Vol 54, No 1 (2023)

In this paper, an attempt to explain the main features of the planetary climate dynamics over the past ~5 Myr is made. In particular, a general cooling from the Pliocene to the Pleistocene, predominant climate variations with periodicities of 100, 41, 23–19 thousand years and the continuous nature of the spectrum are discussed. As a result, it was shown that the decrease in temperature is due to a monotonous decrease of the CO2 concentration during the Cenozoic era. This led to glaciations and restructuring the predominant climate rhythmicity of from 41ka to 100 ka years cycles with an increase in the amplitude of fluctuations. 41 ka, 23 ka and 19 ka year cycles are associated with variations in the position of the planet in its orbit and the elongation of its orbit. 100 ka rhythms exists due to the stochastic resonance of internal variability and eccentricity variations. The continuous spectrum of oscillations reflects the transfer of energy along the spectrum from the energy-carrying range due to the direct cascade, which has a Kolmogorov character. At the same time, energy transfer to the low-frequency region (inverse cascade) is also possible and associated with the effect of the Brownian process. Climate change on a century scales is associated with the inflow of energy from two sides, from long-term and short-term processes. In the first case, it is transfer from the energy-carrying Milankovitch cycles, and in the second case, it is pumping from high frequencies. Therefore, these variations, in a certain sense, are the most difficult for causal analysis. The Dansgaard–Oeschger and Heinrich oscillations, which are included in the range of centenary variations, stand apart, having a specific oceanic-glacial nature.

The paper analyzes 234 radiocarbon dates of the Khvalynian deposits obtained by researchers over more than 50 years of studying the Caspian region. Most of the dates were obtained from shell material, including endemic species of mollusks of the genus Didacna that lived in the early and late Khvalynian basins of the Caspian Sea. The radiocarbon coverage of the Khvalynian stage is in the range of 46–8.3 cal. ka BP. The most ancient dates were obtained from the Khvalynian deposits of the Caspian Sea. The largest number of dates falls within the interval of 17–12.5 cal. ka BP. The development of the early Khvalynian transgression began 40–35 cal. ka BP. During 25–18 cal. ka BP the coastline of the early Khvalynian basin reached levels above 0–5 m asl, and the level of 20–22 m asl developed in the range of 17–13.5 cal. ka BP. After 12.5 cal. ka BP the sea level was falling probably leading to the development of Enotaevkian regression. The Upper Khvalynian deposits dated between 11–8.5 cal. ka BP probably correspond to the development of the late Khvalynian transgression. The age interval for the development of the maximum phase (45–48 m asl) of the Early Khvalynian transgression has not been determined according to the currently available data.

The article presents the results of interdisciplinary (archaeological and palaeoecological) studies conducted in 2018–2021 in the northern part of the Perm Territory at the confluence of the Kosa and Lolog rivers. The main objects of research were the sites of the Mesolithic period and the natural environment of the Late Glacial and Early Holocene. To identify the confinement of archaeological sites to certain landforms within the river valley, the paleochannel method was used. As a result, 2 terraces and a Holocene floodplain were identified. For paleoenvironmental reconstruction palynological and paleocarpological methods were used. The radiocarbon method was used to create a chronological basis for the area of work. The study of the economic activities of Mesolithic groups was based on osteological analysis. In the Late Glacial period the study area was not yet inhabited by ancient people due to unfavorable natural environments. The settlement started only in the second half of the Boreal period of the Holocene, after the formation of the second terrace and the spread of taiga pine and birch forests with the participation of spruce. By this time, the sites of Kosa I and II, located on the banks of the Lolog river were inhabited. The population was mostly engaged in hunting and partly fishing. The natural environments at the beginning of the Atlantic period of the Holocene were still favorable for the existence of human groups here. Formation of the first terrace in the Lolog valley contributed to the colonization of this territory too. The Kosa III site dates back to this time, which population was still mainly engaged in hunting, and probably also fishing. Later, due to the continued lateral migration of the Kosa and Lolog river beds to the east and the emergence of waterlogged floodplains, people left this area and began to inhabit it again only in the Late Holocene.

The results of morphometric analysis based on the SRTM digital elevation model of large enclosed depressions (LEDs) of controversial origin, commonly found on the loess interfluves in the Northern Black Sea region, around the Sea of Azov, at the Western flanks of Caucus Mountains and in the Lower Don basin, are presented in the paper. We have registered 312 LEDs landforms. The morphometric characteristics of landforms vary from 0.4 to 216 km2 for area, from 1 to 21 m for depth, from 0.5 to 13.3 km for width, from 0.7 to 27.5 km for length, from 1 to 4 for elongation coefficient, and from 3.3 to 103.3 m a.s.l for height. The most common depressions have the following parameters: area – 2–4 km2; depth – 2–3 m; width – 1.0–1.5 km; length – 2.5–3.0 km; elongation coefficient – 1.2–1.4; height – 15–20 m a.s.l. There is a correlation between the area and depth of the depressions. The depressions' shape is mostly elongated, e. g. teardrop-shaped, eggshaped, elliptical, triangular, and rarely round. The sharp ends of the egg-shaped depressions always tend to point to the north, and the blunt ones – to the south. We grouped the depressions into seven restricted sites where the differences in size and other morphological features of the LEDs are very small. Within all sites, there is a high consistency of orientation of the long axes of the depressions. The largest depressions around the Sea of Azov and the Western flanks of Caucus Mountains are characterized by longitudinal ridges confined to western side of LEDs. Comparison analysis of sites demonstrated a fan-shaped pattern in changing of the long axes orientation from the NW in the Northern Black Sea region; to the East in the Azov Sea region; to the N in the Western flanks of Caucus Mountains; and the NE in the Central flanks of Caucus Mountains. A radial-centripetal pattern of the erosion network is observed across the territories where LEDs are distributed. Small erosive forms flowing into the center of depressions are represented by very flat and wide gullies and hollows with intermitted channel flow. Such morphological characteristics suggest the relict origin of the erosional forms and, as a result, indicates the pre-Holocene age of the depressions themselves. Morphological and geological data suggests that wind erosion was probably the main factor in the formation of LEDs.