Bulletin of the Mizunami Fossil Museum

Bulletin of the Mizunami Fossil Museum No. 1

The Mizunami group destributes in three mutual related basins i. e. the Kani, the Mizunami and the Iwamura basins from northwest to southeast. Sediments and fossils in these basins are similar and correlate each other. The Mizunami group belongs to the Miocene groups of the Setouchi sedimentary basin (the First Setouchi supergroup) and has close relationship with the Tsuzuki, Ayukawa and Ichishi groups. Vertical change of sedimentary environment in the First Setouchi super group represents a transgressive-regressive phase. It is recognized the existence of three units in the groups. Each units exhibits a transgressive-regressive phase also. Three units have characteristic molluscan assemblages respectively as shown in Table XVI-4. A remarkable change of them is recognized between the upper two units.

Paleoenvironment in the Mizunami sedimentary basin is synthesized in Table XVII-1. Figures XVII-2 and -3 show the palegeography of the Mizunami area and the Setouchi basin respectively.

An attempt to correlate with other Miocene groups in Japan by Ikebe and others (1973) is shown in Table XVIII-1. The Mizunami group is the Early Miocene to the Middle Miocene in age. It belongs to the zones N7 to N10 by Blow (1969).