Patterns and processes of sediment dispersal on the continental slope off Nice, SE France

The distribution of surficial sediments and sediment dispersion patterns on the steep continental slope off Nice (SE France) have been studied using s ide-scan sonar, 3.5 kHz profiles, short piston cores add bottom photographs . The input of terrigenous material to the Bale des Anges, a submarine emba yment bounded by two prominent ridges, is dominated by fluvial input from t he Var River, the Paillon River being only a minor source. The Var River pr ovides very coarse bedload material (gravel and cobble) directly to the hea d of the Var Canyon. Gravel and cobble deposits are found all along the Var Canyon and the Upper Fan Valley of the Var submarine fan and have been sha ped into gravel waves. The fine particles (suspension load) are separated f rom the coarse bedload upon entering the sea and form up to 60-m thick depo sits on the uppermost continental slope of the Bale des Anges. These deposi ts are formed by settling out of sediment plumes. The presence of silt and fine sand laminae that decrease in thickness and frequency away from the Va r River mouth indicate the influence of meso- and hyperpycnal flows on thes e plume deposits. Areas outside the Bale des Anges are not connected to maj or fluvial input and receive only hemipelagic sediments. These primary depo sits are highly unstable and sediment failure due to seismic loading, sedim entary loading or undercutting is frequent. Sediment failure produces secon dary sediment gravity flows that export most of the material to the basin, but also produce turbidity-current over-spill deposits on ridges bounding t he slope canyons and on terraces within the Var Canyon. Slump and debris-fl ow deposits are also observed. At least some of these secondary flows erode the continental slope as cross-cutting chutes on the upper continental slo pe and erosional scours in the Upper-Fan Valley demonstrate. Modern sedimen t dispersal patterns on the continental slope off Nice are proposed as a mo dern analogue to lowstand conditions on continental margins. In fact, the a bsence of a continental shelf together with a steep slope strongly reduces the influence of sealevel on the physiography of the margin. (C) 2000 Elsev ier Science B.V. All rights reserved.