Identification of the Maastrichtian Paleoenvironment of the Western High Atlas Phosphate Series in Morocco: Sedimentology, Sequential Stratigraphy, and Ichnology

The investigation of the Maastrichtian epoch in the Western High Atlas region reveals insights across biostratigraphy, lithostratigraphy, and paleogeography. The study emphasizes fossil and trace fossil identification. Notably, ostracods and Echinoderm assemblages, indicative of the Maastrichtian, in addition to a diversity of Thalassinoïds, Arenicolites and Lockeia-type traces. Paleogeographically, the Maastrichtian marks an Atlantic transgression, resulting in the isolation of the Boulaajlate Basin from the phosphorus-rich Atlantic. The phosphate series in Boulaajlate basin demonstrates rhythmic sedimentation alternating between carbonate and phosphate-rich strata with organic residues. This reflects a phosphatogenesis, associated with intense benthic activity in warm, shallow, well-ventilated environments. On the western sector of Boulaajlate, the phosphate series of the Agadir basin, represents an open connection to the sea, with relatively deep fossiliferous sediments with the absence of phosphatogenesis, and on the eastern side, the phosphate series of Aoulouz, exhibits lagoon-brackish influences a sign that this sector behaves as a group of small sedimentary basins.