Summary in English. / Bibliography: leaves 263-292. / This thesis presents new palaeoenvironmental evidence from the semi-arid lowlands of the West Coast Sandveld, which prompts a fresh synthesis as to the nature of late Quaternary environmental changes in the southwestern Cape's fynbos biome. The study is centred on Verlorenvlei, a remote coastal lake and swamp system which is ideally situated to investigate the complex interactions between late Holocene climate change, vegetation change, sea-level fluctuation, lacustrine/estuarine/fluvial sedimentology and human activity in the Sandveld region. In addition, this region of the West Coast has provided Quaternary scientists with a rich archaeological record against which independent lines of palaeoecological evidence can be evaluated. In support of the study, a wide range of palaeoenvironmental techniques has been applied to sediments sampled from the Verlorenvlei area. Organogenic deposits have been radiocarbondated and subjected to pollen analysis and assorted sedimentological and geoarchaeological assessments. Preliminary fossil pollen data from Elands Bay Cave, assembled for the period following the Last Glacial Maximum until approximately the terminal Pleistocene, are suggestive of moister and possibly cooler conditions in the Sandveld at this time. This is in contrast to prevailing evidence from the summer rainfall region of the subcontinent. Particle size analysis and an assessment of the in situ fossil Mollusca from vibracores, derived from the estuarine reaches of Verlorenvlei, reveal substantive evidence for rapid sea-level fluctuations along the West Coast during the mid-Holocene. Further inland, several mid-Holocene higher sea-levels are reflected in the palynology of lacustrine cores derived from Grootdrift and Klaarfontein. Detailed pollen diagrams, presented from Grootdrift, Klaarfontein, Muisbosskerm and Spring Cave, reflect the regional vegetation history during several periods over the last 7 000 years. There is convincing evidence from these data that the first half of the Holocene - commensurate with the Holocene hypsithermal - was associated with reduced moisture availability, and hence arid conditions along the West Coast. By contrast, there is evidence from the latter half of the Holocene that conditions ameliorated in the Sandveld around 3 000 BP and that moisture was, at this time more freely available. Following a hiatus in sedimentation some time after 4 000 BP, marine conditions are no longer visible in Verlorenvlei, having been replaced by fresh water as the dominant hydrological regime. A high resolution palynological investigation of the Grootdrift wetland sediments has contributed to a detailed palaeolimnological reconstruction of the upper Verlorenvlei system since the time of colonial expansion into the area, some 300 years ago. The picture reveals a sequence of rapid ecological changes in the face of progressive human disturbance. Arising from these insights, a number of recommendations for the management of dryland aquatic ecosystems such as Verlorenvlei, are presented. The significance of these late Quaternary palaeoenvironmental changes, in terms of the biogeography of plants and animals and also in terms of human occupation of the region, is examined.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/13880 |
| Date | January 1997 |
| Creators | Baxter, Andrew James |
| Contributors | Meadows, Michael E, Davies, Bryan |
| Publisher | University of Cape Town, Faculty of Science, Department of Environmental and Geographical Science |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Doctoral Thesis, Doctoral, PhD |
| Format | application/pdf |
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