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
Martha Oliver Withjack2 and Sybil Callaway3
©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.
