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IntroductionThe Toarcian is the highest stage in the Early Jurassic. D’Orbigny in 1852 designated “étage Toarcien”, from the town of Thouars (Toarcium) (Deux-Sèvres, France), but the boundary Pliensbachian - Toarcian is marked by an important unconformity in this locality, and a big question stands: what is missing at the base of the Toarcian (or at the top of the Pliensbachian)? This well-known problem has prevented easy correlations since the beginning of the use of the Toarcian stage. The lower limit of the stage has to be selected elsewhere.