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The AAPG/Datapages Combined Publications Database

AAPG Special Volumes

Abstract


Pub. Id: A169 (1993)

First Page: 71

Last Page: 98

Book Title: M 58: Siliciclastic Sequence Stratigraphy: Recent Developments and Applications

Article/Chapter: Sequence Stratigraphy of Petroleum Plays, Post-Rift Cretaceous Rocks (Lower Aptian to Upper Maastrichtian), Orange Basin, Western Offshore, South Africa: Chapter 4: Recent Applications of Siliciclastic Sequence Stratigraphy

Subject Group: Seismic Stratigraphy, Sequence Stratigraphy

Spec. Pub. Type: Memoir

Pub. Year: 1993

Author(s): A. Muntingh, L. F. Brown Jr.

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 Previous HitseaNext Hit Previous HitlevelNext Hit cycles. During the deposition of third-order, oblique progradational sequence sets (second-order "lowstand Previous HitsystemsNext Hit Previous HittractsNext Hit"), the component third-order lowstand Previous HitsystemsNext Hit Previous HittractsNext Hit shifted far into the basin. During the deposition of a third-order, highly sigmoidal, aggradational set (second-order "highstand Previous HitsystemsNext Hit tract"), however, component third-order highstand Previous HitsystemsNext Hit Previous HittractsNext Hit were stacked along the outer shelf. Consequently, slumping and gravity faulting of distal f ne-grained prodeltaic and slope facies were common and basinward shifts of component third-order lowstand Previous HittractsNext Hit 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 Previous HitsystemsNext Hit Previous HittractsNext Hit.

End_Page 71-------------------------

The most favored petroleum plays and fairways are restricted to lowstand Previous HitsystemsNext Hit Previous HittractsNext Hit 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 basin during progradational supercycles. Deep-basinal lowstand plays are inferred to possess the most favorable petroleum maturation, seals, migration pathways, and combination structural and stratigraphic pinch-out traps.

In addition to supersequence stacking patterns, another important factor affecting the application of sequence-stratigraphic concepts in the Orange Basin is the possible variations within each lowstand system tract along the margin of the basin. Sandy highstand fluvial and deltaic Previous HitsystemsNext Hit Previous HittractsNext Hit within progradational third-order sequence sets support the prediction of adequate lowstand reservoirs in downdip basinal fairways. A constraint on exploration of the lowstand Previous HittractsTop is moderate to deep water, but continued exploration is encouraged by the potential for large reservoir targets.

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