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| Abstract |
It is one of the major problems for the Japanese coal geologists to elucidate the geologic conditions of formation and coalification of the Japanese Tertiary coal that has characteristic nature of hig...h volatite matter and high hydrogen contents than the foreign Paleozoic coal. The Paleogene Ishikari coalfield in the Hokkaido island is selected as an objective area to investigate coalification problem of this characteristic domestic coal. Vitrinite reflectance was measured to indicate degree of coalification both on samples from numerous horizons of different districts in the coalfield and on cutting samples from oil exploring deep drill holes that penetrate the same geologic horizons at the northern extension of the coalfield for comparison. Regional and stratigraphic coalification pattern in the coalfield are delineated and examined by referring to the sedimentational and structural data of the coalfield and the present depth-reflectance gradient of the drill hole samples, which reach to a conclusion that the coalification pattern had been drawn during the later stage of the Hidaka orogenic movement implicating a synorogenic coalification process though the initial pattern was partly deformed by the successive tectonic movement of the latest stage. The characteristic nature of the coal and the coalification pattern would be endowed by the successive geologic events of thick sedimentation that occured in the continually subsiding basin with intermitent and progressive migration and also by simultaneous and successive tectonic movement that took place within a limited geologic time interval and a paleogeothermal condition of low geothermal gradient.show more
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