Formation and evolution of paleo-valleys linked to a subsiding canyon, North Aquitaine shelf (France)

Abstract

High resolution seismic data display four channel sets in front of the Lake of Hourton and the Lake of Lacanau covering a faulted and folded unit (U2) deposited during a high sea level at the end of the Burdigalian. The next unit (U3-1) shows sigmoid to oblique reflections (U3-1) but without apparent channels. However, during the sea level fall at the end of the Langhian, chaotic seismic facies and channels developed. The explanation should be the tectonic phase of the Aquitaine margin with an uplift of the North Aquitaine shelf. This induced the deformation of the unit U2 and provoked the creation of an alluvial plain on the North Aquitaine shelf with the formation of distributary channels (U3-2). The three following sea level falls during the Serravalian could explain the formation of the three other sets of channels (U3-3, U3-4 and U4). The last channels have a reduced mobility and correspond downstream to small paleo-canyons joining southwards the canyon of Cap Ferret. These channels disappear suddenly at the boundary at the Basin of Parentis.