Lithostratigraphic column of the southern Larzac (synthesised from Baudrimont and Dubois, 1989; Delfaud, 1979; Charcosset, 2000). Location in Fig. 3. The Seuil Cévenol is characterised by reduced thicknesses in the Grands Causses basin, which evolve in a non-depositional interval in St-Pierre-de-la-Fage by pinching-out of Sinemurian to Aalenian series. As a result, the Toarcian marly seal unit disappears towards the Seuil Cévenol leading to a unique reservoir unit constituted by Lias, Dogger and Malm carbonates.