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Regional studies of seismic reflection and refraction data in the deep Gulf of Mexico basin outline in considerable detail the distribution of oceanic vs. transitional crust. Oceanic crust forms a narrow east-west belt up to 300 km wide across the deep Gulf. Most current models for early Gulf evolution suggest the belt was emplaced in the Late Jurassic following widespread deposition of salt on rifted and attenuated continental crust (transitional crust). The southern boundary is defined by a zone of prominent salt structures along the northern margin of the Sigsbee salt basin. The northern boundary is obscured below the Texas-Louisiana slope, but is inferred from the distribution of large vertical salt structures. The eastern boundary is clearly marked by onlap and pinch out of thick Jurassic sedimentary sequences. This distribution is corroborated by regional magnetic and gravity data and total tectonic subsidence analysis, and provides constraints for early Gulf basin reconstructions.
An appropriate reconstruction must account for plate motion accommodated by ocean crust formation and extension of continental crust. The data seem most consistent with a model in which the Yucatan block moved generally south and rotated somewhat counterclockwise. This reconstruction implies very little lateral displacement along transform faults between Yucatan and Florida during early basin history. This is supported by seismic stratigraphic studies and DSDP drilling in the southeastern Gulf.
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