Geohistory - Rocks from Continental to Sea Periods
The Ichibu area in Nishinoshima Island, one of the representative fossil locations in the Oki Islands, features an outcrop of sandstone that accumulated on the bottom of a shallow sea around 12 million years ago. It contains numerous shell 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 Northwest Pacific with their habitat extending only as far south as western Honshu. Cold-current and endemic species are present as well. From this, we can infer that the warm current flowing into the Sea of Japan had little influence on the environment of Oki at that time. The cluster is also very different from the shell fossil clusters on Honshu, as they mainly feature warm-climate species.
