AAPG Bulletin, V. 84, No. 5 (May 2000), P. 627-651.

Active Normal Faulting Beneath a Salt Layer: An Experimental Study of Deformation Patterns in the Cover Sequence¹

©Copyright 2000. The American Association of Petroleum Geologists. All rights reserved.
¹Manuscript received January 4, 1999; revised manuscript received August 25, 1999; final acceptance November 15, 1999.
²Mobil Technology Company, Dallas, Texas. Present address: Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854; e-mail: [email protected]
³Mobil Producing Nigeria, Lagos, Nigeria.
We thank Rolf Ackermann, Fred Bowes, Selena Dixon, Gloria Eisenstadt, Karen Fredricks, Malin Ingebrigtsen, Roy Schlische, Ian Sinclair, Dan Shultz-Ela, Bruno Vendeville, and an anonymous reviewer for their help during this study. In addition, Gloria Eisenstadt and Bruno Vendeville provided us with many valuable ideas and insights on experimental modeling. Finally, we thank Mobil Technology Company for its support during this study.

ABSTRACT

Scaled experimental models show that the presence of a viscous layer, such as salt, facilitates the development of extensional forced folds above active normal faults. The geometries of the extensional forced folds and their associated secondary fault patterns depend on the thickness and viscosity of the viscous layer, the thickness of the cover sequence, the strength and ductility of the cover sequence, and the magnitude and rate of displacement on the underlying master normal fault. Increasing the thickness of the viscous layer and the cohesive strength and ductility of the overburden enhances the decoupling between the deep and shallow deformation. Alternatively, increasing the viscosity of the viscous layer, the thickness of the overburden, and the magnitude and rate of displacement on the master normal fault reduces the decoupling between the deep and shallow deformation. Enhanced decoupling facilitates the formation of broad extensional forced folds and the development of detached secondary faults both near and far from the master normal faults. The model-predicted deformation patterns closely resemble those observed in the Gulf of Suez, the Haltenbanken area of offshore Norway, and the Jeanne d'Arc Basin of the Grand Banks, offshore southeastern Canada.