Palaeoenvironmental reconstruction of Kathu Pan, South Africa, based on sedimentological data

Abstract

Several studies have highlighted the importance of collecting well-dated records of palaeoenvironmental changes on desert margins, particularly in the semi-arid interior of southern Africa. Here we describe sediments at three sites in Kathu Pan, a pan complex overlying karstic bedrock at the southern edge of the Kalahari Basin. Sinkholes have exposed sedimentary sequences dating back to the Pleistocene, making it possible to document multiple palaeoenvironmental regimes in this landscape. Using a multi-analytical sedimentological approach, including micromorphology, energy dispersive X-ray spectrometry, electron microprobe, loss-on-ignition, laser diffractometry and luminescence dating, we demonstrate that the sediments at Kathu Pan represent an environment fluctuating among a number of thresholds for accumulation of different kinds of transported and authigenic sediments. Within the Pleistocene sands at the base of our studied sedimentary sequence, the presence of palygorskite, indicative of less extreme evaporative control, represents a semi-arid environment from 156 ± 11 ka to 32 ± 2 ka (Marine Isotope Stages 6–3). Increased moisture availability at 84 ± 4 ka and at 96 ± 5 ka (possibly during Marine Isotope Stages 5a and 5c, respectively) is reflected in the sands by the formation of palygorskite in concert with the deposition and oxidation of organic material. As the climate became increasingly arid, possibly in response to global cooling during the Last Glacial Maximum (21 ± 2 ka), Kathu Pan crossed a threshold, and deposition of CaCO3 dominated over that of palygorskite. In the Holocene beds within our studied unit, alternating CaCO3- and organic-dominated deposits, sometimes in very fine laminae, reflect an increase in the amplitude of either seasonal or annual changes in water availability.