The “Aptian Crisis” of the South-Tethyan margin: New tectonic data in Tunisia

Abstract

The distribution of Cretaceous sedimentary basins in the central Tunisian Atlas is controlled by major faults. The reactivation of these faults and the diapiric activity of the Triassic evaporites has resulted in a complex tectonic history. Most studies show that the Saharan platform in Tunisia, located on the South-Tethyan margin, was compartmentalized by an extensive tectonic phase towards the end of the Aptian, during an episode known as the “Aptian Crisis”. In the study area located in Central-Western Tunisia, the Aptian series of Jebel El Hamra and Jebel El Ajered form the core of an anticlinal fold. The Aptian russet-coloured dolomites (Serj formation) are rimmed by alternating marls and limestones of end-Aptian age and the Fahdene formation composed of Albo-Cenomanian marls. The structural and tectono-sedimentary study of Jebels El Hamra and El Ajered highlights the prominent influence of paleostructures acquired during the evolution of the South-Tethyan basin and their control on the existing geometry of the fold belt. Indeed, the present geometry of folds and faults results directly from the block tectonics developed during the Aptian. This Aptian tectonic style is characterized by extensive and/or transtensive deformation leading to multiscal fracturing in structural blocks. This deformation is characterized by a normal or strike-slip normal fault and drape fold system. The age and the extension direction (SW–NE) are fully consistent with the regional extensional phase probably disturbed by diapirism. This “Aptian Crisis” can be related to the opening of the equatorial Atlantic and Tethys oceans.