Structural style of the southern part of the N-S axis in the Central Tunisian Atlassic foreland: tectonic implications

Nedhir Sebai^1,3, Hamdi Mouakhar², Ines Mahmoudi¹, Ahlem Naily¹, Ferid Dhahri^1,3, Hakim Gabtni⁴, Mohamed Dhaoui⁴ & Noureddine Boukadi^1
1Research Lab LR18ES37: Geodynamics, GeoDigital & Geomaterials, Faculty of Sciences of Tunis, Tunis El Manar University, Tunisia.
²PERENCO Tunisia, 8, Rue Slimane Ben Slimane, El Manar 2, Tunis 2092.
³Department of Earth Sciences, Faculty of Sciences of Gafsa, Gafsa University, Sidi Ahmed Zarroug Campus, 212, Gafsa, Tunisia.
⁴Georesources Laboratory, Centre for Water Research and Technologies, University of Carthage, Soliman, Tunisia.
Corresponding author e-mail: nadhirsbai@gmail.com

The Meknassy-Mezzouna tectonic corridor represents the southern part of the regional scale tectonic structure of the N-S axis in central Tunisia that separates the Central Atlas, to the west, from the eastern foreland basins of Tunisia. It is established within a Mesozoic-Cenozoic cover in a region where both shallow and deep-rooted faults occur. Most of these faults are inherited from the Tethyan rifting and have controlled the deposition of the sedimentary sequences that were deformed during the Atlassic tectonic inversion. The present-day structure of central Tunisia is underlined by a multidirectional fault system locally associated to Triassic salt extrusions. Accordingly, its structural style was significantly controlled by halokinesis and tectonic inheritance. In this region, Triassic evaporites are acknowledged as a decollement level between the faulted ante-Triassic basement and the post-Triassic sedimentary cover dominated by folds and shallow fault-related structures, locally disturbed by Triassic extrusions. In this study, gravity and 2-D seismic surveys, wells and surface geological data are integrated to better understand the subsurface structural architecture of the study area and to detect and map the associated fault network. The interpretation of the gravity data highlights four major fault systems, oriented N-S, NE-SW, NW-SE and E-W. Some faults are deeply rooted into the basement to a more than 5000 m depth, while others of 500 to 2000 m depth are associated with the folds and shallow fault-related structures generated during the Atlassic orogeny. Multistage Mesozoic-Cenozoic extrusions of evaporitic Triassic rocks occurred in privileged weak zones mainly controlled by faults intersection. The tectonic style of the geological structures along the southern part of the N-S axis, in central Tunisia, was visibly controlled by the reactivation of inherited structural features together with salt tectonics.

faults, gravity, halokinesis, tectonics, N-S Axis, Central Tunisia.