Effects of long soil surface residence times on apparent cosmogenic nuclide denudation rates and burial ages in the Cradle of Humankind, South Africa

Prolonged soil surface residence times of up to 1.5 million years in the Cradle of Humankind, South Africa, can lead to significant underestimation of cosmogenic nuclide-derived denudation rates and overestimation of burial ages when using standard assumptions. Researchers analyzed concentrations of 10Be and 26Al in bedrock and soil above Rising Star Cave, where Homo naledi fossils were discovered, revealing that apparent denudation rates derived from soil samples are 2-3 times lower than those from bedrock. Additionally, the 26Al/10Be ratio in soils was significantly lower than the surface production ratio, indicating complex exposure histories. These findings suggest that long near-surface residence times can distort single-nuclide (10Be) catchment-wide denudation rates and burial age estimates if pre-burial ratios are assumed based on surface production alone.

Makhubela, T. V., Kramers, J. D., Scherler, D., Wittmann, H., Dirks, P. H. G. M., & Winkler, S. R. (2019). Effects of long soil surface residence times on apparent cosmogenic nuclide denudation rates and burial ages in the Cradle of Humankind, South Africa. Earth Surface Processes and Landforms, 44(15), 2968–2981. Portico. https://doi.org/10.1002/esp.4723