Progressive Neogene deformation of southern Hedil, Tunisian Atlas

Detailed structural mapping in the southern Hedil region of the northern Tunisian Atlas suggests that the area is characterized by multiple-faulted folds, facing southeast, rather than by the nappes and imbricate thrusts of previous interpretations. Our structural analysis shows that major deformation occurred during the middle Miocene (Langhian-Serravallian). This deformation was progressive and occurred in two discrete phases. In the first phase, shelf-type rocks of Late Cretaceous-early Miocene age were involved in kink-style folding which developed above a gliding surface in Triassic evaporites to form northeast-trending structures. The second phase produced conjugate strike-slip and extensional faulting in these structures. The acute bisectrix of the strike-slip faults, at right angles to the major trends of folding and parallel with the extensional faults, suggests that the maximum principal compressive stress (sigma 1) was directed S38 degrees E and was constant during middle Miocene deformation. This faulted-fold concept contrasts with that suggested in other studies in which the sequence of events is envisioned as faulting followed by folding.