Bulletin of the Mizunami Fossil Museum

Bulletin of the Mizunami Fossil Museum Vol. 51, No. 1

The Miocene sequence in the Hidaka observation well is lithologically divided into A and B formations in ascending order, whose boundary may be unconformable, and the latter is subdivided into B1, B2, B3 and B4 formations.

Diatom fossils and calcareous nannofossils indicate that the A formation, which is Middle Miocene in age, is correlated to the Hiki Group in the Iwadono Hills. On the other hand, the B formation, whose age is late Middle Miocene to Late Miocene, is correlated to the Tokigawa Group.

The “Kazusa Group” overlies unconformably thick Miocene sequences whose geologic ages are slightly different beneath the western part of the Kanto Plain.