A new locality for Lower Cambrian palaeoscolecidan sclerites is described in a section of the western limb of the Chekurovka Anticline. The first finds of palaeoscolecids from the Upper Atdabanian are represented by several sclerites of Wronascolex lubovae (Ivantsov et Wrona, 2004). The Botomian-Toyonian interval is characterized by numerous sclerites of the genus Hadimopanella Gedik, 1977. One species, Hadimopanella luchininae sp. nov., is described as new. Previously known species are illustrated.

The study of Silurian sediments in the central part of the Altai Mountains (Gorny Altai) by limestone dissolution has revealed two groups of spherical objects; large microspheres 90–120 µm and small nanofossils (nanospheres) 5–18 µm in diameter. Their double-layered walls are composed of standard-sized siderite microcrystals replaced by goethite. The Altai microspheres have a low Ca content (<0.5 wt %) so cannot be interpreted as calcispheres. The Altai Silurian microspheres and nanofossils (nanospheres) are tentatively attributed to biomineralized remains of loricae (shell-like envelopes) of various euglenoid alga generations.

—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.

This paper discusses the structure and facies variability of the Silurian mixed terrigenous-carbonate strata and presents new paleontological and biostratigraphic data. It attempts to refine the stratigraphic position and provide new lithologic evidence (markers) for regional manifestations of global sedimentary events (Mulde transgressive-regressive and Linde regressive events) in the Altai sections. The chronostratigraphic position of the Kuimov Horizon, a regional stratigraphic unit, has been defined based on graptolite and conodont faunas.

Tommotiida finds from the Lower Cambrian of the Khairkhan Section located within the Central Tuva trough were characterized for the first time. The assemblages of small shelly fossils are represented by species of the genera typical for the Upper Atdabanian age, such as Tannuolina, Kelanella, Lugoviella, and Microdictyon. Sclerites of four different morphotypes were identified for the Lugoviella ojmuranica species.

This paper describes for the first time the entire Cambrian skeletal problematics from the parametric well Vostok-1 (Tomsk oblast, eastern part of the West Siberian Plate) found in the Lower Cambrian Churbiga Formation, Middle Cambrian Pudzhelga Formation, and Upper Cambrian Kondes and Shedelga formations. The investigation has made it possible to detail the biostratigraphic division of the Lower Cambrian in the studied well using the small shelly fossils and to reveal confinement of the main findings of problematic skeletal remains to the shallow carbonate shelf settings.

Проведено изучение строения и фациальных особенностей силурийского смешанного терригеннокарбонатного типа седиментации. Получены новые палеонтолого-биостратиграфические данные. Высказаны предположения о стратиграфическом положении и литологических свидетельствах (маркерах) региональных проявлений в алтайских разрезах глобальных седиментационных событий трансгрессивно-регрессивного Мульде (Mulde Event) и регрессивного Линде (Linde Event). По граптолитам и конодонтам оценено хроностратиграфическое положение регионального стратона – куимовского горизонта.

The distribution of the main faunal groups of the Atdabanian Age of Early Cambrian in the Altai–Sayan folded area (ASFA) are analyzed. It is shown that Late Atdabanian assemblages of small shelly fossils of the Kuznetsk Alatau and Altai Mountains include in general the same taxa. At that time, these territories were probably situated rather close to each other and connected with the Siberian Platform. A similar result was obtained analyzing the distribution of trilobite assemblages. It is shown that the Western and Eastern Sayan Mountains have more similar forms with Mongolian assemblages. It is also shown that, in the Atdabanian, the greatest taxonomic diversity of trilobites was confined to the areas of the paleobasin where there was accumulation of organogenic carbonate sediments. It is shown that archaeocyaths from ASFA are older than the taxa characteristic of the assemblage from the Nochoroicyathus mariiskii Zone. At the boundary of the Kiya and Kameshki horizons, archaeocyaths sharply increase in abundance and many taxa with the ring and complex internal walls appeared. This boundary is traced throughout the territory of ASFA.

The lower Ust'-Kundat Formation has been studied in detail in a section along the Kiya River (Kuznetsk Alatau, Altai-Sayan folded area). The section was deposited during the Tommotian stage and is a stratotype for the Lower Cambrian Ust'-Kundat sequence comprising several members of the Ust'-Kundat Formation. Member 2 contains newly discovered and previously known species of archaeocyathids near its top found stratigraphically lower than the oldest known archaeocyathan assemblage of the Nochoroicyathus mariinskii biozone. The found archaeocyaths cannot be dated precisely and may have either Tommotian or Atdabanian ages. Small shelly fossils from the same section cover a large stratigraphic range as well. The findings call for updating the age of the upper Ust'-Kundat sequence and the Tommotian upper boundary in the regional stratigraphy of the Altai-Sayan folded area. (c) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

This paper discusses the fossil record, stratigraphy and sedimentary environments of lower Cambrian sequences that crop out in the Salair and Gorny Altai, southern part of western Siberia (Russia).Numerous and well-preserved archaeocyaths and a few small shelly fossils (SSF) have been discovered in carbonate sequences that crop out nearby the Gavrilovka village, Salair. The presence of the Gordonicyathus howelli archaeocyath Zone is established for the first time in this thick sequence of biogenic carbonates, in addition to the Nochoroicyathus mariinskii Zone, which was known previously from the Gavrilovka Formation. Both of these zones are Atdabanian in age. It is likely that accumulation of the Gavrilovka Formation took place in relatively shallow waters, along reef buildups surrounded by lagoons with archaeocyaths.In the Ak-Kaya section of the Gorny Altai, the trilobite species Alacephalus contortus and Poliellaspis rotundata , known previously from the upper Atdabanian, were discovered, only a few meters above horizons bearing lower Botoman trilobites. We may consider that the previously known age range of these two species is slightly longer and should be extended up to the lower Botoman. Alternatively, on the basis of their paleoecological affinity for agitated waters, these trilobites may be interpreted as reworked in lower Botoman strata.

The trilobites Oryctocarella sibirica (Tomash.) and Lancastria plana (Tomash.) from the basal Middle Cambrian in the vicinity of Dolgii Mys Mountain (Batenevsky Ridge, Khakassia) are described. These trilobites were previously described by V.D. Tomashpolskaya, but the original collection was subsequently lost. Repeated finds allowed a detailed study of these species. It is established that relatively small specimens of Oryctocarella sibirica are more similar to Ovatoryctocara granulata. In addition, these species have much in common with the genus Arthricocephalus in morphological characters. New material of Lancastria plana is described in detail. These trilobites were originally assigned to the genus Paraoryctocephalops, although according to the data of Blacker and Peel (1997), they should be transfered to the genus Lancastria.

The Early Cambrian history of the development of the Siberian Platform was marked by events of global significance. In the Early Cambrian the Siberian Platform was the centre of appearance of the first shelly fossils. For this reason, paleobiogeographical features of the distribution of fossils are of interest for scientists as a tool for paleogeographic and paleogeodynamic reconstructions. An analysis of changes in the Early Cambrian biota taxonomic diversity allowed us to reveal two major stages in its development: (1) Late Vendian (Tommotian and Atdabanian Stages): spreading of the Siberian biota worldwide; (2) Late Botomian-Toyonian Stages: an increase in the degree of endemism, extinction of archeocyaths, reduction in organogenic structures, deposition of black shales, and flourishing of trilobites. A permanent increase in the degree of biota endemism, which reached its maximum in the Botomian Stage, and the first appearance of migrants at the generic and species level at the same time, coincided with the first major transgressive phases. The study of the geographic distribution of diverse groups of the Early Cambrian fauna and calcareous algae of the Siberian basin allowed us to identify a number of biofacies of different age, whose boundaries do not coincide. The evolution and change in the taxonomic composition of the Siberian basin biota were affected by events of the first (Salair) phase of the Caledonian orogeny, manifested in the Altai-Sayan region much earlier than in other parts of the world and influencing the geological history of the Siberian Platform. These events resulted in the extinction and appearance of some specific groups of the Tommotian fauna in the Siberian Platform.