Salt tectonics in the Maknassy-Mezzouna region of Tunisia: Example of intrusive and extrusive Triassic evaporites in the central and Southern Atlas

Abstract In the North African Atlas, Triassic sedimentary rocks exhibit a variety of deformation styles that are caused by the interaction between halokinesis, tectonics and sedimentation. This paper aims to present an integrated study documenting the occurrence of salt-tectonic processes in the Maknassy-Mezzouna orogenic system. The interpretation of both, field mapping and seismic data suggests the existence of a complex tectonic evolution of these Triassic evaporites, with the occurrence of Mesozoic extensional/transtensional and Tertiary compressional/transpressional tectonic regime accompanied by sedimentary loading. This evolution took place along three major events of either lateral or vertical migration of Triassic evaporites. The first one is tectonic-driven and is related to the extensional/transtensional tectonic regime, which occurred during the break-up of Pangea and rifting of Neotethyan Ocean in the Early Jurassic. The second remobilization of salt Triassic rock developed during the Cretaceous. The initial mobilization of the Triassic salt was probably induced by sedimentary loading with a limited contribution of tectonic forces. During its third stage of evolution, salt Triassic rocks evolve into salt sheets due to the shortening deformation occurred during Tertiary and Quaternary in relationship with the closure of the Neotethyan realm. Salt migration controls subsidence, generates depocenter shifts and causes thickness variation of the entire post-Triassic sedimentary sequence. The signature of salt Triassic syn-sedimentary control is confirmed by thickness reduction and abrupt variation of structural dip that affects all the sedimentary pile in the flanks of salt sheets. In seismic sections the syn-sedimentary salt tectonic control is observed by geometries like pinching out, thickness reduction, onlap termination geometry as well as unconformities identified along the flanks of the salt sheets.