Depositional Conditions of the Basal Part of the Noborikawa Beds near Akabira Coal Mine. Ishikari Province, Hokkaido.

Abstract

The basal clay of the Noborikawa coal-bearing formation of the Ishikari Series was a thin residual soil on a peneplain developed on the surface of upper Cretaceous formation. It was lateritic and is thought to have formed under semi-arid climatic conditions. Subsequently, when the stage of land depression and rainy condition came, it became residue insitu. In this stage, forests became dense in the area of the margin, or inside, of the shallow wide lake which formed the original basin in which the Ishikari Series was deposited. The lateritic soil was later buried by coal deposits and metamorphosed to kaolinite. The clay bed may be contemporaneous to the Akasaki Beds, the basal Palaeogene formations in northern Kyushu.