The first results of the U–Th–Pb isotope dating of detrital zircons (dZr, N = 130, n = 91) from the middle Danian sandstones (63.9–65.3 Ma) of the Cretaceous–Eocene Novorossiisk–Anapa flysch widely developed in the Sochi synclinorium (southern slope of the Western Caucasus) are presented. The maximum and minimum dZr age is 2973 ± 12 Ma and 318 ± 3 Ma, respectively; weighted average age of the four youngest dZr is 322 ± 7 Ma. There are no signs of erosion products of the Jurassic magmatites involved in the structure of the Greater Caucasus and Crimean Mountains into the sedimentary basin, where the Novorossiisk–Anapa flysch was formed. The results have revealed a high degree of similarity between the provenance signals of the Danian sandstones from the Novorossiisk–Anapa flysch, some Paleogene–Neogene and Early Quaternary (Early Pleistocene) sandstones of the Western Caucasus and Western Cis-Caucasia, red-colored Upper Permian and Lower Triassic sandstones of the Moscow syneclise, as well as Late Quaternary alluvium at lower reaches of the Don and Volga rivers draining vast expanses of the Russian Plate. These facts suggest: (1) the absence of eroded mountain structures of the Greater Caucasus and Crimea in the middle Danian; (2) the main volume of detrital material composing the Novorossiisk–Anapa flysch was formed due to the recycling of Permian–Triassic and younger sequences of the Russian Plate.

The complex body-trace fossils of Vendian soft-bodied biota have been found for the first time in the Central Urals during the study of the Vilukha and Sinii Kamen members of the Chernyi Kamen Formation of the Upper Vendian Sylvitsa Group (Kos’va River area, Perm Krai of Russia). These sedimentary sequences were exposed along the valley of the Shirokovskii Reservoir. Among the fossils, the chuariomorpha-like species Beltanelliformis konovalovi, previously described from the Konovalovka Member of the Chernyi Kamen Formation, was identified. However, the morphological analysis of the new fossil material revealed a number of principal differences from representatives of the genus Beltanelliformis Menner, 1974. It was shown that the taxon B. konovalovi, most likely, does not belong to this genus and probably needs further revision, and, in turn, the fossil locality at the Shirokovskii Reservoir allows us to establish a new area with fossils of the Precambrian mobile organisms.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070061

Macroscopic fossils as composite molds and casts of Ediacara-type soft-bodied organisms were found in the Dzhezhim Formation of the Timan Range for the first time. Among them, representatives of palaeopascichnids, arboreomorphs, chuariomorphids, microbial colonies, and trace fossils were identified. This finding of such a large number of various Ediacaran fossils on the Timan Range not only develops our understanding of their paleogeographic range but also clarifies the age limits of the deposition of the Dzhezhim Formation, the stratigraphic position of which in the Upper Precambrian section was controversial.

Macrofossils of the Vendian soft-bodied organisms were found for the first time in the Vizinga and Ust’-Palega formations of the Upper Precambrian in Chetlasskii Kamen Hill (Middle Timan, Arkhangelsk oblast). Representatives of palaeopascichnids, aspidellamorphs, and possible frondomorphs, trace fossils, and microbially induced arumberiamorph structures were identified among molds and three-dimensional casts of fossils. Previously we revealed Vendian macrofossils in the Upper Precambrian in Dzhezhim-Parma Hill (South Timan, Komi Republic). The discovery of one more locality of various Ediacaran fossils in the middle part of the Timan Ridge significantly expands their paleogeography and also clarifies the time frame of deposition of the Vizinga and Ust’-Palega formations, the position of which in the Upper Precambrian section of Central Timan was debatable.

Here we present new data on the C and O isotopic composition in the Neoproterozoic carbonates of the Ballaganakh and Dal’naya Taiga horizons of the southeastern margin of the Patom paleobasin. In the upper part of the Ballaganakh horizon, a negative δ13С anomaly was established. It is comparable in amplitude and stratigraphic position to the Trezona anomaly, which preceded the Marinoan glaciation. The carbonate layers in the glacial deposits of the Nichatka Fm. of the Dal’naya Taiga horizon have moderately positive δ13С values, and the dolomite horizon at the base of the postglacial sequence is characterized by moderately negative values δ13С which is typical for the cap-carbonate sequence associated with the end of the Marinoan glaciation. In the lower part of the postglacial sequence (the Barakun Fm.), there is a gradual increase in the proportion of calcite in the carbonate component of the rocks and a shift in the isotope composition corresponding to the difference in the fractionation coefficients of stable C and O isotopes for dolomite and calcite. This phenomenon, which is also recorded in the postglacial sequences of Namibia and Canada, indicates that the composition of carbonate minerals was determined by a global change in water chemistry, and not by postsedimentary substitution. The overlying carbonate deposits of the Dal’naya Taiga horizon in the epiplatform part of the Patom paleobasin (Sen Fm.) are depleted in 13С compared to their shelf analogs in the Ura uplift. It has been suggested that carbonate accumulation in the epiplatform and shelf facies of the Patom paleobasin occurred asynchronously. The reconstructed trend of variations in the C isotope composition for the Dal’naya Taiga horizon is characterized by positive and low-amplitude negative δ13С anomalies similar to those in the Doushanto Fm. of China.

A cyclostratigraphic study of the Late Precambrian Zhuya Group (Nikolskoye and Chencha Formations), and Torgo formation in the southern part of the Siberian Platform was carried out to determine the duration of the C-isotope anomaly imprinted in them. The similarity of the ratios of the period lengths of the cyclic components of the magnetic susceptibility in the coeval deposits of the remote sections of the Nikol’skoye and Torgo Formations indicates the connection between the revealed cyclicity and the basin-scale environment changes. According to the astrochronological model, the duration of the formation of the studied intervals of the Nikol’skoye (57 m) and Chencha (147 m) formations was 850 and 2500 ky, respectively. Extrapolation of the data obtained shows that the duration of the C-isotope anomaly of the Zhuya Group in the Vendian reference section on the Ura uplift was about 10 My, which is consistent with most estimates of the Shuram anomaly’s duration and its stratigraphic analogues.

A cyclostratigraphic study of the Late Precambrian Zhuya Group (Nikolskoye and Chencha Formations) and Torgo formation in the south of the Siberian Platform was carried out to determine the duration of the C-isotope anomaly imprinted in them. The similarity of the ratios of the period lengths of the cyclic components of the magnetic susceptibility in the coeval deposits of the remote sections of the Nikol’skoye and Torgo Fms. indicates the connection between the revealed cyclicity and the basin-scale environment changes. According to the obtained astrochronological model, the duration of the formation of the studied intervals of the Nikol’skoye (57 m) and Chencha (147 m) formations was 850 and 2500 ky, respectively. Extrapolation of the data obtained shows that the duration of the C-isotope anomaly of the Zhuya Group in the Vendian reference section of the on the Ura uplift was about 10 My, which is consistent with most estimates of the Shuram anomaly’s duration and its stratigraphic analogues.

New data on the C and O isotope composition in the Neoproterozoic carbonates of the Ballaganakh and Dal’nyaya Taiga regional stages (southeastern margin of the Patom paleobasin (hereafter, Basin) are presented. The negative δ13С anomaly, established in the upper part of the Ballaganakh regional stage, is comparable (in amplitude and stratigraphic position) to the Trezona anomaly, which preceded the Marinoan glaciation. The carbonate layers in glacial deposits of the Nichatka Formation of the Dal’nyaya Taiga regional stage have moderately positive δ13С values. The dolomite unit at the postglacial sequence base is characterized by moderately negative δ13С values that are typical for the cap carbonate sequence associated with the end-Marinoan glaciation. The lower part of the postglacial sequence (Barakun Formation) is characterized by a gradual increase of calcite in the carbonate component of rocks and a shift in the isotope composition corresponding to the difference in the fractionation coefficient of stable C and O isotopes for dolomite and calcite. This phenomenon, recorded in the postglacial sequences of Namibia and Canada as well, indicates that the carbonate mineral composition was governed by a global change in water chemistry rather than postsedimentary alteration. The overlying carbonate rocks of the Dal’nyaya Taiga regional stage in the epicontinental part of the Patom Basin (Sen Formation) are depleted in 13С compared to their shelf analogs in the Ura Uplift. Probably, the carbonates were accumulated asynchronously in the epicontinental and shelf facies of the Patom Basin. The reconstructed trend of variations in the carbon isotope composition for the Dal’nyaya Taiga regional stage is characterized by positive and low-amplitude negative δ13С anomalies similar to those in the Doushantuo Formation (China).

The paleomagnetic data obtained from the Neoproterozoic rocks stratigraphically related to glacial deposits suggest the ice sheets' near-equatorial occurrence. Based on these data, the Snowball Earth hypothesis proposing the Cryogenian period's total glaciations has been developed and became almost a paradigm. Quaternary glacial successions usually contain varves (seasonally laminated deposits) as they were formed in high latitudes. Therefore, we suggest that varves provide an independent sedimentological test of the paleolatitude position of Precambrian glacial deposits. We carried out a sedimentological study on thinly laminated rhythmites in the Neoproterozoic glacial deposits in Southern Siberia, and found that they have features characteristic of seasonal varves. The studied rhythmites interstratify the Bolshoi Patom and Nichatka Formations' diamictites at the base of the Dal'nyaya Taiga Group. The seasonality is clearly manifested in the rhythmites of the Nichatka Formation. The rhythmites are represented by interbedding of millimeter-scale siltstones and mudstones with sandy and gravelly admixture. The coarse-sandy and gravelly component is interpreted as ice-rafted clasts, as it has characteristic features of dropstones and contains unconfined till pellets. Ice rafted clasts saturate siltstone laminas and are practically absent in argillite layers. Thus, argillite laminas can be confidently recognized as deposits of the cold season, during which ice melting and iceberg rafting ceased. On the other hand, siltstone layers with dropstones are deposits of the warmer melting season. The rhythmite's diurnal nature is excluded by its complex structure of the silty layer of the rhythm, which is caused by several sedimentation events separated in time. The entire set of microfacies of the Nichatka Formation rhythmites reveals similarities with varve microfacies produced by variable flows in ice-contact proglacial lakes. The upper part of the Bolshoi Patom Formation's rhythmites is also formed by varve-like pairs of thin siltstone and mudstone laminas. Dropstones are virtually absent in them, and, therefore, the seasonal nature of the rhythm is less confidently established. The siltstone within the rhythm may have a massive or normally graded texture. The argillite is approximately equal in thickness to the siltstone lamina (about 0.5 mm). The thickness of a pair of siltstone and argillite laminas may remain almost constant when more than 50 pairs are observed. This regularity of laminas thickness in rhythmite is not typical of a tidal setting, but it is difficult to rule out this rhythmite's diurnal nature. These deposits display high similarity to varves produced by low energy suspension settling during the melt season. The observed seasonal nature of the rhythmites in the glacial deposits of the Dal'nyaya Taiga Group evidence against the validity of the Snowball Earth hypothesis, which assumes the presence of glacial caps near the equator in the Neoproterozoic. The study was supported by RSF Grant No. 20-77-10066.

Probably the largest negative δ13С anomaly in Earth history called the “Shuram” excursion (SE) had taken place in the Ediacaran period. Determining the duration of SE is needed to resolve its nature and for the stratigraphic correlation of Ediacaran rocks. The cyclostartigraphic method allows to precisely determine the accumulation rates of ancient deposits (the theoretical error is up to 10,000 years), but the testing of the accuracy of the cyclostratigraphic method usually based on biostratigraphy and geochronology meets difficulties for the Precambrian deposits. The reliability of cyclostartigarphic estimates of the SE duration can be determined by the convergence of cyclostratigraphic results obtained from distant sections on different continents and in sections representing different depositional environments. Recently limitations on the SE duration have been obtained in Australia, California, Oman, and China. Recently limitations on the SE duration have been obtained in Australia, California, Oman, and China. Here we present the first cyclostratigraphic estimates of the SE duration from the Zhuya Group of the Patom basin in South Siberia. Two sections of the Zhuya Group were studied, both recording the decrease of the δ13С values up to -12 ‰ in the nadir point and then increase till -9 ‰. In both sections, the cyclicity of variations in magnetic susceptibility (MS) was studied. The first section (57 m, Nikolskoe Fm.) represents sediments deposited on the slope of the carbonate platform. Spectral analysis of the MS variations revealed peaks above 95% significance level on the period lengths of 11.5, 1.73, 1.04, 0.67, 0.51 m with ratios 1/6.6 /11/17/22.3 respectively. This cyclicity is interpreted as a reflection of orbitally forced climate changes, where the longest-period variations correspond to short eccentricity cycles (100 ky). Then, the studied interval lasted approximately 500 ky, and the duration of the entire Nikolskaya Fm., corresponding to the lower third of the SE, is about 2.5 My. The second section belongs to the Torgo Fm. in the Berezovskaya depression, which is the epicontinental part of the Patom Basin. MS variations in the studied 14.2 m interval shows significant peaks at period lengths of 2.3, 0.74, 0.51, 0.38, 0.28, 0.27, 0.25, 0.20 m with ratios 1.00/3.13/4.52/6.10/8.03/8.48/9.19/11.52. In this section, we also interpret the longest-period of the MS variations as a reflection of cycles of short eccentricity (100 ka). Then, the duration of the studied interval is 613 ky. and the SE duration in the whole 200 meters of the Torgo Fm. is estimated as 8.6 My. The obtained preliminary results are in good agreement with those from Australia (ca. 8 My), Oman (7.7 +/- 0.2 My), North America (8.2 +/- 1.2 My), and China (9.1 +/- 1 My). Thus, the influence of Milankovitch's orbital cycles on the formation of carbonate deposits of the Late Precambrian seems to be quite convincing, and the cyclostratigraphic estimate of the duration of the SE about 10 Ma is more and more reliable. Research supported by the Russian Science Foundation (project № 20-77-10066)

A number of ecological and geochemical transformations occurred during late Ediacaran and early Cambrian time, the effects of which are difficult to overestimate. However, the strong linkage of biostratigraphic and chemostratigraphic methods with lithofacies makes the localization of the Precambrian-Cambrian boundary and its correlation with lithologically contrasting sections highly debatable. We analyse the taxonomy and stratigraphic distribution of small skeletal fossils and trace fossils, the carbonate carbon and oxygen isotope composition, and U-Pb detrital zircon age in the Ediacaran-Cambrian transitional interval of the Irkutsk Cis-Sayans Uplift (southwestern Siberian Platform). This interval (Moty Group) comprises a transgressive succession with red-coloured alluvial to deltaic siliciclastic deposits (Shaman Formation) and overlying shallow-marine carbonates (Irkut Formation). The lower Irkut Formation hosts sporadic and poorly preserved tubular Cambrotubulus fossils, which are known from both the terminal Ediacaran Period (c. 550-541 Ma) and the Terreneuvian Epoch (541-521 Ma), and typical Fortunian trace fossils, including an index ichnotaxon of the Cambrian boundary Treptichnus pedum. The biostratigraphic and carbonate carbon isotope data and U-Pb concordia ages of 531.1 +/- 5.2 Ma (mean weighted, 530.6 +/- 5.3 Ma) of the five youngest zircon grains from the lower Irkut Formation indicate that at least the shallow-marine carbonates of the upper Moty Group correspond to the Cambrian Stage 2 (c. 529-521 Ma). In the Irkutsk Cis-Sayans Uplift, the Cambrian Period tentatively began before or during the accumulation of the alluvial to deltaic siliciclastic Khuzhir and Shaman formations, and this crucial divide remained unmarked in the palaeontological and isotopic records.

Lately data have been getting more and more, indicating an unusual, abnormal state of the magnetic field at the boundary of the Precambrian and Phanerozoic. This fact limits significantly the possibility on employing the paleomagnetic approach for creating various paleoreconstructions in this time interval, and it allows a better understanding of the evolution of the Earth's magnetic field. Until recently, there was no exact binding of Lower Cambrian sections bearing an anomalous paleomagnetic record to the chronostratigraphical chart, which did not allow to obtain adequate estimates of the duration of the anomalous state of the magnetic field. In this study we present the results of a paleomagnetic study of the Lower Cambrian terrigenous-carbonate rocks of the Udzha and Anabar uplifts (Emyaksa and Medvezh Formations). New evidence has been obtained of the anomalous the paleomagnetic record in these rocks, which manifests itself in the objective existence of two significantly different directions of the high-temperature magnetization components, the formation of which cannot be explained by a later remagnetization. U-Pb dating of detrital zircons constraints the maximum depositional age of the Manykay and Emyaksa Formations on similar to 520 Ma, what pointing to Atdaban age of studied succession in combination with the faunistic characteristic of the upper part of the Emyaksa Formation. The age constraits obtained indicate on a specific paleomagnetic record, due to the peculiarities of the generation of the geomagnetic field of the terminal Precambrian - Early Cambrian, can be traced back to the Atdaban age, including.

Knowledge on the age and distribution of glacial deposits is essential in order to solve issues surrounding the geological periodization of the Neoproterozoic and the large-scale changes in the environment and biosphere that took place at that time. The glacial origin of diamictites of the Precambrian Chivida Formation on the Yenisei Ridge (on the western periphery of the Siberian Platform) was proposed almost a century ago but has since been disputed. The present study confirms the glacial origin of the Chivida diamictites based on the findings of striated and faceted clasts and other characteristic features of glacial deposits. Results from U-Pb dating of zircon grains from diamictites matrix with and without volcanogenic admixture, tuffaceous sandstones and volcanic breccias interbedding the diamictites of the Chivida Formation are presented. The youngest population of zircon grains revealed in the volcanogenic and tuffogenic rocks of the Chivida Formation is assumed to characterize syn-depositional volcanic activity. Thus, its mean average age (696 +/- 4 Ma) is considered to characterize the glacial sediments' time of deposition. These results prove for the first time the presence of an ice sheet on the Siberian craton during the Sturtian glaciation.

The analysis of paleomagnetic data from Late Neoproterozoic complexes of Siberia and Australia is carried out. We show that the existing paleomagnetic datasets are in a disagreement with the concept of the axial-dipole configuration of the Late Neoproterozoic geomagnetic field: proposed non-actualistic models of the field do not reasonably explain the distribution of the paleomagnetic poles. We carried out analysis of paleomagnetic and virtual geomagnetic poles distribution based on simple geometric calculations. The analysis suggests that the configuration of the Late Neoproterozoic geomagnetic field was determined by the coexistence of a weak, long-lived source that was stably fixed in space, with a main dipole source that experienced sporadic multidirectional jumps within a certain preferred region of the Earth. Predominantly equatorial orientation of the main dipole source is substantiated by paleoclimate proxies. We propose a descriptive non-actualistic model of the Late Neoproterozoic geomagnetic field-the Devious Equatorial Dipole hypothesis, which brings paleomagnetic and paleoclimate data into accordance.

Paleomagnetic results from numerous Early–Middle Devonian volcanic sequences of the Minusa trough, southern Siberia, are presented. The analysis of these data definitely indicates that the geomagnetic field in the Devonian had a specific character, different from both the present field and the field of more ancient geological epochs, and was extremely variable (hyperactive). The anomalies in the paleomagnetic record of the Early–Middle Devonian are not local, peculiar to a particular region, but have a global occurrence. The synthesis of the obtained results with the paleomagnetic data from the coeval volcanics from Scotland shows that during a relatively short time (10–20 Ma), the geomagnetic pole repeatedly changed its location, significantly deviating from the Earth’s rotation axis up to the (paleo)equator and assuming some quasi-stable positions. The arguments suggesting that the specific features of the Devonian paleomagnetic record could probably be induced by the significant contribution of the equatorial dipole to the main geomagnetic field are presented.

The results of U–Pb-isotopic dating of detrital zircons from sandstones of the Proterozoic Pogor`uy Fm. from the northern and southern parts of the Eastern-Angara block of the Yenisei Ridge are presented. The sandstones of the northern part of the Eastern-Angara block are dominated by the Archean and Paleoproterozoic populations of detrital zircons, while in the samples from the southern part of the Eastern-Angara block up to 25% of the Mesoproterozoic age grains have been fixed. The dates of detrital zircons allow us to constrain the maximum sedimentary age of the Pogor`uy Fm. and the entire interval of its formation as 1.2–0.9 Ga. The paleogeographic features of the formation of the Pogor`uy Fm. in the context of existing views on a location of Siberia within the Rodinia supercontinent are considered.