Late Quaternary Turbidity Current Activity on the Var Deep-Sea Fan (Northwestern Mediterranean)
B. Savoye, P. Cochonat, D. J. W. Piper, and H. Nelson
Accurate observations were carried out during several detailed oceanographic surveys conducted from the source area to the distal part of the Var fan lobe. The fan has a morphology suggesting important deposition from both sandy and muddy turbidity currents. Deposition has continued during the Holocene, partly by hyperpycnal flows. Many Holocene turbidites have been observed in cores on the levees. During landfilling operations to extend Nice airport in 1979, a submarine slide affected the muddy prodelta slope, resulting in a tsunami and the cables breaks near and across the lower Var fan valley.
Deep-water SAR and SeaMARC sidescan sonar studies showed fresh gravel waves within the upper valley. Fresh erosion marks on the sea-floor were observed 6 months after the 1979 Nice failure during submersible dives in the lower Var canyon and upper Var fan valley. Backscattering changes of the sonar images along the middle fan valley point out the limit of the sand deposition. Features like sand ridges and erosional scars are observed downslope the fan valley, suggesting that turbidity currents are powerful enough to rework the sea-floor. Recent EM12D and SAR side-scan data show that the distal lobe of the Var fan is located near the northwest Corsican margin covering an area of up to 1900 square km2 at a distance of about 200 km from the head of the canyon. The lobe has a single channel with smaller distributaries, displaying a goose foot like pattern.
Changes through time in abundance and character of turbidity currents suggest that variations in the Quaternary turbidite sedimentation are controlled more by climatic variations than by sea level changes.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California