Genesis and evolution of Permian and Triassic basins in the Pyrenees by regional simple shear acting on older Variscan structures: field evidence and experimental models

Abstract

A sedimentological and structural study of Permian and Triassic basins, Pyrenees (France, Spain), and their underlying Variscan substrate has been made in conjunction with model experiments. We conclude that opening of the basins occured during a regional deformation by simple shear along preexisting basement faults initially situated in first and third quadrants. The opening was developed by block rotation, with accompanying shortening and extension, respectively parallel and normal to the faults. Deposition structures, similar to sedimentary structures observed in the field, were duplicated by experimental models. These models show also that normal faulting or development of a vertical lateral slip conjugate fault system with acute angle bisectrix parallel to the major axis of the basins are not necessarily related to a regional non-ro tational deformation, but can and will occur in the cover if the opening of the basins is due to a regional simple shear, even so if in the underlying basement faults act as strike slip faults.