Cathodoluminescence tools provide clues to depositional history in Miocene and Pliocene mammalian teeth

This paper presents the results of a study which used cathodoluminescence (CL) observations (optical images and SEM spectra) as a tool for assessing diagenetic processes during fossilisation of continental mammalian teeth. The study was performed on fossil teeth of large mammals (Gomphotheriidae, Rhinocerotidae and Hippopotamidae) from Namibia and from Kenya, with ages from the Lower and Middle Miocene to Pliocene. The fossil sites are distinguished by their environmental conditions. They include floodplain deposits, fluvial deposits of the Proto-Orange River and aeolianite deposits in Namibia, and fluvio-lacustrine deposits of different ages in Kenya. Optical CL provides information about the sites' environments and diagenetic processes related to those environments: a blue intrinsic luminescence for the aeolianite deposits and purple to yellowish for floodplain or fluvial deposits. The CL-spectra of these samples show sharp emission bands, which are classically related to late (recent) incorporation of rare-earth elements (REE) substituting in the Ca2+ sites. High-resolution mapping of the distribution of these REE shows a gradient from the enamel interior (low concentrations) to the outer enamel margin (high concentrations).