Interpretação de dados aeromagnéticos do sistema de riftes cenozóicos da Bacia de Campos: estudo de caso no Gráben de São João

Abstract

The Campos Basin is the most prolific Brazilian oil-producing basin where largest oil fields are found and is responsible for more than 84% of all the oil produced in the Country. Six petroleum source rocks have been recognized so far, all believed to be lacustrine rocks of the Early Cretaceous rift system. The oil eventually has migrated through the overlying salt and accumulated in combination traps inTertiary turbidite reservoirs. The oilfields are mainly located in the deep water portion of Campos Basin, where the main exploration risks of the petroleum system include: (a) Identification of Early Cretaceous source rocks; (b) the viability of migration pathways through thick salt layers; and (c) the mechanism for hydrocarbon charging of suprasalt turbidite reservoirs in a deepwater mud-prone system. To address these issues properly, it is necessary to understand the regional tectonic framework and evolution of the southeast Brazilian margin. That portion of the Brazilian continental margin is not a typical passive margin as one would expect from the premises of Plate Tectonics. Several events took place since the Atlantic opening event, leading to the formation of a series of SW-NE striking onshore grabens in the Paleocene-Miocene, along corridors parallel to the present coastline. Those grabens are limited by SE-NW striking transfer faults, reactivated in the Late Cretaceous and in the Cenozoic when occurred the sedimentation of the turbidites. That reactivation was accompanied by abundant volcanism and deep-seated folds attributed to lithospheric buckling. Most all the previous published work was restricted to the analysis of regional datasets such as satellite-derived gravity anomalies, low- resolution shipboard gravity-magnetic surveys and 2D regional seismic lines. In the 2000´s several new high-resolution airborne magnetic surveys were acquired along the shallow water portion of the southeast continental margin. In the present work we integrate and interpret two distinct high-resolution airborne magnetic data in offshore Campos Basin and in the adjacent basement area, in order to build a regional structural model for the entire region. Our main goal is the identification of the subtle NW-SE fault system in the Campos Basin and their continuity to the onshore portion. To that end we have applied several enhancing techniques on the magnetic data. That approach led to the recognition of several NW-SE faults extending from the onshore basement area to the deeper, offshore, portion of Campos Basin. Due to this joint interpretation we were able to resolve the structures that were at the edges. We therefore not only were able to recover the continuity of the structures across the two surveys but also to map entirely new structures.