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Laboratory simulation of fossilization of cyanobacterial cells in the high-carbonate medium in the presence of calcium was carried out for the haloalkaliphilic natronophilic cyanobacterium 'Euhalothece natronophila' Z-M001. This organism was isolated from the Magadi soda lake, where the bioherms consisting of mineralized coccoid cyanobacteria were found in the Quaternary sediments. The structural and chemical heterogeneity of the minerals produced during this process was established, with calcium carbonate and trona being the main products. The differences in the process of cyanobacterial cell carbonatization in soda lakes and marine or freshwater systems were determined. Initial precipitation of calcium carbonate was shown to occur due to a chemical reaction not involving cyanobacteria. At the subsequent stages, amorphous CaCO is sorbed and crystallized on the surface of some of the cells within a cyanobacterial population, resulting in formation of a shell-like mineral layer. The cells embedded in trona in the same system were shown to undergo deformation and destruction. In both cases the mineralized cells were shown to lose their photosynthetic activity. [ABSTRACT FROM AUTHOR]