Abstract
Both the "Ishikari-Kitakami Belt" and "Tomakomai Ridge" are traced from the Kitakami province in northeastern Honshu to the Rebun island off northwestern Hokkaido passing through the Ishikari depression. The former consists of early Cretaceous porphyrites and andesitic volcanic rocks. The basement complex penetrated by Shintotsugawa-1", "Sorachi (MITI)" and "Namporo (MITI)" wells, belongs to the "Ishikari-Kitakami Belt". Both of these tectonic belts correspond to the front of the Northeast Japan Arc, and formed western marginal uplift zone in a geosyncline during the Cretaceous and Palaeogene.
From the Umaoi hill to the Yufutsu offshore area (from north to south), in a narrow belt thick volcanic rocks of the Takinoue stage (early Miocene) unconformably covers the Palaeogene sediments pinching out westward.
Though during which are roughly grouped the Kawabata age (middle Miocene), many isolated subbasins grew in two large basins, which were separated by an uplift zone running through the Rebun island-Kabato-Namporo-Tomakomai into the Tempoku-Hidaka basin in the east and the Ishikari basin in the west. The Hidaka orogenesis influenced only on the development of the Tempoku-Hidaka basin and the uplift zone were not affected any more by the orogenesis.
