编号 1 (2025)

The lithogeochemical characteristics of pelitic and silty-pelitic bottom sediments from a number of areas in the south-western Kara Sea (Baydaratskaya Bay, Pukhuchanskaya Depression, West Kara Step and Novaya Zemlya Depression), samples of which were taken on the 89^th cruise of the R/V “Akademik Mstislav Keldysh” (September 2022). It has been established that the silts contain a significant proportion of the lithogenic component. This is in good agreement with the localization of silt data points on various discriminant diagrams near the reference points of average Paleozoic greywackes and PAAS. The sources of such a component could be either a thin-grained particulated matter of the Ob River, or sedimentary rocks and loose formations of Yamal and Yugra Peninsulars, Vaigach, and Novaya Zemlya. Taking into account the information about the presence in the upper layer of bottom sediments of the south-western Kara Sea of a noticeable amount of fragments of the basic igneous rocks of Novaya Zemlya, the contribution of their erosion products to the composition of the silts could be quite noticeable, but the parameters of the REE spectra in the silts normalized to chondrite are not consistent with such assumption.

The pyrolytic characteristics of dispersed organic matter were determined in clay pulp samples collected from 23 mud volcanoes of the Kerch-Taman area (Crimean-Caucasian region). It belongs to type III kerogen, and its level of change corresponds to the earliest stages of oil generation. It is also shown that the organic matter carried out by volcanoes, by its pyrolytic characteristics, is almost a complete analog of the dispersed organic matter present in the clays of the Maikop series sediments. At the same time, in comparison with the latter, the mud-volcanic pulp has a higher content of bitumoids.

The relationship between the kerogen parameter T_max and different temperature-dependent characteristics of the water (t(Mg-Li) and δ¹⁸O in H₂O) and gas (δ¹³C in CH₄) phases of mud volcanic emissions was found for the first time for the mud volcanic systems of the Kerch-Taman region. These dependences demonstrate that the the gaseous, liquid, and solid phases of mud-volcanic emissions form in a single deep mud-volcanic reservoir and show the overall direction of changes in the composition of fluid systems with rising formation temperatures. Simultaneously, no discernible organic matter contamination of the clay pulp from the surrounding sediments or the walls of the mud-volcanic channel was found.

We present a comparative analysis of the carbonate sedimentation conditions in two Paleoproterozoic basins located in the south-east and north of the Late Archean Karelian craton in the North Onega and Pana-Kuolayarvi synclinories. The carbonate accumulation began in both paleobasins during the Late Jatulian. Carbonate rocks in the Onega sequence are predominantly dolostones, including stromatolite varieties, whereas in the Pan Kuolayarvi succession, they comprise both dolostones and limestones. During the Late Jatulian, cyanobacteria thrive in the coastal marine settings of the Onega basin. Some portions of the basin may have been disconnected from the open sean at this time, facilitating the development of evaporite processes. There was no such diversity of cyanobacterial communities in the Pana-Kuolayarvi basin, and there was no evaporitization. According to geological and lithological data, shallow, lagoon, playa lake and sabha environments existed in the Onega paleobasin in the Late Jatulian time. In the Pana-Kuolayarvi paleobasin, the conditions are shallow, at times with increased water input from the continent, and open marine settings. The geochemical characteristics of the carbonate rocks we obtained lead to the same facies conclusions. The stromatolites in the Onega pleobasin were formed mainly in the intertidal zone, at times the connection of the basin with the open sea was reduced and the conditions approached the lagoon. The oxic conditions existed for a limited time during Jatulian only in the Onega basin. Basically, in the both sedimentation basins the oxygen content was close to the boundary of the transition from disoxic to oxic conditions. Fluctuations in the magnitude of the Ce anomaly in stromatolite laminae reflect changes in the oxygen content in water directly in contact with the stromatolite buildup, which creates the possibility of the existence of oxygen “oases” in the paleobasin with disoxic and oxygen-deficient conditions. Conclusions about redox conditions existing in the paleobasin, based only on geochemical markers, are not sufficient. Conclusions regarding the conditions prevailing in a paleobasin with carbonate sedimentation agree maximally with geological and lithological data based on a set of geochemical characteristics, including REE spectra, values of Ce and Eu anomalies, and ratios of individual lanthanides. These conclusions are supplemented by an analysis of paired correlations between redox-sensitive elements.