http://www.sciencedirect.com/science/article/pii/S1674987114000917     

Miyuki Tahata  Yusuke Sawaki  Yuichiro Ueno  Manabu Nishizawa  Naohiro Yoshida  Toshikazu Ebisuzaki  Tsuyoshi Komiya  Shigenori Maruyama 《地学前缘(英文版)》2015,6(1):121-136

Important ecological changes of the Earth(oxidization of the atmosphere and the ocean) increase in nutrient supply due to the break-up of the super continent(Rodinia) and the appearance of multi-cellular organisms(macroscopic algae and metazoan) took place in the Ediacaran period,priming the Cambrian explosion.The strong perturbations in carbon cycles in the ocean are recorded as excursions in carbonate and organic carbon isotope ratio(δ~(13)C_(carb) and δ~(13)C_(org)) from the Ediacaran through early Cambrian periods.The Ediacaran-early Cambrian sediment records of δ~(13)C_(carb) and δ~(13)C_(org),obtained from the drill-core samples in Three Gorges in South China,are compared with the results of numerical simulation of a simple one-zone model of the carbon cycle of the ocean,which has two reservoirs(i.e.,dissolved organic carbon(DOC) and dissolved inorganic carbon(DIC).The fluxes from the reservoirs are assumed to be proportional to the mass of the carbon reservoirs.We constructed a model,referred to here as the Best Fit Model(BFM),which reproduce δ~(13)C_(carb) and δ~(13)C_(org) records in the Ediacaran-early Cambrian period noted above.BFM reveals that the Shuram excursion is related to three major changes in the carbon cycle or the global ecological system of the Earth:(1) an increase in the coefficient of remineralization by a factor of ca.100,possibly corresponding to a change in the dominant metabolism from anaerobic respiration to aerobic respiration,(2) an increase of carbon fractionation index from 25‰ to 33‰,possibly corresponding to the change in the primary producer from rock-living cyanobacteria to free-living macro algae,and(3) an increase in the coefficient of the organic carbon burial by a factor of ca.100,possibly corresponding to the onset of a biological pump driven by the flourishing metazoan and zooplankton.The former two changes took place at the start of the Shuram excursion,while the third occurred at the end of the Shuram excursion.The other two excursions are explained by the tentative decrease in primary production due to cold periods,which correspond to the Gaskiers(ca.580 Ma) and Bikonor(ca.542 Ma) glaciations.  相似文献   

Swelling–shrinkage properties and soil improvement of compacted expansive soil, Ning-Liang Highway, China     

Yanjun Du  Shenglin Li  Shigenori Hayashi 《Engineering Geology》1999,53(3-4):351-358

In this paper, the swelling–shrinkage properties of the compacted expansive soil in the Huaiyin Section of the Ning-Lian Highway are introduced, and swelling–shrinkage mechanisms are discussed based on changes in soil water content, dry density, material composition and fabric. The improvement of the compacted expansive soil by lime is also discussed briefly. It is concluded that careful attention should be paid to this type of compacted expansive soil.  相似文献   

http://dx.doi.org/10.1016/j.gsf.2016.11.007   总被引：1，自引：1，他引：0  

Tatsuyuki Arai  Shigenori Maruyama 《地学前缘(英文版)》2017,8(2):299-308

Lunar anorthosite is a major rock of the lunar highlands,which formed as a result of plagioclasefloatation in the lunar magma ocean(LMO).Constraints on the sufficient conditions that resulted in the formation of a thick pure anorthosite(mode of plagioclase 95 vol.%) is a key to reveal the early magmatic evolution of the terrestrial planets.To form the pure lunar anorthosite,plagioclase should have separated from the magma ocean with low crystal fraction.Crystal networks of plagioclase and mafic minerals develop when the crystal fraction in the magma(φ) is higher than ca.40-60 vol.%,which inhibit the formation of pure anorthosite.In contrast,when φ is small,the magma ocean is highly turbulent,and plagioclase is likely to become entrained in the turbulent magma rather than separated from the melt.To determine the necessary conditions in which anorthosite forms from the LMO,this study adopted the energy criterion formulated by Solomatov.The composition of melt,temperature,and pressure when plagioclase crystallizes are constrained by using MELTS/pMELTS to calculate the density and viscosity of the melt.When plagioclase starts to crystallize,the Mg~# of melt becomes 0.59 at 1291 C.The density of the melt is smaller than that of plagioclase for P 2.1 kbar(ca.50 km deep),and the critical diameter of plagioclase to separate from the melt becomes larger than the typical crystal diameter of plagioclase(1.8-3 cm).This suggests that plagioclase is likely entrained in the LMO just after the plagioclase starts to crystallize.When the Mg~# of melt becomes 0.54 at 1263 C,the density of melt becomes larger than that of plagioclase even for 0 kbar.When the Mg~# of melt decreases down to 0.46 at 1218 C,the critical diameter of plagioclase to separate from the melt becomes 1.5-2.5 cm,which is nearly equal to the typical plagioclase of the lunar anorthosite.This suggests that plagioclase could separate from the melt.One of the differences between the Earth and the Moon is the presence of water.If the terrestrial magma ocean was saturated with H_2O,plagioclase could not crystallize,and anorthosite could not form.  相似文献   

http://dx.doi.org/10.1016/j.gsf.2016.09.005   总被引：1，自引：1，他引：0  

Toshikazu Ebisuzaki  Shigenori Maruyama 《地学前缘(英文版)》2017,8(2):275-298

We propose the nuclear geyser model to elucidate an optimal site to bear the first life.Our model overcomes the difficulties that previously proposed models have encountered.Nuclear geyser is a geyser driven by a natural nuclear reactor,which was likely common in the Hadean Earth,because of a much higher abundance of ~(235)U as nuclear fuel.The nuclear geyser supplies the following:(1)high-density ionizing radiation to promote chemical chain reactions that even tar can be used for intermediate material to restart chemical reactions,(2)a system to maintain the circulation of material and energy,which includes cyclic environmental conditions(warm/cool,dry/wet,etc.)to enable to produce complex organic compounds,(3)a lower temperature than 100℃ as not to break down macromolecular organic compounds,(4)a locally reductive environment depending on rock types exposed along the geyser wall,and(5)a container to confine and accumulate volatile chemicals.These five factors are the necessary conditions that the birth place of life must satisfy.Only the nuclear geyser can meet all five,in contrast to the previously proposed birth sites,such as tidal flat,submarine hydrothermal vent,and outer space.The nuclear reactor and associated geyser,which maintain the circulations of material and energy with its surrounding environment,are regarded as the nuclear geyser system that enables numerous kinds of chemical reactions to synthesize complex organic compounds,and where the most primitive metabolism could be generated.  相似文献   

Occurrence of phosphatic microfossils in an Ediacaran–Cambrian mid-oceanic paleo-atoll limestone of southern Siberia   总被引：1，自引：1，他引：0  

Yuko Uchio  Yukio Isozaki  Michael M. Buslov  Shigenori Maruyama 《Gondwana Research》2008,14(1-2):183

New phosphatic microfossils were recently discovered in an Ediacaran–Cambrian mid-oceanic paleo-atoll limestone in the southern Gorny Altai Mountains in southern Siberia. Microfossils with calcium phosphate shells are abundant in the limestone that occurs as an exotic block within a Cambrian accretionary complex in the Kurai area. SEM observations confirm that the calcium phosphatic shells are ellipsoidal and equal-sized, about 200–300 μm in diameter. Shell walls are about 1 μm thick. As the absence of external and internal structures hinders a detailed comparison/identification, these microfossils are tentatively treated here as paleontological problematica. EPMA-analysis confirmed the concentration of elements P and Ca in microfossil shells and the absence in the matrix, suggesting the primary phosphatic composition of the shells. Because phosphatic microfossils are generally scarce in the Ediacaran but abundant from the Lower Cambrian, in particular within pre-trilobitic SSF assemblages, the phosphatic fossil-bearing limestone in the Kurai area possibly belongs to the Lower Cambrian. The present find proves that mid-oceanic paleo-seamounts as well as continental shelf domains had already been inhabited by diverse metazoans in the Ediacaran–Cambrian transitional interval.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987115000870     

Hisatoshi Sato  Miyuki Tahata  Yusuke Sawaki  Shigenori Maruyama  Naohiro Yoshida  Degan Shu  Jian Han  Yong Li  Tsuyoshi Komiya 《地学前缘(英文版)》2016,7(4):663-671

Cap Carbonates overlie the Marinoan Snowball Earth-related glacial diamictite,and possibly record the drastic surface environmental change and biological evolution after the Snowball Earth.We conducted on-land drilling from the Liantuo Formation,through the Nantuo,to the lower Doushantuo Formation in the Three Gorges area of South China to collect fresh,continuous samples in the Three Gorges area.We obtained high-resolution chemostratigraphies of δ~(13)C and δ~(18)O values of carbonates from the topmost part of the Nantuo Formation to the Cap Carbonate,in order to decode the detailed surface environmental change in the shallow marine setting.The δ~(13)C chemostratigraphy possesses some unique characteristics:(1) stable δ~(13)C values as a whole,but ubiquitous low δ~(13)C anomalies through the Cap Carbonate,(2) increase of the δ~(13)C values from-3 to +5‰ across the C2/C3 boundary,(3) no δ~(13)C anomaly between the C1 and C2 boundary,and(4) presence of an anomalous high δ~(13)C value(+2.3‰)and a faint positive correlation between δ~(13)C and δ~(18)O values in the C1 unit.Evidence of quite low δ~(13)C anomalies(with a nadir of-41‰),ubiquitous negative δ~(13)C anomalies through the Cap Carbonate,and a high δ~(13)C anomaly accompanied with a faint positive correlation between δ~(13)C and δ~(18)O values in the C1 unit supports decomposition and formation of methane hydrate during Cap Carbonate formation.The drastic increase of δ~(13)C values from the upper C2 to C3 units indicates enhancement of primary productivity and organic carbon burial,possibly due to high continental fluxes after the Snowball Earth event,evidenced by high Sr isotope values.The increase is restricted to the proximal side of the inner shelf in South China,and the timing of the increase of δ~(13)C values of carbonates is earlier at Three Gorges area than any other area,suggesting that the enhancement of primary productivity started in the proximal environment because of higher continental influxes.The increase in oxygen contents of seawater due to the enhanced primary productivity possibly resulted in the emergence of multicellular animals soon after Cap Carbonate deposition.  相似文献   

Highly alkaline,high-temperature hydrothermal fluids in the early Archean ocean     

Takazo Shibuya  Tsuyoshi Komiya  Kentaro Nakamura  Ken Takai  Shigenori Maruyama 《Precambrian Research》2010

Based on the petrology of hydrothermally altered Archean basaltic greenstones, thermodynamic calculations of phase equilibria were conducted to estimate the composition of a high-temperature (∼350 °C) hydrothermal fluid in an Archean subseafloor basalt-hosted hydrothermal system. The results indicate that the hydrothermal fluid was highly alkaline attributed to the presence of calcite in the alteration minerals under a high-CO₂ condition, and predict a generation of SiO₂-rich, Fe-poor hydrothermal fluids in the Archean subseafloor hydrothermal system. The chemically reactive mixing zones between alkaline hydrothermal fluids and slightly acidic-neutral seawater are characterized by inverse pH and chemical polarity to modern hydrothermal systems, leading to extensive precipitation of silica and iron oxyhydroxides on/under the seafloor. Such processes can be responsible for the abiotic formation of voluminous chert and subseafloor silica dike, the mechanism of silicification, and the pH-controlled generation of banded iron formation that has been arising mainly from the redox chemistry in the Archean ocean. Such high-temperature alkaline fluids could have had a significant role not only in the early ocean geochemical processes but also in the early evolution of life.  相似文献   

柴达木盆地北缘早古生代高压——超高压变质带中发现典型超高压矿物——柯石英   总被引：75，自引：11，他引：75       下载免费PDF全文

杨经绥  Shigenori  Maruyama 《地质学报》2001,75(2):175-179

从都兰北带榴辉岩的片麻岩围岩的锆石中发现了柯石英包裹体和石墨包裹体，说明该超高压带的峰期变质作用已达柯石英稳定区间（＞2.8GPa）但小于金刚石的稳定区间（＜3.5GPa），从而确定柴达木盆地北缘存在早古生代超高压变质作用和陆－陆碰撞作用，为中国中部存在一条横贯东西的早古生代（大致500－400Ma）高压超高压变质带的推断提供了新的关键性证据。  相似文献   

Experimental study of migration of potassium ion through a two-layer soil system     

Yan Jun Du  Shigenori Hayashi  Song Yu Liu 《Environmental Geology》2005,48(8):1096-1106

A barrier system based on the hydraulic trap design concept for a landfill was proposed. To study the field scenario in which a clay liner is underlain by a granular layer functioning as a secondary leachate drain layer, a laboratory advection–diffusion test was performed to investigate factors controlling the transport of contaminants in a two-layer soil system. The soils used for this study were Ariake clay and, the underlying layer, Shirasu soil from the Kyushu region of Japan. Potassium (K⁺) was selected as the target chemical species with an initial concentration of 905 mg L⁻¹. The effective diffusion coefficients (D _e) of K⁺ for Ariake clay and Shirasu soil were back-calculated using an available computer program, Pollute V 6.3. Values of D _e derived from this experiment are consistent with previously published ones. The Ariake clay has lower D _e than the Shirasu soil. The hypothesis that mechanical dispersion can be considered negligible is reasonable based on both the observation that the predicted values well fit the experimental data and the analyses of two dimensionless parameters. Parametric analyses show that transport of K⁺ through soils is controlled by advection–diffusion rather than diffusion only, whereas at low Darcy velocity (i.e., ≤10⁻⁹ m s⁻¹), transport of K⁺ will be controlled by diffusion. Applications of the test results and parametric analysis results in practical situations were reviewed.  相似文献   

Orogeny of the Japanese Islands     

Yukio Isozaki  Shigenori Maruyama  Gaku Kimura 《Island Arc》1997,6(1):1-1

  相似文献