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"Le Canyon du Var": Case Study of a Modern Active Proximal Channel

Bruno Savoye, Michael Voisset, Pierre Cochonat, Gerard A. Auffret, Jean-Francois Bourillet, Laurence Droz, Previous HitGillesTop Ollier, Alain Coutelle, Chantal Le Cann, Jean-Marie Auzende, Robert Serge

The Var Canyon and the continental slope along the French Riviera were investigated using SAR, a new deeply towed high-resolution side-scan sonar and 3.5-kHz subbottom profiler package. Later on, a ground-truth operation using the CYANA submersible and Kullenberg cores provided in-situ observations and samples.

The main characteristics of this area are the narrow shelf, the steep continental slope, and very coarse superficial materials. During the Pliocene, an alluvial cone was built on the floor of a deep ria located at the present Var alluvial plain. This detritic cone overlies the Messinian erosion surface. It is totally submarine and formed by pudding stones, conglomerates, and marls. Since the early Quaternary, this large sedimentary body has been dismantled by gravity processes (mass wasting, debris flows, turbidites).

The bed form at the head of the Var Valley (500 m depth) is marked by an anastomosed network eroding the spurs that give the typical herringbone facies of the canyon's flanks. Downslope from this area begins a gravel wave field extending to a water depth of 2,100 m. Wavelength and height appear to be directly controlled by the topography. Downward and according to a break in the slope, the sea floor is characterized by a rhythmic alternance of gravel fields and mud fields (to 2,400 m). The muddy areas are always located on relatively high points of the sea bottom. The significance of these bed forms will be discussed and related to the sedimentary processes which may have operated in this area.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.