An analysis of subfossil cladocerans from the sediment core of Lake Bolshoe Miassovo (Southern Urals) was conducted. In all, 38 cladoceran taxa from 7 families were identified. Most of them fell within the family Chydoridae. Yet, another family, Bosminidae, turned out to be represented by the largest number of individuals. The assemblage was dominated by Bosmina (Eubosmina) longispina. Relatively high concentrations were also characteristic of the Daphnia longispina gr., Chydorus сf. sphaericus, and Alona quadrangularis. The age of the studied core spans the Late glacial and entire Holocene, the maximum age of the sediment core was 13.5 yr BP (Valieva et al., 2023). In the lower layers of the core at the beginning of the Holocene, the discovered Cladocera remains were few and characterized by low species richness. The most significant transformations in the Cladocera community occurred at the end of the Late Dryas - beginning of the Holocene (11400-11950 cal. yr BP), indicating substantial changes in environmental conditions.

Abstract—The paper presents the results of rock magnetic studies and relative paleointensity determinations from sediments of Lake Shira, Khakassia. Carrier minerals of natural remanent magnetization (NRM) were identified through hysteresis loop parameter measurements, thermomagnetic and X-ray diffraction (XRD) analyses. The sediment age was determined by radiocarbon dating; according to age estimates, the studied sediment sequence covers approximately the past 9100 years. To obtain high-quality relative paleointensity results, the determinations were made on linear segments of the pseudo-Arai‒Nagata diagrams. The quality was assessed by the criteria of the number of points in the calculations of slope, quality criterion (q), NRM fraction destroyed in the paleointensity determination interval, and relative paleointensity determination error (σ). According to the rock magnetic studies and XRD analysis, the magnetic carriers are mainly single-domain (SD) and pseudo-single-domain (PSD) magnetite and hematite. The comparison of the obtained relative paleointensity data with model paleointensities calculated for the Shira coordinates from the various models (CALS10K.1b (Korte et al., 2011), PFM9k.1 (Nilsson et al., 2014), HFM.OL1.AL1, CALS10k.2 ARCH10k.1 (Constable et al., 2016)), with absolute paleointensities and with the collection of results from the studies of sedimentary and igneous rocks and archaeomagnetic objects has shown that these data are in good agreement and share common trends. This provides grounds for applying this approach to paleointensity determination from bottom sediments of modern lakes using the pseudo-Thellier method.

An analysis of subfossil Cladocera in a 193-cm sediment core from Lake Beloe (Altai region) was conducted to trace the history of limnological conditions in the lake over the past 4600 years. Currently, a total of 34 Cladocera taxa were identified in the taphocenosis. The greatest cladoceran species richness was observed among littoral forms of Cladocera, reflecting the presence of shallow areas overgrown with macrophytes. The highest concentration of cladoceran remains was observed in the lower horizons of the core (150-191 cm, 3600-4600 cal yr BP). In this zone, the highest values of Hill indices are recorded, indicating high taxonomic diversity in the community. At a depth of 141 cm (3500 cal yr BP), significant changes in community structure occur, with Chydorus cf. sphaericus beginning to dominate. Taxonomic diversity of Cladocera noticeably increases in the upper part of the core.

Relevance. It is known that sedimentary deposits in modern lakes with high sedimentation rates contain detailed paleoclimatic, paleobiological, paleoecological and magnetic records. The study of these parameters allow creation of paleoreconstructions and prediction of future climate behavior. Aim. To identify ecological and climatic events and trends during the Late Quaternary, based on magnetic properties of rocks. Some climate-dependent parameters are not properly used, we are showing that magnetic parameters are sensitive indicators of climate change. Object. Sediments of the Lake Kandrykul (Republic of Bashkortostan). Materials and methods. A set of petromagnetic studies was carried out, including measurements of magnetic susceptibility, normal remanent magnetization in external magnetic field of up to 1.5 T, as well as differential thermomagnetic analysis on induced magnetization and scanning electron microscopy on selected samples. Normal magnetization curves were used to set apart dia-/paramagnetic, ferromagnetic and superparamagnetic components. Results. Seismoacoustic studies showed that the lake bed is smooth, without sharp changes. The maximum water depth is about 16 m, the thickness of sediments reaches 7.5 m. Magnetic susceptibility was measured for three core columns, and the results show good correlation of this parameter between all the cores. Thermomagnetic analysis was used to determine magnetic minerals composition. The Day–Dunlop plot showed the presence of single, pseudo-single and multidomain grains. The authors determined the contribution of dia/para-, ferro-, and superparamagnetic components to the overall magnetic susceptibility. The paper considers the variations in magnetic susceptibility, para-, ferromagnetic components in the context of the Holocene climate changes. Conclusions. Variations in magnetic properties reflect climate changes (i.e. deposition environment). Six zones with different depositional conditions were distinguished based on magnetic susceptibility and its component changes. Additionally, zones with single-domain particles were highlighted based on hysteresis parameters variations. These zones most likely are associated with the remains of magnetotactic bacteria. Joint analysis of paramagnetic, ferromagnetic susceptibility and hysteresis parameters produced information on the effect of total humidity on the bioproductivity of the lake.

This article reports on some preliminary findings of a study on the seismoacoustic profiling of the basin of Lake Turgoyak (Southern Urals) and the magnetic properties of its bottom sediments. In the eastern depressions, the lake sediments are up to 8 m thick. The radiocarbon dating of the sediment samples suggests that the lake is at least 25 000 years old. The seismoacoustic data reveal that the lower part of the section, which is composed of the dense Neopleistocene sediments, accumulated when the water level was lower. The Holocene sediments are poorly consolidated silts up to 4 m thick. The magnetic properties of the sediments were found to be indicative of the environmental conditions and fluctuations in the lake level. The high-amplitude variations in the scalar magnetic values of the sediments point to frequent changes in the sedimentation conditions. The sediments with the highest magnetic susceptibility (χ), natural remanent magnetization (NRM), coercive force (Bc), coercivity of remanence (Bcr), saturation magnetization (Ms), and magnetization remanence (Mrs) are likely to have formed during the periods when sedimentary material was transported by ice, often with a significant influence from wind.

The results of rock magnetic studies and determination of relative paleointensity from sediments of Lake Shira, Khakassia, are presented. The NRMcarrier minerals were determined from the hysteresis parameters, thermomagnetic and X-ray diffraction (XRD) analyses. The age of the sediments was determined by radiocarbon dating. According to these measurements, the column spans about 9100 years. The qualitative determinations of relative paleointensity were obtained from linear segments of the pseudo-Arai–Nagata diagrams. The quality of the determinations was evaluated by the following criteria: number of points used to calculate the slope; quality criterion (q), fraction ofNRMdestroyed in the paleointensity determination interval, and relative paleointensity determination error (σ). According to rock magnetic studies and XRD analysis, the magnetization carriers are represented mainly by single-domain and pseudo-single-domain magnetite and hematite. The comparison of the obtained series of relative paleointensity data with both the model paleointensity values calculated for Shira coordinates from various models (CALS10K.1b [Korte et al., 2011], PFM9k.1 [Nilsson et al., 2014], HFM.OL1.AL1, CALS10k.2 ARCH10k.1 [Constable et al., 2016]) and with absolute paleointensity, as well as the aggregate results of the studies on sedimentary and igneous rocks and on archaeomagnetic objects has shown that these data are in good agreement with each other and have common trends. This provides a rationale for using this methodology to determine paleointensity from sediments of modern lakes using the pseudo-Thellier method.

This paper presents the results of geochemical and petrophysical studies of the Semiluk-Mendym (Domanik) and Kynovian deposits of the Frasnian age of the Devonian system at the Romashkinskoye giant oil field of the Republic of Tatarstan. The biomarker composition of the organic matter of the rocks is shown, its catagenetic maturity and facies conditions of its formation are assessed. In addition, the composition of saturated biomarkers (alkanes, steranes, and triterpanes) of Devonian oils were studied. The correlation «oil-organic matter of rocks» was carried out for oils of the Domanik and Kynovian horizons. It is shown that the differences in the biomarker composition of oils from the Domanik and Kynovian horizons are of practical importance in the field development process, since this allows optimizing the oil production process by evaluating the contributions of oil inflows from different reservoirs. Keywords: Domanik deposits; oil geochemical research; biomarkers; alkanes; terpanes.

A spore-pollen analysis of a 526 cm sediment core retrieved from Lake Bolshoe Miassovo, Southern Urals, was carried out. The obtained data made it possible to reconstruct the vegetation cover in the lake’s catchment area and the climatic situation of the region for 13 400 cal yr BP, which significantly expands and complements the paleogeographic chronicle of the Southern Urals. It was found that in the range of 13 400–12 700 cal yr BP in the conditions of a relatively warm and dry climate of Allerød, periglacial forest-steppe formations were widespread in the studied region. Steppe herb communities and birch-pine sparse woodlands with spruce grew on open landscapes. The pine degradation and replacement of spruce with more cold-resistant larch was most likely caused by a cooling in the period of 12 700–11 700 cal yr BP, which corresponds to the Younger Dryas. The periglacial forest-steppe formations are replaced by birch forests since 11 700 cal yr BP. The significant changes in the vegetation cover of the lake’s catchment area indicate warming and humidification of the climate at the beginning of the Holocene. The dominance of birch forests in the interval of 11 300–10 300 cal yr BP, probably, corresponds to the second half of the Pre-Boreal period. The distribution of pine and spruce in the range of 10 300–8300 cal yr BP indicates a warming of climatic conditions in the Boreal period. Since 8400 cal yr BP the proportion of broad-leaved species in the tree stand increases. The broad-leaved species cover reached its peak between 6000–4500 cal yr BP at the end of the Atlantic - the beginning of the Sub-Boreal period (Holocene climatic optimum). Some cooling of the climate was observed in the range of 4500–2000 cal yr BP, which presumably corresponds to the Sub-Boreal and the beginning of the Sub-Atlantic period. The birch forest with spruce and broad-leaved species grew in the lake’s catchment area. Some aridization and warming of the climate in the Sub-Atlantic period in the range of 1800–1000 cal. yr BP led to an increase in the role of pine and a reduction of spruce in the area around the lake. Since 1800 cal yr BP the vegetation of the territory adjacent to Lake Bolshoe Miassovo was similar to the modern one: pine-birch forests with an admixture of dark coniferous and broad-leaved species prevailed on the territory.

Bottom sediments are the most important “archive” containing information about the development of lake ecosystems. One of the most reliable and widely used methods of studying bottom sediments is diatom analysis (Juze et al., 1949). Currently, it is part of a group of guiding methods used to reconstruct the historical dynamics of the environment and climate (Rudaya et.al., 2012; Palagushkina et.al., 2018). In this work, the history of development of Lake Bolshoe Miassovo (Southern Urals) reconstructed using the taxonomic composition of diatoms found in the 526 cm long sediment core is presented. The maximum age of the sediments in the column was 13 500 years BP. According to the results of the study, 123 taxa of diatoms belonging to 47 genera were identified in the lake sediments. Diatom analysis of the bottom sediments of the studied lake allowed us to identify the main stages of the evolution of the reservoir during the Late Glacial and Holocene. During ~13 200–11 700 yr BP, in the period of a cool climate, the lake was a deep body of water with a constant water level and an extensive zone of shallow waters overgrown with macrophytes; then ~11 700–8500 cal. years BP against the background of cooling, the water level decreased; from ~8500–4600 cal. years BP was the stage of increasing water level in the lake in a warmer and wetter climate; in the period ~4600–2500 cal. years BP there was an increase in productivity of algal communities; during ~2500–800 cal. years BP against the background of decreasing temperature, a deep lake with low mineralized water, and presence of swampy shallow waters with acidification processes in them is finally formed.

Current problems in mature oil fields are high water cut and flow profile estimating of oil and associated brines from different layers. To establish the flow profile in production wells, geophysical research (Production Logging) is traditionally used by lowering special equipment into the well. Production Logging requires production stops and labor costs. Geochemical methods (Production Geochemistry) are used as an alternative solution: sampling is simple and efficient, which makes it possible to cover all the interesting area. Moreover, sampling does not require stopping the well. The geochemical method uses individual indicators of the composition of formation fluids produced from different perforation intervals. In this work, geochemical studies were carried out using wellhead samples from more than 100 wells, with single perforation for carbonate and terrigenous reservoirs. Some wells have joint exploitation of these formations. An automated algorithm was used to identify the distinctive characteristics of each formation based on the composition of the produced brines and oils. Data on the chemical composition of fluids from different development objects made it possible to determine the flow profiles in wells with joint production. Based on the results of the studies, the Devonian reservoir of the field under consideration is divided into 2 parts – northern and southern, which differ in the chemical composition of formation fluids. The same separation of the deposits into 2 parts is noted by field development analysis: over the past 50 years, the main production of oil and associated brines has been concentrated in the southern part of the deposit, confined to the fault, where the active work of the aquifer is assumed. It is recommended to use the obtained data for history matching of the reservoir simulation model.

A spore-pollen analysis of a 526 cm sediment core retrieved from Lake Bolshoe Miassovo, Southern Urals, was carried out. The obtained data made it possible to reconstruct the vegetation cover in the lake’s catchment area and the climatic situation of the region for 13 400 cal yr BP, which significantly expands and complements the paleogeographic chronicle of the Southern Urals. It was found that in the range of 13 400–12 700 cal yr BP in the conditions of a relatively warm and dry climate of Allerød, periglacial forest-steppe formations were widespread in the studied region. Steppe herb communities and birch-pine sparse woodlands with spruce grew on open landscapes. The pine degradation and replacement of spruce with more cold-resistant larch was most likely caused by a cooling in the period of 12 700–11 700 cal yr BP, which corresponds to the Younger Dryas. The periglacial forest-steppe formations are replaced by birch forests since 11 700 cal yr BP. The significant changes in the vegetation cover of the lake’s catchment area indicate warming and humidification of the climate at the beginning of the Holocene. The dominance of birch forests in the interval of 11 300–10 300 cal yr BP, probably, corresponds to the second half of the Pre-Boreal period. The distribution of pine and spruce in the range of 10 300–8300 cal yr BP indicates a warming of climatic conditions in the Boreal period. Since 8400 cal yr BP the proportion of broad-leaved species in the tree stand increases. The broad-leaved species cover reached its peak between 6000–4500 cal yr BP at the end of the Atlantic - the beginning of the Sub-Boreal period (Holocene climatic optimum). Some cooling of the climate was observed in the range of 4500–2000 cal yr BP, which presumably corresponds to the Sub-Boreal and the beginning of the Sub-Atlantic period. The birch forest with spruce and broad-leaved species grew in the lake’s catchment area. Some aridization and warming of the climate in the Sub-Atlantic period in the range of 1800–1000 cal. yr BP led to an increase in the role of pine and a reduction of spruce in the area around the lake. Since 1800 cal yr BP the vegetation of the territory adjacent to Lake Bolshoe Miassovo was similar to the modern one: pine-birch forests with an admixture of dark coniferous and broad-leaved species prevailed on the territory.

The article provides an overview of ion-modified waterflooding technology, also known as low salinity, controlled salinity, or Smart water. This technology is currently considered one of the most promising approaches in the development of oil deposits in carbonate reservoirs due to its economic efficiency and environmental safety. The article discusses the main mechanisms and processes underlying ion-modified waterflooding and presents the results of laboratory studies conducted on core samples from foreign oil deposits. It includes an analysis of several studies, including contact angle measurements and core flooding experiments on core samples from oil deposits in carbonate reservoirs on the eastern side of the Melekess depression in the Republic of Tatarstan. It is important to note that the Vereyian deposits explored in this article are not a typical example of test objects for ion-modified water injection. This is because they are characterized by a low reservoir temperature of 23 °C, which suggests that the efficiency of the technology would likely be lower compared to studies conducted abroad, where reservoir temperatures were significantly higher. For example, Darvish Sarvestani et al. studied reservoir conditions at 90 °C, Yousef et al. – reservoir temperature of 100 °C, and Austad et al. examined the Ekofisk field at 130 °C and the Volhall field at 90 °C in Norway. However, as several studies have indicated, prolonged contact between rock samples and ion-modified water contributes to significant hydrophilization of the rock surface, as confirmed by contact angle measurements. The contact angle decreases from approximately 138.3° to 53.45° after exposure to ion-modified water. Additionally, the core flooding experiment demonstrated a slight increase in the oil displacement coefficient, reaching 9.2%. These findings suggest the potential for enhanced oil recovery by injecting Smart water into the Vereyian sediments, although further research is required to confirm the underlying mechanism.

A major problem in the mature oil fields is the accompanying water production and oil production from different layers. Geochemical signals from different formations and sources can be used for identification flow profile. The study of geochemistry by area allows to establish the migration paths and movement of fluids inside the reservoir. This article focuses on the geochemical composition and isotopic geochemistry of brines and oils, as well as the metal content and the use of fingerprinting for oils (biomarker analysis). It allows to determine: the modes of development of reserves in different parts of the field, the distribution of liquid flows. The main tasks are: identification of geochemical anomalous zones and wells, analysis of the water source in return wells, analysis of communication between geochemical data and cumulative oil recovery. The first step involves selecting candidate wells for sampling. Then reservoir fluid samples are taken, and their unique composition is measured through high-precision mass spectrometric studies (ICP-MS), revealing the content of components to billions of fractions. The "oil fingerprinting" method (GC-MS) is used to identify biomarkers in oil composition and conditions of their origin. Using the developed automated algorithm allows identifying the distinctive characteristics of each reservoir and each phase - water and oil. Graphs and maps are plotted based on the distribution of the identified geoindicators. Geochemical survey was carried out by samples of wellhead samples of more than 100 wells, working for carbonate and terrigenous reservoirs. Area maps of changes in the geochemical background of the field have been constructed. The data of the fluid's geochemical composition from the development objects gave the determining of the inflow profile of each phase in the section of the perforated layers and allowed to compare it with the available geophysical field surveys. The identified difference of oils by the coefficient 2nC29/C28+C30 indicates different stages of hydrocarbons inflow into the traps. In the Devonian system the bright anomalies in the geochemical composition of water and oil were discovered, which are associated with faults and wells with record oil production for the last 50 years, where the actual cumulative production exceeds the volume of the originally estimated recoverable oil. Received data was used in the adaptation of the reservoir simulation model.

Bottom sediments are the most important “archive” containing information about the development of lake ecosystems. One of the most reliable and widely used methods of studying bottom sediments is diatom analysis (Juze et al., 1949). Currently, it is part of a group of guiding methods used to reconstruct the historical dynamics of the environment and climate (Rudaya et.al., 2012; Palagushkina et.al., 2018). In this work, the history of development of Lake Bolshoe Miassovo (Southern Urals) reconstructed using the taxonomic composition of diatoms found in the 526 cm long sediment core is presented. The maximum age of the sediments in the column was 13 500 years BP. According to the results of the study, 123 taxa of diatoms belonging to 47 genera were identified in the lake sediments. Diatom analysis of the bottom sediments of the studied lake allowed us to identify the main stages of the evolution of the reservoir during the Late Glacial and Holocene. During ~13 200–11 700 yr BP, in the period of a cool climate, the lake was a deep body of water with a constant water level and an extensive zone of shallow waters overgrown with macrophytes; then ~11 700–8500 cal. years BP against the background of cooling, the water level decreased; from ~8500–4600 cal. years BP was the stage of increasing water level in the lake in a warmer and wetter climate; in the period ~4600–2500 cal. years BP there was an increase in productivity of algal communities; during ~2500–800 cal. years BP against the background of decreasing temperature, a deep lake with low mineralized water, and presence of swampy shallow waters with acidification processes in them is finally formed.

Abstract. In this study the diatom results of analysis a 510 cm long continuous sediments core from Lake Maloe Miassovo (South Urals, Russia) are presented. The core was collected in July 2018 from central part of the lake from a depth of 7 m. Diatom analysis of samples revealed 38 taxa, belonging to 29 genera and 18 family. The analysis of the ecological structure of the diatom flora of the sediment core sample from the lake under study shows that it is dominated by the Holarctic representatives of benthic and fouling organisms giving preference to the alkaline environmental conditions, which is due to the shallowness of the lake. The prevalence of Staurosira construens Ehrenberg diatom in sediments have been established. Diatom diagram has been divided into two diatom zones on the basis on changing diatom abundances and taxa composition Diatoms were found in low concentrations, or were absent in the lower part of the core of bottom sediments, which could be due to a lack of organic substances, as well as low air and water temperatures. The composition of diatom complexes almost unchanged in the upper part, but their concentration increases significantly.

A core of bottom sediments of 4.98 m depth has been taken from Lake Rubskoe, Ivanovo area (central part of the East European Plain). According to radiocarbon dating, the age of the lower layer of the core is 11 000 cal BP. A study of 23 samples has revealed the remains of 38 taxa of Cladocera (Crustacea: Branchiopoda). According to Lyubarsky’s scale, there are no dominant taxa among the cladocerans; Chydorus cf. sphaericus (Müller, 1776) and Bosmina (Eubosmina) cf. longispina (Leydig, 1860) are subdominant taxa. Typical arctic species that had inhabited the lake at the earlier stages of its formation were replaced by taxa that preferred temperate conditions during the development of the water body. Four faunistic zones have been identified on the stratigrhaphic diagram of the cladoceran community of Lake Rubskoe. An increase in the proportion of Bosmina (Eubosmina) cf. longispina in the layers of 8500 cal BP may have been related to an increase of the pelagic area of the water body at that period. In many cases, it is obvious that the rates of certain taxa in the taphocoenosis of Lake Rubskoe correlate with the climatic changes reported at that time.

The effect of 1-propanol on the transformation of the organic matter (OM) of the domanik rock of the Romashkino field with the Соrg content of 7.26% in supercritical water (SCW) at 374°С was studied. The OM undergoes essential changes in the course of these experiments. According to the Rock-Eval data, addition of 1-propanol to the SCW reaction medium increases the rock production index (PI) by a factor of almost 2, from 0.48 to 0.76, owing to high degree of degradation of the insoluble kerogen, from 22.17 to 0.30 mg g–1 rock (parameter S2). A part of kerogen degradation fragments transforms into resins and aromatic compounds whose content in the extract increases by a factor of more than 2, whereas the content of saturated hydrocarbons (HCs) considerably decreases. As compared to the experiment in straight SCW, insoluble high-carbon substances of carbene/carboid type are absent. The gas phase contains 78.8 rel % СО2, which favors the recovery of high-molecular-mass oil components from the low-permeability domanik rock. The formation of HC gases is indicative of the occurrence of intense degradation processes involving homolytic cleavage of C–C bonds by the radical-chain mechanism. The content of high-molecular-mass n-alkanes C17–C27, phenanthrenes, and dibenzothiophenes in the transformed shale oil increases. The structure of aromatic HCs, resins, and asphaltenes after treatment in SCW with the addition of 1-propanol becomes more condensed, and the content of aliphatic fragments and sulfoxide S=O groups decreases, suggesting the occurrence of dehydrogenation with the elimination of long alkyl chains via cleavage of heteroatomic bonds. In the process, 1-propanol not only acts as a cosolvent but also prevents the recombination of radicals formed in the course of kerogen degradation, which is confirmed by a decrease in the concentration of free radicals in resins and asphaltenes. The structurization of resins and asphaltenes leads to the removal of metals from porphyrin molecules and to a decrease in the paramagnetic properties. After the treatment both with SCW and with SCW + 1-propanol, the resins are characterized by superhyperfine splitting of the line of the vanadyl complex, caused by interaction with the 14N nuclei, which suggests transformations of alkylporphyrins into monocycloalkylporphyrins via dealkylation, demetalation, and hydrogenation. After the autoclave experiments, the structure of mica in the mineral matter of the domanike rock undergoes changes due to segregation of the separate montmorillonite phase.

A study was made of the laws of transformation of the composition of high-viscosity oil under hydrothermal conditions in a porous medium of carbonate rock in the presence of transition metal sulfides formed in situ from an organically soluble precursor. It was determined that the catalysts provide a significant degree of degradation of asphaltenes. When using a catalyst containing nickel and iron in equal proportions, the viscosity becomes an order of magnitude lower than that of the initial oil and reaches a minimum value of 1360 mPa s. Owing to the presence of two different metals in the mixed catalyst makes, a wider range of carbon–heteroatom bonds in resins and asphaltenes of high-viscosity oil can be involved in in the conversion processes. Reducing the viscosity of oil under reservoir conditions makes it possible to increase oil recovery and decrease the carbon footprint of the produced oil due to an increase in the H : C atomic ratio.