--> Abstract: Linked Extensional–Compressional Tectonics in Gravitational Systems of Brazil’s Equatorial Margin, by Maria José R. Oliveira, Joao L.Caldeira, Arnaldo Tanaka, Paulo Santarem, Ivo Trosdtorf Jr., and Pedro V. Zalán; #90082 (2008)

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Linked Extensional–Compressional Tectonics in Gravitational Systems of Brazil’s Equatorial Margin

Maria José R. Oliveira1, Joao L.Caldeira2, Arnaldo Tanaka2, Paulo Santarem1, Ivo Trosdtorf Jr.2, and Pedro V. Zalán2
1Petrobras Research Center, Rio de Janeiro, Brazil
2Petrobras/E&P, Rio de Janeiro, Brazil

Introduction - Gravitational systems with linked extensional–compressional tectonics are a recurring feature along the equatorial margins of Africa and Brazil, the latter being a new frontier for petroleum exploration. In the Pará-Maranhão and Barreirinhas basins, structural systems in arrays were individualized and were designated gravitational gliding cells. Internally, each cell contains a proximal extensional domain, an intermediate transitional domain, and a distal compressional domain in deep waters. In some seismic sections of the Pará-Maranhão Basin it is possible to identify igneous rocks that appear to have had a buttressing effect on the gliding of the sediments. The extensional domain is characterized mainly by synthetic listric normal faults, as well as minor antithetic planar normal faults. The compressional domain, on the other hand, shows thrusts and folds (detachment folds, fault-propagation-folds and fault-bending folds), as described by Zalán (1998, 2005). The transitional domain contains, in its upper levels, normal faults and thrusts, some of them reaching up to the sea floor. The main faults sole on a detachment surface of shales and marls, characterizing a shale tectonic system. The detachment surface for both basins is positioned at depths of about 6 km, as in the Niger Delta (Morley & Guerin, 1996).

Several methods were used to investigate these systems, including structural restoration, physical modeling, numerical modeling and correlation with onshore field data.

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