TESTING THE MICROBIAL MODEL FOR LOW-TEMPERATURE DOLOMITE PRECIPITATION (Invited Presentation)

Recent studies have demonstrated that microorganisms play a significant role in the formation of dolomite at low-temperatures. The majority of this research has targeted bacterial metabolisms, surfaces and their extra-cellular polysaccharides (EPS), yet specific mechanisms of nucleation and precipitation remain elusive. Using mixed microbial consortia and pure cultures of methanogens and heterotrophic bacteria, we precipitated dolomite at 30°C in as few as 40 days. Fluids used in these experiments mimicked marine fluids with a range of Mg/Ca ratios as well as supersaturation of carbonate minerals, including dolomite, calcite, and aragonite. Dolomite did not precipitate in sterile controls nor in vessels containing metabolizing microorganisms. Based on these results and quantification of cell wall functional group density, we propose a surface nucleation model for dolomite precipitation. We propose that low temperature dolomite nucleation and precipitation is not metabolically constrained but rather controlled by the surface character of microbial cells, EPS or potentially other organic carbon in the system. Functional group density of organic matter and microorganisms provides a unifying model for how, when, and where dolomite nuclei form and may provide clues to de-convolute microbial, organogenic and perhaps abiotic sources of dolomite.