Middle Jurassic radiolarians from carbonate manganese nodules in the Otori Formation in the eastern part of the Kuzumaki-Kamaishi Subbelt, the North Kitakami Belt, Northeast Japan

Abstract

A Bajocian to Early Bathonian (Middle Jurassic; Striatojaponocapsa plicarum Zone) radiolarian fauna was recovered from carbonate manganese nodules in siliceous mudstone of the Otori Formation in the North Kitakami Belt (Kuzumaki-Kamaishi Subbelt), Northeast Japan. The Otori Formation mainly consists of white to grey chert, and is marked by Permian red chert and Bajocian to lower Bathonian siliceous mudstone, although their original stratigraphic relationships have not been understood. This formation is tectono-stratigraphically correlatable to the Ryokamiyama Chert Unit of the Ohirayama Unit in the Southern Chichibu Belt in the Kanto Mountains.