Studies on the Oil Geology of the Ishikari Coal-Fields, Hokkaido, Japan (1)

IWAMOTO H., YOSHIDA Y., KOMURA S., SAKAMOTO T.

doi:10.3720/japt.35.258

In the present paper the writers discuss the stratigraphy, tectonics, geophysics, and geochemistry of the Cretaceous of the Ishikari coal fields.<br>The area discussed here in is situated in the central part of Hokkaido. The Cretaceous consists of the Sorachi, Lower Ezo, Middle Ezo, Upper Ezo, and Hakobuchi groups in descending order, ranging Neocomian to Maestrichtian. They are overlain unconformably by the older Paleogene Ishikari group including coal measures and younger Paleogene marine Poronai group.<br>In the northern area predominate pararell folds, of which the Sorachi anticline is the largest, with a general trend of N-S direction. In the southern area, on the contrary, a number of isoclinal or overturned foldings with the same general trend are developed by the more intense tectonic disturbance. Most of these folded structures, are well coinsident to high gravity anomalies.<br>The Cretaceous may be promising for future oil production because of its occupying wide areal distribution and large amount of sediments accompanied with many oil seepages, although the sediments contain smaller content of residual hydrocarbons compared with those of the oil producing areas of Niigata prefecture.<br>The MITT Sorachi, the first test boring well exploring the whole sequences of the Cretaceous and starting in June, 1970, will reveal the more detailed oil-geologic features of the area.

Studies on the Oil Geology of the Ishikari Coal-Fields, Hokkaido, Japan (1)

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