Poor taste in Texas: Tracing dissolved solid origins across the relict margin of the Greater Permian Evaporite Basin, Wichita River Watershed, north-central Texas, USA

The greater Red River system of Texas and Oklahoma, USA, is historically underutilized due to high concentrations of dissolved solids (i.e., Na+, Cl−, SO42−). Catchment geology consists largely of N-striking Permian units that transition downstream from younger, highly soluble marine carbonates and evaporites to older, less soluble terrestrial siliciclastic units. Because Permian marine evaporite-bearing units have distinct Sr and S isotopic compositions, these constituents may effectively trace stratigraphic origins and downstream mixing behavior of the dissolved solid load. This hypothesis was tested for the Wichita River Watershed, an important sub-watershed of the upper Red River Basin. Major ions and stable isotopes (C, H, O, S, Sr) prove to be effective solute tracers in this system because of compositional contrasts between evaporite, carbonate, and silicate lithologic endmembers and the large 87Sr/86Sr range between Permian seawater (<0.707) and continental siliciclastic rocks (>0.710). Western headwaters are close to isotopic equilibrium with outcropping Blaine Formation gypsum, which prospectively correlates with San Andres Formation evaporites in the Permian basin based on comparable 87Sr/86Sr and δ34SSO4 values. Progressive downstream interaction with more radiogenic siliciclastic watershed units increases the dissolved solute 87Sr/86Sr signal to values approaching modern seawater (0.709) above its confluence with the Red River. Sulfur isotopes confirm a persistent Permian evaporite influence over sedimentary pyrite oxidation. These signatures contrast markedly from stream segments whose headwaters do not intersect evaporites. Study results demonstrate the efficacy of Permian evaporite geochemical tracers to characterize spatial variations in the dissolved solid load that directly impact water quality in watersheds intersecting Permian evaporite basins.