Search

Abstract The paper presents data on granites and gneisses recovered by Kulindinskaya-1 hole drilled in the central part of the Siberian Craton. The biotite granites retain a porphyritic texture, correspond to I-type according to their compositional features, are enriched in LREE and moderately depleted in HREE, and have negative Eu, Sr, and Nb and positive Zr anomalies. The U−Pb zircon age of the granites is Neoarchean (2525 ± 10 Ma), with single cores of zircon grains dated at about 2.6 Ga, which likely suggests a crustal source of the granitic magmas. The model age TNd(DM) = 2.77 Ga of the granite shows that the crust from which the initial melts were derived had been formed shortly before the melting episode. In terms of age and all characteristics, the granites are close to those of the Yurubchen massif, which was drilled through in the western part of the Tunguska superterrane. The biotite gneiss was apparently derived from sedimentary rocks and was heavily reworked when the granites were emplaced. The enrichment of the gneiss in Cr and Ni is probably inherited from the sedimentary protolith, whereas the REE, HFSE, and LILE concentrations and distribution in the gneiss are similar to those of the granite. The concordant (D < 1%) U−Pb zircon ages (according to LA-ICP-MS data) broadly vary from 3284 to 2620 Ma, with two major peaks at 2717 and 2678 Ma. The model age of the gneiss TNd(DM) = 2.91 Ga confirms a contribution of the ancient crustal component to the sedimentary protolith of the rock. The minimum age of the detrital zircon, 2.62 Ga, determines the maximum age limit for sedimentation, and the minimum age limit is set by the age of the granite intrusions at 2.53 Ga. According to our data, the Archean gneisses and granites recovered by the Kulindinskaya-1 drillhole probably compose the eastern part of the Neoarchean Tunguska superterrane. Ereminskaya-101 drillhole, which was drilled 20 km northeast of Kulindinskaya-1, recovered gneisses with model ages TNd(DM) from 2.30 to 2.37 Ga, which belong to the adjacent Taimyr−Baikal suture zone with widespread Paleoproterozoic rocks. The contrasting crustal history of the adjacent complexes provides grounds to suggest that they were tectonically combined, which is an additional reason to consider the Taimyr−Baikal suture zone as a Paleoproterozoic collisional orogen.

In 2020–2021 the palaeopascichnid fossils were found in the Krasnaya Gorka Site (Shirokovsky Reservoir, Kosva River area, Perm Region), a type Vendian fossil locality (problematic discoidal casts and arumberiamorph structures) for the Central Urals discovered by Yu.R. Bekker in 1972. In the stratigraphical context, the fossil locality is associated with Chernyi Kamen Formation of the Upper Vendian Sylvitsa Group. The results of morphometric analysis of palaeopascichnid fossils made possible to distinguish three morphological types: Palaeopascichnus delicatus, Yelovichnus gracilis, and Palaeopascichnus linearis. Finding of a large number of palaeopascichnid fossils both develops the understanding of their palaeobiology and taphonomy, and also demonstrates that palaeontological potential of the type fossil locality and one of the most representative section of the Chernyi Kamen Formation has not entirely been realized.

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 tubularCambrotubulusfossils, 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 boundaryTreptichnus 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.

U–Th–Pb (SHRIMP II) isotopic dating of accessory zircons from Vendian (Ediacaran) ash tuffs of the Basa formation section (Asha Group, Southern Ural) was performed for the first time. The concordant age obtained (573.0 ± 2.3 Ma) can be interpreted as the upper age limit of the onset of the Timan Orogeny in the structure of the Southern Urals. Fossil remains of Kuckaraukia multituberculata and several paleopascichnids, belonging to the genera Palaeopascichnus and Orbisiana, were previously found in the rocks of the Upper Basa Subformation, and the first occurrence of Arumberia banksi was established. The age obtained indicates a more ancient age of this Vendian assemblage compared to the previously accepted one.

—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.

The first results of U–Pb (LA–ICP–MS) isotope dating of detrital zircons (dZr) from the Upper Oligocene sands of the Poltava Formation exposed on the southeastern slope of the Voronezh anteclise are presented, providing information on the provenance sources. It is established that the dataset of dZr ages (provenance signal) is characterized by a predominance of ages within the range of 1–2 Ga with a low number of Phanerozoic, Late Proterozoic (younger than 1 Ga), and Archean dates. It is revealed that the cumulative ages of the complexes of the Svecofennian and Sveconorwegian orogens and, to a lesser degree, the Cadomides of Central Europe provide entirely the provenance signal recorded in the sands of the Poltava Formation. The data obtained allow us to refine the paleogeography of the Paratethys northern margin during the Late Oligocene. It has been found that the Poltava Formation was accumulated due to water transport of sediments from intensively eroded structures of western Fennoscandia from the North Sea to the Scythian Sea.

In order to determine the provenance and age of terrigenous-carbonate stratified units exposed in the region of Bagrush Mountains, Bashkirian uplift, U–Pb dating of detrital zircons from these units has been carried out. A comparison of the data results with analogous data on five stratigraphic levels within the Riphean section of the Bashkirian uplift has shown that the studied sequence should be, most likely, correlated to the uppermost Lower Riphean or the lowermost Middle Riphean.

The first U–Pb (LA–ICP–MS) isotope dating of detrital zircons from quartzites of two strata of the Maksyutov metamorphic complex (Southern Urals) was performed. Zircon grains from the Galeevo quartzites are well rounded. The concordant zircon ages fall into the ranges of 529–594, 956–2144, and 2709–2781 Ma; the main age peaks are 544, 551, and 1491 Ma. Zircon grains from the Yumaguzino quartzites are idiomorphic and weakly rounded. The concordant zircon ages fall into the ranges of 497–640 and 957–1027 Ma, forming distinct age peaks of 514, 548, and 605 Ma. The U–Pb ages obtained and their comparison with similar data on the other sequences of the Southern Urals and the Caspian Sea Region indicate the Ordovician age of the protolith of the studied quartzites of the Maksyutov complex.

The paper presents data on dolerite dikes in the Murmansk block in the northeastern Kola Peninsula. The dikes belong to a Middle Paleozoic flood-basalt association, which is a principal element of the large-scale plume–lithospheric process in the area of the Barents Sea. According to their geological, petrological, and geochemical features, the dolerite dikes are classified into two groups: older and younger, which pertain to the initial and final evolution of the large igneous province produced under the effect of the Barents Sea plume at 450–340 Ma. One of the results of the plume–lithosphere interaction was the origin of the Eastern Barents Basin, which is filled with large volumes of basalts, and this predetermined the further subsidence of the area in Meso-Cenozoic time and the accumulation of thick sedimentary sequences with significant hydrocarbon resources. The peripheries of the area with products of basaltic magmatism are marked by alkaline rock complexes. The largest of the latter are the intrusions of the Kola Province and kimberlites in Archangelsk oblast. The dolerites of the dikes abound in xenogenic grains of zircon, which were dated at 2.7, 1.8, 1.3, 0.7 Ga. These age values suggest that the parental melts may have been derived in the lower crust and that the magma-generating processes may have evolved in the root zone of an ancient rift system.

The first results of U–Pb dating of detrital zircons from two samples that characterize the Tauric and Eski-Orda Series of the Cimmerian structural complex of the Crimean Mountains are presented. The strong similarity between the detrital zircons ages from the Lower Tauric Formation of the Tauric Series and the Salgir sequence of the Eski-Orda Series confirms the facial character of the primary relationships of these series. The studied Upper Triassic sandstones had a common source area and were most likely formed in different parts of the same sedimentary basin. It is most likely that this sedimentary basin was part of the continental margin of Baltica. The presence of a significant number of very ancient detrital zircons (>3.0 Ga, including three oldest detrital zircons grains with ages of ~3.9 Ga) in samples suggests that the crystalline complexes represented in the present-day structure of the Ukrainian Shield had very likely been primary sources of these zircons. Crystalline complexes with such ancient ages are extremely rare over the world, but are widely represented in the Podolian and Azov blocks of the Ukrainian Shield.

The first results of U-Pb dating of detrital zircons (dZr) from two samples characterizing the Taurica and Eski-Orda Groups of the Cimmerian structural complex of the Mountainous Crimea are presented. The strong similarity of the sets of ages of dZr from the Lower Taurica Formation of the Taurica Group and the Salgir strata of the Eski-Orda Group confirms the facial character of the primary relationships of these Groups. The studied Upper Triassic sandstones had a common feeding province and were formed, most likely, in different parts of the same sedimentary basin. It is most likely that this sedimentary basin was part of a continental margin of Baltica. The presence in samples of a significant number of dZr with very ancient ages >3.0 Ga (including 3 the oldest dZr grains with ages of ~3.9 Ga) makes the crystalline complexes represented in the present-day structure of the Ukrainian Shield as the very possible primary sources of these zircons. Crystalline complexes with such ancient ages are extremely rare over the world, but are widely represented in the Podolian and Cis-Azov blocks of the Ukrainian shield.

U–Pb dating, Hf-isotope, and trace-element studies on two detrital zircon samples from sandstone interlayers in the Upper Jurassic conglomerates of the Southern coast of the Mountainous Crimea provide new information on the primary crystalline complexes from which those conglomerates were sourced. The U–Pb age spectra of studied zircons suggest that they were most likely sourced from the (meta)sedimentary complexes of the Eastern and Western Pontides blocks and the Dobrogea platform. In particular, a close similarity of the Precambrian age spectra with the detrital zircons from Late Neoproterozoic–Late Paleozoic (meta)sedimentary complexes of the Dobrogea block provides strong supporting evidence for the affinity between the Pre-Mesozoic basement of the Crimea and the Dobrogea platform. The zircons in the first sample were recycled through Dobrogea sedimentary complexes and originated from terranes with Amazonia affinities, while zircons in the second sample were recycled through the Taurides and originated from terranes related to northeastern Africa and Arabia. The strong similarity of the Precambrian parts of the age spectra of the Dobrogea complexes and the sample K15-007 suggests a resemblance of the Crimea’s Pre-Mesozoic foundation and the Dobrogea platform. Initial analytical data are provided in Electronic Supplementary Materials A (ESM A). Descriptions of measurement parameters, methodologies, and constants used to process primary analytical data and some processing results are reported in ESM B (Figs. B1–B8). Schemes of locations within Balkans–Anatolia–Black Sea–Caucasus region the crystalline complexes with Jurassic, Triassic, Permian–Carboniferous, as well as Late Neoproterozoic–Cambrian and Ordovician–Devonian ages are in ESM C (Figs. C1, C3–C5).

The U–Pb dating and Hf isotope systematics of detrital zircons from a sandstone interbed in the section of the upper conglomerate sequence of the Mt. South Demerdzhi were carried out. The dominant populations of detrital zircons in the studied sample characterize episodes of magmatic activity within the source of the Upper Jurassic conglomerates. Magmatism was manifested in the Vendian-Cambrian, Carbon-Triassic and Late Jurassic. The åHf values of detrital zircons of these ages indicate the insignificant role of the ancient (Archean–Early Proterozoic) continental crust in the protolith of magmatic chambers. The similarity of the detrital zircons age distribution from the Middle Jurassic and Upper Jurassic conglomerate strata suggests that they are molasses of the Cimmerian orogen. The absence of products of Middle Jurassic magmatism in molasses of the Cimmerian orogen, which we fixed, limits position of the Cimmerian orogen in the southern part of the Scythian plate. It is shown that the primary source of the Precambrian detrital zircons were mobilized within the Cimmerian orogen the crustal fragments of the Peri-Gondwanan origin, rather than the basement complexes of the East European Platform, similar to the complexes of the Ukrainian shield. The reconstruction of the main stages of the accumulation of the coarse-grained strata of the Mountaineous Crimea in the context of the tectonic evolution of the southern margin of Laurasia during the Mesozoic is presented.

The U–Pb dating and Hf isotope systematics of detrital zircons from a sandstone interbed in the section of the upper conglomerate sequence of the Mt. Southern Demerdzhi were carried out. The dominant populations of detrital zircons in the studied sample characterize episodes of magmatic activity within the source of the Upper Jurassic conglomerates. Magmatism was manifested in the Vendian-Cambrian, Carbon-Triassic, and Late Jurassic. The eHf values of detrital zircons of these ages indicate the insignificant role of the ancient (Archean–Early Proterozoic) continental crust in the protolith of magmatic chambers. The similarity of the detrital zircons age distribution from the Middle Jurassic and Upper Jurassic conglomerate strata suggests that they are molasses of the Cimmerian orogen. The absence of products of Middle Jurassic magmatism in molasses of the Cimmerian orogen, which we fixed, limits position of the Cimmerian orogen in the southern part of the Scythian plate. It is shown that the primary source of the Precambrian detrital zircons were mobilized within the Cimmerian orogen the crustal fragments of the Peri-Gondwanan origin, rather than the basement complexes of the East European Platform, similar to the complexes of the Ukrainian shield. The reconstruction of the main stages of the accumulation of the coarse-grained strata of the Mountaineous Crimea in the context of the tectonic evolution of the southern margin of Laurasia during the Mesozoic is presented.

Detrital zircons of Ordovician terrigenous sequences are studied in various Southern Uralian tectonic units.The age of detrital zircons of the West Uralian and Transuralian megazones, Taganai–Beloretsk Zone, and Kraka allochthons spans from the Late Archean to the end of the Vendian– beginning of the Cambrian; Early Precambrian and Early–Middle Riphean zircons are the most abundant. Vendian–Cambrian detrital zircons are strongly dominant in the Uraltau Zone, Sakmara allochthons, and East Uralian Megazone; the zircons of other ages are absent or extremely rare. The Vendian–Cambrian detrital zircons of all Southern Urals zones probably derive from volcanic and granitic rocks of the marginal continental belt, which are part of the Uraltau Zone, Sakmara allochthons, and East Uralian Megazone. The Lu–Hf isotopic characteristics of Vendian–Cambrian detrital zircons indicate that their parental rocks formed on a heterogeneous basement that includes blocks of juvenile and ancient continental crust. According to a model of the pre-Ordovician tectonic evolution of the Southern Urals, at the end of the Late Riphean, the passive margin of the East European Platform collided with a block on a heterogeneous basement. The formation of the block terminated with the Grenville Orogeny. After collision, a volcano-plutonic belt originated in the Vendian–Cambrian at the actively evolved margin of the East European Platform.

A brief tectonic and geological overview of the fore-Urals and fore-Novaya Zemlya belt of oil and gas accumulation and the results of studying of the conditions for hydrocarbon deposits formation in uplift-thrust structures of its eastern side are presented. It is shown that the early stages of the belt formation are associated with Paleozoic subduction and obduction processes occurring in the transition zone between the Paleo-European continent and Uralian paleo-ocean located eastward (in modern coordinates) the continent. The intensive thrust-folded dislocations of the western verergency are fixed into the eastern side of the fore-Urals and fore-Novaya Zemlya belt of oil and gas accumulation. We associate their formation with the continental collision that occurred during the closure of the Uralian paleo-ocean at the Latest Paleozoic, and in the most northern segments of the belt, probably, at the Earliest Mesozoic. The structural paragenesis of the eastern side of the fore-Urals and fore-Novaya Zemlya belt of oil and gas accumulation includes uplift-thrusts and thrusts, as well as various scaled structural units formed under the conditions of the latitude compression.

The first isotope-geochemical and geochemical characteristics (the “TerraneChrone” method) of previously dated (U-Pb, LA-ICP-MS) detrital zircons from Ordovician sandstones (borehole Ordovician-2, Sol-Iletsk block) are presented. A comparative analysis of the characteristics of the studied zircons and the corresponding characteristics of the complexes composing the possible feeding provinces is carried out.

The primary isotope–geochemical and geochemical characteristics (by the TerraneChrone® technique) are presented for detrital zircons dated previously (U/Pb, LA–ICP–MS dating) from Ordovician sandstones (the Ordovician-2 borehole of the Sol-Iletsk block). The characteristics of the treated zircons were compared to the corresponding parameters of the complexes constituting the possible sources provinces.

Detrital zircons of Ordovician terrigenous sequences are studied in various Southern Uralian tectonic units. The age of detrital zircons of the West Uralian and Transuralian megazones, Taganai–Beloretsk Zone, and Kraka allochthons spans from the Late Archean to the end of the Vendian– beginning of the Cambrian; Early Precambrian and Early–Middle Riphean zircons are the most abundant. Vendian–Cambrian detrital zircons are strongly dominant in the Uraltau Zone, Sakmara allochthons, and East Uralian Megazone; the zircons of other ages are absent or extremely rare. The Vendian–Cambrian detrital zircons of all Southern Urals zones probably derive from volcanic and granitic rocks of the marginal continental belt, which are part of the Uraltau Zone, Sakmara allochthons, and East Uralian Megazone. The Lu–Hf isotopic characteristics of Vendian–Cambrian detrital zircons indicate that their parental rocks formed on a heterogeneous basement that includes blocks of juvenile and ancient continental crust. According to a model of the pre-Ordovician tectonic evolution of the Southern Urals, at the end of the Late Riphean, the passive margin of the East European Platform collided with a block on a heterogeneous basement. The formation of the block terminated with the Grenville Orogeny. After collision, a volcano-plutonic belt originated in the Vendian–Cambrian at the actively evolved margin of the East European Platform.

This paper provides a brief tectonic and geological overview of the Ural– Novaya Zemlya Forebelt of Oil-and-Gas Accumulation and describes the conditions under which the hydrocarbon deposits were formed in the structures of high- and low-angle reverse faults (upthrust-and-thrust) on the eastern side of the belt. It is shown that the early stages of belt formation are associated with Paleozoic subduction and obduction processes that occurred in the transition zone between the Paleo-European continent and the Ural paleo-ocean located eastward (in modern coordinates) of the continent. The intensive cover-folded dislocations of the western vergency are fixed into the eastern side of the Ural–Novaya Zemlya Forebelt of Oil-and-Gas Accumulation. We associate these dislocations with the continental collision that occurred during the closure of the Ural paleo-ocean in the Late Paleozoic, and in the northern-most segments of the belt, probably in the Early Mesozoic. The structural paragenesis of the eastern side of the Ural–Novaya Zemlya Forebelt of Oil-and Gas-Accumulation includes upthrust–thrusts and thrusts, as well as structural units of different sizes, which were formed under the conditions of latitudinal compression.

This study presents the results of U–Pb dating of detrital zircons separated from rocks of the Ai formation. A provenance-signal of local source with an age of approximately 2.07 Ga is derived and an effect of the Ordovician magmatic episode impact on the sedimentary strata is revealed.

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.

The results of U–Pb dating of detrital zircons extracted from rocks of the Ai Formation are presented. A provenance-signal of a local source with an age of about 2.07 Ga has been documented, and the effect of the Ordovician magmatic episode on the sedimentary sequence has been revealed.

The results of U–Pb-isotopic dating of detrital zircons from sandstones of the Proterozoic Pogor’uy Formation, occurring to the north and south of the East Angara block of Yenisei Ridge, are presented. The sandstones of the northern part of the East Angara block are dominated by Archean and Paleoproterozoic populations of detrital zircons, while the samples from the southern part of the East Angara block have been revealed up to 25% of Mesoproterozoic age grains. The detrital zircon ages allow limiting the maximum sedimentary age of the Pogor’uy Fm. and the entire interval of its formation to 1.2–0.9 Ga. The paleogeographic features of the Pogor’uy Fm. deposition in the context of the existing opinions on the location of Siberia within the Rodinia supercontinent were examined.

U/Pb-isotope dating of detrital zircons from conglomerates of the reference section of the Demerdzhi Formation on the western slope of Mount Southern Demerdzhi was carried out. A cluster of the five youngest, reliably dated zircons with an average age of 154.1 ± 0.73 Ma was revealed, which indicates that the formation of conglomerates overlying the studied layer began to form not earlier than in the Late Kimmeridgian. The dating obtained forces us to reconsider the age of the Demerdzhi Formation, which was previously specified as Oxfordian–Early Kimmeridgian. New data on the age of thecoarse-grained sedimentary rocks of the Crimean Mountains advance concepts about Late Jurassic Cimmerian tectonic activity on the northern Tethys margin.

The Bashkir anticlinorium is an extensive outcrop of Precambrian rocks within the Southern Urals, located near the south-eastern edge of the East European Platform (EEP). The Bashkir anticlinorium is subdivided by the Zyuratkul fault into two parts: the Bashkir (western part) and Uraltau (eastern part) Uplifts. The Late Precambrian strata of the Bashkir Uplift were formed at a passive margin of the Volga-Uralian part of Baltica. In contrast, the Late Precambrian strata of the Uraltau Uplift were formed far from its present-day location. Later, the Uraltau Uplift block moved along the Zyuratkul fault to its present-day position with a large-amplitude displacement. This study presents the first results of the integrated (U-Pb age, Hf-isotope and trace-elements contents) study of detrital zircons (dZr) from the Upper Ordovician sandstones of the northern part of the Uraltau Uplift. The integrated characteristics of the studied dZr provide new constraints for their primary sources. A comparison of obtained data with rock types, U-Pb and Hf model ages of the crystalline complexes of the of Volga-Uralia basement, as well as characteristics of dZr from Late Precambrian strata of the Bashkir Uplift and Kazakhstan have revealed that the Upper Ordovician sandstones of the northern part of the Uraltau Uplift contain dZr “alien” to crystalline complexes of Volga-Uralia, Kazakhstan, and Late Precambrian strata of the Bashkir Uplift. The sources of these “alien” dZr were other crustal blocks. A very high similarity of the age spectra of dZr from the Upper Ordovician sandstones, which overlain the Late Precambrian rocks units of the Uraltau and Bashkir Uplifts allows concluding that the spatial conjunction of the Bashkir and Uraltau Uplifts had occurred before the Late Ordovician time. Post-Upper Ordovician sedimentary complexes of the Bashkir and Uraltau Uplifts were sourced from identical feeding provinces in the same sedimentary basin, sealing its composite pre-Upper Ordorvician heterogeneous basement.

This work presents the data on the structure, geochronology, and formation settings of the Ordovician sedimentary and volcanogenic-sedimentary complexes of the Sterlitamak, Mariev, and Imanburluk structural and formational zones located in the western and northwestern frames of the Kokchetav massif (Northern Kazakhstan). In addition, the results of detailed stratigraphic, geochemical, and geochronological studies of the reference section of the Ordovician deposits of the Mariev Zone are given. The studied section is composed of carbonate, terrigenous, and less commonly volcanogenic-sedimentary deposits, confined to a wide stratigraphic interval from Tremadocian Stage of the Lower Ordovician to the lower Sandbian Stage of the Upper Ordovician. For the first time, the study of conodont assemblages made it possible to establish the Early to Middle Ordovician age of the most ancient limestone–dolomite sequence, which was previously conventionally attributed to the Cambrian. The above-lying tuffaceous–terrigenous Kupriyanovka Formation is now attributed to the Middle Ordovician. On the basis of compositional features of the lithoclastic tuffs composing the middle part of the formation, we assume that it was formed within the island arc zone. Limestones from the base of the youngest terrigenous–carbonate Kreshchenovka Formation are attributed to the lower part of the Sandbian Stage of the Upper Ordovician. The study of the geochronology of detrital zircons from terrigenous rocks of the limestone–dolomite sequence has shown that the Early Neoproterozoic quartzite–schist sequences of the Kokchetav massif were the most probable provenance area during its deposition. It was established that there was the change of sedimentation environments from closed lagoons to a relatively deep sea basin with normal salinity and intense circulation of water masses in the northwestern frame of the Kokchetav massif during the Ordovician. During this period of time, there was a sufficiently high level of erosion of provenance areas that resulted in the deposition of thick strata of terrigenous material. A general tendency of the deepening of sedimentation environments from the Early to Late Ordovician was interrupted by sea level rises in the Dapingian and early Darriwilian ages.

We present tectonic implications for hydrocarbon accumulations in the Ural‒Novaya Zemlya Foredeep. Its eastern flank is rich in economical oil and gas deposits mostly localized within the fold-and-thrust belt that was constructed as a result of continent‒continent collision during the Ural Paleoocean closure. On the basis of striking correlation between oil and gas accumulation and fold-and-thrust tectonics we performed geomechanical and petroleum systems modelling that allowed us to propose a new geodynamical model for hydrocarbon accumulations in both fold-upthrust and subthrust structural levels of the Ural‒Novaya Zemlya Foredeep.

The main results are presented on U/Pb-isotope dating of 100 detrital zircons and, selectively, on the Lu/Hf-isotope system of 43 grains from sandstones of the Lopatinskii formation (the lower stratigraphic level of the Chingasan group). Ages from 896 ± 51 to 2925 ± 38 Ma were obtained with a pronounced maximum of ~1890 Ma in the curve of probability density, along with eHf estimates from +8.4 to–15.1, which allow one to throw doubt upon the molasse nature of the Lopatinskii formation.

The results of geochemical study of samples from Riphean–Lower Paleozoic rocks enriched in organic matter (the rocks most likely parental for oil) from the southern part of the Siberian Platform are reported.

The age distribution of detrital zircons from Upper Riphean and Early Carboniferous sandstones of the northwest part of Nordenskiold Land (Spitsbergen Island) was studied. The results obtained supplement the previously known data on the rocks of Precambrian and Paleozoic masses of West Spitsbergen. Integrated consideration of these data showed that the time interval from the Middle Riphean to the Early Carboniferous inclusive might be subdivided into at least five stages characterized by quite different provinces supplying detritus to sedimentary basins. (The relics of these latter are represented in the present structure of western Svalbard.) The most ancient distinguished event of alteration of the sources of sedimentary matter (at the boundary of the Middle and Late Riphean) corresponds to the consolidation time of the ancient basement of Svalbard.

The synthesis of the paleomagnetic data for the Siberian (Siberia) and East European (Baltica) platforms shows that since the Early Paleozoic they could have experienced coherent movements as a part of consolidated continental agglomeration (a composite continent), which also includes the Arctida continent. Based on the paleomagnetic data, the relative positions of the Siberia and Baltica during the Ordovician is reconstructed, and a series of paleogeographical reconstructions describing the drift of the composite continent is suggested. The results of the lithologic–facial analysis of the sedimentation settings within the Ordovician basins of the Siberian and East European platforms and paleoclimatic markers are consistent with the suggested configuration and paleogeographical position of the composite continent. The suggested reconstructions and the ages of detrital zircons from the Early Paleozoic complexes of the platform margins and some objects of the Central Asian Mobile Belt (CAMB) reasonably well agree with the hypothesis (Sengor et al., 1993) which interprets the formation of the structure of CAMB Paleozoides as a result of the evolution of the island arc stretching along the margins of Siberia and Baltica.

The results of U/Pb dating of detrital zircons from sandstones of the Zigalga Formation, which is the base level of the Middle Yurmatu Group of the Bashkir uplift, southwestern Urals, are presented. The U/Pb ages of detrital zircons from sandstones of the Lower, Middle, and Upper Riphean are compared.

This study presents geochemical data on organic-rich rock samples collected from Riphean—Lower Paleozoic strata (potential source rocks) of the southern Siberian Platform and compositional data on hydrocarbon biomarkers (steranes, terpanes, n-alkanes, 12- and 13-methylalkanes, isoprenanes) and diamondoid hyrocarbons from core samples collected from the Kulindinskaya-1 well, which was drilled by RN-Exploration in 2012 within the Katanga saddle.

The first LA–ICP–MS U–Pb isotopic ages of detrital zircons from the Ordovician sandstones of the Sol–Iletsk Block (well 2–Ordovician), located at junction of the East European Platform with the Pre-Caspian Basin and the Pre-Uralian foredeep, are presented. Two detrital zircons with well-defined ages of 561 ± 4 and 570 ± 5 Ma were found in sample K15–501. They confirm the Ordovician age of the sandstones, which earlier had been defined on the basis of seismic–stratigraphic and lithological correlations. The age distribution of the detrital zircons indicates the significant role of Late Precambrian rocks as provenance sources. However, those rocks still remain unknown in the Early Precambrian basement of the Volga–Ural part of the EEP.

New LA-ICP-MS data on the U–Pb isotope age, Hf isotope characteristics, and concentrations of trace elements in zircons from volcanic tuff of the Upper Vendian Sylvitsa Group on the western slope of the Middle Urals are reported.

Analyses of trace elements and Lu/Hf isotopes have been carried out in already U–Pb dated detrital zircons from the Upper Ordovician sandstones of the southern part of the Bashkir Uplift. The concentrations of trace elements in the zircons suggest that they were derived from rocks of intermediate (62%), basic (24%), and felsic (9%) compositions as well as alkaline rocks (2%). The Lu/Hf systematics of the zircons demonstrated a wide variation of both eHf (from +9.5 to–8.7) and model ages of the parental rocks (1.60 Ga < T DM C < 3.28 Ga). Comparison of the isotopic–geochemical characteristics of the detrital zircons from different levels of the Riphean–Paleozoic sequence of the Bashkir Uplift against those from the Early Cambrian Brusov Formation of the Mezen Basin and Early Neoproterozoic Dzhezhim sandstones of Timan Ridge suggests that at the end of the Late Precambrian near the Uralian margin of Baltica a large block of Late Mesoproterozoic–Early Neoproterozoic crust existed, comprising a significant proportion of melanocratic rocks.

Eukaryotic algae rose to ecological relevance after the Neoproterozoic Snowball Earth glaciations, but the causes for this consequential evolutionary transition remain enigmatic. Cap carbonates were globally deposited directly after these glaciations, but they are usually organic barren or thermally overprinted. Here we show that uniquely-preserved cap dolostones of the Araras Group contain exceptional abundances of a newly identified biomarker: 25,28-bisnorgammacerane. Its secular occurrence, carbon isotope systematics and co-occurrence with other demethylated terpenoids suggest a mechanistic connection to extensive microbial degradation of ciliate-derived biomass in bacterially dominated ecosystems. Declining 25,28-bisnorgammacerane concentrations, and a parallel rise of steranes over hopanes, indicate the transition from a bacterial to eukaryotic dominated ecosystem after the Marinoan deglaciation. Nutrient levels already increased during the Cryogenian and were a prerequisite, but not the ultimate driver for the algal rise. Intense predatory pressure by bacterivorous protists may have irrevocably cleared self-sustaining cyanobacterial ecosystems, thereby creating the ecological opportunity that allowed for the persistent rise of eukaryotic algae to global importance., It remains unclear when and why the world’s oceans, once largely occupied by bacteria, became dominated by photosynthetic algae. Here, using fossil lipids in million year old rocks, the authors show that predation after the Snowball Earth glaciations created the opportunity for a global shift to algal ecosystems.