Planktonic foraminiferal biostratigraphy of the Miocene Hatatate Formation in the southwestern part of Sendai City, Northeast Japan.

Abstract

The Hatatate Formation overlying conformably the Moniwa Formation is distributed in the southwestern part of Sendai City, Miyagi Prefecture and its foraminiferal biostratigraphy is presented. The Hatatate Formation is composed mainly of well-sorted fine-grained sandstone intercalating some fine-grained tuff, pumice tuff and scoria beds. This formation exhibits a coarsening-upward sequence, and grades upward into biotite-bearing medium-grained sandstone and coarse- to very coarse-grained sandstone which contains fragments of lapilli and pumice.Planktonic foraminifers were successively detected from the Hatatate Formation. The lowermost to lower part of the formation yields planktonic foraminifers, including Orbulina suturalis, O. universa, Globorotalia peripheroronda, and Grt. ichinosekiensis, and is assigned to the N. 10 planktonic foraminiferal zone of Blow (1969). The middle to upper part of the formation yields abundant foraminifers, including Grt. rikuchuensis, Grt. iwaiensis, and Neogloboquadrina mayeri, and is correlative with the N. 11 to N. 14 planktonic foraminiferal zones of Blow (1969), possibly not ranging up to the N. 15 Zone.