Yenisei Range Research Articles

The Role of Forest Stands Characteristics on Formation of Exterior Migratory Outbreak Spots by the Siberian Silk Moth Dendrolimus sibiricus (Tschetv.) during Population Collapse

The characteristics of Abies sibirica Ledeb.- and Pinus sibirica Du Tour dominated forests stands in outbreak spots formed during a Dendrolimus sibiricus outbreak in 2014–2017 were studied at the stage of population collapse (east of the West Siberian Plain and western foothills of the Yenisei Range). The research was based on the data obtained during ground surveys conducted in 2016 when stands characteristics, the Siberian silk moth population density, and defoliation level were recorded. We classified the studied stands using decision trees and random forest algorithms to identify the key characteristics that determine the formation of outbreak spots. The classification results showed that the characteristics of the detected outbreak spots differ significantly from those previously described for dark coniferous stands of the southern taiga in Siberia. The highest probability of the outbreak spot occurrence in the study area was revealed for stands with the following characteristics: moderately moist site; Siberian stone pine and Siberian fir take 40% or more of stem volume; age of less than 105 years. Another group of forest stands under threat are those sharing the following characteristics: large area (more than 60 ha); stand homogeneity; ground vegetation is dominated by feather mosses; age of more than 120 years; Picea obovata Ledeb. takes a significant share in a stem volume. Such characteristics indicate that during the population collapse, the Siberian silk moth forms outbreak spots in stands that either undergo an early successional stage after previous outbreak or have been slightly damaged during the previous outbreaks due to unfavorable habitat conditions.

Grenville and Valhalla Tectonic Events at the Western Margin of the Siberian Craton: Evidence from Rocks of the Garevka Complex, Northern Yenisei Range, Russia

Grenville and Valhalla Tectonic Events at the Western Margin of the Siberian Craton: Evidence from Rocks of the Garevka Complex, Northern Yenisei Range, Russia

Kinematic indicators in Riphean carbonate rocks of the Siberian Platform Western framing (on the example of the Alad’inskaya Formation)

Introduction. New data on the structure of sections of the Middle Riphean Alad’inskaya Formation at the Kamenskaya subzone of the Yenisei Range (r. Irkineeva) were obtained. These sections indicate the tectonic nature of brecciated and banded dolomite varieties with the associated areas of cavern development, representing promising objects of oil and gas exploration works.Aim. To substantiate the tectonic nature and structural confinement of cavern development areas in dolomites of the Alad’inskaya Formation.Materials and methods. The sections of Alad’inskaya Formation carbonates, located along the Irkineeva river, were studied, including determination of the sample phase composition by the X-ray diffraction method (ARL X’TRA) and examination of samples in sections (Leica DMLR) and by a scanning electron microscope (TESCAN VEGA 3 LMH). Kinematic indicators were studied and classified; a model of structural formation in carbonate rocks was substantiated.Results. A detailed layer-wise description of the studied section, illustrated by various-scale images, was carried out. The kinematic indicators of specified rocks with a reference to a particular section were revealed, described and systematized. A conclusion is made about the genetic association of dolomite breccia, banded dolomites, and cavern development areas with a local thrust, observed at the base of the studied section.Conclusion. The tectonic nature of brecciated and banded dolomites of the Alad’inskaya Formation and the structural control of cavern development areas are substantiated. As a result, the model of structural formation in lamellar carbonates under longitudinal compression is verified.

Age Benchmark of Granulite Metamorphism in the Angara–Kan Block, South Yenisei Range: Evidence from Zircon Dating of Postcollisional Granite–Aplite Dikes

The paper presents isotope–geochronological data on zircons from a granite–aplite dike that cuts garnet–hypersthene gneisses of the Kuzeyev unit of the Neoarchean–Paleoproterozoic Kan Group in the southern extension of the Ishimba–Tatarka regional shear zone, Kan River. The morphology and internal structure of most of the zircon grains indicate that the zircons are metamorphic and xenogenic and were captured by the acidic magma from the host rocks when the magma intruded the granulites. Based on these data, the obtained Paleoproterozoic U–Pb age of 1784 ± 6 Ma can be interpreted as the age of granulite metamorphism. The interpretation of available geological and isotopic data confirms a postcollisional age of the aplite, which was emplaced nearly synchronously with the formation of anorogenic leucogranites of the late phase of the Tarak complex, during the final stage of the formation of the Nuna supercontinent.

Granitoid Anorogenic Magmatism of the Yenisei Range: Evidence of Lithospheric Extension in the Western Part of the Siberian Craton

Granitoid Anorogenic Magmatism of the Yenisei Range: Evidence of Lithospheric Extension in the Western Part of the Siberian Craton

New Data on the Age of Neoproterozoic Volcanic Rocks of the Isakovka Terrane, Sayan–Yenisei Accretion Belt (U–Pb, Zircon)

A Late Neoproterozoic U–Pb zircon age is established for the first time for arc metadacites (691 ± 8.8 Ma) and basalts (572 ± 6.5 Ma) from the Kiselikha Formation of the Kutukas Series. The manifestation of basaltic volcanism is associated with rifting processes. Our studies specify the Late Precambrian stratigraphy of the Yenisei Range and the evolutionary features of the Sayan–Yenisei accretion belt at the Neoproterozoic stage of its history. The fold-and-thrust structures of the junction zone between the Yenisei Range and the West Siberian Plate may be favorable in terms of the search for unconventional oil and gas traps.

C and Sr Isotope Chemostratigraphy and Pb–Pb Age of Carbonate Deposits of the Vorogovka Group (Neoproterozoic), Northwest of the Yenisei Range

The C and Sr isotopic signatures and the Pb–Pb age of carbonate sedimentary rocks of the Vorogovka Group in the reference section in the Vorogovka River valley, northwestern Yenisei Range, were obtained. The deposits of the group ascribed to the Severnaya Rechka, Mutnina, and Sukhaya Rechka Formations fill a large trough, and lithological and textural features indicate a high sedimentation rate. Most of the carbonate rocks are represented by limestones with low Fe/Sr and Mn/Sr ratios and average δ18O value (–6.0 ± 1.6‰ V-PDB), indicating the well-preserved isotope systems of the rocks. The 87Sr/86Sr ratios and δ13С values vary within narrow limits of 0.70816–0.70826 and –1.4 to +0.8‰ for Upper Severnaya Rechka limestones and 0.70818–0.70829 and +1.0 to +2.0‰ for Sukhaya Rechka limestones, respectively. The Pb–Pb isochrone ages of carbonate rocks of the Severnaya Rechka and Sukhaya Rechka formations are 580 ± 40 Ma (MSWD = 1.4) and 565 ± 90 Ma (MSWD = 1.1), respectively. According to chemostratigraphic and isotope-geochronological data, the accumulation of limestones of the Vorogovka Group could have occurred at 580–550 Ma, that corresponds to the Late Vendian or Late Ediacaran. It is evident that the duration of accumulation of Vorogovka Group did not exceed 10–15 m.y. The Vorogovka Trough is different from in the sedimentation pattern from other Late Vendian marginal troughs at the southwestern part of the Siberian Platform and formed independently.

The Upper Riphean of the Yenisei Range: Sr Chemostratigraphy and Pb–Pb Age of Limestones of the Tungusik and Shirokaya Groups

The Pb–Pb isotope age and the Sr isotope signature of the Upper Riphean sedimentary limestones from the south of the Yenisei Range on the western margin of the Siberian Craton were obtained. The Pb–Pb age of carbonate deposits of the Dadykta Formation of the Tungusik Group in the Kamenka facial zone in the east of the Yenisei Range is 1020 ± 20 Ma. The Pb–Pb age of limestone of the Gorevka Formation of the Shirokaya Group in the Glushikha facies zone in the western part of the region is estimated at 1020 ± 70 Ma. The 87Sr/86Sr ratio in limestones of the Dadykta Formation lies within 0.70536–0.70590 and that of the Gorevka Formation lies within 0.70552–0.70578. This coincides with a decrease in the 87Sr/86Sr ratio in a paleo-ocean immediately after the culmination of the Grenville orogeny. The correlation of the Shirokaya Group with the Oslyanka Group of the Kamenka Zone in combination with other data has shown that the accumulation of the Tungusik, Shirokaya, and Oslyanka groups occurred within an interval of 1030–950 Ma. The isotope age of the Middle and Upper Riphean boundary at the base of the Tungusik Group of the Yenisei Range is estimated at 1030 Ma, which is consistent with the age of this boundary in the sections of the Turukhansk Uplift and the Uchur-Maya Region of Siberia. It was revealed that the greater part of the Upper Riphean (Neoproterozoic) in the sedimentary record of the Yenisei Range is missing. The observed facial zoning of the Riphean deposits of the Yenisei Range represents the configuration of the ancient sedimentary basin that existed at the western margin of the Siberian Craton long before the collisional events accompanied by granite intrusions and superimposed metamorphism in the Neoproterozoic.

Geochemistry, Tectonic Settings, and Age of Metavolcanic Rocks of the Isakovskii Terrane, Yenisei Range: Indicators of the Early Evolution of the Paleo-Asian Ocean

The geodynamic nature of the Late Neoproterozoic island-arc dacites (691 ± 8.8 Ma) and rift basalts (572 ± 6.5 Ma) of the Kiselikhinskaya Formation, Kutukasskaya Group, in the Isakovskii terrane is inferred from geochemical data and U–Pb zircon (SHRIMP-II) dates. The volcanic rocks were produced during the late evolutionary history of the Yenisei Range, starting at the origin of oceanic crustal fragments and their accretion to the Siberian craton to the postaccretionary crustal extension and the onset of the Caledonian orogenesis. The reproduced sequence of geological processes marks the early evolution of the Paleo- Asian Ocean in its junction zone with the Siberian craton. The data refine the composition and age of volcanic rocks in the trans-Angara part of the Yenisei Range and specifics of the Neoproterozoic evolution of the Sayan–Yenisei accretionary belt.

Accretionary Tectonics of Rock Complexes in the Western Margin of the Siberian Craton

The geological, geochemical, and isotope-geochronological evidence of the events at the final stage of the Neoproterozoic history of the Yenisei Range is considered (beginning from the formation of fragments of the oceanic crust in the region and their accretion to the Siberian Craton until the postaccretionary stage of crustal tension and onset of the Caledonian orogeny). Based on an analysis of new data on the petrogeochemical composition, age, and geodynamic nature of the formation of contrasting rocks in the composition of tectonic melange of the Near-Yenisei (Prieniseiskaya) regional shear zone, we have found the chronological sequence of events that marks the early stages of the Paleoasian Ocean evolution in the zone of its junction with the Siberian Craton. These events are documented by the continental marginal, ophiolitic, and island-arc geological complexes, each of which has different geochemical features. The most ancient structures are represented by fragments of oceanic crust and island arcs from the Isakovka terrane (700–620 Ma). The age of glaucophane-schist metamorphic units that formed in the paleosubduction zone corresponds to the time interval of 640–620 Ma. The formation of high-pressure tectonites in the suture zone, about 600 Ma in age, marks the finishing stage of accretion of the Isakovka block to the western margin of the Siberian Craton. The final events in the early history of the Asian Paleoocean were related to the formation of Late Vendian riftogenic amygdaloidal basalts (572 ± 6.5 Ma) and intrusion of postcollisional leucogranites of the Osinovka massif (550–540 Ma), which intruded earlier fragments of the oceanic crust in the Isakovka terrane. These data allow us to refine the Late Precambrian stratigraphic scheme in the northwestern Trans-Angarian part of the Yenisei Range and the evolutionary features of the Sayan–Yenisei accretionary belt. The revealed Late Neoproterozoic landmarks of the evolution of the Isakovka terrane are attributed to the terminal phase of the breakup of Rodinia, separation of the Siberian Craton, and opening of the Paleoasian Ocean.

Геохронология гранитов, вмещающих сланцев и руд месторождения золота «Панимба» (Енисейский кряж)

~ ~ ~ Data of isotope geochronological researches of zircons by U-Pb method, also results of Ar-Ar method researches of muscovites from the gold-bearing ores, surrounding schists and granites of the Panimba gold deposit in the Yenisey Ridge are presented. Regional metamorphism of the lower Riphean Kordinskaya suite terrigene sediments, containing ore bodies, took place in the interval of 996,0±32 - 889,0±26,6 Ma. The graniteforming and contact metamorphism of schists in the ore field of the mineral deposit have occurred on a boundary of 868,9±6,5 Ma. The absolute age of the quartz gold sulphide orebearing veins lies in the interval of 817,2±5,3 - 744±17 Ma (by muscovite with Ar-Ar method) and 815,0±37,6 - 762,3±33,3 Ma (by zircon from ore schists with U-Pb method). The long history of development of the Yenisei Range from Upper Archean to Upper Paleozoic was reflected in an accessory zircon of ore schists.

Application of strain analysis to estimate pressure solution processes in regional shear zones

This paper considers the basic principles of the strain analysis method based on the analysis of antitaxial regeneration fibrous fringes around linear rigid inclusions in a low-viscosity rock matrix. This method has been developed for pressure shadows composed of fibrous minerals, whose orientation is controlled by the major elongation direction rather than the orientation of rigid inclusions. This approach is applicable only for rocks exposed to uniform coaxial straining. The strain ellipse is calculated in two ways: for three variably oriented strain markers, it is calculated using Mohr’s circles, and for numerous strain markers by average body ellipse. The strain ellipsoid is calculated using the parameters of a few strain ellipses calculated with three and more non-parallel planes. This paper provides the data on the method testing in reference sites of Dora–Pil’ ore field in the Upper Indigirka district and Vangash area in the Yenisei Range. Regeneration fibrous fringes around fragments of fern fossils and linear rutile metacrystals were used as markers. The results of strain analysis obtained for the reference sites in the Upper Indigirka district made it possible to describe the signs of variable strain stages of developing strike-slip zones making up the Adycha–Taryn Fault Zone. Sublatitudinal ore-bearing strike-slip zones are characterized by a subvertical orientation of the elongation axes X of elongated strain ellipsoids, which are subperpendicular to quartz–carbonate veins and slope kink zones. NW-trending strike-slip zones are characterized by subhorizontal orientation of the Z shortening axes of flattened strain ellipsoids, which are subparallel to the normals of quartz–carbonate veins and veinlets. The results of strain analysis obtained for reference sites in the Vangash area made it possible to describe the thrust strain environment following the metamorphism stage and to reveal specific features in the formation of the strain textures of ore-bearing rocks based on their rheological properties.

Morphological varieties of gold in minerals and mine waste in the weathered crust

The article describes studies into morphology of gold in the initial ore and mining-generated silt in the weathered crust of the Yenisei Range using the methods of optical and electron microscopy. The authors have determined sizes and shapes of gold grains, nature of intergrowth of gold, ore and rock-forming minerals, and microadmixtures characteristic to free gold particles discovered in the initial ore and in old tailings pond.

Radioactive elements in collisional and within-plate Sodic-Potassic Granitoids: Accumulation levels and metallogenic significance

New data are reported on the content of radioactive elements in the Precambrian Na-K granitoids from the southwestern margin of the Siberian Craton, Aldan and Ukrainian shields, and Kursk-Voronezh Massif. Analytical data on other regions were generalized for comparison. Two global epochs of Na-K granitoid magmatism bearing elevated contents of radioactive elements (U, Th, K) were distinguished in the Early Precambrian (in Ga): Neoarchean (2.8-2.6) and Late Paleoproterozoic (1.9-1.75). Mesoarchean (3.1-2.8 Ga) epoch of Na-K granite formation has been additionally distinguished at the Australian, South African, and Canadian shields. These epochs of granitization provided high maturity of the crust: geochemical differentiation of the oldest continental blocks and their geochemical and metallogenic specialization for trace elements and RAE. In the southern margin of the Siberian Craton, the most intense granite formation occurred in the Late Paleoproterozoic. The extended South Siberian belt of collisional and within-plate Na-K granitoids is characterized by intense influx of RAE and other trace elements in the upper crustal shell. The southwestern margin of the craton (Yenisei Range) was spanned by repeated Late Neoproterozoic Na-K granite formation, with wide development of collisional and within-plate Na-K granites having elevated Th content and [Th]/[U] ratio. The higher RAE concentrations are typical of within-plate Paleo and Neoproterozoic granitoids. The highest uranium content was found in the postcollisional and within-plate Na-K granites and subalkaline leucogranites. Uranium ore concentrations were formed at the riftogenic stages of evolution of these crustal blocks, when within-plate subalkaline acid magmatism and accompanying hydrothermal metamorphism overprinted granitized crystalline massifs, including high-U sedimentary and volcanic complexes. Areas with the most favorable geological-geochemical environments for the formation of uranium mineralization were distinguished in the southern margin of the Siberian Craton and its nearest folded framing.

The neoproterozoic Trans-Angara dike belt, Yenisei Range, as an indicator of extension and breakup of Rodinia

The issue of estimation of the geochronological boundaries in the evolution and breakup of the super� continent Rodinia is largely far from a solution. Therefore, the problem of distinguishing and dating the Neoproterozoic complexes, which mark the con� tinental riftogenesis related to the breakup of Rodinia in the Late Neoproterozoic, is still topical [1]. In terms of modern ideas, breakups of ancient supercontinents were caused by deep mantle processes, probably induced by mantle upwellings or plumes [2]. The peri� odic intrusions of highly heated deep material are con� sidered as evidence of such processes within the crust; these intrusions cause a general increase in geoiso� therms, thinning of the lower crust and the lithos� pheric mantle, mafic and ultramafic magmatism (laminated massifs and dike swarms), anorogenic ! ! "#$ %& ’ ( # $ ) & # %&*&$

Pre-Riphean metapelites of the Yenisei Range: Chemical composition, sources of eroded material, and paleogeodynamics

The paper reports data on metapelites (gneisses and crystalline schists) from various Early Precambrian lithostratigraphic units of the Yenisei Range (Kan and Yenisei complexes, Garevka Unit, and Teya Group). A representative selection of 57 samples from the examined vertical section were analyzed for major oxides, LILE, transition elements, HFSE, REE, radioactive elements, and other trace and minor elements. The most important distinctive geochemical feature of metapelites composing most of the vertical section is their elevated concentrations of Al, which are higher than in the Post-Archean Australian Shale (PAAS), K, Rb, Ba, Ga, Sc, Pb, Th, Nb, Y, and REE. These data and the systematics of elements in certain discriminant diagrams testify that the metasedimentary complexes in the sedimentation basin and the rocks associations composing the erosion area (crystalline massifs of the ancient basement of the Siberian craton) were strongly geochemically differentiated and mature. The composition of the eroded crustal material was close to the average composition of the post-Archean continental crust and PAAS. The metapelites of the Kuzeeva Unit in the Kan Complex and Penchenginskaya Formation in the Teya Group were the only ones that could have basic rocks as an additional source of material, as also follows from the elevated Cr concentrations of the rocks and their REE systematics. The three types of REE patterns of the metapelites largely correspond to the composition of the rocks that composed the ancient drainage areas and the degrees of the differentiation and averaging of their terrigenous material. The first predominant type corresponds to PAAS and the averaged composition of the upper continental crust. The second and third types of the REE patterns with high and low LaN/YbN ratios, respectively, and with or without negative Eu anomalies provide evidence of the contribution of tonalite-trondhjemite-granodiorite (TTG) or basite sources typical of granite-greenstone provinces. In certain diagrams, the compositional fields of Early Precambrian metapelites in the Yenisei Range almost exactly coincide with the compositional fields of regional fine-grained Riphean terrigenous rocks. This suggests that the Late Precambrian sedimentary rock sequences inherited their geochemical features from more ancient rocks. The reproduced ancient geodynamic environments in which the Early Precambrian metaterrigenous complexes of the Yenisei Range were accumulated correspond to ensialic continental marginal basins. The rocks of the Kan and Yenisei complexes and the Garevka Unit were formed mostly on active continental margins and, less frequently, on passive margins. The protoliths of metasedimentary rocks of the Teya Group were accumulated in a subplatform environment at a passive margin.

The Sarkhoi Group in East Sayan: Neoproterozoic (∼770–800 Ma) volcanic belt of the Andean type

The Sarkhoi Group localized in the stratotype area is composed of various volcanics and volcanoclastics more than 4 km in total thickness. The volcanics of the lower part are greenschist facies altered rocks ranging from basalt to dacite, and those of the upper part are mainly rhyolitic ignimbrites. The composition, sequence, and facial features of these volcanics show their affinity to the active continental margin. This is confirmed by geochemical data evidencing the participation of the Early Precambrian continental crust in their formation. The U-Pb zircon dating (SHRIMP) of the Sarkhoi volcanics yielded the Neoproterozoic age of the ignimbrites (782 ± 11 Ma, concordant cluster N = 8). The tonalite-trondhjemites of the Sumsunur complex in the Gargan block are plutonic analogs of these volcanic rocks. Coeval granitoids were also revealed in other parts of the Tuva–Mongolian and Dzavhan massifs. The ∼1500 km long Sarkhoi–Dzavhan volcanic belt is a fragment of the Neoproterozoic active continental margin separated from the continent. In the Middle Neoproterozoic, the geodynamic system also included the Oka accretionary prism joining the Sarkhoi continental margin and the Shishkhid island arc. Coeval analogs of the above structures are also reconstructed in the Yenisei Range and Baikal–Muya belt. This suggests that the Sarkhoi belt was initially localized along the margin of the Neoproterozoic Siberian continent. But the exotic origin of the Precambrian massifs in southern Siberia is not ruled out either.

Lower proterozoic metapelites in the northern Yenisei Range: Nature and age of the protolith and the behavior of material during collisional metamorphism

The variable P-T metamorphic conditions studied in the Fe-Al metapelites of the Karpinskii Range Formation are regarded as typical of collision-related metamorphism in the trans-Angara part of the Yenisei Range. Recently obtained geochronologic (SHRIMP-II U-Pb zircon dating) and geochemical data on the distribution of major and trace elements are used to reproduce the composition of the protolith, the facies conditions under which it was formed, the tectonic setting, and the age of the eroded rocks. The metapelites are determined to be redeposited and metamorphosed material of Precambrian kaolinite-type weathering crusts of predominantly kaolinite-illite-montmorillonite-quartz composition. The protolith of the rocks was formed via the erosion of Lower Proterozoic granite-gneiss complexes of the Siberian craton (dated mainly within the range of 1962–2043 Ma) and the subsequent accumulation of this material in a continent-marginal shallow-water basin in a humid climate and tectonically calm environment. These results are consistent with data of lithologic-facies analysis and geodynamic reconstructions of the Precambrian evolution of geological complexes in the Yenisei Range. Mass-transfer analysis with the use of the evaluated rock compositions and calculated chemical reactions indicates that the differences in the REE patterns of metapelites from distinct zones can be explained mostly by the chemical heterogeneity of the protolithic material and, to a lesser extent, by metamorphic reactions at a pressure increase.

Clarkes of concentrations of trace elements in the Riphean fine-grained terrigenous rocks of the Uchur-Maya region and the Yenisei Range

The clarkes of concentrations (Kc) of a wide range of trace elements (Li, Be, B, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, In, Sb, Cs, Ba, REE, Hf, Ta, Hg, Tl, Pb, Bi, Th, and U) were analyzed for fine-gained terrigenous rocks (mudstones, metapelites) from the reference Riphean sections of the Uchur-Maya region and the Yenisei Range. It was established that the shales and mudstones of the Uchur and Aimchan groups in the Riphean hypostratotype section are characterized by moderate (2.5 5) geochemical specialization for Li, B, and Zn. At the same time, the similar rocks of the Lakhanda and Ui groups do not exhibit any distinct geochemical specialization, although they are notably enriched in HREE. The metapelites from the basal formations of the Riphean sedimentary successions in the Yenisei Range are distinctly specialized for B and slightly for Li, Rb, Be, Nb, Ta, Th, Ge, and Cd. In addition, moderate specialization for Cu is characteristic of the metapelites from the Korda and Lopatino formations; for Bi, Sb, Hg, and V, for their analogs from the Potoskui Formation; and, for Hg and Cs, for the similar rocks from the Lopatino Formation. The metapelites of the Lower Riphean Korda Formation from the central zone of the Yenisei Range have elevated contents of significantly more elements (Li, Be, Sc, V, Cr, Co, Ni, Zn, As, Rb, Y, Zr, Nb, Sb, Ag, In, Hf, Hg, and others) than their counterparts from its eastern near-platform part. The mudstones of the ore-bearing (Pb, Zn) Gorevo Formation are characterized by elevated concentrations of several ore elements such as Pb, Cd, As, Sb, and Bi. The elevated Kc values of the rare lithophile and of several ore elements in the metapelites of the Yenisei Range are determined by the high geochemical differentiation of the Early Precambrian blocks constituting the western margin of the Siberian Craton, which were eroded in the Riphean, and the syn-sedimentary riftogenic and intraplate magmatism. On the contrary, the fine-grained and terrigenous rocks from the basal part of the Riphean section in the Uchur-Maya region are compositionally closer to the immature Late Archean substrates or their Early Proterozoic analogs.

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.