--> World’s Largest Petroleum-Bearing Salt Basins: Tectonic Control, Szatmari, Peter; Mohriak, Webster U., #90100 (2009)

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World’s Largest Petroleum-Bearing Salt Basins: Tectonic Control

Szatmari, Peter1
 Mohriak, Webster U.2

1CENPES, Petrobras, Rio de Janeiro, Brazil.
2
E&P, Petrobras,
Rio de Janeiro, Brazil.

Evaporites, especially anhydrite, are widespread worldwide, but large basins thousands of kilometers in diameter, containing hundreds and even thousands of meters of rock salt (halite) and carnallite that control major petroleum provinces, formed only in the geological past, at times when the contact between the salt depositing basin and the world ocean was sharply restricted. These basins formed in an extensional regime at the early stages of ocean opening, as during the early Cretaceous in the
South Atlantic, or in a compressional regime at the last stages in the life of an ocean, when it was being consumed by continental collision. Until the past decades, only salt basins involved in continental collision were well known, because only they were suitably exposed on land. Most important among these collisional salt basins was that of the Williston - western Canada salt basin in the Devonian, and the late Permian (Zechstein) salt basins in the North Sea, Germany and west Texas; in all of them salt played an important role in controlling petroleum accumulations. The salt basin of the Middle East formed in the early stages of ocean opening close to the Proterozoic/Paleozoic boundary, but the present-day structures on surface are compressional because they have been strongly affected by ongoing Tertiary collision and strike slip along the Zagros. Along the North Atlantic extensional salt basins formed during the breakup of Pangea in latest Triassic - early Jurassic times, some were involved in Tertiary collisions, as along the northern margin of western Africa and Iberia. Where the Early Mesozoic evaporite basins are largely unaffected by continental collision, as on the eastern margin of North America and in the Gulf of Mexico, salt tectonics is the major controlling factor for the oil accumulations. Continental breakup between South America and West Africa occurred in the early Cretaceous, somewhat later than between Gondwana and Europe - North America, and the evaporites formed in the early stages of the opening of the South Atlantic controlled most of the oil accumulations discovered along the Brazilian and Angola-Gabon margins. Sea water inflow from the ocean basin to the south, between Argentina and South Africa, was impeded by Early Cretaceous volcanic structures; the sedimentary basins south of this barrier are much less prolific.

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