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Includes abstract. / Includes bibliographical references (leaves 93-102). / This study demonstrates that diatom analysis of lake sediment can provide very detailed information on long and short term climate change, hampered only by inconsistent sediment accumulation at Groenvlei. Further work may provide insight to periods which were not covered in this study.

Atmospheric pollution on the South African high veld is perceived as a concern because of the combination of heavy industry and climatic features that prevail in the region. The frequent occurrence of surface inversions (80 - 90 % of days in the winter months), permits the accumulation of pollutants near ground level. Although industrial stacks, and those of power stations in particular, are generally able to emit gaseous and particulate pollutants above the boundary layer, looping and fumigation of plumes may occur under convective conditions. Under such circumstances, the concentration of pollutants at ground level may be high, especially within 4 km of the stack. Since considerable damage to European and North American ecosystems has occurred as a result of atmospheric pollution, concerns were first raised in a report by Tyson, Kruger and Louw in 1988, that similar effects may be taking place on the eastern highveld region of South Africa. The current study was prompted in direct response to these concerns. The first major objective was to establish long-term monitoring sites whereby changes in the pedosphere in response to atmospheric inputs could be detected. The second objective was to characterise the soil collection and to determine whether any impacts are detectable at this early stage. Arnot power station was selected as the focal point of the study as it is a base-load power station, is the most distant from the industrial centres of Witbank, Middelburg and Gauteng and has been in operation for over twenty years. Fifteen sampling sites located in an arc ranging ENE to SE downwind of the power station were selected. Both topsoil and subsoil were sampled at each site. Details of geographical co-ordinates and site features were noted to enable reproducible resampling. Sampling took place in August 1996, but three sites were visited again in October and resampled to test the reproducibility of sampling. Although not statistically comparable, the soils of each site showed similar results for key analyses, which included EC, pH, organic carbon and acid neutralising capacity.

The Saltpeterkop Carbonatite Complex is a Late Cretaceous (≈76 Ma) volcanic and shallow intrusive magmatic feature located approximately 20 km southeast of Sutherland in the Northern Cape. It is unusual among southern African carbonatite complexes in that it has not been deeply eroded, and retains a significant vestige of its original volcanic features. The main geologic expression of the Complex is a ≈1.5 km diameter tuff ring, located on top of prominently updomed and fractured Beaufort Group (Karoo) sediments, that appears to have formed as the result of a major diatreme-type eruption. The volcaniclastic breccias making up the tuff ring have been heavily altered and silicified by hydrothermal activity, and thick (mm to tens of cm) Fe oxide-rich crusts, which appear to represent the alteration products of Fe-rich carbonatites, are common in this area. Outside of the central ring structure are numerous shallow intrusions (dykes, sills and irregular shapes), satellite breccia pipes and pipe-shaped intrusions that host fresh to only moderately altered igneous rocks. The main igneous rock types include (in decreasing order of abundance): carbonatite, potassic trachyte, olivine melilitite and ultramafic lamprophyre. This thesis provides the first detailed petrographic and geochemical description of these rocks (e.g., major and trace elements) and attempts to explain several aspects of their petrogenesis. The olivine melilitites and ultramafic lamprophyres are the most primitive igneous rocks in the complex and have experienced only minor to moderate extents of differentiation, respectively. They apppear to have been derived by low-degrees of partial melting of a carbonated, likely phlogopite-bearing mantle source. The lamprophyres appear to have been derived by melting at shallower depths than the melilitites based on REE constraints. The carbonatites range from relatively primitive to highly differentiated and they form a nearly continuous compositional range with the ultramafic lamprophyres and melilitites. This seems to argue against a major role for liquid immiscibility in their origin. Their REE content (up to 2 wt.% total REE oxides) correlates with their extent of differentiation. The potassic trachytes are plausibly linked to melts of mafic lower continental crust that has been metasomatised by hydrous potassium-rich carbonatitic melts and which have experienced significant fractional crystallization and assimilation of upper crustal sedimentary rocks during emplacement.