The chemical conditions necessary for the formation of microbialites.
Résumé
Whether biological and/or physico-chemical variations may have changed the abundance of microbialites over geological times remains debated. This calls for a better appraisal of the conditions necessary for the formation of modern microbialites. Here, we compiled datasets from 140 aqueous environments where modern microbialites have been reported, including their respective physico-chemical parameters. By analysing this database, we find that solutions where microbialites form have a relatively high saturation with calcite, the chemical activities of Ca2+ and CO32− being controlled by the solubility of amorphous calcium carbonate (ACC) or monohydrocalcite (MHC) in most of these localities. Further statistical analyses of two databases listing ∼8000 continental aqueous systems show that only a few of them display saturation with ACC/MHC, appearing as candidates for the detection of overlooked microbialites.