Late Pleistocene temperature reconstruction of the interior Kalahari Plateau of Northwestern Botswana

Abstract. Late Quaternary climate reconstructions for southern Africa remain poorly constrained due to the scarcity of paleotemperature data, particularly across the interior, highly elevated Kalahari Plateau. This study addresses the gap by focusing on the Late Pleistocene period in Ngamiland of NW Botswana. We conducted an integrated and multi-proxy mineralogical and isotope geochemical study of marlstones, fossil gastropods, soil concretions, calcretes, and pan and lake sediments from short cores and outcrops of the Kalahari Group near the Tsodilo Hills. Our approach was applied to address the following objectives: (i) identify primary carbonates using petrographic screening, (ii) constrain the hydroclimate using δ¹³C and δ¹⁸O stable isotope signatures and processes, (iii) provide new age constraints of deposition using radiocarbon ¹⁴C dating, and (iv) interpret paleotemperatures by analysing clumped isotopes (∆₄₇) and dual clumped isotopes (∆₄₇-∆₄₈). This multi-proxy approach aimed at defining a robust proxy to reconstruct the Late Pleistocene climate in the interior Kalahari. Our studies revealed that the sediments were deposited between 49.05 ± 1.98 and 24.89 ± 0.13 ka BP ago based on 14C calibrated ages (SHCal20). The marlstones, calcretes and soil concretions are micritic and sparitic with evidence of bioturbation, whereas fossil gastropods are devoid of reworking and suited for paleoclimate studies. The δ¹³C and δ¹⁸O values range between 0.1 and 4.2 ‰ VPDB and -0.3 and 9.4 ‰ VPDB, respectively while measured ∆47 temperatures range between -3.1 and 47.5 ^oC. Stable isotope variations suggest a strong biological control in the soil concretions, whereas the groundwater signature is likely overprinted in the calcretes, and a combination of meteoric and groundwater has influenced the texture of marlstones. The extreme temperatures are attributed to organic contaminants in the sediments. It is interpreted that fossil gastropods retain the primary geochemical signatures based on the stable and clumped isotope variations and therefore represent the most reliable material for climate reconstructions in the region. Our study has provided the first direct temperature estimates of the Late Pleistocene for the interior Kalahari region from these gastropods which appear to be cooler than the present at ~15 ^oC. This study therefore addresses a major data gap in southern African paleoclimate records, which has implication for global climate models.