TECTONIC STRATIGRAPHIC RECORD OF PALEOSTRESS TIME CHANGES IN THE OLIGOCENE BASINS OF THE PROVENCE, SOUTHERN FRANCE

During the Oligocene, extensional tectonics occurred in the European platform, resulting in the formation of the West-European rift system and the Liguro-Provencal rift of the Western Mediterranean. At a later stage, the latter evolved into an oceanic basin. In the Provence, near the West-European rift and the Liguro-Provencal basin, extension induced the formation of numerous irregular grabens. Paleostress reconstructions within these basins, taking stratigraphic information into account, enabled us to reconstruct the tectonic evolution of this area. The existence of three main trends of extension (NNE-SSW, WNW-ESE and NNW-SSE) is demonstrated. By means of relative tectonic chronology as well as direct stratigraphic dating (using synsedimentary faults), we characterize several time changes in paleostress orientation. During a long period of the Oligocene, ESE-WNW-trending extension prevailed, which is related to the West-European rifting. During the late Chattian, significant NNW-SSE extension occurred, related to the Liguro-Provencal rifting preceding the development of the oceanic margin. As shown by paleogeographic maps of Marseilles basin, these changes strongly influenced the distribution of sedimentation and can explain the complex structural patterns of the Provence Oligocene basins.