Sedimentological and palynological events during the Cretaceous-Palaeogene transition in the Middle Atlas (Morocco): Bekrit, Bou Angueur and Oudiksou synclinals

The Cretaceous-Paleogene series in Morocco is a worldwide reference for its richness in phosphate deposits and global geological events. It is characterized by the crisis in the Cretaceous-Tertiary (The KT Extinction) and the... [ view full abstract ]

The Cretaceous-Paleogene series in Morocco is a worldwide reference for its richness in phosphate deposits and global geological events. It is characterized by the crisis in the Cretaceous-Tertiary (The KT Extinction) and the Paleocene-Eocene (The Paleocene-Eocene Thermal Maximum) boundaries. These two events are responsible, respectively, for the extinction of dinosaurs and the demises of 30-50 % of benthic foraminifera.
In the Middle Atlas (west of the Boulmane Meridian), The Cretaceous-Paleogene series are confined in four basins. This series demonstrate a bituminous-phosphate sedimentation rich in fauna, flora and various depositional environment. This preliminary study defines all stages of the Phosphate and bituminous sedimentation of three basins: Bekrit, Bou Anguer and Oudiksou. Also, it introduces the outlines of all the paleoclimatic and paleogeographic events in this area.
The sequence stratigraphy has defined two sedimentaries systems separated by a sequence boundary with a supraregional value. This sequence boundary has identified in the sector of Foum Kheneg. The first sedimentary cycle shows confined sedimentation followed by a genesis of phosphate in this area. The bituminous facies are subdivided into two tracts: the highstand tract and the transgressive tract distinguished by phosphatic debris. The second sedimentary cycle is characterized by a eustatic fall through two periods. The First one has deposed during the Paleocene is represented by continental sedimentation with fine layers marine sedimentation. The second one is distinguished by marine sedimentation which appeared in the Eocene. The limestones depositional environment reveals distribution from high-energy zones to low-energy zones (supra-tidal environment).
The geochemistry of organic matter in the bituminous deposits shows high values. The Analysis by Pyrolysis Rock-Eval exposes hydrocarbon compounds in the bituminous marl and more oxygenated values in the slightly phosphatic bituminous facies. These results confirm that the link between organic matter and phosphate is controlled by a genesis phosphatic environment with a high oxidizing redox potential relative to bituminous shale and connected to a more closed paleogeographic device.
The primary palynological studies of the sedimentary tracts in the Bekrit basin shows relevant results, which are summarized as follow:
-The presence of algae and dinocysts that confirmed a restricted marine paleoenvironment slightly opens at the end of the Cretaceous;
-The presence of pollen and spores, and poverty in marine forms which announced a medium continental level during the Paleocene and Eocene. This can beexplained by the humid climate and proximity from continent back then.