Lower Pliensbachian ammonites from the Folded Middle Atlas, south of Taza (Morocco)

Abstract

In the Middle Atlas range, ammonites from the Pliensbachian remain poorly known. Two Pliensbachian sections, Bab El Hari 1 (BEH1) and Bab El Hari 2 (BEH2), located in the Bab El Hari area (25 km south of Taza town), were studied to improve the record on the Pliensbachian ammonites from the Middle Atlas and Morocco in general. The lithological succession of the section BEH1 (40 m-thick) is divided into two informal formations: a lower, Alternating marlstone and limestone, and an upper, Bedded limestone. The lower formation is divided into three members: Member 1 consists of alternating marlstone and thin limestone beds, containing some ammonites of the Jamesoni Chronozone and a basal level rich in small specimens of the rhynchonellide Sulcirostra brusinai; Member 2, consists of alternating marlstone and limestone beds with some flint nodules, and is the richest in ammonites of the Ibex Chronozone; the upper, Member 3, composed of alternating marlstone and thin limestone beds, contains rare ammonites probably still of the Ibex Chronozone. Its upper part, probably, the Davoei Chronozone, is rich in the large rhynchonellide Sulcirostra brusinai. The Bedded limestone formation, consisting of thin limestone beds separated by stratification planes or thin marlstone layers, yielded rare ammonites probably of the Celebratum Chronozone (lowermost upper Pliensbachian). The section BEH2 (16 m-thick) consists of alternating marlstone and thin limestone beds and is poor in macrofauna. This section provided a single ammonite specimen from the Davoei Chronozone. In section BEH1, three ammonite assemblages have been identified. The first assemblage, dominated by the genus Miltoceras, belongs to the Jamesoni Chronozone; the second assemblage, rich in Tropidoceras, and the third, rich in Metaderoceras and Dubariceras, belong to the Ibex Chronozone. Furthermore, the presence in the identified assemblages of some ammonite species common to the Mediterranean Tethys and the Western European Subboreal Domain indicates marine communications, during the Pliensbachian, between these two paleogeographic domains via the central Atlantic.