The Moroccan Atlas is subdivided into two SW-NE trending zones: a tabular one in the northwest (“Causse moyen-atlasique”) and a folded one (“Moyen-Atlas plisse”) in the southeast. Both show a Paleozoic, partly Carboniferous basement exposed at a few places. It is covered by thick sediments of mainly Mesozoic age. The lower Jurassic consists of carbonate rocks that were deposited on an extended platform. Middle Jurassic sequences are thin on top of the anticlines, but can be very thick in the cores of the synclines. Upper Jurassic deposits have not been clearly identified and a lack of deposition occurs up to the lower Cretaceous. Cretaceous rocks are confined to restricted areas in the center of some synclines as Lower Cretaceous or Maestrichtian beds, which unconformably overlie older rocks.