Heritage Cases

Currently the only working age estimates for the Early Acheulean deposit at Sterkfontein is a faunal date of less than 2 Ma published by Vrba (see Kuman and Clarke 2000 for discussion). Debates based on palaeomagnetic readings and on ESR results have been published, with claims for younger ages of the deposit (e.g., Herries and Shaw 2011). However, these methods do not work well for Sterkfontein and are controversial. And flowstones do not date the actual breccias, because at Sterkfontein many of these are calcite infills that fill voids in breccia, and these are spaces created by subsidence of the breccia. Capping flowstones over deposits also can only provide a minimum age. We have, however, had good success in dating two older members at Sterkfontein using the isochron method of cosmogenic nuclide burial dating (Granger et al. 2015). We here apply to send seven natural chert samples from the Early Acheulean Member 5 West deposit at Sterkfontein to Prof Darryl Granger at Purdue University in the USA, to be dated at the PRIME Lab facility. The advantage of the isochron method is that multiple samples from the same burial depth all share the same post-burial production history. This shared burial history and the differences in the samples’ inherited 26Al and 10Be concentrations allow for the calculation of post-burial production without requiring any assumptions about burial depth or history. In the single sample method, these unknowns must be modelled, which adds to increased uncertainty. Outliers reflecting either sample or reworking problems can also be identified with the isochron method. These seven chert samples were personally selected by Granger during a visit to the site in April this year (but now funds are available for the dating, and hence this application). The samples were selected from the natural rocks retrieved during excavation of the Acheulean deposit and stored at the site laboratory. Samples were specifically selected as items that entered the cave from external sediments, because they need to have been exposed at surface prior to deposit in cave. Adequate shielding from further nuclide production is judged to have occurred for these samples. They are in close association with the Acheulean tools and fauna in this deposit. The sample provenances are as follows: 4 chert samples from Square P/64, 15'0" to 15'7" depth. 3 chert samples from Square Q/63, 15'0" to 16'0" depth. These samples will provide the best dating for Sterkfontein Caves Early Acheulean infill in Member 5 West, Gauteng Province, Cradle of Humankind World Heritage Site. T