Mesozoic geology of the Agulhas Bank, South Africa
This thesis is concerned with the Mesozoic geological history of the Agulhas Bank on the continental shelf off the south coast of South Africa. It incorporates the results of oil exploration activities in the area since 1967: this involved the drilling of 17 boreholes (43 000 m) and the recording of about 24 000 line km of seismic reflection profiles. A structural investigation was facilitated by regional mapping of two key seismic reflectors; these are acoustic basement (horizon D at tile base of the Mesozoic) and a prominent reflector and unconformable horizon (horizon C) within the Lower Cretaceous. An additional two horizons were mapped over part of the Agulhas Bank; they are horizons A (base of the Uppper Cretaceous) and 11 (within the Lower Cretaceous). These reflector horizons were tied to stratigraphic control points in the boreholes. A stratigraphic framework was erected and correlations were established by means of a study of borehole cuttings samples, cores and sidewall cores and a variety of wireline logs. The existing Mesozoic litho-stratrigraphic framework was supplemented by defining reference stratotypes for the Swart¬kops end Sundays River formations. Subsurface stratotypes are defined for two new units; they are termed the Infanta and Alphard Formations. A subsurface reference stratotype for the Alexandria Formation is presented. A chronostratigrapic framework and correlations, which became available through a study of microfauna and microflora were intergrated with structural and lithostratigraphic information. As a consequence four litho-tectonic units are recognised; their evolution is discussed also in terms of varying rates of sediment accumulation. The Mesozoic geologic history of the Agulhas bank is discussed in reference to the plate tectonic history.
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