Trace Element Composition and Classification of the Chinga Iron Meteorite     

K. D. Litasov  A. Ishikawa  I. S. Bazhan  D. S. Ponomarev  T. Hirata  N. M. Podgornykh  N. P. Pokhilenko 《Doklady Earth Sciences》2018,478(1):62-66

A complete microelement analysis of the Chinga meteorite was performed, and the possibility of attributing it together with a number of other iron meteorites into the IVC subgroup, which is transition between IVA and IVB is proposed.  相似文献   

Distinctive erosional and depositional structures formed at a canyon mouth: A lower Pleistocene deep‐water succession in the Kazusa forearc basin on the Boso Peninsula,Japan     

Makoto Ito  Kazuaki Ishikawa  Naohisa Nishida 《Sedimentology》2014,61(7):2042-2062

The canyon mouth is an important component of submarine‐fan systems and is thought to play a significant role in the transformation of turbidity currents. However, the depositional and erosional structures that characterize canyon mouths have received less attention than other components of submarine‐fan systems. This study investigates the facies organization and geometry of turbidites that are interpreted to have developed at a canyon mouth in the early Pleistocene Kazusa forearc basin on the Boso Peninsula, Japan. The canyon‐mouth deposits have the following distinctive features: (i) The turbidite succession is thinner than both the canyon‐fill and submarine‐fan successions and is represented by amalgamation of sandstones and pebbly sandstones as a result of bypassing of turbidity currents. (ii) Sandstone beds and bedsets show an overall lenticular geometry and are commonly overlain by mud drapes, which are massive and contain fewer bioturbation structures than do the hemipelagic muddy deposits. (iii) The mud drapes have a microstructure characterized by aggregates of clay particles, which show features similar to those of fluid‐mud deposits, and are interpreted to represent deposition from fluid mud developed from turbidity current clouds. (iv) Large‐scale erosional surfaces are infilled with thick‐bedded to very thick‐bedded turbidites, which show lithofacies quite similar to those of the surrounding deposits, and are considered to be equivalent to scours. (v) Concave‐up erosional surfaces, some of which face in the upslope direction, are overlain by backset bedding, which is associated with many mud clasts. (vi) Tractional structures, some of which are equivalent to coarse‐grained sediment waves, were also developed, and were overlain locally by mud drapes, in association with mud drape‐filled scours, cut and fill structures and backset bedding. The combination of these outcrop‐scale erosional and depositional structures, together with the microstructure of the mud drapes, can be used to identify canyon‐mouth deposits in ancient deep‐water successions.  相似文献   

Permian Peri‐glacial Deposits from Central Mongolia in Central Asian Orogenic Belt: A Possible Indicator of the Capitanian Cooling Event     

Tatsuya Fujimoto  Shigeru Otoh  Yuji Orihashi  Takafumi Hirata  Takaomi D. Yokoyama  Masanori Shimojo  Yoshikazu Kouchi  Hokuto Obara  Yasuo Ishizaki  Kazuhiro Tsukada  Toshiyuki Kurihara  Manchuk Nuramkhan  Sersmaa Gonchigdorj 《Resource Geology》2012,62(4):408-422

A dropstone‐bearing, Middle Permian to Early Triassic peri‐glacial sedimentary unit was first discovered from the Khangai–Khentei Belt in Mongolia, Central Asian Orogenic Belt. The unit, Urmegtei Formation, is assumed to cover the early Carboniferous Khangai–Khentei accretionary complex, and is an upward‐fining sequence, consisting of conglomerates, sandstones, and varved sandstone and mudstone beds with granite dropstones in ascending order. The formation was cut by a felsic dike, and was deformed and metamorphosed together with the felsic dike. An undeformed porphyritic granite batholith finally cut all the deformed and metamorphosed rocks. LA‐ICP‐MS, U–Pb zircon dating has revealed the following ²⁰⁶Pb/²³⁸U weighted mean igneous ages: (i) a granite dropstone in the Urmegtei Formation is 273 ± 5 Ma (Kungurian of Early Permian); (ii) the deformed felsic dike is 247 ± 4 Ma (Olenekian of Early Triassic); and (iii) the undeformed granite batholith is 218 ± 9 Ma (Carnian of Late Triassic). From these data, the age of sedimentation of the Urmegtei Formation is constrained between the Kungurian and the Olenekian (273–247 Ma), and the age of deformation and metamorphism is constrained between the Olenekian and the Carnian (247–218 Ma). In Permian and Triassic times, the global climate was in a warming trend from the Serpukhovian (early Late Carboniferous) to the Kungurian long and severe cool mode (328–271 Ma) to the Roadian to Bajocian (Middle Jurassic) warm mode (271–168 Ma), with an interruption with the Capitanian Kamura cooling event (266–260 Ma). The dropstone‐bearing strata of the Urmegtei Formation, together with the glacier‐related deposits in the Verkhoyansk, Kolyma, and Omolon areas of northeastern Siberia (said to be of Middle to Late Permian age), must be products of the Capitanian cooling event. Although further study is needed, the dropstone‐bearing strata we found can be explained in two ways: (i) the Urmegtei Formation is an autochthonous formation indicating a short‐term expansion of land glacier to the central part of Siberia in Capitanian age; or (ii) the Urmegtei Formation was deposited in or around a limited ice‐covered continent in northeast Siberia in the Capitanian and was displaced to the present position by the Carnian.  相似文献   

Field observations of meteotsunami locally called “abiki” in Urauchi Bay, Kami-Koshiki Island, Japan     

Toshiyuki Asano  Toru Yamashiro  Norihiro Nishimura 《Natural Hazards》2012,64(2):1685-1706

A seasonal scale field observation extending over a period of 82?days was conducted in Urauchi Bay on Kami-Koshiki Island, to record meteotsunami events, disastrous secondary oscillations locally known as ??abiki.?? The bay has an elongated T-shape topography with a narrow mouth opening westward to the East China Sea. The area has suffered the effects of meteotsunami causing flooding in residential area and damage to fishing fleets and facilities. A comprehensive observation system for sea level, ocean currents and barometric pressure was deployed to cover the regions within and offshore from Urauchi Bay and the open sea near the island of Mejima in the East China Sea. Vigorous meteotsunami events, where the total height exceeded 150?cm, were observed over five-day periods during the observation period. One or two hours prior to the arrival of meteotsunami events at Kami-Koshiki Island, abrupt 1?C2?hPa pressure changes were observed at the Mejima observation site. Pressure disturbances were found to travel eastward or northeastward. The propagation speed was found to nearly coincide with that of ocean long waves over the East China Sea, and as a result, resonant coupling should be anticipated. The incoming long waves were also amplified by geometric resonance with eigen oscillations inherent in the T-shape topography of Urauchi Bay.  相似文献   

Numerical simulation of tidally induced eddies in the Bungo Channel: A possible role for sporadic Kuroshio-water intrusion (kyucho)     

Taira Nagai  Toshiyuki Hibiya 《Journal of Oceanography》2012,68(5):797-806

It is well known that the sudden intrusion of Kuroshio warm water into the Bungo Channel (kyucho) is regulated by spring–neap tidal forcing. In order to clarify the physical background behind this regulation, numerical experiments are carried out using a high-resolution non-hydrostatic three-dimensional model. We first reproduce the strong mixing region off the east coast of the Bungo Channel resulting from tidal flow interaction with complicated land configurations during spring tides; behind islands and headlands, small-scale eddies satisfying an approximate cyclostrophic balance are generated. As a result, averaged over the whole model domain, the tidal-mean energy dissipation rate reaches ≈1.6?×?10^?6?W?kg^?1. The model predicted energy dissipation rates at the location and times of direct microstructure measurements in the Bungo Channel are comparable to the observed values. We next examine whether or not strong tidal mixing thus reproduced can inhibit the northward intrusion of Kuroshio warm water in the Bungo Channel. It is shown that the Kuroshio warm water can (or cannot) pass through the tidal mixing regions off the east coast of the Bungo Channel during periods of weakened (or enhanced) tidal mixing at neap (or spring) tides. This indicates that taking into account the realistic spring–neap modulation of tidal mixing intensity is indispensable to further increase the ability of the existing forecast system for kyucho in the Bungo Channel.  相似文献   

Sound velocity measurements in dhcp-FeH up to 70 GPa with inelastic X-ray scattering: Implications for the composition of the Earth's core     

Yuki Shibazaki  Eiji Ohtani  Hiroshi Fukui  Takeshi Sakai  Seiji Kamada  Daisuke Ishikawa  Satoshi Tsutsui  Alfred Q.R. Baron  Naoya Nishitani  Naohisa Hirao  Kenichi Takemura 《Earth and Planetary Science Letters》2012

We have determined the density evolution of the sound velocity of dhcp-FeH_x (x ≈ 1) up to 70 GPa at room temperature, by inelastic X-ray scattering and by X-ray diffraction. We find that the variation of V_P with density is different for the ferromagnetic and nonmagnetic dhcp-FeH_x, and that only nonmagnetic dhcp-FeH_x follows Birch's law. Combining our results with Birch's law for iron and assuming an ideal two-component mixing model, we obtain an upper bound of the hydrogen content in the Earth's inner core, 0.23(6) wt.% H, corresponding to FeH_0.13(3). The iron alloy with 0.23(6) wt.% H can satisfy the density, and compressional and shear sound velocities of the PREM inner core, assuming that there are no other light elements in the inner core.  相似文献   

Soil organic carbon pools in alpine to nival zones along an altitudinal gradient (4400–5300 m) on the Tibetan Plateau     

Toshiyuki Ohtsuka  Mitsuru Hirota  Xianzhou Zhang  Ayako Shimono  Yukiko Senga  Minguan Du  Seiichiro Yonemura  Shigeto Kawashima  Yanhong Tang   《Polar Science》2008,2(4):277-285

To accurately estimate soil organic carbon (SOC) storage in upper alpine to nival zones on the Tibetan Plateau, we inventoried SOC pools in 0–0.3 m profiles along an altitudinal gradient (4400–5300 m asl). We also studied vegetation properties and decomposition activity along the gradient to provide insight into the mechanisms of SOC storage. The vegetation cover and belowground root biomass showed a gradual increased with altitude, reaching a peak in the upper alpine zone at 4800–4950 m before decreasing in the nival zone at 5200–5300 m.Decomposition activity was invariant along the altitudinal gradient except in the nival zone. SOC pools at lower sites were relatively small (2.6 kg C m⁻² at 4400 m), but increased sharply with altitude, reaching a peak in the upper alpine zone (4950 m; 13.7 kg C m⁻²) before decreasing (1.0 kg C m⁻² at 5300 m) with altitude in the nival zone. SOC pool varied greatly within individual alpine meadows by a factor of five or more, as did bulk density, partly due to the effect of grazing. Inventory data for both carbon density and bulk density along altitudinal gradients in alpine ecosystems are of crucial importance in estimating global tundra SOC storage.  相似文献   

Simultaneous assimilation of surface drifter data, satellite and in situ observations for improved estimates of meso-scale variability in the Kuroshio Extension Region     

Kei Nishina  Yoichi Ishikawa  Toshiyuki Awaji 《Journal of Oceanography》2013,69(2):175-190

In order to better estimate meso-scale variabilities in the energetic Kuroshio Extension (KE) region, simultaneous assimilation of drifter-derived velocity data, together with satellite and in situ hydrographic data, is attempted by using a high-resolution 4-dimensional variational data assimilation (4D-VAR) system. Our experimental results, both with and without assimilation of drifter data (Exp. Drf and Exp. Ref, respectively) for the period during Aug–Oct 2005, show that the reproduced fields in Exp. Drf better reflect the observed meso-scale features such as the KE meandering jet and associated eddies. The adjoint sensitivity analysis indicates that our 4D-VAR system has the ability to provide a more realistic timeseries of the meandering jet structures that play a key role in the intergyre exchange between the subtropical and subarctic gyres in the North Pacific. In addition, the observed information from the surface drifters works to improve the subsurface structure. These results illustrate the advantage of our 4D-VAR simultaneous assimilation with the addition of drifter-derived surface velocity information.  相似文献   

Assessment of mixed layer models embedded in an ocean general circulation model     

Michio Watanabe  Toshiyuki Hibiya 《Journal of Oceanography》2013,69(3):329-338

The atmospheric mixed layer obtained using the Mellor–Yamada model grows slower and becomes shallower than observed, which motivated Nakanishi and Niino (J Meteorol Soc Jpn 87:895–912, 2009) to present a modified version of the Mellor–Yamada model. In this study, incorporating each of the Mellor–Yamada and the Nakanishi–Niino models into an ocean general circulation model, we evaluate its performance in the ocean. Comparing the numerical results with the observed ones in the western North Pacific, the Nakanishi–Niino model is shown to exhibit a better performance than the Mellor–Yamada model under strong wind forcing and sea surface cooling during winter and after passage of typhoons during summer.  相似文献   

青藏高原中南部岩石圈扩张应力场与羊八井地热异常形成机制   总被引：17，自引：3，他引：14       下载免费PDF全文

徐纪人  赵志新  石川有三 《地球物理学报》2005,48(4):861-869

青藏高原中南部地区有着丰富的地热资源,其中羊八井地区存在着温度高达93℃以上,热流值高达364mW/m2的地热奇观.本文利用国际以及中国地震台网资料,详细分析了青藏高原中南部地震活动性和岩石圈脆性破裂深度范围,进而讨论了高地热异常区的岩石圈应力场背景及其动力学机制.研究结果表明,青藏高原地热异常区有高于高原内部平均活动水平的震级为6级左右的中强地震活动,其震中分布呈现出与地热活动相似的、沿近南北向断陷带的带状特征;并且在高热流区域内有高原内部罕见的中深地震活动,地震震源从100km左右深处到地表呈现柱状地震群活动的空间分布等特征.震源机制与应力场研究结果表明,虽然高原中南部应力场主压、主张应力方向与青藏高原的整体特征相符,但是地震发生类型与青藏高原周缘的挤压逆断层型地震完全不同,均属于东西向扩张力作用下的正断层型地震活动,特别是在羊八井高热流区域附近,东西向扩张应力场在岩石圈应力场中起到主导性作用,推测其控制深度可达岩石圈底部100多公里处.青藏高原地热异常区在强烈的近东西向扩张应力场作用下,岩石圈东西向扩张并发生一系列的大规模正断层活动,致使深部软流圈高温热流可以沿着活动正断层及其形成的深裂隙上涌,穿过岩石圈到达地表面,形成了高地热异常区.  相似文献