Features of microbial structures in the "reef - lagoon" system (on example of the Upper Devonian Sedyu reef complex, Southern Timan)

Three types of microbial structures of the Sedyu Reef Comples, exposed in the Southern Timan, were described: skeletal stromatolites, fine-grained stromatolites, and microbial clotted limestones. Skeletal stromatolites were constructed by oxygenic phototrops, cyanobacteria, and made up a significant part of the Sedyu Reef. Clots were resulted from vital activity of ancient heterotrophic bacteria and widespread in the lagoon facies. Fine-grained stromatolites occupied an intermediate position. The dependence of the distribution of different types of microbial structures on the predominance of different functional groups of bacteria was revealed. The bacteria spread, in turn, were regulated by trophic links. The developed hypothetical scheme of the trophic structure of the Sedyu Reef Complex showed the presence of a large trophic loop between the reef and the lagoon, which, in general terms, repeated the modern one.