Search

The paleohydrological settings in the Rostov lowland (Yaroslavl oblast) have been the subject of long-standing of disputes. The concepts for the Holocene fluctuations in the level of Nero Lake differ considerably among researchers. We have studied the structure of bottom sediments and bottom relief in the deepest, northeastern, part of the lake. A bathymetric survey was carried out. Drilling with the selection of undisturbed columns, GPR profiling, radiocarbon dating, and lithological analyses were conducted. Stratigraphic unconformities in the structure of the bottom sediments indicate a drop in the lake level in the Late Glacial and Early Holocene. The level dropped to 87 m asl, which is 7 m lower than the current water level in the lake. The size of the lake at this stage was reduced several times. The transgressive stage was established from 9 to 6.5 ka B.P.: the mean annual level of the lake could have risen up to 91–94 m asl, which is close to the modern level. In the interval from 6.5 to 2.4 ka B.P., a decrease in the level by 1–3 m below the current level is revealed. Then the level begins to grow gradually until it reached the current values 300–500 years ago. The main factor in the fluctuations in the level of Nero Lake in the Holocene is the change in the height of runoff threshold, caused by vertical deformations of the Ustye, Veksa, and Kotorosl river systems. These deformations were associated both with regional changes in fluvial activity and with the self-development of river channels. [ABSTRACT FROM AUTHOR]

Studying the Izborsk-Malskaya Valley, the authors focus on the origin of glaciolacustrine terraces in overdeepened valleys widespread in the Late Valdai (Ostashkov, Weichselian) glaciation areas. In the northern part of the Izborsk-Malskaya Valley were found fragments of the terrace (56–57 m a.s.l.). They are adjacent to the lower parts of its slopes and composed of thin-laminated sands. This terrace could be referred to as the alluvial or kame type. Detailed field and laboratory investigations have made it possible to study the thin-laminated sand formation. It was accumulated in the proglacial lake during the Izborsk–Malskaya valley deglaciation. Later, sand strata were divided by water flow causing the fragments to set apart. The incised stream channel should be associated with the larger water flow rather than the modern Obdekh River. It is likely that dissection of the primary glaciolacustrine surface and fluvial erosion in the valley bottom occurred at the bottom during the proglacial lake discharge approximately 13.3 ka (OSL). The ice-dammed lake was drained relatively rapidly. For this reason, the composition and facies in the upper part of the glaciolacustrine deposits are not variable. Furthermore, additional terraces are absent in the incised stream channel. Thus, the terrace has a glaciolacustrine origin, while its slopes – fluvial erosional one. The new data on the terrace formation process in the northwestern part of the East European Plain differ from the current concepts. Along with the previously described mechanisms of glaciolacustrine terrace formation (abrasion activity of former proglacial lakes, gradual downcutting, or ice-contact slope formation of kame terraces), we should bear in mind the possibility of incision powerful water flows during catastrophic discharges of ice-dammed lakes. Our study of the terrace in the Izborsk-Malskaya Valley gives a clear indication that other similar valleys should be thoroughly examined to revise their age and mechanism of terrace formation. [ABSTRACT FROM AUTHOR]

After the end of the Mikulino interglacial, in connection with the increasing cooling trend, the Scandinavian ice sheet began to form on the territory of Fennoscandia. Its development to the maximum boundaries was accompanied by ice sheet advances or, on the contrary, strong retreats that reflected numerous successions of colder and warmer climate phases over a long period, called the Valdai (Weichselian, Vistulian) ice age. The Scandinavian ice sheet did not reach its maximum simultaneously at the different lobes. The age of the maximum boundary on the continent becomes younger from west to east, which is associated with the paleoclimatic setting in the northern part of Eurasia due to the formation of the extracontinental climate. The climate continentality increased eastward along the periphery of the ice sheet. These climate features and the ice sheet response determined the nature of glacial morphogenesis in the proglacial zone. The conditions for the formation of the peripheral ice sheet and the increase in the number of mudflows and the formation of proglacial lakes were more favorable during the ice sheet degradation than expansion. The forms of active and dead ice, especially the terminal moraines and kames of different types, the valleys of marginal meltwater channels, and outwash plains reflect the stages of warming and degradation of ice sheets. [ABSTRACT FROM AUTHOR]

The use of geological–geomorphological and geochronological (14C, OSL) methods allowed establishing that the bordering mountains of the Chuya basin (Russian Altai) were affected by glaciation as early as the Middle Pleistocene, about 160–180 ka (MIS 6). However, the ice-dammed lake with the highest (up to 2100 m a.s.l.) strandlines in the Chuya and Kurai basins existed later than 90–80 ka, i.e., in the Late Pleistocene. This chronological benchmark limits the influence of the catastrophic outburst floods of the largest lakes on the accumulation of the Inya formation in the Chuya and Katun river valleys. It is confirmed that a large ice-dammed lake existed and had a water level of at least 1730 m a.s.l. in MIS 2 in the Kurai basin. The lake drained no later than 16 ka. Synchronously (about 17–16 ka) the accumulation of diluvial–lacustrine cyclites began in the Inya mouth. It was found that the accumulation of the Saldzhar formation in the Katun River valley between the mouths of the Chuya and Sema rivers was long-lasting during the entire MIS 2 not only as a result of flood events, but also due to gradual hydrological processes. It is necessary to revise the concept adopted by SibRISC in 2018. This concept assumes (i) the absence of ice-dammed lakes in intermont basins of Russian Altai in MIS 2 and (ii) the accumulation of the Inya and Saldzhar catafluvial formations, as well as the high and medium terraces they deposited in the valleys of the Chuya and Katun rivers before 90 ka. [ABSTRACT FROM AUTHOR]

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070115 [ABSTRACT FROM AUTHOR]

In the context of shifting the boundary of the Quaternary down to the level of 2.6 Ma and including the Gelasian Stage in the Quaternary System, the systematization of the original and published data on the geology and paleogeography of the Late Pliocene and Early Pleistocene of Eastern Europe has been carried out. It was established that, at the boundary of the Gauss and Matuyama paleomagnetic epochs, along with the general trend toward cooling and aridization, profound landscape and climate changes occurred and rhythmic fluctuations of the climate intensified. During the period from 2.6 to 1.8 Ma, corresponding to the Gelasian (pre-Tiglian and Tiglian of Western Europe or Paleopleistocene of Eastern Europe), there appeared subarctic landscapes. In the Eopleistocene (1.8–0.78 Ma) and the Early Neopleistocene (0.78–0.42 Ma), the climate became colder, and climatic zonality repeatedly underwent a complex restructuring, gradually approaching the modern one. Glacial deposits (layers of till) occurring in Eastern Europe date back to the Paleopleistocene. Evidence indicates that there were at least three independent glaciations in the Eopleistocene (1.8–0.78 Ma) and possibly four in the Early Neopleistocene. On the basis of studies of stratotypic sections, paragenetic links were established between sediments of different age within glacial and periglacial areas, and the paleogeographic events of the Early Pleistocene of Eastern Europe were correlated with those within the Western European region. [ABSTRACT FROM AUTHOR]