Multi-approach quantification of denudation rates in the Gulf of Lion source-to-sink system (SE France)
Résumé
During the Pliocene and the Quaternary, the Gulf of Lion, the northern passive margin of the Liguro-Provençal basin in the western Mediterranean Sea, received sediments from a 120 000 km2 drainage area constituted by several structural domains. The denudation of mountainous areas, source of this sedimentary supply, results from complex interactions between tectonics, climate, morphology, and rock erodibility. In this study, denudation rates from the present-day and ranging back to the Quaternary and the Pliocene are quantified using four independent methods allowing an investigation over different time scales: 1) compilation of present-day measured sediment fluxes, 2) determination of catchment-scale cosmogenic denudation rates through measurements of in situ-produced 10Be concentrations in sands sampled at the outlet of present-day rivers, 3) estimation of eroded volumes within catchments using a DEM to quantify long-term averaged Quaternary denudation rates, and 4) quantification of sediment volumes deposited within the marine realm of the Gulf of Lion. The results obtained by these four methods are in agreement within the range of uncertainties. The internal part of the Alps exhibits significantly higher denudation rates (∼700 mm ka-1) than those estimated in the other structural domains: 150-250 mm ka-1 in the foreland Alps, ∼100 mm ka-1 in the Pyrenees, and 55-75 mm ka-1 in the Massif Central. The Alpine domain provides at least 80% of the total eroded volume supplied towards the Gulf of Lion. A quantitative geomorphological approach shows that denudation rates are controlled at the first order by catchment morphologies (slope, relief) over different time scales, suggesting glacial conditioning to be the main driver on denudation from the Quaternary to present-day. Throughout the Pliocene-Quaternary, a doubling of denudation rates related to the mid-Pleistocene Revolution (∼0.9 Ma) is highlighted.