EXPLORING THE ROLE OF SURFACE-BOUND CARBOXYL-GROUP DENSITY OF ORGANIC MATTER IN LOW-TEMPERATURE DOLOMITE FORMATION

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 ordered dolomite at low temperatures. This work reveals how surface-bound carboxyl groups, such as those associated with organic matter or microbial biomass, and their density is key in dewatering Mg²⁺, an established rate-limiting step in low temperature dolomite formation. Increased carboxyl group densities of microbial biomass and organic matter are observed in: a.) saline-hypersaline environments, b.) at sharp biogeochemical gradients where cell death rates are high, and in c.) fulvic acid-rich organic matter. This mechanistic insight into low temperature dolomite precipitation is consistent with dolomite formation in depositional environments rich in organic matter and microbial models of dolomite formation and can be applied to other ancient dolomite examples.