Style of Atlassic tectonic deformation and geodynamic evolution of the southern Tethyan margin, Tunisia

Abstract

The structure of the southern Atlas fold-and-thrust belt of Tunisia was investigated using new geologic mapping, seismic reflection data together with the construction of a balanced cross section. The structural architecture of the Tunisian foreland consists in a mixed tectonic style with deep-seated basement faults, shallower décollements within sedimentary cover and salt diapirism. The restoration of the cross section shows a surface shortening of 8.1 km (∼7.3%). Sequential restoration of the balanced cross section has been permitted to decipher the structure and evolution of the southern Tethyan margin of Tunisia. Structural geometry and orientation of the pre-existing Permian (?) to Cretaceous extensional structures controlled subsequent contractional deformation within the sedimentary cover. During the shortening, this inherited tectonic framework controlled the development of ENE-trending thrust-related anticlines such as the Orbata and Chemsi structures, NW-trending lateral ramp such as the Gafsa and Fejej faults and diapir structures as the Beidha anticline. The inversion of the margin can be correlated with the onset of the convergence between Africa and Eurasia. The first phase of the Orbata thrusting growth might occur in late Cretaceous. Continuous inversion of the margin occurred during the Eocene and mainly during the late Miocene to present day. This study underlines the predominant role of inherited basement structures acquired during the evolution of the southern Tethyan margin, and their influence on the geometry of the Atlassic thrust belt. This structural analysis provides new perspectives for future hydrocarbon exploration in this poorly explored region.