Occurrence and Evolution of Salt in Deep Gulf of Mexico
Published:January 01, 1978
Joel S. Watkins, John W. Ladd, Richard T. Buffler, F. Jeanne Shaub, Mark H. Houston, J. Lamar Worzel, 1978. "Occurrence and Evolution of Salt in Deep Gulf of Mexico", Framework, Facies, and Oil-Trapping Characteristics of the Upper Continental Margin, Arnold H. Bouma, George T. Moore, James M. Coleman
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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 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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Framework, Facies, and Oil-Trapping Characteristics of the Upper Continental Margin
The Gulf of Mexico covers an area of more than 1,500,000sq km, has a maximum depth of about 3,700m, and includes many of the geomorphic features of large oceans.The continental shelf, slope, rise, and abyssal plain comprise the major physiographic provinces of the guldf and contain avariety of subprovinces distinguished by topographic character and geomorphic history.
The gulf shelf is a relatively smooth, gently sloping surface marked locally bylow-relief featuresformed by sea-level fluctuation during the Pleistocene, reef growth, near-surface movement of diapiric salt and mud, and faulting. Shelf width varies from about 280km off the Florida and Yucatan Peninsulas to less than 10km at the Mississippi Delta. The continental slope consists of a considerable variety of physiographic subprovinces and individual features that encircle the deep gulf floor.
The distinctive subprovinces of the gulf slope have evolved in response to reef building and constructional sedimentation on the Florida and Yucatan carbonate platforms; erosion, nondeposition, slumping, and fault ing in the Straits of Florida and Yucatan Channel; salt diapirism and differential sedimentation in the region off Texas and Louisiana; the largeaccumulation of mainly Pleistocene sediment on a former continental slope seaward of the Mississippi Delta; tectonic uplift and diapirism in theGolfo de Campeche; and shale mobilization of feastern Mexico. In contrast to the greatly varied, irregular topography of the continental slope,thedeep seafloor of the gulf (composed of continental rise and abyssal plainprovinces) is an almost featureless plain smoothed by turbidite and pelagic sedimentation and marked locally bylow-relief knolls, sedimentary aprons, and small-leveed channels.