2017 Volume 123 Issue 9 Pages 747-764
The Cretaceous non-marine Sasayama Group of Hyogo Prefecture, Japan, has been newly subdivided into the Ohyamashimo and Sawada formations, in ascending order, and this group is described based on the International Stratigraphic Guide. The lower and upper members or formations have been used as informal stratigraphic units. The group can be divided into four lithofacies assemblages reflecting deposition in a gravel bar, sand bar, flood-plain, and crevasse splay/natural levee. The assemblages assigned to the Sasayama Group are interpreted as follows: (1) the group was deposited in an inter-montane basin, as river channel deposits occur in the basin margin, and flood-plain deposits dominate the central area; (2) gravelly river channel environments were common in the early stages of deposition, and these were succeeded by meandering river environments that produced prominent flood-plain and natural levee deposits; and (3) the detection of the clay mineral kaolin by X-ray diffractometry indicates that the reddish-colored soil deposits of the upper Ohyamashimo Formation formed under a semi-arid to semi-humid climate.
