Sedimentary sequences up to 4.71 m thick and up to 24 ka were made by drilling the bottom sediments in three lakes of the Boguty depression. This is the highest mountain (2390–2470 m a.s.l.) and longest sedimentary record for the neighboring areas of Altai, Tuva, and Mongolia, which reflects the course of natural processes in the highest and most arid part of Russian Altai from the Last Glacial Maximum until the present day. As early as in the first stage of this study, the reservoir effect for moraine-dammed Upper Boguty Lake is estimated at 290 years for the present and 1.2 and 1.3 ka for the boundaries at 5.7 and 9.6 ka, respectively. Using a complex of analytical methods, the sedimentological transition zone between the Late Pleistocene glacial–lacustrine clays and the Holocene biogenic–terrigenous silts is identified at 16–13 ka ago; the size of glaciers in MIS-2 and in the Younger Dryas, as well as the time of formation of thermokarst lakes (no later than 8.7 ka), within the upper terminal moraine complex is established. Widespread tree vegetation in the now treeless Boguty depression in the first third of the Holocene is confirmed.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070115

Charcoal is a common material for radiocarbon dating. Meanwhile, it is underestimated as an object of dendrochronological analysis used to date natural and historical–archaeological events with an accuracy of up to a year. The new approach to charcoal sample preparation developed by the authors makes it possible to remove previous restrictions on this fragile material imposed in the dendrochronological studies and to use it as an efficient information source in paleoecology, paleoclimatology, paleogeography, and archaeology. This new method has been applied to construct a 377-year tree-ring chronology using archaeological charcoals from ancient iron-smelting furnaces in the Chuya–Kurai ferrous metallurgy province of the Russian Altai. This tree-ring chronology of charcoal is the first in Russia and the longest in dendrochronological practice throughout the world. Further analysis will provide new information on the nature and archaeological events of the high-mountain region located in the center of Eurasia.

In recent years, dendrochronological analysis in archaeology has undergone a substantial transformation, offering an opportunity to use samples of wood that were previously considered uninformative. One striking example is the analysis of charcoal excavated from archaeological sites. We have studied 448 samples of charcoal collected from metallurgical (iron smelting) furnaces in the Kurai and Chuya basins of the Russian Altai Mountains. Earlier methods of preparing such samples were slow and inefficient. Our approach guarantees fast, simple, and high-quality preparation of a large number of samples of virtually any size and shape. Its advantages include low cost of apparatus, high quality measurement of annual rings, the possibility of efficient remote measurement, no need for verification, and a wider range of measured parameters of the annual ring. Hopefully, the new approach will help to solve the critical problem relating to the construction of a tree-ring chronology in the arid zone of Southern Siberia. Such a c hronology will be highly prospective for assessing the age of wood from numerous mounds in the intermountain depressions of the AltaiSayan region, and year-by-year reconstructions of the humidity regime; and for revealing extreme droughts and other climatic phenomena in this territory.

Application of geological geomorphological and geochronological (14C, OSL) methods allowed to establish that the bordering mountains of the Chuya basin (Russian Altai) were affected by glaciation already in the Middle Pleistocene – about 160–180 ka ago (MIS 6). However, the maximal ice-dammed lake with the highest (up to 2100 m a.s.l.) strandlines both in the Chuya and Kurai basins existed later than 90–80 ka ago, in the Late Pleistocene. This chronological benchmark limits the influence of the cataclysmic outburst floods from the largest ice-dammed 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. It was drained no later than 16 ka ago. Synchronously (about 17–16 ka ago) the accumulation of diluvial-lacustrine cyclites began in the Inya mouth. The Saldzhar formation had been depositing as a result of not only flood events, but also gradual hydrological processes in the Katun river valley between the mouths of the Chuya and Sema rivers during the entire MIS 2. It is necessary to revise the concept adopted by SibRISC in 2018. This concept assumes i) absence of ice-dammed lakes in intermountain basins of the Russian Altai in MIS 2 and ii) accumulation of the Inya and Saldzhar formations deposited by glacial megafloods in the valleys of the Chuya and Katun rivers before 90 ka ago.

The upcoming edition of new stratigraphic scheme of Quaternary deposits of the Altai–Sayan mountain province is based on the concept of cataclysmic draining of the Pleistocene ice-dammed lakes that occurred prior to 90 ka (MIS-5 and earlier). Our geochronological (OSL, 14 C) and paleontological data argue against excluding the Sartansky cryochron (MIS-2) from the epochs of the Altai glaciogenic fluvial catastrophes. The last cataclysmically drained ice-dammed lake in the Chuya Depression existed after 37 ka. The Kurai Depression during MIS-2 was filled with water already by 25 ka and was drained at ~19–16 ka. Draining of the last ice-dammed lake in the Kurai Basin correlates with the onset of the formation of the section of catafluvial-lacustrine cyclites in the Inya River valley (a right tributary of the Katun River) at 17–16 ka (MIS-2). Previously, this section was suggested as a parastratotype of the Saldzhar catafluvial deposits accumulated during MIS-5 in the new edition of the Altai–Sayan stratigraphic scheme. OSL dates (16–12 ka) were obtained for deposits at the margin of the 70-m “Saldzhar” terrace of the Katun River upstream of the mouth of the Chuya River. The paleontological findings of lacustrine fauna in situ allow us to reconsider the concept of the exclusively catafluvial genesis of the Saldzhar deposits of the 60-m terrace of the Katun River, near the mouth of its left tributary, the Sema River. The OSL date (32 ka) of deposits at the base of this terrace indicates the onset of its formation not earlier than the end of MIS-3. The section proposed as the stratotype of the post-Saldzhar Maly Yaloman alluvium with the age 90 ka does not meet the requirements of the Stratigraphic Code, because the contact with the Saldzhar deposits has not been revealed here and genesis of deposits is controversial. At present, 14 С and OSL dates of the Saldzhar sequence and post-Saldzhar alluvium form two non-overlapping clusters, older than 90 and 35–12 ka, which can be connected both with methodological features of age dating and with insufficient geological knowledge. Only one of the eight IRSL and OSL dates obtained for Inya sequence deposits, which compose high (up to 300 m) bars in the Chuya and Katun river valleys, falls within the MIS-6 time, which is insufficient to establish its age as MIS-6 and older. To make correct stratigraphic reconstructions, it is necessary not only to expand a dataset obtained by different geochronological methods but also to study the dated deposits using a complex of geological methods.

Early documentation of the consequences of the Tsambagarav earthquake happened on July 23, 1988 (M = 6.4) compiled by Soviet and Mongolian specialists allowed the authors, using the example of Tsambagarav (Mongolian Altai), to assess the impact of the seismic process on the reduction of mountain glaciation and topography of the trough valleys in the arid region of Central Asia. In 1988, in upper part of the Zuslan river valley, 13 days after the earthquake, the release of a fragment of one of the glaciers gave rise to an ice-rock avalanche << on an air cushion >>. Its deposits with a thickness of up to 30 m blocked the valley over a distance of 5 km. Analysis of space images taken in different time together with field researches revealed that as a result of the earthquake the glacier N degrees 15 simultaneously lost 0.1 km(2) of its tongue (10.4% of total area), as the whole in 1988-2015 it lost 56% of its area, whereas neighboring glaciers N degrees 16 and 17, similar in size and the same exposure, lost significantly less - 35 and 15% of the area, respectively. Rapid shrinking of not only the glacier tongue, but also of its accumulation zone; the established deficit of ice volume in the broken off ice fragment (in comparison with initial assessment), and the abnormally long path of the avalanche made it possible to clarify the factors and mechanism of its initiation: the fall of the ice-snow ledge from the accumulation zone could lead to the rapid release of the broken ice fragment in the tongue part of the glacier. In 2004, 16 years after the avalanche, the buried ice in its deposits was still partially preserved, having completely degraded by 2019. The long time of the ice degradation process was caused by the high content (about half of the volume) of debris that armored the surface of avalanche sediments. The debris material of the avalanche repeats the relief of the underlying Pleistocene moraines, which may complicate the reconstruction of the number, scale and age of glacial events in avalanche hazardous areas. The relatively high rate of leveling of the avalanche traces and, as a consequence, the difficulties of their subsequent identification in the relief allow us to assume a greater number of avalanche releases, including seismic ones, in the recent geological past than it can be established at present in the Altai ridges.

ABSTRACT The available paleosol and paleowood data from the head of the Akkol trough valley, South Chuya range, indicates a climatically driven glacier dynamic in the Russian Altai. Radiocarbon dating of paleosols and paleotree fragments help determine the beginning of the Neoglacial in this high mountain region in the middle of the Holocene. New data limit the advance of the Sofiysky glacier at that time by the front of the Historical moraine. Less so than during the Historical stage (2.3–1.7 cal kBP), glacial activity 5–4 cal kBP is also supported by rapid reforestation. The Akkem moraine in trough valleys of the Russian Altai accumulated prior to the Holocene. The limitations and difficulties of radiocarbon dating of paleosols should be considered when interpreting the dating results.

A 48 km long zone of surface deformation produced by the Ms = 7.3 intracontinental earthquake of 2003 in Gorny Altai is studied in its five segments between the Aktru and Irbistu rivers, where ruptures show the greatest offsets and distinct structural patterns. A total of 554 coseismic ruptures of five slip geometry types are analyzed in terms of length, orientation, and relative percentage. The rupture patterns are discussed with reference to previously published evidence and compared with other strike-slip zones worldwide.

Multidisciplinary studies of various natural archives indicate contrasting changes in the human habitat in the high-mountainous southeastern part of the Russian Altai during the last 20,000 years. This period includes the final stage of the last glaciation and its degradation, the formation of the last giant ice-dammed lakes in the intermountain basins and their cataclysmic draining, considerable transformation of glacial landscapes to modern diverse and mosaic structure. Warmer and more humid climate in the first half of the Holocene was followed by cooling and repeated advances of mountain glaciers. The general trend to cooling and aridization in the second half of the Holocene is the most pronounced during the last two millennia. Deglaciation and final drying of intermountain basins boosted a renovation of the local ecosystems and established an environmental baseline of human occupation in the region. The arid climate, widespread permafrost and low population density determined a good preservation of archaeological heritage in the region, which is located at the crossroad between East and West, North and South. This paper presents the analysis of previously published and new data including newly obtained 14C and OSL dates, which allow to correlate climatically driven landscape transformations with habitat of ancient communities and cultures shifting in the region during the last 20, 000 years, as well as to assess the anthropogenic impact on the environment.

A complicated tectonic and sedimentation history of the high-mountainous south-eastern part of Russian Altai predetermined the presence of sources of ancient organic matter in the region. During the Pleistocene these deposits were affected by various exogenous processes that leads to mixing of young and old carbon in a unique (for each sample) ratio and strongly affects the results of radiocarbon dating. This paper presents the results of multidisciplinary investigations of pedosedimentary sequences and discusses C-14 dating of heterochronous organic matter in paleosols of two locations within the Chuya basin in the chronological context of the late Pleistocene megafloods. In the Kamsug valley reasonable evidence of the oldest (Pleistocene) paleosols in the SE Altai is described for the first time. The mineral composition of sediments and the results of pollen analysis argue for a short-distant redeposition of the Paleogene-Neogene parental substrate. Later it was transformed by Pleistocene pedogenesis: cryogenic processes, particularly solifluction, redox fluctuations resulted in redistribution of Fe and Mn. The analysis of available radiocarbon dates indicates that the contamination of the samples by extraneous carbon and the insufficient data about the features of organic matter of the studied soils don't allow to draw a definite conclusion about the time of the Pleistocene pedogenesis in the region. The presented OSL age 37.0 +/- 3.1 ka (GdTL 3424) predates pedogenesis in this location, as well as the last ice-dammed lake formation in the Chuya basin and its further cataclysmic draining followed by the deposition of cross-bedded gravels and pebbles. In the neighbouring Yamanterek valley radiocarbon dating result for paleosol returns erratic (aged) date due to the influx of ancient organic matter. Similarly, this date cannot serve as the upper chronological limit of ice-dammed lakes existence in the Chuya depression. The radiocarbon ages (9.7-11.3 ka cal BP) of charcoals from the underlying lens of humus sands postdate the last ice-dammed lake with the water level at least 1980 m a.s.l. It was demonstrated that short-distant redeposition of the Paleogene-Neogene sediments in the region preserves their main mineralogical and paleontological features. It gives an opportunity to recognise such redeposited sediments which contain geological carbon. Meanwhile the redeposition followed by pedogenesis introduces younger organic matter. Diagenesis of such originally different organic matter contributes the final pool of organic carbon and results in the formation of heterogenous and heterochronous organic matter. This should be taken into account while 14C dating and interpreting the obtained results.

Для одного из сильнейших (Мs=7,3) современных внутриконтинентальных землетрясений приводится детальное описание пяти фрагментов зоны сейсморазрывов протяженностью 48 км, расположенных между реками Актру и Ирбисту, где сейсморазрывы имеют максимальные амплитуды смещений и формируют закономерный структурный рисунок. Для 554 сейсморазрывов пяти кинематических типов проведен анализ распределения по длинам, ориентировкам, а также анализ соотношения разрывов разных кинематических типов. Рассмотрено строение зоны сейсморазрывов с учетом ранее опубликованных работ, а также в сравнении с другими сдвиговыми зонами Земли.

This paper presents the results of geological, geomorphological, geochronological investigations and the analysis of the biological composition of deposits within the high-mountainous Boguty river basin. The main stages of landscape evolution during the last 14 ka have been investigated through 32 radiocarbon dates. The area is located in the most arid southeastern part of Russian Altai and constitutes the eastern periphery of the Chuya intermountain depression, and the western side of the Chikhachev range. Postglacial landscape development of the upper reaches of the Chuya River began from the degradation of its vast glaciation. By 14 ka cal BP the glaciers had either completely melted or retreated above 2500 m above sea level. As a result, numerous lakes occupied open places and five types of these basins can be seen in the modern topography. They are large moraine-dammed lakes connected with the Boguty River, while some basins have been dammed by uplifted tectonic blocks and numerous lakes are of thermokarst origin or are small cirque lakes and temporal lakes fed by seasonal meltwater from meteoric, ground water and permafrost degradation. Large moraine-dammed lakes within the Boguty basin were developed before the Holocene. The water filling these basins was controlled by the height of moraine dams and by the depth of the Boguty river incision. The moraine-dammed Low Boguty Lake formed earlier than 10 ka cal BP. Its partial draining and transformation of littoral zone into peat bog took place about 8.2-7.6 ka cal BP. As a result of the analysis of biological composition, four stages of water level fluctuations in the lacustrine-boggy system were recognized. The specific geomorphic and sedimentary features in the middle part of the Boguty basin determined the recurrence of debris flow events at about 8-7; 2.9-1; 0.65 and 0.3 ka cal BP, but the last event occurred in June 2017. The occurrence of fossil forest soils dating to about 11-8.5 ka cal BP and of charcoals (Larix sibirica Ledeb) of about 8.5-7.8 ka cal BP indicate a prolonged period of developing forest vegetation in the Boguty basin, which is currently treeless. In general, the data suggest that in SE Altai the climate in the first half of the Holocene was warmer and more humid in comparison with the modern one. The second half of the Holocene has been characterized by colder climate conditions accompanied by aridity intensification, which became especially pronounced during the last 2-1.5 ka.

The high mountainous southeastern part of Russian Altai is characterized by complicated sedimentation history. As a result of tectonic movements, Paleogene, Neogene, and even more old Carboniferous and Jurassic organicrich deposits had been partly uplifted and exhumed on the ridge’s slopes, where during the Pleistocene, they were affected by various exogenous processes including glaciation, glacio-fluvial erosion, winnowing activity of ice-dammed lakes, sliding during lake-draining events, followed by further intensive Holocene erosion, pedogenesis, and permafrost formation/degradation. Remobilized ancient organic matter had been involved into geomorphic and pedogenesis processes and affected the results of radiocarbon dating. Numerous radiocarbon ages obtained revealed several typical problems in interpretation of dating results, which was confirmed by multidisciplinary investigations of associated sediments in a wider regional context. This article presents a discussion on obtained apparent radiocarbon dates of organic material from ten sections of the SE Altai. In addition to radiocarbon analysis, in each case multidisciplinary study was carried out in order to properly interpret obtained dates, as well as to explain the inability of directly using apparent 14C ages as a geochronological basis for paleogeographical reconstruction. The analysis presented is of vital importance for establishing the chronology of formation of large ice-dammed lakes and their cataclysmic draining; revealing chronology and paleoenvironmental conditions of pedogenesis in the highlands of the SE Altai; and estimating the range and magnitude of the tectonically driven topography rebuilding in the post-Neogene time.

The paper presents results of integrated geological, geomorphological, geochronological, and geoarchaeological studies in the basin of Lake Ak-Hol located in southwestern Tuva (Russia), in mountains north of the Great Lakes Basin of Mongolia. The Pleistocene-Holocene history of the basin consisted of several stages recorded in terrain and deposition patterns. The highest stand of Lake Ak-Hol (180m above the present level and 16 times greater area) was due to an ice dam and was coeval to the appearance of organic matter (remnants of higher aquatic plants and algae) in lake sediments about 14 ka cal BP. At the next stage, the lake was impounded by a moraine dam. C-14 ages of buried soils indicate that the level of the ice- and moraine-dammed lake fell to below 222m asl long before 8.5 ka cal BP. Erosion of the moraine dam may correspond to the event of lake drying about 12 ka cal BP evident from a deposition gap in sedimentary cores. That event of sudden drainage may have been the last catastrophic flood into the Great Lakes Basin traceable in the catchment of the Mogen-Buren River. Judging from the obtained C-14 ages of sediments from the Mogen-Buren Valley, ice- and moraine-dammed lakes in the Ak-Hol system underwent cataclysmic outburst floods only before 11.6 ka cal BP. In the Holocene, after the moraine dam failure, the lake level changes were controlled solely by climate. The general decreasing trend was repeatedly interrupted by high stand excursions (up to 15m of relative level rise). Nomad peoples settled on the floor of the highland Ak-Hol basin since the Late Bronze Age. All archaeological sites (from that time to the time of Turkic cultures) mapped in the basin are located above 2220m asl and lack signatures of water erosion, indicating that the lake never rose above that altitude for the past 3 ka years.

Results from geomorphological, sedimentological and geochronological analyses, together with micropaleontological and mineralogical characteristics of lacustrine deposits in five locations within the Kuray intermountain depression, southeast Altai, mountains of south Siberia, support the thesis of repeated formations of ice-dammed lakes during MIS-2 and their draining by high energy floods. Our data suggest that the timing of one of the last cataclysmic draining events in the area can be estimated by an Optically-Stimulated Luminescence (OSL) age of 19.0 +/- 1.1 ka for a sandy layer at the top of the diluvial (i.e. large flood) deposit, revealed in a sedimentary sequence of the 1570 m a.s.l. strandline - one of the lowest preserved strandlines in the western part of the basin. New OSL and radiocarbon ages, augmenting previously published dates, indicate that the last lake to occupy the Kuray depression occurred around 19-16 ka with a depth of at least 170 m in the central part of the basin and to a depth of no less than 220 m near the glacier dam. Lacustrine deposits are represented by two horizons of sandy clays separated by interlayers of mixed-size sands. The mineralogical data, supported by analysis of sedimentological and micropaleontological records, indicate accumulation of a lower lacustrine horizon in a deeper reservoir. Finding of Leucocythere sp.1, Leucocythere sp.2, and Leucocythere dorsotuberosa ostracod species in lacustrine deposits characterizes these reservoirs as periglacial freshwater cold and deep lakes. The presence of well-crystallized mica and chlorite in lacustrine silts and clays from the lower lacustrine horizon indicates cold, dry conditions at the time of their formation, as well as a predominance of physical weathering of rocks within the denudation area. After an abrupt dropping of the lake level around 16 ka, determined from OSL dating, the lake never recovered its former depth. The available radiocarbon ages for organic material in subaerial deposits within the study area and the new OSL ages suggest that the last ice-dammed lake in the Kuray basin was drained between similar to 16.7 and 9.9 ka. The presence of this lake might explain the absence of late Paleolithic surface finds within the basin that remained generally unsuitable for human habitation until its final drying. The last outburst flood passed along the Chuya and Katun river valleys, which had been already carved by older cataclysmic floods, but did not significantly affect the topography downstream of the Kuray-Chuya intermountain depressions. We numerically simulated the draining of a palaeolake in the Kuray basin with the water level 1650 m a.s.l. (maximal depth about 220 m near the dam) with different scenarios of breaching the ice dam. In contrast to a relatively gradual breach of the ice dam due to thermal erosion, an instantaneous dam break due to structural failure can cause an outburst flood with a peak discharge of around 2 x 10(6) m(3) s(-1). The high speeds of the water flow, 1.9-5.6 m s(-1), with the maximum Froude numbers of 0.06-0.22, and peak Shields values of 0.03-0.25 indicate competence to mobilize gravel. Generally, the simulated flow remained subcritical, suggesting that bedforms developed under supercritical flows, such as antidunes, could not have developed, although the development of dunes cannot be precluded. Our data also contribute to the issue of correlating the low lake strandlines in the Kuray basin with the landforms associated with cataclysmic outburst floods.

During the field works in the summer of 2018, in the Lena River delta on the Sardakh-Sisse Island, prints of leaf flora belonging to species of broad and small-leaved deciduous trees were found. The prints found by us are confined to the layer of ferruginous sandstones at the base of the section. The following taxa established: Platanus sp., Alnus sp., Fagus sp., Salix sp. In addition, a fossilized fruit belonging to Magnolia sp. The findings allow to conclude that there are mixed forests in the early-middle Miocene in this region, consisting of coniferous, small- and broad-leaved deciduous species of trees and shrubs.