Overflow Turbidity Currents and Levee Growth on the Var Deep-Sea Fan (NW Mediterranean): Facts and Modelling

B. Savoye, P. Cochonat, M. Naaim, and D. J. W. Piper

Growth patterns in submarine fans reflect the character of turbidty currents transporting sediment to the fan. Because turbity current character is highly linked to climate, sea-level and tectonic activity, these growth patterns, and particularly patterns in levee architecture, may represent an important record of major external forcing changes. Therefore studies of levee architecture and mechanisms of turbidity current overflow are assumed to be fundamental studies toward better understanding the detailed geological archive recorded in submarine fans.

Over the last seven years, several detailed oceanographic surveys were conducted all along the present Var deep-sea fan, so that precise geological observations are now available on the whole system. The fan morphology suggests important deposition from both sandy and muddy turbidity currents. Hyperpycnal flows could significantly contribute to the Var fan sedimentation. The fan has been active through the Holocene and the nature of sedimentation is controlled rather by climate than by sea level changes.

To better understand the link between turbidity processes and the Var fan growth pattern, we investigated turbidity currents in a large water tank using a scale model of the Var fan. Various size and density of turbidity currents were reproduced, allowing to better insight processes inside the canyon and the fan valley and overflow processes over the Var Sedimentary Ridge. The most interesting results concerns the comparison with the catastrophic turbidity current that occurred in 1979 and the location of both depositional areas and preferential overflow paths.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California