--> South Atlantic Deepwater Reservoirs: Responses to Tectonic, Climatic and Eustatic Controls from Two Not-So-Passive Margins, Macgregor, Duncan, #90100 (2009)

Datapages, Inc.Print this page

South Atlantic Deepwater Reservoirs: Responses to Tectonic, Climatic and Eustatic Controls from Two Not-So-Passive Margins

Macgregor, Duncan1

1Neftex Petroleum Consultants, Abingdon, United Kingdom.

South Atlantic passive margins are the focus for many of the world’s best known turbidite reservoirs, the occurrence of which can be shown to be related to high sedimentation rates, hinterland uplifts, wet climates and major lowstands. Both the Brazilian and West African margins show many lines of evidence for syn-drift uplift, including high topography, volcanism, elevated marine surfaces and peneplanation events, AFTA and anomalous source rock maturity trends. Sedimentation rates on both margins show peaks in the Late Cretaceous and Neogene, crudely mimicking the Haq curve, though these peaks are more marked in Africa than in Brazil. The Cretaceous events lead to localised surges in sedimentation and bypass to deepwater while the Neogene events create more even progradational trends with sedimentation rates increasing progressively above a glaciation/eustatic event at base Oligocene.

There are several local variations around these broad trends, with Cretaceous uplift being more evident in south-west Africa and in
Brazil, and Neogene uplift in the Gulf of Guinea hinterland. Sedimentation rates and turbidite reservoir developments are ubiquitously low during arid periods while a higher denudation rate is evident during global glacial periods, possibly due to increased seasonality. It is evident that river systems with the sediment supply of the present day Niger, Congo and Amazon rivers never existed in the Palaeogene or Cretaceous. Late Cretaceous coarse turbidite systems are consequently smaller but may be more geographically widespread.
Models can be built to predict further hidden turbidite systems from our developing knowledge of these three interlinked controls. These focus interest for Cretaceous turbidites on West African regions such as the transform margin. As few onshore basin source rocks are at their maximum burial at Present Day, there are also strong implications for revising charge risk for shallow rift basin plays.


AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil