SMALL SUBMARINE FANS ON THE EASTERN MARGIN OF CORSICA - SEDIMENTARY SIGNIFICANCE AND TECTONIC IMPLICATIONS

The small turbidite systems and their network of distributary channels lying on the base of slope and basin off the eastern margin of Corsica exhibit physiographic and acoustic characteristics similar to those encountered in typical deep-sea fans. In most cases, the fans appear to be connected to sinuous canyons that incise into the shelf break and display varying shapes along the continental slope. They begin as large highly meandering erosional troughs. Then they become progressively depositional and bordered by lateral prominent levees and show evidence of branching. In their most distal part the height of levees decrease and lobes appear unchannelled. Seismically, the lobes are characterized in their middle and lower parts by superposition of channel-levee units, showing high amplitude reflectors with poor penetration in channels, and bedded facies with better penetration on levees. Only the most distal domains located beyond the channelized areas of the lobes are formed entirely by high amplitude reflectors with poor penetration that are interpreted as coarse deposits of sand or silt. The majority of these sand-rich fans, and especially those located in the northern sector of the margin, are related to the insular drainage system of Corsica. The sand-rich fans located in the southern sector may have been structuraly controlled. By the lack of any obvious actual connexion with insular drainage, they suggest earlier association with high continental relief, subsequently removed by erosion or tectonic collapse. The southernmost canyon of this area (Caprera canyon) records structural trends of the Sardinian crystalline basement, and is also probably related to tectonic movements linked with the opening of the Tyrrhenian Sea.