The Préalpes Médianes nappe, located in the Alpine front, is composed by sedimentary rocks, deposited in the northern margin of a vanished ocean named Tethys. These rocks are mainly limestones associated with marIs and clays. The sediments were deposited on the "Briançonnais" terrane from Triassic, 245 millions years ago, to Tertiary, 40 millions years ago. In the beginning of Tertiary, this terrane implicated in the collision between the Apulo-Adriatic Plate and the European Plate. This collision creates the Alps. This study precises the temporal and spatial distribution of Lower Jurassic lithostratigraphic units. A multi-disciplinary approach -Sedimentology, Stratigraphy and Structural Geology - permitted to distinguish between synsedimentary paleotectonics and structures due to the Alpine collision. The analysis of the subsidence shows a strong link between the sedimentary record in the Préalpes basin and tectonics in the basement. These movements are consequences of thermal events in the lithosphere associated with the opening of the Alpine Tethys. During Late Liassic, the sedimentary realm of the Préalpes Médianes evolved as a rim basin of the northern passive margin of this ocean. The geodynamic study integrates data of the Préalpes and from other Briançonnais regions, in updated models of the plate tectonics.
