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ABSTRACT

From widely spaced locations across the northern Gulf of Mexico, seismic reflection data suggest the presence of salt at great depth basinward (south) of the Sigsbee Escarpment. Seismic data from east Alaminos Canyon, central Walker Ridge, and easternmost Atwater Valley display strikingly similar reflection character and geometries in the interval between 7.5 seconds and 10.5 seconds of two-way travel time (TWTT). The salt interval lies between the Middle Cretaceous Sequence Boundary (MCSB) and interpreted basement. Above basement and below the base of autochthonous salt is interpreted an interval of variable thickness, composed of synrift and/or early postrift sediments.

The interpreted salt interval is wedge-shaped and pinches out in a basinward direction. The top of the wedge is undulatory while the wedge base appears relatively flat. Flat lying reflections onlap the wedge from a basinward direction. Other onlapping reflections infill the area between undulations on the wedge surface. Internally, mounded seismic character is observed beneath undulation crests, while a more chaotic reflection character is observed between crests, but between lines reflection character is variable. Clear internal reflection terminations are seen downlapping against the base of the wedge as the wedge pinches out basinward. Undulations in the salt wedge’s upper surface are thought to reflect early salt pillow or salt roller development. Salt within the identified interval and possessing the described reflection character and geometry may represent the basinward depositional limit of deformed autochthonous salt. This depositional limit is thought to lie close to the oceanic-extended continental crust boundary.

Similar wedge-shaped structures within this time interval have not been observed south of the Sigsbee Escarpment in Keathley Canyon or western Walker Ridge. The structures may not exist in this area, may be obscure because of poor/sparse data, or existing structures may have already been overridden by the allochthonous salt.

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