Litho- and biostratigraphic analysis of a number of Ordovician reference sections has been completed in five different blocks of Salair, including West-Berd' (Medvedkovo), East-Berd', Krasnoe, Gurievsk and Eltsovka. Modern data on nine mainly terrigenous and, less often, carbonate-terrigenous sections bearing fossils and composed of carbonate units and volcanic rocks including lavas, as well as tuff and tuff sandstones have been presented. The Ordovician terrigenous sedimentation in the study area was complicated by stages of volcanic sedimentation. Volcanic-sedimentary sequences were documented at four biostratigraphically dated stages in Salair: 1) the Tremadocian, 2) the late Floian, 3) the middle - late Darriwilian, 4) the late Katian - Hirnantian.

Research subject. Sandstones in the Listvenny and Marcheta Formations of the Zasur’ya Series, Gorny Altai. Aim. Reconstruction of the parent rocks and geodynamic position of the sedimentation basin of sandstones of the Zasur’ya Series. Materials and Methods. The stratigraphic position of greywackes was studied. Petrographic descriptions were carried out using whole-rock compositions obtained by X-ray fluorescence (XFR) analysis. The obtained data were analyzed; classification diagrams were compiled. Results. The geological position of the sandstones of the Listvenny Fm. (Molchanikha Locality) and Marcheta Fm. (Marcheta Locality) shows their sediments as part of an accretionary complex. Planar and vertical cross-sections for both localities were constructed. According to petrographic and geochemical data, the sandstones correspond to greywackes, i.e., first-cycle sedimentation rocks. The provenance of the Listvenny sandstones was dominated by intermediate and felsic rocks. The provenance of the Marcheta sandstones was dominated by mafic to intermediate igneous rocks. Conclusions. According to the studied geological and geochemical data, the greywackes of the Listvenny and Marcheta fms. were formed by destruction of an intra-oceanic arc. The sandstones of the Listvenny Fm. accumulated in a back-arc basin, and the sandstones of the Marcheta Fm. accumulated in a forearc basin.

--New and revised previous data based on detailed description of sections have provided better constraints on fauna taxonomy, lithology, and stratigraphy, as well as on biostratigraphic ages of sediments. The lithology and stratigraphy of several key Upper Ordovician sections in the northern Gorny Altai area show that the local units of Sandbian and Katian Savelieva and Bulukhta formations can be used as reference for the regional Ordovician division. It is suggested to include a newly distinguished Bulukhta facies zone, an area of Late Ordovician coarse clastic deposition, into the mapped Ordovician deposits of Gorny Altai. According to paleogeographic reconstructions, the deposition occurred in a large sea gulf surrounded with elevated landmasses exposed to erosion.

New paleontological and biostratigraphic data were obtained for a series of Middle Ordovician sections in the Charysh-Inya and Uimen’-Lebed’ structural-facial zones (SFZ) of the Gorny Altai. Regional stratigraphic stages, namely, the Kuibyshevo and Kostinsky horizons, are discussed in detail. By graptolites, the complete stratigraphic volume of the Kuibyshevo regional unit is defined as following zonal succession: (1) sinodentatus/Cardiograptus/Oncograptus, sinodentatus, (2) austrodentatus, (3) dentatus; and the Kostinsky regional unit within the lentus/balhaschensis/kirgisicus Zone. Beds with conodonts Eoplacognathus pseudoplanus were distinguished in the Batun Section of the Kostinsky Horizon; the same-age beds with conodonts Semiacontiodus asymmetricus–Parapanderodus striatus were distinguished in the Baraniy-1 Section. For the first time in the Voskresenka Formation, in the stratotype of the Kuibyshevo Horizon (Maralikha Section), a brachiopod assemblage was found and identified.

A new version of the Regional stratigraphic chart for the Silurian of West Siberia and explanatory note, compiled in accordance with the Russian Stratigraphic Code, introduce changes, additional and specified data in comparison with the previous chart, adopted as Silurian section of the composite Stratigraphic chart of Paleozoic of the West Siberian Plane approved as the official stratigraphic basis for all types of regional geologic activities. After the meeting in 1998, the Silurian International Standard Stages were completely updated. In accordance with the updated International Standard Stages, in 2012, the Regional stratigraphic chart for Devonian of the West Siberia and a Regional stratigraphic chart for the Cambrian of the Cis-Yenisei part of West Siberia were adopted and approved. In 2020, the Regional stratigraphic chart for the Ordovician of West Siberia was adopted and approved. New paleontological, stratigraphic, lithological, and seismostratigraphic materials on the Silurian deposits of West Siberia have been obtained and generalized. For the first time, an inclusive Regional stratigraphic chart for the Silurian of West Siberia has been compiled.

The paper presents data on the classification, structure, and biota of reef complexes from the Late Ordovician-early Silurian Altai Basin. The early Paleozoic history of the Altai Basin included the early-middle Katian, late Katian, early Hirnantian, late Telychian, and middle-late Sheinwoodian events of large-scale reef formation which produced framework reefs, mud mounds, and coral meadows. The early Paleozoic reefs of the area formed at rates of 40 to similar to 12 cm per thousand years. The late Telychian reef system, which formed in 0.51-1.0 Myr, occupied the largest area of the basin. The lateral extent of reef systems in the Late Ordovician-early Silurian basin of Altai depended more on the rates of vertical and lateral growth, as well as on the previous sea bottom topography and clastic inputs, than on the duration of reef formation. Carbonate deposition in the Altai basins of that time can be simulated with a general model implying formation of distal barrier reefs.

The mountainous Gorny Altai in southern Siberia constitutes the western part of the Altai-Sayan Folded Belt in the northwestern part of the Central Asian orogenic belt, which contains precious records of the lost major Proterozoic-Paleozoic ocean called the Paleo-Asian Ocean (PAO). This paper briefly introduces the latest microfossil (radiolarian and conodont) information recovered from the Lower Paleozoic siliceous and carbonate sequences of the Gorny Altai. The fossils of planktonic biota inhabited in PAO range back to the early Cambrian, in which the world's oldest radiolarians are included. In addition, numerous well-preserved conodonts as well as graptolites were recovered from Cambrian, Ordovician, and Silurian strata in the Gorny Altai. These recorded the Early Paleozoic biodiversity and their secular change both in pelagic and continental margin settings within PAO.

A new version of the Regional stratigraphic chart for the Ordovician of the West Siberian Lowland and the explanatory note, compiled in accordance with the Russian Stratigraphic Code, introduce changes, additional and specified data in comparison with the previous (first edition) chart. Since 1998, the stages of the Ordovician chart were changed completely. New stages – Tremadocian, Floian, Dapingian, Darriwilian, Sandbian, Katian and Hirnantian were adopted by Interdepartmental Stratigraphic Committee of Russia. The independent Regional Stratigraphic Scheme for the Devonian of the West Siberian Lowland and the Regional Stratigraphic Scheme for the Cambrian of the Pre-Yenisei Part of West Siberian Lowland were adopted. The proposed scheme for the Ordovician of West Siberian Lowland fills the lower part of the Ordovician-Silurian interval for the West Siberia. New paleontological, stratigraphical, lithological, seismo-stratigraphical data for the Ordovician of the West Siberian Lowland were obtained and generalized. For the first time independent Regional stratigraphic chart for the Ordovician of the West Siberian Lowland was compiled.

The paper focuses on presumable sources of coarse carbonate material transported into the Visean Northern Kharaulakh basin. The sand to pebble components of the Krestyakh conglomerate unit originated by medium and distant transport by debris flows (turbidity currents) along submarine canyons from the place of their initial littoral deposition to relatively deep accommodation basins. The carbonate material was most likely derived from Ordovician, Silurian, and Devonian sediments, which are currently represented by their analogs in Kotelny Island. The sediments of the Northern Kharaulakh basin store a record of two geological events: (1) middle Visean collision of Siberia with the Laurussian supercontinent and rifting of some terranes off the Siberian сraton, and (2) late Visean collision of the Kara terrane with the northern margin of Siberia.

New data on lithology, stratigraphy and paleontology of the Middle Ordovician strata cropped out in the Teletskoe Lakeside, Altai, are discussed. New section of the Samysh Formation is described. Plates with obtained collection of conodonts and trilobites are presented.

—The paper presents new data on the upper Silurian litho- and biostratigraphy of the Gorny Altai area. Sediments within this interval store a succession of taxonomically representative middle–upper Ludfordian, lower Pridoli, and Lower Devonian (Lochkovian–Pragian) conodont assemblages. The new fauna constraints made a basis for updated correlations of the local and regional stratigraphic units at the Silurian/Devonian boundary of Gorny Altai with the stages of the International Stratigraphic Chart. The correlation results reveal a mismatch between the boundaries of the local and regional Silurian units and the respective boundaries of stages in the International Stratigraphic Chart.

Рассмотрены предполагаемые источники сноса грубообломочного карбонатного материала в визейский бассейн Северного Хараулаха. Установлен генезис псефито-псаммитовых образований крестяхских конгломератов – среднеи дальне-магистральный перенос по подводным каньонам из инициального прибрежного участка накопления за счет деятельности суспензионных потоков в конечный относительно глубоководный участок седиментации. Наиболее вероятным материнским источником масштабного образования карбонатного обломочного материала следует считать ордовикские, силурийские и девонские преимущественно карбонатные осадочные образования, аналоги которых известны на о. Котельный. В Северном Хараулахе, в слагающих его осадочных образованиях наблюдаются феномены проявления двух геологических событий. Первое из них можно сопоставлять со средневизейским столкновением Сибирского палеоконтинента и суперконтинента Лаврусии (Laurussia), с отрывом террейнов от Сибирского кратона, а второе – с поздневизейской коллизией Карского террейна с северной окраиной Сибирского палеоконтинента.

Study of the Ordovician sedimentary sequences of Gorny Altai and Salair has revealed lithological and paleontological features correlating with global sedimentary events: (1) The Acerocare Regressive Event (an initial event in the Early Tremadocian); (2) Black Mountain Transgressive Event (Early Tremadocian); (3) Peltocare Regressive Event (Tremadocian); (4) Kelly Creek Regressive Event (Late Tremadocian); (5) Ceratopyge Regressive Event (Late Tremadocian); (6) Billingen Transgressive Event (Early Floian); (7) Stein Lowstand Event (Middle Darriwilian); (8) Vollen Lowstand Event (Sandbian); (9) Arestad Drowning Event (Middle Sandbian); (10) Frognerkilen Lowstand Event (Early Katian); (11) Linearis Drowning Events 1 and 2 (Middle Katian); (12) Terminal Husbergoya Lowstand Event (Hirnantian); and (13) Hirnantian Lowstand Event (HICE) (Late Ordovician). The chronostratigraphic levels with traces of the global sedimentary events in the Uymen-Lebed structural-facies zone (SFZ) (Gorny Altai) differ from those in the Charysh-Inya and Anui-Chuya SFZ (Altai). In the Ordovician, the Altai basin located in the Charysh-Inya and Anui-Chuya SFZ was a marine area separated from both the Uymen-Lebed basin and the coeval Salair basin. The traces of the global sedimentary and/or biotic events in the Altai and Salair sections can be used as a precise basis for direct correlation of the local stratigraphic units with the units of the International Stratigraphic Chart.

Изучены позднедевонские конодонты из кремнистых и карбонатных пород верхней части акбасайской свиты по левому борту сая Куле Зеравшано-Гиссарской горной области (Узбекистан). Установлено семь конодонтовых зональных ассоциаций франского и фаменского ярусов верхнего девона.

Late Devonian conodonts, recovered from the siliceous and carbonate rocks of the upper part of the Akbasay Formation on the left side of the Kule Gorge, Zeravshan-Gissar mountainous area (Uzbekistan), are studied. Seven conodont associations are defined for the Frasnian–Famennian interval.

The origin and biostratigraphic constraints of the Krestyakh conglomerate remain among most controversial issues in the Late Paleozoic history of the Northern Kharaulakh basin. The Krestyakh conglomerate is a sequence of coarse sand to pebble-size sediments at the base of the Late Paleozoic Verkhoyansk elastic complex. According to geological, lithological, and sedimentation data, the Krestyakh conglomerate in the Atyrdakh Formation is composed of debrites i.e., deposits carried by debris flows that fill submarine canyons. The Verkhoyansk elastic deposition began at the middle Visean stage of the Early Carboniferous.

The first finds of Upper Devonian radiolarians in cherty rocks of the Akbasay Formation, Zeravshan-Gissar mountainous area, are reported. Nineteen species of spherical and spiny forms were identified and assigned to 8 genera. Finds of co-occurring conodonts and radiolarians enabled the refinement of the proposed age of radiolarian associations.