SALT TECTONICS STRUCTURAL STYLES: CONTRASTS AND SIMILARITIES BETWEEN THE SOUTH ATLANTIC AND THE GULF OF MEXICO

Abstract

Abstract The tectonic evolution of the South Atlantic and the Gulf of Mexico salt basins are associated with rupture of Gondwana and the emplacement of oceanic crust in different chronological and geological settings. Salt basins developed diachronously from the Jurassic to the Early Cretaceous, subsequent to an intracontinental rift phase, and were deformed by several tectono-sedimentary episodes in the geologic history, which are responsible for their contrasting halokinetic structural styles. Mechanisms of convergent and divergent radial flow may explain some of the differences between compressional and extensional regimes, but the stratigraphic framework, associated with changing environments of deposition and different episodes of sediment input, controls the formation of extensional and compressional structures, salt mounds, salt diapirs, and salt tongues in different compartments along the sedimentary basins. Allochthonous salt tongues, which have been thoroughly studied in the Gulf of Mexico, are not so spectacularly developed in the South Atlantic, but some deep water structures bear some resemblance to the Sigsbee Scarp. Fold belts associated with proximal extensional regimes giving way to distal compressional regimes have been identified both in the Gulf of Mexico and in the South Atlantic. The occurrence of systematic arrays of counter-regional (landward-dipping) normal faults has been documented both in the Gulf of Mexico and in the South Atlantic. In the deep water province of the Cabo Frio region, this style of salt tectonics resulted in well-developed antithetic faults responsible for large stratigraphic gaps along the salt weld. Late Jurassic to Early Cretaceous autochthonous halokinetic structures, which are often masked by the phenomenal Miocene-Pleistocene progradation that originated salt tongues and other allochthonous structures, can also be visualized in the northeastern Gulf of Mexico. Deep seismic reflection profiles have characterized some enigmatic features offshore the northeastern Brazilian margin. Some of these structures show a moundlike geometry and overlie the rift-drift regional unconformity. Multiple interpretations have been proposed, including tilted rift blocks, reefs, basement highs, volcanic plugs, and even processing artifacts. Some of these features seem to be associated with magmatic activity during the emplacement of oceanic crust, and others occur along fracture zones. On the other hand, some structures show striking evidence of salt tectonics. These features, when analyzed within a basinwide context, have important geologic significance and possible deep-water exploratory plays. Similar structures may be interpreted in the Gulf of Mexico, North Sea, and along the eastern margin of North America.