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Title: Landscape evolution in Namibia and Antarctica : quantifying denudation rates using in-situ cosmogenic isotope analysis
Author: Cockburn, Hermione Anne Phoebe
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1998
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In-situ cosmogenic 10Be, 26A1 and 21Ne concentrations from locations in central Namibia and the Transantarctic Mountains, Antarctica have been used to investigate rates of landscape change in passive margin settings and contrasting hot and cold arid conditions. Concentrations of cosmogenic 10Be and 26A1 in quartz separated from 14 samples from the Gamsberg in central Namibia have been measured using accelerator mass spectrometry. The Gamsberg is a flat-topped residual forming part of the Great Escarpment of central Namibia. Rates of summit denudation range from 0.2 to 0.8 m Ma-1 and rates of slope retreat have been ˜10 m Ma-1 over the past 0.04 to 1.5 Ma. The data indicate that backwearing is much more significant than downwearing but that summit denudation is occurring. Low rates of escarpment retreat of ˜10 m Ma-1 are incompatible with the idea that retreat from the coast has been at a uniform rate since rifting occurred ˜130 Ma BP. The data are consistent with geological evidence and data from apatite fission track thermochronology that suggest that the escarpment retreated rapidly soon after rifting but has not retreated significantly during the Tertiary. Measurements of cosmogenic 10Be and 26A1 from three granite borhardts on the coastal plain of Namibia seaward of the Great Escarpment in the arid/hyper-arid central Namib Desert indicate mean rates of summit lowing ranging from2.2 to 6.3 m Ma-1 over the pat 1-3 x 105 a. Low variability in estimated denudation rates between the sampling sites and the long term persistence of an arid climate implies that a rate of summit lowering of ˜5 m Ma-1 has characterised bedrock exposures in the central Namib for at least the past 10 Ma. It has been demonstrated that in-situ cosmogenic isotope analysis can provide unobtainable data on denudation rates over timescales intermediate between short-term process studied and long-term estimates from techniques such as thermochronology. Cosmogenic isotopes analysis has significant potential for evaluating controls on denudation rates in a range of geomorphic settings and constraining models of long-term landscape evolution.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available