ABSTRACT: Locations and Characteristics of Thin-Bedded Turbidites in Passive-Margin-Setting Submarine Fans

BOUMA, ARNOLD H., School of Geoscience, Louisiana State University, Baton Rouge, LA

Thin beds form an important part of submarine fan deposits. The beds can be found in five different subenvironments: top of a channel fill, channel margin, levee-overbank area, sandwiched between thick layers in the updip nonchannelized depositional lobes, and fan fringe. At present, we are not able to distinguish clearly one depositional subenvironment from the other using thin beds as a criterion.

In the passive margin or Atlantic margin setting of the Gulf of Mexico, and in a number of areas in the Atlantic Ocean, massive sands belonging to a submarine fan can be wet while thin-bedded sandstones may be oil prone. Such a condition makes it important to be able to determine the depositional setting needed to provide information about reservoir geometry, connectivity between successive sandstone layers, porosity/permeability trends, and orientation of the reservoir sands.

Depending on the layer thickness of the thin-bedded turbidites and the sand/shale ratios, recognizing the sandstones on conventional well logs may be difficult. A good seismic survey, however, may permit indication or detection of a channel cross section from which inferences can be drawn as to where thin-bedded sections can be expected. Initial studies on outcrops have shed some light on characteristics of the levee-overbank and channel-top-fill thin-bedded series. Using existing depositional models, circular reasoning commonly is involved in identifying each depositional environment.

AAPG Search and Discovery Article #91014©1992 AAPG GCAGS and GC-SEPM Meeting, Jackson, Mississippi, October 21-23, 1992 (2009)