Study of the patterns of relief formation and its modern development using the example of the Belgorod region. Development of landforms - relief, geological structure and minerals The largest active volcano in Russia...
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78.1.
MESOZOIC FOLDING(Greek mesos middle) development of geosynclines with deep depressions of the earth's crust and the accumulation of powerful sediments, which were folded into folds, raised in the form of mountains, broken through by intrusions of granitic magma and volcanic eruptions that lasted from the end of the Triassic to the beginning of the Paleogene period. In different areas, this folding manifested itself with unequal intensity and at different times; therefore, it has several names.
Mesozoic folding began most early in Southeast Europe, South Asia, and Taimyr; it took a particularly long and intense time along the continental margins of the Pacific Ocean and, after a short break, resumed during the Alpine folding. Its granite intrusions are associated with a variety of minerals and numerous deposits of non-ferrous metals and gold, 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 occurred during the Mesozoic era. It manifested itself most intensively within the Pacific Mobile Belt. There are foldings: ancient Cimmerian, or Indosinian, which appeared in the end. Triassic early Jurassic; Young Cimmerian (Kolyma, Nevada, or Andean); Austrian (at the boundary of the Early and Late Cretaceous) and Laramie. Pacific folding is independently distinguished in areas adjacent to the Pacific Ocean: in the East. Asia, Cordillera and Andes. Ancient Cimmerian folding appeared at the end. Triassic early Jurassic in mountain structures of Crimea, Northern. Dobruja, on Taimyr, in the North. Afghanistan, South-East. Asia, Patagonian Andes and Northeast. Argentina; Young Cimmerian in con. Jurassic early chalk in the Verkhoyansk-Chukotka region, Center. and South-East. Pamir, Karakoram, Center. Iran, the Caucasus, Western Northern Cordillera America, Andes and other areas. Laramie folding one of the youngest eras of Mesozoic folding, manifested itself at the end. chalk beginning Paleogene in the regions of the Northern Rocky Mountains. America, in the Andes South. America, etc.
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 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 of development of the nature of the Earth as a whole.
In the Mesozoic, the foundations of the modern topography 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 connecting the territories of 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 and the Far East, i.e., in a territory with a total area of about 5 million km2. But Mesozoic tectogenesis was also reflected in more ancient structures of 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-Chukchi fold system. Thus, the western 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, in Eastern Siberia and the Far East there are numerous highlands, plateaus, plains (the area of the latter is generally not large) and, finally, the vast Pre-Verkhoyansk regional trough. The manifestation of Mesozoic folding is noted in Kopetdag, Mangyshlak, Donbass, Crimea, and the Caucasus.
In the area of the Mesozoic folded systems of Eastern Siberia and the Far East, the main ones were the Neo-Cimmerian and Laramian movements of the Cretaceous period. The geosynclinal basin extended from the Siberian Platform to the east, i.e., into the territory of the Far East. It was a huge sea in which thick layers of sediment accumulated, amounting to many thousands of meters. In the geosynclinal marine basin there were ancient mountainous mid-land masses: the Kolyma-Indigirsky, Omolon and others, the protrusion of the Siberian platform stood out - the Aldan shield, and in the southeast - the Chinese shield. The accumulation of sediments in the geosynclinal basin occurred due to the erosion and destruction of the ancient middle massifs and the Siberian, De Long, and Okhotsk platforms surrounding the geosyncline. Tectogenesis in the ancient platforms and mountain structures of the Paleozoic, which surrounded the Mesozoid territories from the west, northwest and south, proceeded in a complex and unique manner. One of the indicators of this originality was the different times of tectonic processes and the difference in the forms of their manifestation. But in general, the Mesozoic era in the east of our country ended with the replacement of the maritime regime by the continental one.
The Mesozoic folding was most active between the Kolyma massif and the Siberian platform (Verkhoyansk zone). Fold 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 middle massifs were subject to deep faults, through the cracks of which effusive materials flowed 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 much earlier, the middle massifs of the Precambrian and Paleozoic appeared: 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 Tukuringra-Dzhagdy, Bureinsky, Sikhote-Alin, etc. ridges were also formed. Ancient folding here was accompanied by intense intrusions of granitoids, which caused mineralization.
Mineral resources throughout the Mesozoic folded area of eastern 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 continents that formed the continent of Pangea. Laurasia included Eurasia and North America. They broke away from the mainland and became modern continents between 135 and 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 continent that existed during 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 continent received its name from Laurentia and Eurasia.
Origin
Protocontinent Laurasia is a phenomenon of the Mesozoic era. It is currently 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 attributed to proto-Laurasia. Referring to current thinking, after connecting with the southern continents, Laurasia formed the late Precambrian supercontinent called Pannotia (Early Cambrian), and was never separated again.
Fracture and formation
During the Cambrian era, for the first half a million years, Laurasia was located in equatorial latitudes. The supercontinent began to break apart into Siberia and Northern China, continuing to drift towards the north; in the past time they were further north than 500 million years ago. By the beginning of the Devonian period, Northern China was located near the Arctic Circle and was the northernmost landmass throughout the Carboniferous Ice Age (300-280 million years ago). To date, there is no evidence of major icing of the northern continents. During that cold period, Baltica and Laurentia connected with the Appalachian Mountains platform, allowing for the formation of huge reserves of coal. It is this coal that today forms the basis of the economy of regions such as Germany, West Virginia and part of the British Isles.
In turn, Siberia, moving south, connected with Kazakhstan, a small continent that 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 era, the shield of East China was reunited with Laurasia and Gondwana, resulting in the formation of Pangea. Northern China continued to drift from the near-Arctic latitudes and became the last continent that never connected with Pangea.
Final separation
About 200 million years ago, the procontinent Pangea collapsed. After breaking away, North America and northwestern Africa were separated by the new Atlantic Ocean, while Europe and Greenland (along with North America) were still one. They divided only 60 million years ago in the Paleocene. After this, Laurasia split into Eurasia and Laurentia (present-day 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 torn apart piece by piece. By the end of the Cretaceous and the beginning of the Paleogene periods, the modern post-Gondwanan continents and their parts emerged: South America, Africa (without the Atlas Mountains), Arabia, Australia, and Antarctica.
Gondwana (named after the historical region in Central India), a hypothetical continent that, according to many scientists, existed in the Paleozoic and partially Mesozoic eras in the Southern Hemisphere of the Earth. It included: most of modern South America (to the east of the Andes), Africa (without the Atlas Mountains), o. 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 in the Proterozoic and Upper Carboniferous, extensive glaciation developed on the territory of Gondwana. Traces of the Upper Carboniferous glaciation are known in Central and Southern Africa, southern South America, India and Australia. In the Carboniferous and Permian periods, a unique flora of the temperate and cold zones developed on the mainland, which was characterized by an abundance of glossopteris and horsetails. The collapse of Gondwana began in the Mesozoic, and by the end of the Cretaceous and the beginning of the Paleogene periods, modern continents and their parts separated. Many geologists believe that the destruction of Gondwana was a consequence of the 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. Continental red-colored strata and weathering crust are typical for the Triassic. 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, sediments are more diverse. Among the marine ones are siliceous, carbonate, clayey and glauconitic sandstones; continental - weathering crust deposits predominate, and coal-bearing strata are formed in lagoons. Magmatism manifested itself in geosynclinal areas - the Cordillera and Verkhoyansk-Chukchi, and trap magmatism - on the South American and African platforms. A feature of the Cretaceous deposits is the maximum accumulation of chalk (consists of foraminifera and the remains of coccolithophorid algae shells).
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 by shallow seas (areas adjacent to the Cordillera and the Verkhoyansk-Chukotka geosyncline). The Hercynian fold belts represented areas of dissected relief. The Triassic climate is arid continental, only in the coastal regions (Kolyma, Sakhalin, Kamchatka, etc.) it is moderate. At the end of the Triassic, sea transgression began, which became widespread in the Late Jurassic. The sea extended to the western part of the North American platform, almost the entire East European platform, and to the northwestern and eastern parts of the Siberian platform. The maximum sea transgression occurred in the Upper Cretaceous. The climate of these periods is characterized by alternating humid tropical and dry arid.
79.3.
Geocratic periods in the history of the Earth (from geo... and Greek kratos strength, power), periods of significant increase in land area, as opposed to thalassocratic periods, characterized by an increase in sea area. G.P. are confined to the second half of tectonic cycles, when general uplifts of the earth’s crust transform a significant part of the continents previously flooded by a shallow sea into dry land. They are characterized by a large contrast of climates, in particular a sharp increase in the areas of dry (arid) and cold climatic zones. Typical of the geographic region is the accumulation of continental red-colored strata composed of aeolian, alluvial, and lacustrine sediments of arid plains, partly of true deserts, as well as glacial deposits. No less typical are deposits of internal closed and semi-enclosed sea basins with high salinity in sediments of highly salted lagoons (dolomites, gypsum, salts). Geography can include 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 Anthropocene periods (including the modern era).
Thalassocratic periods in the history of the Earth, periods of widespread 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 subsidence of the earth's crust prevailed over most of the earth's surface, due to which almost everywhere a significant area of continents was flooded by the sea. The increase in the area of the hydrosphere contributed to the development of a humid marine climate with small temperature fluctuations. During the Thalassocratic periods, predominantly 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 fluctuations in sea level (from the Greek éu good, completely and stásis standing still, rest, position), universally traceable slow changes in the level of the World Ocean and associated seas. Eustatic movements (eustasy) were originally identified by E. Suess (1888). Coastline movements are distinguished: 1) as a consequence of the formation of sea depressions, when true changes in sea level occur, and 2) as a consequence of tectonic processes leading to apparent movements of sea level. These fluctuations, causing local transgressions and regressions caused by variously acting tectonic forces, were called deleveling, and wide transgressions and regressions caused by fluctuations in the level of the water shell itself were called hydrokinematic (F. Yu. Levinson-Lessing, 1893). A.P. Pavlov (1896) called negative movements of the coastline geocratic, and the advance of the sea hydrocratic. Among the hypothetical factors determining eustasy, 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 the earth's crust was decisive; later the importance of this factor weakened. Stabilization of the volume of water began, according to A.P. Vinogradov, in the Proterozoic, and from the Paleozoic the volume of the water mass of the hydrosphere changed within insignificant limits; The processes of sedimentation and volcanic outpouring on the bottom of the seas (sedimentoeustasy) and, as a consequence, an increase in the level of the World Ocean are of little importance. Beginning with the Paleozoic, the tectonic factor (tectonoeustasy) was of decisive importance, influencing the change in the capacity of the sea. and oceanic depressions with changes 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. Against the background of tectonoeustasy in recent geological times, the climatic factor in the form of glacioeustasy played a great influence (see Oscillatory movements of the earth's crust, Modern tectonic movements). During glaciations, when water concentrated on the continents, forming ice sheets, the level of the World Ocean dropped by approximately 110x140 m; after melting, glacial waters again entered the World Ocean, increasing its level by approximately 1/3 of its original level. A decrease in temperature and a change in salinity influenced the density of water, due to which the level of the World Ocean in high latitudes differed by several meters from the level of the World Ocean in equatorial regions. The formation of the lowest terrace 3 × 5 m is associated with these factors. Planetary factors (changes in the speed of rotation of the Earth, displacement of the poles, etc.) also played some role in the mechanism of eustasy. The study of eustasy processes is of great importance for historical geology and understanding the peculiarities of the formation of shelf zones, which are associated with the formation of various minerals.
80.2.
Mesozoic climate
Using climatically well-known modern analogues of Mesozoic lithogenetic formations and modern ecological analogues 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 past climatic conditions.
Early and Middle Triassic
The climate of the Mesozoic and especially the Triassic was almost isothermal, therefore the natural zonation of the continent at that time was determined mainly by the distribution of atmospheric precipitation and not so much by the volume as by the mode of its precipitation during the year. For the Early and Middle Triassic, three main natural zones are established within Eurasia: extra-arid (desert), which included the predominant part of Europe, Arabia, Iran, Central and Central Asia; moderately arid (dry savanna), the landscapes of which were dominant in Northern Europe, Western and Southern Siberia, Transbaikalia, Mongolia and Eastern China, and semiarid (moderately wet savanna), covering northeast Asia from Khatanga and Chukotka to the Japanese Islands, and also Southeast Asia.
81.2.
IRIDIUM ANOMALY is an amazing discovery made by American geologist Walter ALVAREZ in 1977 in a gorge near the city of Gubio, 150 kilometers from Rome. At great depths, a thin layer of clay was found with an iridium content 300 times higher than normal. This layer lay at a depth corresponding to the geological boundary between the Mesozoic and Cenozoic - the time when dinosaurs became extinct. Comparing this fact with the fact that usually the content of iridium in the earth's crust is negligible - 0.03 parts by weight per billion, and in meteorites the concentration of this substance is almost 20,000 times higher, Alvarez suggested that the iridium anomaly arose as a result of the fall of a large cosmic body, which caused a global catastrophe 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 an iridium meteorite will be recognized when a specific crater is discovered at the site of its fall .
82.1.
Cenozoic (Cenozoic era) is an era in the geological history of the Earth spanning 65.5 million years, 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 period is divided into Paleogene, Neogene and Quaternary periods (Anthropocene). Historically, the Cenozoic was divided into the Tertiary (Paleocene to Pliocene) and Quaternary (Pleistocene and Holocene) periods, although most geologists no longer recognize this division.
Life in the Cenozoic
The Cenozoic is an era characterized by a wide variety of land, sea and flying animal species.
Geologically, 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 current position near the south pole, the Atlantic Ocean expanded, and at the end of the era South America joined North America. The 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 land, sea and flying species. The Cenozoic can also be called the era of savannas, flowering plants and insects. Birds also evolved significantly during the Cenozoic. Cereals appear among the plants.
82.2.
The stratigraphic division and lithological characteristics of Paleozoic deposits developed in the Belousovsky ore district were developed by us taking into account the definitions of fauna and flora in Carboniferous deposits, as well as spores and pollen in the formations of the Upper and Middle Devonian. The silent rock strata lying between the dated Frasnian and Lower Carboniferous deposits are conventionally assigned to the Famennian. The stratigraphic position of these strata was determined by comparing their lithological composition with faunally dated sections of other areas.
In the Belousovsky ore district of the Irtysh region, the following formations are distinguished: Glubochanskaya B2egv, Shipulinskaya D2gv, Belousovskaya Defri, Garaninskaya Difri, Irtyshskaya Dafmi (?), Pikh-tovskaya (Grebenyushinskaya) Bzgtg, Bukhtarminskaya Cit2 and Maloul -binskaya CinС2. Of these, the first four were established by M.I. Drobyshevsky in 1954. The ore deposits of the deposit, located among hydrothermally altered rocks, are confined to the contact of the Glubochansky formation with the Shipulinsky and Belousovsky formations.
Structurally, the study area covers part of the northeastern wing of the Irtysh anticlinorium, which is complicated by folds and faults of northwestern strike. A characteristic feature of such folds is the tilting of their axial surfaces to the southwest.
All Paleozoic rocks experienced significant changes under the influence of regional contact and, in certain narrow zones, hydrothermal metamorphism. At the base of the stratigraphic section lies a deeply metamorphosed complex of rocks, conventionally attributed to 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 formations are exposed to the surface in small areas. The rest of the area is covered by loose sediments.
82.4.
One of the most important global metallogenic structures is the Mediterranean belt - the product of the ocean, which received the name Tethys from E. Suess. From a 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 to the blessed memory of both scientists this very brief outline of the long and complex history of the Tethys Ocean and the Mediterranean belt.
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, highlighted the “Central Mediterranean Sea” on it. For both scientists, the most convincing evidence for the existence of such a body of water between the northern and southern rows of continents was the striking similarity of Triassic and Jurassic marine faunas from the Alps, through the Himalayas to Indonesia (Timor), which had been established by that time. G. Stille 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 take this view, even though it was based on a fixist premise that has now been completely discredited. It will be further shown that the Tethys Ocean in its long evolution went through a number of stages, including its partial closure and re-opening in another place. The sequence of these stages makes it possible to distinguish the Late Proterozoic-Cambrian Proto-Tethys, the Ordwian-Carboniferous Paleotethys, the Permian-Jurassic Mesotethys and the Jurassic-Paleogene Neo-Tethys, partially overlapping each other in space and time.
Birth of Tethys and Protethys
It is now almost generally accepted that as a result of the Grenville orogeny, about 10 billion years ago, a supercontinent arose, which recently received the name Rodinia. This supercontinent existed until approximately the middle of the Late Riphean, about 850 million years ago, and then began to experience destruction. This destruction began with rifting, which further led to spreading and new formation of the oceans: the Pacific, Iapetus, Paleoasian and Proto-Tethys among them. The birth of this first incarnation of Tethys is proven by the outcrops of ophiolites of Late Riphean age in the Anti-Atlas, the Arabian-Nubian shield on its southern periphery, in the Alps, and the Bohemian Massif on the northern. In the Vendian-Early Cambrian time, the first generation of the Tethys - Prototethys 1 ocean disappeared (partially?) as a result of the Pan-African-Cadoma orogeny, and a significant area was expanded by the Gondwana supercontinent, forming the Epicadomian perigondwanan platform. It formed the oldest foundation of Western Europe, extending north 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 was restored). Remains of its crust are known in the Southern Carpathians, the Balkans (Stara Planina), in northern Transcaucasia (Dzirula massif) and further to the east, in particular in Qilianshan (China). This Vendian-Cambrian basin can be called Proto-Tethys II in contrast to the Late Riphean Proto-Tethys I. It formed possibly along the suture between the Epicadomian Perigondwanan platform and Fennosarmatia (Baltica). 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 era. Prototethys II closed (again partially?) in the second half of the Cambrian and finally at the beginning of the Ordovician thanks to the Salairian orogeny. At the same time, a new ocean was formed - Paleotethys.
Paleotethys
It can be assumed with sufficient reason that this was precisely the ocean basin that later gave rise to the main trunk of European variscids (Hercynids). Its eastern continuation 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 ophiolites of Ordovician age exposed in the Western Alps, Western Carpathians and the Front Range of the Greater Caucasus.
The opening of Paleotethys I was connected from Gondwana to the Epicadomian microcontinent Avalonia and its drift to the north. At the same time, that (large) part of the Epicadomian platform, which remained attached to the Early Precambrian skeleton of Gondwana, separated from the East European craton-Baltica along the “Törnqvist Sea”, underlain by thinned continental crust.
In the left half of the Devonian, the Rhenohercynian back-arc basin opened on the northern periphery of the Paleotethys in the rear of the Middle German crystalline uplift. The ophiolites of the Lizard Peninsula in Cornwall, the MOR-type basalts in the Rhine Shale Mountains and the Sudetenland ophiolites are relicts of the oceanic crust of this basin.
In the middle of the Devonian, a chain of uplifts arose in the central zone of Paleotethys I; it is known as the Nigerian Cordillera. She divided the main ocean basin into two - the northern one, which includes the Saxo-Thuringian and Rhenohercynian variscid zones and finds its southwestern continuation in the Iberian Meseta, and the southern one, which represents Paleotethys proper and can be called Paleotethys II.
Paleotethys I or Reikum entered the final stage of its evolution in the late Paleozoic, transforming into the Variscan fold-thrust belt of Western and Central Europe, the Northern Caucasus, its buried continuation in the south of the Turan young 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 proper begins in the Late Permian-Triassic and lasted until the Late Triassic - Early Jurassic, to the Early Cimmerian orogeny - Mesotethys I or the 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 into the Vardar zone in Yugoslavia and further into the Pontides of northern Anatolia and possibly into central Transcaucasia, where its continuation may be hidden under the molasse of the Kura intermountain trough. Its further continuation can be assumed along the Early Cimmerian suture between the Turanian platform and the Elbrus fold-and-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 Songpan-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, merging with the main basin somewhere in northern Afghanistan, extended through the Kopet Dag, the southern slope of the Greater Caucasus, the Crimean Mountains and all the way to 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 gulf opening eastward into the Pacific Ocean into a continuous oceanic belt dividing Laurasia and Gondwana along its entire length. This division was due to the emergence of the Caribbean, the central Atlantic and the Liguro-Piedmont "ocean". The latter joined in the east with the residual Vardar basin, which was partially closed in the northeast by the 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 the “Cimmerian Continent” of J. Shenger, then crossing the Lesser Caucasus through Lake Sevan and the Akera Valley and reaching Iranian Karadag. Ophiolite outcrops disappear further to the southeast, but reappear in the Sabzevar area south of eastern Elbrus. To the east of the Herirud transform fault, a continuation of Mesotethys II can be seen in the Farakhrud zone of central Afghanistan and further, after crossing another Afghan-Pamir fault, in the Rushap-Pshart zone of the Central Pamirs and, having experienced a new shift along the Pamir-Karakoram 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 Sino-Burman massif (Mogok zone).
The entire eastern part of Mesotethys II, starting from Sabzevar-Farakhrud, was 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 regard belonged to the intra-Senonian, sub-Hercynian tectonic phase.
At the end of the Jurassic, another basin with oceanic or suboceanic crust arose north of the main Mesotethys basin in Europe and extended roughly parallel from the Velis zone of the Alps through the Pieniny "cliff" belt of the Carpathians and onwards, possibly, the Niš-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 Dinarides-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 pulses, starting with the Late Cimmerian and ending with the Pyrenean. And gradually the leading role in the Mediterranean mobile belt passed from the Meso to the Neo-Tethys.
Neo-Tethys
This was the last incarnation of the great ocean. Neo-Tethys 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, Lut block, central Afghanistan, southern Tibet (Lhasa). The opening of the Neoteti sa 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. Neo-Tethys itself extended from the Gulf of Antalya, Cyprus and northwestern Syria around the northern protrusion of the Arabian Plate and then in the rear of the Balochistan ranges and the Himalayas, turning south of the Sunda-Banda arc. As for the western end of Neo-Tethys, two versions are possible: 1) it could have found 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 Dinarides-Ellinides trough - the Budva-Pindos trough. Just as it was in the case of Paleo- and Mesotethys, the main Neotethys basin was accompanied by side and behind-arc basins of different ages and with different 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 Seistan Late Cretaceous-Early Paleogene basin in the extreme east of Iran. The other three, 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. The closure of the Neotethys began in the Senonian and accelerated significantly in the mid-late Eocene, when India and a number of microcontinents that had previously broken off from Gondwanaland, 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 the southeastern protrusion of Europe, leading to the formation of the Indo-Burman chains. As a result, Neotethys turned out to be dismembered 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, Makran, Sunda. Is this really the end of the long history of Tethys or just the beginning of a new one phase of its evolution remains an open question.
Conclusion
Considering that the ocean first formed between Laurasia and Gondwana as a single and separate supercontinents at the end of the Precambrian and finally ceased to exist 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 such a vast water space, even during the period of the existence of Pangea, it was reduced to a very vast gulf comparable in size to the size of the Indian Ocean. However, we can talk about two separate Wilson cycles, separated by the period of the existence of Pangea - the Late Proterozoic-Paleozoic and the Mesozoic-Cenozoic. At the same time, we must admit that the Tethys Ocean during the Proterozoic and Phanerozoic repeatedly and very significantly changed the location and configuration of its the main, axial basin shifted from time to time, mainly in a southern direction, constantly maintaining the role of the water divide between Laurasia and Gondwana or their fragments. These changes did not occur gradually, but spasmodically, and this is what made it possible to distinguish individual stages in the evolution of Tethys and, accordingly, introduce the concepts of Proto-, Paleo-, Meso-, and Neotethys, 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-Cadoma, Caledonian, Hercynian-Variscan, 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 different stages of the evolution of the Tethyan region correspond to the cycles identified a hundred years ago by Marcel Bertrand, and I have proposed to call them Bertrand cycles. In relation to the Wilson cycles, these cycles are of the second order, since they correspond not to complete, but only partial death of the ocean (and at its beginning, a displacement of 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 mini-continents, often superstructured by ensialic volcanic arcs. However, this is completely natural for the intercontinental ocean, for the Mediterranean Sea - Mittelmeer - as M. Neumayr defined it, the same century ago. The separation of continental fragments, their reverse rapprochement 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 The Mediterranean belt along its entire length allows us to better understand the features of metallogeny. However, for now this can only be done partially, in relation to the western part of Tethys and the newest stage of its development, starting with 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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- Mesozoic folding (in English literature - Cimmerian) is the era of folding, in which many mountain ranges appeared, which are now located 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 in 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 passes through the old continent. (from the Latin name of Scotland - Caledonia, Caledonia) - an era of tectogenesis, expressed in a combination 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.
Results of the Hercynian folding era
The Hercynian fold appeared in the late Paleozoic. As a result of Hercynian tectonic processes, geosynclinal development in the Ural-Mongolian and Atlantic geosynclinal belts was completely completed.
In the Ural-Mongolian belt, the Hercynides include the Ural-Novaya Zemlya (1) folded region (the islands of Novaya Zemlya, Vaygach, mountain structures of Pai-Khoi, Ural, Mugodzhar); Tien Shan(2) folded region (Karatau, Ugam, Pskem, Chatkal, Fergana, Zeravshan, Turkestan, Gissar ridges); Dzhungar-Balkhash (3) zone (Zharminsky, Kalbinsky and Narymsky ridges of Kazakhstan); Taimyr-Severozemelskaya (4) folded region (Taimyr peninsula and Severnaya Zemlya archipelago), Mongol-Okhotsk (10) folded region (Mongolian Altai, Gobi Altai, Khingai ridge, Gobi desert, Bureinsky ridge), West Siberian (11) and Scythian-Turanian (12) slabs.
In the Mediterranean belt, geosynclinal development was completed on the territory of the Iberian Peninsula (5), in the northern part of Western Europe (6), within the Kun-Lun (7), Qin-Ling (8) ridges; in Africa - in the Inner Atlas (9).
In the Atlantic belt, the Hercynides include the south of Great Britain (13) and the Mexican-Appalachian (14) region (southwestern Appalachians, Gulf Coast, Florida Peninsula).
In the Pacific geosynclinal belt, geosynclinal development was completed in southern Africa - in the Cape Mountains (15) and in eastern Australia within the Great Dividing Range (16).
By the beginning of the Mesozoic there arose Hercynian structure of the earth's crust, in which the following structural elements are distinguished: areas of more ancient consolidation, Hercynides, geosynclinal belts (Fig. 9.4).
Mesozoic folding covers the Triassic, Jurassic and Cretaceous periods. It manifested itself most intensively in the Mediterranean and Pacific geosynclinal belts. In the Mediterranean belt, the Tibetan-Indochina (1) folded region (southern Tibet, Mekong River basin, Malacca Peninsula) is classified as mesozoids. In the Pacific - (2) Sikhote-Alin, (3) Intra-Cordilleran (Brooks Range, Mackenzie Mountains, Rocky Mountains, Great Basin, Colorado Plateau) and (4) Verkhoyansk-Chukotka (Verkhoyansky, Sette-Daban, Anyuisky, Chersky, Momsky ridges , Yudomsky, Poluosny Ridge, Chukotka Peninsula, Wrangel Island, New Siberian Islands, Laptev Sea) folded areas.
Mesozoic folding led to the emergence of depressions in the Atlantic, Indian and Arctic oceans. IN Mesozoic structure of the earth's crust(Fig. 9.5), formed by the beginning of the Paleogene period, ancient platforms and young platforms (areas of earlier consolidation), mesozoids and geosynclinal areas are distinguished.
Objectives: to introduce the influence of internal and external factors on the formation of relief; show the continuity of relief development; consider the types of natural phenomena, the causes of their occurrence; talk about the influence of man on the terrain.
Equipment: physical map, tables, pictures, video about natural phenomena, books, diagrams.
During the classes
I. Organizational moment
II. Checking homework
1. Repetition of terms and concepts
Platform, shield, folded region, tectonics, paleontology, deposit.
Option 1
1. Stable areas of the earth’s crust are called:
a) platforms;
c) folded areas.
2. The plains are located:
a) at the boundaries of lithospheric plates;
b) on platforms;
c) in folded areas.
3. The mountains are located:
a) on platforms;
b) on slabs;
c) in folded areas.
4. The following ridges rose into the Mesozoic folding:
b) Sikhote-Alin;
c) Caucasus.
5. The reborn mountains are:
b) 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, trogs, sheep's foreheads;
b) ravines, beams;
c) barchans, dunes.
9. The surface of Russia goes down:
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, which continues today, is called:
a) Mesozoic;
b) Cenozoic;
c) Paleozoic.
3. The science of minerals is called:
a) petrography;
b) paleontology;
c) geotectonics.
4. Find a correspondence between the mountains and their highest peaks:
1) Caucasus: a) Victory;
2) Altai; b) Belukha;
3) Sayans; c) Elbrus;
4) Chersky ridge. d) Munku-Sardyk.
5. Choose the correct statements:
a) large plains are located on platforms;
b) aeolian processes create moraines:
c) the Kamchatka peninsulas and the Kuril Islands - the most seismically active zones in 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 correspondence between concepts and their definitions:
1) mud-stone flow;
2) snow melting from mountain slopes;
3) loose clay-boulder glacial deposits.
a) avalanche;
c) moraine,
7. Which map shows the structure of the earth's surface (crust)?
a) on the physical;
b) on geological;
c) on tectonic.
Answers: 1 - in; 2 - b; 3 - a; 4 - 1) c, 2) b, 3) d, 4) a; 5 - a, c, d; 6 - 1) b, 2) a, 3) c; 7 - c.
III. Learning new material
(The following concepts are written on the board: endogenous processes, exogenous processes, volcanism, earthquakes, recent tectonic movements, glaciation, moraines, aeolian relief, dunes, screes, landslides, avalanches, mudflows, erosion.)
Look at the blackboard. We will look at these terms today in class, and remember some of them.
The relief is constantly changing under the influence of exogenous (external) and endogenous (internal) factors.
(The teacher draws a diagram on the board while giving explanations.)
The relief is constantly changing under the influence of exogenous (external) and endogenous (internal) factors. Both of these factors act simultaneously.
Endogenous processes are called neotectonic or recent. They can appear in both mountains and plains.
In the mountains, 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 normal faults are formed. The areas undergo vertical movements, some blocks rise, others fall, forming intermountain basins.
On the platforms, the latest movements are manifested in centuries-old slow fluctuations of the earth's crust, some areas slowly rising, while others are falling at a rate of about 1 cm per year. But there can also be faults on platforms, an example of this is the faults in eastern 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
During the Quaternary period, a huge shell of ice up to 4 km thick buried almost all of Europe. The centers of glaciations were Scandinavia, the Polar Urals, the Putorana Plateau and the Byrranga Mountains on the Taimyr Peninsula. The cold was advancing on the Earth in giant waves. There were several such waves. The formation of glaciers is associated with them. 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. This happened more than 200 thousand years ago. The glacier retreated relatively recently - only 12-15 thousand years ago.
1. Moraine (French moraine) - a geological body composed of glacial deposits. The boulders in 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. The colossal boulder is widely known, which was used as a pedestal for the installation of the monument to Peter 1 in St. Petersburg. This boulder, called the “Thunder Stone,” 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. Delivery to St. Petersburg took two years.
The moraine is an unsorted mixture of clastic material of various sizes - from giant boulders with a diameter of up to several hundred meters, to clay and sandy material formed as a result of the grinding of debris by the glacier as it moves. 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 unlayered.
2. Terminal moraine ridges are the boundaries of glacier movement and represent brought debris material. Enormous terminal moraines and associated water-glacial ridges are located in Finland and on the Karelian Isthmus. These include the Michurinskaya ridge and the 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 ram's foreheads - protrusions of igneous and metamorphic rocks with scratches and scars on the surface; slopes facing the movement of the glacier are gentle, those opposite are steep.
4. Oz (ridge, ridge) is a ridge with rather steep slopes (30-45°), reminiscent of a road embankment. The eskers are usually composed of sand, often with pebbles and gravel; pine loves sandy soils, so it often grows on eskers. There is no consensus on the origin of ozkes. There is a water flow along the glacier, it carries a lot of sand, pebbles, and boulders; Having reached the edge of the glacier, the flow forms a fan, the edge of the glacier retreats, and the cone retreating with it gradually forms a ridge. There is another explanation: a stream flowing on the surface of a glacier or inside it deposits sandy rocks with large fragments along its bed; when the glacier melts, all these sediments fall on the underlying surface, forming a ridge on it. One way or another, eskers are formed by streams flowing along the glacier or in it, which is confirmed by the layering of the rocks that make up the esker, such as is formed by water flows. The height of the escarpment can reach several tens of meters, the length - from hundreds of meters to tens (occasionally even hundreds) of kilometers. The peculiarity of eskers is that they do not take into account the relief at all: an esker ridge can stretch along a watershed, then go down a slope, cross a 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, externally usually difficult to distinguish from a moraine, but the material composing it is better sorted than a moraine and is layered. The origin of kamas, like eskers, is explained in different ways: these can be deposits of lakes that existed on the surface of a glacier or near its edge.
6. Vast areas are occupied by outwash (Il. sand - sand) - surfaces on which sands brought by melted glacial waters are common (Pripyat Polesie, Meshchera Lowland, etc.). Outwash has a characteristic landscape, 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, basins 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 also experienced glacial treatment. Thus, on the northern shores of Lakes Ladoga and especially Onega there are bays that are clearly of glacial origin, this can be seen if only because they extend 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. Mountains where there is glaciation or there was one in the geologically recent past are characterized by steep ridges and sharp peaks; in the top parts there are kars (German kar), bowl-shaped niches with slopes that are steep in the upper parts and gentler below. Karas, or mountain cirques, are formed under the influence of frost weathering, serve as places for the accumulation of snow and the formation of glaciers. When adjacent punishments are connected by their side parts, a protrusion in the form of a three- or four-sided pyramid often remains between them. Karas 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 the solid crystalline rocks perfectly preserve the forms formed during the Quaternary glaciation.
Aeolian landforms
Barchans are a type 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. The shape resembles a horseshoe or sickle. In cross section they have a long and gentle windward slope and a short, steep leeward slope.
Depending on the wind regime, clusters of dunes take different 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 represented mainly by frost weathering.
1. Frost heaving is characteristic of different regions of the cold belt, although it is unevenly developed due to local characteristics of the composition, structure and properties of rocks. Small heaving mounds may arise directly from the increase in the volume of freezing water in the pound. But migration mounds 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 segregated ice formation. This is often associated with peat bogs, to which, when freezing, moisture migrates from rocks with much higher humidity. Such mounds 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 and often ruptures in closed systems. Among such small-polygonal structures one can name medallion spots. When freezing occurs 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 loose rocks of heterogeneous composition, 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 crack zones, with the formation of stone borders.
3. Slope processes in areas of permafrost development include two types: solifluction and kurums (stone flows). Solifluction refers to the slow flow of loose, highly waterlogged dispersed sediments along the slopes. During the seasonal thawing of ice-saturated dispersed pounds of the seasonally thawed layer, they become heavily waterlogged with melt and rainwater, lose their structural connections, transform into a viscoplastic state and slowly move down the slope. In this way, sinter forms in the form of tongues or terraces are formed. Kurums are mobile stone placers in the mountains and plateaus of Eastern Siberia and other areas where rocks come close to the surface. The formation of clastic material in kurums is associated with frost weathering during periodic seasonal freezing and thawing and other processes. Kurums in some places form continuous stone fields (ranging in size from a few hundred square meters to several tens of square kilometers).
4. One of the most famous examples of permafrost degradation is thermokarst. This name was given to the process of thawing underground ice, accompanied by subsidence of the earth's surface, the formation of depressions and shallow thermokarst lakes.
Natural phenomena
Open your 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).
The latest tectonic movements → earthquakes, volcanism.
(To create an image of natural phenomena, you can show the video “Natural Phenomena.”)
Consider the structure of the landslide (according to R.: p. 72; according to B.: Fig. 27 on p. 51).
Reason: gravity → landslides, avalanches, mudflows
What natural disasters are possible in your area? How to protect yourself from dangerous phenomena?
Homework
1. According to R.: § 12, 13.
2. Draw 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 |
Predominant heights, m |
Maximum height, m |
Valdai |
Eastern Europe |
Elevation |
||
Privolzhskaya |
Elevation |
|||
Northern Uvaly |
Elevation |
|||
Smolensk-Moscow |
Elevation |
|||
Central Russian |
Elevation |
|||
Caspian |
Flat lowland |
|||
West Siberian |
Flat lowland |
|||
Sibirskie Uvaly |
North of Western Siberia |
Elevation |
||
North Siberian |
Eastern Siberia |
Hilly lowlands |
||
Central Siberian |
Plateau |
|||
Vitimskoe |
Mountain belt 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 |
|
Mountain belt of southern Siberia |
Mount Belukha, 4506 |
|||
Western Sayan |
Caledonian, Hercynian folds |
Mount Kyzyl-Taiga, 3121 |
||
Eastern Sayan |
Mount Munsu-Sardyk, 3491 |
|||
South of the Russian Plain |
Alpine orogeny |
Mount Elbrus, 5642; Mount Kazbek, 5033; Mount Dykhtau, 5204 |
||
Sikhote-Alin |
Primorye |
Mesozoic folding |
Mount Tordoki-Yani, 2077 |
|
Chersky Ridge |
Northeast Siberia |
Mesozoic folding |
Mount Pobeda, 3147 |
Sections: Geography
Purpose and objectives of the lesson: Continue to form in students an understanding of the peculiarities of the patterns of relief formation and its modern development - the influence of internal and external factors using the example of the Belgorod region. Show the continuity of relief development. To develop the ability to work with maps (tectonic, geological), tables. Talk about the influence of humans on the relief.
Equipment: Physical, tectonic, geological map of Russia and the Belgorod region; geochronological table.
During the classes
I. Organizational moment.
II. Repetition. Checking homework.
Working with cards. Test tasks.
Option 1 |
Option 2 |
| 1. Stable areas of the earth’s crust are called: a) platforms; b) shields; c) folded areas. |
1. The most ancient geological era is called: a) Proterozoic; b) Paleozoic; c) Archean. |
| 2. The plains are located on: a) boundaries of lithospheric plates; b) platforms; c) in folded areas. |
2. The geological era in which we live now is called: a) Mesozoic; b) Cenozoic; c) Paleozoic. |
| 3. Mountains are located on: a) platforms; b) slabs; c) in folded areas. |
3. Which peak corresponds to the Caucasus mountain system? a) Pobeda; b) Belukha; c) Narodnaya; d) Elbrus. |
| 4. The following ridges rose into the Mesozoic folding: a) Altai; b) Sikhote-Alin; c) Caucasus. |
4. Which mountain ranges belong to the Alpine folding? a) Ural; b) Caucasus; c) Altai. |
| 5. Deposits are confined to ancient folded areas: a) coal, oil, gas; b) iron ores, gold. |
5. Which mountains are younger? a) Chersky ridge; b) Caucasian. |
| 6. What is the highest mountain in Russia? a) Folk; b) Elbrus; c) Belukha; d) Victory. |
6. What mountain system does the height of 1896m correspond to? a) Folk; b) Elbrus; c) Belukha; d) Victory. |
| 7. What era of new life are we living in? a) Mesozoic; b) Cenozoic; c) Proterozoic. |
7.The most ancient mountain formation? a) Hercynian; b) Proterozoic; c) Archean. |
Answers: Option 1: 1-a; 2-b; 3-in; 4-b; 5 B; 6-b; 7-b. Option 2: 1-a; 2-b; 3-g; 4-b; 5 B; 6-a; 7-in.
III. Learning new material.
- Look at the blackboard. We will look at these terms in today's lesson.
Erosion, landslides, karst, suffusion phenomena, aeolian processes, technogenic relief.
1. Working with the textbook “Geography of the Belgorod Region” part 1. (make notes in a notebook while working)
- Using Fig. 2 p. 5 of the textbook, answer - what major landform lies at the base of the Belgorod region?
- What tectonic structure is located at the base of the East European Plain?
- What is the name of the projection of the crystalline basement in the Belgorod region? (Voronezh massif).
- How is the Voronezh anteclise, a large tectonic uplift, expressed in relief? (Central Russian Upland).
- Using Fig. 3. Geochronological table and fig. 4. map of the geological structure of the Belgorod region, determine what rocks represent the sedimentary cover? (Rocks of the Cenozoic and Mesozoic eras)
- Where in the region do chalk deposits predominate? (Along the river valleys and in the eastern part of the region).
- According to Fig. 5 page 7 determine what is the thickness of rocks of various systems, deposits, formations?
- Why does the earth's surface in the region have a general slope in the southern and southwestern direction? (The north-eastern part of the region is confined to the arched (elevated) part of the Voronezh massif, and the rest of the territory is located on its southwestern and southern slopes.
- What rocks are associated with terrestrial magnetic anomalies in the region? (The upper part of the crystalline massif represents a series of narrow ridges consisting of layers of ferruginous quartzites (Stary Oskol)).
2. Work according to Fig. 6. with a map of mineral resources of the Belgorod region. Exercise. Answer the questions:
- What mineral resources are represented on the map of the Belgorod region?
- What is the leading mineral resource for the region?
- What iron ore areas can you name?
3. Teacher information about iron ores in the Belgorod region.
On the state balance sheet according to B.o. as of 01/01/1998 there were 14 deposits with balance iron ore reserves of 52.2 billion tons, or 51% of Russia's reserves. Ores are rich or poor in pure iron content. The main reserves of rich iron ore (97.6%) with an iron content of 67-69% are concentrated in the Belgorod iron ore region.
Low-grade iron ores (34.6% - total iron content - ferruginous quartzites) have been explored in the Oskol basin.
The share in iron ore production is 40% of the Russian one. Currently, two mining and processing plants (Lebedinsky, Stoilensky), the KMAruda plant operate on the raw material base of iron ores, and the Yakovlevsky mine for the extraction and processing of KMA iron ores is being built.
The Lebedinskoye iron ore deposit (Fig. on page 10) is one of the unique ones in the KMA basin. Thanks to its huge reserves (22.4 billion tons) and the quality of the ore (no harmful impurities), it is included in the Guinness Book of Records. At the current pace of development of the deposit by Lebedinsky GOK, it will ensure uninterrupted, sustainable operation of the plant for a period of more than 500 years. The Lebedinsky quarry is a huge man-made bowl on the surface of the Earth, which is visible from space orbital stations. Its dimensions: surface length 5000 m, width – 3500 m, depth more than 300 m.
(Physical education pause)
4. Conversation with students.
— As a result of what processes is the relief formed? (internal - endogenous and external - exogenous processes)
Endogenous or internal processes are called newest, which on platforms manifest themselves in secular slow fluctuations of the earth's crust at a speed of 1 cm per year.
Exogenous processes occur under the influence of flowing waters (rivers, mudflows, glaciers), wind, and permafrost.
— What processes are decisive in the formation of the modern relief of the Belgorod region? (exogenous)
Exogenous processes:
- flowing waters(form river valleys, ravines, hollows);
- wind(aeolian - dunes, hilly sands);
- Human(quarries, waste heaps).
The main features of the modern relief of the Belgorod region (Fig. 7. p. 14 Relief of the Belgorod region) began to be created at the end of the Neogene period, after it was freed from the Neogene sea - the last one that covered its territory. The region occupies part of the southern slope of the Central Russian Upland and is an erosion-denudation plain with average heights of about 200 m, dissected by a valley and a ravine-gully network. The maximum elevation of the relief is 276 m on the watershed of the Donetsk Seimitsa, Seim and Korocha rivers. The total length of the gully-beam network on the territory of B.O. about 50 thousand km, which is comparable in length to the length of the equator.
The natural processes that shape the relief on the territory of B.O. are quite diverse. The most common are linear erosion, landslides, karst, suffusion phenomena, aeolian processes, and technogenic relief.
5. Working with the textbook. Find explanations of natural processes in the text on pages 15-16. Read it out loud.
IV. Consolidation.
Students prepare questions for each other on the topic of the lesson and ask them.
V. Homework assignment.
VI. Reflection.
Literature: Geography of the Belgorod region: Textbook. manual for students in grades 8–9 of secondary schools: In 2 parts. Part one. Nature - M.: Moscow State University Publishing House, 2006. - 72 p.
