Linked Extensional-compressional Tectonics in Gravitational Systems in the Equatorial Margin of Brazil
Maria José R . Oliveira, Paulo Santarem, Anderson Moraes, Pedro V. Zalán, João L. Caldeira, Arnaldo Tanaka, Ivo Trosdtorf Jr., 2013. "Linked Extensional-compressional Tectonics in Gravitational Systems in the Equatorial Margin of Brazil", Tectonics and Sedimentation: Implications for Petroleum Systems, Dengliang Gao
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The Pará-Maranhão and Barreirinhas basins in the equatorial margin of Brazil contain gravitational gliding systems composed of three structural domains: a proximal extensional, a distal contractional, and a transitional (or translational) domain between the two others. The main faults of these domains detach on a decollement surface of shales and marls, presumably overpressured. Several methods were applied to investigate these thin-skinned tectonics systems, including interpretation of seismic sections, physical modeling, numerical modeling, restoration of cross sections, and integration with field data. These methods indicated that thrusts developed in a classical backstepping sequence with younger thrusts developing in the hanging wall and with landward migration of depocenters through geologic time. Out-of-sequence thrusts were observed locally. The results of cross section restorations suggested that the total amount of shortening exceeded the total amount of stretching in the basal layers, close to the detachment surface, whereas stretching exceeded shortening in the upper layers. Our conclusions point out that gravitational gliding was caused by the combined effect of sedimentary loading, slope gradient, and probably, pore fluid overpressure, with gliding events being triggered by episodic reactivations of the intervening Romanche and Saint Paul fracture zones.
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The influence of tectonics on sedimentation and hydrocarbon accumulation is different among extensional, strike-slip, and contractional structural styles. Addressing the role of different structural styles and syntectonic sedimentation in petroleum systems is essential to assess the hydrocarbon potential of sedimentary basins. This 18-chapter volume is small enough to focus on the interplay among tectonics, sedimentation, and petroleum systems. Yet it is big enough to cover the diversity of structural styles in important petroliferous sedimentary basins around the globe, including those in west Africa, east Africa, east Brazil, east United States of America, Gulf of Mexico, South China Sea, the Russian Arctic, and the Mediterranean Sea.