Calcareous Microfossil Biostratigraphy of the Uppermost Cenozoic Formations Distributed in the Coast of the Japan Sea

Part 1: Niigata Area

Abstract

Eleven calcareous nannofossil biohorizons are recognized in the Quaternary sequences at six sites drilled in the Northeast Atlantic Ocean during DSDP-IPOD Leg 94. Correlation of those biohorizons with the magnetostratigraphy is established, and ages of all datums are estimated by interpolation between magnetic reversals (TAKAYAMA and SATO, 1986). The calcareous nannofossil and the foraminiferal assemblages of the Nishiyama and the Haizume formations distributed in the Oginojo area, near the type locality of the Haizume Formation, Niigata district are described, and five calcareous nannofossil biohorizons are recognized. Based on the above mentioned results of DSDP-IPOD Leg 94, the middle Nishiyama through the Haizume formations are Pleistocene in age and can be correlated with the interval between the Olduvai and the Jaramillo events of the magnetostratigraphy. This age assignment agrees neither with the magnetostratigraphic interpretations (YOSHIKOSHI, 1983) nor with the fission track datings (MURAMATSU, 1983), which were undertaken in the Oguni area 25 kilometers south of the present area.