Evidence of fault-propagation folds in foreland basin: the case of Chemsi and Belkhir anticlines of southern Tunisian Atlas

Structural analysis of Jebel Chemsi and Belkhir located in southern Tunisian Atlas lead to propose the fault-propagation fold as a model for these anticlines. Geometric analogy is settled after dip surveys and observation of several anticline kinks. Several, independent geomorphologic observations support the hinge migration kinematics characterizing this numerical model. The geomorphological hallmarks used matches to (1) alluvial fan progradation, (2) knick points on longitudinal profiles of channel streams and (3) anomalies on the drainage net in the eastern limits of the fold. These anomalies proved a centrifugal hinge migration of, at least, last folding stages in the direction prospected by the model. Results of numerical modelling using Ramp EM software showed detachment layer at 5.5 km that matches to Triassic series. Shortening amplitude is about 2 km for Jebel Chemsi and 1.5 km for Jebel Belkhir. Locally, we highlighted the role of inherited faults in locating and controlling the compressive deformation. In active tectonic region, the use of geomorphological approach is suitable to highlight the folding kinematics and thus to prove the deformation model. In our case study, many special conditions, such as excellent outcropping resulting of arid climate, constant base level and good lithological contrast, allow objective interpretations