The early Vendian microfossils first found in the Russian plate: Taxonomic composition and biostratigraphic significance

The microfossils studied are discovered for the first time in the Riphean-Lower Vendian deposits, which have been recovered in 2002 by the Kel’tminskaya-1 deep parametric borehole in the Vychegda depression, the northeastern margin of the East European platform. The sampled interval of core section (4825–2347 m) consists of three units: the lower (depth range 4825–3995 m, 5 samples) and middle (depth range 3687–2961 m, 17 samples) carbonate successions overlain by sandstone-siltstone beds (depth range 2907–2347 m, 58 samples). Based on lithological criteria and/or composition of stromatolites, the carbonate successions are correlative with the Yshkemes and Vapol formations of the Upper Riphean of the Timan ridge succession, while the overlying, mostly siltstone succession was correlated with the Vychegda Formation of the southern Timan according to similarity in lithology and mineral composition. Microfossils found in 56 samples occur at 20 microphytological levels and represent different microbiotas. The Yshkemes and Vapol microbiotas of low diversity characterize six lower levels and represent one assemblage, while the diverse and abundant Vychegda microbiota typical of fourteen upper levels is divisible into three successive assemblages. The Vapol stromatolites Inzeria djejimii and Poludia polymorpha along with giant Chuaria and Navifusa present in the Yshkemes-Vapol assemblage suggest that their host deposits correspond to the upper Upper Riphean. The Vychegda assemblages, each of peculiar biostratigraphic specifics and unique in composition, consist of different morphotypes, primarily of large acanthomorphic acritarchs Cavaspina, Polyhedrosphaeridium, Cymatiosphaeridium, Asterocapsoides, and Tanarium, which are known in Scandinavia, Siberia, China, Australia, and India only in the Lower Vendian microbiotas of the Perthatataka type. The comprehensive microphytological characterization of the Lower Vendian in the Vychegda depression and earlier data on the Middle-Upper Riphean microbiotas from the adjacent Mezen syneclise enable a high-resolution biostratigraphic subdivision of the Riphean and Vendian successions in the vast region under consideration.     

Microfossils from cap dolomites of the Lower Vendian Churochnaya Formation in the Polyudov Range (North Urals): Paleoecological approach to interpretation of Late Proterozoic glaciations

Microfossils from silicified varieties of cap dolomites crowning the section of the tillite-bearing Lower Vendian (Ediacaran) Churochnaya Formation in the Polyudov Range (North Urals) are characterized. These microfossils are the first to be found from Vendian sections of the region and from all the terminal post-glacial sediments, one of the most significant global glaciation Marinoan of the African Glacial Era, when glaciers reached the equator. They are represented by remains of hormogonian and chrococcacean cyanobacteria as well as possible green filamentous algae. This microbiotic assemblage is of relatively low diversity, being composed of taxa with wide stratigraphic ranges characteristic of Proterozoic conservative microbiotas developed in shallow-water siliceous-carbonate facies. The lack of phytoplanktonic microfossils in this biota including Pertatataka-type acanthomorphic acritarchs or Ediacaran Complex Acanthomorph Palynoflora (ECAP) is also consistent with the conclusion on shallow-water deposition of the Churochnaya Formation. Moreover, most cyanobacteria representatives occurring in the latter are characteristic of shallow-water arid environments that confirm a theory of significant temperature increase during accumulation of the cap dolomites after termination of the above-mentioned glaciation. In addition to these microfossils, the cap dolomite member of the Churochnaya Formation contains filamentous and coccoidal pseudofossils formed under influence of post-sedimentary fluids. In their morphometric parameters, they resemble structures described from Archean sections as microfossil remains, which may be a key to interpreting their nature.     

Zonal biostratigraphy in the solution of the fundamental and applied problems of geology

The problems of zonal stratigraphy of the early 21st century are discussed. The great advances achieved in recent years in using zones in geological practice are noted. At the same time, attention is drawn to the controversies existing in the interpretation of the concepts “biostratigraphic zone” and “chronozone,” in the methods of drawing the boundaries of such zones, and in the assessment of the spatial scale of zones and in the understanding of them as stratigraphic units.     

The Yudomian of Siberia,Vendian and Ediacaran systems of the International stratigraphic scale

In Russia, the terminal Neoproterozoic formally includes the Vendian of western part of the East European platform and the concurrent Yudoma Group of Siberia. As is shown in this work, the designated subdivisions correspond in the stratotypes only to the upper, Yudomian Series of the Vendian. In the Siberian platform, the Ust-Yudoma and Aim horizons of the Yudomian are tightly interrelated. The lower of them, bearing remains of Ediacaran Fauna, represents the Ediacarian Stage, whereas the upper one containing small-shelled fossils (SSF) corresponds to the Nemakit-Daldynian Stage divided into the trisulcatus and antiqua superregional zones. In more complete sections of the platform periphery, sediments of these subdivisions conformably rest on siliciclastic succession that should be ranked as basal subdivision of the Yudomian. The succession is concurrent to the Laplandian Stage of the East European platform. According to geochronological dates obtained recently, the Yudomian Series spans interval of 600–540 Ma. In the East European platform, the Upper Vendian (Yudomian) begins with the Laplandian basal tillites of synonymous stage. In the west of the platform, tillites are dated at 600 Ma like the Upper Vendian base in Siberia. The next Ediacarian Stage of the East European platform is stratigraphic equivalent of the Redkino Horizon, while summary range of the Kotlin and Rovno horizons is concurrent to that of the Nemakit-Daldynian Stage. The Vendian of Russia is conformably overlain by the Tommotian Stage of the Lower Cambrian. Intense pre-Vendian events constrained distribution areas of the Lower Vendian sediments in Russia. The Lower Vendian deposits of the East European platform are most representative and well studied in the central Urals, where they are attributed to the Serebryanka Group. In Siberia, separate subdivisions representing the Lower Vendian are the Maastakh Formation of the Olenek Uplift, two lower members of the Ushakovka Formation in the Baikal region, and the Taseeva Group of the Yenisei Range. Chronological interval of the Lower Vendian corresponds to 650–600 Ma. The Marinoan Glaciation dated in Australia at 650–635 Ma is concurrent to basal part of the pre-Yudomian interval of the Vendian in Russia, whereas the Laplandian Tillite and Gaskiers Glaciation (600–580 Ma) correspond to onset of the Yudomian Epoch. The new Ediacaran System (Knoll et al., 2004) legalized in the International Neoproterozoic scale is close in range to the entire Vendian (635–544 Ma), although without basal beds (Marinoan Tillite) it deprives the terminal Neoproterozoic of its original sense. Inferiority of the system consists also in its indivisibility into stages. Hence, it is clear that the Vendian System subdivided in detail in Russia should be retained in the rank of terminal system of the Precambrian, one of the basic in general scale of the Neoproterozoic.     

New data on biostratigraphy of the Vendian Nemakit-Daldynian stage in the southern Siberian platform

New paleontological finds in sediments of the Upper Vendian Nemakit-Dadynian Stage from different areas of the southern Siberian Platforms (Yenisei Range, Sayany region, central areas, Patom Highland) are discussed. The base of the Lower Cambrian Tommotian Stage (∼540 Ma) is established at the first appearance level of characteristic small-shelled fossils in the western part of the Patom Highland. This boundary coincides with the episode of a brief sea-level fall and enhanced terrigenous sedimentation in the basin with dominant carbonate sediment deposition. The base of the Purella antiqua Zone (544 Ma), which is registered by paleontological data in the Yenisei Range sections, is marked by the replacement of terrigenous sedimentation by the carbonate one. In the northwestern Yenisei Range, this boundary coincides, in addition, with a major hiatus and subsequent paleobasin extension. The base of the Nemakit-Daldynian Stage (base of the Anabarites trisulcatus Zone, ∼550 Ma) in most sections corresponds to the onset of sea transgression. In addition to small-shelled remains, sediments of this zone contain characteristic ichnofossils and Vendotaenia flora. It is shown that defined boundaries are traceable through the entire southern part of the Siberian Platform. This makes them useful for wider stratigraphic interpretations.     

The Lower Paleogene Biostratigraphic Scale of the Northern Pacific Based on Deep-Water Benthic Foraminifera

Based on the stratigraphic distribution of benthic foraminifera in the lower bathyal–abyssal sediments uncovered by boreholes drilled under the framework of the Deep Sea Drilling Project (DSDP) and Ocean Drilling Project (ODP) in the Northern and Southern Pacific, the Lower Paleogene biostratigraphic zonal scale based on deep-water benthic foraminifera is proposed. The proposed scale includes eight subdivisions: six zones and two subzones. The boundaries of the zonal subdivisions are determined by biotic events (appearance or disappearance (extinction)) of stratigraphically important taxa and are correlated to the zonal scales based on planktonic foraminifera and calcareous nanoplankton. Most of these events are considered to be subglobal.     

Geological structure of the oil-and-gas plays and oil-and-gas potential of the southern Siberian Platform

The paper discusses modern views of the structure of the main producing plays in the southern Siberian Platform: Riphean, Vendian, and Lower Cambrian. The major zones of oil and gas accumulation have been distinguished. Forecast resources have undergone differentiated expert evaluation, and methods for their development have been recommended.     

The first magnetostratigraphic data on the stratotype of the Lopata Formation,Northeastern Yenisei Ridge: Problems of its age and paleogeography of the Siberian Platform at the Proterozoic–Phanerozoic boundary

New paleomagnetic and magnetostratigraphic data are presented for the stratotype of the Upper Riphean Lopata Formation (Teya River, Yenisei Ridge). The paleomagnetic pole calculated is significantly distinct from the Phanerozoic and Riphean poles of the Siberian Platform and is similar to the Late Vendian–Early Cambrian poles of the Madagascar Group. The stratigraphic range studied is characterized by an anomalously high frequency of geomagnetic inversions (15 zones of magnetic polarity), which is comparable with the inversion frequency of the Late Vendian sections of Baltica. These data, along with previous paleontological findings, indicate an age of the Lopata Formation of 555–540 Ma.     

Episodes of development of some major structural elements of Eurasia in connection with distribution of oil-gas provinces (basins) and their resources

The area of Eurasia and the shelves of the marginal and internal seas have been sufficiently investigated by geological, geophysical, and drilling means to formulate a number of regional conclusions about the association between various types of tectonic structures and distribution of the petroliferous provinces (basins). This problem has been considered against the background of platforms of different age, the ancient pre-Riphean (East European and Siberian) and the epi-Paleozoic types (West Siberian and West European, and also the South Caspian intrageosynclinal basin). There are significant differences in their geological evolution, which exerted a direct effect on the distribution of the petroliferous complexes. Within the Siberian Platform, the fundamental stages in downwarping were associated with the deposition of Vendian and lower Paleozoic sediments. The principal stages in the formation of the sedimentary cover of the East European Platform were associated with the Devonian, Carboniferous, and Permian periods.

For all types of structural zones under consideration, an association has heen established between distribution of oil and gas reserves and episodes of development of major structural elements. They define the overall stratigraphic range of the petroleum occurrences within the young and old platform and the fold regions, and also the concentration of the reserves of hydrocarbons in the complexes corresponding to the principal stages of downwarping of the basins.—Authors     

Zonation of the Siberian Ordovician deposits based on pelagic groups of fauna

We summarize data on the biostratigraphic units of the Siberian Ordovician deposits based on pelagic groups of fauna: graptolites, conodonts, and chitinozoans. It is shown that graptolite and conodont zones and beds have a high potential for correlation. We have determined the precise zonal position of most of the lower boundaries of the Ordovician stages and informal Ordovician substages of the International Stratigraphic Chart in the Lower Paleozoic key sections of the Taimyr Peninsula, Siberian Platform, and Altai-Sayan Folded Area.     

A section of Vendian in the east of West Siberian Plate (based on data from the Borehole Vostok 3)

The Borehole Vostok 3 drilled in the east of the West Siberian Plate (Tomsk Region) revealed a Vendian section in the depth range 5002–3870 m, which was subdivided into the Poiga, Kotodzha, and Raiga Formations based on geological, geophysical, and paleontological data. In the Kotodzha and Raiga Formations, typical Upper Vendian fossils of Cloudina hartmanae and Namacalathus sp. were found along with diverse Platysolenites, which are commonly considered to be of zonal significance in Lower Cambrian strata. Hence, the stratigraphic interval with abundant diverse Platysolenites has a wider stratigraphic range than it was believed earlier and seems to cover the Upper Vendian and Lower Cambrian deposits. The Borehole Vostok 3 is the first Siberian occurrence of the fossils Namacalathus, the world's fourth occurrence of the Cloudina-Namacalathus association, and the first site where coexisting Platysolenites and typical Vendian organisms have been found. Therefore, the borehole provides one of the most informative (in paleontological context) Upper Vendian sections.     

Magnetostratigraphy of the Middle–Upper Cambrian Verkhnyaya Lena Group and Lower Ordovician Ust-Kut formation in the southern Siberian Platform

The available paleomagnetic data on the Verkhnyaya Lena Group from different areas of the southern Siberian Platform are revised. The group rests unconformably upon the Lower Cambrian strata and is overlain by Lower Ordovician rocks, which determines conditionally the age of its red-colored deposits. Paleomagnetic correlation of composite sections through the region using defined zones of normal and reversed magnetic polarity serves as a basis for development of the magnetostratigraphic scale for the Verkhnyaya Lena Group. The scale includes nine magnetic zones, which play the role of markers; seven of them are traceable in all the examined sections of the southern Siberian Platform. By the distribution of zones with normal (N) and reversed (R) polarity, the magnetostratigraphic scale is subdivided into three parts. Its lower part is represented by reversed polarity, which is characteristic of the second half of the Lower Cambrian. The middle part is characterized by frequently alternating zones with normal and reversed polarity corresponding to the Middle Cambrian. The upper part of the scale corresponds to the interval of reversed polarity characteristic of the Upper Cambrian and Lower Ordovician. The Middle–Upper Cambrian boundary is located near the last N–R reversal of the geomagnetic field in the Cambrian. The magnetostratigraphic scale includes nine orthozones united into three superzones, which are attributed to two hyperzones of magnetic polarity.     

Neoproterozoic and Lower Cambrian rock complexes in central areas of the Siberian Craton: Their structure and petroleum prospects

The paper summarizes data on the geology, lithology, and geochemistry of petroliferous Riphean, Vendian, and Lower Cambrian rocks in the central parts of the Siberian Craton. The petrological-geological properties of these sediments have been assessed based on results of paleogeographic analysis of these rocks, discrimination of oil reservoirs and oil-source successions, determination of secondary alterations of the rocks, and sources of oil generation and regional migration of hydrocarbons into various traps in zones of possible oiland-gas accumulation.     

Palynostratigraphy of the Upper Cretaceous and Paleogene Deposits in the South of Western Siberia by Example of Russkaya Polyana Boreholes,Omsk Trough

The detailed study of Boreholes 8, 10, and 2 in the Russkaya Polyana district (Omsk Trough) made it possible to reveal the complex structure of the Upper Cretaceous sediments formed in unstable conditions of the marginal part of the Western Siberian basin. The Pokur, Kuznetsovo, Ipatovo, Slavgorod, and Gan’kino formations were subjected to palynological analysis and substantiation of their Late Cretaceous age. Eight biostratigraphic units with dinocysts and five units with spores and pollen from the Albian to the Maastrichtian were identified. The joint application of biostratigraphic and magnetostratigraphic methods made it possible to reveal the stratigraphic breaks in the studied sedimentary stratum and to estimate their scope. The age of the Lower Lyulinvor Subformation was specified in the marginal part of the Omsk Trough. The ingression traces of the Western Siberian basin in the Albian were found for the first time in the considered region.     

The stratotype and facies of the glacial Lower Vendian Nichatka Formation,Chara River basin,Central Siberia

Sediments of the Nichatka Formation are facially studied and thoroughly described, the sections are correlated, and the subformations are recognized. The formation represents a key stratigraphic unit to reveal the origin of the Central Siberian glacial horizon and to correlate it with glacial horizons in other regions of the world, namely, with the Laplandian Horizon of the Lower Vendian, Nantou and Marino tillites, etc. The Nichatka Formation is correlated with the glacial Bolshoi Patom (Dzhemkukan) Formation of the Vendian reference section at the Ura Uplift. Unlike the latter, it is mainly composed of continental glacial deposits and is marked by a complex facies composition. The glacial origin of the Nichatka Formation is reliably determined on the basis of a set of diagnostic characters. This permits a more complete reconstruction of the Early Vendian depositional environments. In addition to typical basal tillites and marginal moraine deposits, the formation includes glaciolacustrine and fluvioglacial sediments along with aquatillites, allotillites, and the glacial fan, including subaqueous, deposits.     

Neoproterozoic ice sheets of the Siberian Platform: U-Pb-LA-ICP-MS ages of detrital zircons from the Bol’shoi Patom formation and the geotectonic position of its provenance

The centers of many Neoproterozoic and Phanerozoic glaciations were located on cratons and crystalline shields not necessarily, as some researchers believe, associated with rifts. An example is the Vendian Bol’shoi Patom glacial formation (Lena River, Yakutia). The U-Pb ages of detrital zircons from this formation imply that it was deposited by glaciers located on the pre-Riphean crystalline shields of the Siberian Platform. Glaciation in this region occurred after cessation of rifting and could not be related to the latter. The Bol’shoi Patom Formation is an element of the Middle Siberian glacial horizon that was deposited during the Marino Glaciation and is traceable along the southern periphery of the Siberian Platform from the Aldan Shield to the Baikal and Sayany regions. This indicates that the Marinoan Glaciation in Siberia involved at least the entire southern part of the Siberian Platform. Rifting was not the single, or even a principal, factor responsible for glaciations, although it could accompany and enhance them simultaneously providing space for sedimentation and conditions for preserving glacial deposits from erosion.     

A new Permian bivalve zonal scale of northeastern Asia. Article 1: Zonal subdivision

Extensive new data obtained during the recent decade on several Permian reference sections in the northern, western, and southern Verkhoyansk region; the Balygychan block; the Omolon massif; and some adjacent regions provided grounds for substantial refining of the Permian bivalve zonal scale of northeastern Asia. The modified version of this scale includes 24 biostratigraphic units ranked as zones, subzones, and faunal beds. Zonal assemblages of bivalve mollusks were refined and supplemented, and the age of the zones was specified and substantiated. The stratigraphic distribution of the defined bivalve taxa is illustrated by a special detailed table.     

C and Sr isotope chemostratigraphy of Vendian-Lower Cambrian carbonate sequences in the central Siberian Platform

We propose a detailed δ¹³C curve for the Vendian and Lower Cambrian (Tommotian) strata of the central Siberian Platform. Two positive carbon isotope excursions identified near the base of the Yuryakh Formation (up to 5.5‰) and in the lower Bilir Formation (up to 5‰) are assigned to the lowermost and middle Tommotian, respectively. This correlation is supported by paleontological data, specific ⁸⁷Sr/⁸⁶Sr values (0.70845-0.70856), and similar C isotope record in coeval Early Cambrian basins. The documented minor vertical oscillations (a few meters) of these isotope excursions relative to the formation boundaries in remote boreholes is presumably caused by the spatiotemporal migration of facies. A high-amplitude negative δ¹³C excursion (-8 to -11‰) in the upper Nepa Regional Stage putatively corresponds to the global Shuram-Wonoka negative carbon isotope excursion (Middle Ediacaran). Carbonates of the lower Nepa Regional Stage (Besyuryakh Formation) demonstrate positive δ¹³C values (up to 5‰) and minimum ⁸⁷Sr/⁸⁶Sr ratios of 0.70796-0.70832. The C and Sr isotope record of the Nepa Regional Stage provides its robust correlation with the Dal’nyaya Taiga and Zhuya Groups of the Patom Foredeep. Micropaleontological data herein reported and glacial diamictites documented at the base of the Vendian sedimentary cover both in the central Patom Foredeep and on its periphery suggest a full stratigraphic volume of the Ediacaran System in the most stratigraphically complete sections of the central Siberian Platform.     

Problems of phytostratigraphy and the correlation of the Lower Jurassic continental sediments in West Siberia and Kuznetsk and Kansk-Achinsk basins

Paleofloral and palynological records of Lower Jurassic sediments in West Siberia, Kuznetsk (Kuzbass), and Kansk-Achinsk basins and their correlation are discussed. In a number of recent papers dedicated to the Jurassic stratigraphy of Siberia this problem is ambiguously treated. The reference palynological scale has been developed for the Jurassic West Siberian sediments and an uninterrupted succession of floral assemblages associated with it and with regional stratigraphic units has been recognized. On this basis the scheme of the correlation between the Lower Jurassic sediments of the Kansk-Achinsk and Kuznetsk basins and West Siberia permitting a better age estimate of coal-bearing deposits, is proposed.