Microfossil assemblages associated with argonaut fossils from the Middle Miocene Fujina Formation, Shimane Prefecture, Southwest Japan

Abstract

Specimens of the fossil argonaut Mizuhobaris izumoensis Yokoyama, a recognized indicator of the influence of the Paleo-Tsushima Warm Current, were obtained continuously through the lower part of the Middle Miocene Fujina Formation near Shinji High School, 30 km west of central Matsue City, Southwest Japan. Ostracode and planktonic foraminiferal assemblages from this site were studied to clarify the depositional environment. A total of 20 ostracode species and 12 planktonic foraminiferal species were obtained. Neither of these assemblages contained tropical species but both contained temperate species. The common presence of M. izumoensis suggests that its occurrence sites may not necessarily reflect the influence of the Paleo-Tsushima Warm Current.