Karsts côtiers et canyons sous-marins de la marge provençale au Cénozoïque : Contrôle géodynamique, eustatique, hydrologique et structural.

Abstract : The Provence Margin is situated in the north-western Mediterranean and constitutes the northern edge of the Liguro-Provençal Basin with the margins of the Gulf of Lion and Ligurian sea. The main objectif of this thesis is the reconstruction of the geodynamic, structural and geomorphologic history of the margin since the Tertiary. This margin is mainly structured by ante-miocene tectonic events. On the Provence Margin, transition between the continental plate and the basin is narrow and characterized by abrupt slopes and associated gravitary instability within the axis of the Cassidaigne canyon. The Provence Margin is characterized by Pyrenean compression and Oligocene extension. The Mesozoïc-Cenozoïc sedimentary pile is dominated by carbonate rocks favorable to water circulation. The origin of the river system in the region is essentially karstic, and the coastal springs of Port-Miou and Bestouan correspond to drowned karstic network that develop along tens of kilometers within the Urgonian limestone, updip of the Cassidaigne Canyon. Previous work suggest (1) that the lack of updip river system and the karst pocket valley shape of the canyon head are the result of an active karstic connexion between the coastal springs and the canyon, (2) that the Provence Margin is not affected by the Messinian erosion and Pliocene transgression, and (3) that Miocene marine transgressions are preserved at higher altitudes than their theoretical level. These facts witness a recent tectonic deformation that is not well understood. This work is based on the integration of geology, geomorphology and hydrogeology with the aim to understand evolution and functioning of coastal karsts and submarine canyons. The main methods are: (1) acquisition and geological interpretation of marine seismic data (2740 km) and 74 shallow coring, (2) the analysis of benchmark levels in terms of tectonics and/or eustasy, (3) hydrogeological survey and electric resistivity imagery of Cassis coastal karst aquifer, (4) 3D geological modeling of land-sea surfaces in the gOcad software, and (5) restoration of the paleotopography since the Tortonian. Results of the seismic interpretation are: (1) a detailed map of the Messinian erosional surface showing an E-W messinian canyon, called "Bandol Canyon", (2) a new geological map and land-sea geological cross sections of the continental shelf that extends from the western Nerthe massif to the Sicié Cape. Sedimentary evolution of the Cassidaigne canyon during the Messinian-Pliocene is genetically linked with the Bandol canyon sedimentation. Two stratigraphic models are proposed to explain the history of their sedimentary filling. Altitude and paleo-bathymetry of marine Miocene transgressions recognized onland and offshore allows the definition of a topographic deformation map at regional scale since the Burdigalian. These 3D topography restorations evidence the tilting of the margin and rejuvenation of reliefs from NE to SW. The evolution of the hydrologic network of the margin, that is coherent with the tectonic restoration, is presented. A deep karst, connected to the lowest network of the Port-Miou cave, emerged during the Messinian in the proximal part of the Cassidaigne canyon. It is confined by southern geologic structures not favorable to karstification. Minor streams, sourced from the Calanque Massif and from the Riou basin, carve the western side of the Cassidaigne canyon. The Bandol canyon, oriented west-east, is mainly incised by the Reppe-Destel and Gapeau rivers.
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Aurélie Tassy. Karsts côtiers et canyons sous-marins de la marge provençale au Cénozoïque : Contrôle géodynamique, eustatique, hydrologique et structural.. Interfaces continentales, environnement. Aix-Marseille Université, 2012. Français. ⟨tel-00830299⟩

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