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Miocene rhodano-provençal architecture basin (Alps, SE France): deformation, physiography and sedimentation relation in a molassic foreland basin

Architecture du bassin rhodano-provençal miocène (Alpes, SE France) : relations entre déformation, physiographie et sédimentation dans un bassin molassique d'avant-pays

Abstract : Inventory and analysis of incised valleys through the “rhodano-provencal” molassic basin (BMRP) results in re-examining the miocene sea submergence and the tectonic deformations of the alpine chain foreland basin. Three great fluviatile erosion stages have been characterized : between late Aquitanian and early Burdigalian, between late Burdigalian and early Langhian and early Tortonian.These Miocene networks who supply the platform and the slope of Lions Gulf provide some elements for a better geodynamic understanding of this area: in particular how the deceleration and the stop of the opening of the Lion Gulf interact with the alpine shortening. The marine Miocene invasions of the peri-alpine furrow are controlled by these successive fluviatile networks existence.The first fluviatile network filling is composed of bioclastic carbonates of “foramol” facies. A high frequency sequential model of an incised valleys complex is proposed.The identification of the three Miocene incised valleys networks allow a completely new BMRP geomorphological evolution analysis. The Aquitano-Burdigalian valleys are generally superimposed and encased in the Oligo-Aquitanian deposits in direct relation with the tectonic foreland basin morphostructural heritage and sign a regional large wavelength deformation reported to a compression stage of this field at the lower Miocene. The next networks are in quasi-conformity with the septentrional pyreneo-provencal structures. They are in relation with the activation of the folds and thrust. They sign a shorter wavelength folded deformation associated, for the late Burdigalian network, to a regional rising. Their superposition underlines the tectonic control perenniality. Their dismantling is the consequence of the folds and thrust activation causing not only depotcenters migration but also of the successive valleys networks whose deformation amplifies the digging.