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Abstract
Oliveira, Maria Jose R ., Pedro V. Zalan, Joao L. Caldeira, Arnaldo Tanaka, Paulo Santarem, Ivo Trosdtorf Jr., and Anderson Moraes,
DOI:10.1306/13351552M1003532
2012 by The American Association of Petroleum Geologists.
Linked Extensional-compressional Tectonics in Gravitational Systems in the Equatorial Margin of Brazil
Maria Jose R. Oliveira,1 Pedro V. Zalan,2 Joao L. Caldeira,3 Arnaldo Tanaka,4 Paulo Santarem,5 Ivo Trosdtorf Jr.,6 Anderson Moraes7
1Petrobras Research Center, Avenida Horacio Macedo, 950, Cidade Universitaria, Rio de Janeiro, Brazil (e-mail: [email protected])
2Petrobras/E
P (Exploration and Production)-Exp, Avenida Republica do Chile 330/16th floor, Rio de Janeiro, Brazil (e-mail: [email protected])
3Petrobras/EP (Exploration and Production)-Exp, Avenida Republica do Chile 330/16th floor, Rio de Janeiro, Brazil(e-mail:[email protected])
4Petrobras/EP (Exploration and Production)-Exp, Avenida Republica do Chile 330/16th floor, Rio de Janeiro, Brazil (e-mail:[email protected])
5Petrobras Research Center, Avenida Horacio Macedo, 950, Cidade Universitaria, Rio de Janeiro, Brazil (e-mail:[email protected])
6Petrobras/EP (Exploration and Production)-Exp, Avenida Republica do Chile 330/16th floor, Rio de Janeiro, Brazil (e-mail: [email protected])
7Petrobras Research Center, Avenida Horacio Macedo, 950, Cidade Universitaria, Rio de Janeiro, Brazil (e-mail: [email protected].)
ACKNOWLEDGMENTS
We thank PETROBRAS for permission to publish this chapter and especially Paulus Van der Ven, Edison J. Milani, Sergio Michelucci, Otaviano Pessoa, and Jose G. Rizzo for the support during this work. We also thank CGG VERITAS for permission to publish the seismic lines. We thank Elisabetta Costa (in memorian, Universita degli Studi di Parma) for running the physical models described here and Fabio Speranza (Instituto Nazionale di Geofisica) for paleomagnetic analysis. We also thank Gabor Tari, Ian Davison, Dengliang Gao, and Peter Szatmari for their peer reviews; Mario Neto C. de Araujo for discussions; and Elcio R. de Lima and Thiago Falcao for the drawings.
ABSTRACT
The Para-Maranhao 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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