Cryogenic Soils in the Chara River Valley (Transbaikalia)

Introduction           

As objects of research in the article, sections of cryogenic soils laid in the summer of 2022 in the valley of the Chara River (Chara basin, northeastern Transbaikalia) at different hypsometric levels are selected - two of them are located on the seven–meter terrace of the Chara River, one on the flat top of the Udokan ridge bordering the Chara basin from the southeast. Thus, we have considered soils belonging to different altitude zones, the contrasting change of which was observed here earlier. The soils in the valley of the Chara River were diagnosed by us as cryogenically-hardened gleezems, and at the top of Udokan the soil profile attributed to peat-lithozems was studied. In general, the soil profiles described and diagnosed by the authors are integrated into the generally accepted ideas about the structure of the soil cover of this territory, moreover, supplementing and clarifying them.

            In addition to morphological descriptions of soils and conclusions about the leading soil-forming processes, conclusions were also drawn about the profile distributions of chemical and physico-chemical properties of the studied soils. To accomplish this task, the authors carried out laboratory processing of 6 soil samples from two sections. Among the types of chemical analytical work carried out by us were the determination of the acidity of soils and the content of easily soluble salts in them in aqueous extract, the determination of the carbonate alkalinity of these soils, as well as the content of organic carbon and the analysis of the granulometric composition of soils.

            The study of all the components of the landscape of the Charskaya basin has recently become very important due to the intensification of the development of the largest in Russia (and the second in the world) proven reserves of copper ores of the Udokan copper deposit and the concomitant development of the entire adjacent territory. Since the qualitative development and development of the territory, especially with such a heterogeneous landscape as in the Charskaya basin, is impossible without the results of detailed studies of nature, it is necessary to further in-depth study of the diversity of soils, the structure of the soil cover, as well as a variety of soil properties.    

Geographical location The sections of cryogenic soils were laid by the authors in early July 2022 in the valley of the Chara river.

The research area is located in the southwestern part of the Charskaya Basin (also called the Verkhnechar Depression), surrounded by the Kodar ranges in the northwest and Udokan in the southeast. Soil studies were conducted at two key sites. One of them (56°45’38.72’ s.w., 118°11’30.12’ v.d.) is located directly near the shore of the Chara river in the area of the confluence of the Belenky Stream into it (Fig. 1). About 10 km north of this site is the tukulan Charsky Sands and the village of Chara, in 8 km to the northeast is the village of Novaya Chara and the station of the same name on the Baikal-Amur Railway (BAM). The second one is on the top of the Udokan ridge (Fig. 2) at an altitude of about 1400 m (56°39’41.20’ s.w., 118°22’36.44’ v.d.), 5 km north of it is the village of Udokan.

Fig. 1. The landscape of the valley of the Chara river in the area of the confluence of the Belenky Stream into it (on the far left – the Charsky Sands tract and chr. Kodar). Photo of D.O. Sergeev, taken with the help of a DJI Mavic Air UAV

Fig. 2. The landscape of Kurum on the slope of hr. Udokan. Photo by A.P. Ginzburg

Geological structure of the territory and quaternary deposits            

Geologically, the northeastern part of the Trans-Baikal Territory is an extremely complex system. The predominant genesis of the rocks common here is igneous, granitoids occupy more than 70% of the area of more than 800,000 ^km2. These formations are confined to the Mongol-Okhotsk (Mongol-Trans-Baikal) mobile belt. Its formation took place in the Archean-Early Cretaceous time and included six major stages of magmatism:

1. Vend–early Cambrian: the foundation of the Caledonian eugeosyncline, the main volcanism with ultrabasic intrusions.

2. Cambrian–Silurian: formation of external carbonate deflections in areas adjacent to the eugeosyncline, mass formation of granites.

3. Devonian: orogenic activation, local development of acidic and mixed volcanism. Intrusions of alkaline earth syenites, granites and alaskan granites.

4. Carbon–Permian: tectonomagmatic activation, intrusive series of gabbro-monzonite-syenite, alkaline-syenite and alkaline-granite composition.

5. Triassic–Cretaceous: a series of tectonomagmatic activations with the laying of volcanotectonic structures, superimposed depressions with intrusions of normal and alkaline earth granodiorite –granite-leucogranite series and outpourings of basaltoids.

6. Quaternary period – rifting and outpouring of alkaline basaltoids.

The geological foundation of the territory of the Charskaya basin is mainly composed of Archean-Proterozoic strata of igneous rocks. These are mainly granites, granodiorites, gabbro, gabbro-diorites, etc. deposits belonging to the lower and upper Archean and lower Proterozoic. These strata are permeated by Lower Proterozoic (granites, granodiorites, gabbro, norites, gabbro-norites, gabbro-diorites, serpentinites) and Late Jurassic (granites, granodiorites, diorites and quartz diorites, granosienites, monzonites) intrusions. In some places, sedimentary rocks of Early Cretaceous, Middle and Late Jurassic age, as well as Lower Paleozoic massifs come to the surface. To the south of the basin, the Pliocene opens-the lower quaternary link of volcanogenic formations of mainly basic composition.

Quaternary deposits occupy almost the entire territory of the bottom of the basin. The youngest of them are Holocene channel facies of alluvium in the valley of the Chary river of sandy granulometric composition. On the right and left banks of the Chara, loamy deposits have a lacustrine genesis (late Pleistocene-Holocene age), in the foothills of the Kodar and Udokan ranges, glacial and water-glacial deposits overlain from above: pebbles, boulders, gravel. 

 Terrain of the territory

The Charskaya basin is an intermountain depression elongated from the southwest to the northeast with a fairly wide flat bottom, fenced from the northwest by the steeper and higher Kodar ridge (heights up to 3,072 m), and from the southeast by a lower and gentle Udokan (heights up to 2,561 m).

The width of the basin in its middle part is about 35 km, the length is around 125 km.

            The marks of absolute heights on topographic maps of this area in the central part of the basin are from 695 (the valley of the Chara river in the area of the confluence of the Apsat River) up to about 792 m (dune massif of the Sands tract). To the north of the village of Novaya Chara, a hill rises to a height of 925.5 m above sea level, the top of which is considered the highest point of the plain part of the basin.

Fig. 3. Schematic profile of the Charskaya basin: 1 – bedrock overlain by low-power loose sediments; 2 – unsorted sands and sandy loams of removal cones and foothill plumes with an abundance of boulders and pebbles; 3 – boulder sandy loams of moraines; 4 – sandy deposits of terraces; 5 – sands, sandy loams and loams of floodplains and low floodplain terraces; 6 – larch forests; 7 – larch-pine and pine-larch forests; 8 – larch woodlands; 9 – spring forests; 10 – swampy meadows and swamps, from ^[1]

              Most of the bottom of the basin is composed of polygenetic sedimentary deposits of considerable thickness, under which outcrops of bedrock are periodically indicated, for example, in the form of a chain of hills up to 200 m high (Fig. 3). In general, the basin is characterized by the predominance of water-glacial and alluvial sandy loam and sandy deposits, mainly fine sands, in the central parts, and along the edges – a wide distribution of glacial boulder-pebble sandy loam and proluvial gravel-pebble deposits. The material of both relief tiers has been substantially reworked by cryogenesis processes ^[1].

Fig. 4. The main parts of the Udokan ridge: 1 – the foothills of the northern slope; 2a – the area of dominance of sharply divided loaches; 2b – the area of dominance of flat-topped loaches; 3 – the Upper Kalar basin; 4 – the foothills of the southern slope, from ^[1]

            The Cenozoic rise of the entire mountainous country of Transbaikalia is considered one of the most important agents of the formation of the mountainous relief of the territory of the region, since it was thanks to this event that modern alternations of mountain-valley sections and the dismemberment of the territory were formed. Tectonic uplift and subsidence eventually led to the presence here of a system of mountain ranges (Kodar, Udokan, Kalarsky, Yankan, etc.) and intermountain basins (Charskaya, Verkhnekalarskaya, etc.). The uplift of the Udokan ridge was accompanied by outpourings of basalts and the creation of extensive summit basalt plateaus. Then the modern appearance of the mountain relief was formed under the influence of the successive change of several epochs of mountain-valley glaciation with interglacials, during which large rivers (Chara, Vitim, etc.) cut through dense igneous rocks ^[1]. At present, the Udokan ridge, depending on geological and geomorphological conditions, is divided into 4 main parts (Fig. 4). The northern foothills are sub-latitudinal elongated flat-topped ridges with heights up to 1200 m, after which the areas occupied by flat-topped loaches are wide in the highlands, and the depression territory occupied by the Verkhnekalar intermountain basin is surrounded by sharply divided loaches (see fig. 4).  

Geocryological conditions The research area is located in the area of continuous permafrost distribution.

The average temperatures of permafrost vary significantly depending on the geomorphological conditions of the occurrence of frozen sediments, as well as depending on their lithological composition. The average temperatures of frozen soils on the surfaces (in the period from 2006 to 2014) vary from +1.5 °C (clumpy-gravelly deposits of the Cranberry Creek valley, height 1338 m) to -6.7 °C (kurum on the slope of the eastern exposure of the cr. Udokan, height 1712 m). The soil temperature at the depth of the sole of the active layer also varies quite widely: from 0.3 ° C (an array of fluttering sands, height 735 m, depth 1 m) to -9.4 ° C (the kurum slope of the southwestern exposure, height 1155 m)^[2]. At the CALM (Circumpolar Active Layer Monitoring program) site, located near the confluence of the Belenky Creek with the Charu River, the depths of seasonal thawing vary from 0.48 to 0.93 m, while the most frequent average values vary between 0.62-0.68 m ^[2]. At a depth of 0.5 m, seasonal fluctuations in soil temperature absolutely do not repeat in the shape of the graph those observed on its surface, only 4-5 months a year significantly differing from its constant value of 0 degrees Celsius. The amplitude of the soil temperature at a depth of 0.5 m in 2007-2008 was 15 degrees (from +1 to -14 ° C), whereas at a depth of 1.3 m for the same period it is approximately 11 degrees. At the same time, on the soil surface, the temperature amplitude for 2007-2008 reached 60 degrees (from +25 to -35 ° C). The two-year course of the kurumnik soil temperature (height 1155 m) on the slope of the Udokan ridge at depths of 0.38, 0.95, 1.5 and 2.05 m largely repeat the shape of the graph of the course of the temperature of the surface air layer, and the amplitudes have values from -34 to +25 ° C (on the surface) and from -30 to +5 °C (at a depth of 2.05 m) ^[3].

            Seasonal thawing on the terraces and floodplain of Chara begins in early May and ends in October, and the thickness of the seasonally thawed soil layer varies greatly from 0.5 to 1.0-3.5 m ^[4]. Small snow cover capacities, low precipitation and wide air temperature amplitudes during the year led to the fact that numerous forms of polygonal relief and re-vein ice (PPL) became widespread on the flat part of the bottom of the basin ^[5-7], which many researchers mistakenly ^[8] considered relics of the Pleistocene epoch, since they evaluated them The age is indirectly determined by the position in the relief, as well as by the granulometric composition of the sediments containing them – medium and large sands with layers of gravel and pebbles ^[8]. Especially often, PZHL are included in the deposits of the first above-floodplain terrace of the Chara River. According to the results of radiocarbon dating obtained by Yu.K. Vasilchuk and co-authors ^[6,7], the ice veins have a radiocarbon age from 7,840 ± 60 to 10,230 ± 95 years, which corresponds to the Early Holocene age. The values of ?18 ^O and ?2 H obtained during the analysis of stable isotopes of oxygen and hydrogen in melt water from PPL are on average -23 and -180, respectively. When converting isotopic data into paleotemperature, it was found that the average winter temperatures during the winter periods of the Holocene optimum (10-7.5 thousand years ago) could be colder than modern ones by 2-3°C, and the average January temperatures by 3-4°C, which contributed to the formation of very large (up to 7 m high) terraces in the sandy sediments of the Chara River PPL ^[5-7]. 

Climate The climatic conditions of the Charskaya basin as a whole are characterized by climate features characteristic of most of Eastern Siberia, while local physical and geographical factors create meso- and microclimatic features on the territory of the basin.

The climate belongs to the sharply continental type, which is due to the remote location from the seas ^[9-12]. The main element of the general circulation of the atmosphere of the northern hemisphere, which forms the climate of the region, is the Siberian (Asian) anticyclone – an area of increased pressure over the northeast of the continental part of Eurasia ^[10].

The average air temperature during the year, according to the meteorological station in the village of Chara (the wide flat part of the bottom of the basin) is -7.8 °C, on average falling in January to -31.8 °C with a historical minimum of -57 °C. In July, the average air temperature is at +16.8 °C, but there are frequent cases of increases to +30 °C or more (the historical maximum is +34 °C). The temperature below 0°C stays in the Spell for 207 days, below -10 °C – about 162 days ^{[9, 11]}.

            On the slopes of the ridges bordering the Charskaya basin, a pronounced temperature inversion is observed when climbing up. So, for example, if the average January air temperature in the village of Chara (708 m above sea level) is -31.8 °C, then at meteorological stations in the village of Nizhny Ingamakit on a spur of the Udokan ridge (1069 m above sea level) ^[9] and the village of Udokan in a narrow high-altitude valley on the Udokan ridge (1570 m above sea level) ^[12] it is higher - -28.9 and -29.2°C, respectively (Fig. 5, A). This pattern is well observed in April, when the air temperatures in Char and Udokan are on average very close (-3.2 and -3 °C, respectively), and in Lower Ingamakit about 4 °C lower (see Fig. 5A).  

5. Average monthly air temperatures (A) and the amount of precipitation (B) in January, April, July and October, as well as the height of snow cover and average monthly temperatures on the soil surface (C)

            The average annual precipitation in this region varies significantly depending on the height above the bottom of the basin. In the village of Chara, the average annual amount of precipitation is 328 mm, whereas when climbing to the village of Udokan, it increases first by about 1.5 times (up to 455 mm in the village of Nizhny Ingamakit), and then by more than 2 times (up to 679 mm in the village of Udokan). The highest humidity is observed in summer, when up to 80-87 mm/month of precipitation falls on average in July (in Char), and in winter the air dries up almost to the complete absence of precipitation (no more than 4 mm / month in January at all three weather stations). The absence of moist air masses is primarily explained by the active activity of the Siberian anticyclone ^{[9, 10]}.

The presence of such a temperature "stage" at an altitude of about 1000 m above sea level also provides an inverse altitude profile of the distribution of precipitation. In all seasons of the year, except spring, the meteorological station Nizhny Ingamakit records a greater amount of precipitation compared to Chara and Udokan. This difference is especially noticeable in autumn, when on average 30 mm of precipitation per month in Nizhny Ingamakit is about twice their level in Char (15.8 mm/month) and Udokan (16.3 mm/month) (Fig. 5B).  

            The low winter precipitation in the village of Chara (3.4 mm/year) explains the relatively small thickness of the snow cover in this area – it reaches its maximum in February, it is equal to 14 cm. Stable snow cover in the Char is established by November (8 cm) and lasts until the end of March (12 cm), and in April – May its capacity decreases to 1-3 cm ^[4]. The snow cover is completely destroyed by the end of May, ceasing to hinder the flow of solar heat warming the soil surface +16 – +21 °C (Fig. 5B).

Hydrological network Hydrological objects in the study area are represented by the Chara River and its tributaries – small and medium-sized rivers and streams.

Chara originates on the slopes of the Kodar ridge and in the lake. The Big Leprindo flows through the area of the basin in the north-east, and then in the north direction. In the area of the village. Novaya Chara and S. Chara several medium and small tributaries flow into it – the Upper Sakukan, Middle Sakukan, Anarga (left), Nirungnakan, Naminngakan, Belenky Creek (right). The Chara River itself belongs to the Lena River basin, being its right tributary along with the Olekma River, with which it joins shortly before the latter flows into the Lena River.

            About 5% of the area of the Lena River basin – one of the largest river basins in Russia and the world - is located in the northern part of the Trans-Baikal Territory, where about 7% of the Lena River flow is also formed ^[13]. The large rivers belonging to this basin – Olekma, Chara, Bugarikhta, Karenga and Kuanda belong mainly to the mountain type with large slopes and rapid flow ^[14]. The length of the Chara river is 851 km, the catchment area is 87.6 thousand ^km2. It has mainly a snow and rain type of nutrition ^[15]. There are two hydrological posts on the Char River – the village of Chara and the village of Bolshoe Leprindo. At both of these posts, the average annual values of water consumption are significantly (correlation coefficients exceed 0.4) related to the amount of precipitation, while the distribution of runoff within the year is very uneven due to contrasting seasons in humidity: during the warm season, rain floods occur on rivers (most often in July and August, which account for the greatest amount of precipitation and as a consequence of river runoff) ^{[13, 15]}.

Fig. 6. The intra–annual course of the amount of precipitation and water consumption averaged over the study area: 1 – the amount of precipitation, mm; 2 - the average monthly water consumption, ^m3/ s (Karenga river, Tungokochen village). According to N.V. Rakhmanova et al. ^[15] 

More than 80% of river runoff is formed in the spring-summer period (Fig. 6), and in winter, especially on small watercourses, the runoff stops altogether due to the complete depletion of groundwater reserves and their freezing. Also, in winter, ice phenomena such as ice formation, ice formation, snowdrifts, and sludge appear in large numbers on the rivers of the region. The duration of all ice phenomena on the Char and its tributaries is approximately 228 days, while the Char is characterized by one of the latest in the region averaged period of onset of ice: stable ice is established here in the area of October 27 (data from the Bolshoe Leprindo g/n) (for comparison, on the Karenga River, on the g/n in the Tungokochen village, on average, ice sets on October 9). The end of all ice phenomena occurs in the interval between May 8 and May 21 ^[15]. Ice, as one of the most common types of ice phenomena on the rivers of northern Transbaikalia, are a serious complication of the engineering and geological conditions of the region. The formation of ice usually occurs within 5-6 months, melting takes about 1-2 months, however, in the northern part of the region, the duration of destruction is mainly determined by the volume of ice. Particularly large ones, such as, for example, the Mururinskaya ice in the upper reaches of the Chara River, do not completely collapse in some years ^{[16, 17]}. Climatic changes in recent years, expressed in the form of an increase in average annual air temperatures from -3.5 to -0.5 °C (according to the meteorological station in Chita) and a slight increase in the average annual precipitation, have led to the fact that groundwater levels have decreased, and the volume of water accumulated in taliks has decreased. Because of this, groundwater that previously participated in ice formation is triggered much faster and transformed at discharge points into surface and subsurface runoff. For this reason, large glaciers that were previously formed annually with a probability of about 100% are now formed episodically, and the volumes of especially large glaciers in the northern Transbaikalia (Srednevakukanskaya, Nizhnegamakitskaya, Mururinskaya, etc.) have decreased by 20-30%, which is significantly more than the usual fluctuations in the annual cycle ^[16].     

Vegetation coverAccording to the scheme of natural zoning of the Trans-Baikal Territory, the studied area belongs to the Kodar Goltsovy (Alpine) district of the Stanovoe Upland natural district.

In the central part of the district, the forest belt on the southern slope is mainly represented by larch trees. Up to 1100-1200 m in their undergrowth, along with cedar elfin (Pinus pumila), there is a spreading birch (Betula divaricata), mosses predominate in the ground cover. Above, a second tier of hanging birch (Betula pendula) and stone birch (Betula ermanii) appear in places, cedar elderberry dominates in the undergrowth, a lot of alder (Duschekia fruticosa), mosses predominate in the cover. On flat areas composed of moraine, there are larch trees with an undergrowth of cedar elfin, with a powerful berry cover. From 1400-1500 m, larch woodlands with a powerful berry cover appear, and on the southern slopes – stunted groves of stone birch, alternating with thickets of elderberry.

For the highlands, the widespread development of fragments of alpine vegetation, on the northern slope occupying significant areas, colorful lawns, rhododendrons (Fig. 7), talniks is typical. On the northern, wetter slope, there is typically a wide distribution of groves of stone birch, sometimes spruce forests; large areas are under thickets of elfin ^{[18, 19]}.

Fig. 7. Vegetation cover of the high-altitude char belt with bagulnik, golden rhododendron and cedar elfin (photo by A. Ginzburg)

The floristic diversity in the Charskaya basin is very large, and the isolated position in the relief leads to the fact that some plant communities here exhibit unique properties and combinations. A.V. Garashchenko ^[18] during a large-scale geobotanical survey of the territory of the Charskaya Basin identified 384 species of vascular plants here and compiled their systematic lists indicating places and features of habitat conditions. According to the results of several seasons of field research expeditions Flora of Siberia (1988-2003), there are 854 of these species in 77 botanical families. The most numerous species from the sedge families (101 species), aster (85 species) and bluegrass (67 species) ^[19].

Soils and soil cover

From the point of view of soil-geographical zoning, a version of which is presented in the Atlas of Transbaikalia ^[20], the area we studied belongs to the Muisko-Udokan highland District of the North Baikal Mountain Province of the East Siberian permafrost-taiga region of the deciduous forest zone of gray forest permafrost soils. In turn, this zone is part of a larger geographical belt – the Boreal (moderately cold). The following conditions of soil formation are considered to be peculiar features of this soil-geographical region: a short biological cycle, sharply dissected mountainous terrain, coarse-grained composition of soil-forming rocks, the presence of permafrost rocks ^[2,5,6].

            The soil cover of Transbaikalia, as well as many other eastern regions of Russia, has not yet been studied in sufficient detail. The reason for this is the combination of a huge area of territory with difficult climatic conditions and its insufficient economic development. N.A. Nogina, in her dissertation on the soils and soil cover of Transbaikalia ^[21], notes that as of the middle of the XX century, even on survey soil maps, the soil cover of the territory of Transbaikalia, Yakutia and the Far East was depicted provisionally, based on the results of a general analysis of the natural situation, and more detailed regional studies of soils have demonstrated their specificity from time to time.

The first data on the soils and soil cover of the territories east of Lake Baikal date back to the 1880s, when fragmentary information about the existence of chernozems and salt marshes here, as well as the widespread distribution of sandy and rocky massifs began to appear. At the beginning of the XX century (1909-1913), the so–called expeditions of the Resettlement Administration were organized, the work on the study of soils during which K.D. Glinka led. Most of these studies were carried out in the steppe and forest-steppe basins of Transbaikalia, mountain taiga areas were not studied. Despite the uniqueness of soils and soil cover structures noted by many soil researchers of that time, not a single type of soil not found in the European part of Russia was identified. In the monograph of L.I. Prasolov ^[22], this stage of accumulation of knowledge about Trans-Baikal soils and their geographical distribution was summarized. The main conclusions of a geographical nature include the following:

1) the nature of the distribution of soils on the territory of Transbaikalia is largely determined by the relief due to most of the area occupied by mountain systems

2) the lowest (600-800 m above sea level) areas of intermountain depressions are occupied by dry–steppe landscapes with chestnut soils, above, at the level of 800-1000 m, chernozems develop, and at altitudes of 1000-1200 m above sea level, gray forest soils are formed (in the Classification and diagnostics of soils of Russia ^[23] - gray), which do not form continuous belts on the slopes of the hollows. Podzolic soils predominate in the mountain taiga (Fig. 8)   

Fig. 8. The scheme of the altitude zone of the slope of the intermountain depression in Transbaikalia at the time of the late 1920s, according to L.I. Prasolov ^[22]. High–altitude landscape zones: 1 – mountain taiga, 2 – mountain forest, 3 - grass-grass, 4 – dry steppe

            In 1932, the LOVIUA expedition under the leadership of S.V. Zonn conducted studies of the soil cover on the territory of steppe and forest-steppe areas of the Selenga River basin, a number of ideas about the geographical distribution of soils in the region were clarified, as well as their morphological and analytical properties were clarified. In the same period, detailed soil surveys began to be carried out point-by-point for the purpose of large-scale mapping of agricultural lands of collective farms and state farms. The critical state of the industrial and agricultural sectors of the USSR in the years after World War II contributed to the activation and intensification of the development of natural resources of the Russian Far East. The need to develop, first of all, the mineral resource base of Transbaikalia also marked a new stage in the study of nature in general and the soil cover of the region in particular. Large-scale research activities were organized by the staff of the V.V. Dokuchaev Soil Institute (Moscow), SOPSa of the USSR Academy of Sciences (Moscow), Irkutsk University named after Zhdanov, etc. Numerous route studies of mountain taiga areas, soil surveys of all steppe and forest-steppe territories of Buryatia were carried out, and a semi-stationary study of soils in areas actively used in agriculture was started. As a result of this stage, a much greater peculiarity of local soils was described than previously it was assumed: if earlier in the classification plan morphological features were expressed only in the names of soils of small taxonomic units, then since the 40-50-ies of the XX century, several new types of soils were introduced into the All-Union classification system, formed with shallow occurrence of permafrost rocks.

            The Trans-Baikal chernozems attract the most attention due to their high fertility ^{[21, 24-26]}. According to N.A. Nogina ^[21], the dry-steppe landscapes framing the most hypometrically low and dry areas of the relief of intermountain basins, at altitudes of 800-1000 m above sea level, are occupied by areas of chernozem-type soils. In her dissertation, three subtypes are distinguished within the type of chernozems: low-humus ("poor") powdery-carbonate transition to chestnut, medium-humus powdery-carbonate chernozems and low-carbonate and carbonate-free chernozems (Fig. 9).   

Fig. 9. Structures of the soil cover of the high-altitude steppe belt on the gentle slopes of the intermountain basins of Transbaikalia. Landscapes: 1 – meadow steppes, 2 – real steppes, 3 – lush meadows, 4 – dry steppes, according to ^[21]

            The high-altitude sub-belt occupied by meadow-steppe plant associations has a very homogeneous soil cover: all autonomous relief positions with uncomplicated drainage are characterized by areas of low- and carbonate-free chernozems, and permafrost-meadow carbonate (and rarely saline soils) are observed in depressions. In the sub-belt of these steppes located below, the diversity of soil formation conditions is greatest within the entire steppe belt: autonomous positions are occupied by medium-humus powdery-carbonate chernozems, in depressions, chernozem-meadow and meadow deep-freezing soils develop. Also, in these territories, there are meadow salt marshes that do not reveal their association with certain elements of the relief, which do not have a wide distribution here. Low-humus powdery-carbonate chernozems are widely distributed in the belt of lush meadows ^[21], where subordinate positions in the relief are occupied by areas of meadow-chernozem soils (sometimes with the participation of meadow salt marshes). The lower part of the steppe belt borders on the bottom of the basin, where the dry-steppe belt with chestnut soils is located (Fig. 10). The soils of the dry steppe zone should also be considered separately.

Fig. 10. Structures of the soil cover of the high-altitude belt of dry steppes on the bottoms of intermountain basins of Transbaikalia. Landscapes: 1 – dry steppes, 2 – meadow-dry steppe lowlands with salt lakes, according to ^[21]

            Compared with the hypometrically higher lying belt of steppes, the dry–steppe belt, which occupies the lowest areas of intermountain basins, is characterized by a less diverse relief, and therefore by soil cover. N.A. Nogina ^[21] distinguishes two predominant types of soils here - chestnut powdery-carbonate and dark chestnut ^{[21, 25]}. In complexes with chestnut soils, salt marshes are often observed, which, in fact, are here a transitional link between chestnut soils in autonomous relief positions and sorov and meadow salt marshes in low-lying areas of salt lake basins (see Fig. 10). The distance of this transition in the conditions of the bottoms of intermountain basins is significantly narrowed, which locally creates a very contrasting soil cover, the areas of which are surrounded by vast territories where the cover is less contrasting. Meadow-chestnut soils are formed on two-three-membered soil-forming rocks of contrasting granulometric composition, at the contact depth of which moisture is provided during wet periods of the year.

Fig. 11. Structures of the soil cover of the high-altitude taiga belt on the slopes of the intermountain basins of Transbaikalia. Landscapes: 1 – north (upper) taiga, 2 – middle taiga, 3 – south taiga, according to ^[21]

            Occupying an intermediate position between the taiga and the steppes, the high-altitude belt of forest-steppes is represented by a combination of permafrost-taiga soils with chernozems, sometimes with chestnut soils. This situation is especially frequent in eastern Transbaikalia on the slopes of the eastern exposure, the driest, where areas of chestnut soils can be observed at altitudes up to 2000 m above sea level, that is, almost on the border of the mountain-taiga belt. With a large depth of seasonal thawing of permafrost rocks (3-5 m) and in conditions of a combination of moist birch forests with undergrowth of willow and yernik with meadows, soils that have no analogues in the soil cover of the European territory of Russia can develop – gleevate, settled or actually permafrost meadow-forest ^[21].   

            The soil cover of the mountain-taiga high-altitude zone is different both in altitude and longitude. Changes in the structure and composition of the soil cover are observed when moving from the bottom up, from the south Taiga sub–belt to the North Taiga, as well as from west to east - from the western (drier) part of Transbaikalia to the eastern (wetter). In the lower part of the taiga high-altitude zone, the background of the soil cover consists of mountain permafrost sod-taiga soils. Rare areas of soils belonging to the podzolic type are confined to the exits of sandy massifs. Permafrost-taiga soils sometimes with signs of podzolization, which are especially pronounced in the eastern part of the region, dominate in the upper middle taiga belt. Deep-freezing illuvial-ferruginous podzols are developed along sandy massifs and exits of highly gravelly sediments. In depressions and poorly drained sediments, permafrost-swamp soils are formed. In the northern (upper) taiga, the most widely represented in the soil cover are mountain permafrost-taiga surface-hardened and surface-peeled soils in the western part of Transbaikalia. In the eastern part, a similar role of the background of the soil cover is played by mountain permafrost-gleetaezh and mountain illuvial-ferruginous podzols (Fig. 11).

            Most of the areas of the char – the upper of the high-altitude belts - are occupied by rocky coarse-grained placers, completely devoid of fine-grained. In this regard, the soil cover is fragmented here. In the western part of the Trans-Baikal Territory, especially on the slopes of the ridges facing the lake. Baikal, mountain-tundra soils are common. Mountain-meadow (subalpine) soils are confined mainly to areas where a large amount of snow accumulates in winter – to the bottoms of cars and trog valleys. On the slopes of the ridges of western Transbaikalia, which have an eastern exposure, char-wasteland soils are common, and mountain-tundra soils are found only in those places where more moisture accumulates – depressions and poorly drained surfaces. In the eastern regions, mountain-tundra soils are again becoming widespread and are found in automorphic positions, mountain-wasteland soils are rare here, mainly in particularly xerophytic positions (Fig. 12).

Fig. 12. Structures of the soil cover of high-altitude char on the tops and near-top surfaces of the ridges of Transbaikalia. Landscapes: 1 – mountain-tundra, 2 – mountain-meadow, according to ^[21].

Note: W – West, B – East

            The most relevant small-scale soil map for the territory of the Trans-Baikal Territory is considered to be a 1:2,500,000 scale map from the National Atlas of Soils of Russia ^[27]. On it, the territory of northeastern Transbaikalia is easily differentiated from the surrounding territory, which is characterized by mountainous terrain. On this scale, the soil cover of the basin is represented as a combination of illuvial-ferruginous podzols with peat- and peat-gley swamp soils (peat and peat bog gley soils). At the same time, the soil-forming rocks in the bottom of the basin are strictly differentiated: sandy deposits are common in the central part, and in the northwestern part of the basin, soils are formed on acidic metamorphic and igneous rocks.

Similar information about the current state of the soil cover is also provided by an earlier soil map of the RSFSR ^[28], with the only exception that only sands are considered as soil-forming rocks within the basin.

Objects and methodsCryogenic soil profiles, soil cover and soil-geochemical catenae representing the high-altitude spectra of soils on the slopes of the Kodar and Udokan ridges are considered as objects of research.

We have directly described three sections of cryogenic soils: two of them on the flat subhorizontal surface of the seven–meter terrace of the Chara river 30-60 m from the river's edge, one on the top of the Udokan ridge on the flat gently sloping surface of the Kurum ^[29]. For a more detailed analysis of such soil cover properties as soil diversity, structure and altitude spectra, additional literature and soil cartographic data were involved. In addition to the morphological features of the soil profiles and the properties of the soil cover, we investigated the chemical and physical properties of these soils – acidity, total content of easily soluble salts, organic carbon content, granulometric composition.

When compiling morphological descriptions of soil profiles and soil classification, classification and diagnostics of soils of Russia were used ^[23].

Soil acidity (pH) and the content of easily soluble salts (TDS, mg/l) were measured in aqueous extracts in a ratio of 1:5 by potentiometric and conductometric methods using stationary pH meter and EC-TDS meter METTLER TOLEDO. In both cases, the extract was made from a soil sample weighing about 5 g, ground with a porcelain pestle in a porcelain mortar, sifted through a sieve with a pore diameter of 1 mm.

The content of organic carbon in soils (C _org.) was measured by the method of I.V. Tyurin with photometric termination. A sample of soil weighing about 1 g, ground with a porcelain pestle in a porcelain mortar, sifted through a sieve with a pore diameter of 0.25 mm, was poured with 10 ml of 0.4 M 1/6 chromium mixture (potassium bichromate – K ₂ Cr ₂ O ₇, diluted (1:1) in sulfuric acid – H ₂ SO ₄). To accelerate the organic carbon oxidation reaction, the extracts of the chromium mixture were heated for 20 minutes in a drying cabinet at 150-160 °C, then cooled, after which the Cr ⁶⁺ ion residue in the extract was titrated with 0.2 M solution of More salt (FeSO ₄·(NH ₄)₂ SO ₄·6H ₂ O) in the presence of 5-6 drops of phenylanthranilic acid (C ₁₃ H ₁₁ NO ₂). The organic carbon content in the soil sample was determined by the following formula:

where V ₁ is the amount of Mohr salt solution (cm ³) used for titration of Cr ⁶⁺ contained in the chromium mixture aliquot (1/6 K ₂ Cr ₂ O ₇) – blank sample; V ₂ is the amount of Mohr salt (cm ³) used for titration of Cr ⁶⁺ remaining after the interaction of the sample soils with an aliquot of chromium mixture (1/6 K ₂ Cr ₂ O ₇); M is the molarity of the solution of More salt; 0.003 is the molar mass of ? S (g/mol); 100 is the conversion coefficient per 100 g of soil; m is the mass of the dry soil sample.

The granulometric composition of the soils was determined by laser granulometry with preliminary grinding of the soil sample with sodium pyrophosphate. The mass of the soil sample, ground in a porcelain mortar with a rubber pestle to avoid the destruction of mineral grains, was 2-3 g. After weighing, 3-5 drops of sodium pyrophosphate (Na ₄ PO ₇) were added to the sample with a pipette, which was used for additional dispersion of colloidal soil particles.

The alkalinity of soils caused by normal carbonates (CO ₃ ^2-) was measured in an aqueous extract in a ratio of 1:4. A sample of air-dry soil weighing 5 g was filled with 20 ml of distilled water and filtered through a paper filter "White tape" with a pore diameter of 0.12 mm into conical flasks. Then two drops of methyl orange indicator (0.1% in H ₂ O) were added to the filtrate, after which the mixture was titrated with a 0.02 M solution of ? H ₂ SO ₄, the end point of titration was fixed by a sharp change in the color of the solution from yellow to pale orange. The calculation of alkalinity from soluble carbonates was carried out according to the formula:

where V _H2SO4 is the volume of a solution of ? sulfuric acid used for titration of a soil sample; M is the molarity of ? sulfuric acid solution; V _tot is the volume of distilled water taken to make an aqueous soil extract; V _al is the volume of an aqueous soil extract taken to determine alkalinity; m is the weight of the sample (g); 2 – coefficient for conversion from bicarbonates to carbonates; 100 – coefficient for expressing the result per 100 g of soil.    

ResultsMorphological properties of soils

            According to the rules of morphological description of the soil profile proposed in the classification and diagnostics of soils in Russia ^[23], set out in the field soil determinant ^[30], the authors described the following properties of soils: thickness, color, moisture, addition, structure, granulometric composition (organoleptically), inclusions, neoplasms, number and size of plant roots, the nature of the transition and the shape of the border.

Soil section Ch-S-22-1 (56°45’38.72’ S.sh., 118°11’30.12’ VD) is laid on a flat subhorizontal surface of a 7–meter terrace of the Chara River about 30 m from its river's edge (Fig. 13), at a height of 3-3.5 m above the river level (abs. height = 728 m above sea level), under a swampy rare-coniferous post-pyrogenic larch taiga with dwarf birch, cedar elfin in the tree-shrub layer, as well as marsh bagulnik, sedges and moss-lichen cover. The ratio of mosses to lichens is approximately 5:1 in the composition of the projective coating.

            O – 0-11 cm, dark brown, poorly decomposed, consisting of plant residues of grasses and shrubs, moss and lichens, moist, loose, abundantly penetrated by roots 2-5 mm in diameter, the transition is gradual in the degree of decomposition of the remains.

            O’ – 11-20 (25) cm, dark brown, darker than the overlying horizon, medium degree of decomposition, consisting of plant residues of grasses and shrubs, moss and lichens, moist, loose, penetrated by roots with a diameter of 2 - 5 mm, the transition is clear in the presence of fine–grained, color and structure, the border is wavy.

            G – 20 (25)-26(30) cm, bright red, wet, compacted, thixotropic, finely sanded silted, structureless, with bluish spots, the transition is clear in color, the border is wavy.

            CG – 26 (30)-34 cm, bluish-gray, wet, dense, thixotropic, finely sanded silted, structureless, with small red spots, the transition is sharp along the upper border of the MMP, the border is smooth.

            CG? – 34... cm, similar to the overlying color, sandy loam-light loamy, silted, permafrost, massive cryogenic texture, low-ice (visually the ice content is ? 30%). 

Soil name: cryogenic-ozhelezenny cryoturbated permafrost gleezem

Fig. 13. Soil profile Ch-S-22-1 – cryogenic-ozhelezenny cryoturbated permafrost gleezem

Soil section Ch-S-22-2 (56°39'41.20" S.sh., 118°22'36.44" VD) is laid on the top of the flat surface of the Udokan ridge, about 3 km from the top of the Cranberry Char and 2 km from the dam of the Udokan copper deposit, on at an altitude of about 1300 m above sea level, on a well-drained stony cobblestone surface of a kurumnik with a rare cedar elfin (Fig. 14). The surfaces of the cobblestones are covered with a cover of scale lichen.

T is 0-12 (27) cm, dark brown, coarse humus, boulder-gravelly, the size of boulders is up to 15 cm across. It consists of remnants of moss, lichens of moderate decomposition and cedar elfin, penetrated by roots up to 2 cm in diameter, the transition is gradual, according to the presence of fine-grained soil and the size of cobblestones.

            R – 12 (27) -40 cm, dark brown, boulder-gravelly, the size of boulders is up to 50 cm across, roots up to 0.5 cm thick are rare, the entire horizon contains small inclusions of peat of a high degree of decomposition, with a small amount of fine earth (up to 20%).

Soil name: permafrost peat-lithozem

Fig. 14. Soil profile Ch-S-22-2 – peat-lithozem permafrost

Soil section Ch-S-22-3 (56°45’33.31’ S.sh., 118°11’9.68’ VD) is laid on a flat subhorizontal surface of a 7-meter terrace of the Chara River about 60 m from its edge, at a height of 3-3.5 m above the river level (absolute height = 730 m above sea level), under a rare-coniferous larch taiga with dwarf birch, cedar elfin in the tree-shrub layer, marsh bagulnik, sedges and moss-lichen cover (Fig. 15).

            O – 0-4 cm, dark brown moss-lichen cover with an admixture of sedges, marsh marsh, dwarf birch, abundantly permeated with roots of woody species up to 2 cm in diameter, the transition is sharp in the degree of decomposition of the litter, the border is smooth.

            Opyr – 4-11 (13) cm, dark brown litter of medium degree of decomposition, raw, loose, permeated with roots of dwarf birch, bagulnik, grasses up to 1 cm in diameter, inclusions of large (up to 2 cm across) black embers, the transition is sharp in color and the presence of fine-grained.

            CG – 11(13)-18(25) cm, light gray-brown with yellowness, moist, compacted, finely sanded silted, structureless, with small (up to 2 mm) roots, with barely noticeable red shapeless spots, with well-defined SiO2 grains (light, transparent), the transition is sharp in the presence of glandular spots and glandular spots, the border is wavy.

            G– 18 (25) – 44 cm, bluish-gray with bright red spots of irregular shape, vertically oriented, along the roots of larches (up to 15 cm), moist, dense, finely sanded silted structureless, with small birch roots (up to 2 mm) and one large larch root with a diameter of 3 cm, with glandular vertically oriented spots, with well-defined SiO2 grains (light, transparent), the transition is sharp along the upper border of the MMP, the border is smooth.

            CG? – 44... cm, similar to the overlying color, permafrost, massive cryogenic texture, low-ice (visually, the ice content is < 30%).

Soil name: cryogenic-ozhelezny permafrost gleezem

Fig. 15. Soil profile Ch-S-22-3 – gleezem cryogenic-ozheleznenny post-pyrogenic permafrost

Fig. 16. Schematic images of soil profiles described in the valley of the Chary River: a) cryogenic-ozhelezem cryoturbated permafrost; b) peat-lithozem permafrost; c) cryogenic-ozhelezem post-pyrogenic permafrost

Physical and chemical properties of soils           

In the course of carrying out a complex of analyses of physical and chemical properties of soils, we investigated the pH, the total content of easily soluble salts, the content of organic carbon and the granulometric composition of 6 soil samples taken in the valley of the Chary River and on the Udokan ridge.

            The pH values in the studied soil profiles vary from 4.85 to 5.44, such values allow them to be attributed to soils with a slightly acidic reaction profile. In the peat-lithozem on Kurum (Fig. 16A), the difference in soil acidity is very significant (0.38 units), which indicates contrasting conditions for the development of fine-grained fraction at different depths, while in the profile of the illuvial-ferruginous subsurface (Fig. 16B), the acidity is distributed even more unevenly along the profile. The most acidic is the upper horizon of Opyr, where the pH drops to 4.85, after which it begins to increase slowly, reaching its maximum (5.3) in the horizon G at depths of 18 (25)-44 cm. The range of pH values in the profile of the illuvial-ferruginous podbura on the 7-meter terrace of the Chara river is 0.45 units. In general, both soils show the same trend in the distribution of pH values in the profile: the upper horizon is significantly more acidic than the underlying ones. The most acidic horizons of soils are visually confined to the highest contents of organic matter, the decomposition products of which, apparently, are weak organic acids that determine the acidity of the situation in the horizons. 

            On the contrary, the content of easily soluble salts in the two soil profiles is very different. If in the peat-lithozem profile on the Udokan ridge, the upper horizon O is significantly more saline than the underlying R (18.86 and 8.1 mg/l, respectively) (Fig. 16A), then in the profile of the illuvial-ferruginous subsurface from the valley of the Chara River, the distribution of TDS values is much more uniform: the average value is 15.32 mg/l, The values vary very narrowly – from 13.6 in the upper horizon of Opyr to 16.71 in the most saline lower frozen CGf? (Fig. 16B). Apparently, the increased salinity of the upper horizons of soils may indicate that easily soluble salts may occur in them as a result of atmospheric precipitation. At the same time, the soils at the top of Udokan are significantly more differentiated in terms of salt content, compared with the Chara Valley. At the same time, the top of Udokan is a drier place compared to the lower high–altitude tiers of the mountain landscape of the basin, therefore, perhaps high humidity may be the reason for a more uniform distribution of salt content, since moisture penetrates more deeply and washes, leveling the profile distribution.

Fig. 17. Profile distributions of pH, TDS, CO ₃ ^2-, C _org. and the content of various granulometric fractions (according to N.A. Kachinsky) in the soil profiles of the valley of the Chary river: a) Peat-lithozem permafrost; b) cryogenic-ozhelezem post-pyrogenic permafrost

             The alkalinity of soils due to soluble carbonates is relatively low. In the studied soil profiles, it varies from 2.4 to 4.8 mmol(-)/100 g. On average, in the section of soil at the top of the ridge (Ch-S-22-2), the carbonate alkalinity is lower than in the soil in the valley of the Chary River (Ch-S-22-3). The upper horizons are generally more alkaline than the lower ones: the alkalinity of the horizon T is 3.2 mmol(-)/100 g, which is 0.8 mmol(-)/100 g higher than in the horizon R. Also, the highest carbonate alkalinity is observed in the upper part of the horizon G, where it reaches a value of 4.8 mmol(-)/100 g, and below it decreases to 4 mmol(-)/100 g. The surface-accumulative nature of the carbonate alkalinity distribution is presumably associated with the introduction of carbonates into soils with atmospheric precipitation, which is consistent with the increased content of easily soluble salts in soil profiles, which is detected especially in the upper horizons.

            The content of organic carbon in the soil, the section of which is laid at the top of the Udokan ridge, reaches 37.8%, and in the horizon R, located below, it decreases dramatically and equals 9.34%. On average, the soil on the terrace of the Chara river contains much less organic carbon. In the upper horizon, its content is 6.8%, and in the underlying mineral horizons it decreases to about 0.9–1.4%. The increased content of organic carbon in the upper parts of the profiles of cryogenic soils of the Charskaya basin marks the organo-accumulative process as one of the leading soil-forming processes here. At the same time, significant differences between the content of _organic matter in the upper and lower horizons of soils indicate a shallow penetration of this process into the soil profile due to unfavorable climatic conditions.

Table 1. Some chemical and physico-chemical properties of soils of the valley of the river Chara and Chr. Udokan

            The granulometric composition of the studied soils is quite homogeneous. This concerns both the comparison of the content of granulometric fractions in the soils of the two landscapes, and the profile distribution of the content of these fractions in the soils. According to the classification of soils of the podzolic type of soil formation according to the granulometric composition of N.A. Kachinsky, used as part of the Classification and diagnostics of soils in Russia ^[23], both of the soils considered belong to sandy loam soils of granulometric composition (see Table 1). The content of physical clay particles in them ranges from 10 to 20%. Moreover, the profile distribution of the content of these particles is very uniform in both soils: in peat-lithozem on kurumnik, the content of physical clay increases to the lower part of the profile from 16.7 to 18.8%, and in cryogenically-hardened gleezem on the above-floodplain terrace, the upper part of the profile is characterized by an almost unchanged content of physical clay in 11.0–11.2%, and in the lowest In the permafrost horizon, G? increases to 14.8% (see Table 1).

Table 2. Granulometric composition of soils of the valley of the river Chara and hr. Udokan

            A more detailed analysis of the granulometric composition of soils and the distribution of percentage concentrations in it over the horizons makes it clear that peat-lithozem has a more uniform distribution of these properties in its profile. The fractions of particles with a diameter of 10-1000 microns are most represented in it, that is, with a diameter larger than the particles of physical clay. Their shares ranged from 24.5 to 30.1% (Table 2).

       Such uniformity of the granulometric composition along the profile and the predominance of a large fraction in it indicates the initial stage of soil formation and the still insignificant processing of mineral grains by soil-forming processes. At the same time, the largest of the fine-grained fractions of soil particles in the granulometric composition of cryogenically-hardened gleezem (Discussion

Diversity of soils of the studied area

Throughout the entire period of studying the diversity of soils in the area of the Charskaya basin, various authors who performed field descriptions of soils attributed the studied sections to several main types. N.A. Nogina ^[21] here, low-carbonate chernozems, powdery-carbonate chernozems and powdery-carbonate "poor" chernozems in the high-altitude zone of the steppes were isolated. Chestnut and dark chestnut were found in the dry steppe zone confined to the bottom of the basin. In the mountain-forest-steppe high-altitude zone, N.A. Nogina described profiles of dark gray forest soils, as well as permafrost meadow-forest, and in the mountain-taiga zone located above, the greatest type diversity was recorded: mountain permafrost-taiga surface-hardened, mountain permafrost-taiga ordinary, mountain permafrost sod-taiga and the podzols are glandular ^[21]. The compilers of the soil map of the Trans-Baikal Territory in the National Atlas of Soils ^[27] note the spread of three main types of soils on its territory: mountain ranges are mainly distributed within the Khentei-Chikoysky highlands in the southwest, on the low plains of the southeast of the region, crossed by relatively low ridges Nerchinsky, Uryumkansky, Borshchovochny, etc. the soils belonging to the chernozem type are mainly represented, in the central and northern parts the dominant type of soils with the structure of the soil cover are podzols (illuvial-ferruginous and illuvial-humus). The Charskaya basin is a flat area, on the elevated parts of which the illuvial-ferruginous and illuvial-humus podzols are mainly represented, that is, the soil cover of the northeastern part of Transbaikalia in this map scale (1:2,500,000) is differentiated into mountain and plain podzols. The low-lying areas of the basin are occupied by areas of peat and peat-bog gleezems, which is partially confirmed by the data of our study on the seven-meter above-floodplain terrace of the Chara River ^[27]. The mountainous territories surrounding the basin, as noted on the soil map of the RSFSR ^[28], are occupied by dry peat mountain ridges on low slopes, and the peaks are practically devoid of soil cover, in its place on the map there is a spread of outcrops of dense rocks and rocky placers ^[30,31].

            The subject of consideration by G.D. Chimitdorzhieva and E.V. Tsybikova ^[32] was the peculiarity of chestnut soils in the southern basins of Siberia. The authors note that in the dry-steppe zone of the Udinsk basin (Buryatia), chestnut soils have a slightly different shade of the humus horizon A than similar soils of western Siberia and the European part of Russia, the shades of the horizon are warmer brown, not brown, recorded in the field descriptions of the soils of Orlova in 1990 in the European part of Russia, Tishchenko and Rydlevskaya in 1936 in Altai and Zavarzina and Demina in 1999 in the Kursk region (cit. according to ^[32]). In the chestnut soils of the Ivolginskaya and Udinskaya basins, soils with a very similar profile structure (A – AB – Vk – Sk) were described, in which, in addition to the main processes of soil formation for chestnut soils, additional signs of salinity are weakly manifested ^[32]. In addition to the chestnut and meadow-chestnut soils noted by many researchers in the bottoms of the basins of Transbaikalia, in the structure of the soil cover of the steppe zone of the Barguzin basin (Upper Kuytun tract. Buryatia) an important place is occupied by cryohumus (soil profile AK – BCA – BCA – Cca – 2Caa), agrokrioarid (soil profile Pw, r – AK – BCA(BCA) – BCA – BCACca – Cca – 2Cca – 3Cca) and agrokriohumus (soil profile P – BCA – BCACca – Cca – 2Cca) of the soil, which significantly separates it from many other intermountain basins of Siberia ^[33].

        In the mountainous regions of the western part of Transbaikalia, L.L. Ubugunov et al. ^[34] within the framework of the trunk of primary soil formation, peat-lithozems and lithozems of coarse humus were isolated, according to descriptions very close to those found by us in the course of this study on the Udokan.

            Diagnostics of soils whose profiles were opened by sections Ch-S-22-1 and Ch-S-22-3 is difficult. On the one hand, properties such as thixotropy and strong gluing indicate that these soils most likely belong to the type of gleezems (department of gleev soils). The assumption about gleezems is especially evident when diagnosing the soil in the section Ch-S-22-1, where the actual morphological properties of soils are also added to the wetness of the surface. An additional argument in favor of classifying the soils under consideration as gleezems is cartographic data that indicate the presence of peat and peat-bog gleezem areas here ^{[27, 28]}. As a counterargument to this point of view, we can cite the fact that various studies of soils in the low-lying areas of the intermountain basins of Transbaikalia note the presence of signs of salinity in them ^{[21, 35]}, and in the soils studied by us, none of the signs listed by them were found either morphologically or chemically analytically. However, the argument against the possibility of calling this soil gleezem is the horizon, the description of which was initially interpreted as signs of BFg, primarily the bright red color of this horizon, which is characteristic of the illuvial–ferruginous horizon of the profiles of the department of alphegumus soils ^[23]. This argument acquires additional force, since when describing the gleezems of the Baikal natural territory ^[36], it is indicated that the gleev horizon in them is bluish-gray, ochre-yellow, or bluish-black spotting, but not bright red or red. Moreover, in the photographic materials applied to the work of L.L. Ubugunov et al. ^[34], the gleev horizon is homogeneous, not differentiated by color.

M.I. Gerasimova, when discussing the results we obtained, suggested that when diagnosing soils on the seven-meter Chara terrace and searching for their position in the local structure of the soil cover, attention should be paid to the recent forest fire in a rare-coniferous larch forest, in which the Ch-S-22-1 section was just laid. V.G. Tarabukina's dissertation ^[37], a review article by A.A.Dymov et al. ^[38], a section on the protection of forest resources of the Komi Republic from fires and their consequences ^[39], etc. are devoted to the study of the transformation of soil properties as a result of upper and lower natural fires in taiga forests. The soils of the harem are compacted, specific and volumetric masses increase in them, water permeability decreases and aeration of the above-frozen horizons improves ^[37]. In the light of these data, the bright red horizon in the upper part of the glued thickness of the soil profile Ch-S-22-1 can be considered as a result of improved air permeability of the upper horizon, or its complete destruction as a result of fire, as evidenced by the color characteristic of oxidized forms of iron (Fe ³⁺) in aerobic conditions. At the same time, the deterioration of water permeability of the soil could just lead to the fact that the groundwater level increased, which is why the conditions of soil formation from more favorable to alfegumus soils were transformed into more suitable for gley. The soil profile Ch-S-22-3, where the oxidation of reduced forms of iron is not so pronounced, and thixotropy is almost not manifested, however, there are obvious signs of a forest fire in the form of embers in the post-pyrogenic horizon of Opyr, perhaps, should be perceived as a subburst, previously transformed into gleezem, and at the moment returning to its original state. Similar processes of self-healing of cryogenic soils (Cryozems and Podburs) after forest fires in larch forests are described by A.A.Dymov et al. ^[38].           

Chemical and physico-chemical properties of soilsStudies in depth into the diversity of chernozem-type soils conducted in western Transbaikalia, firstly, report that the chernozems of the lowland plains are morphologically similar to those observed in the intermountain basins of the northeast ^[32,40], and secondly, indicate that the properties of the chernozems of western Transbaikalia are less favorable for agricultural work, compared with the East Trans-Baikal in intermountain basins.

The humus content in the upper A1 horizons of the Western Trans-Baikal chernozems varies from 3.5 to 5.3% ^[41], whereas in the soils of the Charskaya basin this content ranges from 4.3 to 6.6% ^[21]. The total nitrogen content in the soils of the two parts of the Trans-Baikal Territory is approximately equivalent, it ranges from 0.16 to 0.33% (east) and from 0.05 to 0.52% (west). The situation is similar with soil acidity in an aqueous extract. Thus, the pH of the chernozems of the western Transbaikalia is from 6.6 to 8.9, and in the east – from 5.7 to 8.2. Nevertheless, it is the western Transbaikalia that, due to the relief more convenient for carrying out agrotechnical measures, is more developed in agricultural terms. Chestnut soils of the steppe zone of southwestern Transbaikalia, studied by V.K. Kashin and G.M. Ivanov ^[42] for chromium contamination, are characterized by an aqueous pH from 6.8 to 8.2. The humus content in them is 1.3–2.6%, which is on average similar to the results noted by N.A. Nogina ^[21]: 0.2–3.5%. Powdery-carbonate chernozems in western Transbaikalia contain 2.4–3.7% humus, as well as gray forest soils, the average humus content in which is around 2.7% ^[42].

Arable gray forest soils of Western Transbaikalia, studied in the Duldurginsky district of the Aginsky Buryat Autonomous Okrug of the Chita Region, demonstrate similar values of acidity (pH 5.8 – 6.7), however, the average values of this indicator are lower here than in steppe zones on the bottoms of intermountain basins ^[43], and the authors note that arable soils by about 1 unit The pH is more acidic than the soils of virgin areas: 6,7 and 5,7, respectively. The humus content in these soils does not exceed 4%, decreasing especially strongly during the transition from the upper horizon to the underlying ones: from 3.92 to 1.27% or less. Similar results of measuring the pH of gray forest soils involved in agricultural production of the agro–industrial complex "Alkhanai" (Mogoituysky district, Chita region (currently - Trans-Baikal Territory)), while the humus content in the upper arable horizons of these soils (A1) reached 4.95%, gradually decreasing to the horizon AB1 and below to 1.48% ^[44].

Cryohumus and agrocrioaride soils encountered during the study of the soil cover of the Upper Kuitun tract in the Barguzin basin are characterized by a granulometric composition similar to the soils we studied: the fractions of 250-1000 mm and 50-250 mm are most massively represented. The latter of them often makes up about 50% or more of the total granulometric composition. The content of physical clay in the profile is approximately equal to that found by us during granulometric analysis, in general, the content of a fraction thinner than 10 microns is from 3 to 19%, which corresponds to sandy and sandy loam soils ^[33]. Chestnut soils of the Udinskaya and Ivolginskaya basins, on the contrary, are heavier in granulometric composition. The content of particles of physical clay in them sometimes reaches 27.8%, which, according to N.A. Kachinsky's gradations, corresponds to a light-loamy composition. Many of the described soils ^[32-36] are characterized by either uniform or increasing concentrations of physical clay in soil profiles with depth.

ConclusionThe authors' studies of the morphological and physico-chemical properties of the soils of the valley of the Chary river in the summer of 2022 showed that the described soils on the terrace of the Chary river on sandy loam ancient alluvial deposits belong to the trunk of postlitogenic soil formation, the department of gleev soils, the type of gleezems.

            At the level of subtypes, the soils were divided into cryogenic-hardened cryoturbated permafrost and cryogenic-hardened post-pyrogenic permafrost. The soil on the kurum on the flat top of the xp. Udokan was classified by the authors as peat-lithozem permafrost.

            In the case of the diagnosis of gleezems, certain ambiguities arose associated with the manifestation in the profile of these soils of some morphological and physico-chemical properties, usually characteristic of the type of podburs. These include the bright red coloration of the upper part of the horizon G, which, because of it, can be interpreted as the illuvial-ferruginous horizon BF in the subbura, especially since the horizon G, typical of the Trans-Baikal gleezems, is usually not differentiated, has a uniform bluish color. Also, the sandy loam granulometric composition of these soils is quite easy for gleezem. Nevertheless, factors such as thixotropy (which, however, manifests itself only in one of the two sections on the terrace), increased humidity, strong gluing, waterlogged surface, etc. are, in our opinion, sufficient grounds to classify these soils as gleezems.

            Our next assumption is connected with the postpyrogenicity of the larch forests in which the sections were laid, that the two sections of soils on the above-floodplain terrace belong to different stages of development of these soils. As a result of forest fires that occurred here different times ago, the physical properties of the soils have changed as follows: aeration of the upper soil horizon has improved, water permeability in the lower part of the profile, on the contrary, has become difficult, which led to a change in the washing regime of the subburs to the water–resistant characteristic of the gleezems, which is why there was a gluing. The process of self-healing of harem soils described by various authors can be presented here by the example of these two soil profiles, since signs of a recent fire were encountered by us only in one of the two sections, and in the second the post-pyrogenic subtype was assigned to the soil only by the presence of embers in the Opyr horizon. Accordingly, the dynamic transformation of the podbura into a gleezem under a recently burned larch tree is at an initial stage, and under the forest area where the fire was earlier, the self-healing of the podbura has already progressed further.

            In addition to morphological, we have studied the chemical and physico-chemical properties of soils. The hydrogen pH index of soil acidity has values from 4.9 to 5.4. Both studied soil profiles are characterized by a slight increase in soil acidity with depth. The total content of easily soluble salts in the soil (TDS) is characterized by a surface-accumulative type of distribution. The TDS values do not vary too widely – from 8.1 to 18.9 mg/l. The alkalinity due to normal carbonates in these soils is also relatively low. The values of CO ₃ ^2- are distributed fairly evenly over the profile, ranging from 2.4 to 4.8 mmol(-) /100 g of soil. The content of organic carbon in soils is differentiated both between profiles and within them. Peat-lithozem is characterized by a content with _org. 9.3–37.8%, and gleezem – a range of content With _org. 0.9–6.8%. To the greatest extent, the upper organogenic horizons are enriched with organic carbon, and the underlying horizons contain much less of it, which indicates that the processes of soil formation are not so deep into the profile. On the contrary, the granulometric composition of the soil differs slightly from each other. In the classification system of N.A. Kaczynski, they correspond to sandy loam soils, as evidenced by the fraction fraction of physical clay from 10 to 20%. The content of physical clay in the studied soils is 11.0–18.8%. In peat-lithozem, the proportion of the largest fine-grained fraction (particle diameter 250-1000 microns), along with other fractions larger than physical clay (>10 microns), is up to 30%. At the same time, the proportion of this fraction in gleezem is much lower, and almost half of the particles contained in it have a diameter of 50-250 microns.

            Thus, we studied the morphological and physico-chemical properties of soils, with the help of which their place in the classification of soils of this area was determined, as well as in the structure of the soil cover, which is confirmed by the literary and cartographic data of earlier studies. In the future, the results obtained by us, which are partly preliminary, can be used for a comprehensive description of the landscape of the valley of the Chara River, as well as for various narrow soil-geochemical studies in this region.   

Thanks

The authors are grateful to the head of the Laboratory of Geocryology of the IGE RAS, D.O. Sergeev, for organizing field work and V.A. Palamarchuk, M.Sc. of the ICZ TYUMNTS SB RAS, for assistance in the selection and processing of field materials. The authors are deeply grateful to the professor of the Department of Geochemistry of Landscapes and Geography of Soils, Doctor of Biological Sciences M.I. Gerasimova for her help and advice in classifying soils.