Abstract
The Lower to early Middle Miocene Goto Group is well exposed in Nakadori-jima and Wakamatsu-jima, central part of the Goto Islands, and is divided lithologically into three formations ; Takasaki, Michidoi and Inoseto formations in ascending order. The Goto Gruop exceeds to 3600 m and represents a stratigraphic evolution beginning with thick pyroclastics deposits in lacustrine environment adjacent to volcanoes (Takasaki Formation), passing into fluvial-lacustrine environments (Michidoi Formation), and ending with deltaic environment (Inoseto Formation). The Takasaki and Michidoi formations are identified as continent marginal lake environment of southern portion of rifting of the Japan Sea. The Inoseto Formation is characterized by a dominance of northeast paleocurrent pattern and quartz-rich sandstone. This stratigraphy indicate that the Goto Group identified as the continental river-delta environments on the southern part of rifted Japan Sea. The floral assemblage found at Atotsugi in the Michidoi Formation, middle part of the Goto Group, suggests cooler climate than that of the Daijima-type flora of late Early to earliest Middle Miocene reported from the upper part of the Goto Group.
