From Bureau of Economic Geology, The
University of Texas at Austin (www.beg.utexas.edu).
Bureau Seminar, April 06, 2007
Hydrochemical Variability and Detection of Cross-Formational Flow in the High Plains (Ogallala) and Plateau Aquifer Systems: Crockett and Glasscock Counties, Texas
Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin.
Groundwater in the Early Cretaceous-age Fredericksburg Group (“Edwards”) aquifer ranges from sulfate-poor in southeastern Crockett County to relatively sulfate-rich in the northwest part of the county. Cross plots of sulfate and total dissolved solids suggest that two distinct populations of water types are present and show systematic geographic distributions. Each population is characterized by mixing between fresh recharge water with low dissolved-solid content and more saline sulfate-poor or sulfate-rich groundwater, respectively. End-member mixing models and strontium isotope data mutually support an interpretation of local flow of sulfate-rich groundwater from the Antlers sandstone aquifer (Early Cretaceous-age Trinity Group) into the overlying Edwards aquifer in Crockett County. A strong correlation exists between carbon-14 apparent ages and Mg/Ca values in the Edwards groundwater, which suggests that abundantly available Mg/Ca data might be used as a proxy for carbon-14 apparent age. However, tritium data indicate variable mixing between ancient and modern groundwater, and, therefore, carbon-14 ages are only “effective” ages. Proportions of ancient and modern waters in the mixtures are currently unknown.