All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1794.
Hydrogen utilization potential in subsurface sediments
Frontiers in Microbiology,
7
(JAN)
2016
ISSN: 1664302X
Publisher: Frontiers Media S.A.
Keywords:▾
hydrogen; hydrogenase; iron; manganese; sulfate, Article; ecosystem; enzyme assay; Gulf of Mexico; metabolic activity assay; microbial activity; microbial community; nonhuman; Pacific Ocean; radioactivity; sediment; temperature; Turkey (republic); water analysis
Abstract: ▾ Subsurface microbial communities undertake many terminal electron-accepting processes, often simultaneously. Using a tritium-based assay, we measured the potential hydrogen oxidation catalyzed by hydrogenase enzymes in several subsurface sedimentary environments (Lake Van, Barents Sea, Equatorial Pacific, and Gulf of Mexico) with different predominant electron-acceptors. Hydrogenases constitute a diverse family of enzymes expressed by microorganisms that utilize molecular hydrogen as a metabolic substrate, product, or intermediate. The assay reveals the potential for utilizing molecular hydrogen and allows qualitative detection of microbial activity irrespective of the predominant electron-accepting process. Because the method only requires samples frozen immediately after recovery, the assay can be used for identifying microbial activity in subsurface ecosystems without the need to preserve live material. We measured potential hydrogen oxidation rates in all samples from multiple depths at several sites that collectively span a wide range of environmental conditions and biogeochemical zones. Potential activity normalized to total cell abundance ranges over five orders of magnitude and varies, dependent upon the predominant terminal electron acceptor. Lowest per-cell potential rates characterize the zone of nitrate reduction and highest per-cell potential rates occur in the methanogenic zone. Possible reasons for this relationship to predominant electron acceptor include (i) increasing importance of fermentation in successively deeper biogeochemical zones and (ii) adaptation of H2ases to successively higher concentrations of H2 in successively deeper zones. © 2016 Adhikari, Glombitza, Nickel, Anderson, Dunlea, Spivack, Murray, D'Hondt and Kallmeyer.
1793.
Hydroclimatic variability in the Levant during the early last glacial ( ∼ 117-75 ka) derived from micro-facies analyses of deep Dead Sea sediments
Climate of the Past,
12
(1)
75-90
2016
ISSN: 18149324
Publisher: Copernicus GmbH
Keywords:▾
climate variation; core analysis; deep-sea sediment; interstadial; lake level; Last Glacial; last glaciation; Last Interglacial; marine isotope stage; marl; microfacies; Northern Hemisphere; petrography; sapropel; turbidite, Arctic; Atlantic Ocean; Atlantic Ocean (North); Dead Sea; Greenland; Levant; Mediterranean Region; Mediterranean Sea
Abstract: ▾ The new sediment record from the deep Dead Sea basin (ICDP core 5017-1) provides a unique archive for hydroclimatic variability in the Levant. Here, we present highresolution sediment facies analysis and elemental composition by micro-X-ray fluorescence (ìXRF) scanning of core 5017-1 to trace lake levels and responses of the regional hydroclimatology during the time interval from ca. 117 to 75 ka, i.e. the transition between the last interglacial and the onset of the last glaciation. We distinguished six major micro-facies types and interpreted these and their alterations in the core in terms of relative lake level changes. The two end-member facies for highest and lowest lake levels are (a) up to several metres thick, greenish sediments of alternating aragonite and detrital marl laminae (aad) and (b) thick halite facies, respectively. Intermediate lake levels are characterised by detrital marls with varying amounts of aragonite, gypsum or halite, reflecting lower-amplitude, shorter-term variability. Two intervals of pronounced lake level drops occurred at ∼110-1085 and ∼93-87±7 ka. They likely coincide with stadial conditions in the central Mediterranean (Melisey I and II pollen zones in Monticchio) and low global sea levels during Marine Isotope Stage (MIS) 5d and 5b. However, our data do not support the current hypothesis of an almost complete desiccation of the Dead Sea during the earlier of these lake level low stands based on a recovered gravel layer. Based on new petrographic analyses, we propose that, although it was a low stand, this well-sorted gravel layer may be a vestige of a thick turbidite that has been washed out during drilling rather than an in situ beach deposit. Two intervals of higher lake stands at ∼108-93±6 and ∼87-75±7 ka correspond to interstadial conditions in the central Mediterranean, i.e. pollen zones St. Germain I and II in Monticchio, and Greenland interstadials (GI) 24C23 and 21 in Greenland, as well as to sapropels S4 and S3 in the Mediterranean Sea. These apparent correlations suggest a close link of the climate in the Levant to North Atlantic and Mediterranean climates during the time of the build-up of Northern Hemisphere ice shields in the early last glacial period. © 2016 Author(s).
1792.
High-precision U-Pb geochronologic constraints on the Late Cretaceous terrestrial cyclostratigraphy and geomagnetic polarity from the Songliao Basin, Northeast China
Earth and Planetary Science Letters,
44637-44
2016
ISSN: 0012821X
Publisher: Elsevier B.V.
Keywords:▾
Climate change; Core drilling; Deposition; Drills; Geologic models; Geomagnetism; Sedimentology; Silicate minerals, China; Cyclostratigraphy; Magnetostratigraphy; Santonian-Campanian boundary; Songliao basin; U-Pb geochronology, Geochronology, Cretaceous; cyclostratigraphy; geochronology; magnetic reversal; magnetostratigraphy; uranium-lead dating, China; Songliao Basin
Abstract: ▾ The Cretaceous continental sedimentary records are essential to our understanding of how the terrestrial geologic and ecologic systems responded to past climate fluctuations under greenhouse conditions and our ability to forecast climate change in the future. The Songliao Basin of Northeast China preserves a near-complete, predominantly lacustrine, Cretaceous succession, with sedimentary cyclicity that has been tied to Milankocitch forcing of the climate. Over 900 meters of drill-core recovered from the Upper Cretaceous (Turonian to Campanian) of the Songliao Basin has provided a unique opportunity for detailed analyses of its depositional and paleoenvironmental records through integrated and high-resolution cyclostratigraphic, magnetostratigraphic and geochronologic investigations.Here we report high-precision U-Pb zircon dates (CA-ID-TIMS method) from four interbedded bentonites from the drill-core that offer substantial improvements in accuracy, and a ten-fold enhancement in precision, compared to the previous U-Pb SIMS geochronology, and allow a critical evaluation of the Songliao astrochronological time scale. The results indicate appreciable deviations of the astrochronologic model from the absolute radioisotope geochronology, which more likely reflect cyclostratigraphic tuning inaccuracies and omitted cycles due to depositional hiatuses, rather than suspected limitations of astronomical models applied to distant geologic time.Age interpolation based on our new high-resolution geochronologic framework and the calibrated cyclostratigraphy places the end of the Cretaceous Normal Superchon (C34n-C33r chron boundary) in the Songliao Basin at 83.07. ±. 0.15 Ma. This date also serves as a new and improved estimate for the global Santonian-Campanian stage boundary. © 2016 Elsevier B.V.
1791.
Locating mofettes using seismic noise records from small dense arrays and matched field processing analysis in the NW Bohemia/Vogtland Region, Czech Republic
Near Surface Geophysics,
14
(4)
327 – 335
2016
ISSN: 15694445
Publisher: EAGE Publishing BV
Keywords:▾
Bohemia; Czech Republic; Germany; Vogtland; array; borehole; degassing; earthquake event; earthquake swarm; effective stress; fluid flow; phase velocity; seismic noise
Abstract: ▾ The NW Bohemia/Vogtland region is characterized by currently ongoing geodynamic processes within the intracontinental lithospheric mantle. Among others, this activity results in the occurrence of mid-crustal earthquake swarms and CO2 degassing zones called mofettes. These two natural phenomena are related to each other since it is considered that fluid flow and fluid-induced effective stress can trigger earthquake swarms. At the Earth's surface, they appear spatially separated, but their connection could be explained by the existence of pathways within the crust that allow efficient and permanent fluid transport. However, neither the structure nor the position of such pathways has been imaged yet. With this background, we used a matched field processing analysis within the NW Bohemia/Vogtland region to locate mofettes and investigate their characteristics. Considering the CO2 degassing process as a high-frequency noise source, we chose two different test sites: the Dolní Částkov Borehole, which is an artificial mofette that we used to validate the method, and the South Hartoušov mofette field, a natural CO2 degassing area. On both sites, we measured seismic noise in a continuous mode for several hours (7 hours to 9 hours), with a sampling frequency of 250 samples/second, in multiple campaigns using an array of about 60 × 60 m2 with approximately 30 randomly distributed stations. For the matched field processing computation, the phase velocity c(□) of the study area is required, which we obtained from active seismic experiments with vertical hammer-blow as the source. The phase velocity varies between 200 m/s and 420 m/s for Dolní Částkov and between 100 m/s and 280 m/s for South Hartoušov, both in a frequency range of 7 Hz-60 Hz. With the matched field processing analysis at the artificial mofette in Dolní Částkov, we could relocate the noise source successfully. In the South Hartoušov mofette field, we detected one dominant vertically extended noise source, probably a fluid pathway, as well as a small matched field processing maxima at the surface that can be related to a dry mofette. © 2016 European Association of Geoscientists & Engineers.
1790.
Heat flow pattern at the Chicxulub impact crater, northern Yucatan, Mexico
Journal of Volcanology and Geothermal Research,
311135-149
2016
Abstract: ▾ Along an east-west profile crossing the Chicxulub impact structure in northern Yucatán, México, Curie depths were obtained from statistical-spectral analysis of a grid of aeromagnetic data (256 km wide and 600 km long). These depths were corrected for flight height and depth to the sea floor to determine the geothermal gradient, assuming a temperature of 580 °C for the Curie temperature. Heat flow was then calculated from the geothermal gradients using a value of 2.67 W/m-for the mean crustal thermal conductivity. The results show a conspicuous heat flow high above on the impact basin. In this location, the heat flow is 80 mW/m2 approximately. Available offshore estimates of the depth to the crustal magnetic source bases, on the northern Yucatán platform, and onshore heat flow determination on 8 shallow bore holes, and in a 1511 m deep one, support the existence of this major high heat flow anomaly associated with the impact crater. This high heat flow might be related to the impact through: (1) an uplift of the crystalline basement rocks in the center of the crater; and (2) impact induced radioactive element concentration into the crust below the impact structure. Higher thermal conductivities at the lower crust might also play a key role. Available seismological and thermal property data are compatible with these mechanisms. © 2016 Elsevier B.V.
1789.
First tephrostratigraphic results of the DEEP site record from Lake Ohrid (Macedonia and Albania)
Biogeosciences,
13
(7)
2151-2178
2016
ISSN: 17264170
Publisher: Copernicus GmbH
Keywords:▾
biostratigraphy; Campanian; geochemical method; marine environment; paleoclimate; paleoenvironment; Pleistocene; tephra; tephrochronology; volcanic soil, Abruzzi; Adriatic Sea; Alban Hills; Albania; Apennines; Balkans; Basilicata; Campania [Italy]; Italy; L'Aquila; Lago Grande di Monticchio; Lake Ohrid; Lazio; Macedonia [Southern Europe]; Mediterranean Sea; Mount Somma; Napoli [Campania]; Potenza; Sulmona Basin; Vesuvius; Vico
Abstract: ▾ A tephrostratigraphic record covering the Marine Isotope Stages (MIS) 1-15 was established for the DEEP site record of Lake Ohrid (Macedonia and Albania). Major element analyses (energy dispersive spectroscopy (EDS) and wavelength-dispersive spectroscopy (WDS)) were carried out on juvenile fragments extracted from 12 tephra layers (OH-DP-0115 to OH-DP-2060). The geochemical analyses of the glass shards of all of these layers suggest an origin in the Italian volcanic provinces. They include the Y-3 (OH-DP-0115, 26.68-29.42 ka cal BP), the Campanian Ignimbrite-Y-5 (OH-DP-0169, 39.6±0.1 ka), and the X- 6 (OH-DP-0404, 109±2 ka) from the Campanian volcanoes, the P-11 of Pantelleria (OH-DP-0499, 133.5±2 ka), the Vico B (OH-DP-0617, 162±6 ka) from the Vico volcano, the Pozzolane Rosse (OH-DP-1817, 457±2 ka) and the Tufo di Bagni Albule (OH-DP-2060, 527±2 ka) from the Colli Albani volcanic district, and the Fall A (OH-DP- 2010, 496±3 ka) from the Sabatini volcanic field. Furthermore, a comparison of the Ohrid record with tephrostratigraphic records of mid-distal archives related to the Mediterranean area allowed the recognition of the equivalents of other less known tephra layers, such as the TM24a-POP2 (OH-DP-0404, 102±2 ka) recognized in the Lago Grande di Monticchio and the Sulmona Basin, the CF-V5-PRAD3225 (OH-DP-0624, ca. 163±22 ka) identified in the Campo Felice Basin and the Adriatic Sea, the SC5 (OH-DP-1955, 493.1±10.9 ka) recognized in the Mercure Basin, and the A11/12 (OH-DP-2017, 511±6 ka) sampled at the Acerno Basin, whose specific volcanic sources are still poorly constrained. Additionally, one cryptotephra (OH-DP-0027) was identified by correlation of the potassium X-ray flourescence (XRF) intensities from the DEEP site with those from a short core of a previous study from Lake Ohrid. In these cores, a maximum in potassium is caused by glass shards, which were correlated with the Mercato tephra (8.43-8.63 ka cal BP) from Somma-Vesuvius. The tephrostratigraphic work presented here allows, for the first time, the extension of a consistent part of the Middle Pleistocene tephrostratigraphy of Italian volcanoes as far as the Balkans. The establishment of the tephrostratigraphic framework for the Lake Ohrid record provides important, independent tie points for the age-depth model of the DEEP site sequence, which is a prerequisite for palaeoclimatic and palaeoenvironmental reconstructions. Furthermore, this age-depth model will help to improve and re-evaluate the chronology of other, both undated and dated tephra layers from other records. Thus, the Lake Ohrid record may potentially become the template for the central Mediterranean tephrostratigraphy, especially for the hitherto poorly known and explored lower Middle Pleistocene period. © 2016 Author(s).
1788.
Gyrosigma peisonis var. major var. nov., a new variety of Gyrosigma peisonis (Bacillariophyta) from Lake Qinghai, China
Phytotaxa,
245
(2)
119 – 128
2016
ISSN: 11793155
Publisher: Magnolia Press
Abstract: ▾ The morphology and ultrastructure of Gyrosigma peisonis var. major var. nov., a new variety of Gyrosigma peisonis found in Lake Qinghai (China), are described here on the basis of light and scanning electron microscopy. Most of the morphological features of this new variety are identical to those of the nominal variety Gyrosigma peisonis var. peisonis, but the variety major differs in its distinctly larger cell size and its higher value for the longitudinal/transverse stria density ratio, however. The seasonal variation of this taxon, which was investigated by a sediment-trap study is also discussed. © 2016 Magnolia Press.
1787.
Elemental changes and alteration recorded by basaltic drill core samples recovered from in situ temperatures up to 345°C in the active, seawater-recharged Reykjanes geothermal system, Iceland
Geochemistry, Geophysics, Geosystems,
17
(11)
4772-4801
2016
ISSN: 15252027
Publisher: Blackwell Publishing Ltd
Keywords:▾
Clay alteration; Core drilling; Core samples; Drills; Europium compounds; Geothermal fields; Hydraulic structures; Hydrochemistry; Lithology; Magnesium; Rubidium; Seawater; Uranium, Drill core; Hydrothermal alterations; ICDP; Oceanic crust; Reykjanes, Europium, emplacement; geothermal system; hydrothermal alteration; hydrothermal system; lithology; oceanic crust; recharge; seawater; temperature effect; volcanism, Iceland
Abstract: ▾ Hydrothermal activity results in element exchanges between seawater and oceanic crust that contribute to many aspects of ocean chemistry; therefore, improving knowledge of the associated chemical processes is of global significance. Hydrothermally altered basaltic drill core samples from the seawater-recharged Reykjanes geothermal system in Iceland record elemental gains and losses similar to those observed in samples of hydrothermally altered oceanic crust. At Reykjanes, rocks originally emplaced on the seafloor were buried by continued volcanism and subsided to the current depths (>2250 m below surface). These rocks integrate temperature-dependent elemental gains and losses from multiple stages of hydrothermal alteration that correspond to chemical exchanges observed in rocks from different crustal levels of submarine hydrothermal systems. Specifically, these lithologies have gained U, Mg, Zn, and Pb and have lost K, Rb, Ba, Cu, and light rare earth elements (La through Eu). Alteration and elemental gains and losses in lithologies emplaced on the seafloor can only be explained by a complex multistage hydrothermal alteration history. Reykjanes dolerite intrusions record alteration similar to that reported for the sheeted dike section of several examples of oceanic crust. Specifically, Reykjanes dolerites have lost K, Rb, Ba, and Pb, and gained Cu. The Reykjanes drill core samples provide a unique analog for seawater-oceanic crust reactions actively occurring at high temperatures (275–345°C) beneath a seafloor hydrothermal system. © 2016. American Geophysical Union. All Rights Reserved.
1786.
Electrolyte effects on surface chemistry of basaltic glass in the initial stages of dissolution
Chemical Geology,
42671-84
2016
ISSN: 00092541
Publisher: Elsevier
Keywords:▾
Adsorption; Alkalinity; Aluminum; Basalt; Binding sites; Biological materials; Calcium; Cell membranes; Chemical analysis; Deionized water; Depth profiling; Dissolution; Electrolytes; Geochemistry; Ions; Mass spectrometry; Negative ions; Phase interfaces; Positive ions; Salts; Silicon; Surface chemistry; Zeta potential; Zinc, Alkaline Earth metal cations; Basaltic glass; Charge reversal; Dissolved organic matters; Electrolyte effect; Negative surface charges; Negatively charged surfaces; Secondary neutral mass spectrometry, Glass, concentration (composition); dissolution; electrolyte; experimental study; igneous geochemistry; silicon, Bacteria (microorganisms)
Abstract: ▾ For an understanding of the effect of solution composition on the dissolution rate of basaltic glass detailed knowledge of surface chemistry is important. Here the zeta potential (ζ) as a characteristic parameter of the magnitude of surface charge at the solid-liquid interface was used to determine ionic effects on surface chemistry in initial stages of basaltic glass dissolution. In a systematic approach powdered synthetic basaltic glass was dispersed in solutions of different cations (NO3- salts of Na+, K+, Mg2+, Ca2+, Ba2+, Zn2+, and Al3+) and anions (Na+ salts of F-, Cl-, I-, NO3-, SO42-, C2O42-, HPO42-), each in concentrations of 0.1, 0.5, 1.0, 2.5, and 5.0 mmol/L. ζ was traced in time sequences up to 12,000 h at ideally circumneutral pH. Ion affinities to glass surfaces were characterized by sorption isotherms. A change of glass chemical composition by the formation of altered layers was determined by depth profiling using secondary neutral mass spectrometry (SNMS). The dissolution of the glass was quantified by the amount of Si released after 4000 h.A marked decrease of ζ in deionized water within the first 3 h reaction time is assigned to the desorption of alkali and alkaline earth metal cations from the glass surface and formation of negatively charged SiO- sites. The addition of anions resulted in stronger negative initial ζ values in comparison with the experiment in deionized H2O indicating marked anion adsorption on surface sites, most obvious for F-, C2O42- and HPO42-. The initial ζ was increased upon the addition of divalent cations indicating neutralization of negatively charged surface sites. Over time a striking shift from negative to positive ζ was obtained, most markedly for Ca2+ and Zn2+. The addition of trivalent Al3+ resulted directly in positive ζ indicating a strong adsorption on glass surfaces. With the progress of the experiment the sign of ζ reversed to negative values again. The reason for charge reversal is not fully understood and might be related with cation adsorption exceeding the negative surface charge and a concentration of Fe oxides at the glass surface. After an ~2000 h reaction time ζ adjusted for most electrolyte additions to slightly negative ζ until the end of the experiment, indicating that a final state in the composition of surface sites was reached. The presence of monovalent Na+ and K+ in solution suppressed Si release from the glass, whereas it is accelerated by bivalent cations. It appears that the neutralization of deprotonated ≡Si-O- sites by monovalent cations - their preferential binding is also indicated by chemical analysis - favors polymerization resulting in slower Si release. Upon the addition of Al3+ it is likely that ≡Si-O-Al-O-Si≡ bonds are formed, which can suppress Si release. The presence of F-, C2O42-, and HPO42- clearly enhances glass dissolution, most probably by increasing the coordination of network forming cations, hereby weakening bonds. The observed generation of positive ζ on basaltic glass surfaces is remarkable, and can improve in natural systems the adsorption capability of the basaltic glass surface for negatively charged compounds from pore solution, anions, dissolved organic matter and also bacterial cell walls. © 2016 Elsevier B.V.
1785.
Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640ka sediment sequence from Lake Ohrid (Balkans)
Biogeosciences,
13
(7)
2093-2109
2016
ISSN: 17264170
Publisher: Copernicus GmbH
Keywords:▾
concentration (composition); dilution; environmental conditions; glacial deposit; iron oxide; iron sulfide; magnetic mineral; sediment chemistry; siderite; sulfate; timescale, Balkans; Lake Ohrid
Abstract: ▾ The bulk magnetic mineral record from Lake Ohrid, spanning the past 637 kyr, reflects large-scale shifts in hydrological conditions, and, superimposed, a strong signal of environmental conditions on glacial-interglacial and millennial timescales. A shift in the formation of early di-agenetic ferrimagnetic iron sulfides to siderites is observed around 320 ka. This change is probably associated with variable availability of sulfide in the pore water. We propose that sulfate concentrations were significantly higher before ∼ 320 ka, due to either a higher sulfate flux or lower dilution of lake sulfate due to a smaller water volume. Diagenetic iron minerals appear more abundant during glacials, which are generally characterized by higher Fe/Ca ratios in the sediments. While in the lower part of the core the ferrimagnetic sulfide signal overprints the primary detrital magnetic signal, the upper part of the core is dominated by variable proportions of high- to low-coercivity iron oxides. Glacial sediments are characterized by high concentration of high-coercivity magnetic minerals (hematite, goethite), which relate to enhanced erosion of soils that had formed during preceding interglacials. Superimposed on the glacial-interglacial behavior are millennial-scale oscillations in the magnetic mineral composition that parallel variations in summer insolation. Like the processes on glacial-interglacial timescales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock-magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi-level contribution to environmental reconstructions, since the magnetic properties can mirror both environmental conditions on land and intra-lake processes. © Author(s) 2016.
1784.
Experimental constraints on the relationship between clay abundance, clay fabric, and frictional behavior for the Central Deforming Zone of the San Andreas Fault
Geochemistry, Geophysics, Geosystems,
17
(10)
3865-3881
2016
ISSN: 15252027
Publisher: Blackwell Publishing Ltd
Keywords:▾
Clay minerals; Deformation; Friction; Nanotechnology; Quartz; Serpentine; Silicate minerals; Strike-slip faults; Structural geology; Tectonics, Different proportions; Fabric development; Fault zone; Frictional behavior; Frictional sliding; Random distribution; Shear localizations; Strain localizations, Fault slips, clay mineral; deformation; experimental study; fault gouge; fault zone; friction; petrofabric; San Andreas Fault; slip, California; Parkfield; United States
Abstract: ▾ The presence of smectite (saponite) in fault gouge from the Central Deforming Zone of the San Andreas Fault at Parkfield, CA has been linked to low mechanical strength and aseismic slip. However, the precise relationship between clay mineral structure, fabric development, fault strength, and the stability of frictional sliding is not well understood. We address these questions through the integration of laboratory friction tests and FIB-SEM analysis of fault rock recovered from the San Andreas Fault Observatory at Depth (SAFOD) borehole. Intact fault rock was compared with experimentally sheared fault gouge and different proportions of either quartz clasts or SAFOD clasts extracted from the sample. Nano-textural measurements show the development of localized clay particle alignment along shear folia developed within synthetic gouges; such slip planes have multiples of random distribution (MRD) values of 3.0–4.9. The MRD values measured are higher than previous estimates (MRD 1.5) that show lower degrees of shear localization and clay alignment averaged over larger volumes. The intact fault rock exhibits less well-developed nano-clay fabrics than the experimentally sheared materials, and MRD values decrease with smectite content. We show that the abundance, strength, and shape of clasts all influence fabric evolution via strain localization: quartz clasts yield more strongly developed clay fabrics than serpentine-dominated SAFOD clasts. Our results suggest that (1) both clay abundance and the development of nano-scale fabrics play a role in fault zone weakening and (2) aseismic creep is promoted by slip along clay shears with >20 wt % smectite content and MRD values ≥2.7. © 2016. American Geophysical Union. All Rights Reserved.
1783.
Elevated time-dependent strengthening rates observed in San Andreas Fault drilling samples
Earth and Planetary Science Letters,
450164-172
2016
ISSN: 0012821X
Publisher: Elsevier B.V.
Keywords:▾
Clay minerals; Earthquakes; Friction; Rock drilling; Shear stress; Strike-slip faults; Tribology, Creeping faults; Friction experiments; Linear dependence; Power law relation; Power-law dependences; Recurrence intervals; SAFOD; San Andreas fault, Structural geology, drilling; earthquake recurrence; fault zone; friction; microearthquake; recurrence interval; San Andreas Fault, California; United States
Abstract: ▾ The central San Andreas Fault in California is known as a creeping fault, however recent studies have shown that it may be accumulating a slip deficit and thus its seismogenic potential should be seriously considered. We conducted laboratory friction experiments measuring time-dependent frictional strengthening (healing) on fault zone and wall rock samples recovered during drilling at the San Andreas Fault Observatory at Depth (SAFOD), located near the southern edge of the creeping section and in the direct vicinity of three repeating microearthquake clusters. We find that for hold times of up to 3000 s, frictional healing follows a log-linear dependence on hold time and that the healing rate is very low for a sample of the actively shearing fault core, consistent with previous results. However, considering longer hold times up to ∼350,000 s, the healing rate accelerates such that the data for all samples are better described by a power law relation. In general, samples having a higher content of phyllosilicate minerals exhibit low log-linear healing rates, and the notably clay-rich fault zone sample also exhibits strong power-law healing when longer hold times are included. Our data suggest that weak faults, such as the creeping section of the San Andreas Fault, can accumulate interseismic shear stress more rapidly than expected from previous friction data. Using the power-law dependence of frictional healing on hold time, calculations of recurrence interval and stress drop based on our data accurately match observations of discrete creep events and repeating Mw=2 earthquakes on the San Andreas Fault. © 2016 Elsevier B.V.
1782.
Flowing fluid electrical conductivity logging of a deep borehole during and following drilling: estimation of transmissivity, water salinity and hydraulic head of conductive zones
Hydrogeology Journal
1--17
2016
ISSN: 1431-2174, 1435-0157Abstract: ▾ Flowing fluid electrical conductivity (FFEC) logging is a hydrogeologic testing method that is usually conducted in an existing borehole. However, for the 2,500-m deep COSC-1 borehole, drilled at Åre, central Sweden, it was done within the drilling period during a scheduled 1-day break, thus having a negligible impact on the drilling schedule, yet providing important information on depths of hydraulically conductive zones and their transmissivities and salinities. This paper presents a reanalysis of this set of data together with a new FFEC logging data set obtained soon after drilling was completed, also over a period of 1 day, but with a different pumping rate and water-level drawdown. Their joint analysis not only results in better estimates of transmissivity and salinity in the conducting fractures intercepted by the borehole, but also yields the hydraulic head values of these fractures, an important piece of information for the understanding of hydraulic structure of the subsurface. Two additional FFEC logging tests were done about 1 year later, and are used to confirm and refine this analysis. Results show that from 250 to 2,000 m depths, there are seven distinct hydraulically conductive zones with different hydraulic heads and low transmissivity values. For the final test, conducted with a much smaller water-level drawdown, inflow ceased from some of the conductive zones, confirming that their hydraulic heads are below the hydraulic head measured in the wellbore under non-pumped conditions. The challenges accompanying 1-day FFEC logging are summarized, along with lessons learned in addressing them.
1781.
Grain size of Lake Qinghai sediments: Implications for riverine input and Holocene monsoon variability
Palaeogeography, Palaeoclimatology, Palaeoecology,
44941 – 51
2016
ISSN: 00310182
Publisher: Elsevier B.V.
Keywords:▾
Atlantic Ocean; Atlantic Ocean (North); China; Qinghai; Qinghai Lake; climate change; depositional environment; grain size; Holocene; hydrodynamics; lacustrine deposit; monsoon; reconstruction; solar activity
Abstract: ▾ Grain-size compositions of lake sediments can provide direct information on changes in transporting mechanism and sedimentary environment. Various grain-size parameters have been employed to reconstruct hydrological conditions within the lake and dust influx from outside the lake. Here we present the grain-size results of a 5-m core retrieved from Lake Qinghai, northeastern Tibetan Plateau in order to address the links between Holocene depositional process and climatic change. Our results indicate that two parameters (skewness and grain-size ratio of 8-50/2-8 μm) are sensitive to hydrodynamic changes in Lake Qinghai, which are further linked to the strength of the Asian summer monsoon. Variations of these two parameters reveal that summer monsoon intensity weakened gradually from early to late Holocene, superimposed by persistent centennial variability with dominant periods at 0.35, 0.23 and 0.12 kyr. Comparison of grain-size variations with solar activities and North Atlantic cooling events reveals that solar forcing likely plays an important role in driving centennial monsoon variability. © 2016 Elsevier B.V.
1780.
General design of geophysical logging of the CCSD-SK-2 East Borehole in the Songliao Basin of Northeast China
Earth Science Frontiers,
23
(3)
279 – 287
2016
ISSN: 10052321
Publisher: Science Frontiers editorial department
Keywords:▾
Cements; Deep oil well drilling; Density measurement (specific gravity); Geophysics; Oil well drilling; Oil well drilling equipment; Petroleum prospecting; Well logging; Continental scientific drillings; Cretaceous; Drilling engineering; Geophysical logging; Oil and gas exploration; Scientific objectives; Sedimentary environment; Songliao basin; Boring
Abstract: ▾ CCSD-SK-2 East Borehole is the main borehole of China Continental Scientific Drilling Project in Songliao Basin, which is designed to reach a depth of 6400 m to penetrate Cretaceous strata. Its implementation is important for the research of the Cretaceous sedimentary environment and climate, for the achievement of new breakthroughs in oil and gas exploration, for the enhancement of the deep-drilling level and geophysical logging techniques, etc. Based on the scientific objectives and tasks of this project, combined with the design of drilling engineering and the characteristics of well conditions, the authors carried out the logging design of CCSD-SK-2 East-Borehole,intending to adopt the most advanced equipment to acquire log data. The adopted logging suits include comprehensive logging in openhole and cement-evaluation logging in cased hole. Based on the situation of drilling times and programs, eight times of comprehensive logging and five times of cement-evaluation logging are designed respectively, and comprehensive logging suits in different drilling times are different; taking into account the challenge of high temperature under the depth of 4500 m, logging items are designed including both required and selected ones. This logging design not only seeks to completely acquire all kinds of log data, but also conduces to flexibly deal with complex conditions of the borehole, which would be beneficial to the achievement of scientific goals. © 2016, Editorial Office of Earth Science Frontiers. All right reserved.
1779.
Geological record of meltwater events at Qinghai Lake, China from the past 40 ka
Quaternary Science Reviews,
149279 – 287
2016
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
China; Qinghai; Qinghai Lake; Carbon; Glacial geology; Organic carbon; Carbon effects; Lacustrine record; Meltwater event; Radiocarbon dating; Total Organic Carbon; core analysis; deglaciation; lacustrine environment; marine isotope stage; meltwater; precipitation assessment; radiocarbon dating; sedimentation; total organic carbon; watershed; Lakes
Abstract: ▾ We report here on a previously unpublished sediment core from Qinghai Lake, China, that preserves a continuous record of sedimentation for the past 40 ka. A striking feature of the record is a set of distinct meltwater events recorded at 35, 19 and 14 ka respectively. These events are manifest as distinct pulses of relatively old organic radiocarbon in the sediments. We interpret these as a signal of glacial melting in the Qinghai Lake watershed. The meltwater signals are closely correlated to temperature and precipitation records associated with deglaciation. The events at 19 ka and 14 ka correspond to well-established high latitude Melt Water Pulse (MWP) events during Marine Isotope Stage (MIS) 2, and the 35 ka event corresponds to a period of pervasive high lake levels in western China during late MIS 3. We interpret these anomalous dates as the result of relatively old carbon that was destabilized by the glaciers, and released into the lake as the glaciers melted. The data indicate that this process takes thousands of years. We expect that the approach employed here to identify these events is generally applicable to any lake system with a significant glacial meltwater component. © 2016 Elsevier Ltd
1778.
Geomicrobiological features of ferruginous sediments from lake Towuti, Indonesia
Frontiers in Microbiology,
7
(JUN)
2016
ISSN: 1664302X
Publisher: Frontiers Research Foundation
Keywords:▾
organic matter; organic nitrogen; oxidizing agent; anoxia; Article; atomic absorption spectrometry; biogeochemistry; biosphere; Chloroflexi; Clostridiales; controlled study; Deltaproteobacteria; denaturing gradient gel electrophoresis; Firmicutes; fluorescent lighting; gene sequence; ion chromatography; lake sediment; Methanomicrobiales; microbial community; Nitrospirae; nonhuman; nucleic acid analysis; oxidation reduction reaction; oxygen concentration; phylogeny; polymerase chain reaction; Ruminococcaceae; sulfate reducing bacterium; Thermoplasmatales; total organic carbon
Abstract: ▾ Lake Towuti is a tectonic basin, surrounded by ultramafic rocks. Lateritic soils form through weathering and deliver abundant iron (oxy)hydroxides but very little sulfate to the lake and its sediment. To characterize the sediment biogeochemistry, we collected cores at three sites with increasing water depth and decreasing bottom water oxygen concentrations. Microbial cell densities were highest at the shallow site-a feature we attribute to the availability of labile organic matter (OM) and the higher abundance of electron acceptors due to oxic bottom water conditions. At the two other sites, OM degradation and reduction processes below the oxycline led to partial electron acceptor depletion. Genetic information preserved in the sediment as extracellular DNA (eDNA) provided information on aerobic and anaerobic heterotrophs related to Nitrospirae, Chloroflexi, and Thermoplasmatales. These taxa apparently played a significant role in the degradation of sinking OM. However, eDNA concentrations rapidly decreased with core depth. Despite very low sulfate concentrations, sulfate-reducing bacteria were present and viable in sediments at all three sites, as confirmed by measurement of potential sulfate reduction rates. Microbial community fingerprinting supported the presence of taxa related to Deltaproteobacteria and Firmicutes with demonstrated capacity for iron and sulfate reduction. Concomitantly, sequences of Ruminococcaceae, Clostridiales, and Methanomicrobiales indicated potential for fermentative hydrogen and methane production. Such first insights into ferruginous sediments showed that microbial populations perform successive metabolisms related to sulfur, iron, and methane. In theory, iron reduction could reoxidize reduced sulfur compounds and desorb OM from iron minerals to allow remineralization to methane. Overall, we found that biogeochemical processes in the sediments can be linked to redox differences in the bottom waters of the three sites, like oxidant concentrations and the supply of labile OM. At the scale of the lacustrine record, our geomicrobiological study should provide a means to link the extant subsurface biosphere to past environments. © 2016 Vuillemin, Friese, Alawi, Henny, Nomosatryo, Wagner, Crowe and Kallmeyer.
1777.
Glacial legacies on interglacial vegetation at the Pliocene-Pleistocene transition in NE Asia
Nature Communications,
7
2016
ISSN: 20411723
Publisher: Nature Publishing Group
Keywords:▾
atmospheric gas; climate change; detection method; disequilibrium; glacier dynamics; historical record; interglacial; paleoclimate; paleoecology; paleoenvironment; permafrost; Pliocene; Pliocene-Pleistocene boundary; reconstruction; vegetation dynamics, ecosystem; Far East; global climate; herbivory; interglacial; Larix; multivariate analysis; permafrost; Pleistocene; Pliocene; refugium; vegetation, Chukchi; Elgygytgyn Lake; Far East; Russian Far East; Russian Federation, Larix
Abstract: ▾ Broad-scale climate control of vegetation is widely assumed. Vegetation-climate lags are generally thought to have lasted no more than a few centuries. Here our palaeoecological study challenges this concept over glacial-interglacial timescales. Through multivariate analyses of pollen assemblages from Lake El'gygytgyn, Russian Far East and other data we show that interglacial vegetation during the Plio-Pleistocene transition mainly reflects conditions of the preceding glacial instead of contemporary interglacial climate. Vegetation-climate disequilibrium may persist for several millennia, related to the combined effects of permafrost persistence, distant glacial refugia and fire. In contrast, no effects from the preceding interglacial on glacial vegetation are detected. We propose that disequilibrium was stronger during the Plio-Pleistocene transition than during the Mid-Pliocene Warm Period when, in addition to climate, herbivory was important. By analogy to the past, we suggest today's widespread larch ecosystem on permafrost is not in climate equilibrium. Vegetation-based reconstructions of interglacial climates used to assess atmospheric CO 2-Temperature relationships may thus yield misleading simulations of past global climate sensitivity.
1776.
Gas Production from Methane Hydrate: A Laboratory Simulation of the Multistage Depressurization Test in Mallik, Northwest Territories, Canada
Energy and Fuels,
30
(8)
6210-6219
2016
ISSN: 08870624
Publisher: American Chemical Society
Keywords:▾
Flow of gases; Flow patterns; Gases; Hydration; Methane, Gas production test; Gas-hydrate production; Hydrate dissociation; Laboratory experiments; Laboratory simulation; Reservoir simulator; Three phase system; Transport behavior, Gas hydrates
Abstract: ▾ Gas hydrate production is still in the test phase. It is only now that numerical models are being developed to describe data and production scenarios. Laboratory experiments are carried out to test the rationale of the conceptual models and deliver input data. Major experimental challenges include (I) the simulation of a natural three-phase system of sand-hydrate-liquid with known and high hydrate saturations and (II) the simulation of transport behavior as deduced from field data. The large-scale reservoir simulator (LARS; 210 L sample) at the GFZ has met these challenges and allowed for the first simulation of the gas production test from permafrost hydrates at the Mallik drill site (Canada) via multistage depressurization. At the starting position, hydrate saturation was as high as 90%, formed from dissolved methane only. Whereas gas hydrate dissociation determined the flow patterns in the early pressure stages, the importance of different transport behaviors increased at lower pressure stages and increasing water content. Gas flow patterns as observed in Mallik were recorded. While the conceptual model for the experimental data does agree with the model proposed for Mallik at moderate and low gas production, it is different at high gas production rates. © 2016 American Chemical Society.
1775.
Experimental investigation of the effect of Ca, Fe and Ti on cotectic compositions of the rhyolitic system
European Journal of Mineralogy,
27
(2)
147-159
032015
ISSN: 0935-1221Abstract: ▾ {The effect of the normative anorthite content on the position of cotectic curves in the Qz–Ab–Or–An system has been investigated at 200 MPa and a water activity of 0.5. To simulate compositions as close as possible to those of natural high-silica rhyolites, all investigated compositions also contained ~ 1 wt\% FeO and 0.2 wt\% TiO2. The position of the cotectic curves was deduced from crystallization experiments carried out between 790 and 850°C and using fourteen starting glass compositions containing ~ 3 wt\% H2O. The liquidus phase of the different starting materials was used to constrain the primary fields of quartz, plagioclase and sanidine. The compositions of residual melts coexisting with solid phases were used to define the position of cotectic curves. Compared to the haplogranite system, the eutectic point is shifted away from the Ab apex, and its composition is estimated to be Qz42Ab21Or37 when projected onto the haplogranite system. The implications for the estimation of the depth of magma storage conditions are discussed on the basis of an example from the Snake River Plain high-silica rhyolites.}
1774.
Quaternary climate change and Heinrich events in the southern Balkans: Lake Prespa diatom palaeolimnology from the last interglacial to present
Journal of Paleolimnology,
53
(2)
215-231
2015
ISSN: 09212728
Publisher: Kluwer Academic Publishers
Abstract: ▾ Lake Prespa, in the Balkans, contains an important palaeo-archive in a key location for understanding Quaternary climate variability in the transition between Mediterranean and central European climate zones. Previous palaeoenvironmental research on sediment cores indicates that the lake is highly sensitive to climate change and that diatoms are likely to be strong palaeohydrological proxies. Here, we present new results from diatom analysis of a ca. 91 ka sequence, core Co1215, which spans the time from the end of the last interglacial to the present. Fluctuations in the diatom data were driven primarily by changes in lake level, as a function of shifts in moisture availability. Warmer interglacial (MIS 5, MIS 1) and interstadial (MIS 3) phases exhibit higher lake levels in spite of enhanced evaporative concentration, underlining the importance of changes in precipitation regimes over time. Low lake levels during glacial phases indicate extreme aridity, common to all Mediterranean lakes. Evidence for fluctuations in trophic status is linked, in part, to lake-level change, but also reflects nutrient enrichment from catchment processes. MIS 5a is characterized by the highest lake productivity in the sequence, but low lake levels, which are ascribed primarily to very low precipitation. On a suborbital timescale, the diatoms provide evidence for correlation to the millennial-scale variability recorded in the Greenland oxygen isotope records and clearly reflect the impact of the Heinrich H6, H5 and H3–1 ice-rafting events, suggesting the dominant influence of North Atlantic forcing in this region. Although the highest-amplitude shift in the diatom assemblages occurs during the time of H4 (40–38 ka), it may be superimposed upon the impact of the 39.28 cal ka BP Campanian Ignimbrite volcanic eruption. Diatoms from Lake Prespa core Co1215 display the first strong evidence for the impact of Italian volcanic activity on lacustrine biota in this region. Results emphasize the complexity of diatom response thresholds in different studies across the region. In the case of Lake Prespa, the results highlight the important role of precipitation for maintaining the hydrological balance of the lake, and indirectly, its biodiversity. © 2014, Springer Science+Business Media Dordrecht.
1773.
Rapid reactivation of deep subsurface microbes in the presence of c-1 compounds
Microorganisms,
3
(1)
17 – 33
2015
ISSN: 20762607
Publisher: MDPI AG
Abstract: ▾ Microorganisms in the deep biosphere are believed to conduct little metabolic activity due to low nutrient availability in these environments. However, destructive penetration to long-isolated bedrock environments during construction of underground waste repositories can lead to increased nutrient availability and potentially affect the long-term stability of the repository systems, Here, we studied how microorganisms present in fracture fluid from a depth of 500 m in Outokumpu, Finland, respond to simple carbon compounds (C-1 compounds) in the presence or absence of sulphate as an electron acceptor. C-1 compounds such as methane and methanol are important intermediates in the deep subsurface carbon cycle, and electron acceptors such as sulphate are critical components of oxidation processes. Fracture fluid samples were incubated in vitro with either methane or methanol in the presence or absence of sulphate as an electron acceptor. Metabolic response was measured by staining the microbial cells with fluorescent dyes that indicate metabolic activity and transcriptional response with RT-qPCR. Our results show that deep subsurface microbes exist in dormant states but rapidly reactivate their transcription and respiration systems in the presence of C-1 substrates, particularly methane. Microbial activity was further enhanced by the addition of sulphate as an electron acceptor. Sulphate-and nitrate-reducing microbes were particularly responsive to the addition of C-1 compounds and sulphate. These taxa are common in deep biosphere environments and may be affected by conditions disturbed by bedrock intrusion, as from drilling and excavation for long-term storage of hazardous waste. © 2015 by the authors; licensee MDPI, Basel, Switzerland.
1772.
Rock magnetic and AMS fabrics characterization of suevitic breccias from the Cretaceous-Paleogene Chicxulub impact crater
Revista Mexicana de Ciencias Geologicas,
32
(1)
145-155
2015
Abstract: ▾ Results of a paleomagnetic and magnetic fabrics study of the basal suevitic breccias in the Chicxulub impact crater, Yucatán platform, Gulf of Mexico are presented. The breccias were cored in the Yaxcopoil-1 borehole, which is located at about 62 km radial distance from the crater center. The impactite sequence in the Yaxcopoil-1 borehole is ~100 m thick and formed by six subunits with distinct petrographic and geochemical characteristics. Here we investigate the basal subunit interpreted as: a ground surge in the transient cavity, a melt breccia with clastic material, or an excavation flow from the ejecta curtain interacting with the ejecta plume collapse. Characterization of the magnetic fabrics using rock magnetics and anisotropy of magnetic susceptibility (AMS) are used to investigate on the emplacement mechanism of the suevites. Magnetic hysteresis and k-T curves show that the magnetic mineralogy is dominated by low-Ti titanomagnetites and magnetite. The AMS fabrics record mixtures of oblate and prolate ellipsoids and principal susceptibility axial distributions with relatively high angular scatter, related to turbulent high temperature conditions during ejecta emplacement. Magnetic fabric parameters and principal susceptibility axial distributions correlate with modal composition, relative contents and orientation of melt particles. Results are interpreted in terms of an emplacement mode as an early excavation flow that incorporated ground surge components.
1771.
Rock-magnetic proxies of wind intensity and dust since 51,200 cal BP from lacustrine sediments of Laguna Potrok Aike, southeastern Patagonia
Earth and Planetary Science Letters,
41172 – 86
2015
Keywords:▾
Argentina; Laguna Potrok Aike; Santa Cruz [Argentina]; Dust; Glacial geology; Grain size and shape; Infill drilling; Lakes; Lithology; Magnetism; Magnetite; Minerals; Rocks; Salinity measurement; Silt; Wind; Lake sediments; PASADO; Rock magnetism; Westerly winds; Wind intensity; dust; grain size; lacustrine deposit; Last Glacial; magnetic property; magnetite; remanent magnetization; rock property; Southern Hemisphere; westerly; wind field; Sediments
Abstract: ▾ The sedimentary archive from Laguna Potrok Aike is the only continuous record reaching back to the last Glacial period in continental southeastern Patagonia. Located in the path of the Southern Hemisphere westerly winds and in the source region of dust deposited in Antarctica during Glacial periods, southern Patagonia is a vantage point to reconstruct past changes in aeolian activity. Here we use high-resolution rock-magnetic and physical grain size data from site 2 of the International Continental scientific Drilling Program (ICDP) Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO) in order to develop magnetic proxies of dust and wind intensity at 52°S since 51,200 cal BP. Rock-magnetic analysis indicates the magnetic mineral assemblage is dominated by detrital magnetite. Based on the estimated flux of magnetite to the lake and comparison with distal dust records from the Southern Ocean and Antarctica, kLF is interpreted as a dust indicator in the dust source of southern Patagonia at the millennial time scale, when ferrimagnetic grain size and coercivity influence are minimal. Comparison to physical grain-size data indicates that the median destructive field of isothermal remanent magnetization (MDFIRM) mostly reflects medium to coarse magnetite bearing silts typically transported by winds for short-term suspension. Comparison with wind-intensity proxies from the Southern Hemisphere during the last Glacial period and with regional records from Patagonia since the last deglaciation including marine, lacustrine and peat bog sediments as well as speleothems reveals similar variability with MDFIRM up to the centennial time scale. MDFIRM is interpreted as a wind-intensity proxy independent of moisture changes for southeastern Patagonia, with stronger winds capable of transporting coarser magnetite bearing silts to the lake. © 2014 Elsevier B.V.
1770.
Seismic imaging of the geodynamic activity at the western Eger rift in central Europe
Tectonophysics,
647105 – 111
2015
ISSN: 00401951
Publisher: Elsevier B.V.
Keywords:▾
Alps; Bohemian Massif; Eger; Eifel; France; Germany; Heves; Hungary; Massif Central; Rhineland-Palatinate; Earthquakes; Bohemian massifs; Crustal fluids; Deep seismic reflection profiles; Earthquake activity; Eger rift; Rift systems; Seismic reflectivity; Subsurface structures; Cenozoic; earthquake swarm; geodynamics; rift zone; seismic reflection; seismicity; seismology; upper mantle; Geodynamics
Abstract: ▾ The western Eger rift at the Czech-German border in central Europe is an important geodynamically active area within the European Cenzoic rift system (ECRS) in the forelands of the Alps. Along with two other active areas of the ECRS, the French Massif Central and the east and west Eifel volcanic fields, it is characterized by numerous CO2-rich fluid emission points and frequent micro-seismicity. Existence of a plume(s) is indicated in the upper mantle which may be responsible for these observations. Here we reprocess a pre-existing deep seismic reflection profile '9HR' and interpret the subsurface structures as mapped by seismic reflectivity with previous findings, mainly from seismological and geochemical studies, to investigate the geodynamic activity in the subsurface. We find prominent hints of pathways which may allow magmatic fluids originating in the upper mantle to rise through the crust and cause the observed fluid emanations and earthquake activity. © 2015 Elsevier B.V.