STRUCTURAL CONTROL OF RELICT KARST FEATURES IN THE OWL MOUNTAIN PROVINCE, FORT HOOD MILITARY INSTALLATION, TEXAS

The Owl Mountain Province is a karst landscape located on the eastern peninsula of the Fort Hood Military Installation with Lower Cretaceous Trinity and Fredericksburg Group carbonates found in outcrop and sub-surface. The province is dominated by a broad, dissected plateau capped by Edwards limestone, with interfingering exposures of Comanche Peak and Edwards cropping out along scarps. These scarps reveal significant karst development near Comanche Peak and Edwards boundaries, including caves, rock shelters, tufa, and tafoni associated with upward stoping, and often display significant overprinting by epigenic processes.

Many of these karst features are fracture controlled, with both local and regional trends associated with Balcones uplift and the transverse Belton High. These trends resulted in the development of conjugate joint sets within the province, exerting significant control on cave development and some sub-surface hydrologic flow regimes. Varying permeabilities have partially confined hypogene and/or phreatic waters; these confining units have elevated potentiometric pressures and promoted preferential dissolution along ascending flow paths. Grottos and niches exposed in scarp faces along the trend of major conjugate joint sets are likely remnant cave features exposed by block slope retreat. Tafoni and spongework structures indicate sluggish flow regimes within hypogene systems. The poorly understood, complex interaction of the Edwards and Trinity aquifers within the Cut Plain has created a dynamic flow regime whereby ascending fluids are partially responsible for the suite of features found in the known caves and exposed scarps.