Dolomite Crystal Morphology as an Effective Indicator of Microbial Origins: Evidence from Experimental Simulations and Sedimentary Records

Dolomite formation remains one of the most intriguing puzzles in sedimentary geology, often referred to as the “dolomite problem” . Growing evidence suggests that microbial mediation plays a critical role in overcoming kinetic barriers to dolomite precipitation. This study explores the potential of dolomite crystal morphology as a diagnostic tool for identifying microbial contributions, integrating findings from laboratory simulations and sedimentary records.Controlled experiments reveal that microbial processes produce distinct proto-dolomite crystal morphologies under varying environmental conditions. Cyanobacterium Leptolyngbya boryana induces proto-dolomite precipitation in brackish water, forming characteristic “double-spherical” crystals with hollow interiors and organic inclusions. In contrast, the halophilic bacterium Vibrio harveyi promotes the formation of single-spherical proto-dolomite crystals with unique "pinhole" features on their surfaces, indicative of microbial residue. These results highlight the species-specific influence of microbes on crystal morphology and the critical role of environmental conditions such as Mg/Ca ratios in shaping these mineralization pathways. Sedimentary dolomites from the SG-1 borehole in the Qaidam Basin (NE Tibetan Plateau) predominantly exhibit single-spherical morphologies with surface pinholes, closely resembling those produced by Vibrio harveyi in the laboratory. Although cyanobacterial fossils are present in the sediments, the observed dolomite features strongly suggest that halophilic bacteria were the primary mediators of dolomite precipitation in this system.This study demonstrates that dolomite crystal morphology can serve as a proxy for microbial mediation in carbonate systems. By integrating experimental and sedimentary evidence, these findings advance our understanding of biogenic dolomite genesis and provide insights into reconstructing paleoenvironmental and biogeochemical conditions.