Coniacian–Santonian stratigraphy in Japan: a review

The Coniacian–Santonian stratigraphy of Japan is briefly reviewed. The Coniacian is subdivided into three zones by inoceramids and ammonoids, respectively, and the Santonian consists of a single inoceramid zone, subdivided into two ammonoid zones. The boundary marker species of the Coniacian/Santonian, i.e., Inoceramus (Platyceramus) undulatoplicatus, proposed by the Subcommission on Cretaceous Stratigraphy, is still undiscovered in Japan. It is only possible to indicate the approximate location of the boundary between the two stages. Further research on macrofossils, microfossils and, additionally, carbon isotope stratigraphy are required in order to determine the precise location of Coniacian/Santonian boundary in Japan.