Takahiro Saito¹, Makoto Ito¹

(1) Chiba University, Chiba, Japan

ABSTRACT: Spatial and temporal relationships between sheet-like turbidite packets and channel-overbank systems on a sandy submarine fan: The Late Miocene-Early Pliocene Kiyosumi Formation in the Boso Peninsula, Japan

Sheet-like turbidite packets and channel-overbank systems are interpreted to be major components of a submarine fan. Spatial and temporal relationships between the two major components, however, are not yet clearly understood, in particular, for sand-dominated submarine fans in active margin basin.

Kiyosumi Formation (ca. 850 m thick) is the infill of the Late Miocene-Early Pliocene forearc basin in the Boso Peninsula of Japan and is interpreted to have developed in response to an overall fall in glacioeustatasy (oxygen isotope stages T7-T2) at about 5 Ma. The formation is characterized by thick-bedded turbidites and was interpreted to have developed in a small sandy submarine fan. The Formation was affected by folding and the outcrop belt provides an opportunity to analysis three-dimensional variations in the two major components of a sandy submarine fan, in conjunction with mapping of chronostratigraphic surfaces defined by volcanic ash beds. Three-dimensional analyses of the Kiyosumi Formation indicate that deposition of sheet-like turbidite packets was intimately associated with the lateral migration of depocenters of channel-overbank systems in response to up-fan avulsion. Deposition of a sheet-like turbidite packet is not restricted in a single interchannel low, but rather is spread out over most of the channel-overbank area. Furthermore, some sheet-like turbidite packets are largely contemporaneous with laterally adjacent channel-overbank system. The findings indicate that channel-overbank systems and sheet-like turbidite packets, those are interpreted to correspond, respectively, to slope fans and basin-floor fans of the sequence-stratigraphic model, do not necessarily characterize different parts of a relative sea-level lowstand.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado