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Groundwater Investigation and Associated Source Characterization - Appendix K
Geologic Data - Table of Contents
Surface Geologic Mapping
Direct Observation
Outcrop at CSSA is minimal in area. Creek beds provided the greatest lateral exposure. Direct observation of faulting was only possible at four locations on the CSSA reservation. The fault most clearly expressed at surface, exhibiting slicknsides, stair-step displacement, and fault breccia, is located several hundred yards north of the southern boundary road and was discovered during the initial survey. Due to the limitations of direct observation, stratigraphic continuity was a crucial tool in identifying and delineating structural disturbances.
Stratigraphy
The initial mapping survey and research of published geologic work indicated that lithologies would primarily consist of the upper and lower Glen Rose Formation and occasional Edwards limestone. Morphologically the Edwards is characterized by its resistance to weathering often forming "caprock" and the upper Glen Rose by a weathered "stair-step" pattern. The upper and lower Glen Rose are separated by a thin (1-4 ft.) bed of weather resistant limestone abundant in the foraminifera corbula martinae. The triangular millimeter sized foram is characteristic of this laterally continuous marker bed. The upper portion of the lower Glen Rose is characterized by a 2-8 foot marly limestone zone containing the echinoid Salenia texana. Bed identification relied heavily upon the occurrence of these stratigraphic index fossils due to the similarity of the upper and lower Glen Rose.
Index fossil assemblages were present at fourteen separate localities. The majority of outcrop did not exhibit characteristics unique to either Glen Rose member. Stratigraphic position was determined by outcrop position with respect to the nearest index fossil occurrence incorporating structural data. bed orientation measurements contributed to the structural interpretation, especially in the north and east pastures of the outer cantonment where stratigraphic information was minimal.
Outcrop Locality Station Number Map
Summary of Strike and Dip Data
Stereonet Projection of Strike and Dip Data for the Upper and Lower Glen Rose Formation
Stereonet Projection of Fracture Orientations, Station Number 3S