Dynamics and inversion of the Mesozoic Basin of the Weald-Boulonnais area: role of basement reactivation

The geometry and dynamics of the Mesozoic basins of the Weald-Boulonnais area have been controlled by the distribution of preexisting Variscan structures. The emergent Variscan frontal thrust faults are predominantly E-W oriented in southern England while in northern France they have a largely NW-SE orientation. Extension related to Tethyan and Atlantic opening has reactivated these faults and generated new faults that, together, have conditioned the resultant Mesozoic basin geometries. Jurassic to Cretaceous N-S extension gave the Weald-Boulonnais basin an asymmetric geometry with the greatest subsidence located along its NW margin. Late Cretaceous-Palaeogene N-S oriented Alpine (s.l.) compression inverted the basin and produced an E-W symmetrical anticline associated with many subsidiary anticlines or monoclines and reverse faults. In the Boulonnais extensional and contractional faults that controlled sedimentation and inversion of the Mesozoic basin are examined in the light of new field and reprocessed gravity data to establish possible controls exerted by preexisting Variscan structures.