Miocene calcareous nannofossil and diatom biostratigraphies of the eastern Hokkaido and offshore Yufutsu, Japan

Calcareous nannofossil shows sporadic occurrence from the Miocene formations in Hokkaido, possibly due to its nature province mainly in the pelagic ocean in a low latitude. Despite the rare occurrence, it is significant data to assign the fossil zones and designate the accurate geologic age for the deeper formations under the ground where the index fossil diatoms for the Miocene are dissolved by the diagenesis for the silica mineral phase transition. This report indicates the useful calcareous nannofossil biostratigraphy of the Miocene distributing deeper portion of subsurface in eastern to southern Hokkaido.