Dolomite formation and biogeochemical cycles in the Phanerozoic

Based on present knowledge of the purely chemical controls on the kinetics of massive dolomite formation, the abundance and distribution of dolomite t hroughout the Phanerozoic remains an enigma, sometimes referred to as the ' dolomite problem'. Comparing dolomite abundance to secular variation in sea water chemistry indicates that some changes in seawater chemistry are more likely to have resulted from extensive dolomitization rather than to have c aused it. The recently formulated microbial dolomite model provides the opp ortunity to view the geological history of dolomite formation from a new pe rspective. A biogeochemical approach to the 'dolomite problem' reveals a pl ausible connection between Phanerozoic geochemical cycles and dolomite form ation. In particular, periods of more extensive dolomitization broadly corr elate with diverse indicators of decreased oxygen levels in the atmosphere and oceans. Lowered oxygen levels would have fostered a more active communi ty of anaerobic microbes, including sulphate-reducing bacteria, which in tu rn could have led to more extensive dolomitization of marine carbonates.