Valanginian (Early Cretaceous) ammonite faunas from the western High Atlas, Morocco, and the recognition of western Mediterranean ‘standard’ zones

On the basis of newly collected material, the biostratigraphical significance of Valanginian ammonite assemblages from the western High Atlas, Morocco, is discussed. A critical revision of previously defined regional stratigraphic units correlated with ammonite occurrences shows these units to be diachronous or even to some extent erroneous. Most of the western Mediterranean Lower Cretaceous ‘standard’ ammonite zones and subzones are now recognised and for the first time regional ammonite evidence is given for the Valanginian/Hauterivian stage boundary. The supra-regional value of the basal Valanginian marker, Thurmanniceras otopeta, is questioned here owing to its absence from the working area. The correlation potential of other Valanginian index ammonites, namely Karakaschiceras biassalense, Neocomites (Neocomites) peregrinus, Olcostephanus (Olcostephanus) nicklesi, and Criosarasinella furcillata, is confirmed by their occurrence in the sections studied.