Катагенез органического вещества юрско-меловых отложений юго-запада Енисей-Хатангского регионального прогиба1 Институт нефтегазовой геологии и

—A 6-meter core of the Holocene sediments in Lake Dukhovoe is studied. The material composition of the core is heterogeneous and has clear bedding. Lacustrine sediments are represented by the upper 293 cm. Each bed of the sediments is subjected to microbiological analysis. A high total number of heterotrophic bacteria is revealed in the upper (0–15 cm) and deeper (110–150 cm) sapropel intervals. Sulfate-reducing bacteria are identified only in Chrysophyceae cysts. The CaO/Fe2O3 ratio shows the degree of “carbonate content” of bottom sediments. It is low in the lake sapropel (0.2), which indicates the geochemical specificity (carbonate-free sapropel). Na, Mg, Al, Si, Al, Ca, Fe, Mn, Zr, and Cr concentrations in sapropel are within the average concentrations for the Earth’s crust, shale, and oceanic pelagic clays, while U and Mo concentrations exceed them. Phytoplankton is enriched in phosphorus (biogenic element) and chalcophile elements (Zn, Cd, Sn, Sb, Hg, Pb, and Cu), which characterize the pollution of the modern atmosphere of the Baikal region. Diagenetic processes result in the transformation of the pore waters, namely an increase in mineralization as compared to lake water, an increase in the concentrations of biogenic components (HCO3-, NH4+, NO3-, and PO43-) and a decrease in SO42-. Pyrite framboid accumulations are revealed in organomineral sediments below the horizon of 200 cm, and iron phosphates represented by vivianite are identified in sapropel.

Two cores of the Dulikha peat bog deposits, 4.0 and 5.2 m thick, were studied in detail. The reduction type of diagenesis has been established. Decomposition of the organic matter of the bog deposits begins already in the upper intervals of the section at the earliest stages of diagenesis. Microbiological studies of the peat bog revealed numerous organotrophic, ammonifying, nitrifying, and phosphate-mobilizing microorganisms as well as Fe-Ox and Mn-Ox microorganisms and showed the almost complete absence of sulfate-reducing bacteria (except for the lower intervals of the peat section). The processes of the nitrogen, phosphorus, and carbon cycles are more active than the sulfur cycle processes. The chemical composition of the bog water changes during diagenesis. The contents of HCO3-, NH4+, PO43-, NO3-, and C-org increase in the peat bog section, which is the result of the destruction of organic matter, leading to the transition of the most mobile and labile components into the bog water. The results of physicochemical modeling show that the high content of organic matter significantly changes the chemical composition of the bog water. The enrichment of the latter in Cu, Zn, Sr, Ba, As, Si, Al, and Pb indicates a diagenetic transformation of the bog deposits. A change of oxidizing conditions by reducing ones in the peat bog leads to the reduction of oxidized Fe (III) and Mn (IV) forms to mobile Fe (II) and Mn (II) forms and their subsequent migration from the solid phase of deposits into the bog water. With depth, the reduced S (II) forms become predominant in the peat, which indicates more reducing environmental conditions. The concentration of SO42- decreases in the pore water of the peat-underlying mineral deposits, which marks the beginning of sulfate reduction. This process, however, is very slow in the bog deposits because of the acid environmental conditions and the lower degree of transformation of organic matter.

Пиролитическим методом в варианте Рок Эвал (RE-пиролиз) изучена коллекция торфов Гурского месторождения (Нижнее Приамурье) на ранних этапах диагенеза (в интервале глубин 0–350 см), а также продуцентов органического вещества (ОВ). Пирограммы ОВ торфов являются суперпозицией трех пиков — низкотемпературного с температурой выделения углеводородов ниже 300 о С, промежуточного — в интервале 300–400 о С и высокотемпературного при температуре выше 400 о С. Эти пики представлены липидной, лабильной и керогеновой составляющими ОВ соответственно. Диагенетическая трансформация ОВ сопровождается постепенным уменьшением липидной и лабильной компонент и одновременным возрастанием керогеновой. Наиболее интенсивно этот процесс протекает в верхней части исследованного разреза.

Rock–Eval pyrolysis data were obtained on a collection of peat samples at various diagenesis stages (from depths of 0–350 cm) from the Gurskoe deposit, lower Amur area, and on producers of organic matter (OM). The pyrograms of the peat OM are superpositions of three peaks: (1) a low-temperature one, with temperatures of hydrocarbon release lower than 300°C, (2) an intermediate-temperature peak, with hydrocarbons released at 300–400°C, and (3) a high-temperature one, corresponding to hydrocarbon release at temperatures above 400°C. The peaks correspond to the lipid, labile, and kerogen OM components, respectively. The diagenetic transformation of OM is associated with a gradual decrease in the contents of the lipid and labile components and an increase in the content of the kerogen component. The process is the most intense in the upper part of the vertical section.

—We present results of study of the chemical composition of organic matter (C, H, N, and S) from Holocene sections of lake sapropels with undisturbed stratification penetrated by vibratory drilling of the bottom sediments, down to the underlying rocks, of Lakes Bol’shie Toroki (1.8 m), Minzelinskoe (5 m), Ochki (4.5 m), Dukhovoe (7 m), and Kotokel’ (6 m). We consider methodological approaches to the identification of the sources and genesis of buried organic matter in marine and lacustrine sediments by a number of organogeochemical indicators: data of a biological analysis (biostratification based on layer-by-layer determination of organic relics in bottom sediment sections); hydrocarbon biomarkers (molecular composition of normal aliphatic hydrocarbons (n-alkanes), nitrogen compounds of a protein complex, etc.); and C/N ratio reflecting a difference in the biochemical compositions of bioproducers. The results of biological analysis (biostratification) show that planktonogenic sapropel (phyto- and zooplankton, the autochthonous source of organic matter) in Lake Ochki formed for 10,760 years, and sphagnum and hypnum moss were supplied from the bogged shores (allochthonous source of organic matter). In Lake Minzelinskoe, peaty sapropel formed at the stage of a flooded lowland bog (5905 years ago); since 3980 years ago and till the present, macrophytogenic sapropel has formed. Pyrolytic study (RE pyrolysis and Pyr–GC–MS analysis) of bioproducers and sapropel from Lake Ochki has shown that phytoplankton and zooplankton were the main autochthonous source of OM in the lake, which is confirmed by the identified macromolecules of nitrogen compounds of different compositions. The presence of hopanes indicates the contribution of microorganisms to the formation of OM in the sediments. The organic matter of sapropel has a terrigenous component, which is confirmed by the presence of high-molecular odd-numbered n-alkanes, ketones, and methyl esters of fatty acid. The C/N ratios in the stratified sections of macrophytogenic sapropels of Lakes Bol’shie Toroki and Minzelinskoe fall in the range of values specific to higher aquatic and terrestrial vegetation (C/N = 15–18), whereas the C/N ratios in planktonogenic sapropel of Lake Dukhovoe are typical of marine and lake plankton (C/N = 5.7–8.6).

Organogenic sediments (sapropels) in lakes are characterized by a reduced type of diagenesis, during which organic compounds are decomposed, the chemical composition of the pore waters is modified, and authigenic minerals (first of all, pyrite) are formed. Pyrolysis data indicate that organic matter undergoes radical transformatons already in the uppermost sapropel layers, and the composition of this organic matter is principally different from the composition of the organic matter of the its producers. The sapropels contain kerogen, whose macromolecular structure starts to develop during the very early stages of diagenesis, in the horizon of unconsolidated sediment (0–5 cm). The main role in the diagenetic transformations of organic matter in sediments is played by various physiological groups of microorganisms, first of all, heterotrophic, which amonifying, and sulfate-reducing bacteria. SO42− and Fe2+ concentrations in the pore waters of the sediments are determined to decrease (because of bacterial sulfate reduction), while concentrations of reduced Fe and S species (pyrite) in the solid phase of the sediment, conversely, increase. Comparative analysis shows that, unlike sapropels in lakes in the Baikal area, sapropels in southern West Siberia are affected by more active sulfate reduction, which can depend on both the composition of the organic matter and the SO42− concentration in the pore waters.

The group composition of hydrocarbons (HC) and hetero compounds in the products of stepwise thermolysis of asphaltenes from crude oil of the Usa oilfield at temperatures of 120, 230, 370, 500 and 750°C has been studied. The volatile thermolysis products formed at each step of the process have been studied by gas chromatography–mass spectrometry. It has been found that the main products of stepwise thermolysis of asphaltene molecules are alkylbenzenes (AB) and saturated aliphatic hydrocarbons (SAH), aromatic fragments obtained at 370°C are mainly separate structural blocks of asphaltene molecules, and benzothiophenes (BT) predominate over dibenzothiophenes (DBT) as structural units of asphaltene molecules. It has been shown that with an increase in the process temperature, the alkylbenzenes/saturated aliphatic hydrocarbons ratio (AB/SAH + Alkenes) increases by a factor of 6 to 7; the phenanthrene/alkylbenzenes (PN/AB) ratio and the polycyclic aromatic hydrocarbons/alkylbenzenes (PAH/AB) ratio decrease by ten- and twofold, respectively; and the naphthalenes/alkylbenzenes (NP/AB) ratio increases by two times.

The results of the pyrolytic analysis of products of the organic matter of Sphagnum fuscum , fuscum peat, and humic acids separated from peat with the use of pyrolysis–chromatography–mass spectrometry in the Rock-Eval version are presented. It was shown that Sphagnum fuscum and peat differed only slightly in the degrees of chemical transformation. Benzene, phenol, and their alkyl-substituted homologues predominated in the thermal desorption products of humic acids upon pyrolysis to 400°C. Acetic acid, monohydric phenols, syringol, and guaiacol, which are the basic compounds in the high-temperature fraction, were formed on the pyrolysis humic acids to 700°C from the carbohydrate, phenylpropionic, and guaiacylpropane structural fragments.

The article presents the results of pyrolysis (Rock-Eval) and pyrolysis gas chromatography mass spectrometry analysis of organic matter (OM) in the Holocene sediments of the Black Sea. The studied samples represent two parts of the sedimentary column: coccolith ooze with 2.8% C-org at the top and sapropels oozes with 8.5% C-org at the bottom. The deposition of Holocene sediments was inferred to take place under euxinic conditions, which are more favorable for organic-matter preservation and sapropel deposition during the Old Black Sea stage. The results show that the modern processes of microbially mediated methane oxidation in the Old Black Sea oozes are interpreted as the main cause of their apparently lower degree of diagenetic transformation as compared to that of coccolith oozes. (C) 2017, V.S. Sobolev TOM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

We investigated organic matter (OM) of the Lower Cambrian Sinyaya Formation in the southeast of the Siberian Platform. The studied collection of rocks was divided into groups according to the contents of organic carbon, bitumens, and sulfur and lithologic characteristics. The content and distribution of saturated biomarkers were examined. Lanostanes C30, norlanostanes C29, 28,30-bisnorhopanes, and 2α- and 3β-methylhopanes have been identified in the bitumens. Relationships between the content of organic carbon and the distribution of hopanes, hopane ratios, and 2α-methylhopane index have been established. The conditions of sedimentation, diagenesis, and catagenesis of OM and the generation potential of the rocks have been estimated. It is shown that lanostanes, 28,30-bisnorhopanes, and methylhopanes can be used as biomarkers of the source rocks of the Sinyaya Formation and thus can help to determine the source of bitumens on the northern slope of the Aldan anteclise of the Siberian Platform.

Adamantane hydrocarbons have been isolated from Cenomanian heavy naphthenic oil of the Russkoe field using the thiocarbamide adduction method. Steam distillation of the oil has given a fraction (boiling range 105–150°C) containing 0.36 wt % adamantane, from which a concentrate containing 18.2 wt % C10–C14 adamantane derivatives has been obtained. Adamantane and its derivatives in the crude oil, oil fractions, and concentrate have been identified, and adamantane has been quantified using the gas chromatography—mass spectrometry technique.

Summary Describes the methodology and reconstruction results of the initial (at the beginning of mesokatagenesis) hydrocarbon potential of Bazhenov source rock in the central and southern areas of the West Siberian Basin. The methodology based on basin modeling technic, using pyrolytic and geophysical well logging data.