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Chemical (REE and major elements) and isotope (δ13C, δ18O) composition of carbonate manganese ores and manganese-bearing carbonates of the Usa deposit (Siberia, Russia) were studied. Received data on the composition of REE exhibit both the distinct negative (Ce/Ce*PAAS < 1) and positive (Ce/Ce*PAAS˃1) cerium anomalies and the positive Eu-anomaly (Eu/Eu*PAAS˃1). Negative Eu-anomalies are not observed. The contents of Mn, Fe, REE, and Ce-anomalies show a positive correlation with each other. Ce-anomalies and the amount of manganese and REE in relation to the carbon isotope composition (δ13C) show a negative relationship and indicate that oxidized carbon of organic matter played an important role in the concentration of manganese and REE in manganese ores. The chemical and isotope composition of examined rocks indicates on secondary formation of Mn-ores. Two major phases and sources are distinguished in the ore-forming process characterized by different chemical (REE and ore elements) and isotope composition: (i) high-grade manganese ores (with high contents of REE and light carbon isotope composition) and (ii) low-grade manganese ores (with low contents of REE and heavy carbon isotope composition). [ABSTRACT FROM AUTHOR]

A series of kerogen samples were isolated from Domanik oil shale before and after hydrothermal treatment in an autoclave (at 250–375°C, for 24 h). Than composition of the C1–C5 hydrocarbon gases generated in stepwise (300–800°C) pyrolysis of these kerogens was characterized by gas chromatography. According to the calculated EASY %Ro and Rock-Eval pyrolysis data, the highest maturity level of the organic matter reached by the hydrothermal treatment corresponded to the MC4 stage. As the hydrothermal treatment temperature of the oil shale was elevated up to 325°C, the dry pyrolysis of residual kerogen led to the predominant generation of wet gases in which C2+ prevailed over methane; at temperatures above 325°C, methane was predominant. Based on the pattern of the generation curves plotted individually for C1, C2, C3, C2–C5, and C4–C5 gases, methane was found to have additional sources in the kerogen structure, compared to C2+ gases. Ethane and ethylene are generated simultaneously via the free-radical decomposition of alkyl structures; moreover, at high pyrolysis temperatures, ethane and ethylene have some precursors other than those of C3+ gases. [ABSTRACT FROM AUTHOR]

The composition of hydrocarbon gases formed by pyrolysis of residual Domanik shale kerogen at 800°C, preceded by hydrothermal treatment at 250–375°С, was studied by pyrolytic gas chromatography. Starting from the autoclave temperature of 320–325°C, the hydrothermal treatment of the shale affects the kerogen structures responsible for the formation of C2+ gases in pyrolysis at 800°C. An increase in the temperature of the shale hydrothermal treatment leads to a monotonic increase in the С1/С2+ ratio in the products of the residual kerogen pyrolysis at 800°C. The methane yield at 800°C does not correlate with the content of alkyl structures, determined in kerogen by IR spectroscopy, and the yield of С2+ gases linearly correlates with the content of alkyl structures. [ABSTRACT FROM AUTHOR]

Localization of the finds of natural bitumen in archipelagos in the western segment of the Russian Arctic is considered. The nature of their appearance in relation with the subsurface geothermal regime is discussed. Based on numerical simulation, temperatures and heat flow density are calculated in 2D geometry along seismogeological profiles and in 3D geometry for the isometric structure of Franz Josef Land. It is concluded that all the noted natural bitumen manifestations are genetically related to hydrothermal activity, with signs adequately recorded in the geotemperature field. [ABSTRACT FROM AUTHOR]

The composition of hydrocarbon gases formed by pyrolysis of residual Domanik shale kerogen at 800°C, preceded by hydrothermal treatment at 250–375°С, was studied by pyrolytic gas chromatography. Starting from the autoclave temperature of 320–325°C, the hydrothermal treatment of the shale affects the kerogen structures responsible for the formation of C2+ gases in pyrolysis at 800°C. An increase in the temperature of the shale hydrothermal treatment leads to a monotonic increase in the С1/С2+ ratio in the products of the residual kerogen pyrolysis at 800°C. The methane yield at 800°C does not correlate with the content of alkyl structures, determined in kerogen by IR spectroscopy, and the yield of С2+ gases linearly correlates with the content of alkyl structures. [ABSTRACT FROM AUTHOR]

Abstract—It has been established that the average values of some hydrocarbons biomarker coefficients of bitumens from the Domanik deposits and oils from the Domanik–Tournaisian complex coincide. These are the proportions of C27–C29 steranes, tri-/pentacyclanes ratio, and coefficients 2 × С17/С16 + С18 and 2 × С27/С26 + С28 calculated from n-alkane composition. Such indicators as the Pr/Ph, (Pr + Ph)/(n‑C17 + n‑C18), dia-/reg-steranes, and the sterane/hopane ratios in oils are slightly lower than in the bitumen. The average values of δ13C in asphaltene, resin, aromatic hydrocarbons, and aliphatic hydrocarbons fractions from oils of the Domanik genotype and in the studied bitumens are similar. The carbon isotope composition of asphaltenes in oils is depleted in 13С compared to those of resins and aromatic hydrocarbons, and vice versa in bitumens. A heterogeneous composition of the bacterial flora in the sediments of the Domanik Sea is suggested. In some places, species with high concentrations of diplopterol or hexafunctional bacteriohopanes likely dominated over bacteriohopantetrol. [ABSTRACT FROM AUTHOR]

Hydrothermal liquefaction (HTL) of sewage sludge is considered in the article as an analogue of the natural processes of oil formation (catagenesis). A comparison of the physicochemical composition of primary and secondary sludge with type II kerogen (natural precursor of oil) showed their similarity. Both types of sludge have a slightly higher level of oxygen and nitrogen. The study tested the hypothesis that the elements included in the inorganic part of the oil source rocks can have a catalytic effect on the oil formation processes. For the conducted studies of sludge HTL, the catalysts containing cations and substances found in oil source rocks were chosen: as homogeneous catalysts (KOH, NaOH, NH4Fe(SO4)2, CoCl6, NiSO4, CuSO4, ZnSO4, MoO3) and as heterogeneous catalysts (MgO, Zeolite, Al2O3). The effectiveness of catalysts containing metal ions, zeolite and aluminum oxide has been proven. The highest biocrude yield was achieved in a process with NiSO4 as the catalyst in a dose 2 g per 10 g of sludge: oil yield increased by 34.9% and 63.4% in the processing of primary and secondary sludge, respectively. The use of catalysts provided an increase in fuel HHV by 10.8–12.5%, which is associated with a decrease in oxygen content (by 10.8–43.2%) with a simultaneous increase in carbon (by 7.9–10.9%) and hydrogen (by 6.5–18.7%) content. [ABSTRACT FROM AUTHOR]

Evolutionary transformations of the composition and structure of asphaltenes in different types of organic matter (OM) of sediments and rocks at different lithogenesis stages were studied. Insight into the main steps and processes controlling the transformation of OM asphaltenes in different steps of thermal maturation was gained, and new opportunities for using parameters of the asphaltene structure for constructing geochemical models were revealed. The following trend in variation of bitumen asphaltene parameters in the course of catagenesis was revealed for both genetic forms of OM: directional carbonization of asphaltenes, accompanied by a decrease in the content of hydrogen and an increase in the relative content of aromatic (including condensed) structures and by a decrease in the role of aliphatic substituents. Linear relationship was revealed between the parameters of the composition and structure in the course of thermocatalytic transformations. Three successive stages of thermal maturation of asphaltenes were distinguished. [ABSTRACT FROM AUTHOR]

One of the widely used methods of assessing the maturity of organic matter based on aromatic compounds uses indexes reflecting changes in the relative concentrations of phenanthrene and its methyl-substituted derivates. A set of ratios now widely used in national and international practice (MPHI, MPI-1, MPI-1mod., PP-1, and PHI) is analyzed based on data on these compounds in terrestrial organic matter (OM) recovered by Srednevilyuskaya-27 superdeep well. Equations are derived for calculating synthetic values of vitrinite reflectance based on phenanthrene maturity indexes at meso- and apocatagenesis. Data are presented on typical changes in the relative phenanthrene concentrations and its methyl-substituted derivates under high P–T parameters: the more stable behavior of 2-, 3-, and 1-methylphenanthrene than 9-methylphenanthrene. The relative concentrations of phenanthrene itself are demonstrated to broadly vary at apocatagenesis, and this factor deteriorates the maturity indexes of the phenanthrene ratios. It is necessary to select proper equations for various hydrocarbon systems and determine the boundaries of the transition from positive correlations between phenanthrene indexes with the vitrinite reflectance to negative ones. The obtained results are compared with the classic understanding of the problem. [ABSTRACT FROM AUTHOR]

Tracing interactions during burial-induced organic maturation and associated clay-material alteration is of prime importance for understanding both the individual and combined mineral and organic processes. In the present study the light elements B, Li, O, and H of a sample from oil-prone Eocene Kreyenhagen Shale from San Joaquin Basin (California) were examined. The natural burial-induced temperature increase was simulated by pyrolysis experiments at progressively increasing temperatures (270–365°C) and for varied durations (72–216 h) applied to the whole rock and its <2 μm fraction. The illite structure as well as the K-rich interlayers of the illite-smectite mixed layers were not affected by the pyrolysis experiments and the smectite-rich interlayers did not collapse, while the soluble minerals and the organic matter were altered. The distribution pattern of the rare-earth elements (REEs) from untreated whole rock and of its pyrolyzed equivalents are within analytical uncertainty, which confirms that the changes induced by pyrolysis experiments were minimal in the bulk sample. Conversely, the REEs from the <2 μm fractions were modified significantly, suggesting that the whole rocks and the <2 μm fractions may contain different types of organic materials. Also, only the carbonates, oxides, chlorides, and organic matter were affected together with the smectite-rich interlayers of the illite-smectite structure. Bitumen coating of the smectite interlayers probably increased the amount of B of organic origin in their sites. The δ11B and δ7Li of the successively expelled hydrocarbon phases changed with increasing pyrolysis temperatures, together with the B and Li contents of the hydrocarbon-related fluids. On the basis of the δ11B and δ7Li from pyrolyzed clay fractions, the B released successively was not isotopically homogeneous, probably depending on how the type of organic matter decomposed during the successive pyrolysis steps, and on which components were released. The δ11B of organic-B increased progressively from –2‰ at low experimental temperature up to +9‰ at the highest temperature. The calculated δ7Li that was released also increased relative to the value of the outcropping sample used as a reference, but it remained almost constant from –7‰ at 310°C for 72 h to –8‰ at 365°C for 216 h. The δ18O values of the <2 μm size fractions decreased significantly during pyrolysis above 300°C, but the δD changes were rather modest. The total organic carbon (TOC) remained statistically constant after pyrolysis to 300°C, as did the δ7Li values. The pyrolysis experiments in the present study suggest the presence of bitumen-coated smectite interlayers that could have been misidentified as dehydrated smectite in the literature. Together with abnormal illite K-Ar ages, the occurrence of such bitumen-coated illite-smectite interlayers occurring in source and reservoir rocks could indicate the timing of hydrocarbon maturation relative to illitization. [ABSTRACT FROM AUTHOR]

The regularities were determined for changes in the lithological and geochemical composition of rocks of the Bazhenov Formation (BF) characterized by various degrees of transformation of organic matter (OM). From the M to MK2 stages (140–170–195°C), trends are seen toward (a) an increase of the quantity of limestone–dolomitic interlayers along with the dolomite content; (b) a decrease of the OM content over the entire section; (c) a decrease of the OM and sulfide sulfur concentrations in the pyrite–kerogen band of the roof of the BF; (d) a decrease of the C/S ratio; and (e) an increase of the thickness of the pyrite layer in the transition zone between the BF and overlying sediments along with the growth of the pyrite content. It was concluded that the interval between the M and MK2 stages experienced OM transformation, the migration of transformation products, dolomitization of the rocks, and pyritization of low-carbon rocks in the BF-overlying Podachimovo strata. [ABSTRACT FROM AUTHOR]

A combination of modern analytical methods was used to study terrestrial organic matter from upper Paleozoic rocks in the central part of the Vulyui hemisyneclise (East Siberia) sampled from the depth interval 3370-6458 m penetrated in the Srednevilyuiskaya- 27 superdeep well. In this study, we used 71 core samples to trace depth variations in the geochemical characteristics of organicmatter during middle-late mesocatagenesis and apocatagenesis: organic carbon content (Corg), Rock-Eval pyrolysis parameters (HI, max), carbon isotope composition, thermal maturity (Ro Vt, %), hydrocarbon type composition (hydrocarbons, resins, and asphaltenes), distributions of n-alkanes (TIC), steranes (m/z 217), and terpanes (m/z 191), and standard biomarker indices with increasing degree of thermal maturity. It is shown that during late mesocatagenesis and apocatagenesis, the pyrolysis parameters and biomarker indicators are no longer effective as indicators of organic-matter maturity and genesis. [ABSTRACT FROM AUTHOR]

This is a pioneering study on lateral zoning of groundwater chemistry and authigenic mineralogy in the Oxfordian regional reservoir of the Nadym-Taz interfluve. According to thermodynamic calculations, the nonequilibrium-equilibrium water-rock system lacks equilibrium with primary magmatic minerals, such as albite, anorthite, and microcline, though the water is moderately saline (up to 63.3 g/L) and has been in interaction with rocks for ~165 million years. Authigenic minerals form continuously and successively (kaolinite-montmorillonite-illite-micas-chlorite-albite-microcline) from waters that have certain pH and contents of SiO2, Al, Na, K, Ca, and Mg. The equilibrium of groundwater with primary aluminosilicate minerals impinges on a carbonate barrier, and almost all rocks are more or less strongly carbonatized. Authigenic mineral assemblages from the southern Nadym-Taz interfluve include kaolinite unlike those from the northern part of the region, where albitization is more common. Authigenesis generally decays in the eastern direction. [ABSTRACT FROM AUTHOR]

The zoning of catagenic OM transformation of sediments of the Bazhenovskaya highly carbonaceous formation is analyzed with respect to evolution of pore capacity system in its OM. The regional prospecting criteria of oil beds of the reservoirs related to OM porosity in the formation are formulated on the basis of our studies. [ABSTRACT FROM AUTHOR]

Clay subfractions (SFs) with particles size of 2–5, 0.6–2.0, 0.3–0.6, 0.2–0.3, and 0.1–0.2 μm of two shale samples (Upper Riphean Inzer Formation, South Urals) are studied using transmission electron microscopy, X-ray diffractometry (XRD), and U–Pb, Sm–Nd, Rb–Sr, and K–Ar methods. The SFs are composed of low-temperature 1Md illite; quartz, chlorite, and 2M1 illite are observed only in some coarse SFs. Irrespective of the size, the clay particles are equant. The standardized illite crystallinity indices (CIS) of all SFs are typical of the dia(cata)genesis zone. The CIS value increases, the I002/I001 ratio of XRD patterns decreases, and the K content and K/Rb ratio increase with decreasing particle size of the SFs from 2–5 to 0.1–0.2 μm. Leaching with 1N HCl and 1N NH4OAc and U–Pb, Sm–Nd, and Rb–Sr analysis of untreated SFs, leachate, and residue allowed us to study the isotope systematic of mixing in mobile and silicate material of shales. The 208U/204Pb and 87Rb/86Sr ratios of leachates are lower and the 147Sm/144Nd ratio is higher than those of residues. The leachates are also characterized by less radiogenic Pb and Sr and more radiogenic Nd relative to residues. With decreasing size of SF particles, the U, Pb, Sm, Nd, and Sr contents of leachates gently decrease and the Rb content increases. The 87Rb/86Sr and 87Sr/86Sr ratios of leachates of fine SFs are significantly higher, whereas their 238U/204Pb ratio is lower in comparison with coarse SFs. What is more, the data points of residues of various SFs occur along the mixing lines in the 87Rb/86Sr‒87Sr/86Sr and 1/86Sr‒87Sr/86Sr plots. The data points of corresponding leachates also form linear trends in 238U/204Pb‒206Pb/204Pb, 206Pb/204Pb‒207Pb/204Pb, 147Sm/144Nd‒143Nd/144Nd, and 87Rb/86Sr‒87Sr/86Sr coordinates. Apparent Rb–Sr ages calculated from slopes of "inner isochrons" ("leachochrons") as well as K-Ar ages gradually decrease from 835–836 and 721–773 Ma, respectively, for SFs of 2–5 μm and to 572‒580 and 555‒580 Ma, respectively, for SFs of 0.1–0.2 μm. Thus, the XRD and isotopic data indicate that both clay and mobile shale constituents are mixtures at least of two components, and the silicate phase contains authigenic illites of various ages. First-generation illite abundant in the coarse SFs of 2–5 μm and 0.6–2.0 μm was formed immediately after the deposition of the Inzer sediments and its age of 803–836 Ma is consistent with stratigraphic age of the Inzer Formation. The formation of this illite was facilitated either by lithostatic burial or intense horizontal fluid flow caused by tectonic inversion in the eastern regions of the Uralian paleobasin. The age of the second-generation illite is 572–580 Ma; it was formed as a result of vertical movements or renovation of the composition of the pore fluids during deformations and metamorphism of the South Urals related to the evolution of the Beloretsk metamorphic complex. [ABSTRACT FROM AUTHOR]

The article deals with the chemical structure of kerogen and its transformation in catagenesis of shale formations by the example of the Middle Volga shale formations and the Domanic carbonaceous deposits of the East European Platform. The studies allowed identifying the main distinctive features in the structure of individual structural components of these types of kerogen and refining the models of the fragment of their chemical structure. Some of the oxygen-containing structures are found to be present in the Middle Volga kerogen as carbohydrate moieties and algaenan components, the alkyl chains in which are interlinked by ether bonds, and the structure of the sulfur-containing components can be represented as sulfide (polysulfide) bound n-alkyl structures, in pyrolysis of which low-molecular and high-molecular alkyl-substituted thiophenes, thienyl- and phenylthiophenes are formed. The average S/C value exceeding 0.04 classifies the Upper Jurassic kerogen as Type II-S. The predominant components constituent in the composition of kerogen of Domanic rocks are lipid components, however, its lower aliphaticity is probably due to the higher maturity of organic matter (OM) and to the low ratio of n-alkyl structures to polyaromatic moieties, the formation of which is connected with the rearrangement of polyene and heteroatomic structures in catagenesis. [ABSTRACT FROM AUTHOR]

Samples of Triassic sediments were collected from cores of parametric boreholes drilled on the Admiralteiskii Rise, Franz Josef Land Archipelago, and Fersman structure in the northeastern part of the Barents Sea sedimentary basin. The composition and distribution of hydrocarbon biomarkers ( n -alkanes, isoprenoids, cyclic alkanes, and polyaromatic hydrocarbons) were studied using the GC-MS method and provided information about the genesis, facies conditions of sedimentation, and catagenetic maturity stage of dispersed organic matter (DOM). The Late Mesozoic-Cenozoic uplifting of the region and active magmatic processes significantly influenced the thermal transformation of sediments. The revealed trend is best observed in the sediment section of the Franz Josef Land Archipelago, where the thermal effects led to a radical increase in DOM transformation, up to the AC 1 stage. [ABSTRACT FROM AUTHOR]

More than 1500 measurements of vitrinite reflectance (R° t ), along with mathematical modeling and computing, have been used to map the uppermost Middle Jurassic sediments of the West Siberian basin according to thermal maturity (catagenesis). The thermal maturity varies within the grades PC 3 to AC 2 . Sediments are the least mature along the margins of the basin, and the maturity grade increases progressively toward its central and northern parts (grades MC 1 -MC 2 ). It reaches a maximum in the north (AC 2 ), where the sediments which subsided to large depths became exposed to high temperatures and pressures. The maturity zones of Jurassic sediments in the West Siberian basin form a typical pattern of regional catagenesis. [ABSTRACT FROM AUTHOR]

This study provides geochemical, mineralogical, and isotope data for rocks and ores from Lower Proterozoic black shale formations of the Kodar-Udokan structural and formational zone, which host the Khadatkanda gold-uranium deposit. The results indicate that the uranium and gold mineralizations were formed at different times in relation to different geodynamic settings. The gold mineralization is associated with the inception of the Syulban fault and has a juvenile source. The later Th-U mineralization originated during tectonic rejuvenation of the Syulban fault zone, while the sources of radioactive elements were presumably the underlying sediments of the Kodar Group, which are widespread throughout the area of the Baikal mountain region (BMR). Based on the above results, the Au-U mineralization in the study area can be recognized as unconformity-type deposits, analogous to the well-known deposits of Australia and Canada. In this connection, the Baikal mountain region has a good potential for the discovery of Au-U deposits. [ABSTRACT FROM AUTHOR]

With the development of electron microscopy-based porosity measurement techniques, it is possible to devise new oil and gas reservoir rock classification schemes that would take the geometrical features of the pore space into account. This is associated with the fact that the structure of the pore space of reservoir rocks has a significant effect on the recovery of hydrocarbons upon reservoir processing. For several years, we have carried out microstructural studies of rocks from the productive strata of various fields using cathodoluminescence scanning electron microscopy (SEM) and porometric software for the analysis of SEM images. The investigations show that it is possible to classify reservoirs by the connectivity of pores and pore channels in reservoir rocks. [ABSTRACT FROM AUTHOR]

The article discusses the geochemical features of mature hydrocarbon (HC) systems and their recognition. It mentions that the composition of HC systems in sedimentary sequence is transformed from immature at shallow depths to degraded mature and ultramature oils and condensates at large depths and shows pressure, temperature gradients and a particular type of initial organics. It discusses the isomerization parameters needed to evaluate HC systems.

The peculiarities of the processes of postsedimentary lithification and their dynamics in various geostructural areas (cratons, young platforms, and orogens) are considered. The direct and indirect impacts of geodynamic factors on these processes are substantiated. [ABSTRACT FROM AUTHOR]

The carbon isotope composition of individual n-alkanes in samples of crude oil from the Late Devonian play of the Timan-Pechora basin and rock bitumen that reached the main stage of oil generation has been studied. The carbon isotope composition of individual alkanes of thermal bitumen obtained by autoclaving low-maturity Domanik rocks has been also determined. The carbon isotope composition of individual alkanes of the rock bitumen has been shown to correspond to that of the oil samples, a feature that indicates the syngenetic nature of deposits of these Late Devonian oils. The correlation between the oil and bitumen compositions is also confirmed by matching the composition of acyclic hydrocarbons and polycyclic biomarkers of the test oils and bitumens. For the Domanik organic matter, the carbon isotope composition of n-alkanes has been revealed to depend on the temperature of artificial maturation of the rock organic matter, a finding that potentially increases the reliability of the correlation between the oil and source rock organic matter by the isotope data. [ABSTRACT FROM AUTHOR]

It is shown that the definition of a sedimentary rock that has been given by the classical lithologists L.V. Pustovalov, M.S. Shvetsov, L.B. Rukhin, and U.H. Twonhozhel, among others, does not conform to the modern understanding of the sedimentary process, which covers not only the surface of the planet, but also the Earth's deep interior with high thermodynamic indices (a pressure of up to 8100 kgf/cm and a temperature of up to 800-900°C). [ABSTRACT FROM AUTHOR]

The main (global and regional) Cretaceous events that affected the formation of the Jiamusi-Bureya fragment of the East Asian continental margin are considered to compile a consistent tectonic-sedimentation model of its evolution. The key objects of this margin are the Bureya and Hegang basins, where the epoch of Cretaceous coal accumulation is best expressed. The comparative analysis revealed their similarity. Both the basins were formed in the grabens at the riftogenic stage of the almost amagmatic continental margin. They are characterized by a single Hauterivian-Aptian stage of coal formation as confirmed by new stratigraphic data. Both basins are rich in coal and gas. [ABSTRACT FROM AUTHOR]

Previous studies of postsedimentation and deep rock transformations (the diagenetic, catagenetic, and anchimetamorphic stages) by the author and other Russian lithologists are revised by evaluating the different types of zoning of authigenic mineral formation within terrigenous complexes of different ages in definite structural-tectonic units of continents and their margins. It was emphasized that an intrarock aqueous fluid phase played a dual role in authigenic mineral formation: (1) it served as a medium for internal redistribution of sedimentogenic components or (2) as a carrier of external material. Indicator features of its own newly formed ( A) and allogenic ( A) authigenic minerals are given. It was shown that the background subsidence lithogenesis (SL) of the sedimentary sequence provides the formation of A varieties in the sequence, whereas the prevalence of A marks the superimposed or secondary alterations (SAs) of sedimentary rock. A combination of SL and SA features is demonstrated for different structures: syneclises and anteclises of cratons, rifts, fore troughs, orogens, and others. The SL and SA formation is determined by definite numerous exogenic and endogenic factors, which are often obliterated but integrated by geodynamic settings and geological evolution of sedimentary complexes. According to this conclusion, a new typification scheme of post-sedimentation transformations was proposed on the paleogeodynamic basis. [ABSTRACT FROM AUTHOR]

The catagenesis of the Jurassic-Cretaceous deposits and coals has been comprehensively examined based on a complex of features including the reflectance ( R and R), the qualitative properties, and the petrochemical characteristics (the density and saturation porosity) of the host rocks. The catagenesis of the Jurassic-Cretaceous deposits was studied based on the structural zones in which the coal-bearing deposits occur at different depths ranging from ∼ 10 to 300 m, down to 700m, and from 5 to 3460 m in the Western, Central, and Kyndal zones, accordingly. The following regularities of the changing of the coal's catagenesis have been established: from group 3B to 1G, 2G, and GFL; from gradation PC to MC-MC; and from MC to MC-MC with the changing of the composition of the coals from long-flame coal to gas and gasfat-lean coal. In the intrusive bodies distribution areas breaking through the coal-bearing deposits, the coal seams are metamorphosed to the marks of lean caking and lean coals. The data obtained have made possible the assessment of the hydrocarbon generation in the Jurassic-Lower Cretaceous deposits of the basin. [ABSTRACT FROM AUTHOR]

Abstract: Numerical models are developed to predict the generation, accumulation, and escape of hydrocarbons at the time of sediment accumulation (basin modeling) in the West Siberian geosyneclise during the Jurassic, Cretaceous, and Cenozoic. A theoretical framework for such computer models is presented with a special emphasis on modeling of gas generation during early catagenesis. The study provides a description of the algorithm used for interpretation of simulation results and considers the stages of formation of a shale cap rock during lithogenesis. Peak oil generation began in the Aptian and continued for about 80 Myr until Eocene–Miocene times; gas generation in the late catagenetic window took place from the Valanginian to the Maastrichtian. Numerical simulations show that the major oil-prone source rocks in the South Kara kitchen area were, in the decreasing order of potential, the Bazhenovo (Yanov Stan), Kiterbyut, and Malyshevka Formations. The Upper Jurassic regional rock unit generated over 60% of liquid hydrocarbons and heterocyclic compounds (oils). The major gas-prone source rocks in the area were, in the decreasing order of potential, the Kiterbyut, Malyshevka, Alym, and Bazhenovo (Yanov Stan) Formations. The Lower and Middle Jurassic regional rock units generated about 65% of hydrocarbon gases. Results are presented to quantify the amount of hydrocarbons dissipated due to either the absence or poor effectiveness of confining seals and to explore the role of Cenozoic tectonic processes in the formation of petroleum accumulations in the basin. [Copyright &y& Elsevier]

A preliminary assessment of the source potential of the Jurassic section was obtained using organic geochemical data on samples collected from outcrops on Franz Josef Land and Svalbard archipelagoes as well as boreholes in the Barents Sea basin. The presence of organic-rich shale units with good source potential was reported for the first time within the studied section of Early to Middle Jurassic age, along with well-documented Upper Jurassic source rocks. The study provides an assessment of regional variations in the kerogen type, hydrocarbon generation potential, and maturation of organic matter from Jurassic sediments. [ABSTRACT FROM AUTHOR]

Abstract: We present new data on the material composition of terrigenous deposits in the pre-Jurassic basement of the West Siberian Plate, which formed on the margin of the Kazakhstan paleocontinent. Studies of the sections of several wells drilled in the east of the Kurgan Region showed that the Middle–Upper Devonian and lower Lower Carboniferous continental and littoral deposits are graywackes rich in rock and plagioclase clastics. Quartz grains amount to no more than 3–5%. The rock clastics are mainly volcanics of basic and normal compositions, which were supplied, most likely, from acting volcanoes of the marginal belt. By genesis, these are predominantly tephroids. Along with allothigenic components of sandstones, we consider authigenic minerals, which permit treating the postsedimentational transformation of the Middle Devonian and Early Carboniferous rocks as early catagenesis. By the vitrinite reflectance, the Lower Visean sandstones correspond to gradations MC2 and MC3 (medium catagenesis). [Copyright &y& Elsevier]

This study presents data on the composition of organic matter from the Late Silurian sediments of the Chernov uplift. These sediments are characterized by low C contents, which may reach 1-3% in individual layers. A relatively high thermal maturity of organic matter is confirmed by polycyclic biomarker distributions and Rock-Eval pyrolyisis data. Despite its higher thermal maturity level ( T = 456°C), kerogen in carbonaceous shales from the Padymeityvis River exhibits good preservation of long-chain n-alkyl structures, which are readily identified in the C NMR spectra and by the molecular analysis of the kerogen pyrolysis products. [ABSTRACT FROM AUTHOR]

The results of the latest research by lithologists, including the author, who, jointly with hydrogeologists and geochemists, substantially specified the concepts on the mechanism of the processes of mineral genesis, fluid genesis, and different scale remobilization of sedimentary substances within the stratisphere (the over-metamorphic sedimentary cover of the Earth's crust), where a part of the sediments was transformed to rocks and ores that are completely different in their mineral composition and physical and chemical properties, due to reserves and long before metamorphism, are generalized. Conclusions are made about the openness and self organization of the stratisphere that together with over- and underlying natural systems influenced the orientation and the evolution of the sedimentary process. [ABSTRACT FROM AUTHOR]

Abstract: We have studied for the first time the organic geochemistry of the Vendian thick section stripped by the parametric well Vostok-3 in the depth range 5002–3870 m in southeastern West Siberia. The results point to the aquagene–plankton–derived and bacterial nature of the buried organic matter (OM). At some depth levels, the deposits are enriched in OM (up to 0.7–9.6%). The study of kerogens has shown that the OM is transformed to the apocatagenesis stage. The composition of biomarker hydrocarbons in bitumens has been studied, and the geochemical criteria for the petroleum presence prediction are considered. [Copyright &y& Elsevier]

IR spectroscopy and X-ray diffraction study of insoluble organic matter (IOM) showed that the structural characteristics of its carbonic component depend on the composition of original organic matter and degree of its catagenesis. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents the first comprehensive geochemical data, obtained by modern techniques, on the dispersed organic matter (OM) of Cambrian sediments in the Upper Proterozoic–Paleozoic Cis-Yenisei sedimentary basin (parametric wells Vostok-1 and Vostok-3). The carbonaceous rocks of the Churbiga and Paidugina Formations are the most OM-enriched in the studied Cambrian sections. The OM in these sections is of aquagene (bacterial, plankton-derived) origin. A detailed description of biomarker hydrocarbons has been given for the fraction of saturated hydrocarbons. Also, the high degree of OM catagenesis (apocatagenesis) has been established. Finally, geochemical criteria for predicting the petroleum potential have been considered. [Copyright &y& Elsevier]

Hopane hydrocarbons contained in organic matter from the Lower Cambrian Sinyaya Formation, southeast of the Siberian platform, were analyzed by gas chromatography/mass spectrometry. This study first identified C28 28, 30-bisnorhopane and its homologues present in high concentrations in autochthonous organic matter from East Siberian sedimentary basins. These biomarkers can be used in distinguishing between the sources of naphthides on the northern slope of the Aldan anteclise. Two saturated naphthenic hydrocarbons, C31 homohopene and C31 28-norhomohopene, were also detected. This study provides some details on hopane distribution, organic matter accumulation conditions, and the degree of OM catagenesis. [ABSTRACT FROM AUTHOR]

Abstract: The influence of 6.75 m thick dolerite dike on the sheet coal of the Kaierkan deposit (northwestern Siberian Platform) was studied by organogeochemical methods. It is shown that initial bituminous coal was transformed into anthracite in the immediate vicinity of the dike. Chemical kinetic modeling of the dike-induced cracking of coal''s organic matter was performed, and the maximum paleotemperatures were estimated. [Copyright &y& Elsevier]

Changes in the D/H ratio of sedimentary organic matter (SOM) during thermal maturation have been difficult to interpret because the effects of hydrogen exchange and kinetic fractionations are confounded in natural samples. Recent analytical developments have significantly improved our understanding of the responsible mechanisms. In this paper, we review experimental and field data that document a progressive increase in the D/H ratio of most organic hydrogen at the bulk and molecular levels, and suggest that the transfer of hydrogen from water to organic matter is the most important mechanism leading to those changes. SOM and water in natural petroleum systems approach a pseudoequilibrium D/H fractionation of about -80 to -110%. D/H ratios of organic hydrogen can preserve quantitative information about paleoclimate throughout diagenesis, and some qualitative information through catagenesis. [ABSTRACT FROM AUTHOR]

Clay subfractions (SFs) of <0.1, 0.1–0.2, 0.2–0.3, 0.3–0.6, 0.6–2 and 2–5 μm separated from Middle Riphean shales of the Debengda Formation are studied using the TEM, XRD, K-Ar and Rb-Sr isotopic methods. The oxygen and hydrogen isotope compositions in the SFs are studied as well. The low-temperature illite-smectite is dominant mineral in all the SFs except for the coarsest ones. The XRD, chemical and isotopic data imply that two generations of authigenic illite-smectite different in age are mixed in the SFs. The illite crystallinity index decreases in parallel with size diminishing of clay particles. As compared to coarser SFs, illite of fine-grained subfractions is enriched in Al relative to Fe and Mg, contains more K, and reveals higher K/Rb and Rb/Sr ratios. The Rb-Sr age calculated by means of the leachochron (“inner isochron”) method declines gradually from 1254-1272 Ma in the coarsest SFs to 1038-1044 Ma in finest ones, while the K-Ar age decreases simultaneously from 1225–1240 to 1080 Ma. The established positive correlation of δ18O and δD values with dimensions of clay particles in the SFs seems to be also consistent with the mixing systematics. The isotopic systematics along with data on mineral composition and morphology lead to the conclusion that mixedlayer illite-smectite was formed in the Debengda shales during two periods 1211–1272 and 1038–1080 Ma ago. The first period is likely close to the deposition time of sediments and corresponds to events of burial catagenesis, whereas the second one is correlative with the regional uplift and changes in hydrological regime during the pre-Khaipakh break in sedimentation. [ABSTRACT FROM AUTHOR]

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