Potential of submarine-cave sediments and oxygen isotope composition of cavernicolous micro-bivalve as a late Holocene paleoenvironmental record   总被引：2，自引：1，他引：1  

Akihisa Kitamura  Nagisa Yamamoto  Tomoki Kase  Shu-ichi Ohashi  Mayumi Hiramoto  Hitoshi Fukusawa  Tsuyoshi Watanabe  Tomohisa Irino  Hiroshi Kojitani  Michiyo Shimamura  Ikuo Kawakami 《Global and Planetary Change》2007,55(4):301-316

A sediment layer (43 cm thick) and surface sediments (5 cm thick) in a submarine limestone cave (31 m water depth) on the fore-reef slope of Ie Island, off Okinawa mainland, Japan, were examined by visual, mineralogical and geochemical means. Oxygen isotope analysis was performed on the cavernicolous micro-bivalve Carditella iejimensis from both cored sediments and surface sediments, and the water temperature within the cave was recorded for nearly one year. These data show that: (1) water temperature within the cave is equal to that at 30 m deep in the open sea; (2) the biotic and non-biotic environments within the cave have persisted for the past 2000 years; (3) mud-size carbonate detritus is a major constituent of the submarine-cave deposit, and may have come mainly from the suspended carbonate mud produced on the emergent Holocene reef flat over the past two millennia; (4) the δ¹⁸O-derived temperature (T_δ18_O) of C. iejimensis suggests that the species grows between April and July; (5) the T_δ18_O of C. iejimensis from cored sediments implies that there were two warmer intervals, at AD 340 ± 40 and AD 1000 ± 40, which correspond to the Roman Warm Period and Medieval Warm Period, respectively. These suggest that submarine-cave sediments provide unique information for Holocene reef development. In addition, oxygen isotope records of cavernicolous C. iejimensis are a useful tool to reconstruct century-scale climatic variability for the Okinawa Islands during the Holocene.  相似文献   

Radial diffusion rate of planetesimals due to gravitational encounters     

Keiji Ohtsuki  Hidekazu Tanaka 《Icarus》2003,162(1):47-58

We study the rate of radial diffusion of planetesimals due to mutual gravitational encounters under Hill’s approximations in the three-body problem. Planetesimals orbiting a central star radially migrate inward and outward as a result of mutual gravitational encounters and transfer angular momentum. We calculate the viscosity in a disk of equal-sized planetesimals due to their mutual gravitational encounters using three-body orbital integrations, and obtain a semianalytic expression that reproduces the numerical results. We find that the viscosity is independent of the velocity dispersion of planetesimals when the velocity dispersion is so small that Kepler shear dominates planetesimals’ relative velocities. On the other hand, in high-velocity cases where random velocities dominate the relative velocities, the viscosity is a decreasing function of the velocity dispersion, and is found to agree with previous estimates under the two-body approximation neglecting the solar gravity. We also calculate the rate of radial diffusion of planetesimals due to gravitational scattering by a massive protoplanet. Using these results, we discuss a condition for formation of nonuniform radial surface density distribution of planetesimals by gravitational perturbation of an embedded protoplanet.  相似文献   

Long-term spectral changes in the partial-covering candidate narrow-line Seyfert 1 galaxy 1H 0707–495     

L. C. Gallo  Y. Tanaka  Th. Boller  A. C. Fabian  S. Vaughan  W. N. Brandt 《Monthly notices of the Royal Astronomical Society》2004,353(4):1064-1070

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A huge filamentary structure at z= 0.55 and star formation histories of galaxies at z < 1     

Masayuki Tanaka  Takako Hoshi  Tadayuki Kodama  Nobunari Kashikawa 《Monthly notices of the Royal Astronomical Society》2007,379(4):1546-1556

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Evidence for and implications of sedimentary diapirism and mud volcanism in the southern Utopia highland-lowland boundary plain, Mars     

James A. Skinner Jr.  Kenneth L. Tanaka 《Icarus》2007,186(1):41-59

Several types of spatially associated landforms in the southern Utopia Planitia highland-lowland boundary (HLB) plain appear to have resulted from localized geologic activity, including (1) fractured rises, (2) elliptical mounds, (3) pitted cones with emanating lobate materials, and (4) isolated and coalesced cavi (depressions). Stratigraphic analysis indicates these features are Hesperian or younger and may be associated with resurfacing that preferentially destroyed smaller (<8 km diameter) impact craters. Based on landform geomorphologies and spatial distributions, the documented features do not appear to be specifically related to igneous or periglacial processes or the back-wasting and erosion of the HLB scarp. We propose that these features are genetically related to and formed by sedimentary (mud) diapirs that ascended from zones of regionally confined, poorly consolidated, and mechanically weak material. We note morphologic similarities between the mounds and pitted cones of the southern Utopia boundary plain and terrestrial mud volcanoes in the Absheron Peninsula, Azerbaijan. These analogs provide a context for understanding the geological environments and processes that supported mud diapir-related modification of the HLB. In southern Utopia, mud diapirs near the Elysium volcanic edifice may have resulted in laccolith-like intrusions that produced the fractured rises, while in the central boundary plain mud diapirs could have extruded to form pitted cones, mounds, and lobate flows, perhaps related to compressional stresses that account for wrinkle ridges. The removal of material a few kilometers deep by diapiric processes may have resulted in subsidence and deformation of surface materials to form widespread cavi. Collectively, these inferences suggest that sedimentary diapirism and mud volcanism as well as related surface deformations could have been the dominant Hesperian mechanisms that altered the regional boundary plain. We discuss a model in which detritus would have accumulated thickly in the annular spaces between impact-generated structural rings of Utopia basin. We envision that these materials, and perhaps buried ejecta of Utopia basin, contained volatile-rich, low-density material that could provide the source material for the postulated sedimentary diapirs. Thick, water-rich, low-density sediments buried elsewhere along the HLB and within the lowland plains may account for similar landforms and resurfacing histories.  相似文献   

The first appearance of the red sequence of galaxies in proto-clusters at 2 ≲z≲ 3     

Tadayuki Kodama  Ichi Tanaka  Masaru Kajisawa  Jaron Kurk  Bram Venemans  Carlos De Breuck  Joël Vernet  Chris Lidman 《Monthly notices of the Royal Astronomical Society》2007,377(4):1717-1725

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CaPtO3 as a novel post-perovskite oxide     

Kenya Ohgushi  Yoshitaka Matsushita  Nobuyoshi Miyajima  Yoshio Katsuya  Masahiko Tanaka  Fujio Izumi  Hirotada Gotou  Yutaka Ueda  Takehiko Yagi 《Physics and Chemistry of Minerals》2008,35(4):189-195

Structural, morphological, magnetic, and thermal properties have been investigated for a novel post-perovskite oxide CaPtO₃ synthesized under high pressure. By comparing obtained structural parameters with those for known post-perovskite compounds, we argue that the chemical bond has a strong covalent character. Precise measurements of the Langevin susceptibility χ ₀ = −9.6 × 10⁻⁵ emu/mol and Debye temperature θ ∼ 470 K provide a good opportunity to confirm the reliability of first-principle calculations on predicting physical properties of the Earth’s D” layer.  相似文献   

Fossil Association from the Lower Cambrian Yanjiahe Formation in the Yangtze Gorges Area, Hubei, South China     

GUO Junfeng  LI Yong  HAN Jian  ZHANG Xingliang  ZHANG Zhifei  OU Qiang  LIU Jianni  SHU Degan  Shigenori MARUYAMA  Tsuyoshi KOMIYA 《《地质学报》英文版》2008,82(6):1124-1132

Apart from previously reported Small Shelly Fossils (SSFs), a macroscopic fossil assemblage, comprising abundant algae, cone-shaped tubular fossil forms, and probable impressions of a megascopic metazoan, comes from the Lower Cambrian Yanjiahe Formation in the Yangtze Gorges area of western Hubei Province, south China. The visible fossils are preserved in thin-laminated siltstone or muddy siltstone intercalated between 8–15 mm-thick carbonate deposits, probably representing sedimentary settings of a constrained local depression in the shallow water carbonate platform during the Early Cambrian Meishucunian Stage. The macroscopic fossil association provides significant fossil evidence about the evolution of life from the late Precambrian to the ‘Cambrian explosion’ interval.  相似文献   

Influence of contamination on banded iron formations in the Isua supracrustal belt,West Greenland: Reevaluation of the Eoarchean seawater compositions     

Shogo Aoki  Chiho Kabashima  Yasuhiro Kato  Takafumi Hirata  Tsuyoshi Komiya 《地学前缘(英文版)》2018,9(4):1049-1072

Banded Iron Formations(BIFs) are chemical sediments, ubiquitously distributed in the Precambrian supracrustal belts; thus their trace element compositions are helpful for deciphering geochemical evolution on the Earth through time. However, it is necessary to elucidate factors controlling the whole-rock compositions in order to decode the ancient seawater compositions because their compositions are highly variable. We analyzed major and trace element contents of the BIFs in the 3.8-3.7 Ga Isua supracrustal belt(ISB), southern West Greenland. The BIFs are petrographically classified into four types:Black-,Gray-, Green-and White-types, respectively. The Green-type BIFs contain more amphiboles, and are significantly enriched in Co, Ni, Cu, Zn, Y, heavy rare earth element(HREE) and U contents. However,their bulk compositions are not suitable for estimate of seawater composition because the enrichment was caused by secondary mobility of metamorphic Mg, Ca and Si-rich fluid, involvement of carbonate minerals and silicate minerals of olivine and pyroxene and/or later silicification or contamination of volcanic and clastic materials. The White-type BIFs are predominant in quartz, and have lower transition element and REE contents. The Gray-type BIFs contain both quartz and magnetite. The Black-type BIFs are dominated by magnetite, and contain moderate to high transition element and REE contents. But,positive correlations of V, Ni, Zn and U contents with Zr contents suggest that involvement of detrital,volcanic and exhalative materials influences on their contents. The evidence for significant influence of the materials on the transition element contents such as Ni in the BIFs indicates the transition element contents in the Archean ocean were much lower than previously estimated. We reconstructed secular variations of V,Co, Zn and U contents of BIFs through time, which show Ni and Co contents decreased whereas V, Zn and U contents increased through time. Especially, the Ni and Co contents drastically decreased in the Mesoarchean rather than around the Great Oxidation Event. On the other hand, the V,Zn and U contents progressively increased from the Mesoarchean to the Proterozoic. Stratigraphical trends of the BIFs show increase in Y/Ho ratios and decrease in positive Eu anomaly upwards, respectively. The stratigraphic changes indicate that a ratio of hydrothermal fluid to seawater component gradually decrease through the deposition, and support the Eoarchean plate tectonics, analogous to the their stratigraphic variations of seafloor metalliferous sediments at present and in the Mesoarchean.  相似文献   

Decision-theoretic sensitivity analysis for reservoir development under uncertainty using multilevel quasi-Monte Carlo methods     

Takashi Goda  Daisuke Murakami  Kei Tanaka  Kozo Sato 《Computational Geosciences》2018,22(4):1009-1020

At various stages of petroleum reservoir development, we encounter a large degree of geological uncertainty under which a rational decision has to be made. In order to identify which parameter or group of parameters significantly affects the output of a decision model, we investigate decision-theoretic sensitivity analysis and its computational issues in this paper. In particular, we employ the so-called expected value of partial perfect information (EVPPI) as a sensitivity index and apply multilevel Monte Carlo (MLMC) methods to efficient estimation of EVPPI. In a recent paper by Giles and Goda, an antithetic MLMC estimator for EVPPI is proposed and its variance analysis is conducted under some assumptions on a decision model. In this paper, for an improvement on the performance of the MLMC estimator, we incorporate randomized quasi-Monte Carlo methods within the inner sampling, which results in an multilevel quasi-Monte Carlo (MLQMC) estimator. We apply both the antithetic MLMC and MLQMC estimators to a simple waterflooding decision problem under uncertainty on absolute permeability and relative permeability curves. Through numerical experiments, we compare the performances of the MLMC and MLQMC estimators and confirm a significant advantage of the MLQMC estimator.  相似文献