Late Cretaceous shift from wetter to drier seasonality in the fluvial-coastal depositional record of the Sub-Saharan platform (southern Morocco)

Southern Morocco provides extensive exposures of a fluvial-coastal-shallow marine succession developed between the Albian? and the Early Turonian. The so-called Kem Kem beds represent the lower portion of this succession and are characterized by fluvio-deltaic sandstones at the base (Ifezouane/Gara Sbaa formations) passing upward into coastal mudstones and marls (Aoufous/Douira formations). A robust chronological constraint is available only for the uppermost part of the succession, the Akrabou Formation, which records the establishment of a carbonate platform during the late Cenomanian–Early Turonian. Besides the poor chronostratigraphic constrain there is a broad consensus to place in the Albian the onset of the lower-mid portion of the studied succession, known for its varied vertebrata fossil content including dinosaurs, crocodiles, turtles, and freshwater fishes. This study aims at providing stratigraphic and sedimentological lines of evidence to frame the Kem Kem palaeobiota into a novel depositional model. The fluvial-coastal strata, exposed from the Kem Kem region to the south up to the southern front of the Central High Atlas to the north, are correlated outlining a stratigraphic architecture made of unconformity-bounded sub-units. Facies associations recognized in this succession suggest a temporal variation of the depositional processes in the fluvial-coastal systems. While the lower part of the Ifezouane/Gara Sbaa formations testify a fluvial environment hinting to a moister seasonality along with a deep hydrographic network reorganization, its upper part and the Aoufous/Douira formations, show facies indicating a fluvial environment evolving into a coastal plain with evaporites and fine-grained intercalated deposits hinting to a drier seasonality.