The mineral dolomite is abundant in the geologic record, but scarce in modern environments below 50 °C due to kinetic inhibition. Microbial mediation of dolomite has been documented under a variety of biogeochemical conditions and abiotic synthesis of disordered dolomite phases has been reported using organic and inorganic compounds. Using experimental systems with microbial biomass and carboxylated polystyrene spheres and fluids with a range of marine-type compositions we have determined that surface-bound carboxyl-group density of organic matter is key in forming low temperature dolomite. This work reveals how surface-bound carboxyl groups, such as those associated with organic matter or microbial biomass, and their surface density is key in dewatering Mg, an established rate-limiting step in low temperature dolomite formation. Because increased carboxyl group densities of microbial biomass and organic matter are observed in saline-hypersaline environments, three pure microbial cultures were grown at a variety of ionic strengths to determine how quickly carboxyl group density of these microorganisms changed. Within 10 generations cell wall carboxyl group densities were modified to densities that met or exceeded the threshold value (&gt;0.6 sites Å-2) determined experimentally for dolomite precipitation. These data tie microbial physiology to geochemical conditions that are necessary for the nucleation and precipitation of dolomite at low temperature. More broadly, a nucleation mechanism based on carboxyl group density of organic matter gives insight into low temperature dolomite precipitation in depositional environments rich in organic matter and microbial models of dolomite formation and can be applied to other ancient dolomite examples.

Role of surface-bound carboxyl-group density of organic matter in low-temperature dolomite formation

251st National Meeting (2016)

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