The Saharian Atlas is located between the Tellian domain (in the North) which is a segment of the Tethyan paleomargin and the Saharian platform (in the South), relatively stable since the end of the Paleozoic. In the western part of the Saharian Atlas (between the Moroccan border and the Algiers meridian), the Mesozoic series begins with a thick Triassic evaportitic sequence which formed the maor decollement level during the Tertiary compression. The extensional phase continued during the Early and Middle Jurassic, and resulted in the formation of a subsident intracratonic basin infilled with a thick Mesozoic series (7 to 9 km). To the north (Hauts Plateaux) and to the South (Saharian platform), this basin is bordered by relatively stable Mesozoic areas. During the compressive phases (Tertiary), associated to the genesis of the peri-Mediterranean ranges, the extensional structures were reactivated into reverse faults; the evolution of the Atlas Mesozic basin ended with the formation of Saharian Atlas range, which is a typical inverted basin.