Structures of the Southern Tethyian Margin During the Mesozoic Stage: Case of the Ouarsenis Mountains (Western Algeria)

The opening models of the Tethys between Gondwana and Eurasia are evidenced by several geological models. However, the embryonic phases of this evolution remain unknown due to the rarity of tectono-sedimentary facies. Located in the southern Tellian margin, the Ouarsenis Mountains exhibits an excellent zone where Mesozoic tectonic events are well recorded in the rocks. This area seems to be affected by N90, N120, and N140-trending fault systems. N10, N40, and N70 strike-slip faults are also characterized in this region. Generally, faults are often marked by uplift of Triassic saline material and there are associated with different structures: (i) monocline structures with a strong dip of 80° S, 70° E, and 60° SE respectively at the East, to the south and to the center, (ii) inverted structures (Grand Pic and Bou Malah), and (iii) Liassic formations revealing tectono-sedimentary events from the lower to middle Jurassic where extensional tectonic regimes persisted. A polyphase salt tectonics is observed in the whole of the Ouarsenis Mountains, the effects of which begin from the lower Liassic and continue until the upper Cretaceous related to the first tectonic stage of the Tethyan rifting. The Cenozoic tectonic stage which takes over, gives the current landscape of Ouarsenis. The deformation observed in the Ouarsenis region was interpreted for a long time as the results of compressional tectonic. This new study highlighted the role of diapiric events during the lower–middle Jurassic, reactivated along a main tectonic blocks. The Alpine tectonic inversion is mainly observed at the southern areas of the Tethys Sea. This new interpretation allows us to better explain the Ouarsenis Mountains with introducing the former Mesozoic tectonic inheritance and diapiric activity.