Vol 56, No 4 (2025): NO4 (2025)

В последние годы палеолимнологическое направление в палеогеографии характеризуется небывалым развитием в нашей стране и за рубежом. Озерные отложения являются подробнейшим природным архивом всех изменений климата и ландшафтов на протяжении длительного времени их развития. Новые технические и аналитические возможности отбора проб донных отложений озер и их исследования позволяют получать все более детальные палеогеографические реконструкции и данные о тех или иных параметрах окружающей среды. По результатам 6-й Международной конференции “Палеолимнология Северной Евразии” и Школы молодых ученых, организованной Сибирским федеральным университетом, Институтом биофизики СО РАН (обособленное подразделение Федерального исследовательского центра “Красноярский научный центр” СО РАН (Красноярск) и РГПУ им. А. И. Герцена (Санкт-Петербург) совместно с Институтом лимнологии СО РАН (Иркутск), Институтом географии РАН (Москва), Институтом озероведения (обособленное подразделение ФИЦ “Санкт-Петербургский научный центр РАН”), Санкт-Петербургским государственным университетом (Санкт-Петербург), Северо-Восточным федеральным университетом им. М. К. Аммосова (Якутск), Казанским (Приволжским) Федеральным университетом (Казань), Русским географическим обществом (Палеолимнологическая комиссия Санкт-Петербургского отделения ВОО РГО) и состоявшейся в конце августа 2024 г. в г. Красноярске, сформирован специальный выпуск журнала под названием “Донные отложения озер – сквозь время и пространство”. Специальный выпуск журнала “Геоморфология и палеогеография” состоит из статей, подготовленных участниками конференции на основе представленных ими докладов. Международная конференция “Палеолимнология Северной Евразии” проводится один раз в два года на площадках научных и образовательных учреждений нашей страны по очереди в европейской и азиатской частях (Петрозаводск, 2014 (Институт водных проблем Севера КарНЦ РАН); Якутск, 2016 (СВФУ); Казань, 2018 (КФУ); Иркутск, 2020 (Лимнологический институт СО РАН, дистанционный формат); Санкт-Петербург, 2022 (РГПУ им. А. И. Герцена); Красноярск, 2024 (СФУ)). Отобранные статьи представлены оригинальными научными работами, отражающими широкий спектр палеолимнологических исследований в нашей стране, включая разные регионы (от Кольского п-ова до Магаданской области и Приморья), объекты и тематику исследований. Специальный выпуск журнала состоит из двух крупных разделов: “Озера Европейской части России” и “Озера Сибири и Дальнего Востока”. В статьях представлены не только результаты палеолимнологических исследований современных озер, но и анализируются данные изучения существовавших в прошлом водоемов, следы которых сохранились в толщах четвертичных отложений.

A comprehensive study of the bottom sediments of a lake located at an elevation of 27.0 m on the Barents Sea coast in the Mustatunturi Ridge area, Murmansk region, was carried out. Lithological, diatom, granulometric, geochemical analyses, loss on ignition (LOI) and radiocarbon dating were made. Based on obtained data five sedimentation stages were described, the change in which occurred as a result of the Barents Sea level changeand, probably, a catastrophic event in the Holocene. It has been determined that at first this basin was an uneven seabed, where marine sediments, represented by silt and sand, accumulated. With the intensive uplift of the earth’s surface of the Fennoscandian shield, the basin gradually isolated from the sea, mineragenic sediments are replaced by organogenic ones at the beginning of the Holocene. The formation of transitional organogenic sediments occurred in stable and calm environmental conditions, when the sea level was located slightly below the runoff threshold from the lake, and sea water periodically penetrated into the basin during tides. The repeated ingression of sea water into the lake basin was recorded in the Middle Holocene, which is expressed in the section by the accumulation of poorly sorted mineragenic deposits with inclusions of plant remains, an increase in the grain-size, a decrease of organic material and the dominance of marine species of diatoms. This could have been caused by several reasons, or perhaps a combination of them: the Tapes transgression, the Storegga tsunami, or another catastrophic event. About 8000 years ago, the lake basin was finally isolated from the sea, and freshwater organogenic sediments began to form. The average rate of uplift of the study area over the past 8000 years was 3.5 mm/year.

As a result of drilling of bottom sediments from the ice of the Petrozavodsk Bay of Lake Onega in 2019, the entire section of supralacial sediments was uncovered for the first time, including the upper horizons of the bottom moraine, which, according to seismoacoustic data, overlaps the surface of the bedrock, and the entire thickness of lacustrine glacial and lacustrine sediments. The new data obtained will complement the information under what conditions and to what extent the sedimentary material entering Lake Onega changes during the last glacial–lacustrine-glacial–lake sedimentation cycle. A modern complex of mineralogical and geochemical methods (atomic absorption, mass spectrometry with inductively coupled plasma, X-ray diffraction and X-ray phase, using scanning electron microscopy) has been used to study sediment samples (section SP-0002, thickness 9.86 m). It was revealed that the vast majority of sedimentary material of lacustrine-glacial and lacustrine deposits is represented by particles of pelitic and siltstone-pelitic dimension and is formed mainly by the following minerals: quartz, feldspar, muscovite, illite, chlorite, hornblende. In the upper part of the section (ochreous and homogeneous silt), mineral phases Fe and Mn (goethite, vivianite, siderite, pyrolusite, rhodochrosite) and fragments of diatom shells (SiO_2bio) are added to this group of minerals. Based on new data on the mineral and geochemical composition of the bottom sediments of Lake Onega, according to the calculated lithochemical indices CIA, ICV and modules GM, FM, common features and differences between individual isolated sediment bundles in the continuous section SP-0002 have been established. It has been established that the bottom sediments formed throughout the entire postglacial cycle have a similar mineral and geochemical composition. They are dominated by clastic material mixing products of erosion of Archean and Proterozoic granitoids, volcanogenic-sedimentary and sedimentary rocks of the Baltic crystalline shield, and material from sedimentary rocks of the Russian Plate. The pelitic and siltstone-pelitic dimension of the bulk of the mineral grains, the strong enrichment of bottom sediments with stable minerals and layered silicates, indicates the long-term nature of their transfer or the repeated redeposition of sedimentary material. The revealed weak degree of chemical weathering for sediments from the lower part of the section (lacustrine-glacial varve clays) indicates that intensive physical denudation prevailed in the conditions of nival sedimentogenesis on loose substrates of the catchment areas, as well as the significant role of aeolian transport of a large volume of sedimentary matter. The predominance of mostly moderately weathered material in the packs of homogeneous lake clays and silts, as well as in the “pink horizon” of varve clays, indicates a significant humidification of the climate during their formation.

The study of an ancient lake basin adjacent to the right side of the Ustye River valley (northern macroslope of the Borisoglebsk Upland) was conducted. The set of methods included a detailed study of the catena laid within the coastal zone of the lake basin, hierarchical morphological analysis of sediments and soils at the macro-, meso- and microlevels, granulometric and bulk chemical analysis, general chemical properties and composition of clay mineralogy. The study was supported by OSL dating. The results of the studies do not indicate the existence of a uniform network of periglacial dammed lakes in the Last Glacial Maximum of the Valdai glaciation, primarily due to the absence of a runoff threshold for the lake basins. The lake basin we studied is associated with isolated lake basins with local aquicludes and drainage systems. In the coastal zone, under the thickness of lake sediments at a depth of about 2 meters, a glacial till of Moscow age is exposed. The presence of four different layers of lake sediments is associated with the flooding/drying cycles of the lake basin. All layers show combination of features of both mesomorphic and hydromorphic pedogenesis, reflecting the complex dynamics of the lake basin. Lake sedimentation ended in the Middle Valdai interstadial (31±3 thousand years ago). The subaerial stage of the lake basin evolution was manifested in three stages of aeolian sedimentation 18.5±1.3 (layer III), 16.6±1.3 (layer II) and 12.0±0.9 thousand years ago (layer III). The sediments of the first two stages are represented by thin layers and lenses of sand (layer III) and silty loam (layer II). A mantle of loamy-sandy loam aeolian sediments of the final stage (layer I) universally covers the lake sediments, and beyond the basin – the glacial till. The Bt horizons formed in the glacial till do not differ in the surface and buried bedding, which clearly indicates that the soils formed in glacial tills of Moscow age were under the influence of soil formation during the last interglacial.

When studying the late Pleistocene–Holocene lacustrine sedimentary records from lake cores, the chronological interpretation of the analyzed characteristics is made applying a depth-age model (DAM). Usually, DAM is based on the results of radiocarbon dating. As a rule, the measured value is correlated with the average or median value of the calibrated C age of the corresponding centimeter of the core. This approach ensures the transfer of data from the depth scale of the sedimentary section to the calendar time scale “point to point”, i. e., seemingly, without loss of accuracy. However, in reality it ignores the probabilistic nature of determining calendar age and can thus lead to erroneous chronological reconstructions or an overestimation of their accuracy. We propose an alternative approach that takes into account the probability density function of the calendar age calculated applying the DAM and allows to avoid these problems. By the example of the late Pleistocene–Holocene bottom sediments of the Upper Boguty Lake located in the high-mountain Boguty Depression, South-Eastern Altai, the difference in the application of both approaches to the chronological interpretation of the results of anthracological and spore-pollen analyses is demonstrated. The analyzed sediment characteristics – the charcoal accumulation rate (CHAR) and the content of pollen of woody vegetation in pollen-spore spectra – refer to fundamentally different types of data. Two sample sets represent discrete / relatively continuous measured numerical values and the presence/absence of zero values. It is shown that the chronological reconstruction of both types of data should be carried out taking into account the probability density of the calendar age calculated applying the DAM. Another important issue for correct reconstructions is the appropriate interpretation of zero values of measured characteristics, which is especially important in case of discrete sample. Zero values can be either true, reflecting real changes in the natural paleoenvironmental conditions, or be a result of missing or impossible to determine a specific parameter in a small volume of sediment sample. In each case, the researcher must make an appropriate choice using additional information. In general, the accuracy of the chronological interpretation of the analyzed characteristics of lake sediments and the reliability of the further paleogeographic reconstruction are determined primarily by the quality of the DAM. In this context the presented approach allows us to understand the limitations and accuracy of this reconstruction.

This paper presents a new palynological record from the 144-cm-long, annually-laminated sediment core Shira-2021-II-1, obtained in 2021 from the bottom sediments of the deep-water meromictic Lake Shira, located in the North Minusinsk Basin, south Siberia. Information on the history of vegetation and climate of the region in the Late Holocene is still scarce. New data allows for partially filling this gap in current knowledge. The new record of non-pollen palynomorphs and geochemical indicators of natural environmental change covers the last 3000 years at an average resolution of 21 years. The new results supplement the available regional reconstructions of the climate and dynamics of the hydrological regime of Lake Shira and confirm the assumption that changes in the lake’s hydrology in the Late Holocene were mainly related to large-scale atmospheric circulation processes controlling the water and temperature balance of the Minusinsk Basin. Despite the long regional history of mobile pastoralism, non-pollen palynomorphs and geochemical indicators, as well as available pollen records, suggest the onset of active anthropogenic activity since the second half of the 20th century. In general, the new proxy records show the importance of non-pollen palynomorphs from annually laminated lake sediments for high-resolution temporal reconstructions of lake hydroclimate and general moisture variability in steppe regions of southern Siberia.

Evolution of two coastal paleo-lakes and short-term multi-proxy study (diatom, botanical analyses, and ash content). The age-depth models were made using 10 radiocarbon dates and tephrostratigraphy. The sediments contain tephra from the caldera-forming eruption of 946/947 and 1903 CE. Sedimentation rates and changes in biotic components are estimated. The formation of the “southern” paleolake on the place of a freshened lagoon occurred ~4060 BP. At the initial stage, the diversity of the diatoms in the lake was maximal, although the conditions for diatom development cannot be considered favorable – the concentration of frustules sharply decreased. The swamping began to develop ~3370 yr BP, close to the beginning of the period of prolonged droughts in the region associated with a decrease in the intensity of the summer monsoon. High-resolution records show that the area manifested two “dry” cold events comparable to global ones (2800–2600, 1700–1300 yr BP) and the Little Ice Age with high humidity. The second half of the Medieval Warm Period (945–830 yr BP) was the warmest, and the moisture content decreased. The processes in the Pacific Ocean played a major role in regional hydroclimatic changes, and the links between these climatic changes with the intensity of the summer monsoon, as well as the dynamics of sea surface temperature, El Niño, the activity of the Kuroshio Current, and other factors determining the movement of air masses are considered. The phases of vegetation development of heavily watered bogs formed on the place of coastal lakes are reconstructed. Correlation of the paleoclimatic changes with regional records (northeastern China, South Korea, and Japan) was carried out. The studied sections recorded the passage of extreme hydrological events, including the tsunami of 1026 CE.