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The basic structural and stratigraphic framework of the Gulf of Mexico was established by events that occurred during the Late Triassic and the Jurassic. Cretaceous and Tertiary events only accentuated and modified this framework. During the Late Triassic and Early Jurassic, continental conditions prevailed over most of the southern part of the North American plate. Marine deposition was restricted to parts of western and central Mexico that were covered by embayments of the Pacific Ocean. As the North American plate started to separate from the South American and African plates, tensional grabens began to form in the area. They were filled with red beds and volcanic rocks.
It was not until late in the Middle Jurassic (Callovian) that Pacific marine waters began to reach the Gulf of Mexico area across central Mexico. They intermittently flooded the preexisting grabens and, between floods, evaporated to produce extensive salt deposits (Louann Salt). The salt differed markedly in thickness according to the rate of subsidence in the grabens. Little or no salt was formed in the intervening high areas. During the Late Jurassic, Pacific marine waters progressively covered an increasingly large part of the Gulf of Mexico and surrounding areas as a result of continued subsidence, sea-level rise, or both. Connection with the Atlantic, however, was not established until late Kimmeridgian or Tithonian time.
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