抄録
Diatom assemblages indicative of the lower part of the Crucidenticula kanayae Zone were found in three carbonate concretions collected from the basal part of the Miocene Kamikineusu Formation in southern central Hokkaido. In spite of the fact that the formation has been correlated with the Middle Miocene Kawabata Formation in central Hokkaido on the basis of molluscan evidence, the diatom analysis clarified that the geologic age of the basal part of the formation is 16.9 to 16.7 Ma, latest Early Miocene. The new age data of the Kamikineusu Formation provides some geochronological constraints on the geological history in southern central Hokkaido. Firstly, in the southern part of the Hidaka belt, a part of the Hidaka Supergroup became exposed by an uplift by the latest Early Miocene. Secondly, a transgression occurred in the latest Early Miocene when the sedimentary basin of the Kamikineusu Formation was formed. Thirdly, at least the basal part of the Kamikineusu Formation is correlated with the Takinoue Formation in the Yubari district.
