Reconstruction of the lower Miocene depositional environment in Honshu, Japan

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During this academic year (2000-2001), we studied lower Miocene stratigraphy in Honshu main land form a veiw point of sequence stratigraphy and collected fossils from these strata. We also studied the Sr isotope stratigraphy using molluscan shells collected from these lower Miocene strata. The studied areas includes Echizen costal area and the Fukui City area. Fukui Prefecture. Hota-Mincoka area. Boso Peninsula. Saku-Uchiyama area of Nagano and Gumma Prefectures, Shimonita area of Gumma Prefecture, Chichibu Basin of Saitama Prefecture, Joban coal-field, Fukushima Prefecture and marumori Basin of Miyagi Prefecture. In addition, we Studied lower Miocene of the Iriomote-jima Island, Okinawa Prefecture to understand these floral changes.As a result, we have established the lower Miocene standard section in the Joban coal-field. It covered from 22 Ma to 15 Ma and included two-time warming and cooling events. In general, we obtained successful results of the Sr isotope stratigraphy using mollusean shells. In addition, we also studied lower Miocene from sedimentological view as exemplified by the lower Miocene of the Boso Peninsula using heavry-minerals such as detrital chromian spinel to understand tectonic setting during the early Miocene of the Japanese Islands.Based on these result, we would like to continue the study concerned this project in future by expanding to view from the Pacific gateways and also include Sr isopote stratigraphy of the adjacent area such as Taiwan, Korea, Sakhalin, Kamchatska and so on to clarify lower Miocene paleoenvironments for more wider global scope.