title: Microfossils in cherts from the Middle Riphean (Mesoproterozoic) Avzyan Formation, southern Ural Mountains, Russian Federation.
abstract: A diverse assemblage of well-preserved microorganisms has been detected in black cherts from the approximately 1200 Ma-old Avzyan Formation (Suite) of the southern Ural Mountains, Russian Federation. The lower Kataskin Member contains a diverse, abundant microbiota dominated by mat-forming filamentous cyanobacteria, several types of colonial unicells, and morphologically distinctive stalked cyanobacteria. The upper Revet Member contains a less diverse biota dominated by unicellular cyanobacteria. Palaeoecological evidence indicates that the microbial community of the Kataskin Member inhabited a shallow water, presumably marine, carbonate environment. Revet microorganisms possibly lived in restricted peritidal environments.  The biostratigraphic significance of the Avzyan microbiota is limited. Many of the taxa are long-ranging; they were already abundant in Palaeoproterozoic successions and continue into the Neoproterozoic. Nevertheless, in many respects, the Kataskin assemblage is comparable to those reported from the Middle-Late Riphean deposits of Northern America, Australia and Eurasia. The following taxa are here described: Chroococcaceae-Eogloeocapsa avzyanica Sergeev, Gloeodiniopsis lamellosa Schopf emend. Knoll et Golubic; Entophysalidaceae-Eoentophysalis belcherensis Hofmann; Dermocarpaceae-Polybessurus bipartitus Fairchild ex Green et al.; Nostocaceae-Eosphaeronostoc kataskinicum Sergeev; Nostocaceae or Oscillatoriaceae-Siphonophycus robustum (Schopf) emend. Knoll et Golubic emend. Knoll et al., Siphonophycus sp.; Incertae sedis-Eosynechococcus amadeus Knoll et Golubic.
authors.affiliation: Geological Institute of the Russian Academy of Sciences, Moscow, Russian Federation.
authors.forename: V N
authors.initials: VN
authors.lastname: Sergeev
mesh_terms: D000458:Cyanobacteria / Q000145:classification*; D004783:Environmental Microbiology; D005580:Fossils; D019015:Geologic Sediments / Q000032:analysis / Q000382:microbiology*; D010163:Paleontology; D012426:Russia