Ecostratigraphic Model for Shelf Platform Development of Middle Cretaceous (Stuart City) Limestones of South-Central Texas: ABSTRACT

Abstract

ABSTRACT A new shelf platform model is developed for the Middle Cretaceous strata of South Central Texas based on an ecostratigraphic basin analysis. The concept of ecostratigraphy integrates the various ecologic parameters along time planes so that sequential distribution of magnafacies is observed. Analyses of the Stuart City Trend and associated facies suggest that the shelf platform is formed in a subsiding basin and is developed in two stages. The first involves a platform stage, the second a vertical stacking stage. Shelf platform development is a continuous process beginning in the ramp limestones assigned to the lower Glen Rose Formation. These Trinitian carbonates develop barrier reefs and prograde across the shelf. The debris slope at the base of the barrier reefs forms an elevated platform which maintains the reef organisms within their preferred shallow-water habitat and above the relatively deeper waters of the shelf. When the debris slope reaches the early Fredericksburgian shelf edge, that is maintained by the continental slope, the material is carried beyond the point of stabilization of the debris slope and moves down the continental slope to the abyssal plain. Progradation ceases but barrier-reef development continues and forms a near vertical zone of barrier reefs associated with the continental shelf edge. The barrier trend, which is created at the close of the platform stage, forms the base upon which vertical barrier growth is initiated. In this region, the vertical stage is formed during the Fredericksburgian, continues into the Washitan, and develops as a result of stretched, upward-shoaling cycles.