AAPG Bulletin, V. 82 (1998), No. 5B (May 1998 Part B), P. 1013-1036.

The Evolution of Allochthonous Salt Systems, Northern Green Canyon and Ewing Bank (Offshore Louisiana), Northern Gulf Of Mexico¹

Barry C. McBride,² Mark G. Rowan,³ and Paul Weimer³

©Copyright 1998.  The American Association of Petroleum Geologists.  All Rights Reserved

¹Manuscript received July 22, 1996; revised manuscript received April 15, 1997; final acceptance November 19, 1997.
²Energy and Minerals Applied Research Center, Department of Geological Sciences, Campus Box 250, University of Colorado, Boulder, Colorado 80309. Present address: HS Resources Inc., 1999 Broadway, Suite 3600, Denver, Colorado 80202.
³Energy and Minerals Applied Research Center, Department of Geological Sciences, Campus Box 250, University of Colorado, Boulder, Colorado 80309.

We thank the following companies and their representatives for their tremendous support and input as part of the Gulf of Mexico research consortium at the University of Colorado: AGIP, Amoco, Anadarko, BHP, BP Exploration, Burlington Resources, CXY Resources, Chevron USA, CNG, Conoco, Exxon, Marathon, Mobil, Occidental, PanCanadian, Pennzoil, Petrobras, Phillips Enterprise, Shell, Texaco, Total, Union Pacific, and Unocal. We extend special thanks to Halliburton Geophysical (now Western Geophysical), specifically to Bob Graebner, John Anderson, and Gary White, for the seismic data used in the project. We are indebted to PaleoData Inc. and Art Waterman for use of biostratigraphic data. Software donations from GeoQuest, CogniSeis Development Inc., Landmark, Platte River Associates, and Zeh Graphics are essential to the success of our program and very much appreciated. We appreciate reviews by Albert Bally, Harry Roberts, and, especially, Martin Jackson for his particularly thorough review. We thank Jonathan Irick, Jennifer Crews, and Ryan Crow for drafting. Acknowledgment is made to the Donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support for this research. 

ABSTRACT

The discovery that major episodes of subhorizontal, allochthonous salt flow have occurred in the Gulf of Mexico Basin requires a means of quantifying the evolution of allochthonous salt and associated structures to conduct both basin and petroleum systems analyses. Sequential structural restorations of allochthonous salt systems provide an evolving structural framework for integrating stratigraphic, geophysical, and geochemical data sets. In this study, interpretation of more than 10,000 km (6200 mi) of multifold seismic data, and sequential restoration of eleven profiles, were used to determine the geometry and evolution of allochthonous salt structures within Ewing Bank and northern Green Canyon protraction areas.

The results illustrate the complex geometry of the multilevel salt system and the types of interactions between counterregional and salt-stock canopy models of allochthonous salt system evolution. Sedimentary loading is accommodated by salt sheet extrusion, gravity spreading, gravity gliding, extension, salt evacuation, and contraction. Salt geometry commonly changes dramatically through time because it provides much of the accommodation for sediments and absorbs much of the extension and contraction within its overburden. The positioning and kinematics of extensional and contractional structures are controlled by salt body geometries, salt system interactions, and, most importantly, the topography of the base salt or equivalent salt weld.

The structural restorations also constrain the timing of salt sheet and salt weld formation and document the positive correlation among sedimentation rates, salt flow, and structural deformation. Cross-sectional salt area generally decreases through time in areas of salt evacuation and minibasin formation, but increases in sections crossing growing salt bodies. Three-dimensional restoration is required to determine the three-dimensional kinematics and balance of allochthonous salt tectonics.