The chemical conditions necessary for the formation of microbialites

Whether biological and/or physico-chemical variations may have changed the abun-dance 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 ana-lysing this database, we find that solutions where microbialites form have a relatively high saturation with calcite, the chemical activities of Ca2+ and CO32- being con-trolled by the solubility of amorphous calcium carbonate (ACC) or monohydrocalcite (MHC) in most of these localities. Further statistical analyses of two databases listing similar to 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.

Automated summary

The debate over whether biological and/or physico-chemical variations have affected the abundance of microbialites over time remains unresolved. To better understand the conditions necessary for the formation of modern microbialites, a database of 140 aqueous environments where microbialites have been reported was analyzed. It was found that the solutions where microbialites form have high saturation with calcite, controlled by the solubility of amorphous calcium carbonate (ACC) or monohydrocalcite (MHC). Further analysis of two similar databases of continental aqueous systems suggests that only a small number of them have saturation with ACC/MHC, making them potential candidates for the discovery of overlooked microbialites.