Southern Africa displays a high topography but paradoxically exhibits tectonic stability and low denudation rates. Here the present controls on denudation in southern Africa are investigated by comparing maximum denudation rates for Karoo dolerite surfaces in the region, determined from the abundances of cosmogenic noble gas nuclides (3He, 21Ne and 38Ar) in pyroxenes, with the predictions of a climate-dependent weathering rate model. In general, we find an excellent agreement in the value ranges of both datasets (<4m/Myr), and interpret this as evidence that present denudation in southern Africa is weathering-limited and climatically influenced due to an apparent absence of significant regional neotectonic uplift. The onset of this geodynamic coupling is unknown but may be of considerable antiquity, thus allowing for the prolonged tenure of southern Africa's inherited Cretaceous topography.

Soil erosion has been considered a major problem in South Africa since the early 20th Century, yet the degree to which rates of soil erosion may exceed rates of soil production has not been well constrained by previous studies. Here we present 22 cosmogenic He-3-based maximum denudation rates of Karoo dolerite bedrock surfaces, and interpret these values as local rates of soil production. These generally low soil production rates (<4 m/Myr measured over a 10(5) yr timescale) are in all instances lower than various literature estimates for the corresponding rates of soil erosion in the same catchments, by up to two orders of magnitude. This significant contrast between long term rates of soil production and short term rates of soil erosion suggests that current agricultural practices are unsustainable under prevailing geological conditions.

Southern Africa displays an anomalously elevated landscape with a modal elevation of approximately 1000 m above sea level, even though the region is not associated with convergent plate boundaries or active rifting. The origin and evolution of this region’s topography may be constrained by determining the rates of surface processes on intermediate timescales (103 – 106 yr) with in situ-produced cosmogenic nuclides. Here we present minimum exposure ages and maximum denudation rates for Karoo dolerite surfaces across southern Africa, based on the cosmogenic noble gas inventories (3He, 21Ne) of pyroxene separates. Our minimum exposure ages for vertical and inclined scarp faces vary from ~20 to ~380 ka. Maximum denudation rates for horizontal surfaces are consistently low, and generally less than 3-4 m/Myr. These low denudation rates are compatible with a currently stable landscape, and suggest that southern Africa’s topography developed under a significantly different tectonic and/or climatic regime.

Crassulacean acid metabolism (CAM) photosynthesis, a flexible adaptation to water-stress, has not been shown to occur before the Pleistocene, despite suggestions that CAM first evolved in the Mesozoic or earlier. Here we report on multiple (>= 7) positive organic carbon isotope excursions (delta C-13(org) > -20%) in Late Triassic and Early Jurassic (c. 200 Ma) sedimentary rocks from an arid terrestrial ecosystem in South Africa. These excursions are interpreted as evidence of the episodic dominance of CAM plants in response to heightened aridity in the heartland of Gondwana, and hint at climatic instability in a greenhouse world.