# AAPG Bulletin

Abstract

AAPG Bulletin, V. 87, No. 7 (July 2003),

P. 1123-1144.

## Release faults, associated structures, and their control on petroleum trends in the Recncavo rift, northeast Brazil

### Nivaldo Destro,1 Peter Szatmari,2 Fernando F. Alkmim,3 Luciano P. Magnavita4

1Petrobras Research Center, Ilha do Fundo, Quadra 7, 20179-900, Rio de Janeiro, Brazil; nivaldo@cenpes.petrobras.com.br
2Petrobras Research Center, Ilha do Fundo, Quadra 7, 20179-900, Rio de Janeiro, Brazil
3Department of Geology, Federal University of Ouro Preto, Morro do Cruzeiro, 35400-000, Ouro Preto, Minas Gerais, Brazil
4Petrobras Exploration and Production Department, Antnio Carlos Magalhes Avenue, 1113, 41856-900, Salvador, Bahia, Brazil

## AUTHORS

Nivaldo Destro received his degree in geology and an M.Sc. degree in structural geology from the Escola de Minas of the Federal University of Ouro Preto, where he is also conducting a Ph.D. project. He joined Petrobras in 1986 as an exploration geologist. Currently, he is a structural geologist at Petrobras Research Center in Rio de Janeiro, Brazil. His work has concentrated on the sealing properties of faults.

Peter Szatmari received his diploma in geology from the Eotvos University in Budapest, Hungary and his Ph.D. from the University of Edinburgh, United Kingdom. After a few years as a visiting fellow at Princeton University, United States and working as a consultant, he joined Petrobras Research Center in 1980, teaching and organizing research groups in tectonics. His main interests are the role of Fischer-Tropsch synthesis in petroleum origin and salt tectonics.

Fernando F. Alkmim received his degree in geology from the Escola de Minas of the Federal University of Ouro Preto (1978) and his Dr.rer.nat. degree in geology from the Technical University of Clausthal, Germany (1985). Alkmim is currently a professor at the Federal University of Ouro Preto, teaching field geology and tectonics. His research focuses on fault dynamics and Precambrian geology.

Luciano Magnavita received a degree in geology from the University of Braslia, Brazil, in 1976. He joined Petrobras in 1978, where he worked in the exploration department in Salvador. He obtained a Ph.D. in geology in 1992 from Oxford University, England. Since then, he has been working with several Brazilian basins. His main interests are tectonics and sedimentation in extensional basins, salt tectonics, and sealing processes associated with faulting.

## ACKNOWLEDGMENTS

This paper is a result of a Ph.D. project by N. Destro for Ouro Preto Federal University, Brazil. We thank Maria Alice N. F. de Arago for the helpful contribution in the identification of release faults in the Recncavo rift. Andr A. Bender made thoughtful review and suggestions on an earlier version of this manuscript. Walter B. Maciel and Carlos Eduardo B. de Salles Abreu are thanked for their thoughtful comments on the influence of release faults in the formation of turbidity systems. John H. Shaw, John Lorenz, and an anonymous referee are thanked for their thorough, helpful, and constructive reviews. We thank Petrobras for provision of financial support and permission to publish. F. F. Alkmim received support from CNPq (Brazilian Council for the Scientific and Technological Development) grant #300833/99-7.

## ABSTRACT

Release faults are rift cross faults, which develop to accommodate the variable displacements of the hanging-wall block along the strike of normal faults. Release faults are nearly perpendicular or obliquely oriented to the strike of the normal fault they are related to. They have maximum throws adjacent to the parent normal fault and die out in the hanging wall away from it. They form to release the bending stresses in the hanging wall and do not reflect the orientation of the regional stress field in a basin. Commonly, they show normal-oblique displacements and are preferentially located along the strike ramps. Release faults may also act at the scale of an entire basin, reaching displacements of thousands of meters. Joints, shale, and salt diapirs may develop in association with release faults. Because all these structures represent domains of stress release, they may work as conduits for oil migration and oil traps in extensional basins. This is the case of the Recncavo basin in northeastern Brazil, a Cretaceous failed rift, connected to the eastern Brazilian continental margin basins. In the Recncavo basin, two large-scale release faults, with displacements in the order of 3 km, developed in the hanging wall of the rift border faults and control the location of the main oil fields.

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