Reconstruction of the lower Miocene depositional environment in Honshu, Japan

本学年（2000-2001）从层序地层学的角度研究了本州大陆下中新世地层学，并收集了这些地层的化石。我们还利用这些中新世下地层收集的软体动物壳研究了Sr同位素地层学。研究区域包括越前沿海地区和福井市地区。福井县。Hota-Mincoka区域。Boso半岛。长野县和Gumma县的Saku-Uchiyama地区，Gumma县的下田地区，埼玉县的Chichibu盆地，Joban煤田，福岛县和宫城县的丸森盆地。此外，我们还研究了冲绳县伊里omote-jima岛中新世晚期，以了解这些植物的变化。建立了佐班煤田中新世下标准剖面。它从22 Ma到15 Ma，包括两次变暖和变冷事件。总的来说，我们利用软体动物壳获得了成功的Sr同位素地层学结果。此外，我们还从沉积学角度研究了下中新世，以渤索半岛下中新世为例，利用碎屑铬尖晶石等重矿物来了解日本列岛早中新世的构造环境。在此基础上，我们希望今后将研究范围扩大到太平洋门户，并纳入邻近地区如台湾、韩国、库页岛、堪察加等地的Sr等地层，以在更广泛的全球范围内阐明下中新世古环境。

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.