Reconstruction of sedimentation in the Palaeozoic of the Timan-North Urals region: directions of research, results, problems and objectives

Sedimentation stages differing with lithocomplexes, tectonic events, and a paleogeographic situation are singled out.In the Late Cambrian-Early Ordovician stage sedimentation was defined by thePrecambrian landscape, an erosion of pre-Late Cambrian crusts of weathering,an accumulation of continental and shallow-sea terrigenous deposits in rift valleys.In the Late Ordovician-Early Devonian stage on a carbonate shelf margin local reefs which developed in a barrier reefs system were formed. Lithocomplexesrepresent a combination of carbonate platform-shelfs with variety of facies and reef barriers on the margin and platform-ramps with transgressive tracts facies.In the Middle Devonian-Early Frasnian stage on the Middle Devonian terrigenous-carbonate ramp bioherms were sporadically formed. Various MiddleDevonian horizons lie on Lower Devonian deposits. Lithocomplexes arechangeable in thickness, stratigraphical volume and lateral distribution.In the Middle Frasnian-Tournaisian stage sedimentation occurred in conditionsof an unstable tectonics, fluctuation of sea level and sea waters salinity, andLate Devonian cooling that promoted microbial communities activity. Microbial mounds were formed, and in shallow lagoons there were anoxic bottom waters.In the Late Tournaisian-Middle Carboniferous stage sedimentation was characterized by sedimentation gaps, powerful breccias formation, reduction ofbiogenic accumulation, origination of soil horizons, crusts of weathering, and siderite ores. On a deformed continental margin skeletal mounds developed. In the Late Carboniferous-Early Permian stage bioinduced cements were widespread in skeletal mounds fixing occurrence along a platform margin raisings with accumulation of phosphate-containing deposits. An overlying artinskian flysh formation reflects a deep-water foredeep origination here. In the Late Permian terrigenous sedimentation extended over the platform.