Border Cave cryptotephra analysis

This application is to export sediment samples from the archaeological site Border Cave to the United States for the purpose of cryptotephra analysis. The goal of the analysis is to accurately identify cryptotephra within the sediment samples, which can be used to provide age estimates and precisely link the deposits with other archaeological or environmental archives. Cryptotephra are nonvisible volcanic glass shards that form discrete layers in archaeological or geological deposits (Lane et al., 2014). During a volcanic eruption, cryptotephra can be deposited up to 9000 kms from a source volcano (e.g., Smith et al. 2018). Additionally, each eruption has a unique composition and can be geochemically linked to an independently dated volcanic eruption (Lowe and Alloway, 2014). Because of these properties, cryptotephra can be used to date archaeological sites or link them to paleoenvironmental records with great precision. Smith et al. 2018 recently identified cryptotephra from the Youngest Toba Tuff (YTT), an eruption dating to 74 ka, at Vleesbaai Area B (VBB) and Pinnacle Point 5-6 (PP5-6) in South Africa. YTT and other younger eruptions from East Africa have also been successfully identified at other sites in the region, and papers are being developed for submission (Personal Communications, Dr. Gene Smith). These preliminary results demonstrate the widespread nature of cryptotephra deposits throughout South Africa and the potential to use this technique to precisely date and link archaeological sites throughout the region.

In October 2022, Hirniak collected multiple cryptotephra columns throughout Border Cave, documenting the vertical and horizontal distribution of the volcanic shards. Sampling for cryptotephra involves collecting 5-17 grams of sediment, and all archaeological material is removed. These cryptotephra samples are essential for building a high-resolution age model at Border Cave and understanding this site within a broader environmental context.

Methodology (short):
A total of 484 individual sediment samples were collected from exposed stratigraphic sections at Border Cave, creating a continuous sampling across the entire site. Samples are comprised of sediment only – archaeological and other objects, such as rocks, were removed from samples during the process of collection. If an archaeological object was discovered during sampling, it was recorded using a total station and cataloged with other artifacts from the site. Sample weights range from about 5 to 17 grams, with a mean of 7 grams. Samples will be analyzed at Arizona State University using published protocols (Blockley et al., 2005; Smith et al. 2018).

Statement why this study cannot be done in South Africa: This study cannot be completed in South Africa because there is no laboratory set up to process cryptotephra samples. Currently, Arizona State University and the University of Nevada, Las Vegas are the only two laboratories that are capable of processing extremely low abundance cryptotephra samples. Therefore, following sample collection, these samples must be sent to the USA for further processing.

References:
Blockley, S. P. E. et al. (2005) ‘A new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments’, Quaternary Science Reviews, 24(16–17), pp. 1952–1960. doi: 10.1016/j.quascirev.2004.12.008.
Lane, C. S. et al. (2014) ‘Cryptotephra as a dating and correlation tool in archaeology’, Journal of Archaeological Science. Elsevier Ltd, 42(1), pp. 42–50. doi: 10.1016/j.jas.2013.10.033.
Lowe, D. J. and Alloway, B. (2014) ‘Tephrochronology’, in Encyclopedia of Scientific Dating Methods, pp. 1–26.
Smith, E. I. et al. (2018) ‘Humans thrived in South Africa through the Toba eruption about 74,000 years ago’, Nature, 555(7697), pp. 511–515. doi: 10.1038/nature25967.