Significance of ammonoids and bivalves from the Cretaceous Goshoura Group in Shishi-jima Island, Kagoshima, Japan

The mid-Cretaceous Goshoura Group mainly crops out Goshoura-jima and Shishi-jima Islands, in Amakusa, western Kyushu, Japan, and is composed of fossiliferous non-marine and shallow marine deposits. At the Shichiro-zan section in Shishi-jima Island, the Late Albian and the Early Cenomanian fossil ammonoid and bivalve assemblages are recognized. The Late Albian ammonoid assemblage comprises Mortoniceras rostratum, Stolizckaia sp., Anisoceras sp. and Desmoceras sp. The Early Cenomanian assemblage is characterized by Graysonites adkinsi, Mariella oehlerti and Desmoceras kossmati. As the result, the Shichiro-zan section is correlated to the stratotype section of the lower part of Hokahira Member to the lower part of Gannohana Member, Enokuchi Formation in Goshoura-jima Island. In outer shelf deposits at Shishi-jima Island, the bivalve assemblage is dominated by autochthonous Nanonavis pseudocarinata and parautochthonous Parvamussium yubarense which has not been found in Goshoura-jima Island.