The Caspian Sea is the largest inland water body in the world, its history records evolution of global and regional climate, glacial-interglacial events in the East European Plain and mountainous regions of the Caucasus, Elbrus and Pamir-Alay, and represents a unique object for understanding the evolution of the natural environment and developing regional stratigraphic and paleogeographic schemes in Northern Eurasia. The Caspian Sea played significance role in the migrations of cultural interactions of ancient human populations in the adjacent territories, adding another reason for geoarchaeological studies and reconstruction of history of the basin. This article in the form of a brief review describes the history of the Caspian Sea evolution during the Pleistocene and Holocene, its unresolved or controversial issues, and, as a contribution to solving existing problems, presents articles published in a special issue. The articles are based on the materials of the All-Russian Conference “The Caspian Sea in the Pleistocene and Holocene: Evolution of the Natural Environment and Humans” (Volgograd, 2023), dedicated to the memory of Professor Alexander Adamovich Svitoch (1932–2022), one of the leading experts in Quaternary geology and paleogeography, whose significant contribution to the development of the theoretical foundations of paleogeography, the study of the history of the natural environment of Northern Eurasia entered the annals of Soviet and Russian geology and geography. A special issue of the journal “Geomorphology and Paleogeography” is dedicated to the memory of A.A. Svitoch. 

Based on the results of the spore-pollen analysis of the Aralsor borehole, which uncovered Akchagylian and Apsheronian deposits with a thickness of more than 640 m in the north of the Caspian lowland, determined by the lithology and fauna of the Caspian mollusks, a palinoclimatostratigraphic dissection of late Pliocene – early Pleistocene deposits was performed. The changes in landscape and climatic conditions that occurred during the accumulation of the studied Plio–Pleistocene sediments are reconstructed. It was found that at the beginning of Akchagylian, coniferous forests with heather and birch-pine forests with an admixture of broad-leaved, in places with salt marshes in the south, spread in conditions of cold and dry climate. Against the background of the Akchagylian gradual humidification and warming, dark coniferous forests with tsuga grew on the northern land areas adjacent to the Akchagylian Sea and pine-birch forests with an admixture of broadleaf in the south. The border of Akchagylian and Apsheronian is marked by the change of forest spore-pollen spectra by steppe spectra. Fluctuations, desiccation and cooling of the climate are observed during the Apsheronian, expressed in the development of treeless steppe phytocenoses. A detailed palynological analysis of the Akchagylian and Apsheronian deposits made it possible to identify groups of spore-pollen spectra and nine palinozones, reconstruct flora, vegetation and climatic conditions necessary for climatostratigraphy and further substantiation and improvement of the selected divisions of the quaternary system. 

The Caucasus is the region where the earliest episodes of hominin settlement in Eurasia are recorded. The discovery of a series of stratified Early Palaeolithic sites on the western coast of the Caspian Sea allows us to expand understanding the human exploration history of the Old World. Garaja site, located in the middle reaches of the Kura River in Western Azerbaijan is characterized by impressive archaeological collection, complexity and dynamism of the host sediments. For reconstructing the palaeogeographic history of the site a detailed study of Quaternary deposits, absolute dating using luminescence and analysis of palaeontological and archaeological collections were carried out. At Garaja coastal-marine, lacustrine and alluvial layers are distinguished, described in six lithological units, reflecting major stages of topography evolution and sedimentation conditions. The layers at the base of the section were formed during the Early Bakunian transgression, the middle and upper parts – during the unstable level of the Late Bakunian – Urunjikian transgression and active dynamics of Kura River valley. Analysis of the stone artifacts collection allowed identifying two technological complexes that reflect different stages of human occupation of this area. Absolute ages obtained for the first time for Bakunian deposits show that the pioneer settlement of the territory of the site took place ~445–460 ka and is associated with the Middle Acheulean tradition. This event occurred in the second half of MIS 12 and the Late Bakunian transgression of the Caspian Sea, when a forested multi-branch delta of the Kura River existed here, and forest-steppe landscapes dominated in the interfluve areas. The second stage occurs during 380–370 ka and is associated with the Late Acheulean tradition. The attractiveness of the Garaja area for ancient humans was determined by favorable climatic conditions, the presence of fresh water, accessible stone raw materials, abundant vegetation and numerous hunting objects. For the first time in the Eastern Caucasus, the exact chronology of the Early Palaeolithic site was established and palaeogeographical conditions were reconstructed, which allowed determining position of the archaeological materials of Garaja in the Early Paleolithic cultural mosaic of the region. 

Environment of the Hyrcanian transgressive epoch in the late Pleistocene history of the Caspian Sea is reconstructed on the basis of the results of malacofaunistic and palinological analyses of sediments in the core of boreholes drilled in the areas of engineering-geological research Rakushechnaya and Shirotnaya in the North Caspian. Hyrcanian sediments include 18 species of molluscs, principal part of which are the Caspian endemic; Didacna subcatillus and D. cristata are characteristic species. The malacofaunal composition indicates the salinity of the basin 6–10‰ and its warm water. The consistent change of faunal communities from the Hyrcanian thickness in the borehole IGS 4 of the Korchagin field demonstrates the transgressive development of the basin from shallow water to the basin with its highest level. In the sequence of spore-pollen spectra in these sediments three palinozones and seven subpalinozones are distinguished. They were the basis for reconstruction of the chronicle of climatic and phytocenotic changes and changes in natural conditions, reflecting the development of interglacial forest-steppe and forest landscapes on the territory of the Northern “Pre-Caspian” adjacent to the Hyrcanian basin. Judging by the participation in the composition of the dendropalinoflora of representative species of the Mikulino flora of the south of the Russian Plain, as well as the high content (against the backdrop of the alder pollen dominatiion) of broad-leaved pollen 
and the predominance of pollen Carpinus betulus in the widely complex, the accumulation of the Hyrcanian sediments occurred during a long interval of the thermo-hygrotic stage of the Mikulino interglacial. In the two optimal phases of this warm interval in the adjacent territory of the Northern PreCaspian, broadleaf hornbeams forests with an admixture of oak, lipa and elm and black alder (Alnus glutinosa) trees dominated. In forest communities of intrasonally and automorphic landscapes of interglacial (endothermal) cooling time, alder stands dominated. The climatic conditions of the Hyrcanian warm transgressive stage were more humid, than during the existence of the Late Khazarian Basin, distinguished by the dominance of steppe landscapes. 

Issues of cultural attribution, stratigraphy and chronology of Middle Paleolithic sites in the Caucasus are one of the current topics of Paleolithic science and paleogeography of Eurasia. The discovery of a series of open stratified sites in the valley of the Rubas River (Southern Dagestan) has significantly expanded our understanding of distribution and evolution of Middle Paleolithic cultures in the Eastern Caucasus. Among them, one of the most interesting and significant is the multilayer site of Rubas‑1, within Late Pleistocene deposits of which 8 levels of occurrence of stone artifacts were recorded. These materials were grouped into two complexes, the more ancient of which corresponds to the Late Middle Paleolithic, and the second – to the transitional stages to the Upper Paleolithic. A detailed characterization of the deposits containing archaeological findings, their absolute dating using the optically stimulated luminescence, analysis of exogenous processes and regional features the natural environment evolution were carried out, which allowed establishing the chronology and paleogeographic context of the Middle Paleolithic technocomplexes formation at Rubas‑1. Luminescence dating has been performed on both quartz grains and potassium‑rich feldspars. The validity of the obtained ages was confirmed by standard tests and analyses of relationships of ages from both minerals, which showed high reliability of the resulting chronology. The older complex is associated with sediments formed in the final stages of MIS 5, during the Hyrcanian transgression of the Caspian Sea. The younger complex of artifacts correlates to the second half of MIS 3, when carriers of a different industrial tradition, different from the “classical” complexes of the final Middle Paleolithic of the region, may have penetrated into the Eastern Caucasus, inhabited by Neanderthals.

The Early Khvalynian transgression of the Caspian Sea is one of the largest in the late Pleistocene. In connection with this, an extensive paleo-estuary was formed in the valley of the Volga River and its tributaries. The formation of terraces in the river valleys of the region is thus closely related to the transgressive-regressive dynamics of the Caspian Sea. This paper examines a key section of the river valley. Maliy Karaman (left tributary of the Volga River), its morphology and structure, lithological composition and age of the sediments composing the terraces, to establish the influence of the Early Khvalynian transgression of the Caspian Sea on the structure of the valley. 

Components of the water balance of the Caspian Sea are calculated for a wide range of lake levels (–85–50 m. a. s. l.) and for the two most contrasting climatic epochs over the last several tens of thousands of years: the middle Holocene (6 ka b. p.) and the Last Glacial Maximum (21 ka b. p.), as well as for the pre-industrial conditions (~1850). The eddy-resolving ocean general circulation model INMIO coupled with the CICE ice model are used for the calculations. Climate data of the INM–CM4.8 model for the indicated periods are used as boundary conditions. It is found that the volumes of river inflow required to maintain the lake level at various marks for the Holocene era are lower than the corresponding pre-industrial values by 6–7%. For the Last Glacial Maximum this decrease is 13–14% for regressive states and 20–21% for transgressive ones. Sensitivity of the results is studied to the temporal resolution of boundary meteorological data and to the locations of fresh water inflow into the Caspian Sea. It is shown that excluding the diurnal and intramonthly variability in input data leads to an underestimation of evaporation from the surface of the sea. The greatest influence on this value is exerted by the exclusion of intramonthly variability of the dynamic wind field: this leads to a decrease in the equilibrium runoff by 35%. To correctly simulate the duration of the ice coverage season, it is necessary to take into account the diurnal cycle of incoming radiation and air temperature. The melting period is significantly lengthened when using data at daily or monthly resolution, which has the greatest impact during transgressive states of the Caspian Sea. The redistribution of river mouth locations along the coast does not significantly affect the value of the total equilibrium inflow, which makes it possible to most likely exclude the uncertainty of this value associated with the lack of data on the mutual ratio of discharge of ancient rivers. In addition, estimates of hydroclimatic characteristics of the Caspian region for the middle Holocene and late Pleistocene are provided based on climate modeling carried out within the framework of the PMIP4 project. 

The article summarizes the data on paleogeography, lithology, and biostratigraphy of the Ancient Azov and New Azov deposits of the Sea of Azov (6.5 kyr BP). It is shown that the Black Sea species had a great influence on the flora and fauna during the early stages of the basin formation and the biota of the Sea of Azov began to acquire specific features only 3 thousand years ago. The article describes changes in the fauna of molluscs, the flora of diatoms and pollen spectra at different time stages. Marker taxa for the Ancient and New Azov sediments from different areas of the Sea of Azov are given. Diatom analysis indicates that such species of diatoms as Paralia sulcata, Grammatophora marina, Thalassiosira eccentrica, and Chaetoceros spp. have stratigraphic significance for the Ancient Azov sediments. The New Azov sediments of the open part of the Sea of Azov are characterized by the presence of other diatoms taxa: Actinocyclus octonarius var. ralfsii, A. octonarius var. tonsure, A. pseudopodolicus, Actinoptychus senarius, Thalassiosira decipience, and Chaetoceros spp. Malacological studies indicate that the species Chamelea gallina, Gastrana fragilis, Polititapes aureus, and Loripes obriculatus may be used to distinguish the Ancient and New Azov layers in the open part of the Sea of Azov. Low taxonomic diversity, the absence of gastropods (with the exception of Hydrobia acuta) and the disappearance of Mytilus galloprovincialis shells from sediments characterize the New Azov strata of the Central Taganrog Bay. The results of the spore-pollen analysis indicate that the boundary of the Ancient and New Azov sediments can be identified only by the appearance of pollen – indicators of anthropogenic activity (cultivated cereals and ruderal plants) – registered in sediments of the past 3 thousand years. The authors conclude that it is preferable to use integrated biostratigraphic data combined with the results of radiocarbon dating for the most precise stratigraphic separation of the Quaternary sediments in the Sea of Azov. 

The article is devoted to the study and analysis of the microrelief of the Zavolzhye-Urals region on the elevated erosion-denudation surfaces of the East European Plain (Bugulminsko-Belebeevskaya Upland, Obshchy Syrt and the Subural plateau), denudation basement plains of the southern Trans-Urals (Uralo-Tobolsk plateau) and low mountains of the Southern Urals. The leading role of relict cryogenic processes in its formation is assumed. The morphological and morphometric indicators of the relict permafrost relief (polygonal-block; longitudinal-strip (delley); merged-polygonal and reduced; hilly-depressions microrelief, etc.) are described, and new types of relict cryogenic microrelief (RCM) for the Zavolzhye-Urals region are established and characterized for the first time. The uniqueness of the paleocryogenic genesis of landscape complexes to the steppe zone is confirmed. In drained areas composed of Upper Cretaceous rocks, the microrelief is represented by “chalk polygons”; in areas composed of dispersed rocks – “tufurs”; on Trans-Ural variegated weathering crusts of loamy-clayey composition – “palsa”, on gypsisol- hilly-depressions forms. For the first time in the steppe zone, beaded streams forms have been identified as a type of relict cryogenic relief. The connection has been established between areas with various types of paleocryogenic microrelief and modern relief, geomorphological position and composition of surface sediments. The result of this research was the map-scheme “Relict cryogenic microrelief of the Zavolzhye-Urals region” on a scale of 1:2 500 000.