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

Late Quaternary rates of apparent soil production. bedrock incision. and av erage erosion are determined for the southeastern highlands of Australia us ing in situ produced cosmogenic nuclide concentrations of Be-10 and Al-26. Apparent soil production rates define a steep, inverse exponential function of soil depth with a maximum of 143 in Ma(-1) under zero soil depth. There were no observed soil depths between about 25 cm and zero. however. such t hat the maximum observed rate is about 50 in Ma(-1). The Bredbo River catch ment average erosion rate is 15 +/- I m M-1, and is similar to the average hillslope erosion rate of 16 +/- I in Ma(-1). Bedrock incision rates averag e 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 propaga tion. 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 rapi d stripping of the surrounding saprolite, supporting the view that at least one episodic period of increased denudation has affected the landscape evo lution of the highlands. We test this hypothesis by using a simple landscap e evolution model to reasonably predict the spatial variation of soil depth as well as the emergence of tors. (C) 2001 Elsevier Science Ltd and INQUA. All rights reserved.