2021 Volume 127 Issue 2 Pages 105-120
This paper describes the geology and chronostratigraphy of the Neogene marine sedimentary sequence in the northeastern part of the Sasamori Hills of the Dewa Mountains, Akita Prefecture, Japan. The detailed geological study included reexamination of the lithostratigraphy and establishment of a marine diatom biostratigraphy. The Neogene marine sediments in this area are composed of the Sugota, Onnagawa, Funakawa, and Tentokuji formations, from oldest to youngest. The boundary between the Onnagawa and Funakawa formations, previously considered to be conformable, is now identified as a hiatus with discontinuity from 9.6 to 9.3 Ma. Four glauconite beds have been recognized: three in the Sugota Formation, and one in the Onnagawa Formation. Integrating the diatom biostratigraphy with reported calcareous microfossil biostratigraphy provides the first reliable age estimates for these glauconite beds, which are mostly consistent with ages previously reported for glauconite beds in Japan. Extremely low sedimentation rates are confirmed for the glauconite beds.
