Print this pageIntra-Slope Northwest-Trending Lineaments and Geologic Implications in the Central Campos Basin, Offshore Brazil
Previous regional mapping has shown intra-slope, northwest-trending lineaments in eastern Brazil. Such lineaments, which are common along the South Atlantic passive continental margin, are oblique to the east-west-trending Atlantic oceanic transforms, but the nature and mechanism of formation of the oblique lineaments are unknown. This paper presents high-quality, regional three-dimensional (3-D) seismic data in the central Campos basin that show seismic signature of the lineaments. In the rifted basement and sag basin section below the Aptian salt, we observed changes in structural relief of the rifted basement top and slope gradient of the basal detachment horizon, along with the polarity reversal of the basement half graben. In the post-salt, upper Cretaceous and Tertiary section, we see variations in bathymetry, structural style, trend, sediment thickness, and depositional facies. As opposed to discrete fault planes, the lineaments are shown as zones of perturbation with low seismic coherence. In the sectional view, the lineaments are cored with salt and folds that are relatively steep, thin, and symmetric compared with those associated with listric extensional and contractional faults. In the map view, the long axes of the folds and salt change gradually to become sub-parallel to the lineaments. Seismic stratigraphic analysis indicates that the lineaments have provided accommodation space as canyons or elongate salt-withdrawal mini-basins that have exerted influence to the by-pass, deposition, and back-fill of thick sequences of upper Cretaceous-Tertiary turbidite sands. We interpret that these lineaments are deeply-rooted in the basement associated with the initial rifting and sag phase of the continental margin in the early Cretaceous. In the subsequent passive margin phase of the late Cretaceous and Tertiary, the lineaments have exerted significant influence to the turbidite deposition, salt evacuation, play fairway, and differential gravitational sliding above the basal detachment. The oblique nature of the intra-slope lineaments to the east-west-trending oceanic transforms is strikingly similar to that in the Lower Congo basin, offshore West Africa, suggesting a coherent tectonic process and conjugate rotation history of the two continental margins in association with the breakup of Gondwana and the opening of the South Atlantic in the early Cretaceous.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil