Microbial structures as sedimentary environments indicators in limestones of the Kizel regional substage on the Middle Urals eastern slope
The microbial structures of various genesis are rock-forming components in limestones of the Kizelovian regional substage (the Tournaisian stage) on the Middle Urals eastern slope. Comprehensive petrographic analysis of distinct grains allowed to reconstruct the carbonate platform depositional environments. Microbial structures in this study include: 1) calcitarcha (calcite “spheres” and similar sub-circular microfossils), 2) bioclasts of calcareous green algae, 3) bioclasts of calcified cyanobacteria/calcimicrobes (or calcibionts), 4) most peloids and traces of grains micritization, 5) oncolites (oncoids) and intraclasts of other microbialites. Environmental indicators evidence that sedimentation throughout the Kizelovian time was carried out within the upper subtidal photic zone, in conditions of high salinity and limited water circulation. A distribution of microfacies shows that the basin depth at an average corresponded to the normal wave basis. Microbiota taxonomic composition and bottom configuration features largely determined differences in sediment deposition characteristics. Some carbonate sedimentology terminologic issues are also discussed in this article.