Ostracod-based reconstruction of Late Quaternary playa-lake system evolution within the Makgadikgadi basin, Central Kalahari

The Makgadikgadi Basin (MKB) is a 37,000 km² wide complex playa-lake system in northeastern Botswana. It is a relic of the Paleolake Makgadikgadi, situated in the central part of the Kalahari Basin. Reconstructing the Quaternary depositional and environmental history of the playa-lake system has great significance for revealing the basin's evolution. However, its sedimentary record remained largely unexplored due to methodological challenges. The current study uses a multi-proxy approach integrating AMS ¹⁴C dating of ostracod shells, lithofacies characterization, and ostracod-based biostratigraphy on four ∼1.6 m-long cores collected from the Ntwetwe Pan (Western MKB). The age-depth model and the principal component analysis of ostracod relative abundance data, constrained by key sedimentological variables, effectively defined three statistically significant assemblages and show three major phases of evolution of the MKB: (1) Late Pleistocene (∼29–17 ka BP): Perennial to seasonal, hyperhaline-polyhaline lake, dominated by ostracod assemblage of S. glabrata in association with L. cf. africana; (2) Middle Holocene (∼7.6–5.2): playa margin setting, which formed after a hiatus between ∼17 and 6.3 ka BP, and (3) Middle to Late Holocene (∼5.2 ka BP to present). The last phase is further subdivided into three sub-phases: (i) ∼5.2–1.6 ka BP playa-lake system with semi-permanent, freshwater to oligohaline conditions, which favored Potamocypris group, I. gibba, and Candonopsis spp., (ii) ∼1.6 ka BP, a shift toward nearly desiccated alkaline ephemeral salt pans dominated by desiccation-resistant species, i.e., H. giesbrechtii, and (iii) ∼1 ka BP to present, establishment of the current shallow, high-alkaline brine with high evaporative regimes, dominated by brackish water ostracod species (L. inopinata), indicating seasonally fluctuating playa-lake systems. This multi-proxy core analysis provides a high-resolution archive of Kalahari hydroclimatic variability, revealing a transition from perennial hyperhaline conditions to ephemeral high-alkaline wetlands, associated with progressive regional aridification and shifts in southern African hydroclimate since 29 ka BP.