Evolution of the Atlasic Domain During the Alpine Cycle in the Broader Sense: General Outline of the Evolution of the Tethys

Following the Hercynian orogeny, all the continental blocks remained individualized from the Carboniferous to the Triassic periods. The dislocation of the Pangaea occurred in several stages along two major fractures: the Tethyan fracture and the Atlantic fracture. Morocco was, therefore, in a privileged position, and its history since 200 million years ago was influenced by the opening of the Atlantic Ocean and the birth of the Mediterranean. The Triassic transgression occurs over inherited terranes from the Hercynian and Permian periods. Except in specific regions and around the part of the Pangaea continent located at the intersection of future faults, the post-Hercynian paleotopography was not very pronounced. An open marine domain existed to the East, and the transgression during the upper Triassic period, mainly, was directed toward the West. In view of the Jurassic sedimentation, the Atlas domain differentiates and evolves into two distinct parts:1-A western part corresponding to an open basin to the Atlantic in the process of creation but is closed to the East by the ancient Massif ridge: this is the coastal domain (Essaouira, Agadir basins, etc.); 2-A central and eastern part, represented by the intracontinental basins of the central High Atlas and the eastern or Saharan Atlas, separated by the Tamlelt threshold. Together with the Middle Atlas basin to the north, they constitute the western extensions of the Tethys. In the Lower Cretaceous, the sea occupied restricted areas in Morocco (Rif zone, East of Oujda, and coastal basins). The first transgression occurred in the Valanginian to Aptian. Following the upper Aptian transgression, Morocco has seen a new regression marked by the evolution of continental and lagoon deposits in the Marrakesh region until the middle Cenomanian. In the upper Cenomanian, a major transgression occurred, covering extensive areas in Morocco. The Paleocene to Lutetian is composed of several third-order sequences, which represent successive ingressions followed by the withdrawal of the sea. The sector functioned as an Atlasic chain foreland basin from the Upper Eocene to Oligocene. The siliciclastic deposits of the Neogene and Quaternary fill in this basin called the Haouz of Marrakesh in the north and the Ouarzazate-Sous basin in the south, which is part of a tectonic depression. The basins are not homogeneous and made up of small units with specific sedimentary dynamics and contents. Thus in each one of these units, the deposits have their own organization (alluvial fans, fluvial, and lacustrine), and their distribution is controlled by the morpho-structural setting.