Geophysical and geomorphological investigations of a Quaternary karstic paleolake and its underground marine connection in Cassis (Bestouan, Cassis, SE France)

•Geophysical methods are used to describe the morphology of a coastal polje.•Connection between the polje and a submarine spring through a karst is proposed.•The chronological evolution of this karstic system is detailed.

An original karstic system in a coastal alluvial plain located in a carbonate environment (Cassis, Provence - SE France) was studied using a multi-method approach (electrical resistivity tomography, gravimetric, passive seismic survey), combined with geomorphologic methods, surface observations and drilling. Limestone dissolution and/or cavity collapse led to the development of a polje, which was filled rapidly by erosion of Aptian marls. The combination of several dating and paleoenvironmental proxies indicates that the polje was filled during a glacial period (MIS 6, 8 or 10, i.e. in the 130-360 ka age range). This discovery has implications for the understanding of karst processes. The connection between the polje and the three km-long Bestouan underwater karstic conduit with submarine outlet is strongly suggested by sedimentological studies and geophysical prospections.