Continuous seismic-reflection profiles were recorded along 15 lines across the continental margin of the Gulf of Mexico. The steep slopes off Florida and Yucatan (Florida and Campeche escarpments) appear to have been formed by construction of coral or algal reefs during the Cretaceous Period. The adjacent upper continental slope and continental shelf were formed by prograding and upbuilding of largely calcareous sediments after the death of the Cretaceous reef-building organisms. Off Louisiana, Texas, and part of Mexico the upper continental slope and the continental shelf were formed by progradation and upbuilding of terrigenous sediment contributed largely by the Mississippi River during the Tertiary Period. These sediments buried deeply much of the Early Cretaceous reef.

Considerable alteration of the general structure off Louisiana and Texas resulted from contemporaneous intrusion of salt diapirs. Sediments in the basins between the diapirs were derived partly from the tops of the nearby salt intrusives. The Sigsbee escarpment at the seaward edge of the sedimentary prism off Louisiana and Texas is bordered by a broad ridge of diapirs, to which it may owe its origin. Although diapiric structures are best known north of the Sigsbee escarpment, others are present on the south, at the center of the Gulf basin, and as far south as Golfo de Campeche.

During Early Cretaceous time the reef once almost surrounded the Gulf of Mexico, probably leaving only one narrow connection with the open ocean at the southeast. The narrow opening and the low relative sea level, indicated by reef structure and calcareous algae nearly 3,000 m below present sea level, suggest that water circulation was restricted during Early Cretaceous time. If it had been somewhat more restricted earlier, conditions could have been suitable for the widespread deposition of Late Triassic to Middle Jurassic salt that later fed the diapiric structures.

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