Timan-northern Ural region — a model site for Paleozoic reef formation

The article presents the results of long-term studies of Paleozoic organogenic structures in the Timan-northern Ural region. The article discusses the principles of defining reefs and other organogenic structures, which allow tracing the evolution and stages of the Upper Ordovician-Lower Permian reef formation in the region based on their temporal distribution. Three stages of reef formation have been identified in the Paleozoic of the region, differing in the geometry of organogenic structures, their growth rate, and paleogeographic position. (i) The Middle Katian-Early Emsian stage is characterized by local and barrier reefs of the outer margin of the carbonate shelf, reaching great thickness. (ii) The Middle Frasnian-Early Tournaisian stage is distinguished by the formation of large microbial mounds, both on the outer margin of the shelf and on the margins of shallow-water platforms within the dissected shelf, as well as the appearance of reefs in the coastal zone of the shelf. (iii) The Late Visean-Early Sakmarian stage is characterized by mud, microbial, and skeletal mounds arising on the slopes of depressions and uplifts in the degrading carbonate shelf. The distribution and geometry of organogenic structures were determined primarily by regional tectonic events and global geobiotic processes during this period of Earth's evolution. The uniqueness of this region allows it to be proposed as a model object for the study and understanding of Paleozoic reef formation.