Ammonite biostratigraphy of Central High Atlas. a reference section for Tethyan Domain

The Sinemurian times of the Moroccan Central High Atlas saw important palaeogeographic changes which were of primary importance in the geodynamic evolution of the Atlas Basin. Sedimentation in the subsiding basin was dominated by the hemipelagic, thin bedded sediments of the Aberdouz and Ouchbis formations. The ammonite fauna gives the basis for precise dating of the deposits and recognition of changes of facies along a proximal/distal direction which corresponded to the main breakup of the platform at the turn of Early and Late Sinemurian. This study is concentrated on Sinemurian ammonites of Central High Atlas (Morocco). It refers to four sections namely Bou-Hamid, n’Zala, Tillicht, Foum Zaabel in the High-Atlas of Midelt-Rich and two sections namely Tamadoute, Taguendouf in the High-Atlas of Beni-Mellal. A careful systematic description of 70 taxa belonging to the Phylloceratidae, Juraphyllitidae, Lytoceratidae, Schlotheimiidae, Arietitidae, Echioceratidae, Acanthopleuroceratidae, Oxynoticeratidae, Eoderoceratidae, led to the construction of a detailed biostratigraphical framework for the Sinemurian. Ten horizons were recognized in the Lower Sinemurian (Obtusum Zone) – Upper Sinemurian (Raricostatum Zone) interval up to Lower Carixien (Jamesoni Zone). The bulk of the species show Tethyan paleogeographical affinities and can be correlated with those of the northwestern European standard zonation.