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ABSTRACT: Petroleum Geology of the Akita-Niigata Basin: the Most Important Petroliferous Basin in Japan

Tomoaki Sumii, Yoshio Watanabe, Kisaburo Kodama

The Akita-Niigata basin, in the back-arc region of the northeastern Japan arc, is the most important petroliferous basin in Japan. In this basin, the most important two plays are a lower to middle Miocene volcanic rock play (green tuff play) and a Miocene to Pliocene turbidite play. In the case of the lower-middle Miocene volcanic rock play, the reservoir is porous volcanic/volcaniclastic rocks in a rift-volcanism stage of early to middle Miocene age, preceding the rapid opening of the Japan Sea. The source rock is marine mudstone deposited in the middle Miocene. The trap is a kind of permeability trap; the migration of hydrocarbon is lateral or downward. The horst-like shape of volcanic complex reservoirs was initiated by the tensional block faulting during the rifting a d opening of the Japan Sea. The reservoir of the Miocene-Pliocene turbidite play is middle Miocene-Pliocene turbidite sandstone deposited over the subsiding basin floor, and the source rock of this play is hemipelagic mudstone of middle-upper Miocene age. The trap is a steeply angled anticline closure constructed in the Pliocene-Pleistocene under the compressive tectonic setting. The tectonic setting of northeastern Japan had changed drastically from tensional to compressive. After this tectonic event, the compressive folding and faulting produced many anticlinal trap structures for this play. The source rock in the syncline reached the oil/gas window and produced hydrocarbon, then the oil/gas migrated to the reservoirs of these two plays.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990