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Accueil du site → Master → Afrique du Sud → 2020 → Determination of erosion rates along the Mpumalanga Escarpment using the cosmogenic isotope beryllium-10

University of Johannesburg (2020)

Determination of erosion rates along the Mpumalanga Escarpment using the cosmogenic isotope beryllium-10

Konyana, Sibusiso

Titre : Determination of erosion rates along the Mpumalanga Escarpment using the cosmogenic isotope beryllium-10

Auteur : Konyana, Sibusiso

Université de soutenance : University of Johannesburg

Grade : Magister Scientiae in Geology 2020

Résumé
In this study the chemical separation procedure for cosmogenic beryllium-10 ( 10Be) in quartz for analysis by accelerator mass spectrometry (AMS), as well as the necessary sample preparation procedures, were established, and the methodology was applied to the determination of erosion rates in a section of the eastern Escarpment in the Mpumalanga and Limpopo Provinces of South Africa between 24°30’ S and 27° S, to fill a gap in the existing database of erosion rates along the Southern African Great Escarpment. Sample preparation was done in the Spectrum analytical facility of the Faculty of Science at the University of Johannesburg, the chemical separation was carried out in the ultraclean Wits Isotope Geology Laboratory (WIGL) at the University of the Witwatersrand, and the AMS analyses were carried out at iThemba Labs in Johannesburg. The chemical separation procedure makes use of two successive ion exchange column steps : The first employs an anion ion exchange resin and the second a cation exchange resin. The second one in particular required careful calibration, which was done for two column volumes (1and 2 ml resin respectively), using inductively coupled plasma optical emission (ICP-OES) spectroscopy. The samples analyzed comprised six stream sediments taken in rivers draining the eastern Escarpment to determine catchment-wide erosion rates, as well as five rock samples taken from outcrops close to the escarpment crest, for comparison. Erosion rates determined from the river sediment samples range from 3.9 ± 0.3 to 16.6 ± 1.1 meters per million years (m/Ma), while those for outcrop samples range from 1.77 ± 0.15 to 23.9 ± 3.2 m/Ma. This much larger range for bedrock samples than for river sediments demonstrates, once again, the averaging over catchment areas achieved by analyzing river sand. The range of values obtained is similar to erosion rates determined in other parts of the Great Escarpment, except in the high Drakensberg escarpment east of Lesotho, where values up to 80 m/Ma have been previously determined for stream sediments, and up to 200 for bedrock samples.

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Page publiée le 30 janvier 2021