Extensional salt tectonics in a contractional orogen:: A newly identified tectonic event in the Spanish Pyrenees

A new Coniacian-early Santonian extensional salt tectonics event has been identified in the Cotiella thrust sheet of the central Spanish Pyrenees. We present a new interpretation of the Cotiella thrust system and describe exceptional outcrop examples of postrift, gravity-driven extensional growth faults. The thrust sheet contains three, kilometer-scale extensional faults with as much as 5.5 km of Coniacian-lower Santonian growth strata in their hanging walls. These postrift listric growth faults detached on the prerift Triassic evaporites on the uplifted and eroded southern Ranks of Early Cretaceous rift basins. Early Alpine (late Santonian-Maastrichtian) contractional deformation reactivated and reversed the displacement on both the Early Cretaceous rift faults and some of the postrift-salt detachment faults. Hanging walls of the listric growth faults deformed into major antiforms, but the original extensional geometries are well preserved. Continued Alpine shortening incorporated these reactivated extensional fault systems into the thin-skinned thrust sheets of the southern Pyrenees. These postrift extensional structures account for significant thickness variations in the postrift succession and for along-strike changes in the styles of the thrust structures. The Late Cretaceous extensional salt tectonics is interpreted to result from gravity-induced northward sliding on the Early Cretaceous rift margin, toward the axis of the rift basin. The listric growth faults are similar to those found on the Gulf of Mexico margin, in the southern North Sea, and the South Atlantic margins.