Microbial <scp>EPS</scp>?mediated amorphous calcium carbonate–monohydrocalcite–calcite transformations during early tufa deposition

The Holocene Wolfenden tufa deposit in south-eastern British Columbia, western Canada, preserves a unique record of the earliest stages calcium carbonate deposition resulting from microbial extracellular polymeric substances-mediated precipitation amorphous (ACC) with partial transformation to monohydrocalcite (MHC) and subsequently nanocrystalline calcite. This is first documentation mineralogy involving ACC MHC. Progressive dehydration triggered ACC–MHC–nanocrystalline calcite transformations on bryophytes, algae cyanobacteria sheaths. adsorption substances matrix molecules into ACC–MHC structures preserved polymorph incomplete transformation. Unusual concentrations biofilm filaments provided nucleation sites for precipitation. calcified resulted partially coalesced arrays nanoscale spheroids. Mesocrystalline MHC reconfigured concentric growth layers precipitate bulbous protuberances. Nanocrystalline rhombic faces developed within surfaces Dehydration these substrates micrite fabrics. Recrystallisation obliterated evidence microcrystalline spar domains as widespread encrustation fabric. Localised magnesium during biofilms needle crystals without precursor process. Microbial necessarily critical step phase process, leading has been underappreciated generally not considered. These are proposed possible template other deposits, where obscured by recrystallisation