– a large form of relief, formed as a result of the interaction of external and internal forces with the predominant influence of internal (endogenous) forces.
Morphostructures of flat-platform areas:
Stratified plain– the plain, confined to the platform slab, is composed of layers of the platform cover, lying almost horizontally or slightly inclined. Within the strata plains, separate accumulative lowlands and strata-denudation hills are distinguished.
Basement Plain– a denudation plain formed on dislocated rocks of the crystalline basement of ancient platforms.
Accumulative plains– plains formed as a result of the accumulation of layers of loose sediments. They are divided according to the leading agent of accumulation - endogenous (volcanic plains) or exogenous (marine, alluvial, lake, glacial, etc.); There are also accumulative plains of complex genesis (lacustrine-alluvial, deltaic-marine, alluvial-proluvial, etc.), as well as underwater accumulative plains (for example, abyssal); They are also distinguished by the place of formation (marginal, intermountain, foothill, on slabs of young platforms).
Denudation plains– leveled surfaces formed on the site of a once more elevated and contrasting (for example, mountainous) relief as a result of its destruction and the removal of destruction products under conditions of temporary or long-term predominance of denudation processes.
Stratified denudation plain– an elevated plain on the structures of the Precambrian platform plate, with the predominant development of the surface under the influence of denudation processes.
Monoclinal-stratal-denudation plain(cuesta) - a plain on which there are rows of cuestas parallel to each other - ridges asymmetrical in cross section, produced by erosion and denudation in a gently monoclinal formation of layers of unequal resistance to denudation processes.
Stratified plain– a type of strata-denudation plain, formed in humid and variable-humid climates of the temperate zone.
Stratified step plain(table-step plain) is a type of strata-denudation plain that forms in the humid and variable-humid climates of the tropical zone.
Table relief- a relief dissected by erosion of an elevated plain or plateau composed of horizontally occurring layers of rocks. Characterized by wide flat (table) watersheds, dissected by a few, mostly narrow and steeply sloped valleys. Characteristic of areas of arid climate, as well as areas of development of porous or fractured permeable rocks
Reversed type of morphostructure(inversion relief) – modern character.Morphostructure mountain folded areas:
fold mountains– 1) the type of structure of the newly formed mountains in the region of Alpine folding. Folded mountains arise in mobile zones of the earth's crust and are formed by plicative (without strata ruptures) folded dislocations with a subordinate role of disjunctive dislocations (with strata ruptures - fault, shear, etc.). Rock layers, crushed into folds of varying sizes and steepness, are raised to a certain height, forming ridges - anticlines, intermountain valleys – synclines. In the process of further mountain building, this correspondence is violated. 2) Primary uplifts during bending of the earth’s layers by tectonic movements, mainly in zones of collision of lithospheric plates
Fold-block mountains- a type of mountain structure in the areas of the Hercynian folding, which underwent peneplanation in the Mesozoic and experienced block tectonics in the neotectonic stage. Mountains and mountainous areas that arise during repeated tectonic movements, when folds of rocks that have lost their plasticity and hardened are subject to younger faults into large blocks of the earth's crust, which either rise to form horsts, or are omitted in the form grabens. Block-fold mountains- type of structure of mountains in areas of Mesozoic folding, which were not characterized by the stage of complete peneplanation. Block Mountains- a type of mountain structure associated with ancient platforms or areas of the Baikal and Caledonian folds, which were repeatedly subjected to processes of peniplanation and vertical dismemberment. Block mountains - fault mountains are formed by blocks of the earth's crust, raised along tectonic faults. There are block mountains formed by: a) blocks of horizontally lying rocks, and b) previously folded mountains, later peneplanated. Block mountains are characterized by massiveness, steep slopes and relatively weak dissection. Arising during repeated mountain building, block mountains are usually horsts, separated by grabens - intermountain depressions and tectonic valleys.
Appalachian landform– an inverted type of morphostructure of a mountain region, synclinoria in relief are represented by mountain ranges, and anticlinoria are represented by intermountain plains. Rejuvenated Mountains– an intermediate (middle) stage of mountain development, currently these are mountainous areas of Mesozoic folding, which were not characterized by the stage of complete peneplanation.
Reborn MountainsEpiplatform mountains, activated platforms, are mountain structures that arose on the site of ancient, peneplanated mountain areas as a result of recent movements of the earth's crust. From the era preceding the latest mountain building, highly elevated areas of ancient peneplains (planing surfaces) are preserved in the revived mountains. Examples: Tien Shan, Altai, Rocky Mountains, East African Highlands.
Young (newly formed) mountains- folded mountains formed during the Alpine folding. Young mountains have significant heights, sharp ridge tops, steep slopes, and numerous river gorges. For M.g. characteristic processes of volcanism. Horst- an elevated section of the earth's crust, bounded by tectonic faults (usually faults). Elevated relative to adjacent areas. Horst often appears in the relief in the form of mountain ranges. Graben– a section of the earth’s crust bounded by tectonic faults (faults) and lowered relative to adjacent sections. In relief, large grabens are expressed in the form of depressions occupied by lakes or developed by rivers.Predominant types of morphostructures
are accumulative plains and strata plains and plateaus. Accumulative plains
confined to areas of recent subsidence or slow uplift. They occupy large areas in the Aral Sea region: the northern regions of Kyzylkum, the Aral Sea Karakum, B. and M. Barsuki. Accumulative plains stretch in a continuous strip along mountain structures from the Caspian coast to lake. Alakol. From the side of the mountains, low ridges penetrate into the strip of accumulative plains: the Chu-Ili Mountains, Karatau, Nuratau, spurs of the Kopet Dag, dividing it into isolated sandy deserts - “Kums”: the Caspian Karakums, the Central and South-Eastern Karakums, the Moyynkums, the sands of the southern Balkhash region. The sands of the Aral Karakum region arose as a result of weathering of Cretaceous and Paleogene sandstones. In all other massifs, sands were carried out of the mountains by rivers. These are alluvial, deltaic and alluvial-lacustrine sands. They reach a thickness of 700-900 m and are of Quaternary age.
Plateau-shaped strata plains and plateaus
raised above younger accumulative plains by 100-200 m. Their surface is usually armored with horizontally occurring layers of denudation-resistant rocks. Most often these rocks are limestones and ferruginous sandstones. This type of morphostructure predominates in the western and northern parts of the country. It includes: the Krasnovodsk plateau, the Mangyshlak plateau, Ustyurt, the Turgai plateau, the western part of Betpak-Dala. Often plateaus have clearly defined steep edge ledges (chinks) usually 50-80 m high. The formation of chinks is associated with tectonic, denudation or abrasion processes.
An intermediate position between these two types of morphostructures is occupied by stratified plains and plateaus, covered by a cover of loose sediments of low thickness (10-20 m). This type includes the Zaunguz plateau and the Kyzylkum plateau (the central part of Kyzylkum).
Remnant hills, low mountain ranges and ridges
are confined to the zone of the deep Gissar-Mangyshlak fault, along which intense recent uplifts occur. This type of morphostructure includes the Kyzylkum Hills, Sultan-Uvays, Mangystau and other low-mountain ridges in Mangyshlak.
The development of the relief of the Turan Plain during the Pliocene-Quaternary occurred mainly in arid conditions. This is reflected in the character morphosculptures both accumulative and denudation plains and remnant massifs, in the formation of which the leading role belongs to the wind.
Denudation plains
The northern and western parts of the country are an area of destructive wind activity. They are located where wind speeds are maximum (5.5-8.0 m/sec). At such speeds, deflation—blowing—prevails. The main amount of fine earth lifted by the wind from the surface is carried hundreds and thousands of kilometers away. Here it accumulates only in areas with rich vegetation (in valleys, deltas). During deflation, predominantly negative relief forms appear.
The wind carrying grains of sand has enormous destructive power. It knocks out closed depressions of various sizes (from several centimeters to many kilometers in diameter) even on the granites of the Kazakh hillocks. This process occurs even more intensely on the sedimentary rocks of the Turanian Plain, especially in cases where they are dispersed during the process of salt accumulation. This is precisely what accounts for the abundance of drainless closed basins on the Turanian Plain, especially in its western part. Calculations carried out for the Karynzharyk depression, which has a relative depth of about 300 m, showed that with a material blowing rate of only 1 mm per year, it could have formed in 300 thousand years.
Plains- vast areas of the earth's surface with small (up to 200 m) fluctuations in height and slight slopes.
Plains occupy 64% of the land area. Tectonically, they correspond to more or less stable platforms that have not shown significant activity in recent times, regardless of their age - ancient or young. Most of the land's plains are located on ancient platforms (42%).
Plains are distinguished by absolute and surface height negative-
lying below the level of the World Ocean (Caspian), low-lying- from 0 to 200 m altitude (Amazonian, Black Sea, Indo-Gangetic lowlands, etc.), sublime- from 200 to 500 m (Central Russian, Valdai, Volga uplands, etc.). Plains also include plateau (high plains), which, as a rule, are located above 500 m and are separated from the adjacent plains by ledges (for example, the Great Plains in the USA, etc.). The depth and degree of dissection of them by river valleys, gullies and ravines depends on the height of the plains and plateaus: what
The higher the plain, the more intensely they are dissected.
In terms of appearance, plains can be flat, wavy, hilly, stepped, and in terms of the general slope of the surface - horizontal, inclined, convex, concave.
The different appearance of the plains depends on their origin and internal structure, which largely depend on the direction of neotectonic movements. Based on this feature, all plains can be divided into two types - denudation and accumulative (see diagram 14-A-1-1). Within the former, the processes of denudation of loose material predominate, and within the latter, its accumulation.
It is clear that denudation surfaces have experienced upward tectonic movements for most of their history. It was thanks to them that the processes of destruction and demolition - denudation - prevailed here. However, the duration of denudation may vary, and this is also reflected in the morphology of such surfaces.
With continuous or almost continuous slow (epeirogenic) tectonic uplift, which continued throughout the entire existence of the territories, there were no conditions for the accumulation of sediments. There was only a denudation of the surface by various exogenous agents, and if thin continental or marine sediments accumulated for a short time, then during subsequent uplifts they were carried out of the territory. Therefore, in the structure of such plains, an ancient base comes to the surface - folds cut off by denudation, only slightly covered by a thin cover of Quaternary deposits. Such plains are called basement; It is easy to see that the basement plains tectonically correspond to the shields of ancient platforms and the protrusions of the folded foundation of young platforms. Basement plains on ancient platforms have a hilly topography, most often they are elevated. These are, for example, the plains of Fennoscandia - the Kola Peninsula and Karelia. Similar plains are located in northern Canada. Basement hills are widespread in Africa. As a rule, long-term denudation has cut off all the structural irregularities of the base, so such plains are astructural.
The plains on the “shields” of young platforms have a more “restless” hilly topography, with residual elevations such as hills, the formation of which is associated either with lithological features - more
hard stable rocks, or with structural conditions - former convex folds, microhorsts or exposed intrusions. Of course, they are all structurally determined. This is what, for example, the Kazakh small hills and part of the Gobi plains look like.
Plates of ancient and young platforms, experiencing a stable uplift only during the neotectonic stage of development, are composed of layers of sedimentary rocks of great thickness (hundreds of meters and a few kilometers) - limestones, dolomites, sandstones, siltstones, etc. Over millions of years, the sediments hardened, became rocky and acquired stability to erosion. These rocks lie more or less horizontally, as they were once deposited. Uplifts of territories during the neotectonic stage of development stimulated denudation on them, which did not allow young loose rocks to be deposited there. Plains on slabs of ancient and young platforms are called reservoir. From the surface, they are often covered with loose Quaternary continental sediments of low thickness, which practically do not affect their height and orographic features, but determine their appearance due to morphosculpture (East European, southern part of West Siberian, etc.).
Since strata plains are confined to platform plates, they are clearly structural - their macro- and even mesoforms of relief are determined by the geological structures of the cover: the nature of the bedding of rocks of varying hardness, their slope, etc.
During the Pliocene-Quaternary subsidence of territories, even relative ones, sediments carried away from surrounding areas began to accumulate on them. They filled in all the previous surface irregularities. This is how they were formed accumulative plains, composed of loose, Pliocene-Quaternary sediments. These are usually low-lying plains, sometimes even below sea level. According to the conditions of sedimentation, they are divided into marine and continental - alluvial, aeolian, etc. An example of accumulative plains are the Caspian, Black Sea, Kolyma, Yana-Indigirskaya lowlands composed of marine sediments, as well as the Pripyat, Leno-Vilyuiskaya, La Plata, etc. Accumulative plains , as a rule, are confined to syneclises.
In large basins among the mountains and at their feet, accumulative plains have a surface inclined from the mountains, cut through by the valleys of many rivers flowing from the mountains and complicated by their alluvial cones. They are more complex
We are filled with loose continental sediments: alluvium, proluvium, colluvium, and lake sediments. For example, the Tarim Plain is composed of sands and loess, the Dzungarian Plain is composed of powerful sand accumulations brought from neighboring mountains. The ancient alluvial plain is the Karakum desert, composed of sands brought by rivers from the southern mountains in the pluvial era of the Pleistocene.
The morphostructures of plains usually include ridges These are linearly elongated hills with rounded peaks, usually no more than 500 m high. They are composed of dislocated rocks of different ages. An indispensable feature of a ridge is the presence of a linear orientation, inherited from the structure of the folded region in the place of which the ridge arose, for example, Timansky, Donetsk, Yenisei.
It should be noted that all of the listed types of plains (basement, strata, accumulative), as well as plateaus, plateaus and ridges, according to I. P. Gerasimov and Yu. A. Meshcheryakov, are not morphographic concepts, but morphostructural ones, reflecting the relationship of relief with geological structure 1.
Plains on land form two latitudinal series corresponding to the platforms of Laurasia and Gondwana. Northern Plains Row formed within the framework of the ancient North American and East European platforms, which were relatively stable in recent times, and the young EpiPaleozoic West Siberian platform - a plate that experienced even slight subsidence and is expressed in relief as a predominantly low-lying plain.
The Central Siberian plateau, and in the morpho-structural sense these are high plains - a plateau, was formed on the site of the ancient Siberian platform, activated in recent times due to resonant movements from the east, from the active geosynclinal Western Pacific belt. The so-called Central Siberian Plateau includes volcanic plateaus(Pu-torana and Syverma), tuffaceous plateaus(Central Tunguska), trap plateaus(Tungusskoye, Vilyuiskoye), reservoir plateaus(Priangarskoe, Prilenskoe), etc.
The orographic and structural features of the plains of the northern row are peculiar: beyond the North-
“Plateaus and plateaus are often distinguished only by their appearance and degree of dissection, without taking into account their geological structure. Plateaus are considered less dissected forms of relief and are classified as high plains. Plateaus are usually higher, dissected more intensely and deeper in the marginal parts, so they are classified as mountains.
The Arctic Circle is dominated by low coastal accumulative plains; to the south, along the so-called active 62° parallel, there is a strip of basement hills and even plateaus on the shields of ancient platforms - Laurentian, Baltic, Anabar; in middle latitudes along 50° N. w. - again a strip of stratal and accumulative lowlands - North German, Polish, Polesie, Meshchera, Sredneobskaya, Vilyuiskaya.
On the East European Plain, Yu. A. Meshcheryakov identified another pattern: the alternation of lowlands and hills. Since the movements on the East European Platform were wave-like in nature, and their source in the neotectonic stage was collisions of the Alpine belt, he established several alternating stripes of hills and lowlands, fanning out from the southwest to the east and taking an increasingly meridional direction as they move away from the Carpathians . The Carpathian strip of uplands (Volyn, Podolsk, Prydneprovskaya) is replaced by the Pripyat-Dnieper strip of lowlands (Pripyat, Prydneprovskaya), followed by the Central Russian strip of uplands (Belarusian, Smolensk-Moscow, Central Russian); the latter is successively replaced by the Upper Volga-Don strip of lowlands (Meshchera lowland, Oka-Don plain), then by the Volga upland, Trans-Volga lowland and, finally, by a strip of the Cis-Ural uplands.
In general, the plains of the northern series are inclined to the north, which is consistent with the flow of the rivers.
Southern Plains Row corresponds to the Gond-Van platforms, which have experienced activation in recent times. Therefore, elevations predominate within its boundaries: stratum (in the Sahara) and basement (in southern Africa), as well as plateaus (Arabia, Hindustan). Only within the inherited troughs and syneclises did strata and accumulative plains form (Amazonian and La Plata lowlands, Congo depression, Central Lowland of Australia).
In general, the largest areas among the plains on the continents belong to strata plains, within which the primary plain surfaces are formed by horizontally lying layers of sedimentary rocks, and the basement and accumulative plains are of subordinate importance.
In conclusion, we emphasize once again that mountains and plains, as the main forms of relief on land, are created by internal processes: mountains gravitate towards mobile folded belts
Lands, and plains - to platforms (Table 14). Relatively small, relatively short-lived relief forms created by external exogenous
processes overlap
on large ones and give them a unique appearance. They will be discussed below.
Table 14
Areas of the main types of continental morphostructures (%)
They consist of two tiers: a crystalline plate of Precambrian, Caledonian or Hercynian age and a sedimentary sequence. On the Russian Plain, the sedimentary sequence is represented by marine or lagoonal-continental deposits of all geological periods. On the outskirts of the Baltic shield, near the Gulf of Finland, Cambrian clays are exposed, further to the south, southeast and east Ordovician and Silurian limestones, Devonian sandstones, and Carboniferous clays occur successively. In the Cis-Ural region, the surface is composed of Permian deposits, in the central part of the plain - Mesozoic, and in the south - in the Black Sea and Caspian lowlands - Paleogene and Neogene.
If the platforms had been stationary since their formation, their relief would have been buried under sedimentary strata and not reflected on the surface. In fact, during Meso-Cenozoic time the basement experienced repeated tectonic movements associated with ocean floor movements and Alpine orogeny.
Neotectonic movements manifested themselves in the differentiation of platforms into low and high, in the formation of protrusions and depressions in the foundation of each plate. The newly emerged relief of the basement changed the position of sedimentary strata and created hills and lowlands within the large plains.
The world map clearly shows patterns in the location of high and low plains: 1) on the Laurasian continents, high plains adjoin the Great Ocean (Eastern Siberia and the mid-west of America), and low plains (Eastern European, Western Siberian and western part of America) adjoin the Atlantic. This is due to the formation of oceanic trenches at the end of the Mesozoic, from under which mantle material flowed under the nearest continental massifs (Khain, 1964). This process is currently occurring in the Indian Ocean and is affecting the altitude of the surrounding plains.
Under the influence of lateral pressure from the orogenic belts of the Meso-Cenozoic, all the plates turned out to be broken into blocks by cracks of a complex system. This can be clearly shown using the example of the Baltic Shield, where the plate comes to the surface. This is the Kola Peninsula. The White Sea, the Gulf of Bothnia, and the grabens of Lakes Ladoga and Onega are limited by planes of subsidence.
The protrusions of the foundation are called anteclises, dives - syneclises. They are very large blocks bounded by fault planes. In addition to them, there are protrusions and depressions of smaller sizes, comparable to those listed on the Baltic Shield. The protrusions of the foundation correspond to uplands (Donetsk and Timan ridges. Central Russian and Volga uplands, Siberian ridges, etc.), and the depressions correspond to lowlands (Pechora, Caspian, Oka-Don, etc.).