Vendian Cambrian Research Articles

A Сomparative Analysis of Oils from Carbonate Sediments of the Upper Usolskaya Subformation and the Vendian–Cambrian Pay Horizons in the Central Part of the Nepsko-Botuobinskaya Anteclise

A Сomparative Analysis of Oils from Carbonate Sediments of the Upper Usolskaya Subformation and the Vendian–Cambrian Pay Horizons in the Central Part of the Nepsko-Botuobinskaya Anteclise

Magmatic–Hydrothermal Origin of Fe-Mn Deposits in the Lesser Khingan Range (Russian Far East): Petrographic, Mineralogical and Geochemical Evidence

Iron and iron–manganese deposits form three closely spaced clusters within the Lesser Khingan Range of the Russian Far East. Fe-Mn mineralization is hosted in Vendian–Cambrian carbonates and composed of magnetite, hematite, braunite, haussmanite, rhodochrosite and pyrolusite. The iron–manganese ores are closely associated with explosive intermediate–felsic breccias, magnetite-rich lavas, dolerites and mineralized lithocrystalloclastic tuffs. Magmatic rocks display both concordant and discordant relationships with Fe-Mn mineralization and contain abundant xenoliths of host carbonates. Both magmatic rocks (with the exception of Nb-enriched dolerites) and Fe-Mn ores are characterized by variable enrichments in large-ion lithophile and light rare earth elements and strong depletions in high-field strength elements compatible with the broad subduction setting for explosive volcanism and associated hydrothermal Fe-Mn ore mineralization. Nd-Sr isotope systematics suggest contamination by both ancient and juvenile continental crust and the involvement of recycled pelagic sediment in the formation of Fe-Mn deposits in the Lesser Khingan Range of the Russian Far East.

Structure–Tectonic Characteristics of the Aldan–Maya Potential Petroleum Area Based on the Interpretation of Regional Seismic Data

Abstract —The results of regional geological exploration over the past 18 years within the Aldan–Maya potential petroleum area were used as the basis for the refinement of the geological structure of the study area. The study considers the key structural features of the sedimentary cover of the Aldan–Maya region and major tectonic events that affected its structure. The generalization and interpretation of regional seismic survey data provided the basis for building a series of geoseismic sections and structure maps, which, in turn, were used in structural tectonic zoning of the study area. The map showing outcrops of Riphean formations and groups on the pre-Vendian erosion surface was complied. Tectonic schemes for three structural levels (upper Karelian–Lower Riphean, Middle–Upper Riphean and Vendian–Cambrian) confirmed their fundamental difference. In particular, the large Maya inclined swell was detected only in the topography of the Lower Riphean and is absent in the overlying structures of Middle Riphean–Vendian age, which are represented by weakly differentiated monoclines. The parameters of the major tectonic elements were determined.

Vodorazdelny Granite Massif (Subpolar Urals) and Correlation Problems of the Pre-Ordovician Granitoids and Volcanic Rocks from the Northern Part of the Lyapinsky Anticlinorium

Petrogeochemical features of the Vodorazdelny massif granites (Subpolar Urals, Lyapinsky anticlinorium) indicate these rocks are close to I-granites and were formed in suprasubduction environment. The ratios of the key elements (Rb, Ba, Th, Sr, Y, Nb) suggest that the basites of the melting slab and the fluid separated during their dehydration could participate in the granite generation. The U–Pb age of the main population of magmatogenic zircons is 593 ± 4 Ma and corresponds to the Vendian (Ediacarian). It coincides with the age of the granites from the nearby Vangyr massif (598 ± 5 Ма), as well as with the age of zircon cores from the granites of the Kozhim massif located to the north. Values of εHf(t) from –2 to 0 in magmatogenic zircons with an age corresponding to the age of Vodorazdelny granites indicate a heterogeneous source of melts. The zircons of these granites also contain ancient cores with U–Pb ages from 2200 to 700 Ma, where the values of εHf(t) from +0.8 to +13 indicate the presence of a crust component in the substrate (the substance of the ancient platform basement). Petrogeochemical and isotope-geochronological parameters of granites (and their zircons) do not confirm the validity of attributing of Vodorazdelny granite massif (and its analogues – the Vangyr and Kozhim massifs) to the Cambrian Salner-Mankhambo complex. We consider there are the possibility of separating of independent complex (about 598 Ma, Vendian?) during geological mapping. The presence in the Lyapinsky anticlinorium of several stages of granite generation (Middle Riphean–Vendian–Cambrian), accompanied by metamorphism, and complicate composition of ancient metamorphic strata from this structure basement led to varying isotopic parameters characterizing the heterogeneity of the source of melts, on the one hand, and the convergence of a number of geochemical features, on the other.

The Use of Typomorphic Features of Placer Gold of the Anabar Region for Determining Its Sources

Typomorphic features of placer gold of the Anabar region were studied as predictive-exploration criteria. The target of the study was to determine the typomorphic features of placer gold related to the intermediate sources (paleo-placers) and the supposed nearby primary ore occurrences. Two varieties of placer gold were identified. The first variety is well-rounded high-fineness lamellar gold with a highly modified internal structure. This native gold is associated with intermediate sources, Neogene–Quaternary watershed pebble beds. The second type includes slightly rounded gold with a wide variation in fineness (494‰–999‰). Its indicator is a block heterophase internal structure. The set of typomorphic features of this variety of placer gold indicates the vicinity of the primary source, what was the prerequisite for constructing prospecting traverses in order to find ore occurrences. As a result of these studies, hydrothermal-metasomatic formations with gold-sulfide mineralization were identified. The main primary substrate for them is fractured near-fault carbonate rocks of the Cambrian and Vendian–Cambrian age. Along with this, hydrothermalites developed on slightly cemented fine-pebble quartz conglomerates of the Middle Permian age were found in the core of exploration wells. Two types of metasomatic rocks are identified: quartz-potassium feldspar and jasperoid. The main ore minerals were galena and pyrite, different ratios by sites were revealed. Gold was identified in the form of small particles in the carbonate and siliceous substrate of hydrothermal-metasomatic formations. The lithological factor was one of the leading favorable factors for the ore formation due to the presence of near-fault highly permeable fractured carbonate and slightly cemented terrigenous rocks. The structural control of the studied ore occurrences is determined by their localization in the Mayat–Logoy and Dogoy–Kuoy faults of the Molodo–Popigay system of discontinuous faults. We assume a two-stage formation of the gold ore occurrences: during the first stage, the ore components in the form of primary hydrothermal-sedimentary ores in the near-gault zones were formed. The second stage was related to the processes of the Mesozoic tectonic-magmatic activation, when the intrusion of basite dikes initiated the mobilization of ore components the gold-sulfide occurrences were formed in the near-fault zone as a result of silicic-potassic metasomatosis of the carbonate and terrigenous rocks.

Biostratigraphy of the Devonian–Lower Carboniferous Deposits of the Bambui-Olingda Subzone (South Muya Ridge, Western Transbaikalia)

The results of biostratigraphic studies of the Devonian–lower Carboniferous deposits of the Bambui-Olingda subzone of the Vitimkan-Tsipinsk zone of the Baikal-Vitim fold system are presented. These deposits are isolated from the composition of the Riphean and Vendian–Cambrian formations. Their age was revised on the basis of numerous findings of fauna and flora. The carbonate Bambui and terrigenous Chulegma formations and the terrigenous-carbonate Kadalin stratum are assigned to the Devonian. The volcanogenic-terrigenous Yendekt sequence is dated as late Devonian (Famennian)–early Carboniferous (Tournaisian), while the terrigenous Ognenskaya and Amatkanskaya formations are dated as early Carboniferous (Tournaisian and Visean). Significant changes have been made to the Paleozoic stratigraphy scheme of the subzone. Paleolandscape reconstructions for the Bambui-Olingda basin and coastal land areas in the Devonian–early Carboniferous are proposed. The Devonian carbonate complex was formed in calm conditions of a shallow warm shelf sea. A change in the paleolandscape situation occurred at the Devonian–Carboniferous boundary. Sedimentation of significant thicknesses continued under the conditions of a deepening open shelf-slope paleobasin adjacent to the volcanic zone.

The Isotopic Age and Correlation of Carbonate Rocks of the Ara-Oshei Formation (Tunka Ridge, East Sayan)

Abstract —We present results of Pb–Pb geochronology and Sr- and C- chemostratigraphic study of limestones and dolomites of the Ara-Oshei Formation of the Tunka ridge in East Sayan. The δ13C value of the limestones varies from –0.6 to 2.3‰ PDB, the 87Sr/86Sr ratio is within 0.70851–0.70864, and the Pb–Pb age is 521 ± 21 Ma (MSWD = 0.9). The δ13C value of the dolomites varies from –3.9 to 0.5‰ PDB, the 87Sr/86Sr ratio is 0.70844–0.70882, and the Pb–Pb age is 417 ± 8 Ma (MSWD = 2.5). The U–Pb isotope system of the dolomites was disturbed during the geologic evolution of the region, which led to the rejuvenation of their Pb–Pb age in the Early Devonian. The obtained Sr-chemostratigraphic and Pb–Pb data show that the limestones of the Ara-Oshei Formation accumulated in the early Cambrian. This provides a reliable proof that the limestones are part of the Vendian–Cambrian sedimentary cover of the Tuva–Mongolian massif.

Cyanobacterial Communities of the Zavkhan Association of the Late Vendian and the Paleoenvironment of the Formation of the Vendian–Cambrian Deposits in Western Mongolia

Cyanobacterial Communities of the Zavkhan Association of the Late Vendian and the Paleoenvironment of the Formation of the Vendian–Cambrian Deposits in Western Mongolia

Riphean–Vendian–Cambrian Magmatism of the Mankhambo Block (Subpolar Urals): Geochemical Typification, Correction of Geodynamic Concepts, and the Role of Plume–Lithosphere Interaction

Riphean–Vendian–Cambrian Magmatism of the Mankhambo Block (Subpolar Urals): Geochemical Typification, Correction of Geodynamic Concepts, and the Role of Plume–Lithosphere Interaction

The Vendian–Cambrian Cyclometric Stratigraphic Scale for the Southern and Central Siberian Platform

Abstract —The general Vendian stratigraphic scale of Siberia, with the uncertain age of the Vendian base ranging from 600 to 630– 640 Ma in most of recent publications, remains worse constrained than the Cambrian scale, in which the boundaries of epochs and stages have been well defined. However, the imperfect classical stratigraphic division has been compensated by data on the cyclicity of the Vendian–Cambrian sedimentary section. The Vendian stratigraphy of the Siberian Platform and the related deposition history with cycles of sedimentation and gaps, as well as the hierarchy of sedimentation processes, can be inferred from the succession of alternating clastic, carbonate, and salt units. The cyclicity of geologic processes and their recurrence are attributed to periodic oscillatory motions of the crust. The ranks of these motions correlate with the cyclicity of sedimentary strata, including regocyclites, nexocyclites, and halcyclites separated by gaps. Each Vendian long-period oscillatory motion begins with a regocyclite and ends with a regional-scale gap. The Cambrian section includes one pre-Mayan regional gap at the end of the early Cambrian long-period cycle. Cambrian regocyclites are composed of carbonate subformations and formations in the lower part and alternating salt and carbonate beds in the upper part.

The Provenance of the Vendian Highly Aluminiferous Rocks of the Tunka Bald Mountains, Eastern Sayan: Isotopic, Geochemical, and Mineralogical Evidence

Data on the mineral, chemical, and Nd isotope composition of the highly aluminiferous schists of the Gorlyk Formation in the Tunka Bald Mountains of the Eastern Sayan Range, which are correlated with the Vendian–Cambrian sedimentary cover deposits in the central part of the Tuva–Mongolian Microcontinent, are presented. The highly aluminiferous sediments were deposited on the distal shelf of the microcontinent, and the chemical composition (high Cr, V, and Zr concentrations) of the schists of this formation indicates the acidic and basic–ultrabasic rock erosion products as their precursors. It was established that the protolith of the parametamorphic rocks was probably composed of the fragments of plutonic and volcanic rocks of the destructed Sarkhoi and Dunzhugur island arcs and the metamorphic rocks of the Gargan cratonic block, as well as the weathering crusts that developed on these rocks.

Trace Fossils from the Vendian-Cambrian Transitional Strata of the Igarka Uplift (Northwestern Siberian Platform)

The Vendian–Cambrian transitional strata of the Igarka Uplift (northwestern Siberian Platform), originally erected as the Sukharikha Formation, are one of the key objects revealing evolution of marine ecosystems in the late Vendian. Herein we describe dwelling burrows Skolithos and Arenicolites from dolostones in the middle Sukharikha Formation (Nemakit-Daldynian Regional Stage). High density and local distribution of these burrows in the Sukharikha Formation demonstrate that the terminal Vendian shallow-marine sediments became occupied by vertical-burrowing benthic organisms, mirrored in the geological record as an archetypical Phanerozoic ichnoassemblage (Skolithos ichnofacies).

Reconstruction of the Vendian–Cambrian active continental margin of the Southern Urals: results of studying of detrital zircon from the Ordovician terrigenous rocks

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 Reconstruction of a Vendian–Cambrian Active Continental Margin within the Southern Urals: Results of Detrital Zircons Studying from Ordovician Terrigenous Rocks

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.

Tectonic position of the Early Neoproterozoic–Early Paleozoic metamorphic belts within the Tuva–Mongolian terrane of the Central Asian Orogenic Belt

The Tuva–Mongolian terrane (TMT) of the Central Asian Orogenic Belt is a composite structure with a Vendian–Cambrian terrigenous-carbonate cover. The formation of the northern part of TMT is marked by the granitoids of the Sumsunur Complex with an age of 785 ± 11 Ma. The Sangilen and Khan-Khukhay blocks of its southern part also form a composite structure, which originated during Early Paleozoic(500–490 Ma) low-moderate pressure regional metamorphism reaching amphibolites-granulite facies. The earlier high-pressure metamorphism was established in the Moren Complex of both the blocks. In the Sangilen block, this metamorphism reached conditions of kyanite-garnet-biotite-orthoclase subfacies of amphibolites facies (temperature ~750oC, pressure 9–10 kbar). The upper age limit of this metamorphism is determined by granites with an age of 536 ± 6 Ma, which cut across migmatized biotite gneisses of the Moren Complex. The latter are intruded by the granitoids of the Ortoadir pluton, which were previously dated at 521 ± ± 12 Ma (U-Pb method, TIMS). Its emplacement predated the Early Paleozoic low-moderate pressure metamorphism, the timing of which is constrained by syn- and postmetamorphic granitoids with ages of 496 ± 4 and 489 ± 3 Ma. The age of 513 ± 4 Ma established for the granitoids of the Ortoadir Complex in the Khan-Khukhay Block more accurately constrains the lower age boundary of collision processes. This determined the amalgamation of the fragments of the high-pressure metamorphic belt with basement and carbonate-shelf cover units of the Tuva–Mongolian terrane, as well as the upper age boundary of early metamorphism. The timing of the main mappable structure of the Khan–Khukhay Block and low-moderate pressure regional metamorphism is marked by the synmetamorphic granitoids with an age of 505 ± ± 2 Ma. In general, the metamorphic rocks of the Sangilen, Khan–Khukhay, and Kaakhem blocks can be considered as fragments of the Late Ediacaran high-pressure metamorphic belt, which were amalgamated to the western margin of TMT within 515–505 Ma, after emplacement of the granitoids of the Ortoadir Complex, and were reworked by regional Early Paleozoic low-moderate pressure metamorphism.

The Sukhana Sedimentary Basin, Siberian Platform: Source Rock Characterization and Direct Evidence of Oil and Gas Presence

Abstract —Despite the known large natural bitumen accumulations and oil seeps in several kimberlite pipes along the periphery of the Sukhana sedimentary basin, interpreted as direct evidence of petroleum potential, the basin still remains one of the least studied (by geological and geophysical methods) regions of the Siberian Platform. The platform cover of the basin is composed by Riphean, Vendian, and Cambrian clastic (terrigenous) and carbonate deposits reaching 5.5–6 km in thickness in the central part of the basin. The hydrogeological specifics of the basin is largely governed by its location within the northern geocryological zone (Olenek cryoartesian basin) and is expressed as a continuous distribution of permafrost aggraded into the permafrost zone of unique thickness. Direct indicators of ore and gas presence are the East Anabar, Central Olenek, and Siligir–Markha fields of natural bitumen and oil shows in kimberlite pipes of the Daldyn–Alakit region (Udachnaya pipe). The bituminous-carbonate sediments of the Khatyspyt Formation (Vendian, Ediacaran) and the highly carbonaceous carbonate–siliceous–shaly sediments of the Kuonamka Formation (lower–middle Cambrian) are the Sukhana source rock complexes. The geochemically substantiated genetic relationship between the natural bitumen deposits of the East Anabar field and the organic matter of the Vendian Khatyspyt Formation makes it possible to estimate the area of the spread of the latter far to the west, beyond the axial part of the basin. Gammacerane, inherited from the organic matter of the Khatyspyt Formation and ranking as well-preserved and most characteristic biomarker of these bitumens, provides a compelling evidence of their consanguinity. The bitumen and oil of kimberlite pipes in the south of the basin, in the area of reefs of the Siligir–Markha bar, are similar in all geochemical criteria to oils of the Nepa–Botuobiya anteclise. In particular, in primary geochemical characteristics (12- and 13-monomethylalkanes, unique secosteranes, identical carbon isotope composition, etc.) the oils of the Udachnaya pipe are identical to the Irelyakh oils (oil field in the Mirnyi arch). No accumulations of oil or natural bitumen genetically related to the highly carbonaceous Kuonamka Formation have been found within the basin. At the same time, “intraformational” shows of viscous oil, solid bitumen, and allochthonous bitumen (bitumen extracted with chloroform) were documented directly in the sections of the formation, which makes the sedimentary basin a very attractive target for “shale oil” exploration. As for the regional assessment of the petroleum potential of the entire basin, its axial part (Sukhana depression) complicated by local uplifts is of the greatest interest. Both the Khatyspyt and Kuonamka Formations are widespread there, with the thermal maturity of their organic matter corresponding to the oil window. In addition, the regional reservoirs at the Vendian–Cambrian boundary have good petrophysical properties on both the western and the eastern flanks of the basin.

Sedimentogenic Aspect of Evolution and Hydrocarbon Potential of the Aldan-Maya Sedimentary Basin (Southeast of the North-Asian Craton)

The main features of the lithofacial conditions of formation of the sedimentary complex of the Aldan–Maya Sedimentation Basin (AMSB) are discussed. It is shown that different facies (continental, coastal–marine, and marine) were formed under the conditions of one sedimentation basin of the type of one-side syneclise, which was formed on the eastern slope of the Aldan anteclise of the North Asian Craton, at its contact with the Okhotsk Massif. We distinguish and characterize the main sedimentation stages separated by inversions, magmatic layers, and weathering crusts (from the bottom upward): Pre-Riphean (Late Karelian, Ulkanian); Early Riphean (Uyan–Uchur); Middle–Late Riphean (Kerpyl–Lakhanda–Uisk); and Vendian–Cambrian. Areas of bituminous lithocomplexes are revealed in the sedimentary cover of the AMSB. Structural and sedimentary events in the AMSB are related to the geodynamics of the southeastern zone of the North Asian Craton and to the hydrodynamic regime of the Okhotsk–Pacific sector of the World Ocean. The article is devoted to the problems of comprehensive study of the geology, deep structure, and geodynamics and evaluation of hydrocarbon potential of the AMSB.

Primary Data on U/Pb-Isotope Ages and Lu/Hf-Isotope Geochemical Systematization of Detrital Zircons from the Lopatinskii Formation (Vendian–Cambrian Transition Levels) and the Tectonic Nature of Teya–Chapa Depression (Northeastern Yenisei Ridge)

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.

Geodynamics of the origin of granulites in the Sangilen block of the Tuva–Mongolian terrane, Central Asian Orogenic Belt

The Tuva–Mongolian terrane of the Central Asian Orogenic Belt is a composite structure with a Vendian–Cambrian terrigenous–carbonate cover. The Sangilen block in the southern part of the belt is a smaller composite structure, in which tectono–stratigraphic complexes of different age that were produced under various conditions were amalgamated in the course of Early Paleozoic tectonic cycle. The P–T parameters of the Early Paleozoic metamorphism in the western part of the Sangilen block corresponded to the amphibolite facies. The gneisses of the Erzin Complex contain relict granulite-facies mineral assemblages. The granulites are dominated by metasediments typical of deep-water basins on passive continental margins. The only exception is granulites of the Lower Erzin tectonic nappe of the Chinchlig thrust system: these rocks are metatholeiites, tonalites, and trondhjemites, whose REE patterns are similar to those of MORB. The composition of these granulites and their high Sm/Nd ratios indicate that the rocks were derived from juvenile crust that had been formed in an environment of a mature island arc or backarc basin. It is reasonable to believe that these rocks are fragments of the Late Riphean basement of the Sangilen block. The average 206Pb/238U zircon age of the garnet–hypersthene granulites is 494 ± 11 Ma. With regard for the zircon age of the postmetamorphic granitoids, the granulite-facies metamorphism occurred within the age range of 505–495 Ma. The peak metamorphic temperature reached 910–950°C, and the pressure was 3–4 kbar, which corresponds to ultrahigh-temperature/low-pressure (UHT–LP) metamorphism. The garnet–hypersthene orthogranulites were formed at a temperature that decreased to ~850°C and pressure that increased to ~5.5‒7 kbar. It can be hypothesized that the earlier UHT–LP granulites were produced at an elevated heat flux and were later (in the course of continuing collision) overlain by a relatively cold tectonic slab, and this leads to a certain temperature decrease and pressure increase. This relatively cold slab could consist of fragments of the Vendian elevated-pressure metamorphic belt whose development terminated at the Vendian–Cambrian boundary before the onset of the Early Paleozoic regional metamorphism.

Secondary alterations of globular and platy phyllosilicates of the glauconite–illite series in the Precambrian and Vendian–Cambrian rocks

Previously published and new data on secondary transformations of the globular and platy phyllosilicates of the glauconite–illite series from the Upper Proterozoic terrigenous rocks of the Olenek and Anabar uplifts (East Siberia), Srednii Peninsula (Murmansk coast), and Vendian–Cambrian boundary rocks of the Podolian Dniester area (Ukraine) are generalized for the first time. Plastic deformation, aluminization, chloritization, berthierinization, as well as replacement of phyllosilicates of different morphology by corrensite- chlorite and pyrite at different lithogenesis stages, are considered and lithological-mineralogical characteristics of the glauconite-bearing rocks are reported. The structural, crystal-chemical, genetic, and isotopegeochronological features of di- and trioctahedral phyllosilicates are discussed.