Bedrock erosion and relief production in the northern Flinders Ranges, Australia

Abstract

Cosmogenic 10Be concentrations in exposed bedrock surfaces and alluvial sediment in the northern Flinders Ranges reveal surprisingly high erosion rates for a supposedly ancient and stable landscape. Bedrock erosion rates increase with decreasing elevation in the Yudnamutana Catchment, from summit surfaces (13.96 ± 1.29 and 14.38 ± 1.40 m Myr-1), to hillslopes (17.61 ± 2.21 to 29.24 ± 4.38 m Myr-1), to valley bottoms (53.19 ± 7.26 to 227.95 ± 21.39 m Myr-1), indicating late Quaternary increases to topographic relief. Minimum cliff retreat rates (9.30 ± 3.60 to 24.54 ± 8.53 m Myr-1) indicate that even the most resistant parts of cliff faces have undergone significant late Quaternary erosion. However, erosion rates from visibly weathered and varnished tors protruding from steep bedrock hillslopes (4.17 ± 0.42 to 14.00 ± 1.97 m Myr-1) indicate that bedrock may locally weather at rates equivalent to, or even slower than, summit surfaces. 10Be concentrations in contemporary alluvial sediment indicate catchment-averaged erosion at a rate dominated by more rapid erosion (22.79 ± 2.78 m Myr-1), consistent with an average rate from individual hillslope point measurements. Late Cenozoic relief production in the Yudnamutana Catchment resulted from (1) tectonic uplift at rates of 30-160 m Myr-1 due to range-front reverse faulting, which maintained steep river gradients and uplifted summit surfaces, and (2) climate change, which episodically increased both in situ bedrock weathering rates and frequency-magnitude distributions of large magnitude floods, leading to increased incision rates. These results provide quantitative evidence that the Australian landscape is, in places, considerably more dynamic than commonly perceived.