Boundary stratotype of the Cretaceous Qingshankouan stage in the Songliao Basin - Gang, Han; Wenjing, Zhang; Qinghua, Huang; et al. (Journal of Stratigraphy, 2012)

Assessment of purification and contamination correction methods for analysing the oxygen isotope composition from biogenic silica - Chapligin, B.; Meyer, H.; Bryan, A.; SNYDER, J.; Kemnitz, H. (Chemical Geology, 2012)
Mineral particles and other contaminants cause a serious and undesirable shift in δ 18O values of biogenic silica and should be removed prior to isotope analysis. This problem is particularly significant in the fraction containing clay particles and therefore the fraction <10μm is generally avoided. Here, we present an updated preparation protocol for the <10μm fraction based on known methods, developed using test material from short cores of Lake El'gygytgyn, NE Russia. New contamination assessment and correction techniques are discussed. Best results (low initial weight/high precision and throughput rate) for the <10μm fraction were achieved using geochemical mass-balancing and determining the percentage of contamination by analysing the sample's and end-member's Al 2O 3 with improved Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Energy-Dispersive X-ray Spectroscopy (EDS) protocols or by determining the factor for calculating the percentage of contamination from the Al 2O 3 percentage of clay assemblages. Despite using small initial weights for ICP-OES (10mg) and EDS analysis ( <0.5mg) a sufficiently high precision (for low Al 2O 3 percentages between 0.1 and 1.5%) could be achieved.For the >10μm fraction, point-counting under the light microscope was the preferred option. The different size-fractions from Lake El'gygytgyn samples show a distinct and significantly different species composition (average counts: <10μm: >90% Cyclotella ocellata complex; >10μm: >60% Pliocaenicus seczkinae). Differences in the oxygen isotope composition of these different size fractions could be explained by a species-effect on the δ 18O values. However, this species-effect disappeared after the correction (avg δ 18O <10μm: 19.8±0.6‰; >10μm: 19.8±0.4‰). By comparing these δ 18O values with additional recent water samples, an average 1000 ln α of 39.6‰ for Lake El'gygytgyn sub-recent diatoms was calculated. This tool-kit provides support for the presented improved contamination assessment and corrections and allows utilising smaller initial weight (app. 10mg) and small fractions ( <10μm) for gaining corrected, higher resolution δ 18O records. © 2012 Elsevier B.V..
cited By 32
Keywords: Diatoms; El' gygytgyn; ICP-OES; Species-effect; XRF; Aluminum; Emission spectroscopy; Energy dispersive spectroscopy; Inductively coupled plasma; Isotopes; Lakes; Oxygen; Phytoplankton; Rating; Silica; Contamination; assessment method; biogenic material; biomonitoring; error correction; inductively coupled plasma method; isotopic composition; lake pollution; mass balance; oxygen isotope; pollutant transport; purification; silica; X-ray spectroscopy; Chukchi; Elgygytgyn Lake; Russian Federation; Bacillariophyta; Cyclotella ocellata; Pliocaenicus

Application of conditional simulation of heterogeneous rock properties to seismic scattering and attenuation analysis in gas hydrate reservoirs - Huang, J.W.; Bellefleur, G.; Milkereit, B. (Journal of Applied Geophysics, 2012)
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..
cited By 6
Keywords: 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

Anti-collapse drilling fluids for the Cretaceous scientific drilling in Songliao basin, China: A case study - Cai, J.; Wu, X.; Gu, S. (Applied Mechanics and Materials, 2012)
CCSD-SK1 well was the first Cretaceous scientific drilling well in the world, locating in Songliao basin, Northeast China. It included main well (also called north well) and south well. This paper introduced the anti-collapse drilling fluid technology in main well where the desired continuous coring section was from 164.77 m to 1792.00 m. Continuous technical barriers challenged the intelligence of drilling engineers of this project. First, preserving the wellbore stability was the most critical aspect of continuous core drilling. From top to bottom, the unconsolidated sandstone in the Quaternary super stratum, the water sensitive shale in the Sifangtai group and upper stratum of the Nenjiang group, and the brittle shale of under stratum of the Nenjiang group increased the difficulty of anti-collapse drilling fluid technology. Water invasion into the shale formation often weakens the wellbore and causes problems such as wellbore collapse, shale destabilization and stuck pipe. Fluids should be designed to mitigate these shale problems. Secondly, the openhole strategy imposed the difficulty of maintaining wellbore stability in the second open process (from 245.00 m to the bottom). Finally, the total expense of the well was only one fifth ofsouth well, which was drilled by an oilfield drilling contractor. To overcome these technical challenges, not only different drilling fluid systems such as PAM drilling fluid, DFD-LG-CMC drilling fluid and DFD-NH4HPAN-SAKH drilling fluid were adopted separately, but also technology of feasible viscosity and managed pressure drilling were used. A total of 395 trips had been run in this Cretaceous scientific drilling well and no accidents even dangerous cases occurred. The experience of CCSD-SK1 (main well) explored a successful way of employing economic drilling fluid to preceding similar scientific drilling projects in similar shale formations. © (2012) Trans Tech Publications, Switzerland.
cited By 0
Keywords: Drilling contractors; Managed Pressure Drilling; Northeast China; Open process; Openhole; Scientific drilling; Shale formation; Songliao basin; Stuck pipe; Technical barriers; Technical challenges; Water invasion; Water sensitive; Wellbore; Wellbore stability; Building materials; Civil engineering; Core drilling; Oil field equipment; Oil fields; Shale; Drilling fluids

Correlation of clayey gouge in a surface exposure of serpentinite in the San Andreas Fault with gouge from the San Andreas Fault Observatory at Depth (SAFOD) - Moore, D.E.; Rymer, M.J. (Journal of Structural Geology, 2012)
Magnesium-rich clayey gouge similar to that comprising the two actively creeping strands of the San Andreas Fault in drill core from the San Andreas Fault Observatory at Depth (SAFOD) has been identified in a nearby outcrop of serpentinite within the fault zone at Nelson Creek. Each occurrence of the gouge consists of porphyroclasts of serpentinite and sedimentary rocks dispersed in a fine-grained, foliated matrix of Mg-rich smectitic clays. The clay minerals in all three gouges are interpreted to be the product of fluid-assisted, shear-enhanced reactions between quartzofeldspathic wall rocks and serpentinite that was tectonically entrained in the fault from a source in the Coast Range Ophiolite. We infer that the gouge at Nelson Creek connects to one or both of the gouge zones in the SAFOD core, and that similar gouge may occur at depths in between. The special significance of the outcrop is that it preserves the early stages of mineral reactions that are greatly advanced at depth, and it confirms the involvement of serpentinite and the Mg-rich phyllosilicate minerals that replace it in promoting creep along the central San Andreas Fault. © 2011.
cited By 44
Keywords: Coast range ophiolites; Metasomatic reactions; SAFOD; San Andreas fault; Serpentinite; Smectite clays; Buildings; Clay minerals; Core drilling; Magnesium; Observatories; Strike-slip faults; correlation; creep; fault gouge; fault zone; metasomatism; ophiolite; outcrop; San Andreas Fault; sedimentary rock; serpentinite; smectite; tectonic setting

An emplacement mechanism for the mega-block zone within the Chicxulub crater, (Yucat'an, Mexico) based on chemostratigraphy - Belza, J.; Goderis, S.; Keppens, E.; Vanhaecke, F.; Claeys, P. (Meteoritics and Planetary Science, 2012)
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.
cited By 10

An early first-century earthquake in the Dead Sea - Williams, J.B.; Schwab, M.J.; Brauer, A. (International Geology Review, 2012)
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.
cited By 5
Keywords: chronology; earthquake; Holocene; seismicity; varve; Dead Sea

A study of sediment magnetic mineralogy in Lake Bosumtwi, Ghana: Indications of depositional environment and paleoclimate - Dzirasah, W.; Danuor, S.K.; Menyeh, A.; Peck, J.E. (European Journal of Scientific Research, 2012)
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.

A seasonal cycle of terrestrial inputs in Lake Van, Turkey - Huguet, C.; Fietz, S.; Moraleda, N.; Litt, T.; Heumann, G.; Stockhecke, M.; Anselmetti, F.S.; Sturm, M. (Environmental Science and Pollution Research, 2012)
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.
cited By 8
Keywords: 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

A new model for barberton komatiites: Deep critical melting with high melt retention - Robin-Popieul, Christophe C.M.; Arndt, Nicholas T.; Chauvel, Catherine; Byerly, Gary R.; Sobolev, Alexander V.; Wilson, Allan (Journal of Petrology, 2012)
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.
Keywords: Barberton Greenstone Belt; Archean; concentration (composition); geochemistry; komatiite; magma; mantle plume; modeling; peridotite; petrogenesis; petrology; rare earth element

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 - Hadizadeh, J.; Mittempergher, S.; Gratier, J.-P.; Renard, F.; Di Toro, G.; Richard, J.; Babaie, H.A. (Journal of Structural Geology, 2012)
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.
cited By 46
Keywords: 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

A 250 ka oxygen isotope record from diatoms at Lake El'gygytgyn, far east Russian Arctic - Chapligin, B.; Meyer, H.; Swann, G. E. A.; Meyer-Jacob, C.; Hubberten, H.-W. (Climate of the Past, 2012)
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.
cited By 29
Keywords: 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

500,000 years of environmental history in Eastern Anatolia: The PALEOVAN Drilling project - Litt, T.; Anselmetti, F.S.; Baumgarten, H.; Beer, J.; Cagatay, N.; Cukur, D.; Damci, E.; Glombitza, C.; Haug, G.; Heumann, G.; Kallmeyer, J.; Kipfer, R.; et al. (Scientific Drilling, 2012)
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.
cited By 37
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

40Ar/39Ar ages for deep (∼3.3 km) samples from the Hawaii Scientific Drilling Project, Mauna Kea volcano, Hawaii - Jourdan, Fred; Sharp, Warren D.; Renne, Paul R. (Geochemistry, Geophysics, Geosystems, 2012)
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.
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

2.8 Million years of arctic climate change from Lake El'gygytgyn, NE Russia - Melles, M.; Brigham-Grette, J.; Minyuk, P.S.; Nowaczyk, N.R.; Wennrich, V.; DeConto, R.M.; Anderson, P.M.; Andreev, A.A.; Coletti, A.; Cook, T.L.; Haltia-Hovi, E.; Kukkonen, M.; et al. (Science, 2012)
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.
cited By 339
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

1 The International Continental Scientific Drilling Program - Melezhik, Victor A (Reading the Archive of Earth’s Oxygenation: Volume 1: The Palaeoproterozoic of Fennoscandia as Context for the Fennoscandian Arctic Russia-Drilling Early Earth Project, 2012)

Iron deficiency in pyrrhotite of suevites from the Chesapeake Bay impact crater, USA-A consequence of shock metamorphism? - Mang, C.; Kontny, A.; Harries, D.; Langenhorst, F.; Hecht, L. (Meteoritics and Planetary Science, 2012)
Pyrrhotite from suevite of the 35Ma Chesapeake Bay impact structure (CBIS) shows a shock metamorphism and we report on several mineralogical and magnetic features. Pyrrhotite shows strong brittle deformation with a high density of stacking faults, twinning parallel to the hexagonal (001) planes and average fault distances in the order of 10nm. Although the determination of a superstructure was not possible due to the lattice defects, the reflections of the NiAs subcell, which is typical of all pyrrhotite modifications, were clearly detected. This phase is ferrimagnetic with a Curie temperature (T C) between 350 and 365°C, and suevite with this phase does not show the 34K transition. The most peculiar feature is the low metal/sulfur ratio of 0.81, which indicates a distinctly higher vacancy concentration than for 4C pyrrhotite and a composition close to smythite (Fe 9S 11). This phase carries a stable natural remanent magnetization and is relatively hard magnetic. Steep inclinations of the natural remanent magnetization vector, however, suggest that this phase has been remagnetized by the drilling process. A possible explanation is the magnetic domain size of faultless areas of about 10nm in diameter, which is at the lower limit of the single domain size near the threshold, below which superparamagnetic behavior occurs. The low thermal stability of this phase excludes postshock heating above 300°C for the suevite of the CBIS. Our results imply that the iron-deficient pyrrhotite is produced by shock metamorphism, although an iron loss due to shock has never been reported before for pyrrhotite. © 2012 The Meteoritical Society.
cited By 8

Contributions of gamma-ray spectrometry to terrestrial impact crater studies: The example of Serra da Cangalha, northeastern Brazil - Vasconcelos, M.A.R.; Leite, E.P.; Cr'osta, A.P. (Geophysical Research Letters, 2012)
Several geophysical methods have been used for decades for the identification and exploration of impact craters. Most of them are based on seismic, potential fields and electrical data, focusing on exploration of anomalies caused by changes in physical properties or by structures associated with the formation of the crater. Gamma-ray spectrometry is usually not mentioned among the geophysical methods employed in crater studies, although it is known that impact cratering processes cause a number of physical/chemical changes in the country rocks. These changes include the remobilization of hydrothermal fluids which directly modify the composition of target rocks and, subsidiarily, of soils related to these rocks. Therefore, the distribution of radioactive elements K, Th and U has the potential to map such modifications. We present the analysis of gamma-ray signatures at the Serra da Cangalha impact structure, located in northeastern Brazil, using methods for enhancing K anomalies and also the overall gamma-ray signatures. These results provide valuable information on the distinct zones within the crater and might contribute to the understanding of hydrothermal enrichment processes produced as a result of the impact event. Copyright 2012 by the American Geophysical Union.
cited By 10

Anatomy of the high-frequency ambient seismic wave field at the TCDP borehole - Hillers, G.; Campillo, M.; Lin, Y.-Y.; Ma, K.-F.; Roux, P. (Journal of Geophysical Research: Solid Earth, 2012)
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.
cited By 19
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

Dating deep? Luminescence studies of fault gouge from the San Andreas Fault zone 2.6 km beneath Earth's surface - Spencer, J.Q.G.; Hadizadeh, J.; Gratier, J.-P.; Doan, M.-L. (Quaternary Geochronology, 2012)
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..
cited By 12
Keywords: complexity; deformation; fault gouge; fault zone; luminescence dating; microstructure; resetting; rupture; San Andreas Fault; California; San Andreas; United States

Geochemistry of eolian dust and its elemental contribution to Lake Qinghai sediment - Wan, Dejun; Jin, Zhangdong; Wang, Yinxi (Applied Geochemistry, 2012)
Located at the midpoint of the Asian airborne dust corridor , Lake Qinghai receives substantial dust annually, which may impact the biogeochemical cycles of the system. In order to determine quantitatively the flux and chemical contributions of dust to Lake Qinghai sediment, dust samples were collected monthly at two sites surrounding the lake from June 2009 to May 2011. The results demonstrate similar chemical compositions of dust samples to the local loess, implying strong representativeness of regional dust. The average dust deposition flux is 265.7±55.0g/m 2/a, constituting 56.6±11.7% of the modern sediment, approximating to previous estimates ( 65%). Contributions of dust-derived elements in the sediment differ substantially, with a minimum of 16.7% for Sr and a maximum of 83.9% for Cu. Among these elements, the contribution of lithophile elements (Na, Al, K, Ti, Mn, Fe and Rb) is close to that of the bulk dust; the contributions of mobile elements (Mg, Ca and Sr) are low, only 16.7% (Sr)-26.1% (Mg), whereas potentially harmful metals (Cu, Zn and Pb) have high contributions (70.3-83.9%). Seasonal variations of elemental inputs indicate that springtime contributions dominate the annual dust fluxes for all elements into the sediment, in agreement with the high dust flux in spring. These observations not only quantify the contribution of dust to the sediment of Lake Qinghai, but also highlight the important role of dust in the accumulation of various elements in the sediment, especially for potentially harmful metals. © 2012 Elsevier Ltd.
Keywords: China; Qinghai; Qinghai Lake; Copper; Lakes; Lead; Manganese; Rubidium; Sedimentology; Sediments; Sodium; Strontium; Airborne dusts; Biogeochemical cycle; Chemical compositions; Dust deposition; Dust flux; Dust samples; Eolian dust; Lake Qinghai; Lithophile elements; Mobile elements; Seasonal variation; biogeochemical cycle; eolian deposit; lacustrine deposit; quantitative analysis; seasonal variation; sediment chemistry; Dust

Deep core drilling of three slim geothermal holes, Snake River Plains, Idaho - Delahunty, Chris; Nielson, Dennis L.; Shervais, John W. (Transactions - Geothermal Resources Council, 2012)
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.
Keywords: Core drilling; Geothermal fields; Geothermal; Kimama (Idaho); Kimberly (Idaho); Mountain Home (Idaho); Slim-hole coring; Snake river plains; Wireline; Rivers

Interpreting noble-gas concentrations as proxies for salinity and temperature in the world's largest soda lake (Lake Van, Turkey) - Tomonaga, Y.; Bl{attler, R.; Brennwald, M.S.; Kipfer, R. (Journal of Asian Earth Sciences, 2012)
In this work we present noble-gas concentration profiles measured in the water column and in the sediment pore water of the Earth's largest soda lake: Lake Van (eastern Anatolia, Turkey). The concentrations of noble gases (in particular Ar, Kr, and Xe) in the water body deviate significantly from the expected equilibrium concentrations calculated from the in situ temperature and salinity using existing solubility functions for seawater. The specific chemical composition of the water of the soda lake seems to be responsible for the observed deviations. Our measurements allow the identification and quantification of salinity factors that can be applied to correctly calculate the noble-gas equilibrium concentrations for the lake. These salinity factors provide a solid and robust empirical basis for the interpretation of noble-gas concentration signals measured in the sediment pore water of Lake Van in terms of palaeosalinity and palaeotemperature. © 2012 Elsevier Ltd.
cited By 20
Keywords: chemical composition; concentration (composition); empirical analysis; noble gas; paleoclimate; paleosalinity; paleotemperature; porewater; salinity; temperature; water column; Lake Van; Turkey

Interplay between the Westerlies and Asian monsoon recorded in Lake Qinghai sediments since 32 ka - An, ZhiSheng; Colman, Steven M.; Zhou, Weijian; Li, Xiaoqiang; Brown, Eric T.; Jull, A. J. Timothy; Cai, Yanjun; Huang, Yongsong; Lu, Xuefeng; Chang, Hong; Song, YouGui; Sun, Youbin; et al. (Scientific Reports, 2012)
Two atmospheric circulation systems, the mid-latitude Westerlies and the Asian summer monsoon (ASM), play key roles in northern-hemisphere climatic changes. However, the variability of the Westerlies in Asia and their relationship to the ASM remain unclear. Here, we present the longest and highest-resolution drill core from Lake Qinghai on the northeastern Tibetan Plateau (TP), which uniquely records the variability of both the Westerlies and the ASM since 32ĝ€...ka, reflecting the interplay of these two systems. These records document the anti-phase relationship of the Westerlies and the ASM for both glacial-interglacial and glacial millennial timescales. During the last glaciation, the influence of the Westerlies dominated; prominent dust-rich intervals, correlated with Heinrich events, reflect intensified Westerlies linked to northern high-latitude climate. During the Holocene, the dominant ASM circulation, punctuated by weak events, indicates linkages of the ASM to orbital forcing, North Atlantic abrupt events, and perhaps solar activity changes.

Inferred gas hydrate and permafrost stability history models linked to climate change in the Beaufort-Mackenzie Basin, Arctic Canada - Majorowicz, J.; Šafanda, J.; Osadetz, K. (Climate of the Past, 2012)
Atmospheric methane from episodic gas hydrate (GH) destabilization, the clathrate gun hypothesis, is proposed to affect past climates, possibly since the Phanerozoic began or earlier. In the terrestrial Beaufort-Mackenzie Basin (BMB), GHs occur commonly below thick ice-bearing permafrost (IBP), but they are rare within it. Two end-member GH models, where gas is either trapped conventionally (Case 1) or where it is trapped dynamically by GH formation (Case 2), were simulated using profile (1-D) models and a 14 Myr ground surface temperature (GST) history based on marine isotopic data, adjusted to the study setting, constrained by deep heat flow, sedimentary succession conductivity, and observed IBP and Type I GH contacts in Mallik wells. Models consider latent heat effects throughout the IBP and GH intervals. Case 1 GHs formed at ∼0.9 km depth only ∼1 Myr ago by in situ transformation of conventionally trapped natural gas. Case 2 GHs begin to form at ∼290-300 m ∼6 Myr ago in the absence of lithological migration barriers. During glacial intervals Case 2 GH layers expand both downward and upward as the permafrost grows downward through and intercalated with GHs. The distinctive model results suggest that most BMB GHs resemble Case 1 models, based on the observed distinct and separate occurrences of GHs and IBP and the lack of observed GH intercalations in IBP. Case 2 GHs formed >255 m, below a persistent ice-filled permafrost layer that is as effective a seal to upward methane migration as are Case 1 lithological seals. All models respond to GST variations, but in a delayed and muted manner such that GH layers continue to grow even as the GST begins to increase. The models show that the GH stability zone history is buffered strongly by IBP during the interglacials. Thick IBP and GHs could have persisted since ∼1.0 Myr ago and ∼4.0 Myr ago for Cases 1 and 2, respectively. Offshore BMB IBP and GHs formed terrestrially during Pleistocene sea level low stands. Where IBP is sufficiently thick, both IBP and GHs persist even where inundated by a Holocene sea level rise and both are also expected to persist into the next glacial even if atmospheric CO2 doubles. We do not address the clathrate gun hypothesis directly, but our models show that sub-IBP GHs respond to, rather than cause GST changes, due to both how GST changes propagates with depth and latent heat effects. Models show that many thick GH accumulations are prevented from contributing methane to the atmosphere, because they are almost certainly trapped below either ice-filled IBP or lithological barriers. Where permafrost is sufficiently thick, combinations of geological structure, thermal processes and material properties make sub-IBP GHs unlikely sources for significant atmospheric methane fluxes. Our sub-IBP GH model histories suggest that similar models applied to other GH settings could improve the understanding of GHs and their potential to affect climate. © 2012 Author(s).
cited By 14
Keywords: carbon dioxide; climate variation; gas hydrate; heat flux; Holocene; interglacial; lithology; methane; natural gas; paleoatmosphere; paleoclimate; permafrost; Phanerozoic; sea level change; surface temperature; Arctic Ocean; Beaufort Sea; Beaufort-Mackenzie Basin; Canada; Canadian Arctic; Calluna vulgaris

Impactites: Their Characteristics and Spatial Distribution - Grieve, R.A.F.; Therriault, A.M. (Impact Cratering: Processes and Products, 2012)
cited By 17

Impact-Induced Hydrothermal Activity - Kirsim{ae, K.; Osinski, G.R. (Impact Cratering: Processes and Products, 2012)
cited By 20

Imaging the Mari'ansk'e L'azně Fault (Czech Republic) by 3-D ground-penetrating radar and electric resistivity tomography - Fischer, Tom'aš; Štěpanč'ikov'a, Petra; Karousov'a, Magda; T'aboř'ik, Petr; Flechsig, Christina; Gaballah, Mahmoud (Studia Geophysica et Geodaetica, 2012)
Geodynamic activity in the area of West Bohemia is typified by the occurrence of earthquake swarms, Quaternary volcanism and high flux of mantle-derived CO2. The highest swarm activity occurs beneath the eastern edge of the Cheb basin, which is delineated by the NW-SE trending morphologically pronounced Mari'ansk'e L'azně Fault (MLF) controlling the formation of the basin. The previous trenching survey across the MLF zone has identified several fault strands with possible Quaternary activity. In this paper we present the results of the geophysical survey focused to trace the faults signatures in geophysical sections and to build an image of near surface tectonics. The method of electric resistivity tomography (ERT) along two profiles parallel to the trench identified a strong resistivity contrast between the bodies of sandy gravels in the middle and conductive clayey sands to the west and weathered crystalline basement to the east. The 2-D ground penetration radar (GPR) sections show direct correlation of reflections with lithological boundaries identified in the trench. As expected, the GPR signal amplitudes increase with the resistivities found in the ERT sections. Two of the four faults identified in the trench are indicated in the resistivity and GPR sections. A 3-D GPR measurement has identified a spot of high amplitudes elongated parallel to the MLF trend, which coincides with the high resistivity body. To improve the signal-to-noise ratio of the time slices we stacked the GPR time slices within vertically homogeneous blocks. This provided a contrast image of the sand-gravel body including its boundaries in three dimensions. The detailed analysis of the 3-D GPR cube revealed additional fault that limits the highly reflective sands and appears to be offset by another younger fault. Our results suggest a complex fault pattern in the studied area, which deserves a further study. © 2012 Institute of Geophysics of the ASCR, v.v.i.
Keywords: Bohemia; Czech Republic; earthquake swarm; electrical resistivity; fault zone; geodynamics; ground penetrating radar; lithology; Quaternary; signal-to-noise ratio; three-dimensional modeling; tomography; trend analysis; two-dimensional modeling; volcanism

Holocene climate variability in the Levant from the Dead Sea pollen record - Litt, T.; Ohlwein, C.; Neumann, F.H.; Hense, A.; Stein, M. (Quaternary Science Reviews, 2012)
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.
cited By 125
Keywords: 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

High-temperature, low-H 2O silicic magmas of the yellowstone hotspot: An experimental study of rhyolite from the Bruneau-Jarbidge eruptive center, Central Snake River Plain, USA - Almeev, R.R.; Bolte, T.; Nash, B.P.; Holtz, F.; Erdmann, M.; Cathey, H.E. (Journal of Petrology, 2012)
The phase relations have been investigated experimentally at 200 and 500 MPa as a function of water activity for one of the least evolved (Indian Batt Rhyolite) and of a more evolved rhyolite composition (Cougar Point Tuff XV) from the 12·8-8·1 Ma Bruneau-Jarbidge eruptive center of the Yellowstone hotspot. Particular priority was given to accurate determination of the water content of the quenched glasses using infrared spectroscopic techniques. Comparison of the composition of natural and experimentally synthesized phases confirms that high temperatures ( >900°C) and extremely low melt water contents ( <1·5 wt % H. 2O) are required to reproduce the natural mineral assemblages. In melts containing ∼0·5-1·5 wt % H. 2O, the liquidus phase is clinopyroxene (excluding Fe-Ti oxides, which are strongly dependent on fO. 2), and the liquidus temperature of the more evolved Cougar Point Tuff sample (BJR; ∼940-1000°C) is at least 30°C lower than that of the Indian Batt Rhyolite lava sample (IBR2; 970-1030°C). For the composition BJR, the comparison of the compositions of the natural and experimental glasses indicates a pre-eruptive temperature of at least 900°C. The composition of clinopyroxene and pigeonite pairs can be reproduced only for water contents below 1·5 wt % H. 2O at 900°C, or lower water contents if the temperature is higher. For the composition IBR2, a minimum temperature of 920°C is necessary to reproduce the main phases at 200 and 500 MPa. At 200 MPa, the pre-eruptive water content of the melt is constrained in the range 0·7-1·3 wt % at 950°C and 0·3-1·0 wt % at 1000°C. At 500 MPa, the pre-eruptive temperatures are slightly higher (by ∼30-50°C) for the same ranges of water concentration. The experimental results are used to explore possible proxies to constrain the depth of magma storage. The crystallization sequence of tectosilicates is strongly dependent on pressure between 200 and 500 MPa. In addition, the normative Qtz-Ab-Or contents of glasses quenched from melts coexisting with quartz, sanidine and plagioclase depend on pressure and melt water content, assuming that the normative Qtz and Ab/Or content of such melts is mainly dependent on pressure and water activity, respectively. The combination of results from the phase equilibria and from the composition of glasses indicates that the depth of magma storage for the IBR2 and BJR compositions may be in the range 300-400 MPa (∼≤13 km) and 200-300 MPa (∼≤10 km), respectively. © The Author 2012. Published by Oxford University Press. All rights reserved.
cited By 56
Keywords: concentration (composition); crystallization; experimental study; high temperature; hot spot; lava; magma; phase equilibrium; rhyolite; tectosilicate; volcanic eruption; water content; Idaho; Snake River Plain; United States

Heating-induced changes in the anisotropy of magnetic susceptibility of impact breccias, Chicxulub Crater (Mexico) - Urrutia-Fucugauchi, J.; Delgadillo-Peralta, M.; P'erez-Cruz, L.; Velasco-Villarreal, M. (Studia Geophysica et Geodaetica, 2012)
Initial results of a thermal treatment study on the anisotropy of magnetic susceptibility (AMS) of impact breccias from Chicxulub crater are used to investigate the nature of the magnetic fabrics. Chicxulub impact breccias are heterogeneous materials, with carbonate, basement and melt clasts within carbonate-rich or melt-rich matrix. Samples studied come from the carbonate-rich basal unit Lower Suevite in the Yaxcopoil-1 borehole impactite sequence (core depth interval: 885-895 m). The Lower Suevite is characterized by mixed prolate and oblate ellipsoids with shallow to steep principal susceptibility axes, which had been related to emplacement as an excavation flow with ground-surge components during the early cratering stages. Thermal treatment results in changes in the fabrics with a tendency to oblate fabrics. Stepwise thermal treatment up to 700°C reveals different behaviors for the oblate, neutral and prolate fabrics marked by changes in AMS parameters and principal susceptibility axis orientations. A sample with oblate fabrics and vertical minimum axes showed an increase of magnetic susceptibility at high temperatures, indicating formation of secondary magnetite and fabric enhancement. A sample with neutral ellipsoid showed heating-induced changes towards oblate fabrics and vertical minimum susceptibility axes. Samples characterized by prolate ellipsoids with horizontal maximum axes showed no directional changes. In a sample with apparent intermediate or inverse fabrics, vertical maximum axes showed changes to horizontal inclinations, with the intermediate and maximum axes switching positions. Changes induced by stepwise thermal treatment appear useful to characterize the fabrics of impact lithologies. Further investigation of heating-induced effects in mineralogy, grain size and textural changes is, however, required to relate the different behaviors observed after stepwise thermal treatment with the magnetic mineralogy and emplacement mode of the breccias. © 2012 Institute of Geophysics of the ASCR, v.v.i.
cited By 3

Geothermal systems in the Snake River Plain, Idaho, characterizedby the Hotspot project - Nielson, D.L.; Delahunty, C.; Shervais, J.W. (Transactions - Geothermal Resources Council, 2012)
The Hotspot project has sampled three different geothermal environments in the Snake River Plain (SRP) in Idaho. The project used slim-hole wire line coring in conjunction with a bottom hole temperature probe developed by DOSECC. The first hole at Kimama in the center of the eastern SRP was cored to a depth of 1,915 m. Temperature measurements showed the SRP fresh water aquifer extends to a depth of 965 m and masks the underlying temperature gradient of 74.5°C/Km. A core hole in the town of Kimberly reached a depth of 1,959 m and demonstrated a resource of >50°C from 800 m to the bottom of the hole. A core hole at Mountain Home AFB in the eastern SRP reached a depth of 1,821 m and documents an intermediate- to high-temperature resource.
cited By 13
Keywords: Air Force Base; Bottom-hole temperatures; ID; Kimama; Kimberly; Slim-hole coring; Snake River; Aquifers; Geothermal wells; Rivers; Temperature measurement; Thermal gradients; Geothermal fields

Geological and geochemical characteristics of anoxic event bed in the Qingshankou Formation of Late Cretaceous in Songliao Basin - Gang, Han; Wen-Jing, ZHANG; Qing-Hua, HUANG; Yuan-Lin, MENG (Geoscience, 2012)

Hotspot: The Snake River geothermal drilling project - Initial report - Shervais, John W.; Nielson, Dennis; Evans, James P.; Lachmar, Thomas; Christiansen, Eric H.; Morgan, Lisa; Shanks, W. C. Pat; Delahunty, Christopher; Liberty, Lee M.; Blackwell, David D.; Glen, Jonathan M.; Kessler, James A.; et al. (Transactions - Geothermal Resources Council, 2012)
The Snake River volcanic province (SRP) overlies a thermal anomaly that extends deep into the mantle; it represents one of the highest heat flow provinces in North America. The primary goal of this project is to evaluate geothermal potential in three distinct settings: (1) Kimama site: inferred high sub-aquifer geothermal gradient associated with the intrusion of mafic magmas, (2) Kimberly site: a valley-margin setting where surface heat flow may be driven by the up-flow of hot fluids along buried caldera ring-fault complexes, and (3) Mountain Home site: a more traditional fault-bounded basin with thick sedimentary cover. The Kimama hole, on the axial volcanic zone, penetrated 1912 m of basalt with minor intercalated sediment; no rhyolite basement was encountered. Temperatures are isothermal through the aquifer (to 960 m), then rise steeply on a super-conductive gradient to an estimated bottom hole temperature of ∼98°C. The Kimberly hole is on the inferred margin of a buried rhyolite eruptive center, penetrated rhyolite with intercalated basalt and sediment to a TD of 1958 m. Temperatures are isothermal at 55-60°C below 400 m, suggesting an immense passive geothermal resource. The Mountain Home hole is located above the margin of a buried gravity high in the western SRP. It penetrates a thick section of basalt and lacustrine sediment overlying altered basalt flows, hyaloclastites, and volcanic sediments, with a TD of 1821 m. Artesian flow of geothermal water from 1745 m depth documents a power-grade resource that is now being explored in more detail. In-depth studies continue at all three sites, complemented by high-resolution gravity, magnetic, and seismic surveys, and by downhole geophysical logging.
Keywords: Aquifers; Basalt; Geothermal fields; Geothermal wells; Granite; Isotherms; Natural resources exploration; Rivers; Sedimentology; Volcanoes; Bottom hole temperatures; Downhole geophysical logging; Geothermal resources; Hot spot; Idaho; Lacustrine sediments; Rhyolite; Snake river plains; Sediments

Gas hydrate reservoir modeling and validation - Gloaguen, E.G.; Dubreuil-Boisclair, C.D.B.; Giroux, B.G.; Marcotte, D.M. (Integrated Reservoir Modelling: Are We Doing it Right?, 2012)
The decrease in conventional gas reservoir new discoveries combined with the increase of the market and improvement of the exploitation technologies push the industry to look for unconventional gas resources. Gas hydrates are one of the largest unconventional resource but also one of the less known. In this study, we use a modified bayesian algorithm in order to simulated gas hydrate grades at Mallik, TNO, Canada constrained by 3D seismic acoustic impedances. The results are validated using a high resolution seismic tomographic inversion. Even with the poor quality 3D seismic data, the proposed method is found to be very robust to estimate gas hydrate grades at Mallik.
cited By 0
Keywords: Acoustic impedance; Energy resources; Gases; Hydration; Reservoir management; Resource valuation; Seismology; 3D seismic data; Bayesian algorithms; Gas hydrate reservoir; Gas reservoir; High resolution seismic; Tomographic inversion; Unconventional gas; Unconventional resources; Gas hydrates

Exploration and resource assessment at Mountain Home Air Force Base, Idaho, using an integrated team approach - Breckenridge, R.P.; Nielson, D.L.; Shervais, J.W.; Wood, T.R. (Transactions - Geothermal Resources Council, 2012)
The U.S. Air Force is facing a number of challenges as it moves into the future, one of the biggest being how to provide safe and secure energy to support base operations. A team of scientists and engineers met at Mountain Home Air Force Base near Boise, Idaho, to discuss the possibility of exploring for geothermal resources under the base. The team identified that there was a reasonable potential for geothermal resources based on data from an existing well. In addition, a regional gravity map helped identify several possible locations for drilling a new well. The team identified several possible sources of funding for this well - the most logical being to use U.S. Department of Energy funds to drill the upper half of the well and U.S. Air Force funds to drill the bottom half of the well. The well was designed as a slimhole well in accordance with State of Idaho Department of Water Resources rules and regulations. Drilling operations commenced at the Mountain Home site in July of 2011 and were completed in January of 2012. Temperatures increased gradually, especially below a depth of 2000 ft. Temperatures increased more rapidly below a depth of 5500 ft. The bottom of the well is at 5976 ft, where a temperature of about 140°C was recorded. The well flowed artesian from a depth below 5600 ft, until it was plugged off with drilling mud. Core samples were collected from the well and are being analyzed to help understand permeability at depth. Additional tests using a televiewer system will be run to evaluate orientation and directions at fractures, especially in the production zone. A final report on the well exploitation will be forthcoming later this year. The Air Force will use it to evaluate the geothermal resource potential for future private development options at Mountain Home AFB.
cited By 5
Keywords: Air Force Base; Deep slimhole cores; Department of Water Resources; Geothermal; Resource assessments; Rules and regulations; Scientists and engineers; U.S. Department of Energy; Drills; Geothermal fields; Landforms; Oil well drilling; Military aviation

Delineating ophiolite-derived host rocks of massive sulfide Cu-Co-Zn deposits with 2D high-resolution seismic reflection data in Outokumpu, Finland - Kukkonen, I.T.; Heinonen, S.; Heikkinen, P.; Sorjonen-Ward, P. (Geophysics, 2012)
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.
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

Depositional dynamics in the El'gygytgyn Crater margin: implications for the 3.6 Ma old sediment archive - Schwamborn, G.; Fedorov, G.; Ostanin, N.; Schirrmeister, L.; Andreev, A.; Party (Climate of the Past, 2012)
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.
cited By 15
Keywords: 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

Drilling reveals fluid control on architecture and rupture of the Alpine fault, New Zealand - Sutherland, R.; Toy, V.G.; Townend, J.; Cox, S.C.; Eccles, J.D.; Faulkner, D.R.; Prior, D.J.; Norris, R.J.; Mariani, E.; Boulton, C.; Carpenter, B.M.; Menzies, C.D.; et al. (Geology, 2012)
Rock damage during earthquake slip affects fluid migration within the fault core and the surrounding damage zone, and consequently coseismic and postseismic strength evolution. Results from the first two boreholes (Deep Fault Drilling Project DFDP-1) drilled through the Alpine fault, New Zealand, which is late in its 200-400 yr earthquake cycle, reveal a >50-m-thick alteration zone formed by fluid-rock interaction and mineralization above background regional levels. The alteration zone comprises cemented low-permeability cataclasite and ultramylonite dissected by clay-filled fractures, and obscures the boundary between the damage zone and fault core. The fault core contains a <0.5-m-thick principal slip zone (PSZ) of low electrical resistivity and high spontaneous potential within a 2-m-thick layer of gouge and ultracataclasite. A 0.53 MPa step in fluid pressure measured across this zone confirms a hydraulic seal, and is consistent with laboratory permeability measurements on the order of 10-20 m2. Slug tests in the upper part of the boreholes yield a permeability within the distal damage zone of 10-14 m2, implying a six-orders-of-magnitude reduction in permeability within the alteration zone. Low permeability within 20 m of the PSZ is confirmed by a subhydrostatic pressure gradient, pressure relaxation times, and laboratory measurements. The low-permeability rocks suggest that dynamic pressurization likely promotes earthquake slip, and motivates the hypothesis that fault zones may be regional barriers to fluid flow and sites of high fluid pressure gradient. We suggest that hydrogeological processes within the alteration zone modify the permeability, strength, and seismic properties of major faults throughout their earthquake cycles. © 2012 Geological Society of America.
cited By 122
Keywords: Alpine Faults; Alteration zones; Cataclasite; Damage zones; Deep fault; Drilling projects; Earthquake slip; Electrical resistivity; Fault core; Fault zone; Fluid control; Fluid migration; Fluid pressure gradient; Fluid pressures; Fluid-rock interaction; Hydraulic seals; Hydrogeological; Laboratory measurements; Low permeability; New zealand; Permeability measurements; Pressure relaxation; Regional barriers; Regional levels; Rock damage; Seismic properties; Slip zones; Slug test; Spontaneous potentials; Boring; Clay alteration; Earthquakes; Electric conductivity; Pressure gradient; Rock drilling; Faulting; cataclasite; coseismic process; drilling; earthquake rupture; electrical resistivity; fault slip; fault zone; fluid pressure; mineralization; mylonite; permeability; postseismic process; pressure gradient; Alpine Fault Zone; New Zealand; South Island

Estimation of the stressed state of the rock mass in the area of the Outokumpu deep drill hole (OKU), Finland - Savchenko, Stepan; Gorbatsevich, Feliks (Acta Geodynamica et Geomaterialia, 2012)
The stressed state of the rock mass in the area of the Outokumpu deep drill hole, Finland, was investigated by the boundaryelement method in three mutually orthogonal planes with regard for the massif geological structure. It was found that subhorizontal components of the stress field are determined by tectonic forces acting on the boundaries of the European part of the Eurasian lithospheric plate. In the drill hole vertical section the widest variations of this field gradient occur at the depths of an ophiolite sequence in the range of 1.8-2.0 km.

Evolution of the Lake Titicaca basin and its diatom flora over the last 370,000 years - Fritz, S.C.; Baker, P.A.; Tapia, P.; Spanbauer, T.; Westover, K. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2012)
In recent years, deep drilling undertaken as part of the International Continental Drilling Program has generated multiple long lacustrine sedimentary records to reconstruct continental paleoclimate. In many cases, the tectonic and geomorphic history of these basins is under-constrained and poorly known, which affects the interpretation of climate history from geophysical, geochemical, and paleobiotic proxies in the sedimentary record. In addition, non-analog biotic assemblages that reflect evolutionary processes may constrain the reconstruction of past environments. In the drill-core record of Lake Titicaca, spanning the last . 370. ka, the diatom stratigraphy reflects both the influence of climate and the long-term evolution of the lake basin and its biota. In the upper part of the drill-core sequence, glacial intervals were deep and dominated by freshwater planktic taxa, and peak interglacial intervals were shallow and dominated by benthic species, some with saline affinities. In the basal sections of the drill-core record, benthic diatoms are dominant in both glacial and interglacial units, with freshwater taxa dominating the glacial strata. This suggests that the ancient lake basin was shallower during intervals of both wet and dry climate, and that the modern deep lake may result from a progressive subsidence and deepening of the basin over time. In addition, morphological evolution in one of the major lineages of planktic diatoms, Cyclostephanos, indicates substantial change in the limnological environment that affected species morphology and may have driven speciation. © 2011 Elsevier B.V.
Keywords: Andes; Lake Titicaca; Bacillariophyta; Cyclostephanos; deep drilling; diatom; glacial-interglacial cycle; lacustrine deposit; morphology; paleoclimate; paleoecology; paleoenvironment; paleogeography; paleolimnology; plankton; Quaternary; speciation (biology)

Evidence for a bimaterial interface along the Mudurnu segment of the North Anatolian Fault Zone from polarization analysis of P waves - Bulut, F.; Ben-Zion, Y.; Bohnhoff, M. (Earth and Planetary Science Letters, 2012)
We present results on imaging contrast of seismic velocities across the Mudurnu segment of the North Anatolian Fault Zone (NAFZ) in northwestern Turkey with polarization analysis of early P waveforms generated by near-fault seismicity and recorded by near-fault stations. The analysis uses changes in motion polarity from fault-normal to source-receiver directions to identify early-arriving fault zone head waves on the slow side of the fault, and measure the arrival times of the head and direct P waves. The moveout between the head and direct waves with increasing source-receiver distance along the fault provides an estimate of the average contrast of seismic velocities across the fault. The results indicate that the average contrast of P wave velocities across the Mudurnu segment of the NAFZ is at least 6%, with the south block being the faster side. The findings provide a basis for deriving improved event locations, focal mechanisms and estimated shaking hazard associated with earthquakes on the fault. The analysis technique can be used in other fault zones monitored with sparse seismic instrumentation. © 2012 Elsevier B.V..
cited By 47
Keywords: Analysis techniques; Arrival time; Bi-material interfaces; Direct waves; Event location; Fault zone; Focal mechanism; Head waves; Imaging contrast; Moveout; Near-fault; North Anatolian Fault; North Anatolian Fault Zone; Northwestern Turkey; P waves; P-wave velocity; Polarization analysis; Seismic instrumentation; Seismic velocities; Wave forms; Polarization; Seismic waves; fault zone; focal mechanism; hazard assessment; imaging method; monitoring; normal fault; North Anatolian Fault; P-wave; seismic source; seismic velocity; seismicity; wave velocity; waveform analysis; Turkey

FAR-DEEP Core Archive: Further Opportunities for Earth Science Research and Education - Melezhik, Victor A; Prave, AR (Reading the Archive of Earth’s Oxygenation: Volume 3: Global Events and the Fennoscandian Arctic Russia-Drilling Early Earth Project, 2012)

Fault zone Q values derived from Taiwan Chelungpu Fault borehole seismometers (TCDPBHS) - Wang, Y.-J.; Lin, Y.-Y.; Lee, M.-C.; Ma, K.-F. (Tectonophysics, 2012)
The attenuation factor, Q, at a fault zone is an important parameter for understanding the physical properties. In this study, we investigated the Q value of the Chelungpu Fault, the main rupture of the Mw 7.6 Chi-Chi earthquake, using the 7-level TCDP borehole seismometer array (TCDPBHS). The TCDPBHS was deployed at depths from 945 to 1270m throughout the 1999 ruptured slip zone at 1111m. Three borehole seismometers (BHS1-BHS3) were placed in the hanging wall, and the remaining three (BHS5-BHS7) were placed in the foot wall, with BHS4 near the slip zone. The configuration allowed us to estimate the Q-structure of the recent ruptured fault zone. In this study, we estimated Q values between BHS1 and BHS4, Qs 1 (Qp 1) at the fault zone and between BHS4 to 2km in depth, Qs 4 (Qp 4) beneath the fault zone. We utilized two independent methods, the spectral ratio and spectral fitting analyses, for calculating the Q value of Qs 1 (Qp 1) in order to provide a reliability check. After analyzing 26 micro-events for Qs and 17 micro-events for Qp, we obtained consistent Q values from the two independent methods. The values of Qs 1 and Qp 1 were 21-22 and 27-35, respectively. The investigation for the value of Qs 4 was close to 45, and Qp 4 was 85. These Qp and Qs values are quiet consistent with observations obtained for the San Andreas Fault at the corresponding depth. A low Qs 1 value for the recent Chelungpu Fault zone suggests that this fault zone has been highly fractured. Qs values within the Chelungpu Fault, similar to those within the San Andreas Fault, suggest that the Q structure within the fault zone is sedimentary rock independent. However, the possible existence of fluids, fractures, and cracks dominates the attenuation feature in the fault zone. © 2011 Elsevier B.V.
cited By 11
Keywords: Chelungpu Fault; Drilling projects; Fault-zone attenuation; Qp; Qs; Seismic attenuation; Seismographs; Strike-slip faults; Seismology; borehole; Chi-Chi earthquake 1999; earthquake rupture; fault zone; footwall; San Andreas Fault; sedimentary rock; seismic attenuation; seismograph; slip; Chelungpu Fault Zone; Taiwan

Fault-zone trapped waves: High-resolution characterization of the damage zone of the Parkfield San Andreas fault at depth - Li, Y.-G.; Cochran, E.S. (Imaging, Modeling and Assimilation in Seismology, 2012)
This chapter presents that highly damaged rocks within the San Andreas fault (SAF) at Parkfield form a low-velocity waveguide to trap seismic waves. The amplitudes and dispersion feature of trapped waves are sensitive to the geometry and physical properties of the fault zone due to the constructive interference conditions of these waves. We use faultzone trapped waves (FZTWs) generated by earthquakes and explosions and recorded at a cross-fault surface array and borehole seismographs at the San Andreas Fault Observatory at Depth (SAFOD) site to document fault zone structure and rock damage at seismogenic depths with high-resolution. Observations and 3-D finite-difference simulations of these FZTWs at dominant frequencies of 2-10 Hz show the downward tapering SAF characterized by a 30-40-m wide fault core with the maximum velocity reduction up to 50% embedded in a 100-200-m wide zone with velocities reduced by 25%-35% in average from wall-rock velocities. The width and velocity reduction of the damage zone at 3 km depth delineated by FZTWs are verified by the direct measurements in SAFOD drilling and logging studies at this depth [Hickman et al., 2007]. The results indicate that the localization of severe rock damage on the SAF likely reflects pervasive cracking caused by historical earthquakes on it. The magnitude of damage varies with depth and along the fault strike due to rupture distributions and stress variations over multiple length and time scales. The damage is not symmetric across the main slip plane but extends farther on the southwest side of the main fault trace. Based on the depths of earthquakes generating prominent FZTWs, we estimate that the low-velocity damage zone along the SAF at Parkfield extends at least to depths of 7-8 km. © 2012 Higher Education Press and Walter de Gruyter GmbH & Co. KG, Berlin/Boston.
cited By 6

Foraminiferal repopulation of the late eocene chesapeake bay impact crater - Poag, C.W. (Micropaleontology, 2012)
The Chickahominy Formation is the initial postimpact deposit in the 85km-diameter Chesapeake Bay impact crater, which is centered under the town of Cape Charles, Virginia, USA. The formation comprises dominantly microfossil-rich, silty, marine clay, which accumulated during the final 1.6myr of late Eocene time. At cored sites, the Chickahominy Formation is 16.8-93.7m thick, and fills a series of small troughs and subbasins, which subdivide the larger Chickahominy basin. Nine coreholes drilled through the Chickahominy Formation (five inside the crater, two near the cratermargin, and two 3km outside the crater) record the stratigraphic and paleoecologic succession of 301 indigenous species of benthic foraminifera, as well as associated planktonic foraminifera and bolboformids. Two hundred twenty of these benthic species are described herein, and illustrated with scanning electron photomicrographs. The Chickahominy Formation can be categorized as a single benthic foraminiferal biozone (Cibicidoides pippeni Biozone), subdivided into five subzones, in stratigraphic order from bottom to top: Bulimina jacksonensis Subzone; Lagenoglandulina virginiana Subzone; Uvigerina dumblei Subzone; Bolivina tectiformis Subzone, and; Siphonina jacksonensis Subzone. Two planktonic datums and four benthic datums provide a biochronostratigraphic framework in which to estimate the duration and temporal distribution patterns of discrete microfossil assemblages. Apaleoseral succession from pioneer to equilibrium paleocommunities reflects the temporal and spatial evolution from early unstable benthic paleoenvironments to later stable benthic paleoenvironments. Initial reoccupation of the newly formed crater basin is marked by a dramatic immigration of 32 indigenous species, which replaced the sparse, entirely reworked (allochthonous) foraminiferal assemblages of a preceding inhospitable dead zone. At all nine core sites, attainment of benthic paleoenvironmental equilibrium (29-190kyr postimpact) is signaled by a notable reduction in the number of new immigrant species arriving in the Chickahominy basin. In addition, at five sites inside the crater, early unstable benthic paleoenvironments can be differentiated from later stable benthic paleoenvironments by the presence of an agglutinated Psammosiphonella biofacies in basalChickahominy strata and a shift from short-term to long-term benthic foraminiferal generic dominance facies. Restriction of the dead zone and Psammosiphonella biofacies to intracrater sites indicates unusual benthic paleoenvironmental conditions (warm, saline bottomwater and porewater) derived from the impact, which lasted as long as 350kyr postimpact at one site. Absence of key planktonic foraminiferal and Bolboforma species in early Chickahominy sediments indicates that detrimental effects of the impact also disturbed the upper oceanic water column for at least 80-100kyr postimpact. Nine genera (Bolivina, Uvigerina, Gyroidinoides, Globocassidulina, Angulogerina, Nuttallides, Cibicidina, Caucasina, Epistominella) and two generic groups (buliminids, stilostomellids) are the most abundant taxa among 17 generic dominance facies that characterize Chickahominy core sites. Most dominant taxa were epifaunal or shallow infaunal opportunists, which thrived under conditions of oxygen depletion (dysoxia) and high organic flux rates. After an average of 73kyr of stressed, rapidly fluctuating paleoenvironments, which were destabilized by after-effects of the impact, most of the cored Chickahominy subbasins maintained stable, nutrient-rich, low-oxygen bottom waters and interstitial microhabitats for the remaining 1.3myr of late Eocene time.
cited By 4

Frictional properties and sliding stability of the San Andreas fault from deep drill core - Carpenter, B.M.; Saffer, D.M.; Marone, C. (Geology, 2012)
The strength of tectonic faults and the processes that control earthquake rupture remain central questions in fault mechanics and earthquake science. We report on the frictional strength and constitutive properties of intact samples across the main creeping strand of the San Andreas fault (SAF; California, United States) recovered by deep drilling. We find that the fault is extremely weak (friction coefficient, μ = ∼ 0.10), and exhibits both velocity strengthening frictional behavior and anomalously low rates of frictional healing, consistent with aseismic creep. In contrast, wall rock to the northeast shows velocity weakening frictional behavior and positive healing rates, consistent with observed repeating earthquakes on nearby fault strands. We also document a sharp increase in strength to values of μ > ∼0.40 over <1 m distance at the boundary between the fault and adjacent wall rock. The friction values for the SAF are sufficiently low to explain its apparent weakness as inferred from heat flow and stress orientation data. Our results may also indicate that the shear strength of the SAF should remain approximately constant at ∼10 MPa in the upper 5-8 km, rather than increasing linearly with depth, as is commonly assumed. Taken together, our data explain why the main strand of the SAF in central California is weak, extremely localized, and exhibits aseismic creep, while nearby fault strands host repeating earthquakes. © 2012 Geological Society of America.
cited By 82
Keywords: California; Constitutive properties; Deep drilling; Drill core; Earthquake rupture; Fault strands; Friction coefficients; Friction values; Frictional behavior; Frictional properties; Frictional strength; Low rates; Repeating earthquake; San Andreas fault; Sharp increase; Sliding stability; Stress orientations; Tectonic faults; Core drilling; Creep; Earthquakes; Strike-slip faults; Friction; earthquake mechanism; earthquake recurrence; earthquake rupture; fault geometry; friction; rupture; San Andreas Fault; shear strength; slip rate; stability analysis; stress field; tectonic setting; wall rock; California; San Andreas; United States; Calluna vulgaris

Fifteen new diatom (Bacillariophyta) species from Lake Ohrid, Macedonia - Levkov, Zlatko; Williams, David (Phytotaxa, 2011)

Origin of a rhyolite that intruded a geothermal well while drilling at the Krafla volcano, Iceland - Elders, W.A.; Fridleifsson, G.Ó.; Zierenberg, R.A.; Pope, E.C.; Mortensen, A.K.; Gudmundsson, 'A.; Lowenstern, J.B.; Marks, N.E.; Owens, L.; Bird, D.K.; Reed, M.; Olsen, N.J.; et al. (Geology, 2011)
Magma flowed into an exploratory geothermal well at 2.1 km depth being drilled in the Krafla central volcano in Iceland, creating a unique opportunity to study rhyolite magma in situ in a basaltic environment. The quenched magma is a partly vesicular, sparsely phyric, glass containing 1.8% of dissolved volatiles. Based on calculated H2O-CO2 saturation pressures, it degassed at a pressure intermediate between hydrostatic and lithostatic, and geothermometry indicates that the crystals in the melt formed at 900 °C. The glass shows no signs of hydrothermal alteration, but its hydrogen and oxygen isotopic ratios are much lower than those of typical mantle-derived magmas, indicating that this rhyolite originated by anhydrous mantle-derived magma assimilating partially melted hydrothermally altered basalts. © 2011 Geological Society of America.
cited By 84
Keywords: Anhydrous mantle; Geothermometry; Hydrothermal alterations; Hydrothermally; Icelands; In-situ; Oxygen isotopic; Saturation pressure; Geothermal wells; Glass; Granite; Oxygen; Volcanoes; Well drilling; basalt; geothermal system; hydrogen isotope; hydrothermal alteration; magma assimilation; magma chamber; mantle source; oxygen isotope ratio; rhyolite; volcanology; Iceland; Krafla

Paleosalinity significance of occurrence and distribution of methyltrimethyltridecyl chromans in the Upper Cretaceous Nenjiang Formation, Songliao Basin, China - Wang, L.; Song, Z.; Yin, Q.; George, S.C. (Organic Geochemistry, 2011)
A group of methyltrimethyltridecyl chromans (MTTCs) was found in core samples of Member 1 (K2n1) and Member 2 (K2n2) of the Nenjiang Formation (Upper Cretaceous) from the SK-l southern borehole (Songliao Basin, China). They are assigned for the first time in sediments older than the Tertiary in China. Their composition and distribution are indicative mainly of the redox and salinity conditions in the depositional environment. The δ-MTTC isomer is in relatively higher abundance in samples from enhanced salinity and reducing conditions, but was not detected in samples from aerobic and low salinity environments, while α-MTTC appears to be present in samples from environments with a broad range of salinity and redox conditions. The α-MTTC/γ-MTTC (α/γ) ratio has a similar indication as that of the α/δ ratio and could be used as a corroborative ratio of paleosalinity. A combination of biomarker parameters suggests that the massive lacustrine petroleum-prone source rocks associated with the K2n1 interval were likely developed under a stratified water column with enhanced salinity and an anoxic bottom water layer, associated with a much less saline (fresh to brackish) upper water layer. © 2011 Elsevier Ltd.
cited By 53
Keywords: Bottom water; Depositional environment; Low salinity; Occurrence and distribution; Redox condition; Reducing conditions; Songliao basin; Source rocks; Stratified waters; Upper Cretaceous; Water layers; Anoxic sediments; Saline water; Salinity measurement; biomarker; borehole; Cretaceous; depositional environment; lacustrine deposit; paleosalinity; redox conditions; relative abundance; sampling; source rock; Tertiary; water column; China; Songliao Basin

Outokumpu Deep Drilling Project 2003 - 2010 - Kukkonen, I. (Geological Survey of Finland, 2011)

P- And S-wave velocities and velocity anisotropy of core samples from the Outokumpu 2500 m crustal section: Implications for the nature of seismic reflections - Kern, Hartmut; Mengel, Kurt (Special Paper of the Geological Survey of Finland, 2011)
Laboratory measurements as well as modelling of the physical properties of rock materials are important for the understanding and interpretation of both downhole (logging) and geophysical (surface) observations. On 29 core samples of the Outokumpu scientific drill hole, covering the depth range of 198-2491 m, we calculated the average (isotropic) intrinsic P- and S-wave velocities (V p,Vs) and densities from their modal composition, based on bulk rock (XRF) and mineral chemistry (microprobe), using least squares fitting. For 13 cube-shaped samples representing the main lithologies, we measured P- and S-wave velocities in 3 orthogonal directions at pressures of up to 600 MPa in order to determine their directional dependence and crack sensitivity. Comparison of the calculated velocities with the experimentally derived in situ velocities gave evidence for microcracks that are not completely closed. Microcracks may have an important bearing on the in situ velocities, in addition to the lithological control. Velocity measurements as well as 3D velocity calculations based on neutron diffraction texture measurements revealed that velocity anisotropy and shear wave splitting are important properties of the biotite gneisses that dominate about 70% of the drilled crustal section. Reflection coefficients (Rc) for the various lithological contacts based on modelled and measured velocities provide evidence that the different lithologies of the ophiolite-related assemblage have the potential to cause the marked reflections at 1300-1500 m depth, as revealed by the high-resolution seismic reflection line (OKU-1).
Keywords: Finland; Ita Suomen; Outokumpu; crustal structure; deep drilling; microcrack; ophiolite; P-wave; Proterozoic; S-wave; seismic anisotropy; seismic reflection; seismic wave; wave velocity

P- and S-wave velocities of rocks from the upper 1.5 km crustal section sampled by the Outokumpu Deep Driling Project, Finland - Elbra, Tiiu; Karlqvist, Ronnie; Lassila, Ilkka; Hæggstr{om, Edward; Pesonen, Lauri J. (Special Paper of the Geological Survey of Finland, 2011)
Longitudinal (VP) and shear wave (Vs) velocities of the upper 1.5 km of the Outokumpu Deep Drill Core were measured using a novel ultrasonic instrument. The aim of the laboratory tests was to determine the seismic velocities of rocks as a function of pressure and temperature and to identify parameters that influence these velocities. The velocities differed significantly throughout the core due to variations in mineralogical composition, lithology, fracturing and anisotropy. Notably, even a minor increase in pressure dramatically increased the VP and VS due to microcrack closure. When the pores and microcracks were closed by pressurization, the highest velocities in the upper schist series (33-1314 m) and the ophiolitic series (1314-1515 m) were met within chlorite-sericite schists (VP 5704 m/s, VS 3495 at 30 MPa) and diopside-tremolite skarns (VP 6572 m/s, VS 3752 m/s at 30 MPa), respectively. This new velocity data could improve the interpretation of crustal models by providing constraints on seismic velocities as well as estimates of the seismic impedances and Poisson's ratios in various rock types in the area of the Outokumpu Deep Drill Core.
Keywords: Finland; Ita Suomen; Outokumpu; crustal structure; deep drilling; metasedimentary rock; P-wave; Proterozoic; S-wave; seismic velocity; seismic wave; wave velocity

Paleomagnetism of impact breccias from the Chicxulub crater - Implications for ejecta emplacement and hydrothermal processes - Velasco-Villareal, M.; Urrutia-Fucugauchi, J.; Rebolledo-Vieyra, M.; P'erez-Cruz, L. (Physics of the Earth and Planetary Interiors, 2011)
Results of a paleomagnetic study of 89 samples from impact breccias from the Chicxulub crater are presented and used to investigate on ejecta emplacement, hydrothermal and alteration processes. The impactite sequence sampled in cores from Yaxcopoil-1 borehole is ∼100. m thick and formed by six subunits characterized by petrographic, scan images, geochemical and textural analyses, which point to different emplacement modes. Impact occurred within reverse polarity chron C29r; therefore, magnetization acquired at crater formation and shortly thereafter will present reverse polarity, which is supported by paleomagnetic measurements on melt samples from Yucatan-6 borehole. Results after step-wise thermal and alternating field demagnetization document a pattern of 23 upward and 29 downward inclinations at Yaxcopoil-1 around -33° and 38°, respectively. Measurements of magnetic hysteresis and variation of low-field susceptibility with temperature suggest low-Ti titanomagnetites and magnetite as main magnetic carriers. Petrographic observations indicate the presence of fine-grained magnetite, hematite and Fe-oxyhydroxides, related to hydrothermal alteration processes. Curie points are in the range of 520-580 °C. The wide range of unblocking temperature spectra points to variable grain sizes of a magnetic phase that unblocks around 580 °C. Hysteresis ratio plots indicate most samples fall in the pseudo-single domain field. In some samples, wasp-waist constrained hysteresis loops suggest magnetite and hematite. Analyses of vector plots and coercivity and unblocking temperature spectra do not show apparent differences within and between subunits. Subunits are characterized by distinct textural and compositional differences in size, type and relative abundance of clasts and melt-rich or carbonate-rich matrix types. Bulk properties vary with composition and clast contents, particularly within the Middle Suevite and Brecciated Melt Rock subunits that show higher values, while low values characterize the Lower Suevite carbonate-rich with rare basement clasts subunit. Magnetization acquisition mechanisms are discussed, with reference to impactite characteristics, and may relate to remagnetization from hydrothermal and post-impact alteration processes. © 2011 Elsevier B.V.
cited By 9

Petrophysical properties of the Outokumpu Deep Drill Core and the surrounding bedrock - Airo, Meri-Liisa; S{a{avuori, Heikki; Vuoriainen, Satu (Special Paper of the Geological Survey of Finland, 2011)
Petrophysical laboratory measurements of the Outokumpu Deep Drill Core were carried out in 2005-2008 at the Geophysical Laboratory of the Geological Survey of Finland (GTK). This report describes the pre-processing and measurement procedures and summarizes the measurement results of a total of 1992 samples taken at one-metre intervals along the drill core, representing depths from 55.5 m to 2503.9 m. The determined parameters were density and porosity, magnetic susceptibility and the intensity of remanent magnetization, electrical properties (resistivity and chargeability), P-wave velocity and thermal conductivity. The samples represented different rock types, and their petrophysical parameters showed typical values reflecting the mineralogical variation in the rocks. Generally weak magnetic properties characterize both the drill core samples and the outcropping bedrock (magnetic susceptibilities mainly ≤ 1000 × 10-6 SI). The only magnetically anomalous rocks are serpentinites and other altered ophiolitederived rocks of the Outokumpu assemblage, with susceptibilities of the order of ≥ 10 000 × 10-6 SI. No clear systematic effect of depth along the drill core on density or susceptibility can be observed. P-wave velocity and specific resistivity tend to decrease with depth. The porosity of mica schists increases with depth, but the drill core bulk densities do not change. Microfracturing due to pressure release possibly explains part of this effect. However, the grain densities of mica schists tend to increase with depth. Compared with surface densities, the densities of different rock types in the core are ca. 40 kg/m3 higher than the densities of corresponding rock types exposed around the drilling site (< 100 km). The magnetic properties of different rock types are of about the same intensity. Only black schists on the surface are more highly magnetic than those from the core, suggesting differences in monoclinic / hexagonal pyrrhotite contents.
Keywords: Finland; Ita Suomen; Outokumpu; bedrock; deep drilling; density; electrical property; magnetic susceptibility; metamorphic rock; mica; outcrop; physical property; porosity; remanent magnetization

Paleosecular variation and paleointensity records for the last millennium from southern South America (Laguna Potrok Aike, Santa Cruz, Argentina) - Gogorza, C.S.G.; Sinito, A.M.; Ohlendorf, C.; Kastner, S.; Zolitschka, B. (Physics of the Earth and Planetary Interiors, 2011)
High-resolution paleo- and rock magnetic studies were performed on a group of four sediment cores from Laguna Potrok Aike (Santa Cruz, Argentina) representing the time period AD 1300-2000. The rock magnetic analyses show that the main magnetic mineral is (titano)magnetite with a concentration between 0.01 and 0.08%, and a grain size of 4-15 μm. This study is helpful in order to complete the paleosecular variation (PSV) and paleointensity type curves for South America which do not have a detailed record for the last millennium. The comparison with the study carried out for Lake El Tr'ebol shows a very good agreement, supporting that PSV records of south-western Argentina can be developed into a stratigraphic correlation tool on a regional scale. © 2010 Elsevier B.V.
Keywords: Argentina; Laguna Potrok Aike; Santa Cruz [Argentina]; Iron ores; Lithology; Stratigraphy; ICDP; Paleointensity; Paleosecular variations; PASADO; Southern Hemisphere; core analysis; geochronology; Holocene; magnetic intensity; magnetic survey; paleomagnetism; secular variation; sediment core; Southern Hemisphere; stratigraphic correlation; Minerals

Palynological record from a composite core through Late Cretaceous-early Paleocene deposits in the Songliao Basin, Northeast China and its biostratigraphic implications - Li, J.; Batten, D.J.; Zhang, Y. (Cretaceous Research, 2011)
Two boreholes drilled approximately 75 km apart in the Songliao Basin, Northeast China, have together provided a composite core that represents an almost continuous section through Late Cretaceous-early Paleocene deposits. Eight biozones have been established for this succession of seven formations based on occurrences and associations of biostratigraphically significant palynomorph genera. Seven of these suggest that there was more or less continuous deposition from the late Turonian to the early Paleocene, with the eighth encompassing a Miocene formation that overlies the succession unconformably. This zonation provides a new chronostratigraphic framework for the Late Cretaceous deposits of the Songliao Basin. The ages of most of the formations involved differ from those determined previously. One of the sedimentary units, the Mingshui Formation, includes the Cretaceous/Paleogene boundary, which seems to be indicated by an apparent mass extinction of palynomorph taxa, a comparatively rare occurrence outside North America. The upper Quantou Formation, the lowest unit in the succession, is dated as late Turonian-Coniacian, which is much younger than previously thought. The same applies to the overlying Qingshankou and Yaojia formations, and also to the other three (Nenjiang, Sifangtai and Mingshui) but to a lesser extent, in the conformable succession. The Early/Late Cretaceous boundary must now be located probably below the Quantou Formation, either between it and the underlying Denglouku Formation or within the latter. © 2010 Elsevier Ltd.
cited By 43
Keywords: biostratigraphy; biozonation; chronostratigraphy; Cretaceous; Paleocene; palynology; palynomorph; taxonomy; Tertiary; China; Songliao Basin; Coniacian

Patterns of seismic swarm activity in the Corinth Rift in 2000-2005 - Potanina, M.G.; Smirnov, V.B.; Bernard, P. (Izvestiya, Physics of the Solid Earth, 2011)
Based on the data of the detailed earthquake catalog provided on the website of the Corinth Rift Laboratory, zones of swarm activity are revealed and the variations in the statistical parameters of seismic swarms that occurred in the western part of the Gulf of Corinth are calculated. The preliminary analysis of the catalogue is carried out; the magnitude of completeness and the accuracy of the location of the earth-quake are estimated; the changes in these parameters associated with the development of the observational network are assessed. The b-value (b-values) and the cluster dimension of the set of hypocenters are estimated, and time variations in these parameters in the course of the evolution of swarm activity are revealed. The style of changes in the parameters characterizing the seismic regime during intervals of swarm activity indicates that the process of failure exhibits scale redistribution over the course of time, changing from upscaling (progression from smaller to larger scales) at the stage of increasing seismicity to downscaling (progression from larger to lower scales) at the stage of decay. These particular features of enhancement and reduction of swarm seismicity are qualitatively similar to the scenarios of source preparation and aftershock relaxation of strong earthquakes. The pattern of variations of the swarm seismicity studied is similar to those identified in the previous laboratory and field modeling of various transient modes of seismicity. This fact confirms the relevancy of the retrieved results and conclusions based on the laboratory studies of transient modes, and suggests that the latter have a universal governing mechanism. © 2011 Pleiades Publishing, Ltd.

Permafrost-associated natural gas hydrate occurrences on the Alaska North Slope - Collett, T.S.; Lee, M.W.; Agena, W.F.; Miller, J.J.; Lewis, K.A.; Zyrianova, M.V.; Boswell, R.; Inks, T.L. (Marine and Petroleum Geology, 2011)
In the 1960s Russian scientists made what was then a bold assertion that gas hydrates should occur in abundance in nature. Since this early start, the scientific foundation has been built for the realization that gas hydrates are a global phenomenon, occurring in permafrost regions of the arctic and in deep water portions of most continental margins worldwide. In 1995, the U.S. Geological Survey made the first systematic assessment of the in-place natural gas hydrate resources of the United States. That study suggested that the amount of gas in the gas hydrate accumulations of northern Alaska probably exceeds the volume of known conventional gas resources on the North Slope. Researchers have long speculated that gas hydrates could eventually become a producible energy resource, yet technical and economic hurdles have historically made gas hydrate development a distant goal. This view began to change in recent years with the realization that this unconventional resource could be developed with existing conventional oil and gas production technology. One of the most significant developments was the completion of the BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well on the Alaska North Slope, which along with the Mallik project in Canada, have for the first time allowed the rational assessment of gas hydrate production technology and concepts. Almost 40 years of gas hydrate research in northern Alaska has confirmed the occurrence of at least two large gas hydrate accumulations on the North Slope. We have also seen in Alaska the first ever assessment of how much gas could be technically recovered from gas hydrates. However, significant technical concerns need to be further resolved in order to assess the ultimate impact of gas hydrate energy resource development in northern Alaska. © 2009 Elsevier Ltd.
cited By 192
Keywords: Alaska; Coring; Exploration; Petroleum systems; Resources; Seismic analysis; Energy resources; Gases; Hydration; Natural gas; Natural gas deposits; Natural gas well completion; Natural gas well drilling; Offshore oil wells; Permafrost; Petroleum deposits; Petroleum prospecting; Production; Rating; Resource valuation; Seismology; Stratigraphy; Gas hydrates; core logging; drilling; gas hydrate; gas production; hydrocarbon exploration; hydrocarbon generation; hydrocarbon resource; hydrocarbon technology; natural gas; permafrost; Alaska; North Slope; United States

Petrology of the dril hole R2500 at Outokumpu, Eastern Finland - The deepest dril hole ever driled in Finland - V{asti, Kaj (Special Paper of the Geological Survey of Finland, 2011)
Deep reflection seismic measurements in 2002 across the Outokumpu region revealed numerous reflectors, some of which related to mafic rock assemblages or to rocks that otherwise showed impedance contrasts with their surroundings. Two shallow reflective zones were later targeted for drilling in order to test interpretations of the seismic data. The immediate proximity of the famous Outokumpu ore belt naturally provided an additional incentive for drilling, which was undertaken by NEDRA, a state owned Russian drilling contractor. The Outokumpu region is located within the Paleoproterozoic Karelian schist belt close to the boundary between the Neoarchaean craton in the east and the Paleoproterozoic Svecofennian island arc complex in the west. The Karelian schist belt is divided into the lower Sariolan and Jatulian (2.5-2.1 Ga, mainly autochthonous), and the upper Kalevian (2.1-1.9 Ga) units. The deep drill hole R2500 is located in the allochthonous upper part of the latter unit. The uppermost 2 km of the drill hole consists mainly of mica schist with minor biotite gneiss, chlorite-sericite schist, black schist and hornblende-epidote schist intercalations. Within the interval ca. 1300-1500 m, the mica schist formation encloses a previously unknown assemblage of Outokumpu-type rocks. From ca. 1650 m downwards mica schist is intruded by pegmatitic granitoids, which in turn dominate from ca. 2000 m downwards. The chemical index of alteration (CIA) of the mica schists and biotite gneisses (50.3-65.2) indicates weak to moderate weathering of their source rocks. The lower CIA values of the mica schists probably reflect rapid and subsequent erosion, transportation and re-deposition from large deltas. On the other hand the higher CIA value of the biotite gneisses is a consequence of mineralogy, because it was originally fine-grained shale rich in clay minerals. Chlorite-sericite schist closely resembles mica schist chemically, while the hornblende-epidote schist differs in containing distinctly more CaO and less Na2O and K2O. Black schists are divided into two main types: ordinary black schist and calcareous black schist. The latter type is rich in tremolite and differs chemically mainly in containing less SiO2 and more CaO and MgO. Rocks of the Outokumpu assemblage consist of lithologically diverse rock types ranging from monomineralic serpentinites to various diopside- and/or tremolite-bearing skarns and quartz rocks. A few narrow and strongly schistose mafic dykes, which have been altered to chlorite schists, crosscut skarn. Primarily the Outokumpu-type rock assemblages represent fragments of mantle peridotites affected by hydrothermal and metasomatic alteration. For this reason serpentinites, skarns and quartz rocks usually have trace element concentrations very similar to pyrolite. Although pegmatitic granitoids show significant variations in the modal composition, they are always very leucocratic (M=0.2-4). Chemically all pegmatite types display peraluminous affinities (A/CNK = 1.02-2.08). On A/CNK versus SiO2 and Na 2O versus K2O diagrams pegmatites fall into both S-type or I-type categories.
Keywords: Finland; Ita Suomen; Outokumpu; Archean; biotite; craton; deep drilling; gneiss; granitoid; metasedimentary rock; mica; mineralogy; pegmatite; petrology; Proterozoic; schist; seismic data; seismic reflection; serpentinite; skarn

Physical properties of the Yaxcopoil-1 deep drill core, Chicxulub impact structure, Mexico - Elbra, T.; Pesonen, L.J. (Meteoritics and Planetary Science, 2011)
The Chicxulub structure in Mexico, one of the largest impact structures on Earth, was formed 65Ma by a hypervelocity impact that led to the large mass extinction at the K-Pg boundary. The Chicxulub impact structure is well preserved, but is buried beneath a sequence of carbonate sediments and, thus, requires drilling to obtain subsurface information. The Chicxulub Scientific Drilling Program was carried out at Hacienda Yaxcopoil in the framework of the International Continental Scientific Drilling Program in 2001-2002. The structure was cored from 404m down to 1511m, through three intervals: 794m of postimpact Tertiary sediments, a 100m thick impactite sequence, and 616m of preimpact Cretaceous rocks thought to represent a suite of megablocks. Physical property investigations show that the various lithologies, including the impactite units and the K-Pg boundary layer, can be characterized by their physical properties, which depend on either changes in fabric or on mineralogical variations. The magnetic properties show mostly dia- or paramagnetic behavior, with the exception of the impactite units that indicate the presence of ferromagnetic, probably hydrothermally deposited magnetite and pyrrhotite. The magnetic fraction contributes mainly to enhanced magnetization in the impactite lithologies and, in this way, to the observed magnetic anomalies. The shape and orientation of the magnetic grains are varied and reflect inhomogeneous fabric development and the influence of impact-related redeposition and hydrothermal activity. The Chicxulub impact occurred at the time of the reverse polarity geomagnetic chron 29R, and this finding is consistent with the age of the K-Pg boundary. © The Meteoritical Society, 2011.
cited By 13

Organic geochemical records from Lake Malawi (East Africa) of the last 700years, part II: Biomarker evidence for recent changes in primary productivity - Castañeda, I.S.; Werne, J.P.; Johnson, T.C.; Powers, L.A. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
Relatively few well-dated and high-resolution paleoclimate records of the past few centuries presently exist from tropical East Africa. Here, we examine the bulk and molecular geochemical records of two varved sediment cores from Lake Malawi, which together provide a continuous record of environmental variability in East Africa of the last 730years. We observe a number of changes in the aquatic ecosystem of Lake Malawi, which are likely attributed to both natural climatic forcing and anthropogenic activities. Biomarkers of dinoflagellates (dinosterol) and bacterivorous ciliates (tetrahymanol) display increased accumulation rates from 1900AD to the present, while a simultaneous decrease in accumulation rates of diatom biomarkers (isololiolide/loliolide) is observed. Increased accumulation rates of retene, a compound derived from conifers, are also noted since 1930AD and likely reflect increased soil erosion due to deforestation of the Lake Malawi watershed. Spectral analysis of the high-resolution TOC record indicates a periodicity of 204years, similar to the 206year cycle noted in 14C and 10Be records, suggesting a link between East African climate and solar forcing. © 2010 Elsevier B.V.
cited By 42
Keywords: accumulation rate; biomarker; ciliate; climate variation; deforestation; dinoflagellate; geochemical method; paleoclimate; phytoplankton; primary production; proxy climate record; sediment core; soil erosion; spectral analysis; tropical region; East Africa; East African Lakes; Lake Malawi; Bacillariophyta; Ciliophora; Coniferophyta; Dinophyceae

Organic geochemical records of environmental variability in Lake Malawi during the last 700 years, Part I: The TEX86 temperature record - Powers, L.A.; Johnson, T.C.; Werne, J.P.; Castañeda, I.S.; Hopmans, E.C.; Sinninghe Damst'e, J.S.; Schouten, S. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
We have applied the TEX86 paleothermometer to produce a surface water temperature record for Lake Malawi spanning the past 700years. Over much of the record temperature fluctuates from 24-27°C with a mean of 25°C; however, there has been a substantial increase in temperature of 2.0°C during the past 100years. The TEX86 temperature record reveals a strong similarity to the instrumental record; both records demonstrate warming ( 0.7-1.4°C) over the past 50years as well as a cooling anomaly around 1959. Comparison of the TEX86 temperature record with the proxy records of primary productivity suggests that wind induced upwelling and/or precipitation have a strong influence on the surface temperature of Lake Malawi. © 2010 Elsevier B.V.
cited By 37
Keywords: geochemical method; paleoclimate; paleotemperature; primary production; prokaryote; proxy climate record; surface temperature; surface water; water temperature; East African Lakes; Lake Malawi; Archaea

Melt in the impact breccias from the Eyreville drill cores, Chesapeake Bay impact structure, USA - Bartosova, K.; Hecht, L.; Koeberl, C.; Libowitzky, E.; Reimold, W.U. (Meteoritics and Planetary Science, 2011)
The center of the 35.3Ma Chesapeake Bay impact structure (85km diameter) was drilled during 2005/2006 in an ICDP-USGS drilling project. The Eyreville drill cores include polymict impact breccias and associated rocks (1397-1551m depth). Tens of melt particles from these impactites were studied by optical and electron microscopy, electron microprobe, and microRaman spectroscopy, and classified into six groups: m1-clear or brownish melt, m2-brownish melt altered to phyllosilicates, m3-colorless silica melt, m4-melt with pyroxene and plagioclase crystallites, m5-dark brown melt, and m6-melt with globular texture. These melt types have partly overlapping major element abundances, and large compositional variations due to the presence of schlieren, poorly mixed melt phases, partly digested clasts, and variable crystallization and alteration. The different melt types also vary in their abundance with depth in the drill core. Based on the chemical data, mixing calculations were performed to determine possible precursors of these melt particles. The calculations suggest that most melt types formed mainly from the thick sedimentary section of the target sequence (mainly the Potomac Formation), but an additional crystalline basement (schist/gneiss) precursor is likely for the most abundant melt types m2 and m5. Sedimentary rocks with compositions similar to those of the melt particles are present among the Eyreville core samples. Therefore, sedimentary target rocks were the main precursor of the Eyreville melt particles. However, the composition of the melt particles is not only the result of the precursor composition but also the result of changes during melting and solidification, as well as postimpact alteration, which must also be considered. The variability of the melt particle compositions reflects the variety of target rocks and indicates that there was no uniform melt source. Original heterogeneities, resulting from melting of different target rocks, may be preserved in impactites of some large impact structures that formed in volatile-rich targets, because no large melt body exists, in which homogenization would have taken place. © The Meteoritical Society, 2011.
cited By 3

Optimum design and application of balling-preventing bit - Qinghong, MENG; Hengchun, Zhang; Yule, HU; et al. (Coal Geology & Exploration, 2011)

Millennial-scale Arctic climate change of the last 3.6 million years: Scientific drilling at Lake El'gygytgyn, Northeast Russia - Brigham-Grette, J.; Melles, M.; Minyuk, P.; Koeberl, C. (Oceanography, 2011)
cited By 0

Preface evolutionary and geological history of the Balkan lakes Ohrid and Prespa - Wagner, B.; Wilke, T. (Biogeosciences, 2011)
Keywords: Balkans; Lake Mikri Prespa; Lake Ohrid; geomorphological mapping; historical record; history of geology; lake evolution

Measurement of 10Be from Lake Malawi (Africa) drill core sediments and implications for geochronology - McHargue, L.R.; Jull, A.J.T.; Cohen, A. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
The cosmogenic radionuclide 10Be was measured from drill core sediments from Lake Malawi in order to help construct a chronology for the study of the tropical paleoclimate in East Africa. Sediment samples were taken every 10m from the core MAL05-1C to 80m in depth and then from that depth in core MAL05-1B to 382m. Sediment samples were then later taken at a higher resolution of every 2m from MAL05-1C. They were then leached to remove the authigenic fraction, the leachate was processed to separate out the beryllium isotopes, and 10Be was measured at the TAMS Facility at the University of Arizona. The 10Be/9Be profile from Lake Malawi sediments is similar to those derived from marine sediment cores for the late Pleistocene, and is consistent with the few radiocarbon and OSL IR measurements made from the same core. Nevertheless, a strong correlation between the stable isotope 9Be and the cosmogenic isotope 10Be suggests that both isotopes have been well mixed before deposition unlike in some marine sediment cores. In addition, the correlation of beryllium isotopes to a proxy of lake level TOC (Total Organic Matter) from Lake Malawi indicates that the concentrations of 10Be in the lake sediments result from the combined effects of global and local climates on lake level, local hydrology, and sediment transport in the Lake Malawi basin rather than as a direct response to its production in the atmosphere modulated by the intensity of the Earth's dipole. Therefore, a direct correlation of the 10Be/9Be to a chronology derived from the paleomagnetic variations measured from marine sediments was not possible. Nevertheless, a comparison of the 10Be/9Be chronology, allowing for decay, at Lake Malawi to that of the global marine paleomagnetic record suggests that the bottom of core MAL05-1B is no more than 750ka in age. © 2010.
cited By 10
Keywords: beryllium isotope; cosmogenic radionuclide; geochronology; lacustrine deposit; lake level; marine record; marine sediment; paleoclimate; paleomagnetism; radiocarbon dating; sediment core; sediment transport; East Africa; East African Lakes; Lake Malawi

Mechanical twinning in quartz: Shock experiments, impact, pseudotachylites and fault breccias - Wenk, H.-R.; Janssen, C.; Kenkmann, T.; Dresen, G. (Tectonophysics, 2011)
Increasing use of diffraction methods to study preferred orientation of minerals has established that quartz in deformed rocks not only displays characteristic c-axis orientation patterns, but that there is also generally a distinct difference in the orientation of positive and negative rhombs. In the trigonal quartz crystal structure positive and negative rhombs are structurally different, and particularly negative rhombs (e.g. 01. 1-1) are much stiffer than positive rhombs (e.g. 10. 1-1). Here, we focus on the role of mechanical Dauphin'e twinning under stress as a cause of this difference and illustrate with EBSD measurements ubiquitous twinning in quartz-bearing rocks subjected to high stresses. Characteristic twinning is observed in experimentally shocked sandstones and stishovite-bearing quartzites from the Vredefort meteorite impact site in South Africa. Similar twinning is documented for quartz associated with pseudotachylites from the Santa Rosa mylonite zone in Southern California, whereas quartz in underlying ductile mylonites are more or less twin-free. It suggests that twinning was produced by local seismic stresses that caused fracture and frictional melting on fault surfaces. Quartz-bearing breccias from the SAFOD (San Andreas Fault Observatory at Depth) drilling project also show evidence of twinning and suggest high seismic stresses in the currently creeping segment of the San Andreas Fault at Parkfield. From these observations it appears that Dauphin'e twin microstructures can be diagnostic of high local and transient stresses. © 2011 Elsevier B.V.
cited By 35
Keywords: C-axis orientations; Creeping segment; Diffraction methods; Drilling projects; EBSD; Fault breccia; Fault surfaces; Frictional melting; High stress; Mechanical twinning; Meteorite impact; Mylonites; Preferred orientations; Pseudotachylites; San Andreas Fault; Seismic stress; Shock deformation; South Africa; Southern California; Transient stress; Twin-free; Crystal structure; Meteor impacts; Quartz deposits; Rocks; Seismology; Structural geology; Quartz; breccia; crystal structure; deformation mechanism; ductile deformation; experimental study; microstructure; preferred orientation; pseudotachylite; quartz; San Andreas Fault; twinning; South Africa

Metamorphism as a function of depth in metasedimentary rocks of the Outokumpu Deep Drill Hole - H{oltt{a, Pentti; Karttunen, Petriikka (Special Paper of the Geological Survey of Finland, 2011)
Metamorphic mineral assemblages and mineral compositions were investigated in metasediments of the Outokumpu drill hole from the surface to 2.5 km depth in order to determine the Proterozoic geothermal gradient. The common mineral assemblage of the mica gneisses is biotite-plagioclase-quartz±muscovite. Finegrained garnet and Al silicates (sillimanite, kyanite, andalusite) are locally found, whereas staurolite is rare. Small abundances of leucosome indicating the onset of partial melting are present, especially in the lower parts of the hole, which also show some grain-size coarsening. The Fe and Mg distribution coefficient (KD) between coexisting garnet and biotite increases slightly from the surface to the deeper levels, indicating increasing temperature. The garnet-biotite thermometer shows a slight increase in temperatures from c. 605-610 °C near the surface to c. 620-630 °C at 1200-1500 m depth, indicating an average gradient of 19 °C/km, but the result is within the error limits of the thermometer (±15 °C). Temperatures calculated using Thermocalc software are several tens of degrees higher. Metamorphic pressures calculated using the garnet-biotite-plagioclase- quartz and garnet-muscoviteplagioclase- quartz barometers and the Thermocalc average PT method are in the range from c. 4-9 kbars. Pressures given by fluid inclusion barometry are 2-5 kbars. Geobarometry does not indicate systematic changes as a function of the depth. A clockwise PT path, where pressure increased to 8-9 kbars and was followed by decompression down to the andalusite field, explains the observed mineral assemblages and thermobarometric results.
Keywords: Finland; Ita Suomen; Outokumpu; biotite; fluid inclusion; garnet; gneiss; grain size; iron; magnesium; metamorphism; metasediment; mica; mineralogy; P-T conditions; P-T-t path; partial melting; Proterozoic

Microbiological sampling and analysis of the Outokumpu Deep Drill Hole biosphere in 2007-2009 - It{avaara, Merja; Nyyss{onen, Mari; Bomberg, Malin; Kapanen, Anu; Nousiainen, Aura; Ahonen, Lasse; Hultman, Jenni; Paulin, Lars; Auvinen, Petri; Kukkonen, Ilmo T. (Special Paper of the Geological Survey of Finland, 2011)
Three sampling campaigns were performed during the years 2007-2009 to develop microbiological sampling techniques and to study the deep biosphere in the Outokumpu Deep Drill Hole R2500, drilled into a Palaeoproterozoic sequence of rocks consisting of metasediments, ophiolite-derived altered ultramafic rocks and pegmatitic granite. The results revealed the presence of microbial communities in the saline fluids sampled from the open borehole and fracture systems in the low-porosity crystalline bedrock in Outokumpu. According to the microbiological analyses, the microbial cell density varies from 105 cells ml-1 at the surface to 103 ml-1 at 2350 m depth. The composition of microbial communities in the borehole was found to vary with sampling depth, and the changes appear to be connected to both geological and geochemical factors as well as to fracture zones in the bedrock. Sulphate reducing bacteria and methanogenic archaea are present throughout the borehole water column.
Keywords: Finland; Ita Suomen; Outokumpu; Bacteria (microorganisms); bacterium; bedrock; biosphere; borehole; fracture; granite; groundwater; metasedimentary rock; microbiology; microorganism; sampling; ultramafic rock; water column

Modification of the magnetic mineralogy in basalts due to fluid-rock interactions in a high-temperature geothermal system (Krafla, Iceland) - Oliva-Urcia, B.; Kontny, A.; Vahle, C. (Geophysical Journal International, 2011)
Active high-temperature ( >150 °C) geothermal areas like the Krafla caldera, NE-Iceland, often show distinct magnetic lows in aeromagnetic anomaly maps suggesting a destruction of magnetic minerals by hydrothermal activity. The main alteration processes in such an environment are low-temperature oxidation ( <350 °C, maghemitization) and fluid-rock interactions. We investigated the rock magnetic properties [natural remanent magnetization (NRM) magnetic susceptibility and their temperature and field variation] and the mineralogy, using X-ray diffraction, microscopic methods and electron microprobe analyses, of two drill cores (KH1 and KH3) from the rim of the Krafla caldera. The drill cores have distinctly lower NRM values (average <3 A m-1) compared to younger surface basalts (average 20 A m-1) along with a large variation in magnetic susceptibility (1.3 × 10-7- 4.9 × 10-5 m3 kg-1). The secondary mineral assemblage (sulphides, sphene, rutile and chlorite) indicates an alteration within the chlorite-smectite zone for both cores without depth zoning. Optical miscroscopy in combination with the Bitter technique and backscatter electron microscopy along with the thermomagnetic analyses allow distinguishing two different magnetomineralogical groups of titanomaghemite: (1) titanomaghemite with intermediate titanium concentration and probably high vacancy concentration, and (2) titanomaghemite with low titanium concentration and low vacancy concentration. The mineral assemblages, textures and magnetic properties deduced from the mentioned magnetic measurements indicate two-stage transformation mechanism: (1) Dissolution of titanium at low pH under oxidizing conditions. The ulv{ospinel component of titanomagnetite and ilmenite forms rutile or sphene, and Fe2 + migrates out of the spinel lattice forming titanomaghemite. (2) Formation of pyrite and dissolution of remaining titanomaghemite under reducing and acidic conditions. The latter mechanism produces ghost textures (all titanomaghemite is transformed and only their former grain shapes are preserved), with only paramagnetic minerals left and ferrimagnetic minerals nearly dissolved. This mechanism could explain the significant magnetization loss, which is seen in many local magnetic anomaly lows within the oceanic crust and volcanic islands like Iceland or Hawaii. The production of nanoporous textures in titanomaghemites is suggested as a mechanism for the enhancement of the magnetic susceptibility values related to the hydrothermal alteration of Krafla. © 2011 The Authors. Geophysical Journal International © 2011 RAS.
cited By 21
Keywords: Acidic conditions; Backscatter electron microscopy; Drill core; Ferrimagnetic minerals; Fluid-rock interaction; Geothermal areas; Geothermal systems; Grain shapes; High temperature; Hydrothermal activity; Hydrothermal alterations; Hydrothermal system; Icelands; Krafla caldera; Latter mechanism; Low-temperature oxidation; Magnetic anomalies; Magnetic mineralogy; Magnetic minerals; Magnetization loss; Microscopic methods; Mineral assemblage; Nano-porous; Natural remanent magnetization; Oceanic crust; Oxidizing conditions; Rock magnetic properties; Spinel lattices; Thermomagnetic analysis; Titanomagnetites; Two-stage transformations; Vacancy concentration; Volcanic islands; Basalt; Clay minerals; Concentration (process); Core drilling; Crystallography; Dissolution; Drills; Electron probe microanalysis; Geothermal fields; Lithology; Magnetic susceptibility; Magnetization; Mineralogy; Natural resources management; Oxide minerals; Paramagnetism; Petrography; Rocks; Silicates; Textures; Titanium; X ray diffraction; X ray diffraction analysis; Geomagnetism; basalt; caldera; chlorite; dissolution; geomagnetism; geothermal system; high temperature; hydrothermal activity; hydrothermal alteration; hydrothermal system; magnetic anomaly; magnetic susceptibility; magnetization; mineralogy; natural remanent magnetization; oceanic crust; oxidation; petrology; pyrite; smectite; volcanic island; Iceland; Krafla

Occurrence and distribution of series long-chain alkyl naphthalenes in Late Cretaceous sedimentary rocks of the Songliao Basin, China - Lu, H.; Wang, L.; Song, Z.; Greenwood, P.; Yin, Q. (Geochemical Journal, 2011)
A pair of series straight long-chain 2- and 1-alkyl naphthalenes (aNs) with alkyl chain carbon number up to 30 was detected in late Cretaceous sedimentary source rocks of the onshore Songliao Basin, NE China. Their sedimentary profile was shown to correlate positively with the relative abundances of several higher plant biomarkers including iP-iHMN and phenanthrene and weakly inversely with the relative abundance of alkylbenzenes. In contrast, the aNs distribution shows no relationship with hydrocarbon maturity indicators. The TOC, δ13C profile and other molecular features (e.g., CPI, OEP, Pr/Ph, Ga/C31H) were consistent with transgressive/regressive water cycles of the palaeo-lake of Songliao Basin. Decreasing Pr/Ph values in the upper horizon indicative of increasingly anoxic conditions. The distinctive occurrence and distribution of the long-chain aN compounds on the profile of the SK-1 borehole may imply some unique source inputs under particular lacustrine environmental conditions. Copyright © 2011 by The Geochemical Society of Japan.
cited By 3
Keywords: anoxic conditions; biomarker; Cretaceous; hydrocarbon resource; naphthalene; sedimentary rock; source rock; thermal maturity; total organic carbon; China; Songliao Basin; Embryophyta

Monthly monitoring of gas and isotope compositions in the free gas phase at degassing locations close to the Nov'y Kostel focal zone in the western Eger Rifţ Czech Republic - Br{auer, Karin; K{ampf, Horst; Koch, Ulrich; Strauch, Gerhard (Chemical Geology, 2011)
We report new data on gas and isotope compositions of mantle-derived exhalations from five locations in the Vogtland (Germany)/NW Bohemia (Czech Republic) area, close to the Nov'y Kostel focal zone, recorded by monthly sampling of gases over a three year period. This region is the locus typicus for the term earthquake swarm; since 1985/86 the largest numbers of earthquake swarms in the Vogtland/NW Bohemia have occurred in the Nov'y Kostel focal zone. Mantle-derived degassing has been studied at four locations within the Cheb Basin degassing centre, and at the Wettinquelle spring to the north on the edge of the Cheb Basin. The Bubl'ak and U Mostku locations are on the Počatky Plesn'a Fault Zone (PPZ) while the Kopanina and Dolni Častkov locations are on the Mari'ansk'e L'azně Fault (MLF). The mantle-derived helium content at locations along the PPZ covers the range of the sub-continental lithospheric mantle (SCLM). Along the MLF the 3He/4He ratios are with up to 5.4Ra a little bit lower as at the PPZ locations. The CO2/3He ratios point to a predominantly magmatic source. Depending on the magnitude of gas flux the monthly sampling results indicated various major influences on the fluid signatures at the monitored locations due to seasonal cycles based on the different strong influence of CO2/water interaction. Micro-seismicity occurred repeatedly during the monitoring period and seismically triggered geochemical anomalies were repeatedly observed at the locations close to the focal zone. The 3He/4He ratios drop from 5.9Ra (mean) up to 5.6Ra at Bubl'ak and from 5.6Ra up to 5.3Ra at U Mostku. A decrease in 3He/4He ratios was observed prior to seismic events due to stress accumulation before rupturing, and also after the events due to the release of crustal-derived components within the area of the focal zone. Due to the higher 'helium baseline content' of the Kopanina gas the 3He/4He ratios decreased there only from 4.6 to 4.5Ra. At the Wettinquelle, the most distant from the focal zone, the 3He/4He ratios ranged between 2.3 and 2.5Ra altogether. Superimposed to the seismically induced anomalies a clear three month-lasting increase of mantle-derived helium was observed at the locations on the PPZ. The 3He/4He ratios increased to 6.3Ra at Bubl'ak and to 6.0Ra at U Mostku. An increase in the 3He/4He ratios was also noted at Kopanina (to 4.7Ra) and Dolni Častkov (to 5.4Ra), interpreted as indicating an ascent of less degassed magma (dyke intrusions) from the deeper lithospheric mantle reservoir. Superimposed geochemical effects initiated by the temporal and spatial evolution of a hidden magmatic-driven geodynamic process have therefore been observed in a continental rift system for the first time. © 2011 Elsevier B.V.
Keywords: Bohemia; Cheb Basin; Czech Republic; Germany; Karlovarsky; Vogtland; Carbon dioxide; Degassing; Earthquakes; Gases; Geochemistry; Geologic models; Helium; Isotopes; Magnetic leakage; He ratios; Cenozoic; Earthquake swarms; Magma intrusion; carbon dioxide; Cenozoic; degassing; earthquake swarm; focal mechanism; gas; helium isotope; igneous intrusion; isotopic composition; isotopic ratio; lithospheric structure; magma; mantle chemistry; rift zone; Focusing

Multicellular algae from lower Proterozoic (2.45 Ga) weathering crusts of the Kola Peninsula - Astafieva, Marina M; Rozanov, Alexei Yu; Hoover, Richard B (Instruments, Methods, and Missions for Astrobiology XIV, 2011)

Nanoscale porosity in SAFOD core samples (San Andreas Fault) - Janssen, C.; Wirth, R.; Reinicke, A.; Rybacki, E.; Naumann, R.; Wenk, H.-R.; Dresen, G. (Earth and Planetary Science Letters, 2011)
With transmission electron microscopy (TEM) we observed nanometer-sized pores in four ultracataclastic and fractured core samples recovered from different depths of the main bore hole of the San Andreas Fault Observatory at Depth (SAFOD). Cutting of foils with a focused ion beam technique (FIB) allowed identifying porosity down to the nm scale. Between 40 and 50% of all pores could be identified as in-situ pores without any damage related to sample preparation. The total porosity estimated from TEM micrographs (1-5%) is comparable to the connected fault rock porosity (2.8-6.7%) estimated by pressure-induced injection of mercury. Permeability estimates for cataclastic fault rocks are 10-21-10-19 m2 and 10-17 m2 for the fractured fault rock. Porosity and permeability are independent of sample depth. TEM images reveal that the porosity is intimately linked to fault rock composition and associated with deformation. The TEM-estimated porosity of the samples increases with increasing clay content. The highest porosity was estimated in the vicinity of an active fault trace. The largest pores with an equivalent radius >200nm occur around large quartz and feldspar grains or grain-fragments while the smallest pores (equivalent radius <50nm) are typically observed in the extremely fine-grained matrix (grain size <1 >m). Based on pore morphology we distinguish different pore types varying with fault rock fabric and alteration. The pores were probably filled with formation water and/or hydrothermal fluids at elevated pore fluid pressure, preventing pore collapse. The pore geometry derived from TEM observations and BET (Brunauer, Emmett and Teller) gas adsorption/desorption hysteresis curves indicates pore blocking effects in the fine-grained matrix. Observations of isolated pores in TEM micrographs and high pore body to pore throat ratios inferred from mercury injection suggest elevated pore fluid pressure in the low permeability cataclasites, reducing shear strength of the fault. © 2010 Elsevier B.V.
cited By 53
Keywords: Fault rock; Permeability; SAFOD; San Andreas Fault; TEM; Core samples; Fluids; Ion beams; Mercury (metal); Porosity; Quartz; Rocks; Shear strength; Silicate minerals; Tectonics; Transmission electron microscopy; Structural geology; cataclasite; fault zone; feldspar; fluid pressure; hydrothermal fluid; permeability; porosity; quartz; San Andreas Fault; shear strength; transmission electron microscopy

Neon identifies two billion year old fluid component in Kaapvaal Craton - Lippmann-Pipke, J.; Sherwood Lollar, B.; Niedermann, S.; Stroncik, N.A.; Naumann, R.; Heerden, E.; Onstott, T.C. (Chemical Geology, 2011)
The deep gold mines of the Witwatersrand Basin, South Africa have gained recent attention not only because of investigations of the deep fracture water and associated CH4- and H2-rich gases found there, but because of recent reports of deep microbial communities persisting to depths of almost 3km - an exotic outpost of the Earth's deep biosphere. While shallower fluids in the basin (to approximately 1km) were found to contain abundant populations of methanogens and sulphate-reducing bacteria, the deepest, oldest, most saline fracture waters in the basin hosted hitherto unrecognised low biomass and low biodiversity chemoautotrophic ecosystems independent from the photosphere. Shallow and deep fluids also show distinct differences in gas and fluid geochemistry. Paleometeoric waters are dominated by hydrocarbon gases with compositional and isotopic characteristics consistent with production by methanogens utilising the CO2 reduction pathway. In contrast the deepest, most saline fracture waters contain gases that are dominated by high concentrations of H2 gas, and CH4 and higher hydrocarbon gases with isotopic signatures attributed to abiogenic processes of water-rock reaction. The high salinities (up to hundreds of g/L), highly altered δ18O and δ2H signatures, and both 36Cl and measurements of co-occurring nucleogenic noble gases for these fracture waters are consistent with extensive water-rock interaction over geologically long time scales in these high rock/water ratio environments. While the ultimate origin of these fluids has been attributed alternately to saline waters that penetrated the crystalline basement, formation water, or hydrothermal fluids in some cases, their δ18O and δ2H isotopic signatures have typically been so profoundly overprinted by the effects of long-term water-rock interaction that, for the most saline end-members, little evidence of their primary composition remains. The key objective of the present study is to further investigate the origin of these fluids by integrating for the first time detailed neon isotope analyses on the dissolved gases. Helium isotopic analysis confirmed that there is no significant mantle-derived component associated with these fluids and gases. Neon isotope results show distinct differences in neon composition that correspond to the different fluid geochemical end-members previously identified. Typical crustal neon signatures (type A) are identified in the paleometeoric waters populated with abundant methanogens. In contrast, the deep more saline fracture waters contain an enriched nucleogenic neon signature unlike any previously reported in crustal fluids. These samples show the highest 21Ne/22Ne ratios (0.160±0.003) ever reported in groundwater. Fluid inclusions in these rocks yield even higher 21Ne/22Ne ratios between 0.219 and 0.515, consistent with an extrapolated 21Ne/22Ne value of 3.3±0.2 at 20Ne/22Ne=0. We show that this enriched nucleogenic neon end-member represents a fluid component that was produced in the fluorine-depleted Archaean formations and trapped in fluid inclusions ≥2Ga ago. The observation of enriched nucleogenic neon signatures in deep fracture water implies the release of this billion year old neon component from the fluid inclusions and its accumulation in exceptionally isolated fracture water systems. The observed association of this Archean neon signature with H2-hydrocarbon-rich geogases of proposed abiogenic origin dissolved in the same deep groundwater suggests that the fracture systems have also allowed for the accumulation of various products of water-rock reactions throughout geologic times. One of these fracture systems contained the deepest characterised microbial ecosystems on earth - chemolithotrophs eking out an existence at maintenance levels independent from sunlight. Consequently, the enriched nucleogenic neon isotope signature may indicate regions in the Archaean crust where investigations of the deep biosphere might be focused. © 2011 Elsevier B.V.
cited By 63
Keywords: Abiogenic; Abiogenic origin; Archaean; Archean; Chemolithotrophs; Crustal fluid; Crystalline basement; Deep fluids; Deep fractures; Deep gold mines; Deep groundwaters; Dissolved gas; Endmembers; Fluid components; Fluid geochemistry; Fluid inclusion; Formation water; Fracture systems; Fracture water; High concentration; High salinity; Higher hydrocarbons; Hydro-carbon gas; Hydrothermal fluids; Isotopic analysis; Isotopic characteristics; Isotopic signatures; Key objective; Maintenance levels; Metamorphic fluids; Microbial communities; Microbial eco system; Neon isotopes; Noble gas; South Africa; Subsurface microbiology; Sulphate reducing bacteria; Time-scales; Water rock interactions; Water-rock reactions; Analytical geochemistry; Biodiversity; Biospherics; Ecosystems; Fluids; Fluorine; Fracture; Gallium; Gas fuel analysis; Gold mines; Groundwater; Groundwater geochemistry; Helium; Hydrocarbons; Inert gases; Isotopes; Methanogens; Microbiology; Mineralogy; Rock products; Saline water; Weathering; Neon; concentration (composition); isotopic composition; methanogenesis; microbial community; neon; noble gas; water chemistry; water-rock interaction; South Africa; Witwatersrand

New progress of integrated chronostratigraphy of the Cretaceous in Songliao Basin - Huang, QH; Wu, HC; Wan, XQ; He, HY; Deng, CL (Journal of Stratigraphy, 2011)

Numerical study of gas evolution and transport behaviours in natural gas-hydrate reservoirs - Uddin, M.; Wright, F.; Coombe, D. (Journal of Canadian Petroleum Technology, 2011)
Gas hydrates are a potentially vast untapped source of natural gas. Recent numerical and field studies suggest the Mallik gas-hydrate field in Canada's Mackenzie Delta may represent a technically producible and potentially economically viable reservoir of natural gas. Our initial reservoir simulations using a kinetic reaction approach indicate that gas evolution and transport within porous geologic reservoirs have a significant effect on fluid production characteristics, while field and laboratory data suggest that significant amounts of evolved gas can be trapped for some time within the reservoir, depending on the field operation. In this work, we invoke modelling concepts extensively employed in quantifying gas ex-solution from viscous oils to further assess the kinetic behaviour of gas-hydrate ex-solution through depressurization. Here, the gas bubbles can be categorized into three groups with explicit transport behaviour: small bubbles (water phase), large bubbles (immobile) and connected bubbles (or free gas). These concepts allow the development of a new set of kinetic reactions for hydrate dissociation: one representing the (possibly delayed) conversion of hydrate into water and dispersed gas bubble phases, and one representing the evolution from dispersed bubbles to connected bubbles. These reactions can effectively capture the nonequilibrium fluidflow behaviour observed in field production tests. For modelling of the transport phenomenon, we assumed two explicit mobility formulations: (1) trapped bubbles (no mobility) and a flowing water phase and (2) large connected gas bubbles and flowing water (with relative mobility). Relative mobility can be estimated by using traditional gridblock-relative permeability curves. We then develop a simple mechanistic gas bubble trapping tool as a function of the capillary number, which can easily be incorporated into our numerical simulator. This entrapment of the nonwetting gas-phase results in higher values of critical gas saturation. Two case studies based on alternative representations of a Mallik-like gas-hydrate reservoir demonstrate that significant errors can result in reservoir modelling if these fluid transport phenomena are not adequately represented in numerical simulations. Aspects of the model developed here have been applied to history matching and prediction of natural gas recovery from a clastic, sand-dominated reservoir at the Mallik site.
cited By 21
Keywords: Bubbles (in fluids); Gas hydrates; Gas oils; Gases; Hydration; Kinetics; Natural gas; Natural gasoline plants; Petroleum reservoirs; Transport properties; Critical gas saturation; Gas hydrate reservoir; Hydrate dissociation; Natural gas hydrate reservoir; Natural gas recoveries; Numerical simulators; Relative permeability curves; Reservoir simulation; Natural gas fields

Observations of fault damage zones at reservoir depths - Johri, M.; Zoback, M.D.; Hennings, P. (45th US Rock Mechanics / Geomechanics Symposium, 2011)
We report a study on sub-surface fault damage zones adjacent to faults in a gas field in Southeast Asia and near the San Andreas Fault in central California. The importance of characterizing damage zones arises from the important role that damage zones and natural fractures play in governing fluid flow through low permeability reservoirs. While there are many published studies of exposed damage zones (principally associated with now dormant faults), there is an absence of subsurface data that characterizes damage zones at depth associated with active faults. The first region of study is a fault zone in a gas reservoir in Southeast Asia. A large, basement master fault is associated with twenty-seven seismically-resolvable second-order faults. Five to six fractures per meter are observed in electrical image logs from five wells in the 50-80m wide damage zones of the second-order faults. Damage zones associated with second-order faults adjacent to the San Andreas Fault are studied in well-cemented arkosic sandstones immediately southwest of the main fault at the SAFOD site. Damage zone widths associated with second-order faults are typically on the order of 50-100 meters whereas the damage zone associated with the San Andreas Fault is about 250 meters wide. The density of the third-order faults in damage zones observed in both the areas of study is found to decrease exponentially with distance. © 2011 ARMA, American Rock Mechanics Association.
cited By 3
Keywords: Active fault; California; Damage zones; Electrical images; Fault damage zone; Fault zone; Gas fields; Gas reservoir; Natural fracture; San Andreas Fault; Second orders; Southeast Asia; Sub-surfaces; Subsurface data; Third-order; Flow of fluids; Fracture; Gas industry; Petroleum reservoir engineering; Rock mechanics; Low permeability reservoirs

Postglacial fault drilling in Northern Europe: Workshop in Skokloster, Sweden - Kukkonen, I.T.; Ask, M.V.S.; Olesen, O. (Scientific Drilling, 2011)
cited By 6

Thermal properties of rocks of the borehole Yaxcopoil-1 (Impact Crater Chicxulub, Mexico) - Popov, Y.; Romushkevich, R.; Korobkov, D.; Mayr, S.; Bayuk, I.; Burkhardt, H.; Wilhelm, H. (Geophysical Journal International, 2011)
The results of thermal property measurements on cores from the scientific well Yaxcopoil-1 (1511 m in depth) drilled in the Chicxulub impact structure (Mexico) are described. The thermal conductivity, thermal diffusivity, volumetric heat capacity, thermal anisotropy coefficient, thermal heterogeneity factor, and, in addition, porosity and density were measured on 451 dry and water-saturated cores from the depth interval of 404-1511 m. The acoustic velocities were determined on a subgroup of representative samples. Significant vertical short- and long-scale variations of physical properties related to the grade of shock-thermal metamorphism and correlations between thermal and other physical properties are established. Rocks of the post-impact and impact complexes differ significantly in heterogeneity demonstrating that the impact complex has larger micro- heterogeneity on sample scale. The pre-impact rocks differ essentially from the impact and post-impact rocks in the thermal conductivity, thermal diffusivity, density and porosity. The thermal anisotropy of rocks of all structural-lithological complexes is very low (K = 1.02 ... 1.08), which is similar to the situation in the Puchezh-Katunk and Ries impact structures. Correlations are established between the thermal conductivity and elastic wave velocities measured in laboratory. For limestone-calcarenites, the thermal conductivity (λ) can be calculated from the compressional wave velocity (Vp) using the formula λ= 0.346 Vp + 0.844, and for dolomite-anhydrites this relation has the form λ= 0.998 Vp + 1.163 [for λ in W (m K)-1 and Vp in km s-1]. These correlations are used for downscaling of the sonic velocities to the decimetre scale. The effective medium theory is applied to invert the matrix thermal conductivity and pore/crack geometry from the thermal conductivity measured on the studied samples. Representative experimental data on the thermal properties for all lithological groups encountered by the Yaxcopoil-1 well essentially extend an existing database on the thermal properties of rocks of impact structures and can be used for determination of the heat flow density, interpretation of temperature logging data, theoretical modelling of heat and mass transfer processes and constructing thermal models of the Chicxulub impact structure as well as for the lithological interpretation. The research results confirm the necessity of dense sampling for the thermal property measurements to obtain reliable results in petrophysical and geothermal investigations of impact structure formations. © 2010 The Authors Geophysical Journal International © 2010 RAS.
cited By 17

Project hotspot: Insight into the subsurface stratigraphy and geothermal potential of the snake river plain - Potter, Katherine E.; Bradshaw, Richard; Sant, Christopher J.; King, Jesse; Shervais, John W.; Christiansen, Eric J. (Transactions - Geothermal Resources Council, 2011)
Preliminary stratigraphic sections for Project Hotspot's Kimama drill hole based on gamma and neutron logs correlate well with lithologic observations. The gamma logs document the depth and thickness of sedimentary interbeds, whereas the neutron logs respond to the contrast between massive flow interiors and more porous flow tops. These data show the presence of at least 550 basalt flows (0.1-50 m thick), grouped into at least 30 flow groups, 13 m to 170 m thick (most 20-100 m thick). Flows are designated based upon morphological characteristics, including the presence of rubbly, highly fractured flow tops, massive to vesicular flow interiors, and rubbly flow bases; flow groups are commonly separated by sedimentary interbeds, which range in thickness from 0.2 m to 50 m. Increased conductivity along basalt flow unit contacts and associated fractures is a well-documented trend in the subsurface stratigraphy of the SRP. Determining the location of permeable basalt flow unit contacts and impermeable sediment layers is necessary to understand the flow of groundwater and potentially, geothermal fluid. The compilation of well log data shows an apparent agreement between lithologic and geophysical stratigraphy, with observed basalt flow unit contacts and sediment interbeds at least roughly mirrored by spikes and dips in natural gamma and neutron log signals. Natural gamma logs have the additional capability of identifying more evolved, high potassium basalt compositions through signal peaks that are unrelated to lithologic flow boundaries. These observations demonstrate the usefulness of wireline geophysical data to determine basalt flow group boundaries, flow compositions, and probable fluid transport avenues.
Keywords: Basalt; Geothermal fields; Geothermal prospecting; Groundwater; Neutrons; Potassium; Sedimentology; Stratigraphy; Transport properties; Basalt flow; Drill hole; Flow boundaries; Fluid transport; Geophysical data; Geothermal; Geothermal fluids; Geothermal potential; Group boundary; Hot spot; Morphological characteristic; Neutron log; Porous flow; Rhyolite; Sediment layers; Snake river plains; Subsurface stratigraphy; Well log data; Neutron logging

The PASADO core processing strategy - A proposed new protocol for sediment core treatment in multidisciplinary lake drilling projects - Ohlendorf, Christian; Gebhardt, Catalina; Hahn, Annette; Kliem, Pierre; Zolitschka, Bernd (Sedimentary Geology, 2011)
Using the ICDP (International Continental Scientific Drilling Program) deep lake drilling expedition no. 5022 as an example, we describe core processing and sampling procedures as well as new tools developed for subsampling. A manual core splitter is presented that is (1) mobile, (2) able to cut plastic core liners lengthwise without producing swarf of liner material and (3) consists of off-the-shelf components. In order to improve the sampling of sediment cores, a new device, the core sampling assembly (CSA), was developed that meets the following targets: (1) the partitioning of the sediment into discs of equal thickness is fast and precise, (2) disturbed sediment at the inner surface of the liner is discarded during this sampling process, (3) usage of the available sediment is optimised, (4) subsamples are volumetric and oriented, and (5) identical subsamples are taken. The CSA can be applied to D-shaped split sediment cores of any diameter and consists of a divider and a D-shaped scoop. The sampling plan applied for ICDP expedition 5022 is illustrated and may be used as a guideline for planning the efficient partitioning of sediment amongst different lake research groups involved in multidisciplinary projects. For every subsample, the use of quality flags is suggested (1) to document the sample condition, (2) to give a first sediment classification and (3) to guarantee a precise adjustment of logging and scanning data with data determined on individual samples. Based on this, we propose a protocol that might be applied across lake drilling projects in order to facilitate planning and documentation of sampling campaigns and to ensure a better comparability of results. © 2011 Elsevier B.V.
Keywords: Argentina; Patagonia; Information retrieval systems; Lakes; Sedimentology; Well drilling; Argentina; Core processing; Core sampling; Core slicing; Drilling projects; Inner surfaces; Liner material; Multidisciplinary projects; New devices; New protocol; Off-the-shelf components; Patagonia; Research groups; Sampling campaigns; Sampling plans; Sampling procedures; Sampling process; Scanning data; Scientific drilling; Sediment classification; Sediment core; core logging; deep drilling; lake; partitioning; sampling; sediment core; Anoxic sediments

The Advance of Delta lgR Method and Its Application in Songliao Basin - Huo, Q-L; Zeng, H-S; Fu, Li; Ren, Z-G (Journal of Jilin University(Earth Science Edition), 2011)

The chicxulub multi-ring impact crater, yucatan carbonate platform, Gulf of Mexico - Urrutia-Fucugauchi, J.; Camargo-Zanoguera, A.; P'erez-Cruz, L.; P'erez-Cruz, G. (Geofisica Internacional, 2011)
The Chicxulub impact crater is part of a select group of unique geological sites, being a natural laboratory to investigate crater formation processes and global effects of large-scale impacts. Chicxulub is one of only three multi-ring craters documented in the terrestrial record and impact has been related to the global environmental/climatic effects and mass extinction that mark the Cretaceous/Paleogene (K/Pg) boundary. The crater is buried under 1.0 km of carbonate sediments in the Yucatan peninsula. The buried structure was initially identified from geophysical surveys of the PEMEX oil exploration program in southeastern Mexico. On the surface its influence is marked by the circular ring of cenotes that have formed from differential compaction and fracturing between the impact breccias and surrounding limestone sequences. The crater is about 200 km in rim diameter, half on-land and half off-shore with geometric center at Chicxulub Puerto, making it possible to use land, marine and aerial geophysical methods. The Yucatan carbonate platform is an ideal place to have the crater, tectonically stable with no volcanic activity, having formed by slow deposition of carbonate sediments. These characteristics permit high resolution imagery of the crater underground structure with unprecedented detail. The impact and crater formation occur instantaneously, with excavation of the crust down to 25 km depths in fractions of a second and lower crust uplift and crater formation in the next few hundred seconds. Energy release results in intense fracturing and deformation at the target site, generating seismic waves traveling the whole Earth. Understanding the physics of impacts on planetary surfaces and modeling of crustal deformation and rheological behavior of materials at high temperatures and pressures remain major challenges in geosciences. The K/Pg ejecta layer is the only global stratigraphic marker in the geological record, allowing correlation of events worldwide. In the last 20 years much has been learned about the Chicxulub crater and the K/Pg boundary; however what is perhaps most interesting are the questions remaining, which include fundamental aspects of Chicxulub impact and its environmental effects.
cited By 34

The deep biosphere in terrestrial sediments in the Chesapeake Bay area, Virginia, USA - Breuker, A.; K{oweker, G.; Blazejak, A.; Schippers, A. (Frontiers in Microbiology, 2011)
For the first time quantitative data on the abundance of Bacteria, Archaea, and Eukarya in deep terrestrial sediments are provided using multiple methods (total cell counting, quantitative real-time PCR, Q-PCR and catalyzed reporter deposition-fluorescence in situ hybridization, CARD-FISH). The oligotrophic (organic carbon content of ̃0.2%) deep terrestrial sediments in the Chesapeake Bay area at Eyreville, Virginia, USA, were drilled and sampled up to a depth of 140 m in 2006. The possibility of contamination during drilling was checked using fluorescent microspheres. Total cell counts decreased from 109 to 106 cells/g dry weight within the uppermost 20 m, and did not further decrease with depth below. Within the top 7 m, a significant proportion of the total cell counts could be detected with CARD-FISH.The CARD-FISH numbers for Bacteria were about an order of magnitude higher than those for Archaea. The dominance of Bacteria over Archaea was confirmed by Q-PCR. The down core quantitative distribution of prokaryotic and eukaryotic small sub- unit ribosomal RNA genes as well as functional genes involved in different biogeochemical processes was revealed by Q-PCR for the uppermost 10 m and for 80-140 m depth. Eukarya and the Fe(III)- and Mn(IV)-reducing bacterial group Geobacteriaceae were almost exclu- sively found in the uppermost meter (arable soil), where reactive iron was detected in higher amounts. The bacterial candidate division JS-1 and the classes Anaerolineae and Caldilineae of the phylum Chloroflexi, highly abundant in marine sediments, were found up to the maximum sampling depth in high copy numbers at this terrestrial site as well. A similar high abundance of the functional gene cbbL encoding for the large subunit of RubisCO suggests that autotrophic microorganisms could be relevant in addition to het- erotrophs. The functional gene aprA of sulfate reducing bacteria was found within distinct layers up to ca. 100 m depth in low copy numbers.The gene mcrA of methanogens was not detectable. Cloning and sequencing data of 16S rRNA genes revealed sequences of typi- cal soil Bacteria. The closest relatives of the archaeal sequences were Archaea recovered from terrestrial and marine environments. Phylogenetic analysis of the Crenarchaeota and Euryarchaeota revealed new members of the uncultured South African Gold Mine Group, Deep Sea Hydrothermal Vent Euryarchaeotal Group 6, and Miscellaneous Crenarcheotic Group clusters. © 2011 Breuker, K{oweker, Blazejak and Schippers.
cited By 38
Keywords: Anaerolineae; Archaea; Bacteria (microorganisms); candidate division JS1; Chloroflexi; Chloroflexi (class); Crenarchaeota; Eukaryota; Euryarchaeota; Prokaryota

The Discussion of the Era of the Cretaceous Qingshankou Formation in Songliao Basin (in Chinese with English abstract); [松辽盆地白垩纪青山口组地质时代探讨] - Han, G.; Zhang, W.; Huang, Q. (Science Technology and Engineering, 2011)

The Iceland Deep Drilling Project (IDDP): Planning for the second deep well at Reykjanes - Frioleifsson, G.O.; Albertsson, A.; Elders, W.A.; Sigurdsson, O.; Karlsd'ottir, R.; P'alsson, B. (Transactions - Geothermal Resources Council, 2011)
The Iceland Deep Drilling Project (IDDP) is being carried out by an international industry-government consortium in Iceland, in order to investigate the economic feasibility of producing electricity from supercritical geothermal reservoirs. Modeling suggests that producing superheated steam from a supercritical reservoir could potentially increase power output of geothermal wells by an order of magnitude. To test this concept, the consortium planned to drill a deep well in each of three different geothermal fields in Iceland, namely, Krafla, and at the Hengill and Reykjanes fields in SW-Iceland. In 2009 the drilling of the first deep well, IDDP-1, was attempted in the active central volcano at Krafla in NE Iceland. However the drilling had to be terminated at 2.1 km depth when 900°C rhyolite magma was intersected. The well, IDDP-1, was highly productive, capable of producing some 25 MWe from 380°C superheated steam during a flow test undertaken in 2010. The well was shut in August 2010, to allow the wellhead and surface equipment to be modified to withstand corrosive fluids. Starting in May 2011 flow-testing, wet and dry scrubbing of the steam and a test of a heat exchange system will be conducted. This flow test is expected to last through the rest of 2011. Preliminary results from these tests should be available to report at the GRC Annual Meeting in October 2011. The second deep IDDP well, IDDP-2, could possibly be drilled to 4-5 km depth as early as 2012-2013, into the saline Reykjanes high-temperature field in SW-Iceland. The design of the IDDP-2 well will benefit from lessons learned during drilling of the IDDP-1 at Krafla. Here we review the geological and geophysical characteristics of the Reykjanes field, based on pre-existing and very recent data. According to both 1 dimensional and 3 dimensional interpretations of the new magnetotelluric (MT) data, the IDDP-2 site is located above a major heat source occurring at some 10 km depth.
cited By 17
Keywords: 3-dimensional; Black smokers; Corrosive fluids; Deep drilling; Deep wells; Economic feasibilities; Flow tests; Geothermal reservoir; Heat exchange systems; Heat sources; High temperature; Icelands; Power out put; Super-critical; Superheated steam; Surface equipment; Wet and dry; Deep oil well drilling; Effluent treatment; Geothermal fields; Geothermal prospecting; Supercritical fluids; Geothermal wells

The Lake El'gygytgyn scientific drilling project - conquering Arctic challenges through continental drilling - Melles, M.; Brigham-Grette, J.; Minyuk, P.; Koeberl, C.; Andreev, A.; Cook, T.; Fedorov, G.; Gebhardt, C.; Haltia-Hovi, E.; Kukkonen, M.; Nowaczyk, N.; Schwamborn, G.; et al. (Scientific Drilling, 2011)
Between October 2008 and May 2009, the International Continental Scientific Drilling Program (ICDP) co-sponsored a campaign at Lake El'gygytgyn, located in a 3.6-Ma-old meteorite impact crater in northeastern Siberia. Drilling targets included three holes in the center of the 170-m-deep lake, utilizing the lake ice cover as a drilling platform, plus one hole close to the shore in the western lake catchment. At the lake's center. the entire 315-m-thick lake sediment succession was penetrated. The sediments lack any hiatuses (i.e., no evidence of basin glaciation or desiccation), and their composition reflects the regional climatic and environmental history with great sensitivity. Hence, the record provides the first comprehensive and widely timecontinuous insights into the evolution of the terrestrial Arctic since mid-Pliocene times. This is particularly true for the lowermost 40 meters and uppermost 150 meters of the sequence, which were drilled with almost 100% recovery and likely reflect the initial lake stage during the Pliocene and the last 2.9 Ma, respectively. Nearly 200 meters of underlying rock were also recovered; these cores consist of an almost complete section of the various types of impact breccias including broken and fractured volcanic basement rocks and associated melt clasts. The investigation of this core sequence promises new information concerning the El'gygytgyn impact event, including the composition and nature of the meteorite, the energy released, and the shock behavior of the volcanic basement rocks. Complementary information on the regional environmental history, including the permafrost history and lake-level fluctuations, is being developed from a 142-m-long drill core recovered from the permafrost deposits in the lake catchment. This core consists of gravelly and sandy alluvial fan deposits in ice-rich permafrost, presumably comprising a discontinuous record of both Quaternary and Pliocene deposits.
cited By 66
Keywords: Anoxic sediments; Catchments; Core drilling; Deposits; Drilling platforms; Glacial geology; Meteor impacts; Meteorites; Permafrost; Recovery; Runoff; Sedimentology; Volcanic rocks; Volcanoes; Alluvial fans; Basement rocks; Drill core; Drilling targets; Environmental history; Ice cover; Ice-rich permafrost; Impact events; Information concerning; Lake sediments; Level fluctuation; Meteorite impact; Mid-Pliocene; Pliocene; Pliocene deposits; Scientific drilling; SIBERIA; Underlying rocks; Lakes

Theoretical Basis, Research Advancement and Prospects of Cyclostratigraphy (in Chinese with English abstract);[旋回地层学理论基础、研究进展和展望] - Wu, H.; Zhang, S.; Feng, Q.; Fang, N.; Yang, T.; Li, H. (Earth Science-Journal of China University of Geosciences, 2011)

Spatiotemporal earthquake clusters along the North Anatolian fault zone offshore İstanbul - Bulut, F.; Ellsworth, W.L.; Bohnhoff, M.; Aktar, M.; Dresen, G. (Bulletin of the Seismological Society of America, 2011)
We investigate earthquakes with similar waveforms in order to characterize spatiotemporal microseismicity clusters within the North Anatolian fault zone (NAFZ) in northwest Turkey along the transition between the 1999 İzmit rupture zone and the Marmara Sea seismic gap. Earthquakes within distinct activity clusters are relocated with cross-correlation derived relative travel times using the double difference method. The spatiotemporal distribution of micro earthquakes within individual clusters is resolved with relative location accuracy comparable to or better than the source size. High-precision relative hypocenters define the geometry of individual fault patches, permitting a better understanding of fault kinematics and their role in local-scale seismotectonics along the region of interest. Temporal seismic sequences observed in the eastern Sea of Marmara region suggest progressive failure of mostly nonoverlapping areas on adjacent fault patches and systematic migration of microearthquakes within clusters during the progressive failure of neighboring fault patches. The temporal distributions of magnitudes as well as the number of events follow swarmlike behavior rather than a mainshock/aftershock pattern.
cited By 18
Keywords: Cross correlations; Double differences; Fault kinematics; High-precision; Mainshock; Marmara Sea; Micro-earthquakes; Microseismicity; North Anatolian Fault Zone; Northwest Turkey; Progressive failure; Region of interest; Relative location; Rupture zone; Seismic sequence; Seismotectonics; Source sizes; Spatiotemporal distributions; Temporal distribution; Travel time; Wave forms; Image segmentation; Earthquakes; accuracy assessment; aftershock; earthquake catalogue; earthquake hypocenter; earthquake magnitude; earthquake mechanism; earthquake rupture; earthquake swarm; fault zone; Kocaeli earthquake 1999; microearthquake; spatiotemporal analysis; tectonic setting; Anatolia; Sea of Marmara; Turkey

Low-temperature deformation in calcite veins of SAFOD core samples (San Andreas Fault) - Microstructural analysis and implications for fault rheology - Rybacki, E.; Janssen, C.; Wirth, R.; Chen, K.; Wenk, H.-R.; Stromeyer, D.; Dresen, G. (Tectonophysics, 2011)
The microstructures of four core samples from the San Andreas Fault Observatory at Depth (SAFOD) were investigated with optical and transmission electron microscopy. These samples, consisting of sandstone, siltstone, and fault gouge from phase III of the drilling campaign (3141-3307m MD), show a complex composition of quartz, feldspar, clays, and amorphous material. Microstructures indicate intense shearing and dissolution-precipitation as main deformation processes. The samples also contain abundant veins filled with calcite. Within the inspected veins the calcite grains exhibit different degrees of deformation with evidence for twinning and crystal plasticity. Dislocation densities (ranging from≈3·1012m-2 to ≈3·1013m-2) and twin line densities (≈22mm-1-165mm-1) are used as paleo-piezometers. The corresponding estimates of differential stresses vary between 33 and 132MPa, deduced from dislocation density and 92-251MPa obtained from twin density, possibly reflecting chronologically different maximum stress states and/or grain scale stress perturbations. Mean values of stress estimates are 68±46MPa and 168±60MPa, respectively, where estimates from dislocation density may represent a lower bound and those from twin density an upper bound. The stress estimates are also compatible with residual lattice strains determined with microfocus Laue diffraction yielding equivalent stresses of 50-300MPa in twinned calcite. The lower stress bound agrees with stress estimates from borehole breakout measurements performed in the pilot hole. From these data and assuming hydrostatic pore pressure and a low intermediate principal stress close to the overburden stress, frictional sliding of the San Andreas Fault at the SAFOD site is constrained to friction coefficients between 0.24 and 0.31. These low friction values may be related to the presence of clays, talc, and amorphous phases found in the fault cores and support the hypothesis of a weak San Andreas Fault. © 2011 Elsevier B.V.
cited By 28
Keywords: Amorphous phasis; Calcite grains; Calcite veins; Complex compositions; Crystal plasticity; Deformation process; Differential stress; Dislocation densities; Equivalent stress; Fault core; Fault gouge; Friction coefficients; Frictional sliding; Intermediate principal stress; Lattice strain; Laue diffraction; Line density; Low friction; Low temperature deformations; Lower bounds; Lower stress; Maximum stress; Mean values; Microstructural analysis; Overburden stress; Piezometer; Pilot holes; Residual strains; SAFOD; San Andreas Fault; Scale stress; Siltstones; Upper Bound; Amorphous materials; Calcite; Deformation; Dislocations (crystals); Dissolution; Elasticity; Estimation; Friction; Light transmission; Microstructure; Quartz; Strain; Structural geology; Transmission electron microscopy; Twinning; Carbonate minerals; borehole breakout; calcite; deformation mechanism; dissolution; fault gouge; low temperature; microstructure; precipitation (chemistry); pressure effect; San Andreas Fault; sandstone; siltstone; transmission electron microscopy; twinning; California; San Andreas; United States

Three-component magnetic logging in the Outokumpu Deep Drill Hole - Virgil, Christopher; H{ordt, Andreas; Leven, Martin; Steveling, Erich; K{uck, Jochem; Dietze, Frank (Special Paper of the Geological Survey of Finland, 2011)
In September 2008, the magnetic field in the Outokumpu Deep Drill Hole (OKU R2500) was measured with the G{ottinger Bohrloch Magnetometer (GBM). Unlike previous total field measurements with other tools, the three components of the magnetic field and the tool attitude were measured continuously with a resolution of up to 5 cm. This became possible by utilizing a unique orientation system consisting of three fibre optic gyros. After extensive data processing, the magnetic anomalies along the borehole were obtained in the geographic coordinates North, East and Vertical (WGS-84). Two intervals with significant magnetic anomalies were detected. While the disturbances in the first interval (70-300 m) are either manmade or caused by thin layers of black schist, the second interval (1328-1440 m) is dominated by magnetized rocks of the Outokumpu assemblage. The combined interpretation of core data and in-situ measurements indicates less carbonated serpentinite as the host for magnetic minerals. Furthermore, statistical studies of the magnetisation direction, derived from the GBM measurements, suggest a different geological evolution of the host rocks of the upper and lower section of the Outokumpu assemblage.
Keywords: Finland; Ita Suomen; Outokumpu; Gyros; borehole logging; data processing; deep drilling; magnetic anomaly; magnetic field; magnetometer; metamorphic rock; remanent magnetization

Transmission electron microscopy of omphacite and other minerals in eclogites from the CCSD borehole, China: Indications for their deformation and temperature history - M{uller, Wolfgang Friedrich; Xu, Zhiqin; Brenker, Frank E. (European Journal of Mineralogy, 2011)
Seven eclogite samples from 223 to 584 m depths in the Chinese Continental Scientific Drilling main borehole (CCSDMH) in the Sulu ultrahigh-pressure metamorphic (UHPM) terrane, Eastern China, were studied by transmission electron microscopy (TEM), in order to characterise their microstructures. We observed, among others, omphacite, jadeitic diopside, garnet, amphibole, rutile, Na-rich plagioclase, quartz, K-feldspar, analcime, and diamond (contamination). Omphacite shows a well-known diffusioncontrolled disorder-order phase transition which gives rise to antiphase domains (APDs). In our samples we observed a variation of the APDs' size between ∼5 nm and 2 mm which is correlated with the content in jadeite (Jd) component. The broad maximum of ∼1-2 mm APDs' size is centred on Jd50. This size drops to ∼5-10 nm for Jd37 and Jd66. The size variation can be explained with the T-path of the respective omphacites. While the large APDs of the omphacites formed and coarsened during subduction and exhumation, the smallest APDs formed and grew during exhumation. In contrast to other eclogite occurrences, deformational defects in omphacites from the CCSD-eclogites are mostly very rare. Occasionally, stacking faults parallel to (010), free dislocations with the Burgers vector [001] and those with 1/2[110] connected with antiphase domain boundaries (APBs), deformation twins on (100) and small-angle grain boundaries were observed. The explanation is that most CCSD-omphacites were strongly affected by recrystallisation, which took place above 600 °C during subduction up to its maximum temperature of ∼750 °C and continued during exhumation above 600 °C into the regime of amphibolite facies for several tens of Ma. Garnet shows very rarely crystal defects, while amphiboles usually displayed dislocations and chain multiplicity faults. Rutile of one sample, which contained a few percent Fe, showed fully coherent, nano-sized platelets (Guinier-Preston zones) parallel to (100) and (010). The existence of fluids during retrogression is documented by K-feldspar and analcime in quartz. © 2011 E. Schweizerbart'sche Verlagsbuchhandlung.
Keywords: China; Boreholes; Burgers vector; Crystal defects; Deformation; Feldspar; Garnets; Grain boundaries; High resolution transmission electron microscopy; Metamorphic rocks; Quartz; Titanium dioxide; Transmission electron microscopy; Twinning; Zeolites; Amphibole; Analcime; CCSD; Eclogites; Omphacite; Rutile; Chinese Continental Scientific Drilling Project; crystal structure; deformation mechanism; eclogite; jadeite; microstructure; omphacite; P-T conditions; P-T-t path; phase transition; recrystallization; temperature gradient; transmission electron microscopy; twinning; ultrahigh pressure metamorphism; Transmissions

Tropical East African climate change and its relation to global climate: A record from Lake Tanganyika, Tropical East Africa, over the past 90+kyr - Burnett, A.P.; Soreghan, M.J.; Scholz, C.A.; Brown, E.T. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
Forcing mechanisms of tropical climate in continental areas remain poorly understood, due in large part to a lack of continuous, long-term, high-fidelity records. Sediment core T97-52V from Lake Tanganyika provides new insight into the timing and mechanisms behind East African climate change over the past 90+. kyr. This record is particularly important, because, other than a recently recovered scientific drill core from Lake Malawi, there are no other continuous, well-dated records from East Africa prior to 60. ka. The high resolution age model presented here provides a large degree of age certainty for the past 45+. kyr, and our suite of proxies allows a thorough examination of Lake Tanganyika's dynamics. From core stratigraphy and chemical analyses, we present evidence of a lake level drop greater than 400. m sometime prior to . 90. ka, much greater than that inferred for the LGM, suggesting a period of intense aridity sometime around 100. ka. Additionally, core T97-52. V preserves evidence of worm burrows detected by X-radiographic imagery as indicated by burrow-shaped deposits of iron oxide, indicating a shallow lake at the time of deposition of that material. Intermittently high lake levels between . 78. ka and . 72. ka developed at the same time as a weakened Asian monsoon and a pluvial phase in Northeast Brazil, suggesting a global reorganization of climate, possibly forced by a reduction in orbital eccentricity. Over the past 60. ka this core preserves the same events recorded in a core collected . 100. km away in the southern basin of Lake Tanganyika, including an unexplained increase in biogenic silica at . 37. ka, suggesting that this vast lake is responding coherently across both major bathymetric basins to regional and global climate forcing. © 2010 Elsevier B.V.
cited By 96
Keywords: biogenic deposit; climate change; intertropical convergence zone; lake level; Last Glacial Maximum; paleolimnology; proxy climate record; sediment core; tropical region; X-ray fluorescence; East Africa; East African Lakes; Lake Malawi; Lake Tanganyika

U-Pb ages of shocked zircon grains link distal K-Pg boundary sites in Spain and Italy with the Chicxulub impact - Kamo, S.L.; Lana, C.; Morgan, J.V. (Earth and Planetary Science Letters, 2011)
The U-Pb ages of shocked zircon crystals from the Chicxulub impact crater and Cretaceous-Paleogene (K-Pg) boundary sites in Haiti, the USA, and Canada, and the pattern of decreasing particle size with paleodistance from the crater, have been used as evidence of a genetic link between Chicxulub and the K-Pg boundary. Despite this, the inference that the K-Pg boundary layer formed as a direct consequence of the Chicxulub impact has been repeatedly questioned. Here we present U-Pb (ID-TIMS) ages and textural evidence of shock metamorphosed zircon grains from the K-Pg boundary at Caravaca, Spain, and Petriccio, Italy, that establish a causal connection between the impact and formation of the K-Pg boundary layer. The shocked zircon grains give data that produce a characteristic age pattern, which indicates a primary source age of 549.5 ± 5.7 Ma and a secondary event at the approximate time of impact at 66. Ma. The intensity of the shock features is proportional to the degree of isotopic resetting, and all textural features and ages are analytically identical to those of previously analyzed zircon from Chicxulub and K-Pg boundary sites in North America. Caravaca and Petriccio were > 8000 km from Chicxulub at the time of impact, and are therefore the farthest K-Pg sites identified that can be linked to Chicxulub through the dating of individual shocked zircon grains. We conclude that the combined age data and textural observations provide unambiguous evidence that ejecta from the Chicxulub impact formed the global K-Pg boundary layer. These data cannot be explained by the alternative scenario that the Chicxulub impact occurred . 300. ka prior to the K-Pg boundary. © 2011 Elsevier B.V..
cited By 30

Upper Cretaceous Ostracod biostratigraphy of the CCSD SK-1(south) borehole, Songliao Basin (in Chinese with English abstract); [松辽盆地松科1井南孔晚白垩世介形类生物地层] - Li, S.; Xi, D.; Jing, X.; Huang, Q.; Wang, Z.; Wan, X. (Acta Palaeontolgica Sinica, 2011)

Vesiculation and microlite crystallization induced by decompression: A case study of the 1991-1995 Mt Unzen eruption (Japan) - Cichy, S.B.; Botcharnikov, R.E.; Holtz, F.; Behrens, H. (Journal of Petrology, 2011)
Isothermal decompression experiments were performed to simulate magma ascent at Unzen volcano from the depths of magma storage to shallow crustal levels, corresponding to pressure decrease from 300 to 50 MPa. A partially crystallized synthetic rhyodacitic magma (representing equilibrium conditions at 850°C and 300 MPa) was used as a starting material; this has a composition identical to the groundmass of Unzen rocks erupted in 1991-1995. Decompression rates were varied from 0·0002 to 20 MPa s-1. Experiments conducted with decompression rates ≥0·1 MPa s-1 were decompressed continuously; a multi-step decompression approach was used at decompression rates ≤0·1 MPa s-1. The experiments were fluid-saturated, either containing only water as a fluid component (H2O-bearing) or containing a water and carbon dioxide mixture (H2O + CO2; initial mole fraction of H2O in the fluid 0·6). The experimental products of the H2O-bearing experiments consist of amphibole, pyroxenes, oxides and glass. Plagioclase microlites nucleated and grew only in experiments with the two lowest decompression rates of 0·0005 and 0·0002 MPa s-1. The length of those plagioclases is up to 200-250 μm, which is consistent with the size of plagioclase microlites observed in the natural samples. The experimental products of the H2O + CO2-bearing system are composed of pyroxenes, oxides, glass and plagioclase. Plagioclase microlites in the H2O + CO2-system were already present in the starting assemblage and grew to a maximum size of 80 μm. Equilibrium concentrations of water in the residual glasses at the final pressure of 50 MPa are reached at decompression rates ≤1 MPa s-1 for the H2O + CO2-bearing system and ≤0·1 MPa s-1 for the H2O-bearing system. The bubble number density (BND) values range from 103·7 to 105·6 mm-3 in the H2O-bearing system and from 104·6 to 106·4 mm-3 in the H2O + CO2-bearing systems. In both systems, BND values decrease with decreasing decompression rate from 20 to 0·01 MPa s-1, and increase with decreasing decompression rates < 0·01 MPa s-1, which is interpreted to reflect predominant bubble growth and bubble nucleation, respectively. The onset of crystallization, observed from changes in the chemical composition of the residual melt, occurs at decompression rates < 0·1 MPa s-1. At the lowest decompression rate (0·0002 MPa s-1) the chemical composition of the residual melt in the H2O + CO2-bearing system becomes similar to the natural matrix glass composition. There is no significant variation of the microlite number density (MND) value as a function of the decompression rate. The MND values for plagioclases-only range from 105·4 to 105·7 mm-3, whereas the MND values for the other phases range from 105·3 to 105·9 mm-3. Our experimental MNDPl values are in the range of those from natural samples (105-106 mm-3). We show that the size of microlites nucleating and crystallizing during decompression (plagioclase in our experimental dataset) is useful to constrain magma ascent rates at the onset of the crystallization of the corresponding phase. Based on the size of plagioclase microlites and on the composition of the residual melts, the average magma ascent rates of Unzen magmas in the pressure range 200 to 50 MPa is estimated to be 10-50 m h-1. © The Author 2010. Published by Oxford University Press. All rights reserved.
cited By 39
Keywords: amphibole; chemical composition; decompression; glass; magma; nucleation; oxide; plagioclase; pressure; pyroxene; volcanic rock; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano

Structure and composition of organic matter and isotope geochemistry of the palaeoproterozoic graphite and sulphide-rich metasedimentary rocks from the Outokumpu Deep Drill Hole, eastern Finland - Taran, Ludmila N.; Onoshko, Mariya P.; Mikhailov, Nikolaj D. (Special Paper of the Geological Survey of Finland, 2011)
Graphitic schists from the Outokumpu Deep Drill Hole were investigated in order to reconstruct the structure and composition of organic matter and stable isotope carbon and sulphur geochemistry of graphite, pyrite and pyrrhotite. Core samples of graphitic schists were collected from three depth levels of the Outokumpu Deep Drill Hole. The studied rocks were biotite-(tremolite-) graphite and, occasionally, muscovite (sericite)- and titanite-bearing schists and quartzitic schists. All samples were enriched in sulphides (mostly pyrite and pyrrhotite). Carbon isotope δ13C values of graphitic C were found to vary from -18.4 to -27.4‰. Graphitic schists from the middle part of the core in association with ophiolite-derived serpentinite and other altered ultramafic rocks showed more elevated δ13C values. This suggests incorporation of isotopically heavy carbon species during metamorphism, probably resulting from decarbonation reactions in carbonatebearing rocks. d34S values in the graphitic schists of the Outokumpu Deep Drill Hole were determined to be in range of -3.0 to -9.9‰ for pyrite and -3.8 to -10.8‰ for pyrrhotite. These concentrations could be explained by bacterial reduction of seawater sulphate and, to some extent, by the addition of hydrothermal sulphur. The predominance of aliphatic and oxygen-bearing groups in the bitumen structure suggests a sapropelic origin of the organic matter. Particularities in the distribution of Corganic and chemical changes in the bitumen composition along the core section could be interpreted as evidence of different sources and possibly the re-deposition of organic matter.
Keywords: Finland; Ita Suomen; Outokumpu; Bacteria (microorganisms); bitumen; borehole; carbon isotope; concentration (composition); geochemistry; graphite; isotopic analysis; metamorphism; metasedimentary rock; muscovite; organic carbon; organic matter; Proterozoic; schist; serpentinite; stable isotope; sulfide; ultramafic rock

Spatially explicit analysis of gastropod biodiversity in ancient Lake Ohrid - Hauffe, T.; Albrecht, C.; Schreiber, K.; Birkhofer, K.; Trajanovski, S.; Wilke, T. (Biogeosciences, 2011)
The quality of spatial analyses of biodiversity is improved by (i) utilizing study areas with well defined physiogeographical boundaries, (ii) limiting the impact of widespread species, and (iii) using taxa with heterogeneous distributions. These conditions are typically met by ecosystems such as oceanic islands or ancient lakes and their biota. While research on ancient lakes has contributed significantly to our understanding of evolutionary processes, statistically sound studies of spatial variation of extant biodiversity have been hampered by the frequently vast size of ancient lakes, their limited accessibility, and the lack of scientific infrastructure. The European ancient Lake Ohrid provides a rare opportunity for such a reliable spatial study. The comprehensive horizontal and vertical sampling of a species-rich taxon, the Gastropoda, presented here, revealed interesting patterns of biodiversity, which, in part, have not been shown before for other ancient lakes. In a total of 284 samples from 224 different locations throughout the Ohrid Basin, 68 gastropod species, with 50 of them (= 73.5%) being endemic, could be reported. The spatial distribution of these species shows the following characteristics: (i) within Lake Ohrid, the most frequent species are endemic taxa with a wide depth range, (ii) widespread species (i.e. those occurring throughout the Balkans or beyond) are rare and mainly occur in the upper layer of the lake, (iii) while the total number of species decreases with water depth, the proportion of endemics increases, and (iv) the deeper layers of Lake Ohrid appear to have a higher spatial homogeneity of biodiversity. Moreover, gastropod communities of Lake Ohrid and its feeder springs are both distinct from each other and from the surrounding waters. The analysis also shows that community similarity of Lake Ohrid is mainly driven by niche processes (e.g. environmental factors), but also by neutral processes (e.g. dispersal limitation and evolutionary histories of species). For niche-based mechanisms it is shown that large scale effects such as type of water body or water depth are mainly responsible for the similarity of gastropod communities, whereas small scale effects like environmental gradients affect gastropod compositions only marginally. In fact, neutral processes appear to be more important than the small scale environmental factors, thus emphasizing the importance of dispersal capacities and evolutionary histories of species. © Author(s) 2011.
Keywords: Lake Ohrid; Gastropoda; endemic species; environmental factor; evolutionary biology; gastropod; heterogeneity; spatial analysis; spatial variation; species diversity; spring water; taxonomy; water depth

Project Hotspot: Preliminary analysis of secondary mineralization in basaltic core, Central Snake River Plain - Sant, C.J.; Shervais, J.W. (Transactions - Geothermal Resources Council, 2011)
Project Hotspot offers further understanding of the history and evolution of the Snake River Plain (SRP) through drilling wells in the SRP. The first well at Kimama encountered almost entirely basalt. Kimama drilled through a gradual transition from fresh to altered basalt with depth. The evolution of mineralization with depth at Kimama was initially calcite and some quartz followed by smectite clay minerals (nontronite and saponite) and zeolites. Smectite clay minerals are a great indicator of paleo-temperature of geothermal fluids. Description of the Kimama core, mineral habits, and forthcoming chemical analyses will be discussed in this paper.
cited By 3
Keywords: Geothermal; Geothermometers; Hot spot; Kimama; Snake river plains; Basalt; Calcite; Carbonate minerals; Chemical analysis; Clay; Drilling; Geothermal fields; Geothermal prospecting; Mineralogy; Quartz; Rivers; Clay minerals

Scientific drilling into the San Andreas fault zone - An overview of SAFOD's first five years - Zoback, M.; Hickman, S.; Ellsworth, W. (Scientific Drilling, 2011)
The San Andreas Fault Observatory at Depth (SAFOD) was drilled to study the physical and chemical processes controlling faulting and earthquake generation along an active, plate-bounding fault at depth. SAFOD is located near Parkfield, California and penetrates a section of the fault that is moving due to a combination of repeating microearthquakes and fault creep. Geophysical logs define the San Andreas Fault Zone to be relatively broad ( 200 m), containing several discrete zones only 2-3 m wide that exhibit very low P- and S-wave velocities and low resistivity. Two of these zones have progressively deformed the cemented casing at measured depths of 3192 m and 3302 m. Cores from both deforming zones contain a pervasively sheared, cohesionless, foliated fault gouge that coincides with casing deformation and explains the observed extremely low seismic velocities and resistivity. These cores are being now extensively tested in laboratories around the world, and their composition, deformation mechanisms, physical properties, and rheological behavior are studied. Downhole measurements show that within 200 m (maximum) of the active fault trace, the direction of maximum horizontal stress remains at a high angle to the San Andreas Fault, consistent with other measurements. The results from the SAFOD Main Hole, together with the stress state determined in the Pilot Hole, are consistent with a strong crust/weak fault model of the San Andreas. Seismic instrumentation has been deployed to study physics of faulting-earthquake nucleation, propagation, and arrest-in order to test how laboratory-derived concepts scale up to earthquakes occurring in nature.
cited By 131
Keywords: Active fault; Bounding faults; California; Casing deformation; Chemical process; Deformation mechanism; Deforming zone; Downhole measurements; Earthquake nucleation; Fault creep; Fault gouge; Fault model; Geophysical logs; Horizontal stress; Low resistivity; Measured depths; Micro-earthquakes; Pilot holes; Rheological behaviors; S-wave velocity; San Andreas Fault; Scale-up; Scientific drilling; Seismic instrumentation; Seismic velocities; Stress state; Deformation; Earthquakes; Parks; Rheology; Structural geology; Tectonics

Reduced interannual rainfall variability in East Africa during the last ice age - Wolff, C.; Haug, G.H.; Timmermann, A.; Sinninghe Damst'e, J.S.; Brauer, A.; Sigman, D.M.; Cane, M.A.; Verschuren, D. (Science, 2011)
Interannual rainfall variations in equatorial East Africa are tightly linked to the El Niño Southern Oscillation (ENSO), with more rain and flooding during El Niño and droughts in La Niña years, both having severe impacts on human habitation and food security. Here we report evidence from an annually laminated lake sediment record from southeastern Kenya for interannual to centennial-scale changes in ENSO-related rainfall variability during the last three millennia and for reductions in both the mean rate and the variability of rainfall in East Africa during the Last Glacial period. Climate model simulations support forward extrapolation from these lake sediment data that future warming will intensify the interannual variability of East Africa's rainfall.
cited By 130
Keywords: rain; annual variation; climate modeling; El Nino-Southern Oscillation; flooding; food security; lacustrine deposit; paleoclimate; Pleistocene; precipitation intensity; Africa; article; climate; El Nino; food security; glacial period; lake sediment; priority journal; seasonal variation; Kenya

Role of the deep mantle in generating the compositional asymmetry of the Hawaiian mantle plume - Weis, D.; Garcia, M.O.; Rhodes, J.M.; Jellinek, M.; Scoates, J.S. (Nature Geoscience, 2011)
Linear chains of volcanic ocean islands are one of the most distinctive features on our planet. The longest, the Hawaiiang-Emperor Chain, has been active for more than 80 million years, and is thought to have formed as the Pacific Plate moved across the Hawaiian mantle plume, the hottest and most productive of Earth's plumes. Volcanoes fed by the plume today form two adjacent trends, including Mauna Kea and Mauna Loa, that exhibit strikingly different geochemical characteristics. An extensive data set of isotopic analyses shows that lavas with these distinct characteristics have erupted in parallel along the Kea and Loa trends for at least 5 million years. Seismological data suggest that the Hawaiian mantle plume, when projected into the deep mantle, overlies the boundary between typical Pacific lower mantle and a sharply defined layer of apparently different material. This layer exhibits low seismic shear velocities and occurs on the Loa side of the plume. We conclude that the geochemical differences between the Kea and Loa trends reflect preferential sampling of these two distinct sources of deep mantle material. Similar indications of preferential sampling at the limit of a large anomalous low-velocity zone are found in Kerguelen and Tristan da Cunha basalts in the Indian and Atlantic oceans, respectively. We infer that the anomalous low-velocity zones at the core-mantle boundary are storing geochemical anomalies that are enriched in recycled material and sampled by strong mantle plumes. © 2011 Macmillan Publishers Limited. All rights reserved.
cited By 180
Keywords: asymmetry; data set; geochemical survey; isotopic analysis; mantle plume; Pacific plate; sampling; seismic velocity; volcanic island; Atlantic Ocean; French Southern Territories; Hawaiian Islands; Indian Ocean; Kerguelen; Kerguelen Islands

SAFOD Phase III Core sampling and data management at the Gulf Coast repository - Weymer, B.; Firth, J.; Rumford, P.; Chester, F.; Chester, J.; Lockner, D. (Scientific Drilling, 2011)
cited By 0

Salinity control on long-chain alkenone distributions in lake surface waters and sediments of the northern Qinghai-Tibetan Plateau, China - Liu, Weiguo; Liu, Zhonghui; Wang, Huanye; He, Yuxin; Wang, Zheng; Xu, Liming (Geochimica et Cosmochimica Acta, 2011)
Long-chain alkenones in lacustrine settings are potentially excellent biomarkers for the reconstruction of past terrestrial environmental conditions, and have been found in many different types of lakes around the globe. A wider range of factors influence the occurrence and distribution of alkenones in lake sediments and waters when compared to marine systems. Lake environmental conditions, such as temperature (in particular) and salinity, are among the key factors controlling alkenone distributions in lacustrine settings. Here we investigated alkenone distribution patterns in lakes of the northern Qinghai-Tibetan Plateau, China, and their possible relationship with environmental conditions, by analyzing paired samples of suspended particulate matter in surface waters and surface sediments. Salinity of investigated lake waters ranges from almost 0 to ∼100g/L, while temperature variation among the lakes is minimal, effectively eliminating temperature effects on the alkenone distribution patterns observed here. We show that (1) alkenone concentrations vary substantially between the lakes, yet controlling mechanisms remain elusive; (2) C37/C38 ratios are substantially lower in the lakes of the Qaidam Basin than in the Lake Qinghai region, probably indicating different alkenone producers in the two regions; and (3) large variations in %C37:4 (the percentage of the C37:4 alkenone), determined from both surface waters and sediments, are negatively correlated with salinity. We suggest that the %C37:4 index could be used as a salinity indicator at least on a regional scale, with careful considerations of other potentially complicating factors. However, potential reasons for why salinity could significantly affect %C37:4 values need further investigation. © 2011 Elsevier Ltd.
Keywords: China; Qaidam Basin; Qinghai; Qinghai-Xizang Plateau; alkenone; biomarker; concentration (composition); isotopic ratio; lacustrine deposit; lake water; paleoenvironment; salinity; suspended particulate matter; water temperature

Scientific collaboration on past speciation conditions in ohrid (SCOPSCO): Recent and fossil Ostracods from Lake ohrid as indicators of past environments: A coupled ecological and molecular genetic approach with deep-time perspective - Lorenschat, J.; Scharf, B.; Petkovski, T.; Viehberg, F.; Schwalb, A. (Joannea - Geologie und Palaontologie, 2011)
cited By 2
Keywords: ecosystem approach; fossil record; genetic analysis; molecular analysis; ostracod; paleoenvironment; science and technology; speciation (biology); Lake Ohrid; Ostracoda

Scientific drilling in the Great Rift Valley: The 2005 Lake Malawi Scientific Drilling Project - An overview of the past 145,000years of climate variability in Southern Hemisphere East Africa - Scholz, C.A.; Cohen, A.S.; Johnson, T.C.; King, J.; Talbot, M.R.; Brown, E.T. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
The recovery of detailed and continuous paleoclimate records from the interior of the African continent has long been of interest for understanding climate dynamics of the tropics, and also for constraining the environmental backdrop to the evolution and spread of early Homo sapiens. In 2005 an international team of scientists collected a series of scientific drill cores from Lake Malawi, the first long and continuous, high-fidelity records of tropical climate change from interior East Africa. The paleoclimate records, which include lithostratigraphic, geochemical, geophysical and paleobiological observations documented in this special issue of Palaeo3, indicate an interval of high-amplitude climate variability between 145,000 and 60,000years ago, when several severe arid intervals reduced Lake Malawi's volume by more than 95%. These intervals of pronounced tropical African aridity in the early Late Pleistocene around Lake Malawi were much more severe than the Last Glacial Maximum (LGM), a well-documented period of drought in equatorial and Northern Hemisphere tropical east Africa. After 70,000years ago climate shifted to more humid conditions and lake levels rose. During this latter interval however, wind patterns shifted rapidly, and perhaps synchronously with high-latitude shifts and changes in thermohaline circulation. This transition to wetter, more stable conditions coincided with diminished orbital eccentricity, and a reduction in precession-dominated climatic extremes. The observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical Africa. © 2010 Elsevier B.V.
cited By 76
Keywords: climate variation; lake level; Last Glacial Maximum; marine record; paleobiology; paleoclimate; rift zone; Southern Hemisphere; thermohaline circulation; tropical region; East African Lakes; Kenya; Lake Malawi; Rift Valley; Homo sapiens

Seasonal contributions of catchment weathering and eolian dust to river water chemistry, northeastern Tibetan Plateau: Chemical and Sr isotopic constraints - Jin, Zhangdong; You, Chen-Feng; Yu, Jimin; Wu, Lingling; Zhang, Fei; Liu, Hou-Chun (Journal of Geophysical Research: Earth Surface, 2011)
River waters collected weekly over the whole year of 2007 from the Buha River draining to Lake Qinghai on the northeastern Tibetan Plateau were analyzed for major ions and Sr isotopes. Dissolved loads in the river exhibit distinct seasonal variability in major cation ratios and Sr isotopes over the 1 year period, reflecting seasonal differences in relative inputs from various sources and weathering reactions in the catchment. Distinct geochemical signatures suggest that eolian dust may affect river water chemistry significantly, resulting in a twofold increase influx of dissolved loads during spring relative to winter. It is noticeable that both the lowest and the highest 87Sr/86Sr values of the Buha River waters occurred in the monsoon season, indicating a sensitive response of carbonate versus silicate weathering sources to hydrological forcing on a seasonal basis. A significant decrease in Na/cation, together with lower Sr isotope ratios, is consistent with a greater proportion f carbonate weathering relative to silicate weathering in the early monsoon season. High temperature and increased rainfall during the peak of the monsoon facilitate an increased proportion of ions derived from silicates, partly from groundwaters, to river water. In other seasons, elemental and 87Sr/86Sr ratios vary much less, indicating a constant ratio of silicate to carbonate weathering, consistent with limited variation in discharge. Our results highlight that in a semiarid region where climatic conditions vary seasonally, in addition to silicate and carbonate contributions, supply from eolian dust may also play a significant role in controlling seasonal variations in chemistry of river waters. Copyright 2011 by the American Geophysical Union.
Keywords: Buha River; China; Qinghai; Qinghai-Xizang Plateau; carbonate; catchment; groundwater; high temperature; monsoon; rainfall; river water; seasonal variation; strontium isotope; water chemistry; weathering

Spatial distribution and flux of terrigenic He dissolved in the sediment pore water of Lake Van (Turkey) - Tomonaga, Y.; Brennwald, M.S.; Kipfer, R. (Geochimica et Cosmochimica Acta, 2011)
In this study, the largest ever carried out to measure noble gases in the pore water of unconsolidated sediments in lakes, the emission of terrigenic He through the sediment column of Lake Van was successfully mapped on the local scale. The main input of He to the water body occurs at the borders of a deep basin within the lake, which is probably the remains of a collapsed caldera. The 3He/4He ratio identifies the He injected into the sedimentary column of Lake Van as a mixture of He released from a mantle source and radiogenic He of crustal origin (3He/4He 2.6-4.1×10-6). During passage through the pore space, terrigenic He seems to be further enriched in radiogenic He that is most likely produced in the sediment column. In fact, two distinct trends in isotopic composition can be distinguished in the He injected from the lake basement into the sediments. One of these characterizes samples from the shallow water, the other characterizes samples from the deep basin. However, both of these trends are related to the same source of terrigenic He. The He fluxes determined seem to be characteristic of each sampling location and might be considered as a proxy for the fluid permeability of the deep sediment column. These new findings provide insight into the process of fluid transport within the sediments and into the process of formation of the lake basin. Moreover, the isotopic signature of the He that emanates into the water column of Lake Van is strongly affected by the mixing conditions prevailing in the overlying water body. This fact misled previous studies to interpret the terrigenic He in Lake Van as being solely of mantle origin (3He/4He 10-5). © 2011 Elsevier Ltd.
cited By 26
Keywords: basin evolution; deep-sea sediment; helium; isotopic composition; lacustrine deposit; lake water; mantle source; noble gas; permeability; porewater; sediment chemistry; sedimentary structure; spatial distribution; Lake Van; Turkey

Secondary hydrothermal minerals in buried rocks at the Campi Flegrei caldera, Italy: A possible tool to understand the rock-physics and to assess the state of the volcanic system - Mormone, A.; Tramelli, A.; Di Vito, M.A.; Piochi, M.; Troise, C.; Natale, G.D. (Periodico di Mineralogia, 2011)
The distribution of the alteration assemblages and the related physico-chemical changes induced in the rocks with depth, may provide useful information on the state of the system. Drillholes are the only way to define hydrothermal alteration depth-profiles in variable geological contexts. Deep drillings exploiting programs were conducted since the 1970's by the Agip-Enel Joint Venture in the Quaternary Campi Flegrei caldera (southern Italy), where a geothermal system has been active since at least historical times. New macroscopic and microscopic investigations were performed on selected samples made available by Agip in order to: 1) define the precursor lithology, 2) describe the relationships among texture, mineralogy and depth of the studied core samples and 3) examine the character of the secondary minerals and their distribution with depth and temperature. The new data are integrated with physical properties and elastic parameters of cored rocks, as well as structural information and field data, all available from the physical, seismological, geodetical and volcanological literature. The depth-related multi-parameters profiles provide evidence on the different behavior of the buried rocks beneath the Licola 1, Mofete and San Vito 1 areas, sited in three structurally different sectors of the caldera. The features of the hydrothermally altered rocks are a key to interpret the heterogeneities of the Campi Flegrei substratum, as deduced by velocity, attenuation and scattering P- and S- waves tomography. The time and space distribution of both the eruptive vents and the extruded magma volumes are consistent with the results of our analysis. Therefore, we interpret the observed Campi Flegrei geothermal system as a response to the distribution of volcanic activity in two structurally distinct sectors of the caldera. The central-eastern sector, where the San Vito 1 well was drilled, represents the preferential pathways for both gas escape and magma ascent at least since 8 kyrs, in contrast with the other sites of the caldera where eruptions occurred with minor frequency and magnitude.
cited By 16

Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic - Korte, Christoph; Hesselbo, Stephen P. (Paleoceanography, 2011)
For much of the Mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences. We present a carbon and oxygen isotope and elemental record for part of the Early Jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the Cleveland Basin, UK. The invertebrate isotope record is supplemented with carbon isotope data from fossil wood, which samples atmospheric carbon. New data elucidate two major global carbon isotope events, a negative excursion of ∼2‰ at the Sinemurian-Pliensbachian boundary, and a positive excursion of ∼2‰ in the Late Pliensbachian. The Sinemurian-Pliensbachian boundary event is similar to the slightly younger Toarcian Oceanic Anoxic Event and is characterized by deposition of relatively deepwater organic-rich shale. The Late Pliensbachian strata by contrast are characterized by shallow marine deposition. Oxygen isotope data imply cooling locally for both events. However, because deeper water conditions characterize the Sinemurian-Pliensbachian boundary in the Cleveland Basin the temperature drop is likely of local significance; in contrast a cool Late Pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions. Both the large-scale, long-term and small-scale, short-duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy. Isotope events and the sea level cycles are concluded to reflect processes of global significance, supporting the idea of an Early Jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 Ma. Copyright 2011 by the American Geophysical Union.
Keywords: Cleveland Basin; England; North Yorkshire; United Kingdom; anoxic conditions; benthos; biostratigraphy; brachiopod; carbon isotope; depositional sequence; environmental change; fossil record; glaciation; greenhouse effect; nekton; oxygen isotope; paleoceanography; paleoenvironment; Pliensbachian; sea level change; seafloor; sequence stratigraphy; Sinemurian

Shock metamorphism investigations of quartz grains in clasts from impact breccia of the Eyreville B drill core, Chesapeake Bay impact structure, USA - Bartosova, K.; Koeberl, C. (Meteoritics and Planetary Science, 2011)
The Chesapeake Bay impact structure, approximately 85km in diameter, has been drilled in 2005-2006 at Eyreville (Virginia, USA), to a total depth of 1766m. In the drill cores, the abundance of shock metamorphosed material is very variable with depth. Shocked mineral and lithic clasts, as well as melt particles, are most abundant in suevitic impact breccia section (1397-1451m depth). Shocked quartz (i.e., quartz grains with planar fractures and/or planar deformation features) and melt particles, although rare, are also dispersed in the Exmore Formation unit (444-867m depth). Other lithologies in the Eyreville drill cores show no clear evidence of shock metamorphism. Here, we report on the investigations of 40 samples from the impact breccia section. A total of more than 27,000 quartz grains were examined in about 200 clasts. The abundance of highly shocked clasts tends to decrease with increasing depth. Crystalline clasts derived from the crystalline basement are commonly only slightly shocked (contain generally <10rel% of shocked quartz grains). The clasts of metamorphosed sediments show a low proportion of shocked quartz grains (mostly <10rel%). Sedimentary clasts show a wide range of proportions of shocked quartz grains, with several of them being highly shocked clasts (most values between 0 and 40rel%). Conglomerates show the highest proportion of shocked quartz grains of all types of clasts (up to 83rel%). Polycrystalline quartz clasts are also commonly highly shocked (contain mostly between 10 and 40rel% of shocked quartz grains). These hard nonporous clasts are possibly more liable to show evidence of shock. The investigations suggest that the intensity of shock metamorphism is the result of several parameters, such as original position in the target (both horizontal and vertical) and the properties of each lithology (e.g., grain size, porosity, and amount of matrix). According to the universal-stage investigations, the dominant orientations of planar deformation features in quartz are 101̄3, 101̄2, and also 101̄4. © The Meteoritical Society, 2011.
cited By 1

Short term earthquake forecasts at Koyna, India - Gupta, H.; Shashidhar, D.; Mallika, K.; Rao, N.P.; Srinagesh, D.; Satyanarayana, H.V.S.; Saha, S.; Naik, R.T.B. (Journal of the Geological Society of India, 2011)
Earthquake activity is monitored in real time at the Koyna reservoir in western India, beginning from August 2005 and successful short term forecasts have been made of M ∼ 4 earthquakes. The basis of these forecasts is the observation of nucleation that precedes such earthquakes. Here we report that a total of 29 earthquakes in the magnitude range of 3.5 to 5.1 occurred in the region during the period of August 2005 through May 2010. These earthquakes could broadly be put in three zones. Zone-A has been most active accounting for 18 earthquakes, while 5 earthquakes in Zone-B and 6 in Zone-C have occurred. Earthquakes in Zone-A are preceded by well defined nucleation, while it is not the case with zones B and C. This indicates the complexity of the earthquakes processes and the fact that even in a small seismically active area of only 20 km × 30 km earthquake forecast is difficult. © 2011 Geological Society of India.
cited By 21
Keywords: earthquake magnitude; earthquake prediction; nucleation; observational method; seismic zone; India; Koyna; Maharashtra

Soft-sediment deformation within seismogenic slumps of the Dead Sea Basin - Alsop, G.I.; Marco, S. (Journal of Structural Geology, 2011)
The Late Pleistocene Lisan Formation preserved next to the Dead Sea provides exceptional 3-D exposures of folds and faults generated during soft-sediment slumping and deformation. It is possible to generate a range of four different scenarios associated with overprinting in a single slump event. The progressive evolution of slump systems may be broadly categorised into initiation, translation, cessation, relaxation and compaction phases. Thrust packages typically define piggyback sequences during slump translation, with back-steepening of imbricate faults leading to collapse of folds back up the regional palaeoslope. Detailed evaluation of slumped horizons may also permit structures to be traced across apparently separate and distinct slumped units. The recognition that slumps may be reworked by younger seismically-triggered events suggests that in some cases the seismic recurrence interval may be shorter than previously anticipated. © 2011 Elsevier Ltd.
cited By 140
Keywords: Dead Sea; Folds; Gravity-driven deformation; Mass transport complexes; Slump; Anoxic sediments; Deformation; Earthquakes; Mass transfer; Sedimentology; Gravitation; deformation; earthquake; fold; mass transport; slumping; Dead Sea

Solubility of H2O and CO2 in shoshonitic melts at 1250°C and pressures from 50 to 400MPa: Implications for Campi Flegrei magmatic systems - Vetere, Francesco; Botcharnikov, Roman E.; Holtz, François; Behrens, Harald; De Rosa, Rosanna (Journal of Volcanology and Geothermal Research, 2011)
The solubility of H2O-CO2-bearing fluids in shoshonitic melts relevant to magmas of the Vulcanello peninsula and to mafic melts from magmas erupted at Campi Flegrei (Italy) was experimentally determined at pressures from 50 to 400MPa and at temperature of 1250°C. No quench crystals and less than 1vol.% bubles were observed in the rapid quenched glasses. H2O and CO2 contents in the experimental glasses were determined via Karl-Fischer Titration (KFT) and FTIR spectroscopy. For the quantification of volatile concentrations by IR spectroscopy we have calibrated the absorption coefficients of water-related and carbon-related IR bands for the shoshonitic composition. The determined absorption coefficients are 0.80±0.06L mol-1 cm-1 for the band at 4500cm-1 (OH groups) and 1.02±0.03L mol-1 cm-1 for the band at 5200cm-1 (H2O molecules). CO2 is bound in the shoshonitic glass as CO32- exclusively; its concentration was quantified by the peak height of the low wavenumber band of the doublet near 1430cm-1 using the calibrated absorption coefficient of 356±18L mol-1 cm-1.The H2O solubility in the shoshonitic melts is in the same range as observed for other natural aluminosilicate melts, i.e. 5.12±0.07wt.% at 200MPa and 7.92±0.07wt.% H2O at 400MPa. A non-linear variation of the H2O and CO2 solubility in the melts with increasing mole fraction of H2O (and thus decreasing mole fraction of CO2) in the fluid was observed at each investigated pressure. At 1250°C, the concentration of dissolved carbonate (expressed as CO2 component) in melts coexisting with nearly pure CO2 fluid increases from 307 to 2932ppm (±10% relative) as the pressure increases from 50 to 400MPa. The comparison of the dataset with available models predicting the H2O and CO2 concentrations in silicate melts coexisting with H2O-CO2-bearing fluids shows that the effect of melt composition is not calibrated appropriately in the models.The experimental data are used to re-evaluate the typical pressures of glass inclusions entrapment in phenocrysts from Minopoli2 eruption and the results indicate that the main magma chamber may have been located at a depth of 4000 m. © 2011 Elsevier B.V.
Keywords: Campania [Italy]; Campi Flegrei; Italy; Lipari Islands; Messina [Sicily]; Napoli [Campania]; Sicily; Vulcano; Aluminosilicates; Bearings (structural); Crystals; Fluids; Fourier transform infrared spectroscopy; Glass; Solubility; Water absorption; Campi Flegrei; O; Shoshonitic magmas; Vulcanello; absorption coefficient; carbon dioxide; FTIR spectroscopy; mafic rock; magma; magma chamber; magmatism; phenocryst; shoshonite; silicate melt; solubility; volcanic eruption; volcanic glass; Absorption spectroscopy

Southern hemisphere tropical climate over the past 145ka: Results of the Lake Malawi Scientific Drilling Project, East Africa - Scholz, C.A.; Cohen, A.S.; Johnson, T.C. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
cited By 4

Magnetic anomalies and rock magnetism of basalts from Reykjanes (SW-Iceland) - Dietze, F.; Kontny, A.; Heyde, I.; Vahle, C. (Studia Geophysica et Geodaetica, 2011)
This study presents rock magnetic properties along with magnetic field measurements of different stratigraphic and lithologic basalt units from Reykjanes, the southwestern promontory of the Reykjanes peninsula, where the submarine Reykjanes Ridge passes over into the rift zone of southwestern Iceland. The basaltic fissure eruptions and shield lava of tholeiitic composition (less than 11500 a old) show a high natural remanent magnetization (NRM, Jr) up to 33.6 A/m and high Koenigsberger ratio (Q) up to 52.2 indicating a clear dominance of the NRM compared to the induced part of the magnetization. Pillow basalts and picritic shield lava show distinctly lower Jr values below 10 A/m. Magnetic susceptibility (κ) ranges for all lithologies from 2.5 to 26 × 10-3 SI. Heterogeneously distributed titanomagnetite with small grain sizes is the main carrier of magnetization. Magnetic susceptibility vs. temperature (κ-T) curves reveal multiple Curie temperatures from 35 to 570 °C suggesting different Ti-concentrations in titanomagnetite. A minor oxidation to titanomaghemite is indicated by the irreversibility of some of the κ-T curves. Intra flow variation of the magnetic minerals is relatively high depending on crystallization history and resulting primary composition and amount of titanomagnetite as well as high-temperature oxidation. The total geomagnetic field was measured for regional field variations along three profiles normal to the spreading zone at Reykjanes. These measurements along with the rock magnetic data and field observations were used for modeling the geological subsurface. The models are in agreement with a feeder dyke system related to the youngest Stampahraun 4 fissure eruption in the western part and a hydrothermally active fault system in the eastern part of Reykjanes. Furthermore, topographic features like fault scarps, pillow basalt - hyaloclastite ridges and shield lava are considered. © 2011 Institute of Geophysics of the ASCR, v.v.i.
cited By 7
Keywords: active fault; basalt; fissure; geomagnetic field; geomagnetism; lava; lithology; magnetic anomaly; magnetic mineral; magnetic property; magnetic susceptibility; oxidation; remanent magnetization; rift zone; stratigraphy; tholeiite; titanomagnetite; Atlantic Ocean; Iceland; Reykjanes Peninsula; Reykjanes Ridge

Well logging proxy of the Late Cretaceous palaeoclimate change in Songliao Basin - Wu, XS; Guo, JJ; Huang, YJ; Fu, JW (Journal of Palaeogeography, 2011)

Low strength of deep San Andreas fault gouge from SAFOD core - Lockner, D.A.; Morrow, C.; Moore, D.; Hickman, S. (Nature, 2011)
The San Andreas fault accommodates 28-34-‰mm-‰yr ĝ̂'1 of right lateral motion of the Pacific crustal plate northwestward past the North American plate. In California, the fault is composed of two distinct locked segments that have produced great earthquakes in historical times, separated by a 150-km-long creeping zone. The San Andreas Fault Observatory at Depth (SAFOD) is a scientific borehole located northwest of Parkfield, California, near the southern end of the creeping zone. Core was recovered from across the actively deforming San Andreas fault at a vertical depth of 2.7-‰km (ref. 1). Here we report laboratory strength measurements of these fault core materials at in situ conditions, demonstrating that at this locality and this depth the San Andreas fault is profoundly weak (coefficient of friction, 0.15) owing to the presence of the smectite clay mineral saponite, which is one of the weakest phyllosilicates known. This Mg-rich clay is the low-temperature product of metasomatic reactions between the quartzofeldspathic wall rocks and serpentinite blocks in the fault. These findings provide strong evidence that deformation of the mechanically unusual creeping portions of the San Andreas fault system is controlled by the presence of weak minerals rather than by high fluid pressure or other proposed mechanisms. The combination of these measurements of fault core strength with borehole observations yields a self-consistent picture of the stress state of the San Andreas fault at the SAFOD site, in which the fault is intrinsically weak in an otherwise strong crust. © 2011 Macmillan Publishers Limited. All rights reserved.
cited By 291
Keywords: magnesium; mineral; silicon dioxide; borehole; creep; deformation mechanism; fault gouge; historical record; San Andreas Fault; saponite; serpentine; vertical distribution; article; geography; laboratory; priority journal; strength; United States; California; Parkfield; United States

Dead Sea deep cores: A window into past climate and seismicity - Stein, M.; Ben-Avraham, Z.; Goldstein, S.L. (Eos, 2011)
The area surrounding the Dead Sea was the locus of humankind's migration out of Africa and thus has been the home of peoples since the Stone Age. For this reason, understanding the climate and tectonic history of the region provides valuable insight into archaeology and studies of human history and helps to gain a better picture of future climate and tectonic scenarios. The deposits at the bottom of the Dead Sea are a geological archive of the environmental conditions (e.g., rains, floods, dust storms, droughts) during ice ages and warm ages, as well as of seismic activity in this key region. An International Continental Scientific Drilling Program (ICDP) deep drilling project was performed in the Dead Sea between November 2010 and March 2011. The project was funded by the ICDP and agencies in Israel, Germany, Japan, Norway, Switzerland, and the United States. Drilling was conducted using the new Large Lake Drilling Facility (Figure 1), a barge with a drilling rig run by DOSECC, Inc. (Drilling, Observation and Sampling of the Earth's Continental Crust), a nonprofit corporation dedicated to advancing scientific drilling worldwide. The main purpose of the project was to recover a long, continuous core to provide a high resolution record of the paleoclimate, paleoenvironment, paleoseismicity, and paleomagnetism of the Dead Sea Basin. With this, scientists are beginning to piece together a record of the climate and seismic history of the Middle East during the past several hundred thousand years in millennial to decadal to annual time resolution.
cited By 25
Keywords: archaeology; deep drilling; drilling rig; environmental conditions; paleoclimate; paleoenvironment; paleomagnetism; paleoseismicity; Stone Age; tectonic structure; Dead Sea

Coastal sabkha dolomites and calcitised sulphates preserving the Lomagundi-Jatuli carbon isotope signal - Brasier, A.T.; Fallick, A.E.; Prave, A.R.; Melezhik, V.A.; Lepland, A. (Precambrian Research, 2011)
Palaeoproterozoic Tulomozero Formation carbonates of the Onega basin were targeted by ICDP FAR-DEEP Hole 10B. The recovered rocks contain abundant evidence for Palaeoproterozoic gypsum and anhydrite, particularly in the form of pseudomorphs of inclusion-containing nodules, swallow-tail twinned crystals and evaporite dissolution breccias. Similarly, sand-patch fabric indicates the former presence of surface-covering salt crusts in the Palaeoproterozoic. Atmospheric oxygen and seawater sulphate levels at that time must have been sufficient to allow such sulphates to form. Carbonate δ13C values are considered sedimentary or early diagenetic, predating greenschist facies metamorphism associated with the Svecofennian Orogeny. These carbonate δ13C values range from +7.7 to +15.7‰, with the highest (and lowest) values found in dolostones. The dolostones as well as calcitised calcium sulphates record the Lomagundi-Jatuli signal. However evidence for activity of sulphate-reducing and/or methanogenic bacteria seems to be lacking. Dolomite precipitation (or dolomitisation), calcium sulphate calcitisation and production of the high 13C values (processes which typically involve such bacteria in the Phanerozoic) are thus inferred to have proceeded without the direct influence of sulphate reducers and methanogens. The most plausible explanation for the Lomagundi-Jatuli excursion seems to remain significant sequestration of organic carbon in a location yet to be identified. © 2011 Elsevier B.V.
cited By 22
Keywords: anhydrite; carbon isotope; carbonate; coastal sediment; dolomite; dolostone; gypsum; methanogenesis; organic carbon; oxygen; precipitation (chemistry); pseudomorph; sabkha; seawater; sulfate; Arkhangelsk [Russian Federation]; Onega Basin; Russian Federation; Centroberyx lineatus

Comparative study of infrared techniques for fast biogeochemical sediment analyses - Hahn, A.; Kliem, P.; Ohlendorf, C.; Zolitschka, B. (Geochemistry, Geophysics, Geosystems, 2011)
Analysis of sediment samples in the visible to mid infrared (IR) region requires small amounts of sample material and enables rapid and cost efficient geochemical analysis of mineral and organic sediment components. Here we use geochemical properties (total organic and inorganic carbon, biogenic silica, total nitrogen) from the ICDP deep drilling project PASADO to compare three different IR spectroscopy techniques: Diffuse Reflectance Fourier Transform IR Spectrometry (DRIFTS), Attenuated Total Reflectance Fourier Transform IR Spectroscopy (ATR-FTIRS) and Visible Near IR Spectroscopy (VNIRS). ATR-FTIRS and VNIRS are more rapid techniques compared to DRIFTS. Results show that calibration models developed using DRIFTS are most robust (correlation coefficient: R = 0.92 for TIC, R = 0.84 for BSi, R = 0.97 for TOC, R = 0.95 for TN). However, good statistical performance was also obtained by using ATR-FTIRS and VNIRS. When time and costs are limiting factors, these tools may be given preference for rapid biogeochemical screening. Copyright © 2011 by the American Geophysical Union.
Keywords: Analytical geochemistry; Anoxic sediments; Biogeochemistry; Carbon; Cost benefit analysis; Fourier transform infrared spectroscopy; Near infrared spectroscopy; Organic carbon; Reflection; Sedimentology; Silica; Spectrometry; Spectrum analysis; Attenuated total reflectance; Biogenic silica; Biogeochemical sediments; Calibration model; Comparative studies; Correlation coefficient; Cost-efficient; Deep drilling; Diffuse reflectance; Diffuse reflectance fourier transform infrared; Fourier transform IR spectroscopy; Geochemical analysis; Geochemical properties; Infrared technique; Inorganic carbon; IR spectrometry; Limiting factors; Midinfrared; Near-IR spectroscopy; Organic sediments; Sediment samples; Statistical performance; Total inorganic carbon; Total nitrogen; total organic carbon (TOC); Visible-near infrared spectroscopy; biogeochemistry; calibration; comparative study; FTIR spectroscopy; inorganic carbon; near infrared; sediment analysis; total organic carbon; Fourier transforms

Comparing extension on multiple time and depth scales in the Corinth Rift, Central Greece - Bell, Rebecca E.; McNeill, Lisa C.; Henstock, Timothy J.; Bull, Jonathan M. (Geophysical Journal International, 2011)
The young (<5Ma) Corinth Rift is an ideal natural laboratory to investigate rift deformation mechanisms by comparing extension rates determined by various methods spanning different depth and time ranges. Corinth Rift geodetic extension rates averaged over 5-100 yr have been interpreted to increase from 5 mm yr-1 or less in the east to >10-15 mm yr-1 in the west. We quantify total upper-crust and whole-crust extension on three profiles across the Corinth Rift. Whole-crust extension is greater across the central rift ( 11-21 km) than across the western part of the rift ( 5-13 km). This correlates with the overall rift morphology, which shows maximum basement subsidence, sediment accumulation, rift width and greatest summed Late Quaternary fault displacements in the central basin, but contrasts with the pattern of geodetic extension rates which are greater to the west of the central basin. The E-W increase in strain rates interpreted from geodetic data cannot have persisted over rift history to produce the observed rift morphology. We suggest the discrepancy between short-term and long-term extension patterns is related to shifts in the loci of maximum extension due to fault growth and linkage during Corinth Rift history, and is likely a characteristic of rift development in general. Total upper-crust and whole-crust extension estimates in the western rift, where extension estimates are best constrained, are within error. We propose that uniform pure-shear extension is a viable extension mechanism in the western rift and crustal extension estimates do not require the existence of a major active N-S dipping detachment fault. © 2011 The Authors Geophysical Journal International © 2011 RAS.
Keywords: Central Greece; Greece; Gulf of Corinth; Ionian Sea; Mediterranean Sea; Anoxic sediments; Estimation; Geodesy; Morphology; Sedimentology; Tectonics; Central Basin; Continental tectonics; Crustal extension; Deformation mechanism; Detachment fault; Europe; Fault displacement; Fault growth; Geodetic data; Late quaternary; Natural laboratories; Neotectonics; Sediment accumulation; Sedimentary basin; Time range; active fault; deformation mechanism; detachment fault; extensional tectonics; fault displacement; geodesy; geomorphology; neotectonics; rift zone; sedimentary basin; strain rate; subsidence; upper crust; Strain rate

Consistent trends in the true triaxial strength and deformability of cores extracted from ICDP deep scientific holes on three continents - Haimson, B. (Tectonophysics, 2011)
An extensive true triaxial testing program was carried out on core samples from three ICDP-sponsored deep scientific boreholes, KTB (Germany), SAFOD (United States), and TCDP (Taiwan). The three rocks differ in the processes that formed them and in many of their mechanical properties. However, all three rocks exhibited similar failure mechanism, in which induced or reopened microcracks are primarily aligned with the σ1-σ2 plane, and the developed fault is steeply inclined in the σ3 direction. Rock strength in all tested rocks increases with σ2 when σ3 is kept constant. Thus, the common Mohr-type criteria, which ignore the effect of σ2, typically underestimate rock strength. Rather a 3D criterion that involves all three principal stresses represents well experimental results. Fracture plane slope for the same σ3 steepens as σ2 rises, contrary to Mohr-type criteria. With respect to deformation, the onset of dilatancy increases with σ2. In conclusion, true triaxial tests conducted on cores from three scientific boreholes, revealed important details of mechanical behavior not otherwise observed in conventional triaxial tests. In addition, they show mechanical behavior similarities as related to σ2 effect regardless of rock type. © 2010 Elsevier B.V.
cited By 21
Keywords: Dilatancy; Fault angle; Scientific boreholes; True triaxial strength; True triaxial testing; Deformation; Mechanical engineering; Mechanical properties; Rock mechanics; Testing; Rocks; borehole; deformation; dilatancy; failure mechanism; mechanical property; microcrack; rock mechanics; triaxial test; Germany; Taiwan; United States

Correlation between deep fluids, tremor and creep along the central San Andreas fault - Becken, M.; Ritter, O.; Bedrosian, P.A.; Weckmann, U. (Nature, 2011)
The seismicity pattern along the San Andreas fault near Parkfield and Cholame, California, varies distinctly over a length of only fifty kilometres. Within the brittle crust, the presence of frictionally weak minerals, fault-weakening high fluid pressures and chemical weakening are considered possible causes of an anomalously weak fault northwest of Parkfield. Non-volcanic tremor from lower-crustal and upper-mantle depths is most pronounced about thirty kilometres southeast of Parkfield and is thought to be associated with high pore-fluid pressures at depth. Here we present geophysical evidence of fluids migrating into the creeping section of the San Andreas fault that seem to originate in the region of the uppermost mantle that also stimulates tremor, and evidence that along-strike variations in tremor activity and amplitude are related to strength variations in the lower crust and upper mantle. Interconnected fluids can explain a deep zone of anomalously low electrical resistivity that has been imaged by magnetotelluric data southwest of the Parkfield-Cholame segment. Near Cholame, where fluids seem to be trapped below a high-resistivity cap, tremor concentrates adjacent to the inferred fluids within a mechanically strong zone of high resistivity. By contrast, subvertical zones of low resistivity breach the entire crust near the drill hole of the San Andreas Fault Observatory at Depth, northwest of Parkfield, and imply pathways for deep fluids into the eastern fault block, coincident with a mechanically weak crust and the lower tremor amplitudes in the lower crust. Fluid influx to the fault system is consistent with hypotheses of fault-weakening high fluid pressures in the brittle crust. © 2011 Macmillan Publishers Limited. All rights reserved.
cited By 159
Keywords: mineral; amplitude; correlation; crust; data set; electrical resistivity; fluid; mantle; pressure effect; amplitude modulation; anisotropy; article; biogeographic region; chemical reaction; earthquake; electrical parameters; enzyme kinetics; friction; liquid; nonhuman; porosity; precipitation; priority journal; rock; salinity; san andreas fault; velocity; volcano; California; San Andreas; United States

Deciphering lake and maar geometries from seismic refraction and reflection surveys in Laguna Potrok Aike (southern Patagonia, Argentina) - De Batist, M.; Anselmetti, F.S.; Ariztegui, D.; Haberzettl, T.; Kopsch, C.; Ohlendorf, C.; Zolitschka, B. (Journal of Volcanology and Geothermal Research, 2011)
Laguna Potrok Aike is a bowl-shaped maar lake in southern Patagonia, Argentina, with a present mean diameter of 3.5km and a maximum water depth of 100m. Seismic surveys were carried out between 2003 and 2005 in order to get a deeper knowledge on the lake sediments and the deeper basin geometries. A raytracing model of the Laguna Potrok Aike basin was calculated based on refraction data while sparker data were additionally used to identify the crater-wall discordance and thus the upper outer shape of the maar structure. The combined data sets show a rather steep funnel-shaped structure embedded in the surrounding Santa Cruz Formation that resembles other well-known maar structures. The infill consists of up to 370m lacustrine sediments underlain by probably volcanoclastic sediments of unknown thickness. The lacustrine sediments show a subdivision into two sub-units: (a) the upper with seismic velocities between 1500 and 1800ms-1, interpreted as unconsolidated muds, and (b) the lower with higher seismic velocities of up to 2350ms-1, interpreted as lacustrine sediments intercalated with mass transport deposits of different lithology and/or coarser-grained sediments. The postulated volcanoclastic layer has acoustic velocities of >2400ms-1. The lake sediments were recently drilled within the PASADO project in the framework of the International Continental Scientific Drilling Program (ICDP). Cores penetrated through lacustrine unconsolidated sediments down to a depth of 100m below lake floor. This minimal thickness for the unconsolidated and low-velocity lithologies is in good agreement with our raytracing model. © 2011 Elsevier B.V.
Keywords: Argentina; Laguna Potrok Aike; Santa Cruz [Argentina]; Anoxic sediments; Lakes; Lithology; Refraction; Seismic waves; Seismology; Settling tanks; Submarine geophysics; Surveys; Velocity; Explosive volcanism; Maars; PASADO project; Sedimentary basin; South America; drilling; explosive volcanism; lithology; maar; ray tracing; sedimentary basin; seismic reflection; seismic refraction; seismic survey; seismic velocity; volcaniclastic deposit; Sedimentology

Characterization of bacterial diversity to a depth of 1500m in the Outokumpu deep borehole, Fennoscandian Shield - It{avaara, Merja; Nyyss{onen, Mari; Kapanen, Anu; Nousiainen, Aura; Ahonen, Lasse; Kukkonen, Ilmo (FEMS Microbiology Ecology, 2011)
This paper demonstrates the first microbiological sampling of the Outokumpu deep borehole (2516m deep) aiming at characterizing the bacterial community composition and diversity of sulphate-reducing bacteria (SRB) in Finnish crystalline bedrock aquifers. Sampling was performed using a 1500-m-long pressure-tight tube that provided 15 subsamples, each corresponding to a 100-m section down the borehole. Microbial density measurements, as well as community fingerprinting with 16S rRNA gene-based denaturing gradient gel electrophoresis, demonstrated that microbial communities in the borehole water varied as a function of sampling depth. In the upper part of the borehole, bacteria affiliated to the family Comamonadaceae dominated the bacterial community. Further down the borehole, bacteria affiliated to the class Firmicutes became more prominent and, according to 16S rRNA gene clone libraries, dominated the bacterial community at 1400-1500m. In addition, the largest number of bacterial classes was observed at 1400-1500m. The dsrB genes detected in the upper part of the borehole were more similar to the dsrB genes of cultured SRBs, such as the genus Desulfotomaculum, whereas in the deeper parts of the borehole, the dsrB genes were more closely related to the uncultured bacteria that have been detected earlier in deep earth crust aquifers. FEMS Microbiology Ecology © 2011 Federation of European Microbiological Societies. No claim to original Finnish government works.
Keywords: Bacteriological Techniques; Biodiversity; Colony Count; Microbial; DNA; Bacterial; Finland; Gene Library; Phylogeny; RNA; Ribosomal; 16S; Sulfur-Reducing Bacteria; Water; Water Microbiology; Baltic Shield; Finland; Ita Suomen; Outokumpu; Bacteria (microorganisms); Comamonadaceae; Desulfotomaculum; Firmicutes; uncultured bacterium; bacterial DNA; RNA 16S; water; aquifer; bacterium; bedrock; borehole; community composition; crystalline rock; dominance; electrokinesis; extremophile; groundwater; microbial community; sampling; species diversity; vertical distribution; article; bacterial count; biodiversity; chemistry; classification; Finland; gene library; genetics; Gram negative anaerobic bacteria; isolation and purification; microbiological examination; microbiology; phylogeny

Deep Drilling at the Dead Sea - Stein, M.; Ben-Avraham, Z.; Goldstein, S.; Agnon, A.; Ariztegui, D.; Brauer, A.; Haug, G.; Ito, E.; Yasuda, Y. (Scientific Drilling, 2011)

Deep rock damage in the san andreas fault revealed by P- and S-type fault-zone-guided waves - Ellsworth, W.L. (Geological Society Special Publication, 2011)
Damage to fault-zone rocks during fault slip results in the formation of a channel of low seismic-wave velocities. Within such channels guided seismic waves, denoted by F g, can propagate. Here we show with core samples, well logs and F g-waves that such a channel is crossed by the SAFOD (San Andreas Fault Observatory at Depth) borehole at a depth of 2.7 km near Parkfield, California, USA. This laterally extensive channel extends downwards to at least half way through the seismogenic crust, more than about 7 km. The channel supports not only the previously recognized Love-type- (F L) and Rayleigh-type- (F R) guided waves, but also a new fault-guided wave, which we name F Φ. As recorded 2.7 km underground, F Φ is normally dispersed, ends in an Airy phase, and arrives between the P- and S-waves. Modelling shows that F Φ travels as a leaky mode within the core of the fault zone. Combined with the drill core samples, well logs and the two other types of guided waves, F Φ at SAFOD reveals a zone of profound, deep, rock damage. Originating from damage accumulated over the recent history of fault movement, we suggest it is maintained either by fracturing near the slip surface of earthquakes, such as the 1857 Fort Tejon M 7.9, or is an unexplained part of the fault-creep process known to be active at this site. © The Geological Society of London 2011.
cited By 36
Keywords: earthquake; fault slip; fault zone; P-wave; Rayleigh wave; S-wave; seismic wave; California; San Andreas; United States

Deep scientific drilling to study reservoir-triggered earthquakes in Koyna, Western India - Gupta, H.; Nayak, S. (Scientific Drilling, 2011)
cited By 22

Determination of the optimal sampling interval for cyclostratigraphic analysis by using sampling theorem and accumulation rates - Zhao, Qing-Le; Wu, Huai-Chun; Li, Hai-Yan; Zhang, Shi-Hong (Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences, 2011)

Discovery and focused study of the Chicxulub impact crater - Urrutia-Fucugauchi, Jaime; Camargo-Zanoguera, Antonio; P'erez-Cruz, Ligia (Eos, Transactions American Geophysical Union, 2011)
Three decades ago, a landmark paper by Alvarez et al. [1980] proposed that an asteroid impact 65.5 million years ago was the cause of the mass extinction of about 75% of species, including the dinosaurs, at the boundary between the Cretaceous and Paleogene periods (K-Pg), formerly known as the Cretaceous-Tertiary (K-T) boundary. Alvarez et al. used geochemical studies on carbonate sequences from Italy, Denmark, and New Zealand to study the boundary layer, which was enriched in iridium and other platinum group elements (PGEs) at concentrations well above background levels. They associated these enrichments with the collision of an asteroid that injected large amounts of pulverized debris into the atmosphere, resulting in blockage of solar radiation, global cooling, and a shutdown of photosynthesis.
Keywords: Chicxulub impact crater; history

Discovery of Late Cretaceous foraminifera in the Songliao Basin: Evidence from SK-1 and implications for identifying seawater incursions - Xi, Dang Peng; Wan, Xiao Qiao; Feng, Zhi Qiang; Li, Shun; Feng, Zi Hui; Jia, Jian Zhong; Jing, Xia; Si, Wei Min (Chinese Science Bulletin, 2011)
The Songliao Basin is the largest oil-bearing basin in China. In the absence of sufficient evidence, the possibility of seawater incursion(s) into the Songliao Basin remains controversial. Recently, we discovered relatively abundant foraminifera fossils from units 1 and 2 of the Nenjiang Formation of borehole SK-1. Benthic foraminifera (Gavlinella sp., Anomalinoides sp., Pullenia sp., Haplophragmoides sp., Karrorulina hokkaidoana, Clavulinoides sp.), as well as planktonic foraminifera (Archaeoglobigerina blowi, Archaeoglobigerina cretacea and Hedbergella flandrini), were identified. These fossils were widely distributed in the marine Cretaceous. According to the global distribution of the above-mentioned planktonic foraminifera, the age of these fossil bearing strata appears to be Late Coniacian to Santonian. More importantly, these foraminifera provide direct evidence for marine water incursions into the Songliao Basin during deposition of the Lower Nenjiang Formation. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.
Keywords: Coniacian; Foraminifera; Haplophragmoides; Hedbergella; Pullenia

Chemical and isotope compositions of drilling mud gas from the San Andreas Fault Observatory at Depth (SAFOD) boreholes: Implications on gas migration and the permeability structure of the San Andreas Fault - Wiersberg, T.; Erzinger, J. (Chemical Geology, 2011)
In this contribution we present results from two individual gas monitoring experiments which were conducted during the drilling of the SAFOD (San Andreas Fault Observatory at Depth) boreholes. Gas from circulating drilling mud was monitored during the drilling the SAFOD III side tracks and was later analyzed for δ13C (CH4, C2H6 and C3H8), H/D (CH4) and noble gas isotopes. Furthermore, gas accumulations induced by drill pipe retrieval (trip gas) from the SAFOD MH and the SAFOD III boreholes were also investigated. The data are interpreted in the context of gas migration processes and the permeability structure of the San Andreas Fault (SAF) around two actively deforming zones at 3194m and 3301m borehole depth. Helium isotope ratios of 0.86 Ra at 3203m and between 0.51 and 0.88 Ra at 3262m (Ra is the atmospheric 3He/4He ratio) indicate an improved flow of mantle volatiles between both fault strands. Much lower values were observed at 3147m (0.26 Ra) and 3312m (0.22 Ra). Hydrocarbon concentrations coincide with the occurrence of shale at 3150-3200m and below 3310m depth. The molecular and isotope composition of hydrocarbons and their spatial distributions imply hydrocarbon generation by thermal degradation of organic matter followed by extensive diffusion loss. Carbon isotope data furthermore suggest a thermal maturity of the source rock of approx. 1.4%R0. The concentration of trip gas is generally low in the interval 3100. m-3450. m but exhibits high spatial variability. At 3128. m and 3223. m depth, the trip gas concentrations are as low as in the granite section of the SAFOD Main Hole. Considerable variations of Ra values, trip gas concentrations, and the molecular composition of hydrocarbons when penetrating the active fault strands let us conclude that the permeability of the fault transverse to the fault direction is limited and that the active fault has not been breached over many earthquake cycles such that little or no fluid exchange took place. Diffusion is the dominant mechanism controlling hydrocarbon migration through the fault strands. The elevated Ra values between both fault strands may reflect either episodic or continuous flow of mantle-derived fluids, suggestive of some limited permeability parallel to the fault direction. © 2011 Elsevier B.V.
cited By 35
Keywords: A-thermal; Active fault; Carbon isotopes; Continuous flows; Deforming zone; Diffusion loss; Dominant mechanism; Drilling mud; Drilling mud gas; Fault direction; Fault strands; Fluid exchange; Gas accumulation; Gas concentration; Gas migration; Gas monitoring; Helium isotopes; Hydrocarbon generation; Hydrocarbon migration; Isotope compositions; Mantle volatiles; Molecular compositions; Noble gas isotopes; Organic matter; Permeability structure; SAFOD; San Andreas Fault; Shale gas; Source rocks; Spatial variability; Thermal degradations; Boreholes; Boring; Buildings; Drill pipe; Helium; Hydrocarbons; Inert gases; Isotopes; Observatories; Oil well drilling; Petroleum geology; Shale; Tectonics; Gas permeability; active fault; borehole; chemical composition; diffusion; drilling; helium isotope; hydrocarbon migration; isotopic composition; noble gas; organic matter; permeability; San Andreas Fault; spatial distribution

Characteristics of elastic properties of the crystalline rock samples from the Outokumpu Deep Drill Hole: Results of Acoustopolariscopic Laboratory measurements - Gorbatsevich, Felix F.; Kovalevsky, Mikhail V.; Trishina, Olga M. (Special Paper of the Geological Survey of Finland, 2011)
We present the results of laboratory measurements of the elastic and nonelastic properties of drill core samples from depths of 94-2298 m in the Outokumpu Deep Drill Hole, eastern Finland. A total of 43 cubic rock samples were prepared (30-40 mm side length) and measured with the method of acoustopolariscopy under ambient conditions. In addition, the average velocities were calculated from the modal composition of the rocks. The measurement results provide the complete velocity matrices of the samples with the main components of P-waves as well as S-waves and their anisotropy factors. From the surface down to a depth of ∼1300 m (mostly metasediments), the Outokumpu rocks were found to be strongly anisotropic. The lowest measured anisotropy values were observed in the ∼1300-1600 m depth range (ophiolite-derived altered ultramafic rocks and metasediments). In the lower part of the hole from 1600 m to the hole bottom (metasediments and pegmatitic granite), the velocity anisotropy was variable. The effect of linear acoustic anisotropic absorption (LAAA) is exhibited in samples from the upper and lower sections of the drill hole. We attribute the variations in P- and S-wave velocities and their anisotropies to the variation in rock types and the drilling-induced relaxation of pressure (and to a minor degree temperature), which has resulted in decompaction and the formation of micro-cracks in the drill core. Therefore, a linear decrease in seismic velocities as a function of depth is observed in the laboratory measurements.
Keywords: Finland; Ita Suomen; Outokumpu; borehole; crystalline rock; elastic property; igneous rock; laboratory method; metamorphic rock; metasediment; microcrack; P-wave; S-wave; seismic anisotropy; seismic velocity; ultramafic rock

Earthquake Rupture at Focal Depth, Part I: Structure and Rupture of the Pretorius Fault, TauTona Mine, South Africa - Heesakkers, V.; Murphy, S.; Reches, Z. (Pure and Applied Geophysics, 2011)
We analyze the structure of the Archaean Pretorius fault in TauTona mine, South Africa, as well as the rupture-zone that recently reactivated it. The analysis is part of the Natural Earthquake Laboratory in South African Mines (NELSAM) project that utilizes the access to 3. 6 km depth provided by the mining operations. The Pretorius fault is a 10 km long, oblique-strike-slip fault with displacement of up to 200 m that crosscuts fine to very coarse grain quartzitic rocks in TauTona mine. We identify here three structural zones within the fault-zone: (1) an outer damage zone, 100 m wide, of brittle deformation manifested by multiple, widely spaced fractures and faults with slip up to 3 m; (2) an inner damage zone, 25-30 m wide, with high density of anastomosing conjugate sets of fault segments and fractures, many of which carry cataclasite zones; and (3) a dominant segment, with a cataclasite zone up to 50 cm thick that accommodated most of the Archaean slip of the Pretorius fault, and is regarded as the 'principal slip zone' (PSZ). This fault-zone structure indicates that during its Archaean activity, the Pretorius fault entered the mature fault stage in which many slip events were localized along a single, PSZ. The mining operations continuously induce earthquakes, including the 2004, M2. 2 event that rejuvenated the Pretorius fault in the NELSAM project area. Our analysis of the M2. 2 rupture-zone shows that (1) slip occurred exclusively along four, pre-existing large, quasi-planer segments of the ancient fault-zone; (2) the slipping segments contain brittle cataclasite zones up to 0. 5 m thick; (3) these segments are not parallel to each other; (4) gouge zones, 1-5 mm thick, composed of white 'rock-flour' formed almost exclusively along the cataclasite-host rock contacts of the slipping segments; (5) locally, new, fresh fractures branched from the slipping segments and propagated in mixed shear-tensile mode; (6) the maximum observed shear displacement is 25 mm in oblique-normal slip. The mechanical analysis of this rupture-zone is presented in Part II (Heesakkers et al., Earthquake Rupture at Focal Depth, Part II: Mechanics of the 2004 M2. 2 Earthquake Along the Pretorius Fault, TauTona mine, South Africa 2011, this volume). © 2011 Springer Basel AG.
Keywords: Brittle faulting; Deep mines; earthquake mechanics; earthquake rupture zone; Fault reactivation; Fault rock; Earthquakes; Fracture; Rocks; Tectonics; Fault slips; brittle deformation; cataclasite; displacement; earthquake rupture; fault zone; fracture; quartzite; strike-slip fault; South Africa

Alaska North Slope regional gas hydrate production modeling forecasts - Wilson, S.J.; Hunter, R.B.; Collett, T.S.; Hancock, S.; Boswell, R.; Anderson, B.J. (Marine and Petroleum Geology, 2011)
A series of gas hydrate development scenarios were created to assess the range of outcomes predicted for the possible development of the Eileen gas hydrate accumulation, North Slope, Alaska. Production forecasts for the reference case were built using the 2002 Mallik production tests, mechanistic simulation, and geologic studies conducted by the US Geological Survey. Three additional scenarios were considered: A downside-scenario which fails to identify viable production, an upside-scenario describes results that are better than expected. To capture the full range of possible outcomes and balance the downside case, an extreme upside scenario assumes each well is exceptionally productive.Starting with a representative type-well simulation forecasts, field development timing is applied and the sum of individual well forecasts creating the field-wide production forecast. This technique is commonly used to schedule large-scale resource plays where drilling schedules are complex and production forecasts must account for many changing parameters. The complementary forecasts of rig count, capital investment, and cash flow can be used in a pre-appraisal assessment of potential commercial viability.Since no significant gas sales are currently possible on the North Slope of Alaska, typical parameters were used to create downside, reference, and upside case forecasts that predict from 0 to 71 BM3 (2.5 tcf) of gas may be produced in 20 years and nearly 283 BM3 (10 tcf) ultimate recovery after 100 years.Outlining a range of possible outcomes enables decision makers to visualize the pace and milestones that will be required to evaluate gas hydrate resource development in the Eileen accumulation. Critical values of peak production rate, time to meaningful production volumes, and investments required to rule out a downside case are provided. Upside cases identify potential if both depressurization and thermal stimulation yield positive results. An extreme upside case captures the full potential of unconstrained development with widely spaced wells. The results of this study indicate that recoverable gas hydrate resources may exist in the Eileen accumulation and that it represents a good opportunity for continued research. © 2010 Elsevier Ltd.
cited By 38
Keywords: Alaska North Slope; Capital investment; Cash flow; Changing parameter; Commonly used; Critical value; Decision makers; Depressurizations; Development scenarios; Field development; Gas-hydrate production; Hydrate accumulations; North Slope of Alaska; Production forecasting; Production forecasts; Production rates; Production test; Production volumes; Resource development; Thermal stimulation; US Geological Survey; Forecasting; Gases; Hydration; Investments; Rating; Gas hydrates; forecasting method; gas hydrate; gas production; hydrocarbon reservoir; modeling; resource development; Alaska; North Slope; United States

Lithostratigraphy, physical properties and organic matter variability in Lake Malawi Drillcore sediments over the past 145,000years - Scholz, C.A.; Talbot, M.R.; Brown, E.T.; Lyons, R.P. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
Scientific drill cores recovered from Lake Malawi exhibit a remarkable down-core lithologic variability, and are indicative of radically changing environmental conditions forced by large-amplitude lake-level shifts over the past 150kyr. Here we present detailed lithologic and sedimentary fabric descriptions of the key sedimentary units, along with down-core physical properties data, down-core organic matter geochemistry (TOC, C/N, and δ13C data sets), and images and descriptions from core sections and from sediment smear slide microscopy. These data reveal a fundamental change in Lake Malawi's limnology and regional climate at ca. 60-70ka. Prior to this time the lake was characterized by large-amplitude variations in lake level and water chemistry, but after 60ka the lake remained comparatively high, and the central basin drill site accumulated mainly organic-rich, laminated sediments. Organic matter sources changed dramatically during the different lake stages. During major lake high stands, a mixed assemblage of algal (diatom-dominated), woodland and aquatic macrophyte (C4-pathway), and grassland (C3-pathway) organic matter was deposited, whereas during extreme low lake stages (water depths <200m), when saline, alkaline lakes persisted in the basin, sediments with minimal amounts of algal-dominated organic matter accumulated and were preserved. © 2010 Elsevier B.V.
cited By 18
Keywords: diatom; fossil record; hydrochemistry; lithostratigraphy; macrophyte; organic matter; paleoclimate; paleolimnology; Pleistocene; sediment core; East African Lakes; East African Rift; Lake Malawi; algae; Bacillariophyta

“Earthtime” Project: Dating Precision and Temporal Resolution in the “Deep Time” Record (in Chinese with English abstract);[“地时”(Earthtime)研究计划:“深时”(Deep Time)记录的定年精度与时间分辨率] - Tun, F.; Wang, C.; Zhang, S.; Yang, T.; Mo, X. (Geosciences, 2011)

A 370,000-year record of vegetation and fire history around Lake Titicaca (Bolivia/Peru) - Hanselman, Jennifer A.; Bush, Mark B.; Gosling, William D.; Collins, Aaron; Knox, Christopher; Baker, Paul A.; Fritz, Sheri C. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
Fossil pollen and charcoal analyses of sediments from Lake Titicaca, Peru/Bolivia, provide a record of palaeoclimatic variation spanning four full glacial cycles. Pollen, aquatic microfossils, and charcoal, as well as previously published data including diatom assemblages, carbonate content, and stable carbon isotopic ratios of organic carbon, indicate that interglacials were warm and dry whereas the peaks of glacials were cold and wet. Each of the interglacials documented in the record are somewhat different, with those of MIS 5e and MIS 9 inducing lower lake levels and a drier vegetation signature than those of MIS 7 and 1. The presence of charcoal particles in sediments deposited during previous interglacials provides evidence of the long-term role of fire in shaping Andean ecosystems. © 2011 Elsevier B.V.
Keywords: Andes; Bolivia; Lake Titicaca; Peru; Bacillariophyta; charcoal; depositional environment; diatom; fire history; fossil assemblage; glacial-interglacial cycle; interglacial; lacustrine deposit; microfossil; paleoclimate; palynology; vegetation dynamics; vegetation history

A 500,000-year-long sediment archive drilled in eastern Anatolia - Litt, T.; Anselmetti, F.S.; Çağatay, M.N.; Kipfer, R.; Krastel, S.; Schmincke, H.-U.; Sturm, M. (Eos, 2011)
Sedimentary archives host a wealth of information that can be used to reconstruct paleoclimate as well as the tectonic and volcanic histories of specific regions. Long and continuous archives from the oceans have been collected in thousands of locations by scientific ocean drilling programs over the past 40 years. In contrast, suitable continental archives are rare because terrestrial environments are generally nondepositional and/or subject to erosion. Lake sediments provide ideal drilling targets to overcome this limitation if suitable lakes at key locations have existed continuously for a long time.
cited By 30
Keywords: lacustrine deposit; marine sediment; Ocean Drilling Program; paleoclimate; reconstruction; Anatolia; Turkey

A general viscosity model of Campi Flegrei (Italy) melts - Misiti, V.; Vetere, F.; Freda, C.; Scarlato, P.; Behrens, H.; Mangiacapra, A.; Dingwell, D.B. (Chemical Geology, 2011)
Viscosities of shoshonitic and latitic melts, relevant to the Campi Flegrei caldera magmas, have been experimentally determined at atmospheric pressure and 0.5GPa, temperatures between 840K and 1870K, and H2O contents from 0.02 to 3.30wt.%.The concentric cylinder technique was employed at atmospheric pressure to determine viscosity of nominally anhydrous melts in the viscosity range of 101.5-103Pas. The micropenetration technique was used to determine the viscosity of hydrous and anhydrous melts at atmospheric pressure in the high viscosity range (1010Pas). Falling sphere experiments were performed at 0.5GPa in the low viscosity range (from 100.35 to 102.79Pas) in order to obtain viscosity data of anhydrous and hydrous melts. The combination of data obtained from the three different techniques adopted permits a general description of viscosity as a function of temperature and water content using the following modified VFT equation:logη=-a+bT-c+dT-e·expg·wTwhere η is the viscosity in Pa·s, T the temperature in K, w the H2O content in wt.%, and a, b, c, d, e, and g are the VFT parameters. This model reproduces the experimental data (95 measurements) with a 1σ standard deviation of 0.19 and 0.22 log units for shoshonite and latite, respectively. The proposed model has been applied also to a more evolved composition (trachyte) from the same area in order to create a general model applicable to the whole compositional range of Campi Flegrei products.Moreover, speed data have been used to constrain the ascent velocity of latitic, shoshonitic, and trachytic melts within dikes. Using petrological data and volcanological information (geometrical parameters of the eruptive fissure and depth of magma storage), we estimate a time scale for the ascent of melt from 9. km to 4. km depth (where deep and shallow reservoirs, respectively, are located) in the order of few minutes. Such a rapid ascent should be taken into account for the hazard assessment in the Campi Flegrei area. © 2011 Elsevier B.V.
Keywords: Campania [Italy]; Campi Flegrei; Italy; Napoli [Campania]; Atmospheric pressure; Atmospheric temperature; Atmospherics; Cylinders (shapes); Reservoirs (water); Spheres; Thermal logging; Viscometers; Water content; Campi Flegrei; Concentric cylinders; Falling sphere; Latites; Micropenetration; Shoshonites; air temperature; atmospheric pressure; caldera; experimental study; hazard assessment; magmatic differentiation; P-T conditions; petrology; shoshonite; viscosity; volcanology; Viscosity

A study of rock magnetic properties of serpentinites from the Outokumpu Deep Dril Hole, Finland - Dietze, Frank; Kontny, Agnes (Special Paper of the Geological Survey of Finland, 2011)
This study examined the rock magnetic properties and magnetic mineralogy of serpentinite, skarn, black schist and mica schist of the Outokumpu (OKU) rock type assemblage, which occur between 1314 and 1515 m in the Outokumpu Deep Drill Hole in Eastern Finland. This depth interval is related to pronounced magnetic anomalies. A banded magnetic anomaly pattern, similar to the one observed in the OKU drill cores, is seen in aeromagnetic surveys for the surface in the vicinity of the OKU borehole. Magnetic logging has revealed that the magnetic anomalies are mostly related to the ferrimagnetic serpentinite units in the OKU assemblage. The serpentinite units show a significant scattering of magnetic susceptibility (κ) from 0.04 to 192.7*10-3 SI and natural remanent magnetization (NRM) from 0.06 to 45.1 A/m, indicating a heterogeneous distribution of ferrimagnetic minerals in the ultramafic rocks. The main magnetic minerals are magnetite and pyrrhotite. Furthermore, variation in the K{onigsberger ratio (Q) from below 1 up to 16 indicates that some ultramafic rocks in the OKU assemblage are able to carry a remanent magnetization (Q-ratio > 1). The strong scattering of rock magnetic properties is interpreted to reflect a complex geological history of the studied rocks. Magnetite is known to form during the serpentinization of ultramafic rocks on the sea floor or during subduction-related processes. In the OKU assemblage it was partially decomposed during early deformation stages by listwaenite-birbirite-type carbonatequartz alteration. During subsequent events of regional deformation, the magnetic minerals were deformed or some new formation of magnetic minerals occurred.
Keywords: Finland; Ita Suomen; Outokumpu; borehole logging; deep drilling; magnetic anomaly; magnetic property; magnetic survey; magnetic susceptibility; magnetite; mineralogy; remanent magnetization; rock property; serpentinite; skarn

Applications Study of Geo-drilling Technology (in Chinese with English abstract);[地质钻探技术与应用研究] - Ran, H.; Zhang, J.; Xie, W.; Zhang, Y.; Song, Z.; Xiang, J.; Liu, F.; Feng, Q.; Yan, T.; Jia, M.; Tao, S.; Hu, J. (Acta Geologica Sinica, 2011)

Centimeter-scale sedimentary sequence description of Upper Cretaceous-Lower Paleocene Mingshui Formation: Lithostratigraphy，facies and cyclostratigraphy, based on the scientific drilling (SK1) borehole in the Songliao Basin. - CHENG Ri-Hui, ZHANG Shi-Gong (Earth Science Frontiers, 2011)
Keywords: Songliao Basin; SK1; Mingshui Formation; sedimentary facies; sedimentary sequence; cyclostratigraphy

Aquatic ecosystems of the Yucat'an Peninsula (Mexico), Belize, and Guatemala - P'erez, Liseth; Bugja, Rita; Lorenschat, Julia; Brenner, Mark; Curtis, Jason; Hoelzmann, Philipp; Islebe, Gerald; Scharf, Burkhard; Schwalb, Antje (Hydrobiologia, 2011)
This study presents limnological and morphological characteristics, physical and chemical properties of waters, and geochemistry of surface sediments for 63 aquatic ecosystems located on the karst Yucat'an Peninsula and surrounding areas of Belize and the Guatemalan highlands and eastern lowlands. Our principal goal was to classify the aquatic systems based on their water variables. A principal component analysis (PCA) of the surface water chemistry data showed that a large fraction of the variance (29%) in water chemistry is explained by conductivity and major ion concentrations. The broad conductivity range, from 168 to 55,300 μS cm-1 reflects saline water intrusion affecting coastal aquatic environments, and the steep NW-S precipitation gradient, from 450 to>3,200 mm year-1. Coastal waterbodies Celest'un and Laguna Rosada displayed the highest conductivities. Minimum surface water temperatures of 21.6°C were measured in highland lakes, and warmest temperatures, up to 31.7°C, were recorded in the lowland waterbodies. Most lakes showed thermal stratification during the sampling period, with the exception of some shallow (<10 m) systems. Lakes Chichancanab, Milagros, and Bacalar displayed sulfate-rich waters. Waters of sinkholes had relatively high conductivities (<3,670 μS cm-1) and a broad range of δ18O values (-4.1 to +3.8%). Ca, HCO3, and SO4 dominated the waters of the lowland lakes, whereas Na was the dominant cation in highland lakes. Coastal aquatic ecosystems were dominated by Na and Cl. Cluster analysis based on surface water variables classified aquatic environments of the lowlands and highlands into three groups: (1) lowland lakes, ponds, wetlands, and coastal waterbodies (2) highland lakes, and (3) sinkholes and rivers. A broad trophic state gradient was recorded, ranging from the eutrophic Lake Amatitl'an and the Timul sinkhole to oligotrophic Laguna Ayarza, with the highest water transparency (11.4 m). We used major and trace elements in surface sediments to assess pollution of waterbodies. Lakes Amatitl'an, Atescatempa, El Rosario, Cayuc'on, Chacan-Lara, La Misteriosa, rivers Sub'in and R'io Dulce, the wetland Jamol'un, and the sinkhole Pet'en de Monos showed evidence of pollution and urban development. Their surface sediments displayed high concentrations of As, Cu, Fe, Ni, Pb, Se, Zn, and Zr, which suggest moderate to strong pollution. © Springer Science+Business Media B.V. 2010.
Keywords: Belize [Central America]; Guatemala [Central America]; Mexico [North America]; Yucatan Peninsula; hydraulic conductivity; karst; lake pollution; limnology; morphology; Neotropical Region; physicochemical property; pollution effect; principal component analysis; saline intrusion; surface water; trace element; urban development; water temperature

Attempt to the Late Cretaceous Ostracod Carapace Stable Isotope Measurement–Case Study on the SK1 Drill Cores - Xiao-Qiao, MO; Chao, WANG; et al. (Geoscience, 2011)

Biogenic silica deposition in Lake Malawi, East Africa over the past 150,000years - Johnson, T.C.; Brown, E.T.; Shi, J. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
We report a 150,000. year record of the abundance of biogenic silica (BSi) in drill cores from the northern and central basins of Lake Malawi. The periods of highest diatom burial at both sites occurred around 65-69 and 51-60. thousand years ago (ka) after the termination of prolonged, intense drought in the region. These peaks are believed to reflect elevated delivery of dissolved silica to the lake due to acceleration of chemical weathering in the drainage basin. The droughts that preceded these BSi depositional episodes occurred at precessional frequency, corresponding to times of minimum austral spring (or summer?) insolation in the region prior to 60. ka. Subsequent arid spells have not been as severe due to the reduced amplitude of precessional forcing as a result of the superimposed effect of eccentricity. However, biogenic silica records do not show significant sensitivity to precessional forcing. The BSi burial flux in the north basin displays strong millennial-scale variability since 50. ka, with peak values occurring during cold times in the Northern Hemisphere, as reflected in the Greenland ice core records. We observe no relationship between BSi and deposition of volcanic tephras in this system. The central basin core also displays millennial-scale variability in BSi abundance during the past 50. ky, of comparable magnitude to that in the north basin, but without systematic correlation to the north basin BSi or Greenland ice core records. In general, we conclude that BSi profiles from the north and (probably) south basins are more readily interpreted in terms of regional climate dynamics than are BSi profiles from more central locations in long, narrow tropical rift lakes. Diatom burial rates are suspected to be too influenced by silica limitations imposed by diatom production and burial in the upwelling systems at either end of these low-latitude lacustrine systems. © 2010 Elsevier B.V.
cited By 39
Keywords: biogenic deposit; chemical weathering; diatom; drainage basin; ice core; lacustrine deposit; paleoclimate; sediment core; silica; tephra; tropical region; East Africa; East African Lakes; Lake Malawi; Bacillariophyta

Biomarker seasonality study in Lake Van, Turkey - Huguet, C.; Fietz, S.; Stockhecke, M.; Sturm, M.; Anselmetti, F.S.; Rosell-Mel'e, A. (Organic Geochemistry, 2011)
The endorheic Lake Van in eastern Anatolia (Turkey) is the world's largest soda lake and it is an important site in paleoclimate studies to understand past continental conditions in western Asia. In order to gain further insights into the biomarker signatures in Lake Van's sediments we have analyzed particulate material in sediment traps deployed between August 2006 and July 2007. The biomarkers used were long chain alkenones (LCAs C37-C39, haptophyte lipids), isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs, Archaea membrane lipids) and pigments (chlorins and fucoxanthin). The biomarker fluxes indicate a strong seasonality in export primary productivity and the phytoplankton community structure. The highest total mass and organic carbon fluxes were found in summer, coupled to strong stratification while the lowest mass fluxes occurred in winter at the time of water column mixing. With increasing temperatures in early spring, phytoplankton export productivity grew, coupled with an increase of total mass flux and organic carbon, which might be associated to enhanced nutrient input from snowmelt runoff. The percentage of C37:4 shows some correspondence with observed seasonal changes in Lake Van's stratification structure. We also evaluated the potential applicability of molecular temperature proxies derived from Archaea and haptophyte lipids. The use of the TEX86 proxy was precluded by low GDGT abundances. Estimated LCA temperatures were consistent with temperatures in the photic zone but no seasonality changes were observed despite the wide annual temperature range measured at Lake Van. © 2011 Elsevier Ltd.
cited By 23
Keywords: Archaea; Biomarker flux; Chlorins; Eastern Anatolia; Fucoxanthin; Isoprenoids; Long chain alkenones; Membrane lipids; Organic carbon fluxes; Paleoclimate studies; Particulate materials; Photic zone; Phytoplankton community; Primary productivity; Seasonal changes; Seasonality; Snowmelt runoff; Soda lakes; Strong stratification; Temperature proxy; Temperature range; Total mass; Total mass flux; Water columns; Algae control; Anoxic sediments; Biomarkers; Glycerol; Lipids; Microorganisms; Organic carbon; Phytoplankton; Productivity; Sedimentology; Lakes; biomarker; community structure; isoprenoid; nutrient; organic carbon; paleoclimate; particulate matter; photic zone; phytoplankton; pigment; prokaryote; runoff; seasonality; sediment trap; snowmelt; stratification; temperature profile; water column; Lake Van; Turkey

Centimeter-scale sedimentary sequence description of Upper Cretaceous Nenjiang Formation (lower numbers 1 &2): Lithostratigraphy, facies and cyclostratigraphy, based on the scientific drilling (SK1) borehole in the Songliao Basin. - Wei-Feng, GAO; Pu-Jun, WANG; Ri-Hui, CHENG; Guo-Dong, WANG; Xiao-Qiao, MO; He-Yong, TUN; Shu-Hua, WANG; Mo-Lin, LIANG (Earth Science Frontiers, 2011)

Centimeter-scale sedimentary sequence description of Upper Cretaceous Nenjiang Formation (upper numbers 3-5): Lithostratigraphy, facies and cyclostratigraphy, based on the scientific drilling (SK1) borehole in the Songliao Basin. - Pu-Jun, WANG; Wei-Feng, GAO; Ri-Hui, CHENG; Guo-Dong, WANG; He-Yong, TUN; Xiao-Qiao, MO; Gan-Sheng, YANG; Zhong-Xin, HONG (Earth Science Frontiers, 2011)

Centimeter-scale sedimentary sequence description of Upper Cretaceous Sifangtai Formation: Lithostratigraphy, facies and cyclostratigraphy, based on the scientific drilling (SK1) borehole in the Songliao Basin. - Guo-Dong, WANG; Ri-Hui, CHENG; Pu-Jun, WANG; Wei-Feng, GAO; Cheng-Shan, WANG; Yan-An, LIN; Qing-Hua, HUANG (Earth Science Frontiers, 2011)

Discussion on the geological time of Qingshankou Formation in Songliao Basin (in Chinese); 松辽盆地青山口组地质时代探讨 - Dang, Y. (Petroleum Geology & Oilfield Development, 2011)

Active basins and neotectonics: Morphotectonics of the Lake Ohrid Basin (FYROM and Albania); [Aktive Becken und Neotektonik: Die Morphotektonik des Ohridbeckens (FYROM und Albanien)] - Reicherter, Klaus; Hoffmann, Nadine; Lindhorst, Katja; Krastel, Sebastian; Fern'andez-Steeger, Tom'as; Gr{utzner, Christoph; Wiatr, Thomas (Zeitschrift der Deutschen Gesellschaft fur Geowissenschaften, 2011)
The Lake Ohrid Basin in FYROM (Former Yugoslav Republic of Macedonia) and Albania meets all criteria of an active, seismic landscape: linear step-like fault scarps in the landscape and under water within the lake. Post-glacial (or Late Pleistocene) bedrock fault scarps at Lake Ohrid are long-lived expressions of repeated surface faulting in tectonically active regions, where erosion cannot outpace the fault slip. Other morphotectonic features are wind gaps, wineglass-shaped valleys and triangular facets, which are well preserved. Generally, the faults and fault scarps are getting younger towards the basin centre, as depicted on seismic and hydroacoustic profi les. Additionally, mass movement bodies within the lake and also onshore (rockfalls, landslides, sub-aquatic slides, homogenites, turbidites) are likely to have been seismically triggered. These morphotectonic observations are in line with focal mechanisms of earthquakes in the greater Lake Ohrid area. We investigated the neotectonic history and tectonic geomorphology of the Lake Ohrid Basin by means of an integrated multidisciplinary approach, using tectonic geomorphology and a variety of geophysical and remote sensing methods. © 2011 E.

Earthquake Rupture at Focal Depth, Part II: Mechanics of the 2004 M2.2 Earthquake Along the Pretorius Fault, TauTona Mine, South Africa - Heesakkers, V.; Murphy, S.; Lockner, D.A.; Reches, Z. (Pure and Applied Geophysics, 2011)

Laboratory measurements of the seismic velocities and other petrophysical properties of the Outokumpu deep drill core samples, eastern Finland - Elbra, Tiiu; Karlqvist, Ronnie; Lassila, Ilkka; Hæggstr{om, Edward; Pesonen, Lauri J. (Geophysical Journal International, 2011)
Petrophysical, in particular seismic velocity, measurements of the Outokumpu deep drill core (depth 2.5 km) have been carried out to characterize the geophysical nature of the Paleoproterozoic crustal section of eastern Finland and to find lithological and geophysical interpretations to the distinct crustal reflectors as observed in seismic surveys. The results show that different lithological units can be identified based on the petrophysical data. The density of the samples remained nearly constant throughout the drilled section. Only diopside-tremolite skarns and black schists exhibit higher densities. The samples are dominated by the paramagnetic behaviour with occasional ferromagnetic signature caused by serpentinitic rocks. Large variations in seismic velocities, both at ambient pressure and under in situ crustal conditions are observed. The porosity of the samples, which is extremely low, is either intrinsic by nature or caused by decompaction related to fracturing during the core retrieval. It is noteworthy that these microfractures have dramatically lowered the VP and VS values. From the measured velocities and density data we have calculated the seismic impedances, Young's modulus and Poisson's ratios for the lithological units of the Outokumpu section and from these data the reflection coefficients for the major lithological boundaries, evident in the surveyed section, were determined. The data show that the strong and distinct reflections visible in wide-angle seismic surveys are caused by interfaces between diopside-tremolite skarn and either serpentinites, mica schist or black schist. © 2010 The Authors Geophysical Journal International © 2010 RAS.
Keywords: Finland; Ita Suomen; Outokumpu; Acoustic impedance; Core drilling; Core samples; Drills; Geological surveys; Lithology; Mica; Paramagnetism; Reflection; Seismic waves; Seismology; Silicate minerals; Structural geology; Velocity; Ambient pressures; Black schist; Body waves; Crustal structure; Density data; Drill core; Eastern Finland; In-situ; Laboratory measurements; Mica schists; Microfractures; Paleoproterozoic; Petrophysical; Petrophysical properties; Poisson' s ratio; Reflection coefficients; Seismic impedance; Seismic surveys; Seismic velocities; Young' s Modulus; acoustic property; body wave; crustal structure; geophysics; lithology; Poisson ratio; porosity; schist; seismic survey; seismic velocity; skarn; wave propagation; Young modulus; Acoustic wave propagation

Hydrogeological characteristics of the Outokumpu Deep Drill Hole - Ahonen, Lasse; Kiet{av{ainen, Riikka; Kortelainen, Nina; Kukkonen, Ilmo T.; Pullinen, Arto; Toppi, Taru; Bomberg, Malin; It{avaara, Merja; Nousiainen, Aura; Nyyss{onen, Mari; {Oster, Marjo (Special Paper of the Geological Survey of Finland, 2011)
Extensive hydrogeological studies on the Outokumpu Deep Drill Hole R2500, drilled in 2004-2005, have been carried out during both the drilling phase as well as the post-drilling period. The present paper introduces the main results and characteristics of deep fluids and gases in the 2516 m deep hole drilled into a Paleoproterozoic formation of metasediments, ophiolite-derived altered ultrabasic rocks and pegmatitic granite. The main hydrogeological experiments during drilling were the daily monitoring of drilling fluid electrical conductivity, pH, composition and consumption (loss) of drilling fluid, as well as targeted fluid sampling and hydraulic testing during drilling breaks with the drill stem method. Hydrogeological sampling of the drill hole water with a tube method has been carried out three times to up to 1500-2350 m depths in the post-drilling period, and undisturbed formation fluid was pumped for several weeks from a packer-isolated fracture system at 967 m. The loss of drilling water during drilling was very heavy in the uppermost 1000 m of the hole (1-4 m3 of water per 1 m of drilling), but it decreased to a low level (<1 m3/m) at lower depths, indicating that hydraulically conductive fractures are more frequent in the first kilometre of bedrock than beneath. The hydraulic testing carried out at approximately 500-m depth intervals in 40-70 m thick sections indicated a similar pattern of hydraulic conductivity decreasing with depth: about 7.5 · 10-6 m/s at 500 m, 5.3 · 10-7 m/s at 1000 m, and practically impermeable rock at deeper levels. The electrical conductivity of the drill hole fluid rapidly increased in the post-drilling period due to the discharge of saline water from several fracture systems, and was monitored with repeated down-hole logs. In the uppermost 1000 m, fluid salinity has been in a semi-stable condition since about 2006, but in the deeper parts of the hole electrical conductivity continued to gradually increase in 2008 and 2009, when the most recent downhole logs and fluid sample profiles were obtained. The fluids are Ca-Na-Cl fluids with elevated Mg concentrations at the depths of the ophiolite-derived rocks of the Outokumpu assemblage. The fluids contain abundant gases, with methane and nitrogen being the main components. The stable isotope compositions (δ2H, δ18O) of the saline fluids indicate that they are not meteoric fluids but probably result from long-term water-rock interaction. The results indicate distinct water bodies isolated in fracture zones with minimal hydraulic connections.
Keywords: Finland; Ita Suomen; Outokumpu; bedrock; borehole; deep drilling; electrical conductivity; groundwater; hydraulic conductivity; hydraulic fracture; hydrochemistry; hydrogeology; isotopic composition; magnesium; salt water; stable isotope

Imaging permafrost velocity structure using high resolution 3D seismic tomography - Ramachandran, K.; Bellefleur, G.; Brent, T.; Riedel, M.; Dallimore, S. (Geophysics, 2011)
A 3D seismic survey (Mallik 3D), covering 126 km2 in the Mackenzie Delta area of Canada's north, was conducted by industry in 2002. Numerous lakes and marine inundation create a complex near-surface structure in the permafrost terrain. Much of the near subsurface remains frozen but significant melt zones exist particularly from perennially unfrozen water bodies. This results in an irregular distribution of permafrost ice creating a complex pattern of low and high frequency near-surface velocity variations which induce significant traveltime distortions in surface seismic data. A high resolution 3D traveltime tomography study was employed to map the permafrost velocity structure utilizing first-arrival traveltimes picked from 3D seismic shot records. Approximately 900,000 traveltime picks from 3167 shots were used in the inversion. Tomographic inversion of the first-arrival traveltimes resulted in a smooth velocity model for the upper 200 m of the subsurface. Ray coverage in the model is excellent down to 200 m providing effective control for estimating velocities through tomographic inversion. Resolution tests conducted through horizontal and vertical checkerboard tests confirm the robustness of the velocity model in detailing small scale velocity variations. Well velocities were used to validate tomographic velocities. The tomographic velocities do not show systematic correlation with well velocities. The velocity model clearly images the permafrost velocity structure in lateral and vertical directions. It is inferred from the velocity model that the permafrost structure in the near subsurface is discontinuous. Extensions of surface water bodies in depth, characterized by low P-wave velocities, are well imaged by the velocity model. Deep lakes with unfrozen water, inferred from the tomographic velocity model, correlate with areas of strong amplitude blanking and frequency attenuation observed in processed reflection seismic stack sections. © 2011 Society of Exploration Geophysicists.
cited By 14
Keywords: Lakes; Permafrost; Seismic prospecting; Seismic waves; Seismology; Surface structure; Tomography; Case history; Complex near surfaces; Frequency attenuation; Low and high frequencies; Systematic correlation; Tomographic inversion; Travel time tomography; Velocity analysis; Velocity; arrival time; imaging method; P-wave; permafrost; seismic data; seismic survey; seismic tomography; three-dimensional modeling; travel time; velocity structure; Canada; Mackenzie Delta; Northwest Territories

Influence of the substrate on maar-diatreme volcanoes - An example of a mixed setting from the Pali Aike volcanic field, Argentina - Ross, Pierre-Simon; Delpit, S'everine; Haller, Miguel J.; N'emeth, Karoly; Corbella, Hugo (Journal of Volcanology and Geothermal Research, 2011)

Inter-laboratory comparison of oxygen isotope compositions from biogenic silica - Chapligin, B.; Leng, M.J.; Webb, E.; Alexandre, A.; Dodd, J.P.; Ijiri, A.; L{ucke, A.; Shemesh, A.; Abelmann, A.; Herzschuh, U.; Longstaffe, F.J.; Meyer, H.; et al. (Geochimica et Cosmochimica Acta, 2011)
Several techniques have been introduced in the last decades for the dehydration and release of O2 from biogenic silica (opal-A) for oxygen-isotope analysis. However, only one silica standard is universally available: a quartz standard (NBS28) distributed by the IAEA, Vienna. Hence, there is a need for biogenic silica working standards. This paper compares the existing methods of oxygen-isotope analyses of opal-A and aims to characterize additional possible working standards to calibrate the δ18O values of biogenic silica. For this purpose, an inter-laboratory comparison was organized. Six potential working standard materials were analysed repeatedly against NBS28 by eight participating laboratories using their specific analytical methods. The materials cover a wide range of δ18O values (+23 to +43‰) and include diatoms (marine, lacustrine), phytoliths and synthetically-produced hydrous silica. To characterize the proposed standards, chemical analyses and imaging by scanning electron microscopy (SEM) were also performed. Despite procedural differences at each laboratory, all methods are in reasonable agreement with a standard deviation (SD) for δ18O values between 0.3‰ and 0.9‰ (1σ). Based on the results, we propose four additional biogenic silica working standards (PS1772-8: 42.8‰; BFC: 29.0‰; MSG60: 37.0‰; G95-25-CL leaves: 36.6‰) for δ18O analyses, available on request through the relevant laboratories. © 2011 Elsevier Ltd.
cited By 67
Keywords: biogenic mineral; calibration; comparative study; isotopic analysis; isotopic composition; laboratory method; opal; oxygen isotope; scanning electron microscopy; Bacillariophyta

International Workshop on Deep Scientific Drilling to Study Reservoir Triggered Earthquakes in Koyna, India - Gupta, Harsh; Nayak, Shailesh; Bhaskar Rao, Y. J.; Chadha, R. K.; Bansal, B. K.; Srinagesh, D.; Purnachandra Rao, N.; Roy, Sukanta (Journal of Geological Society of India, 2011)

Intrabasin paleoearthquake and quiescence correlation of the late Holocene Dead Sea - Kagan, E.; Stein, M.; Agnon, A.; Neumann, F. (Journal of Geophysical Research: Solid Earth, 2011)
A comprehensive multisite paleoseismic archive of the late Holocene Dead Sea basin (past 2500 years) is established by constructing two age-depth chronological models of two sedimentary sections exposed at the retreating shores of the modern Dead Sea. Two new paleoseismic study sites studied are the Ein Feshkha Nature Reserve outcrop located at the northern part of the basin and close to an active underwater transverse fault and the east Ze'elim Gully outcrop at the southern part of the basin. Age-depth regression models are calculated for these sections based on atmospheric radiocarbon ages of short-lived organic debris calibrated with a Bayesian model. The uncertainties on individual model ages are smaller than 100 years. The new chronological records are compared to a laminae-counting study of the Ein Gedi core (Migowski et al., 2004) located at the central Dead Sea basin. The Ein Feshkha outcrop yielded the largest number of seismites in the studied time interval (n = 52), while lower numbers of seismites are recovered from the Ze'elim outcrop and Ein Gedi core (n = 15 and 36, respectively). The seismites show no strong dependence on the limnological-sedimentological conditions in the particular sampling sites (they coappear in both shallow and deep water environments and in different sedimentary facies). During time intervals when the chronologies are comparable it appears that the number of seismites is significantly larger in the northern part of the basin (Ein Gedi and Ein Feshkha). Seismic quiescence intervals are apparent at all three sites from 2nd-4th century A.D. and at 500-150 B.C. at Ze'elim and Ein Gedi. Several synchronous seismites appear in all sections (termed here the intrabasin seismites (IBS)). Among them: 1927, 1293, 1202/1212, 749, 551, 419, and 33 A.D. and 31 and mid-2nd century B.C. The recurrence time of the IBS from the 2nd century B.C. to the 14th century A.D. is ∼200 years, compared with ∼100 years for all earthquakes. On a diagram of epicentral distance versus magnitude, historic earthquakes that are correlated with IBS plot in a field of high local intensity. The farther and stronger IBS earthquakes require lower local intensities to be recorded. This study demonstrates that a painstaking effort is still needed for unraveling the seismic history of the Dead Sea basin. The results also indicate that such a study will likely be highly rewarding. Copyright 2011 by the American Geophysical Union.
cited By 58
Keywords: Bayesian analysis; earthquake epicenter; earthquake intensity; earthquake magnitude; fault; geochronology; Holocene; limnology; outcrop; paleoseismicity; radiocarbon dating; sedimentology; seismite; Dead Sea

Lake Malawi's response to megadrought terminations: Sedimentary records of flooding, weathering and erosion - Brown, E.T. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
Sediment records from the northern basin of Lake Malawi provide a means of evaluating the lake basin's response to climate change over the past 75. ky, notably to increased precipitation at the terminations of droughts. Transitions from drier to wetter conditions provide an opportunity to evaluate the system's response to climate shifts. Upon termination of drought episodes at 62 and 72. ka, enhanced precipitation and an associated increase in streampower led to enhanced physical erosion and landscapes were flooded by rising lake waters. These processes appear to have left their mark in the sedimentary record, bringing about a spike of deposition of organic matter (probably of terrestrial origin) at times of increased rainfall. This was immediately followed by a period of deposition of chemically-weathered material that had been retained on the landscape during arid times and mobilized in response to increased precipitation. After this altered material was removed (perhaps a thousand years after the transition to wetter conditions), fresher material, richer in soluble elements including nutrients, was exposed to chemical weathering, leading to substantial diatom blooms. The lag between the onset of wetter conditions and the diatom blooms is inconsistent with significant storage of bioavailable silica in soils in this system. However, biological cycling of silica, including formation and dissolution of phytoliths, may have played a role in mobilization of the silica necessary for the diatom productivity. © 2010 Elsevier B.V.
cited By 34
Keywords: biogenic deposit; chemical weathering; climate change; diatom; dissolution; drought; erosion rate; flooding; lacustrine deposit; lake water; paleoclimate; phytolith; precipitation (climatology); silica; weathering; East African Lakes; Lake Malawi; Bacillariophyta

High-grade contact metamorphism in the Reykjanes geothermal system: Implications for fluid-rock interactions at mid-oceanic ridge spreading centers - Marks, N.; Schiffman, P.; Zierenberg, R.A. (Geochemistry, Geophysics, Geosystems, 2011)
Granoblastic hornfels identified in cuttings from the Reykjanes seawater-dominated hydrothermal system contains secondary pyroxene, anorthite, and hornblendic amphibole in locally equilibrated assemblages. Granoblastic assemblages containing secondary orthopyroxene, olivine, and, locally, cordierite and spinel occur within groups of cuttings that show dominantly greenschist facies hydrothermal alteration. Granoblastic plagioclase ranges continuously in composition from An54 to An96, in contrast with relict igneous plagioclase that ranges from An42 to An80. Typical hydrothermal clinopyroxene compositions range from Wo49En3Fs48 to Wo 53En30Fo17; clinopyroxene from the granoblastic grains is less calcic with an average composition of Wo48En 27Fs25. The hornfels is interpreted to form during contact metamorphism in response to dike emplacement, resulting in local recrystallization of previously hydrothermally altered basalts. Temperatures of granoblastic recrystallization estimated from the 2-pyroxene geothermometer range from 927°C to 967°C. Redox estimates based on the 2-oxide oxybarometer range from log fO2 of -13.4 to -15.9. Granoblastic hornfels comprised of clinopyroxene, orthopyroxene, and calcic plagioclase have been described in a number of ancient hydrothermal systems from the conductive boundary layer between the hydrothermal system and the underlying magma source, most notably in Integrated Ocean Drilling Program Hole 1256D, Ocean Drilling Program Hole 504B, and in the Troodos and Oman ophiolites. To our knowledge, this is the first evidence of high-grade contact metamorphism from an active geothermal system and the first description of equilibrated amphibole-absent pyroxene hornfels facies contact metamorphism in any mid-ocean ridge (MOR) hydrothermal system. This contribution describes how these assemblages develop through metamorphic reactions and allows us to predict that higher-temperature assemblages may also be present in MOR systems. Copyright 2011 by the American Geophysical Union.
cited By 19
Keywords: Feldspar; Geothermal fields; Geothermal prospecting; Hydraulic structures; Igneous rocks; Oceanography; Offshore oil wells; Olivine; Recrystallization (metallurgy); Seawater; Submarine geology; alteration; Average composition; Clinopyroxenes; contact metamorphism; Fluid-rock interaction; Geothermal systems; Geothermometers; Greenschist; Hydrothermal alterations; Hydrothermal system; hydrothermal systems; Hydrothermally; Magma sources; Metamorphic reactions; Mid-ocean ridges; Mid-oceanic ridges; Ocean drilling programs; Oman ophiolite; Orthopyroxene; Metamorphic rocks; clinopyroxene; contact metamorphism; fluid-structure interaction; geothermal system; geothermometry; greenschist facies; hydrothermal alteration; hydrothermal system; mid-ocean ridge; Ocean Drilling Program; P-T conditions; recrystallization; spreading center; Atlantic Ocean; Reykjanes Ridge

Late Pleistocene paleohydrography and diatom paleoecology of the central basin of Lake Malawi, Africa - Stone, J.R.; Westover, K.S.; Cohen, A.S. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
Analysis of sedimentary diatom assemblages (10 to 144. ka) form the basis for a detailed reconstruction of the paleohydrography and diatom paleoecology of Lake Malawi. Lake-level fluctuations on the order of hundreds of meters were inferred from dramatic changes in the fossil and sedimentary archives. Many of the fossil diatom assemblages we observed have no analog in modern Lake Malawi. Cyclotelloid diatom species are a major component of fossil assemblages prior to 35. ka, but are not found in significant abundances in the modern diatom communities in Lake Malawi. Salinity- and alkalinity-tolerant plankton has not been reported in the modern lake system, but frequently dominant fossil diatom assemblages prior to 85. ka. Large stephanodiscoid species that often dominate the plankton today are rarely present in the fossil record prior to 31. ka. Similarly, prior to 31. ka, common central-basin aulacoseiroid species are replaced by species found in the shallow, well-mixed southern basin. Surprisingly, tychoplankton and periphyton were not common throughout prolonged lowstands, but tended to increase in relative abundance during periods of inferred deeper-lake environments. A high-resolution lake level reconstruction was generated by a principle component analysis of fossil diatom and wet-sieved fossil and mineralogical residue records. Prior to 70. ka, fossil assemblages suggest that the central basin was periodically a much shallower, more saline and/or alkaline, well-mixed environment. The most significant reconstructed lowstands are . 600. m below the modern lake level and span thousands of years. These conditions contrast starkly with the deep, dilute, dysaerobic environments of the modern central basin. After 70. ka, our reconstruction indicates sustained deeper-water environments were common, marked by a few brief, but significant, lowstands. High amplitude lake-level fluctuations appear related to changes in insolation. Seismic reflection data and additional sediment cores recovered from the northern basin of Lake Malawi provide evidence that supports our reconstruction. © 2010 Elsevier B.V.
cited By 59
Keywords: deep water; diatom; fossil assemblage; fossil record; lake level; paleoclimate; paleoecology; paleohydrology; periphyton; Pleistocene; seismic reflection; East Africa; East African Lakes; Lake Malawi; Bacillariophyta

Lithology and internal structure of the San Andreas fault at depth based on characterization of Phase 3 whole-rock core in the San Andreas Fault Observatory at Depth (SAFOD) borehole - Bradbury, K.K.; Evans, J.P.; Chester, J.S.; Chester, F.M.; Kirschner, D.L. (Earth and Planetary Science Letters, 2011)
We characterize the lithology and structure of the spot core obtained in 2007 during Phase 3 drilling of the San Andreas Fault Observatory at Depth (SAFOD) in order to determine the composition, structure, and deformation processes of the fault zone at 3. km depth where creep and microseismicity occur. A total of approximately 41. m of spot core was taken from three separate sections of the borehole; the core samples consist of fractured arkosic sandstones and shale west of the SAF zone (Pacific Plate) and sheared fine-grained sedimentary rocks, ultrafine black fault-related rocks, and phyllosilicate-rich fault gouge within the fault zone (North American Plate). The fault zone at SAFOD consists of a broad zone of variably damaged rock containing localized zones of highly concentrated shear that often juxtapose distinct protoliths. Two zones of serpentinite-bearing clay gouge, each meters-thick, occur at the two locations of aseismic creep identified in the borehole on the basis of casing deformation. The gouge primarily is comprised of Mg-rich clays, serpentinite (lizardite ± chrysotile) with notable increases in magnetite, and Ni-Cr-oxides/hydroxides relative to the surrounding host rock. The rocks surrounding the two creeping gouge zones display a range of deformation including fractured protolith, block-in-matrix, and foliated cataclasite structure. The blocks and clasts predominately consist of sandstone and siltstone embedded in a clay-rich matrix that displays a penetrative scaly fabric. Mineral alteration, veins and fracture-surface coatings are present throughout the core, and reflect a long history of syn-deformation, fluid-rock reaction that contributes to the low-strength and creep in the meters-thick gouge zones. © 2011 Elsevier B.V.
cited By 61
Keywords: Casing deformation; Cataclasite; Clay gouges; Deformation process; During phase; Fault gouge; Fault zone; Fault-related rocks; Fluid-rock interaction; Host rocks; Internal structure; Lizardite; matrix; Microseismicity; North American; Pacific plates; Protoliths; SAFOD; San Andreas Fault; Serpentinite; Siltstones; Ultrafine; Whole-rock geochemistry; Buildings; Coatings; Creep; Iron ores; Kaolinite; Lithology; Minerals; Observatories; Plates (structural components); Rock drilling; Rocks; Sandstone; Sedimentology; Serpentine; Structural geology; borehole; creep; deformation; drilling; fault gouge; fault zone; host rock; lithology; observatory; Pacific plate; San Andreas Fault; sandstone; seismicity; shale

Late Pleistocene temperature history of Southeast Africa: A TEX86 temperature record from Lake Malawi - Woltering, M.; Johnson, T.C.; Werne, J.P.; Schouten, S.; Sinninghe Damst'e, J.S. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
We present a TEX86-derived surface water temperature record for Lake Malawi that provides the first continuous continental record of temperature variability in the continental tropics spanning the past 74kyr with millennial-scale resolution. Average temperature during Marine Isotope Stage (MIS) 5A was 26.5°C, with a range from 25.7 to 27.3°C, comparable to Holocene temperatures. MIS 4 was a relatively cold period with temperatures generally decreasing from 25.5°C at 68ka to a minimum of 20°C at 60ka, 1.5-2°C colder than the Last Glacial Maximum (LGM). Termination of MIS 4 is characterized by a rapid increase of 3-4°C in only 0.5kyr. Temperatures were relatively stable throughout MIS 3 at the resolution of this study, with an average of 23.8°C and a range from 25.1 to 22.9°C. The lack of millennial-scale temperature variability during MIS 3 suggests that Lake Malawi's documented response to the bipolar seesaw (Brown et al., 2007) is not reflected in its thermal history. Our temperature estimates for the LGM and Holocene are consistent with a previously published TEX86 record from Lake Malawi with a temperature of 22.6°C for the LGM, 25-26°C in the mid Holocene and 25-28 for the late Holocene. In general the present extended TEX86 record indicates that temperature variability in tropical East Africa during late MIS 5 and MIS 4 was as great as that associated with the deglaciation and Holocene. A decrease in Southern Hemisphere insolation between 70 and 60ka may have played an important role in forcing temperatures during MIS 4, but after 60ka other factors, such as the extent of the polar ice sheets, or atmospheric CO2 may have forced temperature in tropical Africa to a greater extent than local summer insolation. © 2010.
cited By 59
Keywords: deglaciation; Holocene; ice sheet; lacustrine deposit; Last Glacial Maximum; marine isotope stage; surface water; temperature inversion; temperature profile; tropical region; water temperature; East Africa; East African Lakes; Lake Malawi

Late Quaternary lake-level changes of Lake El'gygytgyn, NE Siberia - Juschus, O.; Pavlov, M.; Schwamborn, G.; Preusser, F.; Fedorov, G.; Melles, M. (Quaternary Research, 2011)
Lake El'gygytgyn is situated in a 3.6. Ma old impact crater in northeastern Siberia. Presented here is a reconstruction of the Quaternary lake-level history as derived from sediment cores from the southern lake shelf. There, a cliff-like bench 10. m below the modern water level has been investigated. Deep-water sediments on the shelf indicate high lake levels during a warm Mid-Pleistocene period. One period with low lake level prior to Marine Oxygen Isotope Stage (MIS) 3 has been identified, followed by a period of high lake level (10. m above present). In the course of MIS 2 the lake level dropped to -10 m At the end of MIS 2 the bench was formed and coarse beach sedimentation occurred. Subsequently, the lake level rose rapidly to the Holocene level. Changes in water level are likely linked to climate variability. During relatively temperate periods the lake becomes free of ice in summer. Strong wave actions transport sediment parallel to the coast and towards the outlet, where the material tends to accumulate, resulting in lake level rise. During cold periods the perennial lake ice cover hampers any wave activity and pebble-transport, keeping the outlet open and causing the lake level to drop. © 2011 University of Washington.
cited By 23
Keywords: Climate variability; Deep-water sediments; Holocenes; Ice cover; Impact craters; Lake levels; Lake-level changes; Late quaternary; Marine oxygen isotopes; Sediment core; SIBERIA; Siberian Arctic; Strong waves; Wave activity; Anoxic sediments; Climatology; Isotopes; Sedimentology; Water levels; Lakes; ice cover; lake level; oxygen isotope; Quaternary; sediment core; sediment transport; sedimentation; water level; Chukchi; Elgygytgyn Lake; Russian Federation; Serbia

Late Quaternary stratigraphic analysis of the Lake Malawi Rift, East Africa: An integration of drill-core and seismic-reflection data - Lyons, R.P.; Scholz, C.A.; Buoniconti, M.R.; Martin, M.R. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
Lake Malawi contains a long continuous sedimentary record of climate change in the southern hemisphere African tropics. We develop a stratigraphic framework of this basin over the last . 150 ka by integrating several vintages of seismic-reflection data with recently acquired drill cores. In the seismic-reflection data set, we document three lake-level cycles where progradational delta seismic facies and erosional truncation surfaces mark the basal boundary of each sequence. The clinoform packages and their down-dip, time-equivalent surfaces can be mapped throughout each basin, where each major lowstand surface was followed by a transgression and highstand. On several occasions, lake level dropped as much as 500 m below present lake level (BPLL) in the North Basin and 550 m BPLL in the Central Basin, resulting in a 97% reduction of water volume and 89% reduction of water surface area relative to modern conditions. Evidence for these lake-level fluctuations in the drill cores includes major changes in saturated bulk density, natural gamma ray values, and total organic carbon. During lowstands, density values doubled, while total organic carbon values dropped from . 5% to 0.2%. Coarse-grained sediment and organic matter flux into the basin were higher during transgressions, when precipitation, runoff, sediment supply, and nutrient input were high. This sedimentation pattern is also observed in seismic-reflection profiles, where coarse-grained seismic facies occur at the bases of sequences, and in the drill-core data where the highest total organic carbon values are observed immediately above lowstand surfaces. © 2009 Elsevier B.V.
cited By 93
Keywords: data set; lake level; paleoclimate; sedimentary sequence; sedimentation rate; seismic reflection; seismic stratigraphy; Southern Hemisphere; surface water; total organic carbon; East Africa; East African Lakes; Lake Malawi

Lateral transport of suevite inferred from 3D shape-fabric analysis: Evidence from the Ries impact crater, Germany - Meyer, C.; J'ebrak, M.; St{offler, D.; Riller, U. (Bulletin of the Geological Society of America, 2011)
The transport mechanism of suevite particles during impact cratering is poorly understood and was studied at the 15 Ma Ries crater in southern Germany. Two emplacement modes of suevite deposits are generally discussed: (1) fallback of plume material into the crater and its periphery upon collapse of an ejecta plume; and (2) horizontal transport of ejected material, akin to emplacement of pyroclastic deposits erupting from volcanic centers. In order to differentiate between the two emplacement modes of suevite deposition, we analyzed the shape fabrics of suevite components from two localities outside the Ries crater by fitting shape-fabric ellipsoids to measured shape-fabric ellipses and by applying high-resolution, X-ray- computed tomography to analyze the threedimensional shape and orientation of the suevite particles. We show that the preferred orientation of long axes of elongate particles is disposed either radially or concentrically with respect to the crater center. Our observations indicate that suevite material was not only derived from an ejecta plume, but was transported by lateral flow under viscous conditions upon fallback. This flow regime resembles that known from pyroclastic flows. © 2011 Geological Society of America.
cited By 20

Effect of relative permeability characteristics and gas/water flow on gas-hydrate saturation distribution - Behseresht, J.; Bryant, S. (Proceedings - SPE Annual Technical Conference and Exhibition, 2011)
The descent of the base of gas hydrate stability zone (BGHSZ) through gas accumulated in a sediment is analyzed. A mechanistic model enables estimating hydrate saturation from initial distribution of gas phase saturation in sediment with known grain size distribution. The initial gas phase saturation is estimated from the profile of capillary entry-pressure with depth. The latter is estimated from grain size variations. A mechanistic model is proposed to determine the relative rates of methane and water transport into the HSZ during hydrate formation. The gas accumulation is assumed to be isolated so that methane transport occurs only within it. If water transport occurs only by co-current flow of gaseous and aqueous phases up to the hydrate stability zone (HSZ), it is not possible to create large hydrate saturations from large initial gas saturations due to limitations on water flux imposed by typical relative permeability curves. Thus the observed large hydrate saturations, such as that observed in Mt. Elbert, Alaska and Mallik, NW Territories and deep Indian Ocean, above the BGHSZ suggest another form of water flow: water moves down through accumulated hydrate from above. This requires the aqueous phase to remain connected within the hydrate-bearing sediment. The ratio of aqueous phase permeability in the hydrate-bearing sediment to the aqueous phase relative permeability at residual gas saturation determines hydrate saturation profile. The model is validated against field data from a hydrate-bearing sand unit in Mt. Elbert. Copyright 2011, Society of Petroleum Engineers.
cited By 3
Keywords: Flow of water; Gas permeability; Gases; Grain size and shape; Hydration; Methane; Sediments; Capillary entry pressure; Gas hydrate saturations; Gas hydrate stability zones; Grain size distribution; Hydrate bearing sediments; Relative permeability; Relative permeability curves; Residual gas saturation; Gas hydrates

Hotspot: The Snake River geothermal drilling project - An overview - Shervais, J.W.; Evans, J.P.; Christiansen, E.J.; Liberty, L.M.; Blackwell, D.D.; Glen, J.M.; Kessler, J.E.; Potter, K.E.; Jean, M.M.; Sant, C.J.; Freeman, T.G. (Transactions - Geothermal Resources Council, 2011)
The Snake River volcanic province (SRP) overlies a thermal anomaly that extends deep into the mantle; it represents one of the highest heat flow provinces in North America, and an area with the highest calculated geothermal gradients. This makes the SRP one of the potentially highest producing geothermal districts in the United States. Elevated heat flow is typically highest along the margins of the topographic Snake River Plain and lowest along the axis of the plain, where thermal gradients are suppressed by the Snake River aquifer. Beneath this aquifer, however, thermal gradients rise again and may tap even higher heat flows associated with the intrusion of mafic magmas into a geophysically-imaged mid-crustal sill complex. The primary goal of this project is to evaluate geothermal potential in three distinct settings: (1) the high sub-aquifer geothermal gradient associated with the intrusion of mafic magmas and the release of crustal fluids from the associated wall rocks, (2) the valley-margin settings where surface heat flow may be driven by the up-flow of hot fluids along buried caldera ring-fault complexes, and (3) a more traditional fault-bounded basin with thick sedimentary cover. All settings are found within the central or western Snake River Plain and represent previously untested targets for geothermal exploration. Our first drill site tests the extent of geothermal resources along the axis of the plain, beneath the Snake River aquifer, in an area where elevated groundwater temperatures imply a significant flux of conductive or advective heat flow from below. Our second drill site assesses the geothermal potential of up-flow zones along a buried caldera margin, in an area of known geothermal potential (Twin Falls geothermal district). Further studies will include seismic reflection-refraction surveys, gravity-magnetic surveys, and downhole geophysical logs.
cited By 13
Keywords: Geothermal; Hot spot; Idaho; Rhyolite; Snake river plains; Yellowstones; Aquifers; Basalt; Drills; Geothermal fields; Geothermal wells; Heat transfer; Innovation; Rivers; Thermal gradients; Geothermal prospecting

Late Quaternary (24-10 ka BP) environmental history of the Neotropical lowlands inferred from ostracodes in sediments of Lago Pet'en Itz'a, Guatemala - P'erez, Liseth; Frenzel, Peter; Brenner, Mark; Escobar, Jaime; Hoelzmann, Philipp; Scharf, Burkhard; Schwalb, Antje (Journal of Paleolimnology, 2011)
We inferred late Pleistocene and early Holocene (24-10 ka BP) environmental conditions in and around Lago Pet'en Itz'a,Guatemala from ostracode remains in the lake sediments. Multivariate statistics were run on autecological information for 29 extant ostracode species collected in 63 aquatic ecosystems on the Yucat'an Peninsula along a steep, increasing NW-S precipitation gradient and across a large altitudinal range. Conductivity and water depth are the most important factors that shape ostracode communities. Transfer functions were developed and applied to fossil ostracode assemblages in a 76-m sediment core (PI-6, 85 ka) taken in 71 m of water from Lago Pet'en Itz'a, to infer past shifts in conductivity and water level. Results suggest climate was cold and wet during the Last Glacial Maximum (LGM). Alternating dry and wet conditions characterized the deglacial. Early Holocene climate was warmer and wetter. The LGM was characterized by low ostracode species richness (4 spp.) and abundance (<940 valves g-1), dominance of benthic over nektobenthic taxa, abundant Physocypria globula, conductivity as low as 190 μS cm-1, and clay-rich sediments with relatively high total organic carbon and low C/N ratios (<14), suggesting relatively deeper water at the core site associated with abundant precipitation. Greatest water depth at the core site during the LGM occurred late in the period and was 50 m. The deglacial was characterized by drier conditions, higher ostracode species richness (6 spp.) and abundances up to 18,115 valves g-1, dominance of nektobenthic species, and presence of shallow-water and littoral-zone indicators such as Heterocypris punctata and Strandesia intrepida, conductivity up to 550 μS cm-1, C/N ratios as high as 37, and gypsum deposition. Lowest inferred lake depth at the core site during the deglacial was 20 m. The early Holocene was characterized by high numbers of ostracode remains, up to 25,500 valves g-1, and the presence of L. opesta and P. globula. Cytheridella ilosvayi was absent from late Pleistocene sediments, suggesting it colonized northern Central America during the Holocene. © 2011 Springer Science+Business Media B.V.
Keywords: Guatemala [Central America]; Lake Peten Itza; Peten; Heterocypris punctata; Ostracoda; Physocypria; abundance; aquatic ecosystem; benthos; carbon; community structure; crustacean; deglaciation; dominance; environmental change; environmental conditions; Holocene; intertidal environment; lacustrine deposit; Last Glacial Maximum; lowland environment; multivariate analysis; Neotropical Region; nitrogen; organic carbon; precipitation intensity; sediment analysis; shallow water; species richness; transfer function; water depth

High-frequency Born synthetic seismograms based on coupled normal modes - Pollitz, F. (Geophysical Journal International, 2011)
High-frequency and full waveform synthetic seismograms on a 3-D laterally heterogeneous earth model are simulated using the theory of coupled normal modes. The set of coupled integral equations that describe the 3-D response are simplified into a set of uncoupled integral equations by using the Born approximation to calculate scattered wavefields and the pure-path approximation to modulate the phase of incident and scattered wavefields. This depends upon a decomposition of the aspherical structure into smooth and rough components. The uncoupled integral equations are discretized and solved in the frequency domain, and time domain results are obtained by inverse Fourier transform. Examples show the utility of the normal mode approach to synthesize the seismic wavefields resulting from interaction with a combination of rough and smooth structural heterogeneities. This approach is applied to an 4 Hz shallow crustal wave propagation around the site of the San Andreas Fault Observatory at Depth (SAFOD). © The Author Geophysical Journal International © 2011 RAS.
cited By 2
Keywords: Aspherical; Coupled integral equations; Earth models; Earthquake source; Frequency domains; Full-waveforms; High frequency HF; Inverse Fourier transforms; Normal modes; San Andreas Fault; Seismic wavefields; Structural heterogeneity; Synthetic seismogram; Time domain; Wavefields; Born approximation; Seismology; Three dimensional; Wave propagation; Integral equations; Fourier transform; seismic source; seismic wave; synthetic seismogram; wave field; wave propagation; waveform analysis

Fracture distribution in slimholes drilled for project hotspot: The Snake River Geothermal Drilling Project and the implications for fluid flow - Kessler, J.A.; Evans, J.P. (Transactions - Geothermal Resources Council, 2011)
Project Hotspot: The Snake River Geothermal Drilling Project is an effort to determine the potential for geothermal energy development in the central Snake River Plain, Idaho. Few data regarding the lithologies or distribution of fractures in the vertical profile are available in the central Snake River Plain so drilling provides key data in the vertical profile to help determine the geothermal potential. Three slimhole boreholes are drilled at the Kimama, Kimberly, and Mountain Home sites to depths around 2000 m. Observations of the core will be compared with data in the complete suites of borehole geophysical logs acquired in the holes. The direct observation of lithology and fractures will be used as a constraint on geophysical data to confirm interpretations of mechanical and flow properties of the rocks. Final analysis will then describe the implications for fluid flow. Thin section and permeability test results will be used to evaluate the changes in potential fracture flow characteristics with depth. This effort will provide direct observation of samples at depth and will provide an example of a workflow to connect rock core properties, wireline log responses, and flow properties. Wireline logs can help us understand basic rock properties and the relationships between fracture distribution and rock type. Critical to the development of geothermal systems is the porosity and the potential for fluid flow in the subsurface. The volcanic nature of the formations means there is little primary permeability to contribute to fluid flow. Fractures are the primary mode of fluid transport so the analysis of fractures and the level of saturation in fracture zones are necessary to evaluate the geothermal potential. Preliminary analyses of the core show that fractures exhibit a series of alteration phases, including amygduloidal fine-grained calcite. Despite the nearly zero porosity of the matrix in the rocks, mineralizing fluids appear to form connected pathways in the rock. The borehole geophysical data show where fracture zones exist and whether the porosity produced by the fractures is sufficient for geothermal development.
cited By 3
Keywords: Alteration phasis; Energy development; Flow properties; Fluid transport; Fracture characterization; Fracture distributions; Fracture flow; Fracture zone; Geophysical data; Geophysical logs; Geothermal; Geothermal development; Geothermal drilling; Geothermal potential; Geothermal systems; Hot spot; Log response; Mineralizing fluids; Permeability test; Preliminary analysis; Rock core; Rock properties; Rock types; Slimhole; Snake River; Snake river plains; Thin section; Vertical profile; Wireline logs; Boreholes; Boring; Carbonate minerals; Flow of fluids; Geothermal fields; Geothermal prospecting; Geothermal wells; Lithology; Mechanical permeability; Mechanical properties; Porosity; Rivers; Rocks; Transport properties; Well logging; Fracture

High resolution reflection seismics integrated with deep dril hole data in Outokumpu, Finland - Heinonen, Suvi; Kukkonen, Ilmo T.; Heikkinen, Pekka J.; Schmitt, Douglas R. (Special Paper of the Geological Survey of Finland, 2011)
The Outokumpu area, located in eastern Finland, is well known for its Precambrian Cu-Zn-Co-Ni-Ag-Au sulphide deposits hosted by ophiolite-derived altered ultramafic rocks. In 2004-2005, a 2.5 km deep research borehole was drilled on the south-east side of the main ore belt. The ophiolite-related Outokumpu-assemblage rocks were penetrated at depths of 1.3-1.5 km. The other main lithologies observed in the Outokumpu Deep Drill Hole were mica schist with biotite-gneiss layers (upper 2 km) underlain by pegmatitic granite. In May 2006, high resolution reflection seismic data with 4 m receiver spacing were acquired at the drilling site along two crooked lines to further refine the geological model of the area. The Outokumpu Deep Drilling Project provided an excellent opportunity to correlate high resolution seismic data with drilling results. The main emphasis in the processing of the reflection seismic data was put on static corrections. Substantial topographic variation and a significant velocity contrast between the glacially deposited overburden and the bedrock caused severe travel time variations in the near surface. Results achieved using static corrections carried out with the standard refraction method and using a tomographic approach were compared. Sonic velocity and density logs were used to calculate acoustic impedances and a synthetic seismogram, and theoretical calculations were compared with reflectivity observed in the seismic section. The results indicate that the host rocks of the Outokumpu type deposits are bright reflector packages that can be observed with reflection seismic techniques. The pegmatitic granite shows only weak reflection contrast with the mica schist, but it can be delineated as homogeneous, transparent domains, whereas the mica schist is internally more heterogeneous. A fracture zone at the depth of 967 m can be observed as a sharp sub-horizontal reflector.
Keywords: Finland; Ita Suomen; Outokumpu; borehole; data processing; deep drilling; granite; host rock; lithology; metamorphic rock; ore deposit; pegmatite; seismic data; seismic reflection; seismogram; well logging

Erratum: Intrabasin paleoearthquake and quiescence correlation of the late Holocene Dead Sea (Journal of Geophysical Research (2011) (116) DOI: 10.1029/2011JB008870) - Kagan, E.; Stein, M.; Agnon, A.; Neumann, F. (Journal of Geophysical Research: Solid Earth, 2011)
cited By 6

Evidence of transient increases of fluid pressure in SAFOD phase III cores - Mittempergher, S.; Di Toro, G.; Gratier, J.P.; Hadizadeh, J.; Smith, S.A.F.; Spiess, R. (Geophysical Research Letters, 2011)
The San Andreas Fault Observatory at Depth (SAFOD) in Parkfield, central California, has been drilled through a fault segment that is actively deforming through creep and microearthquakes. Creeping is accommodated in two fault strands, the Southwest and Central Deforming Zones, embedded within a damaged zone of deformed shale and siltstone. During drilling, no pressurized fluids have been encountered, even though the fault zone acts as a permeability barrier to fluid circulation between the North American and Pacific plates. Microstructural analysis of sheared shales associated with calcite and anhydrite-bearing veins found in SAFOD cores collected at 1.5m from the Southwest Deforming Zone, suggests that transient increases of pore fluid pressure have occurred during the fault activity, causing mode I fracturing of the rocks. Such build-ups in fluid pressure may be related to permeability reduction during fault creep and pressure-solution processes, resulting in localized failure of small fault zone patches and providing a potential mechanism for the initiation of some of the microearthquakes registered in the SAFOD site. Copyright © 2011 by the American Geophysical Union.
cited By 29
Keywords: Carbonate minerals; Creep; Drilling fluids; Structural geology; California; Damaged zones; Deforming zone; Fault activity; Fault creep; Fault strands; Fault zone; Fluid circulation; Fluid pressures; Localized failure; Micro-earthquakes; Microstructural analysis; North American; Pacific plates; Permeability barriers; Permeability reduction; Pore fluid pressure; Potential mechanism; San Andreas Fault; Siltstones; Solution process; Shale; creep; fault zone; fluid pressure; microearthquake; microstructure; North American plate; Pacific plate; permeability; San Andreas Fault; shale; siltstone; California; Parkfield; United States

Fault rocks from the SAFOD core samples: Implications for weakening at shallow depths along the San Andreas Fault, California - Holdsworth, R.E.; Diggelen, E.W.E.; Spiers, C.J.; Bresser, J.H.P.; Walker, R.J.; Bowen, L. (Journal of Structural Geology, 2011)
The drilling of a deep borehole across the actively creeping Parkfield segment of the San Andreas Fault Zone (SAFZ), California, and collection of core materials permit direct geological study of fault zone processes at 2-3 km depth. The three drill cores sample both host and fault rocks and pass through two currently active, narrow (1-2 m wide) shear zones enclosed within a broader (ca. 240 m wide) region of inactive foliated gouges. The host rocks preserve primary sedimentary features and are cut by numerous minor faults and small, mainly calcite-filled veins. The development of Fe-enriched smectitic phyllosilicate networks following cataclasis is prevalent in the presently inactive foliated gouges of the main fault zone and in minor faults cutting clay-rich host rocks. Calcite, anhydrite and minor smectitic phyllosilicate veins are interpreted to have formed due to local fluid overpressuring events prior to, synchronous with and after local gouge development. By contrast, the active shear zone gouges lack mineral veins (except as clasts) and contain numerous clasts of serpentinite. Markedly Mg-rich smectitic phyllosilicates are the dominant mineral phases here, suggesting that the fault zone fluids have interacted with the entrained serpentinites. We propose that weakening of the SAFZ down to depths of at least 3 km can be attributed to the pervasive development of interconnected networks of low friction smectitic phyllosilicates and to the operation of stress-induced solution-precipitation creep mechanisms. © 2010 Elsevier Ltd.
cited By 142
Keywords: Fault zone; Phyllosilicate; SAFOD; San Andreas Fault; Smectites; Calcite; Carbonate minerals; Clay minerals; Core drilling; Core samples; Fluids; Sedimentary rocks; Silicate minerals; Structural geology; active fault; core analysis; creep; deformation mechanism; drilling; fault zone; foliation; overpressure; phyllosilicate; San Andreas Fault; shear zone; smectite; stress change; stress field; California; Parkfield; San Andreas; United States

Fish fossils as paleo-indicators of ichthyofauna composition and climatic change in Lake Malawi, Africa - Reinthal, P.N.; Cohen, A.S.; Dettman, D.L. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
Numerous biological and chemical paleorecords have been used to infer paleoclimate, lake level fluctuation and faunal composition from the drill cores obtained from Lake Malawi, Africa. However, fish fossils have never been used to examine changes in African Great Lake vertebrate aquatic communities nor as indicators of changing paleolimnological conditions. Here we present results of analyses of a Lake Malawi core dating back 144ka that describe and quantify the composition and abundance of fish fossils and report on stable carbon isotopic data (δ13C) from fish scale, bone and tooth fossils. We compared the fossil δ13C values to δ13C values from extant fish communities to determine whether carbon isotope ratios can be used as indicators of inshore versus offshore pelagic fish assemblages. Fossil buccal teeth, pharyngeal teeth and mills, vertebra and scales from the fish families Cichlidae and Cyprinidae occur in variable abundance throughout the core. Carbon isotopic ratios from numerous fish fossils throughout the core range between -7.2 and -27.5%, similar to those found in contemporary Lake Malawi benthic and pelagic fish faunas. These results are the first paleo-record of fish fossils from a Lake Malawi sediment core and the first reported δ13C values from Lake Malawi fish fossils. This approach provides a new methodology and framework for interpreting pelagic versus inshore fish faunas, lake level fluctuations and the evolution of the Lake Malawi fish assemblages. © 2010 Elsevier B.V.
cited By 17
Keywords: carbon isotope; cichlid; climate change; cyprinid; fossil assemblage; fossil record; ichthyofauna; lake level; paleoclimate; paleolimnology; pelagic fish; sediment core; stable isotope; Africa; East African Lakes; Lake Malawi; Cichlidae; Cyprinidae; Cypriniformes; Vertebrata

Fluid inclusions in the Outokumpu Deep Drill Core: Implications for palaeofluid evolution and the composition of modern deep saline fluids - Piribauer, Christoph J.; Sindern, Sven; Meyer, F. Michael; Vennemann, Torsten W.; Prochaska, Walter (Special Paper of the Geological Survey of Finland, 2011)
Fluid inclusions in quartz veins in the Outokumpu Deep Drill Core are characterised by high salinities and high homogenisation temperatures in excess of 330 °C. In addition to an aqueous phase, fluid inclusions also contain gaseous phases such as CO2 and CH4. The cation ratios of the dissolved salts are higher than seawater, with Li/Na ratios indicating the influence of magmatic water in deeper parts of the drill hole. Stable isotope (δD, δ18O) signatures point to a metamorphic origin of the palaeofluids. Deep groundwaters in the Outokumpu crystalline basement deviate significantly from fluid inclusions in their stable isotope ratios, which plot to the right of the global meteoric water line in a δD, δ18O diagram. This suggests that they may have formed as a mixture of meteoric and saline waters. In addition, Cl/Br and Na/Br ratios point to chemical exchange with the host rocks. Many models have been proposed to account for the enhanced salinity of deep groundwaters and the shift in the stable isotopes, but our data indicate that the saline fluids are primarily derived through water-rock interaction. The role of fluid inclusions as important contributors to the saline fluids is not supported.
Keywords: Finland; Ita Suomen; Outokumpu; fluid inclusion; groundwater; host rock; isotopic ratio; meteoric water; oxygen isotope; quartz vein; salinity; stable isotope; water-rock interaction

Estimation of q from zero-offset vsp data in gas hydrate-bearing zone - Byun, J.; Yoo, D.-G.; Lee, H.-Y. (Geosystem Engineering, 2011)
Q-factor (or Q) that quantifies the attenuation, the intrinsic property of the material, is a very important required factor in extracting useful subsurface material properties such as lithological information, porosity, permeability, viscosity, and the degree of the saturation from the seismic data. When seismic energy propagates through the gas hydrate-bearing zone and a free gas layer below it, the considerable attenuation occurs and affects the amplitude and wavelet shape of recorded seismic data. Thus Q- factor extracted from seismic data can be used to locate the gas hydrate bearing zone and estimate its reserves. The spectral-ratio method has been widely used in computing the frequency-independent Q's from the zero-offset VSP data because of its ease and fastness. We developed a module of the spectral ratio method, and applied it to the synthetic zero-offset VSP data set and field zero-offset VSP data set. The field data were acquired at Mallik 3L-38 gas hydrate research well in Canada. The Q-factors calculated from the synthetic zero-offset VSP data using the spectral ratio method approached closer to the true values for the medium with low Q-factor than high Q-factor. The changes in the Q-factors extracted from the Mallik zero-offset data using the spectral ratio method agreed well with the boundaries of the layers, including gas hydrate zone, depicted in a reflection image. © 2011 Taylor & Francis Group, LLC.
cited By 1

Geogas transport in fractured hard rock - Correlations with mining seismicity at 3.54km depth, TauTona gold mine, South Africa - Lippmann-Pipke, J.; Erzinger, J.; Zimmer, M.; Kujawa, C.; Boettcher, M.; Heerden, E.V.; Bester, A.; Moller, H.; Stroncik, N.A.; Reches, Z. (Applied Geochemistry, 2011)
An on-site gas monitoring study has been conducted in the framework of an earthquake laboratory (The International NELSAM-DAFGAS projects) at the TauTona gold mine, South Africa. Five boreholes up to 60m long were drilled at 3.54km depth into the highly fractured Pretorius Fault Zone and instruments for chemical and seismic monitoring installed therein. Over the span of 4years sensitive gas monitoring devices were continuously improved to enable the direct observation of geogas concentration variations in the DAFGAS borehole. The major gas concentrations are constant and air-like with about 78% N2, 21% O2, 1% Ar. The geogas components CO2, CH4, He and H2 show the most interesting trends and variations on the minute-by-minute basis and significantly correlate with seismic data, while the 222Rn activity remains constant. Time series and cross correlation analysis allow the identification of different gas components (geogas and tunnel air) and the identification of two processes influencing the borehole gas composition: (1) pumping-induced tunnel air breakthrough through networks of initially water-saturated fault fractures; and (2) seismicity induced permeability enhancement of fault fractures to above ∼5×10-10m2. The current set-up of the gas monitoring system is sensitive enough to quantify the resulting geogas transport during periods of intense blasting activities (including recorded blasts with seismic moment ≤1×109Nm, located within 1000m of the cubby) and, it is suggested, also during induced earthquakes, a final goal of the project. © 2011 Elsevier Ltd.
cited By 24
Keywords: Concentration variation; Cross-correlation analysis; Fault zone; Gas component; Gas compositions; Gas concentration; Gas monitoring; Gas monitoring systems; Hard rocks; Permeability enhancement; Seismic datas; Seismic moment; Seismic monitoring; South Africa; Boreholes; Carbon dioxide; Earthquakes; Fracture; Gas detectors; Gold; Gold mines; Time series; Time series analysis; Gases; borehole; correlation; fault zone; fractured medium; gas transport; gold mine; hard rock; induced seismicity; mining industry; radon isotope; seismic data; time series; South Africa

High pore pressure, or its absence, in the San Andreas fault - Wang, C.-Y. (Geology, 2011)
High pore pressure in the San Andreas fault (California) was hypothesized to explain the prevailing weakness of the fault and may have major implications on the mechanics of earthquakes. However, no evidence of high pore pressure was found in the latest drilling into the San Andreas fault (SAFOD: San Andreas Fault Observatory at Depth) in central California (Zoback et al., 2010). If widely applicable, this result would impact our understanding of earthquake mechanisms on this and other active faults around the world. Here, however, I show that the available evidence from the latest SAFOD drilling may not be sufficient to reject the high pore-pressure hypothesis, and that definite knowledge of pore pressure in the fault zone may require long-term monitoring at the SAFOD site. The inference may also be useful for interpreting results from drilling projects on other active faults. © 2011 Geological Society of America.
cited By 10
Keywords: Active fault; California; Drilling projects; Fault zone; Long term monitoring; San Andreas Fault; Earthquakes; Strike-slip faults; Pore pressure; active fault; earthquake mechanism; fault zone; pore pressure; San Andreas Fault; California; San Andreas; United States

High resolution reflection seismic investigations for defining ICDP drilling sites in the Scandinavian Caledonides - Hedin, P.; Juhlin, C.; Gee, D. G.; Malehmir, A. (AGH University of Science and Technology, 2011)
The Caledonides were once a mountain range of Himalayan dimensions, but are today eroded down to mid crustal levels. In the Scandes, major allochthons are inferred to have been transported hundreds of kilometers from subduction zones along the margin of the Paleozoic Baltica continent onto the Baltoscandian platform. A proposal has been sent to the International Continental Scientific Drilling Program (ICDP) to drill through the long transported allochthons into the Baltica basement. During the summer of 2010 a seismic reflection survey was acquired in the Åre region of western Sweden as a preparation for the COSC deep drilling project. The COSC project will study the fossilized orogenic processes that governed the formation of the Scandinavian Caledonides and test different hypothesis related to orogenesis. The seismic section correlates well with older surveys made in the area, but it also provides a much higher resolution image of the upper few kilometers of the crust. The subsurface is extremely reflective and we interpret a basal d'ecollement, which is one of the main targets with the drilling, to be located at a depth of about 1.5 to 2 km in the eastern parts of the section.

Geomagnetic field intensity and inclination records from Hawaii and the R'eunion Island: Geomagnetic implications - Laj, Carlo; Kissel, Catherine; Davies, Christopher; Gubbins, David (Physics of the Earth and Planetary Interiors, 2011)
We report on new paleointensity and inclination records obtained in Hawaii from 386 samples drilled in 137 subaerial flows of the HSDP2 long basaltic core that we have combined in a composite record with the other Hawaiian results to produce a unique and accurate lava record of absolute geomagnetic field intensity and inclination at Hawaii for the last 405kyr. These data are considered together with published results from La R'eunion Island, for about the same time period in order to compare them to model results. In Hawaii, when recognized excursional periods are omitted, the average VADM (VDM) value is about 8.2×(8.4)×1022Am2 and the inclination is on the average 29.8°, i.e. about 6° shallower than the expected value at this location (GAD value). In the R'eunion Island, we selected published results in which both inclination and intensities values are obtained using modern methods and strict criteria. The average VADM (VDM) is 9.4±2.3 (8.7±2.3)1022Am2 and the average inclination value (when transitional data are ignored) is -44.4±2.4°, about 7° steeper than the GAD value. These results, compared with model intensities predicted by dynamo solutions that incorporate lateral variations in core-mantle boundary heat-flow derived from seismic tomography, are too high for both localities, but they decrease as the amplitude of thermal boundary anomalies increases. With strong boundary heat-flow, the model inclination anomaly at Hawaii fits with the data but at La R'eunion, model inclination anomalies have the wrong sign. This comparison indicates that strong boundary heat-flow anomalies give the best fit to the data and that future improvements will be obtained by proportionally increasing both the Rayleigh number and the amplitude of heat-flow variations. © 2011 Elsevier B.V.
Keywords: Hawaii [United States]; United States; Calluna vulgaris; Electric generators; Seismology; Best fit; Core-mantle boundary; Expected values; Geomagnetic fields; Geomagnetic modeling; Hawaii; Heat-flow; Lateral variations; Model results; Paleointensity; Rayleigh number; Seismic tomography; Subaerial flows; Thermal boundary; Time-periods; amplitude; core-mantle boundary; geomagnetic field; heat flow; numerical model; Rayleigh number; seismic tomography; Geomagnetism

Erratum for Trace element diffusion and viscous flow in potassium-rich trachytic and phonolitic melts, authors Harald Behrens and Matthias Hahn, published in Chemical Geology 259 (2009) 63-77 - Behrens, Harald (Chemical Geology, 2011)

Helium measurements of pore fluids obtained from the San Andreas Fault Observatory at Depth (SAFOD, USA) drill cores - Ali, S.; Stute, M.; Torgersen, T.; Winckler, G.; Kennedy, B.M. (Hydrogeology Journal, 2011)
4He accumulated in fluids is a well established geochemical tracer used to study crustal fluid dynamics. Direct fluid samples are not always collectable; therefore, a method to extract rare gases from matrix fluids of whole rocks by diffusion has been adapted. Helium was measured on matrix fluids extracted from sandstones and mudstones recovered during the San Andreas Fault Observatory at Depth (SAFOD) drilling in California, USA. Samples were typically collected as subcores or from drillcore fragments. Helium concentration and isotope ratios were measured 4-6 times on each sample, and indicate a bulk 4He diffusion coefficient of 3.5 ± 1.3 × 10-8 cm2 s-1 at 21°C, compared to previously published diffusion coefficients of 1.2 × 10-18 cm2 s-1 (21°C) to 3.0 × 10-15 cm2 s-1 (150°C) in the sands and clays. Correcting the diffusion coefficient of 4Hewater for matrix porosity ( 3%) and tortuosity ( 6-13) produces effective diffusion coefficients of 1 × 10-8 cm2s-1 (21°C) and 1 × 10-7 (120°C), effectively isolating pore fluid 4He from the 4He contained in the rock matrix. Model calculations indicate that <6% of helium initially dissolved in pore fluids was lost during the sampling process. Complete and quantitative extraction of the pore fluids provide minimum in situ porosity values for sandstones 2.8 ± 0.4% (SD, n = 4) and mudstones 3.1 ± 0.8% (SD, n = 4). © 2010 Springer-Verlag.
cited By 4
Keywords: concentration (composition); diffusion; fluid dynamics; geoaccumulation; helium; hydrogeology; isotopic ratio; porosity; tortuosity; tracer

Geothermal studies of the Outokumpu Deep Drill Hole, Finland: Vertical variation in heat flow and palaeoclimatic implications - Kukkonen, Ilmo T.; Rath, Volker; Kivek{as, Liisa; Šafanda, Jan; Čermak, Vladimir (Physics of the Earth and Planetary Interiors, 2011)
Detailed geothermal studies of deep drill holes provide insights to heat transfer processes in the crust, and allow separation of different factors involved, such as palaeoclimatic and structural conductive effects as well as advective fluid flow effects. We present high resolution geothermal results of the 2516m deep Outokumpu Deep Drill Hole in eastern Finland drilled in 2004-2005 into a Palaeoproterozoic formation with metasedimentary rocks, ophiolite-derived altered ultramafic rocks and pegmatitic granite. The down-hole temperatures have been logged five times after end of drilling and extend to day 948 after drilling. The hole is completely cored (79% core coverage) and thermal conductivity measurements were done at 1m intervals. The geothermal results on temperature gradient, thermal conductivity and heat flow density yield an exceptionally detailed data set and indicate a significant vertical variation in gradient and heat flow density. Heat flow density increases from about 28 - 32mWm-2 in the uppermost 1000m to 40-45mWm-2 at depths exceeding 2000m. The estimated undisturbed surface heat flow value is 42mWm-2. We present results on forward and inverse transient conductive models which suggest that the vertical variation in heat flow can mostly be attributed to a palaeoclimatic effect due to ground surface temperature (GST) variations during the last 100,000years. The modeling suggests that the average GST was about -3 to -4°C during the Weichselian glaciation. Holocene GST values are within ±2° from the present average GST in Outokumpu (5°C). The topographic hydraulic heads and hydraulic conductivity of crystalline rocks are low which suggests that advective heat transfer in the formation is not significant. The slow replacement of fresh flushing water by saline formation fluids is observed in the hole, but it does not generate significant thermal disturbances in the logs. On the other hand, free sluggish thermal convection is present in the large diameter (22cm) borehole, and temperature variations in the range of few mK to 0.01K occur over times of minutes to tens of minutes. Theory suggests that convection cells are about as tall as the drill hole diameter, and thus the free convection is expected to generate only local thermal 'noise' not affecting the general geothermal results. © 2011 Elsevier B.V.
Keywords: Baltic Shield; Finland; Calluna vulgaris; Boreholes; Climatology; Crystalline rocks; Flow of fluids; Glacial geology; Heat transfer; Hydraulics; Rock drills; Saline water; Thermal conductivity; Thermal logging; Conductive effects; Conductive model; Convection cell; Data sets; Drill hole; Eastern Finland; Fennoscandian Shields; Finland; Fluid flow effect; Geothermal gradients; Ground surface temperature; Heat flow density; Heat flows; Heat transfer process; High resolution; Holocenes; Hydraulic heads; Inverse transient; Large diameter; Metasedimentary rocks; Paleoclimatology; Saline formation; Surface heat flow; Temperature gradient; Temperature variation; Thermal conductivity measurements; Thermal convections; Thermal disturbance; Ultramafic rocks; Vertical variation; drilling; geothermal gradient; granite; heat flow; heat transfer; hydraulic conductivity; hydraulic head; paleoclimate; Proterozoic; thermal conductivity; thermal convection; ultramafic rock; Geothermal energy

Geothermal studies of the Outokumpu Deep Drill Hole - Kukkonen, Ilmo T.; Rath, Volker; Kivek{as, Liisa; Šafanda, Jan; Čermak, Vladimir (Special Paper of the Geological Survey of Finland, 2011)
We present high resolution geothermal results from the 2516 m deep Outokumpu Deep Drill Hole in eastern Finland drilled in 2004-2005 into a Palaeoproterozoic formation with metasedimentary rocks, ophiolite-derived altered ultramafic rocks and pegmatitic granite. Detailed geothermal studies of deep drill holes provide insights into heat transfer processes in the crust, and allow the separation of different factors involved, such as palaeoclimatic and structural conductive effects as well as advective fluid flow effects. The down-hole temperatures of the Outokumpu hole have been logged five times following the end of drilling and extend to day 948 after drilling. The hole was continuously cored (79% core coverage) and thermal conductivity was measured at 1-m intervals. The temperature gradient, thermal conductivity and heat flow density results yield an exceptionally detailed geothermal data set and indicate significant vertical variation in the gradient and heat flow density. This result has important implications for correcting shallow (<1 km) heat flow data in the Fennoscandian Shield. The heat flow density was determined to increase from about 28-32 mW m-2 in the uppermost 1000 m to 40-45 mW m-2 at depths exceeding 2000 m. The estimated undisturbed surface heat flow value was 42 mWm-2. We present results based on inverse transient conductive models that suggest that the vertical variation in heat flow can mostly be attributed to a palaeoclimatic effect due to ground surface temperature (GST) variations during the last 100,000 years. The modelling suggests that the average GST was about -3...- 4 °C during the Weichselian glaciation. Holocene GST values are within ±2 degrees of the present average GST in Outokumpu (5 °C). The topographic hydraulic heads and hydraulic conductivity of crystalline rocks are low, which suggests that advective heat transfer in the formation is not significant. The slow replacement of fresh flushing water by saline formation fluids is observed in the hole, but it does not generate significant thermal disturbances in the logs. On the other hand, free sluggish thermal convection is present in the large diameter (22 cm) borehole, but it generates only local thermal 'noise' in the range of 0.001-0.01 K not affecting the general geothermal results.
Keywords: Baltic Shield; Finland; Ita Suomen; Outokumpu; Calluna vulgaris; borehole; crystalline rock; geothermal gradient; granite; heat flow; heat transfer; hydraulic conductivity; hydraulic head; metasedimentary rock; paleoclimate; surface temperature; temperature gradient; thermal conductivity; thermal convection; ultramafic rock

Extant freshwater ostracodes (Crustacea: Ostracoda) from Lago Peten Itza, Guatemala. - P'erez, Liseth; Lorenschat, Julia; Bugja, Rita; Brenner, M.; Scharf, Burkhard; Schwalb, Antje (Revista de Biologia Tropical, 2010)

Quantification of Microbial Communities in Forearc Sediment Basins off Sumatra - Schippers, Axel; K{oweker, Gerrit; H{oft, Carmen; Teichert, Barbara M.A. (Geomicrobiology Journal, 2010)
Sediments in the Indian Ocean off the coast of the Indonesian island Sumatra were sampled at 25 stations in high resolution near the sediment surface and at three stations up to a maximum depth of 12 meter below seafloor (mbsf) for a quantitative microbial community analysis. Total cell counts were determined applying two different protocols including SYBR Green II as fluorescent staining dye. Total cell counts without detaching cells from sediment particles were 109 cells/ mL sediments at the sediment surface with little variation between all stations. They decreased to 108 cells/ mL at 0.2 to 0.4 mbsf and to 107 cells/ mL below 6 mbsf. The total cell counts after detaching cells from sediment particles were up to one order of magnitude lower above 6 mbsf and showed similar values below. This difference for the two protocols can be explained by a loss of cells during the detachment procedure and/or counting of unspecific signals without detaching cells from sediment particles. Particular phylogenetic and physiological prokaryotic groups were quantified by quantitative, real-time PCR (Q-PCR) targeting 16S rRNA and functional genes. Archaea and Bacteria were found overall in similar 16S rRNA gene copy numbers in the range of the total cell counts at all sediment depths, thus, neither Archaea nor Bacteria could be considered as dominant. The eukaryotic 18S rRNA gene occurred in two orders of magnitude lower numbers than prokaryotic 16S rRNA genes. Fe(III)- and Mn(IV)-reducing bacteria (16S rRNA gene of Geobacteraceae) and sulfate-reducing bacteria (functional gene dsrA) were detected in variable (up to 108 gene copies/ mL sediment) but in always significantly lower numbers than total Bacteria. The proportion of sulfate reducers on the prokaryotic community was between 0.2 and 19%. Calculated aereal sulfate reduction rates were overall low with values between 0.002 and 0.027 mmol m-2a-1, resulting in sulfate reduction rates per cell of 0.0007 and 0.81 fmol cell-1 a-1, similar to published data for other deeply buried marine sediments. Methanogenesis did not seem to play a big role since methane was detected only below 6.5 mbsf, and the functional gene of methanogens and anaerobic methanotrophs mcrA could not be detected in any sample.
Keywords: Greater Sunda Islands; Indian Ocean; Sumatra; Sunda Isles; Archaea; Bacteria (microorganisms); Eukaryota; Geobacteraceae; Prokaryota; bacterium; marine sediment; methanogenesis; microbial community; polymerase chain reaction; prokaryote; quantitative analysis; seafloor

Shear wave splitting in the SAFOD pilot hole using seismic interferometry - Lewis, M.A.; Gerstoft, P. (Society of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010, 2010)
We use noise cross-correlation between stations in the San Andreas Fault Observatory at Depth (SAFOD) pilot hole to extract P and S waves from a noise source at depth and measured anisotropy of the S wave on the horizontal components. The continuous data is recorded at 7 threecomponent stations at depths from 500-800m in the pilot hole. In late September and early October 2004 a noise source is observed propagating from underneath the stations, while in mid and late October the propagating noise signal is absent. This time is consistent with the temporary end of drilling in the SAFOD main-hole for the winter, making drilling activity the likely source of the noise. We cross-correlate between the deepest station and the other six stations in the pilot hole to get an estimate of the P and S wave portions of the Green's function on the vertical and horizontal components, respectably. The velocity of the propagating waves is largely consistent with velocity measurements taken in the borehole when taking into account the angle between the source and receivers. We observe polarization in the S wave, with a fast polarization direction of 120?130?that is 3-4% faster than the slow direction. © 2010 SEG.
cited By 0
Keywords: Boreholes; Geophysical prospecting; Infill drilling; Polarization; Shear flow; Strike-slip faults; Continuous data; Cross correlations; Drilling activity; Polarization direction; Propagating waves; San Andreas fault; Seismic interferometries; Shear wave splitting; Shear waves

Seismotectonic setting of the Karadere-D{uzce branch of the North Anatolian Fault Zone between the 1999 Izmit and D{uzce ruptures from analysis of Izmit aftershock focal mechanisms - G{org{un, E.; Bohnhoff, M.; Bulut, F.; Dresen, G. (Tectonophysics, 2010)
We investigate aftershock focal mechanisms along the eastern part of the Izmit Mw = 7.4 August 17, 1999 rupture zone during the time period August 22, 1999-October 17, 1999. Two spatial clusters of aftershock activity are analyzed representing the Karadere Fault (KF) and the D{uzce Area (DA). Based on an aftershock hypocenter catalogue restricted to events with horizontal and vertical errors < 2 km, we determine fault plane solutions for 221 events. The high number of focal mechanisms at the eastern Izmit rupture zone could be determined only due to the low magnitude-detection threshold of the seismic network and allows to resolve the local deformation pattern with unprecedented precision. Focal mechanisms along the Karadere Fault allow us to identify dominantly dextral strike-slip mechanisms with normal faulting components on NE-SW trending fault planes. Focal mechanisms in the D{uzce Area predominantly exhibit NE-SW extensional normal faulting but also a substantial part of strike-slip faulting. Further subdivision of the data set slightly decreases for the misfit for deeper (z > 10 km) events. North and east of the easternmost end of the Karadere Fault we observe a high variance in stress field orientation correlated with lower b-values. While the Karadere Fault reflects a predominant dextral strike-slip regime with normal faulting components, the D{uzce Area further to the East that also hosted the forthcoming Mw = 7.2 mainshock 87 days after the Izmit earthquake can be subdivided into a dominantly NE-SW extensional normal faulting regime below the D{uzce Basin (DB) and a first-order strike-slip regime along the western D{uzce Fault (DF). We conclude that the D{uzce Basin was set under tension by the Izmit rupture and partly released the slip deficit by extensional faulting on Karadere Fault parallel to the coseismic displacement. At the same time this area and in particular the D{uzce Fault that bounds the D{uzce Basin to the south reflects mostly strike-slip events representing a major asperity along the North Anatolian Fault Zone (NAFZ) before initiating the D{uzce rupture 87 days after the Izmit event. © 2009 Elsevier B.V. All rights reserved.
cited By 26
Keywords: Fault plane solutions; Izmit earthquakes; North Anatolian Fault Zone; Seismotectonics; Stress tensors; Earthquakes; Focusing; Tensors; Aircraft accidents; aftershock; earthquake catalogue; earthquake hypocenter; earthquake magnitude; earthquake rupture; extensional tectonics; fault zone; faulting; focal mechanism; seismotectonics; spatial variation; strike-slip fault; tectonic setting; Anatolia; Duzce; Izmit; Kocaeli [Turkey]; Turkey

Seismic imaging using microseismic events: Results from the San Andreas Fault System at SAFOD - Reshetnikov, A.; Buske, S.; Shapiro, S.A. (Journal of Geophysical Research: Solid Earth, 2010)
We have developed a new passive seismic imaging approach that consists of two steps. First, the hypocenter of the microseismic event is precisely located. Second, this event is treated as a pseudo-active seismic source and the reflections within the recorded wavefield are processed by using a directional migration algorithm in order to construct a high-resolution image of the illuminated subsurface region. In this paper we demonstrate the application of our approach to a number of microseismic events recorded by a borehole array in the San Andreas Fault Observatory at Depth main hole. Results obtained were high-resolution 3-D images of different SE-NW-oriented reflectors related to the San Andreas Fault (SAF) system in the close vicinity of the borehole. To support our approach, we compared our findings with other active and passive seismic images and analyzed the correlation with borehole lithology. We revealed a predominantly satisfactory agreement for both juxtapositions. Furthermore, the stacked image of several microearthquakes provides a spatial characterization of the complex internal structure of the SAF, with much higher resolution than can be obtained from surface seismic reflection data. Copyright 2010 by the American Geophysical Union.
cited By 49
Keywords: algorithm; image resolution; imaging method; microearthquake; San Andreas Fault; seismic data; seismic reflection; seismic source; seismology; stacking; wave field

Sedimentary facies and cyclostratigraphy of the Cretaceous first member of Nenjiang Formation in the Southeast uplift zone, Songliao Basin and its correlation with the CCSD-SK-I. - Youfeng, GAO; Pujun, WANG; Xuejiao, Qu; Guodong, WANG (Acta Petrologica Sinica, 2010)