Abstract
An Early Jurassic strata recently discovered near Yamaoku, Kamiosakabe-mura, Atetsu-gun, Okayama Prefecture, in the Chugoku Mountainland (Maps 1-3) are described., The strata, composed mainly of coarse sandstone, and partly of conglomeratic sandstone and sandy shale, were named the Yamaoku formation., The formation does not show any fine cyclic sedimentation., On the basis of successive changes in lithology and some other facts, the strata are classified into three units as shown in Tables 1-2 and Maps 3-3'., Rock facies and fossil contents of the formation suggest that it was deposited rather rapidly on the metamorphosed Palaeozoic basement., Granitic and volcanic (andesitic to basaltic) detritus were received from the surrounding areas and were deposited in a littoral to brackish (paralic) zone, which was in a somewhat labile condition., Though fossils are scarce (Table 3), the Yamaoku formation may be correlated with a part of the Liassic "Kuruma group" in Nagano, Niigata, and Toyama Prefectures.,
