Abstract
The Sagara Fauna has been regarded as the Middle Miocene to Early Pliocene warm-water molluscan faunal unit in Southwest Japan. Descriptive works, however, have not been enough to discuss the faunal succession in the type section of the Sagara Fauna. This paper reports a molluscan assemblage from shell-concentrated beds in the lower part of the Sagara Group, Shizuoka Prefecture, giving systematic descriptions of the representative species. This assemblage is composed of molluscs transported from shelf depths, such as Phos, Olivella, Megacardita, and Glycymeris. The shell beds are placed in Zone N14 of Blow's planktonic foraminiferal zonal scheme in which the late Middle Miocene global warming condition has been recognized as the Climatic Optimum 2. The warming evidence in Japan is the appearance of tropical to subtropical molluscs from the Kukinaga Group in Tanegashima Island. The molluscan assemblage reported here represents a warm temperate molluscan fauna in the paleo-Kuroshio realm. Moreover, it is noteworthy that the last appearance of the Early to Middle Miocene relict elements and the first appearance of some living species are recognized in this assemblage. This supports a division of the so-called Sagara Fauna into the middle to late Middle Miocene Kukinaga Fauna and the Late Miocene to Early Pliocene Zushi Fauna. We define the Sagara Faunule for the fossil assemblage from the lower part of the Sagara Group, which lived in the warm-temperate region in Southwest Japan during the Climatic Optimum 2.
