Past and present: raw material identification approaches at Umhlatuzana rockshelter, South Africa

Umhlatuzana is an important archaeological site for the study of the Middle and Pleistocene Later Stone Age in South Africa with a largely continuous occupation sequence spanning MIS 4-2 (~70,000 - 10,000 BP). The main technocomplexes represented are Still Bay, Howiesons Poort, Sibudan, final MSA and Robberg (from old to young). Changing selection of raw materials is an important issue in the study of the Middle-to-Later Stone Age transition that appears characterised by a shift in raw material use in addition to a technological organisation. Umhlatuzana was first excavated in 1975 by Jonathan Kaplan who suggested that the lithic assemblage of the Pleistocene deposits consisted mainly of quartz (61%), hornfels (37.6%), and quartzite (1.4%) (Kaplan 1990). Renewed excavations at the site were conducted during 2018 and 2019. This campaign aims to clarify the site’s formation processes employing micromorphological analysis and other techniques (Reidsma et al. 2021, Sifogeorgaki et al. 2020). Micromorphology uses thin sections of undisturbed sediment samples for microscopic studies. The sections allow a petrological inspection of rock fragments embedded in the deposits. Rather unexpectedly, the Umhlatuzana thin sections yield different raw material determinations than Kaplan (1990). While quartz and hornfels are present (around 23% and 25% respectively), they represent a much less sizable proportion than previously reported. Instead, the most prominent raw material observed is a quartz arenite sandstone (42%). Quartzite fragments were not detected.We therefore initiated an in-depth mineralogical and elemental classification of the raw materials. We distinguish 6 raw material types based on the thin section analysis: sandstone, quartz, hornfels, dolerite, chert and diorite. We then determined the elemental composition of the raw material types of the micromorphology samples using p-XRF. Additionally, p-XRF analysis was conducted on c. 100 specimens from the 2018-2019 excavation lithic collection. This allowed us to determine elemental characteristics of the raw materials used during the Pleistocene occupation of the site. Subsequently, p-XRF analysis was systematically performed on a larger sample set of lithics from the site in order to correctly determine their raw material type. The combination of micromorphological and p-XRF analysis of the Umhlatuzana assemblages demonstrates that if only visual inspection is done, the variability of raw materials used ma