Geophysically-BASED structural framework and tectonic evolution of the Brazilian equatorial margin

Abstract

The Brazilian Equatorial Margin (BEM) encompasses a WNW to NW-trending segment along which a complex set of sedimentary basins were developed from the Neobarremian to the Albian. Recent discoveries of hydrocarbon reserves in the continental margins of Ghana, in Africa, and Guyanas/Suriname, in South America, have heightened interest in studying the Equatorial Atlantic margins. In this context, it is crucial to understand better the mechanisms that led to the formation of these basins, whose exploratory potential is still open. Most studies on the BEM either focus on small areas without comparing results to their African counterparts or involve regional reconstructions that overlook hyperextended crustal sections, thus hindering a more accurate fit. This work aims to define the deep crustal architecture of the BEM and delineate the transition from continental to strictly oceanic crust based on the merging of gravimetric, magnetic, and multichannel 2D seismic data from various sources, types, and resolutions. Our findings have allowed us to categorize the BEM into four domains, according to classification schemes and models proposed by Manatschal (2004), Osmundsen and Péron-Pinvidic (2018), Péron-Pinvidic et al. (2013, 2015): proximal (PD), necking zone (NZ), distal domain (DD), and oceanic domain (OD). These domains feature a predominance of Aptian to Albian NW-SE normal and oblique-slip faults, as well as NE-SW folds and thrusts, all of which are associated with E-W strike-slip or oblique-slip faults. The nature of the distal domain zone can vary from gradual to abrupt, depending on its location and the dominant structural style in each margin segment. The oceanward limit of the DD is marked by a continent-ocean boundary (COB) that runs orthogonal to the present-day oceanic fracture zones, unlike what has been reported in other studies. Our defined boundaries ensured a good fit between the continental crusts of the BEM and the African Equatorial Margin (AEM) during the Cenomanian period.