Contribution of seismic velocity studies to structural and lithostratigraphic reconstructions: Salt-intruded corridor ceiling and Lower Turonian Beida anhydrite deposits’ outline in the central–southern Atlas of Tunisia

The Triassic salt dome/ripple ceiling and the Lower Turonian anhydrite Beida distribution are the main geological research objectives in central Tunisia. 2D seismic interpretation and outcrop studies show the thickness and the facies variations of the Turonian deposits identified along the structures recognised in the Gafsa area. Sedimentary distribution in the sub-basin and on the platform zones of the Gafsa plain is controlled by the WNW–ESE salt-intruded Gafsa corridor, the north–south Sidi Ali Ben Aoun and NE–SW Sidi Aïch master strike-slip faults. The conventional seismic velocity enables the extraction of an iso-velocity section that allows us to follow the Sehib-Berda salt-intruded ceiling identified in the Turonian deposits. The interval velocity map was helpful to predict the facies nature and, therefore, to delineate the Lower Turonian anhydrite Beida Formation that filled a local part of the northern Gafsa plain and does not exceed the Sidi Aïch fault to the north and the Sidi Ali Ben Aoun fault to the southeast. The palaeogeographic distribution is the result of a broadly NE–SW extensional tectonic event. The Early Turonian distension is followed by the Middle and Upper Turonian sinistral transtension, causing an inversion of the structuring and a new distribution of the deposits.