The Great Karoo spans the north-central part of South Africa at a major climatic boundary. The characteristics, spatial patterns and drivers of river channel response to Late Quaternary climate changes in the Sneeuberg, South Africa remain unclear due to the discontinuous alluvial stratigraphic record and the lack of dated palaeoclimatic archives. Dendritic channel networks in the upper Sundays River are deeply incised exposing terrace fills of varying thickness (2-6 m), extent (1 - > 10km) and pedogenic overprinting. Channels exhibit 'stepped' long profiles where resistant rock strata (dolerite, sandstone) cross valley floors, but are now partially or completely breached. DGPS surveys, sediment logging, mineral magnetic measurements and radiometric dating (OSL and 14C) were used to determine the source, age structure and depositional process of valley fills and ascribe intensity of pedogenic overprinting. A conceptual model of terrace development in relation to changing conditions of connectivity was tested. First order streams were desensitised to late Quaternary base level changes downstream due to the blocking effect of two barriers, with localised autogenic 'cut and fill'. Contrastingly, the continuity of 4 fill terraces over incised barriers in 2nd-4th order tributaries indicate relatively high sensitivity to post-LGM climatic change. However, deposition of alluvium (T2) inset within periglacial deposits (T1) was partly a complex response to re-connection of the channel network with deep upland colluvial stores resulting in the valleys becoming choked with sediment. This caused a rise in groundwater and formation of extensive (> 10 km2) rootmats on valley floors, restricting depth of subsequent channel entrenchment (T3/T4). This study presents one of the first attempts in South Africa to test and explain terrace genesis and correlation using existing conceptual models for sediment connectivity. The relative roles of periglaciation and fluvial activity are shown to be key influences on dynamics of Quaternary sedimentation, pedogenesis and erosion and help to explain how sediments can be preserved over long periods (104 years) in catchments subject to base level fall.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:706850 |
| Date | January 2016 |
| Creators | Oldknow, C. J. |
| Publisher | University of Liverpool |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://livrepository.liverpool.ac.uk/3002474/ |
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