Research subject. Paleoclimate reconstructions in source area.

Aim. To identify the possibilities and constrains of using a number of geochemical characteristics of mud rocks (CIA, RW index, modules and modular diagrams, etc.) when reconstructing data on the near-surface humidity and mean annual temperatures (MAT) for catchment areas of the geological past.

Key points. The types of climate and paleoclimate classifications, features of paleoclimate reconstruction with a special emphasis on the geochemical composition of fine-grained rocks are considered. N.M. Chumakov's paleoclimate classification is put forward as the most objective. Geochemical criteria are given, according to which it’s possible to reconstruct individual parameters necessary for its application. Thus, it is possible to classify various strata as weathering products of source rocks in a humid, arid/semiarid climate not only using the modular diagrams of Ya.E. Yudovich and M.P. Ketris, but also when studying the titanium geochemistry. In addition, the equation recently proposed by K. Deng et al. allows one to reconstruct the MAT in the area of source rock erosion using the CIA values in a shallow marine and deltaic sediments. However, calculating the CIA index in rocks has a number of constrains, many of which can be overcome. The discussion is supported by several examples of the rational application of the integrated geochemical approach to reconstructing the climate characteristics for Upper Riphean and Upper Vendian strata that bearing red beds, Lower Vendian strata recording glacial and interglacial events, and Upper Devonian formation with a heterogeneous complex of source rock and facies.

Conclusions. It is possible to reconstruct various climate characteristics in paleocatchment area for certain strata using the geochemical characteristics of mud rocks only if they have been comprehensively studied and the researcher takes into account the multifactorial nature of the processes determining their composition.

The object of research is Lower, Middle and Upper Riphean mudrocks in the stratotype area – southern Urals western slope Bashkirian megaanticlinorium. We analyzed major element oxides composition of the 154 samples selected from shales and mudstones.

Research method. Mean annual temperature (MAT) and precipitation (MAP), also as Köppen aridity index (AI_Köppen) was calculated by using different modern approach for ancient catchments. Such computations became possible thanks to CIA values corrected via Al₂O₃–(CaO* + Na₂O)–K₂O diagram and granites actual (not predicted) weathering trend in humid temperate climate. In addition, we apply not only strata but RW-index value clusterization for our data base.

Results. According to estimated paleotemperature values different Riphean catchment areas may be considered as the they existed in humid temperate or cold arid climate. However calculated MAP and AI_Köppen are more likely to be invalid through positive correlation between MAP and MAT variables. That is why we also present few examples of MAP estimation for Upper Riphean era by using AI_Köppen boundary values and MAT values.

Conclusions. We think that such reconstruction tactics as paleotemperature evaluation in complex with subsequent applying of Köppen aridity index and the paleoclimate mineral proxies are the best for the quantitative paleoclimate characteristics estimation for Precambrian and, more than likely, beyond. This approach makes possible computation of the MAP lower limit for humid climates and MAP upper limit for arid climates.

Research subject. The products of epigenetic transformations of carbonate and siliciclastic rocks in the stratotype section of the Upper Riphean Uk Formation (Yuryuzan River near Ust-Katav) in Bashkirian Mega-anticlinorium were identified and studied.

Material and methods. The mineral composition of deposits was determined by X-ray diffraction analysis, the rocks were studied in thin sections under a polarizing microscope, and individual samples were examined using an electron microscope. Post-depositional transformations analysis was used to assess the nature of secondary changes.

Results. Data on the sequence and intensity of both terrigenous and carbonate sediments alterations were obtained. All epigenetic transformations in the rocks of the Uk Formation were divided into gradational (progressive/subsidence epigenesis) and tectonic-fluid (superimposed epigenesis). Gradational transformations include progressive transformations associated with changes in thermobaric conditions over geological time, as well as authigenic native mineralogenesis. Superimposed transformations include authigenic extraneous mineralogenesis (metasomatism and filling of voids), formation of voids, and transformations associated with local changes in temperature and pressure. The superimposed processes (mainly metasomatism) were typical for deposits that initially had the highest permeability: fine-grained sandstones, oolitic limestones, intraclastic limestones and some stromatolitic limestones – they are characterized by a plethora of epigenetic products, which relationships in each case allow us to construct the sequence of processes that took place.

Conclusions. The complex of structural and mineralogical features of rocks indicates progressive transformations at the level of the beginning of late catagenesis, which is consistent with the data literature of organic matter geochemistry, evidenced that the sediments reached the mesocatagenesis substage (“oil window”). The termination of progressive epigenesis is most likely due to the formation of the Ural orogen in the late Paleozoic. The set of secondary changes indicates a significant influence of superimposed epigenetic processes on the sedimentary sequence, but mainly only within the units or layers that could serve as fluid reservoirs (aquifers).

Research subject. The sedimentary sequences of the Ust’-Sylvitsa Formation of the Upper Vendian Sylvitsa Group were studied in Kvarkush-Kamennogorsk Anticlinorium in the sections on Lake Shyrokovsky coastline and Chusovoi City area in the Perm Krai region of Russia.

Results. A three-membered structure of the formation was established, which includes the Lower, Middle, and Upper members. The Lower Member is characterised by sandstones that are thick, brownish, greyish to green-greyish, coarse-grained, and have multi directional herringbone cross-stratification that is often marked by clusters of chocolate-brown flat clay pebbles. The total thickness of the Lower Member is 540 m. The Middle Member (up to 30-m-thick) is represented mainly by massive sandstones without visible stratification and clay pebbles. It reveals marking levels (horizons): a layer of whitish apoclays, from which the U-Pb age of zircon 563 ± 3.5 Ma was previously obtained; and a layer of sandstone with relatively large clasts of feldspar. The section is completed by the Upper Member (up to 80-m-thick), which is characterised by mottled alternation of mudstones, siltstones and sandstones. It also revealed arumberiamorph microbially induced sedimentary structures (Arumberia), as well as levels with ash beds with anomalous whitish to cherry-brown colouring, which may serve as an additional feature in lithostratigraphic correlation of the sequences.

Conclusions. The Ust’-Sylvitsa Formation section in the Lake Shyrokovsky and Chusovoi City area is represented most completely in comparison with the stratotype section on the Chusovaya River near the mouth of the Sylvitsa River, and we propose it as a composite hypostratotype section.

Subject study. Classification of industrial types of magnesite deposits. Aim. To detail the existing classification of magnesite deposits based on a set of defining features.

Materials and methods. Materials – a set of lithological-facies, structuralmineralogical and isotope-geochemical features of magnesite deposits. Method – analysis of both our own and literary data for the classification of industrial types and clarification of their genesis.

Results. The author’s genetic classification of industrial magnesite deposits is given in accordance with the principles of “specific classiology” and the allocation of taxonomic (crystalline structure, shape of ore bodies) and descriptive features of deposits. Two groups of magnesites are distinguished: A – clear-crystalline in pre-Mesozoic sequences and B – cryptocrystalline in Mesozoic-Cenozoic sequences. Within group A, there are sheet-like deposits of crystalline magnesites (A-2) in carbonate strata and lenses of talcbreunnerite stones among hyperbasites (A-3). Both types have signs of hydrothermal-metasomatic formation. This group includes layers of micritic magnesites associated with subaerial coastal-marine conditions and microbial-diagenetic stages of carbonate accumulation (A-1). The second group includes types associated with the weathering crust of hyperbasites: infiltration-residual stockwork (B-1), sheet clastochemogenic (B-2) and biochemogenic sedimentary-diagenetic (B-3). The distribution of stable isotopes forms non-overlapping areas with reduced δ¹⁸O values in the group of crystalline magnesites and a maximum in micritic and even higher values for the group of cryptocrystalline.

Conclusions. The fundamental difference between the identified groups of magnesite deposits lies in the source of Mg: from seawater (types A-1 and A-2) or from hyperbasites (types A-3, Б-1, Б-2 и Б-3).

Research subject. Detrital zircons from the Quaternary deposits from the frame of pyroxenite composing the Shigirsky hills in the western part of the Ufaley block.

Aim. The verification of the Pre-Cambrian dating, evaluation of the substrate type and geotectonic settings of rocks enclosing ultramafites of the Ufaley block.

Materials and methods. U-Pb isotope dating and determination of rare and rare-earth elements in detrital zircon by laser ablation, RSMA investigation of minerals, establishing of zircon nature and provenance and the distance of zircon migration.

Results. Dominant Paleoproterozoic (2100–2000 Ma) maximum for the distribution of detrital zircon age accompanied by lower picks of the Archean and Neoproterozoic-Lower Ordovician age has been established. Detrital zircon was derived from continental-type sources corresponding to igneous and metamorphic rocks of basic, intermediate and acidic composition. The transfer distance was negligible.

Conclusions. Zircon morphology, its internal structure, mineral inclusions, geochemistry and age allow to suggests the similar protolith and joint the Precambrian evolution at least the western part of the Ufaley block and Taratash and Alexandrovsky blocks, which are the fragments of crystalline complexes of the Archean Volga-Uraliya craton. This conclusion supports additionally by similarity in composition of high-Ca mafic-ultramafic rocks known in these blocks.

Research subject. Siderite of Jurassic and Lower Cretaceous sediments of the West Siberian sedimentary basin.

Aim. To determine the patterns of the structure and composition of siderite mineralization and its dependence on sedimentation conditions and stages of changes of surrounding rocks.

Materials and methods. Siderite mineralization in different Jurassic and Lower Cretaceous facies of Western Siberia has been studied. The morphology of siderite was determined by optical and electron microscopy using an energy dispersive spectrometric microprobe. The contents of Fe, Mg, Ca, Mn, Al, Sr were determined in hydrochloric acid extracts using the ICP-MS method. The isotopic composition of C and O in siderites was determined using the FinniganTM MAT 253 isotope ratio mass spectrometer.

Results. A variety of siderite forms has been established. Pelitomorphic and globular siderite predominate, to a lesser extent micro-, fine-crystalline and spherulite. The siderites of continental sediments are cleaner in chemical composition, and increased Ca and Mg contents are recorded in marine sediments. Minor variations of δ¹³C (–5.5...+5.5‰) were noted in marine siderites, and a wide range of δ¹³C values (–8.7...+13.5‰) is typical for continental ones. According to the isotopic composition of oxygen, siderite of continental sediments has a distinctly (depleted isotope) composition (δ¹⁸O – +13.5...+17.6‰) compared with coastal and shallowwater marine (δ¹⁸O – +22.3...+24.4‰). When studying the structural and morphological varieties of siderite, it was found that the early diagenetic generations are characterized by a cleaner composition, while the slightly manifested catagenetic ones are characterized by an increased content of Ca, Mn, and Mg. This pattern can be used when conducting a stadium analysis of enclosing rocks.

Conclusions. Siderite of sandy-siltstone and siltstone-clay rocks of the Jurassic and Lower Cretaceous of Western Siberia were formed under the influence of a number of factors under different conditions and at different stages of diagenesis. They are characterized by a wide range of structural and morphological varieties, a significant range of isomorphic impurities and variability of isotopic composition. According to a number of parameters (content of Ca, Mg, Sr, δ¹⁸O), siderite of continental sediments is distinctly different from marine sediments. Versatile precision studies will facilitate the use of siderite as an indicator of sedimentary environments and post-sedimentation changes.

Research subject. The Upper Jurassic and Lower Cretaceous sections of the left bank of the lower Lena River, opened by a new well (93-80).

Aim of the research is to identify the features of the composition, structure and characterize the conditions of sediment formation.

Methods include the dismemberment and stratification of strata by litho- and biostratigraphic methods, petrographic study of rocks in sections, analysis of data on the mineralogical and chemical composition of rocks obtained by physical–chemical methods. When reconstructing the sediment formation conditions, complex methodological

techniques used in the IPGG SB RAS in genetic interpretations for terrigenous Mesozoic strata of Siberia were used.

Results. It was found that the clay-siltstone part of the section with a basal conglomerate layer (31.8–43.5 м) corresponds to the Buolkalakh Formation (Volgian–Boreal Berriasian). The overlying sandy part (4.0–31.8 м) corresponds to the Kigilakh Formation (Boreal Berriasian(?)–Valanginian). The mineralogical-petrographic and lithochemical characteristics of individual beds and members of the studied section have been revealed. It is reconstructed the directed regressive trend of the formation of the Volgian–Valanginian section, expressed in the change of shallow-marin, coastal-marine and delta environments. At the boundary of the Buolkalakh and Kigilakh Formations a sedimentation regime change was fixed. It is characterized by a significant increase in the rate of terrigenous material entering the basin. It was found that the main sources of demolition were closely located older sedimentary formations rich in quartz, as well as felsic igneous rocks. The parent strata were subject to low and moderate chemical weathering.

Research subject. Turbidite channels of the Achimov formation (Ryazanian-Hauterivian) which occur at the base of the Lower Cretaceous complex of West Siberia. Aim. Identify various types of distribution and feeding turbidite channels, effect on the morphology of underwater fans in order to predict reservoir rocks.

Materials and methods. To interpret facies and classify channels within the Achimov Formation, a complex of core, well log and 3D seismic data on ten West Siberian sites was used. The interpretation and classification effort included the lithofacies, ichnological, electrofacies, sequence-stratigraphic and 3D seismic geomorphological analyses.

Results. The diagnostic features of turbidite channels, their classification based on channel shape and filling, as well as the effect on the morphology of deep-sea fans and the distribution of sand deposits are presented.

Conclusions. Four morphological types of underwater channels have been identified in the Achimov formation of Western Siberia: Erosive; 2) Meandering with an accretion complex without aggradation; 3) Aggrading; 4) Hybrid (mixed). The lateral and time-dependent transformation of the channels has been established. It was noticed that, due to avulsion, most of the deep-sea meandering channels tend to migrate to the left, towards the underwater slope by the effect of the Coriolis force and contour currents, and form fans with left-sided asymmetry. The straightened channels with poor levees form radial fans with high content of sandstones within the cross-section.

Research subject. Bituminous sandstones of the Sheshmian horizon of the Ufimian stage in the Republic of Tatarstan.

Aim. To identify relationships between lithological and petrophysical parameters for paleoreconstructions of the conditions of formation and redeposition of natural bitumen deposits.

Materials and methods. The composition and internal structure of bituminous sandstones were studied by optical microscopy methods (petrographic description of thin sections) and thermogravimetry (quantitative parameters of oil saturation and carbonation), statistical processing of the results of granulometric and petrophysical analyses in Statistica 10 software.

Results. The studied sandstones belong to the graywacke group. Statistical analysis of granulometric and filtration-capacity parameters of bituminous sandstones revealed relationships between certain fractions and the degree of bituminosity. Cluster and factor analysis of lithologic and petrophysical data made it possible to identify integral indicators that can be used to reconstruct the paleofacies of the Sheshmian sandstones. The important role of the Sheshma River valley in the reformation of bitumen deposits in the Neogene-Quaternary time under the influence of Coriolis force has been established. Presence of soda water with high (more than 1 g/l) content of hydrocarbonate-ion is a hydrochemical criterion for searching the deposits of natural bitumen. The present study complements the existing hypotheses of the formation of the Sheshmian bituminous sandstones of the South Tatar arch.

Conclusion. Based on a combined analysis of geological data, lithological and petrophysical parameters, it is suggested that the most bitumen-saturated upper layer of sandstones was formed by eolian processes.

Research subject. Upper Cretaceous sections of the southwestern and central parts of Crimea, which are part of the Cretaceous-Palaeogene cover of the Scythian platform.

Aim. Reconstruction of sedimentation and changes in paleogeography related to sea level fluctuations.

Materials and methods. Outcrop descriptions and petrographical investigations of rocks were conducted. A range of methods including facial analysis and cyclic and sequence stratigraphic techniques were employed.

Results. Six lithological types of beds were identified, with diagnostic characteristics and genetic interpretations proposed. A model of sedimentation environments has been developed that takes into account the diagenetic transformations of sediments under anoxic conditions in the outer ramp. This has made it possible to identify transgressive-regressive layer sequences (cyclothems), determine the position of maximum flooding surfaces, and transgressive surfaces. Based on this, the correlation structures have been refined and detailed. Traces of 12 regional sedimentation cycles have been established. The features of the structures of transgressive and highstand systems tracts from the Cenomanian-Coniacian and Santonian-Maastrichtian sequences were demonstrated. A series of paleogeographic schemes for short intervals of geological time has been compiled.

Conclusions. In the Crimean part of the Late Cretaceous epicontinental basin, sedimentation took place under the conditions of an inner, middle, and outer terrigenous-carbonate ramp that moved northward during periods of transgression and migrated southward during regression (in modern coordinates). At the same time, on large areas, the bottom surface most often remained above the base of storm waves.

Research subject. Oil-source rocks of the inter-salt Devonian complex of the Chervonoslobodsko-Malodushinskaya tectonic stage of the Northern area, tectonic stages of the Central and Southern areas of the Pripyat trough.

Aim. Localization of the oil-source rocks zones, determination the relationship between the quality of oil-source rocks and sedimentation conditions, determination the degree of organic matter transformation in oil-source rocks and the edging of the “oil window” zones.

Methods and material. Bituminological and pyrolytic methods in combination with data on the lithological rock composition.

Results. Oil-bearing rocks have been identified and the quality and degree of transformation of organic matter have been determined. Oil-source rocks localization, their stratigraphic affiliation, and the immersion depth into the “oil window” have their own features in the Central, Southern, and Northern areas of the Pripyat trough.

Conclusion. Sedimentation conditions influence geochemical quality indicators of oil-source rocks. Oil-source rocks of high and medium quality are formed under conditions of carbonate-clay sediment accumulation at paleo-depthes of more than 200 m. The hydrocarbon generation zones are confined to the foothills of the tectonic stages.

Research subject. Placer nephrites of the Vitim Highlands and the Hetian area in northwest China.

Aim. Comparison of mineralogical and geochemical characteristics of nephrite pebbles from the Tsipa River in the north-east of the Republic of Buryatia and the world’s largest accumulation of placer nephrite from the Yurunkash and Karakash Rivers in the Xinjiang Uygur Autonomous Region, Northwest China.

Materials and methods. The mineral composition of placer nephrite from the Vitim Highlands was studied by X-ray diffraction on a PowDix600 powder diffractometer; the diffractograms were interpreted using Almaz software. The chemical composition was studied by SEM (EDX) on a Merlin Carl Zeiss scanning electron microscope equipped with an AZtec X-Max energy dispersion spectrometer (Oxford Instruments). The content of 59 trace elements and rare earth elements was determined by ICP MS method on an iCAP Qc ThermoFisher Scientific inductively coupled plasma mass spectrometer. Statistical processing of the analytical results was carried out using STATISTICA and Excel software programmes.

Results. The main mineral of light-coloured nephrite pebbles is tremolite, which can change into actinolite, accompanied by a significant (10 times) increase in the FeO content with the acquisition of dark green and black colouring of placer nephrite. Petrochemical diagrams Mg/(Mg + Fe²⁺), MgO + FeO–FeO, Al₂O₃– Na₂O + K₂O, SiO₂–CaO + Na₂O + K₂O allowed to obtain distinct differences between the studied objects. All studied nephrite pebbles have common characteristics of rare earth elements (REE) behaviour: negative Eu-anomaly, pronounced right-hand slope, moderate enrichment of light-REEs, practically flat distribution of heavy-REEs.

Conclusions. The genetic similarity of placer nephrite from both nephrite-bearing areas is confirmed by the common distribution of REE in them. The distinctive features of nephrite pebbles of the Vitim Highlands are elevated content of alkalis associated with the participation of acidic intrusions in the formation of the primary source of nephrite, and a developed staining edge acquired under exogenous conditions. Black nephrite of the Karakash River consists predominantly of actinolite, which are formed at elevated levels of ferric oxide. The similarity of alluvial nephrite of the Tsipa, Yurungkash and Karakash rivers testifies to the great prospects of placers in the Vitim region and the need for specialized geological exploration.

Research subject. The Chulymsky bolide, the fall of 1984.

Aim. Identification of diagnostic signs of cometary origin particles extracted from the “trace” of the Chulym cosmic body, analysis of data for its classification by type to a fragment of the comet nucleus.

Materials and methods. Peat columns selected at three points along the flight path of the Chulym cosmic body were studied. An optical microscope “Olympus BX 51M” and a scanning electron microscope “Tescan Vega II” with a prefix for energy-dispersive quantitative microanalysis “Drycool” were used.

Results. The cometary nature of Chulym cosmic body was accepted by the authors as a working hypothesis, according to which a ground–based search was conducted for “traces” of an exploding bolide – a fragment of a comet – in the form of microscopic cosmic particles. The authors consider the version of a thermal explosion of Chulym cosmic body during braking in dense layers of the atmosphere to be the most probable. An initiative expedition was conducted to collect samples containing suspected “traces” of cometary matter. The particles extracted from the samples taken at three points of the Chulym cosmic body trace near Minayevka were studied. The authors attributed some of the detected particles to the substance of the bolide destroyed by the explosion, based on the working hypothesis that the Chulym cosmic body is a fragment of a comet.

Conclusions. The particles found in samples from three sampling points differ in microstructure, which may reflect the interaction of cosmogenic matter with terrestrial matter at different stages of the bolide's flight. Among the particles isolated from the “trace” of the Chulym cosmic body, iron-containing aluminosilicate microspheres with a unique finefiber microstructure turning into nanostructural features that have not been observed previously in particles of volcanic or technogenic origin were identified. Such microspheres can be used as a stratigraphic reference for an impact event, including as a diagnostic feature of cometary matter and its transformation products. Micro- and nanostructures arising during the explosion may have fundamentally new properties and be of interest for the development of materials with new properties, which is important for work in the field of nanotechnology. The detection of thin films of Fe and Ni on particles of terrestrial origin can be used as a diagnostic feature of cometary material in cases of meteoroid explosion with destruction in the atmosphere or on the surface.

Research subject. Previously unknown microbialitic magnesites of the Kunduzak occurrence of the Khalilovsky ultrabasite massif of the Southern Urals.

Aim. On the example of siliceous, phosphate and carbonate biolites, to consider the problem of microbial rock formation and to analyze the role of cyanobacterial biota in this process. Despite successful laboratory experiments on mineralization of cyanobacterial mats, observations in nature show that the productivity of cyanobacteria is not determined by the concentrations of chemical elements in the habitat. Under the same conditions one and the same population of cyanobacteria behaves neutrally or actively accumulates mineral matter. Moreover, the accumulated element is not always dominant in their habitat. Thus, there is every reason to assert that the problem of cyanobacterial rock and ore formation has not been fully solved yet, and additional studies are required for its final closure.

Materials and methods. During the geological mapping of the Kunduzak occurrence, samples of magnesites were taken, which were studied by ISP, scanning electron microscopy, as well as by phase, structural and fluorescence X-ray analysis, in addition to studies in transparent sections. The work was carried out in the laboratories of RUDN, IMGRE, PIN RAS, and RGGRU.

Results. A rich complex of mineralized bacterial forms, which are a fundamental feature of the structure of magnesites, was revealed. These are fragments of cyanobacterial mats and biofilms, cocciform and bacilliform bacteria, remains of glycocalyx, covers of filamentous microfossils, as well as microbiota of unclear systematic position. The development of biomorphosis in magnesites allows us to draw a parallel with the processes of modern magnesite accumulation associated with the activity of the microbial community of cyanobacterial mats. The latter circumstance becomes an irrefutable argument of biogenic (biolitic) nature of magnesite of the Kunduzak occurrence.

Conclusions. In the sediments of the pre-Jurassic weathering crust of ultrabasites, microbialitic magnesites previously undescribed in the literature have been revealed. They belong to the “amorphous” industrial type of ores, and form a bed deposit, which cardinally differs from the neighboring deposits, where magnesite is concentrated in the form of stockwork bodies. The biolitic nature of magnesites is confirmed by a variety of bacterial structures, and an additional feature of these rocks, obviously, are the established anomalies of Dy, Yb and Lu. Microbialitic magnesites were formed in several stages. Their inferred resources are estimated at 130 thousand tons.