for investigations of the influence of heterogeneities on petrophysical properties and thermal field. In the scientific well Yaxcopoil-1 drilled within the frame of the International Continental Deep Drilling Program (ICDP) and as a part of the Chicxulub Scientific Drilling Project (CSDP) high resolution temperature measurements and a dense petrophysical profile measured on core samples at ∼2.2 m depth intervals were recorded. From the calculated vertical component of the thermal gradient and the thermal conductivity measured on the core samples a mean heat flow density of 70.5 ± 1.9 mW m-2 in the depth interval 400-1400 m was determined. On the basis of a simple purely conductive heterogeneous 2D thermal model the effect of the refraction of heat caused by heterogeneities is demonstrated. A statistical investigation shows that if the scales of the heterogeneities influencing the values of the measured thermal conductivity and the calculated thermal gradient are small compared to the length of the borehole the effect of the heterogeneities on the vertical heat flow density can be interpreted as thermal noise. © 2005 Nanjing Institute of Geophysical Prospecting.
335.
In situ thermal conductivity of gas-hydrate-bearing sediments of the Mallik 5L-38 well
Journal of Geophysical Research: Solid Earth,
110
(11)
1-11
2005
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
gas hydrate; sediment property; thermal conductivity
Abstract: ▾ Detailed knowledge about thermal properties of rocks containing gas hydrate is required in order to quantify processes involving gas hydrate formation and decomposition in nature. In the framework of the Mallik 2002 program, three wells penetrating a continental gas hydrate occurrence under permafrost were successfully equipped with permanent fiber-optic distributed temperature sensing cables. Temperature data were collected over a 21-month period after completing the wells. Thermal conductivity profiles were calculated from the geothermal data as well as from a petrophysical model derived from the available logging data and application of mixing law models. Results indicate that thermal conductivity variations are mainly lithologically controlled with a minor influence from hydrate saturation. Average thermal conductivity values of the hydrate-bearing sediments range between 2.35 and 2.77 W m-1 K-1. Maximum gas hydrate saturations can reach up to about 90% at an average porosity of 0.3. Copyright 2005 by the American Geophysical Union.
334.
Impactites of the Haughton impact structure, Devon Island, Canadian High Arctic
Meteoritics and Planetary Science,
40
(12)
1789-1812
2005
Abstract: ▾ Contrary to the previous interpretation of a single allochthonous impactite lithology, combined field, optical, and analytical scanning electron microscopy (SEM) studies have revealed the presence of a series of impactites at the Haughton impact structure. In the crater interior, there is a consistent upward sequence from parautochthonous target rocks overlain by parautochthonous lithic (monomict) breccias, through allochthonous lithic (polymict) breccia, into pale grey allochthonous impact melt breccias. The groundmass of the pale grey impact melt breccias consists of microcrystalline calcite, silicate impact melt glass, and anhydrite. Analytical data and microtextures indicate that these phases represent a series of impact-generated melts that were molten at the time of, and following, deposition. Impact melt glass clasts are present in approximately half of the samples studied. Consideration of the groundmass phases and impact glass clasts reveal that impactites of the crater interior contain shock-melted sedimentary material from depths of >920 to <1880 m in the pre-impact target sequence. Two principal impactites have been recognized in the near-surface crater rim region of Haughton. Pale yellow-brown allochthonous impact melt breccias and megablocks are overlain by pale grey allochthonous impact melt breccias. The former are derived from depths of >200 to <760 m and are interpreted as remnants of the continuous ejecta blanket. The pale grey impact melt breccias, although similar to the impact melt breccias of the crater interior, are more carbonate-rich and do not appear to have incorporated clasts from the crystalline basement. Thus, the spatial distribution of the crater-fill impactites at Haughton, the stratigraphic succession from target rocks to allochthonous impactites, the recognition of large volumes of impact melt breccias, and their probable original volume are all analogous to characteristics of coherent impact melt layers in comparatively sized structures formed in crystalline targets. © The Meteoritical Society, 2005.
333.
Impact structures: What does crater diameter mean?
Special Paper of the Geological Society of America,
3841-24
2005
Abstract: ▾ The diameter of an impact crater is one of the most basic and important parameters used in energy scaling and numerical modeling of the cratering process. However, within the impact and geological communities and literature, there is considerable confusion about crater sizes due to the occurrence of a variety of concentric features, any of which might be interpreted as defining a crater's diameter. The disparate types of data available for different craters make the use of consistent metrics difficult, especially when comparing terrestrial to extraterrestrial craters. Furthermore, assessment of the diameters of terrestrial craters can be greatly complicated due to post-impact modification by erosion and tectonic activity. We analyze the terminology used to describe crater geometry and size and attempt to clarify the confusion over what exactly the term "crater diameter" means, proposing a consistent terminology to help avert future ambiguities. We discuss several issues of crater-size in the context of four large terrestrial examples for which crater diameters have been disputed (Chicxulub, Sudbury, Vredefort, and Chesapeake Bay) with the aim of moving toward consistent application of terminology. © 2005 Geological Society of America.
332.
Hypervelocity collisions into continental crust composed of sediments and an underlying crystalline basement: Comparing the Ries (∼24 km) and Chicxulub (∼180 km) impact craters
Chemie der Erde,
65
(1)
1-46
2005
Abstract: ▾ The Chicxulub and Ries impact craters were excavated from layered continental terrains that were composed of carbonate-bearing sedimentary sequences and underlying crystalline silicate basement materials. The Chicxulub and Ries impact events were sufficiently large to produce complex peak-ring impact craters. The walls of transient craters and excavation cavities, with diameters of 12-16 km for the Ries and 90-100 km for Chicxulub, collapsed to form final crater diameters of ∼24 and ∼180 km, respectively. Debris from both the sedimentary and crystalline layers was ejected during crater formation, but the bulk of the melting occurred at depth, in the silicate basement. The volume of melt and proportion of melt among shock-metamorphosed debris was far larger at Chicxulub, producing a central melt sheet ∼3 km in depth. The central melt sheet was covered with melt-bearing polymict breccias and, at the Ries, similar breccias (crater suevites) filled the central cavity. Also at the Ries (and presumably at Chicxulub), large hill-size megablocks of crystalline basement material were deposited near the transient crater rim. Blocks and megablocks of sedimentary lithologies were ejected into the modification zone between the peak ring and final crater rim, while additional material was slumping inward during crater growth, and buried beneath a fallout deposit of melt-bearing polymict breccias. The melt and surviving clasts in the breccias are dominantly derived from the deeper, basement lithologies. At greater distances, however, the ejecta is dominated by near-surface sedimentary lithologies, large blocks of which landed with such high energy that they scoured and eroded the pre-existing surface. The excavation and ejecta pattern produced lithological and chemical variations with radial distance from the crater centers that evolve from basement components near the crater centers to sedimentary components far from the crater centers. In addition, carbonate (and anhydrite in the case of Chicxulub) was vaporized, producing environmentally active gases. The vaporized volume produced by the Ries impact event was too small to dramatically alter the evolution of life, but the vaporized volume produced by the Chicxulub impact event is probably a key factor in the Cretaceous-Tertiary boundary mass extinction event. © 2004 Elsevier GmbH. All rights reserved.
331.
Hydrothermal processes associated with meteorite impact structures: Evidence from three Australian examples and implications for economic resources
Australian Journal of Earth Sciences,
52
(4-5)
587-605
2005
Abstract: ▾ Meteorite impacts cause conversion of kinetic energy into thermal energy. Part of this thermal energy is used to form a melt sheet, part is dissipated to heat the target rocks and these together with the hot rocks that elastically rebound from the depth of several kilometres (central uplift) activate hydrothermal circulation. Impact-generated hydrothermal systems have been documented from several impact structures world-wide. Three Australian examples-Shoemaker, Woodleigh and Yarrabubba-provide evidence of hydrothermal fluid flow both within and around the structures. Field observations, and petrographic and geochemical data suggest a common evolutionary trend of post-impact hydrothermal activity from early high-temperature alkali metasomatism to a later lower temperature H+ metasomatism, resulting in the overprinting by hydrous mineral assemblages. Hydrothermal systems activated by meteorite-impact events are important because they may also form economic mineral deposits, as is documented for several impact structures in the world. A working model of hydrothermal circulation in terrestrial impact structures posits two main stages: (i) initial high-temperature fluids percolate downward causing widespread alkali metasomatism of the shattered target rocks below the melt sheet, resulting in their modification to rocks of syenitic affinity; and (ii) inflow of meteoric water and progressive cooling of the melt sheet leads to a lower temperature stage, in which hydrothermal fluid flow tends to move upward, resulting in mineral assemblages and alteration patterns that resemble those of epithermal systems. In addition, these fluids can discharge at the surface as hot springs. © Geological Society of Australia.
330.
Hydrothermal activity associated with the Ries impact event, Germany
Geofluids,
5
(3)
202-220
2005
Abstract: ▾ Combined field studies, optical and scanning electron microscopy, and electron microprobe studies of impactites from the Ries impact structure, Germany, have allowed a clearer picture of the hydrothermal system associated with the Ries impact event to be made. Hydrothermal alteration is concentrated within impact-generated suevites in the interior of the crater (crater suevites) and around the periphery (surficial suevites), with minor alteration in the overlying sedimentary crater-fill deposits. The major heat source for the Ries hydrothermal system was the suevite units themselves. Hydrothermal alteration of crater-fill suevites is pervasive in nature and comprises several distinct alteration phases that vary with depth. An early phase of K-metasomatism accompanied by minor albitization of crystalline basement clasts and minor chloritization, was followed by pervasive intermediate argillic alteration (predominantly montmorillonite, saponite, and illite) and zeolitization (predominantly analcite, erionite, and clinoptilolite). Hydrothermal fluids were typically weakly alkaline during the main stage of alteration. In contrast to the crater-fill suevites, alteration within surficial suevites was typically restricted to montmorillonite and phillipsite deposition within cavities and fractures. The pervasive nature of the alteration within the crater-fill suevites was likely due to the presence of an overlying crater lake; whereas alteration within surficial suevites typically occurred under undersaturated conditions with the main source of water being from precipitation. There are exceptional outcrops of more pervasively altered surficial suevites, which can be explained as locations where water pooled for longer periods of time. Hydrothermal fluids were likely a combination of meteoric waters that percolated down from the overlying crater lake and groundwaters that flowed in from the surrounding country rocks. © 2005 Blackwell Publishing Ltd.
329.
High-resolution magnetostratigraphy of late quaternary sediments from Lake Baikal, Siberia: Timing of intracontinental paleoclimatic responses
Global and Planetary Change,
46
(1-4 SPEC. ISS.)
167 – 186
2005
ISSN: 09218181
Publisher: Elsevier B.V.
Keywords:▾
Eastern Hemisphere; Eurasia; Lake Baikal; Russian Federation; World; lacustrine deposit; magnetostratigraphy; paleoclimate; paleomagnetism; Quaternary
Abstract: ▾ Sediment cores retrieved from 6 locations in Lake Baikal were subjected to a paleomagnetic study in order to establish detailed age models based on correlations of relative paleointensity records. Additional data were provided by calibrated accelerator mass spectrometry (AMS) 14C dating, as well as by documentation of geomagnetic excursions like Laschamp at ∼42 ka and Iceland Basin at ∼185 ka. Few intervals were affected by diagenetic features like selective reductive dissolution of magnetite and greigite mineralization (Demory et al., 2005-this issue), and those that were left out of paleointensity records. These records were tuned to the well-dated paleomagnetic record from ODP Site 984 Channell [Channell, J.E.T., 1999. Geomagnetic paleointensity and directional secular variation at Ocean Drilling Program (ODP) site 984 (Bjorn Drift) since 500 ka: comparisons with ODP site 983 (Gardar drift). J. Geophys. Res., B: [Solid Earth], 104 (10):22, 937-22, 951]. The complex shape of the resulting depth/age curves highlights the need for a high-resolution age model. We focused on the climatic boundary between marine isotopic stage (MIS) 7 and 6 where the Iceland Basin paleomagnetic excursion is clearly documented in the North Atlantic Channell et al.[Channell, J.E.T., Hodell, D.A., Lehman, B., 1997. Relative geomagnetic paleointensity and d18O at ODP Site 983 (Gardar Drift, North Atlantic) since 350 ka. Earth Planet. Sci. Lett., 153 (1-2), 103-118] and in Lake Baikal Oda et al. [Oda, H., Nakamura, K., Ikehara, K., Nakano, T., Nishimura, M., Khlystov, O., 2002. Paleomagnetic record from Academician Ridge, Lake Baikal: a reversal excursion at the base of marine oxygen isotope stage 6. Earth Planet. Sci. Lett., 202 (1), 117-132] ; present study). During this period, we provide evidence for a return to cold conditions in the Lake Baikal region simultaneous to the sea surface cooling, but earlier than the global ice volume change observed in North Atlantic planktonic and benthic δ18O records, respectively. The classical strategy of age model reconstruction, based on direct correlation of the climatic record from Lake Baikal sediments with the marine δ18O reference curves is shown here to be unreliable. Moreover, this strategy does not consider (i) the nonlinearity of the age model in Lake Baikal sediments and (ii) the time lags between the global ice volume change and sea surface cooling observed in δ18O marine records. Finally, the "Baikal 200" compilation of the paleointensity records established in this study provides a 200-ka-long synthetic paleomagnetic record for Central Eurasia. © 2004 Elsevier B.V. All rights reserved.