Thick Miocene sediments are distributed in the Ishikari-Teshio Belt along the western side of the Kitami mountain range in the north and the Hidaka mountain range in the south. In the Ishikari-Teshio Belt, sediments of shallow marine origen are widely overlain by turbidite facies sediments. The thickness of turbidite facies sediments attains a few thouthand meters.
Turbidite facies formed by sediment gravity flow, are divided into following 8 lithofacies; conglomerate, sandstone, pebbly sandstone, mudstone, thick bedded turbidites, thin bedded tubidites, slump and pebbly mudstone. The assemblages of the facies above mentioned differ from basin to basin, but in general comglomerate facies dominant in the northern part. The turbidite facies sediments of the Ishikari-Teshio Belt were deposited in a large north-south trough. The trough was subdivided into “Teshio Trough” and “Ishikari Trough” by “44°N. Lat.”.
The north-south trending trough system of Central Hokkaido was formed by the collision of the North American (Okhotsk) Plate and Eurasian (Amurian) Plate.
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