Several reef-building systems occurred during Cambrian-Devonian on the Urals and adjacent regions of the East-European Platform. The first phase was manifested in the Lower Cambrian within a limited area of the western slope of the Urals. The next stage occured on the western slope of Urals during Early to Middle Devonian as a result of Caledonian orogeny. This reef complex is traced on the western slope of the Urals from the Ural River latitude on the south to Barents Sea on the north. Late Devonian bioherms on the territory of the East-European Platform are distributed over a wide area from the Western Urals to the Volga basin. On the east slope of the Urals and in West Siberia bioherms are attributed to marginal structures of depressions.
