2006 Volume 45 Issue 1 Pages 29-39
Conglomeratic beds, whose depositional age is unknown, are distributed around the Terabayashi area at the foot of Mt. Ibuki. These beds are described as the Terabayashi Formation. This formation is divided into four parts : the Lowermost, Lower, Middle, and Upper parts, based on detailed discrimination of lithofacies. The Lowermost part rests on an irregular surface of the basement rock and is composed of varved mud, organic mud, and matrix-supported massive gravels. The Lower and Upper parts are dominated by matrix-supported massive gravel beds, which are deposited as debris-flows. The Middle part consists of lenticular sand beds intercalated in clast-supported massive gravel beds that were deposited as longitudinal bars or lag deposits within channels.
Three volcanic ash beds named the Terabayashi I, II, and III volcanic ash beds in the Lowermost part are described based on their lithofacies, petrographic properties, and chemical composition of volcanic glasses. The Terabayashi I and II volcanic ash beds are correlated with BT60 and BT59 volcanic ash beds in the Takashima-oki core, respectively, based on their characteristic properties. The Takashima-oki core, which was bored at Lake Biwa, represents the typical tephrostratigraphy and tephroclonology of the Kinki district. These correlations of volcanic ash beds show that the depositional age of the conglomeratic beds is around the boundary between oxygen isotope stage 8 and stage 7.
