Construction of the Pyreneo-Languedocian Sedimentary Ridge and associated sediment waves in the deep western Gulf of Lions (Western Mediterranean)

Migrating sediment waves have been recognized in a wide range of marine settings, including turbidite levees adjacent to submarine canyons and valleys. The Pyreneo-Languedocian Sedimentary Ridge (PLSR), located in the Gulf of Lions (North-western Mediterranean), appears similar to such a levee. In an attempt to understand the construction of both the PLSR and associated sediment waves, several scale-studies were done. The data include high and medium resolution seismic reflection profiles and cores collected both on upslope and downslope sides of two successive waves. At a regional scale, the situation of the PLSR was strongly influenced by Pliocene salt tectonics movements that resulted in a basin at the mouth of the Catalano-Languedocian canyons. Later, salt tectonics were chiefly inactive during Quaternary and waves do not result of an extensive superficial tectonic activity. At the scale of the PLSR, the construction occurred during the Quaternary and is divided in three stages recognized on the basis of waves' geometry, sediment supplies changes and spillover source variations. Common sediment wave cross-sections have been identified and suggest a turbidite or a gravity-flow origin. Sedimentological, lithostratigraphical and biostratigraphical studies focus on the last sea-level rise and high stand period. The results support the sediment-wave initiation and the occurrence of sand transfers even during the more recent period. Sand layers and high sedimentation rates characterize the deposits on upstream flanks. Lower rates of deposition correspond with downstream flanks.