Ostracode biostratigraphy of the Lower Cretaceous Wakino Subgroup in northern Kyushu, Japan

Abstract

Nonmarine ostracodes from the Lower Cretaceous Wakino Subgroup in northern Kyushu were studied biostratigraphically. Analysis of abundant fossil ostracodes has led to recognition of 11 assemblages and subassemblages. Vertical changes of these assemblages have made possible biostratigraphical zonation by ostracodes as follows : the Darwinula a. z. (assemblage zone), the transitional a. z. and the large Cypridacean a. z. in ascending order. Using this zonation, the formations of the Wakino Subgroup in the eastern area are correlated with those in the western type area.