Systems tracts and depositional sequences in a carbonate setting: a study of continuous outcrops from platform to basin at the scale of seismic lines

Abstract

The application of sequence stratigraphy concepts to carbonates is feasible and this paper presents an example of its successful application. The continuity and lateral extent of outcropping sedimentary sections observed at the scale of a seismic line from platform to basin in the Southern Vercors Plateau (western Alps, France) confirm the validity of sequence stratigraphy concepts when applied to carbonate depositional systems. From the stratal patterns displayed in outcrop, we determined that carbonate lowstand systems tracts are major components in the basin, even in the deep pelagic realm. Transgressive and highstand systems tracts are very thin, a response to starvation. In contrast, on the shelf, transgressive and highstand systems tracts are the major components. Carbonate lowstand and shelf margin systems tracts pinch out in the vicinity of the offlap break. It clearly appears that the stratal patterns and stratal termination patterns of carbonate systems tracts, especially of carbonate lowstand systems tracts, are basically similar to those of siliciclastic systems tracts. This study documents that carbonate platforms may provide the basin with carbonate clastics during periods of relative sea level falls and lowstand. This is one of the most controversial aspects of the application of sequence stratigraphy concepts in carbonate environments. A second controversial aspect of the application of sequence stratigraphy concepts to carbonate rocks is the distinction between transgressive and regressive facies cycles and depositional sequences and systems tracts. This paper demonstrates that the shoreline position for carbonates (which indicates the facies transgression or regression) is independent of prograding or retrograding shelf breaks. The stratal pattern and facies within systems tracts vary depending on the overall evolution of the accommodation space, i.e. on their position within the transgressive and regressive cycles.