Pleistocene environments in the southern Kalahari of South Africa

Abstract

When considering the pan-African process of human evolution in the Pleistocene it is important to review our understanding of climate on a regional scale, including heterogeneity due to regional variability in the relative strengths of forcing mechanisms. Research in the Kuruman Hills at the southern edge of the Kalahari in South Africa has recently provided new insights into the complexity and distinctiveness of southern African palaeoclimate. Here we compare these records, obtained from Kathu Pan, Wonderwerk Cave, and Mamatwan Mine, focusing on the presence of water bodies from c. 2 million years before present to the end of the Pleistocene. Through the synthesis of multiple proxies we create a picture of localized water availability as it would have affected hominin adaptation. These records are then framed within a larger discussion of regional climate and environmental change. The emerging record from the southern Kalahari suggests that the distribution of zones of rainfall seasonality varied significantly throughout the Pleistocene and a hominin presence is particularly found in association with wetter phases which supported lakes, springs and pans.

Introduction

Many of the hypotheses concerning the relationship between hominin evolution and climate change have been based on the eastern African archaeological record and associated palaeoenvironmental archives (e.g. Potts, 2013; Trauth et al., 2007; Mercader et al., 2021). However, emerging data from long-term research projects in the semi-arid interior of South Africa provides supporting evidence for environmental flexibility of hominins during the Pleistocene (e.g. Chazan et al., 2020; Ecker et al., 2018b; Lukich et al., 2020; Matmon et al., 2015; Vainer et al., 2018). Researchers have attempted to create syntheses of climatic patterns in southern Africa in general (Burrough et al., 2009b; Chase and Meadows, 2007; Gasse et al., 2008; Scott and Lee-Thorp, 2004; Stone, 2014), however, these studies highlight the difficulties of integrating data from various proxies that respond to different forcing factors across vast distances. Although the creation of regional syntheses has most often depended on one particular proxy at many sites to understand palaeoenvironmental changes, combining multiproxy reconstructions in a smaller geographic area can delve deeper into the intricacies of proxy response to one or many climatic systems through time, potentially leading to a more robust overall understanding of the environment at a particular place and time.

Three sites in South Africa's central interior, within 100 km of one another (Fig. 1), provide an opportunity to explore how different proxies respond to climatic change on a constrained local scale. Wonderwerk Cave and Kathu Pan are archaeological sites with associated palaeoenvironmental records located in the Northern Cape province of South Africa, at the margin of the Kalahari Desert and situated within the summer rainfall zone (Fig. 1). Following renewed excavations in the last decade, multi-proxy studies of these sites have produced updated interpretations of the palaeoenvironment in this region throughout the Quaternary (e.g. Chazan et al., 2020; Ecker et al., 2018b; Goldberg et al., 2015; Lukich et al., 2019; Lukich et al., 2020). The nearby Mamatwan mine has also been recently investigated and found to comprise deposits recording environmental change during the Mid-Pleistocene (Matmon et al., 2015; Vainer et al., 2018), although lacking in archaeological material. The variety of dating methods and environmental proxies used at these localities demonstrates the diversity of proxies commonly used in semi-arid regions to reconstruct palaeoenvironments (Table 1). In our sub-tropical research area, aridity and humidity are often interpreted from proxies rather than temperature, as moisture availability is crucial in semi-arid landscapes. Initially, faunal studies pointed to a wetter than present environment being a key environmental component of the Pleistocene in the elevated central interior of South Africa (see review in Brink 2016). This includes specialised grazing ungulates and wetland faunal species such as lechwe (Kobus leche) and waterbuck (Kobus ellipsiprymnus) which went extinct in the region at the end of the Pleistocene (Brink 2016). Other proxies, such as stable isotopes and pan sediments, have since further confirmed the paradigm of a Pleistocene environment defined by open grassland vegetation within a system of active lakes, springs and rivers. This vast area covered parts of the grassland, Nama-Karoo and savanna biomes in Southern Africa. In this paper, we focus particularly on the evidence for water availability at Kathu Pan, Wonderwerk Cave and Mamatwan. This discussion is positioned within a broader overview of nearby sites with palaeoclimatic evidence (Table 1, Fig. 1). This study emphasizes the importance of renewed investigation of previously studied sites using modern methods, especially in regions where the potential for discovering new archives is low and existing records have poor spatial coverage.