ANOTHER STEP TOWARD ANSWERING THE DOLOMITE QUESTION

After years of study of naturally occurring outcrops and attempted synthesis under laboratory conditions, the process of dolomitization is still not well understood. In recent years actively forming CaMg(CO₃)₂ has been observed in South American and Australian lagoons rich in sulfate-reducing bacteria. The discovery of this organic-mediated process only explains a piece to the dolomite mystery and produces more questions such as: Is the naturally forming dolomite restricted to lagoons, swamps, and brackish waters with a particular strain of sulfate-reducing bacteria?

Two sets of experiments were designed to synthesize both organically and inorganically derived dolomites under laboratory conditions. The organic set consisted of six pressure vessels, each with different variables that influence dolomitization, and used multiple strains of sulfate-reducing bacteria that are naturally found in local stagnant, non-saltwater environments. The inorganic set consisted of four pressure vessels, two designed for proto-dolomite precipitation and two designed for ideal dolomite precipitation, each with different controlled variables. The organic vessels were placed into 32°C oven for 2568 hours, and the inorganic vessel were placed into two ovens set at 100°C and 200°C for 1512 hours.

Both the organic and inorganic experiments precipitated carbonates which may contain dolomite, as determined by XRD analysis. Distinction of proto-dolomite versus ideal dolomite is difficult, however. The organic experiments confirm the presence of sulfate-reducing bacteria (strain unidentified). These results indicate that the environment in which organically mediated dolomitization takes place may not be restricted to lagoons and brackish waters; dolomite can precipitate in fresh water environments in the presence of sulfate-reducing bacteria.