The Middle Ordovician to Lower Devonian (Caradoc-Lower Emsian) carbonates are the oldest and most widely pre-served shallow water carbonate strata of the Pechora Urals. Several episodes of reef growth are evident within these strata. The rather well-preserved buildups in shelf, shelf-margin and slope settings provide important insights into the intrinsic and extrinsic processes that affected reef growth along the lower Paleozoic, northeastern European Platform passive margin. Massive corals, branching bryozoans, crinoids and red algae formed bioherms on a carbonate ramp. Hemispherical and laminar stromatolites formed on bioclastic substrates in backreef and lagoonal environments. Small biostromes and bioherms were constructed by ramose corals, stromatoporoids, calcified microbes, crinoids, and diverse shelly metazoa in various shelf-to-basin carbonate settings. Encrusting cyanobacteria and calcified microbes formed microbial boundstone and stromatolites in both isolated and barrier reefs. Microbes, calcareous algae, ramose corals, problematic hydroids and stromatoporoids were the primary builders of the barrier reefs. These organisms are associated with high-diversity assemblages of brachiopods and bivalves. The lower Paleozoic European Platform was overall progradational and features an evolution from a ramp-to-rimmed platform. Initially, reefs on this platform were constructed by a low diversity community, but through the lower Paleozoic, reef builder diversity and reef community complexity increased.

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