A Middle Stone Age occupation identified at Baden-Baden in the grasslands of the Free State, South Africa

In southern Africa, Marine Isotope Stage (MIS) 5 (~ 130 − 71 ka) is a crucial period in the evolution of Homo sapiens but poorly documented in the central interior of the subcontinent. We report here results from Baden-Baden 2, a newly discovered open-air site in the western Free State grasslands of South Africa that documents Middle Stone Age occupations dated to MIS 5. The lithic assemblage differs from known MIS 5 and post-MIS 5 industries and shows similarities with industries typically dated to MIS 6 (~ 191 − 130 ka). In order to geochronologically constrain the occupation of Baden-Baden 2, sediments for optically stimulated luminescence (OSL) dating were collected together with micromorphology blocks to correlate formation processes and luminescence data. Magnetic susceptibility and plant biomarker analyses were used to identify changes in sediment supply and reconstruct past environments, revealing a shift in sediment source or climate regime during the period of human occupation, which took place between 91 ± 8 ka and 75 ± 7 ka. The palaeoenvironment shows three relatively stable phases that match the three broad phases of sediment input identified. The combination of OSL and micromorphology shows extensive bioturbation due to termite activity in the whole sequence. We discuss here the issue of dating quartz grains in bioturbated contexts, using single grain analyses combined with the Finite Mixture Model. Our results suggest that sand at the site was deposited from 106 ± 8 ka, for the base of the sequence, to 120 ± 30 a, for the modern sample at the top. The Baden-Baden 2 assemblage overlaps temporally with different industries in other South African regions, underscoring the need for more systematic investigation of MIS 5 in the interior of South Africa.