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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 49 (1965)

Issue: 3. (March)

First Page: 335

Last Page: 336

Title: Salt Tectonics of the Cuanza Basin, Angola, Portuguese West Africa: ABSTRACT

Author(s): Georges Brognon, Pierre Masson, Georges Verrier, Sherman A. Wengerd

Article Type: Meeting abstract


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The Cretaceous Cuanza basin is located in northwestern Angola on the Atlantic coast of West Africa. This composite basin, 315 km. long, north-south, and 170 km. wide, east-west, consists of an early Cretaceous carbonate-reef barrier-evaporite sequence succeeded by a late Cretaceous clastic-carbonate sequence. The basement is composed of Precambrian crystalline rocks, Paleozoic metasediments, and post-Paleozoic crystalline rocks. Surface of the basin consists of Upper Cretaceous, Paleocene, Eocene, and Miocene strata, with much of the area covered by a thick, red, lateritic, Pleistocene sandy oil.

The middle Aptian sel massif was deposited to a maximum thickness of about 600 meters in response to an early off-shore tectonic welt or fault in the basement, possibly coupled with early Aptian barrier reef growth to create a semi-locked evaporite basin.

Salt tectonism of early to middle Cretaceous age involves (1) regional lateral salt movement of 1 to 15 kilometers, probably initiated by basement faulting; (2) subregional salt shifts in response to clastic loading from the east and barrier reef loading on the west; (3) local to subregional horizontal salt shift and vertical expansion to form anticlines in response to local reef buildup, as well as basement folding and wrenching, and local trough-like clastic loading; (4) final diapiric salt intrusion in waves with amplitudes of 2,000 meters, initiated in Oligocene time, and operative today; (5) Miocene fosse foundering (normal graben faulting) with filling by deltaic clastics; and (6) renewed right lateral wrench-faulting.

An early, low-amplitude Cretaceous regional salt movement, important to initial oil migration and accumulation, was followed by Oligocene diapirism which destroyed several large oil accumulations. Both took place in locales where the initial deposition of the massive salt was the greatest.

Oil exploration of both the pre-salt and post-salt Cretaceous strata in the Cuanza basin today depends upon detailed unravelling of the salt tectonic history.

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Copyright 1997 American Association of Petroleum Geologists