All ICDP Publications with Abstracts
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1469.
Paleoarchean sulfur cycle and biogeochemical surface conditions on the early Earth, Barberton, South Africa
Earth and Planetary Science Letters,
377-378142 – 154
2013
ISSN: 0012821XKeywords:▾
Australia; Barberton Greenstone Belt; Pilbara Block; Western Australia; Biogeochemistry; Gallium; Geodynamics; Isotopes; Pyrites; Quartz; Sedimentology; Sulfur compounds; Tectonics; Disproportionations; Greenstone belts; Hydrothermal environment; Multiple sulfur isotopes; Scientific drilling; Sedimentary environment; Sulfate reduction; Sulfur cycling; anoxic conditions; Archean; atmosphere-biosphere interaction; biogeochemistry; chert; detrital deposit; early Earth; metabasalt; pyrite; seafloor; sulfur cycle; sulfur isotope; tectonics; Sulfur
Abstract: ▾ This study presents the first multiple sulfur isotope dataset on sulfides from the ca. 3.5-3.2 Ga Onverwacht Group in the Paleoarchean Barberton Greenstone Belt (BGB) of South Africa. In situ δ34SCDT and δ33S values of pyrite (n = 568) are reported from a wide range of hydrothermal, volcanic and sedimentary environments and are used to explore Mid-Archean biogeochemical sulfur cycling. Samples are from fresh drill core collected by the Barberton Scientific Drilling Project that intercepted cherts, metabasalts and sheared ultramafics of the ~3.3-3.35 Ga Kromberg Formation; the sedimentary units of the ~3.432 Ga Noisy formation; and the unconformably underlying metabasaltic pillow lavas of the ~3.472 Ga Hooggenoeg Formation.Pyrite in quartz-carbonate-veins in the lower diamictite of the Noisy sequence records the largest range and most negative δ34SCDT values so far reported from an Archean terrain (δ34SCDT = - 55.04 to +27.46‰). The Noisy sediments also contain detrital and diagenetic pyrites with a significant variation in δ33S of between -0.62 to +1.4‰ and δ34SCDT of between -7.00 and +12.6‰, interpreted to reflect tectonic exposure of these early sediments to atmospheric - shallow marine conditions. Early marine pyrites from the Kromberg Cherts also display strong positive δ33S values up to +2.50‰ with narrow range in δ34SCDT values (-6.00 to +1.50‰), whereas hydrothermal veins in the basal ultramafic shear zones preserve magmatic values (~0‰). This study reveals a potential proto-tectonic control on atmospheric, geodynamic and hydrothermal environments available for early sulfate reducing and/or methanogenic microbes in the Paleoarchean.No evidence for microbial sulfate reduction or disproportionation was identified in the Kromberg Cherts, despite previous morphological claims for microbial life. Highly variable and negative δ34SCDT values were found in the Noisy turbidites and Hooggenoeg pillow lava breccia supporting the presence of microbial sulfate reduction in early tectono-sedimentary basins and in the Paleoarchean sub-seafloor, respectively. In light of current controversies surrounding sulfur isotope studies in similar-aged rocks of the Pilbara Craton (West Australia), we argue that microbial elemental sulfur disproportionation was not a preferred metabolic pathway on the Paleoarchean earth. © 2013 Elsevier B.V.
1468.
Paleoatmospheric pCO2 fluctuations across the Cretaceous-Tertiary boundary recorded from paleosol carbonates in NE China
Palaeogeography, Palaeoclimatology, Palaeoecology,
38595-105
2013
ISSN: 00310182Keywords:▾
atmospheric chemistry; borehole; carbon cycle; carbon dioxide; carbonate; crater; Cretaceous-Tertiary boundary; Danian; flood basalt; Maastrichtian; paleoatmosphere; paleoclimate; paleosol; pedogenesis; volcanic eruption, Atlantic Ocean; Bay of Campeche; Chicxulub Crater; China; Deccan; Gulf of Mexico; India; Mexico [North America]; Songliao Basin; Yucatan
Abstract: ▾ A dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the Cretaceous (K)-Tertiary (T) transition following the Chicxulub impact and Deccan Trap eruptions. Here, pedogenic carbonates were collected from drill core of a borehole (SK-1 (N)) straddling the Late Cretaceous and early Paleocene strata in the Songliao Basin, northeast China, to reconstruct atmospheric CO2 concentrations using a paleosol paleobarometer. Our estimates for atmospheric pCO2 from paleosol carbonates range between 277±115ppmv and 837±164ppmv between 67.8Ma and 63.1Ma. One large (~66-65.5Ma) and several small CO2 spikes (~64.7-~64.2Ma) during the latest Maastrichtian to earliest Danian are reported here and incorporated with previously published pCO2 estimates also estimated from paleosol carbonates. These CO2 spikes are attributed to one-million-year-long emplacement of the large Deccan flood basalts along with the extraterrestrial impact at the K-T boundary. © 2013 Elsevier B.V.
1467.
Paleobathymetry and sequence stratigraphic interpretations from benthic foraminifera: Insights on New Jersey shelf architecture, IODP Expedition 313
Geosphere,
9
(6)
1488-1513
2013
ISSN: 1553040XKeywords:▾
Accommodation space; Benthic foraminifera; Foraminiferal assemblages; Highstand systems tract; Individual sequences; Integrated ocean drilling programs; Sequence-stratigraphic interpretation; Short-term variations, Sea level; Stratigraphy; Tectonics, Coastal zones, benthic foraminifera; continental shelf; depositional sequence; Eocene; Miocene; Ocean Drilling Program; parasequence; sequence boundary; sequence stratigraphy; systems tract; transgression, Atlantic Ocean; New Jersey Shelf, Foraminifera
Abstract: ▾ Integrated Ocean Drilling Program (IODP) Expedition 313 drilled three holes (Sites M27, M28, and M29; 34-36 m present water depth) across a series of prograding clinothems from the inner continental shelf of the New Jersey (USA) margin, a region that is sensitive to sea-level change. We examined 702 late Eocene to Miocene samples for benthic foraminiferal assemblages and planktonic foraminiferal abundances. We integrate our results with lithofacies to reconstruct paleobathymetry. Biofacies at all three sites indicate a long-term shallowing-upward trend as clinothems built seaward and sediment fi lled accommodation space. Patterns in biofacies and lithofacies indicate shallowing-and deepening-upward successions within individual sequences, providing the basis to recognize systems tracts, and therefore sequence stratigraphic relationships in early to early-middle Miocene sequences (ca. 23-13 Ma). The clinothem bottomsets and the lower portions of the foresets, which contain the thickest parts of clinothems, yield the deepest water biofacies. Shallower bio facies characterize the sequences in the upper portions of the clinothem foresets and on the topsets. Topsets are characterized by transgressive (TST) and highstand systems tracts (HST). Foresets contain lowstand systems tracts (LST), TSTs, and HSTs. Flooding surfaces mark parasequence boundaries within LSTs, TSTs, and HSTs. Superimposed on the long-term trends, short-term variations in paleowater depth are likely linked to global sea-level changes indicated by global oxygen isotopic variations.
1466.
Paleoflora Assemblages of Late Cretaceous Algae from SK-1s Well in the Songliao Basin (in Chinese); 松辽盆地松科1井南孔晚白垩世藻类化石组合划分
Journal of Stratigraphy,
37
(4)
574-576
2013
1465.
Past climate changes and permafrost depth at the Lake El'gygytgyn site: implications from data and thermal modeling
Climate of the Past,
9
(1)
119-133
2013
ISSN: 18149324Keywords:▾
borehole; climate variation; crater lake; drilling; interdisciplinary approach; Last Glacial Maximum; Little Ice Age; paleoclimate; paleotemperature; permafrost; reconstruction; recovery plan; surface temperature; talik, Chukchi; Elgygytgyn Lake; Russian Federation
Abstract: ▾ This study focuses on the temperature field observed in boreholes drilled as part of interdisciplinary scientific campaign targeting the El'gygytgyn Crater Lake in NE Russia. Temperature data are available from two sites: the lake borehole 5011-1 located near the center of the lake reaching 400 m depth, and the land borehole 5011-3 at the rim of the lake, with a depth of 140 m. Constraints on permafrost depth and past climate changes are derived from numerical simulation of the thermal regime associated with the lake-related talik structure. The thermal properties of the subsurface needed for these simulations are based on laboratory measurements of representative cores from the quaternary sediments and the underlying impact-affected rock, complemented by further information from geophysical logs and data from published literature. <br><br> The temperature observations in the lake borehole 5011-1 are dominated by thermal perturbations related to the drilling process, and thus only give reliable values for the lowermost value in the borehole. Undisturbed temperature data recorded over more than two years are available in the 140 m deep land-based borehole 5011-3. The analysis of these observations allows determination of not only the recent mean annual ground surface temperature, but also the ground surface temperature history, though with large uncertainties. Although the depth of this borehole is by far too insufficient for a complete reconstruction of past temperatures back to the Last Glacial Maximum, it still affects the thermal regime, and thus permafrost depth. This effect is constrained by numerical modeling: assuming that the lake borehole observations are hardly influenced by the past changes in surface air temperature, an estimate of steady-state conditions is possible, leading to a meaningful value of 14 ± 5 K for the post-glacial warming. The strong curvature of the temperature data in shallower depths around 60 m can be explained by a comparatively large amplitude of the Little Ice Age (up to 4 K), with low temperatures prevailing far into the 20th century. Other mechanisms, like varying porosity, may also have an influence on the temperature profile, however, our modeling studies imply a major contribution from recent climate changes. © Author(s) 2013.
1464.
Petrography and geochemistry of impactites and volcanic bedrock in the ICDP drill core D1c from Lake El'gygytgyn, NE Russia
Meteoritics and Planetary Science,
48
(7)
1251-1286
2013
ISSN: 10869379Abstract: ▾ The 3.6 Ma old and 18 km diameter El'gygytgyn impact structure in NE Siberia was drilled in 2008/09 by ICDP (International Continental Scientific Drilling Program). A 517 m long core hole (D1c) was drilled into the outer flank of the central uplift structure, with an overall core recovery of approximately 63%. Thereby, approximately 315 m lake sediments and approximately 202 m impactites were recovered. Here, we present a detailed petrographic and geochemical assessment of the impact breccia and bedrock sections in this core. The 97 m long lower bedrock unit (517-420 m below lake floor [blf]) consists of an ignimbrite. In the overlying upper bedrock unit (420-390 mblf), the core recovered a sequence of similar ignimbrite and several decimeters of mafic rocks. We interpret these units as rocks that are located close to their former, preimpact position, but have been somewhat rotated due to collapse of the central uplift (i.e., it represents parautochthonous basement). From about 390 to 328 mblf occurs a suevite package with an impact melt poor, clast-dominated matrix, and lithic and mineral clasts that cover the entire range of volcanic target rocks known from the El'gygytgyn region. All stages of shock metamorphism (unshocked to melted) were observed in clasts, and in microclasts of the matrix, of suevite from different depths. Immediately below this package, at the contact to the underlying bedrock, occurs a 1 m wide sheared zone within vitrophyric ignimbrite, which we consider the actual crater floor. The uppermost approximately 12 m, from 328-316 mblf depth, seem to comprise reworked suevite, consisting of a mixture of sediments and suevite with more and, on average, stronger shocked minerals than found in the main suevite unit. This includes a small component of glassy spherules and impact melt fragments. Toward the top of this unit, lake sediments progressively become the dominant material in this section. We assume that this unit contains a fallback component from the ejecta plume that was mixed with the first sediments of the postimpact crater lake, and possibly some rocks that slumped off the inner crater wall-similar to a thin layer at the base of the sediment section of borehole LB-5A recovered in Lake Bosumtwi (Ghana). © The Meteoritical Society, 2013.
1463.
Sea-level control of new jersey margin architecture: Palynological evidence from integrated ocean drilling program expedition 313
Geosphere,
9
(6)
1457-1487
2013
ISSN: 1553040XKeywords:▾
Continental margin; Global climate changes; Integrated ocean drilling programs; Organic components; Oxidation resistant; Relative sea level; Sea-level control; Sequence-bounding unconformities, Isotopes; Oxygen; Submarine geology, Sea level, biostratigraphy; chronostratigraphy; continental shelf; glacioeustacy; Miocene; Ocean Drilling Program; palynology; sea level change; sequence boundary; sequence stratigraphy, Atlantic Ocean; New Jersey Margin; New Jersey Shelf
Abstract: ▾ Integrated Ocean Drilling Program Expedition 313 recovered Miocene sequences at Holes M0027A and M0029A on the New Jersey shallow shelf that contain a characteristic acid-resistant organic component. The palynofacies within each sequence refl ects variations in terrigenous versus authigenic fl ux through the Miocene that are associated with sea-level change. Very high ratios of terrigenous versus marine palynomorphs and of oxidation-resistant versus susceptible dinocysts are associated with seismic sequence boundaries, consistent with their interpretation as sequence-bounding unconformities generated at times of low sea level. Comparison of palynological distance from shoreline estimates with paleodepth estimates derived from foraminiferal data allows relative sea level to be reconstructed at both sites. Ages assigned using dinocyst biostratigraphy are consistent with other chronostratigraphic indicators allowing sequence boundaries to be correlated with Miocene oxygen isotope (Mi) events. Paleoclimatic evidence from the pollen record supports the global climate changes seen in the oxygen isotope data. Although chronological control is relatively crude, Milankovitch-scale periodicity is suggested for parasequences visible in thick sequences deposited in relatively deep water where substantial accommodation existed, such as during the early Langhian at Site 29 (Middle Miocene Climatic Optimum). Palyno logical analysis thus supports the long-held hypothesis that glacioeustasy is a dominant process controlling the architecture of continental margins.
1462.
Modern carbon burial in Lake Qinghai, China
Applied Geochemistry,
39150 – 155
2013
ISSN: 08832927Keywords:▾
China; Qinghai; Qinghai Lake; Carbon; Carbon dioxide; Global warming; Sediments; Climatic periods; Different origins; Dissolved inorganic carbon; Dissolved organic carbon; Global carbon cycle; Inorganic carbon; Organic carbon burial rates; Particulate organic carbon; carbon budget; carbon cycle; global warming; lacustrine deposit; organic carbon; sediment chemistry; Lakes
Abstract: ▾ The quantification of carbon burial in lake sediments, and carbon fluxes derived from different origins are crucial to understand modern lacustrine carbon budgets, and to assess the role of lakes in the global carbon cycle. In this study, we estimated carbon burial in the sediment of Lake Qinghai, the largest inland lake in China, and the carbon fluxes derived from different origins. We find that: (1) The organic carbon burial rate in lake sediment is approximately 7.23gm-2a-1, which is comparable to rates documented in many large lakes worldwide. We determined that the flux of riverine particulate organic carbon (POC) is approximately 10 times higher than that of dissolved organic carbon (DOC). Organic matter in lake sediments is primarily derived from POC in lake water, of which approximately 80% is of terrestrial origin. (2) The inorganic carbon burial rate in lake sediment is slightly higher than that of organic carbon. The flux of riverine dissolved inorganic carbon (DIC) is approximately 20 times that of DOC, and more than 70% of the riverine DIC is drawn directly and/or indirectly from atmospheric CO2. (3) Both DIC and DOC are concentrated in lake water, suggesting that the lake serves as a sink for both organic and inorganic carbon over long term timescales. (4) Our analysis suggests that the carbon burial rates in Lake Qinghai would be much higher in warmer climatic periods than in cold ones, implying a growing role in the global carbon cycle under a continued global warming scenario. © 2013 Elsevier Ltd.
1461.
Seismic and well-log inference of gas-hydrate accumulations on Richards Island, Northwest Territories, Canada
Leading Edge,
32
(5)
556-563
2013
ISSN: 1070485X
Publisher: Society of Exploration Geophysicists
Keywords:▾
Acoustic impedance; Gases; Hydration; Permafrost; Petroleum prospecting; Seismic prospecting; Seismic waves; Seismology; Shear waves; Wave propagation; Well logging, Conventional hydrocarbons; High resistivity; Hydrate accumulations; Hydrate bearing sediments; North Slope of Alaska; P- and S-wave velocities; Permafrost area; Seismic evidence, Gas hydrates, detection method; gas hydrate; hydrocarbon exploration; permafrost; S-wave; seismic data; seismic reflection; well logging, Alaska; Canada; Mackenzie Delta; North Slope; Northwest Territories; Northwest Territories; Richards Island; United States
Abstract: ▾ The Mackenzie Delta in Canada's Northwest Territories hosts many permafrost-related gas-hydrate accumulations that were indirectly discovered or inferred from conventional hydrocarbon exploration programs. In particular, gas-hydrate intervals characterized with high saturation show high resistivity and high P-and S-wave velocity on well-log data, are typically found in sand-rich horizons. The acoustic impedance contrast between nonhydrate and hydrate-bearing sediments usually produces strong amplitude reflections on seismic data. Such a signature was previously observed onshore at Mallik, Northwestern Territories (Collett et al., 1999), on the North Slope of Alaska (Collett et al., 2011). Here, we use 2D and 3D seismic reflection data acquired by industry on Richards Island to map and characterize gas-hydrate accumulations beneath a thick permafrost area of the Mackenzie Delta (Figure 1). Specifically, we show new seismic evidences of gas-hydrate accumulations above the Ya Ya and Umiak conventional gas fields. © 2013 by The Society of Exploration Geophysicists.
1460.
1459.
Towards a late Quaternary tephrochronological framework for the southernmost part of South America - the Laguna Potrok Aike tephra record
Quaternary Science Reviews,
7181 – 90
2013
Keywords:▾
Argentina; Laguna Potrok Aike; Santa Cruz [Argentina]; Geology; Natural sciences; Chronology; ICDP-project PASADO; Mt. Burney; Pleistocene; Tephra; Volcanic; community composition; oxide; Quaternary; sediment analysis; tephrochronology; volcanic eruption; Volcanoes
Abstract: ▾ A total of 18 tephra samples have been analysed from the composite sediment sequence from Site 2 of the Laguna Potrok Aike ICDP expedition 5022 from southern Patagonia, Argentina, which extends back to ca 51kacalBP. Analyses of the volcanic glass show that all layers but one are rhyolitic in composition, with SiO2 contents ranging between ca 74.5 and 78wt% and suggest an origin in the Austral Andean Volcanic Zone (AVZ; 49-55°S). Nonetheless, two main data clusters occur, one group with K2O contents between ca 1.5 and 2.0wt%, indicating an origin in the Mt. Burney volcanic area, and one group with K2O contents between ca 2.7 and 3.9wt%, tentatively correlated with Viedma/Lautaro and the Aguilera volcanoes in the northern part of the AVZ. The early Holocene Tephra, MB1 and the late Pleistocene Reclus R1 tephra occur in the upper part of the sequence. Periods with significant tephra deposition occurred between ca 51-44kacalBP, and ca 31-25kacalBP, with a decrease in tephra layer frequency between these two periods. © 2012 Elsevier Ltd.
1458.
Tracking lateral $\delta$13Ccarb variation in the Paleoproterozoic Pechenga Greenstone Belt, the north eastern Fennoscandian Shield
Precambrian Research,
228177--193
2013
1457.
Tracking lateral δ13Ccarb variation in the Paleoproterozoic Pechenga Greenstone Belt, the north eastern Fennoscandian Shield
Precambrian Research,
228177 – 193
2013
1456.
Understanding past climatic and hydrological variability in the mediterranean from Lake Prespa sediment isotope and geochemical record over the last glacial cycle
Quaternary Science Reviews,
66123 – 136
2013
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Albania; Lake Mikri Prespa; Macedonia [Southern Europe]; Geochemistry; Glacial geology; Iron ores; Isotopes; Oxygen; Productivity; Pyrolysis; Sediments; Central Mediterranean; Hydrological variability; Late quaternary; Marine isotope stages; Mediterranean; Reducing conditions; Rock-Eval pyrolysis; Stable isotopes; bottom water; climate effect; hydrological change; lacustrine deposit; lake water; Last Glacial; marine isotope stage; Mediterranean environment; methanogenesis; oxidation; oxygen isotope; paleoclimate; paleoecology; paleohydrology; palynology; preservation; pyrolysis; stable isotope; Lakes
Abstract: ▾ Here we present stable isotope and geochemical data from Lake Prespa (Macedonia/Albania border) over the Last Glacial cycle (Marine Isotope Stages 5e1) and discuss past lake hydrology and climate (TIC, oxygen and carbon isotopes), as well as responses to climate of terrestrial and aquatic vegetation (TOC, Rock Eval pyrolysis, carbon isotopes, pollen). The Lake Prespa sediments broadly fall into 5 zones based on their sedimentology, geochemistry, palynology and the existing chronology. The Glacial sediments suggest low supply of carbon to the lake, but high summer productivity; intermittent siderite layers suggest that although the lake was likely to have mixed regularly leading to enhanced oxidation of organic matter, there must have been within sediment reducing conditions and methanogenesis. MIS 5 and 1 sediments suggest much more productivity, higher rates of organic material preservation possibly due to more limited mixing with longer periods of oxygen-depleted bottom waters. We also calculated lakewater d18O from siderite (authigenic/Glacial) and calcite (endogenic/Holocene) and show much lower lakewater d18O values in the Glacial when compared to the Holocene, suggesting the lake was less evaporative in the Glacial, probably as a consequence of cooler summers and longer winter ice cover. In the Holocene the oxygen isotope data suggests general humidity, with just 2 marked arid phases, features observed in other Eastern and Central Mediterranean lakes. © 2012 Elsevier Ltd.
1455.
Vegetation responses to interglacial warming in the Arctic: examples from Lake El'gygytgyn, Far East Russian Arctic
Climate of the Past,
9
(3)
1211-1219
2013
ISSN: 18149324Keywords:▾
arctic environment; community response; coniferous tree; deciduous tree; dominance; evergreen tree; glacial-interglacial cycle; interglacial; lacustrine deposit; marine isotope stage; paleoecology; palynology; plant community; shrub; tundra; vegetation structure; warming, Arctic; Chukchi; Elgygytgyn Lake; Russian Federation
Abstract: ▾ Preliminary analyses of Lake El'gygytgyn sediment indicate a wide range of ecosystem responses to warmer than present climates. While palynological work describing all interglacial vegetation is ongoing, sufficient data exist to compare recent warm events (the postglacial thermal maximum, PGTM, and marine isotope stage, MIS5) with "super" interglaciations (MIS11, MIS31). Palynological assemblages associated with these climatic optima suggest two types of vegetation responses: one dominated by deciduous taxa (PGTM, MIS5) and the second by evergreen conifers (MIS11, MIS31). MIS11 forests show a similarity to modern Picea-Larix-Betula-Alnus forests of Siberia. While dark coniferous forest also characterizes MIS31, the pollen taxa show an affinity to the boreal forest of the lower Amur valley (southern Russian Far East). Despite vegetation differences during these thermal maxima, all glacial-interglacial transitions are alike, being dominated by deciduous woody taxa. Initially Betula shrub tundra established and was replaced by tundra with tree-sized shrubs (PGTM), Betula woodland (MIS5), or Betula-Larix (MIS11, MIS31) forest. The consistent occurrence of deciduous forest and/or high shrub tundra before the incidence of maximum warmth underscores the importance of this biome for modeling efforts. The El'gygytgyn data also suggest a possible elimination or massive reduction of Arctic plant communities under extreme warm-earth scenarios. © Author(s) 2013.
1454.
Velocity ratio variations in the source region of earthquake swarms in NW bohemia obtained from arrival time double-differences
Geophysical Journal International,
196
(2)
957 – 970
2013
ISSN: 1365246XKeywords:▾
Bohemia; Czech Republic; Geophysical prospecting; Shear flow; Tomography; Transport properties; Velocity; Crustal earthquakes; Double differences; Earthquake location; Earthquake source observations; Earthquake swarms; Monitoring purpose; Velocity variations; Volcano seismology; anomaly; arrival time; earthquake swarm; P-wave; S-wave; seismic source; seismic tomography; seismic velocity; seismology; Earthquakes
Abstract: ▾ Crustal earthquake swarms are an expression of intensive cracking and rock damaging over periods of days, weeks or month in a small source region in the crust. They are caused by longer lasting stress changes in the source region. Often, the localized stressing of the crust is associated with fluid or gas migration, possibly in combination with pre-existing zones of weaknesses. However, verifying and quantifying localized fluid movement at depth remains difficult since the area affected is small and geophysical prospecting methods often cannot reach the required resolution. We apply a simple and robust method to estimate the velocity ratio between compressional (P) and shear (S) waves (vP/vS-ratio) in the source region of an earthquake swarm. The vP/vP-ratio may be unusual small if the swarm is related to gas in a porous or fractured rock. The method uses arrival time difference between P and S waves observed at surface seismic stations, and the associated double differences between pairs of earthquakes. An advantage is that earthquake locations are not required and the method seems lesser dependent on unknown velocity variations in the crust outside the source region. It is, thus, suited for monitoring purposes. Applications comprise three natural, mid-crustal (8-10 km) earthquake swarms between 1997 and 2008 from the NW-Bohemia swarm region. We resolve a strong temporal decrease of vP/vP before and during the main activity of the swarm, and a recovery of vP/vP to background levels at the end of the swarms. The anomalies are interpreted in terms of the Biot-Gassman equations, assuming the presence of oversaturated fluids degassing during the beginning phase of the swarm activity. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.
1453.
Water diffusion in potassium-rich phonolitic and trachytic melts
Chemical Geology,
346149 – 161
2013
ISSN: 00092541Keywords:▾
Experiments; Infrared spectroscopy; Molecules; Pressure effects; Silicates; Water content; Boltzmann-Matano method; Diffusion couple technique; Functional relationship; Phonolite; Piston-cylinder apparatus; Spectroscopic technique; Trachyte; Water diffusion; concentration (composition); diffusivity; infrared spectroscopy; phonolite; potassium; silicate melt; trachyte; water content; Diffusion in liquids
Abstract: ▾ Water diffusivity was investigated in phonolitic and trachytic melts containing up to 6wt.% of dissolved water at temperatures between 1373K and 1673K for running time of 108 to 1186s using the diffusion couple technique. The experiments were performed in an internally heated gas pressure vessel (IHPV) at pressures of 0.2 or 0.3GPa and in a piston cylinder apparatus (PCA) at pressures between 0.5 and 2.5GPa. A newly developed rapid heating and rapid quench device was used for short term experiments in the IHPV. Concentration profiles of hydrous species (OH groups and H2O molecules) and total water (bulk water concentration as sum of OH and H2O molecules) were measured along the cylindrical axis of the diffusion sample using IR micro-spectroscopy. The IR spectroscopic technique was calibrated using a set of samples with bulk water contents measured by Karl-Fischer titration. Electron microprobe traverses show no significant change in relative proportions of anhydrous components along H2O profiles, indicating that our data can be treated as effective binary diffusion between H2O and the rest of the silicate melt.Bulk water diffusivity was derived from profiles of total water using a modified Boltzmann-Matano method as well as using fittings assuming a functional relationship between the total water diffusivity (DH2Ot) and the total water concentration (CH2Ot). The fitting of the profiles indicates that for phonolitic melt the water diffusivity is roughly proportional to water content. The following formulation was derived for the prediction of total water diffusivity (m2/s) as a function of T (K) in the T-range of 1373 to 1673K and CH2Ot:logDH2Ot=-7.11-2.07logCH2Ot-4827-4620logCH2OtT.The experimental data are reproduced by this relationship with a standard deviation of 0.07. log units. Water diffusivity in trachytic melts is similar at the same conditions. A pressure effect on water diffusivity could not be resolved in the range 0.2 to 2.5. GPa for phonolitic or trachytic melts. © 2012 Elsevier B.V.
1452.
Why has the Nazca plate slowed since the Neogene?
Geology,
41
(1)
31-34
2013
ISSN: 00917613DOI:10.1130/G33497.1
Keywords:▾
Convergence rates; Lower mantle; Natural consequences; Nazca plate; Neo genes; Oblique subduction; Seismic tomographic images; South America; Tectonic plates; Thermo-mechanical; Transition zones; View-based, Geology, Tomography, Nazca plate; Neogene; plate motion; seismic tomography; subduction zone; transition zone, Andes
Abstract: ▾ The classic example of the not-well-understood rapid change of tectonic plate motion is the increase and then decrease of the convergence rate between the Nazca and South America plates during the past 25-20 m.y. that coincided with the growth of the Andes Mountains. Currently, the decrease in convergence rate is explained either by the increasing load of the Andes or by the appearance of fl at slab segments beneath South America. Here, we present an alternative view based on a thermomechanical self-consistent (gravity driven) model of Nazca plate subduction. We explain the changes in the convergence rate as a natural consequence of the Nazca plate penetration into the transition zone and lower mantle after long-term oblique subduction of the Farallon plate. The model is consistent with seismic tomographic images of the Nazca plate beneath South America. Our model also shows that the presence of the Andes does not signifi cantly affect the convergence rate between the Nazca and South America plates. © 2012 Geological Society of America.
1451.
Diatoms of Europe: Luticola and Luticolopsis Vol. 7
Publisher
Koeltz Scientific Books, Konigstein
2013
1450.
Sustainable development of the Lake Baikal Region: a model territory for the world
Volume 6
Publisher
Springer Science & Business Media
2013
1449.
Timing of deposition and deformation of the Moodies Group (Barberton Greenstone Belt, South Africa): Very-high-resolution of Archaean surface processes
Precambrian Research,
231236 – 262
2013
ISSN: 03019268Keywords:▾
Barberton Greenstone Belt; Ficus (angiosperm); alluvial deposit; Archean; deformation; deposition; dike; felsic rock; fluvial deposit; geochronology; sandstone; sedimentary rock; siliciclastic deposit; subsidence; tuff; zircon
Abstract: ▾ Thin and largely discontinuous volcanic tuff beds in the alluvial, fluvial, and marginal-marine siliciclastic strata of the Middle Archaean Moodies Group, Barberton Greenstone Belt (BGB), contain rare to abundant zircon. Dating of magmatic zircon grains from five tuff beds and one cross-cutting dike yield ages which span the entire spectrum of BGB history from ca. 3550. Ma to 3215. Ma and show variable degrees of post-depositional alteration until ca. 2500. Ma. The youngest pristine zircon grains in all tuff samples analyzed by CA-ID-TIMS (Chemical-Abrasion Ion-Dissolution Thermal Ion Mass Spectrometry) yield upper intercept and Concordia ages between 3227.6. ±. 0.3 and 3216. ±. 0.3. Ma, and those grains analyzed by LA-SF-ICP-MS (Laser Ablation-Sector Field-Inductively Coupled Plasma-Mass Spectrometry) and SHRIMP (Sensitive High-Resolution Ion Microprobe) yield ages between 3228. ±. 9 and 3214. ±. 9. Ma. Most of these ages are either identical (within error) or significantly older than a CA-ID-TIMS age of 3223.4. ±. 0.3. Ma, obtained from zircon grains of a tuff horizon of the Schoongezicht Formation at the top of the underlying Fig Tree Group. We interpret this age to mark the time of volcanic eruption, whereas the significantly older and overlapping ages of the stratigraphically higher Moodies tuff zircon grains point either to a high degree of magmatic inheritance and/or a detrital contribution from surrounding sedimentary rocks during or after ash-tuff deposition. The minimum age for deposition of Moodies Group sediments and deformation is provided by a LA-ICP-MS zircon U-Pb age of 3219. ±. 9. Ma obtained from an undeformed felsic dike which crosscuts folded Moodies strata. This age overlaps with a precise CA-ID-TIMS U-Pb zircon age of 3216.0. ±. 0.3. Ma obtained from a tuff horizon of the upper Moodies Group. Overall, the new age data collectively imply that the up to 3.7. km-thick, sandstone-dominated Moodies Group was deposited and deformed within <1-14. Ma, and that Moodies strata thus hold the potential to offer a temporal resolution comparable to active- and passive-margin Quaternary strata (~0.1-1. mm/a). © 2013 Elsevier B.V.
1448.
[English]
A two-steps stochastic inversion to estimate gas hydrate grades at the mallik field
Publisher
European Association of Geoscientists and Engineers, EAGE
2013
INRSs, Canada; INRS-ETE, Canada; GSC, Canada; Ecole Polytechnique de Montreal, CanadaKeywords:▾
Acoustic impedance; Acoustic logging; Gases; Hydration; Petrophysics; Seismology; Stochastic systems; Uncertainty analysis, 3D seismic data; Bayesian algorithms; Bayesian frameworks; Gas hydrate saturations; High resolution; Model uncertainties; Petrophysical relationship; Secondary datum, Gas hydrates
1447.
[English]
Continuous mapping of p wave velocity dispersion - A useful tool for reservoir characterization
Page 5554-5558
Publisher
European Association of Geoscientists and Engineers, EAGE
2013
China University of Petroleum, Beijing, China; University of Toronto, CanadaKeywords:▾
Acoustic logging; Acoustic wave velocity; Dispersion (waves); Gas hydrates; Hydration; Mapping; Wave propagation, Continuous mappings; Continuous measurements; Critical frequencies; Cross correlation techniques; Gas hydrate saturations; Laminated sediments; Reservoir characterization; Rock physical properties, Seismic waves
ISBN:
9781629937915
1446.
[English]
Enhanced geothermal system potential for sites on the eastern Snake River Plain, Idaho
Volume 37
,
Page 191-197
2013
Idaho National Laboratory, United States; Idaho State University, United States; Oklahoma University, United States; Idaho Geological Survey, United States; Energy and Geoscience Institute, University of Utah, United States; University of Idaho, United States; Washington State University, United StatesISBN:
9781629932859
1445.
[English]
Fluid-level monitoring using a distributed temperature sensing system during a methane hydrate production test
Volume 4
,
Page 2797-2808
2013
Schlumberger, United States; Japan Oil Gas, and Metals National Corporation, Japan; Natural Resources Canada, CanadaISBN:
9781627481762