Abstract
The Tokai Group occupies the eastern part of the distribution of the Middle Miocene to Middle Pleistocene Second Setouchi Supergroup. The group around Tajimi City is composed of fluvial sediments, and indicates Middle Miocene to Late Pliocene in age. The group around Tajimi City is divided into the Tokiguchi Porcelain Clay Formation and Toki Sand and Gravel Formation with conformable relationship. The former is dominant of sand and mud, and ranges generally between 10 and 30m thickness, while the latter comprises mainly gravel, and its thickness is more than 40m. Lithologically, the Toki Sand and Gravel Formation is composed of two types of gravels; one dominates in chert clasts, and the other dominates in acid volcanic rocks derived from the Nohi Rhyolites. Chert clasts dominate type distributed in the central to northern parts of the study area, and volcanic rock dominate type covers the central to southern parts, approximately. The sedimentary basin around Tajimi City is fault-bounded, and is made up of small basement blocks less than 20 km^2 in area. The formation of small blocks is ascribed to the brittleness around the terrane boundary between the Ryoke and Mino Belts. The characteristics of fault-bounded basin around Tajimi City are common to other basins of the Second Setouchi Supergroup. The basin around Tajimi City, however, never suggests the acceleration of subsiding from 2.5Ma, which is common to other basins of the supergroup, and indicates very low rate of sedimentation.
