Late Valdai Research Articles

Stratigraphy and OSL chronology of the Middle–Upper Pleistocene sedimentary sequence and vegetation history during Late MIS6–MIS5e in the Neva Lowland (St. Petersburg region, Russia)

ABSTRACTThe quarry of the Sverdlov (Etalon) Factory stands out as a unique site in the northwest of the East European Plain since it exposes an almost complete Upper Pleistocene stratigraphic succession. Previous investigations have revealed a sequence of marine sediments deposited during the whole Mikulino Interglacial [Eemian, Marine Isotope Stage (MIS)5e], but the chronology of the Late Pleistocene deposits remains incomplete and requires further update. We present a study of the Middle–Upper Pleistocene units exposed in the Sverdlov Factory quarry by using geological methods, optically stimulated luminescence (OSL) dating and pollen analysis. The lower part of the Sverdlov Factory section comprises glaciomarine/glaciolacustrine varves, which accumulated during degradation of the Late Moscow (Late Saalian, Late MIS6) glaciation and correspond to pollen zone M1 (lower peak of Picea). They are covered by interglacial marine clayey silt that includes all Mikulino regional pollen zones M2–M8. According to a Bayesian model based on K‐rich feldspar luminescence ages, the interglacial marine deposition started 133 ± 8 ka ago and ended 109 ± 7 ka ago. The marine sediments are overlain by lacustrine silt with a K‐rich feldspar age of 119 ± 7 ka, lacustrine/alluvial sand with plant detritus formed 47–41 ka ago, and lacustrine sand and silt without organic matter accumulated ~39 ka ago. The upper part of the section is composed of subglacial till formed during the Late Valdai (Late Weichselian, MIS2) under the Scandinavian Ice Sheet and glaciolacustrine varved deposits of the Baltic Ice Lake. Two ages were acquired using quartz OSL from these varves, 16.9 ± 1.6 and 15.7 ± 1.0 ka, which are assumed to slightly overestimate the true age.

About the possible existence of the Selizharovo proglacial lake

The formation of the incision valley near Selizharovo is associated with the existence of a proglacial lake in the Late Valdai. Geological and hypsometric data indicate its possible level is not lower than 205 m and not higher than 210 m asl. However, at this level of the lake, a incision would not be possible, since the edges of the valley are located at an altitude of 215 – 220 m asl. We assume that the depression at Selizharovo already existed by the beginning of the Late Valdai, and then it deepened and was renewed.

ON THE COLONISATION OF THE CENTRAL RUSSIAN PLAIN IN LATE GLACIAL AND EARLY HOLOCENE ACCORDING TO GEOARCHAEOLOGICAL DATA

Until recently, interpreting archaeological data on the colonisation of the Central Russian Plain during the last glacial epoch (Late Valdai, Vistulian) had been hampered by the prevailing view that vast areas along the ice sheet boundary were submerged by large proglacial lakes. Under the hypothesis that the Tver proglacial lake was covering Upper Volga lowlands and the Dubna depression, these territories would not be habitable until the Pleistocene-Holocene boundary when they finally dried up in the process of deglaciation. In 2018-2021, geoarchaeological investigations were carried out in Zabolotsky peatland (Moscow Region) to test this hypothesis. It was found that during the whole Late Valdai (Vistulian) glacial epoch, the prevailing environmental conditions in the Dubna Lowland were fluvial, rather than lacustrine. Thus, it is entirely plausible that large parts of the Zabolotsky area could already start to become populated at that time. AMS-dating of resin samples from the grooves of bone and hornbeam artefacts attributed to Epigravettian Resseta culture pinpoint the potential timing of this event to circa 15,500 cal BP. During Early Holocene, Zadnepilevo industry was the successor to Resseta tradition. Other populations known to exist in Central Russian Plain during late Pleistocene – early Holocene are attested from Bromme, Ahrensburg, Kultino and Purgasovo culture complexes. The identification of Elin-Bor, Butovo and Ienevo cultures in the Volga-Oka basin during the Mesolithic had been made by tampering with primary data. Therefore, any further allusion to these cultures would be unethical Seasonal migration patterns of both Resseta and Zadnepilevo populations are evidenced not only by data from the Russian Plain, but also from the Scandinavian Peninsula. Here, they are represented by the so-called "eastern pulse" industry. To piece together the cultural and historical development of Eastern and Northern Europe, a substantial increase in field research is needed.

Natural features and geological history of mount Vottovaara (Russian Stonehenge)

The article deals with the issues of physical and geographical features of the territory of Mount Vottovaara (which is the highest point of the West Karelian Upland) and its geological history. It is compared with one of the most famous attractions in the UK – Stonehenge Jam. Hypotheses of the origin and formation of this area are presented. The mountain keeps a large number of secrets, the main and most interesting among which are up to 1,600 individual stones located on its top – components of an ancient cult complex. They can be fully considered seids, many of which resemble unusual stone buildings, and according to a number of researchers who played a cult role and belonged to the culture of the ancient Sami. One of the hypotheses of the origin of the Votovaara seids connects them with the manifestation of glacial exaration processes during the periods of ancient glaciations. Another explains the presence of numerous traces of paleoseismic dislocations by a strong catastrophic palaeo-earthquake that occurred at the end of the Preboreal – the beginning of the Boreal period due to the degradation of the Late Valdai (Ostashkovsky) glaciation and the тrapid removal of glacial load. There is also a hypothesis, partly related to the ancient mythology of a Worldwide Flood, or a catastrophic flood of universal scale. According to one version, it could have happened due to the fall of a large meteorite in the area of the Philippine Sea. The tangential impact of the meteorite led to a shift of the solid earth’s crust along the surface of the liquid mantle, and the shock wave passing through the earth’s crust (compression wave) formed a ridge on the territory of modern Karelia, which includes Vottovaara. Finally, there is a version of the formation of the massif as a result of a powerful volcanic eruption that occurred several million years ago.

PALEOLITHIC SITE SUKHAYA MECHETKA (VOLGOGRAD) IN THE CONTEXT OF STRATIGRAPHY AND PALEOGEOGRAPHY OF THE LOWER VOLGA RIVER AREA

The Sukhaya Mechetka is the most important Middle Paleolithic site in the Eastern Europe. The paper presents the analysis of the section, including its cultural layer, in the context of stratigraphy and paleogeography of the Lower Volga River region. The structure of the section represents 11 main stages of sedimentation and paleogeographic evolution of the site territory, which are closely related to global and regional changes in the climate and the level of the Caspian Sea. The base of the section reflects the stage of a river existence on the territory of the site that flowed into the Volga River estuary, formed by the Early Khazarian transgression of the Caspian Sea at the end of the Middle Pleistocene (MIS 6). A long continental period of evolution under multi-directional climate fluctuations of different amplitudes from the Mikulino interglacial (MIS 5e) till the Late Valdai glacial epoch (MIS 2) is reflected in the middle part of the section. The Late Khazarian and Hyrcanian transgressive basins (MIS 5), as well as the Paleo-Khvalynian stage (MIS 3) of the Caspian Sea did not reach the latitude of Sukhaya Mechetka. The stage of Early Khvalynian transgression (MIS 2, 16 190 ± 200 years ago) during the degradation of Ostashkovo glaciation is expressed in the upper part of the section. Three paleosoils have been found that reflect the warming periods of the MIS 5 stage and are related to its 5e, 5c and 5a sub-stages. The middle paleosoil contains a cultural layer assigned to the Micoquian/KMG community of Northern Eurasia. The climate was moderately warm during the Neanderthal settlement of the territory, steppe landscapes dominated the interfluve, and the forests grew in the balka. The Hyrcanian transgression of the Caspian Sea with an estuary in the Volga River valley predetermined a high erosion basis and the formation of a balka with a wide bottom and gentle banks. A permanent fresh watercourse attracted mammals which were an object of hunting for ancient men. All this, obviously, became a basis for the organization of settlement in the Sukhaya Mechetka balka. Correlation of the section with detailed studied loess-soil sections of the Lower Volga River region makes it possible to determine the age of its cultural horizon in between 97-110 thousand years ago.

Evolution of a proglacial lake in the Izborsko‐Malskaya Valley, Russia, in the Late Glacial

A proglacial lake system formed during the Late Valdai (Weichselian) Ice Sheet recession on the East European Plain. Poor knowledge about chronology, levels and the drainage pathways of ice-dammed lakes does not allow us to fully evaluate their palaeogeographic significance. This study focuses on the Izborsko-Malskaya Valley where fingerprints of a glaciolacustrine environment were found. Based on litho-, biostratigraphic and geochronological data, it is estimated that the proglacial lake in the Izborsko-Malskaya Valley existed from ~14.3 ka cal. BP (the Vashinogorskaya Valley from ~14.9 ka (optically stimulated luminescence)) to 13.2 ka cal. BP. The maximum level was ~72 m a.s.l. (above sea level) and the minimum was ~53 m a.s.l. Sedimentation proceeded mostly in deepwater conditions. The ice-dammed lake in the Izborsko-Malskaya and nearest valleys could have been part of a huge lake on the Pskov lowland which formed after ~15.7 ka cal. BP. The lake level dropped rapidly when the proglacial Lake Pskovsko-Chudskoe (Peipsi) connected with the Baltic Ice Lake. A lacustrine regime was preserved only in the southern portion of the Izborsko-Malskaya Valley after drainage and still exists in the modern lakes. The presented approaches to the ice-dammed lake reconstruction could be useful for the verification of other lakes which existed on the East European Plain.

Landscape development history of the Zabolotsky peat bog in the context of initial settlement of the Dubna River lowland (Upper Volga basin)

Zabolotsky peat bog is a unique biospheric and cultural-historical archive located in the north of the Moscow Region on the territory of the Dubna River lowland. Despite the advances in studying the Zabolotsky region, the question of reconstruction of the primitive population habitat remains unresolved. Until recently, it has been be-lieved that in the Late Valdai period, the Dubna River lowland was covered by the waters of an extensive glacier-dammed Tver paleolake, drained only at the turn of the Pleistocene and Holocene. It was assumed that the lake's existence prevented the settlement of the territory, whereas after its drainage, the shallow residual water pools were actively exploited in the economic activities of the primitive population. However, paleogeographic and ar-chaeological materials have been accumulated during the last two decades that questioned the existence of large dammed lakes in the Upper Volga basin in the Late Valdai time. This paper presents the results of three years (2018–2020) of research, allowing revision of the ideas about the Quaternary geology and development of the geomorphic conditions of this area. A program of research, comprising topographic and geodetic surveys, drilling using a portable boring rig, lithologic description of the core, radiocarbon (AMS) dating, paleo-soil studies, biologi-cal analysis of organic macrofossils, and ground-penetrating radar, has been carried out aimed at reconstruction of the paleogeographic setting and landscape development. Drilling data were used to build the profile across the left bank of the Dubna River floodplain with extension to the low terrace. The lithofacial analysis of samples and AMS dating allowed identifying three generations of ancient riverbeds, the deepest of which (with the bottom at 12 m below the water edge) is more than 30 thousand years old. The biological residues from the dark-coloured loams directly below the peat bottom belong almost exclusively to higher plants, both arboraceous and wetland, which may have been brought in by the floodwaters. The ground-penetrating radar profiles clearly show the boundaries of three electromagnetically homogeneous sedimental layers — the peat, silted peat, and loam. The paleo-geographic data, in conjunction with the geophysical profiling data, indicate the existence of a copious waterway in the lowland (the ancient Dubna River) no later than 15,000–16,000 years ago which formed a floodplain with large features of fluvial paleorelief available for settlement. These data agree well with the new serial AMS-dates for the resin from the grooves of the bone and horn artifacts, which permit extension of the time of the initial de-velopment of the Zabolotsky peat bog by the bearers of the Resseta Culture to 15,500 years ago. The conclu-sions drawn have major significance for the development of an evidence-based chronology of the events and dynamics of the settlement strategy of the population during the transition from the Pleistocene to the Holocene. The new data not only are consistent with the system of global paleoecologic events and history of the develop-ment of the outwash plain zone in Eastern Europe, but also provide the basis for refinement, and, possibly, revi-sion of a range of current concepts.

Tver proglacial lake (Tver region, Russia): myth or reality

Abstract. In this study we aimed to find a Tver proglacial lake in the Upper Volga low land at the Late Valdai that it have been reconstructed by D.D. Kvasov. Our field studies did not verify previously reconstructed lake terraces at 135 140 and 120 125 m a.s.l., though at 140 m a.s.l. we found the Volga River terrace near Seslavie (Tver region, Russia). According to OSL data from this terrace, the Volga River has existed in the Upper Volga lowland ever since the LGM.

The Origin of Terraces in Buried Valleys in the Northwest of the East European Plain

Abstract —The paper considers the origin of terraces that often complicate the slopes of abnormally deep buried valleys in the northwest of the East European Plain. The Izborsk–Maly valley (Pskov Region, Russia), which is half filled with Quaternary sediments, was chosen as the object of study. Since the upper part of the valley remains unfilled, it is possible to study in detail both geologic and geomorphologic structures of its terraced slopes being of particular interest in the context of the origin of buried valleys and the role of substrate in it. The four denudation-terrace levels that have been identified on the slopes of the Izborsk–Maly valley at absolute elevations of 53, 56–58, 70–72, and 75–77 m formed during the destruction of the preglacial karst landscape under the influence of Pleistocene glaciations. The formation of the terraces was probably linked with several stages of overdeepening of the valley and its expansion by the glacial erosion processes, which corresponded to at least two stages of the ice sheet advance in this area. The last stage may have been the beginning of the Late Valdai (Weichselian) glaciation or the activation of the edge of an ice sheet during its Luga phase (~15.7 cal kyr BP). Results of the study suggest that the Izborsk–Maly valley formed in subglacial conditions. The degree of glacial erosion was determined primarily by the coherence of Devonian carbonate-terrigenous rocks hosting the valley and the degree of the area transformation by karst processes. The cirque shape of slopes is the evidence of karst processes expression in pre-glacial time. Analysis of literature data shows that the origin of denudation terraces in the buried valleys in the northwest of the East European Plain has been paid little attention. The obtained data contribute to the study of this problem and provide insights into the origin of buried valleys.

Age and chronostratigraphic position of lacustrine-bog deposits in the Chernaya River basin in the north of the Bolshezemelskaya tundra according to the results of their 230Th/U- and 14C-dating

The main goal of this study was to elucidate the chronostratigraphic position of the sediments of lacustrine-bog stratum from the Ch-14 section located in the sub-latitudinal sector of the Chernaya River in the north of the Bolshezemelskaya tundra. This study presents data on their numerical age and time of their formation, obtained by the parallel 230Th/U and 14С dating of organic-rich layers. According to the results of spore-pollen analysis obtained earlier, the lacustrine-bog sediments were attributed to the Byzovaya (Middle Valdai) interstadial, together with the lake and alluvial deposits from the Ch-3 and Ch-4 sections in the same sector of the Chernaya River. The 230Th/U and 14C age data are in good agreement with each other, especially for the lower boundary of the lacustrine-bog sediments of the Ch-14 section. The time range of the lacustrine-bog stratum accumulation is estimated to be approximately 13.7–13.3 to ~12.0 thousand years ago. Thus, its formation (10.5–6.5 m layer) did not occur in the Middle Valdai, but in the Late Valdai time from the beginning of Allerød to the beginning of the Younger Dryas cooling. It has been suggested that a certain delay of late glacial climatic events took place in the Bolshezemelskaya tundra compared with their age-related estimation by the Greenland isotope-oxygen stages. For the first time, the isochronous approximation approach was applied to obtain the 230Th/U age of such young terrestrial organic-rich deposits. Earlier this approach was usually used in dating similar sediments not younger than MIS-3. The geochronological results presented in this paper allow us to recommend the 230Th/U method for determining the age of late glacial organic-rich deposits and climate events correlated with them.

The Impact of Paleocryogenesis on the Formation of Gray Forest Soils in Central Russia

The paleogeographic development of the natural process in the Late Pleistocene on the East European Plain had a rhythmic pattern with repeated alternation of cold and warm climatic eras. Continental glaciations arising on the East European Plain, in particular, the Late Valdai (Weichselian) glaciation, were reflected in changes in topography formation. Regional paleoenvironmental conditions of the formation of modern soil cover in the area of gray forest soils in central Russia are discussed. The impact of paleocryogenesis on the features of the Holocene soils is considered by the example of Vladimir and Moscow oblasts. In Vladimir oblast, soils were studied in Suzdal district on the territory of the Kibol-5 archaeological site of the early Middle Ages. In Moscow oblast, studied were conducted at the Pushchino key site. The differentiation of soil profiles related to the specificity of parent materials formed under the impact of the Late Weichselian paleocryogenesis with the development of cryogenic microtopography was demonstrated. It was also found that the surface microtopography is predetermined by the buried paleocryogenic polygonal network of elevated blocks (microhighs) and interblock depressions (microlows). The paleocryogenic genesis of this microtopography caused by cryogenic deformation of large wedge-shaped features was confirmed. Large cryogenic wedge-shaped soil features in the study area formed about 22–14 ka ago, which is confirmed by radiocarbon data. The dependence of the Holocene loamy soils in central Russia on the characteristics of parent materials is manifested at the levels of soil profiles, soil horizons, and particular soil properties. It is argued that the presence of Late Pleistocene paleocryogenic features greatly affects the formation of the profiles of Holocene soils and enhances the action of the anthropogenic factor on soil development. As an environmental factor, Late Weichsel paleocryogenesis differentiates soils at the high taxonomic level contributing to the formation of complex soil cover patterns.

Vegetation and Microtheriofauna Dynamics during the Late Glaciation and Holocene in the Yugyd-Va National Park

The results of studies of the Late Pleistocene and Holocene spore–pollen spectra and the microtheriofauna of loose deposits of four cave localities located in the Shchuger and Kozhym river basins within the territory of the Yugyd-Va National Park on the western slope of the Subpolar Urals are discussed. Assessment of the age of sediments from the karst cavities was based on the data of AMS radiocarbon dating of mammalian bones. The speleogenic formations of the localities studied contain layers assigned to the final stage of the degradation of the Polar Ural (Late Valdai) glaciation (Middle to Late Dryas) and to the Preboreal, Boreal, and Subatlantic periods of the Holocene. Cryoxerophilous tundra species predominated (88.3%) in the fossil microtheriofauna assemblage identified for the Allerod. The Middle Dryas and Allerod, the cold and warm periods of the Late Glacial, respectively, were reflected by the spore–pollen spectra. The microtheriofauna on the western slope of the Subpolar Urals remained quite cryophilous by the end of the Late Dryas. The broad distribution of yernik thickets and goosefoot–gramineous–mixed herb assemblages during that time has been established. The vegetation of the western foothills of the Subpolar Urals consisted of grass–shrub tundra with sparse spruce trees during the Late Preboreal cooling period. The microtheriofauna community also had a tundra-like composition. The presence of dark coniferous taiga forests in the south of the Subpolar Urals and sparse spruce–birch forests with pine and dwarf birch in the undergrowth in the north of the area during the Boreal period has been established. The rodent fauna acquired a forest-like character by that time. Northern taiga dark coniferous forests of spruce with a significant admixture of pine developed on the western slope of the Subpolar Urals by the middle of the Subatlantic period, and the content of tundra elements in the stands increased by the end of this period. The microtheriofauna of the studied region had a typical forest appearance characteristic of all Late Holocene taiga communities in northeastern Europe.

Pedostratigraphy and chronology of the Late Pleistocene for the extra glacial area in the Central Russian Upland (reference section Aleksandrov quarry)

New results on stratigraphy and chronology, obtained on the basis of OSL and 14C-dating of paleosols, sediments, and cryogenic deformations in the Aleksandrov quarry situated at the Central Russian Upland, are discussed. Due to the location of the site in a paleodepression, the section presents various stages of soil formation, cryogenesis and sedimentation starting from the Mikulino interglacial to the middle last glacial time. The studied sequence is well preserved and one of the most detailed soil-sedimentary terrestrial archives within Eastern Europe. It reflects climatic variations comprising the timespan from the marine isotopic stage (MIS) 5e to MIS 3. At the base of the paleodepression the pedogenetic stages are extraordinary detailed. Distinct paleosols are alternating with erosion-accumulative stages, forming the Ryshkovo pedolitocomplex during the Mikulino interglacial. During the Early Valdai time two interstadial paleosols were developed, and the Middle Valdai section comprises two main interstadial paleosols as well. In general, interstadial paleosols of the Late Valdai time are absent in the studied quarry. For the first time, the chronological boundaries of the MIS 5e interglacial are recorded and thus, the duration of soil formation could be determined from 12 to 15 thousand years. Furthermore, stages of periglacial conditions during the Early, Middle and Late Valdai time were dated. The obtained ages form the base for a chronostratigraphic framework, which was correlated with those of the loess-paleosol archives of Eastern, Central, and Western Europe.

Periglacial gully erosion on the east European plain and its recent analog at the Yamal peninsula

The net of dry valleys, gullies and shallow hollows is typical for the East European Plain. Dense vegetation usually covers their bottoms and slopes, so the modern erosion there is negligible in the pristine conditions. This erosion landscape formed in periglacial conditions during the terminations of the last two glaciations. The same kind of the erosion landscape is typical for the Arctic regions, especially for the Yamal, Gydan, and Tazovsky peninsulas. The size and the density of such valleys and gullies are quite similar to those existing on the East European Plain, but these erosion features are active there, especially in the conditions of natural or anthropogenic deterioration of the vegetation cover. As the density of dry valley network is an indicator of hydrological conditions in the river basin, the landscapes of the Arctic regions can be used as the modern analogs of the territories with the past periglacial erosion.The recent hydrological characteristics of the west-central Yamal Peninsula were used to estimate the parameters of erosion network at the Khoper River basin, formed in periglacial conditions. For these purposes gully erosion and thermoerosion model GULTEM was verified and calibrated based on the observation of the modern processes on the Yamal Peninsula. The meteorological characteristics were taken from ERA-Interim Reanalysis grid. To calculate the flow characteristics a synthetic hydrological model was used. These verified and calibrated models were used to find the most suitable characteristics of climate and vegetation cover, which can explain the structure and density of the Perepolye dry valley in the Khoper River basin. This dry valley with the main trunk length of 6400 m was formed at the end of the Late Valdai Glaciation (MIS 2). The conditions required for the formation of a periglacial gully of such length were estimated with the GULTEM model. The critical velocity of erosion initiation was within the range 0.8-0.9 m/s, and the surface runoff depth was close to the recent one on the Yamal Peninsula (330 mm). The system of shallow hollows in the Perepolye catchment (the gullies formed at the end of the Moscow Glaciation, MIS 6) is denser and longer than the dry valley system, and the modelling estimates showed that the surface runoff during that period was almost 3.3 times more than the recent one on the Yamal Peninsula.

Основные события эволюции поздневалдайского оледенения в Карело-Кольском регионе с дополнением к ранее опубликованным данным о месторождениях строительных материалов

Основные события эволюции поздневалдайского оледенения в Карело-Кольском регионе с дополнением к ранее опубликованным данным о месторождениях строительных материалов

Aquatic biota response to climate and habitat changes from the Valdai Glaciation to the Meghalayan (Serteya region, Western Dvina Lakeland)

The Serteyka River valley is one of the most important archaeological localities in North-Western Russia. The State Hermitage Museum has conducted research in Serteya since the 1970s. The pile-dwelling remnants located within the Great Serteya Palaeolake Basin (GSPB) are the most prominent excavation. The investigation using precise underwater techniques recovered many exceptional remains of the Neolithic settlement that were preserved below the groundwater level in biogenic deposits. The large-scale studies focused till now primarily on relicts of the human settlement and only scarce environmental data were available before the last decade. A broad environmental archaelogical project using cores of organic deposits has been conducted since 2016 in the framework of Polish-Russian cooperation. The 8 m long STIIa core from the deepest lake point has been investigated. It gives a full sequence of the lake history from the Late Valdai Glaciation to the Middle Ages. Multi-proxy analysis of the STIIa core aims at the reconstruction of regional and local habitat conditions (e.g. climate, hydrology, trophic state, water chemistry, and plant communities) at the lake side during the MIS1.

The Early Khvalynian stage in the Caspian Sea evolution: Pollen records, palynofloras and reconstructions of paleoenvironments

In addressing the controversial issues of the Late Pleistocene paleogeography of the Caspian basin, an important role is given to the results of the spore-pollen analysis and based on them reconstructions of climate and vegetation changes in the Northern Caspian region during the development of the Early Khvalynian transgression. In this paper we present the main results of the palynological study of deposits (chocolate clays and the overlying and underlying layers from the Srednyaya Akhtuba section) of maximum stage of the Early Khvalynian transgression; the materials are illustrated by pollen diagram with the data of spore-pollen analysis and the detailed list of palynoflora recovered from the studied Lower Khvalynian sequences, and complemented with photographs of pollen belonging to the principal autochtonous taxa and, for comparison, to some redeposited palynomorphs. Palynological materials indicate subaqual (brackish marine and freshwater) sedimentation of the sediments studied in periglacial landscapes and, for the most part, under very harsh climatic conditions. The performed climate-stratigraphic reconstructions do not contradict the data of absolute dating on the accumulation of the studied deposits during the Late Valdai (Ostashkov) late Glacial period. During this interval in the territory of the study area, plant communities of the glacial climate — tundra-steppe, periglacial forest-steppe, periglacial steppe, periglacial parklands and periglacial forests — were developed. The widespread occurrence in the composition of the periglacial vegetation cover of the studied region of the yernik formations from Betula nana and shrub communities from Betula fruticosa, B. nana, Alnaster fruticosus, Juniperus, etc. testifies to the severe climatic conditions and, possibly, the existence of sporadic permafrost in the cold stages (stadials) of the Ostashkov Late Glacial period.

Lake sedimentation as an agent of postglacial transformation of interfluves and fluvial landscapes of the Borisoglebsk Upland, Central European Russia

Abstract. Borisoglebsk Upland is considered an example of a secondary upland plain in the marginal zone of the last Middle Pleistocene glaciation. Moraine hills and kames were reworked by glaciofluvial processes and incised by small fluvial forms later. Its postglacial surface drift cover is regularly defined as an undivided complex of mantle loams of dominantly subaerial origin with characteristic cryogenic features and remnants of paleosols. However, some previous studies suggest that lake sedimentation played an important role in the postglacial history of the Borisoglebsk Upland. This paper presents results of a detailed investigation of postglacial sedimentary cover of the eastern part of the Borisoglebsk Upland aimed to reconstruct the co-evolution of surface deposits, soil cover and geomorphic landscapes since degradation of the last Middle Pleistocene glaciation about 150 ka (MIS-6). The study is essentially based on a comprehensive lithological, pedological and geocryological description of postglacial deposits in cores (hand or machine-driven) and open sections, systematic sampling for grain size analysis and selective sampling for 14C absolute dating and monoliths structural examination. The results indicate that most of the surface drifts in this feature consists of stratified lacustrine deposits. Their Late Pleistocene age is stratigraphically confined by the underlying paleosols and incorporated peats of the Mikulino interglacial age (MIS-5) and several organic-rich layers within the lake sequence 14C dated to the Middle Valdai interstadial (MIS-3). Overlying mantle loams and colluvial deposits with cryogenic features and low organic matter content those facially substitute lacustrine sediments were attributed to the Late Valdai stadial (MIS-2). After the Mid-Holocene stabilization, relatively thin colluvial cover identified by the increased amount of organic matter also deposited. We conclude that lacustrine sedimentation is the primary Late Pleistocene agent that transformed the initial glacial topography and most characteristic type of lithodynamics of the eastern Borisoglebsk Upland.

Paleogeographic conditions of Lake formation on Andoma Ice-divide Upland

The results of an integrated study of Late Glacial and Holocene lake-mire deposits on Andoma Ice-divide Upland, located in the Fennoscandian Crystalline Shield-Russian Plate contact zone, are reported. The geomorphological structure of the study area isdescribed. The data obtained show that it was not until the Alleröd, i. e. much later than the Late Valdai glacier had retreated from the study area, that a lake began to form in what is now a mire. This delay was due to some distinctive features of the early deglaciation stages at which dead ice blocks and massifs were formed. The stagnated ice continued to melt until Boreal time. Terrigenous sediments accumulated in the proto-lake in Late Glacial and Preboreal time. They were rapidly succeeded by organic deposits about 7700 B. P. Boreal deposits are assumed to have been completely eroded after the dead ice block damming the lake had completely thawed. As the water level of the lake declined, the lake basin began to get overgrown and peat formation continued. The plant cover development lagged much behind the glacial retreat because dead ice massifs persisted for a long time. The vegetation dynamics from Late Glacial time to the present has been reconstructed. In Late Glacial time, the study area was occupied by tundra dwarf arctic birch-true moss paleocommunities. Open birch woodland, succeeded by sparse birch forests, formed in Preboreal time. Birch forests, succeeded by birch-spruce south-taiga forests, grew in the study area in early Atlantic time. As the climate cooled down at the Atlantic-Subboreal time boundary, spruce and spruce-pine mid-taiga forests began to spread. The contribution of birch increased by the end of the Subatlantic Period.

Postglacial incision-infill cycles at the Borisoglebsk Upland: Correlations between interfluve headwaters and fluvial network

The article discusses postglacial landscape transformation in the Northern Hemisphere Middle Pleistocene glaciation area located in the center of the Russian Plain. We attempted to verify the regional paleogeographic model by reconstructing the Late Pleistocene incision-infill cycles at the Eastern Borisoglebsk Upland based on a comparison of inactive interfluves headwaters and actual fluvial network palaeoarchives. The study was also aimed to determine the past extent of fluvial systems. Interdisciplinary research of the actual and buried topography, lithology and pedogenic properties of surface deposits was carrid out with remote sensing data interpretation, DGPS survey, and detailed description of geological cores involved. The study was followed by analysis of grain size, chemical and organic contents, microstructure, and numerical dating. Integrating the available results, we propose a scenario of the fluvial network transformation at the Eastern Borisoglebsk Upland over the last 150 ka. At least four fluvial incision stages were determined while network extent has significantly changed through the Late Pleistocene. Three can be generally associated with the regional base level decrease – Late Moscow, Late Valdai and Late Holocene and accompanying isolation of the Nero Lake terraces of 130 m, 100–105 m and 95–98 m. Incision stages were separated by landscape stability or aggradation periods those were asynchronous at the middle and upper parts of the fluvial network. The main agent of initial valley infill appears to be local lacustrine sedimentation altered by alluvial and colluvial deposition towards the second half of Valdai. Revealed landscape conditions variability emphasize the importance of comprehensive local correlations for regional retrospective models.