Palaeoflood chronology of blocked-valley lakes in eastern South Africa

Wood, Jamie Callum (2020) Palaeoflood chronology of blocked-valley lakes in eastern South Africa. PhD thesis, University of Gloucestershire. doi:10.46289/9JL99YR8

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Relatively few studies have examined blocked-valley lakes as potential palaeoenvironmental archives and until now radiometric chronologies for these geomorphic features have been limited to 210Pb and radiocarbon dating. With a particular focus on chronicling palaeoflood events, this study aimed to evaluate quartz optically stimulated luminescence dating (OSL) as a technique for dating of clastic sediment within blocked-valley lake deposits upon the Mfolozi catchment, eastern South Africa. A flood chronology was produced for sediments collected from a blocked-valley lake basin on the southern margin of the Mfolozi floodplain, using a combination of OSL, 14C AMS dating and Bayesian modelling. This was complemented by OSL flood chronologies produced for an avulsion channel and a crevasse splay situated on the central and northern areas of the floodplain respectively. The suitability of OSL for dating blocked-valley lake deposits was dependent on the mode of De acquisition. Ages calculated for multi-grain aliquots of fine silt tended to overestimate age owing to partial bleaching, whilst adoption of single-grain OSL enabled De modelling and calculation of appropriate ages. The Mfolozi flood chronologies extended to a maximum of c. 7.2 ka and displayed close relation to regional climatic observations. During phases of climatic warming flood frequency appeared to increase, whilst for climatic cooling flood occurrences decreased until ceasing at lowstands, such as the mid-Holocene neoglacial and Little Ice Age (LIA). Further to the work upon blocked-valley lake sediments, this study investigated the Hydrofluoric acid (HF) etching of quartz grains within the 180-250 μm fraction and the impact of varying treated sample mass and etching time upon naturally-dosed single-grain De distributions. Adoption of strict rejection criteria highlighted sample-dependent systematic changes in overdispersion (OD) with increased HF treatment time whilst De distribution appeared to normalise when treated sample mass was reduced. No variations in central De values were detected across each of the treatment scenarios and it is suggested that the α-component either has a negligible impact upon central De or can not be effectively removed using HF.

Item Type: Thesis (PhD)
Thesis Advisors:
Thesis AdvisorEmailURL
Subjects: G Geography. Anthropology. Recreation > GB Physical geography
Divisions: Schools and Research Institutes > School of Education and Science
Depositing User: Susan Turner
Date Deposited: 24 Apr 2024 11:32
Last Modified: 24 Apr 2024 11:33

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