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ABSTRACT

Seismic interpretation and cross section restoration have been used to evaluate the role of extension in the evolution of allochthonous salt in northern Green Canyon, Ewing Bank, and southwestern Eugene Island. The results show that extenion is relatively rare compared to other areas of the northern Gulf of Mexico, and that this is a direct consequence of the structural geometry of the allochthonous salt system. Much of the Louisiana shelf and slope is dominated by counter-regional salt systems, which are characterized by areally extensive, subhorizontal salt sheets. These sheets, or their equivalent salt welds, serve as detachments for systems of listric growth faults that may accommodate significant down-slope translation of the overburden. In contrast, most of northern Green Canyon is dominated by salt-stock canopy systems, in which the base salt or equivalent weld has considerable structural relief that effectively inhibits down-slope gravity gliding. Deep elliptical depressions in the weld are separated by saddles that underlie passive diapirs; subhorizontal salt sheets are rare and small. The few major normal growth faults are arcuate, curving around the updip and lateral margins of the elliptical lows, and accommodate only minor extension. Reactive diapirs, which grow in response to extension of the overburden, are rare. The relative lack of extension at shallow levels, however, does not preclude the possibility of significant extension at deeper levels.

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