All ICDP Publications with Abstracts
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1019.
[English]
Shear wave splitting in the SAFOD pilot hole using seismic interferometry
Page 4034-4040
Publisher
Society of Exploration Geophysicists
2010
Marine Physical Laboratory, Scripps Institution of Oceanography, United StatesKeywords:▾
Boreholes; Geophysical prospecting; Infill drilling; Polarization; Shear flow; Strike-slip faults, Continuous data; Cross correlations; Drilling activity; Polarization direction; Propagating waves; San Andreas fault; Seismic interferometries; Shear wave splitting, Shear waves
ISBN:
9781617389801
1018.
[English]
Numerical study of gas evolution and transport behaviors in natural gas hydrate reservoirs
Volume 2
,
Page 1274-1303
Publisher
Society of Petroleum Engineers
2010
Alberta Innovates, Canada; Geological Survey of Canada, Canada; Computer Modeling Group, CanadaKeywords:▾
Bubbles (in fluids); Flow of fluids; Gas hydrates; Gas oils; Gases; Gasoline; Hydration; Kinetics; Natural gas; Natural gasoline plants; Petroleum reservoirs; Resource valuation; Transport properties; Wetting, Critical gas saturation; Gas hydrate reservoir; Hydrate dissociation; Natural gas hydrate reservoir; Natural gas recoveries; Numerical simulators; Relative permeability curves; Reservoir simulation, Natural gas fields
ISBN:
9781617820427
1017.
[English]
Electromagnetic methods to monitor gas hydrate distribution and production in layered sediments
Volume 1
,
Page 576-589
Publisher
Society of Petroleum Engineers
2010
Geological Survey of Canada, Canada; Camosun College, Canada; University of Victoria, Canada; University of Toronto, CanadaKeywords:▾
Charcoal; Dissociation; Electric conductivity; Frequency domain analysis; Gases; Gasoline; Heat resistance; Hydration; Ice; Methane; Natural gasoline plants; Resource valuation; Sand; Sediments; Silica; Silt; Time domain analysis, Calorimetric measurements; Electrical impedance spectroscopy; Exothermic crystallization; Frequency-domain methods; Heterogeneous sediments; Natural gas hydrate reservoir; Temporal and spatial sensitivity; Time domain reflectometry, Gas hydrates
ISBN:
9781617820427
1016.
[English]
Analysis of production data for 2007/2008 mallik gas hydrate production tests in Canada
Volume 4
,
Page 2908-2931
Publisher
Society of Petroleum Engineers
2010
Japan Oil Engineering Co., Ltd., Japan; Japan Oil, Gas and Metals National Corporation, Japan; Japan Petroleum Exploration Co., Ltd., Japan; National Institute of Advanced Industrial Science and Technology, Japan; University of Tokyo, Japan; Natural Resources Canada, CanadaKeywords:▾
Aquifers; Boreholes; Bottom hole pressure; Flow of water; Flow rate; Gases; Hydration; Hydraulics; Methane; Oil field equipment; Oil wells; Petroleum prospecting; Pumps; Sand; Software testing; Surface testing; Wellheads, Bottom-hole temperatures; Comprehensive analysis; Depressurization methods; Distributed temperature sensing systems; Exploration and development; Gas-hydrate production; Production performance; Water production rate, Gas hydrates
ISBN:
9781617388866
1015.
Stress field of the earth's crust
Publisher
Springer Netherlands
2010
1014.
Zircon U-Pb ages, REE concentrations and Hf isotope compositions of granitic leucosome and pegmatite from the north Sulu UHP terrane in China: Constraints on the timing and nature of partial melting
Lithos,
117
(1-4)
247 – 268
2010
ISSN: 00244937Keywords:▾
China; Sulu Belt; biotite; granite; granulite facies; hafnium; inclusion; isotopic analysis; isotopic composition; partial melting; pegmatite; rare earth element; retrograde metamorphism; terrane; trace element; Triassic; uranium-lead dating; zircon
Abstract: ▾ Granitic leucosome and pegmatite are widely distributed within biotite-bearing orthogneiss in the northern part of the Sulu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. A combined study of mineral inclusions, cathodoluminescence (CL) images, U-Pb SHRIMP dates, and in situ trace element and Lu-Hf isotope analyses of zircons provided insight into the nature and timing of partial melting in these rocks. Zircon grains separated from biotite-bearing orthogneiss typically have three distinct domains: (1) pre-metamorphic (magmatic) cores with Qtz. +. Kfs. +. Pl. +. Ap inclusions, which record a Neoproterozoic protolith age of ~ 790. Ma, (2) mantles with Coe. +. Phe. +. Ap inclusions that record Triassic UHP age at 227 ± 3. Ma, and (3) narrow rims with quartz inclusions that record HP granulite-facies retrograde metamorphism at ~ 210 ± 3. Ma. In contrast, zircons separated from granitic leucosome have only two distinct domains: (1) the central UHP areas with Coe. +. Phe. +. Ap inclusions record Triassic UHP age of 227 ± 3. Ma, and (2) outer magmatic areas with Qtz. +. Kfs. +. Ab. +. Ap inclusions that record partial melting time of 212 ± 2. Ma. Zircons separated from pegmatite contain mineral inclusions of Qtz. +. Kfs. +. Ap and show regular magmatic zoning from centre to edge. The centres record partial melting time of 212 ± 2. Ma in line with the outer domains of granitic leucosome, whereas the edges give a younger age of 201 ± 2. Ma related to Pb loss and partial recrystallization during late Triassic regional amphibolite-facies retrogression. These data indicate that partial melting in the north Sulu UHP gneissic rocks took place during post-UHP, retrograde HP granulite-facies metamorphism. Pre-metamorphic (magmatic) zircon cores from biotite-bearing orthogneiss give uniform 176Hf/177Hf of 0.28187±0.00003 (2SD; standard deviation) corresponding to εHf(790) and Hf model ages (TDM2) of about -16.3 and 2.41Ga, respectively. This is consistent with the generation of its protolith by reworking of Paleoproterozoic to late Archean crust. In contrast, UHP zircon domains from biotite-bearing orthogneiss and granitic leucosome are characterized by distinct trace element composition with low Lu/Hf (<0.006), low Th/U (<0.1) and considerably higher, 176Hf/177Hf (0.28233±0.00002; 2SD) than the pre-metamorphic cores. The uniform but significantly different Hf isotope composition between the UHP (εHf(227)=-14.6±0.8; 2SD) and pre-metamorphic (-Hf(227)=-27.7) domains indicates equilibration of the Lu-Hf isotope system only within the UHP metamorphic mineral assemblage. The disequilibrium between whole rock and UHP zircon suggests that about two thirds of the whole rock Hf retained in the pre-metamorphic zircon domains. Zircon domains crystallized during partial melting at 212Ma in granitic leucosome and pegmatites have a Hf isotope composition indistinguishable from that of the UHP zircon domains. This suggests that only Hf (and Zr) equilibrated during UHP metamorphism was remobilized during partial melting while pre-metamorphic zircon remained stable or was not accessible. In contrast, the magmatic zircon edges from pegmatite have somewhat lower 176Hf/177Hf (~0.28216) and εHf(t) (-17.6±1.2; 2SD) indicating some release of less radiogenic Hf for instance by dissolution of pre-metamorphic zircon during late regional amphibolite-facies retrogression. © 2010 Elsevier B.V.
1013.
Weathering, Sr fluxes, and controls on water chemistry in the Lake Qinghai catchment, NE Tibetan Plateau
Earth Surface Processes and Landforms,
35
(9)
1057 – 1070
2010
ISSN: 10969837DOI:10.1002/esp.1964
Keywords:▾
China; Qinghai; Qinghai Lake; Qinghai-Xizang Plateau; Budget control; Carbonate minerals; Catchments; Dissolution; Groundwater; Indicators (chemical); Isotopes; Lakes; Lithology; Magnesium; Precipitation (chemical); Rivers; Runoff; Silicates; Soil mechanics; Weathering; Alkaline water; Authigenic carbonates; Budget; Chemical component; Chemical compositions; Eastern Tibetan plateau; Groundwater fluxes; Isotope signatures; Isotopic composition; Isotopic ratios; Lake waters; Late Paleozoic; Magnesium calcite; River systems; Rivers and lakes; Rock sample; Semi-arid conditions; Sr fluxes; Tibetan Plateau; Water budget; Water chemistry; catchment; chemical weathering; concentration (composition); isotopic composition; isotopic ratio; strontium isotope; surface water; water budget; water chemistry; Strontium
Abstract: ▾ Strontium (Sr) concentrations and isotopic ratios have been measured in a series of water and rock samples from most of the major tributaries of the Lake Qinghai basin on the north-eastern Tibetan Plateau. Dissolved Sr and 87Sr/86Sr show ranges of 488-12 240 nmol/l and 0·710497-0·716977, respectively. These data, together with measurements of major cations and anions in rivers and their tributaries and various lithologies of the catchment, were used to determine the contributions of Sr and its isotopic expense to rivers and lakes. Our results demonstrate that the chemical components and 87Sr/86Sr ratios of the alkaline waters are derived from mixing of carbonate and silicate sources, with the former contributing 72 ± 18% dissolved Sr to rivers. The difference in tributary compositions stems from the lithology of different river systems and low weathering intensity under a semi-arid condition. Variation in 87Sr/86Sr ratios places constraint on the Sr-isotopic compositions of the main tributaries surrounding Lake Qinghai. The water chemistry of the Buha River, the largest river within the catchment underlain by the late Paleozoic marine limestone and sandstones, dominates Sr isotopic composition of the lake water, being buffered by the waters from the other rivers and probably by groundwater. However, the characteristic chemical composition of the lake itself differs remarkably from the rivers, which can be attributed to precipitation of authigenic carbonates (low-magnesium calcite, aragonite, and dolomite), though this does not impact the Sr isotope signature, which may remain a faithful indicator in paleo-records. Regarding the potential role of groundwater input within the Lake Qinghai systems in the water budget and water chemistry, we have also determined the Sr concentration and 87Sr/S6Sr ratio of groundwater from diverse environments. This has allowed us to further constrain the Sr isotope systematic of this source. A steady-state calculation gives an estimate for the groundwater flux of 0·19 ± 0·03 x 108 m3/yr, accounting for about 8% of contemporary lake Sr budget. © 2010 John Wiley & Sons, Ltd.
1012.
Ultrasonic velocity of the upper gneiss series rocks from the Outokumpu deep drill hole, Fennoscandian shield - Comparing uniaxial to triaxial loading
Journal of Applied Geophysics,
72
(3)
178 – 183
2010
ISSN: 09269851Keywords:▾
Finland; Ita Suomen; Outokumpu; Core drilling; Cylinders (shapes); Mica; Rock drills; Seismology; Shear waves; Silicate minerals; Ultrasonic velocity; Ultrasonic velocity measurement; Ultrasonics; Wave propagation; Crustal structure; Cylindrical geometry; Drill core; Drill hole; Eastern Finland; Fennoscandian Shields; Measurement device; Mica schists; P- and S-waves; Reflection coefficients; Seismic impedance; Seismic velocities; Triaxial compression; Triaxial loading; Ultrasound; Uni-axial compression; Uniaxial pressures; Wave propagation velocities; compression; crustal structure; data interpretation; geometry; P-wave; S-wave; seismic reflection; seismic velocity; uniaxial strength; wave propagation; Velocity
Abstract: ▾ P- and S-wave propagation velocities in dry mica schist samples obtained from the Outokumpu deep drill hole in Eastern Finland were measured under uniaxial compression in a custom built measurement device. At 300 MPa pressure the obtained velocities (5520 ± 130) m/s and (3270 ± 60) m/s, for P- and S-waves, respectively, agreed with those measured under triaxial compression, (5530 ± 200) m/s and (3300 ± 90) m/s. The increase in Vp with uniaxial pressure was steeper, whereas this was not the case with Vs. These results indicate that ultrasound velocity measurements can be performed under uniaxial compression without the need to alter the cylindrical geometry of a borehole sample. Results obtained with the device can improve the interpretation of seismic crustal structure maps by providing seismic velocity data of the Outokumpu drill core as well as seismic impedances and reflection coefficients measured under crustal conditions. © 2010 Elsevier B.V.
1011.
The thermal regime in the resurgent dome of Long Valley Caldera, California: Inferences from precision temperature logs in deep wells
Journal of Volcanology and Geothermal Research,
198
(1-2)
233-240
2010
ISSN: 03770273Keywords:▾
Caldera; Geothermal; Heat flows; Hydrothermal; Long Valley; Resurgent dome; Temperature log, Boreholes; Domes; Geothermal energy; Geothermal fields; Geothermal logging; Geothermal power plants; Geothermal prospecting; Groundwater; Heat transfer; Temperature control; Volcanoes; Wells, Thermal logging, caldera; crust; dome; geothermal power; groundwater flow; heat flow; hydrothermal system; igneous intrusion; temperature profile; thermal regime; uplift, California; Long Valley Caldera; United States, Calluna vulgaris
Abstract: ▾ Long Valley Caldera in eastern California formed 0.76Ma ago in a cataclysmic eruption that resulted in the deposition of 600km3 of Bishop Tuff. The total current heat flow from the caldera floor is estimated to be ~290MW, and a geothermal power plant in Casa Diablo on the flanks of the resurgent dome (RD) generates ~40MWe. The RD in the center of the caldera was uplifted by ~80cm between 1980 and 1999 and was explained by most models as a response to magma intrusion into the shallow crust. This unrest has led to extensive research on geothermal resources and volcanic hazards in the caldera. Here we present results from precise, high-resolution, temperature-depth profiles in five deep boreholes (327-1,158m) on the RD to assess its thermal state, and more specifically 1) to provide bounds on the advective heat transport as a guide for future geothermal exploration, 2) to provide constraints on the occurrence of magma at shallow crustal depths, and 3) to provide a baseline for future transient thermal phenomena in response to large earthquakes, volcanic activity, or geothermal production. The temperature profiles display substantial non-linearity within each profile and variability between the different profiles. All profiles display significant temperature reversals with depth and temperature gradients <50°C/km at their bottom. The maximum temperature in the individual boreholes ranges between 124.7°C and 129.5°C and bottom hole temperatures range between 99.4°C and 129.5°C. The high-temperature units in the three Fumarole Valley boreholes are at the approximate same elevation as the high-temperature unit in borehole M-1 in Casa Diablo indicating lateral or sub-lateral hydrothermal flow through the resurgent dome. Small differences in temperature between measurements in consecutive years in three of the wells suggest slow cooling of the shallow hydrothermal flow system. By matching theoretical curves to segments of the measured temperature profiles, we calculate horizontal groundwater velocities in the hydrothermal flow unit under the RD that range from 1.9 to 2.8m/yr, which corresponds to a maximum power flowing through the RD of 3-4MW. The relatively low temperatures and large isothermal segments at the bottom of the temperature profiles are inconsistent with the presence of magma at shallow crustal levels. © 2010.
1010.
The New Jersey margin scientific drilling project (IODP expedition 313): Untangling the record of global and local sea-level changes
Scientific Drilling
(10)
26-34
2010
ISSN: 181689571009.
The great oxidation event recorded in Paleoproterozoic rocks from Fennoscandia
Scientific Drilling,
923--29
2010
1008.
Spatial and temporal variations of Rb/Sr ratios of the bulk surface sediments in Lake Qinghai
Geochemical Transactions,
11
2010
ISSN: 14674866Keywords:▾
China; Qinghai; Qinghai Lake; accumulation rate; catchment; lacustrine deposit; rubidium; sediment chemistry; spatial variation; strontium; surficial sediment; temporal variation; terrigenous deposit; weathering
Abstract: ▾ The Rb/Sr ratios of lake sediments have been suggested as indicators of weathering intensity by increasing work. However, the geochemistry of Rb/Sr ratios of lake sediments is variable between different lakes. In this study, we investigated the spatial and temporal patterns of Rb/Sr ratios, as well as those of other major elements in surface sediments of Lake Qinghai. We find that the spatial pattern of Rb/Sr ratios of the bulk sediments correlates well with that of the mass accumulation rate, and those of the terrigenous fractions, e.g., SiO2, Ti, and Fe. The temporal variations of Rb/Sr ratios also synchronize with those of SiO2, Ti, and Fe of each individual core. These suggest that Rb/Sr ratios of the surface sediments are closely related to terrigenous input from the catchment. Two out of eight cores show similar trends between Rb/Sr ratios and precipitation indices on decadal scales; however, the other cores do not show such relationship. The result of this study suggests that physical weathering and chemical weathering in Lake Qinghai catchment have opposite influence on Rb/Sr ratios of the bulk sediments, and they compete in dominating the Rb/Sr ratios of lake sediments on different spatial and temporal scales. Therefore, it is necessary to study the geochemistry of Rb/Sr ratio of lake sediments (especially that on short term timescales) particularly before it is used as an indicator of weathering intensity of the catchment. © 2010 Xu et al; licensee BioMed Central Ltd.
1007.
The distribution of methylated-2-methyltrimethyltride-cylchromans and geochemical implication in Nenjiang Formation of the Late Cretaceous from Songliao Basin
Geochimica,
39469-478
2010
1006.
The convincing identification of terrestrial meteorite impact structures: What works, what doesn't, and why
Earth-Science Reviews,
98
(1-2)
123-170
2010
Abstract: ▾ In the geological sciences it has only recently been recognized how important the process of impact cratering is on a planetary scale, where it is commonly the most important surface-modifying process. On the Moon and other planetary bodies that lack an appreciable atmosphere, meteorite impact craters are well preserved, and they can commonly be recognized from morphological characteristics, but on Earth complications arise as a consequence of the weathering, obliteration, deformation, or burial of impact craters and the projectiles that formed them. These problems made it necessary to develop diagnostic criteria for the identification and confirmation of impact structures on Earth. Diagnostic evidence for impact events is often present in the target rocks that were affected by the impact. The conditions of impact produce an unusual group of melted, shocked, and brecciated rocks, some of which fill the resulting crater, and others which are transported, in some cases to considerable distances from the source crater. Only the presence of diagnostic shock-metamorphic effects and, in some cases, the discovery of meteorites, or traces thereof, is generally accepted as unambiguous evidence for an impact origin. Shock deformation can be expressed in macroscopic form (shatter cones) or in microscopic forms (e.g., distinctive planar deformation features [PDFs] in quartz). In nature, shock-metamorphic effects are uniquely characteristic of shock levels associated with hypervelocity impact. The same two criteria (shock-metamorphic effects or traces of the impacting meteorite) apply to distal impact ejecta layers, and their presence confirms that materials found in such layers originated in an impact event at a possibly still unknown location. As of 2009 about 175 impact structures have been identified on Earth based on these criteria. A wide variety of shock-metamorphic effects has been identified, with the best diagnostic indicators for shock metamorphism being features that can be studied easily by using the polarizing microscope. These include specific planar microdeformation features (planar fractures [PFs], PDFs), isotropization (e.g., formation of diaplectic glasses), and phase changes (high pressure phases; melting). The present review provides a detailed discussion of shock effects and geochemical tracers that can be used for the unambiguous identification of impact structures, as well as an overview of doubtful criteria or ambiguous lines of evidence that have erroneously been applied in the past. © 2009 Elsevier B.V. All rights reserved.
1005.
The chicxulub asteroid impact and mass extinction at the cretaceous-paleogene boundary
Science,
327
(5970)
1214-1218
2010
Abstract: ▾ The Cretaceous-Paleogene boundary ∼65.5 million years ago marks one of the three largest mass extinctions in the past 500 million years. The extinction event coincided with a large asteroid impact at Chicxulub, Mexico, and occurred within the time of Deccan flood basalt volcanism in India. Here, we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction. Notably, a single ejecta-rich deposit compositionally linked to the Chicxulub impact is globally distributed at the Cretaceous-Paleogene boundary. The temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations (for example, darkness and cooling) lead us to conclude that the Chicxulub impact triggered the mass extinction.
1004.
The 2008 West Bohemia earthquake swarm in the light of the WEBNET network
Journal of Seismology,
14
(4)
665 – 682
2010
ISSN: 13834649Keywords:▾
Bohemia; Czech Republic; Germany; Vogtland; earthquake epicenter; earthquake event; earthquake magnitude; earthquake mechanism; earthquake swarm; fault plane; focal mechanism; peak acceleration; seismic moment; seismicity; strong motion
Abstract: ▾ A swarm of earthquakes of magnitudes up to ML = 3.8 stroke the region of West Bohemia/Vogtland (border area between Czechia and Germany) in October 2008. It occurred in the Nový Kostel focal zone, where also all recent earthquake swarms (1985/1986, 1997, and 2000) took place, and was striking by a fast sequence of macroseismically observed earthquakes. We present the basic characteristics of this swarm based on the observations of a local network WEBNET (West Bohemia seismic network), which has been operated in the epicentral area, on the Czech territory. The swarm was recorded by 13 to 23 permanent and mobile WEBNET stations surrounding the swarm epicenters. In addition, a part of the swarm was also recorded by strong-motion accelerometers, which represent the first true accelerograms of the swarm earthquakes in the region. The peak ground acceleration reached 0.65 m/s2. A comparison with previous earthquake swarms indicates that the total seismic moments released during the 1985/1986 and 2008 swarms are similar, of about 4E16 Nm, and that they represent the two largest swarms that occurred in the West Bohemia/ Vogtland region since the ML = 5.0 swarm of 1908. Characteristic features of the 2008 swarm are its short duration (4 weeks) and rapidity and, consequently, the fastest seismic moment release compared to previous swarms. Up to 25,000 events in the magnitude range of 0.5 < ML < 3.8 were detected using an automatic picker. A total of nine swarm phases can be distinguished in the swarm, five of them exceeding the magnitude level of 2.5. The magnitude-frequency distribution of the complete 2008 swarm activity shows a b value close to 1. The swarm hypocenters fall precisely on the same fault portion of the Nový Kostel focal zone that was activated by the 2000 swarm (ML ≤ 3. 2) in a depth interval from 6 to 11 km and also by the 1985/1986 swarm (ML ≤ 4.6). The steeply dipping fault planes of the 2000 and 2008 swarms seem to be identical considering the location error of about 100 m. Furthermore, focal mechanisms of the 2008 swarm are identical with those of the 2000 swarm, both matching an average strike of 170° and dip of 80° of the activated fault segment. An overall upward migration of activity is observed with first events at the bottom and last events at the top of the of the activated fault patch. Similarities in the activated fault area and in the seismic moments released during the three largest recent swarms enable to estimate the seismic potential of the focal zone. If the whole segment of the fault plane was activated simultaneously, it would represent an earthquake of ML ~5. This is in good agreement with the estimates of the maximum magnitudes of earthquakes that occurred in the West Bohemia/Vogtland region in the past. © 2010 Springer Science+Business Media B.V.
1003.
Testing the spatial and temporal framework of speciation in an ancient lake species flock: The leech genus Dina (Hirudinea: Erpobdellidae) in Lake Ohrid
Biogeosciences,
7
(11)
3387 – 3402
2010
ISSN: 17264189Keywords:▾
Balkans; Lake Ohrid; Dina; Erpobdellidae; Hirudinea; Hirudinida; biotic factor; endemic species; geological record; hybridization; leech; molecular analysis; paleobiogeography; Pleistocene; Pliocene; population structure; spatial analysis; speciation (biology); watershed
Abstract: ▾ Ancient Lake Ohrid on the Balkan Peninsula is considered to be the oldest ancient lake in Europe with a suggested Plio-/Pleistocene age. Its exact geological age, however, remains unknown. Therefore, molecular clock data of Lake Ohrid biota may serve as an independent constraint of available geological data, and may thus help to refine age estimates. Such evolutionary data may also help unravel potential biotic and abiotic factors that promote speciation events. Here, mitochondrial sequencing data of one of the largest groups of endemic taxa in the Ohrid watershed, the leech genus Dina, is used to test whether it represents an ancient lake species flock, to study the role of potential horizontal and vertical barriers in the watershed for evolutionary events, to estimate the onset of diversification in this group based on molecular clock analyses, and to compare this data with data from other endemic species for providing an approximate time frame for the origin of Lake Ohrid. Based on the criteria speciosity, monophyly and endemicity, it can be concluded that Dina spp. from the Ohrid watershed, indeed, represents an ancient lake species flock. Lineage sorting of its species, however, does not seem to be complete and/or hybridization may occur. Analyses of population structures of Dina spp. in the Ohrid watershed indicate a horizontal zonation of haplotypes from spring and lake populations, corroborating the role of lake-side springs, particularly the southern feeder springs, for evolutionary processes in endemic Ohrid taxa. Vertical differentiation of lake taxa, however, appears to be limited, though differences between populations from the littoral and the profundal are apparent. Molecular clock analyses indicate that the most recent common ancestor of extant species of this flock is approximately 1.99 ± 0.83 million years (Ma) old, whereas the split of the Ohrid Dina flock from a potential sister taxon outside the lake is estimated at 8.30 ± 3.60 Ma. Comparisons with other groups of endemic Ohrid species indicated that in all cases, diversification within the watershed started ≤2 Ma ago. Thus, this estimate may provide information on a minimum age for the origin of Lake Ohrid. Maximum ages are less consistent and generally less reliable. But cautiously, a maximum age of 3 Ma is suggested. Interestingly, this time frame of approximately 2-3 Ma ago for the origin of Lake Ohrid, generated based on genetic data, well fits the time frame most often used in the literature by geologists. © Author(s) 2010.
1002.
Tephrostratigraphy and tephrochronology of lakes Ohrid and Prespa, Balkans
Biogeosciences,
7
(10)
3273 – 3288
2010
ISSN: 17264189Keywords:▾
Italy; Lake Mikri Prespa; Lake Ohrid; Pantelleria; Sicily; Trapani; data set; Holocene; Pleistocene; stratigraphy; succession; tephrochronology; volcanic eruption
Abstract: ▾ Four cores from Balkans lakes Ohrid and Prespa were examined for recognition of tephra layers and cryptotephras, and the results presented along with the review of data from other two already published cores from Lake Ohrid. The six cores provide a previously unrealised tephrostratigraphic framework of the two lakes, and provide a new tephrostratigraphic profile (composite) for the Balkans, which spans from the end of the Middle Pleistocene to the AD 472. A total of 12 tephra layers and cryptotephras were recognised in the cores. One is of Middle Pleistocene age (131 ka) and correlated to the marine tephra layer P-11 from Pantelleria Island. Eight volcanic layers are Upper Pleistocene in age, and encompass the period between ca. 107 ka and ca. 31 ka. This interval contains some of the main regional volcanic markers of the central Mediterranean area, including X-6, X-5, Y-5 and Y-3 tephra layers. The other layers of this interval have been related to the marine tephra layers C20, Y-6 and C10, while one was for the first time recognised in distal areas and correlated to the Taurano eruption of probable Vesuvian origin. Three cryptotephras were of Holocene age. Two of which have been correlated to Mercato and AD 472 eruptions of Somma-Vesuvius, while the third has been correlated to the FL eruption from Mount Etna. These recognitions provide a link of the Ohrid and Prespa lacustrine successions to other archives of the central Mediterranean area, like south Adriatic, Ionian, and south Tyrrhenian seas, lakes of southern Italy (Lago Grande di Monticchio, Pantano di San Gregorio Magno and Lago di Pergusa) and Balkans (Lake Shkodra). © 2010 Author(s).
1001.
Tectonostratigraphic units and stratigraphic sequences of the nonmarine Songliao basin, northeast China
Basin Research,
22
(1)
79-95
2010
ISSN: 0950091XKeywords:▾
alluvial fan; asthenosphere; Cretaceous; deformation mechanism; depocenter; extension; fan delta; floodplain; geodynamics; hydrocarbon reservoir; Jurassic; lacustrine deposit; lithostratigraphy; plate motion; rifting; sediment thickness; sedimentary sequence; seismic reflection; subduction; subsidence; systems tract; tectonostratigraphy; temperature effect; upwelling; volcanism, China; Pacific Ocean; Sea of Okhotsk; Songliao Basin
Abstract: ▾ Through tectonostratigraphic analysis of the nonmarine, intracontinental Songliao basin in northeast China, four episodes of deformation are recognized: mantle upwelling, rift, postrift thermal subsidence and structural inversion. The episodes are related to regional geodynamics and plate motions. Each episode is associated with a specific stratigraphic signature. The first period of deformation occurred during the Middle and Late Jurassic when asthenospheric upwelling heated, thinned and stretched the lithosphere. These events may have been caused by the narrowing of the Okhotsk Sea through subduction. This deformation is characterized by doming, extension, widespread volcanism and intrusion, and erosion. Volcanics interfinger with alluvial fan and alluvial plain facies systems tracts. The second rifting episode began in the latest Jurassic and continued into the Early Cretaceous. It resulted in the formation of a large number of isolated, NNE-trending fault blocks of 'basin-and-range' style. Rifting may have been caused by the formation and subduction of the Izanagi and Pacific Plates. Coal-bearing fluvial, floodplain, lacustrine and fan-delta strata and widespread volcanic rocks filled the fault-block basins. Volcanic strata hundreds to several thousand meters thick in the Huoshiling and Yingcheng Formations record multiple intrusive events during the rifting stage in the basin. These events were concurrent with episodes of intrusion and volcanic eruption in northeast China. The third phase of regional postrift deformation and subsidence, which began with the Lower Cretaceous Denglouku Formation, was caused by lithospheric cooling and extension, modulated by multiple compressional events. Subsidence in the Songliao basin permitted accumulation of thick postrift deposits, in contrast with other Cretaceous basins in Mongolia and northeast Asia. Three compressional episodes, which episodically interrupted the long-term cooling subsidence, originated from development of the Okhotsk suture and subduction of the Pacific plate. In the Early Cretaceous, pronounced compression originated from closure of Okhotsk Sea, forming the mountain ranges of Daxinganling, which provided sediment to the northern part of the basin. In the Late Cretaceous, the intensity of compression from the Pacific margin increased through time, causing westward migration of depocentres and uplift in the east until the end of Cretaceous. Postrift strata, typically 3000-4000 m thick with a maximum thickness of 6000 m, extend beyond the rift blocks and onlap the basin margins to form a large uniform basin. Early thermal subsidence strata include alluvial fan, fluvial, floodplain, shallow lacustrine and delta facies tracts, overlain by large deltaic and lacustrine facies. Late postrift environments featured by large lakes in the basin centre rimmed by delta, fluvial and floodplain environments. Reflection seismic profiles show that strong structural inversion, including folding and uplift, began at the end of the Nenjiang Formation and culminated at the end of the Cretaceous. The main compressional stress field changed from NW to NWW at the end of the Cretaceous, which caused changes in the direction of folding. During the rifting stage, several sets of gas-bearing reservoirs formed in association with coal-bearing source rocks in fluvial and deltaic strata with reservoir-quality volcanics and fluvial and fan-delta sandstone. Thick, widespread mudstone deposited in deep lakes during the postrift stage contains abundant organic matter, and is an important source rock and regional cap rock. Good reservoirs occur in deltaic and fluvial strata. Because of the episodic compressional events that alternately caused subsidence and uplift, reservoirs are sandwiched between source rocks, providing direct fluid communication from source to reservoir. © 2009 The Authors. Journal Compilation © Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.
1000.
Target and impact deposits at Rochechouart impact structure, France
Special Paper of the Geological Society of America,
465509-541
2010
Abstract: ▾ The 200 Ma, 24-km-diameter Rochechouart impact structure was formed in granitic intrusive and metamorphic rocks of Variscan age (400-300 Ma) close to the margin of the Mesozoic sea. Fractured basement and autochthonous breccias form a several-decameter-thick semicontinuous zone over an 18-20-km-diameter zone. Impact melt rocks, suevite, and polymict lithic breccia are spread over an ∼15 km inner zone, forming a centro-symmetric deposit inclined 0.6°N. No topographic expression of the central uplift exists. The crater floor is at the same elevation (∼±50 m) over a zone at least 20 km in diameter, corresponding to the central part of the original crater. The pre-erosional diameter of the crater is probably larger than previously thought and possibly reached 40-50 km. The structure appears much less eroded than previously thought, as the sequence of crater fill is complete as exposed near Chassenon. The suevite in Chassenon is capped by an ash-like horizontal deposit of very glass-poor, fine-grained, lithic debris derived from basement rocks. Material with similar grain size and composition is observed in centimeter-to meter-thick multilayered glassbearing intercalations (dikes) cutting through the suevite. The integrity of the Chassenon sequence strikingly contrasts with the age and morphology of the structure, implying that a rapid and thick sedimentary deposit has covered the crater to protect it from erosion. The impactoclastic top deposit also firmly constrains the thickness and volume of the initial crater fill, which appear extremely depleted (by a factor of 5 or more) compared with similar-sized impact structures and model-based calculations. This anomaly remains unexplained. All the impactites, including the glass-poor and glass-free impactites, are characterized by a prominent K-metasomatism signifying pronounced postimpact hydrothermal activity. Exposed in isolated occurrences from the center to the periphery of the inner 15-km-diameter zone, impact melt rocks are extremely unlikely to have formed a continuous sheet. They display a large variety of textures, grading from pure melt rock into basal suevite, which are distinct in composition, texture, and setting from the main suevite body forming the top of the impact deposit. Heterogeneity and relative inefficiency in mixing are characteristic of the whole impact deposit, resulting in heterogeneous melts at the scale of hand specimens, but also at the kilometer scale, as suggested by close ties between the composition of melt-bearing rocks and the subjacent target rocks.. © 2010 The Geological Society of America. All rights reserved.
999.
Summary of physical properties measured at several boreholes penetrating through the Chelungpu fault in central Taiwan
Terrestrial, Atmospheric and Oceanic Sciences,
21
(4)
655-673
2010
ISSN: 10170839Keywords:▾
borehole; Chi-Chi earthquake 1999; earthquake magnitude; fault plane; physical property; rupture; well logging, Taiwan
Abstract: ▾ On 20 September 1999, the Ms 7.6 Chi-Chi earthquake ruptured the Chelungpu fault in central Taiwan. After the earthquake, several boreholes of different depths were drilled. Those boreholes penetrated the fault plane. The physical (mechanical, thermal, hydraulic, electric, and magnetic) parameters were measured either on the core samples or through well-loggings. Results are significant for studies of the Chelungpu fault. However, the measured results are published in different articles and reports. It is not convenient for the earth scientists to take advantage of those results. Hence, those results are compiled and described in this paper. In addition, the correlations among a few parameters are also reported.
998.
Stress-dependence of the permeability and porosity of sandstone and shale from TCDP Hole-A
International Journal of Rock Mechanics and Mining Sciences,
47
(7)
1141-1157
2010
ISSN: 13651609
Publisher: Elsevier BV
Keywords:▾
Digital storage; Mechanical permeability; Microcracks; Porosity; Road construction; Rock pressure; Sandstone; Unloading, Confining pressures; Effective pressure; Log-log plots; Permeability and porosities; Stress dependence; Stress history; Stress-dependent; Three orders of magnitude, Shale
Abstract: ▾ We utilize an integrated permeability and porosity measurement system to measure the stress dependent permeability and porosity of Pliocene to Pleistocene sedimentary rocks from a 2000m borehole. Experiments were conducted by first gradually increasing the confining pressure from 3 to 120MPa and then subsequently reducing it back to 3MPa. The permeability of the sandstone remained within a narrow range (10-14-10-13m2). The permeability of the shale was more sensitive to the effective confining pressure (varying by two to three orders of magnitude) than the sandstone, possibly due to the existence of microcracks in the shale. Meanwhile, the sandstone and shale showed a similar sensitivity of porosity to effective pressure, whereby porosity was reduced by about 10-20% when the confining pressure was increased from 3 to 120MPa. The experimental results indicate that the fit of the models to the data points can be improved by using a power law instead of an exponential relationship. To extrapolate the permeability or porosity under larger confining pressure (e.g. 300MPa) using a straight line in a log-log plot might induce unreasonable error, but might be adequate to predict the stress dependent permeability or porosity within the experimental stress range. Part of the permeability and porosity decrease observed during loading is irreversible during unloading. © 2010 Elsevier Ltd.
997.
Stratigraphic analysis of lake level fluctuations in Lake Ohrid: An integration of high resolution hydro-acoustic data and sediment cores
Biogeosciences,
7
(11)
3531 – 3548
2010
ISSN: 17264189Keywords:▾
Lake Ohrid; acoustic data; biodiversity; chronology; coastal zone; endemic species; geochemical method; habitat type; karst; lacustrine deposit; lithology; oligotrophic environment; paleoenvironment; Pliocene; resolution; sediment core; seismic data; stratigraphy; water depth; water level
Abstract: ▾ Ancient Lake Ohrid is a steep-sided, oligotrophic, karst lake that was tectonically formed most likely within the Pliocene and often referred to as a hotspot of endemic biodiversity. This study aims on tracing significant lake level fluctuations at Lake Ohrid using high-resolution acoustic data in combination with lithological, geochemical, and chronological information from two sediment cores recovered from sub-aquatic terrace levels at ca. 32 and 60 m water depth. According to our data, significant lake level fluctuations with prominent lowstands of ca. 60 and 35 m below the present water level occurred during Marine Isotope Stage (MIS) 6 and MIS 5, respectively. The effect of these lowstands on biodiversity in most coastal parts of the lake is negligible, due to only small changes in lake surface area, coastline, and habitat. In contrast, biodiversity in shallower areas was more severely affected due to disconnection of today sub-lacustrine springs from the main water body. Multichannel seismic data from deeper parts of the lake clearly image several clinoform structures stacked on top of each other. These stacked clinoforms indicate significantly lower lake levels prior to MIS 6 and a stepwise rise of water level with intermittent stillstands since its existence as water-filled body, which might have caused enhanced expansion of endemic species within Lake Ohrid. © Author(s) 2010.
996.
Spatial variability of recent sedimentation in Lake Ohrid (Albania/Macedonia)
Biogeosciences,
7
(10)
3333 – 3342
2010
ISSN: 17264189Keywords:▾
Lake Ohrid; anthropogenic source; assessment method; biodiversity; biogeochemistry; catchment; chemical composition; concentration (composition); grain size; heterogeneity; lacustrine deposit; land use; metal; pigment; Pliocene; sedimentation; spatial variation; surficial sediment
Abstract: ▾ Lake Ohrid is likely of Pliocene age and thus commonly referred to as the oldest existing lake in Europe. In this study spatial variability of recent sediment composition is assessed using >50 basin wide distributed surface sediment samples. Analysis of biogeochemical bulk parameters, selected metals, pigment concentrations as well as grain size distributions revealed a significant spatial heterogeneity in surface sediment composition. It implies that sedimentation in Lake Ohrid is controlled by an interaction of multiple natural and anthropogenic factors and processes. Major factors controlling surface sediment composition are related to differences in geological catchment characteristics, anthropogenic land use, and a counterclockwise rotating surface water current. In some instances processes controlling sediment composition also seem to impact distribution patterns of biodiversity, which suggests a common interaction of processes responsible for both patterns.
995.
Spatial pattern of modern sedimentation rate of Qinghai Lake and a preliminary estimate of the sediment flux
Chinese Science Bulletin,
55
(7)
621 – 627
2010
ISSN: 18619541Abstract: ▾ We investigated the spatiotemporal distribution of 137Cs radioactivity in surface sediment of Qinghai Lake, and developed the spatial pattern of sedimentation rate. The 137Cs inventory is higher near the estuary/bank area, but lower at the central lake. On the other hand, the average 137Cs activity is lower near the estuary/bank area, but higher at the central lake. The mass accumulation rate (MAR) and the fluxes and contents of the terrestrial detritus (e.g. SiO2, Fe2O3, and Ti) are higher near the estuary/bank area, but lower at the central lake. The chemical/biogenic deposits (e.g. the autogenic carbonates) take up higher fractions at the central lake. These suggest that the spatial pattern of recent sedimentation rate is dominated by the deposition of terrestrial detritus. The average MAR (0.0337g cm-2a-1) was estimated based on those of different cores of Qinghai Lake and was verified by a Ca mass-balance method. The fluxes of total lake sediments, terrestrial detritus, and direct atmospheric deposits were also estimated. © Science China Press and Springer-Verlag Berlin Heidelberg 2009.