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Geological and Geophysical Interpretation of Salt Deposition and Tectonic Styles in the South Atlantic and North Atlantic Evaporite Basins

Mohriak, Webster U.1; Szatmari, Peter 2; Anjos, Sylvia 1
1 E&P, Petrobras, Rio de Janeiro, Brazil.
2 Cenpes, Petrobras, Rio de Janeiro, Brazil.

This work compares the geological and geophysical interpretation of salt structures in the South Atlantic and North Atlantic sedimentary basins, focussing on the Eastern Brazilian and West African continental margins, the most prolific salt basins in the South Atlantic.

Several episodes of evaporite deposition are recognized in the Brazilian basins, which are characterized by Paleozoic evaporites in the onshore intracratonic basins and Mesozoic (Aptian) evaporites along the continental margin. Paleozoic and Mesozoic evaporite sedimentation is recognized in the North American and NW Europe sedimentary basins, from the Permian Zechstein evaporites in North Sea and North German basins, to the Late Triassic/Early Jurassic salt basins along the Canadian and NW African continental margins.

The salt tectonics structural styles vary within the framework of intracontinental to divergent margin development. We discuss the similarities and differences in evaporite depositional facies, magmatic intrusions affecting salt layers, and the controls of halokinesis on the petroleum systems. Most of the hydrocarbon discoveries in the Brazilian and African margin are related to post-salt turbidite reservoirs, but recent discoveries in the deep-water salt basins along the Brazilian margin indicate that pre-salt plays will represent an important contribution to hydrocarbon production in the nearby future.

Regional seismic interpretation and potential field (gravity and magnetic) data over the Eastern Brazilian and West African margins suggest a very thick autochthonous salt layer deposited over rifted continental crust and particularly above the thick sag basin in the transition zone from continental to oceanic crust. Salt tectonics domains vary from highly extensional on the platform to highly compressional at the crustal limit, where recumbent folds, thrust faults are allocththonous salt tongues are recognized. The North Atlantic divergent margin basins (offshore Canada and Morocco) are also characterized by a thick salt mass in deep waters, and allochthonous salt has been identified in several segments of these margins, forming important exploratory plays that have been minimally tested.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009