A type-section of the Lias and Dogger <"Marine Jurassic") of the southwestern margin of the Basquecantabrian Basin (Cantabria, Palencia and Burgos provinces) has been stablished based on both outcrop and subsurface data (well logs and seismic sections). Three potential hidrocarbon reservoirs are defined for this domain, the Hettangian Basal Dolomitic-Evaporitic Unit, the Lower Sinemurian Shallow Carbonate Ramp and the Middle Dogger Neritic and Pelagic Ramps, that mightget hidrocarbons from middle liassic organic-rich marls and black shales source-rocks developed in the adjacent Polientes-Sedano Basin