| Abstract |
The Sasebo coal field is divided into two areas, the east and the west, by the Sasagawa thrust fault which runs northeast by north. It has long been well known that the qualities of coal of the Sasebo... group in the west are quite different from those in the east. Although there have been many opinions to explain this difference, nothing has been done of clarifying the relation between the grade of coalification and the causes of coalification in quantitative way. Since Hoi'l"D.A (1960) found analytically that in Japanese coal the volatile matter is not always available for showing the rank of coalification, the author used carbon content (d. a. f.) for the index of coalification in this paper. In regard to this coal field, carbon content of each coal seam such as the Ose-goshaku, Matsuura-sanjaku, Fukuiichimai and Sammai-mono increases gradually from the east to the west respectively (figs. 8-13). Having studied the relation between the index of coalification and the causes of the promotion of coalification, the author came to the conclusion that the difference of coalification is mainly due to the difference of overlying sediments which are greater in thickness in the west than in the east. Such geological evidences as radial faults, dome structure, and rapid increasing of carbon contents in the east and north sides of the dome suggest the existence of deep-seated igneous mass in the southwestern part of this coal field. Consequently, the thermal effect of this expected igneous body and also the effect of the tectogenetic movements, including the lateral pressure resulting from the compression of the Sasagawa thrust fault, might have accelerated the difference of the grade of coalification between the both areas. Therefore, the fact that has not been able to explain only by the thickness of the overlying sediments is easily interpreted by these two effects. Further, the difference of coalification, which is shown by the lateral change in thickness of each formations, is presumed to be made step by step during the deposition of the Nojima group and the Hirado formation and during the tectogenetic movement, and also during the accompanying local differential erosion. And it is inferred that the most remarkable displacement of the Sasagawa fault occurred after the grade of coalification became distinct to a considerable extent between the east and the west.show more
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