All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1569.
Coseismic velocity change associated with the 2011 Van earthquake (M7.1): Crustal response to a major event
Geophysical Research Letters,
41
(13)
4519-4526
2014
ISSN: 00948276
Publisher: Blackwell Publishing Ltd
Keywords:▾
Acoustic noise; Drops; Earthquakes; Structural geology, 2011 Van earthquake/Turkey; Ambient noise; Broadband station; Close proximity; Coseismic slips; Frequency ranges; Temporal resolution; Velocity changes, Velocity
Abstract: ▾ Monitoring coseismic velocity changes is a major challenge, since the Earth crust has to be uniformly sampled at preseismic, coseismic, and postseismic stages using repeating active or natural sources. Here we investigate the crustal response to the 2011 Van/Turkey earthquake using ambient noise, which provides the best possible temporal resolution. Combined recordings from the nearest five broadband stations are analyzed for a time period of 6 months framing the main shock. We observe a coseismic velocity decrease of up to 0.76% in the vicinity of the main shock in the frequency range of 0.05-0.3 Hz. The velocity drop is largest at close proximity to the earthquake hypocenter and decreases systematically with distance. We also find a correlation between coseismic velocity decrease and the amount of coseismic slip on the rupture plane. The observed velocity drop shows the drastic response of the brittle crust in response to a major earthquake. Key Points A coseismic velocity change The 2011 Van earthquake Scaling between the velocity change and slip ©2014. American Geophysical Union. All Rights Reserved.
1568.
Cyclostratigraphy and orbital tuning of the terrestrial upper Santonian-Lower Danian in Songliao Basin, northeastern China
Earth and Planetary Science Letters,
40782-95
2014
ISSN: 0012821X
Publisher: Elsevier
Keywords:▾
Astronomical time scale (ATS); Continental environments; Cyclostratigraphy; Late cretaceous; Songliao basin, borehole; cyclostratigraphy; Danian; eccentricity; geological record; magnetostratigraphy; paleoclimate; paleoecology; paleoenvironment; proxy climate record; Santonian; seafloor spreading; stratigraphic boundary; thorium; timescale, Atlantic Ocean; Atlantic Ocean (South); China; Songliao Basin
Abstract: ▾ The Songke-1 north (SK-1n) borehole recovered a continuous, 1541.66 m Late Santonian-Early Danian terrestrial succession in Songliao Basin (SB), northeastern China. It provides a unique record for improving our understanding of continental paleoclimate and ecological system in Cretaceous greenhouse world. Here we use thorium (Th) logging data as a paleoenvironmental and paleoclimatic proxy to conduct a detailed cyclostratigraphic study on the SK-1n core. Power spectra, evolutionary fast Fourier transformation and wavelet analysis all reveal significant decameter- to meter-scale sedimentary cycles in the Nenjiang (K2n), Sifangtai (K2s) and Mingshui (K2m) formations. The ratios of cycle wavelengths in these stratigraphic units are ~20:5:2:1, and are interpreted as Milankovitch cycles of 405 kyr and 100 kyr eccentricity, 38.4 kyr obliquity and 20 kyr precession cycles, respectively. An astronomical time scale (ATS) is established by tuning filtered 405 kyr eccentricity cycles to a target curve of the astronomical solution La2010d based on the magnetostratigraphic time framework of the SK-1n borehole. This ATS provides precise numerical ages for stratigraphic boundaries, biozones, geological and geophysical events, and serves as a basis for correlation of strata and events between marine and terrestrial systems. The Cretaceous/Paleogene (K/Pg), Campanian/Maastrichtian, Santonian/Campanian boundaries are estimated at core depths of 318 m, 752.8 m and 1751.1 m, respectively. A ~3.8 myr-long hiatus between the Nenjiang (K2n) and Sifangtai (K2s) formations occurs from 76.1 to 79.9 million years ago. The ages and durations of magnetochrons C33r to C30n are precisely estimated and provide new constraints on the Late Cretaceous Geomagnetic Polarity Time Scale (GPTS) and South Atlantic sea-floor spreading rates. © 2014 Elsevier B.V.
1567.
Dating Palaeoproterozoic glacial deposits of the Fennoscandian Shield using detrital zircons from the Kola Peninsula, Russia
Precambrian Research,
246281--295
2014
1566.
Deep permeability of the San Andreas Fault from San Andreas Fault Observatory at Depth (SAFOD) core samples
Journal of Structural Geology,
6499-114
2014
ISSN: 01918141
Publisher: Elsevier Ltd
Keywords:▾
Clay minerals; Deformation; Flow of fluids; Fracture; Mechanical permeability; Observatories; Rock pressure; Shearing; Strike-slip faults, Confining pressures; Fault gouge; Low matrix permeability; Maximum displacement; Representative sample; SAFOD; San Andreas fault; Shear displacement, Core samples, confining pressure; country rock; displacement; fault gouge; permeability; San Andreas Fault; sedimentary rock; serpentinite; shear zone, California; San Andreas; United States
Abstract: ▾ The San Andreas Fault Observatory at Depth (SAFOD) scientific borehole near Parkfield, California crosses two actively creeping shear zones at a depth of 2.7km. Core samples retrieved from these active strands consist of a foliated, Mg-clay-rich gouge containing porphyroclasts of serpentinite and sedimentary rock. The adjacent damage zone and country rocks are comprised of variably deformed, fine-grained sandstones, siltstones, and mudstones. We conducted laboratory tests to measure the permeability of representative samples from each structural unit at effective confining pressures, Pe up to the maximum estimated in situ Pe of 120MPa. Permeability values of intact samples adjacent to the creeping strands ranged from 10-18 to 10-21m2 at Pe=10MPa and decreased with applied confining pressure to 10-20-10-22m2 at 120MPa. Values for intact foliated gouge samples (10-21-6×10-23m2 over the same pressure range) were distinctly lower than those for the surrounding rocks due to their fine-grained, clay-rich character. Permeability of both intact and crushed-and-sieved foliated gouge measured during shearing at Pe≥70MPa ranged from 2 to 4×10-22m2 in the direction perpendicular to shearing and was largely insensitive to shear displacement out to a maximum displacement of 10mm. The weak, actively-deforming foliated gouge zones have ultra-low permeability, making the active strands of the San Andreas Fault effective barriers to cross-fault fluid flow. The low matrix permeability of the San Andreas Fault creeping zones and adjacent rock combined with observations of abundant fractures in the core over a range of scales suggests that fluid flow outside of the actively-deforming gouge zones is probably fracture dominated. © 2013.
1565.
Design and development of the discharge system of IDDP-1
Geothermics,
4958-65
2014
ISSN: 0375-6505Keywords:▾
Krafla, IDDP-1, Geothermal well head, Geothermal well discharge, Geothermal superheated steam, Corrosion, Erosion
Abstract: ▾ The initial discharge of IDDP-1 took place in March 2010 and the well was discharged intermittently until July 2012. In the beginning a mixture of steam and water flowed from the well but soon the fluid became superheated and enthalpy gradually increased, approaching 3200kJ/kg. The flow rate from the well was up to 50kg/s. The design condition at well head turned out to be challenging due to high pressure, temperature, corrosion and erosion. Valves, rated for higher pressure and temperature, failed during operation. Five different designs of discharge systems were installed. The well had to be quenched when the master valves failed. Plans for its future are still being evaluated.
1564.
Characterizing oxygen isotope variability and host water relation of modern and subfossil aquatic mosses
Geochimica et Cosmochimica Acta,
130212 – 228
2014
1563.
Biomarker characteristics of source rocks in Well SK1 in Songliao Basin
Earth Sci. Front.,
21
(2)
265-274
2014
1562.
Distinct lake level lowstand in Lake Prespa (SE Europe) at the time of the 74 (75) ka Toba eruption
Climate of the Past,
10
(1)
261 – 267
2014
ISSN: 18149324
Publisher: Copernicus GmbH
Keywords:▾
Arctic; Greater Sunda Islands; Greenland; Indonesia; Lake Mikri Prespa; Sumatra; Sunda Isles; Dreissena; benthos; bivalve; data set; dating method; ice core; karst; Quaternary; radiocarbon dating; sedimentology; tephrochronology; volcanic eruption
Abstract: ▾ The 74 (75) ka Toba eruption in Sumatra, Indonesia, is considered to be one of the largest volcanic events during the Quaternary. Tephra from the Toba eruption has been found in many terrestrial and marine sedimentary deposits, and acidity peaks related to the eruption have been used to synchronize ice core records from Greenland and Antarctica. Seismic profiles and sedimentological data from Lake Prespa on the Balkan Peninsula, SE Europe, indicate a lake level lowstand at 73.6 ± 7.7 ka based on ESR dating of shells. Tephrostratigraphy, radiocarbon dating and tuning of the total organic carbon content with the NGRIP isotope record, corroborate that the lake level lowstand was a short-term event superimposed on the general cooling trend at the end of MIS 5, most likely at the onset of the Greenland Stadial GS-20. Acknowledging that tectonic events or karst processes could have triggered this lake level lowstand, the chronological correspondence between the lowstand and the Toba eruption is intriguing. Therefore a Toba-driven short-term shift to aridity in the Balkan region, leading to lake level changes and triggering spatial expansion events in one of the lake's most abundant benthic species, the carino mussel Dreissena presbensis, cannot be excluded. © Author(s) 2014.
1561.
A 600,000 year long continental pollen record from Lake Van, eastern Anatolia (Turkey)
Quaternary Science Reviews,
10430-41
2014
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Eastern Anatolia; Lake vans; Long continental pollen record; Near East; Paleoclimates, climax; deciduous tree; deep drilling; glacial-interglacial cycle; ice core; paleoclimate; paleoecology; palynology; Quaternary; sedimentary sequence; water depth, Black Sea; Caspian Sea; Lake Van; Mediterranean Sea; Turkey
Abstract: ▾ Lake Van is the fourth largest terminal lake in the world (38.5°N, 43°E, volume 607km3, area 3570km2, maximum water depth 460m), extending for 130km WSW-ENE on the eastern Anatolian high plateau, Turkey. The sedimentary record of Lake Van, partly laminated, obtains a long and continuous continental sequence that covers multiple interglacial-glacial cycles. Promoted by the potential of the sedimentary sequence for reconstructing the paleoecological and paleoclimate development of the Near East, a deep drilling operation was carried out in 2010 supported by the International Continental Scientific Drilling Program (ICDP). The 219m long continental pollen record presented here is based on a well-dated composite profile drilled on the so-called Ahlat Ridge in water depth of 360m encompassing the last 600,000 years. It is the longest continuous continental pollen record of the Quaternary in the entire Near East and central Asia obtained to date. The glacial-interglacial cycles and pronounced interstadials are clearly reflected in the vegetation development based on millennial-scale time resolution. In general, the glacial/stadial vegetation is characterized by dwarf-shrub steppe and desert steppe, whereas the climax vegetation of past interglacials can be described as oak steppe-forest similar to the present interglacial in this sensitive semi-arid region between the Black, Caspian, and Mediterranean Seas. By comparing the Lake Van pollen record with other western Asian and southern European long continental pollen sequences as well as marine and ice-core records, the regional variability of the climate signals is also discussed. © 2014.
1560.
Late Cretaceous palynology and paleoclimate change: Evidence from the SK1 (South) core, Songliao Basin, NE China
Science China Earth Sciences,
57
(12)
2985-2997
2014
ISSN: 16747313
Publisher: Science Press (China)
Keywords:▾
Climate change; Ecology; Water, dinoflagellate; Late cretaceous; Paleoclimates; Songliao basin; spores and pollen, Core samples, borehole; climate variation; Cretaceous; dinoflagellate cyst; dominance; fossil assemblage; microfossil; paleoclimate; paleoecology; paleoenvironment; palynology; sediment core; species diversity; warming, China; Songliao Basin, Dinophyceae
Abstract: ▾ Cretaceous climate was warmer than today. The Songliao Basin contains one of the most important Late Cretaceous non-marine deposits in China for the research of the paleoenvironment and paleoclimate. This research is based on core samples from the SK1(S) borehole. The strata sampled are the upper part of the Quantou Formation to member 2 of the Nenjiang Formation, where spores, pollen, dinoflagellates, and other microfossils are abundantly preserved. Based on analysis of the spores and pollen fossils from the core samples, the following six fossil assemblage zones have been recognized in ascending order: The Cicatricosisporites-Cyathidites-Pinuspollenites, Schizaeoisporites-Cyathidites-Classopollis, Cyathidites-Schizaeoisporites, Schizaeoisporites-Cyathidites-Proteacidites, Proteacidites-Cyathidites-Dictyotriletes, and the Lythraites-Callistipollenites-Schizaeoisporites zones. The six fossil zones range from the late Cenomanian to early Campanian. The Late Cretaceous dinoflagellate cysts in the Songliao Basin are of high abundance and low diversity. Specific phytoplankton types reflect salinity changes of the Songliao Lake. Paleoecology of the dinoflagellates suggests that sediments of members 2 and 3 of the Yaojia Formation (K2y2+3) were deposited in a freshwater environment, whereas members 2 and 3 of the Qingshankou Formation (K2q2+3) and members 1 and 2 of the Nenjiang Formation (K2n1+2) were deposited in freshwater to brackish water environments. Combined with the paleoecology of dinoflagellates and the palynomorph biozones, valuable information of the paleoclimate was provided. The quantitative analyses of spores and pollen fossils, such as vegetation type, climate type, and humidity type, diversity and dominance, indicate a relatively sub-humid, mid-subtropical paleoclimate, with slight climatic fluctuation and/or temporal change. © 2014, Science China Press and Springer-Verlag Berlin Heidelberg.
1559.
10Be content in clasts from fallout suevitic breccia in drill cores from the Bosumtwi impact crater, Ghana: Clues to preimpact target distribution
Meteoritics and Planetary Science,
49
(3)
394 – 411
2014
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ Rocks from drill cores LB-07A (crater fill) and LB-08A (central uplift) into the Bosumtwi impact crater, Ghana, were analyzed for the presence of the cosmogenic radionuclide 10Be. The aim of the study was to determine the extent to which target rocks of various depths were mixed during the formation of the crater-filling breccia, and also to detect meteoric water infiltration within the impactite layer. 10Be abundances above background were found in two (out of 24) samples from the LB-07A core, and in none of five samples from the LB-08A core. After excluding other possible explanations for an elevated 10Be signal, we conclude that it is most probably due to a preimpact origin of those clasts from target rocks close to the surface. Our results suggest that in-crater breccias were well mixed during the impact cratering process. In addition, the lack of a 10Be signal within the rocks located very close to the lake sediment-impactite boundary suggests that infiltration of meteoric water below the postimpact crater floor was limited. This may suggest that the infiltration of the meteoric water within the crater takes place not through the aerial pore-space, but rather through a localized system of fractures. © The Meteoritical Society, 2014.
1558.
14C chronostratigraphy for Qinghai lake in China
Radiocarbon,
56
(1)
143 – 155
2014
ISSN: 00338222DOI:10.2458/56.16470
Keywords:▾
China; Qinghai; Qinghai Lake; accelerator mass spectrometry; age determination; chronostratigraphy; lacustrine deposit; lake ecosystem; radiocarbon dating; reservoir; total organic carbon
Abstract: ▾ Radiocarbon accelerator mass spectrometry (AMS) techniques were used to date total organic carbon and plant seeds in the 1Fs core sequence (36°48′N, 100°08′E) from Qinghai Lake, China. This core was drilled ~18 m into Qinghai Lake sediments as part of an international cooperative research project, "Scientific Drilling at Qinghai Lake in the Northeastern Tibetan Plateau: High-Resolution Paleoenvironmental Records of Eastern Asia Linked to Global Change," which began in 2004. Based on the differences in lithology and total organic content (TOC) in core 1Fs, the core was divided into 3 sections for age-modeling purposes: the upper ~499 cm lacustrine silty clay to clay; the middle unit of silty clay with silt layers from 499-901 cm; and the lower 901-1861 cm silty clay, loess-like silt, and fine sand layers. Three different approaches are applied to the reservoir age problem. First, a simple linear regression gives an offset of 1342 yr. If the core is divided into three sections, linear regressions can be applied separately for the three segments, which results in an age estimate for the average hardwater effect of ~135 yr BP for the surface section up to 499 cm. If extrapolated for deeper sections, these results imply a higher reservoir offset for those two sections, which may be as much as 1143 and 2523 yr, but this assumes that there are no discontinuities in the core. A third approach using a wiggle-matching approach gave an offset of 196 yr. This study concludes that the reservoir age of Qinghai Lake is complex, but these new data add to our understanding of the 14C chronology of Qinghai Lake for the last 32 ka. © 2014 by the Arizona Board of Regents on behalf of the University of Arizona.
1557.
3D interpretation by integrating seismic and potential field data in the vicinity of the proposed COSC-1 drill site, central Swedish Caledonides
Geological Society, London, Special Publications,
390
(1)
301--319
2014
ISSN: 0305-8719, 2041-4927DOI:10.1144/SP390.15
Abstract: ▾ Skip to Next Section The scientific drilling project COSC (Collisional Orogeny in the Scandinavian Caledonides), designed to study key questions concerning orogenic processes, aims to drill two fully cored boreholes to depths of c. 2.5 km each at carefully selected locations in west-central Sweden. The first of these, COSC-1, is scheduled for start late spring 2014 and will target the Seve Nappe Complex, characterized by inverted metamorphism and with parts that have evidently been subjected to hot ductile extrusion. In this study available seismic sections have been combined with surface geology to produce a 3D interpretation of the tectonic structures in the vicinity of the COSC-1 borehole. Constrained 3D inverse gravity modelling over the same area supports the interpretation, and the high-density Seve Nappe Complex stands out clearly in the model. Interpretation and models show that the maximum depth extent of the Seve Nappe Complex is less than 2.5 km, consistent with reflection seismic data. The gravity modelling also requires underlying units to comprise low-density material, consistent with the Lower Allochthon, but the modelling is unable to discern the décollement separating the allochthons from the crystalline Precambrian basement.
1556.
A "slice-and-view" (FIB-SEM) study of clay gouge from the SAFOD creeping section of the San Andreas Fault at ~2.7km depth
Journal of Structural Geology,
69
(PA)
234-244
2014
ISSN: 01918141
Publisher: Elsevier Ltd
Keywords:▾
Clay fabrics; SAFOD; San Andreas fault; SEM and TEM; Smectites, Creep, creep; deformation; fault gouge; fault zone; magnesium; San Andreas Fault; scanning electron microscopy; seismicity; smectite; transmission electron microscopy
Abstract: ▾ The San Andreas Fault is one of the most studied earthquake-generating structures on Earth, but the reason that some sections are anomalously weak, and creep without apparent seismicity, remains poorly understood. Here, we present results from nanoscale (FIB-SEM) 3D microstructural observations of weak (friction coefficient of 0.095) SAFOD clay fault gouge containing serpentinite clasts, recovered from the active Central Deforming Zone at ~2.7km vertical depth. Our nanoscale observations confirm that frictional slip and extreme weakness occurvia deformation of smectite clay that forms a shear fabric within the fault zone. We infer that creep initiates by fracture-controlled, substrate growth of oriented Mg-smectite on R, P and Y shears, followed by clay smearing and ductile flow of an evolving and expanding clay matrix. At the crystal-scale, pervasive sliding occurs along hydrated smectite interlayers and surfaces occupied by exchangeable Mg- and Ca-ions, with slip typically spaced at 3-5 lattice layers apart. We conclude that the strength and seismic behaviour of major tectonic faults at shallow crustal levels evolves as clay fabric develops with accumulated fault slip. © 2014 Elsevier Ltd.
1555.
A 60,000-year record of hydrologic variability in the Central Andes from the hydrogen isotopic composition of leaf waxes in Lake Titicaca sediments
Earth and Planetary Science Letters,
408263 – 271
2014
Keywords:▾
Lake Titicaca; Central Andes; Holocenes; Hydrogen isotopic composition; Last glacial period; Stable hydrogen isotope; Summer monsoon; deglaciation; glacial lake; Holocene; hydrogen isotope; isotopic composition; Last Glacial Maximum; monsoon; precipitation (chemistry); sediment core; stable isotope; summer; Younger Dryas
Abstract: ▾ A record of the hydrogen isotopic composition of terrestrial leaf waxes (δDwax) in sediment cores from Lake Titicaca provides new insight into the precipitation history of the Central Andes and controls of South American Summer Monsoon (SASM) variability since the last glacial period. Comparison of the δDwax record with a 19-kyr δD record from the nearby Illimani ice core supports the interpretation that precipitation δD is the primary control on δDwax with a lesser but significant role for local evapotranspiration and other secondary influences on δDwax. The Titicaca δDwax record confirms overall wetter conditions in the Central Andes during the last glacial period relative to a drier Holocene. During the last deglaciation, abrupt δDwax shifts correspond to millennial-scale events observed in the high-latitude North Atlantic, with dry conditions corresponding to the Bølling-Allerød and early Holocene periods and wetter conditions during late glacial and Younger Dryas intervals. We observe a trend of increasing monsoonal precipitation from the early to the late Holocene, consistent with summer insolation forcing of the SASM, but similar hydrologic variability on precessional timescales is not apparent during the last glacial period. Overall, this study demonstrates the relative importance of high-latitude versus tropical forcing as a dominant control on glacial SASM precipitation variability. © 2014 Elsevier B.V.
1554.
A fixed sublithospheric source for the late Neogene track of the Yellowstone hotspot: Implications of the Heise and Picabo volcanic fields
Journal of Geophysical Research: Solid Earth,
119
(4)
2871-2906
2014
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
basalt; caldera; deformation; hot spot; ignimbrite; lithospheric structure; Neogene; North American plate; volcanic eruption; volcanic landform, Idaho; Snake River Plain; United States; Yellowstone River
Abstract: ▾ The Heise and Picabo volcanic fields of eastern Idaho are part of the more extensive time-transgressive Yellowstone-Snake River Plain hotspot track. Calderas associated with these two silicic volcanic fields are buried under 1 to 3 km of younger basalt, so their locations and eruption record histories have been based on analysis of silicic units along the margins of the eastern Snake River Plain along with some limited geophysical data. A 1.5 km borehole penetrating through basalt into underlying silicic rocks provides new data we used to reassess caldera locations and the timing of eruptions of these volcanic fields. Using these new caldera locations, we calculate an extension-adjusted rate of 2.35 cm/yr for the North American plate over the last 6.66 m.y. and a velocity of 2.30 cm/yr over the 10.27 m.y. Recalculation of a previously determined plate velocity-based migration of the deformation field surrounding the eastern Snake River Plain yields an extension-adjusted rate of 2.38 ± 0.21 cm/yr. These migration rates all fall within the previously published range of North American plate velocities of 2.2 ± 0.8 cm/yr, 2.4 cm/yr, and 2.68 ± 0.78 cm/yr based on a global hot spot reference frame. The consistency of these rates suggest that over the last 10 m.y., the Yellowstone hot spot is fixed with respect to the motion of the North American plate and therefore consistent with a classical deep-sourced hotspot model. ©2014. American Geophysical Union. All Rights Reserved.
1553.
Biogeochemical variability during the past 3.6 million years recorded by FTIR spectroscopy in the sediment record of Lake El'gygytgyn, Far East Russian Arctic
Climate of the Past,
10
(1)
209-220
2014
ISSN: 18149324Keywords:▾
accumulation rate; climate variation; FTIR spectroscopy; glacial-interglacial cycle; paleoclimate; Quaternary; regression analysis, Chukchi; Elgygytgyn Lake; Far East; Russian Federation
Abstract: ▾ A number of studies have shown that Fourier transform infrared spectroscopy (FTIRS) can be applied to quantitatively assess lacustrine sediment constituents. In this study, we developed calibration models based on FTIRS for the quantitative determination of biogenic silica (BSi; <i>n</i> Combining double low line 420; gradient: 0.9-56.5%), total organic carbon (TOC; <i>n</i> Combining double low line 309; gradient: 0-2.9%), and total inorganic carbon (TIC; <i>n</i>Combining double low line 152; gradient: 0-0.4%) in a 318 m-long sediment record with a basal age of 3.6 million years from Lake El'gygytgyn, Far East Russian Arctic. The developed partial least squares (PLS) regression models yield high cross-validated (CV) <i>R</i>2CV Combining double low line 0.86-0.91 and low root mean square error of cross-validation (RMSECV) (3.1-7.0% of the gradient for the different properties). By applying these models to 6771 samples from the entire sediment record, we obtained detailed insight into bioproductivity variations in Lake El'gygytgyn throughout the middle to late Pliocene and Quaternary. High accumulation rates of BSi indicate a productivity maximum during the middle Pliocene (3.6-3.3 Ma), followed by gradually decreasing rates during the late Pliocene and Quaternary. The average BSi accumulation during the middle Pliocene was ∼3 times higher than maximum accumulation rates during the past 1.5 million years. The indicated progressive deterioration of environmental and climatic conditions in the Siberian Arctic starting at ca. 3.3 Ma is consistent with the first occurrence of glacial periods and the finally complete establishment of glacial-interglacial cycles during the Quaternary. ©Author(s) 2014.
1552.
A scaling law to characterize fault-damage zones at reservoir depths
AAPG Bulletin,
98
(10)
2057-2079
2014
ISSN: 01491423
Publisher: American Association of Petroleum Geologists
Keywords:▾
Boreholes; Decay (organic); Well logging, Density decay; Fault damage zone; Fracture density; Geologic environment; Reservoir flow; San Andreas fault; Second orders; Seismic image, Strike-slip faults, damage mechanics; fault geometry; fault plane; fault propagation; fracture zone; sandstone; seismic stratigraphy; simulation, California; California; San Andreas; United States
Abstract: ▾ We analyze fracture-density variations in subsurface fault-damage zones in two distinct geologic environments, adjacent to faults in the granitic SSC reservoir and adjacent to faults in arkosic sandstones near the San Andreas fault in central California. These damage zones are similar in terms of width, peak fracture or fault (FF) density, and the rate of FF density decay with distance from the main fault. Seismic images from the SSC reservoir exhibit a large basement master fault associated with 27 seismically resolvable second-order faults. A maximum of 5 to 6 FF/m (1.5 to 1.8 FF/ft) are observed in the 50 to 80 m (164 to 262 ft) wide damage zones associated with second-order faults that are identified in image logs from four wells. Damage zones associated with second-order faults immediately southwest of the San Andreas Fault are also interpreted using image logs from the San Andreas Fault Observatory at Depth (SAFOD) borehole. These damage zones are also 50-80 m wide (164 to 262 ft) with peak FF density of 2.5 to 6 FF/m (0.8 to 1.8 FF/ft). The FF density in damage zones observed in both the study areas is found to decay with distance according to a power law F = F0r-n. The fault constant F0 is the FF density at unit distance from the fault, which is about 10-30 FF/m (3.1-9.1 FF/ft) in the SSC reservoir and 6-17 FF/m (1.8-5.2 FF/ft) in the arkose. The decay rate n ranges from 0.68 to 1.06 in the SSC reservoir, and from 0.4 to 0.75 in the arkosic section. This quantification of damage-zone attributes can facilitate the incorporation of the geometry and properties of damage zones in reservoir flow simulation models. Copyright © 2014. The American Association of Petroleum Geologists. All rights reserved.
1551.
Abrupt deglaciation on the northeastern Tibetan Plateau: Evidence from Lake Qinghai
Journal of Paleolimnology,
51
(2)
223 – 240
2014
ISSN: 09212728
Publisher: Kluwer Academic Publishers
Keywords:▾
China; Qinghai; Qinghai Lake; Qinghai-Xizang Plateau; climate conditions; deglaciation; environmental indicator; Holocene; paleoclimate; precipitation (climatology); sediment analysis; timescale
Abstract: ▾ We inferred the climate history for Central Asia over the past 20,000 years, using sediments from core QH07, taken in the southeastern basin of Lake Qinghai, which lies at the northeastern margin of the Tibetan Plateau. Results from multiple environmental indicators are internally consistent and yield a clear late Pleistocene and Holocene climate record. Carbonate content and total organic carbon (TOC) in Lake Qinghai sediments are interpreted as indicators of the strength of the Asian summer monsoon. Warm and wet intervals, associated with increased monsoon strength, are indicated by increased carbonate and TOC content. During the glacial period (~20,000 to ~14,600 cal year BP), summer monsoon intensity remained low and relatively constant at Lake Qinghai, suggesting cool, dry, and relatively stable climate conditions. The inferred stable, cold, arid environment of the glacial maximum seems to persist through the Younger Dryas time period, and little or no evidence of a warm interval correlative with the Bølling-Allerød is found in the QH07 record. The transition between the late Pleistocene and the Holocene, about 11,500 cal year BP, was abrupt, more so than indicated by speleothems in eastern China. The Holocene (~11,500 cal year BP to present) was a time of enhanced summer monsoon strength and greater variability, indicating relatively wetter but more unstable climatic conditions than those of the late Pleistocene. The warmest, wettest part of the Holocene, marked by increased organic matter and carbonate contents, occurred from ~11,500 to ~9,000 cal year BP, consistent with maximum summer insolation contrast between 30°N and 15°N. A gradual reduction in precipitation (weakened summer monsoon) is inferred from decreased carbonate content through the course of the Holocene. We propose that changes in the contrast of summer insolation between 30°N and 15°N are the primary control on the Asian monsoon system over glacial/interglacial time scales. Secondary influences may include regional and global albedo changes attributable to ice-cover and vegetation shifts and sea level changes (distance from moisture source in Pacific Ocean). The abruptness of the change at the beginning of the Holocene, combined with an increase in variability, suggest a threshold for the arrival of monsoonal rainfall at the northeastern edge of the Tibetan Plateau. © 2013 Springer Science+Business Media Dordrecht.
1550.
Advances of continental scientific drilling programs in China
International Journal of Earth Sciences and Engineering,
7
(1)
5-15
2014
ISSN: 09745904
Publisher: CAFET INNOVA Technical Society
Abstract: ▾ Continental scientific drilling is an important scientific and engineering project that has been attracting world-wide attentions. Since International Continental Scientific Drilling Program (ICDP) was founded in 1996, great advances have been brought about in many fields of earth sciences by continental scientific drilling. As one of the three founding members of ICDP, China has also achieved a lot of developments in continental scientific drilling. This paper summarizes the continental scientific drilling projects in China, such as the Chinese Continental Scientific Drilling (CCSD), the Lake Qinghai Scientific Drilling Project(CESD), and the preliminary progresses of the third approved ICDP project of China--the Chinese Cretaceous Continental Scientific Drilling Project(SK-I,SK-II project). The implementing Wenchuan Fault Scientific Drilling Program (WFSD) is also included in the paper. Their scientific objectives, drilling and coring situations and drilling equipment used in the project are all introduced. © 2014 CAFET-INNOVA TECHNICAL SOCIETY.
1549.
Advances of continental scientific drilling programs in China
International Journal of Earth Sciences and Engineering,
7
(1)
5-15
2014
ISSN: 09745904
Publisher: CAFET INNOVA Technical Society
Abstract: ▾ Continental scientific drilling is an important scientific and engineering project that has been attracting world-wide attentions. Since International Continental Scientific Drilling Program (ICDP) was founded in 1996, great advances have been brought about in many fields of earth sciences by continental scientific drilling. As one of the three founding members of ICDP, China has also achieved a lot of developments in continental scientific drilling. This paper summarizes the continental scientific drilling projects in China, such as the Chinese Continental Scientific Drilling (CCSD), the Lake Qinghai Scientific Drilling Project(CESD), and the preliminary progresses of the third approved ICDP project of China--the Chinese Cretaceous Continental Scientific Drilling Project(SK-I,SK-II project). The implementing Wenchuan Fault Scientific Drilling Program (WFSD) is also included in the paper. Their scientific objectives, drilling and coring situations and drilling equipment used in the project are all introduced. © 2014 CAFET-INNOVA TECHNICAL SOCIETY.
1548.
Ambient noise analysis in the eastern sea of Marmara region in northwest Turkey: Lateral variations of the crustal velocity field
Bulletin of the Seismological Society of America,
104
(4)
1954-1963
2014
ISSN: 00371106
Publisher: Seismological Society of America
Keywords:▾
Acoustic noise; Frequency bands; Group velocity dispersion; Light velocity; Wave propagation, Azimuthal dependence; Cross correlations; Cross-correlation analysis; Group velocity dispersion curve; Low group velocity; North Anatolian Fault Zone; Seismic velocities; Spectral dependences, Earthquakes, ambient noise; crustal structure; dispersion; earthquake hypocenter; North Anatolian Fault; S-wave; seismic noise; seismic velocity; seismicity; spectral analysis, Sea of Marmara; Turkey
Abstract: ▾ We analyze the ambient seismic-noise field in order to investigate the crustal structure at the North Anatolian fault zone (NAFZ) in northwest Turkey. We focus on the eastern Sea of Marmara section, where the NAFZ is in the final phase of the seismic cycle prior to an expected major (M >7) earthquake. We apply crosscorrelation analysis of the seismic ambient noise to determine the spectral dependence of the seismic velocity in order to image the crustal structure at seismogenic depth. Time-domain cross correlations are calculated for available station pairs in the target area. Interstation distances span 0.3-90 km. Here, the vertical component is analyzed in order to recover fundamental-mode Rayleigh waves in the 0.05-1.1 Hz frequency range. Group velocity dispersion curves are obtained for selected correlation paths in particular to address the azimuthal dependence of the velocity field. In the frequency band of interest, average group velocities range between ~1:8 and 3:5 km=s. Dispersion curves corresponding to the north-south-trending paths crossing the main NAFZ fault branch below the eastern Sea of Marmara show low group velocities between ~1:5 and 1:8 km=s, which is well explained by the 3-4 km-deep Çi{dotless}narci{dotless}k basin, located between the two major fault branches, the Princes Islands and Armutlu fault segments. In contrast, ray paths restricted to within the mainland of Istanbul and the Armutlu peninsulas (primarily trending east-west) show higher group velocities up to 3:2 km=s. By averaging the dispersion curves, we determine an optimized 1D S-wave velocity model for the eastern Sea of Marmara region, allowing for a significant improvement in hypocenter determination for local seismicity.
1547.
Annealing the chicxulub impact: Paleogene yucatàn carbonate slope development in the chicxulub Impact Basin, Mexico
SEPM Special Publications,
105282-304
2014
Abstract: ▾ Stratigraphic analysis of the Yaxcopoil-1 core (Yax-1) and seismic analysis of offshore two-dimensional (2D) seismic data provide insight into the Paleogene history of the Chicxulub impact basin and Yucatàn platform development. Ten facies were identified based on core and petrographic analysis. Slope sediments include redeposited and background facies. The former are carbonate supportstones and finer-grained facies with evidence of soft sediment deformation deposited as gravity flows. Background facies are shales and mud-wackestone interpreted as sub-storm wave base suspension deposits. Depositional setting ranged from a steep bathyal slope inside the crater rim to neritic outer carbonate platform environments of the seaward prograding Yucatàn platform. Through sequence stratigraphic analysis of Yax-1, we documented five sequences based on identification of transgressive and maximum flooding surfaces and facies stacking patterns. Biostratigraphic ages are equivocal, but they imply that sequences 1 and 2 are Early Paleocene, sequences 3 and 4 are Early Eocene, and sequence 5 is Middle Eocene. Coarse-grained redeposited carbonates in lower sequences 1 to 4 indicate slope gravity flow processes. Upper sequence 3 records the first evidence of fine-grained turbidites, indicating progradation of the Yucatàn platform. By the top of sequence 4, facies indicate that the platform margin had prograded over the position of Yax-1. Seismic analysis identified six units, the lower five of which appear to correlate with cored Yax-1 sequences. The geometry and distribution of seismic units A and B indicate deposition confined to the western and central parts of the basin. Unit C, with two sets of clinoforms, records a major progradational event in the eastern part of the basin likely related to Yax-1 sequence 3 turbidites. Mainly parallel reflectors in seismic units D and E indicate relatively level bottom conditions similar to the environments of facies in upper sequence 4 and 5. The tops of units D and E, in proximal settings, are erosionally truncated. This unconformity marks the base of unit F, which is characterized by discontinuous reflectors and is restricted to the northeastern portion of the basin. Stratal patterns in seismic units C to E are more controlled by relative sea-level change, as suggested by the development of clinoforms and regional unconformities. If Chicxulub and others like the Chesapeake Bay structure are representative, large marine impacts in tectonically quiescent regions may dominate local depositional environments for millions to tens of millions of years postimpact before returning control to eustasy. Copyright © 2013 SEPM (Society for Sedimentary Geology).
1546.
Displacement and dynamic weakening processes in smectite-rich gouge from the Central Deforming Zone of the San Andreas Fault
Journal of Geophysical Research: Solid Earth,
119
(3)
1777-1802
2014
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
clay; coseismic process; dehydration; displacement; fault gouge; grain size; microstructure; pore pressure; San Andreas Fault; smectite; stress analysis, California; San Andreas; United States
Abstract: ▾ The strength of clay-rich gouge from the Central Deforming Zone (CDZ) of the San Andreas Fault (SAF) was measured using a high-speed rotary shear apparatus to evaluate the potential for unstable slip along the creeping segment of the SAF. Wet and dry gouge was sheared at 0.1-1.3 m/s, 0.5-1.5 MPa normal stress, and 1-20 m displacement. CDZ gouge is weaker wet than dry and exhibits displacement strengthening to peak friction followed by weakening to steady state strength that decreases with increasing velocity. A clay foliation (Unit 2) develops from the initial microstructure (Unit 1) during the first 1.5 m of slip coincident with increasing strength. Subsequent weakening occurs during shear within Unit 2, and subsequently with development of a localized foliated slip zone (Unit 4) and fluidized material (Unit 3). Displacement and dynamic weakening result from slip along clay foliation assisted by shear-heating pressurization of pore fluid in wet gouge and additional grain-size reduction and possible clay dehydration in dry gouge. Peak strength is proportional to normal stress, but steady state strength is insensitive to normal stress probably because pore pressure approaches the normal stress. As such, CDZ gouge is weak at coseismic rates relative to interseismic creep strength. The potential for sustaining rupture propagation into the CDZ from an adjacent seismic segment is sensitive to the relationship used to extrapolate the critical weakening displacement from experimental to in situ conditions. Rupture propagation from a microseismic patch within the CDZ is unlikely, but sustained propagation from a large earthquake (e.g., Parkfield event) may be possible. ©2014. American Geophysical Union. All Rights Reserved.
1545.
Alkenone distribution in Lake Van sediment over the last 270ka: Influence of temperature and haptophyte species composition
Quaternary Science Reviews,
10453-62
2014
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Algae; Biomarkers; Lakes; Paleolimnology; Salinity measurement; Sediments, Alkenones; Haptophyte species; Lake vans; Long chain alkenones; Paleoproxy; Paleotemperature proxy; Paleotemperatures; Species composition, Population distribution, alga; alkenone; biomarker; fossil record; lacustrine deposit; paleolimnology; paleotemperature; reconstruction; spatial distribution; temperature effect, Lake Van; Turkey
Abstract: ▾ Fossil long-chain alkenones have been used for several decades to reconstruct past ocean surface water temperatures and gained recent interest as a paleotemperature proxy for continental lake settings. However, factors besides temperature can affect alkenone distributions in haptophyte algae, and alkenone compositions can differ between haptophyte species. Alkenone-biosynthesizing haptophyte algae are genetically much more diverse in lakes than in the marine realm, and species-level variations in alkenone compositions could have implications for alkenone paleothermometry. Here, we performed a paired analysis of alkenone distributions and haptophyte species compositions using ancient DNA in up to 270ka-old sediments of Lake Van in Turkey to reveal a possible species-effect on fossil alkenone distributions and paleotemperature estimates. The same predominant haptophyte in Lake Van today prevailed also since the last ~100ka. However, a calibration of alkenone paleotemperature especially in the oldest analyzed intervals is complicated due to a more complex haptophyte species composition predominated by a haptophyte (LVHap_6), which is phylogenetically different from sequences recovered from currently existing lakes including Lake Van and from haptophyte species existing in culture. The predominance of LVHap_6 coincided with the presence of alkenone MeC38:3 and relatively high MeC37:3/4 (2.4) and MeC38:4/5 ratios (3.0). Uk37 index values in the sediment core over the last 270ka reflect relative changes in past temperature and are additionally linked to haptophyte species composition. A sustained period of high salinity, as indicated by pore-water salinity measurements, could potentially have triggered the succession of haptophytes as sources of alkenones in Lake Van. © 2014 The Authors.