Microfossil assemblages from the Late Jurassic to Early Cretaceous Nikoro pelagic sediments, Tokoro Belt, Hokkaido, Japan

Abstract

The Tokoro Belt in Hokkaido constitutes one of the major ophiolitic belts in the Japanese Islands. In order to clarify the origin of the Tokoro ophiolitic rocks which are represented by the Nikoro Group, new micropaleontologic data of the Nikoro pelagic sediments are presented in this paper as regards radiolarians, calcareous nannofossils and foraminifers. The results show that 1) the age of the Nikoro Group ranges from the Kimmeridgian to the early Albian, and 2) the Nikoro pelagic rocks were deposited in a seamount environment near an oceanic ridge in the paleoequatorial productive region, where the paleodepth was about 1000 m and above the CCD. -Authors