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Review of clastic rift plays along the rift borders of the central South Atlantic margins

Ian Davison
Review of clastic rift plays along the rift borders of the central South Atlantic margins (in Petroleum systems in 'rift' basins, Paul J. Post (editor), James Coleman (editor), Norman C. Rosen (editor), David E. Brown (editor), Tina Roberts-Ashby (editor), Peter Kahn (editor) and Mark Rowan (editor))
Papers presented at the Gulf Coast Section, Society of Economic Paleontologists and Mineralogists Foundation Annual Bob F. Perkins Research Conference (December 2015) 34: 836-855

Abstract

The clastic fill of the rifted grabens in the central South Atlantic includes several fields containing over 1 billion barrels of oil in place. The largest fields are mainly hosted by continental fluvial and aeolian sandstones deposited near the base of the rift, before rift topography was fully developed. Footwall erosion progressively eroded back the main fault scarps, and normal faults propagated through the footwall to create terraces along the rift borders. This increased the potential drainage area on the footwall, so eventually, large alluvial fans developed in the hanging wall along the main rift border faults. The basement clast-supported conglomerates scatter seismic energy; and on seismic data, the top of the fan can appear to be the intact crystalline basement. Even when drilled, the top of the fan can still be mistaken for true basement due to the large size of the clasts. Some important oil fields are hidden below these marginal alluvial fans, within prerift and early rift fluvial and eolian sandstones and in lacustrine turbidite sandstone reservoirs. It is suggested that more fields may be found in West Africa using the model of the sub-fan terrace play. The large amount of footwall denudation of dense basement rocks can lead to unloading of the adjacent basin, as well as the footwall, when the crust has a finite flexural strength. The resulting uplift and erosion produce an 'End of Rift' unconformity, and it is suggested this process is likely to have caused the so called 'Breakup' unconformity on continental margins, rather than this being due to initiation of ocean spreading.


ISSN: 1544-2462
Serial Title: Papers presented at the Gulf Coast Section, Society of Economic Paleontologists and Mineralogists Foundation Annual Bob F. Perkins Research Conference
Serial Volume: 34
Title: Review of clastic rift plays along the rift borders of the central South Atlantic margins
Title: Petroleum systems in 'rift' basins
Author(s): Davison, Ian
Author(s): Post, Paul J.editor
Author(s): Coleman, James, Jr.editor
Author(s): Rosen, Norman C.editor
Author(s): Brown, David E.editor
Author(s): Roberts-Ashby, Tinaeditor
Author(s): Kahn, Petereditor
Author(s): Rowan, Markeditor
Affiliation: Earthmoves, Camberley, United Kingdom
Affiliation: Bureau of Ocean Energy Management, New Orleans, LA, United States
Pages: 836-855
Published: 20151201
Text Language: English
Publisher: Society of Economic Paleontologists, Gulf Coast Section (GCSSEPM) Foundation, Houston, TX, United States
ISBN: 978-1-944966-00-3
Meeting name: 34th GCSSEPM Foundation Bob F. Perkins-Rosen research conference on Petroleum systems in 'rift' basins
Meeting location: Houston, TX, USA, United States
Meeting date: 20151213Dec. 13-16, 2015
References: 43
Accession Number: 2020-013096
Categories: Economic geology, geology of energy sourcesApplied geophysics
Document Type: Serial Conference document
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., sketch maps
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute.
Update Code: 202009
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