All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1519.
Drilling into the track of the yellowstone hot spot
Eos,
95
(10)
85-86
2014
ISSN: 00963941
Publisher: American Geophysical Union
Keywords:▾
ash; climate change; drilling; hot spot; mantle plume; volcanic eruption; volcanic ash, Idaho; Snake River Plain; United States; Yellowstone Volcanic Plateau
Abstract: ▾ The Yellowstone supervolcano erupted roughly 640,000 years ago, covering much of North America in a thick coat of ash. Material ejected from the volcano devastated the surrounding area, and particles injected into the atmosphere changed the Earth's climate. Over the past 18 million years the Yellowstone hot spot has powered a series of similar eruptions. In southern Idaho, the 640-kilometer-long Snake River Plain traces the path of the Yellowstone hot spot over this period. ©2014. American Geophysical Union. All Rights Reserved.
1518.
Facies characterization based on physical properties from downhole logging for the sediment record of Lake Van, Turkey
Quaternary Science Reviews,
10485-96
2014
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Physical properties, Downholes; ICDP; Lake sediments; Paleoclimates; PALEOVAN; Quaternary; Tephra, Cluster analysis, basalt; chemical composition; clay; cluster analysis; depositional environment; facies; lacustrine deposit; paleoclimate; paleolimnology; physical property; Pleistocene; sediment core; sedimentation; silt; tephra; volcanic eruption; volcanogenic deposit; well logging, Lake Van; Turkey; Turkey
Abstract: ▾ Lake Van (Turkey) is the 4th largest terminal lake in the world and is located at a key position for climatic reconstruction. The ICDP project 'PALEOVAN' is a deep-drilling campaign initiated in the summer of 2010 to enhance the understanding of paleoclimatic and paleoenvironmental conditions in the Middle East for a period of 550,000 years. Multiple coring of two sites (Northern Basin and Ahlat Ridge) at a water depth of up to 360m has been performed. The sedimentary record is mainly composed of clayey silts and tephra deposits that were supplied by four volcanic sources: 1) the Süphan volcano, located on the northern shore, 2) the Nemrut volcano, 15km west of the westernshore, 3) the Incekaya volcano, on the southwestern shore and 4) intralake eruptive centers. The dominant chemical composition of the volcanic sources is known from studies of land deposits.High-quality downhole logs have been acquired from both sites. To construct a continuous lithological profile, 180m of downhole logging data from the Ahlat Ridge have been analyzed by cluster analysis. To improve the differentiation of the sediments, two elemental intensity profiles from x-ray fluorescence core-scanning (calcium and zirconium) performed on the composite profile core material were added to the cluster analysis. Five cluster units were derived and transformed into three tephra and two clayey silt units. To compare the two clayey silt units with the composite profile from the visual core description (VCD) that showed 15 lithological units, the composite profile was classified into two major groups of lacustrine sediments: banded clayey silts (interpreted as glacial deposits) and laminated clayey silts (interpreted as interglacial deposits). Despite this simplification, no correlation between the two clayey silt units derived from cluster analysis and the banded and laminated clayey silts could be found. The following reasons are proposed: (a) the comparability of the datasets was limited by significant depth shifts of up to 2.5m between the composite profile based on the VCD and the downhole measurements in hole 2D of the Ahlat Ridge, (b) a correlation was difficult to ascertain from the vertical resolution of the downhole logging data and the extremely detailed core description in mm-scale, (c) mixed signals were obtained because of prevailing thin layers and intercalations of different lithotypes and (d) cluster analysis was difficult to perform because the contrast within the input data is too low (possibly background sedimentation) to distinguish between glacial and interglacial deposits. Tephra units are characterized by contrasting properties and differ mainly in their magnetic susceptibility, spectral gamma ray components (uranium, thorium and potassium) and XRF-intensities of calcium and zirconium. Tephra units have been linked to the dominant volcanic composition of the deposited tephra layers and partly to the volcanic sources. Depth trends are derived with prevailing basaltic deposits in the bottom part (128m-210m below lake floor) and are gradually outweighed by the highly differentiated (dacitic and rhyolitic/trachytic) products towards the top of the record. © 2014 Elsevier Ltd.
1517.
Eustasy, its controlling factors, and the limno-eustatic hypothesis - Concepts inspired by Eduard Suess
Austrian Journal of Earth Sciences,
107
(1)
115-131
2014
ISSN: 02517493
Publisher: Austrian Geological Society
Abstract: ▾ For many years Eduard Suess dealt with the phenomenon of displaced shorelines and the search for explanations for their genesis and the controlling factors. In the year 1888 Suess introduced the term eustatic movements referring to the global synchroneity of marker events in marine successions of the Earth history. Since the times of Suess, rapid scientific progress has considerably widened our understanding of the processes involved in changing sea levels. Eustasy now describes global sea-level changes that play a major role in controlling the development, structure and distribution of marine sedimentary successions. Relative (regional and local) and global (eustatic) sea-level fluctuations are controlled by a variety of endogenic and exogenic processes. Mantle convection and resulting gravity anomalies and tectonism, and climate changes are the main drivers, and apply at different temporal and spatial scales. The long-term sea-level record, i.e. 1st to 2nd order cycles and stratigraphic sequences, occurring over millions to tens of millions of years, is mainly controlled by the internal dynamic history of the Earth, e.g., the changing rates of ocean crust production. Short-term eustatic sea-level changes during ice house phases of Earth's climate are clearly controlled by waxing and waning of continental ice sheets. However, significant short-term, i.e. 10s kyr to a few Myr (3rd to 4th order cycles), sea-level changes during greenhouse episodes of Earth history are still enigmatic. Such cycles are often explained by the presence of ephemeral ice sheets even during the hottest greenhouse phases ("hothouse periods") of the Phanerozoic climate history such as the mid-Cretaceous. We argue that the effect of groundwater storage and release on sea-level change, particularly important during ice-free greenhousephases, has been and is widely underestimated in its order of magnitude. It is considered to constitute a water volume that is about equivalent to today's ice volume, thus corresponding to a potential sea-level change of up to ca. 50 m applying isostatic adjustment. Groundwater storage, including both freshwater and saline pore waters, strongly exceeds lake and river storage capacities. We introduce the term "limno-eustatic" to describe the effect of water volumes that are bound to groundwater and lake storage on sea-level fluctuations and cycles during major greenhouse phases of Earth history. Based on these terms the dimension of purely ice-driven glacio-eustatic processes can be better differentiated. The limno-eustatic hypothesis may be testable given high-resolution stratigraphic correlations between marine and continental lake archives during supposed ice-free periods of Earth history. Lake-level and sea-level fluctuations should be in an out of phase relation, i.e. a major marine sea-level lowstand should correspond to a lake-level highstand, and vice versa. Preliminary tests using selected stratigraphic levels of the Late Cretaceous record of the long-lived lacustrine Songliao basin in China indicate such an outof- phase relation, and thus support the limno-eustatic hypothesis as a mechanism to explain significant short-term sea-level fluctuations during greenhouse climate phases.
1516.
Frictional properties of exhumed fault gouges in DFDP-1 cores, Alpine Fault, New Zealand
Geophysical Research Letters,
41
(2)
356-362
2014
ISSN: 00948276
Publisher: American Geophysical Union
Keywords:▾
Friction; Mica deposits, Alpine Faults; Fault friction; Frictional stability; New zealand; Plate boundaries; strike-slip, Strike-slip faults, deep drilling; experimental study; fault zone; friction; pore pressure; stress field; temperature effect, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ Principal slip zone gouges recovered during the Deep Fault Drilling Project (DFDP-1), Alpine Fault, New Zealand, were deformed in triaxial friction experiments at temperatures, T, of up to 350°C, effective normal stresses, σn′, of up to 156 MPa, and velocities between 0.01 and 3 μm/s. Chlorite/white mica-bearing DFDP-1A blue gouge, 90.62 m sample depth, is frictionally strong (friction coefficient, μ, 0.61-0.76) across all experimental conditions tested (T = 70-350°C, σn′ = 31.2-156 MPa); it undergoes a transition from positive to negative rate dependence as T increases past 210°C. The friction coefficient of smectite-bearing DFDP-1B brown gouge, 128.42 m sample depth, increases from 0.49 to 0.74 with increasing temperature and pressure (T = 70-210°C, σn′ = 31.2-93.6 MPa); the positive to negative rate dependence transition occurs as T increases past 140°C. These measurements indicate that, in the absence of elevated pore fluid pressures, DFDP-1 gouges are frictionally strong under conditions representative of the seismogenic crust.
1515.
Frictional strength, rate-dependence, and healing in DFDP-1 borehole samples from the Alpine Fault, New Zealand
Tectonophysics,
630
(C)
1-8
2014
ISSN: 00401951
Publisher: Elsevier
Keywords:▾
Boreholes; Boring; Earthquakes; Friction; Interfaces (materials); Locks (fasteners); Seismology; Velocity, Alpine Faults; Earthquake nucleation; Friction experiments; Frictional behavior; Frictional strength; Scientific drilling; Seismicity; Velocity-weakening, Faulting, borehole; earthquake mechanism; earthquake rupture; failure mechanism; friction; lithology; plate boundary; saturation; seismicity, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ The Alpine Fault in southern New Zealand is a major plate-boundary fault zone that, according to various lines of evidence, may be nearing the end of its seismic cycle and approaching earthquake failure. In order to better characterize this fault and obtain a better understanding of its seismic potential, two pilot boreholes have been completed as part of a larger drilling project. Samples representative of the major lithologic subdivisions of the fault zone at shallow (~ 100. m) depths were recovered and investigated in laboratory friction experiments. We show here that materials from within and very near the principal slip zone (PSZ) tend to exhibit velocity strengthening frictional behavior, and restrengthen (heal) rapidly compared to samples of the wall rock recovered near the PSZ. Fluid saturation causes the PSZ to be noticeably weaker than the surrounding cataclasites (μ = 0.45), and eliminates the velocity-weakening behavior in these cataclasites that is observed in dry tests. Our results indicate that the PSZ has the ability to regain its strength in a manner required for repeated rupture, but its ability to nucleate a seismic event is limited by its velocity-strengthening nature. We suggest that seismogenic behavior at depth would require alteration of the PSZ material to become velocity weakening, or that earthquake nucleation occurs either within the wall rock or at the interface between the wall rock and the PSZ. Coseismic ruptures which propagate to the surface have been inferred for previous earthquakes on the Alpine Fault, and may be facilitated by the slightly weaker PSZ material and/or high rates of healing in the PSZ which support fault locking and eventual stress drops. © 2014 Elsevier B.V.
1514.
Gas hydrate dissociations in Mallik hydrate bearing zones A, B, and C by depressurization: Effect of salinity and hydration number in hydrate dissociation
Journal of Natural Gas Science and Engineering,
2140-63
2014
ISSN: 18755100
Publisher: Elsevier B.V.
Keywords:▾
Aquifers; Dissociation; Gas industry; Gases; Horizontal wells; Hydration; Molecular dynamics; Petroleum reservoirs, Depressurizations; Hydrate dissociation; Hydration number; Salinity; Simulation, Gas hydrates
Abstract: ▾ The Mallik gas hydrate deposit was found to consist of 3 distinct, highly concentrated, high quality zones of structure I hydrate with partial occupancy of 5.75-6.2. Earlier simulation studies focused on history matching the 6 days production test of the lower zone, assuming 100% hydrate occupancy. The focus of the current study is on a simulation comparison of the expected response of the three hydrate bearing zones (lower, middle and upper) of the Mallik well 2L-38 to a single vertical well depressurization test. Additionally, a revised history match of the bottom zone field test considering partial gas occupancy of the hydrate, and a further assessment of the kinetic dissociation model are studied. This study extends the previously developed model found to successfully represent the physical and thermodynamic mechanisms involved with hydrate dissociation in the Mallik field test.The simulation results indicate that hydrate production from the middle hydrate zone is feasible and attractive, while production from the upper zone is not, due to its low pressure/temperature condition. Generally speaking, all three zones showed a similar role of the bottom aquifer in determining the water and gas flows, and all three zones showed an upward gas migration block by different existing hydrate layers. This effect is contrary to gas production from conventional gas reservoirs and indicates that the use of horizontal wells in such reservoirs may not be attractive.This study has also explored the role of partial gas cavity occupancy in the lower zone production characteristics and a re-history match of the 6 days Mallik production test showed an improved match and some indication about partial occupancy close to 6.88. Finally an in-depth examination of a previously reported laboratory scale study of methane hydrate decomposition and some observations from even smaller scale molecular dynamics study gave exciting clues of how to further interpret and improve our kinetic gas hydrate model, to be used at multiple time and length scales. Such an improved model has been proposed and awaits further testing and matching of appropriate data. © 2014.
1513.
Glacial forcing of central Indonesian hydroclimate since 60,000 y B.P.
Proceedings of the National Academy of Sciences of the United States of America,
111
(14)
5100 – 5105
2014
ISSN: 00278424
Publisher: National Academy of Sciences
Keywords:▾
runoff; titanium; article; canopy; climate; climate change; ecosystem; geochemistry; glacial interglacial variability; glacial period; Holocene; hydroclimate; hydrology; ice sheet; Indonesia; interglacial; lake; marine isotope stage 3; Northern Hemisphere; paleoclimate; precipitation; priority journal; sea surface temperature; sediment; stratigraphy; tropical rain forest; vegetation
Abstract: ▾ The Indo-Pacific warm pool houses the largest zone of deep atmospheric convection on Earth and plays a critical role in global climate variations. Despite the region's importance, changes in Indo-Pacific hydroclimate on orbital timescales remain poorly constrained. Here we present high-resolution geochemical records of surface runoff and vegetation from sediment cores fromLake Towuti, on the island of Sulawesi in central Indonesia, that continuously span the past 60,000 y.We show that wet conditions and rainforest ecosystems on Sulawesi present during marine isotope stage 3 (MIS3) and the Holocene were interrupted by severe drying between ∼33,000 and 16,000 y B.P. when Northern Hemisphere ice sheets expanded and global temperatures cooled. Our record reveals little direct influence of precessional orbital forcing on regional climate, and the similarity between MIS3 and Holocene climates observed in Lake Towuti suggests that exposure of the Sunda Shelf has a weaker influence on regional hydroclimate and terrestrial ecosystems than suggested previously. We infer that hydrological variability in this part of Indonesia varies strongly in response to high-latitude climate forcing, likely through reorganizations of the monsoons and the position of the intertropical convergence zone. These findings suggest an important role for the tropical western Pacific in amplifying glacial-interglacial climate variability.
1512.
High temperature instruments and methods developed for supercritical geothermal reservoir characterisation and exploitation—The HiTI project
Geothermics,
4990-98
2014
ISSN: 0375-6505Keywords:▾
High temperature, Supercritical, Downhole, Geothermometers, Televiewer, Basalt experiments
Abstract: ▾ During the early years of the Iceland Deep Drilling Project (IDDP), development of three distinctive technological and scientific approaches were formalised and then carried out until 2010 within a European funded project called HiTI (high temperature instruments for supercritical geothermal reservoir characterisation and exploitation). These approaches were: (1) development of several downhole instruments allowing them to function up to 300°C and 400°C, (2) identification of two new Na/Li cation ratio geothermometric relationships valid at very high temperature, (3) tracer testing with high temperature tolerant organic isomers and finally and (4) basalt rock deformation and petrophysical properties laboratory investigations at high temperature and pressure conditions.
1511.
Hydraulic and acoustic properties of the active Alpine Fault, New Zealand: Laboratory measurements on DFDP-1 drill core
Earth and Planetary Science Letters,
39045-51
2014
ISSN: 0012821XKeywords:▾
Alpine Faults; Drilling projects; Fault mechanics; Hydrologic process; Laboratory measurements; Low permeability; Petrophysics; Thermal pressurization, Elastic moduli; Mechanical permeability; Research laboratories; Wave propagation, Acoustic properties, acoustic property; active fault; core analysis; drilling; fault zone; hydraulic property; permeability; well logging, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ We report on laboratory measurements of permeability and elastic wavespeed for a suite of samples obtained by drilling across the active Alpine Fault on the South Island of New Zealand, as part of the first phase of the Deep Fault Drilling Project (DFDP-1). We find that clay-rich cataclasite and principal slip zone (PSZ) samples exhibit low permeabilities (≤10-18m2), and that the permeability of hanging-wall cataclasites increases (from c. 10-18 m2 to 10-15 m2) with distance from the fault. Additionally, the PSZ exhibits a markedly lower P-wave velocity and Young's modulus relative to the wall rocks. Our laboratory data are in good agreement with in situ wireline logging measurements and are consistent with the identification of an alteration zone surrounding the PSZ defined by observations of core samples. The properties of this zone and the low permeability of the PSZ likely govern transient hydrologic processes during earthquake slip, including thermal pressurization and dilatancy strengthening. © 2013 Elsevier B.V.
1510.
High temperature metamorphism in the conductive boundary layer adjacent to a rhyolite intrusion in the Krafla geothermal system, Iceland
Geothermics,
4942-48
2014
ISSN: 0375-6505Keywords:▾
Krafla, IDDP-1, Geothermal, Contact metamorphism
Abstract: ▾ A rhyolite magma body within the Krafla geothermal system that was encountered at a depth of 2.1km during drilling of the IDDP-1 borehole is producing high temperature metamorphism within a conductive boundary layer (CBL) in adjacent host rocks. Cuttings recovered during drilling within a few meters of the intrusive contact in IDDP-1 are mainly comprised of granoblastic hornfelses, the rock type which confirms the presence of the CBL at the base of the IDDP-1 bore hole. The two pyroxenes in these hornfelses record temperatures that are in the range of 800–950°C. The minimum heat flow across the CBL is 23Wm−2. Country rocks at distances beyond 30m of the intrusive contact are essentially unaltered, implying that they have been emplaced very recently and/or as yet unaffected by hydrothermal fluid flow.
1509.
{Modeling volcano growth on the Island of Hawaii: Deep-water perspectives}
Geosphere,
9
(5)
1348-1383
October2013
ISSN: 1553-040XAbstract: ▾ {Recent ocean-bottom geophysical surveys, dredging, and dives, which complement surface data and scientific drilling at the Island of Hawaii, document that evolutionary stages during volcano growth are more diverse than previously described. Based on combining available composition, isotopic age, and geologically constrained volume data for each of the component volcanoes, this overview provides the first integrated models for overall growth of any Hawaiian island. In contrast to prior morphologic models for volcano evolution (preshield, shield, postshield), growth increasingly can be tracked by age and volume (magma supply), defining waxing alkalic, sustained tholeiitic, and waning alkalic stages. Data and estimates for individual volcanoes are used to model changing magma supply during successive compositional stages, to place limits on volcano life spans, and to interpret composite assembly of the island. Volcano volumes vary by an order of magnitude; peak magma supply also varies sizably among edifices but is challenging to quantify because of uncertainty about volcano life spans. Three alternative models are compared: (1) near-constant volcano propagation, (2) near-equal volcano durations, (3) high peak-tholeiite magma supply. These models define inconsistencies with prior geodynamic models, indicate that composite growth at Hawaii peaked ca. 800–400 ka, and demonstrate a lower current rate. Recent age determinations for Kilauea and Kohala define a volcano propagation rate of 8.6 cm/yr that yields plausible inception ages for other volcanoes of the Kea trend. In contrast, a similar propagation rate for the less-constrained Loa trend would require inception of Loihi Seamount in the future and ages that become implausibly large for the older volcanoes. An alternative rate of 10.6 cm/yr for Loa-trend volcanoes is reasonably consistent with ages and volcano spacing, but younger Loa volcanoes are offset from the Kea trend in age-distance plots. Variable magma flux at the Island of Hawaii, and longer-term growth of the Hawaiian chain as discrete islands rather than a continuous ridge, may record pulsed magma flow in the hotspot/plume source.}
1508.
Pyrite morphology in the first member of the Late Cretaceous Qingshankou Formation, Songliao Basin, Northeast China
Palaeogeography, Palaeoclimatology, Palaeoecology,
385125-136
2013
ISSN: 00310182Keywords:▾
anoxic conditions; bottom water; Cretaceous; depositional environment; diagenesis; hydrocarbon resource; lake water; mudstone; pyrite; redox conditions; size distribution; source rock, China; Songliao Basin
Abstract: ▾ The study of sedimentary pyrite morphological characteristics provides useful information on depositional environments and early diagenic processes and can be used as an indicator of redox conditions in ancient lake bottom waters. The results of this study in the Songliao basin in northeastern China show that euhedral crystals and framboids are the dominant pyrite forms in the mudstones of the first member of the Qingshankou Formation (K2qn1). The framboidal size distribution indicates that during the deposition of K2qn1, redox conditions in the bottom water fluctuated from oxic-dysoxic to euxinic-anoxic to oxic-dysoxic. The presence of euxinic-anoxic bottom water suggests that an anoxic event developed in the Songliao ancient-lake and continued for 196ka. The development of an anoxic bottom environment was the most important factor in hydrocarbon source rock formation in the Songliao Basin. © 2012 Elsevier B.V.
1507.
Reconstruction of palaeoprecipitation based on pollen transfer functions - the record of the last 16ka from Laguna Potrok Aike, southern Patagonia
Quaternary Science Reviews,
71175 – 190
2013
Keywords:▾
Argentina; Laguna Potrok Aike; Patagonia; Santa Cruz [Argentina]; Moisture; Statistical methods; Transfer functions; ICDP-project PASADO; Late quaternary; Modern pollen samples; Palaeoclimate; Pollen; Precipitation reconstruction; Southern Hemisphere; carbonate; concentration (composition); environmental factor; Holocene; numerical model; pollen; precipitation (climatology); reconstruction; Southern Hemisphere; temperature effect; Lasers
Abstract: ▾ Based on modern pollen samples from different vegetation units in southern Patagonia, showing a close relation to yearly amounts of precipitation and mean annual temperatures, different pollen-climate transfer functions are developed and tested. Comparing the performance of MAT (Modern Analogue Techniques), WA (Weighted Average), as well as WAPLS (Weighted Average Partial Least Square) statistical techniques, it is possible to determine the statistically most robust model (WAPLS for precipitation). This transfer function is then used to estimate palaeoprecipitation amounts based on Laguna Potrok Aike pollen results for the last 16,000 years. Generally, the results of the precipitation model indicate less precipitation during the Lateglacial and alternating wet and dry periods during the Holocene. The Holocene started with higher amounts of precipitation until about 8kacal.BP, followed by a period with lower amounts between 8 and 2.5kacal.BP, while the Late Holocene shows a general increase in precipitation. Comparisons with former shoreline reconstructions and carbonate concentrations in the sediments of Laguna Potrok Aike not always show similarities due to the complex environmental factors recorded by these proxies. Moreover, changes in the moisture availability due to the interplay of precipitation and temperature, cannot be reconstructed directly. Nevertheless, the general long-term trend of palaeoprecipitation is in accordance with the absolute moisture content in the air, which is determined mainly by temperature: during cold periods with less absolute moisture, the model shows less precipitation. Moreover, the model also points to a relation with the position and strength of the Southern Hemisphere Westerlies. © 2013 Elsevier Ltd.
1506.
Quantitative and qualitative constraints on hind-casting the formation of multiyear lake-ice covers at Lake El'gygytgyn
Climate of the Past,
9
(3)
1253-1269
2013
1505.
Pliocene warmth, polar amplification, and stepped pleistocene cooling recorded in NE Arctic Russia
Science,
340
(6139)
1421-1427
2013
ISSN: 00368075
Publisher: American Association for the Advancement of Science
Keywords:▾
carbon dioxide, climate variation; cooling; ice sheet; Northern Hemisphere; paleoclimate; Pliocene-Pleistocene boundary; proxy climate record; sea level change, arctic climate; article; carbon dioxide tension; cooling; glacial period; glaciation; greenhouse gas; ice sheet; Pleistocene; Pliocene; priority journal; summer, Arctic Ocean; Russian Federation
Abstract: ▾ Understanding the evolution of Arctic polar climate from the protracted warmth of the middle Pliocene into the earliest glacial cycles in the Northern Hemisphere has been hindered by the lack of continuous, highly resolved Arctic time series. Evidence from Lake El'gygytgyn, in northeast (NE) Arctic Russia, shows that 3.6 to 3.4 million years ago, summer temperatures were ∼8°C warmer than today, when the partial pressure of CO2 was ∼400 parts per million. Multiproxy evidence suggests extreme warmth and polar amplification during the middle Pliocene, sudden stepped cooling events during the Pliocene-Pleistocene transition, and warmer than present Arctic summers until ∼2.2 million years ago, after the onset of Northern Hemispheric glaciation. Our data are consistent with sea-level records and other proxies indicating that Arctic cooling was insufficient to support large-scale ice sheets until the early Pleistocene.
1504.
Preliminary estimation of Lake El'gygytgyn water balance and sediment income
Climate of the Past,
9
(4)
1455-1465
2013
ISSN: 18149324Keywords:▾
catchment; data acquisition; estimation method; fluvial deposit; outflow; paleoclimate; residence time; seasonal variation; terrestrial ecosystem; uncertainty analysis; water budget, Chukchi; Elgygytgyn Lake; Russian Federation
Abstract: ▾ Modern process studies of the hydrologic balance of Lake El'gygytgyn, central Chukotka, and the sediment income from the catchment were carried out during a field campaign in spring and summer 2003. Despite high uncertainties due to the limited data, the results provide important first estimates for better understanding the modern and past sedimentation processes in this basin. Formed ca. 3.6 million years ago as a result of a meteorite impact, the basin contains one of the longest paleoclimate records in the terrestrial Arctic. Fluvial activity is concentrated over the short snowmelt period (about 20 days in second part of June). Underground outflow plays a very important role in the water balance and predominates over surface outflow. The residence time of the lake water is estimated to be about 100 yr. © 2013. CC Attribution 3.0 License.
1503.
Potential and limits of OSL, TT-OSL, IRSL and pIRIR290 dating methods applied on a Middle Pleistocene sediment record of Lake El'gygytgyn, Russia
Climate of the Past,
9
(2)
719-733
2013
1502.
Pleistocene sequence stratigraphy of the shallow continental shelf, offshore New Jersey: Constraints of integrated ocean drilling program Leg 313 core holes
Geosphere,
9
(1)
74-95
2013
ISSN: 1553040XKeywords:▾
biofacies; biostratigraphy; continental shelf; eustacy; incised valley; integrated approach; lithofacies; marine isotope stage; nanofossil; Ocean Drilling Program; paleoceanography; paleoenvironment; Pleistocene; Pleistocene-Holocene boundary; sea level change; seismic stratigraphy; sequence stratigraphy; thalweg; transgression, New Jersey; United States
Abstract: ▾ We used cores and logs from Integrated Ocean Drilling Program (IODP) Expedition 313 to generate biostratigraphic, lithofacies, biofacies, and geochemical data that constrain the ages and paleoenvironments of Pleistocene sequences. We integrate sequence stratigraphy on cores with new seismic stratigraphic data to interpret the Pleistocene history of the Hudson shelf valley and paleoenvironmental and sea-level changes on the inner to middle continental shelf. Improved age control compared to previous studies is provided by integrated calcareous nannofossil biostratigraphy, Sr isotopic stratigraphy, and amino acid racemization. We recognize four upper Pleistocene-Holocene sequences: sequence uP1 is correlated with Marine Isotope Chrons (MIC; "chron" is the correct stratigraphic term for a time unit, not "stage") 7 or 5e, sequence uP2 with MIC 5c, sequence uP3 with MIC 5a, and sequence uP4 with the latest Pleistocene to Holocene (MIC 1-2). However, within our age resolution it is possible that sequences uP2 and uP3 correlate with MIC 4-3c and 3a, respectively, as suggested by previous studies. Lower Pleistocene sequences lP1 and lP2 likely correlate with peak interglacials (e.g., MIC 31 and MIC 45 or 47, respectively). Thus, we suggest that preservation of sequences occurs only during peak eustatic events (e.g., MIC 45 or 47, MIC 31, and MIC 5), unless they are preserved in eroded valleys. The architecture of the Pleistocene deposits at Sites M27 and M29 is one of thin remnants of highstand and transgressive systems tracts, with lowstand deposits only preserved in the thalwegs of incised valleys. Incised valleys at the bases of sequences uP3 (IODP Site M27) and uP2 (IODP Site M29) document more southward courses of the paleo-Hudson valley, compared to the more southeastward course of the MIC 1-2 paleo-Hudson valley. The patchy distribution of Pleistocene sequences beneath the New Jersey inner-middle continental shelf is due to low accommodation during an interval of large eustatic changes; this predicts that sequences in such settings will be discontinuous, patchy, and difficult to correlate, consistent with previous studies in Virginia and North Carolina. © 2013 Geological Society of America.
1501.
Petrophysical characterization of the lacustrine sediment succession drilled in Lake El'gygytgyn, Far East Russian Arctic
Climate of the Past,
9
(4)
1933-1947
2013
ISSN: 18149324Keywords:▾
bedrock; biogenic deposit; clastic sediment; diagram; drilling; interglacial; lacustrine deposit; mass movement; meteorite; petrology; physicochemical property; redox conditions, Chukchi; Elgygytgyn Lake; Russian Federation
Abstract: ▾ Seismic profiles of Far East Russian Lake El'gygytgyn, formed by a meteorite impact some 3.6 million years ago, show a stratified sediment succession that can be separated into subunits Ia and Ib at approximately 167 m below lake floor (Combining double low line∼3.17 Ma). The upper (Ia) is well-stratified, while the lower is acoustically more massive and discontinuous. The sediments are intercalated with frequent mass movement deposits mainly in the proximal areas, while the distal region is almost free of such deposits at least in the upper part. In spring 2009, a long core drilled in the lake center within the framework of the International Continental Scientific Drilling Program (ICDP) penetrated the entire lacustrine sediment succession down to ∼320 m below lake floor and about 200 m farther into the meteorite-impact-related bedrock. Downhole logging data down to 390 m below lake floor show that the bedrock and the lacustrine part differ significantly in their petrophysical characteristics. The contact between the bedrock and the lacustrine sediments is not abrupt, but rather transitional with a variable mixture of impact-altered bedrock clasts in a lacustrine matrix. Physical and chemical proxies measured on the cores can be used to divide the lacustrine part into five different statistical clusters. These can be plotted in a redox-condition vs. input-type diagram, with total organic carbon content and magnetic susceptibility values indicating anoxic or oxic conditions and with the Si/Ti ratio representing more clastic or more biogenic input. Plotting the clusters in this diagram allows identifying clusters that represent glacial phases (cluster I), super interglacials (cluster II), and interglacial phases (clusters III and IV). © Author(s) 2013.
1500.
Reevaluation of siderophile element abundances and ratios across the Cretaceous-Paleogene (K-Pg) boundary: Implications for the nature of the projectile
Geochimica et Cosmochimica Acta,
120417-446
2013
Abstract: ▾ The discovery over 30years ago at Gubbio (Italy) and Caravaca (Spain) of an enrichment in the concentrations of iridium (Ir) and the other platinum group elements (PGE) by up to four orders of magnitude (Irmax=0.10-87ng/g) compared to average continental crustal background levels remains one of the most important discoveries in the Earth sciences. Since then, similar anomalies have been detected in more than 120 Cretaceous-Paleogene (K-Pg) boundary sites worldwide. Highly elevated Ir and other siderophile element abundances in roughly chondritic ratios are considered strong indicators for the presence of a meteoritic contribution in impact-related lithologies (melt rocks, impact ejecta material, etc.), delivered when an extraterrestrial object strikes Earth. The presented work adds 113 unpublished PGE analyses of 38 K-Pg sections worldwide to the existing literature. The analytical protocol relied on for this purpose consisted of a combination of a nickel-sulfide fire assay pre-concentration technique and subsequent trace metal determination via inductively coupled plasma-mass spectrometry (ICP-MS). Through repeated determination of key siderophile elements (i.e., Cr, Co, Ni, and PGE), the importance of sampling, nugget effects, and analytical methodologies applied becomes more apparent. Even more critically, these analytical effects are superimposed by the local syn- and post-depositional conditions that have affected the pristine meteoritic signature of the K-Pg impactor, including potential fractionation during vaporization and condensation, dissimilar PGE carrier phases, terrestrial PGE input, sedimentation rate, reworking, diagenesis, bioturbation, and chemical diffusion. While chondrite-normalized PGE patterns of individual sites appear relatively flat (i.e., chondritic), strong variations in siderophile element content and inter-element ratios exist between K-Pg locations, inter-laboratory measurements, and replicate analyses, hampering a precise projectile identification using (highly) siderophile elements. Only when considering improved databases of siderophile element concentrations in meteorites, in combination with linear regression analysis to calculate inter-element ratios from a large suite of ejecta deposit sites, the nature of the K-Pg projectile can be resolved. Application of this methodology to an extensive data set of continental and marine sites, very proximal to distal to the Chicxulub impact structure, supports a carbonaceous chondritic impactor (type CM or CO). © 2013 Elsevier Ltd.
1499.
Rock magnetic records of the Qingshankou Formation of SK-1 south borehole in Songliao Basin, Northeast China, and their paleoclimate implications
Palaeogeography, Palaeoclimatology, Palaeoecology,
38571-82
2013
ISSN: 00310182Keywords:▾
borehole; climate variation; Cretaceous; detrital deposit; diagenesis; lacustrine deposit; lake level; magnetic field; magnetic mineral; magnetic susceptibility; magnetite; Milankovitch cycle; orbital forcing; paleoclimate; pyrite; remanent magnetization; uplift, China; Songliao Basin
Abstract: ▾ The south borehole (SK-1s) of the China Cretaceous Continental Scientific Drilling project (Songke 1) penetrated the Late Cretaceous lacustrine sediments in the central depression of the Songliao Basin, Northeast China, in order to reveal the terrestrial records of the Cretaceous climate changes. High-resolution rock magnetic records were obtained on the Qingshankou Formation (K2qn) of SK-1s. The results indicate that detrital magnetite is the main remanence-carrier of the K2qn Formation; while both magnetite and paramagnetic minerals, including clay minerals and pyrite, dominantly contribute to magnetic susceptibility. Although reductive diagenesis may have more or less effect on the magnetic signals of the K2qn Formation, they recorded ancient lake-level changes well, resulting both from the tectonic development of the basin and from the Milankovitch astronomical paleoclimatic changes. The first-order vertical trends of the rock magnetic records were controlled by the shallowing-upwards of the lake-level, caused by the tectonic uplift of the basin. The short-term variations of the rock magnetic records were controlled by the lake-level periodical drift, caused by the fluctuations of the rainfall of the catchment area of the basin, which were controlled by astronomical orbital forcing. In addition, the magnetic records also distinguished two most anoxic periods during the lacustrine anoxic event 1 (LAE1): the sections of 1758-1761m and 1769-1771.5m, which may suggest the two most active periods of surface productivity of the lake. © 2013 Elsevier B.V.
1498.
Relaxation of concentration variance: A new tool to measure chemical element mobility during mixing of magmas
Chemical Geology,
3358-23
2013
ISSN: 00092541Keywords:▾
Centrifuge experiments; Chemical exchange; Compositional gradients; Contact areas; Crystal growth and dissolution; Dual effect; Dynamic condition; Dynamic process; Effective tool; Electron microprobes; Element mobility; Exponential increase; Folding dynamics; Fractional crystallization; High temperature; High viscosities; Initial composition; La-ICP-MS; Magma mixing; Major and trace elements; Major elements; Mixing process; Natural melts; New parameters; Pressure and temperature; Rheological property; Rotating speed; Scale-invariant; Silicate melts; Up-hill diffusion, Barium; Centrifuges; Chemical elements; Crystal growth; Diffusion; Dynamics; Experiments; Mixing; Niobium; Rheology; Rubidium; Silicates; Sodium; Spectrometry; Viscosity; Zirconium, Process control, alkali basalt; centrifugal model test; concentration (composition); country rock; dissolution; element mobility; experimental study; fractional crystallization; igneous geochemistry; magma; P-T conditions; reaction kinetics; rheology; silicate melt; trace element
Abstract: ▾ The ability of chemical elements to diffuse in silicate melts is central to igneous processes. It controls the rates of phase transitions such as crystal growth and dissolution kinetics, the rate of homogenization of compositional gradients generated by fractional crystallization and assimilation of country rocks as well as one of the most intriguing processes of all, magma mixing.A very useful measure, commonly used to quantify the rate of homogenization of chemical elements in silicate melts, is the diffusion coefficient. It is widely approximated to be of a constant value (at a fixed pressure and temperature) for a melt with a given composition and rheology. When dealing with magma mixing processes, melts with different initial compositions and rheological properties (e.g. basalt and rhyolite) coexist in the same system. Under such circumstances, the compositional and rheological dependence of diffusion coefficients must be considered, leading to a considerable increase of complexity in the modeling of magma mixing. Yet, an additional and even more dramatic increase in complexity is due to the fact that the mixing of magmas is undoubtedly a very dynamic process. Scale-invariant distributions of filaments of different melts are generated by stretching and folding dynamics. This has a dual effect on the mobility of chemical elements. On the one hand their mobility increases because of an exponential increase of contact area. On the other hand, mobility can be buffered by the different diffusivities in the melts (larger in the low-viscosity than in the high-viscosity melt). Uphill diffusion of chemical elements is likely to develop at the interface between interacting magmas, further increasing the complexity of the process.Here we aim to understand chemical element mobility during melt homogenization in a magma mixing event under dynamic conditions. We have performed experiments by mixing phonolitic and alkali-basaltic melts. The mixing process was induced using a high-temperature centrifuge apparatus. The rotating speed and acceleration during all experiments were 1850. rpm and 1000. g, respectively. Experiments were performed for 5, 20 and 120. min. Samples were arranged in a buoyantly unstable geometry, with the denser material placed at the inner side of the rotating circle, resulting in injection of the mafic melt into the felsic melt during rotation. The temperature during experimental runs was 1200 (± 1)°C.From the resultant glasses, vortex-like structures generated by repeated stretching and folding dynamics were observed at the interface between the two melts. The concentrations of major and trace elements were then measured along interfaces by electron microprobe and LA-ICP-MS. The mobility of each element was next quantified by calculating the decrease (or relaxation) of concentration variance with time. The first notable result is that for major and trace elements, concentrations variance decays exponentially. The exponent of the exponential function is then chosen as a measure of element mobility. Our results show clearly that different chemical elements homogenize in the melt at differing rates. Amongst the major elements Na is the fastest element followed by Al, Mg, Ca, K and Si. The trace elements, Ba, Rb, Sr, Nb and Zr exhibit similar mobilities. The REE display the lowest mobility and they show a systematic decrease from light to heavy.The results from this study indicate that the decay of concentration variance is a robust tool for obtaining new insights into chemical exchanges during the mixing of silicate melts. Concentration variance includes in a single measure an expression of the influence of all possible factors (e.g. viscosity, composition, fluid-dynamic regime) controlling the mobility of chemical elements during the mixing of two liquids. A new parameter, the Relaxation of Concentration Variance (RCV), is proposed as an effective tool for quantifying the homogenization of chemical elements during the mixing of silicate melts. © 2012 Elsevier B.V.
1497.
REPORT ON THE ICDP WORKSHOP DOVE “DRILLING OVERDEEPENED ALPINE VALLEYS”(COMO AND VALTELLINA, 3-5 APRIL 2013)
Alpine and Mediterranean Quaternary,
26
(1)
vii--ix
2013
1496.
Response of methanogenic archaea to Late Pleistocene and Holocene climate changes in the Siberian Arctic
Global Biogeochemical Cycles,
27
(2)
305-317
2013
ISSN: 08866236Keywords:▾
Genetic fingerprints; Holocene climate change; Lipid biomarkers; Methane concentrations; Methanogenic activity; Methanogenic archaea; Methanogenic community; Temperature changes, Deposits; Ethers; Experiments; Genes; Glycerol; Methanation; Methane; Methanogens; Permafrost; Phospholipids; RNA; Sediments; Soils, Climate change, biomarker; climate variation; concentration (composition); Holocene; lipid; methane; methanogenesis; paleoclimate; permafrost; Pleistocene; prokaryote, Arctic; Kurungnakh Island; Lena Delta; Russian Federation; Sakha; Siberia
Abstract: ▾ In order to investigate the link between the methane dynamics in permafrost deposits and climate changes in the past, we studied the abundance, composition, and methane production of methanogenic communities in Late Pleistocene and Holocene sediments of the Siberian Arctic. We detected intervals of increased methane concentrations in Late Pleistocene and Holocene deposits along a 42 ka old permafrost sequence from Kurungnakh Island in the Lena Delta (northeast Siberia). Increased amounts of archaeal life markers (intact phospholipid ethers) and a high variety in genetic fingerprints detected by 16S ribosomal ribonucleic acid gene analyses of methanogenic archaea suggest presently living and presumably active methanogenic archaea in distinct layers predominantly in Holocene deposits, but also in deep frozen ground at 17 m depth. Potential methanogenic activity was confirmed by incubation experiments. By comparing methane concentrations, microbial incubation experiments, gene analysis of methanogens, and microbial life markers (intact phospholipid esters and ethers) to already partly degraded membrane lipids, such as archaeol and isoprenoid glycerol dialkyl glycerol tetraethers, we demonstrated that archaeol likely represents a signal of past methanogenic archaea. The archaeol signal was used to reconstruct the response of methanogenic communities to past temperature changes in the Siberian Arctic, and the data suggest higher methane emissions occurred during warm periods, particularly during an interval in the Late Pleistocene and during the Holocene. This new data on present and past methanogenic communities in the Siberian terrestrial permafrost imply that these microorganisms will respond to the predicted future temperature rise in the Arctic with increasing methane production, as demonstrated in previous warmer periods. ©2012. American Geophysical Union. All Rights Reserved.
1495.
Revisiting wildfires at the K-Pg boundary
Journal of Geophysical Research: Biogeosciences,
118
(4)
1508-1520
2013
Abstract: ▾ The discovery of large amounts of soot in clays deposited at the Cretaceous-Paleogene (K-Pg) boundary and linked to the ~65 Ma Chicxulub impact crater led to the hypothesis that major wildfires were a consequence of the asteroid impact. Subsequently, several lines of evidence, including the lack of charcoal in North American sites, were used to argue against global wildfires. Close to the impact site fires are likely to be directly ignited by the impact fireball, whereas globally they could be ignited by radiation from the reentry of hypervelocity ejecta. To-date, models of the latter have yet to take into account that ejection - and thus the emission of thermal radiation - is asymmetric and dependent on impact angle. Here, we model: (1) the impact and ejection of material, (2) the ballistic continuation of ejecta around a spherical Earth, and (3) the thermal pulse delivered to the Earth's surface when ejecta reenters the atmosphere. We find that thermal pulses in the downrange direction are sufficient to ignite flora several thousand kilometers from Chicxulub, whereas pulses at most sites in the uprange direction are too low to ignite even the most susceptible plant matter. Our analyses and models suggest some fires were ignited by the impact fireball and ejecta reentry, but that the nonuniform distribution of thermal radiation across the surface of the Earth is inconsistent with the ignition of fires globally as a direct and immediate result of the Chicxulub impact. Instead, we propose that the desiccation of flora by ejecta reentry, as well as the effects of postimpact global cooling/darkness, left much of the terrestrial flora prone to fires, and that the volume of soot in the global K-Pg layer is explained by a combination of syn- and postimpact wildfires. Key Points K-Pg thermal radiation from re-entering ejecta is simulated with a new 3D model Radiation varied with distance and direction from Chicxulub Wildfires were ignited in some directions, but they were not global ©2013. American Geophysical Union. All Rights Reserved.