--> From Fan Axis to Fan Margin - Example From a Slope Setting, South-western Karoo Basin, South Africa, by Willem Van Der Merwe and De Ville Wickens; #90037 (2005)

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From Fan Axis to Fan Margin - Example From a Slope Setting, South-western Karoo Basin, South Africa

Willem Van Der Merwe and De Ville Wickens
University of Stellenbosch, Stellenbosch, South Africa

The south-western Karoo Basin hosts the Permian-aged Tanqua Fan Complex, a three-dimensionally exposed deep water Succession comprising five fine-grained individual fan systems. The latter are sand-rich, between 20 and 60 m in thickness, with interfan units comprising finely-laminated shale and silty shales of hemi-pelagic and turbiditic origin.

The basin floor to slope fans outcrop over approximately 650 km2, are progradational and laterally continuous. Although deposited in a basin flanked by an orogenic belt, the fan complex has depositional characteristics similar to fans deposited in passive margin settings.

Depositional characteristics of the Hangklip Fan (Fan 5) reflect a slope setting where local tectonic control seemed to have played a major role in the distribution and regional development of channel-fill and overbank depositional elements. Palaeotransport directions of the channel-fill complexes roughly correspond to the structural trend of synclines and anticlines in the study area. These axial channel-fills correlate with a succession of thin, ripple-laminated beds, up to 100 m thick and about 10 km away. This thin-bedded succession, in places associated with single channel-fills, is now interpreted as stacked fan margin/overbank deposits, genetically related to the Hangklip channel-fill complex.

Highly erosive, stacked slope channels, seemingly controlled by subtle early structural features were able to construct a significant thickness of regionally well-developed stacked overbank. deposits, marginal to a fan axis. These facies changes occur over relatively short distances which hold significant implications on the prediction of and the heterogeneity of reservoir facies in slope settings.