Successions that characterize the eastern southern Alps have been compared with coeval units drilled in the Alpine foreland (Po and Veneto plains, northern Adriatic Sea). The eastern southern Alps are composed of a carbonate platform-plateau, drowned in the Early Jurassic (Trento platform and plateau); a basin formed in the Early Jurassic (Belluno Basin) and a carbonate platform that lasted from the Jurassic to the Cretaceous (Friuli platform). Integration of stratigraphic and geophysical data illustrates the extensional architecture of the Alpine foreland subsurface. At the beginning of the Jurassic, peritidal successions were widespread everywhere except for the Belluno Basin. A reorganization of the Early Jurassic paleogeography affected the southern Alps around the Sinemurian–Pliensbachian boundary: the Pliensbachian successions were deposited in the central-western areas of the Trento platform whereas, elsewhere in the same platform and in the northern Friuli platform, Pliensbachian units are missing, replaced by an unconformity surface covered by crinoidal sands that have also been found in the subsurface. The Belluno Basin is recognizable in seismic profiles under the Veneto Plain. Southward (northern Adriatic Sea and Po plain), the basin between the Trento and the Friuli platforms, here called the “northern Adriatic Basin,” possesses a stratigraphy different from that of the Belluno Basin. The northern Adriatic Basin drowned later, and seismic profiles indicate that it was wider and bounded by groups of small synsedimentary faults instead of the major faults displacing the Belluno Basin. The northern Adriatic Basin can be interpreted as the northeastern extension of the Umbro-Marchean Basin of central Italy.