Re-examination of the lithostratigraphy of Hokusetsu Subgroup in the southeastern part of the Miocene Shidara basin, eastern Aichi Prefecture, central Japan: Proposal of the Umedaira Sandstone Member

Abstract

©The Geological Society of Japan 2021 673 Abstract: The Hokusetsu Subgroup in the eastern Shidara basin, eastern Aichi Prefecture, central Japan, is the lower part of the Miocene Shidara Group. In ascending stratigraphic order, the subgroup consists of the Kawakado, Shimoda, Tsubosawa, and Kuroze formations, which formed during a continuous transgression. Re-examination of the lithostratigraphy of the Hokusetsu Subgroup in the eastern Shidara basin has revealed a thick sandstone formation in the upper part of the Shimoda Formation, which otherwise consists mainly of mudstone. The sandstone beds, which had previously been considered part of the Kawakado Formation, clearly extend to the north where they interfinger with the mudstone of the Shimoda Formation. The existence of these newly identified sandstone beds in the Shimoda Formation, named the Umedaira Sandstone Member, suggests that the Hokusetsu Subgroup formed not only by simple transgression, but also by the influence of tectonic movements. The Umedaira Sandstone Member may be the key to clarifying Miocene tectonics in the Shidara Basin. レター