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AAPG Bulletin
Abstract
AAPG Bulletin, V.
2004. The American Association of Petroleum Geologists. All rights reserved.
Salt tectonics on the Angolan margin, synsedimentary deformation processes
Xavier Fort,1 Jean-Pierre Brun,2 Francois Chauvel3
1G
osciences Rennes, University of Rennes 1, UMR CNRS 6118, 35042 Rennes Cedex, France; Norsk Hydro ASA, Oil 
Energy, Exploration, N-0246 Oslo, Norway; [email protected]; [email protected].
2Lithosphere Team, Gosciences Rennes, University of Rennes 1, UMR CNRS 6118, 35042 Rennes Cedex, France; [email protected]
3Mobil North Sea Limited Grampian House, GHGW Cubicle 67, Union Row, Aberdeen, AB10 ISA, United Kingdom; [email protected]
AUTHORS
Xavier Fort earned an M.S. degree in geology (1998) and a Ph.D. in geology (2002) from the University of Rennes 1, France. His thesis topic concerned salt tectonic processes of the Angolan margin. He is now working as a consultant for Norsk Hydro and extended his interest in salt tectonics to Canada, Gulf of Mexico, and Brazil.
Jean-Pierre Brun is a professor of tectonics at University Rennes 1, France. His research mainly concerns structural geology, basin development, and lithosphere deformation, with application to the European Variscides, Aegean, Atlantic passive margins, and the North Sea. Through analog modeling, he is especially interested in the mechanics of brittle-ductile systems, with particular application to salt tectonics.
Francois Chauvel received his postgraduate degree in geology from the University of Rennes in 2001. He then went on to specialize in petroleum geoscience and graduated in 2003 with an M.Sc. degree from the French Petroleum Institute (IFP) in Paris. In 2003, Francois joined ExxonMobil, and he currently works as a production geologist on the Beryl field in Aberdeen, Scotland.
ACKNOWLEDGMENTS
This work was funded by Norsk Hydro (Norway). We are grateful to Bjorn Rasmussen for initiating the project. Thanks are due to Norsk Hydro and Western Geophysical for permission to use the seismic data presented in this paper. We also thank Jean-Jacques Kermarrec (Gosciences Rennes) for constant help and advice during experiments and Michael Carpenter for editing the English style. We are very grateful to Linn Arnesen, John Gjelberg, Nils Telnas, Arnd Wilhelms (Norsk Hydro), Susanne Sperrevik, Paul Valle (Norsk Hydro and University of Bergen), Giovanni Bertotti, and Stphanie Dupr (Vrije University, Amsterdam) for extremely fruitful discussions at various stages of the work. We would also like to thank the editor and the three referees and especially Mark Rowan for suggestions of improvement.
ABSTRACT
Seismic data from the Angolan margin and laboratory experiments on brittle-ductile 
models
are used to study thin-skinned deformation above the salt at margin scale, which is characterized by extension upslope and contraction downslope. The initial geometry of the salt basin was wedging out, both landward and seaward, and the salt was entirely covered by sediments at the onset of gravity-driven deformation. Downslope contraction is accommodated by upslope extension. The upslope extensional domain is subdivided into three subdomains with (1) sealed tilted blocks, (2) growth fault and rollover systems, and (3) extensional diapirs. We interpret this particular arrangement of extensional structures as directly resulting from variations in mechanical coupling between brittle (sediments) and ductile (salt) layers
. The downslope contractional domain is subdivided into three subdomains with (1) diapirs squeezed at late stage, (2) polyharmonic folds and thrust faults developed at early stage, and (3) folds and thrusts developed at late stage. This structural zoning results from the initiation of contraction at a distance from the salt toe and further migration of contraction immediately downslope and upslope.
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