Corresponding relief form of the Mesozoic folding. Areas of Mesozoic folding

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78.1.

MESOZOIC FOLDING(Greek mesos - middle) - the development of geosynclines with deep folds of the earth's crust and the accumulation of powerful sediments that were crumpled into folds, raised in the form of mountains, broken through by intrusions of granite magma and volcanic eruptions that continued from the end of the Triassic to the beginning of the Paleogene period. In different areas, this folding manifested itself with unequal intensity and non-simultaneously, in connection with this it has several names.

The earliest Mesozoic folding began in South-Eastern Europe, South Asia, and Taimyr; it took a particularly long and intensive course along the continental margins of the Pacific Ocean and, after a short break, resumed already in Alpine folding. A variety of minerals and numerous deposits of non-ferrous metals and gold are associated with its granite intrusions, especially in North America and Northeast Russia.

Mesozoic Folding

Mesozoic folding is a set of geological processes of folding, mountain building and granitoid magmatism that took place during the Mesozoic era. It manifested itself most intensively within the Pacific mobile belt. Folding is distinguished: ancient Cimmerian, or Indosinian, manifested in con. Triassic - early Jurassic; Young Cimmerian (Kolyma, Nevada, or Andean); Austrian (at the turn of the Early and Late Cretaceous) and Laramian. Pacific folding stands out independently in areas adjacent to the Pacific Ocean: in the East. Asia, the Cordillera and the Andes. Ancient Cimmerian folding manifested itself in con. Triassic - early Jurassic in the mountainous structures of the Crimea, Sev. Dobruja, in Taimyr, in the North. Afghanistan, Southeast. Asia, Patagonian Andes and Northeast. Argentina; Young Cimmerian - in con. Jurassic - early chalk in the Verkhoyansk-Chukotka region, Center. and South East. Pamir, in Karakoram, Center. Iran, in the Caucasus, in the West. Cordillera Sev. America, Andes and other areas. The Laramian folding, one of the youngest epochs of the Mesozoic folding, manifested itself in the con. chalk - early Paleogene in the regions of the Rocky Mountains North. America, in the Andes South. America and others.

Areas of Mesozoic folding

By the end of the Paleozoic era, as already mentioned, all geosynclines and mobile areas turned into vast rigid fields. As a result of the upward movements of the earth's crust, they were freed from sea waters. A theocratic regime was established.

The Mesozoic era (the era of middle life) began, the era of a new, higher stage in the development of the nature of the Earth as a whole.

In the Mesozoic, the foundations of the modern relief of our planet were laid, including within the territory of the CIS, and the main outlines of the continents and oceans were determined.

Mesozoids occupy vast spaces, closing and linking the territories of the more ancient parts of the consolidation of the earth's crust. Various forms of Mesozoic folding are expressed in the east and northeast of Siberia, the Far East, i.e., in a territory with a total area of ​​about 5 million km2. But the Mesozoic tectogenesis was also reflected in more ancient structures - the Precambrian, Baikal and Paleozoic stages.

The Mesozoic structures include Eastern Transbaikalia, the south of the Far East with Sikhote-Alin, and the Verkhoyansk-Kolyma-Chukotka fold system. Thus, the west of the Pacific geosynclinal belt belongs to the Mesozoic structures. The modern surface of the East Siberian part and the Far East is characterized by a wide distribution of mountain structures. In addition to the typical mountainous terrain, Eastern Siberia and the Far East include numerous highlands, plateaus, plains (the area of ​​the latter is generally not large) and, finally, the Predverkhoyansk marginal trough, which is extensive in territory. The manifestation of Mesozoic folding is noted in the Kopetdag, Mangyshlak, Donbass, in the Crimea, the Caucasus.

In the area of ​​the Mesozoic fold systems of Eastern Siberia and the Far East, the Neo-Cimmerian and Laramian movements of the Cretaceous period were the main ones. The geosynclinal basin extended from the Siberian platform to the east, i.e., within the territory of the Far East. It was a huge sea, in which thick layers of sediments accumulated, amounting to many thousands of meters. In the geosynclinal sea basin there were ancient mountainous median land masses: Kolyma-Indigirsky, Omolonsky and others, the ledge of the Siberian platform - the Aldan shield, and in the southeast - the Chinese shield stood out. The accumulation of sediments in the geosynclinal basin occurred due to the erosion and destruction of the ancient median massifs and the platforms surrounding the geosyncline - the Siberian, De Long, and Okhotsk. Tectogenesis in the ancient platforms and mountain structures of the Paleozoic, which surrounded the Mesozoic territories from the west, northwest and south, proceeded in a complex and peculiar way. One of the indicators of this originality was the difference in time of tectonic processes and the difference in the forms of their manifestation. But in general, the Mesozoic era in the east of the territory of our country ended with the change of the marine regime to the continental one.

The most active Mesozoic folding manifested itself between the Kolyma massif and the Siberian platform (Verkhoyansk zone). Folding movements here were accompanied by volcanic eruptions and intrusions of granitoids, which led to diverse and very rich mineralization (rare metals, tin, gold, etc.). The median massifs were subjected to deep faults, through the cracks of which effusives poured onto the surface. The mesozoids of Eastern and Northeastern Siberia are characterized by folded zones with anticlinal and synclinal structures.

The geological development of the south of the Far East is similar to the development of the northeast. Folded structures were also formed during the Mesozoic stage of tectogenesis, but the median massifs of the Precambrian and Paleozoic arose much earlier: the Zeya-Bureya plate and the Khanka massif, which was the outskirts of the Manchurian platform. In the Poleozoic, the cores of the axial parts of the ridges were formed - Tukuringra-Dzhagdy, Bureinsky, Sikhote-Alin, etc. Ancient folding here was accompanied by intense intrusions of granitoids, which caused mineralization.

Mineral resources throughout the territory of the Mesozoic folding of the east of Siberia and the Far East are diverse. Mineralization zones are usually confined to ancient hard massifs (or to their edges): iron ores, non-ferrous metal ores, tungsten, molybdenum, gold, etc. Deposits of hard and brown coal, gas, oil, etc. are associated with sedimentary deposits.

78.2.

Laurasia is the northern of the two pra-continents that formed the pro-continent of Pangea. Eurasia and North America were part of Laurasia. They broke off from the parent continent and became modern continents from 135 to 200 million years ago.

In ancient times, Laurasia was a supercontinent and was part of Pangea, which existed in the late Mesozoic era. This continent was formed by those territories that today are the continents of the Northern Hemisphere. In particular, it was Laurentia (the mainland that existed in the Paleozoic era in the eastern and central parts of Canada), Siberia, the Baltic, Kazakhstan, as well as the north and east continental shields. The mainland got its name from Laurentia and Eurasia.

Origin

The primal continent of Laurasia is a phenomenon of the Mesozoic era. At present, it is believed that the continents that formed it, after the collapse of the Motherland (1 billion years ago), formed one supercontinent. To avoid confusion with the name of the Mesozoic continent, it was simply assigned to proto-Laurasia. Referring to current ideas, after joining with the southern continents, Laurasia formed a late Precambrian supercontinent called Pannotia (Early Cambrian), and was no longer separated.

Fault and formation

During the Cambrian epoch, Laurasia was in equatorial latitudes for the first half a million years. The supercontinent began to break up into Siberia and northern China, continuing to drift northward; in the past they were further north than 500 million years ago. By the beginning of the Devonian period, North China was located near the Arctic Circle and was the northernmost land during the entire era of the Carboniferous Ice Age (300-280 million years ago). To date, there is no evidence of a large icing of the northern continents. During that cold period, Baltica and Laurentia merged with the Appalachian Plateau, which made it possible to form huge reserves of coal. It is this coal that today is the basis of the economy of such regions as Germany, West Virginia and part of the British Isles.

In turn, Siberia, moving south, connected with Kazakhstan - a small mainland, which today is considered the result of a volcanic eruption in the Silurian era. At the conclusion of these reunions, Laurasia changed its form significantly. At the beginning of the Triassic, the shield of East China reunited with Laurasia and Gondwana to form Pangea. Northern China continued to drift from the near-Arctic latitudes and became the last mainland that never connected with Pangea.

final separation

About 200 million years ago, the breakup of the pro-continent Pangea took place. Having broken away, North America and northwest Africa were separated by the new Atlantic Ocean, while Europe and Greenland (being together with North America) were still one. They separated only 60 million years ago in the Paleocene. After that, Laurasia split into Eurasia and Laurentia (now North America). Ultimately, India and the Arabian Peninsula were annexed to Eurasia.

78.3.

The collapse of Gondwana began in the Mesozoic, Gondwana was literally pulled apart piece by piece. By the end of the Cretaceous - the beginning of the Paleogene periods, the modern post-Gondwanan continents and their parts - South America, Africa (without the Atlas Mountains), Arabia, Australia, Antarctica - separated.

Gondwana (after the name of the historical region in Central India), a hypothetical continent, which, according to many scientists, existed in the Paleozoic and partly Mesozoic eras in the southern hemisphere of the Earth. It included: most of modern South America (east of the Andes), Africa (without the Atlas mountains), about. Madagascar, Arabia, the Hindustan Peninsula (south of the Himalayas), Australia (to the west of the mountain ranges of its eastern part), and, possibly, most of Antarctica. Proponents of the hypothesis of the existence of Gondwana believe that extensive glaciation developed on the territory of Gondwana in the Proterozoic and Upper Carboniferous. Traces of the Upper Carboniferous glaciation are known in Central and South Africa, in the south of South America, in India and Australia. In the Carboniferous and Permian periods, a peculiar flora of the temperate and cold zones developed on the mainland, which was characterized by an abundance of glossopteris and horsetails. The disintegration of Gondwana began in the Mesozoic, and by the end of the Cretaceous - the beginning of the Paleogene periods, modern continents and their parts separated. Many geologists believe that the destruction of Gondwana was the result of a horizontal expansion of its modern parts, which is confirmed by paleomagnetism data. Some scientists suggest not the expansion, but the collapse of individual sections of Gondwana, which were on the site of the modern Indian and South Atlantic Oceans.

79. 2 .

Features of sedimentation. The Triassic is characterized by continental red-colored strata and weathering crusts. Marine sediments were localized in geosynclinal areas. Trap magmatism manifested itself on a large scale on the Siberian, South American and southern African platforms. There are three types - explosive, lava and intrusive (sills). In the Jura, precipitation is more diverse. Among marine - siliceous, carbonate, clayey and glauconite sandstones; continental - sediments of the weathering crust predominate, and coal-bearing strata are formed in the lagoons. Magmatism manifested itself in the geosynclinal regions - Cordillera and Verkhoyansk-Chukotka, and trap - on the platforms - South American and African. A feature of the Cretaceous deposits is the maximum accumulation of writing chalk (consists of foraminifera and remains of shells of coccolithophorid algae).

Paleogeography of the Mesozoic. The formation of the supercontinent Pangea-2 is associated with the greatest regression of the sea in the history of the Earth. Only small areas adjacent to the geosynclinal belts were covered with shallow seas (the areas adjacent to the Cordillera and the Verkhoyansk-Chukotka geosyncline). Hercynian folded belts represented areas of dissected relief. The climate of the Triassic is arid continental, only in the coastal regions (Kolyma, Sakhalin, Kamchatka, etc.) is it moderate. At the end of the Triassic, the transgression of the sea begins, which was widely manifested in the late Jura. The sea extended into the western part of the North American Platform, almost the entire East European Platform, and into the northwestern and eastern parts of the Siberian Platform. The maximum transgression of the sea manifested itself in the Upper Cretaceous. The climate of these periods is characterized by the alternation of humid tropical and dry arid.

79.3.

Geocratic periods in the history of the Earth (from geo... and Greek kratos - strength, power), periods of a significant increase in land area, as opposed to thalassocratic periods, characterized by an increase in sea area. Geographic areas are confined to the second half of tectonic cycles, when general uplifts of the earth's crust turn into land a significant part of the continents previously flooded by a shallow sea. They are characterized by a great contrast of climates, in particular, a sharp increase in the areas of dry (arid) and cold climatic zones. Typical of hydrogeological deposits is the accumulation of continental red-colored strata composed of eolian, alluvial, and lacustrine sediments from arid plains, partly true deserts, and glacial deposits. No less typical are deposits of internal closed and semi-enclosed marine basins with high salinity of sediments from highly saline lagoons (dolomites, gypsum, salts). The G. p. can be attributed: the end of the Silurian and a significant part of the Devonian periods, the end of the Carboniferous, Permian and part of the Triassic periods, the Neogene and Anthropogenic periods (including the modern era).

Thalassocratic periods in the history of the Earth, periods of wide distribution of seas on the surface of modern continents. They are contrasted with geocratic periods, which are characterized by a significant increase in land area. In terms of time, the Thalassocratic periods refer to the middle of tectonic cycles (stages), when most of the earth's surface was dominated by subsidence of the earth's crust, due to which, almost everywhere, a significant area of ​​the continents was flooded with the sea. The increase in the area of ​​the hydrosphere contributed to the development of a humid maritime climate with small temperature fluctuations. During the Thalassocratic periods, mainly marine sedimentary strata accumulated, among which carbonate rocks played an important role. Thalassocratic periods include the Middle Cambrian, Upper Silurian, Middle and early Late Devonian, Early Carboniferous, and Late Cretaceous.

80.1.

Eustatic sea level fluctuations (from the Greek éu - good, completely and stásis - standing still, rest, position), ubiquitous slow changes in the level of the World Ocean and its associated seas. Eustatic movements (eustasia) were originally identified by E. Suess (1888). Coastline movements are distinguished: 1) as a result of the formation of sea troughs, when true changes in ocean level occur, and 2) as a result of tectonic processes, leading to apparent movements in ocean level. These fluctuations, which cause local transgressions and regressions caused by variously acting tectonic forces, were called deleveling, and wide transgressions and regressions, due to fluctuations in the level of the water shell itself, were called hydrokinematic (F. Yu. Levinson-Lessing, 1893). A.P. Pavlov (1896) called the negative movements of the coastline geocratic, and the advance of the sea hydrocratic. Among the hypothetical factors that determine eustasia, there is a change in the total volume of ocean water in the geological history of the Earth, which was determined by the evolution of the continents. At the initial stages of the development of the earth's crust, the importance of juvenile waters in E. to. was decisive; later the importance of this factor weakened. According to A.P. Vinogradov, the stabilization of the volume of water began in the Proterozoic, and since the Paleozoic, the volume of the water mass of the hydrosphere has changed within insignificant limits; Of little importance are the processes of sedimentation and volcanic outpouring at the bottom of the seas (sedimentoeustasia) and, as a consequence, the rise in the level of the World Ocean. Starting from the Paleozoic, the tectonic factor (tectonoeustasia), which affects the change in the capacity of the sea, was of decisive importance. and oceanic depressions with a change in the relief and structure of the ocean floor and adjacent continents. Apparently, ch. fluctuations in the level of the World Ocean are associated with the development of the system of mid-ocean ridges and with the phenomenon of spreading of the seabed - spreading. Against the background of the action of tectonoeustasia in recent geological time, the climatic factor in the form of glacioeustasia played a great influence (see Oscillatory movements of the earth's crust, Recent tectonic movements). During glaciations, when water was concentrated on the continents, forming ice sheets, the level of the World Ocean dropped by approximately 110-140 m; after melting, glacial waters again entered the World Ocean, raising its level by approximately 1/3 of its original level. A decrease in temperature and a change in salinity at the same time affected the density of water, due to which the level of the World Ocean at high latitudes differed by several meters from the level of the World Ocean in equatorial regions. These factors are associated with the formation of the lowest terrace - 3-5 m. Planetary factors also played a certain role in the mechanism of eustasia (changes in the speed of the Earth's rotation, displacement of the poles, etc.). The study of eustasy processes is of great importance for historical geology and understanding of the features of the formation of shelf zones, which are associated with the formation of various minerals.

80.2.

Mesozoic climate

Using well-known climatically modern analogs of Mesozoic lithogenetic formations and modern ecological analogs of Mesozoic vegetation and the Mesozoic organic world, as well as using paleothermic data, we obtain the necessary data for an approximate quantitative assessment of the climatic conditions of the past.

Early and Middle Triassic

The climate of the Mesozoic and especially the Triassic was almost isothermal, so the natural zonality of the mainland at that time was determined mainly by the distribution of precipitation and not so much by volume as by the mode of precipitation during the year. For the early and middle Triassic within Eurasia, three main natural zones are established: extra-arid (desert), which included the predominant part of Europe, Arabia, Iran, Central and Central Asia; moderately arid (dry savanna), whose landscapes were dominant in Northern Europe, Western and Southern Siberia, Transbaikalia, Mongolia and Eastern China, and semiarid (moderately humid savanna), covering northeast Asia from Khatanga and Chukotka to the Japanese Islands, and also Southeast Asia.

81.2.

Iridium anomaly - an amazing discovery made by the American geologist Walter ALVARES in 1977 in a gorge near the city of Gubio, which is 150 kilometers from Rome. At great depths, a thin layer of clay was found with an iridium content 300 times higher than the norm. This layer lay at a depth corresponding to the geological boundary between the Mesozoic and Cenozoic - the time when the dinosaurs became extinct. Comparing this fact with the fact that usually the content of iridium in the earth's crust is negligible - 0.03 weight parts per billion, and in meteorites the concentration of this substance is almost 20,000 times greater, Alvarez suggested that the iridium anomaly arose as a result of the fall of a large cosmic body that caused a global disaster that killed the dinosaurs. This assumption remains a hypothesis. Meanwhile, iridium anomalies with approximately the same concentration as in the Gubio gorge have already been found in many places on the planet - in Denmark, Spain, on the coast of the Caspian Sea. But the final version of the fall of the iridium meteorite will be recognized when a specific crater is discovered at the site of its fall .

82.1.

Cenozoic (Cenozoic era) - an era in the geological history of the Earth with a length of 65.5 million years, starting from the great extinction of species at the end of the Cretaceous period to the present. Translated from Greek as "new life" (καινός = new + ζωή = life). The Cenozoic is divided into the Paleogene, Neogene and Quaternary period (anthropogen). Historically, the Cenozoic was divided into periods - the Tertiary (from the Paleocene to the Pliocene) and the Quaternary (Pleistocene and Holocene), although most geologists no longer recognize such a division.

Life in the Cenozoic

The Cenozoic is an era characterized by a great variety of terrestrial, marine and flying animal species.

In geological terms, the Cenozoic is the era in which the continents acquired their modern shape. Australia and New Guinea separated from Gondwana, moved north and eventually moved closer to Southeast Asia. Antarctica took its present position at the South Pole, the Atlantic Ocean expanded, and at the end of the era, South America joined North America. Cenozoic is the era of mammals and angiosperms. Mammals have undergone a long evolution from a small number of small primitive forms and have become distinguished by a wide variety of terrestrial, marine and flying species. Cenozoic can also be called the era of savannas, flowering plants and insects. Birds also largely evolved in the Cenozoic. Cereals appear among plants.

82.2.

The stratigraphic subdivision and lithological characterization of the Paleozoic deposits developed in the Belousovsky ore region were developed by us taking into account the definitions of fauna and flora in the Carboniferous deposits, as well as spores and pollen in the formations of the Upper and Middle Devonian. Silent strata of rocks lying between the dated Frasnian and Lower Carboniferous deposits are conditionally assigned to the Famennian. The stratigraphic position of these strata was determined by comparing their lithological composition with faunistically dated sections from other regions.

The following suites are distinguished in the Belousovsky ore region of the Irtysh region: Glubochanskaya - B2e-gv, Shipulinskaya - D2gv, Belo-Usovskaya - Defri, Garaninskaya - Difri, Irtyshskaya - Dafmi (?), Pikhtovskaya (Grebenyushinskaya) - Bzgtg, Bukhtarma - Cit2 and Maloul -Binskaya - Cin-C'2. Of these, the first four were identified by M.I. Drobyshevsky in 1954. The contact of the Glubochanskaya suite with the Shipulinskaya and Belousovskaya suites is associated with ore deposits of the deposit located among hydrothermally altered rocks.

Structurally, the area under study covers a part of the northeastern flank of the Irtysh anticlinorium, which is complicated by folded and faulty faults with a northwestern strike. A characteristic feature of such folds is the tilting of their axial surfaces to the southwest.

All rocks of the Paleozoic underwent significant alteration under the influence of regional contact and, in some narrow zones, hydrothermal metamorphism. At the base of the stratigraphic section lies a deeply metamorphosed complex of rocks, conditionally attributed to the pre-Middle Devonian age. This complex is represented by biotitized, epidotized amphibole-pyroxene gneisses and mica-quartz schists, which are exposed in the erosion section in the core part of the Irtysh anticlinorium in the southeast of the region. The rocks of the listed suites come to the surface in small areas. The rest of the region is covered with loose sediments.

82.4.

One of the most important global metallogenic structures is the Mediterranean belt - a product of the ocean, which received the name Tethys from E. Suess. From the metallogenic standpoint, the Mediterranean belt was specially studied by the outstanding followers of V.I. Smirnov and my late friend G.A. Tvalchrelidze, and I would like to dedicate this very brief outline of the long and complex history of the Tethys Ocean and the Mediterranean belt to the blessed memory of both scientists.

The concept of "the Tethys ocean" appeared at the end of the last century (1893) in the famous work of E. Suess "The Face of the Earth". Somewhat earlier, another Austrian geologist M. Neumayr, who compiled the first world paleogeographic map of the Jurassic period, singled out the "Central Mediterranean Sea" on it. For both scientists, the most convincing proof of the existence of such a body of water between the northern and southern rows of the continents was the striking similarity of the Triassic and Jurassic marine fauna from the Alps, through the Himalayas to Indonesia (Island of Timor), which had been established by that time. G. Shtille expanded this concept in time and showed that the Tethys Ocean arose already in the late Precambrian, after the "Algonkian fragmentation" he identified. In this paper, I proceed from this point of view, despite the fact that it was based on a fixist premise, which is now completely discredited. Further it will be shown that the Tethys Ocean in its long evolution went through a series of stages, including its partial closure" and re-opening elsewhere. The sequence of these stages makes it possible to distinguish between the Late Proterozoic-Cambrian Proto-Tethys, the Ordwic-Carboniferous Paleo-Tethys, the Permian-Jurassic Mesotethys and the Jurassic-Paleogene Neotethys partially overlapping each other in space and time.

Birth of Tethys and Protethys

At present, it is almost generally accepted that as a result of the Grenville orogeny, about 10 billion years ago, a supercontinent arose, recently called Rodinia. This supercontinent existed until approximately the middle of the Late Riphean, about 850 million years ago, and then began to experience destruction. This degradation began with rifting, leading further to spreading and neoformation of the oceans: the Pacific, Iapetus, Paleoasian, and Prototethys among them. The birth of this first incarnation of Tethys is proved by the outcrops of late Riphean ophiolites in the Anti-Atlas, the Arabian-Nubian shield on its southern periphery, in the Alps, the Bohemian massif - on the northern one. In the Vendian-Early Cambrian time, the first generation of the Tethys ocean - Prototethys 1 disappeared (partially?) as a result of the manifestation of the Pan-African-Kadomian orogeny and a significant area increased the Gondwanan supercontinent, forming the Epicadoman Perigondian platform. It formed the oldest foundation of Western Europe, rubbing northward to the English Midlands and the edge of the East European ancient platform.

But very soon the destruction of this newly formed continental crust began and the ocean basin reappeared (or recovered). The remnants of its bark are known in the Southern Carpathians, the Balkans (Stara Planina), in the northern Transcaucasia (Dziruli massif) and further to the east, in particular in Qilianshan (China). This Vendian-Cambrian basin may be called Proto-Tethys II, in contrast to the Late Riphean Proto-Tethys I. It formed, perhaps, along the suture between the Epicadoman Perigondian platform and Fennosarmatia (Baltic). It is interesting that the same two generations of ophiolites are known in the south of Siberia (Eastern Sayan) and in Western Mongolia, which belonged to the Paleoasian Ocean in this epoch. Prototethys II closed (partially again?) in the second half of the Cambrian and finally at the beginning of the Ordovician due to the Salair orogeny. At the same time, a new ocean, the Paleothethys, was formed.

paleotethys

It can be assumed with sufficient reason that this was precisely the ocean basin that later gave rise to the main stem of the European variscids (hercynides). Its eastern extension can be seen in the North Caucasus and further up to Qinling in Central China. In accordance with the age of ophiolites, two generations of basins are oceanic or suboceanic, i.e. thinned and reworked continental crust can be distinguished. The older one is documented by Ordovician ophiolites exposed in the Western Alps, Western Carpathians, and the Peredovy Ridge of the Greater Caucasus.

The opening of Paleo-Tethys I was related from Gondwana to the Epikadomian microcontinent Avalonia and its northward drift. At the same time, that (large) part of the Epicadomian platform, which remained attached to the Early Precambrian core of Gondwana, separated from the East European Craton-Baltic along the "Tornquist Sea", underlain by thinned continental crust.

In the left half of the Devonian, the Renohercynian back-arc basin opened up on the northern periphery of the Paleo-Tethys in the rear of the Middle German crystalline uplift. The ophiolites of the Lizard Peninsula in Cornwall, the MOR basalts in the Rhine Shale Mountains, and the ophiolites of the Sudetes are relics of the oceanic crust of this basin.

In the middle of the Devonian, however, a chain of uplifts arose in the central zone of Paleo-Tethys I; it is known as the Ligerian Cordillera. She subdivided the main oceanic basin into two - the northern one, which includes the Saxo-Thuringian and Renohercynian Variscid zones and finds its southwestern continuation in the Iberian Meseta, and the southern one, representing Paleotethys proper and could be called Paleotethys II.

Paleotethys I or Reikum entered the final stage of its evolution in the Late Paleozoic, transforming into the Varisian fold-thrust belt of Western and Central Europe, the North Caucasus, its buried continuation in the south of the young Turan platform, the Hindu Kush, the southern zone of the Southern Tien Shan, the Northern Pamirs, Kunlun and Qinling.

Paleotethys closed completely only in its western part, west of the meridian of Vienna and Tunisia, forming Pangea. Further to the east, it was inherited by Mesotethys.

Mesotethys

The history of Mesotethys itself begins in the Late Permian-Triassic and lasted until the Late Triassic - Early Jurassic, to the Early Cimmerian orogeny - Mesotethys I or Late Jurassic - Early Cretaceous - Mesotethys II. The main basin of Mesotethys I extended from the border region of Northern Hungary - Southern Slovakia in the Inner Carpathians through the basement of the superimposed Pannonian basin to the Vardar zone in Yugoslavia and further to the Pontides of northern Anatolia and possibly to central Transcaucasia, where its continuation may be hidden under the molasses of the Kura intermountain trough. Its further continuation may be assumed along the early Cimmerian suture between the Turan platform and the Elbrus fold-thrust system on both sides of the South Caspian Basin in Northern Iraq. Further to the east, Mesotethys I can be traced through the southern zone of the Northern Pamirs, the southern slope of Kunlun and Qinling, the famous Sunpan-Kanze triangle and, with a turn to the south, through Yunnan, Laos, Thailand, Malaya - the classical region of the Indosinids or early Cimmerids (early Yangshanids in China). The northern branch of Mesotethys I, which merged with the main basin somewhere in northern Afghanistan, extended through the Kopetdag, the southern slope of the Greater Caucasus, the Crimean Mountains and up to the northern Dobruja, where its blind end was located.

Mesotethys I was replaced by Mesotethys II at the end of the Middle Jurassic (Late Bathonian-Callovian). At this time, Tethys was transformed from a wide bay, opening to the east into the Pacific Ocean, into a continuous oceanic belt, separating Laurasia and Gondwana along its entire length. This division was due to the emergence of the Caribbean, the central Atlantic and the Liguro-Piedmontese "ocean". The latter entered into a connection in the east with the residual Vardar basin, partially closed in the northeast by Early Cimmerian folding. But further to the east, the continuation of this basin, unlike Mesotethys I, deviated south from the Pontides and extended on the other side of J. Shenger's "Cimmerian Continent", then crossing the Lesser Caucasus through Lake Sevan and the Akera valley and reaching the Iranian Karadag. Ophiolite outcrops disappear further to the southeast, but reappear in the Sabzevar area south of eastern Elbrus. To the east of the transform Harirud fault, the continuation of Mesotethys II can be seen in the Farahrud zone of central Afghanistan and further, after crossing another, the Afghan-Pamir fault, in the Rushap-Pshart zone of the Central Pamir and, having experienced a new fault along the Pamir-Karakorum fault, in the Bangong zone -Nujiang of central Tibet. Then this basin, like Mesotethys I, turned to the south (in modern coordinates) and continued in Myanmar to the west of the Sinobirman massif (Mogok zone).

The entire eastern part of Mesotethys II, starting from Sabzevar-Farakhrud, finally closed as a result of the late Cimmerian orogeny. The western, European part also experienced this diastrophism, in particular, the Vardar zone, but here it was not final. The decisive role in this respect belonged to the intra-Senonian, sub-Hercynian tectonic phase.

At the end of the Jurassic, another basin with oceanic or suboceanic crust arose to the north of the main Mesotethys basin in Europe and extended roughly parallel from the Velis zone of the Alps through the Pieninsky "cliff" belt of the Carpathians and further, possibly, the Nish-Troyan zone of eastern Siberia - western Bulgaria. The most important role in the closure of this basin was played by the Australian orogenic phase in the mid-Cretaceous.

This northern basin was not the only one in the Mesozoic Tethys system. The other was the Budva-Pindos basin in the Dinarids-Hellenids and its probable continuation in the Taurus system of southern Anatolia. The third was the back-arc basin of the Greater Caucasus. The final closure of both basins occurred in the Late Eocene. But in the meantime, two more back-arc basins formed in the Late Cretaceous-Early Paleocene:

Black Sea and South Caspian.

Thus, the closure of the European and West Asian segments of Mesotethys II occurred gradually, through a series of compression impulses, starting from the Late Cimmerian and ending with the Pyrenean. And gradually the leading role in the Mediterranean mobile belt passed from Meso to Neotethys.

neotethys

It was the last incarnation of the great ocean. Neotethys was located south of Mesotethys and was formed due to the separation and drift to the north of several fragments of Gondwana - Adria (Apulia), central Iran, the Lut block, central Afghanistan, southern Tibet (Lhasa). The opening of the Neotetis was preceded by continental rifting, most clearly expressed in its eastern Himalayan-Tibetan segment, where it began in the Late Permian. Spreading in the Neotethys region continued from the Late Triassic-Early Jurassic to the Late Cretaceous-Early Paleogene. Neotethys proper stretched from the Gulf of Antalya, Cyprus and northwestern Syria around the northern ledge of the Arabian Plate and then to the rear of the Balochistan chains and the Himalayas, turning to the south of the Sunda-Banda arc. As for the western end of Neotethys, two versions are possible: 1) it could find its blind end somewhere between Adria and Africa, in the area of ​​the Ionian Sea and Sicily; 2) it could represent a continuation of the southwestern Dinarid-Ellinid trough - the Budva-Pindos trough. Just as it was in the case of the Paleo- and Mesotethys, the main basin of the Neotethys was accompanied by side and behind arc basins of various ages and with various degrees of destruction and transformation of the continental crust and the role of spreading. One of them is the Levant Sea of ​​Jurassic age, the other is the Late Cretaceous-Early Paleogene Seistan basin in the extreme east of Iran. Three others, in the extreme west, are the Tyrrhenian Neogene basin in the rear of the Calabrian arc and the Aegean basin of the same age in the rear of the subduction zone of the same name, and finally, the Adaman Sea of ​​the same age, in the extreme east, behind the Sunda subduction zone. Closing of the Neotethys began in the Senonian and accelerated significantly in the Middle-Late Eocene, when India and a number of microcontinents that had previously broken away from Gondwana, from Adria in the west to Transcaucasia and the Bitlis-Sanandaj-Sirijak microcontinent in the east, collided with the southern edge of Eurasia, and the same process manifested itself between the Indian Plate and southeastern ledge of Europe, leading to the formation of the Indo-Burmese chains. As a result, Neotethys turned out to be dissected and only some of its remnants were preserved in the Mediterranean and the Black Sea-South Caspian region and in the Gulf of Oman, as well as relict subduction zones - Calabrian, Aegean, Makranskaya, Sunda. Is this really the end of the long history of Tethys or just the beginning of a new phase of its evolution remains an open question.

Conclusion

Considering that the ocean first formed between Laurasia and Gondwana as a single and separate supercontinent at the end of the Precambrian and finally ceased to function as a whole by the Oligocene, we can consider this huge time interval as corresponding to the Wilson cycle, since at no point in this interval can we assume the absence of such a vast starry space, even during the existence of Pangea, sometimes it was reduced to a very vast bay comparable in size to the size of the Indian Ocean. However, we can talk about two separate Wilson cycles separated by the period of existence of Pangea - the Late Proterozoic-Paleozoic and Mesozoic-Cenozoic. the main, axial basin shifted from time to time, mainly to the south, constantly maintaining the role of the water division between Laurasia and Gondwana or their fragments. These changes did not occur gradually, but abruptly, and this is what made it possible to distinguish between individual stages in the evolution of Tethys and, accordingly, to introduce the concepts of Proto-, Paleo-, Meso-, and Neo-Tethys, despite the fact that some intervals of their "life" overlap one another. . The closure of these changing oceans was due to orogeny, long known under the names of the Baikal-Kadom, Caledonian, Hercynian-Varisian, Cimmerian, and Alpine. Each of these orogenies was accompanied by the accretion of new terranes to Eurasia, which, as a rule, was compensated by the separation of other terranes from Gondwana. Some of these newly accreted terranes later experienced at least partial mobility regeneration, but others remained attached to Eurasia, increasing its size. These various stages in the evolution of the Tethyan region correspond to the cycles identified a hundred years ago by Marcel Bertrand, and I proposed to call them the Bertrand cycles. In relation to the Wilson cycles, these cycles are of the second order, since they correspond not to the complete, but only to the partial extinction of the ocean (and its initial shift in the axis of its opening). It should be emphasized that the internal structure of the Tethyan region, or the Mediterranean mobile belt, during each stage of evolution remained complex and, in addition to the main basin, included several of its branches of different sizes, micro- and minicontinents, often built on ensialic volcanic arcs. However, this is quite natural for the intercontinental ocean, for the Mediterranean Sea - Mittelmeer - as it was defined by M. Neumayr, the same century ago. Separation of continental fragments, their reciprocal approach and, in general, their mutual movements were determined not only by rifting and spreading, not only by subduction, collision and obduction, but also to a large extent by transform faults and shifts. It goes without saying that a complete decoding of the complex history and structural development Mediterranean belt. Throughout their entire length, it also makes it possible to better understand the features of metallogeny. However, so far this can only be done partially, with respect to the western part of the Tethys and the latest stage of its development, starting from the Mesozoic. Therefore, this remains a task for the future and clearly requires international and multidisciplinary (stratigraphy, paleontology, lithology, petrology, tectonics, geophysics, geochemistry) research.

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General information

The eastern part of Russia is characterized by the extensive development of Mesozoic and Alpine folded mountain regions, which are part of the Pacific fold belt. Mesozoids are mountainous folded regions that completed their geosynclinal development in the Cretaceous period. However, typical platform development within them has not yet begun. The earth's crust has not acquired sufficient strength and power here. Examples of them are the Verkhoyansk-Kolyma (Verkhoyano-Chukotka) and Far Eastern (Sikhote-Alin) regions.

The Verkhoyansk-Kolyma region occupies vast expanses of the northeastern part of Russia. In the north, this region is washed by the Laptev and East Siberian seas. It also includes the Novosibirsk, De Long, Lyakhovsky, Wrangel and other islands.

Stratigraphy

Precambrian deposits found within the most ancient massifs of the Verkhoyansk-Kolyma region. They are represented by deeply metamorphosed gneisses, crystalline schists, and amphibolites. In composition and appearance, these rocks are close to the rocks of the Archean complex of the Aldan Shield of the Siberian Platform.

Proterozoic formations are represented by various slates, quartzites, marbled limestones. The deposits are intruded by granite intrusions. The total thickness of the Precambrian strata is over 5 km.

breeds Paleozoic group combine deposits of the Cambrian - Permian age. Paleozoic formations come to the surface only in the cores of anticlinoria. At the same time, Permian deposits are developed more widely. In the Paleozoic group, two strata are distinguished. Lower includes breeds from Cambrian to Lower Carboniferous. It is represented by alternating limestones, marls, dolomites, shales, sandstones.

There are interlayers of conglomerates (Devonian) and effusive rocks (Cambrian, Devonian). There are intrusions of gabbrodiabases and granites. The total thickness of the Paleozoic terrigenous-carbonate sequence is more than 15 km.

With erosion, it overlies the Verkhoyansk complex, which includes Upper Paleozoic and lower mesozoic(Middle and Upper Carboniferous, Permian, Triassic, Lower and Middle Jurassic). The complex is composed of uniformly interbedded dark gray and black sandstones, shales with occasional limestone interbeds. Its thickness exceeds 10 km.

Mesozoic group(Upper Jurassic - Cretaceous) is widespread within the Verkhoyansk-Kolyma region. Upper Jurassic It is represented by terrigenous coal-bearing deposits with interlayers of conglomerates and effusives (porphyrites and diabases) with a total thickness of more than 2 km. Lower Cretaceous It is composed of volcanogenic-terrigenous strata with interlayers of coal. Thickness up to 1 km. Along the coast of the Sea of ​​Okhotsk, the Lower Cretaceous volcanogenic formations are up to 3 km thick. Upper Jurassic and Lower Cretaceous deposits of the Verkhoyansk complex are metamorphosed and folded into various folds. Only within the ancient median massifs of the Verkhoyansk-Kolyma region do they lie almost horizontally.

Upper Cretaceous everywhere unconformably occurs and is composed of typically continental sediments. These are sands, clays, sometimes with interlayers of coal (lower reaches of the Kolyma and Indigirka rivers). Acid effusives and their tuffs are widespread. The thickness of the Upper Cretaceous is up to 1 km.

deposits Cenozoic group are not widespread. Paleogene It is represented by thin sandy-clayey continental sediments and rather significant effusive strata of acidic composition.

Neogene deposits are known in river basins and intermontane depressions. These are continental terrigenous sediments of small thickness.

Lntropogenic formations consist of glacial, alluvial, deluvial and marine sediments up to 100 m thick.

- (Pacific folding Yenshan folding), the era of tectogenesis, which manifested itself during the Mesozoic era mainly along the periphery of the Pacific approx. The main phases are Cimmerian (late Jurassic, early Cretaceous; Crimea and northeast Russia), Laramian (late ... ... Big Encyclopedic Dictionary

mesozoic folding- The era of mountain building, which manifested itself during the Mesozoic era mainly along the periphery of the Pacific Ocean, the main phases are the Cimmerian and Laramian folding ... Geography Dictionary

- (Pacific folding, Yenshan folding), the era of tectogenesis, which manifested itself during the Mesozoic era mainly along the periphery of the Pacific Ocean. The main phases are Cimmerian (late Jurassic, early Cretaceous; Crimea and Northeast Russia), ... ... encyclopedic Dictionary

The totality of geological processes of folding, mountain building and granitoid magmatism that took place during the Mesozoic era. It manifested itself most intensively within the Pacific mobile belt. Distinguish folding: ... ... Geographic Encyclopedia

- (Pacific folding, Yeishan folding), the era of tectogenesis, which manifested itself during the Mesozoic era ch. arr. on the periphery of the Pacific Ch. Cimmerian phases (late Jurassic, early Cretaceous; Crimea and S.V. Russia), Laramian (late Cretaceous, beginning ... ... Natural science. encyclopedic Dictionary

Manifested during the Mesozoic era, ch. arr. within the Pacific mobile belt. Recently (and by some tectonists even now) the S. m. was considered as part of the Alpine folding. The main phases of S. m. appeared non-simultaneously in ... ... Geological Encyclopedia

• Mesozoic folding (in English literature - Cimmerian) - the era of folding, in which many mountain ranges appeared, which are now in Central Asia.

Related concepts

The Atlantic (Greek: Ατλαντικα) is a hypothetical ancient continent that formed in the Proterozoic about 2 billion years ago from various platforms located on the territory of modern West Africa and Eastern South America. The name was proposed by Rogers in 1996 and comes from the Atlantic Ocean that now runs through the old continent. (from the Latin name of Scotland - Caledonia, Caledonia) - the era of tectogenesis, expressed in the totality of geological processes (intense folding, mountain building and granitoid magmatism) at the end of the early - beginning of the middle Paleozoic (500-400 million years). It completed the development of geosynclinal systems that existed from the end of the Proterozoic - the beginning of the Paleozoic, and led to the emergence of folded mountain systems - the Caledonides. The term was introduced by the French geologist M. Bertrand in 1887.

Objectives: to introduce the influence of internal and external factors on the formation of relief; show the continuity of the development of the relief; consider the types of natural phenomena, the causes of their occurrence; talk about the influence of man on the relief.

Equipment: a physical map, tables, pictures, a video about natural phenomena, books, diagrams.

During the classes

I. Organizational moment

II. Checking homework

1. Repetition of terms and concepts

Platform, shield, folded area, tectonics, paleontology, deposit.

Option 1

1. Stable areas of the earth's crust are called:

a) platforms

c) folded areas.

2. Plains are located:

a) at the boundaries of lithospheric plates;

b) on platforms;

c) in folded areas.

3. Mountains are located:

a) on platforms;

b) on the plates;

c) in folded areas.

4. Ridges rose into the Mesozoic folding:

b) Sikhote-Alin;

c) the Caucasus.

5. The revived mountains are:

b) the Caucasus;

6. Deposits are confined to ancient folded areas:

a) coal, oil, gas;

b) iron ores, gold;

c) both.

7. The largest coal basins are:

a) Samotlor, Kansko-Achinsky;

b) Tunguska, Lensky;

c) Urengoy, Yamburg.

8. Landforms of glacial origin include:

a) moraines, troughs, sheep foreheads;

b) ravines, beams;

c) dunes, dunes.

9. The surface of Russia is falling:

b) to the north;

c) to the west;

d) to the east.

Answers: 1 - a; 2 - b; 3 - in; 4 - b; 5 - a; 6 - b; 7 - b; 8 - a;

Option 2

a) Proterozoic;

b) Paleozoic;

c) Archean.

2. The geological era that continues now is called:

a) Mesozoic;

b) Cenozoic;

c) Paleozoic.

3. The science of minerals is called:

a) petrography;

b) paleontology;

c) geotectonics.

4. Find a match between mountains and their highest peaks:

1) Caucasus: a) Victory;

2) Altai; b) Beluga whale;

3) Sayans; c) Elbrus;

4) Chersky Ridge. d) Munku-Sardyk.

5. Choose the correct statements:

a) large plains are located on platforms;

b) eolian processes create moraines:

c) the Kamchatka and Kuril Islands peninsulas - the most seismically active zones of Russia;

d) the main part of the mountains is located in the west and north of Russia;

e) the Ural Mountains are located between the Russian and West Siberian plains.

6. Find a match between concepts and their definitions:

1) mud-stone stream;

2) snow removal from mountain slopes;

3) loose clay-boulder glacial deposits.

a) an avalanche

c) moraine

7. Which map shows the structure of the earth's surface (crust)?

a) on the physical;

b) on the geological;

c) on the tectonic.

Answers: 1 - in; 2 - b; 3 - a; 4 - 1) c, 2) b, 3) d, 4) a; 5 - a, c, e; 6 - 1) b, 2) a, 3) c; 7 - c.

III. Learning new material

(Concepts are written on the board: endogenous processes, exogenous processes, volcanism, earthquake, latest tectonic movements, glaciation, moraines, eolian relief, dunes, talus, landslides, avalanches, mudflows, erosion.)

Look at the desk. We will consider these terms in the lesson today, and remember some.

The relief is constantly changing under the influence of exogenous (external) and endogenous (internal) factors.

(The teacher draws a diagram on the board while making explanations.)

The relief is constantly changing under the influence of exogenous (external) and endogenous (internal) factors. Both of these factors operate simultaneously.

Endogenous processes are called neotectonic or recent. They can appear both in the mountains and on the plains.

In the mountains, the movements of the earth's crust are most active. In the Caucasus, movements occur at a speed of 5-8 cm per year, in young mountains, where the earth's crust is plastic, movements are accompanied by the formation of folds. In areas of ancient folding (Urals, Altai, Sayans, etc.), where the earth's crust is more rigid, faults and faults are formed. The sites make vertical movements, some blocks rise, others fall, forming intermountain basins.

On the platforms, the latest movements are manifested in secular slow fluctuations of the earth's crust, some areas slowly rise, while others fall at a rate of about 1 cm per year. But there can also be faults on the platforms, for example, faults in East Africa (Great African Rifts).

Exogenous processes are processes that occur under the influence of flowing waters (rivers and glaciers, mudflows), permafrost, and wind.

Glacial landforms

In the Quaternary period, a huge shell of ice up to 4 km thick buried almost all of Europe under it. The centers of glaciation were Scandinavia, the Polar Urals, the Putorana Plateau and the Byrranga Mountains on the Taimyr Peninsula. Giant waves were the onset of cold on Earth. There were several such waves. They are associated with the formation of glaciers. Since the Cambrian, scientists have counted up to five such glaciations. At the beginning of the Quaternary period, the great glaciation began for the fifth time. It happened more than 200 thousand years ago. The glacier retreated relatively recently - only 12-15 thousand years ago.

1. Morena (French moraine) - a geological body composed of glacial deposits. The boulders in the moraines consist mainly of granites and gneisses. In addition to rounded boulders, on the surface of the moraine there are sometimes large, up to several tens of meters in diameter, poorly rounded boulders of rapakivi granites - outliers. A colossal boulder is widely known, which was used as a pedestal for the installation of a monument to Peter 1 in St. Petersburg. This boulder called "Thunderstone" was found near the village of Lakhta on the shores of the Gulf of Finland. Its length is 13 m, width - 7 m, height - 8 m. It took two years to deliver it to St. Petersburg.

The moraine is an unsorted mixture of clastic material of very different sizes - from giant boulder blocks with a diameter of up to several hundred meters to clay and sandy material formed as a result of the grinding of debris by a glacier during its movement. It is difficult to note any pattern in the distribution of fragments of different sizes in the body of the glacier; therefore, the rocks deposited by the glacier are unsorted and non-layered.

2. End moraine ridges - this is the boundary of the movement of the glacier, represents the brought clastic material. The grandiose terminal moraines and associated glacier ridges are located in Finland and on the Karelian Isthmus. These include the Michurinskaya ridge, Northern Uvaly, which are a water-glacial formation.

3. On the Baltic and Canadian shields, the rocks are smoothed by the glacier, there are numerous sheep foreheads - ledges of igneous and metamorphic rocks with scratches and scars on the surface; the slopes facing towards the movement of the glacier are gentle, the opposite slopes are steep.

4. Oz (ridge, ridge) is a ridge with rather steep slopes (30-45 °), resembling a road embankment. The eskers are usually composed of sand, often with pebbles and gravel; pine loves sandy soils, so it often grows on lakes. There is no consensus on the origin of the Oz. A water stream goes along the glacier, it carries a lot of sand, pebbles, boulders; having reached the edge of the glacier, the flow forms an alluvial cone, the edge of the glacier recedes, and the cone receding with it gradually forms a ridge. There is another explanation: a stream flowing along the surface of a glacier or inside it deposits sandy rocks with large fragments along its channel; when the glacier melts, all these deposits fall on the underlying surface, forming a ridge on it. One way or another, eskers are formed by streams going along or in a glacier, as evidenced by the layering of the rocks that make up the oz, such as water streams form. The height of the oz can reach several tens of meters, the length - from hundreds of meters to tens (occasionally even hundreds) of kilometers. The peculiarity of the ozes is that they do not take into account the relief at all: the esker ridge can stretch along the watershed, then go down the slope, cross the valley, rise again, then go into the lake, forming a long peninsula, dive and emerge on the other side. And so on, until its length is enough.

5. Kom (English kate or German katt - ridge) is a hill, outwardly usually difficult to distinguish from moraine, but the material that composes it is sorted better than moraine, layered. The origin of kams, as well as ozes, is explained in different ways: these may be deposits of lakes that existed on the surface of the glacier or near its edge.

6. Vast areas are occupied by sands (Isl. sand - sand) - surfaces on which sands are widespread, brought by melted glacial waters (Pripyat Polissya, Meshcherskaya lowland, etc.). There is a characteristic landscape on the sands, but they are also not particularly perceived as landforms.

7. Lakes in glacial basins. Exaration occurs unevenly, because the rocks underlying the glacier are not equally stable. As a result, hollows are formed, usually elongated in the direction of glacier movement. Most of the lakes of Karelia and Finland, as well as the Canadian Shield, are located in such basins. The basins of large lakes are tectonic troughs, but they have also experienced glacial treatment. So, on the northern shores of Ladoga and especially Onega lakes there are bays that are clearly of glacial origin, this can be seen if only because they are elongated from northwest to southeast, which is a common direction for Karelian lakes.

8. Ice moves in streams in mountain valleys, expanding and deepening them, forming trough-shaped valleys - troughs (German trog - trough).

9. For mountains where there is glaciation or it was in the geologically recent past, steep ridges and sharp peaks are characteristic; in the near-top parts there are kars (German kar), bowl-shaped niches with slopes that are steep in the upper parts and more gentle below. Kara, or mountain cirques, are formed under the action of frosty weathering, serve as a place for the accumulation of snow and the formation of glaciers. When adjacent kara are connected by their side parts, a protrusion in the form of a three- or four-sided pyramid often remains between them. Kars and trogs can be seen not only in the mountains, where there is modern glaciation. There are almost no glaciers in the mountains of Transbaikalia, but in solid crystalline rocks, the forms formed during the Quaternary glaciation are perfectly preserved.

Aeolian landforms

Dunes are a kind of dunes, relief mobile formations of sand in deserts, blown by the wind and not fixed by plant roots. They reach a height of 0.5-100 m. They resemble a horseshoe or sickle in shape. In cross section, they have a long and gentle windward slope and a short, steep leeward slope.

Depending on the wind regime, the accumulations of dunes take various forms. For example, there are dune ridges stretched along the prevailing winds or their resultant; dune chains transverse to mutually opposite winds; dune pyramids in places of convection of vortex flows, etc.

Without being fixed, dunes under the influence of winds can change shape and mix at a speed of several centimeters to hundreds of meters per year.

Thermal landforms in our country are mainly represented by frost weathering.

1. Frost heaving is typical for various regions of the cold belt, although it is developed unevenly due to local features of the composition, structure and properties of rocks. Small bumps of heaving can occur directly from the increase in the volume of freezing water in a pound. But migration hillocks have large values, when new volumes of water migrate to the freezing front from the underlying thawed part of the soil, which is accompanied by intense segregation ice formation. This is often associated with peat bogs, to which, when freezing, moisture migrates from rocks with much higher humidity. Such hillocks were observed in Western Siberia.

2. In such a cold climate, small polygonal structural forms are also developed, associated with cracking of the soil into small polygons, uneven freezing of the seasonally thawed layer and the development of stresses in closed systems, and often ruptures. Among such small-polygonal structures, medallion spots can be mentioned. When freezing from above and along cracks inside the landfill, hydrostatic pressure is created, the liquefied soil of the upper permafrost crust breaks through and spreads over the surface. The second type of polygonal structural forms are stone rings and polygons. This occurs in compositionally heterogeneous loose rocks containing inclusions of stone fragments (crushed stone, pebbles, boulders). As a result of repeated freezing and thawing, large clastic material is pushed out of the rock to the surface and moves towards the fracture zones, with the formation of stone borders.

3. Slope processes in permafrost development areas include two types: solifluction and kurums (stone streams). Solifluction is understood as a slow flow along the slopes of loose, highly waterlogged dispersed deposits. During the seasonal thawing of ice-saturated dispersed pounds of the seasonally thawed layer, they are strongly waterlogged by melt and rain waters, lose their structural bonds, pass into a viscoplastic state, and slowly move down the slope. In this way, sinter forms are formed in the form of tongues, or terraces. Kurums are mobile stone placers in the mountains and plateaus of Eastern Siberia and other regions where rocks approach the surface close to the surface. The formation of clastic material of kurums is associated with frosty weathering during periodic seasonal freezing and thawing and with other processes. Kurums in some places form continuous stone fields (from the first hundreds of square meters to several tens of square kilometers in size).

4. One of the most famous examples of permafrost degradation is thermokarst. This name was given to the process of thawing of underground ice, accompanied by subsidence of the earth's surface, the formation of depressions, shallow thermokarst lakes.

Natural phenomena

Open textbooks, find a map of the latest tectonic movements (according to R.: Fig. 26 on p. 26; according to B.: Fig. 22 on p. 46).

Recent tectonic movements → earthquakes, volcanism.

(To create an image of natural phenomena, you can show the video film "Spontaneous Natural Phenomena".)

Consider the structure of a landslide (according to R.: p. 72; according to B.: Fig. 27 on p. 51).

Reason: gravity → landslides, avalanches, mudflows

What natural phenomena are possible in your area? How to protect yourself from dangerous phenomena?

Homework

1. According to R.: § 12, 13.

2. Put on the contour map the relief forms formed under the influence of external factors. To do this, come up with and write down symbols for these landforms in the map legend.

Additional material

Plains of Russia

Name	Geographical position	landform	Prevailing heights, m	Maximum height, m
Valdai	Eastern Europe	Elevation
Privolzhskaya		Elevation
Northern Ridges		Elevation
Smolensk-Moscow		Elevation
Central Russian		Elevation
Caspian		flat lowland
West Siberian		flat lowland
Siberian Ridges	North of Western Siberia	Elevation
North Siberian	Eastern Siberia	hilly lowland
Central Siberian		Plateau
Vitim	Belt of mountains of Southern Siberia	Plateau
Yano-Indigirskaya	Northeast Siberia	Lowland
Kolyma		Lowland

Mountains of Russia

Name	Geographical position			Highest peak, m
Ural	East of the Russian Plain		Hercynian folding	Mount Narodnaya, 1895
	The belt of mountains in southern Siberia			Mount Belukha, 4506
Western Sayan			Caledonian, Hercynian folding	Mount Kyzyl-Taiga, 3121
Eastern Sayan				Mount Munsu-Sardyk, 3491
	South of the Russian Plain		Alpine orogeny	Mount Elbrus, 5642; Mount Kazbek, 5033; mountain Dykhtau, 5204
Sikhote-Alin	Primorye		Mesozoic folding	Mount Tordoki-Yani, 2077
Chersky Ridge	Northeast Siberia		Mesozoic folding	Mount Pobeda, 3147