Recycling of the Kalahari Duricrusts with implications for the long-term resilience of cratonic landscapes

Continental duricrusts cover >10% of Earth’s land surface and play a fundamental role in preserving cratonic landscapes, yet the diagenetic processes controlling their formation and their relationship to long-term landscape evolution remain poorly constrained. Here we present a comprehensive high-resolution analysis of duricrust diagenesis in the Kalahari Basin, southern Africa, integrating optical and cathodoluminescence petrography, electron microprobe elemental mapping, LA-ICP-MS geochemistry, stable and radiogenic isotope analysis, and cosmogenic nuclide dating to reconstruct the evolution of the African Surface.
Analyses from contrasting structural blocks north and south of the Okavango Rift Zone reveal a complex six-phase diagenetic sequence spanning the Pleistocene to Recent, with evidence for Kalahari Duricrust preservation extending to Neogene age in the northern block. Palustrine micrite of 1.4–1.1 Ma display depleted stable isotope values (δ¹³C: –8.2 to –6.8‰; δ¹⁸O: –9.0 to –7.1‰), indicating precipitation from meteoric waters in an open system influenced by rift subsidence. Subsequent phases include fractured filling cements that concentrate metals under reducing conditions, evaporative Sr–Mg-rich cements (Sr: 6067±1659 ppm; Mg/Ca: 0.53; δ¹³C: –2.0 to –1.6‰) indicating hypersaline closed-basin conditions, void-filling calcites recording fluid mixing, extensive silicification and replacement under humid conditions, and late fracture fillings in evaporative settings.
Cosmogenic nuclide burial dating establishes a chronological framework revealing episodic formation with major unconformities at 1.4-1.1 Ma and 0.74±0.14 Ma, coinciding with regional structural reorganization. Exposure and burial ages of 135-140 ka from the southern structural block document the most recent landscape-forming event during the MIS6-MIS5 transition.
Our findings demonstrate that the African Surface in the Kalahari represents a dynamic system where weathering on structural highs supplies solutes that precipitate as duricrusts in adjacent basins through episodic diagenetic recycling. The continuum of in situ alteration and laterally transported cementation explains how duricrusts simultaneously archive ancient weathering signals while remaining subject to ongoing transformation. This duality provides a process-based explanation for the resilience of cratonic landscapes and establishes duricrusts as critical archives for reconstructing Earth’s long-term surface evolution, challenging traditional models of passive landscape preservation in favor of active internal reorganization.
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