The intersection of archaeological material with the landscape is investigated using OSL dating of landforms associated with Middle Stone Age (MSA) archaeology in the Makgadikgadi basin, Botswana. In this study, MSA archaeological sites on the Makgadikgadi pan floor date to two dry periods in the basin during the late Quaternary. Site formation at one site occurred during dry, or seasonally dry conditions that followed a period of high lake levels between 128 ± 18 ka and 81 ± 6 ka. The site was buried by sediments from a subsequent period of high lake levels dating to between 72 ± 5 ka and 57 ± 8 ka. At other investigated sites, the archaeological material was most likely deposited during a second dry period sometime after this. Overlying dunes are much younger (late Holocene) than the late Pleistocene lakebed sediments associated with the archaeological sites. Rapid burial of the archaeological sites by clayey sands has resulted in limited disturbance and weathering of archaeological material which appears to have only been exposed very recently, perhaps in the last 350 years when conditions have been particularly dry and susceptible to deflation. The spatial patterning of both sediment accumulation and deflation strongly influences archaeological visibility both within and around the Makgadikgadi basin.
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The Quiescent Model: Several researchers (e.g. McFarlane and Eckardt, 2006; Moore et al., 2012) not unreasonably suggest that following the reorganization of fluvial inflow systems, Makgadikgadi effectively dried up in the mid-Pleistocene leaving an exposed basin floor that was dry or seasonally dry and, by comparison to the Pliocene and early Pleistocene, was hydrologically inactive during the late Quaternary and Holocene. Evidence cited to support this idea comes from in-situ surface archaeology, namely artefacts assigned to the Early Stone Age (ESA) on the floor of the 945 m asl Palaeolake Magkadikgadi configuration, 6 km north of Gweta (McFarlane and Segadika, 2001), and at Ngcaezini Pan, 18 km north of Gweta (Robbins and Murphy, 1998) between the 945 and 920 m elevation palaeo-lake shorelines. The implication is that the basin must have been dry since the ESA, a techno-typological era that ended elsewhere in southern Africa ∼300 kyrs ago (Wurz, 2020). Similarly, Grove (1969), whose work identified and mapped the shorelines of the palaeolake system, suggested high-lake stands must have pre-dated the Middle Stone Age (MSA) deposits that had been identified by Bond and Summers (1954) on the Nata River that feeds into Sua Pan in the east (Fig. 3a). Since Grove's work, other MSA sites have been recorded right across the Makgadikgadi basin (e.g. Ebert, 1979; Ebert and Hitchcock, 1978; Hitchcock, 1982; Robbins, 1987; Van Waarden, 2010). While both the ESA and MSA material in the basin have no established chronology, the implication of their presence on the lakebed as in-situ sites (i.e. the material has not been washed into the basin from the shorelines) is that a period of hydrological quiescence has prevailed since these artefacts were deposited.Fieldwork was carried out under research permit EWT 8/36/4 XXXV (9), issued April 22, 2016 by the Botswana Ministry of Environment, Wildlife and Tourism (ref EWT 8/36/4 XXXV (52)), extended on June 29, 2018 by the Botswana Ministry of Environment, Natural Resources, Conservation and Tourism (ref ENT 8/36/4 XXXXII (43)). The project was funded by Research Project Grant RPG-2015-344 awarded by the Leverhulme Trust. Additional funding and resources were gratefully received from the University of Botswana, the University of Oxford, the University of Brighton, and the University of Oslo. The archaeological aspects of the project would not have been possible without the significant contribution to fieldwork by students from the University Botswana including Topo Mpho Chengeta, Cathy Legabe, Casper Lekgetho, Jane Masisi, Agang Motlaleng and Oratile Rt Ramore. SLB would also like to acknowledge contributions from the Returning Carers Fund and the Trapnell Fund, at the University of Oxford. We also wish to acknowledge the support of the National Museum of Botswana for laboratory space and equipment loans. Our appreciation goes to the local communities of Gweta and Nata and to Ralph Bousfield and Natural Selection for generous advice, access to the field research station, facilities and storage, and field assistance. We also thank the owners and staff of Gweta Lodge for field assistance and sharing of local knowledge and assistance with community engagement. Finally we would like to thank two anonymous reviewers for their positive and helpful suggestions to improve the manuscript.
The project was funded by Research Project Grant RPG-2015-344 awarded by the Leverhulme Trust . Additional funding and resources were gratefully received from the University of Botswana , the University of Oxford , the University of Brighton , and the University of Oslo . The archaeological aspects of the project would not have been possible without the significant contribution to fieldwork by students from the University Botswana including Topo Mpho Chengeta, Cathy Legabe, Casper Lekgetho, Jane Masisi, Agang Motlaleng and Oratile Rt Ramore.
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