--> Abstract: Anatomy and Stratigraphic Development of a Lower Slope to Base-of-Slope Siliciclastic Wedge from the Tanqua Depocentre, SW Karoo Basin, South Africa, by Willem C. Van der Merwe, De Ville Wickens, David Hodgson, Steve Flint, and Richard Wild; #90082 (2008)

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Anatomy and Stratigraphic Development of a Lower Slope to Base-of-Slope Siliciclastic Wedge from the Tanqua Depocentre, SW Karoo Basin, South Africa

Willem C. Van der Merwe1, De Ville Wickens2, David Hodgson1, Steve Flint1, and Richard Wild3
1Department of Earth & Ocean Sciences, University of Liverpool, Liverpool, United Kingdom
2Geology, Geography and Environmental Studies, University of Stellenbosch, Stellenbosch, South Africa
3Reservoir Characterization Unit, Chevron Energy Technology Company, Houston, LA

Permian deep-water deposits of the Tanqua depocentre, SW Karoo Basin, South Africa, include Unit 5, an approximately 100m thick lower slope to base-of-slope sand-rich deep-water succession, with its upper and lower boundaries clearly defined by regionally-developed mudstone. It is underlain by point-sourced sand-rich basin-floor fans, and succeeded by progradational deltaic deposits. This unit is exposed for approximately 50km in an oblique strike direction and >20km in a dip direction, which has allowed an extensive outcrop-based dataset to be collected. This is augmented by four research boreholes positioned roughly down-dip from the main outcrop area.

Unit 5 consists of several discrete stages of stratigraphic growth that manifested in several areas of channelisation across the outcrop belt, suggesting multiple entry points across the slope. Channel-fill depositional elements are arranged in complexes and complex sets, and associated with stacked sheet-like sandstone units down-dip from and lateral to them. Packages of thin-bedded, ripple-laminated deposits are interpreted to represent a combination of distal frontal splay deposits from earlier up-dip slope feeder systems, and lateral spill deposits formed during channel incision, aggradation and abandonment. The ratio of frontal: lateral splay deposits at any section depend upon the stratigraphic position and spatial location with respect to the genetically related channel-complex. Sedimentological criteria for establishing the depositional setting of thin-bedded facies include stratigraphic packaging and bed thickness (thickening upward trends and greater average bed thickness in frontal deposits), abrupt changes in palaeoflow, and beds with wedge geometries and isolated channel forms (lateral deposits).

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