Geometry and kinematics of the South Atlas Front, Algeria and Tunisia

Abstract

The South Atlas Front is the structural boundary between the Sahara platform and the Atlas mountains. It is frequently indicated as a foreland dipping monocline known as the Sahara Flexure. Earlier work generally considered that such a cover structure resulted from direct inversion of basement faults. This assumption is not applicable to the studied area which is situated close to the Algeria-Tunisia border: our study demonstrates a thin-skinned style characterised by ramp-related folds. Ten parallel balanced cross sections give an interpretation for the South Atlas Front from Negrine to Gafsa, about 100 km along strike. The geometry at depth of each cross section is defined by forward modelling of each individual anticline. The depth-to-detachment is defined using the geometric characteristics of the fault-propagation folds well exposed along the deformation front. In all sections, the modelling is consistent with basal décollements located within Cretaceous stratigraphic levels. Lateral changes of the tectonic style accommodated by tear faults are observed. They seem related to lateral variations in the efficiency of the based décollement faults inducing either a jump of the décollement to another level or the development of en-échelon folds. The modelling predicts small rotations of cover sheets separated by large-scale tear faults.