All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
378.
The use of field dependence of AC susceptibility for the interpretation of magnetic mineralogy and magnetic fabrics in the HSDP-2 basalts, Hawaii
Earth and Planetary Science Letters,
238
(1-2)
110 – 129
2005
ISSN: 0012821XKeywords:▾
Hawaii [(ISL) Hawaiian Islands]; Hawaii [United States]; Hawaiian Islands; North America; oceanic regions; Pacific islands; Pacific Ocean; United States; Western Hemisphere; World; Basalt; Composition effects; Grain size and shape; Magnetic susceptibility; Magnetite; Mineralogy; Oxidation; Field dependence; Magnetic fabrics; Magnetic mineralogy; Titanomagnetite; basalt; magnetic field; magnetic susceptibility; titanomagnetite; Geochemistry
Abstract: ▾ We applied the field dependence parameter χHd (%) = [(k300A/m-k30A/m)/k300A/m] × 100 given by de Wall for the subaerial and submarine basalts drilled by the 3109 m deep HSDP-2 borehole on Hawaii in order to verify the hypothesis that mainly composition controls the field dependence of AC susceptibility in titanomagnetite of natural occurrences. When we used this parameter, our data showed a significant scattering compared to data presented in earlier studies. In addition to composition, the effect of measurement temperature, grain size and anisotropy on the field dependent susceptibility were examined and found to be critical. The impact of grain size is weaker than the other effects. It cannot be totally excluded that the observed effects arise indirectly through an overlap of the other effects for the investigated basalts. The most important factor for the variation of field dependence is the degree of oxidation, causing a modification of the titanomagnetite composition or formation of titanomaghemite, and the mixing of Ti-rich with Ti-poor titanomagnetites, which strongly reduces the χHd parameter. Field dependence is not only related to titanomagnetite composition, especially for intermediate titanomagnetites with TCs between 100 and 300 °C. Temperature dependent susceptibility measurements at different field amplitudes for these intermediate types showed at constant geometry of the k(T) curve great differences in susceptibility, resulting in significant changes of the field dependence parameter over the temperature interval from - 100 to 260 °C. herefore variations of the ambient measurement temperatures are able to influence the field dependence. The second important effect is the degree of particle shape and alignment, which controls the field dependence in different orientations especially for the intermediate titanomagnetite, which is intensively intergrown with elongated hemoilmenite grains. As a consequence, samples with higher degrees of anisotropy exhibit differences of the field dependence parameter if measured parallel to kmax or kmin axis. Therefore, in addition to compositional effects and the temperature dependence, the magnetic fabric has to be considered for the interpretation of field dependent susceptibility measurements. The influence of intrinsic (Ti-content, magnetocrystalline anisotropy), and extrinsic (shape and alignment of grains) factors for the interpretation of the degree of anisotropy has to be kept in mind when interpreting AMS data in terms of strain rates experienced by moving lava during emplacement. © 2005 Elsevier B.V. All rights reserved.
377.
The outline of mallik 2002 gas hydrate production research well program
Nihon Enerugi Gakkaishi/Journal of the Japan Institute of Energy,
84
(2)
88-92
2005
ISSN: 09168753Abstract: ▾ It is estimated that significant amount of methane hydrate resources are deposited offshore Japan and the Research Consortium of Methane Hydrate Resources in Japan (MH21 Research Consortium) was established to undertake the "Japan's Methane Hydrate Exploitation Program" which was prepared by the Ministry of Economy, Trade and Industry and announced in 2001. MH21 Research Consortium planned onshore tests of gas production from gas hydrate reservoir and the Mallik 2002 Gas Hydrate Production Research Well Program was formed in which eight bodies participated from five countries. The test site was located in onshore Mackenzie delta of Northwestern Canada. The swamp feature of the site restricted the whole test operation only in winter when frozen firm ground and transportation road are formed. From December 25th 2001 to March 14th 2002, one gas production test well and two observation wells were drilled. Pressure draw down test using MDT and a hot water circulation test were tried , and the latter test yielded 468m3 dissociated gas from the hydrate reservoir, which was the first success of gas production from naturally deposited gas hydrate reservoir. In December 2003, Mallik International Symposium was held in Chiba, Japan with more than 200 researchers' participation from thirteen countries. The success of the Mallik Program was officially announced for the first time at the Symposium.
376.
The Iceland Deep Drilling Project: A search for deep unconventional geothermal resources
Geothermics,
34
(3)
269 – 285
2005
375.
The ICDP lake Bosumtwi drilling project: A first report
Scientific Drilling,
123 – 27
2005
ISSN: 18168957
Publisher: Copernicus GmbH
Keywords:▾
Coremaking; Lakes; Continental scientific drillings; Core material; Drilling projects; Impact craters; Scientific results; Infill drilling
Abstract: ▾ The 10.5 -km-diameter, 1.07-Ma Bosumtwi impact crater was the subject of a multi-disciplinary and international drilling effort of the International Continental Scientific Drilling Program (ICDP) from July to October 2004. Sixteen different holes were drilled at six locations within the lake, to a maximum depth of 540 m. A total of about 2.2 km of core material was obtained. Despite some technical and logistical challenges, the project has been very successful and it is anticipated that the first scientific results will be available in late 2005. © 2005 Copernicus GmbH.
374.
The 40Ar/39Ar dating of core recovered by the Hawaii Scientific Drilling Project (phase 2), Hilo, Hawaii
Geochemistry, Geophysics, Geosystems,
6
(4)
2005
ISSN: 15252027Abstract: ▾ The Hawaii Scientific Drilling Project, phase 2 (HSDP-2), recovered core from a ∼3.1-km-thick section through the eastern flanks of Mauna Loa and Mauna Kea volcanoes. We report results of 40Ar/39Ar incremental heating by broad-beam infrared laser of 16 basaltic groundmass samples and 1 plagioclase separate, mostly from K-poor tholeiites. The tholeiites generally have mean radiogenic 40Ar enrichments of 1-3%, and some contain excess 40Ar; however, isochron ages of glass-poor samples preserve stratigraphic order in all cases. A 246-m-thick sequence of Mauna Loa tholeiitic lavas yields an isochron age of 122 ± 86 kyr (all errors 2<r) at its base. Beneath the Mauna Loa overlap sequence lie Mauna Kea's postshield and shield sequences. A postshield alkalic lava yields an age of 236 ± 16 kyr, in agreement with an age of 240 ± 14 kyr for a geochemically correlative flow in the nearby HSDP-1 core hole, where more complete dating of the postshield sequence shows it to have accumulated at 0.9 ± 0.4 m/kyr, from about 330 to <200 ka. Mauna Kea's shield consists of subaerial tholeiitic flows to a depth of 1079 m below sea level, then shallow submarine flows, hyaloclastites, pillow lavas, and minor intrusions to core bottom at 3098 m. Most subaerial tholeiitic flows fail to form isochrons; however, a sample at 984 m yields an age of 370 ± 180 kyr, consistent with ages from similar levels in HSDP-1. Submarine tholeiites including shallow marine vitrophyres, clasts from hyaloclastites, and pillow lavas were analyzed; however, only pillow lava cores from 2243, 2614, and 2789 m yield reliable ages of 482 ± 67, 560 ± 150, and 683 ± 82 kyr, respectively. A linear fit to ages for shield samples defines a mean accumulation rate of 8.6 ± 3.1 m/kyr and extrapolates to ∼635 kyr at core bottom. Alternatively, a model relating Mauna Kea's growth to transport across the Hawaiian hot spot that predicts downward accelerating accumulation rates that reach ∼20 m/kyr at core bottom (DePaolo and Stolper, 1996) is also consistent with all reliable ages except the deepest. Copyright 2005 by the American Geophysical Union.
373.
Radiolytic H2 in continental crust: Nuclear power for deep subsurface microbial communities
Geochemistry, Geophysics, Geosystems,
6
(7)
2005
ISSN: 15252027Abstract: ▾ H2 is probably the most important substrate for terrestrial subsurface lithoautotrophic microbial communities. Abiotic H2 generation is an essential component of subsurface ecosystems truly independent of surface photosynthesis. Here we report that H2 concentrations in fracture water collected from deep siliclastic and volcanic rock units in the Witwatersrand Basin, South Africa, ranged up to two molar, a value far greater than observed in shallow aquifers or marine sediments. The high H2 concentrations are consistent with that predicted by radiolytic dissociation of H2O during radioactive decay of U, Th, and K in the host rock and the observed He concentrations. None of the other known H2-generating mechanisms can account for such high H2 abundance either because of the positive free energy imposed by the high H2 concentration or pH or because of the absence of required mineral phases. The radiolytic H 2 is consumed by methanogens and abiotic hydrocarbon synthesis. Our calculations indicate that radiolytic H2 production is a ubiquitous and virtually limitless source of energy for deep crustal chemolithoautotrophic ecosystems. Copyright 2005 by the American Geophysical Union.
372.
Structure and stress state of Hawaiian island basalts penetrated by the Hawaii Scientific Drilling Project deep core hole
Journal of Geophysical Research: Solid Earth,
110
(7)
1 – 8
2005
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
Hawaiian Islands; oceanic regions; Pacific islands; Pacific Ocean; World; ocean island basalt; stress field; structural geology; volcanic island
Abstract: ▾ As part of the Hawaii Scientific Drilling Project (HSDP), an exploratory hole was drilled in 1993 to a depth of 1056 meters below sea level (mbsl) and a deeper hole was drilled to 3098 mbsl in 1999. A set of geophysical well logs was obtained in the deeper hole that provides fundamental information regarding the structure and the state of stress that exist within a volcanic shield. The acoustic televiewer generates digital, magnetically oriented images of the borehole wall, and inspection of this log yields a continuous record of fracture orientation with depth and also with age to 540 ka. The data depict a clockwise rotation in fracture strike through the surficial Mauna Loa basalts that settles to a constant heading in the underlying Mauna Kea rocks. This behavior reflects the depositional slope directions of lavas and the locations of volcanic sources relative to the drill site. The deviation log delineates the trajectory of the well bore in three-dimensional space. This path closely follows changes in fracture orientation with depth as the drill bit is generally prodded perpendicular to fracture strike during the drilling process. Stress-induced breakouts observed in the televiewer log identify the orientations ot the maximum and minimum horizontal principal stresses to be north-south and east-west, respectively. This stress state is attributed to the combination of a sharp break in onshore-offshore slope that reduces stress east-west and the emergence of Kilauea that increases stress north-south. Breakouts are extensive and appear over approximately 30% of the open hole. Copyright 2005 by the American Geophysical Union.
371.
Stable isotope record of post-impact fluid activity in the core of the Yaxcopoil-1 borehole, Chicxulub impact structure, Mexico
Special Paper of the Geological Society of America,
384223-238
2005
Abstract: ▾ Carbon, oxygen, and hydrogen isotope results from carbonate and silicate fractions of altered core samples from the Yaxcopoil-1 borehole drilled into the 65 Ma Chicxulub impact crater provide constraints on the physico-chemical parameters of the hydrothermal solutions, and their likely origin. Yaxcopoil-1 impactites were initially permeated with calcite and halite at ambient temperature. This was followed by thermal metamorphism (diopside after igneous augite) and widespread Na-K metasomatism (feldspar after igneous plagioclase), which were overprinted by abundant lower-temperature clay and calcite. Silicate fraction isotopic values have δ 18O SMOW values between 10 and 23% indicating important isotopic exchange between impact melt (∼8%) and Cretaceous limestone (∼26%). Heavier δ 18 O values occur over depth intervals with intense feldspar alteration (813-833 m and 864-872 m). The δD SMOW values (-34 to -54%) are chiefl y infl uenced by smectite abundance and roughly mirror δ 18 O values. Carbonate fraction δ 18 O SMOW values (22-30%) are controlled by calcite contents, and several exceed the limestone signature. Most δ0.13C PDB (-1 to +2%) values also cluster around that of local limestone, but a number are signifi cantly lighter (down to -7%). Isotopic and fluid inclusion results indicate hydrothermal fluid temperatures between 270 and 100 °C, high salinities (∼20%), and minor kerogen contents. These data are compatible with mineralogical constraints, which further support an increase in oxidation state with decreasing temperature. Isotopic data point to a saline CO 2 -bearing fluid mixed with small amounts of reduced carbon, and decarbonation and infi ltration processes. Combined results are most consistent with a basinal oilfi eld saline brine that was driven by impact-induced heat. © 2005 Geological Society of America.
370.
Spinel-bearing spherules condensed from the Chicxulub impact-vapor plume
Geology,
33
(4)
293-296
2005
DOI:10.1130/G21136.1
Abstract: ▾ Formation of the giant Chicxulub crater off Mexico's Yucatan Peninsula coincided with deposition of the global Ir-rich Cretaceous-Tertiary (K-T) stratigraphic boundary layer ca. 65 Ma. The boundary is marked most sharply by abundant spherules containing un-altered grains of magnesioferrite spinel. Here we predict for the first time the sequential condensation of solids and liquids from the plume of vaporized rock expected from oblique K-T impacts. We predict highly oxidizing plumes that condense silicate liquid droplets bearing spinel grains whose compositions closely match those marking the actual boundary. Systematic global variations in spinel composition are consistent with higher condensation temperatures for spinels found at Atlantic and European sites than for those in the Pacific. © 2005 Geological Society of America.
369.
Seismic structure and location of a CO2 source in the upper mantle of the western Eger (Ohře) Rift, central Europe
Tectonics,
24
(5)
1 – 23
2005
ISSN: 02787407Keywords:▾
Central Europe; Eurasia; Europe; Ohre River; carbon dioxide; lithospheric structure; seismic velocity; upper mantle
Abstract: ▾ P-SV conversions provide new insights into the lithosphere of the western Eger (Ohře) Rift, a presently active CO2 emanation area, Quaternary volcanic field, and earthquake swarm region in central Europe. Gas and isotope (He and C) mapping of free gas phases in mineral springs and mofettes proved the origin Of CO2-dominated gases from a subcrustal magmatic fluid reservoir. Analyzing teleseismic data from several seismic networks in the western Bohemian Massif the source region of these gases was investigated Moho Ps conversions have 3 to 4.5 s delay. Crustal thicknesses vary between 27 and 38 km; vp/vs ratios vary between 1.63 and 1.81. Beneath the western Eger Rift an approximately 40 km wide Moho updoming up to 27 km exists. Locally observed weak conversions indicate a complex Moho transition zone in this area. A local "6 s phase" possibly originates at a discontinuity in approximately 50 to 60 km depth or may represent multiples from velocity inversions at the base of the upper crust. Moho updoming and the distribution of the "6 s phase" coincide with the CO2 degassing fields and the positions of Quaternary volcanoes at the surface. We hypothesize the release of CO2-dominated fluid/magma from isolated melt reservoirs in the depth range of 60 to 30 km, separation of CO2 from the melt at 29 to 21 km depths, and CO2 transport through the crust. The geophysical indications may point to presently active magmatic underplating beneath the study area, supporting the results of gas geochemical and isotope investigations. This is the first attempt that combines seismic and gas geochemical data for a tectonic model. Our model may be transferable to other continental rift areas worldwide. Copyright 2005 by the American Geophysical Union.
368.
Scientific results of conduit drilling in the Unzen Scientific Drilling Project (USDP)
Scientific drilling,
118--22
2005
367.
Scientific results from the Mallik 2002 gas hydrate production research well program, Mackenzie Delta, northwest territories, Canada: Preface
Bulletin of the Geological Survey of Canada
(585)
iii-iv
2005
ISSN: 00687626
Publisher: Energy, Mines and Resources Canada
DOI:10.4095/220702
Keywords:▾
gas hydrate
366.
Scientific drilling reached the magma path of 1990-95 eruption of Unzen Volcano
AIST Today (International Edition)
(16)
13
2005
ISSN: 1346602XAbstract: ▾ The subsurface structure and magma ascending mechanism of Unzen Volcano was investigated by Unzen Scientific Drilling project (USDP) not only by scientific drillings but also related by geophysical and geochemical studies. A hole was drilled to reach the conduit of the Heisei eruption inorder to clarify the ascending and degassing process of magma and to understand the mechanism of an eruption. There was a conduit zone near the area right under Mt.Fugen at around the sea level, where old and new conduits including the Heisei conduit were concentrated within approximately 500 meters. The temperature in the conduit zone was approximately 200°C, lower than expected before the drilling resulted from quick cooling due to hydrothermal activities.
365.
Recent research on the Chesapeake Bay impact structure, USA - Impact debris and reworked ejecta
Special Paper of the Geological Society of America,
384147-170
2005
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Argon; Binary alloys; Crystalline materials; Crystalline rocks; Debris; Feldspar; Fluidization; Geochronology; Lead alloys; Mica; Quartz; Rocks; Sediments; Silicate minerals; Structural geology; Zircon, Cataclastic; Chesapeake; Crater; Dinofl agellate; Ejecta; Impact; Nannofossil; Resurge; Shock; SHRIMP, Meteor impacts, abrasion; cataclasite; Cretaceous; ejecta; Eocene; fluidization; impact structure; ion microprobe; leucogranite; melt; muscovite; quartz; research; sand; zircon, Chesapeake Bay; United States
Abstract: ▾ Four new coreholes in the western annular trough of the buried, late Eocene Chesapeake Bay impact structure provide samples of shocked minerals, cataclastic rocks, possible impact melt, mixed sediments, and damaged microfossils. Parautochthonous Cretaceous sediments show an upward increase in collapse, sand fluidization, and mixed sediment injections. These impact-modifi ed sediments are scoured and covered by the upper Eocene Exmore beds, which consist of highly mixed Cretaceous to Eocene sediment clasts and minor crystalline-rock clasts in a muddy quartz-glauconite sand matrix. The Exmore beds are interpreted as seawater-resurge debris flows. Shocked quartz is found as sparse grains and in rock fragments at all four sites in the Exmore, where these fallback remnants are mixed into the resurge deposit. Crystalline-rock clasts that exhibit shocked quartz or cataclastic fabrics include felsites, granitoids, and other plutonic rocks. Felsite from a monomict cataclasite boulder has a sensitive high-resolution ion microprobe U-Pb zircon age of 613 ± 4 Ma. Leucogranite from a polymict cataclasite boulder has a similar Neoproterozoic age based on muscovite 40 Ar/ 39 Ar data. Potassium-feldspar 40 Ar/ 39 Ar ages from this leucogranite show cooling through closure (∼150 °C) at ca. 261 Ma without discernible impact heating. Spherulitic felsite is under investigation as a possible impact melt. Types of crystalline clasts, and exotic sediment clasts and grains, in the Exmore vary according to location, which suggests different provenances across the structure. Fractured calcareous nannofossils and fused, bubbled, and curled dinofl agellate cysts coexist with shocked quartz in the Exmore, and this damage may record conditions of heat, pressure, and abrasion due to impact in a shallow-marine environment. © 2005 Geological Society of America.
364.
Re-evaluating the age of the Haughton impact event
Meteoritics and Planetary Science,
40
(12)
1777-1787
2005
Abstract: ▾ We have re-evaluated the published age information for the Haughton impact structure, which was believed to have formed ∼23 Ma ago during the Miocene age, and report new Ar/Ar laser probe data from shocked basement clasts. This reveals an Eocene age, which is at odds with the published Miocene stratigraphic, apatite fission track and Ar/Ar data; we discuss our new data within this context. We have found that the age of the Haughton impact structure is ∼39 Ma, which has implications for both crater recolonization models and post-impact hydrothermal activity. Future work on the relationship between flora and fauna within the crater, and others at high latitude, may resolve this paradox. © The Meteoritical Society, 2005.
363.
Late glacial and Holocene vegetation and regional climate variability evidenced in high-resolution pollen records from Lake Baikal
Global and Planetary Change,
46
(1-4 SPEC. ISS.)
255 – 279
2005
ISSN: 09218181
Publisher: Elsevier B.V.
Keywords:▾
Eastern Hemisphere; Eurasia; Lake Baikal; Russian Federation; World; Abies; Acer pensylvanicum; Alnus; Amaranthaceae; Artemisia; Betula; Betulaceae; Picea; Pinus sylvestris; climate variation; Holocene; late glacial; paleoclimate; palynology; vegetation history
Abstract: ▾ High-resolution pollen records from Lake Baikal revealed considerable regional differences in the vegetation development and pronounced climate variability during the last glacial-interglacial transition and Holocene. Correlation between cores was successfully based on a chronology constructed from AMS 14C dating of pollen concentrates. Comparison to other radiocarbon-dated pollen sequences from the Baikal region suggests that the chronology presented is very reliable, and thus correlation to other dated events can easily be performed. Pollen indices, which reflect relative changes in major vegetation types and limitations of growing conditions by moisture availability and temperature, demonstrate near-synchronous vegetation changes, which suggest synchronous large-scale climate variation across the Baikal region. Due to the limited influence of human impact in the Lake Baikal region, the pollen data illustrate that, in the continental interior of NE Eurasia Holocene, climate variability was very pronounced. After initial warming and a strong increase in relative moisture (ca. 16 cal ka BP), the Bølling-Allerød-like event was punctuated by three cool and dry events. These events, dated between ca. 15 and 13 cal ka BP, can be compared to coolings as recorded in GISP 2 oxygen isotope records from Greenland ice cores. An expansion of Betula sect. Nanae/Fruticosae, Artemisia and Chenopodiaceae marks the Younger-Dryas (YD)-like cooling event (ca. 12.5-12 cal ka BP). High temperatures and favourable moisture conditions during the first part of Holocene favoured the optimum development of dark coniferous taiga between 11-7.5 cal ka BP in the south and 10-8 cal ka BP in the northeast. A fir and spruce decline in the southern mountains (ca. 9.5-8.5 cal ka BP) can be related to the 8.2 cal ka BP cooling event. The pronounced mid-Holocene cooling event and a transition towards dry conditions (ca. 8-7 cal ka BP) preceded the nearly synchronous regional expansion of pine taiga. Maximum distribution of Scots pine forests marks the Holocene thermal optimum (ca. 6.5-5.7 cal ka BP), which was followed by two subsequent cooling events (ca. 5.5-4.5 cal ka BP) at the Atlantic-Subboreal transition. A subsequent temperature optimum in the southeastern Baikal region ended with pronounced cooling during the Subboreal-Subatlantic transition (ca. 3-2.5 cal ka BP). A late spread of shrub alders may evidence the beginning of the Little Ice Age. © 2004 Elsevier B.V. All rights reserved.
362.
Late-Quaternary lowstands of lake Bosumtwi, Ghana: Evidence from high-resolution seismic-reflection and sediment-core data
Palaeogeography, Palaeoclimatology, Palaeoecology,
216
(3-4)
235 – 249
2005
ISSN: 00310182
Publisher: Elsevier B.V.
Keywords:▾
Africa; Ashanti; Eastern Hemisphere; Ghana; Lake Bosumtwi; Sub-Saharan Africa; West Africa; World; lake level; lowstand; Quaternary; seismic survey
Abstract: ▾ Results from the first high-resolution, single-channel seismic-reflection survey of tropical Lake Bosumtwi, Ghana, and sedimentological data from a 14C-dated sediment piston core were used to revise and extend the basin's late-Quaternary lake level history. We report four seismic sequence boundaries and an exposure surface from a sediment core, which are interpreted as erosional surfaces formed at times of drastic low lake level. The youngest erosional surface occurs as much as 31 m below present lake level (bpll) and up to 0.7 m below the present sediment-water interface. This most recent unconformity observed in the seismic data is interpreted to be coeval with the basin-wide late-Holocene dry period between 0.5 and 1 cal ky BP (calendar years before present). Another exposure surface observed in a sediment core is based on an abrupt contact separating low density, wet, clay rich sediments from underlying high density, compact, silt-rich and rootlet-rich sediments, and is interpreted to have developed prior to 16.8 cal ky BP when the lake was ∼60 m bpll. Three older, erosional surfaces occur at depths of ∼92±3, 102±3, and 107±4 m bpll, suggesting numerous lowstands in Lake Bosumtwi during the late-Pleistocene. By extrapolation of average sedimentation rates (0.41 m/ky) from the upper ∼10.5 m of sediment, we estimate the ages of these older lowstands to be ∼65, ∼86, ∼108 cal ky BP. The lowstands of Lake Bosumtwi evidenced from the seismic and sediment core data are interpreted as a response to increased aridity in this part of the equatorial tropics and may correlate to other observed continent-wide shifts in African climate over the past 100 ky, and possibly to rapid climatic shifts observed at high latitudes. Determining the precise timing of these lowstands will ultimately reveal much about the drought dynamics of tropical and subtropical Africa. © 2004 Elsevier B.V. All rights reserved.
361.
Introduction to "progress towards reconstructing past climate in Central Eurasia, with special emphasis on Lake Baikal"
Global and Planetary Change,
46
(1-4 SPEC. ISS.)
1 – 7
2005
ISSN: 09218181
Publisher: Elsevier B.V.
Keywords:▾
paleoclimate
360.
Buried treasure
Mechanical Engineering,
127
(SUPPL.)
8-11
2005
ISSN: 00256501Abstract: ▾ The potential of offshore deposits of methane hydrates as energy resource is discussed. The efforts to develop methods that would make production of methane from hydrate both technologically feasible and economically viable are also presented. Methane hydrate is a very efficient storehouse of energy, and when dissociated, a single cubic foot of solid hydrate releases as much as 180 cubic feet of methane gas. work at the Mallik site in the Canadian Arctic has established that production of methane from hydrates is technologically feasible. The US national methane hydrate research program is now performing field and laboratory studies designed to accelerate the commercially viable production of methane from hydrate in Alaska.
359.
Detrital input and early diagenesis in sediments from Lake Baikal revealed by rock magnetism
Global and Planetary Change,
46
(1)
145-166
2005
ISSN: 0921-8181
Publisher: Elsevier B.V.
Keywords:▾
Lake Baikal, Late Quaternary, Rock magnetism, Diagenesis, Detrital input
Abstract: ▾ A rock magnetic study was performed on sediment cores from six locations in Lake Baikal. For a comprehensive approach of the processes influencing the rock magnetic signal, additional data are presented such as total organic carbon (TOC), total sulphur (TS), opal, water content and relative variations in iron and titanium measured on selected intervals. In glacial sediments, the magnetic signal is dominated by magnetite, which is considered to be of detrital origin. This predominance of magnetite is interrupted by distinct horizons of authigenic greigite, probably confined to reductive microenvironments. In interglacial stages, besides dilution by biogenic silica and a decreasing detrital input, the weakness of the rock magnetic signal is also due to a reductive dissolution of magnetic particles. The magnetic assemblage is strongly linked to the redox history of interglacial sediment. In the oxidised bottom sediments of Lake Baikal, a biogenic magnetite is observed [Peck, J.A., King, J.W., 1996. Magnetofossils in the sediments of lake Baikal, Siberia. Earth Planet. Sci. Lett. 140 (1–4), 159–172]. After burial under the redox front, the magnetite is preferentially dissolved, and detrital hematite remains dominant when the sedimentation rate is low and when the residence time of the magnetite close to the redox boundary is long. During these low sedimentation rate conditions, the redox front is preserved [Granina, L., Müller, B. and Wehrli, B., 2004. Origin and dynamics of Fe and Mn sedimentary layers in Lake Baikal. Chem. Geol. 205 (1-2), 55-72]. At constant sedimentation rate and fast burial, the magnetite is preserved or transformed into greigite when sulphate-reducing conditions are reached in the sediment. In interglacial sediments, the magnetic assemblages depict changes in the sedimentation rate, which are traced using the ratio of magnetite over hematite (S-ratio). At the beginning of interglacials, the sedimentation rate is constant with an assemblage magnetite+greigite (high S-ratio), and at the end of some interglacials, the sedimentation rate decreases with a predominance of hematite (low S-ratio).
358.
Depth constraints on nonlinear strong ground motion from the 2004 Parkfield earthquake
Geophysical Research Letters,
32
(14)
1-5
2005
ISSN: 00948276Keywords:▾
Boreholes; Cracks; Earthquakes; Geologic models; Rock mechanics; Seismic waves; Seismology; Structural geology, Depth constraints; Earthquake sequences; Ground motion; Shallow crust, Tectonics, arrival time; damage; earthquake; ground motion; S-wave, California; North America; Parkfield; United States; Western Hemisphere; World
Abstract: ▾ We use the two target repeating earthquake sequences of SAFOD to identify time varying properties of the shallow crust in the Parkfield area at the surface and in shallow boreholes. At the surface, we find that the 2004 Parkfield earthquake caused direct S wave delays exceeding 7 ms, and S coda delays exceeding 15 ms. We attribute these delays to cracks formed or opened during the strong shaking of the Parkfield earthquake. Observations at depth show that the direct S wave arrival time was much less affected by the Parkfield earthquake. This provides evidence that damage caused by strong shaking (nonlinear strong ground motion), is limited to the very near surface (<100 m). Copyright 2005 by the American Geophysical Union.
357.
Crustal and uppermost mantle structure of the Bohemian Massif based on CELEBRATION 2000 data
Journal of Geophysical Research: Solid Earth,
110
(11)
1 – 21
2005
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
Bohemian Massif; Central Europe; Eurasia; Europe; crustal structure; mantle structure; seismic tomography
Abstract: ▾ The deep structure of the Bohemian Massif (BM), the largest stable outcrop of Var scan rocks in central Europe, was studied using the data of the international seismic refraction experiment Central European Lithospheric Experiment Based on Refraction (CELEBRATION) 2000. The data were interpreted by seismic tomographic inversion and by two-dimensional (2-D) trial-and-error forward modeling of P and S waves. Additional constraint on crustal structure was given by amplitude modeling using the reflectivity method and gravity modeling. Though consolidated, the BM can be subdivided into several tectonic units separated by faults, shear zones, or thrusts reflecting varying influence of the Cadomian and Variscan orogeneses: the Saxothuringian, Barrandian, Moldanubian, and Moravian. Velocity models determine three types of crust-mantle transition in the BM reflecting variable crustal thickness and delimiting contacts of tectonic units in depth. The NW area, the Saxothuringian, has a highly reflective lower crustal layer above Moho with a strong velocity contrast at the top of this layer. This reflective laminated lower crust reaches depths of 26-35 km and is characteristic for the Saxothuringian unit, which was subject to eastward subduction. The Moldanubian in the central part is characterized by the deepest (39 km) and the most pronounced Moho within the whole BM with a strong velocity contrast 6.9-8.1 kin s-1. A thick crust-mantle transition zone in the SE, with velocity increase from 6.8 to 7.8 km s-1 over the depth range of 23-40 km, seems to be the characteristic feature of the Moravian overthrusted by the Moldanubian during Variscan collision. Copyright 2005 by the American Geophysical Union.
356.
Climate and the collapse of Maya civilization
American Scientist,
93
(4)
322 – 329
2005
ISSN: 00030996
Publisher: Sigma Xi, Scientific Research Society
Keywords:▾
Social aspects; Collapse; Maya civilization; archaeological evidence; demography; Climatology
Abstract: ▾ During its Classic period (250-950 A.D.), Maya civilization reached a zenith. At its peak, around 750 A.D., the population may have topped 13 million. Then, between about 750 and 950 A.D., their society imploded. The Maya abandoned what had been densely populated urban centers, leaving their impressive stone edifices to fall into ruin. The demise of Maya civilization (which archaeologists call "the terminal Classic collapse") has been one of the great anthropological mysteries of modern times. What could have happened? Scholars have advanced a variety of theories over the years, pinning the fault on everything from internal warfare to foreign intrusion, from widespread outbreaks of disease to a dangerous dependence on monocropping, from environmental degradation to climate change. Some combination of these and other factors may well be where the truth lies. However, in recent years, evidence has mounted that unusual shifts in atmospheric patterns took place near the end of the Classic Maya period, lending credence to the notion that climate, and specifically drought, indeed played a hand in the decline of this ancient civilization.
355.
Chicxulub impact ejecta from the Cretaceous-Paleogene (K-P) boundary in northeastern México
Special Paper of the Geological Society of America,
384191-221
2005
Abstract: ▾ The combined petrological and rock magnetic study of the Cretaceous-Paleogene (K-P) boundary in northeastern México revealed compositionally and texturally complex Chicxulub ejecta deposits. The predominant silicic ejecta components are Fe-Mg-rich chlorite and Si-Al-K-rich glass spherules with carbonate inclusions and schlieren. Besides these silica phases, the most prominent ejecta component is carbonate. Carbonate occurs as lithic clasts, accretionary lapilli, melt globules (often with quench textures), and as microspar. The composition of the spherules provides evidence for a range of target rocks of mafi c to intermediate composition, presumably situated in the northwestern sector of the Chicxulub impact structure. The abundance of carbonate ejecta suggests that this area received ejecta mainly from shallow, carbonate-rich lithologies. Rare μm-sized metallic and sulfi dic Ni-Corich inclusions in the spherules indicate a possible contamination by meteoritic material. This complex composition underlines the similarities of ejecta in NE México to Chicxulub ejecta from K-P sections worldwide. Although the ejecta display a great variability, the magnetic susceptibility, remanence, and hysteresis properties of the ejecta deposits are fairly homogeneous, with dominantly paramagnetic susceptibilities and a weak ferromagnetic contribution from hematite and goethite. The absence of spinels and the ubiquitous presence of hematite and goethite points to high oxygen fugacity during the impact process. The microfacies and internal texture of the ejecta deposits show welding and fusing of components, as well as evidence for liquid immiscibility between silicic and carbonate melts. No evidence for binary mixing of ejecta phases was found. Therefore, Chicxulub ejecta in NE México probably derived from less energetic parts of the ejecta curtain. However, welding features of ejecta particles and enclosed marl clasts and/or benthic foraminifera from a siliciclastic environment suggest interaction of the-still hot-ejecta curtain with northern Mexican shelf sediments. In addition, an initial ground surge-like ejecta-dispersion mode seems possible. © 2005 Geological Society of America.
354.
Chicxulub Crater Seismic Survey prepares way for future drilling
Eos, Transactions American Geophysical Union,
86
(36)
325-328
2005
Abstract: ▾ Sixty-five million years ago, a large meteorite hit the Earth and formed the ∼200-km-wide Chicxulub crater in Yucatán, Mexico. The well-known, massive extinction event at the Cretaceous-Tertiary (K-T) boundary appears to have been caused, at least in part, by this impact. In the first few seconds after impact the surface of the Earth was pushed down to form a cavity ∼35 km deep, and in the next few hundred seconds this cavity collapsed to form a multi-ring basin with an inner peak ring. To examine the rings and subsurface structure of this superbly preserved impact crater, a seismic experiment was shot across the crater in January and February 2005 by a team of scientists from Mexico, the United States, and the United Kingdom (Figure 1).