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

The Aquitaine shelf in France is a storm-dominated shelf similar to the Cal ifornian 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 s haped into various bed forms corresponding to the contrasted physical proce sses operating at different water depths and time-scales. These bed forms a re: a) sand patches separated by depressions or 'furrows', b) large transve rse dunes and c) large wave ripples. The overall architecture of the sand c over is considered as resulting from the stacking of several storm beds. Du ring the last post-glacial sea-level rise, the magnitude of reworking proce sses 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 consta nt and reworking mainly affected the upper 1-2 m of sediment on the inner s helf. Deeper than about 20-30 m below sea-level, present-day reworking appe ars as being limited to the upper tenths of centimeters, during major storm s. Winnowing of Pleistocene coarse-grained sediments as well as of transgre ssive sand patches provide the material for this thin upperlying highstand deposit, still in equilibrium with present processes. (C) 2000 Ifremer / CN RS / IRD / Editions scientifiques et medicales Elsevier SAS.