Abstract:
The origin of dolomite has remained an enigmatic issue of earth sciences. Dolomite mineral is generally considered as a replacement phase of pre-exsisting carbonate. However, a microbial/organogenic dolomite model has been recently proposed, suggesting that dolomite can also be directly precipitated from solutions with the aid of microorganisms or organic matters, thus providing new insight into the old enigma. This paper reviews the latest progress on the microbial/organogenic dolomite model and discusses how to improve such model. Microbes facilitate low-temperature dolomite formation primarily by enhancing the saturation state with respect to dolomite. Furthermore, the negatively-charged microbial cell walls can be functioned as template for dolomite nucleation. Microbial dolomite normally displays spherical, dumbbell and cauliflower-like morphologies. Microbially-induced dolomite formation can be facilitated by elevated salinity. The role of sulfate on microbial dolomite formation still awaits resolution. The recent studies have also demonstrated that microbial exopolymeric substances (EPS) play an important role in the dewatering of Mg-H2O complexes. In the similar manner with microbial EPS, natural organic matters can also catalyze dolomite precipitation. However, growing evidence shows that microbes could only precipitate proto-dolomite rather than ordered-dolomite. More studies are required to improve our understanding of the alteration of microbial/organogenic dolomite during burial~diagenesis