Evolution of the Atlas Mountains (Morocco) and Adjacent Sedimentary Basins:  Implications for Hydrocarbons

GOMEZ, FRANCISCO, MUAWIA BARAZANGI, Institute for the Study of the Continents, Cornell University, Ithaca, NY 14853, USA; WELDON BEAUCHAMP, ARCO International, Plano, TX  75075, USA; AHMED DEMNATI, ONAREP, Rabat, Morocco

     The High and Middle Atlas Mountains of Morocco represent Early Mesozoic continental rifts associated with the opening of the central Atlantic Ocean.  These rift basins subsequently contracted and uplifted during the Cenozoic (i.e., "inversion tectonics") in response to convergence between the African and Eurasian plates.  Structurally, the Atlas Mountains present both contractionally reactivated rift-related faults, and younger moderately dipping thrust faults.  The High Atlas displays pure contraction, whereas the Middle Atlas is transpressional.  Cenozoic sedimentary basins adjacent to the Atlas mountains record these tectonic processes.  Stratigraphic evidence suggests that the main episode of mountain buliding has occurred since the Neogene.
     Understanding the context of these adjacent basins and their structural relationships with the Atlas ranges has implications for hydrocarbon exploration.  The Ouarzazate and Tadla "foreland" basins flanking the bivergent central High Atlas contain up to 1 km of Cenozoic strata, and the intermontane Missour Basin, located between the High and Middle Atlas ranges, contains but a thin veneer of Cenozoic strata.  Although depositional burial of potential Paleozoic and Cretaceous source rocks is insufficient, the basin margins may be sufficiently buried beneath overthrusts from the Atlas Mountains.  Furthermore, the Missour Basin also contains inverted rift structures.  Another example, the Guercif Basin, develops abruptly along strike of the Middle Atlas as an extensional basin relating to the interference during the Neogene between the Middle Atlas and the Rif thrust belt farther to the north.  Neogene strata locally exceed 2.5 km in thickness, and thus place potential Paleozoic and Mesozoic source rocks within the "oil window".