--> Sedimentological and Structural Interactions Between Mobile Salt and Carbonate Systems in SE Mexico

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Sedimentological and Structural Interactions Between Mobile Salt and Carbonate Systems in SE Mexico

Abstract

Abstract

Carbonate platform(s) founded on salt structures offer significant opportunities for the development of reservoir facies. During the Jurassic and Cretaceous, SE Mexico was mainly basinal. Coeval movement of Callovian salt initiated by tectonics and loading, led to the development of intrabasinal highs (salt swells) on which carbonate platforms grew. Development of these platforms initiated with the deposition of low energy mound facies and slumping down their margins. Platforms then developed further, either by uplift of the salt high or upward growth of the platform above wave base. Facies include peritidal platform interior with bioclast grainstone shoals on the margins. Associated slope deposits include bioclastic and lithoclastic carbonate breccias and turbidites. Uplift of the platform above sea level may lead to erosion, karstification and reworking. If the underlying salt is dissolved this may lead to collapse brecciation. Salt withdraw may occur at any time, causing collapse of the platform that will then be preserved as a body of collapse breccia enclosed by basinal facies. Provenance of clasts within these breccia bodies would be dominated by platform interior facies with an absence of clasts derived from basinal or carbonate slope settings. Salt movement continued to influence reservoir development after deposition as it migrated through the sedimentary succession. Salt withdrawal structures are recognised by cross-cutting bodies of breccia in a matrix of sheared mud rock, stratigraphic anomalies such as misplaced bodies of evaporites, unusually thick or thin units, and stratigraphic units out of sequence. Bodies of stratified breccio-conglomerate that lack evaporites but contain reworked exotic clasts may represent salt emerging on the sea floor with dissolution of evaporites and reworking of insoluble clasts. Mesozoic sections of SE Mexico were particularly suitable for the interaction of salt and carbonate sedimentation because depositional conditions were favourable to carbonate production. Examples of Cenozoic carbonates are fewer in number because of the deeper-water nature of the basin system. The interaction of salt and carbonates in this southern part of the Gulf of Mexico should be taken as seriously by explorationists as the interaction of salt and siliciclastics on its northern side.