Influence of rift basin geometry on the subsequent postrift sedimentation and basin inversion: The Organyà Basin and the Bóixols thrust sheet (south central Pyrenees)

The extensional period in the Bay of Biscay-Pyrenean domain during the Early Cretaceous influenced subsequent Upper Cretaceous contractional Alpine structures of the Pyrenean orogen. In the Pyrenees, the Lower Cretaceous rift system shows en echelon geometries for different basins, with the Organya Basin being one of the most important. This basin is located in the southern central Pyrenees, and the inversion of its W-E southern margin has been related to the development of the Boixols thrust sheet, the northernmost of the south Pyrenean thrust sheets. Detailed interpretation of outcrop and seismic reflection data has revealed the presence of a NNW-SSE trending relay area, which corresponds to the western boundary of the Organya Basin. The postrift facies belts parallel this boundary. The geometry of the contractional structures shows related variations such as changes in the structural relief and the plunge and the wavelength across this relay area. The synorogenic sediments also show characteristic thickness variations and onlap geometries perpendicular to thrust-transport direction. These evidences highlight the presence of this extensional margin and corroborate its influence in the subsequent stages of the evolution of the area. Seismic, well, and field data have been incorporated into a 3-D structural model in order to better understand the 3-D geometry of the study area.