We investigated the morphological and architectural variability of four sandbanks, from the same area, at intermediate depths (from 50 to 120m) along the continental shelf of Western Brittany (France) in the Iroise Sea, a dispersive shelf exposed to large storms. In order to identify the parameters controlling the variability of sandbanks morphologies and architectures, we analyzed geophysical data (seismic, reflectivity and bathymetry) from several oceanographic cruises. Preliminary results reveal internal architectures composed of 4 to 5 seismic units for each bank. They are interpreted as controlled by the stepwise flooding of the Armorican basement shelf during the last transgression. This igneous basement that outcrops on the seafloor up to 100m deep has constrained local tidal circulation and swell exposure during the progressive flooding of the shelf, which explains the very contrasting morphologies and internal architectures of these coeval banks on the Iroise Sea shelf.