Abstract
A sedimentary complex of the Takatori Formation (Ashio Belt) in the central Yamizo Mountains is divided into six units bounded by basal thrust faults. Each unit recognized as a chert-clastic sequence consists of siliceous claystone, bedded chert, siliceous shale, laminated shale, and alternating beds of sandstone and shale in ascending order. These chert-clastic sequences constitute thrust sheets forming a westward-inclined imbricate structure. Based on conodont and radiolarian assemblages, we estimated that the geologic age of these chert-clastic sequences is from the Early Triassic Spathian to the Late Jurassic Tithonian. The age of accretion is presumed to be from Kimmeridgian to Tithonian of the Late Jurassic. This is later than the age of accretion of the Ashio Belt in the Kuzuu area, to the west of the Yamizo Mountains.
