Bulletin of the Mizunami Fossil Museum

Bulletin of the Mizunami Fossil Museum No. 3

Many samples were collected from Miocene Mizunami group distributed at the neighbourhood　of Shuku in Mizunami City, Gifu Prefecture, Japan. This study is on the basis of the samples. Mizunami group is composed of the Toki lignite bearing, Hongo, Akeyo and Oidawara formations in ascending order (Itoigawa, 1974). Radiolarian fossils are generally well-preserved in the Oidawara formation, but they are not seen in the other formations. The radiolarian assemblage in the Oidawara formation is characterized by Spongoplegma Variabile together with the species such as Melittosphaera magnaporulosa, M. hokurikuensis, Rhodosphaera nipponica, Sphaerostylus yatsuoensis, Ommatodiscus haeckelii, Cyrtocapsella tetrapera, C. cornuta, Stichocorys delmontensis and Eucyrtidium calvertense etc.

Judging from the present results, the Oidawara formation is correlated to Melittosphaera magnaporulosa Zone (Early Miocene–lowest Middle Miocene) of Neogene Radiolarian Zonation

in Japan which was proposed by the writers (Nakaseko and Sugano, 1972).