日本海側に発達する最上部新生界の石灰質微化石層序 ＩＩ 北陸堆積盆地

Abstract

On the basis of calcareous nannofossil assemblages in samples recovered at six sites in the North Atlantic Ocean during DSDP-IPOD Leg 94, eleven calcareous nannofossil biohorizons are recognized in the Quaternary sequences deposited at middle and high latitudes. Correlation of these biohorizons with the magnetostratigraphy is established, and ages of all datums are estimated by interpolations between magnetic reversals (CLEMENT and ROBINSON, 1987; TAKAYAMA and SATO, 1987). The calcareous nannofossil and the foraminiferal assemblages of the Yabuta and the Junicho formations in Toyama Prefecture and the Omma formation at its type locality in Kanazawa City are described in detail. Based on the above mentioned results of DSDP-IPOD Leg 94, the Yabuta, the Junicho and the Omma formations are late Pliocene, Plio-Pleistocene and Pleistocene in age, respectively.In 1984, small mammalian fossil bone of Stegodon aurorae (elephant) was found from the upper Omma formation. This level of S. aurorae is probably referred to the stratigraphic interval between the calcareous nannofossil biohorizon (5) (0.83Ma) and the Brunhes/Matuyama boundary of the magnetostratigraphy (0.73Ma).The Omma formation overlies unconformably the Saikawa formation. In contrast to the Omma formation, the Saikawa formation contains middle to lower Miocene calcareous nannofossils. The upper Miocene and the Pliocene sediments are, therefore, completely missing between these two formations.