Late Campanian radiolarians obtained from the Ryujin Formation in the Hidakagawa Group, Northern Shimanto Belt, Kii Peninsula, Japan

Abstract

The Ryujin Formation, occupying a wide area in the Cretacesous Hidakagawa Group of Shimanto Belt in the Kii Peninsula, Southwest Japan, has been considered to be an accretionary complex of late Campanian in age. Radiolarian fossils of the age evidence have been found from only the western part of the Hidakagawa Group. In this article, we report radiolarian fossils of the Amphipyndax tylotus interval zone newly found from the central part of the Hidakagawa Group. Therefore the geologic age of the Ryujin Formation was firmly established to be a late Campanian.