All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1244.
Deep core drilling of three slim geothermal holes, Snake River Plains, Idaho
Transactions - Geothermal Resources Council,
36 1641 – 647
2012
ISSN: 01935933ISBN:
978-162276434-1
Abstract: ▾ A deep core drilling project focused on evaluating the geothermal potential of the Snake River Plains in southern Idaho. Slim-hole continuous diamond coring and associated geophysical surveys were used to sample different geothermal environments. Three locations were drilled with target depths as follows: Kimama 1915 m, Kimberly 1959 m, and Mountain Home 1821 m. All total depths were accomplished or exceeded. A continuous core sample was produced and down-hole temperature while drilling was collected.
1243.
Anatomy of the high-frequency ambient seismic wave field at the TCDP borehole
Journal of Geophysical Research: Solid Earth,
117
(6)
2012
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
ambient noise; borehole; coda; correlation; drilling; geophysical array; in situ measurement; numerical model; seismic source; seismic wave; signal-to-noise ratio; wave field; wave propagation; wave scattering, Taiwan
Abstract: ▾ The Taiwan Chelungpu-fault Drilling Project (TCDP) installed a vertical seismic array between 950 and 1270 m depth in an active thrust fault environment. In this paper we analyze continuous noise records of the TCDP array between 1 and 16 Hz. We apply multiple array processing and noise correlation techniques to study the noise source process, properties of the propagation medium, and the ambient seismic wave field. Diurnal amplitude and slowness patterns suggest that noise is generated by cultural activity. The vicinity of the recording site to the excitation region, indicated by a narrow azimuthal distribution of propagation directions, leads to a predominant ballistic propagation regime. This is evident from the compatibility of the data with an incident plane wave model, polarized direct arrivals of noise correlation functions, and the asymmetric arrival shape. Evidence for contributions from scattering comes from equilibrated earthquake coda energy ratios, the frequency dependent randomization of propagation directions, and the existence of correlation coda waves. We conclude that the ballistic and scattered propagation regime coexist, where the first regime dominates the records, but the second is weaker yet not negligible. Consequently, the wave field is not equipartitioned. Correlation signal-to-noise ratios indicate a frequency dependent noise intensity. Iterations of the correlation procedure enhance the signature of the scattered regime. Discrepancies between phase velocities estimated from correlation functions and in-situ measurements are associated with the array geometry and its relative orientation to the predominant energy flux. The stability of correlation functions suggests their applicability in future monitoring efforts. Copyright 2012 by the American Geophysical Union.
1242.
An emplacement mechanism for the mega-block zone within the Chicxulub crater, (Yucatán, Mexico) based on chemostratigraphy
Meteoritics and Planetary Science,
47
(3)
400-413
2012
Abstract: ▾ To better constrain the emplacement mechanism of the so-called "mega-block zone," a structurally complex unit of target rocks within the Chicxulub impact structure, the stratigraphic coherence of this zone is tested using its strontium isotopic composition. Forty-eight samples across the 616m sequence of deformed Cretaceous rocks in the lower part of the Yaxcopoil-1 core, drilled by ICDP in 2002, were analyzed for their 87Sr/ 86Sr isotope ratio. The oceanic anoxic event 2 (OAE2 event), located near the base of the core forms the only stratigraphic anchor point. From this point upward to approximately 1050m depth, the 87Sr/ 86Sr trend shows small oscillations, between approximately 0.7074 and 0.7073, characteristic of Cenomanian to Santonian values. This is followed by an increase to approximately 0.7075, similar to the one reported in the seawater strontium curve during the Campanian. Scattered Sr isotope ratios are attributed to local diagenetic effects, such as those expected from the possible presence of hot, impact-induced dikes and hydrothermal fluid flow, originating from the thick central melt sheet. The absence of Upper Maastrichtian Sr isotope values may result from the removal of upper target lithologies during the impact cratering process. Based on these results, the displaced Cretaceous sequence in Yax-1 appears to have preserved its stratigraphic coherence. During the modification stage, it probably moved as a whole into the annular basin during collapse of the crater wall, thereby breaking up into discrete units along previously weakened detachment zones. This model is consistent with the emplacement mechanism postulated by Kenkmann et al. (2004). © 2012 The Meteoritical Society.
1241.
An early first-century earthquake in the Dead Sea
International Geology Review,
54
(10)
1219-1228
2012
ISSN: 00206814Keywords:▾
chronology; earthquake; Holocene; seismicity; varve, Dead Sea
Abstract: ▾ This article examines a report in the 27th chapter of the Gospel of Matthew in the New Testament that an earthquake was felt in Jerusalem on the day of the crucifixion of Jesus of Nazareth. We have tabulated a varved chronology from a core from Ein Gedi on the western shore of the Dead Sea between deformed sediments due to a widespread earthquake in 31 BC and deformed sediments due to an early first-century earthquake. The early first-century seismic event has been tentatively assigned a date of 31 AD with an accuracy of 5 years. Plausible candidates include the earthquake reported in the Gospel of Matthew, an earthquake that occurred sometime before or after the crucifixion and was in effect borrowed by the author of the Gospel of Matthew, and a local earthquake between 26 and 36 AD that was sufficiently energetic to deform the sediments at Ein Gedi but not energetic enough to produce a still extant and extra-biblical historical record. If the last possibility is true, this would mean that the report of an earthquake in the Gospel of Matthew is a type of allegory. © 2012 Copyright Taylor and Francis Group, LLC.
1240.
A study of sediment magnetic mineralogy in Lake Bosumtwi, Ghana: Indications of depositional environment and paleoclimate
European Journal of Scientific Research,
82
(1)
95 – 114
2012
ISSN: 1450216X
Publisher: EuroJournals, Inc.
Abstract: ▾ Lake Bosumtwi in Ghana, has been the focus of international paleoclimate research during which continuous sediment cores were recovered for mutliproxy paleoclimate studies. Seventy-six (76) samples of the top 2-8 cm of the sediments were collected at different locations throughout the lake with Ekman dredge to determine indications of depositional environment and paleoclimate. The percentage (%) water and percentage (%) organic matter contents, and the magnetic mineralogy of the sediment samples were determined. The magnetic measurements carried out include isothermal remanent magnetization (IRM), anhysteric remanent magnetisation (ARM) and magnetic susceptibility. The results showed that the percentage (%) water and percentage (%) organic matter contents increased with increasing water depth. The magnetic susceptibilities of the samples increased with increasing water depth, whereas the percentage (%) frequency dependence of susceptibility has a gentle increase with water depth. Most parameters measured show an abrupt change at about 18 m water depth. Values for S-ratio averaged 0.93, indicating the presence of low coercivity magnetic minerals such as maghemite and magnetite. These low coercivity minerals in the surface sediments were deposited in the presently warm and wet interglacial climate with reduced Sahara/Sahel dust influx to Ghana. © EuroJournals Publishing, Inc. 2012.
1239.
A seasonal cycle of terrestrial inputs in Lake Van, Turkey
Environmental Science and Pollution Research,
19
(8)
3628-3635
2012
ISSN: 09441344Keywords:▾
biological marker, alkane; anthropogenic source; bacterium; biomarker; catchment; climate change; dust storm; eolian deposit; freshwater sediment; lake pollution; pollen; saline lake; seasonality; sediment trap; snowmelt; soil microorganism; terrestrial deposit, article; chemistry; environmental monitoring; lake; microbiology; pollen; season; Turkey (republic); water pollutant, Biological Markers; Environmental Monitoring; Lakes; Pollen; Seasons; Soil Microbiology; Turkey; Water Pollutants, Chemical, Lake Van; Turkey, Embryophyta; Tracheophyta
Abstract: ▾ Lake Van in Turkey is the world's largest soda lake (607 km3). The lake's catchment area is estimated to be ~12,500 km2, and the terrestrial input is carried through eolian, riverine, snowmelt and anthropogenic paths. Extent and seasonality of the terrestrial inputs to the lake have not been studied, but it is essential to evaluate its environmental status and to assess the use of environmental proxies to estimate the lake's response to climate changes. This study aims to measure seasonal changes in terrestrial input of natural and anthropogenic origin as recorded by the fluxes of pollen and biomarkers of soil bacteria and vascular or higher plants, as well as petrogenic biomarkers in monthly resolved sediment traps from August 2006 to July 2007. Fluxes of pollen, soil and higher plant biomarkers seem to be related to precipitation and snowmelt in autumn and spring. In addition, dust storms, which are common during the summer months, may have resulted in long-distance transport. Anthropogenic biomarker fluxes indicate year-round petrogenic contamination although some mature biomarker fluxes are higher in summer and in late winter-spring. The relative changes between petrogenic markers indicate variations in the pollutant sources. © 2012 Springer-Verlag.
1238.
A new model for barberton komatiites: Deep critical melting with high melt retention
Journal of Petrology,
53
(11)
2191 – 2229
2012
ISSN: 14602415Keywords:▾
Barberton Greenstone Belt; Archean; concentration (composition); geochemistry; komatiite; magma; mantle plume; modeling; peridotite; petrogenesis; petrology; rare earth element
Abstract: ▾ The oldest well-preserved komatiites, and the type examples, are found in the Barberton Greenstone Belt in South Africa (3·5-3·3 Ga). All three komatiite types are present, commonly within the same stratigraphic unit. Al-depleted komatiites have low Al/Ti, relatively high concentrations of incompatible elements and depleted heavy rare earth elements (HREE); Al-undepleted komatiites have chondritic Al/Ti and flat HREE patterns; and Al-enriched komatiites have high Al/Ti, low concentrations of incompatible elements, enriched HREE and extremely depleted light rare earth elements. Based on a comprehensive petrological and geochemical study, we propose a new melting model for the formation of these magmas. The basis of the model is the observation, from published experimental studies, that at great depths (~13 GPa) the density of komatiitic liquid is similar to that of solid peridotite. At such depths, melting in a rising mantle plume produces near-neutrally buoyant komatiite melt that does not escape from the residual peridotite. As the source ascends to shallower levels, however, the pressure decreases and the density difference increases, eventually making melt escape possible. Al-depleted komatiites form first at about 13 GPa by equilibrium melting under conditions in which a large proportion of melt (30-40%) was retained in the source and the residue contained a high proportion of garnet (15%). Al-undepleted and Al-enriched komatiites form by fractional melting at intermediate to shallow depths after the escape of a large proportion of melt and after exhaustion of residual garnet. This model reproduces the chemical characteristics of all komatiite types in the Barberton belt and can probably be applied to komatiites in other parts of the world. © The Author 2012. Published by Oxford University Press. All rights reserved.
1237.
A microstructural study of fault rocks from the SAFOD: Implications for the deformation mechanisms and strength of the creeping segment of the San Andreas Fault
Journal of Structural Geology,
42246-260
2012
ISSN: 01918141Keywords:▾
Cataclasis; Foliated gouge; Pressure solution; SAFOD; San Andreas fault; Shear localizations, Clay minerals; Creep; Electron microscopy; Fracture; Image processing; Strike-slip faults; Structural geology; X ray powder diffraction; X ray spectroscopy, Shear flow, asperity; creep; deformation mechanism; fault gouge; fault zone; foliation; microstructure; San Andreas Fault; seismicity; shear zone; slip, California; San Andreas; United States
Abstract: ▾ The San Andreas Fault zone in central California accommodates tectonic strain by stable slip and microseismic activity. We study microstructural controls of strength and deformation in the fault using core samples provided by the San Andreas Fault Observatory at Depth (SAFOD) including gouge corresponding to presently active shearing intervals in the main borehole. The methods of study include high-resolution optical and electron microscopy, X-ray fluorescence mapping, X-ray powder diffraction, energy dispersive X-ray spectroscopy, white light interferometry, and image processing.The fault zone at the SAFOD site consists of a strongly deformed and foliated core zone that includes 2-3 m thick active shear zones, surrounded by less deformed rocks. Results suggest deformation and foliation of the core zone outside the active shear zones by alternating cataclasis and pressure solution mechanisms. The active shear zones, considered zones of large-scale shear localization, appear to be associated with an abundance of weak phases including smectite clays, serpentinite alteration products, and amorphous material. We suggest that deformation along the active shear zones is by a granular-type flow mechanism that involves frictional sliding of microlithons along phyllosilicate-rich Riedel shear surfaces as well as stress-driven diffusive mass transfer. The microstructural data may be interpreted to suggest that deformation in the active shear zones is strongly displacement-weakening. The fault creeps because the velocity strengthening weak gouge in the active shear zones is being sheared without strong restrengthening mechanisms such as cementation or fracture sealing. Possible mechanisms for the observed microseismicity in the creeping segment of the SAF include local high fluid pressure build-ups, hard asperity development by fracture-and-seal cycles, and stress build-up due to slip zone undulations. © 2012 Elsevier Ltd.
1236.
A 250 ka oxygen isotope record from diatoms at Lake El'gygytgyn, far east Russian Arctic
Climate of the Past,
8
(5)
1621-1636
2012
ISSN: 18149324Keywords:▾
air temperature; arctic environment; diatom; glacial-interglacial cycle; ice core; isotopic composition; lacustrine deposit; Last Glacial Maximum; marine isotope stage; oxygen isotope; sediment core; silica, Antarctica; Arctic; Chukchi; Dome Concordia; East Antarctica; Elgygytgyn Lake; Russian Federation
Abstract: ▾ In 2003 sediment core Lz1024 was drilled at Lake El'gygytgyn, far east Russian Arctic, in an area of the Northern Hemisphere which has not been glaciated for the last 3.6 Ma. Biogenic silica was used for analysing the oxygen isotope composition (δ18Odiatom) in the upper 13 m long section dating back about 250 ka with samples dominated by one taxa in the <10 μm fraction (Cyclotella ocellata). Downcore variations in δ18O values show that glacial-interglacial cycles are present throughout the core and δ18Odiatom-values are mainly controlled by δ18Oprecipitation. Changes reflect the Holocene Thermal Maximum, the Last Glacial Maximum (LGM) and the interglacial periods corresponding to MIS 5.5 and MIS 7 with a peak-to-peak amplitude between LGM and MIS 5.5 of Δ18O = 5.3‰. This corresponds to a mean annual air temperature difference of about 9 °C. Our record is the first continuous δ18Odiatom record from an Arctic lake sediment core directly responding to precipitation and dating back more than 250 ka and correlates well with the stacked marine δ18O LR04 (r = 0.58) and δD EPICA Dome-C record (r = 0.69). With δ18O results indicating strong links to both marine and ice-core records, records from Lake El'gygytgyn can be used to further investigate the sensitivity of the Arctic climate to both past and future global climatic changes. © Author(s) 2012.
1235.
500,000 years of environmental history in Eastern Anatolia: The PALEOVAN Drilling project
Scientific Drilling
(14)
18-29
2012
ISSN: 18168957
Publisher: Copernicus GmbH
Keywords:▾
Inert gases; Lakes; Sediments; Single crystals, Compositional evolution; Continental scientific drillings; Drilling projects; Earthquake activity; Environmental history; Lacustrine sediments; Mediterranean sea; Semi-arid region, Infill drilling
Abstract: ▾ International Continental Scientific Drilling Program (ICDP) drilled a complete succession of the lacustrine sediment sequence deposited during the last -500,000 years in Lake Van, Eastern Anatolia (Turkey). Based on a detailed seismic site survey, two sites at a water depth of up to 360 m were drilled in summer 2010, and cores were retrieved from sub-lake-floor depths of 140 m (Northern Basin) and 220 m (Ahlat Ridge). To obtain a complete sedimentary section, the two sites were multiple-cored in order to investigate the paleoclimate history of a sensitive semi-arid region between the Black, Caspian, and Mediterranean seas. Further scientific goals of the PALEOVAN project are the reconstruction of earthquake activity, as well as the temporal, spatial, and compositional evolution of volcanism as reflected in the deposition of tephra layers. The sediments host organic matter from different sources and hence composition, which will be unravelled using biomarkers. Pathways for migration of continental and mantle-derived noble gases will be analyzed in pore waters. Preliminary 40Ar/39Ar single crystal dating of tephra layers and pollen analyses suggest that the Ahlat Ridge record encompasses more than half a million years of paleoclimate and volcanic/geodynamic history, providing the longest continental record in the entire Near East to date.
1234.
40Ar/39Ar ages for deep (∼3.3 km) samples from the Hawaii Scientific Drilling Project, Mauna Kea volcano, Hawaii
Geochemistry, Geophysics, Geosystems,
13
(5)
2012
ISSN: 15252027
Publisher: Blackwell Publishing Ltd
Keywords:▾
Hawaii [(ISL) Hawaiian Islands]; Hawaii [United States]; Hawaiian Islands; Mauna Kea; United States; Infill drilling; Thermal plumes; Accumulation rates; Chemical and physical characteristics; Hawaii; Mauna keas; Ocean island basalts; Paleomagnetic record; Scientific drilling; volcanology; argon-argon dating; mantle plume; ocean island basalt; paleomagnetism; petrology; regression analysis; tholeiite; timescale; uncertainty analysis; volcanology; Volcanoes
Abstract: ▾ The Hawaii Scientific Drilling Project recovered core from a 3.5 km deep hole from the flank of Mauna Kea volcano, providing a long, essentially continuous record of the volcano's physical and petrologic development that has been used to infer the chemical and physical characteristics of the Hawaiian mantle plume. Determining a precise accumulation rate via 40Ar/ 39Ar dating of the shield-stage tholeiites, which constitute 95-98% of the volcano's volume is challenging. We applied 40Ar/ 39Ar dating using laser- and furnace-heating in two laboratories (Berkeley and Curtin) to samples of two lava flows from deep in the core (∼3.3 km). All determinations yield concordant isochron ages, ranging from 612 ± 159 to 871 ± 302 ka (2σ; with P ≥ 0.90). The combined data yield an age of 681 ± 120 ka (P = 0.77) for pillow lavas near the bottom of the core. This new age, when regressed with 40Ar/39Ar isochron ages previously obtained for tholeiites higher in the core, defines a constant accumulation rate of 8.4 ± 2.6 m/ka that can be used to interpolate the ages of the tholeiites in the HSDP core with a mean uncertainty of about ±83 ka. For example at ∼3300 mbsl, the age of 664 ± 83 ka estimated from the regression diverges at the 95% confidence level from the age of 550 ka obtained from the numerical model of DePaolo and Stolper (1996). The new data have implications for the timescale of the growth of Hawaiian volcanoes, the paleomagnetic record in the core, and the dynamics of the Hawaiian mantle plume. Copyright 2012 by the American Geophysical Union.
1233.
2.8 Million years of arctic climate change from Lake El'gygytgyn, NE Russia
Science,
337
(6092)
315-320
2012
ISSN: 00368075
Publisher: American Association for the Advancement of Science
Keywords:▾
arctic environment; climate modeling; climate prediction; climate variation; greenhouse gas; ice sheet; interglacial; marine isotope stage; precipitation (climatology); sediment core, arctic climate; article; benthos; climate change; greenhouse effect; greenhouse gas; interglacial; lake; priority journal; Quaternary (period); Russian Federation; seasonal variation; summer, Antarctica; Arctic; Chukchi; Elgygytgyn Lake; Russian Federation; West Antarctic Ice Sheet; West Antarctica
Abstract: ▾ The reliability of Arctic climate predictions is currently hampered by insufficient knowledge of natural climate variability in the past. A sediment core from Lake El'gygytgyn in northeastern (NE) Russia provides a continuous, high-resolution record from the Arctic, spanning the past 2.8 million years. This core reveals numerous "super interglacials" during the Quaternary; for marine benthic isotope stages (MIS) 11c and 31, maximum summer temperatures and annual precipitation values are ∼4° to 5°C and ∼300 millimeters higher than those of MIS 1 and 5e. Climate simulations show that these extreme warm conditions are difficult to explain with greenhouse gas and astronomical forcing alone, implying the importance of amplifying feedbacks and far field influences. The timing of Arctic warming relative to West Antarctic Ice Sheet retreats implies strong interhemispheric climate connectivity.
1232.
Major environmental change and bonebed genesis prior to the triassic-jurassic mass extinction
Journal of the Geological Society,
169
(2)
191 – 200
2012
ISSN: 00167649
Publisher: Geological Society of London
Keywords:▾
South Wales; United Kingdom; Wales; Vertebrata; Barium alloys; Isotopes; Lithology; Carbon isotope excursions; Central atlantic magmatic provinces; Environmental change; Environmental crisis; Sedimentary organic matter; Sedimentological data; Sedimentological evidence; Triassic-Jurassic boundary; carbon cycle; environmental change; geochemistry; Jurassic; mass extinction; organic matter; paleoenvironment; petrogenesis; phosphate; phosphatization; redox conditions; Rhaetian; sedimentology; stratigraphic boundary; stratigraphy; vertebrate; water column; Organic carbon
Abstract: ▾ We present new geochemical and sedimentological data from marginal marine strata of Penarth Bay, south Wales (UK) to elucidate the origin of widespread but enigmatic concentrations of vertebrate hard parts (bonebeds) in marine successions of Rhaetian age (late Triassic). Sedimentological evidence shows that the phosphatic constituents of the bonebeds were subjected to intense phosphatization in shallow current dominated settings and subsequently reworked and transported basinward by storms. Inter bedded organic-rich strata deposited under quiescent and poorly oxygenated conditions record enhanced phosphorus regeneration from sedimentary organic matter into the water column and probably provided the main source of phosphate required for heavy bonebed clast phosphatization. The stratigraphically limited interval showing evidence for oxygen depletion and accelerated P-cycling coincides with a negative 4‰ organic carbon isotope excursion, which possibly reflects supra-regional changes in carbon cycling and clearly predates the 'initial isotope excursion' characterizing many Triassic-Jurassic boundary strata. our data indicate that Rhaetian bonebeds are the lithological signature of profound, climatically driven changes in carbon cycling and redox conditions and support the idea of a multi-pulsed environmental crisis at the end of the Triassic, possibly linked to successive episodes of igneous activity in the central Atlantic Magmatic Province.
1231.
Dating deep? Luminescence studies of fault gouge from the San Andreas Fault zone 2.6 km beneath Earth's surface
Quaternary Geochronology,
10280-284
2012
ISSN: 18711014Keywords:▾
complexity; deformation; fault gouge; fault zone; luminescence dating; microstructure; resetting; rupture; San Andreas Fault, California; San Andreas; United States
Abstract: ▾ This study aims to assess whether luminescence emission from fault gouge samples from the San Andreas Fault Observatory at Depth (SAFOD) can be used to determine the age distribution of distinct deformation microstructures. Such age determination could help constrain some of the proposed micromechanical models for shear localization in fault gouge, in addition to providing more accurate time constraint on the seismic cycle itself. The mechanism by which previously trapped charge is reset in minerals in fault gouge is thought to be a combination of frictional heating and mechanical deformation, and these processes may be localized to grain surfaces. An added dating complexity specific to deep samples is the high ambient temperature conditions, which act as a barrier to charge storage in lower energy trapping sites. In this work luminescence experiments are being conducted on minerals from whole-rock samples of intact fault gouge from the SAFOD Phase III core. Initial studies indicate (i) the thermal and radiation history of the mineral lattice can be assessed with TL, (ii) trap resetting is evident in both TL and IRSL data, (iii) a small charge-trapping window between drill hole ambient temperature of ∼112 °C and higher energy lattice excitation via rupture events is evident in TL data from ∼300 to 400 °C, and we tentatively link the source of IRSL to TL within this 300-400 °C region, (iv) IRSL data have low natural intensity but good luminescence characteristics, and (v) SAR IRSL D e data have high over-dispersion but demonstrate ages ranging from decades to centuries may be measured. © 2012 Elsevier B.V..
1230.
Application of conditional simulation of heterogeneous rock properties to seismic scattering and attenuation analysis in gas hydrate reservoirs
Journal of Applied Geophysics,
7783-96
2012
ISSN: 09269851Keywords:▾
Borehole logging; Compressional; Conditional simulations; Distribution of gas; Elastic medium; Elastic properties; Finite-difference modeling; Gas hydrate reservoir; Heterogeneous environments; Heterogeneous rocks; Hydrate accumulations; Leaky modes; Model spaces; Multiscales; Numerical experiments; Petrophysical; Petrophysical models; Petrophysical properties; Pore space; Reservoir models; Resonance scattering; Rock properties; Seismic energy; Shear-wave velocity; Subsurface lithology; Vertical seismic profiles, Anoxic sediments; Energy dissipation; Experiments; Gases; Hydration; Petroleum reservoirs; Scattering; Seismic waves; Seismology; Shear flow; Three dimensional, Gas hydrates, algorithm; borehole logging; computer simulation; elastic property; gas hydrate; heterogeneous medium; rock property; S-wave; saturation; seismic attenuation; seismic data; three-dimensional modeling; wave propagation; wave scattering; wave velocity, Canada; Northwest Territories
Abstract: ▾ We present a conditional simulation algorithm to parameterize three-dimensional heterogeneities and construct heterogeneous petrophysical reservoir models. The models match the data at borehole locations, simulate heterogeneities at the same resolution as borehole logging data elsewhere in the model space, and simultaneously honor the correlations among multiple rock properties. The model provides a heterogeneous environment in which a variety of geophysical experiments can be simulated. This includes the estimation of petrophysical properties and the study of geophysical response to the heterogeneities. As an example, we model the elastic properties of a gas hydrate accumulation located at Mallik, Northwest Territories, Canada. The modeled properties include compressional and shear-wave velocities that primarily depend on the saturation of hydrate in the pore space of the subsurface lithologies. We introduce the conditional heterogeneous petrophysical models into a finite difference modeling program to study seismic scattering and attenuation due to multi-scale heterogeneity. Similarities between resonance scattering analysis of synthetic and field Vertical Seismic Profile data reveal heterogeneity with a horizontal-scale of approximately 50. m in the shallow part of the gas hydrate interval. A cross-borehole numerical experiment demonstrates that apparent seismic energy loss can occur in a pure elastic medium without any intrinsic attenuation of hydrate-bearing sediments. This apparent attenuation is largely attributed to attenuative leaky mode propagation of seismic waves through large-scale gas hydrate occurrence as well as scattering from patchy distribution of gas hydrate. © 2011 Elsevier B.V..
1229.
Delineating ophiolite-derived host rocks of massive sulfide Cu-Co-Zn deposits with 2D high-resolution seismic reflection data in Outokumpu, Finland
Geophysics,
77
(5)
WC213–WC222
2012
ISSN: 00168033
Publisher: Society of Exploration Geophysicists
Keywords:▾
Finland; Outokumpu; Pohjois-Karjala; 3D modeling; Acoustic impedance; Acoustic logging; Cobalt alloys; Cobalt compounds; Copper alloys; Copper compounds; Deposits; Geophysical prospecting; Magnesite; Mica; Mica deposits; Ores; Reflection; Seismic response; Seismic waves; Structural geology; Sulfur compounds; Ternary alloys; Zinc alloys; Zinc deposits; Zinc sulfide; Europe; High resolution seismic; Reflective structure; Seismic impedance; Seismic reflection data; Seismic reflection method; Synthetic seismogram; Vibroseis; acoustic property; cobalt; copper; crustal structure; host rock; logging (geophysics); massive sulfide; mica; mining; ophiolite; ore deposit; reflectivity; schist; seismic data; seismic reflection; seismic wave; seismogram; upper crust; vibroseis; wavelength; zinc; Rocks
Abstract: ▾ Seismic reflection data was applied to a study of the upper crustal structures in the Outokumpu mining and exploration area in eastern Finland. The Cu-Co-Zn sulfide ore deposits of the Outokumpu area are hosted by Palaeoproterozoic ophiolite-derived altered ultrabasic rocks (serpentinite, skarn rock, and quartz rock) and black schist within turbiditic mica schist. Mining in the Outokumpu area has produced a total of 36 Mt of ore from three historical and one active mine. Seismic data comprises 2D vibroseis data surveyed along a network of local roads. The seismic sections provide a comprehensive 3D view of the reflective structures. Acoustic rock properties from downhole logging and synthetic seismograms indicate that the strongly reflective packages shown in the seismic data can be identified as the host-rock environments of the deposits. Reflectors show excellent continuity along the structural grain of the ore belt, which allows correlating reflectors with surface geology, magnetic map, and drilling sections into a broad 3D model of the ore belt. Massive ores have acoustic properties that make them directly detectable with seismic reflection methods assuming the deposit size is sufficient for applied seismic wavelengths. The seismic data revealed numerous interesting high-amplitude reflectors within the interpreted host-rock suites potentially coinciding with sulfides. © 2012 Society of Exploration Geophysicists.
1228.
Holocene climate variability in the Levant from the Dead Sea pollen record
Quaternary Science Reviews,
4995-105
2012
ISSN: 02773791Keywords:▾
Atlantic Ocean; Atmospheric conditions; Bayesian statistics; Climate condition; Climate cycle; Dead sea; Environmental conditions; Holocene climate variability; Holocenes; Hydrological condition; Late Holocene; Model-based OPC; Natural vegetation; Near East; Paleoclimatology; Palynology; Pollen data; Rapid shifts; Sea surface temperature (SST); Sediment core; Sedimentary records; Short time intervals; Temporal variation; Water composition, Sedimentology; Structural analysis, Climatology, Bayesian analysis; climate conditions; climate cycle; climate variation; desert; environmental disturbance; Holocene; Neolithic; paleoclimate; paleotemperature; palynology; precipitation (climatology); quantitative analysis; reconstruction; sea surface temperature; sediment core; temporal variation; vegetation dynamics; water level; water quality, Dead Sea; En Gedi; Levant; Mediterranean Region; Occupied Territories; West Bank
Abstract: ▾ The Dead Sea, located at the deepest place on continent and between the subtropical Mediterranean zone and the desert, reflects in its water composition and levels, and sedimentary records the hydrological conditions in the southern Levant region. Temporal variations in rainfall and temperatures of the Holocene Levant are reconstructed here from pollen data recovered from a sediment core drilled at the Ein Gedi shore, applying a novel biome model based on Bayesian statistics. Our results suggest that the region was arid and warm in the early Holocene period (~10-6.5 ka cal BP), wetter and colder in the mid Holocene (6.3-3.3 ka cal BP), and drier and warmer in the late Holocene (~3.2 ka cal BP to present). These periods comprise multi-centennial climate cycles that are characterized by rapid changes in temperature and precipitation reflecting Sea Surface Temperature (SST) and atmospheric conditions over the Atlantic Ocean. The pollen record responds within a short time interval to the climate conditions and marks rapid shifts from Mediterranean to desert environmental conditions and back in the southern Levant region. We also evaluate our results in the light of possible disturbances of the natural vegetation, e.g. the possibility of forest decrease, since the Neolithic. © 2012 Elsevier Ltd.
1227.
Magnetotelluric Studies at the San Andreas Fault Zone: Implications for the Role of Fluids
Surveys in Geophysics,
33
(1)
65-105
2012
ISSN: 01693298
Publisher: Kluwer Academic Publishers
Keywords:▾
Creep; Fluids; Magnetotellurics; Strike-slip faults; Volcanic rocks, Electrical conductivity; High-conductivity zones; Interconnected porosity; Magnetotelluric studies; Metamorphic fluids; Non-volcanic tremors; San Andreas fault; Weakening effect, Structural geology, deformation mechanism; electrical conductivity; fault zone; high pressure; magnetotelluric method; porosity; rheology; San Andreas Fault, California; San Andreas; United States
Abstract: ▾ Fluids residing in interconnected porosity networks have a significant weakening effect on the rheology of rocks and can strongly influence deformation along fault zones. The magnetotelluric (MT) technique is sensitive to interconnected fluid networks and can image these zones on crustal and upper mantle scales. MT images have revealed several prominent electrical conductivity anomalies at the San Andreas Fault which have been attributed to the presence of saline fluids within such networks and which have been associated with tectonic processes. These models suggest that ongoing fluid release in the upper mantle and lower crust is closely related to the mechanical state of the crust. Where fluids are drained into the brittle crust, and where these fluids are kept at high pressures, fault creep is supported. Fluid fluxes from deeper levels, in combination with meteoric and crustal metamorphic fluid inflow, and in response to fault creep, leads to high-conductivity zones developing as fault zone conductors in the brittle portion of crust. In turn, the absence of crustal fluid pathways may be characteristic for mechanically locked segments of the fault. Here, MT models suggest that fluids are trapped at depth and kept at high pressures. We speculate that fluids may infiltrate neighboring rocks and in their wake induce non-volcanic tremor. © 2011 Springer Science+Business Media B.V.
1226.
Depositional dynamics in the El'gygytgyn Crater margin: implications for the 3.6 Ma old sediment archive
Climate of the Past,
8
(6)
1897-1911
2012
ISSN: 18149324Keywords:▾
alluvial fan; crater lake; depositional environment; displacement; flooding; matrix; nearshore environment; permafrost; reconstruction; sediment core; sediment transport; sedimentology; sliding; turbidity; water column, Chukchi; Elgygytgyn Lake; Russian Federation
Abstract: ▾ The combination of permafrost history and dynamics, lake level changes and the tectonical framework is considered to play a crucial role for sediment delivery to El'gygytgyn Crater Lake, NE Russian Arctic. The purpose of this study is to propose a depositional framework based on analyses of the core strata from the lake margin and historical reconstructions from various studies at the site. A sedimentological program has been conducted using frozen core samples from the 141.5 m long El'gygytgyn 5011-3 permafrost well. The drill site is located in sedimentary permafrost west of the lake that partly fills the El'gygytgyn Crater. The total core sequence is interpreted as strata building up a progradational alluvial fan delta. Four macroscopically distinct sedimentary units are identified. Unit 1 (141.5-117.0 m) is comprised of ice-cemented, matrix-supported sandy gravel and intercalated sandy layers. Sandy layers represent sediments which rained out as particles in the deeper part of the water column under highly energetic conditions. Unit 2 (117.0-24.25 m) is dominated by ice-cemented, matrix-supported sandy gravel with individual gravel layers. Most of the Unit 2 diamicton is understood to result from alluvial wash and subsequent gravitational sliding of coarse-grained (sandy gravel) material on the basin slope. Unit 3 (24.25-8.5 m) has ice-cemented, matrix-supported sandy gravel that is interrupted by sand beds. These sandy beds are associated with flooding events and represent near-shore sandy shoals. Unit 4 (8.5-0.0 m) is ice-cemented, matrix-supported sandy gravel with varying ice content, mostly higher than below. It consists of slope material and creek fill deposits. The uppermost metre is the active layer (i.e. the top layer of soil with seasonal freeze and thaw) into which modern soil organic matter has been incorporated. The nature of the progradational sediment transport taking place from the western and northern crater margins may be related to the complementary occurrence of frequent turbiditic layers in the central lake basin, as is known from the lake sediment record. Slope processes such as gravitational sliding and sheet flooding occur especially during spring melt and promote mass wasting into the basin. Tectonics are inferred to have initiated the fan accumulation in the first place and possibly the off-centre displacement of the crater lake. © Author(s) 2012.
1225.
Lithosphere structure of the NE Bohemian Massif (Sudetes) - A teleseismic receiver function study
Tectonophysics,
564-56512 – 37
2012
ISSN: 00401951Keywords:▾
Bohemian Massif; Sudetes; Seismology; Central Europe; ratio; Lithosphere-asthenosphere boundary; Lithospheric structure; Moho discontinuity; Permo-Carboniferous volcanism; asthenosphere; Carboniferous; crust-mantle boundary; crustal structure; lithospheric structure; magma chamber; Moho; observational method; Permian; S-wave; seismic tomography; seismic velocity; velocity structure; volcanism; Structural geology
Abstract: ▾ In 2004 and 2005 a passive seismic experiment was carried out in the northern and northeastern part of the Bohemian Massif (Sudetes) to study the lithospheric structure. We present results from Ps and Sp receiver function analyses. With one exception, Moho depth at stations in the northwestern part of the study area varies between 28 and 32km. Thicker crust up to 35km was mapped toward the south (Moldanubian unit) and toward the east (Moravo-Silesian and Brunovistulian units) confirming results from previous active seismic measurements. There exists a relatively sharp step in Moho depth between units of the central Sudetes (~30km) and the Moravo-Silesian unit (~35km). The v p/v s ratios inverted from primary and multiple Moho Ps conversions hint for different crustal compositions of the units. Toward the Carpathian thrust we have no clear indications for any crustal root or slab beneath the western Carpathians. However, our data suggests a deepening of the Moho or at least a complicated crust-mantle transition in this area. Additional Ps phases were observed between 6 and 10s delay time in the Sudetes. These phases cannot be explained by Moho reverberations, but are most probably caused by low velocity zones in the middle crust or lithospheric mantle as shown by modeling of theoretical receiver functions. The stations showing these abnormal phases are located in the area of Permo-Carboniferous basins on probably Teplá-Barrandian crust. Therefore we assume that the phases hint at a mid-crustal low velocity zone between 16 and 20km depth, which is interpreted as a felsic solidified magma reservoir of the Permo-Carboniferous volcanism beneath the Sudetic Basins. Sp receiver functions show phases with negative polarity at 9 to 12s lead time on average, which we interpret as lithosphere-asthenosphere boundary at about 80 to 110km depth. © 2012 Elsevier B.V.
1224.
Late Quaternary sedimentological and climate changes at Lake Bosumtwi Ghana: New constraints from laminae analysis and radiocarbon age modeling
Palaeogeography, Palaeoclimatology, Palaeoecology,
361-36249 – 60
2012
ISSN: 00310182Keywords:▾
Ashanti; Ghana; Lake Bosumtwi; Sub-Saharan Africa; calibration; climate change; core analysis; drought; glacial-interglacial cycle; graphitization; heat transfer; Heinrich event; Holocene; laminar flow; moisture content; paleoclimate; radiocarbon dating; sedimentation rate; uncertainty analysis
Abstract: ▾ The Lake Bosumtwi sediment record represents one of the longest and highest-resolution terrestrial records of paleoclimate change available from sub-Saharan Africa. Here we report a new sediment age model framework for the last ~. 45. cal kyr of sedimentation using a combination of high-resolution radiocarbon dating, Bayesian age-depth modeling and lamination counting. Our results highlight the practical limits of these methods for reducing age model uncertainties and suggest that even with very high sampling densities, radiocarbon uncertainties of at least a few hundred years are unavoidable. Age model uncertainties are smallest during the Holocene (205. yr) and the glacial (360. yr) but are large at the base of the record (1660. yr), due to a combination of decreasing sample density, larger calibration uncertainties and increases in radiocarbon age scatter. For portions of the chronology older than ~. 35. cal kyr, additional considerations, such as the use of a low-blank graphitization system and more rigorous sample pretreatment were necessary to generate a reliable age depth model because of the incorporation of small amounts of younger carbon. A comparison of radiocarbon age model results and lamination counts over the time interval ~. 15-30. cal kyr agree with an overall discrepancy of ~. 10% and display similar changes in sedimentation rate, supporting the annual nature of sediment laminations in the early part of the record. Changes in sedimentation rates reconstructed from the age-depth model indicate that intervals of enhanced sediment delivery occurred at 16-19, 24 and 29-31. cal kyr, broadly synchronous with reconstructed drought episodes elsewhere in northern West Africa and potentially, with changes in Atlantic meridional heat transport during North Atlantic Heinrich events. These data suggest that millennial-scale drought events in the West African monsoon region were latitudinally extensive, reaching within several hundred kilometers of the Guinea coast. This is inconsistent with a simple southward shift in the mean position of the monsoon rainbelt, and requires changes in moisture convergence as a result of either a reduction in the moisture content of the tropical rainbelt, decreased convection, or both. © 2012 Elsevier B.V.
1223.
Late Pleistocene and Holocene contourite drift in Lake Prespa (Albania/F.Y.R. of Macedonia/Greece)
Quaternary International,
274112 – 121
2012
ISSN: 10406182Keywords:▾
Lake Mikri Prespa; chronostratigraphy; contourite; drift behavior; glacial deposit; Holocene; ice cover; interglacial; lake level; lithology; marine isotope stage; Pleistocene; sediment core; sedimentary sequence; sedimentation
Abstract: ▾ Hydro-acoustic surveys and coring campaigns at Lake Prespa were carried out between 2007 and 2009. This paper presents hydro-acoustic profiles and provide lithological and chronostratigraphical information from three up to 15.75 m long sediment sequences from the Macedonian side of the lake. The sediment sequences comprise glacial and interglacial sediments likely deposited from the end of Marine Isotope Stage (MIS) 5 to present day. The information implies a distinct change of sedimentation patterns at the Pleistocene/Holocene transition and the establishment of a relatively strong Holocene current system and deposition of channel-related contourite drift in Lake Prespa. Potential causes for the establishment of this current during the Holocene include significant lake level change, reduced winter ice cover, and/or higher aeolian activity. © 2012 Elsevier Ltd and INQUA.
1222.
Late Cretaceous chronostratigraphy (Turonian-Maastrichtian): SK1 core Songliao Basin, China
Geoscience Frontiers,
3
(4)
357-367
2012
ISSN: 16749871
Publisher: Elsevier B.V.
Keywords:▾
age determination; charophyte; chronostratigraphy; cyclostratigraphy; lithostratigraphy; Maastrichtian; ostracod; palynomorph; Turonian, China; Songliao Basin, Characeae; Ostracoda
Abstract: ▾ Non-marine ostracodes, charophytes and palynomorphs are abundant in most Cretaceous lacustrine basins of East Asia. However, their ranges are not directly integrated with marine biota that defines the Cretaceous stages. Non-biotic events such as magnetochrons and radiometric ages in these terrestrial deposits enable their correlation with marine strata. The SK1 north and south composited cores in the Songliao Basin present a continuous section of Upper Cretaceous non-marine fossil and magnetochron successions in superposed order. These chronostratigraphic events are integrated with marine events by an X/Y graphic plot between the core data and a global database of Global Section and Stratotype Points (GSSP) and key reference sections. This plot projects stage boundaries in marine sections into the SK1 section and interpolates numerical ages to the first and last occurrences of biota and to lithostratigraphic boundaries. This stratigraphic experiment tests and refines age calibrations based on both manual interpolation of depths to numerical ages and cyclostratigraphy. Ages derived by interpolation are similar and ages by cyclostratigraphy are older because stage boundaries are calibrated to a different age scale. © 2011, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.
1221.
Late Cretaceous biostratigraphy and paleoenvironmental reconstruction based on non-marine ostracodes from well SK1 (south), Songliao Basin, northeast China
Hydrobiologia,
688
(1)
113-123
2012
ISSN: 00188158Keywords:▾
biostratigraphy; Cretaceous; deep water; fossil record; ostracod; paleoecology; paleoenvironment; reconstruction; salinity, China; Songliao Basin, Ostracoda
Abstract: ▾ High-resolution biostratigraphy has been established on the basis of fossil ostracodes from cores of the Cretaceous Continental Scientific Drilling borehole-Songke 1 (south) (SK1(s)) in the Songliao Basin, northeast China. More than 80 species belonging to 13 genera have been identified and 15 ostracode assemblage zones have been recognized. On the basis of ostracode paleoecological analysis, paleoenvironments, for example lake levels and salinity, have been reconstructed. Two inferred deep-water phases occurred during the deposition of the lower Qingshankou and lower Nenjiang formations, whereas shallower water phases probably occurred during deposition of the upper Quantou and uppermost Qingshankou to Yaojia formations. The salinity of paleo-Songliao lake is interpreted as predominantly freshwater to oligohaline. Oligohaline to mesohaline water environments may have occurred during the first and middle third members of the Qingshankou formation and the lower first and lower second members of the Nenjiang formation. © 2011 Springer Science+Business Media B.V.
1220.
Isotopic evidence for a sizeable seawater sulfate reservoir at 2.1 Ga
Precambrian Research,
19278--88
2012