Print this pageTectonic Control During Earth History of World's Largest Petroleum-Bearing Salt Basins
Evaporites are widespread worldwide in many stratigraphic sequences, but large evaporite basins are few. Basins measuring thousands of kilometers that accumulated hundreds and often thousands of meters of halite and carnallite, and often control rich petroleum provinces (as in the South Atlantic region) formed only during short intervals of time when communication with the world ocean was sharply restricted. Two end-member classes of large evaporite basins may be recognized: basins formed in divergent tectonic setting at the early stages of ocean opening, and those formed in covergent setting when the ocean 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 were 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 these basins, salt played an important role in controlling petroleum accumulations. The Latest Proterozoic salt basin of the Middle East formed during the early stages of ocean opening, but its present-day structures on surface are compressional, because the basin was involved in 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 of these were also involved in Tertiary collisions, as along the northern margin of western Africa and in Iberia. Where the Early Mesozoic evaporite basins are largely unaffected by continental collision, as in the Eastern margin of North America and also in the Gulf of Mexico, salt tectonics is the major controlling factor of 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 resulting evaporites 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