All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1444.
[English]
The future of geothermal energy: The shale gas analogy significant electrical EGS resource areas in the US
Volume 37
,
Page 117-122
2013
Huffington Department of Earth Sciences, Southern Methodist University, Dallas, TX, United StatesISBN:
9781629932859
1443.
[English]
Thermo-hydro-mechanical sand production model in hydrate-bearing sediments
Publisher
European Association of Geoscientists and Engineers, EAGE
2013
Technion - Israel Institute of Technology, Israel; Japan Oil, Gas and Metals National Corporation, Japan1442.
5.1 FAR-DEEP core archive and database
Reading the Archive of Earth’s Oxygenation
Page 493--502
Publisher
Springer
2013
493--5021441.
6.1 The imandra/varzuga Greenstone Belt
Reading the Archive of Earth’s Oxygenation
Page 505--590
Publisher
Springer
2013
505--5901440.
A unique find of the earliest multicellular algae in the Lower Proterozoic (2.45 Ga) of the Kola Peninsula
,
Doklady Biological Sciences
Volume449
,
Page 96--98
SP MAIK Nauka/Interperiodica
2013
1439.
Total organic carbon isotopes: A novel proxy of lake level from Lake Qinghai in the Qinghai-Tibet Plateau, China
Chemical Geology,
347153 – 160
2013
ISSN: 00092541Keywords:▾
China; Qinghai; Qinghai Lake; Qinghai-Xizang Plateau; Cladophora; Potamogeton; Ruppia; Carbon; Isotopes; Organic carbon; Photosynthesis; Sedimentology; Slow light; Surficial sediments; Carbon isotopic composition; Depositional environment; Isotopic composition; Lake levels; Lake Qinghai; Lake-sediment records; Qinghai Tibet plateau; Total Organic Carbon; carbon isotope; environmental change; green alga; isotopic composition; lacustrine deposit; lake level; precipitation (chemistry); sediment chemistry; total organic carbon; water depth; Lakes
Abstract: ▾ The isotopic compositions of total organic carbon (TOC) in lakes have been widely used to interpret paleoclimatic changes and the depositional environments of lake sediments. However, the main factors that affect the carbon isotopes of TOC (source of organic material, water condition and others) may vary in different lake sediment records, which have limited the applicability of organic carbon isotopes in explaining biogeochemical and environmental changes in lakes. In this study, the organic carbon isotopic compositions of aquatic plants and surface sediments from Lake Qinghai and the living terrestrial plants and surface soils around the lake were systematically investigated to identify the sources of TOC in the sediments and the significance of the organic carbon isotopes of sedimentary TOC. We found that the aquatic plants in the deep water areas (>10m) were primarily dominated by Cladophora, but submerged plants (Potamogeton and Ruppia L.) are the dominant species in shallow water (<10m). The Cladophora have negative δ13Corg values (-33.6‰ to -28.6‰) that are caused by C3-like photosynthesis, but the submerged plants have enriched δ13Corg values (-17.8‰ to -15.4‰) that are caused by C4-like photosynthesis. In addition, the δ13Corg values of Cladophora become more negative with increasing water depth because of the slow photosynthetic rate caused by the weak light intensity at depth. The isotopic data indicate that the carbon isotopes of organic material in the surface sediments are primarily controlled by the types of aquatic plant and that the δ13Corg values of TOC can be used to indicate the variation of the water depth (lake level). The organic carbon isotopic data from the 1F core showed that the water was shallow (<10m) because of intense evaporation related to high temperatures even though precipitation sharply increased in the warm period during the early-mid Holocene. The lake level reached its maximum level at 3ka. © 2013 Elsevier B.V.
1438.
Time evolution of chemical exchanges during mixing of rhyolitic and basaltic melts
Contributions to Mineralogy and Petrology,
166
(2)
615-638
2013
ISSN: 00107999Keywords:▾
chaotic dynamics; concentration (composition); element mobility; experimental study; magma chemistry; mixing; rhyolite; tectonic evolution; tectonic setting; time series analysis
Abstract: ▾ We present the first set of chaotic mixing experiments performed using natural basaltic and rhyolitic melts. The mixing process is triggered by a recently developed apparatus that generates chaotic streamlines in the melts, mimicking the development of magma mixing in nature. The study of the interplay of physical dynamics and chemical exchanges between melts is carried out performing time series mixing experiments under controlled chaotic dynamic conditions. The variation of major and trace elements is studied in detail by electron microprobe and Laser Ablation ICP-MS. The mobility of each element during mixing is estimated by calculating the decrease in the concentration variance in time. Both major and trace element variances decay exponentially, with the value of exponent of the exponential function quantifying the element mobility. Our results confirm and quantify how different chemical elements homogenize in the melt at differing rates. The differential mobility of elements in the mixing system is considered to be responsible for the highly variable degree of correlation (linear, nonlinear, or scattered) of chemical elements in many published inter-elemental plots. Elements with similar mobility tend to be linearly correlated, whereas, as the difference in mobility increases, the plots become progressively more nonlinear and/or scattered. The results from this study indicate that the decay of concentration variance is in fact a robust tool for obtaining new insights into chemical exchanges during mixing of silicate melts. Concentration variance is (in a single measure) an expression of the influence of all possible factors (e.g., viscosity, composition, and fluid dynamic regime) controlling the mobility of chemical elements and thus can be an additional petrologic tool to address the great complexity characterizing magma mixing processes. © 2013 Springer-Verlag Berlin Heidelberg.
1437.
Seismic evidence of shallow gas from Lake Van, eastern Turkey
Marine and Petroleum Geology,
48341-353
2013
ISSN: 02648172Keywords:▾
Bright spots; Enhanced reflections; Lake vans; Pockmarks; Shallow gas, Chimneys; Hydrostatic pressure; Lakes; Sediments; Seismology; Volcanoes, Gases, deltaic deposit; facies analysis; hydrocarbon reservoir; hydrostatic pressure; lacustrine deposit; mud volcano; permeability; pockmark; seismic reflection; tephra; turbidite; venting, Lake Van; Turkey
Abstract: ▾ Analysis of multi-channel seismic reflection and chirp data from Lake Van (eastern Turkey) reveals various shallow gas indicators including seismic chimneys, enhanced reflections, bright spots, mud volcanoes, pockmarks, and acoustic blanking. The enhanced reflections, suggesting the presence of free gas, are most dominant and observed at more than 200 locations. They are characterized by very-high amplitude reflections and occur in both deep and shallow sedimentary sections. Some enhanced reflections are accompanied by very subtle seafloor expressions such as mounds, which may suggest active venting activity. Seismic chimneys or columnar zones of amplitude blanking have been observed in much of the surveyed area. Seismic chimneys in the study area cannot be associated with any known faults that would act as migration pathways for deep fluids. This suggests that the observed structures in Lake Van sediments allow the preferential emission of gases which might be for a large share of biogenic origin. The acoustic blanking, characterized by transparent or chaotic seismic facies, is seen in the eastern part of the lake. The lakeward edge of the acoustic blanking largely coincides with the 100m water depth contour, indicating that (past) changes of the hydrostatic pressure may be responsible for the distribution of these anomalies. Mound-like features, interpreted as mud volcanoes, occur in a few locations. The presence of these features may suggest active gas emission. Very strong amplitude anomalies or bright spots with negative polarity, indicating gas-charged zones, are also seen in a number of locations. Pockmarks are observed only in the northeastern part of the study area. The scarce occurrence of pockmarks in the study area might be ascribed to a higher permeability of the lake sediments or to the absence of the substrate/reservoir providing the critical mass of gases necessary to produce such features. Turbidites, tephra layers, and deltaic deposits have the potential to provide ideal conditions to allow the sediments to act as a gas reservoir. © 2013 Elsevier Ltd.
1436.
Structural Preconditions of West Bohemia Earthquake Swarms
Surveys in Geophysics,
34
(4)
491-519
2013
ISSN: 01693298
Publisher: Kluwer Academic Publishers
Keywords:▾
Aquifers; Faulting; Groundwater resources; Hydrostatic pressure; Image enhancement; Inverse problems; Refraction; Roofs; Seismic waves; Structure (composition); Tomography; Velocity; Water levels, 9hr reflection profiles; Bohemian massifs; CEL09 refraction profiles; Earthquake swarms; Gravity model; Saxothuringian, Earthquakes, earthquake magnitude; earthquake mechanism; earthquake swarm; gravity field; Hercynian orogeny; hydrostatic pressure; inverse analysis; refraction; slab; subduction; tomography, Bohemian Massif; Cheb Basin; Czech Republic; Germany; Karlovarsky; Vogtland
Abstract: ▾ The West Bohemia and adjacent Vogtland are well known for quasi-periodical earthquake swarms persisting for centuries. The seismogenic area near Nový Kostel involved about 90 % of overall earthquake activity clustered here in space and time. The latest major earthquake swarm took place in August-September 2011. In 1994 and 1997, two minor earthquake swarms appeared in another location, near Lazy. Recently, the depth-recursive tomography yielded a velocity image with an improved resolution along the CEL09 refraction profile passing between these swarm areas. The resolution, achieved in the velocity image and its agreement with the inverse gravity modeling along the collateral 9HR reflection profile, enabled us to reveal the key structural background of these West Bohemia earthquake swarms. The CEL09 velocity image detected two deeply rooted high-velocity bodies adjacent to the Nový Kostel and Lazy focal zones. They correspond to two Variscan mafic intrusions influenced by the SE inclined slab of Saxothuringian crust that subducted beneath the Teplá-Barrandian terrane in the Devonian era. In their uppermost SE inclined parts, they roof both focal zones. The high P-wave velocities of 6,100-6,200 m/s, detected in both roofing caps, indicate their relative compactness and impermeability. The focal domains themselves are located in the almost gradient-free zones with the swarm foci spread near the axial planes of profound velocity depressions. The lower velocities of 5,950-6,050 m/s, observed in the upper parts of focal zones, are indicative of less compact rock complexes corrugated and tectonically disturbed by the SE bordering magma ascents. The high-velocity/high-density caps obviously seal the swarm focal domains because almost no magmatic fluids of mantle origin occur in the Nový Kostel and Lazy seismogenic areas of the West Bohemia/Vogtland territory, otherwise rich in the mantle-derived fluids. This supports the hypothesis of the fluid triggering of earthquake swarms. The sealed focal domains retain ascending magmatic fluids until their critical pressure and volumes accumulated cause rock micro-fractures perceived as single earthquake bursts. During a swarm period, the focal depths of these sequential events become shallower while their magnitudes grow. We assume that coalescence of the induced micro-fractures forms temporary permeability zones in the final swarm phase and the accumulated fluids release into the overburden via the adjacent fault systems. The fluid release usually occurs after the shallowest events with the strongest magnitudes ML > 3. The seasonal summer declines of hydrostatic pressure in the Cheb Basin aquifer system seem to facilitate and trigger the fluid escape as happened for the 2000, 2008, and 2011 earthquake swarms. The temporary fluid release, known as the valve-fault action, influences the surface aquifer systems in various manners. In particular, we found three quantities, the strain, mantle-derived 3He content in CO2 surface sources and ground water levels, which display a 3-5 months decline before and then a similar restoration after each peak earthquake during the swarm activities. The revealed structure features are particularly important since the main Nový Kostel earthquake swarm area is proposed as a site for the ICDP project, 'Eger Rift Drilling'. © 2013 Springer Science+Business Media Dordrecht.
1435.
Shock experiments up to 30 GPa and their consequences on microstructures and magnetic properties in pyrrhotite
Geochemistry, Geophysics, Geosystems,
14
(1)
64-85
2013
ISSN: 15252027
Publisher: Blackwell Publishing Ltd
Keywords:▾
Coercive force; Experiments; Magnetic properties; Microstructure, Coercivity of remanence; Extraterrestrial material; Grain-size reduction; Mechanical deformation; Mechanical twinning; pyrrhotite; Saturation isothermal remanent magnetizations; shock, Iron ores, crystal structure; deformation; experimental study; grain size; lithology; magnetic property; microstructure; pyrrhotite; remanent magnetization; temperature effect
Abstract: ▾ Shock experiments with pressures ranging from 3 to 30 GPa have been conducted on a mixed assemblage of hexagonal and monoclinic pyrrhotite. All samples were studied with respect to their particular shock-induced microstructures and magnetic properties at high and low temperatures. Up to 8 GPa, microstructures in shocked pyrrhotite are characterized by mechanical deformation producing a damage of the crystal structure. At pressures of 20 GPa and upward, amorphization and mechanical twinning are the dominant structural features induced by shock. Within the lower-pressure range coercivity, saturation isothermal remanent magnetization and coercivity of remanence increase with shock pressures, in agreement with more single-domain (SD)-like behavior. Simultaneously, the λ-peak of hexagonal pyrrhotite decreases and the 34 K transition of monoclinic pyrrhotite broadens and is depressed. Magnetic hardening is triggered by grain-size reduction, but also by the formation of SD within discrete multidomain grains. Planar deformation features subdivide such multidomain grains into lath-shaped domains with average sizes lying in the SD range. The planar deformation features disappear at 20 GPa and irregular, nanometer-sized "amorphous domains" occur instead. Pressure release from 30 GPa finally triggers partial melting of pyrrhotite. The sharp interfaces between molten and crystalline pyrrhotite document a rapid change of thermal conditions. Within molten pyrrhotite, quenched iron crystals occur. The presence of native iron strongly influences the magnetic properties, depending on the particular amount in the studied sample and likely affects the magnetic properties of impact lithologies on Earth and extraterrestrial material. ©2013. American Geophysical Union. All Rights Reserved.
1434.
Shock experiments up to 30 GPa and their consequences on microstructures and magnetic properties in pyrrhotite
Geochemistry, Geophysics, Geosystems,
14
(1)
64-85
2013
Abstract: ▾ Shock experiments with pressures ranging from 3 to 30 GPa have been conducted on a mixed assemblage of hexagonal and monoclinic pyrrhotite. All samples were studied with respect to their particular shock-induced microstructures and magnetic properties at high and low temperatures. Up to 8 GPa, microstructures in shocked pyrrhotite are characterized by mechanical deformation producing a damage of the crystal structure. At pressures of 20 GPa and upward, amorphization and mechanical twinning are the dominant structural features induced by shock. Within the lower-pressure range coercivity, saturation isothermal remanent magnetization and coercivity of remanence increase with shock pressures, in agreement with more single-domain (SD)-like behavior. Simultaneously, the λ-peak of hexagonal pyrrhotite decreases and the 34 K transition of monoclinic pyrrhotite broadens and is depressed. Magnetic hardening is triggered by grain-size reduction, but also by the formation of SD within discrete multidomain grains. Planar deformation features subdivide such multidomain grains into lath-shaped domains with average sizes lying in the SD range. The planar deformation features disappear at 20 GPa and irregular, nanometer-sized "amorphous domains" occur instead. Pressure release from 30 GPa finally triggers partial melting of pyrrhotite. The sharp interfaces between molten and crystalline pyrrhotite document a rapid change of thermal conditions. Within molten pyrrhotite, quenched iron crystals occur. The presence of native iron strongly influences the magnetic properties, depending on the particular amount in the studied sample and likely affects the magnetic properties of impact lithologies on Earth and extraterrestrial material. ©2013. American Geophysical Union. All Rights Reserved.
1433.
Source mechanisms of the 2000 earthquake swarm in the West Bohemia/Vogtland region (Central Europe)
Geophysical Journal International,
194
(2)
979 – 999
2013
ISSN: 1365246XKeywords:▾
Bohemia; Czech Republic; Germany; Vogtland; Faulting; Seismic waves; Shear waves; Accidental error; Dynamics and mechanics of faulting; Earthquake source observations; Earthquake swarms; Fracture and flows; Intra-plate process; Moment magnitudes; Source mechanisms; data inversion; earthquake magnitude; earthquake swarm; faulting; focal mechanism; ground motion; intraplate process; moment tensor; P-wave; SH-wave; source parameters; Earthquakes
Abstract: ▾ An earthquake swarm of magnitudes up to ML = 3.2 occurred in the region of West Bohemia/Vogtland (border area between Czech Republic and Germany) in autumn 2000. This swarmconsisted of nine episodic phases and lasted 4 months. We retrieved source mechanisms of 102 earthquakes with magnitudes between ML = 1.6 and 3.2 applying inversion of the peak amplitudes of direct P and SH waves, which were determined from ground motion seismograms. The investigated events cover the whole swarm activity in both time and space. We use data from permanent stations of seismic network WEBNET and from temporal stations, which were deployed in the epicentral area during the swarm; the number of stations varied from 7 to 18. The unconstrained moment tensor (MT) expression of the mechanism, which describes a general system of dipoles, that is both double-couple (DC) and non-DC sources, was applied. MTs of each earthquake were estimated by inversion of three different sets of data: P-wave amplitudes only, P- and SH-wave amplitudes and P-wave amplitudes along with the SH-wave amplitudes from a priori selected four 'base' WEBNET stations, the respective MT solutions are nearly identical for each event investigated. The resultant mechanisms of all events are dominantly DCs with only insignificant non-DC components mostly not exceeding 10 per cent. We checked reliability of the MTs in jackknife trials eliminating some data; we simulated the mislocation of hypocentre or contaminated the P- and SH-wave amplitudes by accidental errors. These tests proved stable and well constrained MT solutions. The massive dominance of the DC in all investigated events implies that the 2000 swarmconsisted of a large number of pure shears along a fault plane. The focal mechanisms indicate both oblique-normal and oblique-thrust faulting, however, the oblique-normal faulting prevails. The predominant strikes and dips of the oblique-normal events fit well the geometry of the main fault plane Nov'y Kostel (NK) and also match the strike, dip and rake of the largest ML =4.6 earthquake of a strong swarm in 1985/86. On the contrary, the 2000 source mechanisms differ substantially from those of the 1997-swarm (which took place in two fault segments at the edge of the main NK fault plane) in both the faulting and the content of non-DC components. Further, we found that the scalar seismic moment M0 is related to the local magnitude ML used by WEBNET as M0 ∝ 101.12ML, which differs from the scaling law using moment magnitude Mw, that is M0 ∝ 101.5 ML. © The Authors 2013.
1432.
Source parameters of earthquakes in the reservoir-triggered seismic (RTS) zone of Koyna-Warna, Western India
Natural Hazards,
69
(1)
965-979
2013
ISSN: 0921030X
Publisher: Kluwer Academic Publishers
Keywords:▾
earthquake event; earthquake magnitude; earthquake trigger; focal mechanism; reservoir-induced seismicity; seismic moment; seismic zone; source parameters; spectral analysis; stress analysis; waveform analysis, India
Abstract: ▾ New empirical relations are derived for source parameters of the Koyna-Warna reservoir-triggered seismic zone in Western India using spectral analysis of 38 local earthquakes in the magnitude range ML 3.5-5.2. The data come from a seismic network operated by the CSIR-National Geophysical Research Institute, India, during March 2005 to April 2012 in this region. The source parameters viz. seismic moment, source radius, corner frequency and stress drop for the various events lie in the range of 1013-1016 Nm, 0.1-0.4 km, 2.9-9.4 Hz and 3-26 MPa, respectively. Linear relationships are obtained among the seismic moment (M0), local magnitude (ML), moment magnitude (Mw), corner frequency (fc) and stress drop (Δσ). The stress drops in the Koyna-Warna region are found to increase with magnitude as well as focal depths of earthquakes. Interestingly, accurate depths derived from moment tensor inversion of earthquake waveforms show a strong correlation with the stress drops, seemingly characteristic of the Koyna-Warna region. © 2013 Springer Science+Business Media Dordrecht.
1431.
Spatial and temporal variability in sedimentological and geochemical properties of sediments from an anoxic crater lake in West Africa: Implications for paleoenvironmental reconstructions
Palaeogeography, Palaeoclimatology, Palaeoecology,
37496 – 109
2013
ISSN: 00310182Keywords:▾
Ashanti; Ghana; Lake Bosumtwi; West Africa; correlation; data set; environmental change; geochemical survey; lake ecosystem; land use change; organic matter; paleoenvironment; parameterization; pelagic deposit; principal component analysis; spatiotemporal analysis; stable isotope
Abstract: ▾ The physical, inorganic and organic geochemical and stable isotopic characteristics of lacustrine sediments can provide valuable insights into past environmental changes, provided that the environmental controls on these characteristics are well understood. In the present study, a set of 155 modern vegetation, catchment soil, river sediments and lake surface sediment samples are used to characterize the spatial patterns of TOC, TN, C/N ratios, stable isotope, major element, and particle size distributions within Lake Bosumtwi, a meromictic crater lake in West Africa. Spatial variations in sediment characteristics are strongly correlated with depth and distance from shore, reflecting the dominant influence of lake level on the relative proportions of littoral and pelagic depositional systems and their impact on the physical and geochemical properties of lacustrine sediments. This is supported by a principal component analysis, which indicates that 65% of the variance in the dataset is explained by depth-related variability in the sedimentary components. Variations in sedimentary organic matter reflect the combined influences of productivity, preservation and the relative proportions of aquatic and terrestrial organic matter sources. Grain size and Si content are dominantly influenced by the delivery of clastic materials from the watershed to the lake, whereas Fe and Ca appear to be most strongly influenced by the delivery of reduced metals and nutrients from the anoxic hypolimnion to the surface. With the exception of grain size, all of the sediment parameters record synchronous century-scale variability over the past ~2.5ka, consistent with independent evidence for changes in lake level. However, the magnitude of changes in sediment characteristics differs, reflecting different sensitivities to water depth, particularly in the deepest part of the lake basin where the sediment cores were collected. However, even the parameters with the most linear and strongly significant relationships with depth (e.g., TOC, TN) significantly overestimate the magnitude of lake level changes, suggesting that these parameters may be best suited to qualitative paleolake level reconstructions. Over the last 2 centuries, changes in C/N and δ13C became decoupled from the other geochemical proxies and the inferred rise in lake level. We hypothesize that this reflects the influence of anthropogenic land use change on the composition of terrestrial organic matter sources contributing to the lake. This result highlights the potential difficulties in reconstructing past environmental changes from indirect proxy measurements when those proxies may be subject to multiple varying controls. © 2013 Elsevier B.V.
1430.
Stable isotope values (δ18o & δ13c) of multiple ostracode species in a large neotropical lake as indicators of past changes in hydrology
Quaternary Science Reviews,
6696 – 111
2013
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Guatemala [Central America]; Lake Peten Itza; Peten; algae; Heterocypris punctata; Limnocythere; Ostracoda; Climate change; Fluid dynamics; Geochemistry; Hydrodynamics; Isotopes; Mixing; Sediments; System stability; Water levels; Autecology; Environmental change; Holocenes; Lake level changes; Neotropics; Ostracoda; Stable isotopes; abundance; autecology; benthos; fossil assemblage; fossil record; hydrodynamics; isotopic composition; lake level; Neotropical Region; ostracod; oxygen isotope; paleoecology; paleohydrology; paleolimnology; Pleistocene-Holocene boundary; seasonal variation; sediment core; stable isotope; taphonomy; Younger Dryas; Lakes
Abstract: ▾ Modern lake hydrodynamics, ostracode species autecology, stable isotopes (δ18O and δ13C) of multiple ostracode species, ostracode taphonomy and sediment geochemistry were studied to improve interpretation of the late Pleistoceneeearly Holocene (~24-10 ka) stable isotope record of ostracodes in sediment core PI-6 from Lago Petén Itzá, northern Guatemala. Oxygen and carbon stable isotopes in modern and fossil species assemblages of Lago Petén Itzá were used as indicators of changes in the balance between evaporation and precipitation, past lake level and carbon source. Ostracode taphonomy was used to detect past periods of strong currents, high-energy environments, and possible partial or full mixing of the lake. The modern lake water isotopic composition displays clear seasonal differences that are independent of lake level fluctuations. Modern benthic species displayed lower δ18O and δ13C values than nektobenthic species, with differences of 3.0‰ and 5.3‰, respectively. Valves of nektobenthic species display higher values of d13C because these ostracodes live in shallower environments among abundant algae and aquatic plants, where productivity is high. The benthic species Limnocythere opesta Brehm, 1939 displayed the smallest average offset from d18O water (0.3‰) and the largest offset from δ13CDIC values (4.1‰) among studied ostracode species. Nektobenthic species Heterocypris punctata Keyser, 1975 displayed the smallest difference relative to the δ13CDIC values (0.1‰). Late Pleistoceneeearly Holocene climate conditions and water levels in Lago Petén Itzá can be summarized as follows: 1) high lake levels and cold conditions (Last Glacial Maximum [LGM], ~24-19 ka), 2) fluctuating lake levels and cold conditions (Heinrich Stadial 1 [HS1], ~19-15 ka), 3) high lake levels and warm and wetter conditions (Bølling-Allerød [BA], ~15-13 ka), 4) low lake levels and dry conditions (Younger Dryas [YD], ~13-11.5 ka) and 5) high lake levels and warm and wetter conditions (early Holocene, ~11.5-10.0 ka). Average lake level fluctuation in Lago Petén Itzá during the late Pleistoceneeearly Holocene was as much as ~25 m. Ostracode analyses suggest that the LGM was characterized by relatively low d18O (4.7 to 6.0&), and d13C values (7.1 to 6.4‰) in ostracode valves, high inferred water depths and high percentages of broken adult and juvenile valves (>66%), suggesting a high-energy environment, strong currents, partial to full mixing, downslope transport, colder water temperatures and wetter conditions. An increase in the relative abundance of the benthic species L. opesta and higher numbers of broken valves suggest heavy precipitation events during the LGM (~23.7, 21.7, 20.8 and 20.1 ka). HS1 was predominantly dry, but we identified times when lake levels were slightly higher, at the onset of the deglacial and a brief period (~17-16 ka) between HS1b and HS1a. All studied climate proxies indicate wetter and warmer conditions and lake system stability during the BA. Lake levels dropped during the YD and gradually increased during the Preboreal and early Holocene. We demonstrate that modern and fossil ostracode isotopic signatures, species assemblages and taphonomy can be used together with physical and geochemical variables in Lago Petén Itzá sediments to make high-resolution inferences about late Pleistoceneeearly Holocene environmental changes in the lowland Neotropics. © 2012 Elsevier Ltd.
1429.
Stable isotopic evidence for climate and basin evolution of the Late Cretaceous Songliao basin, China
Palaeogeography, Palaeoclimatology, Palaeoecology,
385106-124
2013
ISSN: 00310182Keywords:▾
basin evolution; Campanian; carbon isotope; Cenomanian-Turonian boundary; Coniacian; hydrological response; Maastrichtian; marine isotope stage; ostracod; oxygen isotope; paleoclimate; Santonian; stable isotope; strontium isotope, China; Nen Basin; Songliao Basin, Coniacian; Ostracoda
Abstract: ▾ Because of the need to understand the links and feedbacks of the carbon cycle during times of global greenhouse conditions numerous studies have focused on the Cretaceous climate. Much of what we know about this warm period in Earth's history comes from the study of ocean sediments recovered from both ocean drill cores and marine sediments exposed at the Earth's surface. In contrast, there are few studies of Cretaceous terrestrial sediments. The Songliao basin located in northeast China offers a unique opportunity to understand Cretaceous paleoclimate of terrestrial settings because it contains a nearly complete record of lacustrine sediments deposited throughout the Cretaceous and there is an active drilling program to recover core from this paleolake. We present carbon, oxygen and strontium isotopic data from ostracods collected from two drill cores (SK-1 (N) and SK-1 (S)) that cover a time interval that extends from the Turonian through the Maastrichtian. These data record robust isotopic trends with numerous carbon and oxygen isotope shifts that are both rapid and long-term. We tentatively interpret this record to reflect changes in both global climate and regional basin evolution. In the Turonian and Coniacian Qingshankou Formation we observe several carbon isotope shifts that appear to be correlative to marine isotopic records based upon timing and magnitude of the isotopic changes. We suggest that the carbon isotope record in the Songliao basin reflect the decrease in carbon isotope ratios following the strong positive excursion at the Cenomanian/Turonian boundary, a positive isotope excursion in the late Turonian, and the negative isotope shift that occurs at the Turonian/Coniacian boundary. Upward in the section, however, the marine and Songliao isotopic records diverge as sediment sources shift from the southwest, east and north to more northerly. Strontium isotopes record the change in source region as they increase markedly between the Coniacian/Santonian Yaojia and Santonian/Campanian Nenjiang Formations. As this is the first isotopic record of the Songliao basin we are cautious about many of our interpretations of these isotopic data. Yet it is clear that with tighter age constraints and focused sampling centered on many of the isotope excursions presented here will allow for a deeper understanding of the terrestrial response to changing climate and the hydrologic response to basin evolution. © 2012 Elsevier B.V.
1428.
Statistical classifi cation of log response as an indicator of facies variation during changes in sea level: Integrated Ocean Drilling Program Expedition 313
Geosphere,
9
(4)
1025-1043
2013
ISSN: 1553040XKeywords:▾
cluster analysis; continental margin; core logging; depositional environment; depositional sequence; hydrocarbon exploration; lithofacies; lithology; lithostratigraphy; Miocene; Ocean Drilling Program; sea level change; sediment chemistry; sequence stratigraphy; shelf sediment; siliciclastic deposit, Atlantic Ocean; New Jersey Margin
Abstract: ▾ In this study, a novel application of a statistical approach is utilized for analysis of downhole logging data from Miocene-aged siliciclastic shelf sediments on the New Jersey Margin (eastern USA). A multivariate iterative nonhierarchical cluster analysis (INCA) of spectral gamma-ray logs from Integrated Ocean Drilling Program (IODP) Expedition 313 enables lithology within this siliciclastic succession to be inferred and, through comparison with the 1311 m of recovered core, a continuous assessment of depositional sequences is constructed. Signifi cant changes in INCA clusters corroborate most key stratigraphic surfaces interpreted from the core, and this result has particular value for surface recognition in intervals of poor core recovery. This analysis contributes to the evaluation of sequence stratigraphic models of large-scale clinoform complexes that predict depositional environments, sediment composition, and stratal geometries in response to sea-level changes. The novel approach of combining statistical analysis with detailed lithostratigraphic and seismic refl ection data sets will be of interest to any scientists working with downhole logs, especially spectral gamma-ray data, and also provides a reference for the strengths and weaknesses of multi component analysis applied to continental margin lithofacies. The method presented here is appropriate for evaluating successions elsewhere and also has value for hydrocarbon exploration where sequence stratigraphy is a fundamental tool. © 2013 Geological Society of America.
1427.
Stress rotation and recovery in conjunction with the 1999 Izmit Mw 7.4 earthquake
Geophysical Journal International,
196
(2)
951-956
2013
ISSN: 0956540XKeywords:▾
Earthquake dynamics; Regional stress field; Seismic cycle; Seismicity and tectonics; Seismotectonic settings; Spatial analysis; Spatio-temporal changes; Stress-field orientation, Fault slips; Stresses; Transform faults, Earthquakes, aftershock; coseismic process; focal mechanism; Kocaeli earthquake 1999; normal fault; seismicity; seismotectonics; spatial analysis; stress field; strike-slip fault; transform fault, Akyazi; Sakarya; Turkey
Abstract: ▾ Local rotations of the stress field might serve as an indicator to characterize the physical status of individual fault segments during the seismic cycle. In this study we focus on the pre-, 2-month aftershock- and post-seismic phase of the 1999 Mw7.4 Izmit earthquake in northwestern Turkey. Using a compilation of focal mechanism data we investigate spatiotemporal changes of the stress field orientations and find distinct variations along individual fault segments. Whereas the regional stress field prior to the Izmit earthquake and following the 2-month aftershock sequence reflects a stable strike-slip regime, the early aftershock period is dominated by EW-extension below the Akyazi Basin. During the 2-month aftershock period we find significant changes from strike-slip to normal-faulting during the main shock following by a systematic backrotation to the pre-main shock stress regime. This backrotation commences first in the Akyazi Plain hosting a co-seismic slip deficit of ≤3m and propagates then further to the east towards the Karadere and Düzce faults where the Düzce Mw 7.1 main shock nucleated 87 d later. Our results confirm that spatiotemporal stress field rotations are a useful indicator for variations of the seismotectonic setting during the seismic cycle. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.
1426.
Sulfate reduction controlled by organic matter availability in deep sediment cores from the saline, alkaline lake van (Eastern Anatolia, Turkey)
Frontiers in Microbiology,
4
(JUL)
2013
ISSN: 1664302X
Publisher: Frontiers Research Foundation
Keywords:▾
organic matter; sulfate, alkalinity; article; biogeochemical cycling; biosphere; carbon nitrogen ratio; ion pair chromatography; lake ecosystem; limit of quantitation; macromolecule; mathematical model; microbial activity; nonhuman; particle resuspension; pH measurement; reduction; reduction kinetics; relative density; salinity; sedimentology; sulfate reduction; total organic carbon; water sampling
Abstract: ▾ As part of the International Continental Drilling Program deep lake drilling project PaleoVan, we investigated sulfate reduction (SR) in deep sediment cores of the saline, alkaline (salinity 21.4%, alkalinity 155 m mEq-1, pH 9.81) Lake Van, Turkey. The cores were retrieved in the Northern Basin (NB) and at Ahlat Ridge (AR) and reached a maximum depth of 220 m. Additionally, 65-75 cm long gravity cores were taken at both sites. SR rates (SRR) were low (≥22 nmol cm-3 day-1) compared to lakes with higher salinity and alkalinity, indicating that salinity and alkalinity are not limiting SR in Lake Van. Both sites differ significantly in rates and depth distribution of SR. In NB, SRR are up to 10 times higher than at AR. SR could be detected down to 19 mblf (meters below lake floor) at NB and down to 13 mblf at AR. Although SRR were lower at AR than at NB, organic matter (OM) concentrations were higher. In contrast, dissolved OM in the pore water at AR contained more macromolecular OM and less low molecular weight OM. We thus suggest, that OM content alone cannot be used to infer microbial activity at Lake Van but that quality of OM has an important impact as well. These differences suggest that biogeochemical processes in lacustrine sediments are reacting very sensitively to small variations in geological, physical, or chemical parameters over relatively short distances. © 2013 Glombitza, Stockhecke, Schubert, Vetter and Kallmeyer.
1425.
Three-dimensional seismic velocity model of the west Bohemia/Vogtland seismoactive region
Geophysical Journal International,
195
(2)
1251 – 1266
2013
ISSN: 1365246XKeywords:▾
Bohemia; Czech Republic; Germany; Vogtland; Earthquakes; Elastic moduli; Poisson ratio; Seismic waves; Seismographs; Shear waves; Velocity; Wave propagation; Body waves; Controlled-source seismologies; Crustal structure; Europe; Seismic tomography; arrival time; body wave; bulk modulus; crustal structure; earthquake hypocenter; earthquake swarm; isotropy; P-wave; Poisson ratio; S-wave; seismic data; seismic source; seismic tomography; seismic velocity; seismic zone; seismology; tectonic setting; three-dimensional modeling; Three dimensional
Abstract: ▾ In this paper, we present a smooth 3-D seismic model WB2012 for theWest Bohemia/Vogtland earthquake swarm region derived by means of seismic tomography. Inverted data were represented by a set of 2920 P-wave traveltimes from controlled shots fired in a framework of different experiments and a set of 11339 P- and S-wave arrival times from 661 local earthquakes between 1991 December and 2010 March. We used a standard tomographic approach for independent calculation of P- and S-wave velocity fields in a rectangular grid whose size was 1 km in all coordinates. The traveltimes and rays were calculated by a numerical solution of the eiconal equation. While locating seismic events, our new WB2012 model yielded arrival time residuals on average by 13 per cent lower and hypocentre depths by 0.95 km shallower compared to the locations of the foci in the standard 1-D vertically inhomogeneous isotropic velocity model of the West Bohemia swarm region WB2005. Further, we converted the Pand S-wave velocities to the bulk modulus K and Poisson's ratio ν. The bulk modulus (~40- 70 GPa) correlates acceptably with the tectonic and geological structure of the area. The anomalously low values of the Poisson's ratio (~0.15) are typical for the most active focal zones of Nový Kostel and Lazy in West Bohemia. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.
1424.
Synoptic climatology and recent climate trends at Lake El'gygytgyn
Climate of the Past,
9
(3)
1271-1286
2013
ISSN: 18149324Keywords:▾
air temperature; climate change; dominance; freezing; low pressure; paleoclimate; seasonality; sediment core; synoptic meteorology; temperature inversion; thermodynamics, Chukchi; Elgygytgyn Lake; Russian Federation
Abstract: ▾ We developed a synoptic climatology for Lake El'gygytgyn, Chukotka Russia, and explored modern climate trends affecting air temperatures there to aid in paleoclimate reconstructions of a 3.6 million-year-old sediment core taken from the lake. Our self-organized mapping (SOM) approach identified 35 synoptic weather patterns, based on sea level pressure, that span the range of synoptic patterns influencing the study domain over the 1961-2009 NCEP/NCAR analysis period. We found strong seasonality in modern weather patterns, with summer weather primarily characterized by weak low pressure systems over the Arctic Ocean or Siberia and winter weather primarily characterized by strong high pressure over the Arctic Ocean and strong low pressure in the Pacific Ocean. In general, the primary source of variation in air temperatures came from the dominant patterns in each season, which we identify in the text, and nearly all of the dominant weather patterns here have shown increasing temperatures. We found that nearly all of the warming in mean annual temperature over the past 50 yr (about 3°C) occurred during sub-freezing conditions on either side of summer (that is, spring and fall). Here we found that the most summer-like weather patterns (low pressures to the north) in the shoulder seasons were responsible for much of the change. Finally, we compared the warmest 15 yr of the record (1995-2009) to the coolest (1961-1975) and found that changes in thermodynamics of weather were about 3 to 300 times more important than changes in frequency of weather patterns in controlling temperature variations during spring and fall, respectively. That is, in the modern record, general warming (local or advected) is more important by orders of magnitude than changes in storm tracks in controlling air temperature at Lake El'gygytgyn. We conclude with a discussion of how these results may be relevant to the paleoclimate reconstruction efforts and how this relevancy could be tested further. © Author(s) 2013.
1423.
Temporal variation of b value associated with M ~4 earthquakes in the reservoir-triggered seismic environment of the Koyna-Warna region, Western India
Journal of Seismology,
17
(1)
189-195
2013
ISSN: 13834649
Publisher: Kluwer Academic Publishers
Keywords:▾
earthquake event; earthquake magnitude; earthquake precursor; earthquake prediction; earthquake trigger; loading; reservoir-induced seismicity; seismic isolation; temporal variation; unloading, India; Koyna; Maharashtra; Warna
Abstract: ▾ It is generally found that the b values associated with reservoir-triggered seismicity (RTS) are higher than the regional b values in the frequency magnitude relation of earthquakes. In the present study, temporal and spatial variation of b value is investigated using a catalog of 3,000 earthquakes from August 2005 through December 2010 for the Koyna-Warna region in Western India, which is a classical site of RTS globally. It is an isolated (30 × 20 km2) zone of seismicity where earthquakes of up to M ~5 are found to occur during phases of loading and unloading of the Koyna and Warna reservoirs situated 25 km apart. For the Warna region, it is found that low b values of 0. 6-0. 9 are associated with earthquakes of M ~4 during the loading phase. The percentage correlation of the occurrence of an M ≥ 4 earthquake with a low b value outside the 1σ or 2σ level is as high as 78 %. A drastic drop in the b value of about 50 % being reported for an RTS site may be an important precursory parameter for short-term earthquake forecast in the future. © 2012 Springer Science+Business Media B.V.
1422.
Tephrostratigraphic studies on a sediment core from Lake Prespa in the Balkans
Climate of the Past,
9
(1)
267 – 287
2013
ISSN: 18149332Keywords:▾
Balkans; Campania [Italy]; Ischia; Italy; Lake Mikri Prespa; Napoli [Campania]; age; archaeology; biostratigraphy; chemical composition; fragmentation; numerical model; paleoenvironment; sediment core; tephrochronology
Abstract: ▾ A detailed tephrostratigraphic record, which dates back to Marine Isotope Stage (MIS) 5b (ca. 91 kyr), has been established from a 17.76 m long core (Co1215) from Lake Prespa (Macedonia, Albania and Greece). A total of eleven tephra and cryptotephra layers (PT0915-1 to PT0915-11) were identified, using XRF scanning, magnetic susceptibility measurements, and macro- and microscopic inspection of the sediments. The major element composition of glass shards and/or micro-pumice fragments indicates that the tephras and cryptotephras originate from the explosive volcanism of Italy. Eight tephra and cryptotephra layers were correlated with specific volcanic eruptions: the AD 512 eruption of Somma-Vesuvius (1438 cal yr BP), the Mercato eruption of Somma-Vesuvius (8890 ± 90 cal yr BP), the Tufi Biancastri/LN1-LN2 eruption of the Campi Flegrei (14 749 ± 523 cal yr BP and 15 551 ± 621 cal yr BP), the SMP1-e/Y-3 eruption of the Campi Flegrei (30 000-31 000 cal yr BP), the Campanian Ignimbrite/Y-5 eruption of the Campi Flegrei (39 280 ± 110 cal yr BP), the SMP1-a event of Ischia Island (around 44 000 cal yr BP) and the Green Tuff/Y-6 eruption of Pantelleria Island (around 45 000 cal yr BP). One tephra could be attributed to the volcanic activity of Mount Etna, but probably represents an unknown eruption at ca. 60 000 cal yr BP. Cryptotephras PT0915-6 and PT0915-10 remain unclassified so far, but according to the presented age-depth model these would have been deposited around 35 000 and 48 500 cal yr BP, respectively. Some of the tephras and cryptotephras are recognised for the first time in the Balkan region. The tephrostratigraphic work provides important information about ash dispersal and explosion patterns of source volcanoes and can be used to correlate and date geographically distant paleoenvironmental and archaeological archives in the central Mediterranean region. Moreover, the tephrostratigraphic work in combination with radiocarbon and electron spin resonance (ESR) dating is a precondition for paleoclimatic reconstructions inferred from the sediment succession Co1215. © 2013 Author(s).
1421.
Testing the ureilite projectile hypothesis for the El'gygytgyn impact: Determination of siderophile element abundances and Os isotope ratios in ICDP drill core samples and melt rocks
Meteoritics and Planetary Science,
48
(7)
1296-1324
2013
Abstract: ▾ The geochemical nature of the impactites from International Continental Scientific Drilling Project-El'gygytgyn lake drill core 1C is compared with that of impact melt rock fragments collected near the western rim of the structure and literature data. Concentrations of major and trace elements, with special focus on siderophile metals Cr, Co, Ni, and the platinum group elements, and isotope ratios of osmium (Os), were determined to test the hypothesis of an ureilite impactor at El'gygytgyn. Least squares mixing calculations suggest that the upper volcanic succession of rhyolites, dacites, and andesites were the main contributors to the polymict impact breccias. Additions of 2-13.5 vol% of basaltic inclusions recovered from drill core intervals between 391.6 and 423.0 mblf can almost entirely account for the compositional differences observed for the bottom of a reworked fallout deposit at 318.9 mblf, a polymict impact breccia at 471.4 mblf, and three impact melt rock fragments. However, the measured Os isotope ratios and slightly elevated PGE content (up to 0.262 ng g-1 Ir) of certain impactite samples, for which the CI-normalized logarithmic PGE signature displays a relatively flat (i.e., chondritic) pattern, can only be explained by the incorporation of a small meteoritic contribution. This component is also required to explain the exceptionally high siderophile element contents and corresponding Ni/Cr, Ni/Co, and Cr/Co ratios of impact glass spherules and spherule fragments that were recovered from the reworked fallout deposits and from terrace outcrops of the Enmyvaam River approximately 10 km southeast of the crater center. Mixing calculations support the presence of approximately 0.05 wt% and 0.50-18 wt% of ordinary chondrite (possibly type-LL) in several impactites and in the glassy spherules, respectively. The heterogeneous distribution of the meteoritic component provides clues for emplacement mechanisms of the various impactite units. © The Meteoritical Society, 2013.
1420.
Testing the ureilite projectile hypothesis for the El'gygytgyn impact: Determination of siderophile element abundances and Os isotope ratios in ICDP drill core samples and melt rocks
Meteoritics and Planetary Science,
48
(7)
1296-1324
2013
ISSN: 10869379Abstract: ▾ The geochemical nature of the impactites from International Continental Scientific Drilling Project-El'gygytgyn lake drill core 1C is compared with that of impact melt rock fragments collected near the western rim of the structure and literature data. Concentrations of major and trace elements, with special focus on siderophile metals Cr, Co, Ni, and the platinum group elements, and isotope ratios of osmium (Os), were determined to test the hypothesis of an ureilite impactor at El'gygytgyn. Least squares mixing calculations suggest that the upper volcanic succession of rhyolites, dacites, and andesites were the main contributors to the polymict impact breccias. Additions of 2-13.5 vol% of basaltic inclusions recovered from drill core intervals between 391.6 and 423.0 mblf can almost entirely account for the compositional differences observed for the bottom of a reworked fallout deposit at 318.9 mblf, a polymict impact breccia at 471.4 mblf, and three impact melt rock fragments. However, the measured Os isotope ratios and slightly elevated PGE content (up to 0.262 ng g-1 Ir) of certain impactite samples, for which the CI-normalized logarithmic PGE signature displays a relatively flat (i.e., chondritic) pattern, can only be explained by the incorporation of a small meteoritic contribution. This component is also required to explain the exceptionally high siderophile element contents and corresponding Ni/Cr, Ni/Co, and Cr/Co ratios of impact glass spherules and spherule fragments that were recovered from the reworked fallout deposits and from terrace outcrops of the Enmyvaam River approximately 10 km southeast of the crater center. Mixing calculations support the presence of approximately 0.05 wt% and 0.50-18 wt% of ordinary chondrite (possibly type-LL) in several impactites and in the glassy spherules, respectively. The heterogeneous distribution of the meteoritic component provides clues for emplacement mechanisms of the various impactite units. © The Meteoritical Society, 2013.