All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1594.
Seismic stratigraphy of Lake Van, eastern Turkey
Quaternary Science Reviews,
10463-84
2014
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Drills; Faulting; Infill drilling; Mass transfer; Sedimentation; Seismic waves; Seismology; Stratigraphy, Ahlat ridge; Lake vans; Northern basins; Seismic reflections; Tatvan basin, Lakes, delta; drilling; fault; geomorphology; lacustrine deposit; lake evolution; sedimentation; seismic reflection; seismic stratigraphy; turbidity, Lake Van; Turkey
Abstract: ▾ More than 1500km of multi-channel seismic reflection profiles combined with ICDP (International Continental Scientific Drilling Program) drilling data, provide important insights into the stratigraphic evolution of Lake Van, eastern Turkey. Three major basins (Tatvan, Northern and the Deveboynu basins) comprise the main lake basin and are separated by morphological highs (Ahlat ridge and Northern ridge). Moreover, NE-SW faults, parallel to the general tectonic lineament of the area, dominate the entire basin and are in charge of creating graben and half-graben structures. Well-developed prograding deltaic sequences on top of the basement were recognized by seismic stratigraphy analysis. Most likely, they formed during the initial flooding of Lake Van ~600ka. The Tatvan basin sediments are dominated by mass-flow deposits of various origins alternating with undisturbed lacustrine sediments including distinct tephra layers. Faulting along the Tatvan basin margins may have triggered margin-wide slope failures. Ahlat ridge started to form between ca340ka-290ka. Since then, Ahlat ridge was sheltered from major mass-flows due to its elevation. Hence, slow lacustrine sedimentation has prevailed throughout lake history on Ahlat ridge, which was the location of the main drill site during the ICDP. Several lake level fluctuations are evident on the eastern slope area but the deep basins were permanently covered by water. A significant lake-level low stand (ca600kaBP) was found at ~610m below present lake level. The setting of the lake changed at about 30ka. Tectonic activity appears to have waned significantly as the mass-transport deposition decreased across the Tatvan basin while normal undisturbed lacustrine sedimentation prevailed. A different setting is found in the Northern basin from ca90ka to Present, especially due to the strong influx of mostly volcaniclastic turbidites causing sedimentation rates to be about 3.5 times higher (drill Site 1), than at Site 2 (Ahlat ridge). © 2014 Elsevier Ltd.
1593.
Seismic velocity variations at TCDP are controlled by MJO driven precipitation pattern and high fluid discharge properties
Earth and Planetary Science Letters,
391121-127
2014
ISSN: 0012821XAbstract: ▾ Using seismic noise based monitoring techniques we find that seismic velocity variations (dv/v) observed with the borehole array of the Taiwan Chelungpu-fault Drilling Project (TCDP) are controlled by strong precipitation events associated with the Madden-Julian Oscillation (MJO), a dynamic intraseasonal atmospheric pattern in the tropical atmosphere. High-frequency noise (>1 Hz) excited by steady anthropogenic activity in the vicinity of the TCDP allows daily resolution of dv/v time series. Relatively large fluid discharge properties control the equilibration of the ground water table and hence seismic velocities on time scales smaller than the average precipitation recurrence interval. This leads to the observed synchronous 50-80 day periodicity in dv/v and rainfall records in addition to the dominant annual component. Further evidence for the governing role of hydraulic properties is inferred from the similarity of observed dv/v timing, amplitude, and recovery properties with dv/v synthetics generated by a combined model of ground water table changes and diffusive propagation of seismic energy. The lapse time (τ) dependent increase of dv/v amplitudes is controlled by the sensitivity of the diffuse wave field sampled at 1100 m depth to shallower water level fluctuations. The significant vertical offset between stations and water level explains the direct τ dependence which is opposite to the trend previously inferred from measurements at the surface. © 2014 Elsevier B.V.
1592.
Seismically triggered anomalies in the isotope signatures of mantle-derived gases detected at degassing sites along two neighboring faults in NW Bohemia, central Europe
Journal of Geophysical Research: Solid Earth,
119
(7)
5613 – 5632
2014
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
Bohemia; Czech Republic; Germany; Vogtland; carbon dioxide; carbon isotope; degassing; earthquake swarm; earthquake trigger; fault zone; geodynamics; helium isotope; igneous geochemistry; intraplate process; isotopic analysis; isotopic ratio; magmatism; nitrogen isotope; spatial distribution; temporal distribution
Abstract: ▾ The Vogtland and NW Bohemia region is known for its earthquake swarms; the most intensive swarm since 1985/86 occurred in October 2008. To find further indications for the interaction of ascending mantle-derived fluids and the occurrence of earthquake swarms, detailed fortnightly studies of gas compositions (CO2, N2, Ar, He, H2, and CH 4) and isotope ratios (δ13C, δ15N, and 3He/4He) were carried out between October 2008 and April 2011 at four locations close to the Nový Kostel focal zone and at the Wettinquelle spring (Bad Brambach). From the start of the 2008 earthquake swarm seismically induced isotope-geochemical anomalies were recorded at locations along the Počatky-Plesná fault zone (PPZ) and were, for the first time, also found at degassing locations on the Mariánské LáznÄ• fault zone (MLF). Variations were observed in both the temporal and spatial distributions of the anomalies as well in anomaly strengths, probably due to the positions of these fault zones relative to the focal zone, and to differences in fluid migration pathways. Prior to both the 2000 and 2008 swarms, 3He/4He ratios>6Ra were recorded at the Bublák mofette. These anomalous pre-seismic 3He/ 4He ratios suggest that both the 2000 and 2008 swarms may have been associated with the supply of fresh magma from a less degassed reservoir in the lithospheric mantle. The temporal δ13CCO2 pattern from detailed studies at Bublák between 2005 and 2011 indicates progressive magma degassing, as well as seismically induced variations in the δ13C, providing additional support to the interpretation derived from the 3He/4He ratios. Key Points Isotope anomalies detected in gases from different faults after earthquakes A pre-seismic increase in 3He/4He (> 6 Ra) indicates magma ascent from mantle Isotope monitoring is an excellent way to track active geodynamic processes ©2014. American Geophysical Union. All Rights Reserved.
1591.
Site selection for the well IDDP-1 at Krafla
Geothermics,
499-15
2014
ISSN: 0375-6505Keywords:▾
IDDP-1 well site at Krafla, Superheated and supercritical reservoir conditions, MT-resistivity data
Abstract: ▾ This paper describes the site selection for the IDDP-1 well within the Krafla volcano in 2008. In a feasibility study in 2003, 12 potential well sites within three geothermal areas were suggested and prioritized to meet the goal of finding supercritical temperatures and pressures together with high permeability. In 2006 one of these priority sites was selected within the Krafla field, but in autumn 2007 due to its proximity to the Krafla power plant a new location had to be selected only a few months before drilling. Choice of that new site was justified by new MT-resistivity survey data, seismic data and information from an earlier nearby production well, K-36.
1590.
Stratigraphy and otolith microchemistry of the naked carp Gymnocypris przewalskii (Kessler) and their indication for water level of Lake Qinghai during the Ming Dynasty of China
Science China Earth Sciences,
57
(10)
2512 – 2521
2014
ISSN: 16747313
Publisher: Science Press (China)
Keywords:▾
Carbonate minerals; Fish; Offshore oil well production; Stratigraphy; Topography; Water levels; Fishbone; Lake levels; Lake Qinghai naked carps; lapillus; Oxygen isotopes; Lakes
Abstract: ▾ Otoliths are biogenic carbonate minerals in the inner ear of teleost fish, whose compositions can record the physical and chemical conditions of the ambient water environment inhabited by individual fish. In this research, the fishbones and otoliths of naked carp sampled near the Bird Island, offshore Lake Qinghai, were dated and analyzed for mineralogy and microchemical compositions. Comparing the microchemical compositions of ancient otoliths with those of modern otoliths, we conclude that the ancient naked carps inhabited a relict lake formed when the lake shrank from a high lake level, by combining with the AMS-14C ages of fishbones and otoliths, the stratigraphy and surrounding topography of the sample site. AMS-14C dating results of ancient fishbones and otoliths show that these naked carps lived from 680 to 300 years ago, i.e. during the Ming Dynasty of China. The X-ray diffraction (XRD) patterns demonstrate that the ancient lapillus is composed of pure aragonite, identical to modern one, indicating that the mineral of lapillus didn’t change after a long time burial and that the ancient lapillus is suitable for comparative analysis thereafter. Microchemical results show that both ratios of Mg/Ca ((70.12±18.50)×10−5) and δ18O ((1.76±1.03)‰) of ancient lapilli are significantly higher than those of modern lapilli (average Mg/Ca=(3.11±0.41)× 10−5 and δ18O=(−4.82±0.96)‰). This reflects that the relict water body in which the ancient naked carp lived during the Ming Dynasty was characterized by higher Mg/Ca and δ18O ratios than modern Lake Qinghai, resulting from strong evaporation after being isolated from the main lake, similar to today’s Lake Gahai. Based upon the stratigraphy and altitude of naked carp remains, it can be inferred that the altitude of lake level of Lake Qinghai reached at least 3202 m with a lake area of 4480 km2 during the Ming Dynasty, approximately ∼5% larger than it is today. © 2014, Science China Press and Springer-Verlag Berlin Heidelberg.
1589.
The effects of solar irradiation changes on the migration of the Congo Air Boundary and water levels of paleo-Lake Suguta, Northern Kenya Rift, during the African Humid Period (15-5ka BP)
Palaeogeography, Palaeoclimatology, Palaeoecology,
3961 – 16
2014
ISSN: 00310182Keywords:▾
Atlantic Ocean; Congo Margin; Kenya; Rift Valley; Suguta Valley; Congo; East African Rift; Kenya; Kenya Rift; Rift Valley; Suguta Valley; atmospheric pressure; irradiation; migration determinant; paleoatmosphere; paleolimnology; pressure gradient; radiocarbon dating; shoreline; solar radiation; water level; atmospheric pressure; grain size; highstand; insolation; irradiation; monsoon; Northern Hemisphere; pressure gradient; rift zone; summer; water level
Abstract: ▾ The water-level record from the 300. m deep paleo-lake Suguta (Northern Kenya Rift) during the African Humid Period (AHP, 15-5. ka BP) helps to explain decadal to centennial intensity variations in the West African Monsoon (WAM) and the Indian Summer Monsoon (ISM). This water-level record was derived from three different sources: (1) grain size variations in radiocarbon dated and reservoir corrected lacustrine sediments, (2) the altitudes and ages of paleo-shorelines within the basin, and (3) the results of hydro-balance modeling, providing important insights into the character of water level variations (abrupt or gradual) in the amplifier paleo-Lake Suguta. The results of these comprehensive analyses suggest that the AHP highstand in the Suguta Valley was the direct consequence of a northeastwards shift in the Congo Air Boundary (CAB), which was in turn caused by an enhanced atmospheric pressure gradient between East Africa and India during a northern hemisphere insolation maximum. Rapidly decreasing water levels of up to 90. m over less than a hundred years are best explained by changes in solar irradiation either reducing the East African-Indian atmospheric pressure gradient and preventing the CAB from reaching the study area, or reducing the overall humidity in the atmosphere, or a combination of both these effects. In contrast, although not well documented in our record we hypothesize a gradual end of the AHP despite an abrupt change in the source of precipitation when a decreasing pressure gradient between Asia and Africa prevented the CAB from reaching the Suguta Valley. The abruptness was probably buffered by a contemporaneous change in precession producing an insolation maximum at the equator during October. Whether or not this is the case, the water-level record from the Suguta Valley demonstrates the importance of both orbitally-controlled insolation variations and short-term changes in solar irradiation as factors affecting the significant water level variations in East African rift lakes. © 2013 Elsevier B.V.
1588.
Stratigraphy, alteration mineralogy, permeability and temperature conditions of well IDDP-1, Krafla, NE-Iceland
Geothermics,
4931-41
2014
ISSN: 0375-6505Keywords:▾
IDDP-1, Krafla, Alteration, Magma, Superheated conditions
Abstract: ▾ The stratigraphy, alteration mineralogy and temperature conditions in well IDDP-1 were established through drill cutting analyses and geophysical logs. The stratigraphy comprises basaltic lava and hyaloclastite sequences extending to 1362m succeeded by an intrusive complex. Intrusions comprise basaltic dykes, dolerites and below 2020m, granophyre and felsites. Rhyolitic magma was intersected below 2100m. Alteration reflects cooling in the upper ∼1500m of the reservoir. Below 1600m temperature follows the boiling-point-depth curve. Alteration minerals are scarce in vicinity to the feed zone at 2035–2080m correlating with a superheated steam zone above the magma, but estimated bottom-hole temperature is ∼500°C.
1587.
Structural geology of impact craters
Journal of Structural Geology,
62156-182
2014
Abstract: ▾ The formation of impact craters is a highly dynamic and complex process that subjects the impacted target rocks to numerous types of deformation mechanisms. Understanding and interpreting these styles of micro-, meso- and macroscale deformation has proved itself challenging for the field of structural geology. In this paper, we give an overview of the structural inventory found in craters of all size ranges on Earth, and look into the structures of craters on other planetary bodies. Structural features are discussed here that are caused by i) extremely high pressures and temperatures that occur during the initial passage of the shock wave through the target rock and projectile, ii) the resulting flow field in the target that excavates and ejects rock materials, and iii) the gravitationally induced modification of the crater cavity into the final crater form. A special focus is put on the effects that low-angle impacting bodies have on crater formation. We hope that this review will help both planetary scientists and structural geologists understand the deformation processes and resulting structures generated by meteorite impact. © 2014.
1586.
Surirella subrotunda sp. nov. and Surirella parahelvetica sp. nov., two new diatom (Bacillariophyta) species from Lake Prespa, Macedonia
Phytotaxa,
156
(3)
145 – 155
2014
ISSN: 11793155
Publisher: Magnolia Press
Abstract: ▾ The genus Surirella is highly diverse and many taxa are reported as endemic, especially from ancient lakes and tropical continental regions. In ancient Lake Ohrid, 25 different Surirella species have been identified by different authors, five are considered to be endemic for the lake. In contrast, research on its sister Lake Prespa has been less rigorous and data for recent and fossil species of Surirella is very sparse. The number of Surirella taxa reported from Lake Prespa is 11; only one is considered an endemic for both lakes, Ohrid and Prespa. In this study, taxa from the genus Surirella were observed in a number of recent and fossil samples from Lake Prespa. Two taxa possess unique characters that distinguish them from known species. Their formal descriptions, based on detailed LM and SEM observations, are presented here. Surirella subrotunda sp. nov. is differentiated from other similar species by its valve outline, size, and shape of median area; it has been observed only in fossil diatom samples from core Co1215 recovered from Lake Prespa. Surirella parahelvetica sp. nov. is distinguished by its size, valve outline, number of alar canals and stria density. © 2014 Magnolia Press.
1585.
The 2011 expedition to the El'gygytgyn impact structure, Northeast Russia: Toward a new geological map for the crater area
Meteoritics and Planetary Science,
49
(6)
978-1006
2014
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ El'gygytgyn is a 3.6 Ma, 18 km diameter, impact crater formed in an approximately 88 Ma old volcanic target in Northeast Siberia. The structure has been the subject of a recent ICDP drilling project. In parallel to those efforts, a Russian-German expedition was undertaken in summer 2011 to investigate the permafrost soil, lake terraces, and the volcanic rocks of the southern and eastern crater rim. This provided the unique opportunity for mapping and sampling of the volcanic target rocks around a large part of this complex impact structure. Samples from 43 outcrops were collected and analyzed petrographically and geochemically. The results were combined with earlier mapping outcomes to create a new geological map of this impact structure and its immediate environs, at the scale of 1:50,000. Compositions of our rock suites are compared with the lithologies of the 2009 ICDP drill core. The ignimbrite described as lower bedrock in the ICDP drill core shows petrographically and chemically strong similarities to the rhyolitic and rhyodacitic ignimbrites observed on surface. The suevite sequence exposed in the ICDP drill core is a mixture of all observed target rocks at their respective proportions in the area. In contrast to previous studies, the calculated average target composition of El'gygytgyn takes the contribution of the basic target rocks into consideration: mafic and intermediate rocks approximately 7.5%, and felsic rocks approximately 92.5%. © The Meteoritical Society, 2014.
1584.
The Bow City structure, southern Alberta, Canada: The deep roots of a complex impact structure?
Meteoritics and Planetary Science,
49
(5)
872-895
2014
Abstract: ▾ Geological and geophysical evidence is presented for a newly discovered, probable remnant complex impact structure. The structure, located near Bow City, southern Alberta, has no obvious morphological expression at surface. The geometry of the structure in the shallow subsurface, mapped using downhole geophysical well logs, is a semicircular structural depression approximately 8 km in diameter with a semicircular uplifted central region. Detailed subsurface mapping revealed evidence of localized duplication of stratigraphic section in the central uplift area and omission of strata within the surrounding annular region. Field mapping of outcrop confirmed an inlier of older rocks present within the center of the structure. Evidence of deformation along the eastern margin of the central uplift includes thrust faulting, folding, and steeply dipping bedding. Normal faults were mapped along the northern margin of the annular region. Isopach maps reveal that structural thickening and thinning were accommodated primarily within the Belly River Group. Evidence from legacy 2-D seismic data is consistent with the subsurface mapping and reveals additional insight into the geometry of the structure, including a series of listric normal faults in the annular region and complex faulting within the central uplift. The absence of any ejecta blanket, breccia, suevite, or melt sheet (based on available data) is consistent with the Bow City structure being the remnant of a deeply eroded, complex impact structure. Accordingly, the Bow City structure may provide rare access and insight into zones of deformation remaining beneath an excavated transient crater in stratified siliciclastic target rocks. © The Meteoritical Society, 2014.
1583.
The concept of the Iceland deep drilling project
Geothermics,
492-8
2014
ISSN: 0375-6505Keywords:▾
Iceland Deep Drilling Project, Supercritical geothermal fluid systems
Abstract: ▾ Calculations discussed in the Iceland Deep Drilling Project feasibility study in 2003 indicated that, for same volumetric flow rate of steam, a geothermal well producing from natural supercritical fluid would have the potential to generate power outputs an order of magnitude greater than from conventional high-temperature wells (240–340°C). To reach supercritical hydrous fluid conditions in natural geothermal systems requires deep drilling to a minimum depth of some 3.5–5km were temperature conditions can be expected to range between 400 and 600°C in reasonably active high-temperature fields. Three geothermal fields in Iceland, Reykjanes, Hengill and Krafla, were selected as suitable locations for deep drilling to test this concept in search of natural supercritical geothermal fluid systems.
1582.
Late Glacial to Holocene climate change and human impact in the Mediterranean: The last ca. 17ka diatom record of Lake Prespa (Macedonia/Albania/Greece)
Palaeogeography, Palaeoclimatology, Palaeoecology,
40622 – 32
2014
ISSN: 00310182
Publisher: Elsevier
Keywords:▾
Albania; Greece; Lake Mikri Prespa; Macedonia [Greece]; anthropogenic effect; aridity; climate variation; community composition; diatom; Holocene; lake level; late glacial; Mediterranean environment; moisture content; paleoclimate; paleoecology; paleolimnology; paleoproductivity; palynology; Younger Dryas
Abstract: ▾ Lake Prespa (Macedonia/Albania/Greece) occupies an important location between Mediterranean and central European climate zones. Although previous multi-proxy research on the Late Glacial to Holocene sequence, core Co1215 (320cm; ca. 17cal ka BP to present), has demonstrated its great value as an archive of Quaternary palaeoclimate data, some uncertainty remains in the interpretation of climate change. With the exception of oxygen stable isotope data, previous palaeolimnological interpretation has relied largely on proxies for productivity. Here, existing interpretation is strengthened by the addition of diatom data. Results demonstrate that shifts in diatom assemblage composition are driven primarily by lake-level changes and thus permit more confident interpretation of shifts in moisture availability over time, while corroborating previous interpretation of catchment- and climate-induced productivity shifts. An inferred cold, arid shallow lake phase between ca. 17.1 and 15.7cal ka BP is not only followed by a high-productivity phase from ca. 15.7cal ka BP with Late Glacial warming, but also is the first evidence for a gradual increase in lake level, in line with other regional records. Clear evidence for a Younger Dryas climate reversal between ca. 13.1 and 12.3cal ka BP is followed by an unusually gradual transition to the Holocene and deeper, oligotrophic-mesotrophic lake conditions are reached by ca. 11.0cal ka BP. In contrast to the arid episode from ca. 10.0 to 8.0ka inferred from positive 18δOcalcite values, rapid diatom-inferred lake-level increase after the start of the Holocene suggests high moisture availability, in line with palynological evidence, but with only very subtle evidence for the impact of an 8.2ka cold event. The maintenance of high lake levels until 1.9cal ka BP, and the peak of inferred humidity from ca. 7.9 to 6.0cal ka BP, matches the oxygen stable isotope profile and confirms that the latter is driven primarily by evaporative concentration rather than reflecting regional shifts in precipitation sources over time. During the Late Holocene progressive eutrophication is inferred between 1.9 and present. Two shallow phases at ca. 1.0cal ka BP and at ca. 100years ago probably represent an aridity response which is added to increase human impact in the catchment. Overall, the study is important in confirming previous tentative inferences that Late Glacial to Holocene moisture availability has strong affinity with other sites in the Eastern Mediterranean. It also tracks the pattern of North Atlantic forcing. © 2014 Elsevier B.V.
1581.
Comparative study of geophysical and soil-gas investigations at the Hartoušov (Czech Republic) natural CO2 degassing site
Environmental Earth Sciences,
72
(5)
1421 – 1434
2014
ISSN: 18666280
Publisher: Springer Verlag
Keywords:▾
Czech Republic; Carbon; Carbon capture; Climate change; Degassing; Electric conductivity; Geology; Moisture; Risk assessment; Soil moisture; Soils; Electrical resistivity tomography; Evaluation of methods; Meteorological condition; Permeable structures; Preferential pathways; Self potential; Self-potential anomalies; Structural information; carbon dioxide; carbon sequestration; climate change; comparative study; degassing; electrical resistivity; leakage; permeability; radon; risk assessment; underground storage; Carbon dioxide
Abstract: ▾ Our study at this natural analog site contributes to the evaluation of methods within a hierarchical monitoring concept suited for the control of CO2 degassing. It supports the development of an effective monitoring concept for geological CO2 storage sites-carbon capture and storage as one of the pillars of the European climate change efforts. This study presents results of comprehensive investigations along a 500-m long profile within the Hartoušov (Czech Republic) natural CO2 degassing site and gives structural information about the subsurface and interaction processes in relation to parameters measured. Measurements of CO2 concentrations and investigation of the subsurface using electrical resistivity tomography and self-potential methods provide information about subsurface properties. For their successful application it is necessary to take seasonal variations (e.g., soil moisture, temperature, meteorological conditions) into consideration due to their influence on these parameters. Locations of high CO2 concentration in shallow depths are related to positive self-potential anomalies, low soil moistures and high resistivity distributions, as well as high δ13C values and increased radon concentrations. CO2 ascends from deep geological sources via preferential pathways and accumulates in coarser sediments. Repetition of measurements (which includes the effects of seasonal variations) revealed similar trends and allows us to identify a clear, prominent zone of anomalous values. Coarser unconsolidated sedimentary layers are beneficial for the accumulation of CO2 gas. The distribution of such shallow geological structures needs to be considered as a significant environmental risk potential whenever sudden degassing of large gas volumes occurs. © 2014 Springer-Verlag Berlin Heidelberg.
1580.
Late cretaceous-early paleocene ostracod biostratigraphy of scientific drilling Sk1(N) in the Songliao Basin, northeast China
Journal of Paleontology,
88
(4)
786-798
2014
ISSN: 00223360
Publisher: Paleontological Society
DOI:10.1666/13-076
Keywords:▾
biostratigraphy; community structure; Cretaceous; Danian; fossil record; Maastrichtian; new species; ostracod; Paleocene; paleoenvironment; taxonomy, China; Songliao Basin
Abstract: ▾ Cretaceous non-marine deposits are widespread in China and have been studied comprehensively. The Songliao Basin in northeast China is thought to be well suited for investigation of Cretaceous biostratigraphy. However, despite much research having been conducted in the basin, little is known about its Late Cretaceous biostratigraphy and paleoenvironment. Here, we establish a high-resolution biostratigraphy of the Late Cretaceous based on ostracods from borehole SK1(n) in the Songliao Basin, northeast China. As part of the present study, 45 species assigned to 20 genera have been recovered, with one new species (Ilyocypris bisulcata n. sp.) and five ostracod assemblages: the Cypridea gunsulinensis-Mongolocypris magna assemblage, which is marked by the first occurrence (F.O.) of Ilyocyprimorpha with nodes and spines; the Ilyocyprimorpha-Limnocypridea sunliaonensis-Periacanthella assemblage, which ranges from the F.O. of Ilyocyprimorpha with nodes and spines to the F.O. of Strumosia sp.; the Strumosia inandita assemblage from the F.O. of Strumosia sp. to the lower occurrence (L.O.) of Strumosia inandita; the Talicypridea amoena-Metacypris kaitunensis-Ziziphocypris simakovi assemblage from the F.O. of Mongolocypris apiculata (Cea) and Talicypridea amoena to the F.O. of Ilyocypris sp.; and the Ilyocypris assemblage from the F.O. of Ilyocypris sp. to the L.O. of Ilyocypris bisulcata n. sp. Moreover, the zonal fossil Ilyocypris bisulcata n. sp. of Zone 5 is here described for the first time from the upper Mingshui Formation, and Paleocene charophyte genera including Neochara and Grovesicahra have been found to coexist with the Zone 5 fauna. The age of the Ilyocypris Assemblage is assigned to the latest Maastrichtian to the earliest Danian. Copyright © 2014, The Paleontological Society.
1579.
Comparison of petrophysical properties of impactites for four meteoritic impact structures
Meteoritics and Planetary Science,
49
(5)
896 – 920
2014
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ We reanalyzed and compared unique data sets, which we obtained in the frame of combined petrophysical and geothermal investigations within scientific drilling projects on four impact structures: the Puchezh-Katunki impact structure (Vorotilovo borehole, Russia), the Ries impact structure (Noerdlingen-73 borehole, Germany), the Chicxulub impact structure (ICDP Yaxcopoil-1 borehole, Mexico), and the Chesapeake impact structure (ICDP-USGS-Eyreville borehole, USA). For a joined interpretation, we used the following previously published data: thermal properties, using the optical scanning technique, and porosities, both measured on densely sampled halfcores of the boreholes. For the two ICDP boreholes, we also used our previously published P-wave velocities measured on a subset of cores. We show that thermal conductivity, thermal anisotropy, porosity, and velocity can be correlated with shock metamorphism (target rocks of the Puchezh-Katunki and Ries impact structures), and confirm the absence of shock metamorphism in the samples taken from megablocks (Chicxulub and Chesapeake impact structure). The physical properties of the lithic impact breccias and suevites are influenced mainly by their impact-related porosity. Physical properties of lower porosity lithic impact breccias and suevites are also influenced by their chemical composition. These data allow for a distinction between different types of breccias due to differences concerning the texture and chemistry and the different amounts of melt and rock clasts. © The Meteoritical Society, 2014.
1578.
Chemical composition of sediments in Baikal deep-water boreholes as a basis for reconstructions of climatic and environmental changes
Russian Geology and Geophysics,
55
(1)
1 – 17
2014
ISSN: 10687971Keywords:▾
Akademichesky Ridge; Barguzin River; Buryatia; Lake Baikal; Russian Federation; Bacillariophyta; borehole; chemical composition; clay mineral; climate variation; deep water; drainage basin; environmental change; environmental indicator; Miocene; Pleistocene; Pliocene; reconstruction; sediment chemistry; silica; stratigraphic correlation
Abstract: ▾ Earlier reconstructions of climatic and environmental changes from data of deep-water drilling on the Akademichesky Ridge in Lake Baikal were based both on the content of biogenic silica or the abundance of diatom valves and on the results of X-ray diffraction (XRD) analysis of the sediment mineralogy. It was established that clay minerals are the main carrier of information about climatic variations in a drainage basin. The content of biogenic silica strictly correlates with two chrystallochemical parameters: the abundance of smectite beds in illite-smectite and the abundance of illite. However, detailed analysis of clay minerals calls for exclusive XRD techniques without mass determination of minerals in the sediments of long Baikal cores. We propose a new approach to determine the mineral composition of bottom sediments, based on their chemical composition. We compared the average chemical compositions of Pleistocene, Pliocene, and Miocene core sediments from the boreholes BDP-96 and BDP-98 and sediments of the Paleo-Barguzin River avandelta and recognized groups of chemical elements marking warm and cold climatic periods. However, the difference in the chemical compositions of sediments in warm and cold periods is insignificant. Since an XRD analysis of mineral composition is usually performed for short time intervals, it was necessary to identify cold and warm intervals by the mineral composition calculated from the chemical composition of sediments. The mineral contents were estimated using the Selektor software. Based on the average contents of chemical elements, we computed the mineral composition of the bottom sediments throughout the BDP-98 section and studied its warm and cold periods. We have established that feldspars weakly respond to climatic changes, their contents show minor variations in warm and cold epochs, whereas the contents of mica minerals change seriously. Thus, clay minerals, together with biogenic silica, are a good indicator of paleoclimatic environmental changes. © 2014 V.S. Sobolev IGM, Siberian Branch of the RAS.
1577.
Chronostratigraphy of Huoshiling Formation in the Songliao Basin, NE China: An overview
Earth Science Frontiers,
21
(2)
234-250
2014
ISSN: 10052321
Publisher: Science Frontiers editorial department
Keywords:▾
Isotopes; Volcanic rocks, Chronostratigraphy; Huoshiling Formation; Jurassic-Cretaceous; Jurassic-Cretaceous boundary; Magnetostratigraphy; Shahezi formations; Songliao basin; Volcanic eruptions, Plants (botany)
Abstract: ▾ The chronostratigraphy, sequence and distribution of Huoshiling Formation (H-Form) in the Songliao Basin are discussed and summarized on the basis of biostratigraphy, isotopic dating, lithostratigraphy as well as magnetostratigraphy. The H-Form is the first rifting basin stage with the filling sequence of mainly volcanic rocks in northeastern China and adjacent areas. Laterally, it is characterized by the widespread distribution, remarkable variation in volcanic eruption time and scale between fault depressions. The H-Form yielded plant megafossils in a wide range of periods. The sporo-pollen assemblages show a blooming age of the early Cretaceous. Characteristic megaspore fossil and magnetostratigraphy indicate the age of the Jurassic. Overlying sequence of the H-Form is also concerned in order to constrain its time span. The bottom of Yingcheng Formation is 130 Ma, the duration of Shahezi Formation is about 10 Ma, so that the top age of the H-Form should be ca. 140 Ma. The minimum duration of H-Form is calculated ca. 8 Ma, and its bottom age ought to approach about 150 Ma. The isotopic age dating on the volcanic rocks of H-Form mainly ranges from 140 Ma to 150 Ma. All these evidences above suggest that the age of H-Form can be well constrained from the Tithonian to the Berriasian or to the bottom of the Valanginian. The Jurassic-Cretaceous boundary(J/K boundary) in the Songliao Basin probably exists inside the Huoshiling Formation.
1576.
Chronostratigraphy of the 600,000 year old continental record of Lake Van (Turkey)
Quaternary Science Reviews,
1048-17
2014
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Argon; Glacial geology; Ice control; Isotopes; Lakes; Organic carbon; Sediments; Single crystals; Stratigraphy, ICDP project PALEOVAN; Long terrestrial paleoenvironmental records; Magnetostratigraphy; Radiometric dating; Tephrostratigraphy, Ice, argon-argon dating; chronostratigraphy; lithostratigraphy; magnetostratigraphy; NorthGRIP; paleoclimate; Quaternary; radiometric method; sediment core; sediment property; sedimentary sequence; tephrochronology; total organic carbon, Lake Van; Turkey
Abstract: ▾ Lake Van sediment cores from the Ahlat Ridge and Northern Basin drill sites of the ICDP project PALEOVAN contain a wealth of information about past environmental processes. The sedimentary sequence was dated using climatostratigraphic alignment, varve chronology, tephrostratigraphy, argon-argon single-crystal dating, radiocarbon dating, magnetostratigraphy, and cosmogenic nuclides. Based on the lithostratigraphic framework, the different age constraints are compiled and a robust and precise chronology of the 600,000 year-old Lake Van record is constructed. Proxy records of total organic carbon content and sediment color, together with the calcium/potassium-ratios and arboreal pollen percentages of the 166-m-long event-corrected Ahlat Ridge record, mimic the Greenland isotope stratotype (NGRIP). Therefore, the proxy records are systematically aligned to the onsets of interstadials reflected in the NGRIP and synthesized Greenland ice-core stratigraphy. The chronology is constructed using 49 age control points derived from visual synchronization with the Greenland ice-core stratigraphy using the GICC05 timescale, an absolutely-dated speleothem timescale (e.g., Hulu, Sanbao, Linzhu cave) and the Epica Dome C timescale. In addition, the uppermost part of the sequence is complemented with four ages from Holocene varve chronology and three calibrated radiocarbon ages. Furthermore, nine argon-argon ages and a comparison of the relative paleointensity record of the magnetic field with reference curve PISO-1500 confirm the accuracy of the age model. Also the identification of the Laschamp event via measurements of 10Be in the sediment confirms the presented age model. The chronology of the Ahlat Ridge record is transferred to the 79-m-long event-corrected composite record from the Northern Basin and supplemented by additional radiocarbon dating on organic marco-remains. The basal age of the Northern Basin record is estimated at ~90ka. The variations of the time series of total organic carbon content, the Ca/K ratio, and the arboreal pollen percentages illustrate that the presented chronology links ice-marine-terrestrial stratigraphies and that the paleoclimate data are suited for reconstructions and modeling of the Quaternary and Pleistocene climate evolution in the Near East at millennial timescales. Furthermore, the chronology of the last 250ka can be used to test other dating techniques. © 2014 Elsevier Ltd.
1575.
Clay mineral records of the Erlangjian drill core sediments from the Lake Qinghai Basin, China
Science China Earth Sciences,
57
(8)
1846 – 1859
2014
ISSN: 16747313
Publisher: Science in China Press
Keywords:▾
China; Qinghai; Qinghai Lake; Qinghai-Xizang Plateau; Clay minerals; Climate change; Grain size and shape; Kaolinite; Tectonics; Clay mineral assemblages; Grain size distribution; Lake Qinghai; Paleoclimates; Paleoenvironmental change; Qinghai Tibet plateau; Tectonic uplift; Weathering conditions; clay mineral; grain size; Miocene; paleoclimate; paleoenvironment; proxy climate record; sediment core; uplift; weathering; Lakes
Abstract: ▾ Located at the northeastern margin of the Qinghai-Tibet Plateau (QTP) in the Asian interior, the Lake Qinghai is sensitive to environmental change and thus an outstanding site for studying paleoenvironmental changes. Thick deposits in the Lake Qinghai provide important geological archives for obtaining high-resolution records of continental environmental history. The longest drilling core obtained from the Lake Qinghai, named Erlangjian (ELJ), reached about 1109 m and was investigated to determine its clay mineral assemblage and grain size distributions. Clay mineralogical proxies, including type, composition, and their ratios, as well as the illite crystallinity (KI) and chemical index (CI), in combination with grain size data, were used for reconstructing the history of paleoenvironmental evolution since the late Miocene in the Lake Qinghai Basin. The clay mineral records indicate that the clay mainly comprise detritus originating from peripheral material and has experienced little or no diagenesis. The proportion of authigenic origin was minor. Illite was the most abundant clay mineral, followed by chlorite, kaolinite, and smectite. Variations of clay mineral indexes reflect the cooling and drying trends in the Lake Qinghai region, and the grain size distribution is coincided with the clay minerals indexes. The paleoclimatic evolution of the Lake Qinghai Basin since the late Miocene can be divided into five intervals. The climate was relatively warm and wet in the early of late Miocene, then long-term trends in climate change character display cooling and drying; later in the late Miocene until early Pliocene the climate was in a short relatively warm and humid period; since then the climate was relatively colder and drier. These results also suggest multiple tectonic uplift events in the northeastern QTP. © 2014 Science China Press and Springer-Verlag Berlin Heidelberg.
1574.
Climate variability over the last 92 ka in SW Balkans from analysis of sediments from Lake Prespa
Climate of the Past,
10
(2)
643 – 660
2014
ISSN: 18149324
Publisher: European Geosciences Union
Keywords:▾
Balkan; Turkmenistan; algal bloom; climate variation; electron spin resonance dating; mountain region; Northern Hemisphere; paleoclimate; palynology; phytoplankton; primary production; radiocarbon dating; sediment core; tephrochronology; transboundary cooperation
Abstract: ▾ The transboundary Lake Prespa (Albania/former Yugoslav Republic of Macedonia/Greece) has been recognized as a conservation priority wetland. The high biodiversity encountered in the catchment at present points to the refugial character of this mountainous region in the southwestern Balkans. A lake sediment core retrieved from a coring location in the northern part of the lake was investigated through sedimentological, geochemical, and palynological analyses. Based on tephrochronology, radiocarbon and electron spin resonance (ESR) dating, and cross correlation with other Northern Hemisphere records, the age model suggests that the basal part of core Co1215 reaches back to 92 ka cal BP. Here we present the responses of this mid-altitude site (849 m a.s.l.) to climate oscillations during this interval and assess its sensitivity to millennial-scale variability. Endogenic calcite precipitation occurred in marine isotope stages (MIS) 5 and 1 and is synchronous with periods of increased primary production (terrestrial and/or lacustrine). Periods of pronounced phytoplankton blooms (inferred from green algae and dinoflagellate concentrations) are recorded in MIS 5 and MIS 1 and suggest that the trophic state and lake levels underwent substantial fluctuations. Three major phases of vegetation development are distinguished: the forested phases of MIS 5 and MIS 1 dominated by deciduous trees with higher temperatures and moisture availability, the open landscapes of MIS 3 with significant presence of temperate trees, and the pine-dominated open landscapes of MIS 4 and MIS 2 with lower temperatures and moisture availability. Our findings suggest significant changes in forest cover and landscape openness, as well as in the properties of the vegetation belts (composition and distribution) over the period examined. The study area most likely formed the upper limit of several drought-sensitive trees (temperate tree refugium) at these latitudes in the Mediterranean mountains. © Author(s) 2014.
1573.
Comparative mineral chemistry and textures of SAFOD fault gouge and damage-zone rocks
Journal of Structural Geology,
68
(PA)
82-96
2014
ISSN: 01918141
Publisher: Elsevier Ltd
Keywords:▾
Corrensite; Fault gouge; SAFOD; San Andreas fault; Saponite; Shearing-enhanced reactions, corrensite; creep; damage; deformation; fault gouge; mineralogy; San Andreas Fault; saponite; sedimentary rock; serpentinite; shear zone; texture
Abstract: ▾ Creep in the San Andreas Fault Observatory at Depth (SAFOD) drillhole is localized to two foliated gouges, the central deforming zone (CDZ) and southwest deforming zone (SDZ). The gouges consist of porphyroclasts of serpentinite and sedimentary rock dispersed in a foliated matrix of Mg-smectite clays that formed as a result of shearing-enhanced reactions between the serpentinite and quartzofeldspathic rocks. The CDZ takes up most of the creep and exhibits differences in mineralogy and texture from the SDZ that are attributable to its higher shearing rate. In addition, a ~0.2-m-wide sector of the CDZ at its northeastern margin (NE-CDZ) is identical to the SDZ and may represent a gradient in creep rate across the CDZ. The SDZ and NE-CDZ have lower clay contents and larger porphyroclasts than most of the CDZ, and they contain veinlets and strain fringes of calcite in the gouge matrix not seen elsewhere in the CDZ. Matrix clays in the SDZ and NE-CDZ are saponite and corrensite, whereas the rest of the CDZ lacks corrensite. Saponite is younger than corrensite, reflecting clay crystallization under declining temperatures, and clays in the more actively deforming portions of the CDZ have better equilibrated to the lower-temperature conditions. © 2014.
1572.
Comparison of petrophysical properties of impactites for four meteoritic impact structures
Meteoritics and Planetary Science,
49
(5)
896-920
2014
Abstract: ▾ We reanalyzed and compared unique data sets, which we obtained in the frame of combined petrophysical and geothermal investigations within scientific drilling projects on four impact structures: the Puchezh-Katunki impact structure (Vorotilovo borehole, Russia), the Ries impact structure (Noerdlingen-73 borehole, Germany), the Chicxulub impact structure (ICDP Yaxcopoil-1 borehole, Mexico), and the Chesapeake impact structure (ICDP-USGS-Eyreville borehole, USA). For a joined interpretation, we used the following previously published data: thermal properties, using the optical scanning technique, and porosities, both measured on densely sampled halfcores of the boreholes. For the two ICDP boreholes, we also used our previously published P-wave velocities measured on a subset of cores. We show that thermal conductivity, thermal anisotropy, porosity, and velocity can be correlated with shock metamorphism (target rocks of the Puchezh-Katunki and Ries impact structures), and confirm the absence of shock metamorphism in the samples taken from megablocks (Chicxulub and Chesapeake impact structure). The physical properties of the lithic impact breccias and suevites are influenced mainly by their impact-related porosity. Physical properties of lower porosity lithic impact breccias and suevites are also influenced by their chemical composition. These data allow for a distinction between different types of breccias due to differences concerning the texture and chemistry and the different amounts of melt and rock clasts. © The Meteoritical Society, 2014.
1571.
Caldera subsidence in extensional tectonics
Bulletin of Volcanology,
76
(10)
1 – 7
2014
1570.
Compressional and shear-wave velocities from gas hydrate bearing sediments: Examples from the India and Cascadia margins as well as Arctic permafrost regions
Marine and Petroleum Geology,
58
(PA)
292-320
2014
ISSN: 02648172
Publisher: Elsevier Ltd
Abstract: ▾ Shear wave velocity data have been acquired at several marine gas hydrate drilling expeditions, including the India National Gas Hydrate Program Expedition 1 (NGHP-01), the Ocean Drilling Program (ODP) Leg 204, and Integrated Ocean Drilling Program (IODP) Expedition 311 (X311). In this study we use data from these marine drilling expeditions to develop an understanding of general grain-size control on the P- and S-wave properties of sediments. A clear difference in the downhole trends of P-wave (Vp) and S-wave (Vs) velocity and the Vp/Vs ratio from all three marine regions was observed: the northern Cascadia margin (IODP X311) shows the highest P-wave and S-wave velocity values overall and those from the India margin (Expedition NGHP-01) are the lowest. The southern Cascadia margin (ODP Leg 204) appears to have similar low P-wave and S-wave velocity values as seen off India. S-wave velocity values increase relative to the sites off India, but they are not as high as those seen on the northern Cascadia margin. Such regional differences can be explained by the amount of silt/sand (or lack thereof) occurring at these sites, with northern Cascadia being the region of the highest silt/sand occurrences. This grain-size control on P-wave and S-wave velocity and associated mineral composition differences is amplified when compared to the Arctic permafrost environments, where gas hydrate predominantly occurs in sand- and silt-dominated formations. Using a cross-plot of gamma ray values versus the Vp/Vs ratio, we compare the marine gas hydrate occurrences in these regions: offshore eastern India margin, offshore Cascadia margin, the Ignik-Sikumi site in Alaska, and the Mallik 5L-38 site in the Mackenzie Delta. The log-data from the Arctic permafrost regions show a strongly linear Vp-Vs relationship, similar to the previously defined empirical relationships by Greenberg and Castagna (1992). P- and S-wave velocity data from the India margin and ODP Leg 204 deviate strongly from these linear trends, whereas data from IODP X311 plot closer to the trend of the Arctic data sets and previously published relationships. Three new linear relationships for different grain size marine sediment hosts are suggested:. a)mud-dominated (Mahanadi Basin, ODP Leg 204 & NGHP-01-17): Vs=1.5854×Vp-2.1649b)silty-mud (KG Basin): Vs=0.8105×Vp-1.0223c)silty-sand (IODP X311): Vs=0.5316×Vp-0.4916We investigate the relationship of gas hydrate saturation determined from electrical resistivity on the Vp/Vs ratio and found that the sand-dominated Arctic hosts show a clearly decreasing trend of Vp/Vs ratio with gas hydrate saturation. Though limited due to lower overall GH saturations, a similar trend is seen for sites from IODP X311 and at the ash-dominated NGHP-01-17 sediment in the Andaman Sea. Gas hydrate that occurs predominantly in fractured clay hosts show a different trend where the Vp/Vs ratio is much higher than at sand-dominated sites and remains constant or increases slightly with increasing gas hydrate saturation. This trend may be the result of anisotropy in fracture-dominated systems, where P- and S-wave velocities appear higher and Archie-based saturations of gas hydrate are overestimated. Gas hydrate concentrations were also estimated in these three marine settings and at Arctic sites using an effective medium model, combining P- and S-wave velocities as equally weighted constraints on the calculation. The effective medium approach generally overestimates S-wave velocity in high-porosity, clay-dominated sediments, but can be accurately used in sand-rich formations. © 2014.