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Mapping and classification of modern and ancient shelf margins provide a basis for a concise post-rifting history of the Gulf of Mexico basin. Many hydrocarbon occurrences in the basin can be related to styles of shelf margins and their associated slope with implications for frontier exploration in deep-water facies. Seven basic types of shelf margins have been recognized.
1. Reef-dominated carbonate margins surrounded the deep basin during the Early and middle Cretaceous. This category can be subdivided into: (a) low-relief, short-lived (ca. 10 m.y.) margins in Louisiana and Texas (Stuart City and Sligo), and (b) high-relief (1 to 3 km; 3,280 to 9,843 ft), long-lived (ca. 40 m.y.) margins elsewhere (Florida, Campeche, and Blake escarpment, Golden Lane, El Abra), which are typically associated with fore-reef talus.
2. Sigmoidal progradational carbonate margins developed landward of drowned mid-Cretaceous margins of the Florida and Yucatan platforms during the Cenozoic. Large-scale gravity slides with rollover structures have occurred along the Yucatan slope contemporaneously with deposition of sigmoidal carbonate margins.
3. Carbonate ramps with little or no seismic expression characterized the Late Jurassic, when a deep marine basin was first established, an the Late Cretaceous, following drowning of mid-Cretaceous carbonate platforms.
4. Stable progradational clastic margins with well-developed, undeformed, large-scale clinoform stratification are relatively rare in the Gulf basin. Modern examples are limited to offshore Alabama and Veracruz.
5. Unstable progradational clastic margins result from gravity sliding of the continental slope, commonly associated with salt and shale diapirism, which obscures large-scale clinoform stratification. Growth faults with major expansion and rollover characterize the shelf margin; folds and/or thrust faults characterize the lower slope. This type of shelf margin has dominated the northwestern Gulf during the Cenozoic, and now extends from offshore Mississippi to offshore Veracruz. Numerous episodes of deltaic progradation to the shelf margin have been identified in Texas and Louisiana; these clastic influxes have prograded the shelf edge as much as 350 km (215 mi).
6. Tectonically active progradational clastic margins are present in Tabasco and eastern Veracruz. There the shelf margin has prograded up to 200 km (125 mi) since the early Miocene in an area of active compression and sinistral wrench faulting. Interaction of basement tectonics with diapirs and probably gravity sliding has created great structural complexity in thick Neogene deltaic sequences.
7. Tectonically active sediment-bypassing margins characterize the early Tertiary. The continental margins of Veracruz and Cuba underwent major compressional deformation and did not develop broad constructional shelves; instead, most sediment was probably bypassed to the deep basin. At the same time, a deep-water foreland basin, probably with a similar type of margin, extended into Chiapas and central Guatemala.
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