Duricrust Diagenesis in the Kalahari Basin With Implications for Mineral Recycling and the Long-Term Resilience of Cratonic Landscapes

Duricrusts cover more than 10% of Earth’s land surface. They armor cratonic landscapes and retard erosion, yet the diagenetic processes governing their internal evolution remain incompletely understood. We present an integrated micro-analytical study of duricrust diagenesis in the Kalahari Basin, southern Africa, combining cathodoluminescence petrography, electron microprobe elemental mapping, laser ablation ICP-MS, stable and radiogenic isotope geochemistry, and cosmogenic nuclide dating.

Two sites on contrasting structural blocks flanking the Okavango Rift Zone, comprising predominantly calcareous duricrusts, reveal a six-facies paragenetic sequence spanning the Middle Pleistocene. The northern site (KPH) records open-system meteoric-phreatic cementation with depleted stable isotope values (δ¹³C: −8.2 to −6.8‰; δ¹⁸O: −9.0 to −7.1‰) and progressing radiogenic ⁸⁷Sr/⁸⁶Sr signatures indicating interaction with Archaean crystalline basement. The southern site (OKW) preserves an evaporative concentration sequence yielding carbonates with extreme strontium enrichment (median 6452 ppm) and high Mg/Ca ratios (median 0.61), followed by aggressive dissolution and replacement by authigenic Mg-silicates during humid intervals.

Cosmogenic nuclide burial ages of 1.4–1.1 Ma for palustrine carbonates at KPH, capped by aeolian sand emplaced by 0.74 ± 0.14 Ma, and exposure ages of 145–352 ka of the granitoid-gneiss plateau at OKW, demonstrate that duricrust formation and modification in structural blocks situated less than 200 km apart record contrasting histories of accumulation, stripping, and re-cementation. Together, the chronological framework reveals that mineral recycling within duricrust profiles can proceed orders of magnitude faster than basin-average erosion.

Within the limits of the two studied profiles, these results show that duricrusts represent dynamic recycling systems in which arid phases build reactive mineral reservoirs that are rapidly dissolved and reprecipitated during humid phases. Solute transport from structural highs to adjacent lows derives from various sources, through both surface and subsurface pathways in fractured host rocks, maintaining chemical reactivity within apparently stable landscapes. Cratonic landscape resilience thus arises from continuous internal reorganization rather than passive preservation.