Crystal Geyser, Utah: Active Travertine Deposits of a Cold-water Carbon Dioxide-driven Geyser and Related Ancient Deposits of the Little Grand Wash Fault
An active travertine sloping terraced deposit has been precipitated from the cool waters erupting from Crystal Geyser, located on the eastern bank of the Green River, near the town of Green River, Utah, since 1936. The conduit of water to the surface is an abandoned oil well, which tapped into an aquifer at depth. Below the modern ochre travertine is an older deposit, which has a gray color and is a naturally occurring precursor to the modern one. Eruptions are fueled by pressure generated by the build-up of CO2. Genetically related ancient travertine deposits are found in the immediate proximity of the modern deposit, derived from fluid flow channeled through the Little Grand Wash Fault. A combination of abiotic and biotic activity contributes to the development of the modern deposit. The travertine is composed of various concentrations of calcite and aragonite, but calcite generally dominates. The iron-oxide lending the travertine its ochre color is due, in part, to filamentous iron-oxidizing bacteria, possibly Leptothrix. Textures created by iron-oxide-precipitating bacteria strongly resemble those of the ancient micro-fossil Frutexites. Abiotic constituents include pisoids and intraclasts. Intraclasts serve as the nuclei for larger pisoids. The pisoids develop their coatings tumbling inside the well vent and are expelled during eruptions. Pisoid nuclei may contain spherulites, formed both abiotically and biotically as a result of bacteria induced carbonate precipitation. Plant material, diatoms, and siliciclastics are cemented into the deposit. Carbonate textures include sparry mosaics composed of anhedral to subhedral crystals, sparse occurrences of poikilotopic cement, disrupted "lacy laminations" formed by cyanobacteria, columnar crusts, spherulites, radiating isopachous cements, and feathery crystal splays. The deposit displays laminations that range from less than 1 mm to 2 cm, often undulating due to the turbulent nature of the environment and as a result of the formation of rimstone pool and micro-terrace morphologies. The ancient aragonite deposits consists of needle-like to bladed crystals. Laminations of aragonite are truncated by iron-oxide laminae that also display textures similar to Frutexites. Iron-oxides are more pronounced in samples collected from the deposit in the nearby ridge and they may display a convoluted pattern consistent with the deforming activities of the fault.