Ordovician–Silurian Carbonate Platforms on the Western Slope of the Urals: Conventional Model Revised

Based on analysis of taxonomic identifications of previously collected fossils combined with the results of a lithological study, some traditional models are revisited, and the nature of cyclic units in the sections of the western megazone of the Urals is re-interpreted. Lists of ichthyofauna from the Kuba River Formation stratotype (Middle Ural, Silurian, Ludlow) suggest a gap in the transgressive sequence of shelf carbonates. It is expressed as a blended unconformity corresponding to most of the Gorstian Stage. The sedimentary nature of the cyclic units of the Ordovician–Silurian mega-sequence are due to the irregular rate of tectonic subsidence and not related to eustatic fluctuations.