Paper No. 4
Presentation Time: 9:00 AM
PHYSICAL HETEROGENEITIES AND SALINE SPRING GEOCHEMISTRY
MAAS, Benjamin J., Geology and Geophysics, Louisiana State University, Department of Geology and Geophysics, E235 Howe-Russell, Baton Rouge, LA 70803, HEADD, Brendan, Earth & Planetary Sciences, The University of Tennessee, Department of Earth and Planetary Sciences, 306 EPS Building, Knoxville, TN 37996 and WICKS, Carol, Geology and Geophysics, Louisiana State University, E237 Howe-Russell Geoscience Complex, Baton Rouge, LA 70803, bmaas1@lsu.edu
Horizontal and vertical permeability, a by-product of speleogenesis and tectonic forces, produce basin scaled heterogeneous flow most evident at springs. Commonly sedimentary sequences are more heterogeneous vertically than laterally, and because of this, the flow path the water follows in the subsurface affects the geochemical signature of individual springs. However, how the geochemistry of individual springs is affected by the flow path of the water, the sedimentary sequence and heterogeneous permeability over small spatial areas, i.e. hundreds of meters, is not well understood. The hypothesis is heterogeneous permeability will influence the geochemistry of thermal saline springs over a small spatial area due to the dependence of geochemistry on water rock interactions. The goal of this study is to analyze the geochemistry of thermal spring waters so that a better understanding of how the major and minor ions vary in a small heterogeneous system may be obtained.
Water samples from six thermal saline springs were collected over four sampling trips from south-central Oklahoma. The field area is predominately composed of Upper Cambrian and Lower and Middle Ordovician aged carbonate bedrock that has been karstified by hypogenic speleogenesis, which has resulted in the formation of numerous conduits. Additionally tectonic features related to the Hunton Anticline and the Bromide Fault are present, and add to the heterogeneous permeability of the site. Though the thermal springs are located within a 200-m area, the spring waters have concentrations of calcium, chloride, magnesium, sodium, and sulfate that span an order of magnitude. A saline solution and meteoric water are the dominant water types, as indicated by the geochemistry, and each of thermal spring has a different percentage of the two water types. Only one of the thermal springs has chloride and sodium concentrations that plot on a seawater dilution line which indicates that the water chemistry is not simply the result of halite dissolution. The differences between the thermal spring water geochemistry indicate there are poorly connected flow networks in the subsurface that are being affected by the individual flow paths through the different stratigraphic units.
