The Late Quaternary history of the Caspian Sea remains controversial. One of the major disagreements in this debate concerns the stratigraphic correlation of various deposits in the Caspian Basin. In this paper we identify and date, for the first time, the Enotaevka regression, lying between the two major phases of the largest Late Quaternary Caspian Sea transgression, the Khvalynian transgressive epoch, and provide a minimum estimate of sea level decrease during this regression. The River Volga is the major source of water to the Caspian; the Lower Volga region is unique in its record of palaeogeographic events, and this provides the opportunity to build a single stratigraphic and palaeogeographic history for the Pleistocene of Central Eurasia. Here we use luminescence to establish a new chronology for the largest Late Quaternary transgressive epoch of the Caspian Sea. The existing radiocarbon chronology does not allow the resolution of the two transgressive phases of this epoch (Early and Late Khvalynian). Based on clear palaeontological and geomorphological evidence, these must be very different in age, but shells associated with both transgressions gave very scattered ages of between 8 and 50 ka. This ambiguity has led to considerable discussion concerning the existence or otherwise of a deep Enotaevka regression phase between the two Khvalynian transgressions. Recently we have again identified these deposits at Kosika, on the right valley side of the Volga River. The new luminescence chronology described here, based on quartz OSL and K-feldspar pIRIR(290) ages, allows us to reconstruct the complicated history of Late Quaternary sedimentation in the southern part of the Lower Volga valley. The Kosika section reflects the following major stages: (1) the earlier Khazarian transgressive epoch; (2) a decrease in the sea level with the development of a freshwater lake/lagoon in the Volga valley; and (3) the Khvalynian transgressive-regressive epoch, including both the Early and Late Khvalynian transgressive periods, and the intercalated Enotaevka regression. Sea level during the early stage of the Khvalynian transgression reached Kosika at about 23-22 ka (approx. -1 to -2 m asl). This event is of the same age as the "grey clay" strata at the base of the Leninsk section marine unit (Kurbanov et al., 2021), also formed at the beginning of the Early Khvalynian transgression. Around 15-14 ka the Khvalynian basin moved to a regressive stage, and in the northern part of the Lower Volga the top part of the well-known 'Chocolate Clay' accumulated. In the southern part of the valley marine accumulation stopped at about 12-13 ka. This allows us to reconstruct a decrease in Early Khvalynian basin sea level between 15-14 ka and 13-12 ka ago, of about similar to 15 m. At the Kosika section sediments derived from the Enotayevka regression are visible as a weakly developed palaeosol with evidence of surficial erosion, and these sediments are now dated to 13-12 ka. At 8.6 +/- 0.5 ka, during the period of the Mangyshlak regression, aeolian deflation processes reworked sediments deposited by immediately preceding Late Khvalynian transgression.

The normally-closed Caspian Sea is known for large changes in relative sea-level (of similar to 170 m) during the late Quaternary. These transgressive/regressive events influenced the topography, sedimentation and ecosystems of a large area, of up to 1 million km(2). The Volga River has played an important role in the water balance of the Caspian Quaternary basins but our understanding of the temporal evolution is poorly constrained. Recent studies on the evolution of the Lower Volga have focused mainly on the subaerial sequence of loess-palaeosol series corresponding to a long-duration Caspian low stand (the so-called "Atelian regression" from similar to 90 to similar to 25 ka). In this study we address, for the first time, the temporal evolution of the Volga River during the late Quaternary, as recorded in the many layers of alluvial sands at the Raygorod reference section. This 50 m high outcrop contains a complicated sequence of different types of interlayered alluvium (channel and floodplain facies), a loess-palaeosol sequence with a weakly developed palaeosol, and marine sediments of the Khvalynian transgression (Chocolate Clay facies). The new chronology, based on 35 samples, is derived using optically stimulated luminescence (OSL) analysis of sand-sized quartz, with support from post-infra-red infra-red stimulated luminescence (post-IR IRSL) from K-rich feldspar grains to date the older parts of the section. The new ages identify five stages of the topography development in the northern parts of the Lower Volga: (1) an MIS 5a flood-plain in deltaic/estuary environments (>90 ka) during a high-stand of the Caspian Sea (Hyrcanian transgression); (2) a transition from deltaic/estuary conditions to a river valley with normal alluvial sedimentation and sporadic stabilization reflected in palaeosol development (80-70 ka); (3) a palaeo-Volga channel migration at elevations of 4-8 m msl during 69-62 ka, evidence of a brief increase in Caspian Sea-level and blocking of the Volga flow; (4) a subaerial stage with high-speed accumulation of loess during MIS 4 to MIS 2, containing one weakly developed palaeosol (MIS 3c) and pedocomplex of three combined palaeosols of the beginning of MI52 (30-24 ka); (5) a rapid Khvalynian transgression, starting at the Raygorod location at similar to 18.3 ka, with relatively weak marine erosion of the top 40-60 cm of loess cover, presumably because of the rapid migration of the coastline in the flat Northern Caspian Lowland.

We present a detailed luminescence chronology of the loess-palaeosol sequences in the Lower Volga region of Russia at the Leninsk site - an important palaeogeographic archive describing the climate and environmental conditions of regressive stages of the Caspian Sea. The chronology of these sediments has received very little attention compared to the under- and overlying marine deposits. The degree of bleaching was addressed by making use of the differential resetting rates of quartz and feldspar. Our results show that the quartz OSL and feldspar pIRIR(50)(,)(290) signals were sufficiently bleached before deposition and uncertainties in bleaching have a negligible impact on the reliability of the luminescence ages. The combined quartz OSL and K-feldspar pIRIR(50)(,)(290) chronology constrains the main stages of the Northern Caspian Lowland evolution during the Late Quaternary. During early MIS 5 (130-120 ka), the northern part of the Lower Volga was covered by a shallow brackish water estuary of the warm Late Khazarian Caspian Sea transgression. After similar to 122 ka, the Volga incised the Northern Caspian Lowland surface following sea-level decrease and the start of subaerial conditions at Leninsk. Loess accumulation rate increased towards the end of MIS 5 and two palaeosols of presumably MIS 5c and MIS 5a age formed, exhibiting features evidencing a dry, cold climate, influenced by long seasonal flooding by the Volga River. Cryogenesis affecting the MIS 5a soil is a regional phenomenon and is dated to between similar to 70 and 90 ka. The overlying thick Atelian loess unit formed during the cold periods of MIS 4 and MIS 3. Clear erosional features at the top of the Atelian loess are constrained by luminescence to similar to 35 to similar to 24 ka, allowing reconstruction of erosion of 150-200 cm of loess.

The article is concerned with some features of the morphological structure of abandoned lands of the southern taiga of Central European Russia compared to the arable soils from the 1988–1990 survey period. A conjugate study of macro-, meso- and microstructure and some soil properties has made it possible to identify two groups of features by which the chronosequence elements – arable soils and abandoned lands differ from each other. The first group characterizes features of post-agrogenic transformation (development of sod-forming processes, increase in macrofauna activity, improvement in structure), which are caused by a change in the type of land use and are typical of the meadow overgrowth stage of self-restoration. The second group of features diagnoses changes in redox conditions and the regime of soil moistening during the last 30 years between surveys. Growth of hydromorphism, appearance of stagnic properties and some changes in carbonate state have been noted in all modern profiles of abandoned lands on loamy continuous and lithic discontinuous parent materials. The appearance of these features was accompanied by changes in the regional climatic conditions.

Morphological descriptions of cryogenic soils of the taiga zone are very important for diagnostics and classification of soils of northern regions. The development of geocryogenic processes depends on locally specific climatic and lithological factors. Previous studies on cryometamorphic soils (svetlozems) formed on Mid-Pleistocene loamy parent materials have been focused on their hydrological and thermal regimes. This article presents the results of meso-and micromorphological analyses of mesomorphous loamy soils formed in autonomous (interfluve) areas under seasonal freezing conditions. The permafrost features of the studied soils were formed during cold climatic cycles of the Pleistocene-Holocene period. The modern pedogenesis develops under increasingly hydromorphic conditions untypical for autonomous soils of the taiga zone of the West Siberian Plain. As a result, processes of peat accumulation and gleyzation have developed in such soils. However, gley features are absent in cryometamorphic soils. In their upper layers, iron undergoes oxidation and concentrates within granular peds during freezing. In their lower horizons (from the 40 cm depth), Fe-nodules are assimilated within platy peds (as a result of cryogenic restructuring of silty-clayey groundmass) and relic clay coatings are fragmented. The vertical differentiation of cryogenic features within the studied soil profiles can be associated with changes in climatic conditions during the Pleistocene-Holocene period.