EVERTS, ARNOUT J. W., JAN STAFLEU, and WOLFGANG SCHLAGER, Vrije Universiteit, Institute for Earth Sciences, Amsterdam, Netherlands

ABSTRACT: Sequences and Stratal Patterns of the Vercors Carbonate Platform (Lower Cretaceous, SE France) in Outcrop and Seismic Model

Large-scale stratal geometries of a Lower Cretaceous carbonate platform

can be studied in outcrop in the Southern Vercors (SE France). We focussed on the Barremian interval, where the Vercors platform displays an overall climbing progradation geometry. Progradation was intermittent: phases of rapid progradation alternated with phases of toe-of-slope retreat during which the clinoforms were covered by basinal sediments. However, clinoforms and basinal sediments show gradational boundaries and complex interfingering patterns rather than discrete onlap or downlap surfaces. Furthermore, petrographical analysis indicates gradual changes in sediment composition. Therefore we interpret the rhythms of progradation and retreat of the Vercors platform as gradual and symmetric shifts of the facies belts. Most of these shifts occurred when the platform was flooded, s nce both the prograding and retreating units can be traced for several kilometers across the platform top.

In order to evaluate these outcrop geometries in terms of seismic stratigraphy we produced two-dimensional seismic models. In particular at relative low frequencies (e.g. 25 Hz), the interfingering relationships between clinoforms and basinal sediments usually show up as lapout patterns (downlap and onlap in case of prograding and retreating clinoforms respectively) on the seismic lines. Only at frequencies of 75 Hz or higher the gradual and symmetrical character of the facies shifts emerges.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.