PIPER, DAVID, Atlantic Geoscience Centre, Dartmouth, Nova Scotia, Canada, and BRUNO SAVOYE,* IFREMER, Plouzane, France

ABSTRACT: Processes of Late Quaternary Turbidity Current Flow and Deposition on the Var Deep Sea Fan, Northwest Mediterranean Sea

Late Quaternary sedimentation patterns on the Var deep-sea fan are known from high-resolution seismic boomer profiles (vertical resolution < 1 m), piston cores, SAR side-scan sonargraphs, and submersible dives. Foram biostratigraphy and radiocarbon dating provide chronologic control that is seismically correlated across the fan. Regional erosional events correspond to the isotopic stage 2 and 6 glacial maxima.

A widespread surface sand layer was deposited from the 1979 turbidity current, which broke two submarine cables. Numerical modeling constrains its character. A small slide on the upper prodelta developed into an accelerating turbidity current, which eroded sand from the Var canyon. The current was 30 m thick in the upper valley, expanding downflow to >120 m, where it spilled over the eastern Var sedimentary ridge at a velocity of 2.5 ms-1. Other Holocene turbidity currents (with a 103-yr recurrence interval) were muddier and thicker, but also deposited sand on middle fan-valley levees and are inferred to have had a similar slide-related origin.

Late Pleistocene turbidity currents deposited on the high Var sedimentary ridge. The presence of sediment waves and the cross-flow slope inferred from levee asymmetry indicate that some flows were hundreds of meters thick, with velocities of 0.35 ms-1. Estimated times for deposition of thick levee mud beds are many days to weeks. Late Pleistocene flows therefore are interpreted to result from hyperpycnal flow of glacial outwash in the Var River. Variation in late Pleistocene-Holocene turbidite sedimentation thus is controlled more by changes in sediment supply than by sea level.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.