THE AMMONITES FROM THE LATE SINEMARIAN FROM THE CENTRAL HIGH-ATLAS (RICH, MOROCCO) - PALEONTOLOGICAL AND BIOSTRATIGRAPHICAL POINTS-OF-VIEW

The examination of more than 25 ammonite taxa and their biostratigraph ic succession in an exceptionally complete and fossiliferous section n ear Rich in the Central High Atlas Mountains (Morocco) indicates there are 10 basic biochronological units (= assemblages) for a period exte nding from the end of the Early Sinemurian to the Late Sinemurian. The se are the most precise biostratigraphical data so far collected in No rth Africa for the Oxynotum and Raricostatum zones. The many newly acq uired data for the Early Sinemurian and Obtusum zone complete and/or c onfirm an initial horizon scale recently proposed for the Beni-Mellal area of the High Atlas Mountains. Some 25 per cent of the forms identi fied in this paper are new and one species, Asteroceras langi nov. sp. , is described. The regional distinctiveness of the fauna, which is ve ry marked throughout the period under consideration, makes correlation with other Mediterranean regions difficult and more difficult still w ith North Western Europe. Consequently the widely accepted subzone sca le cannot be used. Quantified analysis of morphologies shows a correla tion between shell coiling patterns and variations in argillaceous sup ply.