Interpretação sismoestratigráfica em bacia oceânica profunda na margem equatorial brasileira: porção leste da Bacia Potiguar e Alto de Touros

Abstract

The Brazilian Equatorial Margin (BEM) deep-water regions present important geological features, although few explored beyond continental shelf-break. The main objective of this study is to characterize seismically syn and post-rift sequences and some seamounts which are part of the Fernando de Noronha Ridge (FNR) in deep-water basins offshore northeastern Brazil. We used 2D post-stack high resolution seismic sections to distingue syn and post-rift tectonic phases. The syn-rift stage is marked by discontinuous and locally parallel reflectors with low amplitude and low frequencies, which are offset by normal faults in half-grabens. The post-rift stage is characterized by continuous-parallel reflectors with low to high amplitude and frequency. The volcanic intrusions affected syn-rift and post-rift sequences and partially confines deep-water basins deposits. That happened once the pre-existent material and the material deposited after the seamount rises were partially confined by continental slope and one or two seamounts. Some volcanic vents reach the ocean bottom and form dome-shaped features. Both volcanic episodes seem to have created volcanoclastic deposit marked by disorganized/chaotic seismic pattern with few continuous reflectors, indicating interbedded magma flows with sedimentary material. Seismic interpretation indicates two periods of volcanic activity: (a) Early Eocene to Late Miocene for seamounts and, (b) Neogene, for volcanic vents. Although deeper water regions can hold key points about the BEM formation and on future could represent oil and gas reservoirs, deep-water basins deposits remain poorly studied in this portion of BEM. In this sense, our paper provides a first insight about deep-water basin deposits on syn and post-rift stages and how they are affected by volcanism on area.