High resolution analysis of cooling process in northern Japan during the Middle Miocene period based on microfossils.

本文对日本北方从北海道到关东、北陆诸道的中中新世浅海沉积物进行了岩石地层学和有孔虫生物地层学研究，获得了以下结果：（1）将北海道的几个中中新世浅海沉积物划分为15 Ma以前、15- 12 Ma和12 Ma以后三类。2)Togeshita组在其早期（仅在Rumoi中部）和中期（螺纹部分）沉积于亚滨海环境，但在其他部分沉积于半深海深度。3)在北海道东南部上国地区的大安斋川组中发现了一种亚热带大型有孔虫Miogypsina。4)银山组为11.5 ~ 10.5Ma的浅海沉积。其组合显示为中温带气候。5)日本关东乌山地区小幡组的岩石组合显示了暖温带浅海的海侵序列。6)对东波地区的黑泽谷组、东别所组、天居山组和诺托半岛的七尾组、关之花组、须须组、东因内组和宝寿寺组进行了取样、沉积相分析和有孔虫分析。7)8）中新近纪气候适宜期后的降温事件具有穿时性。它始于CA。在日本北方东北省中部地区，在10 Ma以后，在北方和北海道东部地区，在12 Ma以后。

Based on the lithostratigraphy and foraminiferal biostratigraphy on the Middle Miocene shallow-marine deposits in northern Japan, from Hokkaido to Kanto and Hokuriku provinces, the following results were obtained.1) Several Miocene shallow-marine deposits in Hokkaido are discriminated into three categories of their ages deposited, before 15Ma, 15-12Ma, and after 12Ma. 2) The Togeshita Formation was deposited at sublittoral environment in its earlier (only in the central part of Rumoi) and middle stages (whorl part), but at bathyal depth in the others. 3) A subtropical larger foraminifer, Miogypsina, is found in the Ooanzaigawa Formation of Kaminokuni region, southeast Hokkaido. 4) The Ginzan Formation in Obanazawa, Northeast Province, is a shallowmarine deposits in 11.5〜10.5 Ma. Its assemblage indicates mild-temperate climate. 5) The assemblages in the Kobana Formation in Karasuyama, Kanto Province, indicate transgressive succession in warm-temperate shallow marine. 6) Sampling, sedimentary facies analysis and foraminiferal analysis are performed for the Kurosedani, Higashibessho, Tenguyama formations in Tonami region, the Nanao, Sekinohana, Suso, Higashi-innai, and Hojuji formations in Noto Peninsula. 7) A foraminiferal database system is constructed and tentatively began to use it. 8) The cooling event after the Mid-Neogene climatic optimum was diachronous. It began in ca. 12Ma at northern and eastern Hokkaido, but after 10Ma at middle part of Tohoku Province of northern Japan.