Contribution of statistical analysis of facies to stratigraphic correlations. Example from the Upper Toarcian and Aalenian in the Quercy area (SW France)

We aim at showing the results of a statistical analysis of sedimentary faci es in four Upper Toarcian - Aalenian cross-sections, located in the Quercy area (NW Bassin aquitain). In a Multiple Analysis of Correspondences (MAC), different characters of both microfacies and macrofacies have been studied . An automatic clustering was applied in order to group the samples charact eristic of the same palaeoenvironment. The first axis, of the MAC would be linked to the internal-external polarity of the platform, the second axis t o the faunal diversity and the fourth one to the hydrodynamics. No interpre tation can be given for the third axis. The Fl - score series of the sample s with chronological arrangement is linked with transgressive - regressive tendencies. A regression occurs from the Upper Toarcian until the Aalenian - Bajocian limit. Moreover, six transgressive regressive half-cycles have b een considered as belonging to the Upper Toarcian and seven to the Aalenian .