All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
2094.
Abrupt or gradual? Change point analysis of the late Pleistocene-Holocene climate record from Chew Bahir, southern Ethiopia
Quaternary Research (United States),
90
(2)
321-330
2018
ISSN: 00335894
Publisher: Cambridge University Press
Keywords:▾
Hierarchical systems; Principal component analysis, Change-point analysis; Dansgaard-Oeschger cycles; Holocenes; Humid periods; Late Pleistocene; Paleoclimatology; Southern Ethiopian Rift; Younger Dryas, Climate change
Abstract: ▾ We used a change point analysis on a late Pleistocene-Holocene lake-sediment record from the Chew Bahir basin in the southern Ethiopian Rift to determine the amplitude and duration of past climate transitions. The most dramatic changes occurred over 240 yr (from 15,700 to 15,460 yr) during the onset of the African Humid Period (AHP), and over 990 yr (from 4875 to 3885 yr) during its protracted termination. The AHP was interrupted by a distinct dry period coinciding with the high-latitude Younger Dryas stadial, which had an abrupt onset (less than 100 yr) at 13,260 yr and lasted until 11,730 yr. Wet-dry-wet transitions prior to the AHP may reflect the high-latitude Dansgaard-Oeschger cycles, as indicated by cross-correlation of the potassium record with the NorthGRIP ice core record between 45-20 ka. These findings may contribute to the debates regarding the amplitude, and duration and mechanisms of past climate transitions, and their possible influence on the development of early modern human cultures. © University of Washington. Published by Cambridge University Press, 2018.
2093.
Abnormally high natural radioactivity zones in the main borehole of the Continental Scientific Drilling Project of Cretaceous Songliao Basin: Geophysical log responses and genesis analysis [松科2井东孔营城组高放射性异常层测井响应特征及成因初探]
Acta Geophysica Sinica,
61
(11)
4712-4728
2018
ISSN: 00015733
Publisher: Science Press
Keywords:▾
Acoustic logging; Acoustic spectroscopy; Boreholes; Boring; Core analysis; Gamma rays; Geophysics; Groundwater; Infill drilling; Neutron logging; Nuclear magnetic logging; Nuclear magnetic resonance spectroscopy; Petroleum prospecting; Radioactivity; Uranium, Continental scientific drillings; Elemental capture spectroscopy; Genesis; Geophysical information; Log response; Natural radioactivity; Songliao basin; Uranium mineralization, Oil well logging, abnormality; adsorption; borehole; Cretaceous; geophysical survey; mineralization; nutrient enrichment; paleoclimate; potassium; radioactivity; radionuclide; thorium; uranium; well logging, China; Songliao Basin
Abstract: ▾ SK-2 East Borehole (SK-2e) is the main borehole of Continental Scientific Drilling Project of Cretaceous Songliao Basin, which is designed to acquire the geophysical log data in the whole borehole, to provide accurate, comprehensive geophysical information for resource exploration and research on paleoclimate and paleoenvironment. Among various well logging methods, natural gamma-ray logging and natural gamma-ray spectral logging can measure natural gamma-ray intensity and uranium (U), thorium (Th), potassium (K) contents, and are effectively applied to radioactive deposit exploration, especially to uranium exploration and research. Conventional logging (including resistivity, acoustic, density and neutron logging) and special logging (including nuclear magnetic resonance, resistivity imaging and elemental capture spectroscopy logging) can obtain lithologic and physical parameters of strata, offering strong support for uranium exploration. In this study, the natural gamma-ray log data was used to identify abnormally high natural radioactivity zones. Based on conventional log data, special log data and previous geological research achievements, the characteristics and genesis of radioactive abnormality were analyzed. The results show that two abnormally high natural radioactivity zones are located in deep-seated Yingcheng Formation. And their depths are 3096.8~3102.8m (Layer I) and 3168.3~3170.9 m (Layer II) respectively. According to the comprehensive analysis of various log data and core data, Layer I is conglomerate, with the maximum gamma of 360 API and high uranium content (20.5~29.3 ppm). Therefore, Layer I has uranium mineralization potential. Analysis shows that tectonic conditions and epigenetic alteration are probably the key factors affecting uranium enrichment which causes abnormally high gamma-ray intensity. It was speculated that fault movements, volcanic activity, and the basin's uplift and erosion provide uranium-bearing groundwater, oil and gas with the migration channel to I layer. The epigenetic reduction of oil and gas eventually leads to uranium enrichment of Layer I. Layer II consists of agglomerate lava and tuff, with the maximum gamma of 250 API, high thorium content (22.4~37.3 ppm) and high uranium content (5.9~11.0 ppm). The rhyolitic components of high thorium content and uranium adsorption by clay minerals may cause the abnormally high gamma-ray intensity in Layer II. The abnormally high radioactivity zones of Yingcheng Formation in SK-2e are characterized by deep burial depths and high uranium contents, indicating uranium prospecting potential in deep zones of Songliao Basin. © 2018, Science Press. All right reserved.
2092.
A unified effective medium model for gas hydrates in sediments
Geophysics,
83
(6)
MR317-MR332
2018
ISSN: 00168033
Publisher: Society of Exploration Geophysicists
Keywords:▾
Algorithms; Elastic moduli; Friction; Gases; Hydration; Models; Neutron logging; Sediments; Shear waves; Spheres; Velocity; Wave propagation, Effective medium model; Friction coefficients; Gas hydrate saturations; Heterogeneous environments; Neutron porosity logs; P- and S-wave velocities; Rock physics; Unconsolidated sediment, Gas hydrates, algorithm; bulk modulus; gas hydrate; numerical model; P-wave; S-wave; sediment analysis; shear modulus; surface roughness; wave velocity
Abstract: ▾ A unified effective medium model is developed to incorporate the endpoints of perfectly smooth and infinitely rough sphere components and to allow partitioning between rough and smooth grains. We incorporate the unified model into the framework for gas hydrates in unconsolidated sediments using pore-fluid and rock-matrix configurations for grain placement, while reviewing other developments that have taken place in the past four decades. The unified rock-matrix model is validated with data available from the 2002 Mallik gas hydrates project well 5L-38. Gas-hydrate saturation and neutron-porosity logs from this well are used to generate synthetic P- and S-wave velocity models for several values of the friction coefficient. First, we overlaid crossplots of P- versus S-wave velocities for synthetic and measured velocities, and we compared the match until a good choice was found for the friction coefficient. Second, we plotted the synthetic velocities as separate logs of P- and S-wave velocities for each friction coefficient; the synthetic velocity logs were then overlaid on the measured velocities calculated from the sonic logs. Results of a direct comparison of the synthetic and measured velocity logs provide valuable insights into the validation of the unified effective medium model. Recognizing the significance of the Hertz-Mindlin-type effective medium models for gas hydrates in unconsolidated sediments, we incorporate the previous efforts into a single "unified" model and define a common nomenclature. Although we attempt to assign a single friction coefficient value to each hydrate window, it is not surprising that in a real and heterogeneous environment, the value might vary with depth, as it does here at the larger spatial scales. We determine and quantitatively estimate that gas hydrates in sediments are well-predicted with a friction coefficient closer to a smooth sphere model than a rough sphere model. © 2018 Society of Exploration Geophysicists. All rights reserved.
2091.
A study of secondary pyrite deformation and calcite veins in SAFOD damage zone with implications for aseismic creep deformation mechanism at depths >3 km
Journal of Structural Geology,
11714-26
2018
ISSN: 01918141
Publisher: Elsevier Ltd
Keywords:▾
Calcite; Microstructure; Pyrites; Strike-slip faults; Structural geology; Transform faults, Aseismic creep in the SAF; Calcite veins; Creep deformation mechanisms; Deformation behavior; Deformation mechanism; Pressure solution; SAFOD; Seismogenic zones, Creep, calcite; cathodoluminescence; creep; deformation mechanism; pressure solution; pyrite; vein (geology)
Abstract: ▾ Previous studies of the San Andreas Fault damage-zone samples from the San Andreas Fault Observatory at Depth (SAFOD) have identified a variety of tectonic microstructures including pressure solution cleavage, calcite-sealed fractures vein fabric, and pyrite and anhydrite hydrothermal fracture sealing. Understanding the deformation provenance of the damage zone rocks and operative deformation mechanism(s) based on preserved microstructures provide insight into overall deformation behavior of the entire seismogenic zone in the creeping section of this transform fault. We analysed the deformation of hydrothermal secondary pyrite in connection with network of calcite veins in a sample of foliated ultracataclasites bordering the actively creeping Southwestern Deforming Zone (SDZ), using SEM, EBSD and CL microscopy. The results show that calcite veins associated with the pressure solution cleavage are crosscut by the secondary pyrite deformed under a range of P-T conditions. Relatively undeformed secondary pyrite is found sealing implosion microbreccia. Our review of previously available data indicates that the damage zone rocks may represent a collage of structural and compositional domains from both locked and creeping sections of the SAF. This interpretation together with results of this study suggest that weak-clay frictional deformation mechanism(s) is likely to be the predominant aseismic creep mechanism at depths below the SAFOD. © 2018
2090.
A new approach to probabilistic lava flow hazard assessments, applied to the Idaho National Laboratory, eastern Snake River Plain, Idaho, USA
Geology,
46
(10)
895-898
2018
ISSN: 00917613
Publisher: Geological Society of America
DOI:10.1130/G45123.1
Keywords:▾
Floods; Intelligent systems; Monte Carlo methods; Probability, Annual probabilities; Effusive eruptions; Hazard Assessment; Idaho national laboratories; Nuclear facilities; Recurrence rates; Snake river plains; U.S. Department of Energy, Hazards
Abstract: ▾ We present a new probabilistic lava flow hazard assessment for the U.S. Department of Energy's Idaho National Laboratory (INL) nuclear facility that (1) explores the way eruptions are defined and modeled, (2) stochastically samples lava flow parameters from observed values for use in MOLASSES, a lava flow simulator, (3) calculates the likelihood of a new vent opening within the boundaries of INL, (4) determines probabilities of lava flow inundation for INL through Monte Carlo simulation, and (5) couples inundation probabilities with recurrence rates to determine the annual likelihood of lava flow inundation for INL. Results show a 30% probability of partial inundation of the INL given an effusive eruption on the eastern Snake River Plain, with an annual inundation probability of 8.4 × 10-5 to 1.8 × 10-4. An annual probability of 6.2 × 10-5 to 1.2 × 10-4 is estimated for the opening of a new eruptive center within INL boundaries. © 2018 Geological Society of America.
2089.
A MIS 9/MIS 8 speleothem record of hydrological variability from Macedonia (F.Y.R.O.M.)
Global and Planetary Change,
16239 – 52
2018
2088.
A leaf wax biomarker record of early Pleistocene hydroclimate from West Turkana, Kenya
Quaternary Science Reviews,
186225 – 235
2018
2087.
A high-resolution, 60 kyr record of the relative geomagnetic field intensity from Lake Towuti, Indonesia
Physics of the Earth and Planetary Interiors,
2759 – 18
2018
ISSN: 00319201
Publisher: Elsevier B.V.
Keywords:▾
Greater Sunda Islands; Lake Towuti; Malili Lakes; South Sulawesi; Sulawesi; Sulawesi; Sunda Isles; Geomagnetism; Lakes; Lithology; Magnetic fields; Magnetization; Repair; Sedimentology; Sediments; Stratigraphy; Anhysteretic remanent magnetizations; Earth's magnetic field; Environmental history; Laschamp excursions; Magnetic field variations; Natural remanent magnetization; Normalizing parameters; Relative paleointensity; geological record; geomagnetic field; lacustrine deposit; magnetic intensity; ophiolite; paleoenvironment; paleointensity; paleomagnetism; reconstruction; stratigraphic correlation; Magnetism
Abstract: ▾ Past changes in the Earth's magnetic field can be highlighted through reconstructions of magnetic paleointensity. Many magnetic field variation features are global, and can be used for the detailed correlation and dating of sedimentary records. On the other hand, sedimentary magnetic records also exhibit features on a regional, rather than a global scale. Therefore, the development of regional scale magnetic field reconstructions is necessary to optimize magnetic paleointensity dating. In this paper, a 60 thousand year (kyr) paleointensity record is presented, using the core TOW10-9B of Lake Towuti, located in the island of Sulawesi, Indonesia, as a part of the ongoing research towards understanding the Indonesian environmental history, and reconstructing a high-resolution regional magnetic record from dating the sediments. Located in the East Sulawesi Ophiolite Belt, the bedrock surrounding Lake Towuti consists of ultramafic rocks that render the lake sediments magnetically strong, creating challenges in the reconstruction of the paleointensity record. These sediment samples were subject to a series of magnetic measurements, followed by testing the obtained paleointensity records resulting from normalizing natural remanent magnetization (NRM) against different normalizing parameters. These paleointensity records were then compared to other regional, as well as global, records of magnetic paleointensity. The results show that for the magnetically strong Lake Towuti sediments, an anhysteretic remanent magnetization (ARM) is the best normalizer. A series of magnetic paleointensity excursions are observed during the last 60 kyr, including the Laschamp excursion at 40 kyr BP, that provide new information about the magnetic history and stratigraphy of the western tropical Pacific region. We conclude that the paleointensity record of Lake Towuti is reliable and in accordance with the high-quality regional and global trends. © 2017 Elsevier B.V.
2086.
3.4 Ga biostructures from the Barberton greenstone belt of South Africa: New insights into microbial life; [Strutture biosedimentarie di 3.4 miliardi di anni fa del Barberton greenstone belt in Sudafrica: nuove prospettive sull’origine della biosfera primitiva]
Bollettino della Societa Paleontologica Italiana,
57
(1)
59 – 74
2018
2085.
Increased frequency of torrential rainstorms during a regional late Holocene eastern Mediterranean drought
Quaternary Research (United States),
89
(2)
425-431
2018
ISSN: 00335894
Publisher: Cambridge University Press
Keywords:▾
Climatology; Debris; Drought; Floods, Dead sea; Debris flows; Holocenes; Lake sediments; Levant; Paleoclimates; Red sea, Thunderstorms, atmospheric circulation; cyclone; debris flow; drought; facies analysis; flood; geological record; Holocene; lacustrine deposit; microfacies; paleoclimate; paleohydrology; rainstorm; trough, Dead Sea; Indian Ocean; Levant; Mediterranean Region; Red Sea [Indian Ocean]
Abstract: ▾ Identifying climates favoring extreme weather phenomena is a primary aim of paleoclimate and paleohydrological research. Here, we present a well-dated, late Holocene Dead Sea sediment record of debris flows covering 3.3 to 1.9 cal ka BP. Twenty-three graded layers deposited in shallow waters near the western Dead Sea shore were identified by microfacies analysis. These layers represent distal subaquatic deposits of debris flows triggered by torrential rainstorms over the adjacent western Dead Sea escarpment. Modern debris flows on this escarpment are induced by rare rainstorms with intensities exceeding >30 mm h-1 for at least one hour and originate primarily from the Active Red Sea Trough synoptic pattern. The observed late Holocene clustering of such debris flows during a regional drought indicates an increased influence of Active Red Sea Troughs resulting from a shift in synoptic atmospheric circulation patterns. This shift likely decreased the passages of eastern Mediterranean cyclones, leading to drier conditions, but favored rainstorms triggered by the Active Red Sea Trough. This is in accord with present-day meteorological data showing an increased frequency of torrential rainstorms in regions of drier climate. Hence, this study provides conclusive evidence for a shift in synoptic atmospheric circulation patterns during a late Holocene drought. Copyright © University of Washington. Published by Cambridge University Press, 2018.
2084.
Depositional environment of the Late Santonian lacustrine source rocks in the Songliao Basin (NE China): Implications from organic geochemical analyses
Organic Geochemistry,
124215-227
2018
ISSN: 01466380
Publisher: Elsevier Ltd
Keywords:▾
Analytical geochemistry; Biomarkers; Deposition; Paraffins; Seawater; Sediments, Depositional environment; Lacustrine source rocks; Marine transgression; Organic-rich sediment; Organic-rich source rock; Santonian; Stable carbon isotopes; Water columns, Organic carbon, anoxic conditions; biomarker; carbon isotope; Cretaceous; depositional environment; estuarine environment; euphotic zone; Jurassic; macrophyte; organic geochemistry; organic matter; outcrop; phenanthrene; Santonian; seawater; sediment chemistry; sedimentary basin; source rock; total organic carbon; water column, China; Songliao Basin, algae; Embryophyta
Abstract: ▾ The Songliao Basin (SLB) located in northeastern China is one of the largest Cretaceous continental sedimentary basins in the world. The SLB is filled with sediments deposited in the Upper Jurassic, the Lower Cretaceous and the Upper Cretaceous epochs. The Nenjiang Formation (K2n) is subdivided into five members, where Member 2 (K2n2) was deposited in the late Santonian in the lower part of the Nenjiang Formation. This member is characterized by a thick succession of organic-rich source rocks. However, the complexity of the depositional environment raises questions about the specific factors that drove this accumulation of organic material. Here, we present data on the total organic carbon (TOC) contents and their stable carbon isotope values (δ13Corg), as well as biomarker data from 50 outcrop samples collected from the Yuewangcheng (YWC) section, in the southeastern SLB. According to the variations of the bulk organic parameters (TOC and δ13Corg) and biomarker indices, the profile could be divided into three stages (stages I–III). The distribution of biomarkers (n-alkanes, steranes and hopanes) and δ13Corg values indicate that the organic matter (OM) in the Lower K2n2 is derived largely from algae and macrophytes, with a minor input from bacteria and land plants. The water column was stratified, as indicated by the presence of gammacerane. Variations in the pristane/phytane (Pr/Ph) and aryl isoprenoids relative to phenanthrene ratio (A-i/P) suggest that bottom waters were anoxic during Stage I (31.5–26.0 m) and Stage II (26.0–16.3 m), with the anoxic layer impinging on the euphotic zone and a relative oxic environment at Stage III (16.3–0 m). This brackish environment persisted in the water over the interval represented by the section, as reflected by methytrimethyltridecyl chromans (MTTCs) Index (MTTCI) and α-MTTC/γ-MTTC ratios. Marine transgressions, with subsequent seawater incursions, can be detected with the presence of 24-n-propyl-cholestanes and 24-isopropyl-cholestanes in the Lower K2n2 sediments, especially during Stage I. These seawater incursions are closely correlated with anoxic conditions and the deposition of organic-rich source rocks. © 2018 Elsevier Ltd
2083.
Crystallization and partial melting of rhyolite and felsite rocks at Krafla volcano: A comparative approach based on mineral and glass chemistry of natural and experimental products
Chemical Geology,
483603 – 618
2018
2082.
Design and application of an immersive virtual reality system to understanding the cores of the “SK2” (in Chinese with English abstract); [松科二井岩芯认知沉浸式虚拟现实系统设计与开发]
China Mining Magazine,
27
(S2)
268-271
2018
2081.
Experimental microbial alteration and Fe mobilization from basaltic rocks of the ICDP HSDP2 drill core, Hilo, Hawaii
Frontiers in Microbiology,
9
(JUN)
2018
ISSN: 1664302X
Publisher: Frontiers Media S.A.
Keywords:▾
glass, abiotic stress; Article; bacterial growth; biotic stress; chemical analysis; glucose intake; Gram negative bacterium; Hawaii; incubation time; microbial activity; microbial colonization; microbial growth; organismal interaction; pH; scanning electron microscopy
Abstract: ▾ The interaction of a single bacterial species (Burkholderia fungorum) with basaltic rocks from the ICDP HSDP2 drill core and synthetic basaltic glasses was investigated in batch laboratory experiments to better understand the role of microbial activity on rock alteration and Fe mobilization. Incubation experiments were performed with drill core basaltic rock samples to investigate differences in the solution chemistry during biotic and abiotic alteration. Additionally, colonization experiments with synthetic basaltic glasses of different Fe redox states and residual stresses were performed to evaluate their influence on microbial activity and surface attachment of cells. In biotic incubation experiments bacterial growth was observed and the release of Fe and other major elements from drill core basaltic rocks to solution exceeded that of abiotic controls only when the rock sample assay was nutrient depleted. The concentration of dissolved major elements in solution in biotic colonization experiments with synthetic basaltic glasses increased with increasing residual stress and Fe(II) content. Furthermore, the concentration of dissolved Fe and Al increased similarly in biotic colonization experiments indicating that their dissolution might be triggered by microbial activity. Surface morphology imaging by SEM revealed that cells on basaltic rocks in incubation experiments were most abundant on the glass and surfaces with high roughness and almost absent on minerals. In colonization experiments, basaltic glasses with residual stress and high Fe(II) content were intensely covered with a cellular biofilm. In contrast, glasses with high Fe(III) content and no residual stress were sparsely colonized. We therefore conclude that structurally bound Fe is most probably used by B. fungorum as a nutrient. Furthermore, we assume that microbial activity overall increased rock dissolution as soon as the environment becomes nutrient depleted. Our results show that besides compositional effects, other factors such as redox state and residual stress can control microbial alteration of basaltic glasses. © 2018 Stranghoener, Schippers, Dultz and Behrens.
2080.
In situ carbon mineralization in ultramafic rocks: Natural processes and possible engineered methods
Energy Procedia,
14692--102
2018
2079.
Implementation Overview of Chinese Continental Scientific Drilling (CCSD) Project and Technical Systems of Core Boring (in Chinese with English abstract); [我国大陆科学钻探工程实施概况及其取心钻进技术体系]
Acta Geologica Sinica,
92
(10)
1971-1984
2018
2078.
High-resolution reflection seismics reveal the structure and the evolution of the Quaternary glacial Tannwald Basin
Near Surface Geophysics,
16
(6)
593 – 610
2018
2077.
High-latitude vegetation and climate changes during the Mid-Pleistocene Transition inferred from a palynological record from Lake El'gygytgyn, NE Russian Arctic
Boreas,
47
(1)
137-149
2018
ISSN: 03009483
Publisher: Blackwell Publishing Inc.
Keywords:▾
biome; climate variation; forest; herb; paleoclimate; palynology; Pleistocene; shrub; uplift; vegetation, Arctic; China; Chukchi; Elgygytgyn Lake; Qinghai-Xizang Plateau; Russian Federation
Abstract: ▾ A continuous pollen record from Lake El'gygytgyn (northeastern Russian Arctic) provides detailed information concerning the regional vegetation and climate history during the Mid-Pleistocene Transition (MPT), between 1091 ka (end of Marine Isotope Stage (MIS) 32) and 715 ka (end of MIS 18). Pollen-based qualitative vegetation reconstruction along with biome reconstruction indicate that the interglacial regional vegetation history during the MPT is characterized by a gradual replacement of forest and shrub vegetation by open herbaceous communities (i.e. tundra/cold steppe). The pollen spectra reveal seven vegetation successions that have clearly distinguishable glacial-interglacial cycles. These successions are represented by the intervals of cold deciduous forest (CLDE) biome scores changing from high to low, which are basically in phase with the variations of obliquity from maxima to minima. The dominating influence of obliquity forcing on vegetation successions contradicts with the stronger power of eccentricity, as demonstrated by the result of wavelet analysis based on landscape openness reconstruction. This discrepancy shows that a single index is insufficient for catching signals of all the impacting factors. Comparisons with vegetation and environmental changes in the Asian interior suggest that global cooling during the MPT was probably the key force driving long-term aridification in the Arctic region. The accelerated aridification after MIS 24–22 was probably caused by the additional effect of the Tibetan Plateau uplift, which played an important role on intensification of the Siberian High and westerly jet systems. © 2017 Collegium Boreas. Published by John Wiley & Sons Ltd
2076.
Heat flow and geothermal gradients of the Campania region (Southern Italy) and their relationship to volcanism and tectonics
Journal of Volcanology and Geothermal Research,
36523 – 37
2018
ISSN: 03770273
Publisher: Elsevier B.V.
Keywords:▾
Campania [Italy]; Italy; Calluna vulgaris; Buildings; Heat transfer; Tectonics; Transport properties; Brittle-ductile transition zone; Campania; Distribution of temperature; Geothermal gradients; Magma reservoirs; Thermal anomalies; Volcanic district; Volcanism; geothermal gradient; heat flow; magma chamber; mass transport; tectonic evolution; temperature gradient; thermal convection; volcanism; Geothermal energy
Abstract: ▾ The heat flow and distribution of temperatures at depth in the Campania region were analysed and correlated with the volcanism and tectonics of the area. The temperature data, a part of the inventory of the AGIP, SAFEN and ENEL Companies (Inventario delle Risorse Geotermiche Nazionali), were gathered during drilling campaigns that began in 1940. The Campania region is characterised by the presence of two active and high-risk volcanic districts (the Campi Flegrei, Ischia and Vesuvius) emerging at the western boundary of the Campania Plain structural graben, and by the outcropping of the carbonate basement along the borders of the plain. The thermal anomalies have been correlated to different processes: the rising of the upper mantle (at about 20 km depth), the heat flow mass transport due to advection of hot fluids above magma reservoirs and the pure conductive heat transport of deeper crust. Furthermore, the presence of the carbonate basement has possibly buffered the deeper crustal thermal processes. The data also provided an estimation of the brittle-ductile transition zone that has been compared with the seismicity cut-off depth of the area. © 2018 Elsevier B.V.
2075.
Hadean zircon from a 3.3 Ga sandstone, Barberton greenstone belt, South Africa
Geology,
46
(11)
967 – 970
2018
DOI:10.1130/G45276.1
2074.
Gas and seismicity within the Istanbul seismic gap
Scientific Reports,
8
(1)
2018
ISSN: 20452322
Publisher: Nature Publishing Group
Keywords:▾
article; earthquake; sediment; Turkey (republic); Marmara Sea
Abstract: ▾ Understanding micro-seismicity is a critical question for earthquake hazard assessment. Since the devastating earthquakes of Izmit and Duzce in 1999, the seismicity along the submerged section of North Anatolian Fault within the Sea of Marmara (comprising the "Istanbul seismic gap") has been extensively studied in order to infer its mechanical behaviour (creeping vs locked). So far, the seismicity has been interpreted only in terms of being tectonic-driven, although the Main Marmara Fault (MMF) is known to strike across multiple hydrocarbon gas sources. Here, we show that a large number of the aftershocks that followed the M 5.1 earthquake of July, 25th 2011 in the western Sea of Marmara, occurred within a zone of gas overpressuring in the 1.5-5 km depth range, from where pressurized gas is expected to migrate along the MMF, up to the surface sediment layers. Hence, gas-related processes should also be considered for a complete interpretation of the micro-seismicity (~M < 3) within the Istanbul offshore domain. © 2018 The Author(s).
2073.
Formation of large-scale impact melt dikes: A case study of the Foy Offset Dike at the Sudbury impact structure, Canada
Earth and Planetary Science Letters,
495224-233
2018
Abstract: ▾ Hypervelocity impacts frequently result in the formation of dikes in the crater floor and central uplift. Impact melt-bearing dikes in large terrestrial impact basins – such as the Offset Dikes at the Sudbury impact structure – occur at a large scale, often tens of meters wide and several kilometers in length. The Offset Dikes host significant Ni–Cu–PGE deposits, which include several well-known mines, such as Totten and Copper Cliff that have been mined for nearly 100 years. The Offset Dikes typically consist of a clast- and sulfide-rich core and clast-poor margins. Their formation has been a subject of debate for decades. The most widely proposed model is the early emplacement of clast-poor impact melt shortly after the impact event, followed by the later emplacement of clast- and sulfide-rich impact melt in the center of the dike. An alternative hypothesis is that a single pulse of clast-rich impact melt flowed into the fractured target rocks and flow differentiation resulted in a clast-rich core and a clast-poor margin. In this study, we examine field and petrographic relationships of the Foy Offset Dike to better understand its emplacement. Our results show that the characteristics of the Foy Offset Dike – namely the gradational nature of the contact between the clast-rich and clast-poor phases, the alignment of clasts sub-parallel to this contact, the geochemical similarities and the presence of sulfides within both phases of the dike – are more consistent with the single injection and flow differentiation hypothesis. © 2018 Elsevier B.V.
2072.
Fluid Flux in Fractured Rock of the Alpine Fault Hanging-Wall Determined from Temperature Logs in the DFDP-2B Borehole, New Zealand
Geochemistry, Geophysics, Geosystems,
19
(8)
2631-2646
2018
ISSN: 15252027
Publisher: Blackwell Publishing Ltd
Keywords:▾
Aquifers; Boreholes; Flow of fluids; Fracture; Groundwater; Groundwater resources; Hydrogeology; Mechanical permeability; Rocks, Diffusive process; geothermal; Orders of magnitude; Surrounding rock mass; Temperature anomaly; Temperature recovery; Temperature signal; Thermal disturbance, Thermal logging, aquifer; borehole logging; fluid flow; fractured medium; geothermal system; groundwater; hanging wall; hydrogeology; permeability; rock mechanics; temperature gradient, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ Sixteen temperature logs were acquired during breaks in drilling of the 893m-deep DFDP-2B borehole, which is in the Alpine Fault hanging-wall. The logs record various states of temperature recovery after thermal disturbances induced by mud circulation. The long-wavelength temperature signal in each log was estimated using a sixth-order polynomial, and residual (reduced) temperature logs were analyzed by fitting discrete template wavelets defined by depth, amplitude, and width parameters. Almost two hundred wavelets are correlated between multiple logs. Anomalies generally have amplitudes <1°C, and downhole widths <20m. The largest amplitudes are found in the first day after mud circulation stops, but many anomalies persist with similar amplitude for up to 15 days. Our models show that thermal and hydraulic diffusive processes are dominant during the first few days of re-equilibration after mud circulation stops, and fluid advection of heat in the surrounding rock produces temperature anomalies that may persist for several weeks. Models indicate that the fluid flux normal to the borehole within fractured zones is of order 10−7 to 10−6 m s−1, which is 2–3 orders of magnitude higher than the regional flux. Our approach could be applied more widely to boreholes, as it uses the thermal re-equilibration phase to derive useful information about the surrounding rock mass and its fluid flow regime. ©2018. American Geophysical Union. All Rights Reserved.
2071.
Design and Application of Long Servce Life Bit in Hard Rock Drilling for " SK-Ⅱ" Well
Exploration Engineering (Rock & Soil Drilling and Tunneling),
45
(2)
56-60
2018
2070.
Facies architecture of Miocene subaqueous clinothems of the New Jersey passive margin: Results from IODP-ICDP Expedition 313
Geosphere,
14
(4)
1564-1591
2018
ISSN: 1553040X
Publisher: Geological Society of America
Keywords:▾
Deposits; Erosion; Floods; Sand; Sea level; Sedimentology; Seismic waves; Seismology; Storms; Tectonics, Continental scientific drillings; Depositional environment; Depositional models; Facies architecture; Global sea level rise; Recurrence intervals; Sediment distribution; Sedimentary architecture, Sediments, continental margin; depositional environment; facies analysis; Miocene; passive margin; progradation; reconstruction; sea level change; spatial distribution, Atlantic Ocean; New Jersey Shelf
Abstract: ▾ Understanding the history, causes, and impact of sea-level changes is a challenge for our societies that face accelerated global sea-level rise. In this context, improvement of our knowledge of sea-level changes and shoreline migration at geological time scales is critical. The preserved, laterally correlative sedimentary record of continental erosion on passive margins has been used to reconstruct past sea level. However, the detailed nature of a basic clinothem progradational pattern observed on many of these margins is still poorly known. This paper describes the sedimentary facies and interprets the depositional environments and the architecture of the clinothems of the New Jersey shelf (offshore northeastern USA) to depict the origin and controls of the distribution of the sediment on the margin. We analyze 612 cores totaling 1311 m in length collected at three sites 60 km offshore Atlantic City, New Jersey, during International Ocean Discovery Program-International Continental Scientific Drilling Program (IODP-ICDP) Expedition 313. The three sites sampled the lower to middle Miocene passive margin sediments of the New Jersey shelf clinothems. We also collected wireline logs at the three sites and tied the sedimentary architecture to the geometry observed on seismic profiles. The observed sediment distribution in the clinoform complex differs from that of current models based on seismic data, which predict a progressive increase in mud and decrease in sand contents in a seaward direction. In contrast, we observe that the clinoforms are largely composed of muds, with sands and coarser material concentrated at the rollover, the bottomset, and the toe of the slope. The shelf clinothem topsets are storm-influenced mud whereas the foreset slope is composed of a mud wedge largely dominated by density current deposits (e.g., low-density turbidites and debrites). The architecture of the clinothem complex includes a composite stack of ~30-m-thick clinothem units each made up of four systems tracts (Transgressive, Highstand, Forced- Regressive, and Lowstand Systems Tract) building individual transgressiveregressive sequences. The presence of mud-rich facies deposited during highstands on the topset of the clinoform, 40-60 km offshore from the sand-prone shoreface deposit (observed in the New Jersey onshore delta plain), and the lack of subaerial erosion (and continental depositional environments) point to a depositional model involving a subaerial delta (onshore) feeding a distant subaqueous delta. During forced regressions, shelf-edge deltas periodically overstep the stacks of flood-influenced, offshore-marine mud wedges of the New Jersey subaqueous delta, bringing sand to the rollover and building up the large-scale shelf-prism clinothems. The clinothem complex develops on a gently dipping platform with a ramp-like morphology (apparent dip of 0.75°-0.5°) below mean storm wave base, in 30-50 m of water depth, 40-60 km seaward of the coastal area. Its shape depends on the balance between accommodation and sedimentation rates. Subaqueous deltas show higher accumulation rates than their subaerial counterparts and prograde three times further and faster than their contemporaneous shoreline. The increase in the intensity of waves (height and recurrence intervals) favors the separation between subaqueous and subaerial deltas, and as a consequence, the formation of a flat topset geometry, a decrease in flood events and fluvial discharge, an overall progressive decrease in sediment grain size (from sequence m5.45, ca. 17.8-17.7 Ma, onwards), as well as an increase in sedimentation rates on the foresets of the clinoforms. All of these are recognized as preliminary signals that might characterize the entry into the Neogene icehouse world. © 2018 The Authors.