The Neoproterozoic glacial formations of the North and Middle Urals
Nickolay M. Chumakov, 2011. "The Neoproterozoic glacial formations of the North and Middle Urals", The Geological Record of Neoproterozoic Glaciations, Emmanuelle Arnaud, Galen P. Halverson, Graham Shields-Zhou
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In the North and Middle Urals, four Neoproterozoic diamictite-dominating units are known: the Churochnaya, Tany and Koyva formations and Lower Starye Pechi Subformation. A glacial origin for the diamictites is indicated by a number of characteristic features such as erratic stones, striated and faceted clasts, shales with dropstones, preferential orientation of elongated stones, the wide distribution and confinement to certain stratigraphic levels of the deposits, and the association with distinct post-glacial dolostones. Most diamictites were deposited in a glaciomarine environment and sourced from an ice sheet on the East European craton. The Churochnaya Formation also contains subordinate terrestrial and probably seasonal sea ice deposits. This formation accumulated on a glaciated continental shelf, while the Tany, Koyva and Starye Pechi formations were deposited on the outer shelf and continental slope of the eastern margin of the East European Craton. The Middle Ural sections contain the White Sea (Ediacaran) Metazoa assemblage, typical late Neoproterozoic microfossils, stromatolite associations, and radiometric dates obtained from volcanic tuffs, granosyenites, trachytes and trachyandesites. The combined data suggest that the Lower Starye Pechi Subformation was deposited in the middle of the Ediacaran Period (Early Vendian). The Churochnaya Formation of the North Urals and the Tany and Koyva formations of the Middle Urals were likely deposited in the late Cryogenian period (Early Vendian).
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In recent years, interest in Neoproterozoic glaciations has grown as their pivotal role in Earth system evolution has become increasingly clear. One of the main goals of the IGCP Project No. 512 was to produce a synthesis of newly available information on Neoproterozoic successions worldwide similar in format to Hambrey & Harland’s (1981) Earth’s pre-Pleistocene Glacial Record. This Memoir therefore consists of a series of overview chapters followed by site-specific chapters. The overview chapters cover key topics including the history of research on Neoproterozoic glaciations, identification of glacial deposits, chemostratigraphic techniques and datasets, palaeomagnetism, biostratigraphy, geochronology and climate modelling. The site specific chapters for 60 successions worldwide include reviews of the history of research on these rocks and up-to-date syntheses of the structural framework, tectonic setting, palaeomagnetic and geochronological constraints, physical, biological, and chemical stratigraphy, and descriptions of the glaciogenic and associated strata, including economic deposits.