--> Paleogeographic Mapping of the South Atlantic: Jurassic Through Albian Evolution, Henry, Steven G.; Danforth, Al; Kumar, Naresh; Venkatraman, Sujata, #90100 (2009)

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Paleogeographic Mapping of the South Atlantic: Jurassic Through Albian Evolution

Henry, Steven G.1
 Danforth, Al4
 Kumar, Naresh2
 Venkatraman, Sujata3

1RIFTT, Las Cruces, NM.
2Growth Oil and Gas, Richardson, TX.
3ION-GX Technology, Houston, TX.
4Consultant, Houston, TX.

Based on the improved pre-salt imaging provided by the recently acquired BrasilSPAN (2008), and CongoSPAN (2005 and 2007) pre-stack depth migrated seismic data, Jurassic through Albian stratal relationships have been interpreted, and six-geologic-time intervals have been mapped. These maps support a model of diachronous rifting for the opening of the South Atlantic. Understanding the timing and spatial relationships of these rifting events is the key to successful pre-salt exploration on both sides of the Atlantic.

Two distinct periods of rifting have been identified. Rifting in the Valanginian failed to create oceanic crust, but generated the space in which both a syn-rift and a thick overlying sag-basin developed. The sag basin appears to have subsided with little or no crustal faulting. The Lagoa Feia (Brazil) and the Falcão/Organic Bucomazi (Angola) source rocks were deposited in the upper sequences of the sag-basin.

A younger, Barremian-age rifting event was successful in separating Africa from South America. This rifting was highly volcanic with many eruptive centers over the majority of the crust extended during the Barremian rifting. At the western limit of the Barremian faulting in Brazil and the eastern limit in Angola, the sag basin has been faulted and becomes part of the pre-rift for this younger event. Aptian salt appears to have been first deposited overlying the sag basins, and then the salt transgressed into the actively subsiding Barremian syn-rift grabens.

This interpreted geologic history is illustrated for the Santos /Campos in the west, and the Benguela /Kwanza /Congo /Gabon basins in the east, using paleo-geographic maps for six time intervals beginning in the Jurassic and continuing until the Albian. These maps are useful for visualizing the diachronous rifting and associated development of basins. Models on the mechanics of rifting will need to include these newly imaged deep pre-salt reflectors.

Understanding how and when these basins developed is fundamental for pre-salt exploration. In the Santos Basin, the successful Tupi play is located at the junction of the sag basin and the western limit of Barremian rifting, while the Jupiter discovery lies in the faulted sag basin caused by the Barremian rifting. On the African side, the deepwater pre-salt has been penetrated by only a few wells, but much of what has been learned on the Brazilian side can be applied to the African counterpart of this emerging new pre-salt play.

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