Sequence Stratigraphy of Alluvial Strata in the Alpine Foreland Basin, French Alps

Trevor Elliott, Neville E. Jones

The Digne-Valensole Basin is the foreland basin of the French Alps. It contains an Oligocene to late Pliocene succession the upper part of which is a 1200m thick section of alluvial deposits that represents the terminal phase of the basin-fill. Detailed investigations of the facies, palaeocurrents and provenance of these fluvial strata has revealed a series of independent river systems each with identifiable drainage basins, entry points and pathways in the basin. The ancient river systems coincide remarkably with the present-day river systems of this region suggesting that the present-day system was already established by Miocene times. The fluvial deposits can be sub-divided into 5 sequences defined by erosional unconformities or sequence boundaries that can be correlat d between the independent river systems, clearly indicating that the controls on sequence development were of regional, basin-wide scale. A distinctive feature of these sequence is that the erosional unconformities are not only recognized by an abrupt change in fluvial style but also by pronounced changes in sediment provenance. Since the hinterland on which the drainage basins were established was tectonically quiescent at the time of alluvial deposition the provenance changes are felt to reflect river capture events that were prompted by increased headward erosion during periods of relative sea level fall. This point is particularly clear in the Messinian unconformity which formed in response to the desiccation of the Mediterranean and can be correlated throughout the entire region (e. . Rhone valley and delta area, Nile delta).

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995