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Basement Structure and Jurassic Evolution of the Southern Gulf of Mexico Salt Province

Abstract

There is now a general consensus that the salt basins in the northern and southern Gulf of Mexico originated as a single basin that was split apart during basin opening. As such, we expect the crustal structure and salt tectonics in the Mexican Gulf of Mexico to be related to the better-studied conjugate margin on the northern side of the basin. This presentation provides an overview of the regional geology of the Isthmian salt basin in Mexico, and compares and contrasts it with the Central Louann salt basin in the offshore US. The Isthmian salt basin can be divided into the Yucatan and Campeche salt provinces, separated across the nose of the Yucatan platform. The two salt provinces have very different crustal configurations and salt-tectonic styles. The Yucatan salt province to the east comprises a long, seaward dipping thin-salt detachment, overlain by a Jurassic extensional province accommodating many tens of km of translation. Locally present at the seaward end of this extensional province is a trough in the base of salt several km deep, in which most of the salt in the province is found. The province is a mirror image of the conjugate margin offshore Florida, and is interpreted to record extension and seaward salt flow occurring during early widening of the Gulf of Mexico Basin. The Campeche salt province to the east, by contrast, has a relatively flat-lying salt detachment, with no large phase of Jurassic extension. The crustal trough observed at the seaward end of the Yucatan province is absent here. Thick salt is much more abundant in the Campeche province than in Yucatan. There is a strong overprint of Tertiary shortening in Campeche, caused by basement shortening from the Chiapas fold-and-thrust belt. The absence of strong Jurassic extension and seaward salt flow suggests that the Campeche salt province originated as an interior basin, separated from the rest of the Louann basin by a series of basement ridges. Thus the Campeche and Yucatan salt provinces are interpreted to have had very different histories from salt deposition onwards. Salt in the Yucatan province flowed seaward during widening of the Gulf of Mexico basin, whereas salt in the Campeche province was relatively static, perched in an interior basin. During the Tertiary, Campeche's proximity to the Chiapanecan orogenic belt resulted in a compressional overprint not experienced elsewhere.