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Title: Reconstructing the Quaternary denudation history of the Orange River basin, southern Africa using cosmogenic 10Be and 26Al analysis
Author: Butler, Jonathan J.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2007
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Cosmogenic-nuclide based estimates of denudation rates applicable over time scales of 104 – 106 years exist for some localities in southern Africa, but there have been no equivalent catchment-wide studies in the Orange basin, the primary drainage basin of the subcontinent. In this study a regional-scale picture of catchment-wide denudation based on 10Be and 26Al is presented that shows rates varying from ~ 2 to ~ 50 mm ka-1. These rates are consistent with existing cosmogenic-derived site-specific estimates. The cosmogenic-derived denudation rates presented here, which provide mean rates over time scales of 104 – 105 years, also provide a benchmark against which rates estimated by other methods for the past few decades in catchments in the central Orange Basin can be compared. Such comparisons reveal that short-term denudation rates, which in some cases at least have been influenced by anthropogenic factors, have been up to two orders of magnitude higher than the longer term cosmogenic-derived rates. The major knickpoint on the Orange River, the Augrabies Falls, exerts a fundamental control on landscape evolution across the two-thirds of the basin area upstream, but the rates of channel incision above and below the Falls have not previously been constrained. Site-specific cosmogenic nuclide concentration of 10Be and 26Al from channel bed and interfluve samples from a range of sites across the complex anabranching channel system of the Augrabies Falls region indicate that channel incision rates in the higher gradient zone above the main falls average ~ 40 mm ka-1, whereas rates in the gorge section below the main falls are typically ~ 10 mm ka-1. Rates of denudation on interfluves of ~3 mm ka-1 show that local relief is increasing, albeit very slowly.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available