Quantification de la subsidence etdu réajustement isostatique messinien àpartir de paléomarqueurs sédimentaires :exemples en Méditerranée Occidentale

Passive marginsare characterised by an important tectonic and thermal subsidence, which favours a good preservation of sedimentary sequences. This sedimentation in turn enhances the subsidencebecause of loading effects. We present here a direct method based on sedimentary markers seen on seismic data, to evaluate total subsidencerates from the coast to the outer shelf and to the deep basin in the Gulf of Lion, from the beginning of massive salt deposition up to present day (the last circa 6 Ma) with minimal theoretical assumptions. On the shelf, the Pliocene-Quaternary subsidenceshows a seaward tilt reaching a rate of 240 m/Ma ( 15 m/Ma) at the shelf break (70 km from the present day coastline) (i.e. a total angleof rotationof 0.88°(0.16°/Ma).We also quantifed for the first time the Messinian salinity crisis isostatic rebound of the outer shelf. This value is reaches up to 1.3 km of uplift during the crisis around the Herault-Sete canyon heads (around 1.8 km/Ma). On the slope, we also find a seaward tilting subsidencefrom Km 90 to Km 180 with a measured angle of 1.41°. From 180 Km to the deepest part of the basin, the total subsidenceis then almost vertical and reaches 960 m/Ma ( 40 m/Ma) during the last 5.7 Ma ( 0.25 Ma) in the deepest part of the basin. The subsidenceis organised in three compartments that seem related to the very deep structureof the margin during the opening of the Liguroprovencal basin. These very high total subsidencerates enable high sedimentation rates along the margin with sediments provided by the Rhone river flowing from the Alps, which in turn enable the detailed record of climate evolution during Pliocene-Quaternary that make of the Gulf of Lion a a unique archive. These results have been extended in 3D during Estelle Leroux PhD but also onland during Stephane Molliex postdoc and towards the Valencia basin were similar measurements are under process within Romain PellenPHD (see their respective presentations).