3-D internal architecture of methane hydrate-bearing turbidite channels in the eastern Nankai Trough, Japan     

Satoshi Noguchi  Naoyuki Shimoda  Osamu Takano  Nobutaka Oikawa  Takao Inamori  Tatsuo Saeki  Tetsuya Fujii 《Marine and Petroleum Geology》2011,28(10):1817-1828

The reservoir architecture of methane hydrate (MH) bearing turbidite channels in the eastern Nankai Trough, offshore Japan is evaluated using a combination of 3-D seismic and well data. On the 3-D seismic section, the MH-bearing turbidite channels correspond to complex patterns of strong seismic reflectors, which show the 3-D internal architecture of the channel complex. A seismic-sequence stratigraphic analysis reveals that the channel complex can be roughly classified into three different stages of depositional sequence (upper, middle, and lower). Each depositional sequence results in a different depositional system that primarily controls the reservoir architecture of the turbidite channels. To construct a 3-D facies model, the stacking patterns of the turbidite channels are interpreted, and the reservoir heterogeneities of MH-bearing sediments are discussed. The identified channels at the upper sequence around the β1 well exhibit low-sinuosity channels consisting of various channel widths that range from tens to several hundreds of meters. Paleo-current flow directions of the turbidite channels are typically oriented along the north-northeast-to-south-southwest direction. High-amplitude patterns were identified above the channels along the north-to-south and north-northeast-to-south-southeast directions. These roughly coincide with the paleo-current flow of the turbidite channels. An interval velocity using high-density velocity analysis shows that velocity anomalies (>2000 m/s) are found on the northeastern side of the turbidite channels. The depositional stage of the northeastern side of the turbidite channels exhibits slightly older sediment stages than the depositional stages of the remaining channels. Hence, the velocity anomalies of the northeastern side of the channels are related to the different stages of sediment supply, and this may lead to the different reservoir architectures of the turbidite channels.  相似文献   

Distribution of phytoplankton in the East China Sea in the winter of 1993   总被引：3，自引：1，他引：3  

Ken Furuya  Kiyo Kurita  Tsuneo Odate 《Journal of Oceanography》1996,52(3):323-333

Phytoplankton distribution and its relationship to water masses were investigated in the East China Sea from February 15 to March 10, 1993. Diatoms, dinoflagellates and coccolithophorids were examined by the Utermöhl method. Two distinct phytoplankton assemblages were identified: a shelf and oceanic assemblage. The shelf community was characterized by a high abundance of diatoms, particularly, a benthic diatomParalia sulcata, and the oceanic community by numerical dominance of coccolithophorids and occurrence of surface warm-water species of diatoms. A boundary of both communities was located at the shelf edge that coincided with the shelf side of a Kuroshio front.P. sulcata was the most dominant in the inner shelf area throughout the water column. The occurrence of this species near the surface was considered to be a good indicator of the enhanced vertical mixing driven by winter monsoon. The species survives under extremely low light intensity near the bottom during the stratified periods in summer. During the winter time when light condition at the bottom becomes most unfavorable, resuspension and upward traveling of the species due to enhanced vertical mixing seem to be advantageous to acquire suitable light condition. Because of its predominance, possible importance ofP. sulcata is suggested in material cycling on the shelf, particularly near the bottom.  相似文献   

Unquenchable high-pressure perovskite polymorphs of MnSnO3 and FeTiO3     

Kurt Leinenweber  Wataru Utsumi  Yoshihiko Tsuchida  Takehiko Yagi  Kei Kurita 《Physics and Chemistry of Minerals》1991,18(4):244-250

New high-pressure orthorhombic (GdFeO₃-type) perovskite polymorphs of MnSnO₃ and FeTiO₃ have been observed using in situ powder X-ray diffraction in a diamond-anvil cell with synchrotron radiation. The materials are produced by the compression of the lithium niobate polymorphs of MnSnO₃ and FeTiO₃ at room temperature. The lithium niobate to perovskite transition occurs reversibly at 7 GPa in MnSnO₃, with a volume change of -1.5%, and at 16 GPa in FeTiO₃, with a volume change of -2.8%. Both transitions show hysteresis at room temperature. For MnSnO₃ perovskite at 7.35 (8) GPa, the orthorhombic cell parameters are a=5.301 (2) A, b=5.445 (2) Å, c=7.690 (8) Å and V= 221.99 (15) ų. Volume compression data were collected between 7 and 20 GPa. The bulk modulus calculated from the compression data is 257 (18) GPa in this pressure region. For FeTiO₃ perovskite at 18.0 (5) GPa, cell parameters are a=5.022 (6) Å, b=5.169 (5) Å, c=7.239 (9) Å and V= 187.94 (36) ų. Based on published data on the quench phases, the FeTiO₃ perovskite breaks down to a rocksalt + baddelyite mixture of FeO and TiO₂ at 23 GPa. This is the first experimental verification of the pressure-induced breakdown of a perovskite to simple oxides.  相似文献   

Using HED meteorites to interpret neutron and gamma‐ray data from asteroid 4 Vesta          下载免费PDF全文

Andrew W. Beck  David J. Lawrence  Patrick N. Peplowski  Thomas H. Prettyman  Timothy J. McCoy  Harry Y. McSween Jr  Michael J. Toplis  Naoyuki Yamashita 《Meteoritics & planetary science》2015,50(8):1311-1337

Here, we construct a comprehensive howardite, eucrite, and diogenite (HED) bulk chemistry data set to compare with Dawn data. Using the bulk chemistry data set, we determine four gamma‐ray/neutron parameters in the HEDs (1) relative fast neutron counts (fast counts), (2) macroscopic thermal neutron absorption cross section (absorption), (3) a high‐energy gamma‐ray compositional parameter (C_p), and (4) Fe abundance. These correspond to the four measurements of Vesta made by Dawn's Gamma Ray and Neutron Detector (GRaND) that can be used to discern HED lithologic variability on the Vestan surface. We investigate covariance between fast counts and average atomic mass (<A>) in the meteorite data set, where a strong correlation (r² = 0.99) is observed, and we demonstrate that systematic offsets from the fast count/<A> trend are linked to changes in Fe and Ni concentrations. To compare the meteorite and GRaND data, we investigate and report covariance among fast counts, absorption, C_p, and Fe abundance in the HED meteorite data set. We identify several GRaND measurement spaces where the Yamato type B diogenites are distinct from all other HED lithologies, including polymict mixtures. The type B's are diogenites that are enriched in Fe + pigeonite + diopside ± plagioclase, relative to typical, orthopyroxenitic diogenites. We then compare these results to GRaND data and demonstrate that regions north of ~70°N latitude on Vesta (including the north pole) are consistent with type B diogenites. We propose two models to explain type B diogenite compositions in the north (1) deposition as Rheasilvia ejecta, or (2) type B plutons that were emplaced at shallow depths in the north polar region and sampled by local impacts. Lastly, using principal component (PC) analysis, we identify unique PC spaces for all HED lithologies, indicating that the corresponding GRaND measurables may be used to produce comprehensive lithologic maps for Vesta.  相似文献   

Source parameters of central California earthquakes on February 24 and September 4, 1972     

Tuneto Kurita 《Physics of the Earth and Planetary Interiors》1976,13(1):18-36

The directivity function method is combined with an earthquake sequence study to obtain the reliable estimates of rupture area and rupture velocity of two right-lateral strike-slip earthquakes occurring along the San Andreas fault zone in central California. By utilizing a significant difference in velocity structure on both sides of the main fault, a modified version of the directivity function is formulated and applied to near-field SH waves. On assuming aftershock areas following their step-wise increase with time as rupture areas, an extensive systematic search for the best fit between the observed and theoretical directivity functions is made for a combination of both source parameters. The rupture at the February 24, 1972 earthquake (M_L = 5.0) propagated unilaterally with an average velocity of about 2.3 km/sec. It produced a rectangular area, the horizontal and vertical lengths being about 5 and 2 km, respectively. The rupture at the September 4, 1972 earthquake (M_L = 4.6) was of bilateral, yielding a nearly square rupture area of which side length is about 2 km. The rupture velocity of this earthquake, though some ambiguities resulting from a lower quality of the observed directivity function, is estimated at 1.9 km/sec or less. A difference in average rupture velocity between both earthquakes might imply its dependence on the ambient tectonic environment such as represented by local stress and humidity. By taking into account a post-earthquake creep increase of about 3.0–3.5 cm observed at a creepmeter station situated over the focus of the February 24, 1972 earthquake, its stress drop and seismic moment are estimated at about 10 bar and 10²³ dyn · cm, respectively. The above procedure has a broad applicability for recovering reliable estimates of source parameters, especially when it is combined with a synthetic approach.  相似文献   

Experimental studies of He and Ar degassing during rock fracturing     

M. Honda  K. Kurita  Y. Hamano  M. Ozima 《Earth and Planetary Science Letters》1982,59(2):429-436

We studied degassing of He and Ar from granite, basalt and volcanic tuff samples which were subjected to uniaxial compression. From the samples which were fractured in the dilatant region He was always degassed, while degassing of Ar dependent not only on the dilatancy, but also on the type of rock and the compressional conditions such as wet, room dry or vacuum conditions. It is concluded that degassing of rare gases from the compressed samples depends primarily on the generation of new surface area by dilatancy.  相似文献   

A synthetic seismicity model for the Xianshuihe fault, southwestern China: simulation using a rate- and state-dependent friction law   总被引：1，自引：0，他引：1  

Naoyuki Kato  Xinglin Lei  Xueze Wen 《Geophysical Journal International》2007,169(1):286-300

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A deep near-infrared survey around the giant radio galaxy PKS 1343–601     

T. Nagayama  P. A. Woudt  C. Nagashima  Y. Nakajima  D. Kato  M. Kurita  T. Nagata  H. Nakaya  M. Tamura  K. Sugitani  K. Wakamatsu  S. Sato 《Monthly notices of the Royal Astronomical Society》2004,354(4):980-990

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Continuing observation of disturbed reproductive cycle and ovarian spermatogenesis in the giant abalone, Haliotis madaka from an organotin-contaminated site of Japan   总被引：1，自引：0，他引：1  

Horiguchi T  Kojima M  Takiguchi N  Kaya M  Shiraishi H  Morita M 《Marine pollution bulletin》2005,51(8-12):817-822

Histological examination of gonads as well as chemical analysis of organotin compounds in tissues of the giant abalone, Haliotis madaka, was conducted to evaluate continuing endocrine disruption in abalone populations in Japan. Abalone specimens were collected from two different areas, Tsushima as a reference site and Jogashima as a site representative of declining abalone populations where serious organotin contamination had been observed, each month from January 1998 to March 1999. Scores were given to the development stages of reproductive cells in the ovary and testis. The degree of sexual maturation was evaluated by calculating the mean value of a histogram of these scores for the reproductive cells of each abalone. The temporal variations in degree of sexual maturation showed that female and male abalone from Tsushima matured synchronously, while those from Jogashima did not, which were similar to results of the previous study during September 1995–November 1996. Approximately 19% of the female abalone from Jogashima were masculinized with an ovo-testis, which was also similar to the result of the previous study. The masculinization of female abalone is reported to be induced by tributyltin (TBT) and triphenyltin (TPhT) from antifouling paints. Concentrations of the sum of butyltins (TBT, dibutyltin (DBT) and monobutyltin (MBT): ΣBTs) and the sum of phenyltins (TPhT, diphenyltin (DPhT) and monophenyltin (MPhT): ΣPhTs) in the muscle of abalone from Jogashima (n = 73) of 7.8 ± 9.0 ng/g wet wt. and 4.5 ± 6.8 ng/g wet wt., respectively, were significantly higher than those from Tsushima (n = 87) of 4.7 ± 4.9 ng/g wet wt. and 0.8 ± 1.7 ng/g wet wt., respectively (p < 0.05 for ΣBTs; p < 0.001 for ΣPhTs), although concentrations of TBT and TPhT in the muscle of abalone from Jogashima (n = 73) of 2.2 ± 2.5 ng/g wet wt. and 5.8 ± 5.1 ng/g wet wt., respectively, were insignificantly and significantly higher than those from Tsushima (n = 87) of 0.4 ± 0.6 ng/g wet wt. and 0.5 ± 0.9 ng/g wet wt., respectively, (p > 0.05 for TBT; p < 0.001 for TPhT). Thus, endocrine disruption as well as contamination by organotins in the giant abalone from Jogashima is still persisting.  相似文献   

The emplacement of in situ greenstones in the northern Hidaka belt: The tectonic relationship between subduction of the Izanagi–Pacific ridge and Hidaka magmatic activity     

Futoshi Nanayama  Jun Tajika  Toru Yamasaki  Hiroshi Kurita  Hideki Iwano  Tohru Danhara  Takafumi Hirata 《Island Arc》2021,30(1):e12403

Greenstone bodies emplaced upon or into clastic sediments crop out ubiquitously in the Hidaka belt (early Paleogene accretionary and collisional complexes exposed in the central part of northern Hokkaido, NE Japan), but the timing and setting of their emplacement has remained poorly constrained. Here, we report new zircon U–Pb ages for the sedimentary complexes surrounding these greenstones. The Hidaka Supergroup in the northern Hidaka belt is divided into four zones from west to east: zones S, U, and R, which contain in situ greenstones; and zone Y, which does not. Detrital zircons in zones S, U, and R have early Eocene U–Pb ages (55–47 Ma) and these strata are intruded by early Eocene granites (46–45 Ma), indicating that they were deposited between 55 and 46 Ma. Therefore, in situ greenstones in the northern Hidaka belt can only be explained by the subduction of the Izanagi–Pacific Ridge during 55–47 Ma. In contrast, the deposition of zone Y (the Yubetsu Group, younging to the west) began by 73–71 Ma, indicating that the accretionary prism in front of the paleo-Kuril arc formed at the same time as that in the Idonnappu zone and grew continuously until 48 Ma. The plutonic rocks that intruded the Hidaka belt are roughly divided into three stages: (1) early Eocene granites intruded the northern Hidaka belt at 46–45 Ma, during subduction of the Izanagi–Pacific Ridge; (2) the upper sequence of the Hidaka metamorphic zone was metamorphosed by magmatism at 40–37 Ma associated with the collision of the paleo-Kuril arc and NE Asia; and (3) younger granites intruded the entire Hidaka belt at 20–17 Ma in association with asthenospheric upwelling caused by back-arc expansion.  相似文献