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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The Ncogene turbidite systems of Green Canyon and Ewing Bank lease areas in the northern Gulf of Mexico are amajor exploration play. The regional sequence stratigraphy for this area has been interpreted to help define the potential areas for future exploration. Data base consists of 6300 miles of 2-D multifold seismic data well log data for 175, wells, and biostratigraphy from 180 wells. Four main intervals have been identified, which reflect different kinds of turbidite systems based upon lithologies and seismic facies. Exploration concepts must be different in each of the four intervals because of the different nature of the turbidite systems. Paleoecology data indicate that deposition of these turbidite systems occurred in bathyal water depths. Lower Pliocene sediments (5.5 to 3.0 Ma) include the 5.5, 4.2 and 3.8 sequence boundaries. The interval consists of sandrich turbidite systems. The upper Pliocene interval (3.0 to 1.4 Ma) comprises the 3.0, 2.6, 2.4, 1.9 sequence boundaries. The interval is thin in the eastern portion of the area and becomes thicker to the west. Sands develop only in the western portion of the area. The interval corresponds to when the Mississippi River avulsed to farther in the western Gulf of Mexico and sediment supply decreased significantly. The lower Pleistocene interval (1.4 to 0.7 Ma) includes the 1.4, 1.1 and 0.8 Ma sequence boundaries. The interval is predominantly shale-rich with localized sands developing in channel-levee systems and unchannelized sands. The upper Pleistocene interval (0.7 Ma to Present) consists of shale-dominated turbidite systems. Notable submarine canyons develop in this interval to the east.

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Seismic profiles, well logs, biostratigraphic data, and cross section restorations were integrated to investigate the relationships between salt tectonics and sedimentation in northern Green Canyon, Ewing Bank, and southwestern Eugene Island. Preliminary results address three aspects of salt-sediment interaction. First, minibasins have characteristic stratigraphic stacking patterns that evolve from ponded to bypass settings. The transition may occur entirely within the slope environment or be associated with shelf progradation through the minibasin. The shift can sometimes be related to salt evacuation, and in other cases to regional variations in the location and volume of clastic input. Second, different types of salt bodies have varying bathymetric expressions that may affect sequence thicknesses and facies development: reactive diapirs are overlain by graben at the sea floor; passive diapirs usually create asymmetric highs, with smooth slopes on some flanks and steep scarps on others; and diapirs modified by contraction are marked by broad topographic highs. Third, models of salt sheet emplacement by extrusion at the sea floor have important implications for the spatial and temporal shifting of sedimentation patterns. Salt bodies originally covered by condensed sections become major minibasins, while bathymetric lows that serve as turbidite conduits and depocenters may be overridden by allochthonous salt sheets. Because complex salt/sediment geometries in any area are genetically linked to surrounding basins and salt bodies, the interactions between deformation and sedimentation can be understood only by reconstructing the regional evolution of both salt and sediments. Although a daunting task, such efforts will aid in the exploration for hydrocarbons, especially in the sub-salt province.