Relationship between gravitational flap structures in the backlimb of anticlinal breakthrough Fault-Propagation Folds: case study of the Southern-Central Tunisian Atlas

The development of orogenic belts structures in the Southern-Central Tunisian Atlas is influenced by the evolution of tectonic activities during different phases, which are also closely linked to the formation of gravitational collapse structure. The typical example is that of the northern flank of the Jebel Orbata particularly the Ben Zannouch fold. It is an asymmetrical anticline interpreted by the model of “Fault Propagation Folds”. The development of the Ben Zannouch structures is resulted from landslides, scree falls and inverted layers plunging to the south. The direction of resulted gravitational structure is parallel to the main thrust direction of the Bou Omrane anticline. The thrust activity of Bou Omrane fault is associated to the important paleo-slope facing south and plastic lithology (incompetent marl layers) of outcropped series, facilitates the development of the Ben Zannouch Flap structure. The definition of gravitational collapse structures for the first time in Tunisia particularly in the northern flank of the Jebel Orbata is controlled by many principal structural conditions: fragmentation of the landslide surfaces, rheology and topography. Other regional factors can be distinguished in the Southern-Central Tunisian Atlas as the seismic activity of the pre-existing Gafsa fault reactivated during compressive phases and the weather conditions during the postglacial period.