Dr Amara Masrouhi, the assistant professor from University of Gabès, Tunisia is the invited researcher of OT-Med (within the framework of OT-Med mobility fellowships). He presented the talk entitled: "Tectonique salifère: exemples du Maghreb à la la Provence" on Monday 16th December 2013 at 14h30 in the conference room CEREGE at Saint Charles, Marseille.

ABSTRACT

As at many passive margins, in the North African margin and Provencal domain, salt-related structures are dominant features. Salt structures in North Africa and Provence domain expose Triassic salt (200–250 Ma). In the North-eastern part of the Atlas fold-thrust-belt (North Tunisia and North-eastern Algeria), there are numerous outcrops of salt structures with a NE-SW prevailing strike. The Meso-Cenozoic history of the North African margin has been classically divided into two major intervals. A Triassic-Upper Cretaceous cycle when the south-Tethyan margin was passive margin and a second post-Senonian cycle characterized by a compressive tectonic episode intercalated with periods of relative tectonic quiescence related to the collision of the African and European plates in the Tertiary. The context of the extensional tectonic regime related to the Cretaceous margin structural setting offers at least two factors allowing salt to extrude onto the sea floor and flow downslope toward deeper marine conditions: (i) tectonic extension, which weakened the overburden units by forming the main normal faults and creating the space for the salt to rise. This tectonic regime was also responsible for a sub-marine slope, on which salt can flow and spread; (ii) differential sedimentation, which drove the salt. In southeastern France, the Vocontian basin is located between the internal alpine zone to the east and the Massif Central to the west. The Vocotian basin is characterized by major faults system (e.g., Nîmes fault, Durance fault, the Mont Ventoux structures that delimits the vocotian basin to the south). Detailed geologic mapping, structural analysis, and the construction of cross-sections are used to reconstruct the structural evolution of the Suzette diapir. Two main periods of diapirism are highlighted. (i) During Jurassic–lower Cretaceous period salt was likely flowed at the sediment–water interface forming a sheet of allochthonous salt concordant with the underlying sediments and related to the diapir. (ii) During Oligocene time, a second period of extension, faults were reactivated, the Suzette diapir is trigged again and inversion of the topography was probably occurred with a southwest dip. Consequently, a second salt sheet coincides with Oligocene extension and the southwest slope. Thus, we propose that the salt sheet of the southern part region corresponds to a second salt sheet extruded during Oligocene from the reactivated Suzette diapir. In inverted passive margin (e.g. North Maghreb and Southeast France); the superposition of extensional and contractional deformation usually determines the diapir emplacement and evolution. Data can demonstrate a probable relationship Diapirism/Extension for which the symmetric extension triggers a diapir structure in the graben axis and an asymmetric extension triggers preferentially large allochthonous salt sheets.