Stratral architectures of late Quaternary regressive–transgressive cycles in the Roussillon Shelf (SW Gulf of Lions, France)

Abstract

A seismic and sequence stratigraphy scheme of the southwestern area of the Gulf of Lions Shelf (NW Mediterranean Basin) is presented, through the analysis of high-resolution seismic profiles obtained with a Minisparker system and calibrated with published seismic and core data of the adjacent Languedoc area. The observed stratigraphic architecture records the repetition of four regressive–transgressive cycles, which constitute high-frequency depositional sequences (DSs). Regressive intervals dominate the generation of shelf sedimentary architecture. Within regressive intervals, the identification of progressively shallower clinoforms, from proximal to distal in a downdip direction, constitutes a strong indicator of the occurrence of forced regressions. This stratigraphic pattern documents the preservation of potential sand-prone reservoirs encased within widespread regressive wedges and directly connected with organic matter rich muds, as distally there is no sharp basal contact between the two. The unusual preservation of pre-Last Glacial Maximum transgressive deposits is attributed to the combined influence of previous shelf topography and dominant wave regime. The most significant transgressions were recorded by shallow-water deposits in distal, middle and proximal locations. Distal and proximal deposits develop over relatively steep surfaces, which caused slower transgressions and favoured the generation of wave-dominated coastal deposits. In contrast, middle deposits show moderate development over a smooth shelf profile as a consequence of rapid shoreline translation. The analysis of spatial changes of regressive–transgressive cycles provided important information about the nature of shelf processes and about the relative significance of regressive versus transgressive intervals within each individual DS, whose development was led by recent, high-frequency sea-level cycles. Dominance of 120 ka cycles would imply that transgressive deposits represent a partial record of glacial–interglacial transgressions. Dominance of 20 ka cycles is not favoured by the fact that the preservation of Quaternary deposits is apparently limited on the shelf.