Nº 1 (2023)

On the basis of lithological and gas geochemical studies and a comprehensive interpretation of the available materials, the main factors of the formation and distribution of grain size distribution, water-physical properties, organic saturation, concentrations and geochemical parameters of hydrocarbon gases in seafloor sediments of geostructures of the western part of the East Siberian Sea are summarized and analyzed. It has been established that the sediments of the northern and central parts of the study area are represented by aleurite-pelites, the southern ‒ by aleurite-pelite-psamites with variations in C_org values ‒ 0.6–2.0%, natural humidity and density ‒ 18–43% and 1.5–2.0 g/cm³, open porosity ‒ 17–33%, the concentrations of methane and its homologues are 0.001–5.934 and 0.00003–0.0312 cm³/kg, the molecular mass of the hydrocarbons fraction, the “wetness”, “dryness” coefficients, and the coefficients of the transformation are 16.05–22.6 g/mol, 0.2–51%, 1–1999, 0.2–50.8 and δ¹³С‒СН₄ (–82.7…–38.4‰). Based on the values of gas geochemical parameters, eleven types of gas sources were identified in bottom sediments. In the process of research, it was found that the formation of hydrocarbon anomalies in sediments is mainly associated with their reservoir properties, C_org content and depths of their sampling, as well as with the complex influence of geological factors, the main of which are the gas saturation of the underlying sediments and the type of gas sources, discontinuous and plicative tectonics, geostructures position, thickness of Quaternary deposits, coal and gas content and age of the folded base. To a lesser extent, anomalies of hydrocarbon gases are associated with the lithological composition and density parameters of sediments.

The article presents the results of a study of changes in the chemical composition of Pleistocene sediments from Hole 858B, 38.6 m deep with a temperature gradient of 10‒11°C/m, drilled in the Middle Valley of the Juan de Fuca oceanic ridge (Northeast Pacific) in the “Dead Dog” hydrothermal field, in 20 m from “black smoker” with a temperature of 276°C. The content of petrogenic elements in these sediments was studied by XRD. For the first time, data on a large set of trace elements were obtained for this object using the ICP MS method. The change in the chemical composition of sediments occurred in the process of solution-rock interaction under conditions of a rapid increase in temperature downwards the section. In the Unit I, in its upper part (1.97‒10.41 m), the sediments are slightly altered at a temperature of about 17°C. In the lower part of the Unit I (12.70‒25.31 m) under conditions of average temperature (112‒197°C), the change in the content of petrogenic elements and trace elements is well pronounced. The chemical composition of the sediments of the Unit IIB and the Unit IID (25.31‒38.6 m) is most strongly changed in the temperature range from 112‒197°С to 320‒330°С. Changes in the content for most macroelements and trace elements in the sediments of Unit IIB and Unit IID are similar, with the difference that the decrease in the content of chemical elements is more pronounced in the sediments of the Unit IID. In them, the content of Cu, Zn, Ga, Rb, Sr, Ag, Cd, Sb, Cs, Ba, Tl, Bi, except for U, is significantly lower than in background sediments. The sediments of the the IID, as well as the sediments of the Unit IIB, contain less Ca, Na, K, P and more Mg. A lower content of chemical in these sediments can be considered as their removal from sediments under the process of solution-sediments interaction and enrichment of the solution with them, and their higher content, as its introduction into sediments from solution and, accordingly, depletion of these chemical elements in the solution. The results of studying the chemical composition of metalliferous sediments (Unit III, 0‒1.97 m) and sulfide layer IV (10.41‒12.70 m), as well as the chemical composition of unaltered background sediments from Holes 855A, C, D are presented.

This article provides the first modern overview of fossil resin finds in West Central Asia – far beyond the traditional resin-bearing areas, both in Russia and in northern Western Europe. Based on little-known facts and random references scattered in the geological literature, the main locations of fossil resins have been revisited and described, and the level of their study has been assessed. Peculiarities of molecular structure of fossil resins of Priaralie using IR spectroscopy has been studied for the first time. It is shown that the resins of this region, previously described as amber (in modern understanding – succinite), are not such, but are represented by exclusively fragile varieties – retinite, gedanite and do not represent practical interest as jeweller raw material.