An imbrication model for the Rajang Accretionary Complex in Sarawak, Borneo     

E. Honza  J. John  R. M. Banda 《Journal of Asian Earth Sciences》2000,18(6):281

The structural framework of the Rajang Accretionary Complex is interpreted on the basis of field surveys conducted around the Lupar Fault Zone in southwestern Sarawak. Bedding dips in the Rajang Accretionary Complex are generally southward, while the complex as a whole becomes younger northward. The complex is interpreted as a series of thrust slices formed by accretion at a subduction trench. Each slice forms a unit 10 to 15 km in width. Thrust slices of this order of this order of magnitude are consistent with those formed by accretion processes at modern subduction trenches. It is suggested that accretion of Late Jurassic to Cretaceous oceanic crust occurred initially from the Pacific (eastern) side of Borneo in the Late Cretaceous, forming part of an arc system extending all along the eastern margin of Asia from Japan to Kalimantan. Subsequently, in the Early Tertiary, due to bending of the southern end of the arc system in Borneo, the direction of subduction changed, so that accretion occurred from the north.  相似文献   

Role of the ocean in controlling atmospheric CO2 concentration in the course of global glaciations     

Akira Oka  Eiichi Tajika  Ayako Abe-Ouchi  Keiko Kubota 《Climate Dynamics》2011,37(9-10):1755-1770

Responses of ocean circulation and ocean carbon cycle in the course of a global glaciation from the present Earth conditions are investigated by using a coupled climate-biogeochemical model. We investigate steady states of the climate system under colder conditions induced by a reduction of solar constant from the present condition. A globally ice-covered solution is obtained under the solar constant of 92.2% of the present value. We found that because almost all of sea water reaches the frozen point, the ocean stratification is maintained not by temperature but by salinity just before the global glaciation (at the solar constant of 92.3%). It is demonstrated that the ocean circulation is driven not by the surface cooling but by the surface freshwater forcing associated with formation and melting of sea ice. As a result, the deep ocean is ventilated exclusively by deep water formation in southern high latitudes where sea ice production takes place much more massively than northern high latitudes. We also found that atmospheric CO₂ concentration decreases through the ocean carbon cycle. This reduction is explained primarily by an increase of solubility of CO₂ due to a decrease of sea surface temperature, whereas the export production weakens by 30% just before the global glaciation. In order to investigate the conditions for the atmospheric CO₂ reduction to cause global glaciations, we also conduct a series of simulations in which the total amount of carbon in the atmosphere?Cocean system is reduced from the present condition. Under the present solar constant, the results show that the global glaciation takes place when the total carbon decreases to be 70% of the present-day value. Just before the glaciation, weathering rate becomes very small (almost 10% of the present value) and the organic carbon burial declines due to weakened biological productivity. Therefore, outgoing carbon flux from the atmosphere?Cocean system significantly decreases. This suggests the atmosphere?Cocean system has strong negative feedback loops against decline of the total carbon content. The results obtained here imply that some processes outside the atmosphere?Cocean feedback loops may be required to cause global glaciations.  相似文献   

Evidence for ocean water invasion into the Chicxulub crater at the Cretaceous/Tertiary boundary     

Kazuhisa GOTO  Ryuji TADA  Eiichi TAJIKA  Timothy J. BRALOWER  Takashi HASEGAWA  Takafumi MATSUI 《Meteoritics & planetary science》2004,39(7):1233-1247

Abstract The possibility of ocean water invasion into the Chicxulub crater following the impact at the Cretaceous/Tertiary boundary was investigated based on examination of an impactite between approximately 794.63 and 894.94 m in the Yaxcopoil‐1 (Yax‐1) core. The presence of cross lamination in the uppermost part of the impactite suggests the influence of an ocean current at least during the sedimentation of this interval. Abundant occurrence of nannofossils of late Campanian to early Maastrichtian age in the matrices of samples from the upper part of the impactite suggests that the carbonate sediments deposited on the inner rim margin and outside the crater were eroded and transported into the crater most likely by ocean water that invaded the crater after its formation. The maximum grain size of limestone lithics and vesicular melt fragments, and grain and bulk chemical compositions show a cyclic variation in the upper part of the impactite. The upward fining grain size and the absence of erosional contact at the base of each cycle suggest that the sediments were derived from resuspension of units elsewhere in the crater, most likely by high energy currents association with ocean water invasion.  相似文献   

Heterogeneity of the 1980 Izu-Hanto-Toho-Oki earthquake rupture process     

Eiichi Fukuyama  Kojiro Irikura 《Geophysical Journal International》1989,99(3):711-722

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Corundum-bearing mafic granulites in the Horoman (Japan) and Ronda (Spain) Peridotite Massifs: Possible remnants of recycled crustal materials in the mantle     

Tomoaki  Morishita  Eiichi  Takazawa  Shoji  Arai  Masaaki  Obata  Tadahiro  Kodera  Fernando  Gervilla 《Island Arc》2006,15(1):2-3

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Mechanisms of uranium mineralization by the yeast Saccharomyces cerevisiae     

Toshihiko Ohnuki  Takuo Ozaki  Fuminori Sakamoto  Eiichi Wakai  Haruyuki Iefuji 《Geochimica et cosmochimica acta》2005,69(22):5307-5316

We determined the association of uranium in yeast cells S. cerevisiae grown in medium containing high (1 g · L^-1) or low (0.2 g · L^-1) concentrations of phosphate after exposure for 96 h to a 4 × 10^-4 mol · L^-1 U(VI) solution at pH 3.2 or 4.7. The analysis was made using a field emission scanning electron microscope equipped with energy dispersive spectroscopy (FESEM-EDS), transmission electron microscopy (TEM), and visible diffuse reflectance spectrometry. Cells grown in the high-phosphate medium rapidly accumulated U(VI) from solution at pH 3.2 over the first 24 h, followed by a slow uptake until 96 h, whereas in cells grown in low-phosphate medium, U(VI) accumulation reached a steady state within 24 h. FESEM-EDS analyses revealed the formation of a U(VI)-bearing precipitate on the yeast cells grown in high-phosphate medium after only 48 h exposure; no precipitate was detected on cells grown in low-phosphate medium up to 96 h. These results suggest that sorption onto the cell surfaces was the dominant process initially. Analysis of the U(VI)-bearing precipitates by all three methods demonstrated the presence of H-autunite, HUO₂PO₄ · 4H₂O. Thermodynamic calculations suggest that the chemical compositions of the solutions containing yeast grown in high-phosphate medium were undersaturated with respect to H-autunite, but were supersaturated with ten times more U(VI) and P than were actually observed. Apparently, the sorbed U(VI) on the cell surfaces reacts with P released from the yeast to form H-autunite by local saturation. The U(VI) uptake by yeast cells grown in high phosphate medium at pH 4.7, along with the thermodynamic calculation, indicated that more H-autunite is precipitated in neutral pH solution than in acid solution. Thus, U(VI)-phosphate mineralization on the cells of microorganisms should be taken into account for predicting U(VI) mobility in the environment.  相似文献   

The 16°40′ S triple junction in the North Fiji Basin (SW Pacific)     

Y. Lafoy  J. M. Auzende  E. Ruellan  P. Huchon  E. Honza 《Marine Geophysical Researches》1990,12(4):285-296

During the last three years, the North Fiji Basin (SW Pacific) has been intensively studied on three oceanographic cruises carried out by French, American and Japanese ships. One of the main goals of these cruises was to study by means of precise SeaBeam, SEAMARC II, seismic and magnetic surveys, the active spreading system and its associated hydrothermal processes. The North Fiji basin, bounded by the major Pacific and Indo-Australian plates, shows a complex polyphased tectonic evolution. One of the last phases of this evolution is the functioning since 3 Ma of a NS spreading center in the axial part of the basin. The tectonic instability of the area resulted in a permanent rearrangement of the ridge axis. Among others, the 16°40′ S triple junction is one of the major manifestations of such an instability. Sinistral strike-slip motion 1 Ma ago, along the North Fiji Fracture Zone induced the change in direction of two segments of the axis from NS to N15 and N160. The first segment is characterized by a typical spreading ridge similar to various parts of the EPR, while the second shows an atypical ‘en echelon’ fan-shape opening. The N15 and N160 ridges converging with the North Fiji Fracture Zone constitute the 16°40′ S Ridge-Ridge-Fracture Zone triple junction. The detailed morphologic and kinematic study of this junction allows us to understand one of the mechanisms of the deformation in the North Fiji basin.  相似文献   

The New Britain trench and 149° embayment,Western Solomon Sea     

D. L. Tiffin  H. L. Davies  E. Honza  J. Lock  Y. Okuda 《Geo-Marine Letters》1987,7(3):135-142

The western New Britain Trench contains relatively thin sediment fill in the east, compared to the west where a sequence of thick turbidites is ponded behind a basement high in the trench axis, The trench trends toward Huon Gulf, but intersects the Trobriand Trench at an acute angle at the 149° Embayment, where both trenches end. Seismic structure west of the trench is incoherent, related to incipient collision of the Indian-Australia Plate and the South Bismarck Plate. The collision suture is marked by the Markham Canyon, continuous in its upper reaches with the Ramu-Markham Fault Zone on shore.  相似文献   

Neogene geological history of the Tohoku Island Arc system     

Eiichi Honza  Hideo Kagami  Noriyuki Nasu 《Journal of Oceanography》1977,33(6):297-310

The Pacific-type orogeny in the Tohoku Island Arc is discussed using marine geological and geophysical data from both Pacific and Japan Sea along the Tohoku region. The Tohoku Arc is divided into three belts; inner volcanic and sedimentary belt, intermediate uplifted belt and outer sedimentary trench belt. Thick Neogene sediments which are distinguished in several layers by continuous seismic reflection profiling occur on both sides of the intermediate belt. The dominant structural trend of the Neogene layers is approximately parallel to the coast line and to the axis of the Japan Trench and has a extension of approximately 100 km in each unit on the Pacific side. The trench slope break is an uplifted zone of Neogene layers. The structural trend of the upper continental slope and outer shelf is relative uplift of the landward side. Tilted block movement toward the west is the dominant structural trend on the Japan Sea side. Structural trends which can be seen in both the inner and outer belts may suggest horizontal compressional stress of east to west. Orogenesis and tectogenesis in the Tohoku Arc has been active since early Miocene or latest Oligocene. It may be implied that the Japan Trench was not present during Late Cretaceous to Paleogene, as is suggested by the volcanism of the Tohoku Arc. The basic framework of the present structure was formed during late Miocene to early Pliocene in both the inner and outer belts. Structural movements were reactivated during late Pleistocene.  相似文献   

Carbon cycle and climate change during the Cretaceous inferred from a biogeochemical carbon cycle model   总被引：3，自引：0，他引：3  

Eiichi Tajika 《Island Arc》1999,8(2):293-303

The carbon cycle and climate change during the Cretaceous are reconstructed by using a carbon cycle model, and discussed. The model takes into account the effects of the enhanced magma eruption and organic carbon burial rates, both of which characterize the carbon cycle during the Cretaceous. The result for the CO₂ variation is roughly consistent with the pattern of paleoclimate change inferred from the geological record. The CO₂ level during the mid-Cretaceous is estimated to be 4–5 times the present atmospheric level, corresponding to a surface temperature of 20–21°C. The warm, equable Cretaceous resulted from the effects of tectonic forcing such as enhanced CO₂ degassing, although the enhanced organic carbon burial has a tendency to decrease the CO₂ level. The organic carbon burial rate during the Cretaceous is generally larger than those for the Cenozoic, and is characterized by three major peaks (~ 1.5–1.8 times the present-day value) corresponding to the major oceanic anoxic events. In the case for the extensive mantle plume degassing, although the CO₂ levels are only 10% higher than those for the standard case during 120–100 Ma, the causes for the enhanced CO₂ levels would be quite different. If the globally averaged surface temperature had increased due to paleogeographic forcing effects, the greenhouse effect of CO₂ (and thus the CO₂ level) should be lower than the values estimated for the standard case. If the CO₂ levels are similar to, but the surface temperature is higher than, those for the standard case, either the parameter β (an influence of the Himalayas–Tibetan Plateau on the global weathering today) may be unreasonably large or the dependence of the silicate weathering rate on the CO₂ partial pressure and the surface temperature should be much weaker than those previously proposed.  相似文献