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Sequence Stratigraphy of Petroleum Plays, Post-Rift Cretaceous Rocks (Lower Aptian to Upper Maastrichtian), Orange Basin, Western Offshore, South Africa

By
A. Muntingh
A. Muntingh
Soekor (Pty) Ltd. Parow, South Africa
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L.F. Brown, Jr.
L.F. Brown, Jr.
Consultant Georgetown, Texas U.S.A.
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Published:
January 01, 1993

Abstract

The interpretation of viable siliciclastic lowstand petroleum plays and fairways within post-lower Aptian (112–68 Ma) Cretaceous passive-margin rocks underlying 90,000 km2 of the Orange Basin, offshore South Africa, was carried out using seismic- and sequence-stratigraphic concepts and methods. Twenty-three fundamental third-order, type 1 depositional sequences and five composite third-order, type 1 sequences comprising 12 fourth-order sequences were identified, provisionally dated, correlated, and mapped.

The sequences compose four third-order progradational and/or aggradational sequence sets (second-order supersequences) bounded by second-order, type 1 unconformities. Control of the stacking patterns of third-order sequence sets was probably an interplay between basin subsidence and first- and second-order eustatic sea level cycles. During the deposition of third-order, oblique progradational sequence sets (second-order "lowstand systems tracts"), the component third-order lowstand systems tracts shifted far into the basin. During the deposition of a third-order, highly sigmoidal, aggradational set (second-order "highstand systems tract"), however, component third-order highstand systems tracts were stacked along the outer shelf. Consequently, slumping and gravity faulting of distal fine-grained prodeltaic and slope facies were common and basinward shifts of component third-order lowstand tracts were highly constrained. A positive aspect of the aggradational third-order sequence set, however, is its potential for supplying large volumes of reservoir-quality sands to basin-floor fans during lowstand fluvial entrenchment of the third-order highstand fluvial/deltaic systems tracts.

The most favored petroleum plays and fairways are restricted to lowstand systems tracts within highly progradational, third-order sequence sets. These plays comprise third-order incised valley-fill, prograding (deltaic) wedge, and basin-floor prospects that shifted far into the

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Contents

AAPG Memoir

Siliciclastic Sequence Stratigraphy: Recent Developments and Applications

Paul Weimer
Paul Weimer
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Henry Posamentier
Henry Posamentier
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American Association of Petroleum Geologists
Volume
58
ISBN electronic:
9781629810997
Publication date:
January 01, 1993

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