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Geologic History of North and Northeastern Brazilian Margin: Controls Imposed by Seafloor Spreading on the Continental Structures
Six sedimentary basins underlie the North Brazilian Shelf between latitude 5°N and latitude 8°S. Four of these basins (clockwise from the northernmost: Foz-do-Amazonas, Barreirinhas, Potiguar, and Recife-Joao Pessoa) lie partly onshore. The remaining two, Ceara and Piaui, located between the Barreirinhas and Potiguar basins, lie almost entirely offshore.
The six basins contain a lowermost interval of continental and transitional marine sediments ranging in age from Aptian in the west to Maastrichtian in the east. Shallow marine carbonates, followed by younger open marine sands and shales, overlie the continental sequence in all basins. These basins contain up to 4 km of sediments, except the Foz-do-Amazonas which contains more than 8 km.
The evolution of these basins is intimately related to the spreading history of the equatorial Atlantic Ocean which began to open during Early Cretaceous time. Westward extensions of oceanic fracture zones form the boundaries of Recife-Joao Pessoa and Ceara basins. These basins do not have a shelf-edge high and display a half-graben structure in cross section. The Piaui and Barreirinhas basins have a shelf-edge high and display a graben structure in cross section. The Potiguar and Foz-do-Amazonas basins, although bounded by shelf-edge highs related to oceanic fracture zones, are different from the other four because some of their structures formed before the opening of the equatorial Atlantic.
Close control of the basin boundaries by oceanic fracture zones suggests that these zones formed during the initial opening of the South Atlantic. Whereas some fracture zones appear to follow old weakness zones in the Precambrian Shield, others trend at large angles to the shield fabric. A complete evaluation of the geologic history and hydrocarbon potential of this area can only be carried out within the framework of the history of the adjacent ocean basin.
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