Eocene Banda and Kushinoyama basalts from southern Okayama district, southwest Japan

Abstract

The recently discovered middle Eocene Banda (41.2±1.0 Ma) and Kushinoyama (46.1±1.1 Ma) basalts occur in the southern Okayama district, near the Seto Inland Sea, Chugoku region, southwest Japan. Middle Eocene to Oligocene igneous rocks were known only from a narrow belt along the Japan Sea in the Chugoku region; thus, this discovery shows that Paleogene igneous activity also occurred in the southern parts of the region.

The Banda Basalt unconformably overlies the sandstones and conglomerates of the Kitagata Formation, placing the deposition of the formation in the middle Eocene or earlier.