Problems of Late Pleistocene History of Central Japan

Along the coasts of Japan characteristic coastal terraces that were probably formed during the marine transgressions of the Riss-Würm Interglacial are recognized. This interglacial transgression in Japan has been named the “Shimosueyoshi Transgression.” It is very difficult to determine the chronologic situation of Pleistocene events without definitive evidence. Pleistocene volcanic ash, usually called “loam” in Japan, is very useful as an indicator horizon for the correlation of the geologic events of the Pleistocene. An especially good indicator horizon of regional extent is the pumice bed Pm-I of the Shinshu loam, which originated from the eruption of the Ontake volcano in the vicinity of the Japanese Alps. Recently this pumice bed Pm-I has been found in the middle of the Shimosueyoshi loam beds (tephra beds) in South Kanto. Tephrochronologic study by means of Pleistocene volcanic ash indicates that the formation of fluvial terraces has occurred independently of climatic changes.