Recent research and geological mapping have shown problems with officially accepted chronostratigraphic scales for the Pleistocene of Siberia, especially in their uppermost parts. Results of 21st century studies, using latitudinal correlation of late Quaternary events reflected in Upper Pleistocene and uppermost Middle Pleistocene stratigraphic units of glaciated northern Russia, provide a solid basis for updating these scales. This correlation uses stratigraphic marker levels traceable by characteristic paleoclimatic proxies supported by modern geochronometry. This principle levels are represented by descriptions of the rocks of the main temperate and cold stages (thermomers and cryomers in the Russian Stratigraphic Code) with examples of their mass dating in key sections. Summarized, they would support the important parts of the regional chronostratigraphic scales. The most valuable feature of modern chronometry is that it is a statistically robust chronological framework, which is provided by series of datings. It is also important to control correlations using collateral instrumental dating methods. Under discussion herein are four major correlation levels established from sedimentological, paleontological and chronometric proxies and traceable as climatoliths—i.e., paleoclimate-based stages – from Timan to Taimyr. Correlation of underlying strata is largely dependent on Upper Pleistocene data. A correlation table is proposed as an aid in developing new regional stratigraphic schemes.
A study of the geology of the Verkhnyaya Gora strata in the Berezhekovo-5 section of the Kurtak geoarcheological region, based on numerous detailed outcrops, shows its deluvial-solifluctional genesis. The results of the analysis of the therio- and malacofaunas from the Verkhnyaya Gora strata suggest that the most probable age of host deposits, based on the summary of all available paleontological data, is early Neopleistocene. Most of the small mammal fauna from the Verkhnyaya Gora strata at the Berezhekovo-5 locality formed during the MQR 5 biochron (up to the boundary with the MQR 4 biochron) and corresponds to the level of late Vyatkino faunas of Western Siberia and late Tiraspol’ faunas of Eastern Europe. Ecological characteristics of the identified small mammal taxa allows the recognition of three biochronologically close but ecologically distinct faunal assemblages: steppe, forest-steppe, and periglacial. Considering the biochronological interpretation of the microtheriofauna, the presence of remains from multiple faunal assemblages in mixed state within the Verkhnyaya Gora strata can be explained by accumulation of paleontological material during the MQR 5 biochron against the background of changing landscape-climatic environments spanning Marine Isotope Stages (MIS) 16 to the onset of MIS 13. Thus, an early Quaternary age for the subaerial Verkhnyaya Gora strata in the stratotype Berezhekovo-5 section, Kurtak region, Yenisei River, is deemed substantiated for both the local stratigraphic scheme of the Minusinsk Basin and the regional stratigraphic scheme of the Altai-Sayan mountain region.
The chronology, size, and drainage patterns of ice-dammed lakes in the high-mountain depressions of the Russian Altai, as well as their influence on topography changes and sedimentation of the main valleys during the Pleistocene, remain highly debatable. The main reason is different interpretation of key sections and landforms; the different sets of research methods; the objective difficulties of applying numerical dating techniques; and the discrepancies in chronological determinations obtained by different dating techniques. A comprehensive geological and geomorphological study based on OSL and 14C dating allowed us to propose our own version of Pleistocene events in the upper Chuya River basin. The age of glaciolacustrine deposits in the Chagan key section indicates powerful glaciation in the mountainous framing of the Chuya Depression as early as the Middle Pleistocene—ca 160–180 ka ago (MIS 6). However, the ice-dammed (probably single) lake, which left the highest (up to 2100 m a.s.l.) shorelines preserved in the topography on the slopes of the Chuya and Kurai Depressions, existed no earlier than 90–80 ka ago, i.e., in the Late, not Middle Pleistocene, probably in MIS 4. The view that the Chuya Depression was filled in MIS 4 to a level of 2250 m a.s.l. does not yet have a geochronological basis; existing calculations of the volume of the single Kurai-Chuya lake at this level are purely hypothetical. The last lake in the Chuya depression, with a level of about 1890 m a.s.l., existed during the Last Glacial Maximum (MIS 2) about 37 (25)–16 (14) ka ago, and was drained over a short period of time. The Kurai Depression in MIS 2 was occupied by lake at least 25 ka ago. Around 19 ka ago the Kurai paleolake had a water level of 1730 m a.s.l. (depth up to 270 m near the dam) and extended as a narrow bay into the Chuya Valley between the Kurai and Chuya depressions. Sharp and significant drop in the lake’s level occurred at that time, but about 16 ka ago its level was still no lower than 1570 m a.s.l. No later than 16–14 ka ago the main part of the Kurai Depression had completely drained. The damming of not only the old but also the new Chuya River valley at the outlet of the Kurai Depression by the Maashey Glacier, and subsequently by its moraines, was a key reason for the change of direction of flow of the Chuya River. At the beginning of the Holocene, small lakes of non-glacial origin existed at the mouths of both depressions and in the Chuya Valley between them. The comprehensive description of studied sections applying geochronological, geological, paleontological and geomorphological methods allows us to classify them as key sections for reconstructing the Pleistocene evolution history of the Chuya and Kurai Depressions and the Altai highlands as a whole. Refinement of the stratigraphic scale of the Altai Quaternary deposits should be considered based on the results of these studies.
Ideas about the age and climatic conditions of the Valdai interstadials on the Russian Plain are based on biostratigraphic and limited 14C dating data. The chronometric reference of the Valdai interstadial deposits is not always reliable, including due to the use of the 14C method at the limit of its accuracy. Their paleobotanical characterization is complicated due to the lower specificity of plant complexes in contrast to interglacial deposits. This makes it difficult to conduct spatiotemporal correlations of Upper Pleistocene warmings stages over a large territory. We applied a comprehensive approach to the study of Upper Pleistocene buried peat deposits in a well-known section near the Verkhnie Nemykari village in the Smolensk region based on their 230Th/U and 14C dating and paleobotanical study. It has been revealed that the lower peat in the section accumulated during the pre-optimal and optimal phases of the Mikulino Interglacial. The 230Th/U age of the peat layers corresponding to the interglacial optimum is 112–106 ka, which is consistent with previously obtained 230Th/U dates for Mikulino organogenic deposits on the Russian Plain. The upper peat layer was dated using 230Th/U and 14C methods. The close age intervals were obtained in the range of 50–40 ka. According to paleobotanical data, a successive change in forest vegetation took place during the accumulation of the upper peat horizon: birch forests, spruce-birch forests, spruce-pine forests with larch, and spruce-birch-pine forests. These new data suggest that the upper peat horizon was formed during the Middle Valdai period, in the initial phases of MIS 3, under relatively favorable interstadial conditions that were slightly cooler than interglacial conditions. Despite the tentative age estimate of the upper peat layer, we propose to extend this comprehensive approach to a new study of known sections containing Valdai interstadial deposits. In combination with OSL dating of minerogenic deposits, this approach is promising for clarifying issues of chronostratigraphy of Upper Neopleistocene interstadial deposits in the Russian Plain.
This paper proposes a substantial refinement of the regional stratigraphic scheme of Upper Neopleistocene loess deposits in the central East European Plain. The Aleksandrov quarry is considered as the main stratotype section of the late Neopleistocene. A variety of modern paleogeographic methods, including paleosol, biostratigraphic, radiocarbon (14C) and optically stimulated luminescence (OSL) dating, were used in this study. During the Mikulino Interglacial, the Ryshkovo paleosol MIS 5e (marine isotope stage) or Ryshkovo pedolithic complex formed under accumulative mesorelief conditions. During the first Early Valdai cooling, permafrost episodes appeared in the Seim loess (MIS 5d), the eponymous cryogenic horizon (CH). The Valdai Early Glacial (MIS 5c-5a) is recorded not by one, as previously believed, but by two interstadial paleosols in the Chermeninsk horizon: Kukuevo (MIS 5c) and Streletsk (MIS 5a), separated by the Mlodat loess and CH (MIS 5b). At the beginning of the Valdai Pleniglacial, a significant increase in cryogenesis was noted, which was accompanied by the formation of the Selikhovodvor CH (MIS 4). In the Middle Pleniglacial (MIS 3), not one but two paleosols formed and were better preserved in the Leningrad horizon: Aleksandrov and Bryansk. Under accumulative conditions, the structure of the deposits becomes more complex, with the addition of the Gidrouzel and Monastyrshchino paleosols, which reflect more fractional climatic rhythms. In the Late Pleniglacial (Ostashkov horizon, MIS 2), several paleosols were identified that do not yet have a stratigraphic significance, with the exception of the Divnogorsk pedolithic complex, which records repeated pulses of pre-Holocene warming. The proposed scheme has been shown to be more detailed than Velichko’s scheme. The structures of the Upper Neopleistocene deposits in glacial and non-glacial regions of the central East European Plain have been correlated. Similarities in the structures of loess-soil sections from the first half of the late Neopleistocene in the Central Russian Upland, the Azov region, the Lower Volga region, and the Ciscaucasus have been demonstrated. Correlating the structures of the sections of the Central Russian Upland, the Donetsk Ridge, and the Volyn Upland demonstrated interregional similarities in the reflection of climatic signals by paleosols. This confirms the global (astronomical) causes of the major climatic rhythms in the Neopleistocene.
