Stratigraphic correlations of the main Jurassic events in the Western Mediterranean Tethys (western Algeria and eastern Morocco)

Along the Saharan margin and northwards, several SW-NE palaeogeographical units differentiated progressively during the Early Jurassic in relation to tectonic and eustatic movements. In western Algeria and eastern Morocco, the following areas are defined from south to north :Atlas furrow (Eastern High Atlas, Ksour Mountains), High Plains and High Plateaux stable shoal, Tlemcen domain with several basins and ridges and the Alpine Tell-Rif. The dynamic evolution can be divided into major episodes which were diachronous :the basins and furrows differentiated centrifugally, along a south-north trend perpendicular to the present day structures. Large Carbonate Platforms. The build-up of large, shallow and diachronous initial carbonate platforms began during the Hettangian and ended during the Pliensbachian. Their diachronous break-up extended from the Semicostatum Zone (Early Sinemurian) to the Domerian. These platforms were a barrier and the environment was often confined or restricted. Partition. This occurred from the Sinemurian to the Domerian. It was provoked by interacting factors : acceleration of subsidence and reduced carbonate production related to periodic eustatic rises of the sea level. Locally, the availability of terrigenous quartz-rich sediment compensated for the subsidence, so that subsequently progradation of carbonates was possible. If the sedimentation rate was too low, the area subsided rapidly and became a limited deep basin (The french term ''ombilic'' will be used in this paper). Rosso-Ammonitico facies and slope deposits were widespread. A mosaic of small basins and ombilics. These local structures are separated by more or less large shoals: Sedimentation was highly controlled by differential subsidence owing to strong extensional movements (mainly tilted blocks). The coeval carbonate platforms were small and narrow. They developed on the High Plains shoal and along the margins of the Tlemcen and Atlas furrows. Their basinward progradation became significant during the late Bajocian in the Atlas. Final homogenization stage. During an interval ranging from Early Bajocian (Middle-Atlas) to Callovo- Oxfordian (Tlemcen Domain), the basins became less divided and they received more uniform marry sedimentation. Turbidites were deposited from the Late Bajocian (Ksour Mountains) to the Oxfordian (Tlemcen and Saida). Progradation of terrigenous material caused filling of the main basins at the south of the Tell. Turbidites (flysch-like) and radiolarites accumulated in the internal parts of the Tell-Rif. Late Jurassic differentiation. In the southern and western sectors (Moroccan Atlas, Ksour), sedimentation became continental. In the northern areas of the Extra-Alpine Domain (mainly Tlemcen Domain), a new carbonate platform developed on the deltaic deposits. Open sea and pelagic sedimentation became general in the Tell-Rif Alpine Domain (e.g. Ouarsenis Massif).