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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
2004. The American Association of Petroleum Geologists. All rights reserved.
Analysis of submarine slumping in the Gabon continental slope
Nabil Sultan,1 Pierre Cochonat,2 Florence Cayocca,3 Jean-Fran
ois Bourillet,4 Jean-Louis Colliat5
ois Bourillet,4 Jean-Louis Colliat51Institut Fran
ais de Recherche pour l'Exploitation de la Mer (IFREMER), Laboratoire Environnements S
dimentaires, Dpartement Gosciences Marines, P.O. Box 70, 29280 Plouzan, France; [email protected]
2Institut Franais de Recherche pour l'Exploitation de la Mer (IFREMER), Head Office, 155, rue Jean Jacques Rousseau, 912130 Issy-les-Moulineaux, France; [email protected]
3Institut Franais de Recherche pour l'Exploitation de la Mer (IFREMER), Laboratoire Environnements Sdimentaires, Dpartement Gosciences Marines, P.O. Box 70, 29280 Plouzan, France; [email protected]
4Institut Franais de Recherche pour l'Exploitation de la Mer (IFREMER), Laboratoire Environnements Sdimentaires, Dpartement Gosciences Marines, P.O. Box 70, 29280 Plouzan, France; [email protected]
5Total EP, Avenue Larribau, 64018 Pau Cedex, France; [email protected]
AUTHORS
Nabil Sultan received his Ph.D. in geotechnics from the Ecole Nationale des Ponts et Chausses, Paris, France. He joined Institut Franais de Recherche pour l'Exploitation de la Mer (IFREMER) in 2000. His main interests are laboratory and field geotechnical tests, mathematical and constitutive models in geomechanics, and slope stability and flow in porous media.
Pierre Cochonat received his Ph.D. in applied geology from the Universit Scientifique et Mdicale de Grenoble, France. He has 26 years experience in engineering geology and sedimentology. His main field of scientific interest has been the study of sedimentary processes on slope and deep-sea sediments. He is now deputy director of Ocean Research and manager of the Continental Margin Programme at IFREMER.
Florence Cayocca graduated as a civil engineer from Ecole Nationale des Ponts et Chausses, Paris, France. After a master's degree in ocean engineering at the University of California, Santa Barbara, she completed her Ph.D. in morphodynamic modeling at IFREMER. Since then, she has worked there on sediment-transport numerical modeling on the slope and in coastal seas.
Jean-Franois Bourillet graduated in 1982 from the Ecole Nationale Suprieure de Gologie de Nancy, France. He joined IFREMER in 1982 for submarine mining exploration. His main interests are coring operations, bathymetry processing, slope stability, and sedimentology of the Gulf of Biscay (western Europe).
Jean-Louis Colliat received his Ph.D. in geotechnics from the University of Grenoble, France, in 1986. He joined Geodia in 1986, then Elf in 1991, becoming Total in 2000. His main interests are offshore geotechnical engineering, from soil investigation, design studies, and offshore installation works.
ACKNOWLEDGMENTS
Authors are very grateful to B. Savoye, head of the ZaiAngo (Zaire and Angola) project at IFREMER, and A. Morash, head of the Deep Offshore Project at Total, for their financial support and data supplies. An insightful review of two anonymous reviewers helped to improve an earlier version of the manuscript.
ABSTRACT
The Gabon continental slope is selected as a case study for slope-stability analysis because of evidence of previous slide activities. Different types of data were collected from the continental slope in the Gulf of Guinea off west Africa during Guiness and ZaiAngo surveys. The offshore investigation was carried out using swath bathymetry and associated imagery, deep-towed high-resolution subbottom profiles, side-scan sonar images, observation from remotely operated vehicle Victor, and Kullenberg cores. These data reveal different examples of seafloor instabilities commonly related to fluid-escape features. These slides occur on the continental slope at low declivities, showing that slope gradient has a secondary role on the marine slope instability with respect to external triggering mechanisms such as fluid flow, earthquake, shallow gas, and gas hydrates. One case of mass slide with small downslope displacement was studied on the Gabon slope.
In this work, a pseudo
three-dimensional slope-stability analysis (Sultan et al., 2001) was undertaken. Three scenarios of instability were tested to identify the possible trigger mechanism of the observed slide instability: (1) under static gravity loading, (2) under earthquakes, and (3) under upward fluid flow. Simulation results show that static stability of the area is satisfactory. However, the stability is very sensitive to fluid escape. These results agree with sonar images showing seepage features aligned along the upslope limit of the observed slide.
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