New Mexico Geological Society Annual Spring Meeting — Abstracts

CO₂-rich springs of the western U.S. associated with Quaternary travertine and lacustrine carbonate deposits, record long-lived interactions of deeply-sourced (“endogenic”) fluids with the near-surface hydrologic regime. Springs occur along faults and fracture zones associated with continental extension (e.g., Rio Grande rift, Basin and Range, Arizona transition zone). Upwelling waters may emerge as springs along basin margins or they may mix with aquifer waters in the shallow hydrologic system. They represent diffuse degassing and a generally unrecognized flux of CO₂ into regional aquifers, and also impair water quality via high solute loads and the presence of elevated trace metal concentrations (e.g., arsenic). Geochemical mixing models indicate that only a small component of saline, radiogenic, hydrothermal fluid is needed to produce observed spring chemistries. He and C isotopes are suggestive of a deep crustal or mantle origin for the gases, linking them to magmatism and extensional tectonics. Both cool (20-35ºC) and hot springs (40-80ºC) share geochemical similarities to the chemolithotrophic microbial ecosystems found in oceanic hydrothermal systems related to extensional tectonic settings (black and white smokers at mid-ocean ridges). Microbial community analysis reveals the presence of microorganisms utilizing many of the same metabolic pathways found in oceanic hydrothermal settings. Cloning and sequencing of amplified 16S rRNA genes using universal primers identifies organisms with >95% similarity to marine denitrifiers and thermophiles, as well as novel forms (<90% 16S rRNA gene similarity). Results reveal a microbial community strikingly uncharacteristic of known terrestrial springs. Bacterial communities are similar among sampled locales in CO, AZ and NM, and include many Gamma-proteobacteria sequences that exhibit strong similarity to halophilic and marine bacteria representatives from cold seeps, hydrothermal vents, saline lakes, and Arctic brine ice. Archaeal sequences are dominated by thermophilic Crenarchaeota, detected in marine and terrestrial volcanic environments. These results suggest that the springs harbor microbial communities similar to marine vent systems and seeps due to similarities in the geochemical environment.