The Ichibu area in Nishinoshima Island, a hotspot for fossils in the Oki Islands, features an outcrop of sandstone deposited on the bottom of a shallow sea 12 mln years ago. It contains numerous fossils of about 20 different species such as scallops.
Few warm-current species are confirmed in this fossil cluster. Many represent temperate climate species of the Norht-West Pacific with habitat extending as far south as western Honshu Island. Cold-current and endemic species are present as well. From that, we can infer the warm current flowing into the Sea of Japan had little influence on the environment of Oki at the time. The cluster is also very different from the shell fossil clusters on Honshu Island, as they predominantly feature warm-climate species.