Geomorfologiâ i paleogeografiâ

Comprehensive investigations of the northern coast of the Sambian (Kaliningrad) Peninsula, that included geomorphological survey, lithostratigraphic description of the section logs, diatom, botanical and LOI analyses, radiocarbon dating, and GNSS survey relating lithological boundaries and sampling levels to the sea level and determining terrace elevations, were performed. New data on the regional palaeogeographic settings of the Late Glacial period and the stages of development of the large proglacial basin, the Baltic Ice Lake (BIL) were obtained. It has been established that after the degradation of the last glaciation, erosional (subaquatic) processes prevailed in the coastal area, while in the interval of 14–13 cal kyr BP subaerial conditions established at the study site, and tree-moss phytocenoses formed during the Allerød warming. At the end of the warming period there was a shallow, isolated lake, with decreasing depth. During the Younger Dryas oscillation, ca. 12 000 cal kyr BP, the area was flooded by waters of a vast freshwater, ultra-oligotrophic basin with high content of suspended fine mineral particles. The conditions of a shallow bay of the BIL sheltered from the main basin by a moraine ridge at least 4–5 m high, are suggested for this period. The lake drainage took place around 11 660 cal kyr BP. Since then, no accumulation or alternating accumulation and erosion conditions prevailed in the study site until the late Holocene. The obtained results allow us to speak about two stages of flooding of the northern coast of the Sambia Peninsula during the Late Glacial, possibly caused by the BIL transgressions. The occurrence of BIL deposits in the northern part of the Sambia Peninsula above sea level suggests that the Late Glacial basin level in the study area may have exceeded the present sea level.

Since 2014, the joint research team from the Institute of Earth Sciences, Northern Water Problems Institute KRC RAS, the Science Park of Moscow State University, as well as FSBI “VNIIOkeangeologia”, and Herzen State Pedagogical University of Russia has begun a study of Quaternary deposits of Onega and Ladoga Lakes, the largest Russian lakes located on the eastern periphery of the Baltic crystalline shield. Using large volume of data collected in previous studies, and new data obtained by multichannel seismoacoustic profiling and heavy gravity corers, as well as new methods for core analysis the main attention was paid to the geological development of these lakes in the Late Pleistocene-Holocene. The study of the lake Quaternary deposits makes it possible to accurately understand the dynamics of the Scandinavian Ice Shield retreat from the North-Western territory of the Russian Federation. At the same time, the major influence of the glaciers on the lakes formation during its degradation makes it possible to draw regional paleogeographic correlations, starting from the Baltic and ending with the White Sea. The history of the lake basins formation is also of considerable interest, given that there are practically no Phanerozoic deposits. The geological section of the lakes is represented by both Archean-Proterozoic and Quaternary formations.

The article discusses the analysis of new data obtained using multichannel seismoacoustic profiling and long sediment cores (Lake Onega), results of mathematical modeling of cycles of lake basins development (glacial, glacial-lake, lacustrine), and their correlation with the paleogeographic development of the White Sea.

The macrophyte pollen is a valuable source of information about lake level changes. Continuing our previous studies on the use of the macrophytes pollen analysis in the paleolimnology we studied the Lake Vitalievskoye sediments sequence of on the Valaam Island (the northern part of Lake Ladoga). To confirm the results of pollen analysis we conducted lithological and diatom analyzes. The macrophytes distribution of the island lakes at the present time has been established with the help of geobotanical and pollen analyzes of the lacustrine surface sediments. As a result, a comprehensive study made it possible to establish the stages of the Lake Vitalievskoye development during the Late Holocene: The Lake Ladoga Bay stage with a slight overgrowth of aquatic vegetation; the lake isolation stage of the from Lake Ladoga, when macrophytes disappeared from the lake, and the lake independent development stage, when their maximum distribution occurred and later began to decline as a result of the human impact. According to our research of the Valaam Island lakes we have received new data about the modern distribution of macrophytes in the island lakes, their dynamics in the Late Holocene. We also conducted a methodological study establishing the macrophytes pollen role in studying the small island lakes history and the Lake Ladoga level.

The relative sea-level changes for the time interval of ~12.1–9.1 ka cal BP were reconstructed on the eastern coast of the Gorlo Strait using the results of paleolimnological, GPR and geomorphological analyses conducted in the basin of the Srednyaya Tret’ Lake (7.3 m a.s.l., 66.014009° N, 41.086294° E), as well as UAV surveying of the lake surroundings. Bottom sediments of the lake were studied from the four core sections and correlated with each other according to the results of GPR data interpretation. Lithostratigraphic descriptions of bottom sediment cores, grain-size and diatom analyses, radiocarbon dating (AMS), determination of LOI, C_org content and C_org /N_org ratio were performed. We present the reconstruction of the coastlines at heights of 4–5 and 12–15 m formed by currents and/or wave processes within the lower Ruch’i River valley and Srednyaya Tret’ Lake according to field observations and interpretation of space images. As a result, the position of the relative sea-level and the chronology of the Late Glacial (Younger Dryas) transgression and the early stages of the Holocene (Tapes) transgression were refined. Late glacial transgression finished earlier than ~12.1 ka cal BP, and its relative level was probably no higher than 15 m a.s.l. After a deep regression, the relative sea-level approached the modern again ~9.5 ka cal BP, and at the Tapes transgression maximum (~9.1 ka cal BP) it was near the lake runoff threshold (∼5 m). Though the coastline was near the lake basin, sea waters never entered the lake. Sands, carried by the wind, accumulated in the part of the basin facing the coast. The the Srednyaya Tret’ Lake basin was gradually filled by fresh water according to the results of diatom analysis.

The article discusses the first results of studying the structure of the bottom topography and bottom sediments of Chukhlomskoe Lake (Kostroma Region, Chukhlomsky District). We analyzed the lake bottom topography based on the results of our bathymetric survey and discovered two hollows with maximum depths diverging from the lake’s center towards the city of Chukhloma. The maximum depth inside the hollows (and for the entire lake) reaches 5.4 m, and the average lake depth is 2.2 m. There are two steps seen in the bottom topography; 2.0–2.4 m and 1.5–1.8 m. The bottom sediment structure of Chukhlomskoe Lake was revealed by drilling from the ice with two boreholes (with lengths of 9.45 and 7.45 m, located in the area of background depths and inside the hollow, respectively). Five radiocarbon AMS dates were obtained for the core from the hollow’s bottom. The sedimentary sequences of the pre-Holocene part of both cores show high similarity in structure and depths of the marker horizons identified by a set of lithological analyses. The structure and thickness of Holocene sediments differ significantly. In the area of background depths, the Holocene organo-mineralogenic silt is 3.8 m, and inside the hollow, the thickness of this layer is only 1.45 m. Moreover, hiatuses in sedimentation were documented in the structure of the Holocene sediment inside the hollow. The age of hiatuses, based on the sedimentary model, was estimated as 10.6–5.3 and 4.9–0.06 thousand years ago. A probable mechanism for the origin of hollows is localized erosion caused by wind currents in a highly shallow lake. An additional erosion factor can be the degassing of bottom sediments, which leads to the loosening of the bottom layer of sediments, which makes them susceptible to erosion. The cutoff of sediment erosion inside the hollow coincided in time with the construction of a dam on the Veksa River and a rise in the lake level by 1.0–1.5 m in the 1960s.

A spore-pollen analysis of a 526 cm sediment core retrieved from Lake Bolshoe Miassovo, Southern Urals, was carried out. The obtained data made it possible to reconstruct the vegetation cover in the lake’s catchment area and the climatic situation of the region for 13 400 cal yr BP, which significantly expands and complements the paleogeographic chronicle of the Southern Urals. It was found that in the range of 13 400–12 700 cal yr BP in the conditions of a relatively warm and dry climate of Allerød, periglacial forest-steppe formations were widespread in the studied region. Steppe herb communities and birch-pine sparse woodlands with spruce grew on open landscapes. The pine degradation and replacement of spruce with more cold-resistant larch was most likely caused by a cooling in the period of 12 700–11 700 cal yr BP, which corresponds to the Younger Dryas. The periglacial forest-steppe formations are replaced by birch forests since 11 700 cal yr BP. The significant changes in the vegetation cover of the lake’s catchment area indicate warming and humidification of the climate at the beginning of the Holocene. The dominance of birch forests in the interval of 11 300–10 300 cal yr BP, probably, corresponds to the second half of the Pre-Boreal period. The distribution of pine and spruce in the range of 10 300–8300 cal yr BP indicates a warming of climatic conditions in the Boreal period. Since 8400 cal yr BP the proportion of broad-leaved species in the tree stand increases. The broad-leaved species cover reached its peak between 6000–4500 cal yr BP at the end of the Atlantic - the beginning of the Sub-Boreal period (Holocene climatic optimum). Some cooling of the climate was observed in the range of 4500–2000 cal yr BP, which presumably corresponds to the Sub-Boreal and the beginning of the Sub-Atlantic period. The birch forest with spruce and broad-leaved species grew in the lake’s catchment area. Some aridization and warming of the climate in the Sub-Atlantic period in the range of 1800–1000 cal. yr BP led to an increase in the role of pine and a reduction of spruce in the area around the lake. Since 1800 cal yr BP the vegetation of the territory adjacent to Lake Bolshoe Miassovo was similar to the modern one: pine-birch forests with an admixture of dark coniferous and broad-leaved species prevailed on the territory.

Numerous modern lakes appeared in the intermountain basins and on the high-elevation plateaus of Altai within the immediate distribution of glaciation in the Neo-Pleistocene. There is little known about the geochemical processes of autigenic mineral formation in lake systems under conditions of nival sedimentogenesis. The study of cores of bottom sediments of 8 high-altitude lakes of Altai showed that the waters of the lakes are fresh bicarbonate with variations in the cationic composition of Ca–Na. The bottom sediments of lakes are characterized by different ratios of mineral detrital material, autigenic minerals (calcite, gypsum, pyrite, illite) and mortmass of plant residues. In the bottom sediments of lakes located within the same basin (Bertek or Tarkhatinskaya), the absolute concentrations of elements differ within one standard deviation, with the exception of significant variations in the contents of individual elements (Mo, U, Li, Be). The enrichment of bottom sediments of lakes (Argamdzhi, Teply Klyuch, Krasnoe) with these elements is associated with the presence of ore concentrations (Mo, U, Li, Be) in the local catchment areas of a single lake. The mineral associations of the sediments of the studied lakes differ from each other in the composition of autigenic minerals, and from rocks, soils of catchment areas in the composition of layered silicates. In the composition of fine-scaled, tangled fibrous aggregates of the bottom sediment illite, the amount of iron is 2-4 times greater than in the composition of lamellar aggregates of micas, chlorites from rocks, soils of catchment areas. Cryogenic processes have determined the crystallization of gypsum nodules in the lakes Argamdzhi and Small Tarkhatinskoye; and calcite aggregates in Zerlyukol-Nur and Large Tarkhatinskoye in significant volumes for lakes with fresh water composition.