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GEOREF RECORD

Evolution of the Cretaceous Astrid thrust belt in the ultradeep-water Lower Congo Basin, Gabon

Martin P. A. Jackson, Michael R. Hudec, David C. Jennette and Richard E. Kilby
Evolution of the Cretaceous Astrid thrust belt in the ultradeep-water Lower Congo Basin, Gabon
AAPG Bulletin (April 2008) 92 (4): 487-511

Abstract

The Lower Congo Basin contains the greatest salt-based fold and thrust belt off Africa's Atlantic margin. Our study area in the Anton Marin and Astrid Marin exploration blocks is in the northern part of the basin. Gravity-driven tectonic shortening began soon after the Aptian salt deposition, forming gentle, west-trending, salt-cored anticlines, which, together with salt diapirs, created a template for later thrusting. In the Late Cretaceous, a thrust front propagated landward into the study area, and thrusts formed above salt anticlines and diapirs. Formation of a hanging-wall wedge of growth strata was recorded when each thrust fault ruptured the seabed. Thrusting began after widespread salt thinning, as autochthonous salt was expelled into older, passive diapirs. Thinning stiffened the detachment, so that thrusts verge strongly seaward. Structural restorations, dip-corrected isochron maps, and fault-activity graphs all show that the landward edge of the thrust belt propagated landward. Three main pulses of shortening episodically reactivated thrust faults as the thrust front broke landward. As thrusting culminated, precursor passive diapirs were squeezed and extruded small allochthonous sheets. Translation culminated in major erosional scouring, from which we infer epeirogenic slope steepening in the Late Cretaceous. As shortening spread updip into the previously extensional domain during the Late Cretaceous to Paleogene, older extensional faults were inverted, and new extensional faults formed orthogonally, parallel to the regional paleoslope. The structural pattern, created in the Late Cretaceous when the paleoslope dipped southward, remains recognizable in the little-deformed Neogene strata, although the present continental slope dips westward.


ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 92
Serial Issue: 4
Title: Evolution of the Cretaceous Astrid thrust belt in the ultradeep-water Lower Congo Basin, Gabon
Affiliation: Bureau of Economic Geology, Austin, TX, United States
Pages: 487-511
Published: 200804
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
References: 38
Accession Number: 2008-084421
Categories: Economic geology, geology of energy sourcesStructural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: sects., sketch maps
S07°00'00" - S03°00'00", E08°00'00" - E12°00'00"
Secondary Affiliation: Apache Corporation, USA, United StatesShell Exploration and Production Company, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States
Update Code: 200825
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