A dense grid of multifold seismic reflection lines was combined with results of DSDP Leg 77 to subdivide the Lower Cretaceous section in the deep southeastern Gulf of Mexico into four seismic sequences (I to IV). Age and gross lithologic assignments were made by correlation with DSDP holes 535 and 540. Isochron and seismic facies maps were constructed for each sequence. These data document the complex filling of the deep southeastern Gulf of Mexico by pelagics and fine-grained carbonate debris shed from the adjacent growing Early Cretaceous margins on the east and west. This sedimentation accompanied subsidence of a rifted continental (transitional) crust formed during the early rift history (Late Triassic-Jurassic) of the Gulf basin.

The oldest unit (IV, Hauterivian-Berriasian) thins to the east, whereas unit III (Barremian-Aptian) thins to the west, suggesting a depocenter or source area shift to the east. A chaotic, hummocky, discontinuous unit (II, Aptian-mid-Albian) thinning to the south indicates deposition, in part, by northeast- or northwest-source debris flows from the flanking margins. Unit I (mid-Albian-Early Cenomanian) is a tabular parallel to subparallel sequence grading to more discontinuous facies at the base of the Florida escarpment, suggesting an eastern source. A prominent regional unconformity, characterized by erosional truncation, forms its cap. This corresponds to a 50-m thick pebbly limestone unit encountered in DSDP holes 97 and 540 that may span the entire Upper Cretaceous.

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