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

Abstract

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 10 Be and 26 Al. Apparent soil production rates define a steep, inverse exponential function of soil depth with a maximum of 143 m Ma À1 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 À1. The Bredbo River catchment average erosion rate is 1571 m Ma À1 , and is similar to the average hillslope erosion rate of 1671 m Ma À1 . Bedrock incision rates average 9 m Ma À1 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 À1 , 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. r

Erosion in northwest Tibet from in‐situ‐produced cosmogenic 10Be and 26Al in bedrock

“…This is because the study area is located in a low-relief plateau and in fact our results are consistent with that obtained for the interior of the Tibetan plateau (Lal et al, 2003). Previous comparison of erosion rates for bedrock and catchment sediments shows that the differences are within a factor of two Clapp et al (2000) 240 30 29 ± 6 active to five (Bierman, 1994;Heimsath et al, 2001). Clearly the tremendous difference in denudation rate within different time intervals in northwest Tibet is not an artifact of dating material.…”

On the potential for regolith control of fluvial terrace formation in semi-arid escarpments

“…Globally, α has been measured between 0.017 and 0.042 cm −1 (Heimsath et al, 2001(Heimsath et al, , 2005. The highest values result in slightly thinner soils that are equivalent within error to the modelled soil thicknesses using α = 0.03 cm −1 (see Norton et al, 2014).…”

A Simple Model of the Variability of Soil Depths

“…The San Gabriel Mountain data of Southern California [45] demonstrate the variation of soil depths along a gradient in topographic relief, and thus erosion rates, but not of climate. We have found particle size data for only five of the data sets below, and even in some of these cases we had to generate a median particle size from graphic representations of what are considered to be typical distributions of particle diameters for a given texture [48].…”