Where is the Lower Leonard Shelf? A Depositional Model for the Blalock Lake Southeast and Powell 8300 Fields, Glasscock County, Texas

Lithofacies and microfacies analysis of reservoir rocks from the Blalock Lake Southeast field indicate in-situ mound and intermound facies. Mounds grew on remnant Strawn paleohighs across a broad carbonate ramp. Two-dimensional seismic sequence stratigraphy does not confirm a well-defined shelf margin. Rocks from the Powell 8300 field are grainstone and debris-flow facies sourced from the adjacent mounds of the Blalock Lake Southeast field. The authors recognize six major lateral facies in the two field areas: the mound facies, a flanking crinoid mudstone, apron talus, intermound peloidal mudstones, capping grainstones, and downdip grainstone and debris flows. This depositional model also includes a globally documented eustatic sea level fall in the overall transgressive upper Wolfcamp - lower Leonard cycle. The perpendicular depositional trends of the mound facies and the grainstone-debris-flow facies are useful tools that can be applied to exploratory and development efforts.