Contrôle tectonique et images sismiques de méga-structures syn-sédimentaires miocènes dans le Sahel de Mahdia — Tunisie orientale

Abstract

The seismic interpretation of the El Jem - Mahdia region data by the seismo-stratigraphic and seismo-tectonic analysis of miocene horizons shows the existence of kilometrics syn-sedimentary mega-structures in the grabens. The implicate sedimentary series are hundreds of meters thick. The progressive angular unconformities and a lenticular reeflike mega-structure take place along importants bordering geophysical faults; N110 fault of Mahdia and N175 fault of El Jem, that limit the miocene grabens. The syn-sedimentary structures of the El Jem graben are langhian-serravallian age. The Mahdia graben structure has serravallien to tortonian age. The mega-structures had been induced the permanent activity, during the Langhian - Serrvallian, of deep normal wrench faults producing internal rotations of tilted blocks and structueral and material migration. This phenomenon generates graben zones with continuous subsidence (progressive unconformities) and high zones with positive movements (reef structure). The seismo-stratigraphic and seismo-tectonic analysis of these mechanisms make it possible to individualise a multi-directional extension of miocene period extending from the Langhian to the Tortonian in the Mahdia Sahel.