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| New Insights into Petroleum Geoscience Research
Through Collaboration Between Academia & Industry, 15-16th April
2003 The Grological Society, Burlington House, London |
| Wild, R., King, R., van Lente, B., Flint, S.,
Hodgson, D. & Potts, G. Tectono-stratigraphic controls on the development of a sub-marine slope system: The Tanqua Karoo, South Africa. |
| Sediment supply and slope physiology in foreland
basins are primarily controlled by the formation of the orogenic belt. Changes
in routing and storage of sediment and the gradient and morphology of the basin
slope have significant implications on the stratigraphic evolution of submarine
slope systems through time and space. The SLOPE Project aims to better
understand the impact of hinterland and seabed deformation, as well as changes
in climate, provenance and relative sea-level, on the sequence stratigraphic
development of submarine slope systems by integrating sedimentological,
geochemical, petrographic and tectonic studies in the Tanqua Karoo basin, South
Africa. The Permian Tanqua Basin is interpreted as a foreland basin that formed in front of a major oroclinal bend in the Cape Fold Belt, consisting of two limbs, the Cederberge and Swartberg ranges. Each limb is structurally different, suggesting spatial separation during formation. However, basin sediments observed both north and south of the CFB indicate that the Hexriver syntaxial structure post-dates the two branches thus explaining the structural variation. In the basin, a series of prograding submarine fans overlie a thick succession of starved basin floor shales. The Koedoesberg Formation, a 300-m-thick fine-grained submarine slope system, prograded over the submarine fans, and is capped by extensive shallow-marine systems. Palaeocurrent and provenance studies indicate a point source origin for the sediments of the Tanqua outside of the fold belt. It is proposed that the structural separation described above facilitated sediment bypass of the CFB into the Tanqua sub-basin. The identification of a ramp profile indicates low rates of basin subsidence during Koedoesberg Formation times. This interpretation is based on stacking patterns, types of architectural elements and a pronounced cyclicity to the facies. Genetic sedimentary units are recognisable in outcrop gamma-ray logs and integration of this technique will aid sequence stratigraphic analyses and reservoir characterisation. |
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