MAJOR TECTONIC FEATURES IN THE SOUTHEASTERN BRAZILIAN MARGIN

A regional geophysical and geological dataset has been integrated to analyse the major tectonic elements along the southeastern Brazilian margin, from the Espírito Santo towards the Santos basins, the most prolific oil provinces offshore Brazil. The diverse tectono-sedimentary domains identified along the continental margin are related to the Mesozoic-Cenozoic tectonic reactivations, particularly the syn-rift extensional processes associated with the separation of the West African and South American plates in the Late Jurassic – Early Cretaceous. These processes are responsible for synthetic and antithetic normal faults that formed half-grabens and grabens within the mainland and offshore, which were filled by continental volcanics and siliciclastic rocks in the Neocomian - Barremian. Subsequent to this syn-rift phase, the transitional phase (Aptian age) is associated with siliciclastic and carbonate sediments deposited above a regional unconformity (breakup unconformity) that heralds the continental drift phase and forms a sag basin that underlies the Aptian evaporites. The regionally extensive, thick evaporite layers that occur both along the Eastern Brazilian and West African margins suggest the occurrence of an elongated and shallow gulf that was periodically invaded by sea waters during the first marine ingressions of the nascent Atlantic Ocean. The presence of a highly mobile evaporite layer resulted in the development of a characteristic tectonic style marked by salt diapirs and salt walls associated with extensional and compressional structures. The outermost boundary of the salt layers seem to correlate with the feather edge of seaward-dipping reflectors that correspond to volcanic wedges formed during the inception of oceanic crust, which is related to propagators that advanced northwards by rupturing the crust and upper mantle. Several major tectonic features are associated with syn-rift and post-rift magmatic episodes, particularly in the southern Santos Basin (Florianópolis platform), in the northern Santos and southern Campos basins (Cabo Frio region), and in the Abrolhos region of the Espirito Santo Basin.