Seismic Stratigraphy of the Onshore Portion of Pernambuco Basin: Evidence of Break-Up during Middle Albian for the South Atlantic Rift in Northeast Brazil; #30324 (2014)

The present study brings new evidence about the age of the rift event alongside the eastern portion of Northeast Brazilian continental margin, which encompasses the Pernambuco, Paraíba and Natal Platform basins, investigating the record of the coastal portion of Pernambuco Basin. This region encompasses the basins northward of Alagoas Basin, linking the distensive marginal domain to the transforming domain of the Equatorial Atlantic Brazilian margin (Figure 1).This region represents the last link between Africa and South America (Rand and Mabesoone, 1982), and along the Brazilian margin, it was influenced by the nature of the sub-domains related to crustal blocks which formed the Borborema Province (Van Schmus et al., 2008; Araujo et al., 2013). This province represents a large set of Archean/Paleoproterozoic and Mesopreterozoic/neoproterozoic terrains, the relations of which were controlled by crustal-scale shear zones (Neves et al., 2000; Araujo, 2013) (Figure 1). Each of those basins is intimately linked to one of the primary subdomains. The Pernambuco Basin is related to the Pernambuco-Alagoas Massif and is bounded by the Maragogi High (south) and by the Pernambuco Shear Zone (PESZ) (north); the Paraíba Basin is related to the Central domain of Borborema and is bounded by the PESZ and the Patos Shear Zone PASZ (north); the Natal Platform is related to the Northern Domain and is bounded by the PASZ and the Touros High (north) (Barbosa and Lima Filho, 2006) (Figure 1). Additionally, the basins are located between two oceanic plateaus (Pernambuco to the south and Touros to the north), which most likely formed as a result of the interaction between basement lineaments and fracture zones during the extension of the margins (Fainstein and Milliman, 1979; Long et al., 1986). However, the Pernambuco Plateau is often associated with the Santa Helena Hotspot, considering its position between Northeast Brazil and Equatorial Guineau, which occurred approximately 100 m.y. ago (Jackson et al., 2000; Ngako et al., 2006). In fact, it was previously proposed that the rift breakup in this region occurred during the Albian (Matos, 1999), after its northward propagation from the Alagoas Basin during the Aptian. The marginal region of these basins formed, together with the Benue Trough and Rio Muni-Douala basins, a giant orthogonal structure bounded by large shear zones (Matos, 1999). Additionally, Turner et al. (2008) proposed that the breakup in the region of the Pernambuco Basin occurred approximately 104 m.y. ago. The first seismic reflection surveys-based investigation along the Brazilian Margin (Asmus and Carvalho, 1978) proposed a general tectonosedimentary model for this region, which led to the interpretation of a poor petroliferous potential. Subsequently, the region attracted few studies in three decades, resulting in one of the less studied regions of the Brazilian margin. This poor understanding was influenced by certain aspects which were found in the platform regions to the north of the PESZ: (1) high basement with shallow sedimentary cover between 400 and 200 m along the coastal zone of the Paraíba Zone and between 200 and 100 m along the Natal platform coastal zone (Barbosa and Lima Filho, 2006); (2) the age of sedimentary deposits spans from Turonian to Danian-Eocene with a lack of evaporite deposits; (3) in the platform region, the sedimentary cover thickness was estimated at only 1 to 2 km (Fainstein and Milliman, 1979; Barbosa and Lima Filho, 2006); and (4) the platform is narrow, and the shelf break is notably abrupt, creating a regional bypass zone to the oceanic basin (Barbosa and Lima Filho, 2006; Lima Filho and Barbosa, 2010). However, these characteristics are not shared by the Pernambuco Basin and its plateau, which is positioned to the south of the ZCPE (Figure 1). Since the 1980’s, it has been known that the region which encompasses the Pernambuco marginal basin possesses a plateau implanted over continental crust with an expressive sedimentary cover (Fainstein and Milliman, 1979; Alves and Costa, 1986; Mello et al., 1988). However, the lack of wells in the offshore portion and geophysical surveys caused a delay in exploration activities. The region only received attention in recent years, and the exploratory programs that are being developed will reveal the real petroliferous potential of the Pernambuco Basin. This study was based on reanalyzing the only deep well, drilled in the coastal zone of Pernambuco Basin and the only three seismic lines executed in its onshore portion. We proposed a major revision in the stratigraphic column of the basin with the inclusion of two new units in the Aptian-Albian clastic succession. Additionally, we proposed that the rift in that region developed in two phases, and the break-up occurred in the Lower-Middle Albian and the first drift phase in the onshore region is represented by an Upper Albian siliciclastic marine-influenced formation. Further, the stratigraphic relations observed in the seismic data suggested that the magmatism could have started in the Lower Albian and the existence of compressional features points to late stages of transpressive reactivation of Precambrian basement faults.