Abstract The strength degradation of two marl formations (Pamplona marls in Spain and Abadia marls in Portugal) is analysed in the paper. In the case of Pamplona marls, a number of large-scale direct shear tests on natural and saturated specimens of the undisturbed material were performed. Tests on marl–concrete interfaces were performed and are also presented. Both cases analysed show that the saturation of the marl leads to a strong reduction of friction and effective cohesion. Negative effects of suction changes on the mechanical behaviour of the marls were investigated in more detail in suction controlled tests on Abadia marls, a more plastic material. A numerical simulation of wetting effects on a marl fragment of finite size helps to identify the nature of degradation mechanisms, which are associated with the development of tensile surfaces inside the marl matrix. They, in turn, are due to the expansive behaviour of the clay fraction of the marl relative to suction changes.

Abstract A synthesis of the knowledge about the Lusitanian Basin is presented here, focusing on its stratigraphic record, sedimentary infill, evolution, and petroleum systems. Petroleum system elements are characterized, including Palaeozoic and Mesozoic source rocks, siliciclastic and carbonate reservoirs, and Mesozoic and Tertiary seals and traps. Related processes, such as organic matter maturation and hydrocarbons migration are also discussed. The characteristics of these elements and processes are analysed and implications for deep offshore exploration are discussed.