ABSTRACT: Outcrop Expression at Seismic Scale of Systems Tracts During Transgressive and Regressive Periods in a Carbonate Setting

T. Jacquin, C. Ravenne, P. R. Vail

One of the major features of Barremian-Aptian sedimentation in the southern Vercors Mountains, France (northern sub-Alpine mountain chain), is the conformity of the Barremian paleotopography with the present topography. The extremity of the southern Vercors plateau corresponds to the shelf-slope transition: the shelf facies are present on the plateau, the slope facies on the southern slopes, and the basin facies is present south of the plateau. The other main feature of the Vercors is the thickness and lateral extent of the outcropping sedimentary section, comparable with the scale of seismic sections. Thus, the outcrop sequence stratigraphy interpretations can be made at seismic scales.

From the early Barremian to the early Aptian, six depositional sequences are present in the northern sub-Alpine mountain chain. The so-called Urgonian limestones (inner shelf facies) are limited to the highstand systems tracts of the three last depositional sequences. During the period of these highstands, the basin was starved. The lowstand periods are characterized by deposition of huge bioclastic progradational sequences. The tops of the lowstand system tracts are the maximum progradation of bioclastic facies into the basin for each sequence. The maximum progradation occurred near the early Barremian/late Barremian boundary. After this time the margin changed from overall progradation to overall retrogradation. This change from progradation to retrogradation is interpreted to be re ated to an acceleration in the rate of tectonic subsidence close to the early Barremian/late Barremian boundary.

Field examples document at seismic scales the changes in systems tract thicknesses and variations in stratal patterns and lithofacies within systems tracts during the transgressive and regressive phases of the major transgressive/regressive facies cycles.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990