Tidal amplification and along‐strike process variability in a mixed‐energy paralic system prograding onto a low accommodation shelf,Edgeøya,Svalbard     

Ingrid Anell  Valentin Zuchuat  Anna Daniela Rhnert  Aleksandra Smyrak‐Sikora  Simon Buckley  Gareth Lord  Harmon Maher  Ivar Midtkandal  Kei Ogata  Snorre Olaussen  Per T. Osmundsen  Alvar Braathen 《Basin Research》2021,33(1):478-512

The study describes the depositional development and sediment partitioning in a prograding paralic Triassic succession. The deposits are associated with the advance of large prism‐scale clinoforms across a shallower platform area. Approaching the platform, the limited accommodation and associated relative higher rates of deposition generated straighter clinoforms with lower foreset angles. The vertical restriction across the platform is interpreted to have amplified the tidal signature. Sediment was redistributed from the coast into increasingly sandy delta‐front deposits, compared to offshore equivalents. The deposits comprise extensive compound dune fields of amalgamated and increasingly clean sandbodies up‐section. Rapid deposition of significant amounts of sand led to differential subsidence and growth‐faulting in the delta front, with downthrown fault blocks further amplifying the tidal energy through funnelling. A mixed‐energy environment created along‐strike variability along the delta front with sedimentation governing process‐regime. Areas of lower sedimentation were reworked by wave and storm‐action, whereas high sedimentation rates preserved fluvially dominated mouth bars. A major transgression, however, favoured tidally dominated deposits also in these areas, attributed to increasing rugosity of the coastline. Formation of an extensive subaqueous platform between the coast and delta front dampened incoming wave energy, and tidally dominated deposits dominate the near‐shore successions. Meanwhile formation of wave‐built sand‐bars atop the platform attest to continued wave influence. The strong tidal regime led to the development of a heterolithic near‐shore tidally dominated channel system, and sandier fluvial channels up‐river. The highly meandering tidal channels incising the subaqueous platform form kilometre wide successions of inclined heterolithic stratification. The fluvially dominated channels which govern deposition on the delta plain are narrower and slightly less deep, straighter, generally symmetric and filled with cleaner sands. This study provides important insight into tidal amplification and sand redistribution during shallowing on a wide shelf, along with along‐strike process‐regime variability resulting from variations in sediment influx.  相似文献   

Book reviews     

S. J. Gibowicz  John W. Rudnicki  Vladimir Pinsky  Gary Mavko  William L. Power  A. V. Koloskov  Randall Lee Mackie  Yu. N. Korenkov  Kei Katsumata 《Pure and Applied Geophysics》1991,135(1):135-164

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Flow behavior of large-scale pyroclastic flows — Evidence obtained from petrofabric analysis     

Tadahide Ui  Keiko Suzuki-Kamata  Rumi Matsusue  Kei Fujita  Hideya Metsugi  Mami Araki 《Bulletin of Volcanology》1989,51(2):115-122

The grain orientations within the matrix of two large-scale welded, two small-scale nonwelded and two nonwelded low-aspect ratio pyroclastic flow deposits are measured to analyze flow behavior. Preferred grain alignments are especially apparent in the middle part of layer 2 of each deposit. Preferred grain alignments do not vary laterally within a 10 m interval. The grain alignments obtained are radial from the source caldera, especially in proximal to medial and plateau-forming facies of pyroclastic flow deposits. Grain alignments are controlled by valley-channel directions for the valley-ponded facies of pyroclastic flow deposits, especially at medial to distal locations. Such local topographic factors strongly affect the data for high-aspect ratio and smallscale deposits, and weakly affect the data for widespread low-aspect ratio pyroclastic flow deposits. This work suggests that grain alignment analysis should be used with care when attempting to determine the location of an unknown source.  相似文献   

Spatial trends of nitrate pollution and groundwater chemistry in Shimabara,Nagasaki, Japan   总被引：1，自引：0，他引：1  

Kei Nakagawa  Hiroki Amano  Hiroshi Asakura  Ronny Berndtsson 《Environmental Earth Sciences》2016,75(3):234

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Application of a Simulation Model for the Formation of Methane Hydrate to the Nankai Trough and the Blake Ridge: Natural Examples of Two End-member Cases     

Kei Baba  Arata Katoh 《Resource Geology》2004,54(1):125-135

Abstract. Simulation experiments with a one-dimensional static model for formation of methane hydrate are used to demonstrate models of hydrate occurrence and its generation mechanism for two end-member cases. The simulation results compare well with experimental data for two natural examples (the Nankai Trough and the Blake Ridge).
At the MITI Nankai Trough wells, the hydrate occurrence is characterized by strongly hydrated sediments developing just above the BGHS. Such occurrence can be reproduced well by simulation in which the end-member case of upward advective fluid flow from below the BGHS is set. The strongly hydrated sediments is formed by oversaturated solution with free gas which directly enters the BGHS by the upward advective fluid flow. The recycling of dissociated methane of preexisting hydrate also contributes to the increase of hydrate saturation.
At the Site 997 in the Blake Ridge area, the hydrate occurrence is characterized by thick zone with poorly hydrated sediments and no hydrate zone developing above the hydrate zone. Such occurrence can be reproduced well by simulation in which the end-member case of in-situ biogenic production of methane in the sediment of methane hydrate zone is set. The distribution pattern of hydrate saturation is basically controlled by that of TOC. However, the hydrate concentration near the bottom of the hydrate zone is increased by the effect of recycling of dissociated methane of pre-existing hydrate. No hydrate zone expresses the geologic time needed until the local concentration of methane exceeds the solubility by gradual accumulation of in-situ biogenic methane with burial.  相似文献   

Solubilities of nitrogen and noble gases in silicate melts under various oxygen fugacities: implications for the origin and degassing history of nitrogen and noble gases in the earth     

Akiko Miyazaki  Hajime Hiyagon  Kei Hirose 《Geochimica et cosmochimica acta》2004,68(2):387-401

Solubility experiments for nitrogen and noble gases (Ar and Ne) in silicate melts were conducted using two experimental configurations: one was conducted at 1 atmospheric pressure, T =1300°C and oxygen fugacity (fO₂) of IW + 0.9 (i.e., 0.9 log units higher than the iron-wüstite buffer) and the other at high pressures (P_total ∼ 2 × 10⁸ Pa), 1500°C and fO₂ ∼ IW + 6. For the former experiment, isotopically labeled-nitrogen (¹⁵N¹⁵N-enriched) was used to distinguish dissolved nitrogen from contaminating atmospheric or organic nitrogen and to examine dissolution mechanisms of nitrogen in silicate melts. The results obtained for the two series of experiments are consistent with each other, suggesting that Henry's law is satisfied for fN₂ of up to ∼250 atm (2.5 × 10⁷ Pa). The results are also consistent with our earlier results (Miyazaki et al., 1995) obtained at highly oxidizing conditions (fO₂ ∼ IW + 10). All these results support physical dissolution of nitrogen as N₂ molecules in silicate melts for fO₂ from ∼IW + 10 down to ∼IW. The observed solubility (Henry's constant) of nitrogen (3-5 × 10⁻⁹ mol/g/atm) is comparable to that of Ar (2-4 × 10⁻⁹ mol/g/atm), and much lower than that of Ne (11-14 × 10⁻⁹ mol/g/atm) at 1300°C. A preliminary experiment was also performed for partitioning of nitrogen and noble gases between clinopyroxene (cpx) and basaltic melt using a piston cylinder-type apparatus at 1.5 GPa and at 1270 to 1350°C. The obtained cpx/melt partition coefficient of nitrogen is 0.06, slightly lower than those of noble gases (∼0.1 for Ne to Xe), suggesting that nitrogen is as incompatible as or even slightly more incompatible than noble gases. The present results imply that a large nitrogen/Ar fractionation would not be produced by magmatic processes. Therefore, the two orders of magnitude difference between the N₂/³⁶Ar ratios in the Earth's atmosphere (∼10⁴) and that in the mantle (∼10⁶) must be explained by some other processes, such as incomplete segregation of metal blobs into the core and their later oxidation.  相似文献   

GHR1 Zircon – A New Eocene Natural Reference Material for Microbeam U‐Pb Geochronology and Hf Isotopic Analysis of Zircon     

Michael P. Eddy  Mauricio Ibaez‐Mejia  Seth D. Burgess  Matthew A. Coble  Umberto G. Cordani  Joel DesOrmeau  George E. Gehrels  Xianhua Li  Scott MacLennan  Mark Pecha  Kei Sato  Blair Schoene  Victor A. Valencia  Jeffrey D. Vervoort  Tiantian Wang 《Geostandards and Geoanalytical Research》2019,43(1):113-132

We present multitechnique U‐Pb geochronology and Hf isotopic data from zircon separated from rapakivi biotite granite within the Eocene Golden Horn batholith in Washington, USA. A weighted mean of twenty‐five Th‐corrected ²⁰⁶Pb/²³⁸U zircon dates produced at two independent laboratories using chemical abrasion‐isotope dilution‐thermal ionisation mass spectrometry (CA‐ID‐TIMS) is 48.106 ± 0.023 Ma (2s analytical including tracer uncertainties, MSWD = 1.53) and is our recommended date for GHR1 zircon. Microbeam ²⁰⁶Pb/²³⁸U dates from laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) and secondary ion mass spectrometry (SIMS) laboratories are reproducible and in agreement with the CA‐ID‐TIMS date to within < 1.5%. Solution multi‐collector ICP‐MS (MC‐ICP‐MS) measurements of Hf isotopes from chemically purified aliquots of GHR1 yield a mean ¹⁷⁶Hf/¹⁷⁷Hf of 0.283050 ± 17 (2s, n = 10), corresponding to a εHf₀ of +9.3. Hafnium isotopic measurements from two LA‐ICP‐MS laboratories are in agreement with the solution MC‐ICP‐MS value. The reproducibility of ²⁰⁶Pb/²³⁸U and ¹⁷⁶Hf/¹⁷⁷Hf ratios from GHR1 zircon across a variety of measurement techniques demonstrates their homogeneity in most grains. Additionally, the effectively limitless reserves of GHR1 material from an accessible exposure suggest that GHR1 can provide a useful reference material for U‐Pb geochronology of Cenozoic zircon and Hf isotopic measurements of zircon with radiogenic ¹⁷⁶Hf/¹⁷⁷Hf.  相似文献   

Electrical resistivity of fcc phase iron hydrides at high pressures and temperatures     

Kenji Ohta  Sho Suehiro  Kei Hirose  Yasuo Ohishi 《Comptes Rendus Geoscience》2019,351(2-3):147-153

We measured the electrical resistivity of face-centered-cubic (fcc) structured iron hydrides at high pressures up to 65 GPa and high temperatures in a laser-heated diamond anvil cell. The results indicate that the resistivity of stoichiometric fcc FeH_x (x ～ 1.0) is smaller than that of fcc Fe at the same pressure and temperature conditions. The same behavior was also observed in fcc FeNiH_x (x ～ 1.0). On the other hand, hydrogen-poor fcc FeH_x (x < 0.77) showed a resistivity comparable to that of the fcc phase of pure iron. Therefore, we conclude that the stoichiometric fcc Fe (–Ni) hydride is more conductive than Fe (–Ni) with the same crystal symmetry, and the impurity resistivity of hydrogen in Fe is vanishingly small. Even if hydrogen is the major light element in the Earth's core, it would have little influence on the electrical and thermal conductivity of Fe–Ni alloys, and hence the thermal evolution of the core.  相似文献   

Composition and pressure dependence of lattice thermal conductivity of (Mg,Fe)O solid solutions     

Akira Hasegawa  Kenji Ohta  Takashi Yagi  Kei Hirose  Yoshiyuki Okuda  Tadashi Kondo 《Comptes Rendus Geoscience》2019,351(2-3):229-235

We measured the lattice thermal conductivities of Fe_0.98O wüstite and iron-rich (Mg,Fe)O magnesiowüstite using the pulsed light heating thermoreflectance technique with a diamond anvil cell up to 61 GPa at 300 K. We found that the thermal conductivity of wüstite does not show a monotonic increase as a function of pressure, contrary to that of MgO periclase. Rocksalt (B1) to rhombohedral B1 transition is likely to induce an abnormal pressure response in the conductivity of wüstite. Our results also show that magnesiowüstite has a lower conductivity than that of MgO and FeO endmembers due to a strong iron impurity effect, which is well reproduced by a model considering phonon-impurity scattering in a binary solid solution.  相似文献   

Pyrene induces a reduction in midbrain size and abnormal swimming behavior in early-hatched pufferfish larvae     

Yuki Sugahara  Masahumi Kawaguchi  Tatsuya Itoyama  Daisuke Kurokawa  Yasuhiko Tosa  Shin-Ichi Kitamura  Itsuki C. Handoh  Kei Nakayama  Yasunori Murakami 《Marine pollution bulletin》2014

Spills of heavy oil (HO) have an adverse effect on marine life. We have demonstrated previously that exposure to HO by fertilized eggs of the pufferfish (Takifugu rubripes) induces neural disruption and behavioral abnormality in early-hatched larvae. Here, two kinds of polycyclic aromatic hydrocarbons, pyrene and phenanthrene, were selected to examine their toxic effects on larval behavior of another pufferfish species (T. niphobles). Larvae exposed to pyrene or phenanthrene exhibited no abnormalities in morphology. However, those exposed to pyrene but not phenanthrene swam in an uncoordinated manner, although their swimming distance and speed were normal. The optic tectum, a part of the midbrain, of pyrene-exposed larvae did not grow to full size. Thus, these findings are indicated that pyrene might be a contributor to the behavioral and neuro-developmental toxicity, although there is no indication that it is the only compound participating in the toxicity of the heavy oil mixture.  相似文献