| It is hypothesized that several major springs in Trans-Pecos Texas are partially recharged by a regional flow system that originates in the Salt Basin and flows through the Apache Mountains into the Toyah Basin. This flow system appears to be influenced by regional fracture trends in the bedrock. This hypothesis is tested by means of three separate investigations involving groundwater geochemistry, fracture orientation, and isotopic character. Groundwater geochemical data from over 1600 samples were reduced to composite records that represent the distribution of major ions in the study area. These records were used to identify geochemical trends and to trace groundwater flow paths. Fracture traces in the study area were mapped using aerial photograph analysis and preexisting maps of the region. Length-weighted rose diagrams were used to identify predominant structural trends and to compare those trends to regional groundwater flow paths. Well and spring water samples from the study area were collected and analyzed for 87Sr/86Sr, δD, and δ18O. The stable isotopes were used to distinguish local from regional recharge, while strontium isotopes were used to trace groundwater flow paths.; Results of the geochemical analysis delineate hydrochemical facies and indicate that the springs are recharged by both local and regional components. The fracture study results indicate that distinct fracture trends exist, and these trends correlate to the regional groundwater flow paths and suggest that fractures are controlling groundwater flow. Stable isotope values from the regional flow path are significantly lighter than expected, suggesting that recharge occurred during the cooler and wetter climate of the late Pleistocene-early Holocene. 87Sr/86Sr values from samples along the regional flow path are anomalously high from interaction of groundwater with alluvial fill sediments derived from exposed Precambrian and early Paleozoic rocks at the upgradient end of the flow system. The strontium data appear to trace a plume of high 87Sr/86Sr values that correspond to the regional flow paths. 87Sr/86Sr and major ion chemistry indicate mixing of at least three end members in the regional flow system, and strontium and ion data suggest that a fourth Na/Cl water is also influencing water chemistry. |
