All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1694.
Clay mineral formation and fabric development in the DFDP-1B borehole, central Alpine Fault, New Zealand
New Zealand Journal of Geology and Geophysics,
58
(1)
13-21
2015
ISSN: 00288306
Publisher: Taylor and Francis Asia Pacific
Keywords:▾
active fault; borehole; clay mineral; fault gouge; fault zone; mineralogy; smectite; water-rock interaction, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ Clay minerals are increasingly recognised as important controls on the state and mechanical behaviour of fault systems in the upper crust. Samples retrieved by shallow drilling from two principal slip zones within the central Alpine Fault, South Island, New Zealand, offer an excellent opportunity to investigate clay formation and fluid-rock interaction in an active fault zone. Two shallow boreholes, DFDP-1A (100.6 m deep) and DFDP-1B (151.4 m) were drilled in Phase 1 of the Deep Fault Drilling Project (DFDP-1) in 2011. We provide a mineralogical and textural analysis of clays in fault gouge extracted from the Alpine Fault. Newly formed smectitic clays are observed solely in the narrow zones of fault gouge in drill core, indicating that localised mineral reactions are restricted to the fault zone. The weak preferred orientation of the clay minerals in the fault gouge indicates minimal strain-driven modification of rock fabrics. While limited in extent, our results support observations from surface outcrops and faults systems elsewhere regarding the key role of clays in fault zones and emphasise the need for future, deeper drilling into the Alpine Fault in order to understand correlative mineralogies and fabrics as a function of higher temperature and pressure conditions. © 2015 The Royal Society of New Zealand.
1693.
Characterizing clay mineralogy in Lake Towuti, Indonesia, with reflectance spectroscopy
Journal of Paleolimnology,
54
(2-3)
253 – 261
2015
ISSN: 09212728
Publisher: Kluwer Academic Publishers
Keywords:▾
Greater Sunda Islands; Lake Towuti; Malili Lakes; South Sulawesi; Sulawesi; Sulawesi; Sunda Isles; clay mineral; fluvial deposit; lacustrine deposit; paleolimnology; relative abundance; spatial variation; spectroscopy
Abstract: ▾ We tested the use of visible to near-infrared (VNIR) reflectance spectroscopy to characterize the relative abundances of clay minerals in sediments from Lake Towuti, a large tectonic lake in Sulawesi, Indonesia. We measured VNIR spectra of lake and river sediments from Lake Towuti and its catchment to identify clay minerals, fit major VNIR absorption features with a modified Gaussian model to estimate relative abundances of these minerals, and compared these absorptions to the samples’ chemistry to test the utility of VNIR spectroscopy to characterize sediment compositional variations. We found that major absorptions are caused by vibrations of Al–OH in kaolinite (2.21 μm), Fe–OH in nontronite (2.29 μm), Mg–OH in saponite and serpentine (2.31 μm), and Mg–OH in serpentine (2.34 μm). This was confirmed with X-ray diffraction data. The correlations between absorption band areas for Fe–OH, Al–OH, and Mg–OH vibrations and Fe, Al and Mg concentrations, respectively, are statistically significant, varying between r = 0.51 and r = 0.90, and spatial variations in inferred clay mineralogy within the lake are consistent with variations in the geology of the catchment. We conclude that VNIR spectroscopy is an effective way to characterize the clay mineralogy of lake sediments, and can be used to investigate changes in mineral inputs to lake deposits. © 2015, Springer Science+Business Media Dordrecht.
1692.
Changes in hot spring temperature and hydrogeology of the Alpine Fault hanging wall, New Zealand, induced by distal South Island earthquakes
Geofluids,
15
(1-2)
216-239
2015
ISSN: 14688115
Publisher: Blackwell Publishing Ltd
Keywords:▾
earthquake; exhumation; fluid flow; geothermal system; hanging wall; hydrogeology; permeability; temperature anomaly; thermal spring; uplift, Alpine Fault Zone; New Zealand; South Island; Southern Alps
Abstract: ▾ Thermal springs in the Southern Alps, New Zealand, originate through penetration of fluids into a thermal anomaly generated by rapid uplift and exhumation on the Alpine Fault. Copland hot spring (43.629S, 169.946E) is one of the most vigorously flowing, hottest of the springs, discharging strongly effervescent CO2-rich 56-58°C water at 6 ± 1 l sec-1. Shaking from the Mw7.8 Dusky Sound (Fiordland) 2009 and Mw7.1 Darfield (Canterbury) 2010 earthquakes, 350 and 180 km from the spring, respectively, resulted in a characteristic approximately 1°C delayed cooling over 5 days. A decrease in conductivity and increase in pH were measured following the Mw7.1 Darfield earthquake. Earthquake-induced decreases in Cl, Li, B, Na, K, Sr and Ba concentrations and an increase in SO4 concentration reflect higher proportions of shallow-circulating meteoric fluid mixing in the subsurface. Shaking at amplitudes of approximately 0.5% g Peak Ground Acceleration (PGA) and/or 0.05-0.10 MPa dynamic stress influences Copland hot spring temperature, which did not respond during the Mw6.3 Christchurch 2011 aftershock or other minor earthquakes. Such thresholds should be exceeded every 1-10 years in the central Southern Alps. The characteristic cooling response at low shaking intensities (MM III-IV) and seismic energy densities (approximately 10-1 J m-3) from intermediate-field distances was independent of variations in spectral frequency, without the need for post-seismic recovery. Observed temperature and fluid chemistry responses are inferred to reflect subtle changes in the fracture permeability of schist mountains adjacent to the spring. Permanent 10-7-10-6 strains recorded by cGPS reflect opening or generation of fractures, allowing greater quantities of relatively cool near-surface groundwater to mix with upwelling hot water. Active deformation, tectonic and topographic stress in the Alpine Fault hanging wall, where orographic rainfall, uplift and erosion are extreme, make the Southern Alps hydrothermal system particularly susceptible to earthquake-induced transient permeability. © 2014 The Authors Geofluids Published by John Wiley & Sons Ltd.
1691.
Carbonate deposition in the Palaeoproterozoic Onega basin from Fennoscandia: a spotlight on the transition from the Lomagundi-Jatuli to Shunga events
Earth-Science Reviews,
14765--98
2015
ISSN: 00128252
Publisher: Elsevier
Keywords:▾
bitumen; carbon isotope; carbonate platform; depositional environment; dolomite; lithostratigraphy; organic matter; Proterozoic; sediment core, Arkhangelsk [Russian Federation]; Fennoscandia; Onega Basin; Russian Federation
Abstract: ▾ Several deep drillholes were made in the Onega palaeobasin by the Fennoscandian Arctic Russia-Drilling Early Earth Project (FAR-DEEP) of the International Continental Scientific Drilling Program (ICDP). These provided fresh core material documenting the Lomagundi-Jatuli Isotopic Event (LJIE), its termination, and the start of the Shunga Event (SHE) of an enhanced accumulation of organic matter. The cored section represents the most complete known record of the end of the LJIE.The late phase of the LJIE, recorded in FAR-DEEP Core 11A, is represented by the upper part of the Tulomozero Formation (TF), a 300-m-thick unit composed of variegated dolostones, siltstones and shales. Accumulated under oxic conditions on a shallow-water carbonate platform, the TF hosts the earliest known thick formations of halite and massive anhydrite. Low-temperature greenschist facies metamorphism caused partial recrystallisation of the rocks; however, a primary carbonate phase, the dolomite, exhibits a negligible degree of post-depositional alteration of the carbon isotope system. The dataset of 46 bulk-carbonate analyses of carbon and oxygen isotopes yielded δ13Ccarb ranging between +6.8 and +11.8‰, and revealed a positive excursion from +8 to +11.8‰ followed by a decline to +8‰ towards the top of the 300-m-thick succession.The cored part of the overlying Zaonega Formation (ZF) recovered in holes 12AB and 13A is an 800-m-thick unit composed of mixed siliciclastic-carbonate facies with numerous mafic lava flows and tuff beds intruded by gabbro sills. The formation represents an unprecedented episode of enhanced accumulation of organic-rich rocks and preserves the earliest known supergiant, petrified oilfield, all typifying the SHE. The sedimentological, petrographic, geochemical and C- and O-isotopic study of over 800m of core throughout the ZF suggests that the initial carbonate deposition occurred in a lacustrine environment, then rapidly proceeding through a lagoonal setting to a rifted deepwater shelf, and finally to a carbonate platform. Both the deepwater shelf and the platformal settings are marked by organic-rich environments. The primary dolomite was potentially exposed to syn- and post-depositional hydrothermal/metasomatic alterations, organic matter diagenesis, metamorphic mineral reactions, CO2 degassing, and finally a low-temperature, post-metamorphic calcitisation resulting in overall large fluctuations of δ13Ccarb between -22 and +8‰. The dataset of over 413 bulk-carbonate analyses of carbon and oxygen isotopes, screened petrographically and geochemically against post-depositional alteration, revealed 28 least-altered samples within three stratigraphic intervals, suggesting multiple positive and negative δ13Ccarb excursions throughout over 1000m of stratigraphy. A shift from +5 to +9‰ followed by a drop to near zero values marks the lower part of the ZF. A δ13Ccarb decline from +8‰ to below zero in the middle and upper part of the ZF defines the end of the LJIE. A subsequent prominent negative excursion down to -6‰ does not show convincing isotopic evidence for influence of methanogenesis, and hence appears to be of primary depositional origin. An erratic positive excursion in the uppermost part of the drilled section indicates return of δ13Ccarb to a near normal marine value. © 2015 Elsevier B.V.
1690.
An innovative optical and chemical drill core scanner
Scientific Drilling,
1913--16
2015
ISSN: 1816-34591689.
Age-depth model of the past 630 kyr for Lake Ohrid (FYROM/Albania) based on cyclostratigraphic analysis of downhole gamma ray data
Biogeosciences,
12
(24)
7453 – 7465
2015
ISSN: 17264170
Publisher: Copernicus GmbH
Keywords:▾
Lake Ohrid; age determination; benthos; carbonate; climate signal; cyclostratigraphy; gamma ray radiation; glacial-interglacial cycle; lacustrine deposit; oxygen isotope; potassium; precipitation (chemistry); sedimentation rate
Abstract: ▾ Gamma ray (GR) fluctuations and potassium (K) values from downhole logging data obtained in the sediments of Lake Ohrid from 0 to 240 m below lake floor (b.l.f). correlate with fluctuations in δ18O values from the global benthic isotope stack LR04 (Lisiecki and Raymo, 2005). GR and K values are considered a reliable proxy to depict glacial-interglacial cycles, with high clastic input during cold and/or drier periods and high carbonate precipitation during warm and/or humid periods at Lake Ohrid. Spectral analysis was applied to investigate the climate signal and evolution over the length of the borehole. Linking downhole logging data with orbital cycles was used to estimate sedimentation rates and the effect of compaction was compensated for. Sedimentation rates increase on average by 14 % after decompaction of the sediment layers and the mean sedimentation rates shift from 45 cm kyr-1 between 0 and 110 m to 30 cm kyr-1 from 110 to 240 m b.l.f. Tuning of minima and maxima of gamma ray and potassium values versus LR04 extrema, in combination with eight independent tephrostratigraphical tie points, allows establishing of a robust age model for the downhole logging data over the past 630 kyr. © Author(s) 2015.
1688.
Accelerating Neoproterozoic research through scientific drilling
Scientific Drilling,
1917-25
2015
ISSN: 18168957
Publisher: Copernicus GmbH
Keywords:▾
Energy resources; Mechanical engineering, Neoproterozoic; Scientific drilling, Drilling
1687.
Abrupt climate and vegetation variability of eastern Anatolia during the last glacial
Climate of the Past,
11
(11)
1491-1505
2015
ISSN: 18149324
Publisher: Copernicus GmbH
Keywords:▾
carbon isotope; catchment; charcoal; climate variation; concentration (composition); Dansgaard-Oeschger cycle; GRIP; humidity; marine sediment; moisture; proxy climate record; stable isotope, Anatolia; Arctic; Greenland; Greenland Ice Sheet; Lake Van; Turkey
Abstract: ▾ Detailed analyses of the Lake Van pollen, Ca / K ratio, and stable oxygen isotope record allow the identification of millennial-scale vegetation and environmental changes in eastern Anatolia throughout the last glacial (∼ 111.5-11.7 ka BP). The climate of the last glacial was cold and dry, indicated by low arboreal pollen (AP) levels. The driest and coldest period corresponds to Marine Isotope Stage (MIS) 2 (∼ 28-14.5 ka BP), which was dominated by highest values of xerophytic steppe vegetation. <br><br> Our high-resolution multi-proxy record shows rapid expansions and contractions of tree populations that reflect variability in temperature and moisture availability. These rapid vegetation and environmental changes can be related to the stadial-interstadial pattern of Dansgaard-Oeschger (DO) events as recorded in the Greenland ice cores. Periods of reduced moisture availability were characterized by enhanced occurrence of xerophytic species and high terrigenous input from the Lake Van catchment area. Furthermore, the comparison with the marine realm reveals that the complex atmosphere-ocean interaction can be explained by the strength and position of the westerlies, which are responsible for the supply of humidity in eastern Anatolia. Influenced by the diverse topography of the Lake Van catchment, more pronounced DO interstadials (e.g., DO 19, 17-16, 14, 12 and 8) show the strongest expansion of temperate species within the last glacial. However, Heinrich events (HE), characterized by highest concentrations of ice-rafted debris (IRD) in marine sediments, cannot be separated from other DO stadials based on the vegetation composition in eastern Anatolia. In addition, this work is a first attempt to establish a continuous microscopic charcoal record for the last glacial in the Near East. It documents an immediate response to millennial-scale climate and environmental variability and enables us to shed light on the history of fire activity during the last glacial. © Author(s) 2015.
1686.
A high-resolution Late Glacial to Holocene record of environmental change in the Mediterranean from Lake Ohrid (Macedonia/Albania)
International Journal of Earth Sciences,
104
(6)
1623 – 1638
2015
ISSN: 14373254
Publisher: Springer Verlag
Keywords:▾
Albania; Lake Ohrid; Macedonia [Southern Europe]; Mediterranean Region; climate oscillation; environmental change; geochemistry; Holocene; late glacial; paleoclimate; paleoenvironment; paleolimnology; sediment core; stable isotope
Abstract: ▾ Lake Ohrid (Macedonia/Albania) is the oldest extant lake in Europe and exhibits an outstanding degree of endemic biodiversity. Here, we provide new high-resolution stable isotope and geochemical data from a 10 m core (Co1262) through the Late Glacial to Holocene and discuss past climate and lake hydrology (TIC, δ13Ccalcite, δ18Ocalcite) as well as the terrestrial and aquatic vegetation response to climate (TOC, TOC/N, δ13Corganic, Rock Eval pyrolysis). The data identifies 3 main zones: (1) the Late Glacial–Holocene transition represented by low TIC and TOC contents, (2) the early to mid-Holocene characterised by high TOC and increasing TOC/N and (3) the Late Holocene–Present which shows a marked decrease in TIC and TOC. In general, an overall trend of increasing δ18Ocalcite from 9 ka to present suggests progressive aridification through the Holocene, consistent with previous records from Lake Ohrid and the wider Mediterranean region. Several proxies show commensurate excursions that imply the impact of short-term climate oscillations, such as the 8.2 ka event and the Little Ice Age. This is the best-dated and highest resolution archive of past Late Glacial and Holocene climate from Lake Ohrid and confirms the overriding influence of the North Atlantic in the north-eastern Mediterranean. The data presented set the context for the International Continental scientific Drilling Program Scientific Collaboration On Past Speciation Conditions in Lake Ohrid project cores recovered in spring–summer 2013, potentially dating back into the Lower Pleistocene, and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history. © 2014, Springer-Verlag Berlin Heidelberg.
1685.
Microbial abundance in lacustrine sediments: a case study from Lake Van, Turkey
International Journal of Earth Sciences,
104
(6)
1667-1677
2015
ISSN: 14373254
Publisher: Springer Verlag
Keywords:▾
biosphere; lacustrine deposit; microbial activity; microbial community; microbial ecology; relative abundance, Lake Van; Turkey
Abstract: ▾ The ICDP “PaleoVan” drilling campaign at Lake Van, Turkey, provided a long (>100 m) record of lacustrine subsurface sedimentary microbial cell abundance. After the ICDP campaign at Potrok Aike, Argentina, this is only the second time deep lacustrine cell counts have been documented. Two sites were cored and revealed a strikingly similar cell distribution despite differences in organic matter content and microbial activity. Although shifted towards higher values, cell counts from Lake Potrok Aike, Argentina, reveal very similar distribution patterns with depth. The lacustrine cell count data are significantly different from published marine records; the most probable cause is differences in sedimentary organic matter composition with marine sediments containing a higher fraction of labile organic matter. Previous studies showed that microbial activity and abundance increase centimetres to metres around geologic interfaces. The finely laminated Lake Van sediment allowed studying this phenomenon on the microscale. We sampled at the scale of individual laminae, and in some depth intervals, we found large differences in microbial abundance between the different laminae. This small-scale heterogeneity is normally overlooked due to much larger sampling intervals that integrate over several centimetres. However, not all laminated intervals exhibit such large differences in microbial abundance, and some non-laminated horizons show large variability on the millimetre scale as well. The reasons for such contrasting observations remain elusive, but indicate that heterogeneity of microbial abundance in subsurface sediments has not been taken into account sufficiently. These findings have implications not just for microbiological studies but for geochemistry as well, as the large differences in microbial abundance clearly show that there are distinct microhabitats that deviate considerably from the surrounding layers. © 2015, The Author(s).
1684.
A GCM comparison of Pleistocene super-interglacial periods in relation to Lake El'gygytgyn, NE Arctic Russia
Climate of the Past,
11
(7)
979-989
2015
ISSN: 18149324
Publisher: Copernicus GmbH
Keywords:▾
boreal forest; climate forcing; climate modeling; greenhouse gas; heat transfer; lake ecosystem; land surface; marine isotope stage; paleoclimate; paleoenvironment; Pleistocene; proxy climate record, Arctic Ocean; Chukchi; Elgygytgyn Lake; Russian Federation; Russian Federation
Abstract: ▾ Until now, the lack of time-continuous, terrestrial paleoenvironmental data from the Pleistocene Arctic has made model simulations of past interglacials difficult to assess. Here, we compare climate simulations of four warm interglacials at Marine Isotope Stages (MISs) 1 (9 ka), 5e (127 ka), 11c (409 ka) and 31 (1072 ka) with new proxy climate data recovered from Lake El'gygytgyn, NE Russia. Climate reconstructions of the mean temperature of the warmest month (MTWM) indicate conditions up to 0.4, 2.1, 0.5 and 3.1 °C warmer than today during MIS 1, 5e, 11c and 31, respectively. While the climate model captures much of the observed warming during each interglacial, largely in response to boreal summer (JJA) orbital forcing, the extraordinary warmth of MIS 11c compared to the other interglacials in the Lake El'gygytgyn temperature proxy reconstructions remains difficult to explain. To deconvolve the contribution of multiple influences on interglacial warming at Lake El'gygytgyn, we isolated the influence of vegetation, sea ice and circum-Arctic land ice feedbacks on the modeled climate of the Beringian interior. Simulations accounting for climate-vegetation-land-surface feedbacks during all four interglacials show expanding boreal forest cover with increasing summer insolation intensity. A deglaciated Greenland is shown to have a minimal effect on northeast Asian temperature during the warmth of stages 11c and 31 (Melles et al., 2012). A prescribed enhancement of oceanic heat transport into the Arctic Ocean does have some effect on Lake El'gygytgyn's regional climate, but the exceptional warmth of MIS l1c remains enigmatic compared to the modest orbital and greenhouse gas forcing during that interglacial. © Author(s) 2015.
1683.
Earth science: Deadly combination
Nature,
527
(7577)
172-173
2015
DOI:10.1038/527172a
Abstract: ▾ New evidence suggests that seismic waves from the Chicxulub meteorite impact doubled the eruption rate of lavas on the opposite side of the planet - a combination that led to the mass extinction at the end of the Cretaceous period. © 2015 Macmillan Publishers Limited. All rights reserved.
1682.
Continuous 1.3-million-year record of East African hydroclimate, and implications for patterns of evolution and biodiversity
Proceedings of the National Academy of Sciences of the United States of America,
112
(51)
15568-15573
2015
ISSN: 00278424
Publisher: National Academy of Sciences
Keywords:▾
water, Article; atmospheric moisture; biodiversity; catchment; cichlid; climate change; clinical effectiveness; East African; freshwater environment; hydroclimate; lake; Middle Pleistocene; molecular evolution; nonhuman; paleoclimate; priority journal; species diversity; tropic climate; Africa; animal; climate; ecosystem; evolution; history; paleontology; time factor, Africa, Eastern; Animals; Biodiversity; Biological Evolution; Cichlids; Climate; Climate Change; Ecosystem; History, Ancient; Lakes; Paleontology; Time Factors
Abstract: ▾ The transport of moisture in the tropics is a critical process for the global energy budget and on geologic timescales, has markedly influenced continental landscapes, migratory pathways, and biological evolution. Here we present a continuous, first-of-its-kind 1.3-My record of continental hydroclimate and lake-level variability derived from drill core data from Lake Malawi, East Africa (9-15° S). Over the Quaternary, we observe dramatic shifts in effective moisture, resulting in large-scale changes in one of the world's largest lakes and most diverse freshwater ecosystems. Results show evidence for 24 lake level drops of more than 200 m during the Late Quaternary, including 15 lowstands when water levels were more than 400 m lower than modern. A dramatic shift is observed at the Mid-Pleistocene Transition (MPT), consistent with far-field climate forcing, which separates vastly different hydroclimate regimes before and after ∼800,000 years ago. Before 800 ka, lake levels were lower, indicating a climate drier than today, and water levels changed frequently. Following the MPT high-amplitude lake level variations dominate the record. From 800 to 100 ka, a deep, often overfilled lake occupied the basin, indicating a wetter climate, but these highstands were interrupted by prolonged intervals of extreme drought. Periods of high lake level are observed during times of high eccentricity. The extreme hydroclimate variability exerted a profound influence on the Lake Malawi endemic cichlid fish species flock; the geographically extensive habitat reconfiguration provided novel ecological opportunities, enabling new populations to differentiate rapidly to distinct species.
1681.
Episodes of environmental stability versus instability in Late Cenozoic lake records of Eastern Africa
Journal of Human Evolution,
8721 – 31
2015
1680.
Initial seismic observations from a deep borehole drilled into the Canadian Shield in northeast Alberta
International Journal of Earth Sciences,
104
(6)
1549 – 1562
2015
ISSN: 14373254
Publisher: Springer Verlag
Keywords:▾
Alberta; Canada; Canadian Shield; borehole; craton; metamorphic rock; seismic reflection; seismic velocity; vertical seismic profile
Abstract: ▾ The availability of a deep borehole in northeastern Alberta provides an unprecedented opportunity to study the in situ metamorphic craton rocks. This borehole reaches a depth of 2.4 km, with 1.8 km in the crystalline rocks, and is the only known borehole allowing access into the deeper rocks of the metamorphic Canadian Shield. In 2011, a zero-offset vertical seismic profile (VSP) was acquired to assist in the interpretation of seismic reflection data and geophysical logs. Three sets of upgoing tube waves interpreted from the raw profile correspond to the small-scale fluctuations in the borehole diameters and fracture zone in the crystalline rocks. A comparison between sonic log velocities and VSP velocities reveals a zone with increased velocity that could be due to the change in rock composition and texture in the basement rocks. The final processed profile is used to generate corridor stacks for differentiating between primary reflections and multiples in the seismic reflection profile. Analysis of the zero-offset VSP verifies existing log interpretation on the presence of fractures and the possible lithological changes in the metamorphic rocks of the Canadian Shield. © 2014, The Author(s).
1679.
Mediterranean climate since the Middle Pleistocene: A 640 ka stable isotope record from Lake Ohrid (Albania/Macedonia)
Biogeosciences Discussions,
12
(16)
13427 – 13481
2015
ISSN: 18106277
Publisher: Copernicus GmbH
Keywords:▾
Lake Mikri Prespa; Lake Ohrid; Mediterranean Region; biodiversity; calcite; carbon isotope; endemic species; glacial-interglacial cycle; lacustrine deposit; lake water; Mediterranean environment; oxygen isotope; Pleistocene; population structure; sediment core; siderite; stable isotope; temperature effect
Abstract: ▾ Lake Ohrid (Macedonia/Albania) is an ancient lake with a unique biodiversity and a site of global significance for investigating the influence of climate, geological and tectonic events on the generation of endemic populations. Here, we present oxygen (δ18O) and carbon (δ13C) isotope data on carbonate from the upper ca. 248 m of sediment cores recovered as part of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project, covering the past 640 ka. Previous studies on short cores from the lake (up to 15 m, < 140 ka) have indicated the Total Inorganic Carbon (TIC) content of sediments to be highly sensitive to climate change over the last glacial-interglacial cycle, comprising abundant endogenic calcite through interglacials and being almost absent in glacials, apart from discrete bands of early diagenetic authigenic siderite. Isotope measurements on endogenic calcite(δ18Oc and δ13Cc) reveal variations both between and within interglacials that suggest the lake has been subject to hydroclimate fluctuations on orbital and millennial timescales. We also measured isotopes on authigenic siderite (δ18Os and δ13Cs) and, with the δ18OCc and δ18Os, reconstruct δ18O of lakewater (δ18Olw) through the 640 ka. Overall, glacials have lower δ18Olw when compared to interglacials, most likely due to cooler summer temperatures, a higher proportion of winter precipitation (snowfall), and a reduced inflow from adjacent Lake Prespa. The isotope stratigraphy suggests Lake Ohrid experienced a period of general stability through Marine Isotope Stage (MIS) 15 to MIS 13, highlighting MIS 14 as a particularly warm glacial, and was isotopically freshest during MIS 9. After MIS 9, the variability between glacial and interglacial δ18Olw is enhanced and the lake became increasingly evaporated through to present day with MIS 5 having the highest average δ18Olw. Our results provide new evidence for long-term climate change in the northern Mediterranean region, which will form the basis to better understand the influence of major environmental events on biological evolution within the lake. © Author(s) 2015.
1678.
Erratum to Orogenic paleofluid flow recorded by discordant detrital zircons in the Caledonian foreland basin of northern Greenland [Lithosphere, 7, 2, (2015), 138-143] DOI: 10.1130/L420.1
Lithosphere,
7
(2)
206-206
2015
ISSN: 19418264
Publisher: Geological Society of America
DOI:10.1130/L395.1
Keywords:▾
Caledonian orogeny; detrital deposit; foreland basin; geochronology; lithosphere; lithostratigraphy; orogenic belt; zircon, Arctic; Greenland
1677.
Magma mixing enhanced by bubble segregation
Solid Earth,
6
(3)
1007-1023
2015
ISSN: 18699510
Publisher: Copernicus GmbH
Keywords:▾
Advection; Basalt; Cylinders (shapes); Glass; Mixing; Silicates; Viscosity, Compositional gradients; Diffusion gradients; Magmatic temperatures; Orders of magnitude; Reduced viscosity; Rheological modelling; Viscous resistance; Volatile contents, Computerized tomography, advection; bubble; chemical alteration; chemical composition; entrainment; experimental study; igneous geochemistry; magma assimilation; mixing; rhyolite; silicate melt
Abstract: ▾ In order to explore the materials' complexity induced by bubbles rising through mixing magmas, bubble-advection experiments have been performed, employing natural silicate melts at magmatic temperatures. A cylinder of basaltic glass was placed below a cylinder of rhyolitic glass. Upon melting, bubbles formed from interstitial air. During the course of the experimental runs, those bubbles rose via buoyancy forces into the rhyolitic melt, thereby entraining tails of basaltic liquid. In the experimental run products, these plume-like filaments of advected basalt within rhyolite were clearly visible and were characterised by microCT and high-resolution EMP analyses. <br><br> The entrained filaments of mafic material have been hybridised. Their post-experimental compositions range from the originally basaltic composition through andesitic to rhyolitic composition. Rheological modelling of the compositions of these hybridised filaments yield viscosities up to 2 orders of magnitude lower than that of the host rhyolitic liquid. Importantly, such lowered viscosities inside the filaments implies that rising bubbles can ascend more efficiently through pre-existing filaments that have been generated by earlier ascending bubbles. MicroCT imaging of the run products provides textural confirmation of the phenomenon of bubbles trailing one another through filaments. This phenomenon enhances the relevance of bubble advection in magma mixing scenarios, implying as it does so, an acceleration of bubble ascent due to the decreased viscous resistance facing bubbles inside filaments and yielding enhanced mass flux of mafic melt into felsic melt via entrainment. In magma mixing events involving melts of high volatile content, bubbles may be an essential catalyst for magma mixing. <br><br> Moreover, the reduced viscosity contrast within filaments implies repeated replenishment of filaments with fresh end-member melt. As a result, complex compositional gradients and therefore diffusion systematics can be expected at the filament-host melt interface, due to the repetitive nature of the process. However, previously magmatic filaments were tacitly assumed to be of single-pulse origin. Consequently, the potential for multi-pulse filaments has to be considered in outcrop analyses. As compositional profiles alone may remain ambiguous for constraining the origin of filaments, and as 3-D visual evidence demonstrates that filaments may have experienced multiple bubbles passages even when featuring standard diffusion gradients, therefore, the calculation of diffusive timescales may be inadequate for constraining timescales in cases where bubbles have played an essential role in magma mixing. Data analysis employing concentration variance relaxation in natural samples can distinguish conventional single-pulse filaments from advection via multiple bubble ascent advection in natural samples, raising the prospect of yet another powerful application of this novel petrological tool. © 2015 Author(s).
1676.
Low resistivity and permeability in actively deforming shear zones on the San Andreas Fault at SAFOD
Journal of Geophysical Research: Solid Earth,
120
(12)
8240-8258
2015
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
active fault; deformation; electrical resistivity; fault gouge; permeability; porosity; San Andreas Fault; sediment core; shear zone, California; Parkfield; United States
Abstract: ▾ The San Andreas Fault Observatory at Depth (SAFOD) scientific drill hole near Parkfield, California, crosses the San Andreas Fault at a depth of 2.7 km. Downhole measurements and analysis of core retrieved from Phase 3 drilling reveal two narrow, actively deforming zones of smectite-clay gouge within a roughly 200 m wide fault damage zone of sandstones, siltstones, and mudstones. Here we report electrical resistivity and permeability measurements on core samples from all of these structural units at effective confining pressures up to 120 MPa. Electrical resistivity (~10 Ω-m) and permeability (10-21 to 10-22 m2) in the actively deforming zones were 1 to 2 orders of magnitude lower than the surrounding damage zone material, consistent with broader-scale observations from the downhole resistivity and seismic velocity logs. The higher porosity of the clay gouge, 2 to 8 times greater than that in the damage zone rocks, along with surface conduction were the principal factors contributing to the observed low resistivities. The high percentage of fine-grained clay in the deforming zones also greatly reduced permeability to values low enough to create a barrier to fluid flow across the fault. Together, resistivity and permeability data can be used to assess the hydrogeologic characteristics of the fault, key to understanding fault structure and strength. The low resistivities and strength measurements of the SAFOD core are consistent with observations of low resistivity clays that are often found in the principal slip zones of other active faults making resistivity logs a valuable tool for identifying these zones. © Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
1675.
Lateglacial and Holocene climatic changes in south-eastern Patagonia inferred from carbonate isotope records of Laguna Potrok Aike (Argentina)
Quaternary Science Reviews,
114189 – 202
2015
Keywords:▾
Argentina; Laguna Potrok Aike; Patagonia; Santa Cruz [Argentina]; Budget control; Calcite; Calcium; Calcium carbonate; Carbon; Carbonation; Climate change; Glacial geology; Isotopes; Lakes; Oxygen; Sediments; Calcium isotopes; Carbon isotopes; ICDP; Ikaite; Lake sediments; Oxygen isotopes; PASADO; Southern south america; Strontium isotopes; carbonate; climate variation; evaporation; Holocene; ikaite; isotopic composition; lacustrine deposit; late glacial; oxygen isotope; paleoclimate; paleotemperature; proxy climate record; strontium isotope; westerly; Strontium
Abstract: ▾ First results of strontium, calcium, carbon and oxygen isotope analyses of bulk carbonates from a 106m long sediment record of Laguna Potrok Aike, located in southern Patagonia are presented. Morphological and isotopic investigations of μm-sized carbonate crystals in the sediment reveal an endogenic origin for the entire Holocene. During this time period the calcium carbonate record of Laguna Potrok Aike turned out to be most likely ikaite-derived. As ikaite precipitation in nature has only been observed in a narrow temperature window between 0 and 7°C, the respective carbonate oxygen isotope ratios serve as a proxy of hydrological variations rather than of palaeotemperatures. We suggest that oxygen isotope ratios are sensitive to changes of the lake water balance induced by intensity variations of the Southern Hemisphere Westerlies and discuss the role of this wind belt as a driver for climate change in southern South America. In combination with other proxy records the evolution of westerly wind intensities is reconstructed. Our data suggest that weak SHW prevailed during the Lateglacial and the early Holocene, interrupted by an interval with strengthened Westerlies between 13.4 and 11.3kacalBP. Wind strength increased at 9.2kacalBP and significantly intensified until 7.0kacalBP. Subsequently, the wind intensity diminished and stabilised to conditions similar to present day after a period of reduced evaporation during the "Little Ice Age". Strontium isotopes (87Sr/86Sr ratio) were identified as a potential lake-level indicator and point to a lowering from overflow conditions during the Glacial (~17kacalBP) to lowest lake levels around 8kacalBP. Thereafter the strontium isotope curve resembles the lake-level curve which is stepwise rising until the "Little Ice Age". The variability of the Ca isotope composition of the sediment reflects changes in the Ca budget of the lake, indicating higher degrees of Ca utilisation during the period with lowest lake level. © 2015 Elsevier Ltd.
1674.
Late Glacial and Early Holocene cyclic changes in paleowind conditions and lake levels inferred from diatom assemblage shifts in Laguna Potrok Aike sediments (southern Patagonia, Argentina)
Palaeogeography, Palaeoclimatology, Palaeoecology,
42720 – 31
2015
1673.
Lake Qinghai sediment geochemistry linked to hydroclimate variability since the last glacial
Quaternary Science Reviews,
12263-73
2015
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Animals; Arid regions; Calcium; Carbonate minerals; Dust; Geochemistry; Glacial geology; Lakes; Minerals; Precipitates; Rubidium; Sedimentology, Asian dust; Hydroclimate; Lake Qinghai; Lake waters; Sediment geochemistries, Sediments, aragonite; calcium carbonate; chemical composition; climate variation; eolian process; lacustrine deposit; Last Glacial; Northern Hemisphere; ostracod; paleoclimate; sediment chemistry; semiarid region; shell, China; Qinghai; Qinghai Lake, Ostracoda
Abstract: ▾ Geochemistry of basin sediments from semi-arid regions is valuable to understand past hydroclimatic changes. Here, we investigate the links of sedimentary geochemistry (Rb, Sr, Ca/Zr, TOC, and %CaCO3), carbonate mineralogy and ostracod shell δ18O of Lake Qinghai, a basin proximal to major dust production centers at mid-latitudes of the Northern Hemisphere, to changes in depositional conditions and hydroclimate during the past 32ka. Surface lacustrine sediments are characterized by low-Rb, high-Sr, low-Rb/Sr, high-%CaCO3 and high-Ca/Zr values, in contrast to the chemical compositions of eolian loess (high-Rb, low-Sr, high-Rb/Sr, low-%CaCO3, and low-Ca/Zr). A direct comparison of soluble Ca and Sr in two short cores with instrumental water discharge data suggests that lacustrine precipitates in Lake Qinghai are dominated by authigenic aragonite formed under Ca2+-limited water conditions, and that the accumulation rate of aragonite dominantly depends on solute fluxes into the lake during the rainy seasons (late May to September). Our high-resolution down-core records show that sediments during the last glacial (~32-19.8ka) had high-Rb, low-Sr, low-%CaCO3, and low-Ca/Zr, indicating eolian dust (loess) accumulation in a desiccated basin under dry glacial conditions, further supported by grain size and pollen results. This type of sedimentation was maintained during the last deglacial (~19.8-11.5ka), but interrupted by episodic lacustrine precipitates with high-Sr, high-%CaCO3, high-Ca/Zr, and low-Rb. At ~11.5ka, sedimentary Rb/Sr, Ca/Zr, %CaCO3 and TOC show dramatic and permanent changes, implying an abrupt shift in the atmospheric circulation at the onset of the Holocene in the Lake Qinghai region. Lacustrine precipitates have persisted throughout the Holocene with a maximum during the early to mid-Holocene (~10.5-8.0ka). Since ~8.0ka, the gradual and significant decreases in aragonite and Sr accumulations in tandem with increasing dust deposit and more positive ostracod δ18O may be linked to a weakening of Asian summer monsoons during the mid-to-late Holocene. Overall, our records appear to show a high sensitivity of sediment development and geochemistry in Lake Qinghai to the regional hydroclimate changes since the last glacial. © 2015 Elsevier Ltd.
1672.
Laboratory study on ultra high temperature water base mud
Drilling Fluid and Completion Fluid,
32
(1)
10–13 and 97
2015
ISSN: 10015620
Publisher: North China Petroleum Administration Drilling Technology Research Institute
Abstract: ▾ A high temperature water base drilling fluid was formulated with sodium bentonite and attapulgite, and a high temperature water-in-oil stabilizer, MG-H2 which is synthesized through emulsion polymerization. Laboratory evaluation of the drilling fluid showed that, after aging at 240 °C, the drilling fluid still retained satisfactory rheology and filtration properties. It had good inhibitive capacity and was resistant to contamination caused by the introduction of 10% clay, or a combination of 5% NaCl and 1% CaCl2. It also had good lubricity at high temperature. The formulation of this high temperature drilling fluid lays the foundation for the formulation of an ultra-high temperature drilling fluid, say, 260 °C, for the drilling of the Well Songke-2.
1671.
Investigations related to scientific deep drilling to study reservoir-triggered earthquakes at Koyna, India
International Journal of Earth Sciences,
104
(6)
1511-1522
2015
ISSN: 14373254
Publisher: Springer Verlag
Keywords:▾
borehole; deep drilling; earthquake; earthquake hypocenter; fault zone; heat flow; lidar; reservoir; seismic zone; seismicity; trigger mechanism, Deccan; India; Koyna; Maharashtra, Calluna vulgaris
Abstract: ▾ Artificial water reservoir-triggered earthquakes have continued at Koyna in the Deccan Traps province, India, since the impoundment of the Shivaji Sagar reservoir in 1962. Existing models, to comprehend the genesis of triggered earthquakes, suffer from lack of observations in the near field. To investigate further, scientific deep drilling and setting up a fault zone observatory at depth of 5–7 km is planned in the Koyna area. Prior to undertaking deep drilling, an exploratory phase of investigations has been launched to constrain subsurface geology, structure and heat flow regime in the area that provide critical inputs for the design of the deep borehole observatory. Two core boreholes drilled to depths of 1,522 and 1,196 m have penetrated the Deccan Traps and sampled the granitic basement in the region for the first time. Studies on cores provide new and direct information regarding the thickness of the Deccan Traps, the absence of infra-Trappean sediments and the nature of the underlying basement rocks. Temperatures estimated at a depth of 6 km in the area, made on the basis of heat flow and thermal properties data sets, do not exceed 150 °C. Low-elevation airborne gravity gradient and magnetic data sets covering 5,012 line km, together with high-quality magnetotelluric data at 100 stations, provide both regional information about the thickness of the Deccan Traps and the occurrence of localized density heterogeneities and anomalous conductive zones in the vicinity of the hypocentral zone. Acquisition of airborne LiDAR data to obtain a high-resolution topographic model of the region has been completed over an area of 1,064 km2 centred on the Koyna seismic zone. Seismometers have been deployed in the granitic basement inside two boreholes and are planned in another set of six boreholes to obtain accurate hypocentral locations and constrain the disposition of fault zones. © 2014, Springer-Verlag Berlin Heidelberg.
1670.
Investigating uncertainties in empirical green’s function analysis of earthquake source parameters
Journal of Geophysical Research: Solid Earth,
120
(6)
4263-4277
2015
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Abstract: ▾ I use a well-recorded earthquake sequence to investigate the uncertainties of earthquake stress drops calculated using an empirical Green’s function (EGF) approach. The earthquakes in the largest (M~ 2.1) repeating sequence targeted by the San Andreas Observatory at Depth (SAFOD), Parkfield, California, are recorded by multiple borehole stations and have simple sources, well-constrained stress drops, and abundant smaller earthquakes to use as EGFs. I perform three tests to estimate quantitatively the likely uncertainties to arise in less optimal settings. I use EGF earthquakes with a range of cross-correlation values and separation distances fromthe main earthquakes. The stress dropmeasurements decrease by a factor of 3 as the quality of the EGF assumption decreases; a good EGF must be located within approximately one source dimension of the large earthquake, with high cross correlation. I subsample the large number ofmeasurements for the main earthquakes to investigate the expected stress drop uncertainties in studies where fewer stations or EGFs are available. If only one measurement is available, the uncertainties are likely to be at least 50%. The uncertainties decrease to <20% with five ormore measurements; usingmultiple EGFs is a good alternative to multiple stations. To investigate the effects of limited frequency bandwidth, I recalculate the corner frequencies after progressively decimating the sample rate. Decreasing the high-frequency limit of the bandwidth decreases the estimate of the corner frequency (and stress drop). The corner frequency may be underestimated if it is within a factor of 3 of the maximum frequency of the signal. © 2015. American Geophysical Union. All Rights Reserved.