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Abstract


AAPG Studies in Geology 56: Atlas of Deep-Water Outcrops, 2007
chapter-143
DOI: 10.1306/12401022St563308

Chapter 143: Karoo Basin, South Africa: Deep-water Basin-floor and Slope Deposits of the Laingsburg Depocenter

Stephen S. Flint, David M. Hodgson, Peter J. Sixsmith, Martin Grecula, H. De Ville Wickens

Abstract

The Middle Permian Laingsburg Formation includes a range of basin-floor and slope deposits that are well exposed around the town of Laingsburg. These deposits overlie postglacial shales (Prince Albert and Whitehill Formations), muddy turbidites and ashes (Collingham Formation), and mudstones, silty turbidites, and mass-transport complexes (Vischkuil Formation). The Laingsburg Formation attains a thickness of 850 m (2800 ft) and comprises six deep-water turbidite complexes, informally called Fan A and Units B to F, each separated by a significant thickness (10–90 m [33–295 ft]) of hemipelagic and turbiditic mudstones. Fan A is interpreted as a basin-floor submarine fan, constituting approximately 40% of the Laingsburg Formation with a thickness of 350 m (1150 ft) southeast of Laingsburg. Unit B, deposited in a lower-slope setting, attains a thickness of 80–150 m (262–492 ft), and Units C to F (middle to upper-slope setting) have thicknesses ranging between 10–100 m (33–328 ft). The overlying Fort Brown Formation represents upper-slope to shelf-edge deposits. The complete Vischkuil/Laingsburg Formations succession is interpreted as a low-order falling-stage and lowstand systems tract to two basinwide low-order depositional sequences. Fan A is divisible into seven regionally mappable, sand-rich, high-frequency sequences with distinctive stacking patterns. Units B–F are interpreted as high-frequency, lowstand systems tracts within the low-order composite sequence.


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