Cementstones origin in the upper silurian lagoon deposits of the Northern Urals

The Upper Silurian proximal lagoon deposits, widely developed in the Ilych River basin, were previously studied in detail. One of the surprising fabrics in them is large (up to 1.0 m in diameter) areas with zonal cements (cementstones), there are different points of view on their origin. The samples of these cementstones investigated by microscopic and isotopic methods, have a complex morphology characterized by horizontal and vertical element alterations. This internal texture is conditioned by centripetal zonal radial-fibrous calcite growth with thin layers of fine-grained dolomites. Most of the proposed interpretations (recrystallized stromatoporoids, stromatactis fabric, or methane spring cannels) were rejected because one or more cementstone features contradicted them. The paleokarst interpretation at least has no contradictions in all three characteristics considered: morphological, lithological, and geochemical. The 13C values of cementstones (and the host rocks at the boundary with them) vary within 0.9-1.95 ‰ (PDB), while the 18O values have narrower variations (25.51-25.88 ‰ SMOW in one case and 25.11-25.48 ‰ SMOW in the other case). In addition, these 18O values are higher than those in the host rocks.