All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1319.
High-temperature thermomagnetic properties of vivianite nodules, Lake El'gygytgyn, Northeast Russia
Climate of the Past,
9
(1)
433-446
2013
1318.
Identity and typification of Diploneis ostracodarum, Diploneis budayana and Diploneis praeclara (Bacillariophyta)
Phytotaxa,
137
(1)
15 – 26
2013
ISSN: 11793163Abstract: ▾ A lectotype and isolectotype for Navicula budayana Pantocsek = Diploneis budayana (Pantocsek) Hustedt, Navicula ostracodarum Pantocsek = Diploneis ostracodarum (Pantocsek) Jovanovska, Nakov & Levkov and Navicula praeclara Pantocsek = Diploneis praeclara (Pantocsek) Cleve-Euler from Köpecz, Neogene fossil deposits in Romania have been made. Typification for each species was based on Pantocsek's original images and material deposited at the Hungarian Natural History Museum (BP). Unfortunately, the type slides for Diploneis budayana, D. ostracodarum and D. praeclara were lost or destroyed during the course of World War II. Therefore, authentic material from the type locality Köpecz at BP was used to designate the lectotypes for these three species. Detailed LM and SEM observations have been assigned for each taxon, in order to ascertain the variation in valve morphology. Taxonomic descriptions and comments are made for each species. Typification of taxa described by Pantocsek would potentially affect further stratigraphic, comparative or molecular phylogenetic work not just for Tertiary floras but for Recent floras as well. In particular, studies concerning comparisons of these species between localities, such as Lake Ohrid, will greatly benefit from this work. The outcome of such studies will shed light on the evolutionary and biogeographic history of diatoms in the context of geologic events on the Balkan Peninsula. © 2013 Magnolia Press.
1317.
Seismic and sedimentological evidence of an early 6th century AD earthquake at Lake Ohrid (Macedonia/Albania)
Climate of the Past Discussions,
84333–4355
092012
1316.
Seismic imaging of the Scandinavian Caledonides to define ICDP drilling sites
Tectonophysics,
554–55730--41
2012
ISSN: 0040-1951Keywords:▾
Reflection seismic, Collisional orogeny, Borehole, Migration, Continental Scientific Drilling, Scandinavian Caledonides
Abstract: ▾ A 36 kilometer long high resolution 2D seismic reflection profile was acquired in the summer of 2010 to be used in the planning of the COSC (Collisional Orogeny in the Scandinavian Caledonides) Deep Drilling Project. Two fully cored boreholes, each to c. 2.5 km depth, are planned for the Åre-Mörsil area of west-central Sweden in order to increase our understanding of orogenic processes and, in particular, the tectonic evolution of the Scandinavian Caledonides. Besides providing important sub-surface structural information in the vicinity of the potential drill sites, the seismic profile also provides detailed, high resolution images previously not available for the uppermost few kilometers in the region. The subsurface is highly reflective and very complex down to at least 9 km depth (the limit of decoded data) with clear reflections spanning the entire length of the profile. Correlation with previous regional reflection seismic and magnetotelluric surveys has been achieved by acquisition of a short (7 km) connecting profile. A clearly defined reflection, present in the new profile at depths between c. 2.5 km in the east and c. 4.5 km in the west and with an average westwards dip of c. 3.5°, apparently defines the base of the Lower Allochthon. Closer to the Caledonian front, this sole thrust overlies the Cambrian alum shale formation, which rests unconformably on the autochthonous Precambrian crystalline basement. The latter is remarkable for its deep internal reflectivity which is probably related to mafic intrusions in a dominantly granitic host-rock; their deformation may be of both Caledonian and older (e.g. Sveconorwegian) age. The new high resolution seismic data provide the basis for locating the first borehole in the Seve Nappe Complex. They also demonstrate that the second hole, designed to penetrate the Caledonian basement, will have to be located further east than was originally planned.
1315.
Revisiting elastic anisotropy of biotite gneiss from the Outokumpu scientific drill hole based on new texture measurements and texture-based velocity calculations
Tectonophysics,
570-571123 – 134
2012
ISSN: 00401951Keywords:▾
Finland; Outokumpu; Pohjois-Karjala; Acoustic wave velocity measurement; Anisotropy; Neutron diffraction; Poles; Seismic waves; Textures; Angular resolution; Averaging method; Averaging technique; Biotite gneiss; Counting statistics; Crystal preferred orientations; Deep drilling; Drill hole; Elastic anisotropy; Finland; Gneiss; Grain shapes; Micropores; Neutron diffraction data; P-wave velocity; Pole figure; Pole figure analysis; Preferred orientations; Rietveld technique; Self-consistent averaging; Texture measurement; Texture patterns; Time of flight; Velocity calculations; biotite; crystal property; elastic property; gneiss; measurement method; neutron diffraction; P-wave; preferred orientation; seismic anisotropy; seismic velocity; texture; Mica
Abstract: ▾ A sample of biotite gneiss from the Outokumpu deep drilling project in Finland was investigated by Kern et al. (2008) for crystal preferred orientation and elastic anisotropy. Considerable differences between measured acoustic velocities and velocities calculated on the basis of texture patterns were observed. Measured P-wave anisotropy was 15.1% versus a Voigt average yielding 7.9%. Here we investigate the same sample with different methods and using different averaging techniques. Analyzing time-of-flight neutron diffraction data from Dubna-SKAT and LANSCE-HIPPO diffractometers with the Rietveld technique, much stronger preferred orientation for biotite is determined, compared to conventional pole-figure analysis reported previously. The comparison reveals important differences: HIPPO has much better counting statistics but pole figure coverage is poor. SKAT has better angular resolution. Using the new preferred orientation data and applying a self-consistent averaging method that takes grain shapes into account, close agreement of calculated and measured P-wave velocities is observed (12.6%). This is further improved by adding 0.1. vol.% flat micropores parallel to the biotite platelets in the simulation (14.9%). © 2012.
1314.
Reading the Archive of Earth’s Oxygenation: Volume 1: The Palaeoproterozoic of Fennoscandia as Context for the Fennoscandian Arctic Russia-Drilling Early Earth Project
1313.
Reading the Archive of Earth’s Oxygenation: Volume 3: Global Events and the Fennoscandian Arctic Russia-Drilling Early Earth Project
1312.
Reconstructing Holocene environmental change in Lake Ohrid (Macedonia/Albania) using diatom as proxies
Macedonian Journal of Ecology and Environment,
14
(1-2)
7–18
2012
1311.
Seismic evidence of up to 200m lake-level change in Southern Patagonia since Marine Isotope Stage 4
Sedimentology,
59
(3)
1087 – 1100
2012
Keywords:▾
Argentina; Laguna Potrok Aike; Magellan Strait; Patagonia; Santa Cruz [Argentina]; Anoxic sediments; Climate change; Glacial geology; Isotopes; Seismic waves; Argentina; ICDP project PASADO; Laguna potrok aike; Lake-level variations; Patagonia; Seismic reflection profiles; climate variation; desiccation; dune; ice core; lacustrine deposit; lake level; marine isotope stage; paleoclimate; sedimentation; seismic reflection; shoreline; transgression; unconformity; water level; Lakes
Abstract: ▾ Maar lake Laguna Potrok Aike is located north of the Strait of Magellan (south-eastern Patagonia). Seismic reflection profiles revealed a highly dynamic palaeoclimate history. Dunes were identified in the eastern part of the lake at approximately 30 to 80m below the lake floor, overlying older lacustrine strata, and suggest that the region experienced dry conditions probably combined with strong westerly winds. It is quite likely that this can be linked to a major dust event recorded in the Antarctic ice cores during Marine Isotope Stage 4. The dunes are overlain by a series of palaeo-shorelines indicating a stepwise water-level evolution of a new lake established after this dry period, and thus a change towards wetter conditions. After the initial, rapid and stepwise lake-level rise, the basin became deeper and wider, and sediments deposited on the lake shoulder at approximately 33m below present-day lake level point towards a long period of lake-level highstand between roughly 53·5kacal. bp and 30kacal. bp with a maximum lake level some 200m higher than the desiccation horizon. This highstand was then followed by a regressional phase of uncertain age, although it must have happened some time between approximately 30kacal. bp and 6750yrscal. bp. Dryer conditions during the Mid-Holocene are evidenced by a dropping lake level, resulting in a basin-wide erosional unconformity on the lake shoulder. A second stepwise transgression between ca 5·8 to 5·4kacal. bp and ca 4·7 to 4kacal. bp with palaeo-shorelines deposited on the lake shoulder unconformity again indicates a change towards wetter conditions. © 2011 The Authors. Journal compilation © 2011 International Association of Sedimentologists.
1310.
Scientific drilling and biological evolution in ancient lakes: Lessons learned and recommendations for the future
Hydrobiologia,
682
(1)
3-25
2012
ISSN: 00188158Keywords:▾
adaptation; biogeography; divergence; drilling; fossil record; interdisciplinary approach; lake; paleoclimate; paleoenvironment; paleolimnology; phylogenetics; reconstruction; resolution; salinity; sediment core; speciation (biology)
Abstract: ▾ Scientific drilling to recover sediment core and fossil samples is a promising approach to increasing our understanding of species evolution in ancient lakes. Most lake drilling efforts to date have focused on paleoclimate reconstruction. However, it is clear from the excellent fossil preservation and high temporal resolution typical of lake beds that significant advances in evolutionary biology can be made through drill core studies coordinated with phylogenetic work on appropriate taxa. Geological records can be used to constrain the age of specific lakes and the timing of evolutionarily significant events (such as lake level fluctuations and salinity crises). Fossil data can be used to test speciation and biogeographic hypotheses and flesh out phylogenetic trees, using a better-resolved fossil record to estimate timing of phylogenetic divergences. The extraordinary preservation of many fossils in anoxic lake beds holds the hope of collecting fossil DNA from the same body fossils that improve our understanding of morphological character evolution and adaptation. Moreover, fossils allow calibration of molecular clocks, which are currently largely inferential. Lake Malawi Drilling Project results provide some guideposts on what might be expected in a drilling project for studies of evolution. The extreme variability in lake level and environmental history that most ancient lakes experience (exemplified by the Lake Malawi record) demonstrates that no one drilling locality is likely to provide a complete record of phylogenetic history for a radiating lineage. Evolutionary biologists should take an active role in the design of drilling projects, which typically have interdisciplinary objectives, to ensure their sampling needs will be met by whatever sites in a lake are ultimately drilled. © 2011 Springer Science+Business Media B.V.
1309.
Seismic anisotropy in the crystalline upper crust: Observations and modelling from the Outokumpu scientific borehole, Finland
Geophysical Journal International,
189
(1)
541 – 553
2012
ISSN: 1365246XKeywords:▾
Finland; Outokumpu; Pohjois-Karjala; Anisotropy; Cracks; Mica; Seismology; Stiffness; Three dimensional; Velocity; Angle-dependent; Cratons; Downholes; Effective medium model; Elastic stiffness; Finland; Forward modelling; In-situ; Intrinsic anisotropy; Scientific drilling; Seismic anisotropy; Seismic velocities; Shear wave splitting; Three component; Upper crust; Velocity model; Vertical seismic profiles; accuracy assessment; biotite; borehole; crystallization; forward modeling; fracture zone; homogeneity; in situ measurement; observational method; P-wave; S-wave; seismic anisotropy; seismic velocity; stiffness; three-dimensional modeling; upper crust; wave splitting; well logging; Seismic prospecting
Abstract: ▾ Seismic velocity anisotropy measurements are made of a fractured metamorphic formation from the 2.5-km-deep International Continental Scientific Drilling Programme (ICDP) borehole in Outokumpu, Finland. Three component walk-away vertical seismic profile (VSP) measurements are made along two source-line azimuths at three receiver depths (1000, 1750 and 2500 m) and incidence angle-dependent qP- and qS-wave velocities are extracted with a τ-p method. The highest qP-wave anisotropy, 13.6 per cent (v fast= 6160 m s -1, v slow= 5370 m s -1), is measured between 1000- and 1750-m depth, with anisotropy of up to 9.4 per cent (v fast= 6090 m s -1, v slow= 5540 m s -1) measured between 1750 and 2500 m depth. The top ∼1300 m of the region is composed of a homogeneous, strongly intrinsically anisotropic biotite-rich schist, and is sampled by the shallowest walk-away profile. Anisotropy of up to 11.1 per cent (v fast= 5950 m s -1, v slow= 5320 m s -1) is measured by the walk-away VSP between 50 and 1000 m depth, along with shear wave splitting averaging 5 per cent (180 m s -1). Laboratory-derived intrinsic anisotropy of the schist cannot by itself explain the degree or orientation of the anisotropy measured in the walk-away VSPs, however, a model which modifies the intrinsic stiffnesses by the inclusion of a single set of dipping, aligned cracks allows the observed in situ velocities to be reproduced. Forward modelling of the qP-wave walk-away VSP measurements from 50 to 1000 m depth is undertaken using an effective medium model to develop a 3-D velocity model of this region. An orthorhombic medium is used to represent the intrinsic anisotropy of the biotite-rich schist, and a single set of aligned cracks is added to give a bulk elastic stiffness. The resulting model predicts the schist to have an overall anisotropy of 16.8 per cent, with qP-wave velocities of up to 6315 m s -1. The accuracy of the model is assessed through its fit to the walk-away VSP measurements as well as a comparison to known geology of the region. © 2012 The Authors Geophysical Journal International © 2012 RAS.
1308.
Seismicity-based estimation of the driving fluid pressure in the case of swarm activity in Western Bohemia
Geophysical Journal International,
191
(1)
271 – 281
2012
ISSN: 1365246XKeywords:▾
Bohemia; Czech Republic; Diffusion in liquids; Estimation; Faulting; Diffusion process; Earthquake dynamics; Earthquake source; Earthquake swarms; Fluid pressures; Hydro-fracture; Migration patterns; Overpressure; Pressure increase; Seismicity pattern; Stress changes; Stress redistribution; earthquake precursor; earthquake swarm; fault; fluid pressure; fracture; geostatistics; seismic migration; seismic source; seismicity; seismology; Earthquakes
Abstract: ▾ Two recent major swarms in Western Bohemia occurred in the years 2000 and 2008 within almost the same portion of a fault close to Novy Kostel. Previous analysis of the year 2000 earthquake swarm revealed that fluid intrusion seemed to initiate the activity whereas stress redistribution by the individual swarm earthquakes played a major role in the further swarm evolution. Here we analyse the new swarm, which occurred in the year 2008, with regard to its correlation to the previous swarm as well its spatiotemporal migration patterns. We find that (i) the main part of the year 2008 activity ruptured fault patches adjacent to the main activity of the swarm 2000, but that also (ii) a significant overlap exists where earthquakes occurred in patches in which stress had been already released by precursory events; (iii) the activity shows a clear migration which can be described by a 1-D (in up-dip direction) diffusion process; (iv) the migration pattern can be equally well explained by a hydrofracture growth, which additionally explains the faster migration in up-dip compared to the down-dip direction as well as the maximum up-dip extension of the activity. We use these observations to estimate the underlying fluid pressure change in two different ways: First, we calculate the stress changes induced by precursory events at the location of each swarm earthquake assuming that observed stress deficits had to be compensated by pore pressure increases; and secondly, we estimate the fluid overpressure by fitting a hydrofracture model to the asymmetric seismicity patterns. Both independent methods indicate that the fluid pressure increase was initially up to 30 MPa. © 2012 The Authors Geophysical Journal International © 2012 RAS.
1307.
Possible earthquake trigger for 6th century mass wasting deposit at Lake Ohrid (Macedonia/Albania)
Climate of the Past,
8
(6)
2069 – 2078
2012
ISSN: 18149332Keywords:▾
Lake Ohrid; depositional environment; earthquake trigger; environmental change; geochemical method; Holocene; sedimentology; seismic data; tephrochronology; volcanic eruption
Abstract: ▾ Lake Ohrid shared by the Republics of Albania and Macedonia is formed by a tectonically active graben within the south Balkans and suggested to be the oldest lake in Europe. Several studies have shown that the lake provides a valuable record of climatic and environmental changes and a distal tephrostratigraphic record of volcanic eruptions from Italy. Fault structures identified in seismic data demonstrate that sediments have also the potential to record tectonic activity in the region. Here, we provide an example of linking seismic and sedimentological information with tectonic activity and historical documents. Historical documents indicate that a major earthquake destroyed the city of Lychnidus (today: city of Ohrid) in the early 6th century AD. Multichannel seismic profiles, parametric sediment echosounder profiles, and a 10.08 m long sediment record from the western part of the lake indicate a 2 m thick mass wasting deposit, which is tentatively correlated with this earthquake. The mass wasting deposit is chronologically well constrained, as it directly overlays the AD 472/AD 512 tephra. Moreover, radiocarbon dates and cross correlation with other sediment sequences with similar geochemical characteristics of the Holocene indicate that the mass wasting event took place prior to the onset of the Medieval Warm Period, and is attributed it to one of the known earthquakes in the region in the early 6th century AD. © Author(s) 2012.
1306.
Quaternary coastline evolution of Lake Ohrid (Macedonia/Albania)
Central European Journal of Geosciences,
4
(1)
94 – 110
2012
ISSN: 18961517Abstract: ▾ Lake Ohrid (between FYR of Macedonia and Albania), situated in an active tectonic region of the Balkanides, is characterized by N - S trending active faults. To reconstruct the Holocene shoreline evolution we investigated the coastline using sediment cores and geophysical methods to image sedimentary and tectonic structures. We revealed areas of differing sedimentation regimes. The plains north and south of the lake are dominated by clastic input related to climate variations and uplift/erosion, whereas the steep western and eastern margins are controlled by recent tectonics. Furthermore, no evidence for a much higher lake-level during the Holocene was found in the plains north and south of the lake, except rare temporary floodings. This is supported by mappings of the limestone cliffs around Lake Ohrid, which yielded no evidence for abrasional platforms or notches as indicators for past highstands. © 2012 Versita Warsaw and Springer-Verlag Wien.
1305.
Mollusc biodiversity in a European ancient lake system: Lakes Prespa and Mikri Prespa in the Balkans
Hydrobiologia,
682
(1)
47 – 59
2012
ISSN: 15735117Keywords:▾
Lake Mikri Prespa; Bivalvia; Gastropoda; Mollusca; assessment method; biodiversity; biogeography; conservation management; endemic species; extinction; habitat conservation; heterogeneity; mollusc; population decline; Red List; spatial distribution; species conservation; species richness; taxonomy; visualization
Abstract: ▾ The spatial distribution of (endemic) biodiversity in ancient and potentially ancient lakes in Europe is poorly understood. Examples include Lakes Prespa and Mikri Prespa in the Central Balkans. Utilizing information of the most species-rich taxon in these lakes, the Mollusca, we therefore attempt to statistically assess and visualize the spatial distribution of biodiversity, to analyse biogeographical patterns, and to carry out a conservation assessment. We estimate that at least 40 (sub)species (29 gastropod and 11 bivalve taxa) occur in the lakes. For both lakes combined, 37. 5% of the mollusc taxa are endemic. In general, the mollusc richness in Lake Mikri Prespa is lower than in Lake Prespa and less heterogeneously distributed. The highest species richness can be seen on the western and south eastern shores of Lake Prespa. Based on the presence/absence of genera, a minimum spanning tree analysis supports the sister lake relationship of both lakes, which, in turn, are most closely related to lakes in the western Balkans and not to nearby Lake Ohrid. The IUCN red list assessment revealed (A) a tendency towards mollusc faunal change, (B) a contemporary decline and potential loss of mollusc diversity, and (C) that all endemic species are of conservation concern. © 2011 Springer Science+Business Media B.V.
1304.
Platinum group element abundances in the upper continental crust revisited - New constraints from analyses of Chinese loess
Geochimica et Cosmochimica Acta,
9363-76
2012
Abstract: ▾ Platinum group element (PGE) abundances in the upper continental crust (UCC) are poorly constrained with published values varying by up to an order of magnitude. We evaluated the validity of using loess to estimate PGE abundances in the UCC by measuring these elements in seven Chinese loess samples using a precise method that combines NiS fire assay with isotope dilution. Major and trace elements of the Chinese loess show a typical upper crustal composition and PGE abundances are consistent with literature data on Chinese loess, except for Ru, which is a factor of 10 lower than published values. We suggest that the high Ru data and RuN/IrN values of Chinese loess reported by Peucker-Ehrenbrink and Jahn (2001) (Geochem. Geophys. Geosys. 2, 2001GC000172) are an analytical artifact, rather than a true geochemical characteristic of loess because likely sources of loess are not significantly enriched in Ru and transport and deposition processes cannot preferentially enrich Ru in loess. The effect of eolian fractionation on PGE abundances in loess appears to be limited because Chinese loess from different locations shows similar PGE patterns and concentrations. This conclusion is supported by strong positive correlations between the PGE (except for Pt) and other compatible elements such as Fe2O3, Ni, Cr, Co. Using a compilation of PGE data for loess from China, Argentina and Europe, including our data but excluding one sample with an anomalously high Pt content, we propose average PGE abundances for global loess of Ir = 0.022 ppb (ng/g), Ru = 0.030 ppb, Rh = 0.018 ppb, Pt = 0.599 ppb, and Pd = 0.526 ppb, and suggest that these are the best current estimates for the PGE abundances of the UCC. © 2012 Elsevier Ltd.
1303.
Physical properties of surface outcrop cataclastic fault rocks, Alpine Fault, New Zealand
Geochemistry, Geophysics, Geosystems,
13
(1)
2012
ISSN: 15252027
Publisher: Blackwell Publishing Ltd
Keywords:▾
Clay alteration; Friction; Grinding (comminution); Kaolin; Kaolinite; Mechanical permeability; Physical properties; Shear flow; Strain rate; Strengthening (metal); Tribology, Alpine Faults; Cataclasite; Effective normal stress; Fault gouge; Fault rock; Friction coefficients; Frictional sliding; Low strain rates; New zealand; Pore fluid pressure; Rate dependence; Shear failure; Smectites; Surface exposure; surface rupture; Surface ruptures; True triaxial; Unified analysis, Surface properties, cataclasite; earthquake rupture; fault; fault gouge; fault zone; friction; outcrop; permeability; physical property; plate tectonics, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ We present a unified analysis of physical properties of cataclastic fault rocks collected from surface exposures of the central Alpine Fault at Gaunt Creek and Waikukupa River, New Zealand. Friction experiments on fault gouge and intact samples of cataclasite were conducted at 30-33MPa effective normal stress (n) using a double-direct shear configuration and controlled pore fluid pressure in a true triaxial pressure vessel. Samples from a scarp outcrop on the southwest bank of Gaunt Creek display (1) an increase in fault normal permeability (k=7.45×10-20 m2 to k=1.15×10-16 m2), (2) a transition from frictionally weak (=0.44) fault gouge to frictionally strong (=0.50-0.55) cataclasite, (3) a change in friction rate dependence (a-b) from solely velocity strengthening, to velocity strengthening and weakening, and (4) an increase in the rate of frictional healing with increasing distance from the footwall fluvioglacial gravels contact. At Gaunt Creek, alteration of the primary clay minerals chlorite and illite/muscovite to smectite, kaolinite, and goethite accompanies an increase in friction coefficient (=0.31 to =0.44) and fault-perpendicular permeability (k=3.10×10-20 m2 to k=7.45×10-20 m2). Comminution of frictionally strong (=0.51-0.57) cataclasites forms weaker (=0.31-0.50) foliated cataclasites and fault gouges with behaviors associated with aseismic creep at low strain rates. Combined with published evidence of large magnitude (Mw∼8) surface ruptures on the Alpine Fault, petrological observations indicate that shear failure involved frictional sliding within previously formed, velocity-strengthening fault gouge. Copyright 2012 by the American Geophysical Union.
1302.
Petrologic characteristics and genesis of dolostone from the campanian of the SK-I well core in the Songliao Basin, China
Geoscience Frontiers,
3
(5)
669-680
2012
ISSN: 16749871
Publisher: Elsevier B.V.
Keywords:▾
bacterium; black shale; borehole; Campanian; carbon isotope; carbonate; diagenesis; dolostone; lithostratigraphy; mudstone; oxygen isotope; petrology; precipitation (chemistry); pyrite, China; Songliao Basin, Foraminifera
Abstract: ▾ The well SK-I in the Songliao Basin is the first scientific borehole targeting the continental Cretaceous strata in China. Oval concretions, thin laminae and beds of dolostone are found intercalated within mudstone and organic-rich black shale in the Nenjiang Formation of Campanian age. Low ordered ferruginous dolomite is composed of euhedral-subhedral rhombs with cloudy nucleus and light rims formed during the diagenesis, which are typical features of replacement. The heavy carbon isotopes (δ13CPDB - 1.16-16.0) are results of both the fermentation of organic matter by microbes and degassing of carbon dioxide during the period of diagenesis, and the presence of light oxygen isotopes (δ18OPDB - 18.53∼-5.1) is a characteristic feature of fresh water influence which means the carbonate may have been altered by ground water or rainwater in the late diagenesis. Marine water incursions into the normally lacustrine basin have been proved by both the salinity of Z value and the occurrence of foraminifera in the same strata where dolomite occurs. Pyrite framboids observed by SEM are usually enclosed in the dolomite crystals or in the mudstones, supporting the sulfate reducing bacteria (SRB). The formation of both dolomite and pyrite are associated with marine water incursions, which not only supply magnesium ion for dolomite, but also result in limited carbonate precipitation in the basin. The presence of pyrite framboids indicates the development of an anoxic environment associated with salinity stratification in the lake. The dolomite in the Nenjiang Formation is the results of marine water incursions, diagenetic replacement of calcareous carbonate and sulfate reducing bacteria (SRB). © 2012 Elsevier B.V. All rights reserved.
1301.
Petrographic investigation of melt and matrix relationships in Chicxulub crater Yaxcopoil-1 brecciated melt rock and melt rock-bearing suevite (846-885m, units 4 and 5)
Geochimica et Cosmochimica Acta,
861-20
2012
Abstract: ▾ The drill core from the International Continental Drill Program's Chicxulub Scientific Drilling Project Yaxcopoil-1 (Yax-1) borehole, in the annular trough of the Chicxulub crater, exhibits from 794 to 895. m a continuous sequence of impactites consisting of reworked fallout, fallout suevite, and brecciated impact melt rock. These impact breccias exhibit a complex history of deposition, fracturing, matrix emplacement and hydrothermal alteration. Detailed investigation of the mineralogy and chemistry of these breccias has led to a better understanding of the complex events involved in their formation. We find that the paragenesis of the brecciated impact melt rock (unit 5, 861-885. m) involved fracturing of melt rock and early K-metasomatism during a hydrothermal alteration episode as suggested by earlier work. However, the present work has identified the role of multiple episodes of precipitation of Mg-rich phyllosilicates and formation and dissolution of accessory minerals in a relatively high temperature (>300. °C) hydrothermal event. The earliest matrix formation event involved precipitation of Mg-rich phyllosilicate, accessory quartz, calcite, apatite, and andradite garnet from a hydrothermal fluid with a brine or seawater component. The fluid could have partly incorporated elements and shock-metamorphosed mineral phases derived from sedimentary lithologies, including calcite and dolomite that underwent complex phase transformations such as melting, decomposition and possible back-reactions. The discovery of andradite garnet in the matrix confirms the presence of an early high temperature hydrothermal event previously identified by mineralogical, stable isotope and fluid inclusion studies. The mineral assemblage, including Mg-rich saponite, suggests the involvement of seawater by comparison with similar alteration assemblages in hydrothermal systems involving seawater around the world. The presence of a later, low-temperature phase of the hydrothermal system, with different fluid chemistry is indicated by the partial dissolution of andradite garnet, and continued precipitation of matrix phyllosilicate minerals, but without the accessory quartz, abundant calcite or andradite, and without an accompanying K-metasomatism event. © 2012 Elsevier Ltd.
1300.
Past and present mercury flux to a West African crater lake (Lake Bosomtwe/Bosumtwi, Ghana)
Science of the Total Environment,
420340 – 344
2012
ISSN: 18791026Keywords:▾
Air Movements; Air Pollution; Environmental Monitoring; Environmental Pollution; Geologic Sediments; Ghana; History, 19th Century; History, 20th Century; Lakes; Mercury; Ashanti; Ghana; Lake Bosumtwi; Anoxic sediments; Atmospheric chemistry; Atmospheric movements; Lakes; Lead; Mercury (metal); Sedimentology; cesium 137; lead 210; mercury; Africa; Atmospheric mercury; Atmospheric mercury deposition; Atmospheric transport; Crater lake; Global mercury emissions; Lake areas; Lake sediments; Long-range atmospheric transport; Mercury concentrations; Mercury depositions; Mercury fluxes; Past and present; Sediment core; Small catchment; West Africa; catchment; concentration (composition); crater lake; deposition; lacustrine deposit; mercury (element); meromictic lake; sediment core; article; catchment; chemical analysis; chemical composition; concentration (parameters); controlled study; geographic distribution; Ghana; isotope labeling; lake; lake sediment; pollution transport; priority journal; sedimentation rate; trend study; water pollution; Lake pollution
Abstract: ▾ Lake sediment cores have been used to reconstruct mercury deposition patterns in many parts of the world; however, no studies to date have used these methods in West Africa, nor are there any published measurements of mercury deposition to this region. We measured mercury in a 210Pb dated sediment core from a meromictic crater lake in West Africa (Lake Bosomtwe, Ghana). Lake Bosomtwe has a very small catchment area to lake area ratio (1.1) and the sediment mercury profile is expected to reflect past and present atmospheric mercury deposition to the lake. Mercury concentrations in sediments as well as mercury flux to the sediments increased from the mid-1800s to latter half of the 1900s, however there has been a sharp decline in mercury flux to Lake Bosomtwe in recent decades. The recent decline in mercury flux to Lake Bosomtwe's sediments does not appear to be consistent with trends in local, regional or global mercury emissions, and may instead reflect declining global atmospheric mercury concentrations or declining European emissions, highlighting the importance of long-range atmospheric transport of mercury. © 2012 Elsevier B.V.
1299.
Observation and scaling of microearthquakes from the Taiwan Chelungpu-fault borehole seismometers
Geophysical Journal International,
190
(1)
665-676
2012
ISSN: 0956540XKeywords:▾
Apparent stress; ChiChi earthquake; Coseismic slips; Drill sites; Drilling projects; Earthquake source; GPS survey; Inter-seismic periods; Iterative technique; Main shock; Method analysis; Micro-earthquakes; Observation data; Seismic moment; Seismotectonics; Self-similarities; Site effects; Source dimensions; Source parameters; Source time functions; Static stress; Stress drop; Tectonic structure; Thrust belts; Thrust faults, Boring; Drills; Drops; Faulting; Seismographs, Earthquakes, Chi-Chi earthquake 1999; decollement; deformation; earthquake magnitude; fold and thrust belt; microearthquake; seismic moment; seismicity; seismograph; seismotectonics; source parameters; tectonic structure; thrust fault, Chelungpu Fault Zone; Taiwan
Abstract: ▾ Microearthquakes with magnitude down to 0.3 were detected by the Taiwan Chelungpu-fault Drilling Project Borehole Seismometers (TCDPBHS). Despite the large coseismic slip of 12m at the drill site during the 1999 Chi-Chi earthquake, our studies show very little seismicity near the TCDPBHS drill site 6 yr after the Chi-Chi main shock. The microearthquakes clustered at a depth of 9-12 km, where the Chelungpu thrust fault turns from a 30° dipping into the horizontal decollement of the Taiwan fold-and-thrust tectonic structure. Continuous GPS surveys did not observe post-slip deformation at the larger slip region and no seismicity was observed near the drill site. Therefore we suggest that the thrust belt above the decollement is locked during this interseismic period. We further investigated source parameters of 242 microearthquakes by fitting ω -2-shaped Brune source spectra to our observation data using a frequency-independent Q model. We find that the static stress drop increases significantly with increasing seismic moment. However, due to the intense debate on this topic of scaling-relations and the related self-similarity of earthquakes, we further improve the data analysis and correct for path and site effects using the Projected Landweber Deconvolution (PLD) method for events within some clusters. The PLD method analyses the source time functions of the larger and the smaller event by an iterative technique. As a result we received source dimensions and stress drops of larger events including path and site effect corrections. The results from the PLD method are less scattered and also show a positive relation between static stress drop and seismic moment. We find a similar positive trend for the apparent stress scaling with seismic moment. © 2012 The Authors Geophysical Journal International © 2012 RAS.
1298.
Non-Gaussian gas hydrate grade simulation at the Mallik site, Mackenzie Delta, Canada
Marine and Petroleum Geology,
35
(1)
20-27
2012
ISSN: 02648172Keywords:▾
Bayesian algorithms; Bayesian simulation; Bimodal distribution; Gas hydrate reservoir; Log data; Non-Gaussian; Non-linear distribution; Reservoir modeling; Standard deviation; Statistical relationship; Stochastic simulations; Total porosity; Well log data; Work-flows, Acoustic impedance; Estimation; Gases; Hydration; Stochastic models; Stochastic systems; Three dimensional; Three dimensional computer graphics; Well logging, Gas hydrates, acoustics; Bayesian analysis; borehole; gas field; gas hydrate; pixel; stochasticity; well logging, Canada; Mackenzie Delta; Northwest Territories
Abstract: ▾ For the past decades, gas hydrate reservoirs have beneficiated from an increasing attention in the academic and industrial worlds. As a result, there is a growing need to develop specific and comprehensive gas hydrate reservoir characterization methods. This study explores the use of a stochastic Bayesian algorithm to integrate well-logs and 3D acoustic impedance in order to estimate gas hydrate grades (product of saturation and total porosity) over a representative volume of the Mallik gas hydrate field, located in the Mackenzie Delta, Northwest Territories of Canada. First, collocated log data from boreholes Mallik 5L-38 and 2L-38 are used to estimate the statistical relationship between acoustic impedance and gas hydrate grades. Second, conventional stochastic Bayesian simulation is applied to generate multiple gas hydrate grade 3D fields integrating log data and lateral variability of 3D acoustic impedance. These equiprobable scenarios permit to quantify the uncertainty over the estimation, and identify zones where this uncertainty is greater. Contrary to conventional stochastic reservoir modeling workflows, the proposed method allows integrating non Gaussian and non linear distributions. This permits to handle bimodal distributions without using complex stochastic transforms. The results present gas hydrate grade values that are in accordance with well-log data. The relatively low standard deviation calculated at each pixel using all realizations suggests that gas hydrate grades is well explained by acoustic impedance and log data. © 2012 Elsevier Ltd.
1297.
1296.
New insights into paleoenvironmental changes in Laguna Potrok Aike, southern Patagonia, since the Late Pleistocene: The PASADO multiproxy record
Holocene,
22
(11)
1323 – 1335
2012
Keywords:▾
Argentina; Laguna Potrok Aike; Patagonia; Santa Cruz [Argentina]; diatom; lacustrine deposit; paleoclimate; paleoecology; paleoenvironment; palynology; Pleistocene; proxy climate record; sediment core; stable isotope
Abstract: ▾ A series of long sediment cores was retrieved from Laguna Potrok Aike, Southern Patagonia, within the framework of PASADO (Potrok Aike Maar Lake Sediment Archive Drilling Project), an ICDP (International Continental Scientific Drilling Program) lake drilling project. This maar lake, located at 52°S, 70°W in the Province of Santa Cruz (Argentina), in the southernmost continental area of the world, is one of the few permanent lakes in the region, providing a unique continuous paleoclimatic and paleoecological lacustrine record for the last glacial cycle. Previous multiproxy studies of this site have characterized the environmental history of these dry lands in the Patagonian Steppe for the last 16 cal. ka BP. This new series of sediment cores provides a much longer record of climate variability in Southern Patagonia since 51.3 cal. ka BP. Using a multiproxy strategy, a set of samples (mostly from core catcher material) was analyzed for physical properties, rock magnetism, geochemistry, CNS elemental analysis, stable isotopes, pollen and diatoms. This preliminary multiproxy limnogeological interpretation sheds new light on the regional Pleistocene and Holocene environmental history, revealing lake-level variations through time and identifying time windows of interest where higher resolution analyses will be carried out. © The Author(s) 2011.
1295.
Monitoring the West Bohemian earthquake swarm in 2008/2009 by a temporary small-aperture seismic array
Journal of Seismology,
16
(2)
169 – 182
2012
ISSN: 13834649Keywords:▾
Bohemia; Czech Republic; aftershock; earthquake catalogue; earthquake magnitude; earthquake swarm; frequency analysis; microearthquake; monitoring; polarization; seismic moment; temporal variation
Abstract: ▾ The most recent intense earthquake swarm in West Bohemia lasted from 6 October 2008 to January 2009. Starting 12 days after the onset, the University of Potsdam monitored the swarm by a temporary small-aperture seismic array at 10 km epicentral distance. The purpose of the installation was a complete monitoring of the swarm including micro-earthquakes (M L < 0). We identify earthquakes using a conventional short-term average/long-term average trigger combined with sliding-window frequency-wavenumber and polarisation analyses. The resulting earthquake catalogue consists of 14,530 earthquakes between 19 October 2008 and 18 March 2009 with magnitudes in the range of - 1.2 ≤ M L ≤ 2. 7. The small-aperture seismic array substantially lowers the detection threshold to about M c = - 0.4, when compared to the regional networks operating in West Bohemia (M c > 0.0). In the course of this work, the main temporal features (frequency-magnitude distribution, propagation of back azimuth and horizontal slowness, occurrence rate of aftershock sequences and interevent-time distribution) of the recent 2008/2009 earthquake swarm are presented and discussed. Temporal changes of the coefficient of variation (based on interevent times) suggest that the swarm earthquake activity of the 2008/2009 swarm terminates by 12 January 2009. During the main phase in our studied swarm period after 19 October, the b value of the Gutenberg-Richter relation decreases from 1.2 to 0.8. This trend is also reflected in the power-law behavior of the seismic moment release. The corresponding total seismic moment release of 1.02×10 17 Nm is equivalent to M L,max = 5. 4. © 2011 Springer Science+Business Media B.V.