Sand bodies at the shelf edge in the Gulf of Lions (Western Mediterranean): Deglacial history and modern processes.

The outer continental shelf of the Gulf of Lions is covered by thick, mainly regressive, sand deposits. A combination of seismic, sedimentological and geochronological methods allows us to demonstrate that a veneer of transgressive sand bodies, few m to less than 1 m thick, reworks these deposits. They take the form of sand ridges and transverse dunes that formed at different periods. In fact, the low-gradient outer shelf of the Gulf of Lions displays a complete record of deglacial history, including not only transgressive deposits that formed during sea-level rise, but also bedforms that still evolve under episodic high-energy events that occur under more highstand conditions. Core lithology, 14C dates and regional sea-level curve suggest that the formation of the sand ridges was favoured during a period of deceleration of sea-level rise, such as during the Younger Dryas event. The dunes are part of a “mobile carpet” (here U160). The deposition of this marine sand veneer is possibly related to the interplay between different factors that trigger the turning on/off for bottom currents sand deposition/transport on the outer shelf. In fact, the sands appear to have been reworked intermittently due to high-energy conditions in shallow water depth (currents, wave regime and wind-driven circulation) as well as they form current ridges superimposed to the transgressive deposits in the westernmost part of the studied area (at the Bourcart Canyon's head).