Strontium, neodymium and lead isotope systems for tracing cultural ochre provenance

Strontium (Sr), neodymium (Nd) and lead (Pb) isotope ratios have been a key component of the geochemist's toolkit for understanding the provenance of rocks from geological settings. The application of these radiogenic isotope systems to the study of ochre provenance from archaeological contexts has not been exhaustively explored; however recent studies have predominantly focused on Pb isotopes in metal objects and dietary Sr as a proxy for deciphering migration patterns. This paper presents the first application of Sr, Nd and Pb isotopic systems to ochre pigments, using a combination of Sr, Nd and Pb isotope ratios to fingerprint ochre sources in Australia and Kenya. To validate this method, three sources within Australia and one source in Kenya have been characterised using Sr, Nd and Pb isotope ratios to quantify both the intra-source and inter-source variation. Strontium and neodymium isotope variation observed in the studied sources demonstrates that the combination of these two isotopic systems can be used to distinguish between sources. Further, this research also reveals that Pb isotope ratios when analysed in conjunction with Sr and Nd isotope ratios, assist in the identification of differences within the sub-sources sampled. This study provides a framework for the future provenance of archaeological ochres to their source locations and proof of concept to utilise Sr, Nd and Pb to trace the cultural movement and exchange of ochre.