Relations between Anticlinal Structure and Coal Deposits near the Akabira Mine, Ishikari Province, Hokkaido

Abstract

The "Sorachi Anticline" lies between the Akabira and Mojiri coal mines, Ishikari Province, Hokkaido. The basement structure is an embryonic anticline which was formed after deposition of Cretaceous formations. A second anticline occurs in the stages of coal seams which belong to Wakkanabe and Bibai coal-bearing formations. The axis of the embroyonic anticline nearly coincides with the second anticline. Both anticlines remained through periods of coal deposition of the Ishikari Series. In two stages of coal deposition, coal seams are often interpreted as composite by interpolation of bands or partings of sandstone and shale. The partings gradually increase in thickness towards east or west from the axis, so that the subordinate seams of coal become separate from each other. The main cause of the splitting of the thick seams of the anticlinal axis into a number of progressively thinner seams away from the axis is differential subsidence that has taken place in the Sorachi Coal Field.