EVIDENCE FOR A MIDDLE SHELF TO SHELF MARGIN ENVIRONMENT: FACIES ANALYSES AND DEPOSITIONAL ENVIRONMENT OF THE OWL MOUNTAIN PROVINCE, FORT HOOD MILITARY INSTALLATION, TEXAS

The Owl Mountain Province is a plateaued, karst landscape located in the eastern section of the Fort Hood Military Installation and characterized by Lower Cretaceous Fredericksburg Group carbonates. The topography is capped by thick sequences of the Edwards limestone; steep scarps and incised valleys along the edges host inter-fingering outcrops of the Edwards and Comanche Peak limestones, and the lower valleys are covered by alluvial sediments and intermittent outcrops of the Walnut Clay. These formations were deposited to the north and west of the main Edwards trend, and are thought to be one of the isolated shoals that developed in a restricted environment on the Comanche Shelf associated with the western flank of the Belton High.

In order to correlate and understand the depositional environment and facies development of the study area, detailed surface mapping and stratigraphic analyses of vertical and lateral facies changes have been ongoing in the Owl Mountain Province, with 21 distinct bio-and-lithofacies identified based on bulk rock descriptions. Measured sections and thin section analyses have provided evidence of a complex middle shelf to shelf margin environment that is associated with a shallow shoal. Evidence found thus far includes facies that are typical of a middle shelf environment, dominantly wackestone with mudstone and packstone common; there are also potential grainstone facies though they are less common. Bedding types and sedimentary structures found within the study also indicate a middle shelf to shelf margin environment, these include nodular-marly/flaser bedding, argillaceous thin-bedded, tabular and irregular laminations, as well as cross bedding.