Trace element and Pb and Sr isotope investigation of tooth enamel from archaeological remains at El-Kurru, Sudan: Evaluating the role of groundwater-related diagenetic alteration

Abstract

Abstract This study reports new trace element and Pb and Sr isotope compositions of tooth enamel from archaeological remains at a Medieval (Christian) cemetery located adjacent to the Kushite royal cemetery of El-Kurru, Sudan. The archaeological site of El-Kurru is located along the Nile River on the southern edge of the Nubian Plateau; the bedrock geology consists of Neoproterozoic crystalline basement and is overlain by fluvial sandstones and mudstones of Cretaceous age. El-Kurru is situated between two well-developed drainage basins, and in the past has been subjected to periodic (wadi-related) flooding as a result of intense local precipitation events. Enamel samples were taken from 18 individuals of varying ages and both sexes. Trace element abundances for a significant number of samples record elevated concentrations relative to modern (“in-vivo”) enamel, including Pb and U; however, the abundances for both elements do not correlate significantly with the contents of the remaining trace elements (Ba, Fe, Mg, Mn, Nd, Sr) investigated here. The calculated enrichment factors for all trace elements studied here relative to average crustal values are not consistent with exposure to Pb ores for human purposes, which is corroborated by the Pb isotope results. The Sr isotope compositions define 2 main groups that yield 87Sr/86Sr ratios that are either higher or lower than 0.7072 with similar Sr abundances (range between ~100 and ~400\xa0ppm). The Pb isotope compositions are extremely variable and correlate well with their corresponding U/Pb ratios; the former overlap Pb isotope ratios for proximal Neoproterozoic rocks belonging to the Saharan Metacraton and Arabian Nubian Shield tectonic provinces. The combined trace element abundances and Sr and Pb isotope compositions for the enamel samples located within the Christian cemetery at El-Kurru are best interpreted to record interaction with groundwater that occurred post-mortem during flooding events. As reported in previous anthropological studies of a similar nature, the Pb isotope results reported here are particularly sensitive to monitoring post mortem diagenetic alteration given their extremely low abundances in non-altered tooth enamel. In contrast, the 87Sr/86Sr ratios have been minimally perturbed by post mortem alteration, and therefore most likely represent individuals with distinct Sr isotopic signatures inherited from different geographic regions.