The study compares the elemental composition of asphaltenes with the parameters of hydrocarbon biomarkers and Precambrian insoluble organic matter (OM) of the Aldan–Maya depression. The elemental composition of the asphaltenes was found to depend on the pyrolytic characteristics of the OM. Using asphaltene compositions in combination with biomarker parameters, the genetic and catagenetic features of difficult-to-study objects such as Precambrian bitumens can be characterized more accurately and reliably. The elemental composition of the asphaltenes was shown to correlate with the aromatic parameters that reflect the OM maturity. In contrast, the parameters of the asphaltenes show essentially no correlation with biomarker data for the saturated components.

The distribution of biomarker hydrocarbons in samples from Ust’-Mayskaya-366 well in the Aldan–Maya depression, Siberian platform, was studied in detail using modern techniques to elucidate biogeochemical features of Precambrian source organic matter (OM) and naphthides generated by it. To correlate OM and assess the effect of migration on biomarker parameters, allochthonous and mixed bitumens (AllB and MB, respectively), as well as open-pore bitumens (OPB) extracted from the uncrushed rocks of the Neryuen, Ignikan, Kandyk, Ust-Kirbin (Riphean), and Sardana (Vendian) formations were studied in comparison with the autochthonous bitumen (AutB) of the source-rock horizon of the Neryuen Formation. Saturated cyclanes and aromatic-fraction compounds from this well were analyzed for the first time. The Neryuen mudstones are enriched in organic matter (TOC > 1 MC_3^1 (Tmax = 452–465°C). The maximum in tricyclanes C19–31 in almost all of the studied samples falls onto C23, as in the Neryuen AutB. Even homologues of 3,7-dimethylalkanes found in the Neryuen AutB and Ust-Kirbin MB, as well as those detected in trace amounts in the Neryuen and Ignikan MBs and in the OPBs of the Sardana Formation, were apparently disseminated during migration. All bitumens were found out to contain 12- and 13-monomethylalkanes, which are most abundant in the Kandyk OPBs. These compounds can likely be accumulated during migration. The migrated bitumens differ from the AutB in containing a higher proportion of steranes C29 (up to C29/nC27 > 2) and a higher nC27/nC17 ratio (up to >1). Relationships with the bitumen coefficient was found for Pr/Ph, nC27/nC17, ΣnCi/ΣizoCi in acyclic hydrocarbons, C29/C27 in steranes, C35/C34 in homohopanes, hopane/tricyclane ratios; these parameters are likely susceptible to effects of migration. The most probable source of the Riphean bitumens was mainly the carbonaceous rocks of the Neryuen horizon, and the variations in characteristics were caused by catagenesis and migration processes of accumulation or dissemination of low-molecular-weight mobile compounds. The OPBs of the Sardana Formation differ from the Riphean ones. The upper two bitumens are immature parautochthonous, and the others are probably a mixture of Riphean and Vendian bitumens, which were influenced by solutions from the Sardana base-metal stratiform deposits (which is located at approximately 35 km southeast occurs of the area) and the Perevalnoye deposit (at about 20 km), whose mineralization is of Vendian age.

Сatagenetic transformations of asphaltenes of organic matter (OM) from recent sediments and fossil rocks were studied on rocks sampled from different sedimentary basins (Timan-Pechora, Mezen, West Siberian, Kuznetsk, Aldan-Maya and Middle Amur) of Russia. Changes in the elemental composition of asphaltenes were analyzed with the Veselovsky’s model of the formation of major groups of fossil fuels using cO parameter (cO = (O/8 – N)/(C/3)) as compared with the total carbon based on elemental analysis. Just as the Van-Krevelen diagram, the plot built in C–cO coordinates for OM of various genetic forms demonstrates a significant difference in the asphaltenes composition evolution during catagenesis. At the same time, the cO parameter has notably increased in asphaltenes of both types of OM. Structural transformations of asphaltenes during catagenesis were identified in the course of high-resolution NMR (nuclear magnetic resonance) spectroscopy. The research results comprise data on carbon distributions in the aromatic and aliphatic groups in the investigated asphaltenes of different type OM of sediments and rocks at different stages of lithogenesis. A correlation between the asphaltene composition and structural parameters depending on thermocatalytic transformations is revealed. The asphaltenes of terrestrial organic matter are distinguished by higher cO values and different carbon yields of aromatics (higher) and aliphatics (lower) throughout the catagenesis phase. The highly transformed marine OM is marked by surge condensation of aromatic rings in asphaltenes, which makes them similar to asphaltenes of the terrestrial type OM.

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.

Changes in the elemental composition of asphaltenes in organic matter (OM) of different origin, with particular focus on their evolution from proto- to mesocatagenesis, were analyzed in samples of Devonian bituminous shales and brown coals from the Kuznetsk Basin and samples of Cenozoic brown coals and clays from the Middle Amur Basin. The composition of asphaltenes (protoasphaltenes) of different origin is shown to be differentiated as early as the stage of sedimentation: terrestrial asphaltenes are enriched in carbon and hydrogen, while sapropelic asphaltenes contain more oxygen (heteroelements). It is discovered that the formation of the two evolutionary catagenetic branches of asphaltene compositions corresponds to the onset of protocatagenesis. Both sapropelic and terrestrial OM undergo different transformations during diagenesis (at the sediment–protocatagenesis interface), with sapropelic OM subjected mainly to drastic carbonation with parallel hydrogenation, while redistribution of oxygen and hydrogen concentrations associated with a dramatic loss of the latter observed in the terrestrial OM (if the of carbon concentration level is constant). Further changes in the composition of asphaltenes within these branches take place during the mesocatagenesis through apocatagenesis, during which the evolutionary branches converge again.

In the Neoproterozoic of the Aldan-Maya depression, the rocks of the Malgin (MF), Tsipanda (TF) and Kumakha (KF) Formations are enriched in organic matter (OM) and can be classified as source rocks. High generation potential is typical for the MF and TF (267–511 mg HC/g TOC). The thermal maturity level of OM corresponds to MC12 grade (Tmax is 438–443ºC). Based on the biomarker distribution, the biological precursors of OM in these formations are mostly prokaryotes, including cyanobacteria (hopanes, acyclic biomarkers) and to a lesser extent eukaryotes (the presence of steranes С27-C30) that lived in the Precambrian (the presence of 12- and 13-monomethylalkanes) marine (absence of continental biomarkers, the distributions of acyclic alkanes and steranes) basin with clayey sedimentation (high content of diasteranes). The absence of steranes in some samples (the absence of eukaryotes in the source OM), the MF is likely to have been partly deposited before the emergence of eukaryotes. Most samples have elevated concentrations of low-molecular tricyclanes (2C19-20/C23-26>1), which can be attributed to the specificity of the source biota, although it is not typical for marine OM. A rare homologous series of 2,7-dimethylalkanes that has been recently found by other researchers in some Precambrian strata is present in several samples of the MF and KF and totally absent from all samples of the TF. This may indicate the differences in its biota, depositional environments or its evolution during diagenesis and catagenesis. A distinctive feature of the TF is the high content of ethylcholestanes (C29/C27=2.5).

Актуальность исследования обусловлена необходимостью расширения ресурсной базы в месторождениях Байкитской антеклизы. Нахождение двух типов нефтей может быть обязано дополнительному источнику, что повышает перспективы района. Однако вариации в составе нефтей могут быть также связаны с высоким катагенезом и миграционными эффектами, поэтому необходима оценка влияния этих факторов на состав нефтей. Цель: определить влияние генетического, катагенетического и миграционного факторов на углеводороды-биомаркеры нефтей Байкитской антеклизы, выделить районы преимущественного влияния каждого из них. Объекты: нефти Байкитской антеклизы. Методы: сопоставление характеристик углеводородов-биомаркеров, полученных с помощью хромато-масс-спектрометрии, в насыщенной и ароматической фракциях нефтей, оценка влияния на их состав вклада из разных нефтематеринских формаций, катагенеза и миграции, группировка нефтей по преобладанию влияния этих факторов. Результаты. Дана характеристика углеводородов-биомаркеров насыщенной и ароматической фракций нефтей рифейских и вендских коллекторов Байкитской антеклизы. На основании этих характеристик, отличающихся от полученных ранее характеристик наиболее распространенных и типичных древних нефтей Сибирской платформы, сделано заключение о влиянии вклада из верхнерифейской ирэмэкенской толщи в двух нефтях на востоке Куюмбинского месторождения, а также влияние вклада из вероятно вендских нефтематеринских формаций в нефтях из вендских коллекторов. Главными фактором формирования состава большинства нефтей Куюмбинского месторождения был высокий катагенез, усиленный за счет миграционных эффектов в сторону обогащения низкомолекулярными соединениями. Вероятно, несколько нефтей являются смесью двух компонентов, имеющих разный катагенез, причём более преобразованный обогащён насыщенными, в том числе циклическими, соединениями, а менее преобразованный – ароматическими.

The relevance of the research is conditioned by the necessity to expand the resource base of the Russian Far East. The study of sedimentary basins and their hydrocarbon potential, the development of new forecast technologies for traditional and unconventional hydrocarbon fields is a priority for the Russian Academy of Sciences for many years. The evaluation of source rocks based on levels of their enrichment with the organic matter and its generation potential will provide valuable data for basin modeling. Besides, given that the Ushumunskoe source rocks have not been studied by organic geochemical methods, the present study sets out to clarify the conditions of the organic matter accumulation, and to reconstruct landscapes and biota in the Cenozoic Era. The aim of the research is to characterize the biological source of the organic matter, conditions of its accumulation, diagenetic settings and the level of the Ushumunskoe source rocks maturity. Objects of the research are the Ushumunskoe coals, clays and siltstones from the Middle Amur sedimentary basin. Methods: comparison of the results of pyrolysis and isotope analysis of the organic matter and characteristics of biomarker hydrocarbons obtained using chromatography-mass spectrometry in saturated and aromatic fractions of bitumen extracts, evaluation of sources, as well as diagenetic and catagenetic conditions of organic matter. Results. The Paleogene-Neogene source rocks of the Ushumunskoe brown coal field in the Middle Amur sedimentary basin were studied by the methods of organic geochemistry for the first time. The organic matter of the studied samples has signs of both terrestrial and sapropelic types. The organic carbon isotopic composition, n-alkanes distribution, the presence of kaurane, beyerane, phyllocladanes (biomarkers of higher plants Podocarpaceae and Araucareaceae) in the saturated fraction of extractable bitumens, retene (biomarker of conifers) in the aromatic fraction indicate the terrestrial (humic) nature of organic matter. At the same time, in most samples the aromatic fraction characteristics correspond to the sapropelic organic matter, which is evidenced by low concentrations of phenanthrenes, high concentrations of mono- and triaromatic steroids, distributions of methyldibenzothiophenes, and probable presence of long-chain alkylnaphthalenes (biomarkers of lake algae Botryococcus braunii). Phytane concentrations are significantly higher, than pristane, and half of the samples according to the hydrogen index (HI) values belong to type II. Due to the absence of marine deposits in the study area, type II is probably a mixture of type I (lacustrine) and III (continental). Moreover, judging by the HI variations throughout the section, depositional environments changed repeatedly from lacustrine to peatbog and vice versa. In some samples, the maxima in the acyclic isoprenoids fall on i-C-21 and i-C-22, possibly due to the significant contribution of archea to the original living substance. According to the high concentrations of dibenzothiophenes, the organic matter underwent diagenesis with high content of hydrogen sulfide in sediment. Probably, the duality of signatures (terrestrial and sapropelic) is associated with the specificity of the initial biota in this basin and is characteristic of its age and/or geographical localization. The vitrinite reflectance data, pyrolytic characteristics, high carbon preference index in n-alkanes, the presence of biohopanes and hopenes, almost complete absence of typical steranes and terpanes, and distribution of triaromatic steroids are interpreted as indications of immature organic matter, with the latter potentially enhancing such a duality of characteristics.

The relevance of the research is caused by the need to expand the resource base in the fields of the Baykit anteclise. Occurrence of two types of oils may be caused by additional source, which increases the prospects of the area. However, variations in the composition of oils may also be associated with high catagenesis and migration effects; therefore, an assessment of the influence of these factors on composition of oils is necessary. The aim of research is to determine the influence of genetic, catagenetic and migration factors on biomarker hydrocarbons in the oils of the Baykit anteclise, to identify areas of preferential influence of each of them. Objects of the research are the oils of the Baykit anteclise. Methods: comparison of the characteristics of biomarker hydrocarbons obtained using gas chromarography-mass spectrometry in saturated and aromatic fractions of oils, assessment of the impact on their composition of the contribution from different source formations, catagenesis and migration, grouping of oils by the predominance of the influence of these factors. Results. The author has characterized biomarker hydrocarbons of saturated and aromatic fractions of the oils from Riphean and Vendian collectors of the Baykit anteclise. Based on the characteristics, which differ from the previously obtained characteristics of the most common and typical ancient oils of the Siberian platform, the author made a conclusion on the impact of the contribution from the Upper Riphean Iremekensky stratum in two oils in the east of the Kuyumbinskoye field, as well as the contribution of probably Vendian oil source formations in oils from Vendian collectors. The main factor in the formation of the composition of most oils of the Kuyumbinskoe field was high catagenesis, enhanced by migration effects towards the enrichment of low molecular weight compounds. Probably, several oils are a mixture of two components with different catagenesis, moreover, more transformed component is enriched with saturated, including cyclic compounds, and less transformed - with aromatic compounds.

Актуальность исследования обусловлена необходимостью расширения российской ресурсной базы Дальнего Востока. Изучение осадочных бассейнов и их углеводородного потенциала, разработка новых технологий прогноза традиционных и нетрадиционных месторождений углеводородного сырья остается приоритетным направлением Российской АН на многие годы. Оценка обогащенности пород органическим веществом и его генерационного потенциала поможет в работах по бассейновому моделированию. Настоящие исследования нужны также для: уточнения обстановок накопления органического вещества; реконструкции ландшафтов и биологического мира в кайнозое. Цель: охарактеризовать биологический источник органического вещества, условия его накопления, обстановки диагенеза и уровень катагенетической зрелости в породах Ушумунского буроугольного месторождения. Объекты: угли, глины и алевриты Ушумунского буроугольного месторождения Среднеамурского осадочного бассейна. Методы: сопоставление данных пиролиза и изотопного анализа органического вещества и характеристик углеводородов-биомаркеров, полученных с помощью хромато-масс-спектрометрии в насыщенной и ароматической фракциях битумоидов, оценка источников, диагенетических обстановок и катагенетической преобразованности органического вещества. Результаты. Породы палеогена и неогена Ушумунского буроугольного месторождения Среднеамурского осадочного бассейна впервые изучены методами органической геохимии. Органическое вещество исследованных образцов имеет признаки как террагенного (гумусового), так и аквагенного (сапропелевого) типов. Изотопный состав углерода органического вещества, распределение н-алканов, наличие каурана, биерана, филлокладанов (биомаркеров высших растений Podocarpaceae и Araucareaceae) в насыщенной фракции битумоидов, ретена (биомаркера хвойных растений) в ароматической фракции свидетельствуют о террагенной природе органического вещества. Вместе с тем в большинстве образцов характеристики ароматической фракции соответствуют аквагенному органическому веществу: низкие концентрации фенантренов, высокие – моно- и триароматических стероидов, распределение метилдибензотиофенов, вероятное присутствие длинноцепочечных алкилнафталинов – биомаркеров озерных водорослей Gloeocapsomorpha prisca и Botryococcus braunii. Также в большинстве образцов концентрации фитана значительно выше, чем пристана, и половина образцов согласно водородному индексу HI относится к типу II (аквагенный морской). Морских отложений в районе исследований нет, по-видимому, тип II является смесью типов I (аквагенный озерный) III (континетальный). Причем, судя по изменениям HI по разрезу, режим осадконакопления менялся неоднократно с озерного до торфяно-болотного и обратно. В ряде образцов максимумы в составе ациклических изопреноидов приходятся на i-С21 и i-С22, возможно, из-за значительного вклада организмов домена археа в исходное живое вещество. Согласно высоким концентрациям дибензотиофенов, органическое вещество пережило диагенез с избытком серы в осадке. Вероятно, двойственность признаков (террагенные и аквагенные) связана со специфичностью исходной биоты этого бассейна и является характерной для ее возрастной и/или географической локализации. Низкие значения показателей отражательной способности витринита, пиролитические характеристики, резкое преобладание соединений с нечетным числом атомов в молекуле в н-алканах, наличие биогопанов и гопенов при почти полном отсутствии типичных стеранов и терпанов, распределение триароматических стероидов соответствуют катагенетически незрелому органическому веществу, и, возможно, недостаточная зрелость усиливает эту двойственность характеристик.

We present results of lithological and geochemical studies of Paleozoic deposits stripped by drilling within the Ledyanskaya area in the north of the Tunguska syneclise. The studied section has a terrigenous sulfate-carbonate composition and is complicated by trap intrusions. We have established that the Ordovician-Devonian sedimentation proceeded within an epicontinental basin, with its depth varying from supralittoral to lower sublittoral zones. In the Carboniferous and Permian, coastal-continental sedimentation was predominant; in the Late Permian it was accompanied by volcanic activity. Analysis of the poroperm properties of rocks has distinguished three potential oil reservoirs: Silurian reef carbonate deposits and Ordovician and Carboniferous sand horizons. The Lower Silurian argillaceous-carbonate rocks and Devonian carbonate-sulfate-clay members, halite beds, dolerite bodies, and tuffaceous rocks are probably confining beds of these reservoirs. Geochemical study of organic matter has shown several possible sources of hydrocarbons: Upper Proterozoic deposits, Lower and Middle Cambrian Kuonamka complex, Middle Devonian Yukta Formation, and Upper Paleozoic coal-bearing deposits. (C) 2017, V. S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.