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The AAPG/Datapages Combined Publications Database
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Multifold seismic reflection investigations have provided data pertinent to the problem of origin and mode of deformation of salt in the Gulf of Mexico. The Challenger seismic unit which contains Jurassic salt covered the Jurassic abyssal basin and onlapped the Campeche and West Florida continental margins; it is thought to have onlapped the Texas-Louisiana, Rio Grande, and East Mexican margins as well. The unit has an estimated average thickness of 1.5 km and a maximum thickness of at least 2.5 km. Onlap and pinchout of the Challenger unit and isostatic considerations suggest that the unit was deposited on a seafloor several thousand meters below sea level. The data are inconclusive with respect to the question of whether the salt was deposited in deep water or whether t e surface of the Gulf was greatly lowered.
The principal dissimilarity of the Challenger from overlying units derives from mobilization of salt within the Challenger. The causes of localization of salt mobilization are not clear, but salt mobility is developed best in areas where the lower, seismically transparent part of the Challenger is thickest.
The volume of salt within the Challenger equals an estimated 20 to 50 times the volume of salt in present Gulf waters. An accumulation of this magnitude required continuous replacement from the world ocean and could not have resulted from a single episode of drying-up of the Gulf of Mexico.
Four modes of salt mobilization and emplacement can be recognized: (1) geographically random diapirism continuously active from Jurassic to present in the Texas-Louisiana Shelf and upper slope, Campeche Knolls, and Sigsbee Knolls; (2) formation of sinuous, subparallel ridges beneath the Mississippi cone, probably due to differential sediment loading of the prograding delta; (3) Pleistocene overthrusting of a salt "tongue" in the central Sigsbee Scarp; and (4) late Miocene-early Pliocene mobilization of Jurassic stratiform salt in the Campeche Knolls province.
The Mexican Ridges, which some investigators have suggested are cored by salt, appear to be cored with shale.
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