Dissolved silica-driven dolomite precipitation in the Great Salt Lake, Utah, and its implication for dolomite formation environments

Since the discovery of dolomite, numerous attempts have been made to understand its precipitation mechanism at Earth's surface conditions. One such mechanism relies on a relationship with microbial life, where laboratory synthesis experiments have shown that specific organic molecules, such as polysaccharides, exopolymeric substances and hydrogen sulphide can promote dolomite precipitation. Other mechanisms for precipitating dolomite focus on abiotic chemical environments, such as adding dissolved silica, which lower the dehydration energy barrier for the surface Mg2+-water complex and promote disordered dolomite precipitation. Modern occurrences of dolomite in the Great Salt Lake, Utah, have been studied since the early 20(th) Century. The distribution of primary dolomite in the Great Salt Lake is spatially heterogeneous, with only the carbonate mud in the South Arm and ridge-site between desiccation cracks in the North Arm being dominated by dolomite and calcite, while stromatolites in both Arms and ooidal sands in the North Arm are composed entirely of aragonite. It was proposed that dolomite precipitation in the Great Salt Lake was possibly induced by microbial activities such as organic degradation, bacteria sulphate reduction, or other microbial metabolic by-products. However, these hypotheses could not explain the lack of dolomite in microbial mats, especially in the North Arm, which is constituted by mostly aragonite with no dolomite. Our results suggest that dissolved silica concentration is the primary control for dolomite and Mg-clay formation in the Great Salt Lake. Even though the North Arm has a much more concentrated Mg and Ca water from lack of freshwater input, dissolved silica levels in the South Arm (>0.5 mm) and the Ridge-site (ca 0.5 mm) are much higher than in the North Arm (m). Our finding could also provide a new proxy for reconstructing climate changes in the Great Salt Lake area based on dolomite content variation. Phanerozoic dolomite abundance variations may be linked to global CO2 level that facilitates global chemical weathering and dissolved silica input into palaeo-ocean.