Proposed Analyses of Chemicals for finding the botanical origin of residues at Sibhudu

MOTIVATION FOR THE CHEMICAL ANALYSES
In the South African Middle Stone Age (MSA), adhesive substances form the perhaps most informative material class available to archaeologists. This is so because investigating the know-how involved in adhesive production may shed light on evolutionary concepts, such as complex cognition and the advent of cumulative culture. Adhesive must be produced with techniques that imply complicated thought processes and knowledge transfers. Previous work on adhesives from Sibhudu Cave (under permit 21038, see: Schmidt et al. 2024, https://doi.org/10.1016/j.jhevol.2024.103578) has shown that some of them were produced by pyrolysis, using the leaves of local plants. The production processes involved burning these leaves near flat stone surfaces, onto which the adhesives are deposited by condensation, and from where they can be collected by scraping with a stone tool. Podocarpus may have been one of those plants. This plant is part of the vegetation record at Sibhudu until the end of the Howiesons Poort at this site, around 62,000 years ago, but the resin has not yet been securely identified on the tools. Other plants may also have been used to produced adhesives. This opens important questions about these foragers’ knowledge and understanding of their botanical environment. What was the botanical origin of these adhesives in different periods? Do they reflect the available plant resources at different times? Alternatively, did these foragers have an intimate knowledge of the available botanical resources and their potential for adhesive making, selecting them according to specific criteria? These questions can be answered by understanding which plant species were actually used for making adhesives at different times in the Sibhudu sequence, investigating the botanical environment available to the Sibhudu inhabitants and evaluating the potential quality of these plants for adhesive making. Our approach will be based on chemical readings that can be made in Tübingen (Gas Chromatograph-Mass Spectrometry, Infrared Spectroscopy). The methodology will aim at identifying chemical characteristics and biomarkers that are specific to plants found in the Sibhudu environment. Further, the tools listed in this application have mineral residues visible on their hafting edges and these imply that mineral components were part of compound adhesives used at the site. We will therefore also conduct analyses of the binders (Raman Spectroscopy and X-Ray Diffraction), hoping to shed light on the complete set of raw materials used for adhesive making at Sibhudu.
For the analyses, the pieces will be transported to Germany, where the analytical competences are available. Technical difficulties in the Wits laboratories have made it impossible to analyse the material there. The results will be analysed together with Prof. Wadley who has extensive knowledge of local plants and the Archaeology of Sibhudu. Together, we project the publication of a peer-reviewed publication that makes available our dataset on the plant types and other raw materials used for adhesive making at two periods of the MSA, the Stillbay and the Howiesons Poort.