Late Quaternary erosion in southeastern Australia: A field example using cosmogenic nuclides

Late Quaternary rates of apparent soil production, bedrock incision, and average erosion are determined for the southeastern highlands of Australia using in situ produced cosmogenic nuclide concentrations of ¹⁰Be and ²⁶Al. Apparent soil production rates define a steep, inverse exponential function of soil depth with a maximum of 143 m Ma^-1 under zero soil depth. There were no observed soil depths between about 25 cm and zero, however, such that the maximum observed rate is about 50 m Ma^-1. The Bredbo River catchment average erosion rate is 15 ± 1 m Ma^-1, and is similar to the average hillslope erosion rate of 16 ± 1 m Ma^-1. Bedrock incision rates average 9 m Ma^-1 and suggest that the higher rates of hillslope erosion may be in response to a pulse of incision, perhaps generated by knickpoint propagation. Bedrock erosion rates inferred from a tor profile average 3.8 m Ma^-1, with higher rates on other, more weathered tor tops. An aboveground tor profile of nuclide concentrations is consistent with a simple model of rapid stripping of the surrounding saprolite, supporting the view that at least one episodic period of increased denudation has affected the landscape evolution of the highlands. We test this hypothesis by using a simple landscape evolution model to reasonably predict the spatial variation of soil depth as well as the emergence of tors.