SOME PECULIARITIES OF THE EVOLUTION OF THE CALCAREOUS ALGAE CALCIBIONTA AT THE VENDIAN-CAMBRIAN BORDER

At the Vendian-Cambrian border large-scale calcification of algae wide ly abundant in the Riphean began. This phenomenon coincided with the b eginning of a great regressive cycle, which took place all over the wo rld. Calcareous algae are combined into the formal group Calcibionta, and most of them are the off-spring of cyanobacteria, which died out a t the end of the Mesozoic. By the type of calcareous-shell formation, Calcibionta have no analogs among the present-day algae. Their shells did not preserve traces of the cell structures of filaments and coloni es, which is confirmed by study of Calcibionta obtained on dissolving rocks in acetic acid. In Cambrian basins with the carbonate type of se dimentation Calcibionta were the main producers of organic matter.