Study on the Stratigraphy and Sedimentation Environment in the Miike Coal Field

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The writer has studied the stratigraphy and deposition environment in the Miike coal field from the synthesized geological deta of the underground survey, drilling and physical prospecting. The Miike coal field, having crystalline schists in the north and granites in the south as its basement, is bounded by the Chikugo barrier on the southern margin, by the Minenosu barrier on the western margin and by the upheaval in the Amagi and Oma mountain blocks on the eastern margin, and is open to the south. This coal field is, by its geological structure, divided into two basins, that is, the Omuda basin in the south and the Yamato basin in the north. The Palaeogene Shiranuhi Series of the Miike coal field is composed, in ascending order, of Ginsui, Komenoyama, Tooka, Nanaura, Kattachi and Yotsuyama formations, all conformable with each other. There are 4 burried hills, named Nakajima, Saragakibiraki, Kurosakibiraki and Kurosaki in the Yamato basin ; and on the upheaval of these burried hills, the lower parts of the Palaeogene deposits are not seen. These Palaogene deposits are thin near the burried hills but are thicker in the basin among these burried hills. The Palaeogene deposits are unconformably covered by the Neogene Yame group in the north and by the diluvial deposits in the southe. Denudation of the Palaeogene deposits has been stronger in the central district than in the north and south districts ; accordingly, the upper parts of the Yotsuyama formation are not seen anywhere in the Miike cool field. The Neogene basin has the sothern margin trending NE to ENE, stretching from Saragakibiraki and Nakajima in the south of Yanagawa to Oda, Nakagawara, Kanematsu and Kurogi, the eastern margin trending NNE, stretching from Kitakawachi in the north of Kurogi to Yamada, Yoshitsune, Fujiyama and Koraguchi, and the northern margin of granites and schists. The base rocks of this basin are crystalline schists in the eastern margin and Palaeogene rocks partly in the southern margin. The writer determined the boundary of the Palaeogene formations from the cycle of sedimentation. The Ginsui formation of the Akazaki group which is terrestrial deposits, is defined by the last terrestrial deposits as lower boundary. The Komenoyama formation of the Omuda group which is marine to brackish deposits, is defined by the dark gray shale of fresh water type as lower boundary and by the last marine deposits as upper boundary. The Tooka formation of the Omuta group which is brackish deposits containing the Miike main coal seam, is defined by the grayish white sandstone, abounding in quartz and feldspar, of the brackish type as lower boundary and by the fresh water deposits laid on the Miike main coal seam as upper boundary. The Nanaura formation of the Omuta group which is marine to brackish deposits contaning the Miike upper coal seam, is defined by the Orthaulax zone as the lower boundary and by the fresh water deposits containing No.1 upper coal seam as the upper boundary. The Kattachi formation of the Manda group which is marine to fresh water deposits containing No.2 upper coal seam and showing 3 cycles of sedimentation, is defined by the Kattachi fossil zone as lower boundary and by the last brackish deposits as upper boundary. The Yotsuyamo formrtion which is marine to brackish deposits and has 4 cycles of sedimentation, is defined by the Yotsuyama fossil zone as lower boundary.
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Study on the Stratigraphy and Sedimentation Environment in the Miike Coal Field

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