飯山市西方大川層中の関屋テフラ層(SK)と新潟地域および掛川層群のテフラ層との対比

概要

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The Sekiya Tephra Bed (SK) is intercalated in the Plio-Pleistocene Ogawa Formation in the western liyama City, Nagano Prefecture. It is about 10m in total thickness and can be divided into three units. In this paper, it is correlated to the Chw-2 Tephra Bed in the Nishiyama Formation in the Niigata region and also to the Iwaname III〜V Tephra Beds in the Kakegawa Group of the Pacific Ocean side. The age of the Sekiya Tephra Bed was inferred to be around 2.2Ma. On the basis of the Sekiya and T4 (SK110) (around 1.63Ma) Tephra Beds, the Ogawa Formation (about 1600m in thickness) was suspected to be 2.5-1.0Ma in age and 88cm/1000yr in the sedimentary rate. This sedimentary basin along the western side of the Chikuma river was inverted to the rapid uplift and tectonic regime after around 1Ma to the present.
新潟大学の論文