Geochemical investigation of the taphonomy, stratigraphy, and palaeoecology of the mammals from the Ouled Abdoun Basin (Paleocene-Eocene of Morocco)
Graphical abstract
Introduction
The phosphate series of the Ouled Abdoun Basin in Morocco, which is exploited in large industrial quarries, is renowned for its Upper Cretaceous-Lower Eocene vertebrate assemblages (e.g., Arambourg, 1952; Bardet et al., 2017). The fauna predominantly comprises sub-autochthonous marine aquatic organisms such as cartilaginous and bony fishes, mosasaurs, and turtles, but occasionally terrestrial remains have also been described, such as non-avian dinosaurs, birds, and mammals (e.g., Gheerbrant et al., 2003; Pereda Suberbiola et al., 2004; Bourdon et al., 2005). The mammals are rare and most of the time scientists come to know about them from private collectors living near the phosphate quarries, and often cannot determine their precise stratigraphic origin. Knowing the stratigraphic origins of the Ouled Abdoun fossils is crucial to elucidating the early Cenozoic evolution of African mammals (e.g., Gheerbrant et al., 2018). Accurate dating of the Ouled Abdoun mammals is also important for knowledge and characterization of the early Cenozoic successive African faunal assemblages.
To tackle the stratigraphic origins of vertebrate remains, geochemical taphonomy is a widely used method (e.g., Staron et al., 2001; Trueman et al., 2003; Metzger et al., 2004; MacFadden et al., 2007; Suarez et al., 2010; Herwartz et al., 2013; Botfalvai et al., 2021). This is based on trace element contents that are absent or occur only in very low concentrations (sub-ppm) in modern bones and teeth, however, after the death of the animals their concentrations increase through the influence of the sedimentary environment (e.g., Elderfield and Pagett, 1986). The most widely used elements are the rare earths (REE) and uranium, which can reach 4–5 orders of magnitude enrichment in fossil material compared to modern concentrations (e.g., Trueman and Tuross, 2002). These elements therefore could reflect the chemistry of the pore fluid in which the vertebrate remains were fossilized. There are several studies using REE chemistry of fossil bioapatite to reconstruct palaeoenvironmental conditions in terrestrial and marine depositional settings (e.g., Trueman et al., 2003; Lécuyer et al., 2004; Shields and Webb, 2004; Kocsis et al., 2009; Žigaitė et al., 2016, Žigaitė et al., 2020), which are all based on the assumption that REEs are quantitatively taken up from the burial environment (e.g., Reynard et al., 1999). During their incorporation into the bioapatite structure, however, fractionation could occur between the light and heavy REEs due to size differences along the REE series and related diffusion (e.g., Trueman et al., 2011; Herwartz et al., 2013). In addition, protracted late diagenetic modification (Kocsis et al., 2010; Herwartz et al., 2011) may further complicate environmental interpretations, especially for older samples (Kowal-Linka et al., 2014). To address these issues, a large number of samples, including different types of materials (e.g., bones, teeth, enamel, and dentine), and multiple in-situ analyses, are needed to evaluate further the origin of the REEs within the bioapatite.
In relation to the Moroccan phosphate series in the Ouled Abdoun and Ganntour basins, the trace element chemistry of nearly 200 marine samples (fish teeth, bones, coprolites) was published in Kocsis et al. (2016). Fractionation and late diagenetic overprint were completely ruled out. All the samples yielded similar, typical oxic seawater REE distributions with heavy REE enrichment and a negative Ce-anomaly. Importantly, however, the Ce-anomalies show a distinct change with stratigraphic level (Kocsis et al., 2016), a trend that is used in this work to assign a stratigraphic age for unprovenanced fossils. Such an approach was successful for the Embrithopoda mammal taxa of Stylolophus minor and S. major in the Ouled Abdoun Basin (Gheerbrant et al., 2018).
The main aim of this study is to further investigate the validity of the trace element provenancing method for the rare mammal fossils with known and unknown origins in the Ouled Abdoun Basin. To help better assess the taphonomy of these remains, major and other trace elements, and strontium isotope ratios (87Sr/86Sr) of selected mammal fossils, were compared with marine end-members such as data from shark teeth. Enameloid 87Sr/86Sr data derived from the latter also provide a proxy for the age of the phosphate beds, through comparing their ratios with the global 87Sr/86Sr record. In addition, some mammal fossils were measured for their stable oxygen and carbon isotopic compositions to get an insight into the ecological conditions of some of these early African placental mammals.
Section snippets
Geological and stratigraphical settings
The Ouled Abdoun Basin is one of the ancient epicontinental marine basins along the Atlantic coast of Africa, where large amounts of phosphorite accumulated during the late Cretaceous - early Eocene period. The basement rocks are covered by Cenomanian-Turonian carbonates followed by yellow marls with possible age within the Coniacian-Campanian interval (El Assel et al., 2013), which were eventually succeeded by the phosphorite series. The top of the succession is either covered by Lutetian
Investigated materials
Several mammal species and/or other fossils from the mammal-related sediment matrix were involved in our research. Some of the fossils have known stratigraphic positions, while the origins of the others are questionable or completely unknown (Table 1). We focused primarily on the trace element compositions of the fossils (Table 1). However, some specimens were also analyzed for the presence of major elements (Ca, P, F), stable oxygen and carbon isotopes, and radiogenic strontium isotopes. The
Major element compositions
The remains of four mammal taxa, Daouitherium rebouli (PM65), Phosphatherium escuilliei (MNHN.F PM25), Hyracoidea indet (MNHN.F PM52), and Ocepeia grandis (PM66) were analyzed for CaO, P2O5 and F content (Table 2, Fig. 2). The Ca/P ratio ranges from 1.70 to 2.02, with the values increasing from enamel to dentine to bone. The F content varies between 0.73 and 3.95 wt% and a similar trend to the Ca/P ratio can be seen, as the lower values come from the enamel, and the highest ones from the bone
Terrestrial, marine, and diagenetic signals
Hard tissues (i.e., bones, teeth) of terrestrial and marine animals record the chemical and isotopic signatures of their respective environments, hence when these remains are fossilized the ancient ecological conditions can be traced in the case of no alteration (e.g., Tütken et al., 2006; Kocsis et al., 2007; Domingo et al., 2009; Reynard and Balter, 2014; Akhtar et al., 2020). Generally, freshwater (e.g., terrestrial drinking sources) has a lower F and Sr content than seawater, while Ba is
Conclusions
The rare but diverse terrestrial mammal fossils from the Ouled Abdoun phosphorite are proven to have a similar diagenetic history to that of the marine fossils. This is reflected by a similar REE distribution and stratigraphy matched Ce/Ce* and Pr/Pr* ratios. The Ce/Ce* variation along the phosphate series either confirmed previous known origins or helped to estimate the stratigraphic provenance of the Ouled Abdoun mammal specimens whose origin was unknown. Exchanges with marine pore fluid
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The research was conducted under L.K.'s Ambizione Research grants (Nr. PZ00P2_126407 & PZ00P2_145115/1 – Switzerland), but in the later phase of the research LK also received support from his URC Grant from Universiti Brunei Darussalam (UBD/PNC2/2/RG/1(325)). The help from both funding agencies is much appreciated. This study benefited from the paleontological “Phosphapal” collaborative Agreement with the Ministère de l'Energie, des Mines, de l'Eau et de l'Environnement (MEMEE), the Office
References (105)
- et al.
Latitudinal temperature gradient during the Cretaceous Upper Campanian Middle Maastrichtian: δ18O record of continental vertebrates
Earth Planet. Sci. Lett.
(2004) - et al.
The retention of primary oxygen isotope compositions of fossil elephant skeletal phosphate
Geochim. Cosmochim. Acta
(1994) - et al.
Distribution of yttrium and rare-earth elements in the Penge and Kuruman iron-formations, Transvaal Supergroup, South Africa
Precambr. Res.
(1996) - et al.
Controls of trace metals in seawater
- et al.
Marine vertebrate faunas from the Maastrichtian phosphate deposits of the Benguérir area (Ganntour Basin, Morocco): biostratigraphy, palaeobiogeography and palaeoecology
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2014) - et al.
Microscopy evidence of bacterial microfossils in phosphorite crusts of the Peruvian shelf: implications for phosphogenesis mechanisms
Chem. Geol.
(2013) Palygorskite in the uppermost Cretaceous-Eocene Rocks from Marrakech High Atlas, Morocco
J. Afr. Earth Sci.
(2004)- et al.
Multiproxy reconstruction of the paleoclimate and paleoenvironment of the Middle Miocene Somosaguas site (Madrid, Spain) using herbivore tooth enamel
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2009) - et al.
Rare earth elements in ichthyoliths: variations with redox conditions and depositional environment
Sci. Total Environ.
(1986) Selected palynomorphs from the Lower to Middle Eocene of the south Atlas Border Zone (Morocco) and their environmental significance
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(1988)
Trace elements in river waters
Phosphatherium escuilliei du Thanétien du bassin des Ouled Abdoun (Maroc), plus ancien proboscidien (Mammalia) d’Afrique
Geobios
Natural and synthetic inhibitors of kallikrein-related peptidases (KLKs)
Biochimie
Strontium isotope age-dating of fossil shark tooth enameloid from the Upper Cretaceous Strata of Alabama and Mississippi, USA
Cretac. Res.
Timescales and mechanisms of REE and Hf uptake in fossil bones
Geochim. Cosmochim. Acta
Rare earth element systematics of fossil bone revealed by LA-ICPMS analysis
Geochim. Cosmochim. Acta
High-resolution dating of deep-sea clays using Sr isotopes in fossil fish teeth
Earth Planet. Sci. Lett.
Geochemical study of vertebrate fossils from the Upper Cretaceous (Santonian) Csehbánya formation (Hungary): evidence for a freshwater habitat of mosasaurs and pycnodont fish
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Protracted diagenetic alteration of REE contents in fossil bioapatites: direct evidence from Lu–Hf isotope systematics
Geochim. Cosmochim. Acta
Comprehensive stable isotope investigation of marine biogenic apatite from the late Cretaceous-early Eocene phosphate beds of Morocco
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Gradual changes in upwelled seawater conditions (redox, pH) from the late Cretaceous through early Paleogene at the northwest coast of Africa: negative Ce anomaly trend recorded in fossil bio-apatite
Chem. Geol.
Predicting animal delta O-18: Accounting for diet and physiological adaptation
Geochim. Cosmochim. Acta
LA-ICP-MS analysis of rare earth elements in marine reptile bones from the Middle Triassic bonebed (Upper Silesia, S Poland): impact of long-lasting diagenesis, and factors controlling the uptake
Chem. Geol.
Rare earth element evolution of Phanerozoic seawater recorded in biogenic apatites
Chem. Geol.
Was the Early Eocene proboscidean Numidotherium koholense semi-aquatic or terrestrial? Evidence from stable isotopes and bone histology
Comp. Rend. Palevol.
Strontium isotope stratigraphy, chapter 7
The first record of a sauropod dinosaur from the Late Cretaceous phosphates of Morocco
J. Afr. Earth Sci.
Concomitant separation of strontium and samarium–neodymium for isotopic analysis in silicate samples, based on specific extraction chromatography
Anal. Chim. Acta
Trace elements and their isotopes in bones and teeth: Diet, environments, diagenesis, and dating of archeological and paleontological samples
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Crystal–chemical controls on rare earth element concentrations in fossil biogenic apatites and implications for paleoenviromental reconstructions
Chem. Geol.
Has the REE composition of seawater changed over geologic time
Chem. Geol.
Hypomaturation enamel defects in Klk4 knockout/LacZ knockin mice
J. Biol. Chem.
Heterogeneous rare earth element (REE) patterns and concentrations in a fossil bone: implications for the use of REE in vertebrate taphonomy and fossilisation history
Geochim. Cosmochim. Acta
Geochemical taphonomy of shallow marine vertebrate assemblages
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Fractionation of rare earth elements within bone mineral: a natural cation exchange system
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Isotope compositions (C, O, Sr, Nd) of vertebrate fossils from the Middle Eocene oil shale of Messel, Germany: implications for their taphonomy and palaeoenvironment
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Palaeoenvironment and palaeoclimate of the Middle Miocene lake in the Steinheim basin, SW Germany: a reconstruction from C, O, and Sr isotopes of fossil remains
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Early diagenesis of bone and tooth apatite in fluvial and marine settings: constraints from combined oxygen isotope, nitrogen and REE analysis
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Reconstructing first-order changes in sea level during the Phanerozoic and Neoproterozoic using strontium isotopes
Gondwana Res.
A record of the δ44/40Ca and [Sr] of seawater over the last 100 million years from fossil elasmobranch tooth enamel
Earth Planet. Sci. Lett.
Les vertébrés fossiles des gisements de phosphates (Maroc-Algérie-Tunisie)
Bioapatite 87Sr/86Sr of the last woolly mammoths – implications for the isolation of Wrangel Island
Geology
Les vertébrés fossiles des phosphates crétacés-paléogènes (72,1-47,8 Ma) du Maroc, in Zouhri, S. ed., Paléontologie des Vertébrés du Maroc: état des connaissances
Mém. Soc. Géol. France
Changes in Sr/Ca, Ba/Ca and 87Sr/86Sr ratios between two forest ecosystems in the northeastern USA
Biogeochemistry
X’ marks the spot! Sedimentological, geochemical and palaeontological investigations of Late Cretaceous (Maastrichtian) vertebrate fossil localities from Vălioara Valley (Densus-Ciula Formation, Hateg Basin, Romania)
Cretac. Res.
Earliest African neornithine bird: a new species of Prophaethontidae (Aves) from the Paleocene of Morocco
J. Vertebr. Paleontol.
Clay mineralogy of Cretaceous and Cenozoic sediments off the Moroccan margin, Deep Sea Drilling Project sites 415, 416
Initial Rep. Deep Sea Drill. Proj.
Tectonics, climate and the diversification of the tropical African terrestrial flora and fauna
Biol. Rev.
Linking species diversification to palaeo-environmental changes: a processbased modelling approach
Glob. Ecol. Biogeogr.
Mise en évidence d’un Sénonien gypseux sous la série phosphatée du bassin des Ouled Abdoun: Un nouveau point de départ pour l’origine des zones dérangées dans les mines à ciel ouvert de Khouribga, Maroc
Estud. Geol.
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