Regional restoration across the Kwanza Basin, Angola: Salt tectonics triggered by repeated uplift of a metastable passive margin

Michael R. Hudec,¹ Martin P. A. Jackson²

¹Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, University Station, Box X, Austin, Texas 78713-8924; email: [email protected]

²Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, University Station, Box X, Austin, Texas 78713-8924

AUTHORS

Mike Hudec received his Ph.D. from the University of Wyoming. He has worked for Exxon Production Research and taught at Baylor University. He joined the Bureau of Economic Geology in 2000, where he is codirector of the Applied Geodynamics Laboratory. His current research interests include palinspastic restoration of salt structures, salt-sheet emplacement mechanisms, and minibasin initiation.

Martin Jackson received his Ph.D. from the University of Cape Town in 1976, taught at the University of Natal, and joined the Bureau of Economic Geology in 1980. He established and codirects the Applied Geodynamics Laboratory. His current research interests include salt-sheet emplacement mechanisms, passive-margin tectonics, and behavior of salt in orogenic belts.

ACKNOWLEDGMENTS

We thank WesternGeco for providing the seismic data on which much of our regional section was based, Seismic MicroTechnology for providing Kingdom Suite, and Paradigm Geophysical for use of Geosec-2D. We also thank Sonangol for their help in the publication of this paper. Review comments by Bill Brumbaugh, Webster Mohriak, and Mark Rowan were extremely helpful. Diagrams were drafted by Nancy Cottington, David Stephens, and Pat Alfano under the direction of Joel L. Lardon and by the authors. Publication was authorized by the director, Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin.

The project was funded by the Applied Geodynamics Laboratory consortium, which comprises the following oil companies: Anadarko Petroleum Corporation, BHP Petroleum (Americas) Inc., BP Production Company, ChevronTexaco, ConocoPhillips, EnCana, Eni S.p.A., ExxonMobil Upstream Research Company, Marathon Oil Company, Petroleo Brasileiro, S.A., Repsol YPF, Total, Unocal, and Woodside Energy Ltd.

ABSTRACT

Restoration of a 375-km (230-mi)-long section across the Kwanza Basin, Angola, shows three stages of deformation detaching on Aptian salt, each caused by basement tectonics. First, tilting related to postrift thermal subsidence initiated early Albian deformation, shortly after salt deposition ended. Deformation waned in the late Albian, probably because of thinning of salt lubricant beneath the extensional province. The second phase of deformation was triggered by hitherto unrecognized crustal uplift beneath the continental rise around 75 Ma (Campanian). Uplift led to salt extrusion and seaward advance of the Angola salt nappe over the abyssal plain. Exposure of the nappe toe removed the buttress provided by abyssal-plain cover, which rejuvenated seaward translation. Third, Miocene basement uplift below the shelf steepened the bathymetric slope and greatly accelerated downslope translation. This deformation is now slowing because accelerated sedimentation on the abyssal plain reduced the relief of the system and blocked salt-nappe advance.