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Abstract:
THE " CAUSSE COMTAL " (AVEYRON, FRANCE): GEOLOGY, HYDROGEOLOGY AND INVENTORY OF MAIN CAVES - The " Causse Comtal " (S = 265 km2) forms a sedimentary bridge between the " Causses du Quercy " in the west and the " Grands Causses " in the east. With a middle humid climate (P = 1000 mm/y, T = 9,4 °C, Evap. = 450-500 mm/y), this plateau karst presents two aquifer levels in the Lower and Middle Jurassic separated by a marly layer. These formations cover a paleozoic basement (sandstone, argillite from Carboniferous and Permian, crystalline rocks). The hydrogeological basins are controlled by E-W reverse faults due to the N-S pyrenean compression. The main spring is near Salles-la-Source in the western part (average discharge: 840 l/s; flood : 10 m3/s); it drains a 50-55 km2 area. The morphological and speleological evolution is subordinated to an erosion surface from Upper Cretaceous - Tertiary. Often stopped up (blocking), the numerous fossil caves probably date from the end of Cenozoic era. The large subterranean passages (active or semi-actives galleries; ex.: Tindoul de la Vayssière) are plio-quaternary.