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We summarize data on the biostratigraphic units of the Siberian Ordovician deposits based on pelagic groups of fauna: graptolites, conodonts, and chitinozoans. It is shown that graptolite and conodont zones and beds have a high potential for correlation. We have determined the precise zonal position of most of the lower boundaries of the Ordovician stages and informal Ordovician substages of the International Stratigraphic Chart in the Lower Paleozoic key sections of the Taimyr Peninsula, Siberian Platform, and Altai-Sayan Folded Area. [ABSTRACT FROM AUTHOR]

Based on the inventory, revision, and analysis of stratigraphic, paleontological, and lithofacies data on the area of Ordovician deposits in the southern Siberian Platform (Irkut amphitheater), the refined and detailed schemes of biofacies zonation of this paleobasin are substantiated. Schemes of zonation have been compiled for the Nyaian, Ugorian, Kimaian, Mukteian, Volginian, Kirenskian-Kudrinian, Chertovskian, and Baksanian Horizons of the regional Ordovician stratigraphic chart of the Siberian Platform. The schemes present biofacies different in lithologic composition, spread of dominant groups of fauna, and hydrochemical regime (normal-marine salinity, freshwater, or high salinity). It is shown that contrasting changes in paleogeographic environments and the spread of faunal communities under changing environmental conditions were influenced by the transgression-regression cyclicity of the evolution of the Siberian Platform paleobasin and by the proximity of the land. Specific groups of fauna localized in particular facies are described. These groups are regarded as communities that were the first to occupy the littoral zones of epicontinental sea basins in the Ordovician. [ABSTRACT FROM AUTHOR]

The new-generation regional stratigraphic chart of the Siberian Platform was accepted by the Interdepartmental Stratigraphic Committee of Russia in April 2013. Two main supplements to the chart of 1979 were made: (1) the new scale of stages, accepted by the International Commission on Stratigraphy in 2008, was presented for the Ordovician System along with the previous British standard and (2) the nomenclature of the regional stratigraphic units was supplemented by the Mukteian Horizon, which occupies an intermediate position between the Vikhorevian and Volginian Horizons. The first substantiation of the necessity of viewing this stratigraphic interval as an independent horizon was made in 1980, after it had become possible to use well cores for a more precise definition of the paleontologic characteristics and boundaries of the Vikhorevian Horizon, originally detected from several isolated sections in the Irkut amphitheater with an indistinct boundary with the overlying Volginian Horizon. Recent data, particularly those from drilling, permit a more complete paleontological substantiation of the Mukteian Horizon, consideration of its distribution in different structure-facies zones, and correlation of type sections. [ABSTRACT FROM AUTHOR]

Abstract: The results of studying Ordovician ostracods from the southeastern Siberian Platform are presented. Ordovician sections are described in brief from outcrop and core studies. Four of the ostracod zones distinguished in the Ordovician strata of the Siberian Platform have been found in the Volgian, Kirenskian–Kudrinoan, Chertovskayan, and Baksanian Horizons. Stratigraphic correlation takes into account the available data on the distribution of other groups (e.g., conodonts and cephalopods).. [Copyright &y& Elsevier]

Abstract: We analyze new geologic and geophysical data, which confirm Trofimuk’s (1960) high evaluation of the petroleum potential of the Silurian–Devonian sediments in the northwestern Siberian Platform. Priority targets are set for geologic exploration aimed at testing his scientific predictions. [Copyright &y& Elsevier]

Abstract: The Altai-Sayan Fold Belt epitomises how Phanerozoic island-arc continental crust contributed to the growth of the Palaeo-Eurasian continent. Its formation is dominated by the closure of the Palaeo-Asian Ocean (PAO) when island-arc systems and Gondwana-derived terranes accreted to the Siberian margin. Relics of the PAO related tectonic units and associated granitoids occur along the ophiolitic Charysh–Terekta–Ulagan–Sayan suture (CTUSs) between Gorny-Altai and Altai-Mongolia. Zircon LA-ICP-MS U/Pb dating of this igneous record constrains the multi-stage geodynamic PAO evolution. Primitive Kuznetsk-Altai island-arc crust formed at the Siberian margin during the Ediacaran–Early Cambrian (525–555Ma). This island-arc matured during the Middle–Late Cambrian (~510Ma) and was consumed by PAO subduction in the Late Cambrian–Early Ordovician (480–490Ma) forming the Siberian Early Caledonian accretion–collision belt. South of the CTUSs, granitic magmatism occurred within Gondwana-derived Altai-Mongolia during the Middle–Late Ordovician (450–470Ma) Palaeo-Kazakhstan assembly and during a Silurian–Early Devonian (400–425Ma) Andean-type collision. Middle–Late Devonian (360–395Ma) granitoids were emplaced as a result of the collision of Altai-Mongolia with Siberia. During final Pangaea amalgamation, the suture was strike-slip reactivated (associated magmatism ~295Ma). The youngest (220–255Ma) sampled granitoids originated in an intra-plate setting. [Copyright &y& Elsevier]

Abstract: Gold mineralization of the Tardan deposit is of different spatial occurrences and is related to different hydrothermal-metasomatic formations, the main ones being skarn-magnetite bodies, metasomatites of mineralized crush zones, and metasomatites of argillizitic-rock association. The formation of gold mineralization was a multistage process related to the repeated magmatism of the Tannu-Ola complex. It took place in a wide temperature range (400–150 °C), which determined the diversity of produced mineral assemblages. The gold mineralization associated with magnetite bodies shows a spatial correlation with magnesian and calcareous skarns and is localized in plagiogranites and gabbro-diorites of the Tannu-Ola complex intruded in the Late Ordovician. Gold mineralization that occurs in crush zones and along the fault sutures in moderate- and low-temperature hydrothermal-metasomatic rocks (propylites, beresites, serpentinites, and argillizites) formed somewhat later than skarns as a result of the intrusion of granite dike bodies. Comparative analysis of different types of gold mineralization showed both a change of mineral assemblages of the gold mineralization during the ore formation and some geochemical difference between gold and gold-bearing ores. In passing from early to late occurrences of native gold, its fineness decreases, the contents of admixtures correspondingly increase, and the gold composition changes. Gold of high-temperature rocks is rich in Cu (up to 17%), and gold of low-temperatures rocks has higher contents of Ag and Hg. [Copyright &y& Elsevier]