The Late Mesozoic evolution of the Central High Atlas domain (Morocco): suggestions from the paleo-drainage record of the Adrar Aglagal syncline

This paper illustrates the results of a stratigraphic, sedimentologic and structural study of the continental succession exposed at the core of the Adrar Aglagal syncline, located at the southern front of the Central High Atlas (Morocco). This structure deforms a Lower Jurassic-Upper Cretaceous succession, resting unconformably on Triassic clastic and volcanic deposits. Marine-transitional Lower Jurassic limestone, dolomite and gypsum crop out at the syncline's limbs whereas the core is characterized by a continental clastic succession which is the local expression of a sedimentary complex regionally known as Couches Rouges (red beds). These continental successions, attesting to a Middle Jurassic-Lower Cretaceous regressive phase, have different interpretations in the frame of the tectono-sedimentary evolution of the Central High Atlas. According to some authors these red beds record localized early compressive-transpressive stages of deformation, others refer them to a period of tectonic quiescence. Facies analysis and recognition of unconformities have allowed a stratigraphic revision and a new subdivision of these, mostly fluvial, deposits in five units. Paleocurrent analysis, compositional data and the evidence of syn-depositional growth of the syncline support a picture of crustal shortening that affected this axial portion of the Central High Atlas in a period considered tectonically quiescent. This case study supports the hypothesis that the Moroccan Atlas system experienced significant relief formation, as the consequence of the peculiar geodynamic setting in which the northern margin of the Africa plate was located during the Mesozoic.