| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1995: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1994: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
The nature and evolution of the Paleogene basins on land and under the sea in the eastern margin of East Asia continent were examined to elucidate their origins, tectonic settings and sedimentary sequences. Those basins are grouped into three main provinces ; the West Japan Sea (WJSP), Shelf (SP) and Forearc-Trench Provinces (FTP), among which the distribution and the sedimentological and structural features are very different with one another. The WJSP occupies the West Honshu and North Kyushu and shows a half-graven structure trending in a northwestern direction. It consists of the Middle Eocene to Early Oligocene non-marine sequence with coal and volcanogenic beds frequently in the lower, and the Upper Oligocene shallow-marine sequence in the upper, which are bounded by a ravinement surface. It might be comparable to an aulacogen prior the serious opening of the Japan Sea. The SP and the FTP are correspond to the forearc shelf and the deep forearc-trench basins, respectively. The SP
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extends widely from the Yaeyama Islands and west of Diaoyudao Ridge to West Kyushu, and the FTP is traceable from Kyushu to the south Ryukyu. The SP is made up of a non-and shallow-marine successions, and is characterized by the regional folds and normal faults that are accompanied with strike-ship faulting, structurally. The FTP is defined well as the subduction complex and is cmposed of deep-marine fan sediments at deep-marine terrace and trench. Three ravinement surfaces and two sequence boundaries were defined. Among them the ravinment surface between the Eocene and the Oligocene, and the type1 sequence boundary in the mid-Oligocene (30Ma) shows marked changes of paleodepth, that seems to be correlative to the eustatic curve (Haq et al., 1988). The analyzes of sedimentary facies, cycles and paleocurrent suggest that the growing of the subduction complexes were attributed to the development of a delta-fed fan system. The oblique-slip margin with trench erosion on the south and the orthogonal convergent margin on the north were assumed for the subduction process of the Philippine Sea Plate beneath the East Asia continent during Eocene. Less
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