Bacias Sedimentares da Margem Continental Brasileira
Sedimentary Basins of the Brazilian Continental Margin
Webster Ueipass Mohriak Petrobras
The Brazilian continental margin has been the object of study of severalbasin analysis projects in the last few decades. Technological advances in the acquisition, processing and interpretation of the large geological and geophysical datasets obtained by the petroleum industry resulted in outstanding advances in the geological interpretation and substantial development of new concepts related to the tectono-sedimentary evolution of the continental margin, with directimplications in the evaluation of the exploratory potential. This work presents an integrated review of the tectono-sedimentary evolution of the basins along the Brazilian continental margin, from the transform-related domains in the equatorial margin towards the divergent domains of the South American plate. This review focus on the sedimentary basins along the equatorial margin (Foz do Amazonas,Pará–Maranhão, Barreirinhas, Ceará, and Potiguar) and along the transversal and divergent domains of the plate, from the northeastern and eastern region (Pernambuco–Paraíba, Sergipe–Alagoas, Jacuípe, Camamu, Almada, Jequitinhonha, Cumuruxatiba), and extending to the southeastern and southern regions (Espírito Santo, Campos, Santos and Pelotas). A number of aborted rifs (example, Tacutu andTucano) developed during the Gondwana breakup and during the continental drift phase are also discussed. The syn-rift phase of the sedimentary basins along the continental margin is associated with extensional processes, which are responsible for synthetic and antithetic normal faults that formed half-grabens and grabens. These were filled with siliciclastic and carbonate lacustrine continentalsediments deposited during the Neocomian and Barremian. The southeastern and southern segments of the margin are characterized by a large igneous province dated as Upper Jurassic to Early Cretaceous, with tholeiitic basalts underlying the syn-rift sediments, whereas in the northeastern Brazilian margin the syn-rift sediments are underlain by Paleozoic to Mesozoic pre-rift sediments. The transitional phase(Aptian age) is associated with siliclastic and carbonate sediments deposited above a regional unconformity (breakup unconformity) that heralds the continental drift phase, which is associated with evaporite sedimentation between the Sergipe–Alagoas and Santos basins, suggesting the occurrence of an elongated and shallow gulf, which was subsequently invaded by
Parte I – Geologiamarine waters during the first marine ingressions of the nascent Atlantic Ocean. The presence of salt (halite) in the evaporites resulted in the development of a characteristic tectonic style marked by diapirs and extensional and compressional structures. The marine megasequence may be divided into a transgressive marine supersequence, with the establishment of a carbonate platform that grades intomarls and shales (Albian to Turonian), and a regressive marine supersequence (Santonian to Tertiary), with carbonate and siliciclastic facies extending from the platform toward the deep water region. The equatorial margin is characterized by a few aborted rifts along the continental platform and in the onshore region (for example, the Caciporé, Tacutu and S. Luís rifts), and by some sedimentarybasins that are characterized by an extensional phase followed by transcurrent movements associated with wrench tectonics and transform faults, forming compressional structures (e.g., along the western part of the Ceará Basin). Following the inception of oceanic crust (whose limit with the continental crust´s characterized by an abrupt segmentation by transform faults), the thermal subsidence...