The Middle Pleistocene to Holocene tephrostratigraphy of the Takashima-oki core from Lake Biwa, central Japan

Thick sequences of sediments have been deposited in the Lake Biwa basin for the last 400,000 years providing useful data for Quaternary stratigraphical and paleo-environmental studies. As the Takashima-oki core taken from Lake Biwa contains a large number of key tephra beds, it is one of the types of stratigraphical cores for the Middle Pleistocene to Holocene period in the Kinki district. Previously, the tephras in this core were studied for their tephro-stratigraphical and chronological values, but the refractive indices of their heavy minerals were not measured until this study. To do this we used a temperature variation type refractometer and correlated the refractive index of volcanic glass shards with heavy minerals in each tephra. Their correlation coefficients are not so high, thus each refractive index is a useful value as an independent variable parameter for the correlation with tephra in other areas.