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Albian Rift Systems in the Northeastern Brazilian Margin: An Example of Rifting in Hyper-extended Continental Crust

Abstract

The progress of petroleum exploration toward ultra-deep waters along the Brazilian coast resulted in the acquisition of seismic reflection data with record as deep as 30 km (18 sec TWT), making possible the drilling of exploration wells in the distal rifted northeastern Brazilian margin. The interpretation of this dataset allowed not only the visualization of the Albian marine rift system along the entire coast, but also the identification of the boundary between the continental and the oceanic crusts and their internal structures as well. The rheological behavior of the upper and lower portion of the continental crust controls the geometry of rifted blocks, which can show a brittle or a ductile pattern, from high angle faulted blocks to rotated ones. In the northeastern Brazilian margin, covering the coast from southern Bahia to Pernambuco, these rift basins occur as half-grabens showing flip-flop geometry with its related magmatism, which occurs as extrusive magma, sills and dykes. Aptian salt domes are also present in some Albian grabens, in opposition to synchronous thermal marine basins in the Espírito Santo basin to the south, where the thickness of the Cenomanian sag section is thicker. Northward from Espírito Santo basin, the Jacuípe and Sergipe-Alagoas basins are characterized by intense magmatism represented by large intrusions and magmatic flows, sometimes as SDR's. Further north, the Pernambuco-Paraíba basin presents a typical half-graben geometry associated with huge igneous intrusive features. Wells drilled in the rift system confirmed Albian age to the rift sediments interbedded with pillow-basalts 400 meters thick. Magmatic bodies that crop out in onshore Pernambuco-Paraíba basin dated with 40Ar-39Ar method provided ages between 94–102 Ma, compatible with the age of the extrusive and intrusive features mapped in seismic lines located in the deep water domain. Furthermore, organic-rich marine shales drilled in the Albian rifts are candidates to the source rocks of Upper Cretaceous oil fields found in Sergipe-Alagoas basin. Therefore, the regional architecture of the Albian rift system plays an important role to better understand the geological evolution of the northeastern Brazilian margin.