Natalia Olegovna Kovaleva

The high sensitivity of plants, and, consequently, the 13C/12C isotope ratio in their tissues, to fluctuations in air humidity and temperature, as well as to the concentration of carbon dioxide in the atmosphere, makes it possible to use this parameter as an accurate paleoclimatic indicator and biomarker of nodule genesis. Concretions from the gray forest soil of the Moscow region were studied using computed microtomography, biochemical analysis, and metagenomic sequencing. The composition of stable and radioactive carbon isotopes was determined in ferruginous-manganese nodules. It has been shown for the first time that the age of the concretions of light gray forest soils formed on cover noncalcareous loess-like heavy loamy parent rocks exceeds 1600 years. At the same time, the carbon isotopic composition of different fractions of nodules reveals in them the remains of modern plant species (from –26,3 to –27,4 δ13C, ‰) and confirms the leading role of woody plant lignin in the formation of nodules. The species composition of microorganisms differs in different fractions of concretions, makes the isotope composition of fine fractions heavier, and changes as soil hydromorphism increases. Drainage causes irreversible degradation of concretions, and first of all, their large fractions.

The practice of using isotope analysis in archaeological research, which has been developing in recent years, requires knowledge of the features of isotope fractionation in cultural layers and buried soils. The structural properties of geoarchaeological monuments are determined by local relief, climate, vegetation, landscape hydrology, physical and chemical properties of soil-forming and underlying rocks, and the existence of crops, and therefore their isotopic signature has a complex cumulative character. The aim of the study was to study the variability of the carbon isotope composition of soils, rocks and cultural layers of various landscape parts of geoarchaeological mounds in different natural zones of the Russian Plain from the standpoint of identifying general climatic trends and the contribution of the anthropogenic factor to carbon isotope fractionation. The defensive ramparts of the Dmitrovsky Kremlin (Moscow region), Davydovsky settlement (Tambov region), Vodyansky settlement (Volgograd region), necropolises of the Zhereno and Kvetun archaeological complexes (Bryansk region) were chosen as objects of study. It is shown that a significant variability in the carbon isotope composition is typical for soils and cultural layers of geoarchaeological monuments of different natural zones and makes it possible to identify the stages of stable soil formation on the surface of embankments and the stages of backfilling structures. The isotopic ratios decrease in the humus horizons of daytime and buried soils. An increase in isotopic ratios is characteristic of the cultural layers of geoarchaeological monuments in all natural zones and marks the epochs of the existence of cultures, however, the mechanisms of this process require further research. Despite the predominant distribution of herbaceous vegetation on the day surface of the sites, the isotope signature of buried soils reflects the type of dominant zonal vegetation and, through features of the type of photosynthesis, makes it possible to reconstruct the climate features of the region at various chronostages of the existence of objects.