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Abstract

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 on lapped the Texas-Louisiana, RioGrande,and East Mexican margins as well. The unit has an estimated average thickness of 1.5 km and a maximum thickness of at least2.5km.On lap and pinch out of the Challenge run it and isostatic considerations suggest that the unit was deposit edona sea floor several thousand meters below sea level.The data are inconclusive with respect to the question of whether the salt was deposited indeep water or whether the surfaceof 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 are as where the lower,seismically transparent part of the Challenger is thickest.

The volume of salt with in the Challenger equals an estimated 20 to 50 times the volume of salt inpresent 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 upperslope, Campeche Knolls,and Sigsbee Knolls;(2)formation of sinuous,sub parallel ridges beneath the Mississippi cone,probably due to differential sediment loading of the prograding delta;(3)Pleistocene over thrusting of a salt“tongue”in the central Sigsbee Scarp;and(4)late Miocene-early Pliocene mobilization of Jurassic stratiformsalt 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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