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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The Upper Cretaceous Izumi Group is narrowly distributed along the M. T. L. from the Izumi Mountain range in the Kii peninsula to the Asan Mountains in Shikoku. The Izumi Group in the study area which is situated in the western part of the Izumi Mountains, composed mainly of “classic” turbidites and re-sedimented coarse clastics. The coarse clastics which consist of pebbly sandstone, pebbly mudstone and massive sandstone are mainly exposed in a limited area along the northern margin of the Izumi Group province and are inferred to be channel-fill sediments. On the basis of the analyses of sedimentary structure and texture, it is ascertained that these coarse clastics are divided into four types, viz. normal graded sandstone (Type I), inverse to normal graded sandstone (Type I'), slurry sandstone with inverse to normal graded part (Type II) and massive sandstone (Type III). It is supposed that the normal graded part of type I and I' was deposited from high-density turbulent suspension. The inverse graded part constituting the basal part of type I' is interpreted to have been formed by dispersive pressure resulting from high concentration of grains during an early stage of deposition. The type II must have been deposited from debris flow under the condition of turbulent to laminar fashion. The type III may have been deposited from modified grain flow referred by Lowe (1982).

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