The Upper Cenomanian–Lower Turonian of the Preafrican Trough, Morocco

Abstract

The Upper Cenomanian–Lower Turonian deposits of the Preafrican Trough, Morocco, are composed by fossil-rich limestones accumulated in environments ranging from the peritidal zone to the outer ramp. Two distinct domains appear during the Late Cenomanian; to the east and south-east, shallow-water sedimentation predominates in the peritidal zone and the inner ramp, while, to the west and north-west, sedimentation develops on the mid-ramp and outer-ramp. The late Cenomanian Oceanic Anoxic Event 2, OAE2, is well recorded by δ13C excursions in all the depositional environments, even in shallow water. Despite the lack of black shale deposits, the presence of buliminids indicates occasionally dysoxic conditions in the western domain during the OAE2. The maximum flooding and deepening phase (drowning) is dated as Early Turonian (post-OAE2), associated with outer ramp sedimentation over the whole area. Dysoxic conditions, indicated by laminated and silicified limestones rich in buliminids, prevail at the scale of the Preafrican Trough. Shallower marine environments and oxic conditions appear once again at the end of the Early Turonian.