TESSON, M., Laboratoire de Geochimie et Sedimentologie Marine, Universite de Perpignan, Perpignan, France, and G. P. ALLEN, TOTAL Centre Scientifique et Technique, St. Remy les Chevreuse, France
ABSTRACT: Reservoir Stratal Geometry within a Pleistocene Shelf-Edge Lowstand Complex
A grid of 3000 km of high resolution seismic profiles on the Rhone continental shelf (SE France) indicates the existence of a regional sediment wedge which extends from the mid-shelf to the continental slope. This wedge is interpreted as a lowstand complex accumulated during the latest Pleistocene glacial period. It attains a thickness of 150 m. at the shelf break, onlaps landward onto a regional unconformity, and forms an overall regressive system which has resulted in the progradation of the slope by more than 15 km.
The wedge is composed of several seaward prograding mud and sand units which represent successive episodes of shoreface progradation. These units attain a thickness of 20-80 m. at the shelf break and can be correlated regionally. Each is bounded by an upper transgressive ravinement surface, a lower downlap surface, and onlaps updip onto a regional unconformity within the wedge. Each unit constitutes a separate reservoir related to a coastal progradation of several tens of km. During progradation, each unit was affected by episodic small-scale relative sea level falls, which resulted in unconformities and reservoir discontinuities within the prograding clinoforms.
Seaward tilting of the shelf occurred between each regressive unit, thereby creating accommodation for the succeeding unit. The interaction between high frequency glacio-eustatic cycles and the isostatic shelf tilting resulted in a complex pattern of coastal onlaps. The landward onlap termination of the individual units forms both landward and seaward stepping patterns. Each unit, therefore constitutes either a parasequence or a type 2 depositional sequence, depending on the location of the hinge line and the amplitude of sea level change.
AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.