Student and ECR Research Support Award (June 2021) - Irini Sifogeorgaki

Geoarchaeological work on a South African Middle and Later Stone Age site

Irini Sifogeorgaki, Leiden University

As part of my PhD research, I am studying the formation processes of Umhlatuzana rockshelter. Umhlatuzana rockshelter is located in KwaZulu-Natal, South Africa and is one of the few sites with a sequence spanning the Middle to Later Stone Age transition (∼40–20 ka), making it an important site documenting this drastic technological reorganization in southern Africa. Having a deep understanding of the events and processes that concluded in the creation of the site allows us to better analyse and interpret its lithic technocomplexes. In addition, the geoarchaeological study can reveal a wide variety of information, for example, palaeoenvironmental proxies (i.e., botanical remains) and anthropogenic features (i.e., trampling features, hearths). The geoarchaeological methods I apply include soil micromorphology (the study of undisturbed samples of the stratigraphic profile under the microscope), as well as other mineralogical (i.e., XRF, FTIR), sedimentological (i.e., particle size, fabric), and geochemical (i.e., pH, Loss on Ignition) analyses conducted on bulk (loose) sediment samples.

Umhlatuzana rockshelter, site view

Umhlatuzana was first excavated in 1975 by Jonathan Kaplan (Kaplan, 1990). Kaplan suggested the deposits at Umhlatuzana underwent large-scale sediment displacement. The integrity of the archaeological assemblages was thus considered dubious and their role in the larger discussion about the development of human behavior in southern Africa was therefore limited. In 2018 and 2019, the project I work and is based at Leiden University, conducted renewed excavations at the site to clarify the formation processes and to further investigate the archaeological assemblage. So far, an updated stratigraphy of the site was published in Sifogeorgaki and others (2020) while an in-depth geochemical study of the sequence together with preliminary micromorphology results was published in Reidsma and others (2021).

I am currently finalizing an in-depth micromorphological analysis to address outstanding questions on the formation processes of the site, the most prominent of which relate to the following:

 The degree in which bioturbation affects the integrity of the archaeological finds. Bioturbation features are clearly visible within the thin sections however it is not completely clear whether this smaller-scale sediment mixing could lead to substantial dislocation of the artefacts. An accurate assessment of this is crucial for the study of the archaeological assemblage.

      OSL dating of the sequence has proven complex with some samples demonstrating high overdispersion values. Micromorphological samples located in close proximity to OSL samples need to be carefully assessed for sediment mixing, distribution of quartz grains, and formation of secondary minerals. This will assist in accurate dating of the sequence which is of immense importance for estimating the timing of the Middle to Later Stone Age transition.

In order to ensure accurate interpretations of the micromorphology samples and conduct additional analyses, I arranged a collaboration with Prof. Takis Karkanas and the Weiner Lab in Athens, Greece. Prof. Karkanas is a prominent geoarchaeologist with years of experience in conducting site formation processes research in settings similar to Umhlatuzana rockshelter. He also has experience with micromorphological research in South Africa, and thin sections from South African sites comparable to Umhlatuzana are currently in the Weiner Lab reference collection. In October2021, Dr. Karkanas and I looked at the Umhlatuzana micromorphological thin sections together. During this time, also performed additional XRD and FTIR analyses in bulk sediment samples, and SEM-EDS analysis on the thin sections. The travel and accommodation costs for this visit were covered by the SAS research support bursary.

Taking micromorphological samples

The facilities of the Wiener lab include microscopes with smaller magnifications than the ones I had available at Leiden University. The use of these microscopes allowed me to distinguish various sections in which the deposits appeared unaltered. This suggests that the bioturbation activity is not as severe as first estimated, which in turn makes for a more secure archaeological context. Another prominent outcome of the Wiener lab visits concerns the mineralogical identification of various secondary phosphate minerals. This provides insights into the geochemistry of the deposits and is important for accurate OSL dating results. One of the phosphate minerals that was identified is extremely rare and has only been reported in 25 locations worldwide, none of which is in Africa.

Micromorphological analysis allows for observations in different scales

With the support of the SAS, I visited the Wiener Lab in Athens to solve outstanding geoarchaeological questions by conducting additional analyses and by getting mentorship from a prominent researcher (Dr. Karkanas). The results of this research are of great archaeological significance and will be presented in two upcoming open-access, peer-reviewed articles: One focuses on the site formation processes and geoarchaeology of Umhlatuzana rockshelter. The second focuseson dating the Umhlatuzana deposits. Stay tuned!

If you want to follow my research journey, I post frequent updates on my Twitter account: @sifogeoarch

Papers on Umhlatuzana rockshelter:

Kaplan, J., 1990. The Umhlatuzana Rock Shelter sequence: 100 000 years of Stone Age history. Natal Museum Journal of Humanities. 2, 1–94.

Sifogeorgaki, I., Klinkenberg, V., Esteban, I., Murungi, M., Carr, A. S., Van den Brink, V. B., Dusseldorp, G. L., 2020. New Excavations at Umhlatuzana Rockshelter, KwaZulu-Natal, South Africa: A Stratigraphic and Taphonomic Evaluation. The African Archaeological Review. 37(4), 551.

Reidsma, F., Sifogeorgaki, I., Dinckal, A., Huisman, H., Sier, M., van Os, B., Dusseldorp, G., 2021. Making the invisible stratigraphy visible: a grid-based, multi-proxy geoarchaeological study of Umhlatuzana rockshelter, South Africa. Frontiers in Earth Science.

Pecha Kucha-styled presentation on the geoarchaeology of Umhlatuzana rockshelter:

‘Finding resolution for the Middle to Later Stone Age transition in South Africa’ Project Webpage