Some peculiarities of the evolution of the calcareous algae Calcibionta at the boundary between Vendian and Cambrian

At the Vendian-Cambrian boundary calcification process commenced largely in algae being common in the Riphean. This event coincided with the start of an extensive regression cycle which occurred worldwide. Calcareous algae are united into the formal group Calcibionta and are for the most part a branch of cyanobacteria which had extinguished by the end of Mesozoic time. The mode of formation of calcareous sheath in calcibionts has no analogs among modern algoflora and prevents the preservation of evidence of the cellular structure of filaments or colonies, the fact supported by calcibionts found after the rocks had been dissolved in acetic acid. In Cambrian basins with carbonate type of sedimentation, Calcibionta were the major producers of organic matter.