Recent research and geological mapping have shown problems with officially accepted chronostratigraphic scales for the Pleistocene of Siberia, especially in their uppermost parts. Results of 21st century studies, using latitudinal correlation of late Quaternary events reflected in Upper Pleistocene and uppermost Middle Pleistocene stratigraphic units of glaciated northern Russia, provide a solid basis for updating these scales. This correlation uses stratigraphic marker levels traceable by characteristic paleoclimatic proxies supported by modern geochronometry. This principle levels are represented by descriptions of the rocks of the main temperate and cold stages (thermomers and cryomers in the Russian Stratigraphic Code) with examples of their mass dating in key sections. Summarized, they would support the important parts of the regional chronostratigraphic scales. The most valuable feature of modern chronometry is that it is a statistically robust chronological framework, which is provided by series of datings. It is also important to control correlations using collateral instrumental dating methods. Under discussion herein are four major correlation levels established from sedimentological, paleontological and chronometric proxies and traceable as climatoliths—i.e., paleoclimate-based stages – from Timan to Taimyr. Correlation of underlying strata is largely dependent on Upper Pleistocene data. A correlation table is proposed as an aid in developing new regional stratigraphic schemes.
A study of the geology of the Verkhnyaya Gora strata in the Berezhekovo-5 section of the Kurtak geoarcheological region, based on numerous detailed outcrops, shows its deluvial-solifluctional genesis. The results of the analysis of the therio- and malacofaunas from the Verkhnyaya Gora strata suggest that the most probable age of host deposits, based on the summary of all available paleontological data, is early Neopleistocene. Most of the small mammal fauna from the Verkhnyaya Gora strata at the Berezhekovo-5 locality formed during the MQR 5 biochron (up to the boundary with the MQR 4 biochron) and corresponds to the level of late Vyatkino faunas of Western Siberia and late Tiraspol’ faunas of Eastern Europe. Ecological characteristics of the identified small mammal taxa allows the recognition of three biochronologically close but ecologically distinct faunal assemblages: steppe, forest-steppe, and periglacial. Considering the biochronological interpretation of the microtheriofauna, the presence of remains from multiple faunal assemblages in mixed state within the Verkhnyaya Gora strata can be explained by accumulation of paleontological material during the MQR 5 biochron against the background of changing landscape-climatic environments spanning Marine Isotope Stages (MIS) 16 to the onset of MIS 13. Thus, an early Quaternary age for the subaerial Verkhnyaya Gora strata in the stratotype Berezhekovo-5 section, Kurtak region, Yenisei River, is deemed substantiated for both the local stratigraphic scheme of the Minusinsk Basin and the regional stratigraphic scheme of the Altai-Sayan mountain region.
The chronology, size, and drainage patterns of ice-dammed lakes in the high-mountain depressions of the Russian Altai, as well as their influence on topography changes and sedimentation of the main valleys during the Pleistocene, remain highly debatable. The main reason is different interpretation of key sections and landforms; the different sets of research methods; the objective difficulties of applying numerical dating techniques; and the discrepancies in chronological determinations obtained by different dating techniques. A comprehensive geological and geomorphological study based on OSL and 14C dating allowed us to propose our own version of Pleistocene events in the upper Chuya River basin. The age of glaciolacustrine deposits in the Chagan key section indicates powerful glaciation in the mountainous framing of the Chuya Depression as early as the Middle Pleistocene—ca 160–180 ka ago (MIS 6). However, the ice-dammed (probably single) lake, which left the highest (up to 2100 m a.s.l.) shorelines preserved in the topography on the slopes of the Chuya and Kurai Depressions, existed no earlier than 90–80 ka ago, i.e., in the Late, not Middle Pleistocene, probably in MIS 4. The view that the Chuya Depression was filled in MIS 4 to a level of 2250 m a.s.l. does not yet have a geochronological basis; existing calculations of the volume of the single Kurai-Chuya lake at this level are purely hypothetical. The last lake in the Chuya depression, with a level of about 1890 m a.s.l., existed during the Last Glacial Maximum (MIS 2) about 37 (25)–16 (14) ka ago, and was drained over a short period of time. The Kurai Depression in MIS 2 was occupied by lake at least 25 ka ago. Around 19 ka ago the Kurai paleolake had a water level of 1730 m a.s.l. (depth up to 270 m near the dam) and extended as a narrow bay into the Chuya Valley between the Kurai and Chuya depressions. Sharp and significant drop in the lake’s level occurred at that time, but about 16 ka ago its level was still no lower than 1570 m a.s.l. No later than 16–14 ka ago the main part of the Kurai Depression had completely drained. The damming of not only the old but also the new Chuya River valley at the outlet of the Kurai Depression by the Maashey Glacier, and subsequently by its moraines, was a key reason for the change of direction of flow of the Chuya River. At the beginning of the Holocene, small lakes of non-glacial origin existed at the mouths of both depressions and in the Chuya Valley between them. The comprehensive description of studied sections applying geochronological, geological, paleontological and geomorphological methods allows us to classify them as key sections for reconstructing the Pleistocene evolution history of the Chuya and Kurai Depressions and the Altai highlands as a whole. Refinement of the stratigraphic scale of the Altai Quaternary deposits should be considered based on the results of these studies.
Ideas about the age and climatic conditions of the Valdai interstadials on the Russian Plain are based on biostratigraphic and limited 14C dating data. The chronometric reference of the Valdai interstadial deposits is not always reliable, including due to the use of the 14C method at the limit of its accuracy. Their paleobotanical characterization is complicated due to the lower specificity of plant complexes in contrast to interglacial deposits. This makes it difficult to conduct spatiotemporal correlations of Upper Pleistocene warmings stages over a large territory. We applied a comprehensive approach to the study of Upper Pleistocene buried peat deposits in a well-known section near the Verkhnie Nemykari village in the Smolensk region based on their 230Th/U and 14C dating and paleobotanical study. It has been revealed that the lower peat in the section accumulated during the pre-optimal and optimal phases of the Mikulino Interglacial. The 230Th/U age of the peat layers corresponding to the interglacial optimum is 112–106 ka, which is consistent with previously obtained 230Th/U dates for Mikulino organogenic deposits on the Russian Plain. The upper peat layer was dated using 230Th/U and 14C methods. The close age intervals were obtained in the range of 50–40 ka. According to paleobotanical data, a successive change in forest vegetation took place during the accumulation of the upper peat horizon: birch forests, spruce-birch forests, spruce-pine forests with larch, and spruce-birch-pine forests. These new data suggest that the upper peat horizon was formed during the Middle Valdai period, in the initial phases of MIS 3, under relatively favorable interstadial conditions that were slightly cooler than interglacial conditions. Despite the tentative age estimate of the upper peat layer, we propose to extend this comprehensive approach to a new study of known sections containing Valdai interstadial deposits. In combination with OSL dating of minerogenic deposits, this approach is promising for clarifying issues of chronostratigraphy of Upper Neopleistocene interstadial deposits in the Russian Plain.
This paper proposes a substantial refinement of the regional stratigraphic scheme of Upper Neopleistocene loess deposits in the central East European Plain. The Aleksandrov quarry is considered as the main stratotype section of the late Neopleistocene. A variety of modern paleogeographic methods, including paleosol, biostratigraphic, radiocarbon (14C) and optically stimulated luminescence (OSL) dating, were used in this study. During the Mikulino Interglacial, the Ryshkovo paleosol MIS 5e (marine isotope stage) or Ryshkovo pedolithic complex formed under accumulative mesorelief conditions. During the first Early Valdai cooling, permafrost episodes appeared in the Seim loess (MIS 5d), the eponymous cryogenic horizon (CH). The Valdai Early Glacial (MIS 5c-5a) is recorded not by one, as previously believed, but by two interstadial paleosols in the Chermeninsk horizon: Kukuevo (MIS 5c) and Streletsk (MIS 5a), separated by the Mlodat loess and CH (MIS 5b). At the beginning of the Valdai Pleniglacial, a significant increase in cryogenesis was noted, which was accompanied by the formation of the Selikhovodvor CH (MIS 4). In the Middle Pleniglacial (MIS 3), not one but two paleosols formed and were better preserved in the Leningrad horizon: Aleksandrov and Bryansk. Under accumulative conditions, the structure of the deposits becomes more complex, with the addition of the Gidrouzel and Monastyrshchino paleosols, which reflect more fractional climatic rhythms. In the Late Pleniglacial (Ostashkov horizon, MIS 2), several paleosols were identified that do not yet have a stratigraphic significance, with the exception of the Divnogorsk pedolithic complex, which records repeated pulses of pre-Holocene warming. The proposed scheme has been shown to be more detailed than Velichko’s scheme. The structures of the Upper Neopleistocene deposits in glacial and non-glacial regions of the central East European Plain have been correlated. Similarities in the structures of loess-soil sections from the first half of the late Neopleistocene in the Central Russian Upland, the Azov region, the Lower Volga region, and the Ciscaucasus have been demonstrated. Correlating the structures of the sections of the Central Russian Upland, the Donetsk Ridge, and the Volyn Upland demonstrated interregional similarities in the reflection of climatic signals by paleosols. This confirms the global (astronomical) causes of the major climatic rhythms in the Neopleistocene.
The paper compares the variations in several weathering indices (CIA, CIA–K, CIAcorr, MIA (o), MIA (r), and (ω) in clayey rocks of most representative Riphean shelf sedimentary sequences (1.75–0.6 Ga) of the Bashkirian Meganticlinorium (South Urals, a stratotype section) and the Uchur–Maya region (Southeast Yakutia, a Riphean hypostratotype) and their changes in paleosols of the same period from other world regions (USA, Australia, and Scotland). It is thus found that variations in intensity of chemical weathering, which are reflected in bulk chemical composition of the Riphean fine-grained clastic/clayey rocks of South Urals and Southeast Yakutia, are smoother than those in paleosols. This is likely due to the mineral and chemical composition of clayey rocks of shelf associations is more averaged than that of rocks with similar granulometry in continental sedimentation areas. Despite this, our results can be considered an additional argument in favor of a previous conclusion on approximately constant on-land weathering intensity over the last three billion years of the Earth’s geological evolution. The constant weathering intensity during the Riphean (i.e., over a period of >1 Ga) allows us to assume that various global and subglobal processes and events, such as the formation and breakup of supercontinents (including the presence of many continental blocks in the equatorial region at the peak of Rodinia assembly), the formation of large igneous provinces, the changes in atmospheric composition, and paleoclimatic perturbations, had a minor impact on weathering intensity. This issue however requires careful consideration in the future.
Results of comprehensive study of the Upper Cretaceous deposits in the Miroshniki and Krasny Yar sections (Tersa depression) and Splavnukha section (Karamysh depression) are presented. The vertical distribution of benthic foraminifera is the basis for the detailed subdivision and correlation of the clay–carbonate deposits of the Bannovka and Volsk formations within the Ulyanovsk–Saratov Trough. The features of the distribution of benthic and planktonic foraminifers, inoceramides, belemnites, sea urchins, crinoids, brittlestars, and sponges in the Turonian and Coniacian sediments of the Lower Volga region are identified. The analysis of the distribution of benthic foraminifera allows the most detailed subdivision of rocks and the determination of the position of the Turonian–Coniacian boundary within a monotonous carbonate succession of the Gubkino Horizon. The differences in sequence of zonal units and their thickness are interpreted as a result of partial isolation of the studied structural zones during the formation of the northern part of the Don–Medveditsa swell.
During the 20th century, no ostracods zonal scales for the Jurassic of the East European Platform (EEP) were recognized. At that time, only ostracod assemblages characterizing substages or some ammonite zones were described. First-generation scales, developed at the turn of the 20th and 21st centuries, consisted of ostracod beds correlated at best with substages and were therefore poorly detailed. The second-generation scale, comprising zones, subzones, and beds correlated with ammonite zones, is currently the most detailed of all Jurassic micropaleontological scales of the EEP, second only to ammonites. A third-generation ostracod scale, based on phylogenetic and paleogeographic reconstructions, is now under development. It consists of lineage zones and migration zones and is correlated with ammonite biohorizons.
This paper presents new data on the stratigraphy, palaeogeography, and chronology of Upper Pleistocene marine deposits from the eastern Chukotka Peninsula. Particular emphasis is placed on the reconstruction of transgressive events attributed to Marine Isotope Stages (MIS) 5 and 3. The palaeogeographical interpretation is based on published data on molluscan assemblages, foraminifera, diatoms, and pollen spectra, which indicate periods of climatic amelioration and relative sea-level rise. New chronological constraints are obtained using two independent absolute dating methods: electron spin resonance (ESR) applied to marine mollusc shells, and infrared optically stimulated luminescence (IR-OSL) applied to sandy deposits, including both those containing and those devoid of shell material. ESR and IR-OSL dating link the 105–78 ka interval—corresponding to the latter half of MIS 5—with part of the Valkatlen–Konergin transgressive-regressive cycle. IR-OSL ages from overlying sands and gravelly deposits (41.7–39.3 ka) are attributed to the Amguema transgression and correlate with the Malokhet climatic optimum recognised in Western Siberia during MIS 3. This interval represents a regional phase of climatic amelioration accompanied by a rise in sea level. The combined application of ESR and IR-OSL dating provides a robust chronostratigraphic framework for major Upper Pleistocene palaeogeographical events in eastern Chukotka. Comparison of the established age intervals with marine successions from the western sector of the Eurasian Arctic and Alaska reveals the pan-Arctic synchronicity of transgressive–regressive cycles during MIS 5 and MIS 3. The results refine the stratigraphic position of Upper Pleistocene marine deposits in Chukotka and improve interregional correlations of Late Quaternary palaeogeographical events.
Prospects of petromagnetic and related methods for detecting traces of meteorite events in sedimentary successions were evaluated on the example of the Ordovician section of the Lynna River (Leningrad oblast), which reliably contains extraterrestrial matter associated with the Ordovician meteorite event. Traces of these events can serve as markers for the global correlation of sedimentary sequences, which is particularly important when the application of other methods is limited for various reasons. It has been established that classical petromagnetic methods do not reveal clear anomalies in the section interval enriched with meteoritic material and, accordingly, are ineffective for the purpose of searching for traces of global impact events. X‑ray fluorescence (XRF) analysis has demonstrated the best practical potential for detecting increased concentrations of chromium and titanium relative to the rest of the section in the interval enriched with meteoritic material. These increased concentrations are likely associated with the Ordovician meteorite event.
The migration pathways of Western European Glyptocythere Brand et Malz, 1962 during the Bajocian–Bathonian and their expansion into the seas of the East European Platform (EEP) through the northern migration corridor (Pripyat Trough), with the formation of allopatric neoendemic species, are traced. The precise stratigraphic range of the Ukrainian species G. losoviensis Permyakova, 1970, G. aff. tuberosa (Khabarova, 1955) (= G. regulariformis Brand et Malz in Brand and Fahrion, 1962 sensu Permyakova, 1978), G. aff. tuscila Brand et Malz, 1966, G. aff. tenuisulcata Brand et Malz in Brand and Fahrion, 1962, G. crassicostata Permyakova, 1970, and G. multa Permyakova, 1970 is established at the end of the Parkinsoni Zone, in the boundary interval of the Truellei (Densicosta) and Bomfordi subzones. These species can be considered characteristic of the G. tuberodentina ostracod Zone, which is recognized in Ukraine. The species G. aspera (Khabarova, 1955), G. tuberosa (Khabarova, 1955), G. praerimosa (Khabarova, 1955), and G. strigata (Khabarova, 1955) are distributed in the Michalskii Zone and serve as index species for the G. aspera ostracod Zone, which has also been traced in the Dnieper–Donets Basin. The G. aspera Zone is widely recognized in the south of Central Russia (Kursk and Belgorod regions), the Volga Region, and western Kazakhstan. In the Lower Volga Region, it corresponds to the Michalskii Zone and the lower part of the Besnosovi Zone (including the O. issae biohorizon). The upper part of the Besnosovi Zone (the O. calvum and O. besnosovi biohorizons) is characterized by a different assemblage of Glyptocythere that evolved in the Central Russian Sea: G. bathonica Tesakova, 2022, G. khabarovae Tesakova, sp. nov., G. scissa Tesakova, sp. nov., G. transversa Tesakova, sp. nov., and G. kiklica Tesakova, sp. nov. During the late Bajocian–early Bathonian, the genus Glyptocythere evolved in the EEP through four parallel lineages. The systematics and evolution of two of these lineages (reticulate and some ribbed Glyptocythere) have been published previously. This article examines the taxonomy and development of two other lineages of ribbed Glyptocythere.
The results of U–Pb isotope dating (LA-ICP-MS) of zircons from metatuffaceous sandstones of the Shidzhatmaz (sample DN223A) and Dolina Narzanov (sample DN224A) Formations within the Bechasyn Zone on the northern slope of the Greater Caucasus are presented. The minimum age estimates for zircons from the studied metatuffaceous sandstones of the Shidzhatmaz and Dolina Narzanov Formations, taking into account the error, are very similar. The weighted mean of the youngest coherent zircon dates from metatuffaceous sandstones of the Dolina Narzanov Formation is 544 ± 5 Ma (based on 5 dates), while that from the Shidzhatmaz Formation metatuffaceous sandstones is 545 ± 5 Ma (based on 6 dates). The weighted mean of the 9 youngest coherent dates of zircons from both samples is 544 ± 4 Ma. The Shidzhatmaz and Dolina Narzanov Formations are assigned to the Upper Riphean on the certified second-generation State Geological Map. Our results reliably constrain the ages of the Shidzhatmaz and Dolina Narzanov Formations not older than the latest Vendian (Ediacaran). The zircons extracted from the metatuffaceous sandstones of both formations are dominated by age groups ranging from 700 to 540 Ma, with distinct frequency peaks at 557 and 630 Ma, which are nearly identical for samples from both formations. This pattern of zircon age distribution is highly typical of clastic rocks from Upper Precambrian and Lower Paleozoic sequences that form tectonic blocks interpreted as Peri-Gondwanan terranes and widespread in Western and Central Europe, on the Atlantic coast of North America, in North Africa, Anatolia, and Arabia. In this context, it is concluded that the metatuffaceous sandstones of the Dolina Narzanov and Shidzhatmaz Formations were most likely formed in close proximity to a large volcanic edifice that developed on the Northern periphery of Gondwana (in Peri-Gondwana) with enhanced magmatic activity occurring at approximately 630 and 557 Ma. The Dolina Narzanov Formation is composed of the erosion products of the upper part of the volcanic edifice, while the structurally overlying Shidzhatmaz Formation is made of the erosion products of its lower part and the basement.
New data on the composition of nannoplankton and planktonic foraminiferal assemblages were obtained during a detailed study of boundary deposits of the Maikopian Group and the Siyaki Formation (Pteropod beds) in the Islamdag section (Shemakha-Gobustan region of Azerbaijan). Finds of stratigraphically important species in the assemblages of both microplankton groups including the zonal species Sphenolithus heteromorphus, allowed for a direct correlation with the NN5 Zone of the Martini scale. The definition of boundaries and range of the Tarkhanian regional stage in the Islamdag section is substantiated, and its correlation with the Tarkhanian stratotype and reference sections of the Eastern Paratethys is performed. The stages of evolution of microplankton assemblages are recognized and correlated with the Tarkhanian subdivisions, which provides an expanded micropaleontological characteristics of the top of the Maikopian Group and of the bottom of the Siyaki Formation.
As a result of lithofacies studies and analysis of geological data available, Riphean–Vendian boundary deposits from different regions of the Southern Urals (Tolparovo, Krivaya Luka, and Tirlyansky) were correlated. In the first two regions, a lithological marker of glacial-diamictite deposits with vertical change of terrigenous facies has been established, from shallow-sea tidal sediments with signs of superposition of marinoglacial sedimentation to deeper ones corresponding to the conditions of underwater delta-type outflow cones or fjords. Owing to the strong tectonization and metamorphism of the Riphean–Vendian deposits, the sequence of formations in the Tirlyansky region considered as the Arshinian series is ambiguous and their correlation with other areas is difficult. We propose a new interpretation of the position of the Arshinian series formations. The series is based on volcanics of the Igonino Formation, reflecting the stage of rifting. Higher in the section, there are sandy-clay deposits of the Bainas formation (and its inferred facies analog, the Shum Formation), accumulated in mobile shallow water environment. These deposits are correlated with those which underly diamictites in the Tolparovo and Krivaya Luka regions. The upper part of the section is represented by glacial diamictite conglomerates of the Makhmutovo Formation. Under this interpretation of the position of the Arshinian series formations, a single Riphean–Vendian boundary marinoglacial level can be traced throughout the Bashkir meganticlinorium in its western and eastern frames. Therefore, it can be included in the Upper Precambrian stratigraphic scale of the Southern Urals.
The article analyzes modern isotope datings of sedimentary sequences of the Serebryanka (Middle Urals) and lower part of the Asha (Southern Urals) groups. The affiliation of diamictites/tillite-like conglomerates of the Serebryanka Group and the Staropechny Formation to the Laplandian glacial horizon, as well as the problem of the stratigraphic position of the Bakeevo Formation of the Asha Group (uppermost part of the Upper Riphean or the Lower Vendian) are discussed. Possible correlation options are considered both with the involvement of the provisions of stratigraphic codes of different years, and on the basis of comparison with the type sequences of the Lapland glacial horizon of the Northern Norway (the lower part of the Vestertana Group) and the Vilchanka Group of the Orsha Depression (Republic of Belarus).
This paper presents the results of a study of fossil remains of large Quaternary mammals from the Berezhekovsky sector of the Kurtak archaeological region (Krasnoyarsk Krai, Central Siberia), conducted in 2023. Taphonomic, morphological, and spatial analysis of the paleofaunal material collected on a coastal shoal enabled the assignment of specific find assemblages to distinct stratigraphic horizons. Based on preservation type, four groups of finds were identified: one is attributed to the middle Neopleistocene, and three to the Kazantsevo, Karginsky, and Sartan horizons to—the late Neopleistocene. The preservation types of bone remains for the two upper horizons of the scale correspond to those of remains from various Paleolithic sites in the Krasnoyarsk district. The studied paleontological material supplements faunal lists for various horizons of the stratigraphic scale and will subsequently allow for a refinement of the stratigraphic subdivision scheme for Quaternary deposits in the Kurtak region.
The Late Pleistocene of Northern Eurasia remains a subject of active scientific debate, particularly in the context of climate change. This study presents a palaeoenvironmental analysis for the interval of Marine Isotope Stage (MIS) 5 (approximately 130 to 70 ka), including the first warming phase of interglacial rank. Special attention is given to a detailed study of the Voka key section on the south-eastern coast of the Gulf of Finland. This section is remarkable for the completeness of its geological and palaeontological record, which allows a deeper understanding of the Late Pleistocene palaeogeographic history, especially during the latter half of MIS 5. Climatic and stratigraphic analysis was carried out using the palynological method, while the chronological framework of palaeoclimatic events was established by infrared optically stimulated luminescence (IR-OSL) dating. This allowed the dynamics of the first Late Pleistocene warming of interglacial rank to be traced, correlating with the Mikulino interglacial in the Eastern European Plain. Comparison of the results with electron spin resonance (ESR) dating of mollusc shells from palaeoshelf deposits in climatically highly sensitive regions of Eurasian North confirmed the synchronicity of major palaeogeographic events in both terrestrial and marine ecosystems during MIS 5. Our interdisciplinary research provides new data that contribute to reconstructions of Late Pleistocene palaeogeographic events and refine our understanding of climate dynamics during MIS 5.
According to the stratigraphic scheme of the Quaternary deposits of Belarus, the Pleistocene Belovezhian Stage includes three substages (Borkovian, Nizhninian and Mogilevian). Palynological research and palynology-based interregional correlation of the studied deposits suggest that these substages can be considered as stages, which supports proposals put forward previously by Belarusian geologists and paleontologists. The materials presented also indicate that the Korchevian interglacial, identified as a part of the Narevian glacial, is coeval with the Mogilevian Substage (Stage).
The results of the geological, geochronological, and micropaleontological studies of the Cambrian–Ordovician volcanic and sedimentary formations of the Sarysu-Teniz watershed in the west of Central Kazakhstan are presented, which allowed for a detailed stratigraphic division. It is shown that they formed in the interval from the end of the Early Cambrian ( 515 Ma) to the end of the Middle Ordovician. The first findings of conodonts made it possible to expand the age range of accumulation of siliceous-terrigenous strata (Kusheke Formation), covering the interval from the top of the Floian Stage to the Darriwilian Stage of the Lower and Middle Ordovician. The results of U–Th–Pb isotope-geochronological (LA-ICP-MS) study of detrital zircon from sandstones indicate the predominance of Precambrian provenance areas in the accumulation of Lower–Middle Ordovician strata (Kokdombak and Kushekinskaya formations). It has been shown that the studied complexes of the Sarysu-Teniz watershed are stratigraphic and facies analogs of the volcanic and sedimentary complexes of the Jalair–Naiman zone, the formation of which was associated with the evolution of the Cambrian–Early Ordovician island arc system.
Terrigenous sedimentation conditions and provenance in the Segozero structure, Karelian Craton, which predates the Lomagundi–Jatuli Event (LJE) (2.20–2.06 Ga) are deciphered based on lithology, geochemistry, and U–Th–Pb zircon geochronology. The section of this structure is a stratotype of the Jatulian Group, which comprise three formations (from bottom to top): Jangozero, Medvezhegorsk, and Tulomozero, each consisting of two units. Their lower parts consist of terrigenous rocks, whereas the upper parts are composed of basalts of the Jangozero and Medvezhegorsk formations and carbonates of the Tulomozero Formation. The lower terrigenous unit (Jangozero Formation) is composed of quartz sandstones with shales interbeds, which are anomalously enriched in Al2O3, K2O, TiO2,Th, Nb, Zr, REE, W, and Ga, and contains zircon with the age of 2.7 and 2.9 Ga. Granitoids of the Vodlozero domain, which were altered in situ to lateritic paleosoil, were the sources of these rocks. The homogeneity and a large volume of the lower terrigenous unit suggest a significant thickness of the pre-Jatulian paleosoil on the Karelian Craton, indicating high atmospheric oxygen content prior to the LJE. The middle terrigenous unit (Medvezhegorsk Formation) is composed of quartz and arkose sandstones with siltstone and mudstone interbeds, which formed as a result of erosion of weakly weathered granitoids with age of 2.7 Ga, probably, upon active extension and increasing the depth of the basin. The upper terrigenous unit (Tulomozero Formation) combines geochemical characteristics of the lower and middle terrigenous units with a significant contribution of mafic material and could have formed during erosion and redeposition of the underlying sedimentary rocks and basalts. The lithology of terrigenous rocks indicate the predominance of fluvial processes during sedimentation and formation of an alluvial–deltaic succession and a general transgressive trend. The lithology of terrigenous rocks and their association with basaltic volcanism indicate a rifting environments of the Jatulian basin. The reconstructed NW direction of material transport by channel flows is correlated with NW orientation of the rift. The data on oxygen-rich atmosphere and intracontinental rift evolution of the Jatulian basin, which accumulated carbonate rocks of the Tulomozero Formation with positive δ13C values, are additional arguments in favor of canonical LJE model and a leading role of regional factors responsible for this event.
