ABSTRACT

Carbonate ramp and carbonate shelf depositional models are utilized in interpreting Lower Cretaceous carbonate stratigraphy in the Gulf of Mexico province. The lower Glen Rose (upper Trinity) high-energy, rudist reef and grainstone complex began on a low-relief carbonate ramp profile and prograded seaward over slightly deeper water, low-energy, lime mudstones and wackestones with a resultant growth of some 1.250 ft vertically over a horizontal distance of 30 miles. During late Glen Rose, Fredericksburg, and Washita time, this same high-energy facies complex built about 1,300 ft vertically in a horizontal distance of 6 miles, creating a marked break in slope between the shallow water of the shelf and a shelf margin and the adjacent deeper water of the ancestral Gulf of Mexico. This topographic break in slope changed a carbonate ramp to a carbonate shelf profile of deposition. A faster rising sea level, perhaps a result of a more rapid rate of sea-floor spreading, probably accounts for the pronounced vertical buildup.

Regional cross sections of Fredericksburg and Washita strata show the shallow-water depositional attributes of carbonates on the Central Texas platform. High-energy grainstone and rudist reef complexes separate these shallow-water carbonates and evaporites front deeper water strata in the East Texas basin and, during Washita time, in the McKnight basin.

Density and acoustical contrasts present within the prograding lower Glen Rose strata deposited on a ramp profile and in the upper Glen Rose, Fredericksburg, and Washita strata deposited at the shelf margin are sufficient to recognize the character of these buildups on reflection seismic profiles.

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