Sedimentary processes and facies on the northern Aquitaine shelf, France.

The Aquitaine shelf in France is a storm-dominated shelf similar to the Californian shelf in the US. It exhibits a thin veneer (about 1-2 m) of sandy sediments overlying coarse-grained deposits. This surficial sand sheet is shaped into various bed forms corresponding to the contrasted physical processes operating at different water depths and time-scales. These bed forms are: a) sand patches separated by depressions or 'furrows', b) large transverse dunes and c) large wave ripples. The overall architecture of the sand cover is considered as resulting from the stacking of several storm beds. During the last post-glacial sea-level rise, the magnitude of reworking processes progressively decreased as a result of increasing water depth. This is demonstrated by the overall upward thinning and fining of elementary storm beds. Since ca. 4000 years BP, sea-level has remained approximately constant and reworking mainly affected the upper 1-2 m of sediment on the inner shelf. Deeper than about 20-30 m below sea-level, present-day reworking appears as being limited to the upper tenths of centimeters, during major storms. Winnowing of Pleistocene coarse-grained sediments as well as of transgressive sand patches provide the material for this thin upperlying highstand deposit, still in equilibrium with present processes.