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Three-Dimensional Geometry and Evolution of a Composite, Multilevel Salt System, Western Eugene Island, Offshore Louisiana
Mark G. Rowan (1), Paul Weimer (1), Peter B. Flemings (2)
Seismic data from southwestern Eugene Island (EI), in the northern Gulf of Mexico, have been interpreted to determine the three-dimensional geometry of allochthonous salt. The main feature is a multilevel salt weld consisting of numerous lows separated from each other by ramps and saddles. Shallow portions of the weld surface commonly overhang deeper portions of the same weld system, producing a complex, almost spiraling geometry. Isolated salt diapirs are connected by the weld system and are usually found either over the saddles or near the edges of the shallow overhangs. Major normal faults, including those bounding the EI-330 minibasin, are preferentially located over the ramps in the weld surface.
The observed geometry was combined with the results of sequential restoration of several north-south profiles to determine a model for the three-dimensional evolution of the salt system. A fundamental component of the model is that the lows in the weld surface mark the location of original isolated salt bodies. These formed salt glaciers at the sea floor during periods of slow sedimentation and/or fast salt flow. Once the deep salt source was exhausted, the topographically elevated salt fountains collapsed gravitationally, initiating basin formation and salt withdrawal; thus, the original salt bodies became the locations of major depocenters flanked by growth faults rising from the ramps in the weld surface. Displaced salt moved up and laterally to higher levels, forming amalgamated sheets at the sea floor, which in turn became segmented into diapirs through a combination of extension and differential loading.
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