Geological structure. The geological structure of the territory What does the geological structure mean
The Prikazansky District is located in the east of the Russian Platform. The Precambrian crystalline basement, exposed by boreholes at a depth of about 1800 m, is overlain by a thick layer of sedimentary rocks of the Paleozoic group. It includes deposits of the Devonian, Carboniferous, Permian systems. Only rocks of the Upper Permian, Neogene and Quaternary system emerge on the day surface, which make up the modern relief of the region.
The Upper Permian includes deposits of the Kazan and Tatar stages, lying on a washed out, strongly karstized surface of gypsum and anhydrite of the Lower Permian. The total thickness of the Upper Permian deposits is about 250 m. They are exposed in numerous outcrops in the valleys of the Volga and its tributaries, in gullies and ravines, and have also been penetrated by a large number of boreholes.
The formations of the Kazanian stage are represented by two substages, the lower and the upper, which differ sharply from each other lithologically and faunistically. Sandstones, sandy limestones, clays and marls with a total thickness of 30–35 m are involved in the formation of the Lower Kazan substage. (Scientific guide to Kazan and its environs, 1990)
The Kazanian Stage is represented in the west mainly by marine formations and is characterized by a diverse fauna of foraminifers, brachiopods, pelecypods, gastropods, bryozoans, corals, nautiloids, and conodonts. To the east, there is a depletion of the marine fauna and its gradual replacement by brackish and continental ones. From east to west, the layer thickness decreases from 190–200 m to 15–20 m.
The Upper Kazanian substage is widespread. Four strata (layers) are distinguished in its composition: Prikazanskaya, Pechishchinskaya, Upper Uslonskaya and Morkvashinsky. The structure of the Upper Kazanian substage is characterized by significant facies variability and distinct rhythm. In the west, types of sections are developed, entirely represented by marine formations with a corresponding complex of faunal remains. In the east, the sections of the substage consist of formations of continental facies with freshwater shell fauna, bones of terrestrial vertebrates, and rich plant complexes. Between the two extreme types of sections there is a fairly wide (50-100 km) transition zone, within which marine layers alternate with continental red-colored deposits.
Urzhum deposits are widespread in the territory of the Republic of Tatarstan, composing many watershed and watershed spaces. In its western part, they are developed almost everywhere. The lower boundary of the stage is clearly marked here by the change in the section of gray-colored carbonate-argillaceous rocks with the remains of the marine fauna of the Kazan Age. In the eastern part, the Urzhum deposits make up the tops of the watersheds, the lower boundary of the stage is drawn along the sole of alluvial sandstones and conglomerates, which are eroded on lacustrine clayey-siltstone rocks containing a complex of pelecypods and ostracods characteristic of the Upper Kazanian substage. In the rest of the territories, the Urzhum deposits were exposed by boreholes under the overlying Upper Permian, Cretaceous, Jurassic, Neogene and Quaternary formations.
The deposits of the upper (Tatar) division (P 3) are represented by the Severodvinsk and Vyatka stages. In the most complete sections, their thickness reaches 150-200 m.
Sediments of the Severodvinian stage are relatively widespread in the western part of the Republic of Tatarstan, where they form the watersheds of the Volga and Sviyaga, Maly Cheremshan and Bolshaya Sulcha rivers and their tributaries. They also come to the surface in the cliffs of the right slope of the Volga valley and in the valleys of its right-bank tributaries. In the eastern part of the territory of the republic, Serodvinian deposits form the watersheds of the Sheshma and Zai, Zai and Ik, Dymka and Bolshoi Kandyz rivers. The lower boundary of the stage is clearly marked by the change of pale-colored carbonate-argillaceous rocks with pelecypods and otstracods of the Urzhum Age by bright-colored sandy-silty-argillaceous rocks of the Severodvinsk Age, containing the Late Permian faunistic complex.
Neogene deposits (N) within the territory of the Republic of Tatarstan are represented by formations of alluvial, less often alluvial-lacustrine and lacustrine-marsh origin, which formed in the late Neogene (Pliocene).
Formations of the Quaternary period (Q) are ubiquitous in the territory of the Republic of Tatarstan, absent only on the steep slopes of river valleys. Quaternary formations cover Permian, Mesozoic, Neogene deposits and are characterized by a significant diversity, complexity of structure, great diversity of facies and lithological composition, and variability of thicknesses. The formation of Quaternary formations was determined by the structure of the relief, the composition of the underlying rocks, the nature of the latest tectonic movements, as well as climatic features.
Modern (Holocene, Q IV) alluvial deposits compose floodplain terraces and channels of most of the rivers of the Republic of Tatarstan. Floodplain deposits are mainly represented by quartz sands, cross-layered with interlayers of sandy loams, loams; interlayers of coarser sands and pebbles with pebbles of local rocks appear in the lower horizons. The total thickness of the Holocene (modern) alluvium is 25-30 m. Lacustrine-alluvial deposits of the Holocene are represented by sands, loams, clays, gray silty sandy loams with remains of organic matter. The thickness of these deposits is from 1-2 to 10-12 m. Modern biogenic (marsh) deposits are represented by peat, clays, loams up to 1-2 m thick. Man-made deposits associated with human activities are distributed mainly in cities and other settlements , in places of mining, along the lines of railways and highways. (Geological monuments of nature of the Republic of Tatarstan, 2007)
Bedrock layers generally lie quietly, forming 4 brachyanticlinal folds with an amplitude of about 40-60 m, related to the southern tip of the Vyatka swell (Verkhneuslonskaya, Kamskoustinskaya, Kazanskaya and Kinderskaya).
The upper terraces are separated from the lower ones by a well-defined ledge 29-50 m high. They have a complex geological and geomorphological structure. Directly near the ledge there is a Middle Pleistocene terrace, the absolute height of which varies from 80 to 140 m (30-90 m above the level of the reservoir)
The alluvium composing the high Middle Pleistocene terrace has a two-membered structure. The lower suite (35-40 m) is represented by “normal” (humid) alluvium with a distinct division into channel and floodplain facies. The upper suite is periglacial alluvium, represented mainly by sands. It can be assumed that the anomalously high sections of this terrace (120-140m) are partly formed by blown sands. The Early Pleistocene terrace is a basement one - it is composed of “normal” alluvium, the base of which lies 10-30 m above the low water of the old Volga.
The most ancient element of the valley of the entire Volga is a deep (up to minus 100-200 m) erosion incision made by alluvial and lacustrine deposits of the Akchagyl stage of the Upper Pliocene. These deposits also go beyond the incision and in some places form a late Pliocene accumulative plain, strongly reworked by erosion in the Quaternary. In some places they underlie the alluvium of the Middle Pleistocene terrace or form the basement of the Early Pleistocene alluvium. Less distinctly under the alluvium of the Holocene, late and middle Pleistocene, the alluvium of a less deep (up to minus 10-20 m) erosion cut, called G.I. Goretsky Vedensky, can be traced. It is of Early Pleistocene age and is younger than the alluvium of the Early Pleistocene basement terrace.
The wide distribution of carbonate and sulphate rocks of the Lower Permian and the Kazanian stage led to the intensive development of karst processes. In the Prikazansky region, karst is developed everywhere, but the intensity of its development is not the same and is controlled by relief, tectonics, and rock composition.
Karst phenomena are confined primarily to river valleys, because the watershed spaces are composed of non-karst rocks of the Tatar stage. The karsting sequence of the Kazanian stage is most highly elevated in the vaults of the brachyanticlines, which creates favorable conditions for karsting.
Basically, karst is associated with vertical and horizontal circulation of groundwater in the thickness of the Upper Kazanian substage, which lies above the level of rivers, i.e. with processes in the zone of active karst. These are non-pressure descending type bicarbonate-calcium waters.
The historical and administrative center of Kazan is located on the left bank of the Kazanka. This is primarily the Kremlin, built on a cape-like ledge of a high Middle Pleistocene terrace. A ledge of high terraces divides the city into two parts - upper and lower. A similar division is more clearly visible in the old left-bank part of the city.
Middle Permian (Biarmian) deposits (P 2) occupy more than 2/3 of the territory of the Republic of Tatarstan under Quaternary formations. The deposits form the surface of the pre-Quaternary relief; in the southwest they are overlain by Mesozoic rocks, and in the valleys of large rivers - by Neogene formations. Absent only in some parts of paleorivers. The middle section includes deposits of the Kazan and Urzhum stages. Their total thickness reaches 300 m. (Scientific guide to Kazan and its environs, 1990)
Kabirova Kamila
Chugunova Valeria
Relief
The Prikazansky district is located in the east of the Russian platform. (Scientific guide to Kazan and its environs, 1990) Kazan - oldest city in the Middle Volga region - located on the left bank of the Volga in the lower reaches of its small, 112 km long tributary of the Kazanka. In this section, the Volga, crossing the southern part of the Vyatka swell, is cut into limestones and dolomites of the Kazanian stage of the Upper Permian. Rounding the Verkhneuslonskaya brachianticline, the Volga abruptly changes the direction of the current from east to south. The width of its ancient valley decreases to 10 km, but a pronounced asymmetry of the slope remains. The steep and high right slope is composed of bedrock, the left one is formed by a series of Quaternary alluvial terraces, on which the city lies.
After the construction of the Kuibyshev hydroelectric complex in 1957, a reservoir was formed that flooded the floodplain near Kazan and partially the first floodplain terraces. The lower reaches of the Kazanka turned into a bay. The Volga came close to the walls of the Kremlin. Small areas of the first terrace above the floodplain and the high floodplain that are not flooded by the reservoir are protected by a dam. The width of the reservoir near Kazan varies from 3 to 7 km.
The main part of the city is located on two terraced levels, separated by a well-marked ledge 20-25 m high, dividing the city into upper and lower parts. This division has not only geomorphological significance, but also socio-economic. The upper part of the city is in all respects more comfortable and environmentally friendly. The lower part was inhabited by ordinary working people.
The lower part of the city is located on the second Late Pleistocene terrace above the floodplain, which was called the first terrace in earlier works. Its surface lies at a height of 15-18 m above the low water level of the old Volga and 4-7 m above the level of the reservoir. In the rear part of the terrace, swampy depressions were traced, most of which were filled up.
In the southern part of the city, near the foot of the ledge of high terraces, there is a system of interconnected Kaban lakes: Lower (or Near), Middle (or Far) and Upper. Their areas are respectively 0.6; 1.2; 0.25 km2. These are Late Pleistocene oxbow lakes of the Volga, heavily complicated by karst. The deepest is the Middle Boar - about 25m.
The upper part of the city is located on high Middle and Early Pleistocene terraces, morphologically almost indistinguishable. Their absolute heights fluctuate within 80-120 m, relative under the low water of the Volga - 40-80 m, above the level of the reservoir - 30-70 m.
Before filling the Kuibyshev reservoir in the floodplain of the Volga, adjacent to the city from the west, large areas were washed, the surface of which merged with the surface of the second terrace above the floodplain. Port facilities, a stadium and other buildings were placed on these sites. To protect them from flooding, embankment dams were built.
The spread of the ledge separating the upper and lower terraces largely determined the direction of the streets and the general layout of the historical part of the city. Along the ledge on the lower terrace, Sverdlov, Pavlyukhin, Orenburg tract streets also stretch.
The ledge and the surface of the upper terraces are cut by deep gullies and young ravines, longer (up to 3 km) on the slopes to the Volga and shorter (up to 1 km) on the slopes to the Kazanka and its right tributary the Knox. The formation of the vast majority of ravines is due to human activity - the reduction of forests, plowing of land, the extraction of pottery and brick loam, the laying of roads and streets descending the ledge. IN last years after the construction and streamlining of storm sewers, the growth of ravines stopped. Many short ravines in the central part of the city have been filled in. (Middle Voga, 1991)
Ravines also develop more intensively on the right bank, where their average density is 0.5 - 1.0 km/km 2 . On the left bank, ravines dissect the ledge of high terraces and the slopes of the valleys of small rivers, their average density does not exceed 0.1 km / km 2. The development of ravine erosion is due to human activity - deforestation, plowing of land - which began in the time of the Bulgar state, but proceeded especially intensively in the 19th century. IN forest areas ravines sometimes appear only on the slopes along the roads after showers of exceptional strength. The densest ravine network develops in loams, the less dense one develops in the clay-marl stratum of the Tatarian stage. Such are the differences in the rate of growth of ravines. Along with primary ravines, secondary ravines cut into the bottoms of Pleistocene gullies are widespread. There are especially many such ravines on the right slope of the Volga valley. Their formation was facilitated by the intensive erosion of the right slope by the Volga, due to which many beams became "hanging". Stationary observations in various regions of the Middle Volga region show that 2/3 of the growth of ravines in length occurs due to the runoff of melt water. (Scientific guide, 1990)
On the right bank of the Kazanka, a near-terrass depression of a low floodplain terrace was occupied by a peat bog (Kizichesky swamp). Currently, intensive residential development is being carried out here on the poured soils.
Gilmanova Aigul
Climate
Republic of Tatarstan
The territory of the Republic of Tatarstan is characterized by a temperate-continental type of climate in the middle latitudes with warm summer and moderately cold winters.
Climate formation is significantly affected by the predominance of western air transport in the troposphere in the lower stratosphere. Air masses moving from Atlantic Ocean, soften and moisten the local climate, despite the considerable distance from the ocean. At the same time, air masses also come here from other, including sharply continental regions, such as Siberia and Kazakhstan. (Scientific guide to Kazan and surroundings, 1990).
Kazan
Due to the fairly frequent entry of air masses from the west, Kazan has a rather high relative humidity: in the cold half-year (November-March) about 80-85%, in the warm half-year (April-October) about 60-80%, the average annual 76%. The annual amount of precipitation is about 500 mm, in the warm period about 340 mm falls, in the cold about 160 mm. In the annual course, the maximum amount of precipitation occurs in the summer months. February and March are the least irrigated in terms of precipitation. Prevailing winds: south, west, southeast and southwest. In summer, the frequency of northern and northwestern winds increases.
Despite the great distance from the oceans and seas, the climate of Kazan is characterized by a high frequency of significant and continuous cloudiness. From September to May inclusive, the frequency of cloudy sky conditions is over 50%, and in the autumn-winter months it is over 70%. In autumn and winter, cloud systems are more often observed, extending into the hundreds and thousands. These are altostratus, nimbostratus and stratus clouds, usually covering the entire sky. In summer, on the contrary, altocumulus, cumulus, cumulonimbus and stratocumulus clouds have a greater frequency.
Accumulations of products of condensation and sublimation of water vapor in the surface layer of the atmosphere impair visibility. Depending on the degree of turbidity, fog or haze occurs. In the cold season, with heavy snowfall combined with strong winds throughout the territory of the Republic, in particular in the city of Kazan and its environs, blizzards are observed, which are classified as dangerous phenomena. Heavy rain, hail, thunderstorms are also included here.
The main features of the climate of Kazan and its environs in terms of climatic indicators are as follows: the annual value of the total radiation is about 3500 mJ / m 2, its maximum in June is about 610 mJ / m 2, the minimum in December is about 30 mJ / m 2, mean annual temperature about +3.7◦С, the warmest month is July with an average monthly air temperature of about +20◦С, the coldest month is January with an average monthly temperature of about -13◦С.
The absolute maximum air temperature in July reached 38◦С, in January -4◦С, on the contrary, the absolute minimum dropped in January to -47◦С, in July to -3◦С. According to the absolute minimum air temperature in Kazan, there are only two months without negative temperatures - July and August, and according to the absolute minimum temperature on the soil surface, only one - July. Thus, fluctuations in air temperature and soil surface in Kazan and its environs are very large.
annual course temperature parameters simple, solar-conditioned. The maximum radiation balance and turbulent heat transfer falls in June, the maximum air temperature in July (July 20-25). On average, about 13 days this month have an average daily temperature in the range of 20-25◦С, about 12 days with an average daily temperature of 15-20◦С. There are about four hot days with an average daily temperature of 25-30◦С.
In winter, in January, on average, there are about 14 days with an average daily temperature ranging from -5 to -15◦С. There are six days with an average daily temperature from -15 to -20◦С, five to six days from -20 to -30◦С. Hard frosts with an average daily temperature below -30◦С do not occur annually.
Climatic characteristics of the seasons.
The calendar seasons - spring, summer, autumn, winter - do not coincide with the climatic and phenological seasons in duration and dates of beginning and end.
The beginning of spring is conditionally taken as the date of a stable transition of the average daily air temperature through 0ºС and the date of destruction of the stable snow cover. For the Kazan region, these are March 31 - April 3 and April 9-11, respectively. The date of transition of the average daily air temperature through 15 ºС, observed on May 26-30, is taken as the end of spring.
Spring is characterized by a rapid increase in temperature due to an increase in the influx of solar radiation and a decrease in cloudiness. In spring, the conditions of atmospheric circulation change: the western transport from the Atlantic Ocean, which is especially intense in winter, weakens in spring, and the meridional circulation intensifies, which is associated with intrusions of warm air masses from the south and intrusions of cold air masses from the Arctic. Sharp drops in temperature, accompanied by precipitation, occur during the rapid movement of Arctic air masses to the south in the rear of cyclones.
In March, in the last winter month, the average monthly air temperature in Kazan is 4.7-5.8 ºС, in April 4.2-5.1 ºС, the average May temperature is 12.6-13.3 ºС.
Early spring is characterized by late frosts. The number is increasing precipitation. Precipitation falls mainly in the form of rain; snowfalls are observed only in the first half of April. In April and May, the number of hours of sunshine noticeably increases due to an increase in the length of the day and a decrease in cloudiness. Days with partly cloudy prevail. The wind regime changes due to the seasonal restructuring of the air pressure field.
At the end of May - beginning of June, a warm, often hot weather. The end of spring - the beginning of summer, conventionally taken as the date of the transition of the average daily air temperature through 15 ºС, for the end of summer - the transition of the average daily temperature through 10 ºС downwards, which is celebrated in Kazan on September 19-22.
During the summer period, various types of weather are observed: warm and humid, hot with short-term heavy rainfall, climatically hot dry and windy weather, cool rainy and cool dry.
The climatic and weather conditions of summer in the Kazan region are formed mainly under the influence of the transformation of relatively cold air masses entering here. The average number of hours of sunshine for four summer months outside the city is 1003. The temperature regime of summer in Kazan is quite uniform. On the outskirts of the city, temperatures are approximately 1ºC lower. In summer, due to the increase in the absolute moisture content of air masses and the frequency of cyclonic processes, the moisture circulation increases. Therefore, heavy precipitation falls during the summer months. During the entire summer season, a semi-clear sky condition prevails. The prevailing wind directions in summer are western, northwestern and northeastern. The frequency of southwestern and northeastern winds is noticeably less.
Unfavorable weather phenomena in the summer season for the climate of Tatarstan and the Kazan region are showers, thunderstorms, hail, dry winds, and droughts. The onset of autumn in the Kazan region is characterized by a relatively sharp decrease in air and soil temperatures, an increase in the number of cloudy and rainy days, increased winds, and an increase in relative humidity air. The specified weather conditions usually coincide with the end of the frost-free period and the transition of the average daily air temperature through 10 ºС downwards. In Kazan, this transition takes place on September 19-22. From August to September, the amount of precipitation decreases by approximately 10 mm. The partial pressure of water vapor decreases by an average of 4-5 hPa. In autumn, cloudiness increases, the number of cloudy days increases. The frequency of winds of the southwestern and southern directions increases, the frequency of winds of the northern half of the horizon decreases. Autumn is characterized by an increased frequency of fogs, which is extremely unfavorable for the operation of various modes of transport.
With the transition of the average daily air temperature through 0ºС downwards (30.10-2.11) and the appearance of snow cover (27.10-1.11), winter sets in. But since for some time the air temperature either rises or falls, and as a result of which the snow cover melts during this period, which lasts for three weeks, it is called pre-winter. Winter is established from the moment when the air temperature passes through -5ºС with the formation of a stable snow cover. Winter with pre-winter lasts five months - from November to March. The winter period is characterized by higher wind speeds, which cause snow, low and general blizzards. There are few days with high rainfall in winter. Precipitation, which usually falls in solid form, forms a snow cover. In protected areas (forests, city parks, buildings), the depth of snow cover is noticeably greater. Blizzards are unfavorable weather phenomena. Along with strong winds, hard frosts should include ice, frost, fogs. In Kazan and its environs, there are on average about 10 days with ice and more than 20 days with frost a year. An unfavorable manifestation of the climate in the winter period can be attributed to relatively long periods of time with very low temperatures. Strong prolonged frosts were observed in January and February 2006.
The relief, hydrography, vegetation, soil and snow cover cause territorial diversity in the distribution of individual climatic indicators. However, these climatic differences fit within the framework of a larger zone, whose climate features are determined by radiation and circulation factors. The influence of relief on a number of climate indicators can be traced quite clearly. And in this regard, of paramount importance are such aspects of the relief as its absolute height, the prevailing slopes, their orientation in relation to the prevailing air currents, as well as dissection, the impact of which is manifested primarily in the creation of microclimatic differences. (The climate of Kazan and its changes in the modern period, 2007)
Geological structure
The territory of the Russian Federation is occupied mainly by platforms - ancient and young. The ancient East European and Siberian platforms (cratons) have an Early Precambrian crystalline basement and a Late Precambrian-Phanerozoic sedimentary cover. They are separated by the Late Proterozoic-Paleozoic-Mesozoic Ural-Okhotsk mobile belt(or Ural-Mongolian), which also borders Siberian platform from the south (see tectonic map). southern framing East European Platform is the Mediterranean (Alpine-Himalayan) late Proterozoic-Phanerozoic mobile belt, which retains high mobility. To the east of the Siberian platform and the Precambrian massifs - Bureya and Khanka - stretches the marginal continental Western Pacific Mobile Belt separating Eurasia from the basin Pacific Ocean. This belt has not finished its development yet. The folded structures of the Ural-Okhotsk and Mediterranean mobile belts are partially overlain by the Phanerozoic sedimentary cover of young platforms (Barents-Pechora, West Siberian and Scythian). Some sections of ancient platforms and mobile belts that entered into platform development were involved in repeated mountain building in the course of further evolution. Repeatedly manifested epiplatform orogeny in the south of Siberia (Altai, Sayan, Baikal, Transbaikalia) led to the formation of the Central Asian inland mountain belt. In the south of Eastern Siberia is Baikal rift system .
The northern periphery of Russia, covering the wide Arctic shelf, is a passive margin of the Arctic Ocean. At the bottom of the shelf seas, the structural elements of the land continue. The eastern periphery is the active margin of the Pacific Ocean with all its characteristic elements: marginal seas (Bering, Okhotsk, the northern part of Japan), volcanic arcs (Kuril, Kamchatka, the western end of the Aleutian-Komandorskaya) and deep-water trenches.
East European platform
Takes up almost all European part territory of Russia, with the exception of the Timan Ridge, the Pechora Lowland, the western slope of the Ural Mountains, Ciscaucasia, the northern slope of the Greater Caucasus, and is represented by its northern, central, eastern and southeastern parts. The largest structural elements of the East European Platform are Baltic Shield And Russian stove .
Baltic Shield covers the Kola Peninsula and Karelia, is composed of outcropping and exposed Kola superdeep well rocks of the crystalline basement, whose age is from 1.7 to 3.2 billion years, i.e., Early Proterozoic and Archean. The Kola, Karelian, and White Sea megablocks stand out in the structure of the shield. Within the Kola and Karelian megablocks, Archean formations predominate, represented by gneisses, granitoids, crystalline schists, and amphibolites, among which greenstone belts are distinguished, composed of basic and ultrabasic volcanic rocks, metamorphosed mainly in greenschist facies. The belts are associated with ferruginous quartzites Olenegorsk group of deposits(Kola Peninsula) and Kostomuksha field(Karelia) iron ores. In the southern part of the Kola megablock, the Pechenga-Imandra-Varzug rift structure extends, filled with a thick volcanic-sedimentary series of the Lower Proterozoic. The Pechenga deposit of copper-nickel ores is associated with ultrabasic igneous rocks that make up bedded intrusions. Within the Karelian megablock, Lower Proterozoic terrigenous flyschoid formations are developed along its western periphery (marginal part of the Svecofene belt). To the east, strike-slip depressions are common - grabens filled with volcanic-sedimentary rocks of the Lower and clastic strata of the Middle Proterozoic. The Archean-Early Proterozoic complexes of Karelia are cut through by intrusions of Middle Proterozoic rapakivi granites. The Kola and Karelian megablocks are separated by the Belomorian megablock, an Archean-Early Proterozoic granulite-gneiss belt, characterized by a higher degree of metamorphism and a very complex structure.
Within Russian plate the foundation is covered by a sedimentary cover and occurs at depths of 0–2 km in domes anteclise(Voronezh, Volga-Ural) up to, as a rule, 3-5 km in the central parts syneclise(V Caspian syneclise up to 20 km or more). The basement of the Voronezh anteclise, which comes to the surface in the upper reaches of the Don and in quarries Kursk magnetic anomaly(KMA), is composed of Archean blocks separated by a narrow, elongated in the meridional direction, band of terrigenous rocks and ferruginous quartzites of the Lower Proterozoic, to which large deposits of iron ore (KMA) are confined. Internal structure The Archean and partially Early Proterozoic basement of the Volga-Ural anteclise is characterized by great complexity and has a scaly-thrust character. Ancient continental rifts are buried under the sedimentary cover of the Russian Plate - aulacogens, dissecting the foundation of the East European Platform. These include the Central Russian rift system, its southeastern (Pachelma) and northern branches, the Dnieper-Donetsk, Kamsko-Belsky, Vyatsky, Dono-Medveditsky, and other aulacogenes. These structures are mainly confined to the base of the syneclise, over some of them there are deformation zones of the sedimentary cover, swells. The aulacogenes are made up of a complex of Riphean and Lower Vendian rocks: continental clastic, partly shallow-marine carbonate deposits hosting mafic volcanic rocks. Some structures also contain Devonian terrigenous and volcanogenic formations. The sedimentary cover is composed of Upper Vendian and entire Phanerozoic rocks; its section reaches its greatest thickness and fullness in syneclises - Moscow, Mezen, Caspian and the youngest Ulyanovsk-Saratov. Shallow-marine terrigenous-carbonate, partly continental gray- and red-colored, sometimes lagoonal gypsum-saline deposits predominate; bauxites and phosphorites are also present. In the Caspian syneclise, the thickness of the cover exceeds 20 km; the basement lacks the granite metamorphic layer characteristic of the continental crust. A distinctive feature of its sedimentary occurrence is the presence in the section of deep-sea deposits of the upper part of the Devonian - lower part of the Permian, overlain by a thick layer of salts of the Kungurian stage of the Lower Permian, which is associated with the occurrence salt tectonics. Oil and natural combustible gas deposits are confined to the sedimentary cover of the East European Platform ( Volga-Ural oil and gas province And Caspian oil and gas province), coal ( Moscow region coal basin), aluminum ores represented by bauxites (Tikhvinskoye, Severoonezhskoye deposits), phosphate ores represented by phosphorites (Vyatsko-Kamskoye, Egoryevskoye deposits), stone ( Baskunchak) and potassium ( Verkhnekamskoye field) salts, writing chalk, refractory clays and building stone.
Platform magmatism on the East European Platform is manifested in the aulacogenes formed and revived in the Paleozoic (Dnieper-Donetsk, Vyatka), in the northern part of the Baltic Shield (Khibiny ring pluton of alkaline-ultrabasic rocks of Devonian age, containing deposits of apatite-nepheline ores; Lovozero pluton, with associated with deposits of rare earth ores). On the northern slope of the Mezen syneclise, there are kimberlite pipes, to which primary diamond deposits are confined. Arkhangelsk diamondiferous region(pipes "Arkhangelskaya", named after Lomonosov, "Pionerskaya", named after Karpinsky-1, named after Karpinsky-2, "Pomorskaya" and named after V. Grib).
Siberian platform
It is located in Central and Eastern Siberia, between the Yenisei and Lena. The foundation of the Siberian Platform protrudes to the surface within Aldano-Stanovoi shield(in the southeast) Anabar Shield(in the north), and is also exposed in a small area in the extreme northeast of the platform - at the top of the Olenyok arch. It is composed of Early Precambrian, mainly Archean, formations, partially reworked in the Early Proterozoic.
In the building Aldano-Stanovoi shield the Aldan (northern) and Stanovoi (southern) megablocks stand out. The Aldan megablock, composed mainly of Archean rocks, is divided by submeridional thrust faults into 3 blocks: Olekma (western), Batomg (eastern) - granite-greenstone, and Central Aldan - granulite-gneiss. Deposits of ferruginous quartzites (Tarynnakh and Gorkit deposits of magnetite ores) are confined to the greenstone belts of the late Archean and, probably, early Proterozoic. In the southwestern part of the Aldan megablock, the Early Proterozoic Udokan rift basin is located, filled with a thick sequence of continental clastic rocks hosting cupriferous sandstones, with which the largest Udokan deposit copper ores. The Stanovoi megablock, which experienced intensive tectonothermal reworking in the Early Proterozoic, is pushed over the Aldan megablock. Archean rock complexes are zoned metamorphosed and intruded by large layered plutons of gabbro-anorthosites and granite intrusions of high alkalinity of the late Early Proterozoic. During the period of the Mesozoic activation of the Stanovoy zone, the formation of Late Jurassic-Early Cretaceous batholiths of granitoids took place. Deposits of ores of gold (Kuranakhskoe ore field), iron (Taiga, Chineyskoe), rare earth elements and apatite (Seligdarskoe) are associated with igneous rocks of epochs of tectonomagmatic activation of the shield. From the south, the Stanovoi megablock is bounded by the North Tukuringra Fault, along which the Aldan-Stanovoi Shield is pushed over the folded structures of the Ural-Okhotsk mobile belt. At the latest stage, the Stanovaya zone was involved in intense uplift and became part of the Central Asian belt of revived mountains.
Anabar Shield composed mainly of Archean rocks metamorphosed in granulite facies. In its southeastern part, Early Proterozoic primary sedimentary and volcanogenic formations are common, which also protrude to the surface at the top of the Olenyok arch. In the northern marginal part of the Anabar shield is the Popigai astrobleme with the unique shock-metamorphic deposits of industrial diamonds Skalnoye and Udarnoye confined to it.
The basement rock complex includes the Early Proterozoic formations of the Akitkan volcanoplutonic belt, which extends along the northwestern shore of Lake Baikal and plunges northeast under the sedimentary cover.
Foundation Lena-Yenisei plate, which is the area of distribution of the platform cover, is dissected by a series of differently oriented aulacogens (Kotui, Udzhinsky, Oleneksky, Turukhano-Norilsky, Irkineevsky, Urinsky, Vilyui paleorift system), filled with Riphean shallow-marine terrigenous-carbonate and partly continental clastic deposits, including volcanites. During the Paleozoic, some aulacogenes experienced inversion or regeneration. In the section of revived aulacogens (Vilyui paleorift, etc.), there are Middle Upper Devonian volcanics overlain by the Upper Devonian saliferous sequence, which is associated with the manifestation of salt-dome tectonics in the upper horizons of the platform cover. In the structure of the Lena-Yenisei plate, syneclises are distinguished: Prisayansko-Yenisei, Tungusskaya, Vilyuiskaya, within which the thickness of the sedimentary cover is 3–7 km (in the north of the Tunguska syneclise, 12 km). These structures are separated and framed by anteclises (the largest are Anabar-Olenyok, Aldan and Nepa-Botuobinsk). At their tops, the foundation lies at depths of 0–2 km. The platform cover is composed of shallow-marine and continental rocks of the Middle - Upper Riphean and Vendian - Phanerozoic. In the Sayan-Yenisei syneclise, filled with deposits of the Cambrian, Ordovician and Silurian, there is a thick sequence of stone and potassium salts of the Cambrian age (Bratskoye, Usolskoye deposits). The southern part of the syneclise, sandwiched between the folded structures of the Eastern Sayan and the Baikal-Patom highlands, forms the so-called. Irkutsk amphitheater. To the northeast of it, between the marginal part of the Nepa-Botuoba anteclise and the thrust front of the Baikal-Patom folded region, there are the Pre-Patom trough and the Angara-Lena dislocation zone, where the Cambrian-Silurian deposits are torn from the basement and crushed into a system of folds of northeast strike . It is confined to the Nepa dislocation zone within the Nepa-Botuoba anteclise Nepa-Gazhensky potassium-bearing basin. Within the Tunguska syneclise, the Middle Carboniferous-Permian coal-bearing series is widespread ( Tunguska coal basin), overlain by the Upper Permian–Lower Triassic trap complex. As a result of the metamorphism of coals of the Tunguska series under the contact action of intrusions of the basic composition, graphite deposits arose (Noginskoye, Kureyskoye). Rich sulfide copper-nickel ores with cobalt and platinoids ( Norilsk group of fields). To the northeast of the Tunguska syneclise is the Maimecha-Kotui trough, notable for its Triassic alkaline-ultrabasic formation with large ring plutons (Gulinsky), which are associated with deposits of titanomagnetite, apatite, nepheline, and rare earth ores. The western limit of the Tunguska syneclise is the Turukhano-Norilsk dislocation zone, the southwestern limit is the small Baikit anteclise, within which oil deposits have been identified in the Riphean carbonate rocks (oil and gas bearing area). The Upper Riphean and Vendian-Lower Cambrian deposits of the Nepa-Botuobinsk anteclise, which separates the Tunguska syneclise from the Vilyui syneclise, contain oil and gas deposits (the Nepa-Botuobinsk region Lena-Tunguska oil and gas province). The Vilyui syneclise is located above the Vilyui paleorift system and is made up of Jurassic-Cretaceous shallow-marine and continental coal-bearing deposits ( Lena coal basin). Its eastern marginal part is superimposed by the shallow Lower Aldan Basin, within which continental terrigenous sediments of the Paleogene and Neogene are developed. To the north of the syneclise in the direction of the Anabar massif, a strip of kimberlite pipes extends, with which primary diamond deposits are associated. Yakutsk diamond province(Udachnaya, Yubileinaya, Mir, International, Zarnitsa, Aikhal, Krasnopresnenskaya pipes) and diamond placers. In the southern half of the Siberian Platform, small superimposed depressions are developed, filled with Jurassic continental coal-bearing deposits: the Kansko-Taseevskaya, superimposed on the northern part of the Sayan-Yenisei syneclise; Irkutsk, located in the western part of the "amphitheater" (brown coal basins); a chain of rift depressions - grabens along the overthrust of the Stanovoi megablock of the Aldan-Stanovoi Shield (Chulmanskaya, Tokinskaya, etc. - South Yakutsk coal basin).
Ural-Okhotsk (Ural-Mongolian) mobile belt
The belt stretches across Eurasia from the Barents Sea to the Sea of Okhotsk and consists of two segments. The northern (Ural-Siberian) segment separates the East European and Siberian platforms. Southern (Central Asian) separates the Siberian platform from the Sino-Korean one. In the structure of the belt, folded systems of different ages (from Baikalides to mesozoids) are distinguished, formed within Paleoasian ocean, partially covered by covers of the West Siberian and Barents-Pechora young platforms.
South Barents-Timan fold system of Baikal age, the formations of which underlie the sedimentary cover of the Barents-Pechora Plate and come to the surface on the Rybachy and Kanin peninsulas and in the Timan Ridge, is located in the northwest of the mobile belt. Its outer (southwestern) zone is composed of Riphean terrigenous deposits of the continental slope and foot of the ancient East European continent (Baltic). To the east, igneous rocks, probably of island-arc origin, play a significant role. In Pai-Khoi and the Polar Urals, the Baikalid system is sharply unconformably overlain by Hercynian structures.
Ural fold-thrust system Hercynian age extends along the eastern edge of the ancient East European platform and is separated from it by a chain edge deflections. The system is separated by the Main Ural Fault - a gently sloping overthrust– into two longitudinal megazones: the western and eastern slopes. The megazone of the western slope is underlain by the submerged foundation of the East European Platform and is composed of formations of its Paleozoic passive margin - shelf terrigenous and carbonate rocks of the Ordovician - Lower Carboniferous. The deposits are crumpled into folds, disturbed by overthrusts, sometimes covered with plates ophiolites transferred from the eastern slope megazone. The latter has a more complex structure, in which ophiolites are involved, which are relic oceanic crust of marginal (back-arc) and interarc seas, complexes of volcanic arcs of the Late Ordovician - Early Carboniferous, Late Devonian-Early Carboniferous flysch. Sedimentary-volcanogenic complexes of the eastern slope megazone are intruded by Late Paleozoic granitoids, with which skarn-magnetite ores are associated (Goroblagodatskoye deposit, Vysokogorskaya group), and by earlier gabbro-peridotites of the Platinum-bearing belt of the Urals (titanomagnetite vanadium-bearing deposits of Gusevogorskoye, Kachkanarskoye with platinoids). Numerous deposits of copper-pyrite-polymetallic ores (Gaiskoye, Sibayskoye, Blyavinskoye, Uchalinskoye, etc.) are associated with island-arc volcanic rocks. The folded formations of the system are thrust in the west over the foredeeps filled with Upper Paleozoic-Triassic deposits. The structure of the eastern slope of the Urals is complicated by rift grabens filled with the coal-bearing formation of the Upper Triassic - Lower Jurassic (Chelyabinsk lignite basin).
In the north, the structures of the Urals are butt-jointed with Pai-Khoi-Novaya Zemlya folded system early Mesozoic age. The Paleozoic formations composing it have a certain similarity with the deposits of the megazone of the western slope of the Urals. On Severny Island of the Novaya Zemlya Archipelago, Paleozoic platform deposits are conformably underlain by Upper Proterozoic rocks, which sharply unconformably overlie the Middle Proterozoic metamorphic basement. Similar relationships give grounds to single out here the epigrenville platform massif - Svalbard (Barents), which limits the South Barents structures of Baikal age from the north. The Kara astrobleme is superimposed on the Pai-Khoi segment of the system.
In the east, the folded formations of the Urals are covered by a sedimentary cover. West Siberian Platform(slabs), along the eastern edge of which intensely deformed rocks are exposed folded system of the Yenisei Ridge Baikal age. The Riphean formations of the Yenisei Ridge are represented by terrigenous and terrigenous-carbonate flyschoid deposits of the continental slope and foot of the ancient Siberian continent (Siberia). Black shales contain the bodies of gold ores of the giant Olimpiada deposit. In the northwest of the fold system, there are ophiolites and island-arc volcanic rocks of the Riphean age, which formed in an active continental margin setting.
North of the Siberian platform is located Taimyr fold system, separated from it by a deep (over 14 km) Yenisei-Khatanga trough. There are three zones within the system. The central one has a complex fold-thrust structure; among thrust scales there are plates composed of island-arc volcanic rocks and ophiolites of the Riphean. In the northern zone and on the islands of the Severnaya Zemlya archipelago, terrigenous deposits of the Upper Riphean appear, which are sediments of the foot and slope of the Precambrian continental block, similar to the Svalbard one and, possibly, constituting its eastern extension. The southern zone is superimposed on the submerged edge of the Siberian Platform; it was formed by the Lower-Middle Paleozoic shelf carbonate rocks of the underwater margin of the ancient Siberian continent. The section of deposits of the Upper Paleozoic and the beginning of the Mesozoic resembles the sedimentary cover of an ancient platform. The thick sequences that form the southern zone of the Taimyr fold system are intensively dislocated and disturbed by overthrusts facing the platform. Deformations in this area date back to the end of the Triassic - Jurassic - beginning of the Cretaceous.
Salairo-Caledonian-Hercynian Altai-Sayan folded region located in the south of Western and Central Siberia. In the northeast, it adjoins the Siberian Platform. The region has a very complex structure and consists of differently oriented folded zones of different ages: Salair structures of the Eastern Sayan, Kuznetsk Alatau and Mountain Shoria, Eastern Tuva, Dzhida zone; Caledonian structures of the Western Sayan, Gorny Altai; Hercynian structures of Rudny Altai, Salair Ridge. Within its limits, a number of median arrays ( microcontinents), for example, the Gargano-Khamar-Dabansky with an Early Proterozoic basement and an Upper Riphean-Lower Cambrian cover. In the structure of folded zones, an important role is played by island-arc volcanic-sedimentary rocks and ophiolites (East Sayan-Kuznetsk and Dzhida zones, Eastern Tuva and the Salair ridge), terrigenous flyschoid formations (West Sayan and Gorno-Altai zones). Within Rudny Altai, rocks of the Middle Devonian–Early Carboniferous volcanoplutonic association are widespread. The intermountain Middle-Late Paleozoic Minusinsk depression is filled in the lower part with volcanogenic and clastic molasses Devonian, and then coal-bearing strata of the Upper Paleozoic and Jurassic ( Minusinsk coal basin). Within the intermountain Kuznetsk trough, the Devonian-Early Carboniferous marine terrigenous-carbonate formation is widespread, which is overlain by the Upper Paleozoic coal-bearing series ( Kuznetsk coal basin- one of the largest in the world, the largest in Russia in terms of coking coal reserves), Triassic traps and Jurassic continental deposits with coals.
To the west of the Altai-Sayan region is located Irtysh-Zaisanskaya fold-integument system late Hercynian age, occupying an axial position in the structure of the Ural-Okhotsk belt. In its central part, in the fault zone, Ordovician-Early Devonian ophiolites are developed, olistostromes, metamorphic complexes. The Irtysh-Zaisan system extends into Russia from Kazakhstan. To the north, the folded formations submerge under the cover of the West Siberian young platform, being exposed on the right bank of the Ob to Novosibirsk and Tomsk (Tom-Kolyvan zone); to the north, the structure of the system was traced by drilling to the latitude of Norilsk.
In the east, the Altai-Sayan region merges with structures Baikal-Patom folded region, composed of Riphean terrigenous-carbonate deposits of the paleomargin of the Siberian Platform, island-arc complexes of the Late Proterozoic and Cambrian ages. Within its limits, relics of the oceanic crust of the marginal seas of the same age, represented by ophiolites, have been established. Huge areas are occupied by the Middle Paleozoic Angara-Vitim granite batholith. In the north of the region, in the black shale strata of the Upper Proterozoic, the largest gold ore deposit in Russia was discovered Dry Log .
The Hercynian-Mesozoic Mongolian-Okhotsk fold-integument system. From the south, it is limited by the Priargunsky and Bureya massifs with a Precambrian basement, and in the east it articulates with the northern end of the Sikhote-Alin fold system. The Mongolian-Okhotsk system arose on the site of the basin, which in the Late Paleozoic and Mesozoic was the bay of the Pacific Ocean. Deformations in this area are dated in the west by the Late Paleozoic, in the east by the Mesozoic (late Jurassic).
Significant areas in the north of the Ural-Okhotsk belt are covered by a sedimentary cover, which belongs to the young Barents-Pechora and West Siberian platforms, separated by the Ural-Novaya Zemlya fold system. Foundation Barents-Pechora platform - Baikal, in the north of the Barents Sea - Grenville. In the southern part of the platform (on land), the cover is composed of Paleozoic shallow-water and partly continental deposits; to the north, within the Barents Sea, powerful complexes of the Mesozoic also take part in its structure. Oil and gas fields are associated with the sedimentary cover of the platform ( Timan-Pechora oil and gas province and East Barents Province) and coal ( Pechora coal basin).
West Siberian platform(megasyneclise), which continues in the southern part of the Kara Sea, has a folded Paleozoic and partly Precambrian basement, broken by a network of rift depressions, which are filled with Triassic clastic strata containing basalts. Salairids and hercynides of the Altai-Sayan region, the Irtysh-Zaisan system, the Caledonides of the Kazakh uplands, and the Central Kazakhstan massif (microcontinent) are traced under the cover of Meso-Cenozoic sediments. The sedimentary cover is represented by continental and shallow-marine terrigenous rocks of the Jurassic - Cenozoic (in some places in the section there is a Paleozoic complex), which are associated with oil and gas fields ( West Siberian oil and gas province). The northeastern branch of the West Siberian platform is the Yenisei-Khatanga trough, at the base of which a Triassic (possibly older) rift extends. The trough is filled with oil and gas bearing Jurassic and younger sediments. It separates the ancient Siberian platform from the southern zone of the Taimyr fold system and, like it, is superimposed on the northern margin of the platform.
Western Pacific Mobile Belt
The belt covers the North-East and the Far East of Russia. It is located to the east of the Siberian platform, Bureya and Khanka Precambrian massifs and consists of several folded areas. In the north is the Late Mesozoic Verkhoyansk-Chukotka fold-cover region, within which the Verkhoyansk-Kolyma (in the west) and Novosibirsk-Chukotka (in the east) fold systems are distinguished. The Verkhoyansk-Kolyma system over most of its area is underlain by the submerged basement of the Siberian Platform and is composed of Riphean-Jurassic carbonate and terrigenous deposits of its passive paleomargin, folded into large linear folds. In the central part of the system, there is the Kolyma-Omolon massif (microcontinent) with an Early Precambrian basement and a gently deformed Riphean-Mesozoic cover. To the west of it, in accordance with folded structures, there is a chain of late Jurassic granite plutons with gold and tin mineralization (the Deputatskoye, Odinokoye, etc. deposits). In the Chersky Ridge, ophiolites have been identified that mark the boundary between the ancient Siberian continent and the basin with oceanic crust that separated the Kolyma-Omolon microcontinent from it in the Early Paleozoic. The Verkhoyansk-Kolyma system is thrust in the west onto the Cis-Verkhoyansk marginal trough, which extends along the eastern periphery of the Siberian Platform and is filled with Cretaceous and partially Cenozoic coal-bearing molasses.
The Novosibirsk-Chukotka fold system covers the Novosibirsk archipelago (partially), the southern parts of the East Siberian and Chukchi seas, and the northern coast of Chukotka. Paleozoic and Mesozoic terrigenous-carbonate deposits of the passive margin of the hypothetical Hyperborean platform, which is the northern limit of the system, take part in its structure. In the south, island-arc volcanic rocks have been identified. The Novosibirsk-Chukotka and Verkhoyansk-Kolyma fold systems are separated by the South Anyui suture zone, which has a very complex fold-thrust structure and is marked by Jurassic ophiolites and Late Jurassic-Early Cretaceous granite intrusions. In the west, the Novosibirsk link of the Novosibirsk-Chukotka system is separated from Taimyr by a young rift basin of the Laptev Sea that emerged at the end of the Early Cretaceous. Along the southern part of this sea and its coast, the Lena-Anabar zone of the Verkhoyansk-Kolyma system extends to the west, adjoining the southern zone of the Taimyr fold system and together with it pushing over the Siberian platform. To the east of the Novosibirsk archipelago, there are rift troughs of the East Siberian and Chukchi seas, formed in the middle of the Cretaceous and superimposed on the southern part of the Hyperborean platform and the northern part of the Novosibirsk-Chukotka system.
In the southeast, the Verkhoyansk-Chukotka folded region is limited Okhotsk-Chukotka volcano-plutonic belt the middle of the Cretaceous, superimposed on a folded and metamorphic base of different ages. The belt is composed of terrestrial volcanic rocks of basic, intermediate, and felsic composition, which are closely related to intrusive massifs of gabbro, diorites, granodiorites, and granites. Adjacent to it is the Late Mesozoic-Cenozoic Koryak-Kamchatka folded area, which is a complex accretionary complex, which includes island-arc formations of the Paleozoic, Mesozoic and Paleogene. The youngest element of the area is the Miocene-modern volcanic arc of Eastern Kamchatka (Shiveluch, Klyuchevskaya Sopka, Tolbachik volcanoes, etc.) and the Kuril Islands, which limits the Sea of Okhotsk depression from the southeast. The shallow-water part of the sea is considered by some scientists as a block with an ancient continental crust (microcontinent), and by others as a Miocene oceanic plateau included in the accretionary complex. The deep-water South Okhotsk (Kuril) basin, located in the rear of the Kuril volcanic arc, is a captured section of the oceanic plate or, according to other researchers, back-arc basin .
From the west, the Sea of Okhotsk depression is limited by the Cenozoic Sakhalin fold-cover system. In its structure, two megazones are distinguished, separated by a steep fault - a shift. In the eastern megazone, island-arc complexes are developed, the upper age limit of which corresponds to the end of the Miocene. The western megazone is composed of a thick layer of Upper Cretaceous–Paleogene terrigenous deposits accumulated in a deep-water trench, which adjoined the East Sikhote-Alin volcano-plutonic belt of the corresponding age from the east. The western megazone of the Sakhalin system is separated from the named belt by the newest rift graben of the Tatar Strait, which arose in the Miocene and opens in the south into the newly formed basin of the Sea of Japan. The fold-thrust structures of the system are superimposed by a large depression filled with Pliocene molasse, to which the North-East Sakhalin region is confined. Okhotsk oil and gas province, continuing on the eastern shelf of the island.
Late Mesozoic Sikhote-Alin fold-cover system It is located on the mainland and adjoins the ancient Bureya and Khanka massifs from the east. It extends to the mouth of the Amur, where it merges with the Mongol-Okhotsk fold system. The Sikhote-Alin system is divided by the NE-trending Central Sikhote-Alin strike-slip into two megazones. The western one is a complex accretionary complex formed at the beginning of the Cretaceous. Olystostromes play an important role in its structure. melange, which include Paleozoic, Triassic and Jurassic ophiolites and limestones. The formations of the complex are intruded by Early Cretaceous granites and overlain by Lower Cretaceous flysch. Repeated deformations with the introduction of granite intrusions occurred in the middle of the Cretaceous. The eastern megazone is composed of Upper Cretaceous–Paleogene volcanic rocks of the marginal volcanoplutonic belt.
Mediterranean (Alpine-Himalayan) mobile belt
The belt covers the extreme south of the European part of Russia. It includes the Crimean peninsula, the Ciscaucasia, the northwestern subsidence and the northern slope of the Greater Caucasus. The flat part of the Crimean peninsula and Ciscaucasia in tectonic terms correspond to the young Scythian platform(plate) with a Paleozoic (mainly) folded base, unconformably overlain by a Permian-Lower Triassic molasse and a cover of Middle Jurassic and younger terrigenous and carbonate sediments. In the eastern part of the platform, under a slightly deformed cover, Upper Triassic felsic volcanic rocks occur, and Jurassic rocks are present in the section of the cover. evaporites(large Gremyachinskoe deposit of potassium salts). Oil and natural combustible gas deposits are confined to the Scythian Plate and the forward troughs of the Greater Caucasus ( North Caucasian oil and gas province). Between the Scythian and East European platforms there is a narrow folded zone of the Karpinsky Ridge(Donetsk-Caspian) of Paleozoic age, which arose as a result of inversion of the eastern link of the Dnieper-Donetsk rift system. Folded Devonian-Carboniferous-Lower Permian and Triassic formations of the zone are overlain by Jurassic-Cenozoic platform deposits.
In the south, the Scythian platform is separated by a discontinuous strip of foredeeps (West-Kuban, or Indolo-Kuban; East Kuban, Terek-Caspian) from the cover-folded mountain structures of the Mountainous Crimea and the Greater Caucasus, which are part of the Dobrudzhan-Crimean-Caucasian-Kopetdag branch of the Alpine - The Himalayan belt, the folded systems of which were formed in the Cenozoic within the Mesozoic-Cenozoic Neotethys ocean (see Art. Tethys). At the base of the incision mountain-folded structure of the Crimean Mountains overlie: intensely deformed sandy-argillaceous flysch of the Upper Triassic - Lower Jurassic, Middle Jurassic island-arc volcanics and volcanogenic-sedimentary strata, which are overlain by Upper Jurassic reef limestones (in the southwest - conglomerates, in the eastern part - flysch), Lower Cretaceous terrigenous-carbonate rocks and monoclinally overlying Upper Cretaceous - Eocene marl-carbonate deposits. The southern flank of the orogen is lowered along faults below the level of the Black Sea within the limits of the underwater margin of the Crimean Peninsula. There are chains of Middle Jurassic hypabyssal intrusions of gabbro, diorites, and plagiogranites (Ayudag, Plaka, Kastel, etc. massifs along the southern slope of the Crimean Mountains).
north slope mountain-fold structure of the Greater Caucasus is a gently sloping monocline composed of shelf sediments of the Upper Jurassic - Paleogene. This structure was formed due to the tectonic uplift of the southern edge of the Scythian platform. In the Rocky, Peredovy, and Glavny (Vodorazdelny) ranges of the Central Caucasus, fold-cover complexes of the Baikal and Hercynian ages, including Lower Paleozoic ophiolites, protrude from under obliquely deposited Mesozoic deposits. The Upper Proterozoic and Lower Middle Paleozoic formations are intruded by Late Paleozoic, Mesozoic and Cenozoic granite intrusions. The skarn marbles in the contact zone of the young intrusion are dated Tyrnyauz field complex tungsten-molybdenum ores. In the Eastern Caucasus, the Paleozoic complex plunges under a thick lower and middle Jurassic black shale sequence accumulated in the axial part of the marginal basin of the Neotethys Ocean. The foredeeps are filled with thick Oligocene-Neogene molasses. In the axial zone of the Terek-Caspian trough, the Tersky and Sunzha swells are localized, containing large oil deposits (fields in Dagestan, Chechnya and Ingushetia). The foredeeps are separated by the transverse Mineralovodsko-Stavropol uplift, within which manifestations of Neogene-Quaternary magmatic activity are known, including the Elbrus and Kazbek volcanoes in the Greater Caucasus, dissected by erosion laccoliths Caucasian Mineral Waters. Between the folded structures of the Mountainous Crimea and the Greater Caucasus is located Kerch-Taman transverse trough, composed of a thick layer of dislocated deposits of the Oligocene - Neogene, incl. clayey Maikop series, which is associated with the manifestation of clay diapirism and mud volcanism on the Kerch and Taman peninsulas.
THE USSR. Geological structure The largest elements of the structure of the earth's crust on the territory of the USSR: the East European and Siberian platforms and the folded geosynclinal belts separating them - the Ural-Mongolian, separating the East European platform from the Siberian and enveloping the latter from the south; Mediterranean, bordering the East European platform from the south and southwest; Pacific, forming the outskirts of the Asian continent; part of the Arctic, located within the northern coast of the Chukotka Peninsula. Within the folded geosynclinal belts, there are: young regions that have not yet completed their geosynclinal development, which are active modern geosynclines (the peripheral part of the Pacific belt); areas that completed geosynclinal development in the Cenozoic (the south of the USSR, belonging to the Alpine geosynclinal folded area), and more ancient areas that form the foundation of young platforms. The latter, depending on the time of the end of the processes of geosynclinal development, folding and metamorphism of sedimentary strata, are divided into folded areas of different ages: Late Proterozoic (Baikal), Middle Paleozoic (Caledonian), Late Paleozoic (Hercynian, or Varisian) and Mesozoic (Cimmerian). The geosynclinal type of the structure of the earth's crust arises at earlier stages of development. Subsequently, geosynclinal areas turn into the foundation of platforms, which is then covered by a cover of platform sediments (platform slabs) in lowered areas. Thus, in the course of the development of the earth's crust, the geosynclinal stage is replaced by a platform stage with a two-story structure typical of platforms. During the formation of the foundation of the platforms, the oceanic crust of the geosynclinal belts is transformed into the continental crust with a thick granite-metamorphic layer. In accordance with the age of the foundation, the age of the platforms is also determined. The foundation of the ancient (Precambrian) platforms was formed mainly by the beginning of the Riphean (Late Proterozoic). Among the young platforms, there are: epibaikalian (the upper Proterozoic is involved in the foundation structure, and Paleozoic, Mesozoic and Cenozoic rocks are developed in the cover), epipaleozoic (the foundation was formed in the Paleozoic, and the cover was formed in the Mesozoic - Cenozoic) and epimesozoic (Mesozoic rocks participate in the foundation structure). ). Some areas of ancient platforms and geosynclinal belts, which turned into young platforms, in the course of further evolution turned out to be covered by repeated processes of orogeny (epiplatform orogeny), which manifested itself many times in Siberia (Stanovoi Range, Western Transbaikalia, Sayan Mountains, Altai, Gissar-Alai, Tien Shan and etc.). The structural regions of the land continue directly on the bottom of the shelf seas, bordering the north, east, and partly northwest. territory of the USSR. ancient platforms. The East European platform includes 2 basement protrusions on the surface - the Baltic Shield and the Ukrainian crystalline massif - and the vast Russian Plate, where the basement is submerged and covered by a sedimentary cover. The Archean, Lower and Middle Proterozoic strata participate in the basement structure. Archean rocks form numerous massifs, within which 2 rock complexes of different composition and age are distinguished. Older rocks (over 3000 million years ago) compose the lower horizons of the Kola series on the Kola Peninsula (biotite and amphibole gneisses and amphibolites), and on the Dnieper area of the Ukrainian massif (between Zaporozhye and Krivoy Rog), rocks of the Konsko-Verkhovtsevo series are similar in composition . In Podolia and the Bug basin, the oldest rocks are represented by pyroxene-plagioclase garnet gneisses and charnockites. The younger Archean complex (from 2600 to 3000 Ma) consists of thick series of biotite, two-mica, amphibole gneisses, amphibolites, crystalline schists, quartzites, and marbles. This complex is typically expressed along the shores of the White Sea (Belomorskaya series). The processes of metamorphism, which the rocks of the White Sea complex underwent at the beginning of the Proterozoic, were accompanied by the formation of granite massifs and migmatites. The Archean massifs are separated by bands of Lower Proterozoic (from 1900 to 2600 Ma) folded structures composed of gneisses, schists, quartzites, and diabases, which were subjected to strong folding and granitization at the end of the Early Proterozoic and repeated (superimposed) metamorphization in the Middle and locally Late Proterozoic ( 1750-1600 and 1500-1350 Ma). The Middle Proterozoic rocks on the Baltic Shield and the Ukrainian massif lie unconformably and are represented by quartzites, phyllites, diabases, and dolomitic marbles (Jatulian of Karelia, Jotnium of Finland, Ovruch series of Ukraine). These sequences are characterized by metamorphism products of kaolin weathering crusts, which could have been formed in a calm tectonic setting. They represent deposits of the most ancient Middle Proterozoic cover, after the accumulation of which large massifs of porphyritic rapakivi granites (1670-1610 Ma) were emplaced. These are the youngest granite intrusions in the platform basement. The depth of the foundation on the Russian plate varies from several hundred m(on elevations) up to several thousand meters. m(in the hollows). The largest uplifts are the Voronezh, Belorussian and Volga-Ural anteclises. Among the depressions, the Moscow, Baltic, and Caspian syneclises stand out. The submerged parts of the platform adjoining the Urals, the Timan Ridge, and the Carpathians correspond to pericratonic subsidences (Pritimansky, Kama-Ufimsky, and Transnistrian). A special type of structures - Aulacogens ,
often forming entire systems. The largest system of aulacogenes is the Central Russian system, which stretches from Valdai to the Timan region. The Orsha-Kresttsovskiy, Moscow, Ladoga, and Dvina aulacogens have been established in the northern, western, and central parts of the Russian Plate, and the Pachelmskiy, Kazhimskiy, Verkhnekamskiy, and other aulacogens have been established in the East. Aulacogens and pericratonic troughs are the oldest basins of the Russian Plate. Aulacogens are filled with Riphean deposits. The pericratonic troughs are composed of Riphean and Vendian deposits. The eastern part of the Pripyat-Dnieper-Donetsk aulacogen was formed in the Riphean, but as a separate structure it was formed in the Devonian. Carboniferous and Permian deposits in its eastern part (Donetsk coal basin) are crumpled into folds. The rocks that fill the syneclises range in age from the Vendian to the Cenozoic and form the upper stage of the structures of the Russian Plate. The largest snneclise, the Moscow one, separates the protrusion of the basement of the Baltic Shield in the north from the Voronezh and Volga-Ural anteclises in the south and southeast. In its axial part, Triassic and Jurassic rocks are developed, on the wings - Permian and Carboniferous. The foundation in its central part is submerged to a depth of 3-4 km. The horizontal position of the cover on the wings is complicated by flexures. The deepest is the Caspian depression (on the southeast platform), the thickness of its sedimentary cover exceeds 20 km, the structure of the basement and lower horizons of the cover is unknown; According to geophysical data, the basement rocks in the center of the depression are characterized by an increased density close to that of basalt, and the structure of the cover is complicated by numerous domes of Permian salt. Vendian and Cambrian deposits are developed in the Moscow and Baltic syneclises and in pericratonic troughs (Transnistria). They are represented by clays with sandstones, in some places - tuffs. Ordovician and Silurian deposits occur on the western platform (clay shales with graptolites and limestones). The Ordovician includes oil shales - kukersites. Devonian deposits (argillaceous-carbonate, gypsum-bearing and saline) are developed everywhere on the Russian Plate; near faults, volcanic tuffs and diabases are known in them; bituminous limestones and clays are characteristic of the east of the platform. Carboniferous deposits are mainly represented by limestones and dolomites. A coal-bearing suite is associated with the Lower Carboniferous. In the Donets Basin, carbon forms a powerful (up to 18 km)
a series of sandstones, limestones, clays alternating with coal seams. Permian and Triassic deposits are common in syneclises (detrital rocks, dolomites, gypsum). Large reserves of rock salt are associated with the Lower Permian deposits. The Jurassic and Lower Cretaceous deposits in the central regions of the platform are represented by characteristic dark clays and glauconite sands with phosphorites. In the section of the widespread Upper Cretaceous deposits of the southern regions, marls and writing chalk are developed; in the north there are many clay-siliceous rocks. Marine sandy-argillaceous Cenozoic deposits are found in the southern part of the Russian Plate. The Siberian platform has an ancient, predominantly Archean basement, whose highly metamorphosed rocks (gneisses, schists, marbles, quartzites) are exposed within two basement projections (the Anabar massif and the Aldan shield). Among the Archean rocks, there are the Lower Archean (Iengra series, etc.), which make up several large massifs, and the younger ones, the Upper Archean, framing the ancient massifs (Timpton, Dzheltulinskaya series, etc.); on the Aldan shield and the Stanovoy uplift, the basement rocks are intruded by Precambrian, Paleozoic, and Mesozoic intrusions of granites and syenites. The Lower Archean complexes form dome-shaped folded structures, the Upper Archean - large systems of linear folds northwest. prostrations. Under the sedimentary cover within the Central Siberian Plateau, according to aeromagnetic survey data, submerged ancient massifs (Tunguska, Tyungsky) are established, which are framed by Upper Archean fold systems. Several platform troughs and uplifts are located in the cover area. The northwestern part of the platform is occupied by the Paleozoic Tunguska syneclise. In the east is the Mesozoic Vilyui syneclise, which opens into the deep Upper Jurassic-Cretaceous trough near Verkhoyansk, which separates the Siberian platform from the Verkhoyansk-Chukotka region of Mesozoic folding. The Mesozoic Khatanga and Leno-Anabar depressions stretch along the northern edge of the platform. A relatively uplifted block between these troughs forms the complex Anabar anteclise with outcrops of Proterozoic and Cambrian deposits. To the south of the platform, along the upper reaches of the river. Lena, an elongated shallow Angara-Lena trough extends, filled with Cambrian (with a thickness of rock salt), Ordovician and Silurian deposits. The southeastern edge of the trough is characterized by a system of ridge-like folds and faults; in the north it is separated from the Tunguska depression by the Katanga uplift. Near the southern border of the platform, a series of depressions with coal-bearing Jurassic deposits stretches: Kanskaya and Irkutskaya - along the northern spurs of the Eastern Sayan; Chulmanskaya, Tokkinskaya, and others - in the south of the Aldan shield. The platform cover includes Upper Proterozoic, Paleozoic, Mesozoic, and Cenozoic deposits. Thick strata of sandstones and algal limestones stand out in the composition of the Upper Proterozoic deposits. Cambrian deposits are widespread, absent only on shields. Ordovician and Silurian deposits are known in the western and central parts. Devonian and Lower Carboniferous - marine carbonate-terrigenous strata in the north and east, continental - in the south. In the basin of the river. Vilyui, they contain basic tuffs and lavas. Continental coal-bearing deposits of the Middle and Upper Carboniferous, Permian, as well as thick tuffaceous and lava series of the Triassic (Siberian traps) fill the Tunguska syneclise. Numerous trap intrusions are developed along its margins, on the slopes of the Anabar anteclise and in the southern areas of the platform, forming linear zones along faults that cut the basement and cover deposits. In addition to Upper Paleozoic trap intrusions and explosion pipes with kimberlites corresponding in age, similar Devonian and Jurassic igneous bodies are known. The Jurassic-Cretaceous Vilyui syneclise overlies the Paleozoic aulacogenes. Mesozoic deposits are represented by clastic rocks interbedded with brown coal and limestone (in the north). The Siberian platform, in contrast to the East European one, at the end of the Proterozoic and the beginning of the Paleozoic was an area of general subsidence and almost universal accumulation of marine, which means. degree of carbonate deposits. In the second half of the Paleozoic, in the Mesozoic and Cenozoic, it was relatively uplifted and mainly continental deposits accumulated on it. The Siberian platform is distinguished by a high degree of tectonic activity. It has many faults that cross the cover, and flexures; basic and alkaline magmatism is widely manifested. Folded geosynclinal belts. By the beginning of the Mesozoic, the Ural-Mongolian belt acquired the structure of a platform, the base of which is formed in different areas by folded systems of different ages: Baikal and Salair, Caledonian, Hercynian. The cover on the Baikalids and Salairids is formed by Paleozoic, Mesozoic, and Cenozoic deposits (on the Hercynides, only Mesozoic and Cenozoic). Paleozoic and Precambrian rocks come to the surface in basement projections (modern mountainous regions of the Urals, Tien Shan, Central and Eastern Kazakhstan, Altai, Sayan, Transbaikalia, Taimyr, etc.). The sedimentary cover covers the foundation within the Timan-Pechora, West Siberian, northern parts of the Turan and Bureya plates. The structures of the Baikal folding zone form an arc around the Siberian platform from the northwest. and S.-W., and come to the surface in Northern Taimyr, in the Yenisei Ridge, Eastern Sayan and in the Baikal region. Under the cover, the eastern margins of the West Siberian Plate, the Baikal structures extend along the left bank of the river. Yenisei. The Baikal region also includes the Bureinsky massif in the Amur, Zeya, and Bureya basins, partially covered by a sedimentary cover, as well as the area extended along the northeastern edge of the East European Platform (Timan Ridge, basement of the Pechora syneclise). In the structure of the regions of Baikal folding, the main role is played by thick Precambrian, especially Upper Proterozoic strata, folded into complex linear folds. They are represented by various types of sedimentary and sedimentary-volcanic geosynclinal formations. Upper Riphean, in places Vendian, clastic accumulations belong to molasses. Large massifs of granitoids of the Late Riphean - Vendian are widespread, but there are also younger alkaline intrusions (Devonian, Jurassic - Cretaceous). The Baikalides of the Eastern Sayan are adjacent to the west and east by structures of Early Caledonian or Salair folding, in whose structure thick marine and volcanic geosynclinal sequences of the Upper Proterozoic and Lower and Middle Cambrian play the greatest role, forming linear folds. The Salairid molasse complex begins in the Upper Cambrian, which is represented by red clastic accumulations. The role of the Salair folding and intrusive granptoid magmatism is significant in areas previously classified as Baikal (Baikal-Vitim highland, etc.). The areas of Caledonian folding cover part of Altai and Tuva, as well as the Northern Tien Shan and Central Kazakhstan. In the structure of the Caledonides, Cambrian and Ordovician sedimentary and sedimentary-volcanogenic rocks are widely developed, crumpled into linear folds. Precambrian is exposed in the cores of anticlinorians, on the massifs. The Silurian and younger deposits are usually represented by molasses and terrestrial volcanic rocks. In some places (Northern Tien Shan), the Caledonian structures are melted through by huge massifs of Lower Paleozoic (Ordovician) granitoids. The areas of the Baikal, Salair and Caledonian foldings are characterized by large intermontane depressions (Minusinsk, Rybinsk, Tuva, Dzhezkazgan, Teniz), filled with marine and continental, often molasse formations of the Devonian, Carboniferous and Permian. The basins are superimposed structures, but some (Tuva) follow the largest deep faults. The Hercynian folded areas include the Urals with the Cis-Ural foredeep, Gissar-Alai and part of the Tien Shan (Turkestan, Zeravshan, Alai, Gissar, Kokshaltau ridges), the Balkhash part of Central Kazakhstan, the Zaisan lake area, Rudny Altai and a narrow strip of eastern Transbaikalia, squeezed between the edge of the Siberian platform and the Bureya massif (Mongol-Okhotsk folded system). Hercynian folded structures are formed mainly by marine geosynclinal sedimentary and volcanogenic formations of the Lower Paleozoic, Devonian and Lower Carboniferous, collected in linear folds and often forming extensive tectonic covers. Precambrian metamorphic rocks within them come to the surface in the cores of anticlinoria. In separate intermountain depressions, they are overlain by continental molasses of the Upper Carboniferous and Permian. Sedimentary and volcanogenic rocks in the Hercynian regions are intruded by large granite massifs (Upper Carboniferous - Permian). Late Paleozoic (Hercynian) intrusions are also developed in areas of earlier folding epochs. Within the vast area of plates of the Ural-Mongolian belt, the basement is composed of the same folded systems as in the mountainous areas, but they are covered by a sedimentary cover. The basement contains separate Late Proterozoic (Baikal) massifs, which are bordered by younger Caledonian and Hercynian systems of structures. The rocks of the Jurassic, Cretaceous, Paleogene, Neogene and Anthropogenic, represented by marine and continental sedimentary rocks, play the main role in the structure of the plate cover. Continental, volcanogenic and coal-bearing deposits of the Triassic - lower Jurassic are made by separate grabens (Chelyabinsk and others). The complete section of the cover on the West Siberian Plate is represented below by continental coal-bearing deposits (Lower and Middle Jurassic), marine clay-sandstone strata of the Upper Jurassic - lower Cretaceous, continental strata of the Lower Cretaceous; marine clay-siliceous strata of the Upper Cretaceous - Eocene, marine clays of the Oligocene. Neogene and Anthropogenic deposits are usually continental. The Mesozoic-Cenozoic cover lies almost horizontally, forming separate arches and troughs; in some places flexures and faults are noted (see West Siberian oil and gas basin). Within the Ural-Mongolian belt, Neogene processes of epiplatform orogeny appeared, due to which the basement is often bent and split into separate blocks raised to different heights. These processes were most intensive in Gissar-Alai, Tien Shan, Altai, Sayan, Cisbaikalia and Transbaikalia. The Mediterranean belt is located to the southwest. and south of the East European platform. Along the Gissar-Mangyshlak deep fault, its structures are in contact with the structures of the Ural-Mongolian belt. The Mediterranean belt on the territory of the USSR includes the outer and inner zones. Outer zone (Scythian plate, South part Turan plate, Tajik depression and Northern Pamir) is a young platform. Within its limits, the Mesozoic and Cenozoic form a gently dipping platform cover on a folded, metamorphosed, and intrusion-cut Paleozoic and Precambrian basement. The Tajik depression and the Northern Pamirs in the Neogene - Anthropogen were covered by orogeny, as a result of which the Mesozoic and Cenozoic deposits of the platform cover were crumpled into folds here. The Scythian plate, which includes the plain territories of the Crimea and Ciscaucasia, has a basement, which includes blocks of Upper Proterozoic rocks (fragments of Baikal structures), soldered together by a folded geosynclinal Paleozoic. The Baikal massifs have a cover of gently dipping Paleozoic deposits intruded by Late Paleozoic intrusions. The platform cover ubiquitously includes Cretaceous to Anthropogenic deposits. The lower horizons of the cover (Triassic - Jurassic) are not ubiquitous - they often occur in grabens. In some places they are dislocated, broken through by intrusions (Kanevsko-Berezansky folds of the North Caucasus, Tarkhankutsky folds of the Crimea). In the structure of the cover, clay-sand strata (Lower Cretaceous, Paleogene) and marl-Cretaceous strata (Upper Cretaceous) are developed. They make up a number of depressions and projections, on which the largest are the Stavropol arch, the Simferopol ledge, the Kuma and Azov depressions. The depth of the sole of the cover on the uplifts 500 m, in deflections up to 3000-4000 m. The southern part of the Turan Plate has a basement consisting of a number of Precambrian massifs (Central Karakum, Kara-Bogaz, North Afghan, etc.), overlain by a rock cover (Carboniferous, Permian, and Triassic), which is cut through by Late Paleozoic intrusions. The massifs are separated by Paleozoic fold systems (Tuarkyr, Mangyshlak, Nuratau). Large graben-like basement depressions are filled with dislocated marine terrigenous and volcanogenic Triassic deposits (Mangyshlak, Tuarkyr, Karabil). The cover of the plate as a whole is formed by a series of deposits from the Jurassic to the Anthropogenic. The thickest cover is developed in the southeast, in the Murghab and Amudarya depressions. The central part of the plate is occupied by a large uplift - the Karakum arch; to the west are elevated zones - the Tuarkyr meganticline and the Kara-Bogaz arch. Along the northern border, from the Caspian to the Aral Sea, the Mangyshlak system of uplifts stretches. The folded structures observed in the cover are due to faults in the basement. The inner zone of the Mediterranean belt (Carpathians, Mountain Crimea, Caucasus, Kopetdag, Middle and Southern Pamirs) is distinguished by the fact that the Mesozoic and Cenozoic deposits in it are represented by the geosynclinal type of formations. The separation of the outer and inner zones began from the late Triassic - Jurassic. The Ukrainian Carpathians form part of the Carpatho-Balkan arc. On the territory of the USSR, it is formed mainly by the Cretaceous and Paleogene flysch series. A subordinate role is played by the protrusions of the base of geosynclinal complexes (Lower Mesozoic, Paleozoic, and Precambrian). The Carpathians are characterized by a complex folded structure with numerous thrusts. The Eastern Carpathians are separated from the East European Platform by the deep Carpathian marginal foredeep, on which they are thrust. Mountain Crimea is a separate anticlinal structure, the southern wing of which is submerged under the Black Sea level. In the core of the Crimean anticline uplift, sandy-argillaceous, carbonate and volcanogenic deposits of the geosynclinal type (Upper Triassic, Jurassic, partly Lower Cretaceous) are exposed. The northern flank is formed by flat-lying Cretaceous-Paleogene platform-type rocks. The main manifestations of intrusive and effusive magmatism belong to the Middle Jurassic (diorites, granodiorites, gabbro, spilites, keratophyres, etc.). The complex folded structure of the meganticlinorium of the Greater Caucasus is formed by Paleozoic, Mesozoic, and Paleogene geosynclinal complexes of different composition, disturbed by numerous faults and broken by intrusions of different ages. Metamorphic rocks of the Upper Precambrian are exposed in the cores of the most uplifted structures. Precambrian and Paleozoic rocks compose the pre-Alpine base, Mesozoic and Paleogene - the Alpine geosynclinal complex; its thickness reaches maximum values along the southern slope of the Greater Caucasus. The structure of the meganticlinorium is asymmetrical. Sandy-argillaceous and carbonate rocks of the Jurassic, Cretaceous, Paleogene on its northern flank lie predominantly gently, monoclinally, on the southern flank they lie steeply, crumpled into folds, complicated by overthrusts. The Upper Jurassic-Paleogene deposits in the west and east of the southern flank are represented by flysch series. To the north of the Greater Caucasus are the Indolo-Kuban and Terek-Caspian marginal troughs of the Neogene age, and to the south is the Riono-Kura zone of intermountain depressions, which separates the meganticlinoria of the Greater and Lesser Caucasus. In the geological structure of the Lesser Caucasus, the main role belongs to sedimentary-volcanic formations of the Jurassic, Cretaceous and Paleogene ages (including ophiolite complexes). The structure of the Lesser Caucasus is a bloc. Large areas are overlain by thick gently sloping Neogene and Anthropogenic lava sequences. The Kopetdag is a relatively simple folded structure formed on the surface by carbonate-argillaceous complexes of the Cretaceous and Paleogene ages with folds overturned to the north towards the Pre-Kopetdag trough, which separates the Kopetdag from the Turan plate. K S.-Z. from the Kopetdag, on the continuation of the Kopetdag marginal deep fault, there is the Big Balkhan meganticline with outcrops in the core of the geosynclinal Jurassic rock complex. The wings of the meganticline are formed by Cretaceous and Paleogene deposits of the platform type. Within the limits of the Central Pamirs, sedimentary geosynclinal complexes of the Paleozoic and Mesozoic ages, collected in complex folds, complicated by thrusts, are developed, and in the Southern Pamirs, Precambrian metamorphic rocks and large massifs of granites of various ages are developed. The Pacific Belt covers the territory east of the Siberian Platform and the Bureya Massif. Its eastern boundary is the system of the Kuril-Kamchatka and Aleutian deep-sea trenches. The general orientation of the belt is close to meridional. The Pacific belt includes the Mesozoic folded regions (Verkhoyansk-Chukotka and Sikhote-Alin) and the structures of the modern geosynclinal region - geoanticlinal uplifts (Kamchatka, Sakhalin, Kuril Islands), as well as the depressions of the marginal seas (Japan, Okhotsk and Bering). The Verkhoyansk-Chukotka folded region occupies the northeast. THE USSR. Within its boundaries, Permian, Triassic, and Jurassic deposits are most widely developed (on the surface), forming several anticlinal and synclinal zones. The geosynclinal complex (cf. Carboniferous - Upper Jurassic) is formed by a powerful series of marine clay-sandstone deposits, among which volcanic rocks occupy a subordinate place. The largest put. The structures of the region are the Verkhoyansk meganticlinorium, the Sette-Dabana anticlinorium, Anyui, Chukotsky, Tas-Khayakhtakhsky, Momsky, Polousnensky, etc. last three an important role belongs to the mesozoid base complex. The most important negative structure is the Yano-Indigirskaya (Yano-Kolyma) synclinor zone, composed of Triassic-Jurassic deposits on the surface. The molasse orogenic complex (Upper Jurassic - lower Cretaceous), largely coal-bearing, fills the Verkhoyansk marginal trough, as well as several large internal inherited troughs and intermountain depressions (Oldzhoyskaya, Momsko-Zyryanovskaya). An important role in the structure of the region belongs to the protrusions of the base, sometimes covered by a cover of Paleozoic and Mesozoic deposits (Kolyma, Okhotsk, Omolon, Chukotka and other massifs). Late Jurassic - Early Cretaceous and Late Cretaceous - Paleogene granitoids form batholiths along the zones of deep faults. Upper Cretaceous - Cenozoic (post-geosinklinal) complex is limitedly developed; composed mainly of continental coal-bearing and volcanic series. In the lower reaches of the river Yana, Indigirka, Kolyma, Cenozoic rocks cover geosynclinal and orogenic structures with a cloak, composing a platform cover lining the shelves of the Laptev and East Siberian seas. The Sikhote-Alin folded area differs from the Verkhoyansk-Chukotka one in the wide distribution of volcanic-siliceous strata of the Middle and Upper Paleozoic and Mesozoic, as well as in the later completion of geosynclinal sedimentation (2nd half of the Late Cretaceous). At the end of the Cretaceous and in the Cenozoic, the Sikhote-Alin region underwent orogeny with the accumulation of clastic and volcanic rocks. The Mesozoic structures are separated from the modern geosynclinal region located to the east by a system of deep faults that controlled volcanic eruptions and intrusions during the Late Cretaceous and Cenozoic. The position of the faults corresponds to the Okhotsk-Chukotka and East Sikhote-Alin marginal volcanic belts - zones of development of the Cretaceous and Paleogene effusives. The modern geosynclinal region includes the Koryak Highlands, the Kamchatka Peninsula, the Kuril and Commander Islands, about. Sakhalin and the bottom of the adjacent seas - Bering, Okhotsk, Japan. The eastern boundary of the region is the deep-water Kuril-Kamchatka trench, which separates the modern geosynclinal region from the Pacific Ocean depression. The location of the trench corresponds to the outcrop of a zone of deep-focus earthquakes (the Zavaritsky-Benioff zone), associated with the largest deep faults in the earth's crust and upper mantle. The ridges of the islands are considered as positive. geosynclinal structures (geoanticlines), deep-water basins (Bering Sea, South Kuril) and deep-water trenches (Kuril-Kamchatsky, Aleutian) are negative structures (geosynclinal troughs), in the section of the earth's crust of which there is no "granite" layer. Part of the bottom of the Sea of Okhotsk and the Sea of Japan is submerged rigid median massifs among linearly elongated geosynclinal troughs and geoanticlinal uplifts. Most of the modern geosyncline Far East is an area of sedimentation and is characterized by active seismicity and intense volcanism (volcanoes of Kamchatka and the Kuril Islands). The main role in the geological structure is played by thick sedimentary and volcanogenic-sedimentary complexes of the Cretaceous, Paleogene and Neogene ages, as well as Anthropogenic deposits collected in systems of folded structures. More ancient rocks are of Triassic - Jurassic age. Paleozoic and Mesozoic metamorphic complexes are developed in Kamchatka. On the Kuril Islands, the most ancient are Upper Cretaceous volcanics, sandy-argillaceous deposits. Cm. cards.
M. V. Muratov, V. M. Zeisler, E. S. Chernova, E. A. Uspenskaya.
We will consider geological formations in the order of the traditional geological presentation, first describing the lithological composition and the igneous rocks that cut through them, and then the tectonics. The age of rocks located in the Irkutsk region is very diverse - from the oldest Precambrian strata, with an absolute age of over 2 billion years, to Cenozoic and modern formations.
For convenience of consideration, the entire territory of the Irkutsk region is usually divided into a number of regions: 1) South-Western, Southern Baikal and Khamar-Daban; Western and Northwestern Baikal region; 3) Eastern Sayan and Sayan area; 4) Baikal-Patom Highlands.
A. Precambrian complexes
Archean and Early Proterozoic formations belong to the oldest Precambrian rock complexes in the territory of the Irkutsk region. Archean complexes within the region are distributed in the South-Eastern Sayan region in the basins of the Irkut, Kitoy, Belaya rivers, in the Southern and South-Western Baikal regions (the area of the Circum-Baikal railway), and the Proterozoic ones compose small areas in the Eastern Sayan, spurs of the Khamar-Dabansky, Primorsky , Baikal and Akitnan ranges, in the Olkhon region, on the Baikal-Patom highlands.
Southwestern and Southern Baikal region, Mt. Khamar-Daban. The oldest rocks within this region and the region as a whole are the Early Archean formations within the Sharyzhalgai outcrop of the platform basement, represented by three relatively monotonous highly metamorphosed strata: the Shumikhinskaya, Zhidoiskaya and Zoginskaya suites, combined by geologists into the Sharyzhalgai series.
The rocks of the Sharyzhalgai series of the early Archean are exposed along the shore of the lake between the sources of the river. Hangars in the east and the village. Kultuk in the west and traced further to the northwest in the Sayan region. The rocks of this series can be best studied along the southern coast of the oe. Baikal along the Circum-Baikal Railway, where for almost 80 km it is possible to trace the section of the most ancient granular complex. The series is overlain by deposits of the Upper Proterozoic Olkha Formation, and in some places by the Continental Jurassic (source of the Angara River). From the south and southwest, the distribution area of the rocks of the Sharyzhalgai series is limited by the zone of the Main Sayan Fault.
The Sharyzhalgay Group is dominated by rocks of the granulite facies of metamorphism formed at the highest pressures and temperatures. In the course of a drop in temperature and pressure, these granulites, for the most part, at a later time, were everywhere transformed into various migmatites, gneissic granites, and other rocks of grintoid appearance.
Granulites are preserved as relic sites in fields of migmatites in the form of two-pyroxene-hornblende, two-pyroxene-biotite, diopside-hornblende, hypersthene-hornblende-biotite crystalline schists and ultramafic rocks represented by pyroxenites and olivine pyroxenites.
Based on the predominance of dark-colored minerals, plagioclase gneisses are classified as hypersthene-biotite, garnet-biotite, garnet-hypersthene-biotite, two-pyroxene, etc.
Marbles play a very subordinate role. They are exposed in the area of Belaya Vyemka and the port of Baikal. Relics of dolomitic marble are observed here, which is the source for a variety of widespread products of its granitization - magnesian-skarn formation: calciphyres, pyroxene, spinel-pyroxene skarns and other rocks. Nepheline-bearing skarns, nepheline syenites, almost monomineral nepheline rocks, as well as rocks with red and blue spinel and phlogopite veins attract special attention here.
In areas of distribution of rocks of the granulite facies, there are specific Archean rocks - charnockites and enderbites, observed in the form of veins or bedded bodies, sometimes forming a complex network of veins and isolated segregations.
Late (Early Proterozoic) formations within the ledge include metamorphic rocks of the Slyudyanka series, represented mainly by marbles and calciphyres.
On the whole, the rocks of the Sharyzhalgai block are folded into steep or gently sloping dome-shaped, open folds of submeridional or northwestern strike, complicated by intense fine additional folding.
The northern slopes and the axial part of the ridge. Khamar-Daban in the southern Baikal region is composed of three Proterozoic series of metamorphic rocks: Slyudyanskaya, Khangarulskaya, and Khamardabanskaya.
The Slyudyanka series is most fully exposed and studied in detail along the Slyudyanka and Pokhabikha rivers in the Slyudyansky region. It is represented by rhythmically interbedded biotite, biotite-garnet-cordierite, biotite-diopside-hypersthene, biotite-pyroxene, often with hypersthene, crystalline schists, quartz-diopside rocks in the lower part of the section, and interbedded marbles with horn-exchange-pyroxene crystalline schists, biotite gneisses, quartz-diopside with apatite and wollastonite rocks in the upper. Power series 6300 m.
Deposits of phlogopite, lapis lazuli, wollastonite, diopside, and other rare and beautiful minerals (apatite, spinel, vesuvianite, scapolite) are associated with the Slyudyanka Series. In contrast to the Sheryzhalgai series, the strata of the Slyudyansky complex are distinguished by a large variety of rocks of crystalline schists, gneisses, marbles, specific types of metamorphic rocks (manganese phosphate-bearing, wollastonite).
The Khengarul Group in the lower part is composed mainly of diopside and calcite-diopside gneisses with interlayers of marbles and biotite gneisses with cordierite and hypersthene. The thickness of this part of the section varies from 100-180 to 1000-1500 m. In the upper part, garnet-biotite, biotite-garnet-cordierite, biotite-garnet-sillimanite, biotite-pyroxene, and locally strongly migmatized aluminous gneisses play the main role. Interlayers of marbles and igneous diopside schists and gondites appear in the uppermost part. The total thickness of the Hangzrul series is 3900 m.
Khemardaba, a certain series is distributed in Khamar-Daben in the south of the Slyudyansky region and is composed of extremely diverse metamorphic rocks that arose from clastic and carbonate-clastic primary sedimentary deposits of various initial composition. Most of the series is represented by gneisses: biotite, biotite-garnet, biotite-garnet-sillimanite, and in zones with a lower intensity of metamorphism - shales with biotite, garnet, cordierite, tremolite, passing into very weakly metamorphosed rocks - sandy, carbonaceous, micaceous -carbonate and other shales.
Eastern Sayan and Pri-Sayanye. Here, as well as in the previous region, the bulk of geological formations are composed of Precambrian rocks of the Archean Sharyzhalgai series, Early Proteroeoic rocks of the Derba series, Kamchadal (1000 m), Belorechenskaya (3000 m), Sublukskaya (2000-4000 m) and Sosnovoe Baitsa (700-1000 m) suite. The Derbinskaya series is analogous to the Slyudyanskaya series. The apparent thickness of the Archean rocks is estimated at many thousands of meters.
Proterozoic deposits were probably originally marine and oceanic sediments, as well as volcanic rocks deposited on Archean rocks, subsequently overlain by various platform mantle sedimentary rocks beginning with Vendian deposits. The oldest of the Proterozoic rocks are marbles and quartzites alternating with biotite-garnet and amphibole schists. The Subluk Formation is distributed in the near-platform part of the Sayan region and is composed of quartz porphyry, felsite, tuff, and conglomerates. These more ancient, conventionally Early Proteroic rocks are overlain by the Sosnovy Baits Formation, which consists of rocks of the jaspilite formation: amphibolites, biotite and garnet-biotite-staurolite schists with characteristic horizons of ferruginous quartzites and hemetite-magnetite rocks.
Western Baikal region. For the most ancient complexes (Sharyzhalgais-
whom, Olkhonsky) of this region is very characteristic of
- new variety and high degree metamorphism. At the same time, highly metamorphosed rocks are confined to the border of the Siberian Platform and the folded area (see the map "Tectonics" in the school atlas (Irkutsk region ..., 2009). As you move towards the Baikal folded area, the degree of metamorphism changes from high granulite to low greenschist.
On the territory of the Priolkhonsky Plateau itself and on the slopes of the Primorsky Range adjacent to it from the north-west, formations of four complexes of different ages and different in genesis are represented:
a) Olkhonskaya series - crystalline schists, marbles, metamorphosed mafic and ultrabasic rocks, plagiomigmatites, which are strongly altered in places by low-temperature processes;
b) Anginskaya series of early Proterozoic - amphibolites formed as a result of metamorphism after ancient basalt and ultrabasic volcanic rocks, calcite and dolomitic marbles, schists of calc-silicate composition;
c) the Tsagan-Zaba series of the late Proterozoic - weakly metamorphosed andesitic and basaltic porphyrites, lava and tuff breccias, andesite-basalt tuffs;
d) the rocks of the Primorsky deep fault zone are represented by Early Proterozoic granites, dike pre-Riphean mafic rocks, metamorphic rocks of the Precambrian series and analogues of all these rocks, altered as a result of repeated manifestations of dynamothermal metamorphism, alkaline and silicic metasomatism.
The most remarkable structure of this region is the Early Proterozoic Pribaikalsky volcanic belt, which at one time stretched along the southeastern border of the Siberian continent for a distance of almost 1200 km. The belt is composed of predominantly felsic volcanics with a subordinate amount of mafic and intermediate rocks, lacustrine red-colored and marine shallow-water deposits (conglomerates, gravelstones, sandstones, siltstones, and tuffites) and granitic intrusions solidified at shallow depths.
Baikapo-Patom Highlands. Within the region, the most important and interesting from the point of view of geology are the Mamskeya muscovite-bearing province and the Lena gold-bearing region, within which the rocks of the Upper Proterozoic Teptorginsky series developed from the Precambrian formations, formed in the platform stage from redeposited ancient weathering crusts. The series is composed of gray and pink quartzites, quartzite-sandstones and conglomerates, quartz-sericite-chlorite, ottrelite (chloritoid)-disthene schists, in places with lenses of hematite ores, in the middle part there are horizons of metamorphosed basic effluents and tuffs. The thickness of the series reaches 1800 m. The presence of metamorphosed analogs of bauxites (high-alumina shales), monomineral quartzites in the series indicates the existence of a series of continental breaks in the history of formation, and the presence of wave-cut signs, drying cracks, flysch hieroglyphs, etc., indicates their formation in shallow-water conditions of the passive margin that existed here at that time of the Angara (Siberian) continent.
Vendian deposits are also distinguished here, represented by carbonaceous shales, limestones, siltstones, carbonate breccias in the lower part and quartz and carbonate sandstones in the upper part.
B. Geological formations of the cover of the Siberian Platform
The layered complexes of the sedimentary cover of the Siberian Platform in the territory of the Irkutsk region are best studied within the Irkutsk amphitheater in connection with the study of their oil and gas potential, salt accumulation, and coal formation.
Riphean. Riphean deposits on the Siberian platform mark the beginning of the formation of its cover. In the south of the Siberian Platform and in the Western Baikal region, the so-called three-membered Baikal complex or series of Riphean age is widespread, which overlies older deposits with a sharp unconformity, with basal conglomerates at the base and consists of three formations: the Golousteneka, Uluntui, and Kachergat suites. The Goloustenskaya Formation is composed of arkose sandstones and quartzites alternating with limestones and dolomites. The Uluntui Formation is represented by limestones with interlayers of argillaceous and calcareous shales and siltstones (phosphorite-bearing). Sediments of the Kachergat Formation are gray, red and green sandstones, alternating with siltstones, phyllites and shales. The age of the formations is accepted by most geologists as Middle-Early Riphean. The total thickness of the complex varies from 1000 m in the north to 3500 m in the south.
In the south of the Irkutsk region, the rocks of the complex are overlain by the Vendian Ushakov Formation, which consists exclusively of poorly sorted sandy material with an abundance of mica flakes. In the south of the region, the formation overlies the Upper Riphean Olkha Formation and is overlain by quartzite-like sandstones of the Motskaya Formation of Vendian-Cambrian age.
The rock composition of the Ushakovskaya Formation: quartz siltstones with mica flakes on bedding surfaces, brownish-gray to black mudstones, gravelstones and small-pebble conglomerates of quartz pebbles, less often crystalline rocks and mudstones of the Olkha Formation; sandstones are greenish-gray and reddish-brown, polymictic, rhae-grained, coarse-grained and gravelite, hard, massive and indistinctly bedded, locally bedded with inclusions of green and brown-red mudstones and lenses of glauconite sand.
Vendian-Cambrian and Cambrian. These are deposits of the Vendian-Cambrian Motskaya and Cambrian formations: Usolskaya, Belskaya, Bulaiskaya and Angara.
The Motskei Formation is composed mainly of sandy layers interspersed with siltstones, mudstones, carbonate rocks with interlayers of marls and anhydrites. The marine nature of the deposits indicates to us that at the turn of the Vendian and Cambrian times in the interval 570-530 million years ago, a shallow inland sea existed in the south of the Irkutsk region, and the earth's crust in this place rather slowly sank (sag), since the thickness precipitation grew, but the depth of the sea did not increase
lass. The sea was surrounded by mountains that supplied detrital material (wood, gravel, clay, loam, etc.).
With the beginning of the Cambrian period (535 million years ago), tectonic movements slowed down significantly - the mountains stopped growing, the subsidence stopped. The so-called period of stable standing of the platform in a hot climate began, i.e., the Siberian continent at that time was somewhere in the equatorial latitudes. Sea water flowed from the ocean to the platform, like a hot frying pan. Here it evaporated, leaving layers of rock salt, limestone, dolomite, gypsum and anhydrite (Usolskaya, Velskaya, Bulaiskaya and Angara formations of the Cambrian) with a total thickness of 1300-1800 m. 509 Ma.
The Middle Cambrian in the Angara-Lena trough is distinguished under the name of the Litvintsevskaya suite, which consists of two horizons - the Amga and the May. The boundary of the middle and upper Cambrian is established by the change of trilobite assemblages. In the basin of the upper reaches of the river. Lena, the Litvintsevskaya suite is compared with the Icherskaya suite, in the lower reaches of the river. Angara - with the Zedeevsky suite, in the Lena-Kireng interfluve - with the Munok suite.
During the Middle Cambrian, in all likelihood, the connection between the continental seas and the ocean was broken. The seas begin to dry up, and the carbonates remaining on the surface are weathered and turn into flour (dolomite flour), that is, desert conditions are established in the south of the Irkutsk region.
In the central part of the region, the deposits of the Middle Cambrian are represented by the Verkholenskaya suite, the outcrops of which occupy vast expanses. The bottom, lowest, part of these deposits is composed of clay-marl breccias with fragments of the underlying dolomites of the Angara Formation, which are often laterally replaced by dolomite flour. Higher up are variegated gypsum mudstones, marly dolomites with interbeds of siltstones and sandstones, followed by quartz and carbonate sandstones with interlayers of marls and siltstones, and at the very top there are mainly sandstones. The color of the rocks is predominantly reddish, spotty. The thickness of the Middle Cambrian rocks ranges from 350 to 550 m.
The relationship of the Lower Cambrian and Middle Cambrian rocks can be observed along the banks of large rivers with indented sides (Angara, Belaya, Lena, China, etc.), where the upper parts of the watersheds are composed of clastic (terrigenous) strata of the Middle Cambrian (Verkholenskaya suite), and all the hollows are carbonate rocks. Early Cambrian (Angara Formation).
The deposits of the Late Cambrian are represented by the Ilikta Formation, which consists of red sandstones interbedded with limestones in the lower part. The thickness of the rocks does not exceed hundreds of meters.
Ordovia. Deposits of this period in the territory of the Irkutsk region are quite widespread. The lower part of the system (490-475 Ma) in the northern regions of the region is composed of limestones, dolomites, sandstones, siltstones and partially conglomerates in the lower part, sandstones, limestones, dolomites, siltstones, mudstones in the upper part. closer to
to the south, the upper part of the Lower Ordovician is supplemented by sandstone deposits, gravelstones, siltstones, and again conglomerates. In the river basin Angara in the Irkutsk amphitheater, the lower part of this section is represented by carbonate rocks, and the upper part is composed (from bottom to top) of variegated sandstones, siltstones and mudstones with interlayers of conglomerates, further - mainly gray and variegated sandstones and conglomerates. The subordinate place here is occupied by siltstones and mudstones. Thus, when following from the river basin. Hangars in the river basin. Lena (from south to north) in the sections of the Ordovician there is a decrease in the amount of terrigenous rocks and, accordingly, an increase in carbonate.
The Middle-Upper Ordovician sections are composed of siltstones, mudstones, sandstones, phosphorites, gravelstones, less often conglomerates, limestones, marls, gypsums.
The rocks of the Middle Ordovician (Krivolutsk Stage) are associated with an increased phosphorite content of rocks. The source of the phosphate substance was probably the pre-Krivolutsk weathering crusts, which contained phosphorus in a dispersed form. Marine transgression, which replaced the continental regime, led to resuspension and redistribution of material with the formation of phosphorite nodules, nodules, and nodules in the basal horizons. Phosphorite horizons are almost universally associated with iron ore manifestations in the form of thin lenticular beds of oolitic hematite ores or mineralized siltstones. -
The thickness of the Ordovician deposits varies considerably throughout the region. Within the limits of the Baikal-Lena foredeep it is 1S00 m, in the Prisayansky - 1100-1400 m, and in the central part of the region it is only 600 m.
Silurian and Devonian. Deposits of this age within the territory of the Irkutsk region are very limited in distribution, their thickness is about 100 m. In the Irkutsk amphitheater, this age period includes strata of red-colored rocks occurring above the rocks of the Upper Ordovician; they cannot be divided into departments and tiers. Erosions are observed at the base and at the top of the Silurian sequence. The lower part of the section of the Silurian system in the Angara-Ilimsk region is composed of gray quartz sandstones, variegated mudstones and siltstones with interlayers of greenish-gray dolomites, the upper part is represented by red-colored mudstones and siltstones with interlayers of greenish-gray sandstones and gypsum lenses. The layers rest on the underlying Ordovician rocks without apparent unconformity. The Silurian deposits are comparatively poor in minerals. On the Siberian platform, only gypsum deposits are confined to the Silurian.
A complete section of Devonian deposits with a thickness of about 400 m is found only within the Sayano-Altai folded region, where they are represented by sedimentary-volcanogenic formations.
Carboniferous and Permian systems. The Upper Pleozoic coal-bearing deposits are found in the basins of the Angara, Katanga, Chuni, Taseeva and Nizhnyaya Tunguska rivers and are subdivided into the Carboniferous and Permian systems. The thickness of each system within the Tunguska syneclise is just over 100 m.
The coal content of the Carboniferous and Permian deposits is very uneven both in section and area. When moving from the northern deposits to the southern and eastern ones, the coal content of the Carboniferous and Permian rocks noticeably decreases. The coals are brown to anthracite. The most highly metamorphosed coals are found near trap intrusions. The rocks of the Carboniferous system, which are widespread on the southeastern margin of the Kensko-Teseevskaya depression, previously attributed to the Middle Devonian, were formed in an arid climatic environment, which caused the variegation of the deposits.
Triassic. The rocks of this age are mainly developed within the Tunguska basin and are represented by volcanic-sedimentary formations. In the southern part of the Tunguska basin on the territory of the region, Triassic deposits are united according to lithological features into the Tutonchan and Korvunchan suites. The rocks of the first of the formations are widespread in the basins of the Nizhnyaya Tunguska, Katanga, and Chuna rivers. They are represented by tuffites, tuff sandstones, tuff siltstones, and ash pisolite tuffs. The maximum thickness of the suite is up to 200 m. The age of the rocks is attributed to the late Permian - early Triassic.
The Korvunchanskaya Formation occurs conformably on the Tutonchanskaya Formation or, with erosion, on various horizons of the Upper Paleozoic sequence. It is divided into two subformations. The lower subformation is a derivative of explosive volcanic activity; it accumulated in the conditions of a dissected relief inherited from the regional Tutonchan erosion. Two facies are distinguished in its composition: a facies of overburden sedimentary-pyroclastic rocks and a facies of near-vent pyroclastic rocks.
The facies of the overlying sedimentary-pyroclastic rocks is represented mainly by fine clastic, gravel and ash tuffs. The subordinate place is occupied by large pizolitic tuffs and tuffites. These formations were formed far from the center of the ejection of explosive material, in low landforms. Their thickness varies from 50 to 200 m.
The facies near the vent pyroclastic rocks is composed of xenotuffs, agglomerate tuff breccias, and lapilli tuffs. They are widely distributed within the tuff field and form bizarre outcrops with pillar-like and tower-like weathering forms. The detrital part of pyroclasts is represented by volcanic bombs, lapilli, explosive fragments of basic magma, and fragments of sedimentary rocks.
The upper subformation, like the Tutonchanskaya suite, is composed mainly of tuffaceous-sedimentary rocks, which are distributed locally within the Irkutsk region, mainly along the watershed parts of the rivers. The apparent thickness of the subformation does not exceed 50 m. The total thickness of the Korauchanskaya suite is at least 300 m.
Yura. Jurassic deposits are most widespread in the south of the region. Here, with a long break and structural unconformity, they lie on the Cambrian rocks, filling an asymmetric piedmont trough, elongated from the northwest to the southeast along the Sayan domed uplift that rose in the Jurassic. The entire section here is represented by continental, mainly terrigenous deposits. According to lithology and coal saturation of rocks in the section, three formations are distinguished (from bottom to top): Cheremkhovskaya, Prisayanskaya and Kudinskaya. In addition, the pre-Jurassic weathering crust, represented by siliceous-kaolin, sandy-siliceous breccias and kaolin clays of various colors - white, blue, red, etc., has been preserved in some places in the depressions. Its thickness does not exceed 20-40 m.
The section of Jurassic deposits in the south of the region begins with a thick layer of conglomerates. The thickness of this layer directly below Irkutsk reaches 110 m, its depth is 390-510 m. It consists of conglomerates with interlayers of coarse-grained sand. Pebbles of volcanic rocks predominate - porphyrites and porphyries. Less common are flint and quartz pebbles and very rarely granites, crystalline schists and other rocks. The density of conglomerates varies from loose to very dense. The cement of loose conglomerates is sandy-argillaceous, while that of dense conglomerates is clayey-carbonate and clayey-carbonate-sandy. Toward Baikal, the thickness of the conglomerate horizon increases significantly.
In other places of the region, the Jurassic rocks are distinguished by a somewhat finer-grained set of rocks. For example, the lower parts of the Cheremkhovskaya Formation are generally characterized by coarse-grained and quartz sandstones, light-colored rocks, and sometimes strong buffing of the rocks. Previously, this part of the section was identified as the Zalara Formation and given the significance of the basal one, i.e., the beginning of the section of the Jurassic deposits. The thickness of this part of the suite ranges from 0 to 150 m. The rest of the Cheremkhovo suite is composed of sandstones with horizons and lenses of siltstones, mudstones, and thick coal seams. The thickness of the suite is up to 200-350 m. A very interesting section of the suite can be studied along the river. Angara below the mouth of the river. Balei. Insects of stoneflies, mayflies, dragonflies and other forms of the Early Jurassic age are found here. The Prisoyanskaya suite, according to or with a hidden disagreement, replaces the Cheremkhovo one and is exposed in the vicinity of the city of Irkutsk. The suite is represented by a sequence of massive sandstones, uneven-grained, often cross-bedded with thin interlayers of siltstones and coals. Its thickness is 250-350 m. According to the finds of organic remains in the sediments of the formation (Ferganoconch bivalves, phyllopods, flora remains - ferns, Ginkgo sphenobaiera, etc.), its age is determined as Middle Jurassic.
The Cuban suite is common in the valley of the river. Kuda and in the area of Irkutsk. The lower part of the suite is represented by coarse clastic deposits, the upper part is tuffaceous-sandy. Ash tuffs are also found in the underlying rocks of the Jurassic, which indicates some volcanic activity at that time, presumably in the area of modern Baikal.
Judging by the characteristics of the rocks described above, the conditions of sedimentation in the Jurassic were varied. Coarse-clastic deposits (pebbles, gravelstones, coarse-grained cross-bedded sandstones) are characteristic of fluvial channel deposits. Sandy-siltstone and clayey rocks were formed in the setting of wide river floodplains and lakes. Bog facies favored coal formation.
The total thickness of the Jurassic deposits according to deep well data is 1100 m or more.
The most ancient sedimentary Cenozoic rock complexes (the time interval of their formation is 32-1.6 million years ago) (the Manzur, Bayandaev and Baisha suites of the Neogene and the Bulusa suite of the Paleogene) are represented by unique Paleogene-Neogene deposits that were formed along narrow private depressions Meso-Cenozoic age, the most famous of which are located within the Ust-Orda Buryat district. These sediments are represented by various clays, often high alumina, sandy loams, loams, sands, and brown coals. Occasionally, shell limestones and calcareous fine-grained tuffites are noted. Huge reserves of brick, refractory, drill clay and brown coal are concentrated in these deposits. The thickness of the sediments reaches 250-300 m. They almost everywhere overlap the Cretaceous-Paleogene leveling surface, which is the result of a long uplift or tectonic quiescence of the territory at that time.
Igneous rocks distributed on the territory of the region are diverse in composition, geological age and formation conditions (see the Geological map in the school atlas (Irkutsk region ..., 2009). Precambrian igneous rocks are represented by various granitoids that are exposed within the folded area and basement outcrops platforms to the surface (Sharyzhalgaysky, Biryusinsky and Charsky ledges).
In the Late Proterozoic time, diabases and gabbro-diabases of the Patom complex (the first manifestations of the trap formation on the Siberian Platform) were intruded into the lithified strata of the Riphean Patom Highlands, and fissure intrusions of granitoids of the Vitimkanskopo or Konkuderomakansky complexes penetrated along the zones of Proterozoic faults within the Precambrian rocks.
In the Ordovician-Silurian time, in the vast expanses of the territory of the Irkutsk region adjoining from the south and within the Patom highlands, collisional granitoids of the Angara-Vitim batholith (a real pluton) were formed, which melted vast areas (about 200 thousand km1) and is the largest granite massif the globe.
At the end of the Upper Paleozoic (Devonian-Carboniferous) in the Baikal region, in activated zones of Precambrian faults, alkaline intrusive magmatism manifested itself with the intrusion of nepheline syenites of the Tazheran complex.
Late Paleozoic and Early Meeozoic igneous rocks are represented by Siberian traps of gabbro-dolerites, dolerites, diabases and their numerous varieties of the Angara, Katangsky, Zharovsky and other complexes, small intrusions and dikes of alkaline and subalkaline granitoids in the Baikal region.
Cenozoic igneous rocks are represented by basalts in the Sayan region and Khemar-Daban. Their manifestation is associated with the formation of the Baikal system of depressions and in time refers to the Pliocene - the beginning of the Pleistocene.
Tectonically, the territory of the Irkutsk region covers two geotectonic regions - the southern wedge-shaped ledge of the ancient Siberian platform, known as the Irkutsk amphitheater, and the younger belt of post-platform mountain building (epiplatform orogeny) of the Neogene-Quaternary age, which arose on the site of the Paleozoic platform (Fig. 8 and see Tectonic map in the school atlas (Irkutsk region..., 2009).
The area of epiplatform orogeny consists of ancient Precambrian blocks - fragments of the basement of the Siberian platform (Biryusa, Sharyzhalgay, Narekaya) and folded areas framing them, belonging both to the most ancient platform and newly formed ones.
The Paleozoic structure of the cover of the ancient platform in the territory of the Irkutsk region is complex. Here, areas of monoclinal slightly inclined occurrence of rocks, areas of horizontal occurrence, uplifts, depressions, foredeeps and zones of linear folds are distinguished.
According to the nature of the Jura deposits within the areas of its distribution, the following can be distinguished tectonic structures: 1) the Irkutsk basin and the Rybinsk depression - parts of the piedmont foredeep with a relatively high intensity of oscillatory movements during sedimentation and deformation of Jurassic rocks in the process of Late Mesozoic tectonic movements; 2) Kansky basin - a vast intracontinental basin with a calmer tectonic regime; 3) Angara-Vilyui superimposed trough - a complex depression consisting of a series of relatively shallow depressions and uplifts separating them, connecting the Kansk basin and the southwestern periphery of the Vilyui depression; 4) Vilyui depression - intra-platform trough.
During the epiplatform orogeny, the epipaleozoic platform within the area underwent block folding with the formation of domes, grabens, horsts, depressions, and numerous faults. At the beginning of this tectonic stage of movements, rift volcanism of the basic composition was observed, which manifested itself especially intensively in the Sayan region and Khamar-Daban. The arch formation contributed to the exposure of the Archean rocks of the basement of the ancient platform (Sharyzhalgay, Biryusinsky and Charsky ledges) to the surface and the formation of modern mountain ranges in the south of the region.
QUESTIONS FOR SELF-CONTROL: Where on the territory of the Irkutsk region do the most ancient rocks occur and how old are they? What is remarkable about the Baikal volcanic belt? What kind of rocks, which suites are used in the section of the sedimentary cover of the Siberian Platform on the territory of the Irkutsk region? At what time and at what latitudes was the Siberian continent located, when powerful salt layers formed on it? Under what marine or continental conditions were the Jurassic rocks formed on the territory of the Irkutsk region? 
SIBERIAN ANCIENT PLATFORM. Crystalline basement: 1 - protrusions of the Archean-Lower Proterozoic formations (blocks); 2 - Lower Proterozoic folded zones. Platform cover. Riphean-Lower Paleozoic structural stage: 3 - intraplatform positive forms (uplifts); 4 - depressions with a large amplitude of deflection; 5 - zones of marginal deflections; b - areas of subhorizontal occurrence of rocks. Upper Paleozoic-Lower Meozoic structural stage (Tunguska syneclise): 7 - field of development of normal sedimentary rocks; - field of development of volcanogenic formations. Middle Mesozoic-Cenozoic structural stage: 9 - areas of maximum immersion of the Angara-Vilyuiskoto trough; 10 - Jurassic substage of foothill troughs; 11 - Cenozoic substage of foothill troughs.
FOLDED AREA. 12 - Lower Proteroeoic blocks; 13 - Roman-Paleozoic complexes; 14 - reef basin of Baikal. 15 - zones of intraplatform folds; 16- faults; 17 - boundaries of the Siberian platform. THE NUMBERS ARE INDICATED ON THE MAP. Elevations: 1 - Tulun. 2 - Chuno-Biryuyeinsky, 3 - Angara-Katangsky, 4 - Baikal. Depressions: 5 - Taishetskaya, - Murshaya, 7 - Angara-Vilyuisky trough,
Zones of the internal plates of the Phoomean folds: 8 - Angarsk, 9 - Nepa, 10 - Lena. Marginal troughs: 11 - Pre-Seyansny, 12 - Cis-Baikal, 7 - Bzykalo-Patom, 14 - Memsko-Brdaiba. Foundation protrusions: 15 - Biryueinsky, 16 - Sharyzhalgaisny, 17 - Charsky.
Rice. 8. Tectonic map of the Irkutsk region. Where in the territory of the Irkutsk region are there chalk formations? Are there any Cenozoic igneous formations on the territory of the Irkutsk region and how are they represented? What protrusions of the foundation of the Siberian platform are known in the territory of the Irkutsk region?
The Omsk Region is located within the young West Siberian Platform* (Hercynian Plate). In the geological structure of its territory, a folded basement composed of Paleozoic and pre-Paleozoic rocks and a platform cover with gently sloping Mesozoic and Cenozoic deposits are clearly distinguished.
The foundation has a complex structure and consists of igneous formations (granites, diabases, etc.), volcanic tuffs, and metamorphosed rocks (gneisses, shales) to varying degrees. The basement rocks are folded into complex folds and crossed by faults of northeast and northwest strike. Along these faults, some sections-blocks of the foundation fell, others rose. As a result of tectonic movements of the foundation blocks, deflections and protrusions were formed on its surface.
As scientists have established with the help of the latest geophysical data and satellite images, there are peculiar “basalt windows” in the foundation - blocks made up of oceanic crust, and ring structures.
The surface of the foundation plunges from south to north. So, in the south of the region, the foundation is opened by wells at a depth of several hundred meters, in Omsk - 2936 m, in the Kormilovsky district (state farm "Novo-Alekseevsky") - 4373 m.
The platform sedimentary cover in the lower part of the section repeats the basement topography in its occurrence. Its upper horizons practically do not reflect the surface of the foundation.
The sedimentary rocks of the cover are represented by sands, sandstones, clays, mudstones, etc. A thick sedimentary cover was formed over tens of millions of years over six geological periods (240 million years).
During this time, the earth's crust experienced slow vertical oscillations. When lowering its sea waters flooded vast territories. In the formed warm seas a rich organic world developed, contributing to the formation of marine sedimentary strata. Then the lowering of the earth's crust was replaced by an uplift, the sea became shallow and gradually disappeared, the territory of the region became flat land with numerous lakes and rivers. Terrestrial vegetation was widely developed. These events were repeated many times.
Over the entire geological history of the formation of the West Siberian Plate, a sedimentary cover was formed here, the thickness of which varies from 3000-3500 m in the north to 500-1000 m - at the southern border of the region. The upper part of the cover (250-300 m) is composed of continental Upper Paleogene-Neogene clays, loams and sands. Outcrops of these rocks are exposed along the banks of the river. Irtysh and its tributaries (Fig. 3.), as well as in large lake basins. Most often, these deposits are overlain by thin Quaternary deposits.
Each geological period in the history of the region is marked by characteristic natural conditions and geological processes. To answer the question of what happened in the distant past, it is necessary to travel through the geochronological table (Table 1).
Table 1
GEOCHRONOLOGICAL TABLE
| eras | Periods (duration, million years) | Major geological events | natural conditions | organic world | Rock formation | ||||
| KAYNOZOYSKAYA | Quaternary (anthropogen) 1.8 | Repeated glaciations in the north of the West Siberian Plain, which influenced the natural conditions of the Omsk region. | Repeated flooding, formation of glacial lakes. At the maximum glaciation in the north of the region there was tundra, to the south of it - forest-tundra, then forest-steppe. | Of the animals lived mammoth, woolly rhinoceros, bison, giant deer. The vegetation is close to modern. | Covering loams, sands, sandy loams, loams. Peat, lake sapropel. | ||||
| Neogene (Neogene) 22.8 | Slow vertical movements of the earth's crust - uplifts. Intensive development of rivers. | At the beginning of the Neogene, the plain is covered with coniferous-deciduous forests. The climate is moderately warm and humid. By the end of the period, temperature and humidity decrease. Forest-steppe and steppe appear. | Small-leaved tree species are widely used. Animal world – mastodons, proboscis, ancient horses, rhinos, hippos, saber-toothed tiger, etc. The emergence of man. | Sands, sandy loams, loams, clays, concretions, and lignites formed in lakes, swamps, and rivers. Neogene rocks are found in the bluffs of the Irtysh, Om, Tara, and other rivers. | |||||
| KAYNOZOYSKAYA | Paleogene (Paleogene) 40.4 | At the beginning of the Paleogene, a short uplift of the earth's crust, and then a long subsidence and the advance of the sea on land. At the end of the period, the subsidence was replaced by the rise and retreat of the sea. | For almost 30 million years, the Paleogene Sea existed in the region. At the end of the Paleogene, the mora becomes shallow and breaks up into lake basins. The resulting land was covered with coniferous-deciduous forests with an admixture of heat-loving plants. The climate is warm and humid. | Marine fauna predominates; the Paleogene sea is inhabited by mollusks, fish, and protozoa - radiolarians, diatoms, and others. On land, the flowering of ungulates and predators. | Clays with interlayers of sand accumulated at the bottom of the sea. On land, in lakes - clays, silts, sands, brown coals | ||||
| Mesozoic | Cretaceous (chalk) 79.0 | With the onset of the Cretaceous period, the slow uplift of the earth's crust began, the retreat of the sea. In the second half of the Cretaceous, the earth's crust subsides and the entire area is flooded by the sea. | In the first half of the Cretaceous, the region was a flat land covered with coniferous forests. In the forests grew: pine, spruce, cedar and heat-loving tropical plants. The climate is subtropical, humid. In the future, a warm sea existed on the territory of the region, the water temperature was 20 ° C. From time to time, a cold current penetrated from the north and the water temperature dropped. | The sea was inhabited by cephalopods, fish and other animals, and various algae. | In lakes and rivers, thick strata of predominantly sands and sandstones were formed, to which underground thermal waters are confined. Various clays were formed in the sea - siliceous, calcareous. | ||||
| Jurassic (Jurassic) 69.0 | There was a slow subsidence of the earth's crust, which reached a maximum in the Late Jurassic. This sinking caused the advance of the sea. | In the first epochs of the Jurassic period, the region was represented by a low-lying plain with numerous lakes and rivers. The climate is warm and humid. In the late Jurassic, the entire region was occupied by the sea, which existed for 25 million years. | The sea was inhabited by numerous cephalopods - ammonites, belemnites, fish, algae. Coniferous, ginkgo, and other plants are widespread on land. | Sedimentary rocks accumulated in lakes and rivers - clays and sands, which later turned into mudstones and sandstones. The rocks contain many plant remains and a layer of coals. Clays deposited in the sea contain a large amount of organic substances, from which hydrocarbons (oil and gas) can be formed. | |||||
| Triassic (Triassic) 35.0 | Slow vertical uplifts of the earth's crust. Intensive destruction and erosion of rocks. Locally volcanic. | Raised plain. There were vast forests. The climate is hot, arid. | The forests are dominated by gymnosperms. | Deposits are rare. Mudstones, siltstones, sandstones. Volcanic rocks - diabases. | |||||
| Paleozoic | Perm (Permian) 38.0 | General uplift of the region. The entire territory is a single stable paraplatform linking the Siberian and Russian platforms. | Area of plateaus and uplands with developed erosion processes. The climate is hot and dry. | On land, the development of terrestrial reptiles, conifers, the appearance of ginkgo. At the end of the period, the extinction of trilobites, four-pointed corals. some molluscs and brachiopods. | Clastic material supplied from surrounding mountain structures. | ||||
| Hard coal (carbon) 74.0 | A time of relatively calm tectonic activity. Deflection of the territory and transgression of the sea. At the end of the period, the general uplift of the earth's crust. Sea regression. Volcanic activity is not observed. | The sea is shallow, open, warm with a normal hydrochemical regime. At the end of the period, a large area was drained, a low plain. | The first reptiles. Tree ferns, horsetails and club mosses, the first gymnosperms. Widespread distribution of large insects. In the seas there are bony and cartilaginous fish, invertebrates. | Volcanogenic and normal sedimentary marine rocks of all types. | |||||
| Devonian (Devonian) 48.0 | The regional uplift of the territory caused cracking of the earth's crust, the revival of deep faults, and an outbreak of volcanism. | The land is a desert, on the southern outskirts of which volcanoes were located. | Wide distribution of bony and cartilaginous fish. On land, there are tree-like ferns, horsetails and club mosses. Appearance of the first amphibians and insects. | Volcanogenic sedimentary rocks. clay, sand, limestone. | |||||
| Silurian (Silur) 30.0 | The West Siberian Platform is a continuation of the Siberian Platform. It shows active tectonic processes. | Noticeable restructuring of paleolandscapes. At the beginning of the period, the territory is dominated by mountainous land, at the end by a flat desert plain. | The first land plants (psilophytes). In the seas there are graptolites, corals, brachiopods, trilobites. | Terrigenous sediments, saline and gypsum-bearing, are probable. | |||||
| Ordovician (Ordovician) 67.0 | Deflection of the earth's crust. | The seas are warm and normally salty with numerous islands and underwater volcanoes. | Appearance of the first fish. The flourishing of trilobites, corals. There are bryozoans and graptolites on the seabed. | Effusive and terrigenous formations. | |||||
| Cambrian (Cambrian) 65.0 | Most of the territory of Western Siberia has lost the features of the geosyncline. A para-platform was formed. | Bring the transgression of the sea! to the dismemberment of land. Widespread areas of underwater volcanism. The sea is shallow water with high salinity. | Wide distribution of marine invertebrates: trilobites, archaeocyaths, four-beam corals. Active development of blue-green algae. | Effusive and terrigenous formations. | |||||
| Proterozoic | >2000 | The Ural-Siberian geosynclinal belt occupies the entire space between the Siberian and Russian platforms. Active tectonic processes and volcanism. | Sharply dissected relief. | The appearance of the first plants - algae and invertebrates, sponges, radiolarians, brachiopods, arthropods. worms. | Clayey and carbonate sediments and effusive rocks predominate. | ||||
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