Fig 1.
Map of South Africa with the location of Ga-Mohana Hill (GHN) and key palaeoenvironmental and middle stone age sites discussed in the text.
Dashed lines demarcate summer and winter rainfall zone boundaries (SRZ, WRZ), middle area experiences year-round rainfall (YRZ). Inset map shows the approximate extent of the Kalahari Basin in southern Africa and the location of the region of interest in relation to it. Figure produced in ArcGIS 10 from multiple open source datasets: Kalahari Basin extent from SASSCAL Open Access Data Centre [32]; Digital Elevation Model obtained from USGS Earth Explorer [33]; annual rainfall data from WorldClim 2 [34] and river centrelines accessed from Natural Earth vector data [35].
Fig 2.
Tufa depositional environment context and representative photographs of each of the tufa morphologies identified on the Ga-Mohana hillside.
(A) Schematic profile sketch of Ga-Mohana Hill North Rockshelter (not drawn to scale) illustrating the series of tufa deposits and the archaeological excavation. The excavation layers dated via OSL: DBSR = ~105 ka; OAS = ~31 ka and DBGS = ~15 ka; (B) cliff cascade; (C) step-front cascade; (D) sinuous rim-pool edge; (E) barrage tufa; (F) terrace breccia; (G) tufa dome.
Table 1.
U-Th age data for tufa samples from Ga-Mohana Hill.
The samples are labelled according to the sequence they were collected in but presented in stratigraphic order. Errors on all isotope activity ratios are reported with 2σ uncertainty. All ages have been corrected to account for the effect of detrital Th assuming an estimate for initial 230Th/232Th of 1.5 ± 1.5, and calculated using the 230Th-238U decay constants of Cheng et al. [54] and equation 1 from Hellstrom [47].
Fig 3.
Composite plot of Ga-Mohana Hill tufa formation compared to selected global proxies over the last 120 ka.
(A) LR04 curve [61]; (B) variance of reconstructed sea surface temperatures (SST) from Indian Ocean core MD96-2048 [62]; (C) mean daily summer insolation curve for 27oS [63]; (D) OSL age data from the Ga-Mohana Hill North excavation sediments [27, 36]; (E) tufa U-Th age data with 2σ error bars presented in Table 1. The blue bars highlight clusters of overlapping tufa ages and are defined by the minimum and maximum ages in each range, calculated using the 2σ uncertainty associated with the ages. Based on the presence of the tufa deposits, these periods are inferred to represent episodes of greater water availability on the landscape.
Fig 4.
Comparison of palaeoenvironmental and archaeological records from Ga-Mohana Hill, Kathu Pan, and Wonderwerk Cave.
Archaeological occupation ages for Ga-Mohana Hill [27, 36], Kathu Pan [25, 26, 91, 92] and Wonderwerk Cave [20, 93, 94]. Pale orange bars highlight periods of occupation. Palaeoenvironment proxy data from Ga-Mohana Hill (this study), Kathu Pan [25] and Wonderwerk Cave [19, 20]. Pale blue bars highlight wet periods across the sites. Orange star marks the point at ~71 ka, before which human occupation of the region appears to have been associated with the availability of water.