Evidence of selective tectonic inversion in salt bearing basins inferred from integrated interpretation of gravity and 2D seismic data (Northeastern Tunisia)

This study discusses how tectonic inversion selectively reactivated former extensional structures within the salt bearing basins of northeastern Tunisia. Our approach is based on an integrated interpretation of gravity data and regional 2D seismic profiles. The geological history of the area distinguishes two main tectonic phases: an initial period of predominant Mesozoic extension, followed by a prominent compressional regime that has persisted since the end of Cretaceous, in response to the convergence of African and Eurasian plates. As a result, five distinct episodes of tectonic inversion have been highlighted: Santonian, Late Maastrichtian-Early Paleocene, Upper Lutetian, Burdigalian-Langhian, and Upper Tortonian-Pliocene times. As a consequence, positive inversion reactivated Mesozoic rift basins, generating faulted folds, salt cored folds, and inverted grabens. Indeed, reactivation of pre-existing normal faults was spatially selective, during Cenozoic compression. In fact, the majority of the reactivated faults are located in the northwestern part of the area, and trend predominately N-S to NE-SW, orthogonal to the NW-SE-oriented compressional stress field, established since the Santonian. Therefore, among the triggering factors controlling fault reactivation, the orientation of faults relative to maximum principal paleostress and its magnitude seems to play a key role in tectonic inversion. However, closely space and similar discontinuities can react differently to tectonic inversion, probably due to variations in fault properties such as cohesion and coefficient of friction. Additionally, faults properties like permeability and healing processes must also been taken into account to improve predictions of hydrocarbon prospectivity.