THE MICROBIALITES OF UTAH’S GREAT SALT LAKE: GEOLOGY VS. BIOLOGY

Great Salt Lake in northern Utah contains a wide variety of microbialite structures, but numerous questions remain about their formation and morphology. In particular, is the morphology of the microbialites only related to geologic/environmental conditions, or do different microbial communities play a role in the variety of microbialite shapes and sizes? This unique investigation pairs geologic research methods with microbiological techniques to examine the main drivers of Great Salt Lake microbialite development. Several unique morphologic characteristics exist depending on the microbialite’s location relative to wave energy, proximity to shorelines and bedrock outcrops, as well as other factors. For example, larger, taller, and more well-cemented microbial domes tend to occur in higher-energy environments (e.g., north side of Lady Finger Point, Antelope Island), whereas smaller, low-profile, poorly cemented superficial domes are common in sheltered areas (e.g., Bridger Bay, Antelope Island). Petrographic analysis reveals that microbialites in high-energy environments contain a slightly higher ratio of microbial clots to carbonate grains than structures in low-energy environments. In locales far from bedrock outcrops (e.g., Bridger Bay), the microbialites are composed mostly of clots and carbonate rip-ups, ooids, and pellets, whereas structures near steep bedrock cliffs contain significantly more lithic fragments (e.g., Buffalo Point, Antelope Island). In areas where groundwater might influence microbialite formation, the overall porosity of the structure is less due to denser, travertine-like inclusions. Biologically, all currently submerged microbialites in the South Arm of the lake are covered with a green-brown “living” microbial mat. This living layer was analyzed using next-generation DNA sequencing techniques to determine the microbial community composition at each study location. Bottom line, the microbial community across all sampled sites in the South Arm are not significantly different, indicating that geology/environmental variations are the primary driver of microbialite morphology. This new observation has significant implications regarding our understanding of microbialite formation and the interpretation of ancient analogs in the rock record.