• Broeck, Erik Van Den
• Graillot, Didier
• Peuble, Steve
• Gallice, Frédéric
• Paran, Frédéric
• Jolivet, Joël

Abstract

The positioning of the Ardèche river catchments area and its tributaries depends on a whole organized system which follows a long building process in a context of geological and physiographical spatial accommodations. This context cannot be dissociated from the global parameters like erosion, climate variations and eustatic fluctuations generated by continental drift. The development of the gorges de l'Ardèche stems from these fundamental parameters which over time gave its current appearance to the meandering canyon. The Lower Cretaceous limestones have settled as a result of areas made available during the Upper Jurassic. In a hot and humid climate, the progradation of the Urgonian sedimentary systems leads to progressive fillings of accommodations under the constraints of eustatism and the tectonics causing differential subsidence. The structural diagram of the future gorges de l'Ardèche is initiated in this context. The uplift and the progressive emersion of the Lower Cretaceous platform will take place from the Albian-Cenomanian. Starting from the Upper Cretaceous, materials from surrounding seas or weathering deposits coming largely from the Massif Central induce successive subsidences whose tectonosedimentary deformations will interfere with the previously faulted structures. These evolving morphologies favour aerial flows in constant reorganisation at the roof of sedimentary landfills. Water streams, whose circulation direction is oriented N-S to NE-SO, descend from the Massif Central and allow the settling of braided channels and the formation of valleys of various size, under a tropical climate and according to the eustatic variations of the alpine Tethys located to the south. The question here is to understand the distribution and the direction of river circulations during the Upper Cretaceous and Palaeogene as well as in the Lower Oligocene-Miocene, at the beginning of the incision of the Ardèche canyon in the Neogene. A caracterisation protocol carried out by geochemical ICP-AES analysis of Upper Cretaceous and Paleogene samples, referenced on the geological map 889 of Bourg Saint Andéol, makes it possible to compare the geochemical signatures of unpublished sandstone and clay samples, found on the surface and in the caves of the Ardèche karstic plateaus .(<i>Jolivet</i> et <i>al</i>., 2020).

Topics

• impedance spectroscopy
• surface
• atomic emission spectroscopy
• Auger electron spectroscopy