All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
519.
Joint IODP-ICDP workshop examines challenges of fault zone drilling
Scientific Drilling
(1 SUPPL. 1)
5-16
2007
ISSN: 18168957518.
Joint IODP/ICDP scientific drilling of the Chicxulub impact crater
Scientific Drilling
(4)
42-44
2007
517.
Lake Baikal climatic record between 310 and 50 ky BP: Interplay between diatoms, watershed weathering and orbital forcing
Palaeogeography, Palaeoclimatology, Palaeoecology,
250
(1-4)
50 – 67
2007
ISSN: 00310182Keywords:▾
Eurasia; Lake Baikal; Russian Federation; Aulacoseira baicalensis; Aulacoseira skvortzowii; Bacillariophyta; Cyclotella; Cyclotella minuta; Stephanodiscus; climate change; diatom; interglacial; interstadial; lacustrine deposit; magnetic field; Northern Hemisphere; orbital forcing; proxy climate record; record; spectroscopy; watershed; weathering
Abstract: ▾ The environmental record from Lake Baikal, Russia, from 310 to 50 ky BP (MIS 9a to MIS 3) was interpreted using rock magnetic, UV-Vis spectral, mineralogical, and diatom analyses. The age model was based on a correlation of the diatom and chemical weathering records and the summer insolation curve at 55°N and checked against an age model based on the proxy of relative palaeointensity of the Earth's magnetic field. Peaks in chemical weathering within the watershed, inferred from maximum concentration of magnetic and coloured minerals and mica, the lowest mean Fe oxidation state in silicates and highs in expandable clay minerals correlated with the Northern Hemisphere summer insolation minima at 55°N. Reconstructed changes in weathering intensity are better correlated to insolation patterns than to global ice volume records. We propose a scheme of yet missing palaeoenvironmental interpretation of the diatom assemblage, including also some extinct species. Aulacoseira baicalensis and Aulacoseira skvortzowii were abundant in the early stages of lake flora recovery immediately after deglaciation and during MIS 7e and MIS 5e; periods of more pronounced continental climate and peak chemical weathering. Stephanodiscus formosus var. minor, Cyclotella minuta and Cyclotella ornata dominated in intervals of decreased seasonality and decreased humidity at the end of most interglacial/interstadial diatom zones. Stephanodiscus grandis, Stephanodiscus carconeiformis and Stephanodiscus formosus were ubiquitous between MIS 8 and MIS 5, an interval marked by high seasonality, i.e., large differences between winter and summer insolation, and low humidity revealed by a low hydrolysis of expandable clay minerals in the watershed. Diatom concentrations peaked in the climatic optima of MIS 7e and MIS 5e and in the short periods marked by shifts to warmer conditions in the upper sections of MIS 5: MIS 5c (103-99 ky BP), MIS 5b (90-88 ky BP), and MIS 5a (84-79 ky BP) in which increased humidity resulted in enhanced hydrolysis of clay minerals. No such short similar climatic optimums were found from MIS 9a to MIS 6. Sharp climate deteriorations recorded in the diatom and clay mineral records at 107, 94, and 87 ky BP, however, occurred within 1-2 ky of cold extremes in North Atlantic sea surface temperature emphasizing the strong teleconnections between the two localities. © 2007 Elsevier B.V. All rights reserved.
516.
Late Cenozoic climate changes in China's western interior: a review of research on Lake Qinghai and comparison with other records
Quaternary Science Reviews,
26
(17-18)
2281 – 2300
2007
ISSN: 02773791Keywords:▾
Asia; Atlantic Ocean; Atlantic Ocean (North); China; Eurasia; Far East; Qinghai-Xizang Plateau; Qionghai Lake; Sichuan; Tarim Basin; Xinjiang Uygur; Carbonates; Glaciers; Global warming; Precipitation (meteorology); Sea level; carbonate; Cenozoic; climate change; climate conditions; comparative study; global warming; historical record; Holocene; ice sheet; Last Glacial Maximum; marginal basin; Northern Hemisphere; regional climate; Lake Qinghai; Tibetan Plateau; Climate change
Abstract: ▾ We review Late Cenozoic climate and environment changes in the western interior of China with an emphasis on lacustrine records from Lake Qinghai. Widespread deposition of red clay in the marginal basins of the Tibetan Plateau indicates that the Asian monsoon system was initially established by ∼8 Ma, when the plateau reached a threshold altitude. Subsequent strengthening of the winter monsoon, along with the establishment of the Northern Hemisphere ice sheets, reflects a long-term trend of global cooling. The few cores from the Tibetan Plateau that reach back a million years suggest that they record the mid-Pleistocene transition from glacial cycles dominated by 41 ka cycles to those dominated by 100 ka cycles. During Terminations I and II, strengthening of the summer monsoon in China's interior was delayed compared with sea level and insolation records, and it did not reach the western Tibetan Plateau and the Tarim Basin. Lacustrine carbonate δ18O records reveal no climatic anomaly during MIS3, so that high terraces interpreted as evidence for extremely high lake levels during MIS3 remain an enigma. Following the Last Glacial Maximum (LSM), several lines of evidence from Lake Qinghai and elsewhere point to an initial warming of regional climate about 14 500 cal yr BP, which was followed by a brief cold reversal, possibly corresponding to the Younger Dryas event in the North Atlantic region. Maximum warming occurred about 10 000 cal yr BP, accompanied by increased monsoon precipitation in the eastern Tibetan Plateau. Superimposed on this general pattern are small-amplitude, centennial-scale oscillations during the Holocene. Warmer than present climate conditions terminated about 4000 cal yr BP. Progressive lowering of the water level in Lake Qinghai during the last half century is mainly a result of negative precipitation-evaporation balance within the context of global warming. © 2007.
515.
Rare earth element composition as evidence of the precursor material of Cretaceous-Tertiary boundary sediments at distal sections
Chemical Geology,
232
(1-2)
1-11
2006
Abstract: ▾ The Chicxulub impact event led to a worldwide deposition of impact materials originated from target rocks and the vaporized bolide. Relative contributions of both types of material to the K/T ejecta deposits vary with distance to the crater site. At distal sites (e.g., Agost and Caravaca in the SE of Spain) a major contribution of extraterrestrial material is indicated by different impact signatures, such as Os and Cr isotope composition, abundant microkrystites, platinum group elements and other siderophile elements that are typical of extraterrestrial components. Closer settings to the Chicxulub crater, for example the Blake Nose Plateau in the North American margin, display major continental crustal rock contributions in the ejecta layer. REE compositions provide additional evidence for terrestrial vs. extraterrestrial rock contributions. Previous research has not focused specifically on REE concentrations and corresponding C1- and NASC-normalized patterns. However, normalized REE patterns are already generating supplementary insights into the nature of the original material of the K/T boundary layer. Thus, Blake Nose ejecta C1-normalized patterns indicate a derivation from continental crustal target rocks. In more distal sections REE compositions point to a probable mafic precursor and confirm that extraterrestrial materials represent a major contribution the ejecta layer. © 2006 Elsevier B.V. All rights reserved.
514.
Refining the image of the San Andreas Fault near Parkfield, California using a finite difference travel time computation technique
Tectonophysics,
426
(1-2)
189-205
2006
ISSN: 00401951Keywords:▾
data inversion; fault zone; ray tracing; seismic tomography; seismic zone; travel time, California; North America; Parkfield; United States
Abstract: ▾ The Parkfield Area Seismic Observatory (PASO) was a dense, telemetered seismic array that operated for nearly 2 years in a 15 km aperture centered on the San Andreas Fault Observatory at Depth (SAFOD) drill site. The main objective of this deployment was to refine the locations of earthquakes that will serve as potential targets for SAFOD drilling and in the process develop a high (for passive seismological techniques) resolution image of the fault zone structure. A challenging aspect of the analysis of this data set was the known existence of large (20-25%) contrasts in seismic wavespeed across the San Andreas Fault. The resultant distortion of raypaths could challenge the applicability of approximate ray tracing techniques. In order to test the sensitivity of our hypocenter locations and tomographic image to the particular ray tracing and inversion technique employed, we compare an initial determination of locations and structure developed using a coarse grid and an approximate ray tracer [Thurber, C., Roecker, S., Roberts, K., Gold, M., Powell, M.L., and Rittger, K., 2003. Earthquake locations and three-dimensional fault zone structure along the creeping section of the San Andreas fault near Parkfield, CA: Preparing for SAFOD, Geophys. Res. Lett., 30 3, 10.1029/2002GL016004.] with one derived from a relatively fine grid and an application of a finite difference algorithm [Hole, J.A., and Zelt, B.C., 1995. 3-D finite-difference reflection traveltimes, Geophys. J. Int., 121, 2, 427-434.]. In both cases, we inverted arrival-time data from about 686 local earthquakes and 23 shots simultaneously for earthquake locations and three-dimensional Vp and Vp/Vs structure. Included are data from an active source seismic experiment around the SAFOD site as well as from a vertical array of geophones installed in the 2-km-deep SAFOD pilot hole, drilled in summer 2002. Our results show that the main features of the original analysis are robust: hypocenters are located beneath the trace of the fault in the vicinity of the drill site and the positions of major contrasts in wavespeed are largely the same. At the same time, we determine that shear wave speeds in the upper 2 km of the fault zone are significantly lower than previously estimated, and our estimate of the depth of the main part of the seismogenic zone decreases in places by ∼ 100 m. Tests using "virtual earthquakes" (borehole receiver gathers of picks for surface shots) indicate that our event locations near the borehole currently are accurate to about a few tens of meters horizontally and vertically. © 2006 Elsevier B.V. All rights reserved.
513.
SAFOD Penetrates the San Andreas Fault
Scientific Drilling,
2006
(2)
32-33
2006
ISSN: 1816-8957Abstract: ▾ SAFOD, the San Andreas Fault Observatory at Depth (Fig. 1), completed an important milestone in July 2005 by drilling through the San Andreas Fault at seismogenic depth. SAFOD is one of three major components of EarthScope, a U.S. National Science Foundation (NSF) initiative being conducted in collaboration with the U.S. Geological Survey (USGS). The International Continental Scientific DrillingProgram (ICDP) provides engineering and technical support for the project as well as online access to project data and information (https://www.icdp-online.org/sites/sanandreas/news/news1.html). In 2002, the ICDP, the NSF, and the USGS provided funding for a pilot hole project at the SAFOD site. Twenty scientifi c papers summarizing the results of the pilot hole project as well as pre-SAFOD site characterization studies were published in Geophysical Research Letters (Vol.31, Nos. 12 and 15, 2004).
512.
Scanned core image database and web-sharing of Chinese continental scientific drilling project
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences,
31
(4)
575-577
2006
ISSN: 10002383Abstract: ▾ The only main hole of the Chinese Continental Scientific Drilling (CCSD) Project, the deepest scientific drilling project of all the ICDP projects, reached its depth of over 5000 m, from which more than 4400 m cores were collected. Hence the scanned core image database of CCSD project is also the largest of all the databases of ICDP projects. After various samplings, some cores have been completely damaged or disappeared. To make full use of the scanned core images, an MS ACCESS database was developed, on the basis of the original DIS system. More than 8000 images (about 100 gigabyte) have been efficiently and systematically managed and shared on the Internet with some user-friendly query program and interfaces using the ASP and VB techniques. This new information technology, proved by one year trial test, can not only store permanently and efficiently the original image data, but also help geologists to study efficiently the cores for their scientific purpose.
511.
Seismic characterization and continuity analysis of gas-hydrate horizons near Mallik research wells, Mackenzie Delta, Canada
Leading Edge,
25
(5)
599-604
2006
ISSN: 1070485X
Publisher: Society of Exploration Geophysicists
Keywords:▾
Gases; Hydration; Petroleum prospecting, Clastic sediments; Conventional hydrocarbons; Gas hydrate saturations; Hydrate accumulations; Permafrost region; Potential sources; Significant gas; Three interval, Gas hydrates, clastic sediment; gas hydrate; hydrocarbon exploration; natural gas; permafrost; porosity; supermarket, Arctic; Arctic Ocean; Beaufort Sea; Canada; Mackenzie Delta; Northwest Territories
Abstract: ▾ Gas-hydrate accumulations located onshore in Arctic permafrost regions are seen as a potential source of natural gas. Surprisingly, most of the gas hydrate found in the Mackenzie Delta and Beaufort Sea areas was indirectly discovered or inferred from conventional hydrocarbon exploration programs. One of these occurrences, the Mallik gas-hydrate field (Figure 1), has received particular attention over the last 10 years. Two internationally partnered research well programs have intersected three intervals of gas hydrates and have allowed successful extraction of subpermafrost core samples with significant gas hydrates. The gas-hydrate intervals are up to 40 m thick and have high gas-hydrate saturation, sometimes exceeding 80% of pore volume of unconsolidated clastic sediments with average porosities from 25-40%. At Mallik, the gas-hydrate intervals are located at depths of 900-1100 m and are localized on the crest of an anticline. © 2006 Society of Exploration Geophysicists.
510.
Seeking chemical clues to earthquakes
Chemical and Engineering News,
84
(4)
39-41
2006
ISSN: 00092347
Publisher: American Chemical Society
Keywords:▾
Flow of fluids; Pressure effects; Real time systems; Rocks; Tectonics, Chemical clue; Frictional change; San Andreas Fault; San Andreas Fault Observatory at Depth (SAFOD),, Earthquakes
509.
Seismicity, deformation and seismic hazard in the western rift of Corinth: New insights from the Corinth Rift Laboratory (CRL)
Tectonophysics,
426
(1-2)
7 – 30
2006
ISSN: 00401951Keywords:▾
Gulf of Corinth; Ionian Sea; Mediterranean Sea; active fault; deformation; earthquake magnitude; geophysical survey; normal fault; seismic hazard; seismicity
Abstract: ▾ This paper presents the main recent results obtained by the seismological and geophysical monitoring arrays in operation in the rift of Corinth, Greece. The Corinth Rift Laboratory (CRL) is set up near the western end of the rift, where instrumental seismicity and strain rate is highest. The seismicity is clustered between 5 and 10 km, defining an active layer, gently dipping north, on which the main normal faults, mostly dipping north, are rooting. It may be interpreted as a detachment zone, possibly related to the Phyllade thrust nappe. Young, active normal faults connecting the Aigion to the Psathopyrgos faults seem to control the spatial distribution of the microseismicity. This seismic activity is interpreted as a seismic creep from GPS measurements, which shows evidence for fast continuous slip on the deepest part on the detachment zone. Offshore, either the shallowest part of the faults is creeping, or the strain is relaxed in the shallow sediments, as inferred from the large NS strain gradient reported by GPS. The predicted subsidence of the central part of the rift is well fitted by the new continuous GPS measurements. The location of shallow earthquakes (between 5 and 3.5 km in depth) recorded on the on-shore Helike and Aigion faults are compatible with 50° and 60° mean dip angles, respectively. The offshore faults also show indirect evidence for high dip angles. This strongly differs from the low dip values reported for active faults more to the east of the rift, suggesting a significant structural or rheological change, possibly related to the hypothetical presence of the Phyllade nappe. Large seismic swarms, lasting weeks to months, seem to activate recent synrift as well as pre-rift faults. Most of the faults of the investigated area are in their latest part of cycle, so that the probability of at least one moderate to large earthquake (M = 6 to 6.7) is very high within a few decades. Furthermore, the region west to Aigion is likely to be in an accelerated state of extension, possibly 2 to 3 times its mean interseismic value. High resolution strain measurement, with a borehole dilatometer and long base hydrostatic tiltmeters, started end of 2002. A transient strain has been recorded by the dilatometer, lasting one hour, coincident with a local magnitude 3.7 earthquake. It is most probably associated with a slow slip event of magnitude around 5 ± 0.5. The pore pressure data from the 1 km deep AIG10 borehole, crossing the Aigion fault at depth, shows a 1 MPa overpressure and a large sensitivity to crustal strain changes. © 2006 Elsevier B.V. All rights reserved.
508.
Seismic evidence for asthenospheric updoming beneath the western Bohemian Massif, central Europe
Geophysical Research Letters,
33
(5)
2006
ISSN: 00948276Keywords:▾
Bohemian Massif; Central Europe; Eurasia; Europe; Carbon dioxide; Degassing; Earthquakes; Flow of fluids; Tectonics; asthenosphere; crustal thickness; earthquake swarm; fluid flow; imaging method; mantle process; Asthenospheric updoming; Carbon dioxide mantle-derived degassing; Earthquake swarm activity; Seismology
Abstract: ▾ Detailed images of the lithosphere beneath the western Bohemian Massif were obtained by analysis of more than 8500 P receiver functions. At the intersection of Regensburg-Leipzig-Rostock zone and Eger Rift, crustal thickness decreases to 26 km from approx. 31 km in the surroundings. The receiver functions display a positive phase at about 6 s delay time and a strong negative phase at 7 to 8 s, which coincides with an area of Moho updoming, CO2 mantle-derived degassing and earthquake swarm activity. These phases can be modeled by a velocity increase at 50 km and a velocity decrease at 65 km depth. The velocity decrease, observed over an area of 5300 km2, gives evidence for local asthenospheric updoming and/or a confined body of partial melt, which might be the cause for high CO2 mantle fluid flow and earthquake swarm activity in this recently nonvolcanic, intracontinental rift area. Copyright 2006 by the American Geophysical Union.
507.
Seismic reflections of gas hydrate from perturbational forward modeling
Geophysics,
71
(6)
F165-F171
2006
ISSN: 00168033
Publisher: Society of Exploration Geophysicists
Keywords:▾
Gas hydrates; Mineralogy; Organic compounds; Perturbation techniques; Petroleum reservoirs; Porosity; Reflection, Seismic amplitude; Seismic reflections, Seismology, amplitude; clay; elastic property; porosity; sand; seismic attenuation; seismic reflection; seismic velocity; seismology
Abstract: ▾ We perturb the elastic properties and attenuation in the Arctic Mallik methane-hydrate reservoir to produce a set of plausible seismic signatures away from the existing well. These perturbations are driven by the changes we impose on porosity, clay content, hydrate saturation, and geometry. The key is a data-guided, theoretical, rock-physics model that we adopt to link velocity and attenuation to porosity, mineralogy, and amount of hydrate. We find that the seismic amplitude is very sensitive to the hydrate saturation in the host sand and its porosity as well as the porosity of the overburden shale. However, changes to the amount of clay in the sand only weakly alter the amplitude. Attenuation, which may be substantial, must be taken into account during hydrate reservoir characterization because it lowers the amplitude to an extent that may affect the hydrate-volume prediction. The spatial structure of the reservoir affects the seismic reflection: A thinly-layered reservoir produces a noticeably different amplitude than a massive reservoir with the same hydrate volume. © 2006 Society of Exploration Geophysicists.
506.
Shock re-equilibration of fluid inclusions in crystalline basement rocks from the Ries crater, Germany
Meteoritics and Planetary Science,
41
(2)
247-262
2006
Abstract: ▾ This study examines the effects of shock metamorphism on fluid inclusions in crystalline basement target rocks from the Ries crater, Germany. The occurrence of two-phase fluid inclusions decreases from shock stage 0 to shock stage 1, while single-phase inclusions increase, likely as a result of re-equilibration. In shock stages 2 and 3, both two-phase and single-phase inclusions decrease with increasing shock stage, indicating that fluid inclusion vesicles are destroyed due to plastic deformation and phase changes in the host minerals. However, quartz clasts entrained in shock stage 4 melts contain both single-phase and two-phase inclusions, demonstrating the rapid quenching of the melt and the heterogeneous nature of impact deformation. Inclusions in naturally shocked polycrystalline samples survive at higher shock pressures than those in single crystal shock experiments. However, fluid inclusions in both experimental and natural samples follow a similar trend in re-equilibration at low to moderate shock pressures leading to destruction of inclusion vesicles in higher shock stages. This suggests that shock processing may lead to the destruction of fluid inclusions in many planetary materials and likely contributed to shock devolatilization of early planetesimals. © The Meteoritical Society, 2006.
505.
Post-Chicxulub depositional and diagenetic history of the northwestern Yucatan Peninsula, Mexico
Sedimentary Geology,
183
(1-2)
51-69
2006
Abstract: ▾ The Chicxulub Sedimentary Basin of the northwestern Yucatan Peninsula, Mexico, which was formed because of the largest identified Phanerozoic bolide impact on Earth, became a site of deposition of dominantly marine carbonate sediments during most of the Cenozoic Era. This is a study of the filling and diagenetic history of this basin and surrounding areas. The study makes use of lithologic, biostratigraphic, petrographic, and geochemical data obtained on core samples from boreholes drilled throughout the northwestern Yucatan Peninsula. The core sample data indicate that: 1) The Chicxulub Sedimentary Basin concentrated the deposition of pelagic and outer-platform sediments during the Paleocene and Eocene, and, in places, during the Early Oligocene, as well, and filled during the Middle Miocene, 2) deeper-water limestone also is present within the Paleocene and Lower Eocene of the proposed Santa Elena Depression, which is located immediately south of the Basin, 3) shallow-water deposits are relatively more abundant outside the Basin and Depression than inside, 4) the autigenic and allogenic silicates from the Paleogene formations are the most abundant inside the Depression, 5) sediment deposition and diagenesis within the Basin also were controlled by impact crater topography, 6) the abundance of the possible features of subaerial exposure increases upward and outward from the center of the Basin, and 7) the formation of replacive low-magnesium calcite and dolomite, dedolomitization, dissolution, and precipitation of vug-filling calcite and dolomite cement have been more common outside the Basin than inside. δ18O in whole-rock (excluding vug-filling) calcite from core samples ranges from -7.14‰ to + 0.85‰ PDB. δ13C varies from -6.92‰ to +3.30‰ PDB. Both stable isotopes correlate inversely with the abundance of subaerial exposure features indicating that freshwater diagenesis has been extensive especially outside and at the edge of the Chicxulub Sedimentary Basin. δ18O and δ13C in w hole-rock (excluding vug-filling) dolomite ranges from -5.54‰ to +0.87‰ PDB and -4.63‰ to +3.38‰ PDB, respectively. Most dolomite samples have negative δ18O and positive δ13C suggesting that replacive dolomitization involved the presence of a fluid dominated by freshwater and/or an anomalously high geothermal gradient. Most dolomite XRD-determined mole percent CaCO3 varies between 51 and 56. Replacive dolomite is larger, more euhedral, and less stoichiometric inside the Chicxulub Sedimentary Basin than outside. © 2005 Elsevier B.V. All rights reserved.
504.
Origin and significance of clay-coated fractures in mudrock fragments of the SAFOD borehole (Parkfield, California)
Geophysical Research Letters,
33
(16)
2006
ISSN: 00948276
Publisher: American Geophysical Union
Keywords:▾
Clay; Crystal growth; Rocks; Scanning electron microscopy; Textures; Thin films; Transmission electron microscopy; X ray diffraction analysis, Aqueous fluids; Drilling mud; Fault creep; Slickenfiber striations, Boreholes, bentonite; borehole; calcium; cation; clay; crystal structure; hydration; mudstone; potassium; rock property; sampling; San Andreas Fault; scanning electron microscopy; smectite; texture; transmission electron microscopy; X-ray diffraction
Abstract: ▾ The clay mineralogy and texture of rock fragments from the SAFOD borehole at 3067 m and 3436 m measured depth (MD) was investigated by electron microscopy (SEM, TEM) and X-ray-diffraction (XRD). The washed and ultrasonically cleaned samples show slickenfiber striations and thin films of Ca-K bearing smectite that are formed on polished fault surfaces, along freshly opened fractures and within adjacent mineralized veins. The cation composition and hydration behavior of these films differ from the Namontmorillonite of the fresh bentonite drilling mud, although there is more similarity with circulated mud recovered from 3479 m MD. We propose that these thin film smectite precipitates formed by natural nucleation and crystal growth during fault creep, probably associated with the shallow circulation of low temperature aqueous fluids along this shallow portion of the San Andreas Fault. Copyright 2006 by the American Geophysical Union.
503.
Petrology and thermal structure of the Hawaiian plume from Mauna Kea volcano
Nature,
444
(7119)
605-609
2006
ISSN: 00280836
Publisher: Nature Publishing Group
Keywords:▾
Lithology; Melting; Rocks; Thermal plumes; Uncertain systems; Volcanoes, Hawaiian core; Mauna Kea magmatism; Pyroxenite/eclogite rocks; Tholeiitic lavas, Petrology, aluminum derivative; aluminum trioxide; calcium oxide; chromium trioxide; dipotassium oxide; glass; iron oxide; iron trioxide; magnesium oxide; manganese oxide; nitrogen oxide; oxacillin; oxide; phosphorus pentoxide; potassium derivative; silicon dioxide; titanium dioxide, core analysis; lava; magma; mantle plume; oceanic crust; peridotite; petrology; pyroxenite; thermal structure; tholeiite, article; calibration; crystallization; fractionation; garnet; melting point; peridotite; petrology; priority journal; pyroxenite; rock; volcano
Abstract: ▾ There is uncertainty about whether the abundant tholeiitic lavas on Hawaii are the product of melt from peridotite or pyroxenite/eclogite rocks. Using a parameterization of melting experiments on peridotite with glass analyses from the Hawaii Scientific Deep Project 2 on Mauna Kea volcano, I show here that a small population of the core samples had fractionated from a peridotite-source primary magma. Most lavas, however, differentiated from magmas that were too deficient in CaO and enriched in NiO (ref. 2) to have formed from a peridotite source. For these, experiments indicate that they were produced by the melting of garnet pyroxenite, a lithology that had formed in a second stage by reaction of peridotite with partial melts of subducted oceanic crust. Samples in the Hawaiian core are therefore consistent with previous suggestions that pyroxenite occurs in a host peridotite, and both contribute to melt production. Primary magma compositions vary down the drill core, and these reveal evidence for temperature variations within the underlying mantle plume. Mauna Kea magmatism is represented in other Hawaiian volcanoes, and provides a key for a general understanding of melt production in lithologically heterogeneous mantle. ©2006 Nature Publishing Group.
502.
Petrographic studies of "fallout" suevite from outside the Bosumtwi impact structure, Ghana
Meteoritics and Planetary Science,
41
(11)
1761 – 1774
2006
ISSN: 10869379
Publisher: University of Arkansas
Keywords:▾
Africa; Ghana; Sub-Saharan Africa; West Africa; crater; crystalline rock; ejecta; fallout; impact structure; metasedimentary rock; suevite
Abstract: ▾ Field studies and a shallow drilling program carried out in 1999 provided information about thickness and distribution of suevite to the north of the Bosumtwi crater rim. Suevite occurrence there is known from an ∼1.5 km2 area; its thickness is ≤15 m. The present suevite distribution is likely the result of differential erosion and does not reflect the initial areal extent of continuous Bosumtwi ejecta deposits. Here we discuss the petrographic characteristics of drill core samples of melt-rich suevite. Macroscopic constituents of the suevites are melt bodies and crystalline and metasedimentary rock (granite, graywacke, phyllite, shale, schist, and possibly slate) clasts up to about 40 cm in size. Shock metamorphic effects in the clasts include multiple sets of planar deformation features (PDFs), diaplectic quartz and feldspar glasses, lechatelierite, and ballen quartz, besides biotite with kink bands. Basement rock clasts in the suevite represent all stages of shock metamorphism, ranging from samples without shock effects to completely shock-melted material that is indicative of shock pressures up to ∼60 GPa. © The Meteoritical Society, 2006.
501.
Paleoenvironmental record in Lake Baikal sediments: Environmental changes in the last 160 ky
Palaeogeography, Palaeoclimatology, Palaeoecology,
237
(2-4)
240 – 254
2006
ISSN: 00310182Keywords:▾
Arctic Ocean; Atlantic Ocean; Atlantic Ocean (North); Eurasia; Lake Baikal; Russian Federation; Siberia; Bacillariophyta; climate change; environmental change; fossil record; magnetic susceptibility; paleoenvironment; reflectance; sediment analysis; X-ray diffraction
Abstract: ▾ Measurement of magnetic susceptibility (MS) and diffuse reflectance spectra (DRS) were used to construct environmental proxies in a 6.5 m section of the sediment core VER98-1-13 from the Academician Ridge, Lake Baikal. The interpretation of MS and DRS was supported by X-ray diffraction and microparticle voltammetry to identify the main Fe-bearing minerals. The record of the relative paleointensity of the Earth's magnetic field was used to construct an age model showing the core interval covers the last 160 ky. The time resolution of the record was ∼1 ky. The main environmental changes were recognized by a combination of DRS and MS records and compared to marine isotopic stages in addition to the diatom record from 120 to 60 ky BP so as to demonstrate the importance of these inorganic proxies as paleoenvironmental records. A dramatic climatic deterioration between 66 and 60 ky BP was probably preceded by a dry intermediate stage between 77 and 66 ky BP. The DRS-based proxies of Fe(II) / Fe(III) ratios in the mineral assemblage, MS and/or diatom records clearly reveal 1-2 ky long environmental extremes at 110, 103, 90, 85, 77, 61, 54, 36, 27, 23, and 19 ky BP. The majority of these extremes were contemporaneous with discharges of North Atlantic and Arctic Ocean icebergs (Heinrich events) documenting a teleconnection between the North Atlantic Ocean and East Central Siberia. These sharp changes coincided with a major transition to the colder climatic stages of the last 100 ky. © 2006.
500.
Paleoclimatic variations in West Africa from a record of late Pleistocene and Holocene lake level stands of Lake Bosumtwi, Ghana
Palaeogeography, Palaeoclimatology, Palaeoecology,
242
(3-4)
287 – 302
2006
ISSN: 00310182Keywords:▾
Africa; Ashanti; Ghana; Lake Bosumtwi; Sub-Saharan Africa; West Africa; climate variation; crater lake; highstand; Holocene; ice sheet; lacustrine deposit; lake level; Last Glacial; monsoon; paleoclimate; Pleistocene; radiocarbon dating; Younger Dryas
Abstract: ▾ A detailed investigation of geomorphological evidence of paleoshorelines and exposed stratigraphic sections of lake deposits, combined with a chronology based on radiocarbon dated charcoal and in-situ 14C dating of wave polished bedrock, provide important new constraints on lake level changes of Lake Bosumtwi, Ghana. Thick sequences of laminated silts, alternating with transgressive sands and deltaic gravels, attest to a long history of climatically controlled lake level variations. The post-glacial rise in lake level began sometime after 16.3 ka, reached stable levels first at 14.5 ± 0.6 ka and then rose again after ca. 14.3 ka. A significant lake level regression spanned the interval from 12.6 ± 0.3 to 11.6 ± 0.5 ka, synchronous with the Younger Dryas. Deep lake conditions were reestablished after ca. 11 ka, at which time the lake overtopped the crater. Overflow continued until 8.8 ± 0.5 ka, when another significant but short-lived regression occurred. Deep, but probably not overflowing conditions were again reestablished by > 7.2 ± 0.3 ka and continued until around 3.2 ± 0.1 ka, when lake level dropped precipitously. Multicentury late Holocene highstands occurred at 2.2 ± 0.1 and 1.7 ± 0.2 ka, although these were significantly lower than those registered in the late glacial and early Holocene. The timing of late glacial events is similar to those recorded elsewhere in Africa and the higher latitudes, and likely reflects the dominant control of high latitude northern hemisphere conditions on the African tropics during the times of large northern hemisphere ice sheets. Mid- to late-Holocene variations appear to be less coupled with changes across Africa and elsewhere, suggesting that regional forcing may be more important during warmer periods. © 2006.
499.
Paleoclimate and human evolution workshop
Eos,
87
(16)
161
2006
ISSN: 00963941
Publisher: Blackwell Publishing Ltd
Keywords:▾
human evolution; Neogene; paleoclimate
498.
Origin of Pleistocene-Holocene ashes of the Russian northeast based on trace and rare earth element data
Doklady Earth Sciences,
411
(2)
1351-1356
2006
ISSN: 1028334X
Publisher: Maik Nauka-Interperiodica Publishing
Keywords:▾
Pleistocene-Holocene boundary; rare earth element; trace element; volcanic ash; volcanic eruption
497.
Orbital forcing of continental climate during the Pleistocene: a complete astronomically tuned climatic record from Lake Baikal, SE Siberia
Quaternary Science Reviews,
25
(23-24)
3431 – 3457
2006
ISSN: 02773791Keywords:▾
Eurasia; Lake Baikal; Russian Federation; Siberia; Astronomy; Cell culture; Correlation methods; Glaciers; Lakes; Mathematical models; Sedimentation; age determination; biogenic mineral; climate change; Holocene; insolation; magnetic reversal; orbital forcing; paleoclimate; Pleistocene; precession; proxy climate record; sedimentation rate; silica; Astronomically tuned climatic records; Biogenic silica; Pleistocene paleomagnetic reversals; Regional climate; Climate change
Abstract: ▾ A new composite BDP-96 biogenic silica record over the entire Pleistocene was generated by splicing BDP-96-1 and BDP-96-2 drill cores from Lake Baikal, crosschecked against a similar record from a nearby BDP-98 drill core. A new astronomically tuned age model is proposed based on correlating peak biogenic silica responses with the timing of September perihelia. This target is derived from analysis of regional climate proxy responses during the Holocene, the last interglacial and around paleomagnetic reversals. By resolving virtually every precessional cycle during the Pleistocene, the new age model represents a major improvement compared with previously reported Lake Baikal timescales. The astronomically tuned ages of the Pleistocene paleomagnetic reversals are consistent with published dates. The minimal tuning approach we used (precession only) has also aligned high signal power in a narrow obliquity band, confirming the strong presence of orbital forcing. There are also strong ca 100-ka scale cycles, but these are not aligned with the orbital eccentricity. Despite the location of Lake Baikal in a continental interior that is highly sensitive to insolation forcing, the tuned biogenic silica record reveals a consistent phase difference of -32° (ca 4 ka) relative to insolation in the obliquity band. An inherent lag embedded in a continental proxy record, not driven by global ice volume, is an intriguing finding. Another new observation is that long-term changes in sedimentation rates in Lake Baikal appear to be related to the amplitude of orbital forcing; both amplitudes and sedimentation rates undergo significant changes during MIS 24-MIS 19 interval corresponding to the Middle Pleistocene Transition. With potential for linking continental and marine climato-stratigraphies, the new Baikal record serves a new benchmark correlation target in continental Eurasia, as an alternative to June 65°N insolation and ODP-correlated timescales. © 2006 Elsevier Ltd. All rights reserved.
496.
On Pliocaenicus costatus (Bacillariophyceae) in Lake El’gygytgyn, East Siberia
European Journal of Phycology,
41
(2)
169-178
2006
495.
Occurrence and palaeoenvironmental significance of aromatic hydrocarbon biomarkers in Oligocene sediments from the Mallik 5L-38 Gas Hydrate Production Research Well (Canada)
Organic Geochemistry,
37
(5)
519-538
2006
ISSN: 01466380Keywords:▾
Angiosperm-gymnosperm aromatic ratio (AGAR); Aromatic diterpenoids; Climatic conditions; Gymnosperm markers, Aromatic hydrocarbons; Composition; Environmental impact; Gas chromatography; Hydration; Mass spectrometry; Sediments, Biomarkers, aromatic hydrocarbon; biomarker; geochemistry; Oligocene; paleoenvironment; sediment; vegetation, Canada; North America, Coniferophyta; Gymnospermae; Magnoliophyta
Abstract: ▾ The aromatic hydrocarbon biomarker distributions of thirty Oligocene sediment samples with different lithology (lignite, clay and sand) from the JAPEX/JNOC/GSC et al. Mallik 5L-38 Gas Hydrate Production Research Well, Canada, were analyzed using gas chromatography-mass spectrometry (GC-MS). The compositions vary with lithology, indicating a change in palaeoenvironmental conditions at the time of deposition. Aromatic diterpenoids of the abietane type are more abundant in the lignite samples than in the clay samples and represent a gymnosperm (e.g., conifer) dominated palaeovegetation. In contrast, in the clay samples aromatic triterpenoids are generally preserved as major constituents, indicating angiosperm dominated vegetation. The sand samples contain only minor amounts of aromatic terpenoids, but show a preference for diterpenoid gymnosperm markers. To recognise gymnosperm versus angiosperm dominated palaeoenvironments a new ratio, termed the angiosperm-gymnosperm aromatic ratio (AGAR), has been developed. Thus, the terpenoid distribution in the deltaic sediments provides information on the compositional changes in the plant community at the Mallik site (lignites) and the hinterland (clays) over time. Concomitantly, the changing dominance in the plant communities allows an insight into varying climatic conditions during the late Oligocene in the area. Additionally, the aromatic biomarker composition has been used to assess the level of thermal maturity of the organic matter in the Mallik samples and indicates a prevailing immature character. © 2006 Elsevier Ltd. All rights reserved.