Vol 280

The study is devoted to the quantitative assessment of organic carbon (C_org) deposition rates in the bottom sediments of small lakes located in the south of Western Siberia. The studied water bodies cover a wide range of landscape-climatic conditions and types of sedimentation environments. Despite their local dimensions, the small lakes of the region demonstrate exceptionally high efficiency of long-term carbon burial. It is shown that their capacity to accumulate C_org is comparable to or even exceeds that of such recognized carbon depots as bogs and marine shelves. The work is based on a comprehensive analysis of bottom sediments, including radiometric dating (Pb-210, Cs-137) to determine sedimentation rates and layer ages, as well as morphological, elemental (CHNS analysis), and X-ray diffraction analyses. According to the obtained data, the average C_org deposition rate in the studied lakes reaches 462±29 g/m² per year. It has been established that the majority of carbon (> 50 % in most cases) accumulates specifically in the form of organic matter, even in lakes with intensive intra-basin (authigenic) carbonate formation. The study revealed the main factors controlling carbon accumulation: productivity of aquatic communities (phytoplankton, zooplankton, macrophytes), total sedimentation rate, sediment ash content (mineral fraction proportion), and local morphometric features of the lakes (depth, basin shape). The absence of a clear dependence of carbon deposition rates on landscape zonality underscores the critical importance of considering local conditions when modeling the contribution of small lakes to the global carbon cycle. The obtained results substantially fill gaps in regional carbon assessment and prove the significance of small lakes in the south of Western Siberia as highly efficient and stable natural depots of organic carbon under conditions of continental sedimentation.

This work is devoted to the study of fossil resins from the collection of the Mining Museum using infrared spectroscopy (FTIR). Samples of amber from the Iset River in the Middle Urals, collected in the early 19th century and known as “Kolchedan amber”, were examined. For comparison, fossil resins from other localities in Northern Eurasia were studied: the Peschanka River on the coast of the Barents Sea, the Amderma River on the Yugorsky Peninsula, and the Khatanga River on the Taimyr Peninsula. The obtained data indicate that “Kolchedan amber” belongs to an independent and widespread type of fossil resin in Northern Eurasia, the finds of which are confined to Cretaceous deposits. Previously, this type of resin was identified as “krantzite” for the locality on the Iset River or as “retinite” for localities on the coast of the Arctic Ocean. A comparison with other mineral species of fossil resins is carried out in this work. An analysis of the absorption peaks in the IR spectrum suggests that, according to K.Anderson’s resin classification, “Kolchedan amber” belongs to Class I, which is represented by resins with a predominance of labdane-type diterpenoids. A distinctive and most characteristic feature of the IR spectrum of “Kolchedan amber” is a “comb” consisting of three approximately equal absorption peaks at 936, 909, and 888 cm^–1. An analysis of the systematically significant features of the IR spectrum indicates that the most likely biological source of this type of fossil resin was plants from the Pinaceae family. An additional argument supporting such a biological origin is the comparison of the diagnostic region of the IR spectrum of “Kolchedan amber” with the spectrum of amber from Axel Heiberg Island in the Canadian Arctic, which originated from the resin of the genus Pseudolarix.

This research investigates the operational performance of ejection systems integrated into drilling rock-breaking assemblies. The object of the study is a near-bit reaming-ejection device (RED), which is installed in the bottom hole assembly (BHA) and is intended to improve bottom hole cleaning efficiency during drilling through the operation of integrated ejection systems that ensure effective entrainment of drilling fluid jets from the near-bit region enriched with drilled cuttings and fragmented rock. The subject of the study is the flow of drilling fluid through ejection nozzles with different cross-sectional geometries, which determine the hydrodynamic characteristics of the fluid flow. The design of the near-bit RED combines two systems – a drilling reamer and ejection devices – which makes it possible to reduce the space occupied within the BHA, improve borehole diameter stabilization, and enhance bottom hole cleaning efficiency simultaneously. Computational fluid dynamics simulations of ejection nozzles with various cross-sectional geometries (circle, triangle, square, pentagon, regular hexagon, and specially oriented hexagon) showed that the increase in the velocity of the fluid-flow core issuing from the nozzle model with a specially oriented hexagonal cross-section amounted to approximately 4.5 % compared with the baseline design (circular cross-section) and approximately 5.5 % compared with the remaining models. It was found that the nozzle design with a specially oriented hexagonal cross-section enables the fluid flow to be directed at an angle toward the borehole wall. The results of additional computational fluid dynamic simulations made it possible to establish a relationship between the angle of deviation of the drilling fluid flow from the vertical and the value of the control angle of the specially oriented hexagonal cross-section of the ejection nozzle. This relationship provides an opportunity for purposeful control of the drilling fluid trajectory through modification of the nozzle geometry. This capability may be used for additional sealing of borehole walls without significant deviation from the designed borehole diameter.

This article presents an experimental study of the effect of chromium (III) oxide, recovered from chromium-containing catalyst sludge, on the properties of grouting mortars used for well cementing in permafrost zones. The necessity of modifying grouting mortars to increase the strength of the cement stone for intervals in permafrost formations is justified. A method for reducing Cr(VI) to the stable form Cr(III) has been developed, and Cr₂O₃ has been obtained for use as an active mineral additive. Four grouting mixture compositions are considered: a base mixture, commonly used at sites, based on Portland cement with a setting accelerator; a mixture based on Portland cement; a mixture based on Portland cement with the addition of chromium (III) oxide; and a mixture based on Portland cement with calcium chloride and the addition of chromium (III) oxide. The experiments include testing of the four compositions at two water-to-solid ratios (W/S = 0.4 and 0.5) with an assessment of flowability, compressive and flexural strength, microstructure (microtomography, SEM) and phase composition (XRD) at normal and sub-zero temperatures, including cyclic temperature changes. The data obtained show that at W/S = 0.5, the addition of Cr₂O₃ increases the compressive and flexural strength of the cement stone; a reduction in the content of free Ca(OH)₂ is observed, the proportion of calcium silicate hydrates (CSH) increases, and a more homogeneous and dense microstructure is evident. This modification increases the flowability of the grout, which facilitates better replacement of the drilling fluid. The use of Cr₂O₃ to improve the durability and watertightness of support structures in cryolithozone conditions is clearly advisable.

Climate is one of the key factors controlling sediment accumulation in lacustrine ecosystems. Integrated studies of continuous lake-sediment cores, including radiocarbon dating, grain-size analysis, mineralogical and chemical characterization, and measurements of magnetic properties, enable reconstructions of sedimentation conditions during the Late Quaternary. Such studies are particularly relevant for lakes of the Southern Urals, which are located near a climatic divide and for which episodes of increasing/decreasing moisture have been interpreted inconsistently. This paper presents data on the age, material composition, and genetic features of bottom sediments from lakes Bolshoye Miassovo and Maloye Miassovo. The results show that, based on grain-size distribution, mineral composition, and inorganic geochemistry, the studied lacustrine sediments exhibit a pattern typical of freshwater lakes – the predominance of allothigenic silt-sized particles. This is supported by the structure of allothigenic-input factor F1 derived from factor analysis. Quaternary deposits represented by eluvial, slopewash, colluvial, and alluvial facies were identified as the main source of allothigenic material for the investigated basins. The ICV index and the A-CN-K diagram indicate that the sediments formed predominantly from stable allothigenic minerals of the primary sedimentation cycle, sourced mainly from Quaternary deposits and exposed pre-Quaternary rocks. The transport pathways of allothigenic material are linked to the directions of slope flows and channel networks visible on the Quaternary-deposit map. The integrated analysis allowed us to identify the most informative proxies and to correlate them with global and regional climatic stages and events, including the Bølling warming (~14,700 cal. yr BP), the ~8200 cal. yr BP cooling event, aridization in the Southern Urals (~2000 cal. yr BP), and Bond Event 1 (~1500 cal. yr BP). Additional climate-arid events were identified at ~11,430, ~6100, ~4250, ~3537, and ~1065 cal. yr BP.