A pre-accretional extensional platform of the North African Tethys during the Toarcian-Aalenian (Iguer Awragh-Afennourir syncline, western Middle Atlas, Morocco).

A pre-accretional extensional platform of the North African Tethys during the Tharcian-Aalenian (Iguer Awragh-Afennourir syncline, western Middle Atlas, Morocco). A stratigraphic study and mapping allow defining the particular features of this area of the southwestern Middle Atlas (Morocco) during the Toarcian and the Aalenian. Numerous spectacular variations in thickness and facies are documented by the discovery of coralline build-ups dated to the Late Toarcian. They occur along the palaeostructures. Development of the structures occurred in several stages: (1) initial differentiation during the Early and Middle Toarcian; (2) homogenisation during the Late Toarcian, after the construction of the reefs. The Aalenian history is similar: differentiation (Early Aalenian)-homogenisation (Middle to Late Aalenian). Two palaeostructural trends are evident: SW-NE and transverse SSW-NNE to south-north. These caused separation of several subbasins, which alternatively deepened and shallowed, probably due to the tilting of several blocks to the southwest. (C) 2002 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.