Geochemical investigation of the taphonomy, stratigraphy, and palaeoecology of the mammals from the Ouled Abdoun Basin (Paleocene-Eocene of Morocco)

Lászlό Kocsis (1) , Alex Ulianov (2) , Mustapha Mouflih (3) , Fatima Khaldoune , Emmanuel Gheerbrant (4)

1 Universiti Brunei Darussalam
2 UNIL - Université de Lausanne = University of Lausanne
3 UH2MC - Université Hassan II [Casablanca]
4 CR2P - Centre de Recherche en Paléontologie - Paris

We performed different geochemical analyses of Paleogene terrestrial mammal remains to establish their taphonomy, stratigraphic provenance, and palaeoenvironmental conditions. Rare earth element (REE) results indicate a similar diagenetic history to that of previously investigated marine taxa from these beds. Therefore, the mammal remains were initially deposited in a marine setting, and probably not long after the death of the animals their bodies were washed into the sea. The Ce/Ce* and Pr/Pr* ratios for the mammal fossils were compared with the background dataset from the phosphate mines, which varies with time. This allowed us to characterize the stratigraphic levels bearing the fossils. The provenances of fossils with known origins were confirmed, while remains with unknown origins could be assigned to certain stratigraphic horizons that are compatible with previously proposed phylogenic relationships. Marine diagenesis affected the various skeletal tissues differently, with the largest alteration in the bone and the least or none in the enamel. This is mostly demonstrated by the high F concentration, high Ca/P, and seawater related 87 Sr/ 86 Sr in the bone/dentine samples. Enamel shows the opposite, and retained the most pristine terrestrial values. The δ 18 O PO4 and δ C results from mammal enamel revealed warm (>20°C mean annual temperature-MAT) and dry (<500mm mean annual precipitation) conditions for Paleocene-Eocene period in the region. From the early to mid-Ypresian about +5°C ∆MAT is recorded that might be linked to the Early Eocene Climatic Optimum. Furthermore, the 87 Sr/ 86 Sr ratios derived from shark tooth enameloid fit the global open ocean Sr-isotope record during the latest Paleocene and early Eocene providing further evidence for the age of these phosphate beds in the Ouled Abdoun Basin. However, older marine fossils yielded higher ratios than the global Sr-isotope curve, reflecting an alteration and/or somewhat restricted conditions in the Moroccan coastal basins, possibly triggered by global sea-level changes.

Mots clés: strontium isotopes; phosphorite; bioapatite; rare earth elements; stable isotopes

Domaines: Paléontologie; Systématique, phylogénie et taxonomie; Evolution [q-bio.PE]

Lászlό Kocsis, Alex Ulianov, Mustapha Mouflih, Fatima Khaldoune, Emmanuel Gheerbrant. Geochemical investigation of the taphonomy, stratigraphy, and palaeoecology of the mammals from the Ouled Abdoun Basin (Paleocene-Eocene of Morocco). Palaeogeography, Palaeoclimatology, Palaeoecology, inPress, 577, pp.1-17. ⟨10.1016/j.palaeo.2021.110523⟩. ⟨hal-03269557⟩