What is part of the West Siberian Plain. Geographical location of the West Siberian Plain: description and features

The West Siberian Plain is of the accumulative type and is one of the largest low-lying plains on the planet. Geographically, it belongs to the West Siberian plate. On its territory there are regions Russian Federation and the northern part of Kazakhstan. Tectonic structure West Siberian Plain ambiguous and diverse.

Russia is located on the territory of Eurasia, the largest continent on the planet, which includes two parts of the world - Europe and Asia. The tectonic structure of the Ural Mountains separates the cardinal directions. The map makes it possible to clearly see the geological structure of the country. Tectonic zoning divides the territory of Russia into geological elements such as platforms and folded areas. The geological structure is directly related to the surface topography. Tectonic structures and landforms depend on the region they belong to.

Within Russia there are several geological regions. The tectonic structures of Russia are represented by platforms, folded belts and mountain systems. On the territory of the country, almost all areas have undergone folding processes.

The main platforms within the country are East European, Siberian, West Siberian, Pechora and Scythian. They, in turn, are divided into plateaus, lowlands and plains.

Relief of Western Siberia

The territory of Western Siberia is sinking stepwise from south to north. The relief of the territory is represented by a wide variety of forms and is complex in origin. One of important criteria relief is the difference in absolute elevations. On the West Siberian Plain, the difference in absolute elevations is tens of meters.

The flat terrain and slight elevation changes are due to the small amplitude of plate movement. On the periphery of the plain, the maximum amplitude of uplifts reaches 100-150 meters. In the central and northern parts, the amplitude of the subsidence is 100-150 meters. The tectonic structure of the Central Siberian Plateau and the West Siberian Plain in the late Cenozoic was relatively calm.

Geographical structure of the West Siberian Plain

IN geographically in the north the plain borders the Kara Sea, in the south the border runs through the north of Kazakhstan and covers a small part of it, in the west it is controlled by the Ural Mountains, in the east by the Central Siberian Plateau. From north to south, the length of the plain is about 2500 km, the length from west to east varies from 800 to 1900 km. The area of ​​the plain is about 3 million km 2.

The relief of the plain is monotonous, almost flat, and occasionally the height of the relief reaches 100 meters above sea level. In its western, southern and northern parts, the height can reach up to 300 meters. The subsidence of the territory occurs from south to north. In general, the tectonic structure of the West Siberian Plain is reflected in the terrain.

The main rivers flow through the plain - the Yenisei, Ob, Irtysh, and there are lakes and swamps. The climate is continental.

Geological structure of the West Siberian Plain

The location of the West Siberian Plain is confined to the epihercynian plate of the same name. The basement rocks are highly dislocated and date back to the Paleozoic period. They are covered with a layer of marine and continental Mesozoic-Cenozoic sediments (sandstones, clays, etc.) more than 1000 meters thick. In the depressions of the foundation this thickness reaches up to 3000-4000 meters. In the southern part of the plain, the youngest - alluvial-lacustrine deposits are observed, in the northern part there are more mature - glacial-marine deposits.

The tectonic structure of the West Siberian Plain includes a foundation and a cover.

The foundation of the slab has the appearance of a depression with steep sides on the east and northeast and gentle sides on the south and west. The foundation blocks belong to the pre-Paleozoic, Baikal, Caledonian and Hercynian times. The foundation is dissected by deep faults of different ages. The largest faults of submeridional strike are the East Trans-Ural and Omsk-Pur. The map of tectonic structures shows that the surface of the plate foundation has an Outer Edge Belt and an Inner Region. The entire surface of the foundation is complicated by a system of rises and depressions.

The cover is interlayered with coastal-continental and marine sediments with a thickness of 3000-4000 meters in the south and 7000-8000 meters in the north.

Central Siberian Plateau

The Central Siberian Plateau is located in the north of Eurasia. It is located between the West Siberian Plain in the west, the Central Yakut Plain in the east, the North Siberian Lowland in the north, the Baikal region, Transbaikalia and the Eastern Sayan Mountains in the south.

The tectonic structure of the Central Siberian Plateau is confined to the Siberian Platform. The composition of its sedimentary rocks corresponds to the Paleozoic and Mesozoic periods. Characteristic rocks for it are sheet intrusions, which consist of traps and basalt covers.

The relief of the plateau consists of wide plateaus and ridges, at the same time there are valleys with steep slopes. The average height of the difference in the relief is 500-700 meters, but there are parts of the plateau where the absolute mark rises above 1000 meters, such areas include the Angara-Lena Plateau. To one of the most high areas The territory includes the Putorana plateau, its height is 1701 meters above sea level.

Sredinny ridge

The main watershed ridge of Kamchatka is a mountain range consisting of systems of peaks and passes. The ridge extends from north to south and its length is 1200 km. In its northern part it is concentrated a large number of passes, central part represents large distances between the peaks, in the south there is a strong dissection of the massif, and the asymmetry of the slopes characterizes the Sredinny Range. The tectonic structure is reflected in the relief. It consists of volcanoes, lava plateaus, mountain ranges, and glacier-covered peaks.

The ridge is complicated by lower-order structures, the most striking of which are the Malkinsky, Kozyrevsky, and Bystrinsky ridges.

The highest point belongs to and is 3621 meters. Some volcanoes, such as Khuvkhoytun, Alnai, Shishel, Ostraya Sopka, exceed 2500 meters.

Ural Mountains

The Ural Mountains are a mountain system that is located between the East European and West Siberian plains. Its length is more than 2000 km, its width varies from 40 to 150 km.

The tectonic structure of the Ural Mountains belongs to the ancient folded system. In the Paleozoic there was a geosyncline here and the sea splashed. Beginning with the Paleozoic, the formation of mountain system Ural. The main formation of folds occurred during the Hercynian period.

Intensive folding occurred on the eastern slope of the Urals, which was accompanied by deep faults and intrusions, the dimensions of which reached about 120 km in length and 60 km in width. The folds here are compressed, overturned, and complicated by thrusts.

On the western slope, folding occurred less intensively. The folds here are simple, without thrusts. There are no intrusions.

Pressure from the east was created by a tectonic structure - the Russian Platform, the foundation of which prevented the formation of folding. Gradually, folded mountains appeared in place of the Ural geosyncline.

In tectonic terms, the entire Urals is a complex complex of anticlinoriums and synclinoriums, separated by deep faults.

The relief of the Urals is asymmetrical from east to west. The eastern slope slopes steeply towards the West Siberian Plain. The gentle western slope smoothly transitions into the East European Plain. The asymmetry was caused by the activity of the tectonic structure of the West Siberian Plain.

Baltic shield

It belongs to the north-west of the East European Platform, is the largest protrusion of its foundation and is elevated above sea level. In the northwest, the border passes with the folded structures of Caledonia-Scandinavia. In the south and southeast, shield rocks are submerged under the cover of sedimentary rocks of the East European Plate.

Geographically, the shield is tied to the southeastern part of the Scandinavian Peninsula, to the Kola Peninsula and Karelia.

The structure of the shield involves three segments, different in age - South Scandinavian (western), Central and Kola-Karelian (eastern). The South Scandinavian sector is tied to the south of Sweden and Norway. The Murmansk block stands out in its composition.

The central sector is located in Finland and Sweden. It includes the Central Kola block and is located in the central part of the Kola Peninsula.

The Kola-Karelian sector is located in Russia. It belongs to the most ancient formation structures. In the structure of the Kola-Karelian sector, several tectonic elements are distinguished: Murmansk, Central Kola, White Sea, Karelian, they are separated from each other by deep faults.

Kola Peninsula

Tectonically tied to the northeastern part of the Baltic crystalline shield, composed of rocks ancient origin- granites and gneisses.

The relief of the peninsula has adopted the features of a crystalline shield and reflects traces of faults and cracks. On appearance The peninsula was influenced by glaciers, which smoothed the tops of the mountains.

Based on the nature of the relief, the peninsula is divided into western and eastern parts. The relief of the eastern part is not as complex as the western one. The mountains of the Kola Peninsula are shaped like pillars - at the tops of the mountains there are flat plateaus with steep slopes, and at the bottom there are lowlands. The plateaus are cut by deep valleys and gorges. In the western part there are the Lovozero tundra and the Khibiny Mountains, the tectonic structure of the latter belongs to the mountain ranges.

Khibiny

Geographically, the Khibiny belongs to the central part of the Kola Peninsula and is a large mountain range. The geological age of the massif exceeds 350 million years. Mountain Khibiny is a tectonic structure, which is an intrusive body (frozen magma) complex in structure and composition. From a geological point of view, an intrusion is not an erupted volcano. The massif continues to rise even now, the change per year is 1-2 cm. More than 500 types of minerals are found in the intrusive massif.

Not a single glacier has been discovered in the Khibiny Mountains, but traces of ancient ice are found. The peaks of the massif are plateau-shaped, the slopes are steep with a large number of snowfields, avalanches are active, there are many mountain lakes. The Khibiny are relatively low mountains. The highest elevation above sea level belongs to Mount Yudychvumchorr and corresponds to 1200.6 m.

Features of the geographical location of Western Siberia

Note 1

To the east of the Ural Mountains lie vast expanses of the Asian part of Russia. This territory has long been called Siberia. But due to the diversity of the tectonic structure, this territory was divided into several separate regions. One of them is Western Siberia.

The basis of Western Siberia is the West Siberian Plain. It is bounded in the west by the Ural Mountains, and in the east by the Yenisei River. In the north, the plain is washed by the waters of the Arctic Ocean. The southern borders approach the Kazakh small hills and the Turgai plateau. The total area of ​​the plain is about $3$ million km²$.

The characteristic features of the West Siberian Plain are the following:

• slight fluctuations in altitude over such a vast area;
• the extension from north to south and the almost flat topography determined a clear change in natural zones with latitude (classical latitudinal zoning);
• formation largest areas swamps in the taiga and salt accumulation landscapes in the steppe zone;
• a transitional climate is being formed from the temperate continental Russian Plain to the sharply continental one Central Siberia.

History of the formation of the plain

The West Siberian Lowland lies on the Upper Paleozoic plate. Sometimes this tectonic structure is also called epihercynian. The crystalline slab foundation contains metamorphosed rocks. The foundation sinks towards the center of the slab. The total thickness of the sedimentary cover exceeds $4$ km (in some areas – up to $6-7$ km).

As already mentioned, the foundation of the plate was formed as a result of the Hercynian orogeny. Next, peneplanation (leveling of the relief through erosion processes) of the ancient mountainous country occurred. In the Paleozoic and Mesozoic, troughs formed in the center, and the foundation was flooded by the sea. Therefore, it is covered with a significant thickness of Mesozoic sediments.

Later, during the Caledonian folding era, the southeastern part of the plain rose from the bottom of the sea. In the Triassic and Jurassic, the processes of relief denudation and the formation of sedimentary rocks prevailed. Sedimentation continued into the Cenozoic. During the Ice Age, the north of the plain was under a thick glacier. After its melting, a significant area of ​​Western Siberia was covered with moraine deposits.

Characteristics of the relief of Western Siberia

As already noted, geological history caused the formation of flat relief on the territory of the West Siberian Plain. But a more detailed study of the physical and geographical features of the region showed that the orography of the territory is complex and diverse.

The major relief elements on the plain are:

• lowlands;
• sloping plains;
• hills;
• plateau.

In general, the West Siberian Plain has the shape of an amphitheater, open to the Arctic Ocean. Plateau and upland areas predominate in the western, southern and eastern periphery. In the central regions and in the north, lowlands predominate. The lowlands are represented by:

• Kandinskaya;
• Nizhneobskaya;
• Nadymskaya;
• Purskoy.

Among the plateaus, the Priobskoye Plateau stands out. And the hills are represented by:

• Severo-Sosvinskaya;
• Turinskaya;
• Ishimskaya;
• Chulymo-Yeniseiskaya and others.

The relief includes zones of glacial-marine and permafrost-solifluction processes (tundra and northern taiga), fluvioglacial forms of glaciolacustrine plains (up to the middle taiga) and a zone of semiarid structural-denudation plateaus with erosion processes.

Note 2

Currently, human economic activity plays an important relief-forming role. The development of Western Siberia is accompanied by the development of mineral resources. This causes changes in the structure of rock layers and changes the course of physical and geographical processes. Erosion processes are intensifying. In the south during development Agriculture A large amount of minerals is introduced into the soil. Developing chemical erosion. It is necessary to carefully approach the issues of developing the nature of Siberia.

The West Siberian Lowland covers an area of ​​about 3 million square kilometers. It covers 1/7 of the entire territory of Russia. The width of the plain varies. In the northern part it is about 800 km, and in the southern part it reaches 1900 km.

Regions

The West Siberian Lowland is considered the most densely populated part of Siberia. On its territory there are several large regions, these are such as Omsk, Tyumen and Kurgan, as well as Novosibirsk and Tomsk. The greatest development of the lowland is observed in its southern part.

Climatic conditions

The climate in the lowlands is predominantly continental and quite harsh. Due to the large extent of the West Siberian Plain from north to south, there are significant differences in the climate of the southern part from the northern part. The proximity of the Arctic Ocean plays a big role in the formation of weather conditions, as well as the fact that on the plain there are no obstacles to the movement of air masses from north to south and their mixing.

In the cold season, an area of ​​high pressure appears over the southern part of the lowland, while in the north it decreases. Cyclones form at the boundary of air masses. Because of this, in regions located on the coast, the weather in winter is very unstable. can reach 40 meters per second. Winter throughout the entire territory of such a plain as the West Siberian Lowland is characterized by stable sub-zero temperatures, minimum temperatures can reach -52 o C. Spring comes late and is cold and dry, warming occurs only in May.

In the warm season the situation is reversed. Pressure increases over the Arctic Ocean, causing northerly winds to blow throughout the summer. But they are quite weak. The hottest time within the boundaries of the plain, called the West Siberian Lowland, is considered to be July. During this period in its northern part Maximum temperature reaches 21 o C, and in the south - 40 o C. Such high levels in the south are quite explainable by the fact that the border with Kazakhstan and Central Asia passes here. This is where the heated air masses come from.

The West Siberian Lowland, whose height varies from 140 to 250 m, is characterized by winters with little precipitation. At this time of year, only about 5-20 millimeters falls. The same cannot be said about the warm season, when 70% of annual precipitation falls on the ground.

Permafrost is widespread in the northern part of the lowland. The ground freezes to a depth of 600 meters.

Rivers

So, compare the West Siberian Lowland and the Central Siberian Plateau. A fairly strong difference is that the plateau is rugged a huge amount rec. There are practically no wetlands here. However, there are also a lot of rivers on the plain. There are about 2 thousand of them. All of them together contribute up to 1,200 cubic kilometers of water to the Kara Sea every year. That's an amazing amount. After all, one cubic kilometer contains 1,000,000,000,000 (trillion) liters. Most rivers in Western Siberia are fed by melt water or summer precipitation. Most of the water drains during the warm season. When a thaw occurs, river levels can rise by more than 15 meters, and in winter they are frozen. Therefore, during the cold period, the flow is only 10%.

The rivers of this part of Siberia are characterized by slow currents. This is due to the flat terrain and slight slopes. For example, the Ob River drops only 90 m over 3 thousand km. Because of this, its flow speed does not exceed half a meter per second.

Lakes

There are even more lakes in these parts than rivers. And many times more. There are about a million of them. But almost all of them are small in size. A special feature of the local lakes is that many of them are filled with salt water. They also overflow very heavily in the spring. But over the summer they can significantly decrease in size, and by autumn they can completely disappear. Over the last period, thanks to precipitation, the lakes fill with water again, freeze in winter, and the cycle repeats. This happens not with all reservoirs, but with the so-called “fog” lakes, which occupy the territory of this lowland - the West Siberian Plain. It is also characterized by another type of lake. They occupy natural uneven terrain, various pits and depressions.

Swamps

Another feature of Western Siberia is that it breaks all records for the number of swamps. It was within the boundaries of this lowland that the floods, which are considered one of the largest in the entire globe, spilled. Increased waterlogging is explained by the high content of peat in the ground. The substance is capable of holding a lot of water, which is why “dead” areas appear. The area itself also contributes to the formation of swamps. A plain without drops does not allow water to drain, and it remains in an almost motionless state, eroding and softening the soil.

Natural areas

Due to the fact that Western Siberia is strongly stretched from north to south, transitions are observed in it. They change from tundra in the north to deserts and semi-deserts in the south. Part of the lowland is occupied by the tundra zone, which is explained by the general northern position of the entire territory of the plain. To the south, the tundra gradually turns into forest-tundra, and then into the forest-swamp zone. The latter occupies 60% of the entire territory of Western Siberia.

There is a rather sharp transition to the steppe regions. The most common trees here are birch and aspen. In addition to them, the plowed steppe zone also occupies the extreme southern position in the plain. The West Siberian Lowland, the geographical location of which is directly related to the distribution of zones, also creates favorable conditions for pine forests located on low sandy spits.

The region is rich in representatives of the animal world. For example, about 99 species of mammals live here. Among them are fur-bearing animals such as arctic foxes, weasel and sable. Meet large predators- bears and lynxes. There are also many birds living in this area. Peregrine falcons, hawks and golden eagles are found in the reserves. There are also birds listed in the Red Book. For example, a black stork or a white-tailed eagle.

Mineral resources

Compare the geographical location of the West Siberian Lowland with any other, and it will become clear that about 70% of oil production is concentrated in the described plain. The plain is also rich in coal deposits. The total area of ​​land rich in these resources is estimated at 2 million square meters. km. The timber industry is also well developed. The greatest advantage is given to coal mining in Kuzbass.

Central Siberian Plateau

Compared to the West Siberian Lowland, the Central Siberian Plateau is not swampy due to the fact that it is located on a hill. However, there is a denser river system that is also fed by rain and melting snow. Permafrost is widespread everywhere. The climate on the plateau is sharply continental, which is why, as in the West Siberian Lowland, big differences temperatures in winter. The average in the north reaches -44 o C, and in the south -22 o C. This is also typical for summer period. There is less variety of animals, but bears, reindeer and hares are also found. The plateau is also rich in oil and gas deposits. To this are added various ores and

The West Siberian Plain is one of the largest accumulative lowland plains on the globe. It extends from the shores of the Kara Sea to the steppes of Kazakhstan and from the Urals in the west to the Central Siberian Plateau in the east. The plain has the shape of a trapezoid tapering to the north: the distance from its southern border to the northern reaches almost 2500 km, the width is from 800 to 1900 km, and the area is only slightly less than 3 million km 2.

The relief of the West Siberian Plain is one of the most homogeneous in the world. Occupying an area of ​​2.6 million km², the West Siberian Plain stretches from west to east, from the Urals to the Yenisei, for 1900 km, north to south, from the Arctic Ocean to the Altai Mountains, for 2400 km. Only in the extreme south do altitudes exceed 200 m; the vast majority of the plain has an altitude of less than 100 m above sea level; Alluvial-lacustrine and accumulative relief predominates (also denudation in the south). Relief features characteristic of Western Siberia, such as vast floodplains and huge swamps, are especially common in the northern part of the plain; The relief north of the latitudinal section of the Ob River was formed under the influence of transgressions of the sea and glaciers.

In the northwest and northeast of the West Siberian Plain, the relief is accumulative glacial, formed by glaciers descending from the mountains of the Northern Urals and the Putorana Plateau. The valleys of large rivers are terraced. On the Yamal and Gydan peninsulas there are aeolian dunes. Relatively elevated and dry territories, where the bulk of the population of Western Siberia is concentrated, are located south of 55 ° C. Latitude.

The differentiated subsidence of the West Siberian Plate in the Mesozoic and Cenozoic led to the predominance within its boundaries of processes of accumulation of loose sediments, the thick cover of which levels out the surface irregularities of the Hercynian basement. Therefore, the modern West Siberian Plain has a generally flat surface. However, it cannot be considered as a monotonous lowland, as was recently believed. In general, the territory of Western Siberia has a concave shape. Its lowest sections (50-100 m) are located mainly in the central (Kondinskaya and Sredneobskaya lowlands) and northern (Nizhneobskaya, Nadymskaya and Purskaya lowlands) parts of the country. Along the western, southern and eastern outskirts stretch low (up to 200-250 m) hills: North Sosvinskaya, Turinskaya, Ishimskaya, Priobskoye and Chulym-Yenisei plateaus, Ketsko-Tymskaya, Verkhnetazovskaya, Nizhneeniseiskaya. A clearly defined strip of hills is formed in the inner part of the plain by the Siberian Uvals (average height - 140-150 m), stretching from the west from the Ob to the east to the Yenisei, and the Vasyugan Plain parallel to them.

Some orographic elements of the West Siberian Plain correspond to geological structures: gentle anticlinal uplifts correspond, for example, to the Verkhnetazovskaya and Lyulimvor hills, and the Barabinskaya and Kondinskaya lowlands are confined to syneclises of the base of the plate. However, in Western Siberia, discordant (inversion) morphostructures are also common. These include, for example, the Vasyugan Plain, which formed on the site of a gently sloping syneclise, and the Chulym-Yenisei Plateau, located in the zone of basement deflection.

The West Siberian Plain is usually divided into four large geomorphological regions: 1) marine accumulative plains in the north; 2) glacial and water-glacial plains; 3) periglacial, mainly lacustrine-alluvial plains; 4) southern non-glacial plains (Voskresensky, 1962).
The differences in the relief of these areas are explained by the history of their formation in Quaternary times, the nature and intensity of recent tectonic movements, and zonal differences in modern exogenous processes. In the tundra zone, relief forms are especially widely represented, the formation of which is associated with the harsh climate and widespread permafrost. Thermokarst depressions, bulgunnyakhs, spotted and polygonal tundras are very common, and solifluction processes are developed. Typical of the southern steppe provinces are numerous closed basins of suffusion origin, occupied by salt marshes and lakes; The network of river valleys here is sparse, and erosional landforms in the interfluves are rare.

The main elements of the relief of the West Siberian Plain are wide, flat interfluves and river valleys. Due to the fact that the interfluve spaces account for most of the country's area, they determine the general appearance of the plain's topography. In many places, the slopes of their surfaces are insignificant, the flow of precipitation, especially in the forest-swamp zone, is very difficult and the interfluves are heavily swamped. Large areas are occupied by swamps north of the Siberian line railway, on the interfluves of the Ob and Irtysh, in Vasyugan and Barabinsk forest-steppe.

However, in some places the relief of the interfluves takes on the character of a wavy or hilly plain. Such areas are especially typical of some northern provinces of the plain, which were subject to Quaternary glaciations, which left here piles of stadial and bottom moraines. In the south - in Baraba, on the Ishim and Kulunda plains - the surface is often complicated by numerous low ridges stretching from northeast to southwest.

Western Siberia. Photo: Bernt Rostad

Another important element of the country's topography is river valleys. All of them were formed under conditions of slight surface slopes and slow and calm river flows. Due to differences in the intensity and nature of erosion, the appearance of the river valleys of Western Siberia is very diverse. There are also well-developed deep (up to 50-80 m) valleys of large rivers - the Ob, Irtysh and Yenisei - with a steep right bank and a system of low terraces on the left bank. In some places their width is several tens of kilometers, and the Ob valley in the lower reaches reaches even 100-120 km. The valleys of most small rivers are often just deep ditches with poorly defined slopes; During spring floods, water completely fills them and even floods neighboring valley areas.

Currently, on the territory of the West Siberian Plain there is a slow shift of the boundaries of geographical zones to the south. Forests in many places encroach on the forest-steppe, forest-steppe elements penetrate into the steppe zone, and tundras slowly displace woody vegetation near the northern limit of sparse forests. True, in the south of the country man interferes with the natural course of this process: by cutting down forests, he not only stops their natural advance on the steppe, but also contributes to the shift of the southern border of forests to the north.

West Siberian Plain(West Siberian Lowland) is one of the largest accumulative lowland plains on the globe. It extends from the shores of the Kara Sea to the steppes of Kazakhstan and from the Urals in the west to the Central Siberian Plateau in the east. The plain has the shape of a trapezoid tapering towards the north: the distance from its southern border to the northern reaches almost 2500 km, the width is from 800 to 1900 km, and the area is only slightly less than 3 million km 2. It occupies the entire western part of Siberia from the Ural Mountains in the west to the Central Siberian Plateau in the east, and includes regions of Russia and Kazakhstan. Geographical position The West Siberian Plain determines the transitional nature of its climate between the moderate continental Russian Plain and the sharply continental climate of Central Siberia. Therefore, the country’s landscapes are distinguished by a number of peculiar features: natural areas here are somewhat shifted to the north compared to the Russian Plain, the zone deciduous forests is absent, and landscape differences within the zones are less noticeable than on the Russian Plain.

Geological structure and history of development

The West Siberian Plain is located within the epi-Hercynian West Siberian plate, the foundation of which is composed of intensely dislocated and metamorphosed Paleozoic sediments, similar in nature to similar rocks of the Urals, and in the south of the Kazakh hills. The formation of the main folded structures of the basement of Western Siberia, which have a predominantly meridional direction, dates back to the era of the Hercynian orogeny. They are everywhere covered with a cover of loose marine and continental Meso-Cenozoic rocks (clays, sandstones, marls and the like) with a total thickness of over 1000 m (in the depressions of the foundation up to 3000-4000 m). The youngest, anthropogenic deposits in the south are alluvial and lacustrine, often covered with loess and loess-like loams; in the north - glacial, marine and ice-sea (thickness in some places up to 4070 m).

The tectonic structure of the West Siberian plate is quite heterogeneous. However, even its large structural elements appear in modern relief less clearly than tectonic structures Russian platform. This is explained by the fact that the surface relief of Paleozoic rocks, descended to great depths, is leveled here by a cover of Meso-Cenozoic sediments, the thickness of which exceeds 1000 m, and in individual depressions and syneclises of the Paleozoic basement - 3000-6000 m.

Significant changes in the conditions for the accumulation of sediments occurred in the Neogene. Formations of rocks of Neogene age, outcropping mainly in the southern half of the plain, consist exclusively of continental lacustrine-fluvial deposits. They were formed in the conditions of a poorly dissected plain, first covered with rich subtropical vegetation, and later with broad-leaved deciduous forests of representatives of the Turgai flora (beech, walnut, hornbeam, lapina, etc.). In some places there were areas of savannah where giraffes, mastodons, hipparions, and camels lived at that time.

The events of the Quaternary period had a particularly great influence on the formation of the landscapes of Western Siberia. During this time, the country's territory experienced repeated subsidence and continued to be an area predominantly of accumulation of loose alluvial, lacustrine, and, in the north, marine and glacial sediments. The thickness of the Quaternary cover reaches 200-250 m in the northern and central regions. However, in the south it noticeably decreases (in some places to 5-10 m), and in the modern relief the effects of differentiated neotectonic movements are clearly expressed, as a result of which swell-like uplifts arose, often coinciding with positive structures of the Mesozoic sedimentary cover.

Lower Quaternary sediments are represented in the north of the plain by alluvial sands filling buried valleys. The base of alluvium is sometimes located in them 200-210 m below the modern level of the Kara Sea. Above them in the north usually lie pre-glacial clays and loams with fossil remains of tundra flora, which indicates that a noticeable cooling of Western Siberia had already begun then. However, in the southern regions of the country dark coniferous forests with an admixture of birch and alder predominated.

The Middle Quaternary in the northern half of the plain was an era of marine transgressions and repeated glaciations. The most significant of them was Samarovskoe, the sediments of which form the interfluves of the territory lying between 58-60° and 63-64° N. w. According to currently prevailing views, the cover of the Samara glacier, even in the extreme northern regions of the lowland, was not continuous. The composition of the boulders shows that its food sources were glaciers descending from the Urals to the Ob valley, and in the east - glaciers of the Taimyr mountain ranges and the Central Siberian Plateau. However, even during the period of maximum development of glaciation on the West Siberian Plain, the Ural and Siberian ice sheets did not merge with each other, and the rivers of the southern regions, although they met a barrier, formed by ice, but found their way north in the interval between them.

The sediments of the Samarova strata, along with typical glacial rocks, also include marine and glaciomarine clays and loams that formed at the bottom of the sea advancing from the north. Therefore, the typical forms of moraine relief are less clearly expressed here than on the Russian Plain. On the lacustrine and fluvioglacial plains adjacent to the southern edge of the glaciers, forest-tundra landscapes then prevailed, and in the extreme south of the country loess-like loams formed, in which pollen of steppe plants (wormwood, kermek) is found. Marine transgression continued in the post-Samarovo period, the sediments of which are represented in the north of Western Siberia by the Messa sands and clays of the Sanchugov Formation. In the northeastern part of the plain, moraines and glacial-marine loams of the younger Taz glaciation are common. The interglacial era, which began after the retreat of the ice sheet, in the north was marked by the spread of the Kazantsev marine transgression, the sediments of which in the lower reaches of the Yenisei and Ob contain the remains of a more heat-loving marine fauna than that currently living in the Kara Sea.

The last, Zyryansky, glaciation was preceded by regression of the boreal sea, caused by uplifts of the northern regions of the West Siberian Plain, the Urals and the Central Siberian Plateau; the amplitude of these uplifts was only a few tens of meters. At the maximum stage of development of the Zyryan glaciation, glaciers descended to the areas of the Yenisei Plain and the eastern foot of the Urals to approximately 66° N. sh., where a number of stadial terminal moraines were left. In the south of Western Siberia at this time, sandy-clayey Quaternary sediments were overwintering, aeolian landforms were forming, and loess-like loams were accumulating.

Some researchers of the northern regions of the country paint a more complex picture of the events of the Quaternary glaciation era in Western Siberia. So, according to geologist V.N. Sachs and geomorphologist G.I. Lazukov, glaciation began here in the Lower Quaternary and consisted of four independent eras: Yarskaya, Samarovskaya, Tazovskaya and Zyryanskaya. Geologists S.A. Yakovlev and V.A. The Zubaks even count six glaciations, dating the beginning of the most ancient of them to the Pliocene.

On the other hand, there are supporters of a one-time glaciation of Western Siberia. Geographer A.I. Popov, for example, considers the deposits of the glaciation era of the northern half of the country as a single water-glacial complex consisting of marine and glacial-marine clays, loams and sands containing inclusions of boulder material. In his opinion, there were no extensive ice sheets on the territory of Western Siberia, since typical moraines are found only in the extreme western (at the foot of the Urals) and eastern (near the ledge of the Central Siberian Plateau) regions. During the glaciation era, the middle part of the northern half of the plain was covered with the waters of marine transgression; the boulders contained in its sediments were brought here by icebergs that broke off from the edge of glaciers that descended from the Central Siberian Plateau. Only one Quaternary glaciation in Western Siberia is recognized by geologist V.I. Gromov.

At the end of the Zyryan glaciation, the northern coastal regions of the West Siberian Plain subsided again. The subsided areas were flooded by the waters of the Kara Sea and covered with marine sediments that make up post-glacial marine terraces, the highest of which rises 50-60 m above the modern level of the Kara Sea. Then, after regression of the sea, a new incision of rivers began in the southern half of the plain. Due to the small slopes of the channel, lateral erosion prevailed in most river valleys of Western Siberia; the deepening of the valleys proceeded slowly, which is why they usually have a significant width but small depth. In poorly drained interfluve spaces, the reworking of the glacial relief continued: in the north it consisted of leveling the surface under the influence of solifluction processes; in the southern, non-glacial provinces, where there was more precipitation, especially in the transformation of the relief important role processes of deluvial washout played a role.

Paleobotanical materials suggest that after the glaciation there was a period with a slightly drier and warmer climate than now. This is confirmed, in particular, by the finds of stumps and tree trunks in the deposits of the tundra regions of Yamal and the Gydan Peninsula at 300-400 km. north modern border woody vegetation and the widespread development of relict large-hilly peat bogs in the south of the tundra zone.

Currently, on the territory of the West Siberian Plain there is a slow shift of the boundaries of geographical zones to the south. Forests in many places encroach on the forest-steppe, forest-steppe elements penetrate into the steppe zone, and tundras slowly displace woody vegetation near the northern limit of sparse forests. True, in the south of the country man interferes with the natural course of this process: by cutting down forests, he not only stops their natural advance on the steppe, but also contributes to the shift of the southern border of forests to the north.

Sources

• Gvozdetsky N.A., Mikhailov N.I. Physical geography of the USSR. Ed. 3rd. M., "Thought", 1978.

Literature

• West Siberian Lowland. Essay on Nature, M., 1963; Western Siberia, M., 1963.
• Davydova M.I., Rakovskaya E.M., Tushinsky G.K. Physical geography of the USSR. T. 1. M., Education, 1989.