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Paleocene - Lower Miocene Sequences in the Northern
Gulf: Progradational Slope Salt-Basin Deposition and Diminishing
Slope-Bypass Deposition in the Deep Basin
A very large northern Gulf of Mexico well database containing age, sand and paleoecological information was integrated with published seismic-stratigraphic data to create sequential lower Paleocene (Midway) through lower Miocene deposystem maps. It is apparent from our mapping that allochthonous salt-basin geometry and related depositional styles changed dramatically over that interval. In the early Tertiary, a series of discrete areas of low accumulation represent now-vanished topographic highs that were expressions of near-surface salt canopies. Unlike the modern contiguous (Sigsbee) canopy system, early Tertiary basin-margin canopies developed independently at different times. An East Texas canopy influenced Midway-Wilcox deposition, collapsed in the late Eocene and was succeeded by South Texas and South Louisiana canopies which influenced Jackson-Anahuac deposition. The latter collapsed finally in the earliest Miocene (Lentic jeff). Throughout the period large volumes of sediment were deposited at the shelf-margin behind the canopies, as prograding slope-wedges. There is also evidence, however, that prior to the Liebusella Regression, which terminates late Oligocene deposition, the small discontinuous canopies permitted significant quantities of sediment, including sand to bypass the slope and accumulate in the deep basin in front of advancing salt. These salt-bypass fans of the northern basin-margin merged with the distal facies of deep-basin fan systems fed from uplifted terrain in the Veracruz-Campeche area of Mexico and from rivers draining the southeastern United States through a southeastern Louisiana-northwestern Florida corridor. Continued slope-wedge progradation in the early Miocene overstepped salt that had been displaced from the early Tertiary canopies, re-mobilizing it to form a new canopy. Mapped patterns of accumulation rate support the view that the newly created contiguous salt canopy both buttressed the prograding slope and restricted sediment delivery to the deep Gulf basin. As the modern Sigsbee canopy system developed in the early Miocene, both the volume and sand content of salt-bypass sediments deposited in front of the advancing salt diminished.
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