Sedimentary Facies Distribution of the Upper Cenozoic Fourth- Order Depositional Sequences and Basin-fill Process of the Niigata Back-Arc Sedimentary Basin, Central Japan

Hiroyuki Arato and Koichi Hoyanagi

The Niigata back-arc basin, compartmentarized and characterized by steep slope, large sediment influx related to active island-arc and extremely large depositional rate higher than 200 cm/1,000 year, had been formed at stroke with close relationship to Japan Sea opening in the Middle Miocene age. A large part of this basin has been filled with a thick 2nd-order tectono- sequence by present. Deposition of 3rd-order depositional sequences comprising 2nd-order tectono-sequence is interpreted to correspond with filling-up of subbasins. A lower 3rd-order depositional sequence distributes rather proximal part of the Niigata basin, and an upper one occupies distal part. Stacking pattern of the 3rd-order depositional sequences, therefore, demonstrates a large scale progradational configuration.Their component 4th-order depositional sequences, ranging several tens through hundreds meter in thickness, are suitably recognized on a set of seismic profiles. Those 4th-order depositional sequences consist of depositional systems like fan-delta, fluvial, delta, shelf, slope and basin floor on the basis of assemblages of the observed sedimentary facies and facies associations in many exploratory wells. Sedimentary facies distributions, as a conclusion, are interpreted to reflect faithfully 4th-order relative sea-level cycles in sedimentary basins in the active margin area like the Niigata back-arc sedimentary basin. 3rd-order sequences, composed of those 4th-order sequences, fill subbasins progressively from proximal one to distal. In addition, process of basin evolution ould correspond to 2nd-order tectonic event in the active margin basins.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California