Chemical composition of bottom sediments and pore waters of organic-mineral sediments (sapropel) of Lake Kotokel (Eastern Baikal region) has been studied, based on long drilling cores, 14.5 and 16.5 m. A reduction type of diagenesis has been established, during which destruction of organic matter, transformation of the chemical composition of pore waters and the formation of authigenic minerals occur. Even in the uppermost intervals of sapropel, organic matter is being profoundly transformed and differs significantly in composition from that of bioproducers (plankton). The major role in diagenetic transformations of organic matter belongs to different physiological groups of microorganisms, primarily heterotrophic, amonifying and sulfate-reducing bacteria. During diagenesis, the basic chemical composition of pore waters (HCO3-, SO42-, Cl-, Ca2+, Mg2+, K+, Na+) changes, trace elements (Fe, Mn, Sr, Ba, Pb, As, Co, Ni) redistribute, concentrations of HCO3-, NH4+, PO43- and Si increase; this is caused by destruction of organic matter. In the process of bacterial sulfate reduction in pore waters, the concentration of SO42- decreases along the depth of the section, and in the sediment the proportion of reduced forms of sulfur increases and the isotopic composition of sulphur delta 34S changes. Transformation of chemical composition of pore waters and the activity of microorganisms leads to the formation of authigenic pyrite, rhodochrosite, and barite.

Purpose. The article presents the results of a comprehensive analysis of iron ore fragments found during the explorations of mound no. 51 of the Ust-Tartas site (Vengerovsky distric, Novosibirsk region). The fragments presented shapeless rock debris with ferruginous oxides and a specific. Two fragments turned out to be slag. Three fragments come from burial no. 17 while others were found in the mound fill and the arable layer, obviously moved from their original location. The samples were studied using binocular microscopy, X-ray phase analysis and scanning electron microscopy with energy-dispersive spectrometry.Results. According to the study, the presented goethite ores samples were classified as sedimentary swamp-lake ores of regional and local origin, which is characterized by a lower melting point and high quality of smelted iron. Apparently, the region landscape features made it possible to extract bog ore in the immediate vicinity of the places where the craftsmen lived. It has been suggested that the identified artifacts the professional activity of a Sargat community related to metal production, buried in the investigated mound or participat in the funeral ceremony.Conclusion. The studied site is of great scientific importance for the study of the Sargat culture, as a whole, and the phenomena associated with the Sargat society life. The importance of the methodological component of the samples study should also be emphasized.

—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.

This paper presents results of biogeochemical investigation of the Holocene organic-rich sapropelic sediments of Lake Dukhovoe situated not far from the Baikal. The main source of organic matter in Lake Dukhovoe is phytoplankton, which serves as a biogeochemical barrier where elements are accumulated from water and then buried in the bottom sediments. Microorganisms (e.g., bacteria, micromycete and actinomycetes) play significant role in decomposition of organic matter and formation of organic-mineral complexes in four distinguished types of sapropels: organic, organic-mineral, mineral-organic and mineral. Diagenetic transformations of the Lake Dukhovoe sapropels under influence of mechanical, biochemical, microbiological and physicochemical processes lead to transformation of element speciation. A boundary between oxidizing and reducing diagenesis conditions is at the depth of 167 cm in the sapropel core. Change of the conditions forms geochemical barrier in bottom sediments and control the formation of secondary phases (organic-mineral complexes, diatomite, framboidal pyrite, vivianite, carbonates, etc.) as well as processes of accumulation and leaching of chemical elements. Additionally, high contents of Fe, Mn, Cu, Zn, Pb, Cd, and Mo in the upper 10 cm of the sapropel might have been caused by forest fires and anthropogenic factors. The fact of marcasite formation in the stomatocysts of Chrysophyte algae (golden algae) is new and was established for the first time. Based on the results and geochemical equilibrium modelling, the stomatocysts of Chrysophyte algae can be considered as a microreactor for iron sulfide formation.

Abstract. We present the results of study the Holocene sediments of Itkul Lake, a shal low brackish lake with carbonate sedimentation, located in the eastern part of Baraba lowland (Southwestern Siberia, Novosibirsk Region). A 1.8 m thick core of the Holocene (7.9 14C yr) sediments of Itkul Lake has been studied. Based on the geochemical and lithostratigraphic properties of the bottom sediments, we have established the following stages of the lake evolution: (I) the beginning of sedimentation, 7.8 7.0 14 ka; (II) extreme shallowing with a probable complete drying, ~7.0 5.5 14 ka; (III) rise in the water level, ~5.5 4.3 14 ka; (IV) repeated shallowing, 4.3 2.8 14 ka; and (V) subsequent watering, 2.8 0 14 ka. At present, the lake again tends to shallowing.

Abstract. Our study of the Holocene sediments of shallow saline Lake Bolshoy Bagan located revealed the following stages of the lake evolution: (I) Appearance and maturing of the lake 9.1 5.8 ka BP; (II) rise in water level 5.8 2.3 ka BP; and (III) shallowed lake 2.3 0 ka BP.

The paper presents data on the geochemical processes of postsedimentation transformations of boggy deposits at early diagenesis and the redistribution of chemical elements, including biogenic ones, in the Holocene sections of peat bogs in the Baraba forest-steppe in southern West Siberia. The contents of Fe, Mn, Pb, Hg, Sb, Cd, Cu, and Zn were found out to increase in the upper layers of the peat, whereas the S, N, Ca, and Sr concentrations increase in the middle parts of the peat profiles. The distribution character of various physiological groups of microorganisms in the peat profiles of Ubinskoe and Sherstobitovo peatlands lead to the conclusion that the nitrogen and carbon cycles are more active than that of sulfur. The activity of microorganisms leads to a decrease in pH and Eh in the vertical sections of the peatlands. The high values of $${\text{N}}{{{\text{H}}}_{4}}^{ + }$$ , $${\text{NO}}_{3}^{ - }$$ , TOC, and the chemical oxygen demand in the bog waters of Ubinskoe and Sherstobitovo bogs indicate that active biochemical decomposition and oxidation of organic matter proceed in these bogs. According to their predominant ions, the waters of the bogs belong to the hydrocarbonate class of the calcium group and are characterized by elevated concentrations of Al, Fe, Cu, and Zn, which is caused by the acid composition of the waters. The low pH values of the bog waters and the oxidizing environment facilitated the development of goethite–hydrogoethite mineralization in the upper horizon of peat profiles. The formation of hematite and anhydrite in the middle parts of the peat profiles was probably caused by paleofires. The authigenic minerals formed in the process of early diagenesis are, first of all, pyrite and less often siderite, calcite, and kaolinite. Under reducing conditions, nanoparticles of native Ni and Ni–Cr intermetallic compounds can be formed, and amorphous silica can be deposited at the dissolution of aluminosilicate minerals from the upper peat horizons.

—A 1.8 m thick core of the Holocene (7.9 14C kyr BP) sediments of Lake Itkul’ (Novosibirsk Region) has been studied. Based on the geochemical and lithostratigraphic properties of the bottom sediments, we have established the following stages of the lake evolution: (1) the beginning of sedimentation, 7.8–7.0 14С kyr BP; (2) extreme shallowing with a probable complete drying, ~7.0–5.5 14С ky BP; (3) rise in the water level, ~5.5–4.3 14С kyr BP; (4) repeated shallowing, 4.3–2.8 14С kyr BP; and (5) subsequent watering, 2.8–0 14С kyr BP. At present, the lake again tends to shallowing. We have established that Lake Itkul’ has mineral sediments with a high content of carbonates (up to 64%). The high concentrations of HCO3– and Ca2+ and stable saturation (S/St > 1) of the surface water cause a shift of the carbonate– calcium equilibrium toward the carbonate formation. The studied authigenic carbonates are aragonite and fine-grained aggregates of poorly crystallized calcite particles with different Mg contents. Aragonite is both biogenic (mollusk and ostracode shells) and chemogenic (formed during the lake shallowing). In addition to carbonates, the lacustrine sediments contain mixed-layer aluminosilicates, feldspars, and quartz. The presence of pyrite throughout the sediment section indicates reducing conditions and the activity of sulfate-reducing microorganisms. Carbonates (especially aragonite) are significantly enriched in strontium. Manganese does not form its own minerals but is present as an isomorphic impurity in authigenic carbonates.

Sorption of uranyl ions from uranyl nitrate UO2(NO3)2 · 6H2O solutions by natural and synthetic layered silicates was studied by X-ray diffraction, IR spectroscopy, and high-resolution inductively coupled plasma mass spectrometry. The modifications of some structural parameters of the studied species after they were reacted with uranyl ions are due to a partial incorporation of uranyls into the interlayer spaces of the smectite structure, or the rotation of the tetrahedra of a tetrahedral network and the distortion of octahedra in an octahedral layer. The natural bottom clay samples from the Pacific Ocean and the Sea of Okhotsk have the best sorption properties. This is due to structural defects and the formation of uranium complexes with the iron ions of the smectite structure. Iron present in clay minerals improves their sorption potentials.

На основании минерального состава колонки донных отложений IV озерка оз. Фумарольное проведена палеореконструкция условий формирования осадков. Нижние горизонты отложений сложены преимущественно смектитом в ассоциации с гипсом и ярозитом и перекрыты смектит-каолинитовыми отложениями с большим количеством фрамбоидального пирита и створок диатомовых водорослей. Присутствует слой натечных опал-пиритовых образований и кальцита. Сделан вывод о том, что изначально озерко IV представляло собой грязевой котел с сульфидсодержащими растворами. Затем при снижении уровня воды и выведении донных отложений на поверхность произошло их окисление. Последовавший фреатический взрыв привел к перекрытию окисленных отложений восстановленным веществом нижних горизонтов котла. Далее обстановка осадконакопления сначала соответствовала источнику с развивающимся вокруг грифона циано-бактериальным сообществом, затем сменилась обстановкой мелководного озерка, аналогичной современной. В осадке наблюдаются два слоя пирокластического материала от извержений недалеко расположенных вулканов.

Paleoreconstruction of events involved in the bottom sedimentation has been carried out on the basis of mineral composition of the section of the minor lake IV (Lake Fumarolnoe, Kamchatka) bottom sediments. The lower sediments are composed mainly of smectite in association with gypsum and jarosite; they are overlain by smectite–kaolinite with a large amount of framboidal pyrite and diatom shells. There is also a layer of sinter opal–pyrite units and calcite. It is concluded that initially the minor lake IV was a mud pit with sulfide-bearing solutions. Then, after the lowering of the water level and the partial exposure of the bottom sediments on the surface, the latter were oxidized. The subsequent phreatic explosion provided the covering of oxidized sediments with the reduced substance from the lower horizons of the pit. Further setting of sediment accumulation corresponded to a source with cyanobacterial community developing around the gryphon, and then it changed to that of a shallow-water lake similar to a contemporary one. Sediments also include two layers of pyroclastic material originated from eruptions of neighboring volcanoes.

A crystallochemical analysis of synthetic layered lithium-containing silicates has been performed. It is shown that these compounds have unique properties and structural characteristics. According to the X-ray diffraction data, the initial material possess a layered structure. After filling the material with ethylene glycol, the intensity of the reflection corresponding to the interplanar spacing d001 = 12.3 Å significantly decreased, and two additional peaks arose: strong (d = 16.8 Å) and weak (d = 14.7 Å), which indicates possible presence of three layered phases with different sorption properties in the sample. The samples easily absorb moisture from air. The range of stretching vibrations of OH groups in the IR spectra of synthesized samples corresponds to the spectrum of adsorbed water.

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.