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

By
Stephen Flint
Stephen Flint
1
Stratigraphy Group, Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, United Kingdom
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David Hodgson
David Hodgson
1
Stratigraphy Group, Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, United Kingdom
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Peter Sixsmith
Peter Sixsmith
1
Stratigraphy Group, Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, United Kingdom
2
Present address: chevron, San Ramon, California, USA
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Martin Grecula
Martin Grecula
1
Stratigraphy Group, Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, United Kingdom
3
Present address: Shell Exploration and Production in Europe, Assen, The Netherlands
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H. de Ville Wickens
H. de Ville Wickens
1
Stratigraphy Group, Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, United Kingdom
4
Department of Geology, University of Stellenbosch, Stellenbosch, South Africa
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Published:
January 01, 2008

Abstract

The 230-m (754-ft)-thick Vischkuil Formation and overlying 850-m (2800-ft)-thick Laingsburg Formation represent the early deep-water phase of retro-arc foreland basin stratigraphy in the Karoo basin, South Africa. Using radiometric dates from ashes and thicknesses of pelagic shale decompacted and compared to modern-day depositional rates, the succession is interpreted as a third-order falling stage (FSST) and lowstand systems tract (LST). The upper Vischkuil Formation comprises a series of large-scale mass-transport complexes (MTCs) that can be correlated more than 20 km (12 mi) downdip. Mapping suggests that emplacement of these features created sea-floor topography, which influenced thickness and facies distribution in the lower part of the overlying basal Laingsburg Formation Fan A complex. The N1 road links Cape Town and Johannesburg. When travelling from the south, 1 km (0.6 mi) before the town of Laingsburg, a series of roadcuts expose the Vischkuil and Laingsburg Formations. The upper MTC is well exposed at the western end of the N1 road cut. The Laingsburg Formation comprises six sandstone-dominated intervals (Fan A and Units B-F), each separated by 10–90 m (33–295 ft) of turbiditic and hemipelagic shales. Fan A is 275 m (907 ft) thick in the road cut and has been divided into seven regionally mappable, high-frequency sequences (growth stages), each comprising a sand-prone lowstand systems tract (15–55 m [49–180 ft] thick) and a mudstone-dominated transgressive/highstand systems tract (5–25 m [16–82 ft] thick). Fan A is therefore a composite sequence. The sandstones in the three lower growth stages are relatively dirty, with the occurrence of occasional floating mudstone clasts,

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Contents

AAPG Studies in Geology

Atlas of Deep-Water Outcrops

Tor H. Nilsen
Tor H. Nilsen
Desceased
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Roger D. Shew
Roger D. Shew
University of North Carolina
Wilmington, North Carolina
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Gary S. Steffens
Gary S. Steffens
Shell International E&P
Houston, Texas
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Joseph R. J. Studlick
Joseph R. J. Studlick
Maersk Oil America Inc.
Houston, Texas
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American Association of Petroleum Geologists
Volume
56
ISBN electronic:
9781629810331
Publication date:
January 01, 2008

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