Thin-skinned tectonic deformation within the southern Atlas foreland folds and thrust belts of Tunisia

Abstract

The southern segment of the Oriental Atlas represents a key zone for studying deformation patterns within the North African foreland basins. Our investigation focused on studying deformation within the Orbata, Chemsi, and Belkhir anticlines located in Tunisia. Our structural observations indicate that the deposition of Cretaceous and early Cenozoic sedimentary rocks was affected by numerous normal faults. Compressive deformation from the Miocene to the Quaternary has been documented in (1) fractures, which were studied at various measurement sites and revealed faults, veins, shear joints, conjugate shear joint systems, tension joints, and pressure-solution sets, exhibiting an NNW–SSE shortening direction; and (2) folds, which were examined in three cross sections. The balanced cross-sections and the restored models demonstrate that normal faults influenced the basin geometry. These structures were later inverted to accommodate contractional deformation. Secondary normal fault sets linked to the major faults played a significant role in determining the position of the main thrust systems. This gave rise to the Orbata, Chemsi, and Belkhir anticlines through in-sequence thin-skinned deformation. Structural analysis suggests that the three anticlines originated through fault-propagation folding. The Belkhir anticline displays a simple step configuration, whereas the Orbata and Chemsi anticlines exhibit more complex geometries involving break-out thrusts. During this phase of Cenozoic contractional deformation the detachment levels were within the Triassic series. Seismic line interpretations across the Sidi Mansour Basin validate our results, showing clear thickness variations within the Mesozoic sequence and evidencing a thin-skinned deformational regime.