Includes abstract. / Includes bibliographical references. / Like many of the world’s subtropical regions, the Western Cape of South Africa is highly sensitive to oscillations in the earth’s climate system triggered by major tectonic changes, local variations in orbital forcing, better known as Milankovitch cycles, and its position at the interface between temperate and tropical circulation systems. Regrettably, a dearth of reliable and continuous palaeoenvironmental records means that relatively little is known about how regional environments have been impacted over centennial to multi-millennial timescales. Palaeosols constitute an important stratigraphic marker for past environments and may provide useful validation of pedogenic and other earth system process models. However, the characterisation and analysis of palaeosols has been a largely neglected source of information in the Western Cape, South Africa. This thesis aims to improve the understanding of the environments and climate dynamics using evidences from palaeosols. Various palaeosol-based proxies including geochemistry, mineralogical, macro- and micromorphological, δ13C and δ18O isotope, and selected physico-chemical properties of palaeosols were studied and records obtained for four sites in the Western Cape. A number of chemical weathering indices and geochemical climofunctions were used to calculate weathering intensities, pedogenesis, palaeotemperature and palaeoprecipitation for the various locations using geochemical and stable isotope data. Results of this study indicate that palaeosol-based proxies have the potential to provide snapshots into the palaeoenvironments and palaeoclimate of Western Cape and may complement previous studies done with other proxies such as pollens and diatoms. For example, the interpretation of the pedofeatures (calcareousness, vertic, gleyic, illuviation) - from the micromorphology - of thepalaeosols suggests cyclic patterns of erosion and deposition that correlate with climate changes of the past. Podzolization and laterization are the principal pedogenic processes responsible for the red palaeosol formation at the Cape Peninsula, while calcification and salinization are accountable for the Quaternary palaeosols. Inferences of gleization and lessivage are only evident in the mid-Miocene palaeosol at Langebaanweg. At LBW, pedogenesis was more advanced in the Mid-Miocene and Early Pliocene layers signifying a more humid and warmer climate with more stable landscape. Two major regional climate cycles were evident at the Cape Peninsula: relatively warm and humid subtropical climate which gave rise to the pedogenically modified buried red palaeosol and dry semi-arid Mediterranean climate under which the soils overlying the stone line is currently forming, as seen from the poor horizonation and translocation of materials. Clay mineral assemblages suggest the Quaternary palaeoclimate of the Western Cape has been predominantly characterised by low precipitation and active coastal erosion, which jointly accounted for poor soil profile development. This is in agreement with the early reports obtained from marine records of the African continent (e.g. deMenocal, 2005). A cross plot of the δ13C and δ18O of the carbonate palaeosols indicates they all formed under strong marine influence and C3 plants have been dominant since late Quaternary.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/4849 |
| Date | January 2013 |
| Creators | Eze, Peter Ndubuisi |
| Contributors | Meadows, Michael E |
| 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, Ph D |
| Format | application/pdf |
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