Formation and inversion of salt-detached ramp-syncline basins. Results from analog modeling and application to the Columbrets Basin (Western Mediterranean)

The widespread extensional deformation that took place during Jurassic to Cretaceous times in Western Europe and the North Atlantic margin resulted in the formation of several rift systems. Some of the resulting basins associated with these rifts show broad synclines detached on pre- or syn-kinematic Permian or Triassic salts, and are filled by thick sedimentary successions. The development of these salt-detached ramp-syncline basins has been associated to the extensional motion of ramp/flat extensional sub-salt faults. The shape and kinematics of such faults have usually been established using the architecture of syn-kinematic units and by assuming complete coupling of the hanging wall rocks. Therefore, there are fault interpretations that do not consider the role played by the deep salt layers, which clearly act as an effective detachment, decoupling sub- and supra-salt deformations. Moreover, the complexity of these scenarios further increases due to some of these basins, which, during latest Cretaceous and Cenozoic times, were partially inverted and were often incorporated into fold-and thrust belts. Based on analog models and using the Mesozoic Columbrets Basin (Western Mediterranean) as a case study, the aim of this research is: to decipher the influence of the ramp/flat extensional fault during the syncline development and the interaction with a pre-kinematic salt; and to infer how salt-detached ramp-syncline basins are subsequently inverted. To achieve this goal we carried out an experimental program consisting of eight different sandbox models. Our results show that the main structure formed at the end of the extension is a salt-detached ramp-syncline and that its geometry not only depends on the dip and length of the fault panels, but also on the fault displacement and salt thickness. The inversion of these salt-detached ramp-synclines resulted in a major thick-skinned fault bend anticline with minor thin-skinned contractional structures.