Stratigraphy and Chronology of Widespread Tephra Layers during the Past 430ky in the Kinki District and the Yatsugatake Mountains

Energy dispersive Xray Spectrometry (EDS) was applied to measure the major element composition of volcanic glass shards. One hundred three analytical tephra samples were collected from the Takashima-oki drilling core sample on Lake Biwa, as well as some representative drilling core samples in the Osaka coastal area and Middle Pleistocene tephra layers at the foot of the Yatsugatake Mountains. The ages of the principal tephra layers were estimated from the correlation between the biostratigraphic horizons from the core samples and the oxygen isotope stratigraphy. The estimated ages of the Kg, K-Ah, U-Oki, AT, Aso-4, K-Tz, Aso-3, BT44, BT51, Ata-Th, Aso-1, Ng-1, Kkt and BT72 tephra layers are 3.1ka, 7.3ka, 10.7ka, 29ka, 87ka, 91ka, 133ka, 203ka, 216ka, 238ka, 249ka, 294ka, 334ka, and 349ka, respectively. These principal tephra ages provide the estimated ages of other tephra layers using the sediment accumulation rates in the Takashima-oki core. Consequently, this study has reconstructed the tephrostratigraphy and chronology during the past 430ky. Furthermore, it is pointed out that caldera forming eruptions have occurred at low sea level periods just before the maximum high sea level.