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The East European epikarelian platform is located within Eastern, Northern and Central Europe. Its area is 5.5 million km2. The relief of the East European Platform is almost entirely represented by the plain of the same name. Only on the Kola Peninsula there are mountains with heights up to 1 km. The plain is eroded by rivers belonging to the basins of the Baltic, White, Black and Caspian Seas. The modern boundary of the platform is traced most easily in the east with the Hercynides of the Urals, in the west with the Carpathian Alps, and in the north with the Caledonides of Norway. The boundary of the platform with the Baikalids of the Timan uplift has also been unambiguously established. In other areas, the modern boundary between the pre-Baikalian and later folded systems is overlapped by sedimentary rocks of the cover and is drawn rather conventionally.
platform foundation. In two places on the platform, a significantly eroded crystalline basement was raised to the level of the day surface, forming the extensive Baltic and small Ukrainian shields. On the rest of the platform, called the Russian Plate, the foundation is covered by a sedimentary cover. The basement of the East European Platform is composed of Archean and Early Proterozoic folded structures: Belomorides and Karelids. They form blocks, quite clearly differing in shape and location. Belomorids have a polygonal shape and contain oval formations (nuclear nuclei).
. Sedimentary rocks overlying the crystalline basement of the East European Platform are Riphean to Quaternary in age. At the same time, the entire section of the cover is divided by large stratigraphic breaks into several stages, which have different distributions. Consider the structure of the cover floor by floor. The lowermost first floor of the cover is composed of Riphean and Lower Vendian deposits. Their average thickness is 0.5-3 km. These deposits are not metamorphosed and are disturbed only in aulacogenes. They are composed of sandy-silty-argillaceous sediments of quartz or arkose composition. There are also glacial and volcanogenic formations in a small amount. The second floor of the cover is composed of a continuous section from the Upper Vendian to the Lower Devonian inclusive. The lower horizons of the second stage (Vendian and Cambrian) are represented by fine-clastic sediments of shallow-water and coastal facies. These are mudstones, clays, sandstones with some tuffs and tuffites in the Vendian. Higher up the section it is composed of carbonates - dolomites, argillaceous limestones, marls. Abundance and diversity of organic remains in Ordovician and Silurian carbonate sediments. The Lower Devonian is a regressive complex in which shallow-marine sediments are replaced by freshwater delta-continental ones. The total thickness of deposits on the second floor of the cover ranges from 200 m to 2 km. The third floor is composed of deposits of the Devonian-Triassic age.
The section begins at the top of the Lower Devonian, which is represented by continental, lagoonal, and marine shallow-water terrigenous rocks. The Upper Devonian is represented by carbonate deposits. Salts are also widely developed, there are covers of basalts of the trap formation. The Carboniferous section begins with a carbonate stratum, a coal-bearing stratum lies above, then red-colored clayey-silty rocks occur. Permian deposits are mainly lagoonal and continental formations. The lower horizons of the Permian are represented by carbonate rocks, higher they are replaced by sulfate and chloride sediments, and terrigenous deposits dominate in the upper part.
The section of the third floor of the cover is completed by the Triassic system. These deposits represent a regressive complex of continental terrigenous rocks. Sandstones, siltstones, clays with intercalations of kaolinite, brown iron ore, and siderite nodules are noted among them.
The last fourth floor of the cover is composed of Jurassic-Cenozoic deposits. The Jurassic are represented by gray-colored shallow-marine and continental coal-bearing deposits.
The Paleogene of the Russian Plate is characterized by two types of sections. In the southernmost part of the plate (the Black Sea and Caspian regions), the section is composed of thick moderately deep-water clayey-calcareous deposits. The more northern section is represented by less thick shallow-water and continental deposits: quartz-glauconite sandstones, clays, siliceous sediments, and brown coals. The Neogene deposits of the Russian Plate are characterized by great variability. These are shell limestones, glauconite sands, sandstones, dolomites, brown coals, red clays. Quaternary deposits cover most of the surface of the East European Platform with a mantle ranging in thickness from fractions of a meter to several hundred meters. It is composed of moraine deposits, cross-layered coarse-grained sands and glacial deposits, loess is also common.
Baltic shield, Ukrainian shield, South Baltic monocline, Black Sea monocline, Timan-Pechora uplift zone, Belarusian anteclise, Volga-Ural anteclise, Voronezh anteclise, Cis-Ural foredeep, Carpathian trough, Ryazan-Saratov trough, Pechora syneclise, Baltic syneclise, Ukrainian syneclise, Caspian syneclise, Moscow syneclise.
Siberian platform
The Siberian Platform is located in Central and Eastern Siberia. The surface of the Siberian Platform, in contrast to the East European Platform, is almost entirely a denudation upland with heights from 0.5 to 2.5 km. The surface of the platform is eroded by rivers belonging to the basins of the Kara Sea and the Laptev Sea. The eastern modern boundary of the platform is traced from the mouth of the Lena to the Sea of Okhotsk, first along the Pre-Verkhoyansk marginal trough and then along the Nelkan marginal suture. These structures separate the platform from the Cimmerides of the Verkhoyansk-Chukotka region. The northern and western boundaries are covered by the sediment cover of the West Siberian Plate, therefore, they are conventionally drawn along the relief ledge in the right bank of the Yenisei and Khatanga. The southern boundary of the platform is the most complex, as it is complicated by Mesozoic tectonics and granite intrusions of different ages. The boundary runs from the Uda Bay along the southern slope of the Stanovoy Range to the sources of the Olekma along the North Tukuringra fault, which separates the platforms from the Hercynides of the Mongol-Okhotsk belt. Then, from Vitim, the border sharply turns to the north, reaching almost to the Lena, and again to the south to the southwestern edge of Baikal, thereby skirting the Baikalides of the Baikal-Patom Highlands. Then the border continues in a northwestern direction to the mouth of the Podkamennaya Tunguska, leaving the Baikalides of the Eastern Sayan and the Yenisei Ridge in the west.
platform foundation. The basement of the Siberian Platform is composed of deeply metamorphosed Archean and Lower Proterozoic rocks. The foundation is interrupted by numerous Paleozoic and Mesozoic intrusions. Represented by quartzites, gneisses and amphibolites, on which marbles and graphite occur with disagreement. There are also volcanogenic-sedimentary formations with a thickness of 2-5 km, ferruginous-siliceous formations, terrigenous formations with a thickness of up to 10 km, containing a horizon of cuprous sandstones.
The structure of the platform cover. A typical cover began to form on the Siberian platform earlier than on the East European platform - already at the beginning of the Late Proterozoic. In the section of the cover, several stages are also distinguished, separated by large stratigraphic breaks.
The lower first floor of the cover of the Siberian platform is composed of Riphean deposits. They overlie the Lower Proterozoic with a regional break and angular unconformity, are confined to aulacogenes, and are represented by terrigenous sand and gravel deposits. Higher up the section clastic rocks are replaced by carbonate ones. The second floor of the cover is composed of a continuous section from Vendian to Silurian deposits. The base of the section is composed of terrigenous rocks, which are replaced by dolomites and limestones. The third floor of the cover accumulated from the end of the Middle Devonian to the Triassic. The Devonian part of the section is represented by marine terrigenous-carbonate and continental red-colored deposits, as well as mafic and alkaline volcanic rocks. Salt-bearing strata are also present. The Carboniferous and Permian systems are represented by terrigenous-carbonate marine deposits. They are overlain by Middle Carboniferous and Permian deposits. Top part the Permian system consists of terrigenous-tuffaceous formations.
The Triassic system is represented by volcanogenic formations of the trap formation and numerous mafic intrusions associated with them. These are covers of basalts with a thickness of several to a hundred meters with interlayers of tuffs, tuffites and sedimentary rocks. The fourth floor of the cover is represented by Jurassic-Cretaceous deposits. Jurassic deposits overlie transgressively on rocks of different ages. For the most part, these are gray-colored terrigenous marine deposits, changing in the southern direction of the continental
hoist. The latter are coal-bearing. Cretaceous deposits lie according to the Jurassic and are represented mainly by continental coal-bearing strata. Mesozoic intrusive magmatism is widespread in the south of the platform. The section of the cover of the Siberian platform is completed by Cenozoic deposits of the fifth floor. The Paleogene and Neogene on the underlying strata occur with erosion and are represented by thin continental sediments limited in area. They are represented by quartz and arkose sands, cross-bedded sandstones and clays. The thickness of the deposits reaches several hundred meters.
Quaternary deposits are ubiquitous and are represented by a wide variety of genetic types of continental rocks.
Main structural elements. Turukhansk and Ust-Maya zones of uplifts, Aldan shield, Anabar, Nepa-Botuobinsk, Baikit anteclises, Tunguska, Vilyui, Khatanga syneclises, Baikal-Patom, Cis-Verkhoyansk troughs, Yenisei, Baikal, East Sayan folded zones.
31. Late Paleozoic (Hercynian) stage of the geological history of the Earth.
The Late Paleozoic includes the D-th, C-th and R-th periods, with a total duration of approx. 170 million years
Organic world and stratigraphy. Among marine invertebrates, the leading role belonged to brachiopods, cephalopods (goniatites), corals and protozoa. There are sea lilies and sea urchins. Towards the end, ceratites appear. Of the corals, the most widespread are four-rayed, both colonial and solitary forms, of the simplest - foraminifera. Terrestrial invertebrates of the Late Paleozoic are represented by numerous insects. In the Devonian they are still wingless: scorpions, spiders, cockroaches. In the Carboniferous period, giant dragonflies appear. The appearance and development of insects is closely related to the development of terrestrial vegetation. The extremely active accumulation of plant biomass contributed, on the one hand, to the formation of powerful deposits of peat, which later turned into coal, and, on the other hand, an increase in the oxygen content in the atmosphere. The latter, in turn, led to the intensification of oxidation processes, in As a result, many Permian deposits are brown in color. C - the conquest of land by plants and the appearance of the first amphibians. In the middle of the Devonian, bony fishes replaced the armored fishes. The first reptiles appeared in R.
Composition and structure of deposits. Basic structures. Upper Paleozoic deposits are widespread both within platforms and Caledonian mountain-fold structures, and within geosynclinal belts. Late Paleozoic sedimentation is characterized by a large proportion of continental deposits. The thickness of the Upper Paleozoic deposits on ancient platforms is on average 2-4 km. The epochs of maximum transgressions are characterized by carbonate sediments (dolomites, limestones, rift structures); during regressions, carbonates were replaced by terrigenous sediments and evaporites. A common feature of Carboniferous deposits is the presence of a large amount of coal in them and their wide distribution. Therefore, the Carboniferous period can be called "the first era of coal accumulation" in the history of the Earth. In contrast to the Early Paleozoic, in the Late Paleozoic, tectonic movements were more actively manifested on the ancient platforms, which led to the formation of new structures. One of these structures are aulacogens. On the Siberian platform, increased tectonic activity manifested itself in the form of trap volcanism, which began at the end of the Carboniferous period, and reached its maximum at the end of the Permian - the beginning of the Triassic. Mountain building was accompanied large quantity granitoid intrusions. In place of the troughs and uplifts separating them, complex mountain-folded structures, the Hercynides, arise.
History of geological development. As a result of the Hercynian tectonic stage at the turn of the Paleozoic and Mesozoic, a significant restructuring occurred in the distribution of continents and oceans. The wide distribution of Hercynidae within the Ural-Mongolian and Mediterranean regions indicates the closure of the Paleo-Asian Ocean and the western part of the Tethys Ocean. In this regard, the Epicaledonian continents again turned out to be unloaded into a single continental block - Pangea II, consisting of two parts. In the south, it is Gondwana, which has remained virtually unchanged. In the north - the new continent Laurasia, uniting the North Atlantic continent, the Siberian and Chinese platforms.
Paleogeography and climate. Minerals. In connection with the epochs of transgressions and regressions, the climate of the Late Paleozoic changed rather sharply. The presence of evaporites and red flowers in the deposits of the Early Devonian and Permian indicates the existence of a hot and dry climate during these periods. In the Late Devonian and Carboniferous, on the contrary, the climate was humid and mild, as evidenced by the rapid development of vegetation. In the Carboniferous period, the climatic zoning of the Late Paleozoic was especially pronounced, which is clearly fixed by rocks and fossil remains of animals and, especially, plants. Among sedimentary minerals leading role combustibles play - oil, gas and coal. Oil and gas fields are confined to the marine strata of the Devonian, Carboniferous and Permian. About half of all coal reserves on Earth are of Late Paleozoic age. Sedimentary strata of the Upper Paleozoic contain iron (siderite ores), phosphorites, cuprous sandstones, bauxites, rock and potassium salts, gypsum, etc. Deposits of titanomagnetite, chromite, nickel, cobalt, and asbestos are associated with intrusions of the basic composition. Pyrite-polymetallic deposits are associated with volcanic activity. Deposits of rare and non-ferrous metals are associated with acidic intrusions: lead, zinc, tin, mercury, etc.
45. Conditions for the accumulation of organic matter and its transformation in diagenesis.
organic matter in the earth's crust - the buried remains of living organisms in the process of sedimentation.
The main source of oil hydrocarbons is organic compounds present in a dispersed state in sedimentary rocks of subaqueous, mainly marine, origin. But before these compounds form accumulations of oil and gas, they must go through a complex path of geochemical changes, together with their host sediments, which, from highly watered silts deposited on the seabed, turn into lithified sedimentary rocks.
In the geochemical history of 0B transformation of sedimentary rocks, two main stages can be distinguished: the biochemical transformation of OM, which begins during sedimentogenesis and ends at the diagenesis stage, and the thermocatalytic transformation of 0B (the catagenesis stage), which occurs when sedimentary rocks sink to a depth. Each of these stages has its own operating factors and sources of energy.
Relating to the number of ancient (pre-Riphean) platforms. It occupies a significant part of the eastern and northern, from the Scandinavian mountains to and from the Barents to the Black and Caspian Seas. The border in the northeast and north runs along the Timan Ridge and along the coast of the Kola Peninsula, and in the southwest along a line crossing the Central European Plain near Warsaw and then going northwest through the Baltic Sea and the southern part of the Jutland Peninsula.
In the structure of the East European platform, the ancient pre-Riphean (mainly Karelian, more than 1600 million years) folded crystalline and sedimentary (Epikarelian) calmly occurring on it stand out. The foundation of the East European platform is made up of crumpled into, strongly and, over large spaces turned into and. Areas are distinguished within which these rocks are of very ancient age - older than 2500 million years (massifs Kola, Belomorsky, Kursky, Bugsko-Podolsky, Prydneprovsky, etc.). Between them are the Karelian fold systems, composed of rocks of the Lower Proterozoic age (2600-1600 Ma). In and they correspond to the Svecofennian fold systems; early Precambrian formations within southwestern Sweden, southern Norway, and also Denmark and underwent deep processing in the Gothic (about 1350 million years) and Dalslandian (1000 million years) epochs. The foundation protrudes only in the northwest () and southwest () of the platform. On the rest, larger area, allocated under the name of the Russian plate, the foundation is covered with a cover of sedimentary deposits.
In the western and central parts of the Russian plate, lying between the Baltic and Ukrainian shields, the basement is relatively elevated and shallow, in some places above ocean level, forming the Belarusian and. They are separated from the Baltic Shield by the Baltic Shield (stretching from Riga in a southwestern direction), and from the Ukrainian Shield by a system of graben-like depressions Pripyat-Dnieper-Donetsk, ending in the east with the Donetsk folded structure. To the southwest of the Belorussian anteclise and to the west of the Ukrainian shield, along the southwestern boundary of the platform, the Vistula-Dniester zone of marginal (pericratonic) subsidence extends. The eastern part of the Russian plate is characterized by a deeper basement and the presence of a powerful one. Two syneclises stand out here - the Moscow one, which extends to the northeast almost to Timan, and the Pre-Caspian one (in the southeast) bounded by faults. They are separated by a complexly built buried Volga-Ural anteclise. Its foundation is divided into ledges (Tokmovsky, Tatarsky, etc.), separated by aulacogene grabens (Kazan-Sergievsky, Verkhnekamsky). From the east, the Volga-Ural anteclise is framed by the marginal deep Kama-Ufimskaya depression. Between the Volga-Ural and Voronezh anteclises, the deep Pachelma Riphean aulacogen extends, merging in the north with the Moscow syneclise. Within the latter at a depth found whole system Riphean graben-like depressions with a northeast and northwest strike. The largest of them are the Central Russian and Moscow aulacogenes. Here, the foundation of the Russian plate is submerged to a depth of 3-5 km, and in the Caspian depression, the foundation has the deepest occurrence (over 20 km).
The composition of the sedimentary cover of the East European platform includes deposits from the upper (Riphean) to. The most ancient rocks of the cover (Lower and Middle Riphean), represented by compacted and, are present in marginal depressions, as well as in Finland, Sweden (Iotnian), in Karelia and other areas. In most deep depressions and aulacogenes, sedimentary strata begin with Middle or Upper Riphean deposits (clays, sandstones, basaltic lavas, etc.). The sedimentary strata of the cover are disturbed in places by gentle bends, dome-shaped (vaults) and elongated (swells) uplifts, as well as normal faults. In the Pripyat-Dnieper-Donetsk aulacogen, the Devonian and Permian are developed, and in the Caspian basin - the Permian salt-bearing strata, which are disturbed by numerous salt domes.
The Late Paleozoic history of the East European Platform differs significantly from the Early Paleozoic in the restructuring and complexity of the structure of the platform as a whole. If in the Early Paleozoic subsidence covered only the northwestern and western parts of the platform, then in the Late Paleozoic, the central and eastern regions began to sink.
Devonian. Devonian deposits are very widespread on the platform, they are represented by all three divisions, but the area of their development is very different. The most common deposits are the Middle and especially the Upper Devonian. The Devonian sections of different areas of the platform differ significantly from each other both in composition and in thickness. In the east, between the Volga and the Urals, as well as in the central part, marine carbonate rocks are widely developed (Fig. 91). In the west and northwest, continental red-colored and lagoonal sediments predominate with thin sea layers. On most of the platform, Devonian deposits occur transgressively on various Lower Paleozoic horizons or directly on crystalline basement rocks. II only in the west they gradually replace the Silurian deposits (Polish-Lithuanian syneclise).
At the beginning of the Devonian, almost the entire East European Platform was a vast continent. uplift on-
Rice. 92. Schematic lithological-paleogeographical map of the East European Platform in the middle of the Eifelian. According to S. V. Tikhomirov (1967), with simplification
1 - ^Sweetness of blur; 2 - area of accumulation of deltaic sediments; 3-area of accumulation of dolomite sediments in the sea basin with high salinity; 4 - gypsum and anhydrite; 5 - halite and rock salt; 6 - area of accumulation: carbonate sediments in the marine basin of normal salinity; 7-direction of demolition of clastic material; 8 - platform boundaries;
- - boundaries of areas with different sedimentation environments
The Middle and Upper Devonian deposits are more widespread. From the end of the Early Devonian, a new stage began in the development of the East European Platform, which continued until the end of the Permian. Main Feature This stage was the gradual subsidence of the platform and, as a result, the transgression of the sea. The immersion of individual parts of the platform did not occur simultaneously. At the end of the Early and the beginning of the Middle Devonian, the western margins and partly the central regions were involved in subsidence, i.e., those areas that experienced subsidence in the Early Paleozoic (inherited development) - see fig. 92.
The restructuring of the structural parade ground took place at the end of the Eifelian (Middle Devonian), when the eastern part of the platform began to sink and the sea transgression gradually expanded from the east. The northwestern part of the platform was involved in the uplift; it turned into a vast alluvial coastal plain - an area of continental sedimentation. Only in the middle of the Frankish century, when the maritime transgression reached its maximum, this part of the platform was again flooded with the sea.
Other distinguishing feature The initial stages of the stage under consideration consisted in the fact that in a number of places on the platform, the subsidence was accompanied by the splitting of the basement and the appearance along the faults of narrow, but significant in extent, graben-like troughs - aulacogenes. A striking example is the Dnieper-Donetsk aulacogen, where volcanic activity took place in the Devonian period. Deep faults served as the pathways for the penetration of basic magma. Compared to other parts of the platform, the aulacogen experienced more intense deflection.
At the end of the Devonian period, the platform experienced a short-term uplift, the sea basin was reduced; its waters had an increased salinity (Fig. 93), as evidenced by interlayers of dolomites, gypsum and anhydrites in the upper part of the section.
Carboniferous period. Carboniferous deposits on the East European platform are less common than Devonian ones, they are almost everywhere built according to a single plan, although in some parts of the platform they change significantly both in composition and in thickness; on the Devonian rocks lie with traces of erosion.
After uplift at the end of the Devonian, the East European Platform from the beginning of the Carboniferous began to sink and its territory
Rice. 93. Schematic lithological-paleogeographical map of the East European Platform at the end of the Famennian. According to S. V. Tikhomirov (1967), with simplification
Symbols see fig. 92
was covered by a shallow sea basin. The western margin of this basin, closest to the shore, was often subjected to drying, and terrigenous material transported from the Baltic Shield accumulated here. The eastern part of the platform, adjacent to the Ural-Mongolian geosynclinal belt, subsided most intensively.
At the moments of drainage, conditions were created for the accumulation of coal-bearing deposits (the beginning of the Insea Age). Coals lying among sands and clays form one or more rapidly wedging out seams up to 8 m thick. Coals are brown, of low quality, they contain a lot of moisture (up to 35%) and mineral impurities (45%). Coals are developed in the Moscow region coal basin and used as energy fuel
in. To the northwest, the coal-bearing stratum is replaced by facies clays with bauxites (Tikhvin), and to the east - oil-bearing sands and clays of marine origin. The thickness of coal-bearing deposits is up to 60 m.
The subsidence of the platform in the second half of the Visean led to the expansion of the transgression of the sea from the east and the accumulation of carbonate sediments. The sea basin was distinguished by its large shallowness. at times there were islands overgrown with trees. An increase in the thickness of the carbonate sequence in the east of the platform indicates a more active subsidence of its eastern part compared to the western part.
Deposits of the Middle and Upper Carboniferous form a single stratum of limestones and dolomites. Interlayers of gypsum and anhydrite appear in the upper part of the section, and sands (often oil-bearing) and red-colored clays occur at the base. Almost everywhere (except for the eastern regions) the Middle Carboniferous is eroded and begins from the Moscovian. The thickness varies from 400 m (in the west) to 750 m (in the east).
By the beginning of the Middle Carboniferous, almost the entire platform was uplifted and denuded. With the onset of subsidence in the Middle Carboniferous, marine transgression again spread from the east and reached its maximum in the Moscow Age. As before, the eastern part of the platform experienced the greatest subsidence.
Thus, the formation of Carboniferous deposits on the East European platform took place against the background of a general subsidence, which was interrupted by two phases of short-term uplifts (at the end of the Tournaisian and at the end of the Serpukhovian). These uplifts led to the appearance of erosion in the thickness of the Carboniferous sediments. The steady uplift of the platform began at the end of the Carboniferous and ended in the Permian.
Significantly different features of development in the Carboniferous period were characterized by the Dnieper-Donetsk aulacogen. The section of Carboniferous deposits in the Donets Basin consists of two unequal parts.
The lower part, corresponding to the Tournaisian and most of the Vteanian, is represented by limestones 300–600 m thick. Above, up to the border with the Permian, there follows a colossal coal-bearing series consisting of sandstones, mudstone siltstones with interlayers of limestones and coals. Seams of coal usually lie among mudstones and many of them can be traced for a considerable distance. Up to 300 coal seams are known in the Donbass, of which about 60 are of working capacity. Coals high-quality paralytic. The total thickness of the coal-bearing series in the southeastern part of the basin reaches 18,000 m; its sharp decrease is noted from south to north, less sharp from east to west. The rocks of the coal-bearing series listed above are repeatedly repeated in the section, forming rhythms separated from each other by traces of erosion (Fig. 94).
At the beginning of the Carboniferous period, the processes of sedimentation in the Dnieper-Donetsk aulacogen were the same as in the rest of the platform. At the end of the Early Carboniferous, a radical change occurred - increased deflection began earth's crust and the formation of a powerful coal-bearing series.
Permian period. Permian deposits on the East European platform occupy vast areas. They lie on the underlying rocks according to (with rare exceptions).
Rice. 94. Section of the Devonian and Carboniferous deposits of the Donets Basin (a) and one rhythm of the coal-bearing series (b)
1 - coal-bearing series; 2 - saline deposits; 3 - volcanics (lavas, tuffs); 4 - conglomerates: 5 - sandstones; 6 "- mudstones and siltstones; 7 - limestones; in - coal; * layer
Rice. 95. Schematic lithological-paleogeographical map of the East European Platform (Kazan Age)
Intracontinental alluvial plain: 1 - red-colored sandy-argillaceous deposits, G - pebbles, 3 - coal-bearing deposits; fly around marine sedimentation: 4 - carbonate
precipitation; 5 - dolomite-carbonate sediments, gypsum, anhydrites, b - rock salt; 7 - i.i-." reign of a layer of clastic material; 6 - c:-- sha, where sedimentation did not occur
Sedimentation at the beginning of the Early Permian took place in a shallow marine basin inherited from the Carboniferous, which occupied the eastern part of the platform and the Cis-Ural marginal foredeep. At first, this basin had a connection with the Boreal Ocean and, obviously, with the Paleo-Tethys, which caused normal salt and corresponding temperature regimes. It accumulated mainly carbonate sediments.
As a result of increasing uplift, synchronous with folding movements in the Ural geosynclinal system, the sea basin began to shrink, lost contact with the ocean, and by the end* of the Early Permian turned into a huge salt-producing lagoon.
The sediments of the Upper Permian differ noticeably in composition from those of the Lower Permian. Salt-bearing deposits are gradually replaced by conti-224
dental red-colored sandy-clay, often plastered. Characterized by cross-bedded sandstones, which are alluvial and partly deltaic. In some places the sandstones are oil-bearing. Along with them, there are also carbonate rocks with freshwater fauna. These are sediments from desalinated lakes.
At the beginning of the Late Permian, the platform was an accumulative plain. Huge masses of detrital material were carried away by water flows from mountain ranges paleo-Urals.
In the middle of the Late Permian (Kazan Age), the northern and eastern parts of the platform subsided, which caused a short-term but extensive transgression from the Arctic basin. A huge meridionally elongated sea bay with an unstable salt regime and rather diverse sedimentation conditions arose again (Fig. 95): carbonate sediments formed in its northern part, and halogen sediments formed in its southern part. Submergence also took place in the northwest, the waters of the Zechstein Sea, which at that time occupied significant areas of Western Europe, penetrated here.
At the end of the Permian, the entire East European Platform again turned into land and was a huge accumulative plain. In the east, it was limited by the paleo-Ural mountains, due to the destruction of which very diverse, rapidly replacing each other red sandy-argillaceous sediments (proluvial, river, eolian and lacustrine) were formed.
The Late Paleozoic stage of the development of the East European Platform ended with a general uplift at the end of the Permian, which reached its maximum value in the Triassic. The end of this stage coincided with the end of the Hercynian folding movements in the Ural-Tien Shan geosynclinal region.
The East European Platform constitutes the Precambrian foundation of Europe and determines its main structural and geomorphological features.
The platform lies between the folded structures different ages. In the northwest, it is bordered by the Caledonides - folded mountain formations of the Atlantic mobile zone. In the east, it borders on the Hercynian folded structures of the Ural mobile zone. Hercynian folds frame the platform in the west. Alpine folded formations of the Mediterranean mobile zone adjoin the East European Platform from the south.
For the greater part of its borders, the East European Platform has sharp, secondary outlines. It is articulated with the Caledonides pushed over the platform by a tectonic suture. At all other contacts, the crystalline foundation of the platform is cut off by faults. Its margins are strongly submerged towards the foredeeps separating the platform from the adjacent mountain structures.
The present-day tectonic relief of the East European Platform is determined by the system of pre-Cambrian, Paleozoic, and Cenozoic faults of different ages discussed above. Faults divide the crystalline foundation of the platform into blocks, which determine its hypsometry.
An important role in the tectoorogeny of the platform cover of the East European Plain is played by subtectonic landforms - salt structures and brown coal domes, common in many provinces of the country.
Of great tecto-orogenic importance for the East European Platform are also nested subgeosinclinal folded structures, the only structures of their kind - the Donetsk and Timan ridges.
In the structure of the foundation of the East European Platform, the following are distinguished: the Ukrainian crystalline shield and the Volyn-Podolsk syneclise, or plate, the Baltic shield, the Voronezh anteclise, the Masurian-Belarusian anteclise, the Dnieper-Donetsk depression and the Donetsk ridge, the Black Sea and Caspian depressions, the Baltic syneclise, the Latvian saddle , Orsha-Kresttsovsky trough, Moscow syneclise, Pachelmsky trough, Sursko-Mokshinsky swell, Volga-Ural anteclise, Zhiguli arch, Caspian flexure, Omutinsky trough, Cis-Ural depression system - Abdulinsky trough, Osinskaya depression, Omutinsky trough, Pre-Timan trough and Timan ridge, Pechora syneclise. All these elements of the hypsometry of the crystalline basement are identified on the 1964 tectonic map of Europe. To some extent, they are associated with the distribution of geological formations and elements of the modern geomorphological surface.
These regional structures are characterized: some - shields - as areas of relief of a granite basement, others - uplands - as areas with a predominantly reflected relief, and still others - lowlands - as areas with a typical accumulative relief. The second and third categories of structural-geomorphological regions have a thick platform cover. This indicates the predominance of downward movements in the tectonic development of the East European Platform, starting from the Early Paleozoic. They identified the main feature of the tectonic relief, mostly low-lying plain, which distinguishes it from other continental platforms in the Eastern Hemisphere.
Within the East European platform, the Ukrainian and Baltic crystalline shields are distinguished, located respectively in the south- and north-western parts of the platform.
Ukrainian crystal shield adjacent to the Crimean-Carpathian mobile zone, the location of which reflects its outer edge.
The shield stretches from the northwest to the southeast of the river valley. Goryn to the Sea of \u200b\u200bAzov is almost 1000 km. Its width in some places exceeds 250 km. The distribution of the crystalline basement generally corresponds to the right-bank Dnieper and Azov uplands.
The surface of the crystalline rocks of the shield rises: in the north - the Ovruch ridge - up to 315 m, in the middle part - on the Bug region - up to 320 m and in the south - the Azov Upland - up to 327 m above sea level.
Towards the adjacent depressions, the surface of the shield first decreases gradually, then it is abruptly cut off by faults. In the lowered parts, the blocks of the crystalline basement are submerged to a depth of 3-5 km, and in the axial part of the Dnieper-Donetsk depression, more than 8 km. The marginal parts of the shield are in the form of plates inclined towards the depressions. Morphologically, they resemble shelves and in many cases were. For the most part, coastal marine deposits lie on the surface of its margins, as can be seen on the western, Podolsk, slope of the Ukrainian crystalline shield.
The steep buried slopes of the crystalline Precambrian basement are dissected by deep canyons and valleys, similar to those found on the continental slopes of the ocean floor. Like the latter, the valleys on the slopes of the Ukrainian crystalline shield and other shields have a complex, not yet fully elucidated origin. AT this case tectonics and river erosion played a decisive role in the formation of buried valleys. River valleys were laid down and developed in zones of tectonic disturbances, primarily faults. Marine abrasion, which was repeatedly renewed during the history of the geological development of the shield, when its steep slopes formed sea shores, had a certain significance in the development of the forms of buried valleys.
The age of the denudation surface of the Ukrainian crystalline shield is very ancient and varies in different parts of it. The remains of the most ancient platform cover on the shield are represented by the Ovruch formation. Its terrigenous-volcanogenic sequence is filled by a tectonic trough of an older Precambrian basement. At the end of the Precambrian, a similar cover, apparently, was already widespread on the East European Platform. Based on the occurrence of the Ovruch formation, it can be concluded that by the end of the Precambrian, the Ukrainian crystalline shield, as most of East European platform, as a whole had an already leveled surface. The beginning of the denudation alignment dates back to the late Archean - by the time when the desert crystalline plateau of the platform began to acquire a block structure due to the formation of faults of the Krivoy Rog system.
Between the completion of the formation of the Ovruch Series and the next stage of peneplanation of the shield, the southwestern part of the platform experienced significant uplifts, giving it the appearance of an elevated blocky country. Since the Riphean, especially in the early Paleozoic, there have been sharp deformations of the crystalline basement of the platform. Their consequence was the formation of deep faults, which outlined the main features of the modern tectoorogeny of the platform. The most important structural elements of the Early Paleozoic emplacement on the East European Platform are considered to be faults that limit the Baltic Shield, the Timan Upland, the Pachelma trough, the Dnieper-Donetsk depression, the western slopes of the Ukrainian crystalline shield, and its entire southwestern and southern edges. These also include the establishment of the Mediterranean and Ural mobile zones adjacent to the platform within their present boundaries, the Black Sea and Caspian depressions, as well as the Moscow syneclise.
On the western slopes of the Ukrainian crystalline shield and the entire area of the Volyn-Podolsk syneclise plate that emerged at that time, shelf marine deposits were deposited in the Proterozoic and Early Paleozoic and later. The elephant, slightly inclined to the outer edge of the platform, maintains this position for many geological periods. The faults that bound the shield from the west and east were areas of volcanism. The basalts formed at that time take part in the structure of the local relief. Areas of basalt cover, buried at a considerable depth, were also found in the Dnieper-Donetsk depression.
Throughout the entire Paleozoic, Mesozoic and Paleogene, the Ukrainian crystalline shield experienced noticeable block movements that occurred in the foyer of a general subsidence or uplift. The raised blocks represent islands. Sediments were deposited on the lowered blocks in depressions on the shield surface. The available evidence indicates that already in the Cambrian time, the movement of shield blocks was differentiated. Remains of the Cambrian platform cover were preserved in the depressions of the shield surface in the Bug region, and the Carboniferous one - in the Boltysh depression.
Since the epoch of Jurassic and Cretaceous transgressions, the Ukrainian crystalline shield, apparently, periodically subsided below sea level. The deposits of that time are preserved in depressions and ancient buried valleys on the basement surface. At the beginning of the Paleogene, the territory of the shield throughout its entire length was a highly moistened land covered with abundant vegetation. A powerful brown-coal formation accumulated in its vast low areas. Marine sediments deposited in relief depressions contributed to the general leveling of the surface. During the Neogene period, the territory of the Ukrainian crystalline shield was covered by the sea only partially. The coastline has consistently shifted, approaching the modern one. At the border of the Neogene and the Quaternary, after the Kuyalnik Age, fluctuations in the position of the coastline occurred within the current sea level or slightly exceeded it.
In the structure of the relief of the shield, the marine environment left bright traces in the form of a stepped accumulative relief. These are flat surfaces spread over a large area, limited by weakly pronounced ledges within the location of ancient coastlines. They are most clearly preserved in the Sarmatian, Pontic, Cimmerian and Kuyalnik basins, the Baltic delta plain, as well as the ancient Euxinian, Karangatian and Azov-Black Sea marine terraces, known within the Black Sea lowland.
The last stage in the formation of superimposed elements of the relief of the shield belongs to the Quaternary period. Following the decrease in the level of the Kuyalnitsky basin, the development of modern river systems was completed. In the Pleistocene, in connection with the advance of the ice sheet on the territory of the shield, a number of abrasion and accumulative surface forms were formed, grouped depending on the position of the glaciation edge. A particularly significant place is occupied by landforms associated with moraine, fluvioglacial deposits and loess. Post-glacial geomorphogenesis was expressed in the formation of river terraces, valley-ravine landscapes, and eolian local forms.
The modern geomorphological appearance of the shield was created over a very long time. It includes elements of different ages, reworked and altered to varying degrees by both ancient and modern geological factors. The main features of the relief of the shield create: 1) forms of denudation of the crystalline basement; 2) structural plains; 3) water-genetic and glacigenic superimposed forms of the surface.
The structural-denudation relief of the Ukrainian crystalline shield, in addition to the previously noted factors, depends on the composition of the rocks, their occurrence and structural relationships, subsequently disturbed by faults and smoothed by denudation.
There are many extremely contradictory ideas about the structural features of the shield and the stratigraphy of the constituent sedimentary-metamorphic and igneous complexes. Most of the generalizing materials do not contain the necessary historical-structural and petrogenetic data and are still insufficient for tecto-orogenic conclusions.
On the denudation section of the shield, structural and geomorphological elements are exposed, to a certain extent reflecting the sequence of its formation. The most ancient formations of the shield are spilite-keratophyric sequences developed in the Orekhovo-Pavlograd region of the lower Dnieper region. Their age is 3000-3500 million years (Tugarinov, Voitkevich, 1966). The magnetic anomalies expressed in this area are composed of ultramafic, metabasic, siliceous rocks interbedded with mica schists, ferruginous quartzites interbedded with shales and gneisses. The iron ore concentrations associated with these deposits are located in islands within the zones of anomalies. The most characteristic among them are the areas of Tokmak-Mogila, Kamennaya Mogila and Pervomaisky in the basin of Kamyshevata, Salt, etc.
Mafic and related sedimentary-metamorphic rocks, in our opinion, are the original formations of the continental crust, island land centers, similar to modern islands of oceanic island arcs. The location of the siliceous-iron-ore formation in the central and southeastern parts of the shield also corresponds to the regularities of the location of the tectonic systems of islands on the oceanic-type earth's crust.
In the modern relief, siliceous-iron-ore strata, due to their stability, create uplands - large hills, usually rounded. A striking example of such a relief is Tokmak-Tomb in the Azov region.
Later formations are rows of sedimentary-metamorphic strata, concentrating around the oldest effusive-sedimentary formations. Under conditions of a high degree of metamorphism, the individual features of the sedimentary strata are equalized and in the modern structure of the shield are represented mainly by gneisses and migmatites. Shales and crystalline limestones are of subordinate importance. The regularities of relationships between crystalline strata are obscured by the subsequent fragmentation of fields by faults into blocks, outpourings of mafic lavas, and denudation cut of blocks at different stratigraphic levels.
The most important structural and geomorphological feature of the Ukrainian crystalline shield are numerous plutons. A certain pattern is observed in their location, which consists in the concentration of intrusions depending on the general structural conditions. Three types of pluton tectoorogeny are distinguished. The first category includes relatively small intrusions of granitoids associated with ancient areas of formation of the continental crust. This type of intrusives prevails in the southeastern part of the shield, in the lower Dnieper and Azov regions. The spaces between the ancient areas are occupied by fields of gneisses and migmatites. The latter have a folded, plananticlinal and plaxiclinal structure. G. I. Kalyaev (1965) singled out a number of flat anticlines under the name of domes. The main ones are: Saksagansky, Demurinsky, Krinichansky, Kamyshevakhsky, Pyatikhatsky swell and Zaporozhye anticline uplift. In the structural field of gneisses and migmatites, including plutons, lies the Krivoy Rog zone, bounded by deep faults. Faults are associated with local submeridional folding. The folds are sometimes complicated by conformable intrusions of granitoids. This is the second type of shield plutons.
Intrusions of the second type, associated with folding, are always of considerable size and heterogeneous composition. They are most pronounced in the central part of the shield in the middle Bug region, the Teterev and Sluch basins. The boundary between the southeastern and central, as well as between the central and northern Volyn blocks of the Ukrainian crystalline shield is characterized by fault tectonics. These faults are associated with powerful discordant plutons of the third type - Korostensky, Novomirgorodsky and a number of other smaller formations. These are the latest plutonostructures within the shield.
Many intrusions of the shield take part in the structure of the modern relief. As can be seen from the example of the granites of the river. Kamenka, Stone Graves in the Sea of \u200b\u200bAzov, Korostyshev granites, etc., they make up rocky hills crowned with rocky hills - graves with characteristic forms of weathering. The ranges of rocky uplands generally correspond to the shape and size of the plutons.
The Volyn crystalline block is located in the northern part of the shield, in the basin of the Teterev, Sluch, Ubort and Uzha rivers and is limited by faults. The southern tectonic boundary runs schematically in the direction of Kyiv - Zhytomyr - Chudnov - Slavuta, which approximately coincides with the northern boundary of the distribution of migmatites of the Kirovograd complex. The given boundary is also the boundary of the forest (Polesskaya) and forest-steppe, as well as the northern boundary of the distribution of loess. This testifies to the tectonic, stable activity of the noted structural boundary for a very long period.
The surface of the crystalline basement of the Volyn block has an uneven sedimentary cover. In places of structural and denudation depressions, mainly confined to the fields of distribution of gneisses and migmatites, there is a sedimentary cover with an accumulative relief. The Krasnoarmeiskaya (Pulinskaya) depression, the Korostyshevsky lignite basin, etc., have such a surface. Throughout the rest of the block, the platform cover is characterized by an insignificant thickness, which only smooths out the sharpness of the outlines of crystalline rocks.
Positive landforms are created by outcrops of the crystalline basement. The features of the elevations are determined by the composition of the rocks that make them up and the method of preparation, depending on the denudation factor. These regularities are maintained throughout the territory of the Ukrainian crystalline shield and all shields in general.
In the basin of the Southern Bug, Ingulets, on the Azov crystalline massif and, apparently, in other places where the crystalline basement is cut off by denudation at the level of magma formation centers, dome tectonics of crystalline rocks, first noted by V. A. Ryabenko (1963), is exposed. Domes in the relief are rounded hills with smoothed protrusions, rising several meters or tens of meters above the surrounding area. These morphostructures are especially clearly expressed in the Berdichev region.
Canyons are one of the most common landforms of the Ukrainian crystalline shield. They are located in most cases in fault zones. These are inherited terrain elements. Significant in size and numerous canyons are known in the valleys of Teterev, Sluch, Uzh, Kamenka, etc. The most grandiose canyon in granite is located in the Dnieper valley between Dnepropetrovsk and Zaporozhye.
Weathering forms are exceptionally diverse on the Ukrainian crystalline shield. Within the distribution of granite massifs, heaps of weathering units, limited by tectonic cracks, predominate. Often they take on bizarre outlines. In the area of distribution of the Dnieper glaciation, the surface of crystalline rocks everywhere has traces of ice impact. In the area of Korosten - Shchors, outcrops of red Korosten granite look like smoothed arenas, dotted with glacial scratches and scars, mostly elongated from north-north-west to south-south-east. In the watershed areas, granite outcrops have the shape of sheep's foreheads. Their steep ledges rise to 2-3 m. Forms of glacial denudation to the west of Korosten in the vicinity of the Barashi-Yablonets region are especially indicative. Over a fairly large area, continuous outcrops of gray granites and gneisses have the shape of typical curly rocks.
To the south-west of Korosten, granitoid outcrops smoothed by the glacier form separate rounded hills, occasionally scattered among the sandy plain. The rocks of labradorite are characterized by layered segregations (blocks) with slightly smoothed corners. Charnockite outcrops have peculiar forms of weathering. They accumulate in the form of fragments of variable shape and size. Alkaline igneous rocks form, during weathering, rounded blocks that occur among loose weathering products.
Peculiar geomorphological ensembles formed within the areas of ancient volcanism. They occupy the most significant areas in the junction zone of the Azov crystalline massif and the Donetsk Ridge, as well as in the fault zone that delimits the shield and the Volyn-Podolsk plate. On the northern outskirts of the Azov massif, in the basin of the Wet Volnovakha and the part of the Kalmius valley adjacent to its mouth, volcanic rocks form ridges along the valleys and rocks on the banks of the rivers. In a number of places, ancient lavas have preserved flow structures. In the basalt rocks located on the shores, a well-pronounced prismatic separation is sometimes observed. In the Goryn basin, on the western slopes of the shield, basalt dikes appear as small hills against the background of the smoothed surface of the Polissya Plain.
The distribution area of the Krivoy Rog iron ore formation lies within the steppe accumulative plain. Against the background of the plain, in the sloping parts, the rocks of this formation form rocks, distinguished by a dark color and a metallic sheen. Notable among them is the Eagle Rock in Krivoy Rog - one of the few surviving relief monuments of this type. In the area of deposits of the Krivoy Rog series, landscapes are distinguished by the coloration of iron oxides. This is reflected in geographical names (for example, Zheltye Vody, Zheltorechensk).
In the geomorphology of the Ukrainian crystalline shield, the Ovruch Ridge occupies a special place. Sedimentary-volcanogenic rocks, mainly pyrophyllite schists and quartzites, take part in its structure. Along the bedding planes of quartzites, wind-cut signs are often found, indicating the continental origin of these rocks. The Ovruch series fills depressions in the surface of the crystalline basement and has a slightly noticeable synclinal occurrence. This is a structure of the plaksincline type, trough, characteristic of the platform cover.
The Ovruch Ridge exceeds the adjacent spaces by more than 100 m and is limited by steep slopes. The most elevated part of the ridge is devoid of a cover of post-Cambrian deposits. The lowered areas and slope parts of the ridge are covered with Quaternary deposits, represented by lacustrine, often banded loams and loess rocks 20–30 m thick. Numerous steep-walled ravines that cut through the entire loess layer play an important role in the geomorphology of the Ovruch ridge. Huge alluvial fans are located at the mouths of ravines. In some places, they merge with their edges and form a proluvial terrace bordering its uplift. At the southwestern slope of the ridge in the floodplain of Norin on small area Paleogene sandstone placers are widespread. Huge blocks of it create original features of the landscape, found everywhere where the Paleogene is exposed. Blocks of sandstone usually have a smooth surface and are covered with a dark crust. In addition to the environs of Ovruch, Paleogene sandstones take part in the structure of the relief in the vicinity of the area with. Squirrel - Mount Tochilnitsa, Barashi - Mount Lisuha, etc.
The destruction products of the crystalline basement were the source of material for the formation of sedimentary rocks and associated mineral concentrations. Significant masses of weathering products during geological time, undergoing repeated processing, were removed from it by long distance and only a small part of them was fixed within the shield. In particular, practically valuable mineral concentrations are concentrated in depressions of the surface of the crystalline basement - tectonic depressions, modern and buried valleys, as well as on the slopes of the shield and in the zones of shallow deposits of epicontinental seas that have repeatedly advanced on its territory.
Baltic shield. In the northwest of the East European Platform, the crystalline basement is exposed over a large area of the Baltic Sea basin from the northern coast of the Kola Peninsula to Bornholm Island, in the Baltic Sea - in the south.
Throughout the Baltic Shield has tectonic boundaries. In the north, from the Varanger Fjord to the White Sea, the shield is cut by a deep fault that delimits the Precambrian basement and the Caledonian structures. Relics of Precambrian structures have been preserved in the form of Rybachy and Kildin Islands. Outlines of the Kola Peninsula of fault origin. NW-trending faults extend southeast from the shield into the East European Platform. The origin and development of the Kandalaksha, Onega, and Mezen bays and the Varanger Fjord are obviously connected with sublatitudinal faults. The bath of the Baltic Sea is also a tectonic depression. Its origin is similar to the origin of the Orsha-Kresttsovskiy trough of the basement of the East European Platform, with which the basin of the Baltic Sea, according to the lead, is a syntectonic formation.
The southwestern boundary of the Baltic Shield is also of fault-tectonic origin. In this part, the shield limits a fault that cuts off the outer edge of the platform. It runs from southeast to northwest in the direction of Torun-Koszalin, on the coast of the Baltic Sea, south of about. Bornholm, Ystad, in the south of Scandinavia, Helspnger, on about. Zealand, and through the peninsula of Jutland, at the latitude of the city of Holstebro. The Øresund, Kattegat, and Oslo Straits are located in grabens at the site of submerged blocks of the marginal part of the East European Platform.
In the west, the Baltic Shield borders the Caledonides of the Scandinavian Mountains. The tectonic suture in the form of a flat arc runs from the northeast to the southwest from the upper reaches of the Varangerfjord to Laiswalm and Halgar, in the northern part of the Oslo graben. From the latter, the Precambrian boundary of the Baltic Shield continues in a sprat direction to the west, southwest, in the direction of Buki Fjord. Throughout the western boundary, the masses of Caledonides are pushed to the east, overlapping the crystalline basement of the shield. The thrust front is strongly dissected by denudation and protrudes sharply in the relief, and is of great structural and geomorphological significance.
The crystalline basement of the East European Platform within the Baltic Shield is uplifted to a considerable height and in many areas has mountainous relief. A certain regularity is observed in the distribution of the heights of its surface. The basement is most elevated in the northwestern part and along the tectonic suture with the Caledonides. The surface marks of the crystalline basement reach 1139 m on the Finnmarken plateau, on the northwestern coast of Lake. Sturaele-Tresk 2125 m, south of the river valley. Jungen 580 m, Dalfjell mountains 945 m, Gausta, Southern Norway, 1889 m. The surface of the crystalline basement decreases towards the Baltic Sea.
In the southern part of Finland, the surface of crystalline rocks rises to 105 m - South Salpauselkä, to 235 m - east of Vaza. The eastern part of the Baltic Shield has a relatively lower surface compared to the western one. The fluctuation of heights here ranges from 0, on the coast of the White Sea, to 1189 m in the Khibiny mountains.
The orographic elements of the eastern part of the Baltic Shield have a consistent northwest strike. In this direction stretch the heights of the Kola Peninsula Keiva and the "tundra" Panskiye Lujarvik and others, the Kandalaksha and Onega bays of the White Sea, the Windy Belt ridge, the strip of lakes - Onega, Segozero, Vygozero, Kuito, Topozero, the elevations - West Karelian and Manselka. Most of the valleys of the innumerable lakes of the shield have a northwestern extent.
The orography of the crystalline basement of the Baltic Shield reflects, to a certain extent, the structure and composition of the rocks that take part in its structure.
The first reports on the structure of the Baltic Shield are given in the works of O. I. Mushketov and A. D. Arkhangelsky. Modern ideas about its structure are covered in the works of X. Väyrynen (1954), K. O. Kratz (1963), A. A. Polkanov and E. K. Gerling (1961), as well as in explanatory notes to international tectonic maps of Europe and Eurasia (Tectonics of Europe, 1964; Tectonics of Eurasia, 1966).
The structural field of the Baltic Shield is characterized by the distribution of sedimentary-metamorphic rocks of different ages. The oldest of them are gneisses and gneiss granites, the relict massifs of which have been preserved among later structural formations. The age of these rocks is 2500-3500 million years. Later formations of 1900-2000 and 2000-2500 Ma are represented by biotite, sillimanite-staurolite, amphibole gneisses and amphibolites with magnetite quartzites. These ancient formations of the shield are associated with igneous rocks - peridotites, gabbro-labradorites, gabbro-diabases and granites.
Of the other types of sedimentary-metamorphic rocks on the Baltic Shield, phyllites, micaceous, green, graphite, clayey, shungite and other schists, tuff schists, amphibolites and amphibole schists, quartzites, conglomerates, limestones and dolomites are common. Strongly deformed sedimentary-metamorphic strata are dominated by igneous rocks of diverse composition and age. The most developed among them are granites, syenites and quartz syenites, diorites, gabbro, peridotites, nepheline rocks, diabases, diabase tuffs, etc.
The Precambrian of the Baltic Shield is subdivided into a number of stratigraphic sequences bounded by sharp unconformity surfaces.
On the Baltic Shield, according to X. Väyrynen (1959, p. 53), within Finland, the exposed geological bodies “…are typical deep rocks that cooled at a depth of many kilometers (up to 10-15 km). Thus, we can get some idea of the extent of erosion and the amount of material that was moved from this area of the Earth as a result of slow destruction and transport by flowing water before the earth's surface reached the present level.
The overlying strata were demolished not only over the granites, but also over the shale belts, which meander between the granite areas in the form of seams, and also sometimes compose larger areas. They are primary surface formations, but they have been intruded everywhere by larger or smaller granite and other intrusive masses, which are the same deep rocks as within large massifs. Shales were transformed into mixed gneisses under the influence of intruded granites. This indicates the insular formation of the continental crust of the Baltic Shield.
There are six phases in the development of the main Precambrian structural zone in Finland. According to H. Väyrynen, where granites were intruded into the most ancient, early Archean shales, tectonics manifests itself in the form of plastic deformations. The axial planes of the folds are vertical or steeply inclined, the folds are isoclinal. Granite intrusions are not secant, injection gneisses have not formed here either, granite veins are rare; they are layered, with sharp contacts, often folded together with shales. Proceeding from this, X. Väyrynen wrote (1959, p. 273) that "the earth's crust, on which the shale strata were originally deposited, completely melted under them." The thickness of the sediments of the earth's crust had a thickness of only a few hundred meters. Later, when a thicker crust was formed, the folding was concentrated in separate folded belts flowing around rigid areas and granite areas located between the folding belts.
The structure of the crystalline basement is reflected in the relief. Near Lake Ladoga structures "younger than the last folding of these shales, often open or filled with loose material cracks and fissure belts, which are clearly distinguished in the relief" (Väyrynen, 1959, p. 280).
The structure of the eastern part of the Baltic Shield within Karelia is multi-storey. According to K. O. Kratz (1963), the floors are distinguished:
1) granite-gneiss basement composed of deeply metamorphosed Archean formations; against their background, early and late Proterozoic folded formations protrude;
2) metamorphosed and highly deformed geosynclinal deposits intruded by basic and acidic intrusions; lower Proterozoic;
3) a layer of gently folded weakly metamorphosed subgeosynclinal deposits; Middle Proterozoic;
4) platform, non-metamorphosed Upper Proterozoic and Paleozoic deposits.
The Karelians are considered as part of the Proterozoic folded region. Its folded structures are cut off by denudation and are preserved only in synclinal structural zones. The relatively well-studied Ladoga synclinorium is included among the latter. “It is distinguished by the development of thick, highly dislocated strata of the Sortavala and Ladoga series, cut through by intrusions of ultrabasic, basic and granitoid rocks. The folded structures of the synclinorium are complicated by blocks protruding on the modern surface, composed of the oldest granite-gneiss complex and massifs of post-Ladoga granitoids.
In the Ladoga synclinorium, there are more than a dozen blocks composed of ancient granite gneisses with relics of various gneisses and amphibolites, ranging in size from small to larger, 120-150 km 2. …these granite-gneiss massifs appear as rigid cores of dome-shaped anticlines in the structure of folded shale strata overlying them” (Kratts, 1963, pp. 98, 102). The uplifts are welded together by relatively narrow synclinal zones of complexly folded deeply metamorphosed geosynclinal deposits and deep intrusions of the Lower Proterozoic. This is a typical ancient island structure (Bondarchuk, 1969, 1970).
In the highly dislocated Precambrian sequence of the Baltic Shield, two independent structural complexes are distinguished, corresponding to the main epochs of folding - the Belomorian and Karelian. The older Saami and later Sveko-Finnish formations, significantly reworked, are of subordinate importance in places during folding. The age of the Saami folded complex is considered to be at least 2200 million years. It is composed of sedimentary-metamorphic rocks of the geosynclinal type. These deposits can be traced in the structure of the Belomorian and granulite massifs.
The Belomorian structural stage, or Belomorids, is composed of a series of Archean amphibolites, gneisses, and granite-gneisses with a total thickness of 6000-8000 m. These rocks are crumpled into folds extending in a northwesterly direction. Belomorids have been preserved between massifs of later folding in the areas adjacent to the White Sea and in southern Sweden.
The Belomorids of the Belomorian region have a very complex structure. Here stands out (Tectonics of Europe, 1964) the Central, Ensko-Lukhsky, synclinorium. It separates the Kandalaksha and Primorsky anticlinoria in the northeast and the Keriysko-Kovdovorzsky one in the southwest. The main folds are complicated by dome-shaped anticlines and transverse synclines extending in a northeasterly direction. In the northern part of the Belomorian massif, the folds are overturned mainly to the northeast, and in the southern part, to the northwest. The folded structures of gneisses, which are characteristic of higher sections of the Belomorids, are replaced with depth by plastic flow deformations.
A characteristic feature of the structure of Belomorides are numerous and diverse igneous formations. In the structure of Belomorides, the Belomorian and granulite massifs are especially distinguished. Karelians adjoin them from the northeast and southwest, the articulation with which passes along faults. Intrusions of basic and acid composition are concentrated in the contact zone. Various intrusions are known in the fault zones of the Vetrenoy Belt, in northern Karelia. Faults also separate the Belomorian massif from the granulite massif in the western part. The latter is pushed over the Karelians of Lapland to the south and southwest.
Karelians- Proterozoic folded formations of the Baltic Shield. Their structure has been most thoroughly studied in Karelia (Kratts, 1963) and Finland (Väyuryunen, 1954). In the western part of the shield, apparently, Svecofennids and Gotids syntectonic with Karelids.
Rock complexes of the Archean and Proterozoic age take part in the structure of Karelids. Archean deposits form the foundation of the Karelids and are exposed over a large area of them. They are represented by gneisses, granite gneisses, migmatites, and amphibolites.
Proterozoic formations of Karelids are divided into three subgroups: lower, middle and upper. The most common are the Lower Proterozoic strata, represented by highly metamorphosed deposits. They are collected in vast synclinal zones, elongated in a northwesterly direction. The synclinal zones separate the anticlinal uplifts, on which there are almost no deposits of the Lower Proterozoic. Anticlinal uplifts are composed of Archean formations complicated by later igneous intrusions, predominantly of granite.
The Middle Proterozoic is composed of sedimentary, weakly metamorphosed strata of conglomerates, sandstones, quartzites, carbonate-shale-diabase formations, and shale-volcanogenic rocks. These sequences are collected in gentle folds, often inheriting the strike of the previous Proterozoic folding.
Upper Proterozoic deposits are common in the southern part of the Karelian ASSR. They are represented by strata of quartzites and sandstones and fill gentle synclinal troughs. Late Proterozoic igneous formations are widely developed, which are dominated by rapakivi granites, dolerites and gabbro-alkaline rocks in the northern part of the republic.
Let us characterize the general features of the tectonic structure of the Karelids according to K. O. Kratz (1963). Horst-anticlinal uplifts composed of Archean formations predominate in the modern cut across the area. Narrow folded synclinal zones extend between these uplifts, composed of geosynclinal strata compressed into folds.
The main structural elements of the Karelids (from east to west) are: the Karelian synclinal zone, which is complexly articulated with the Belomorian massif, the Central Karelian massif, the East Finland synclinal zone, adjacent to the Lapland massif in the north, including the Ladoga syncline in the south; in the southwest, the East Finland synclinal zone articulates with the Central Finland and Vyborg massifs; the synclinal zone of the North Norland Karelids.
The structure of the Central Finland synclinal zone is very complex. In addition to plutons, large faults play an important role in its tectoorogeny.
Proterozoic folded structures in the western part of Finland and Sweden are distinguished under the name svecofennids, and in the southern part of Sweden and southeastern Norway - gotids.
In southwestern Finland, the Svecofennids and Karelids articulate in the region of the Central Finland Massif. The latter is a structure similar to the Belomorian massif.
The structure of svecofennids is dominated by graywacke shales, leptites, which are metamorphosed volcanic rocks, volcanic rocks with a total thickness of about 8000 m. The base of these formations is unknown. A characteristic feature of sphecofennids is folded, strongly compressed structures and plastic flow structures in granitization zones. The strike of isoclinal folds is predominantly northwestern, changing in the areas of articulation with massifs.
From east to west and south, the main structural elements of the svecofennids are: the marginal zone of the svecofennids of northern Norland, which articulates with the Karelids in the east; in the south it includes the Skellefte anticlinorium, to the south it is delimited by faults: the synclinal zone of svecofennids of central Norland, the marginal zone of svecofennids of southern Norland, in the southwest bordering on the Värmland granite massif, and in the south including the anticlinorium of svecofennids and the synclinorium of Lake. Melaren, according to which the svecofennids articulate with the gotids.
The Gotids occupy the entire Precambrian region of southern Scandinavia - southern Sweden and the southeastern part of Norway. This entire part of the Baltic Shield is distinguished by a very complex structure of different ages and a different composition of strongly deformed rocks. Grandiose ancient faults are of particular importance in its structure.
Gneisses, granite-gneisses, mica schists, crystalline limestones, quartzites, conglomerates, etc. take part in the structure of the Gotids. In the structure of the Precambrian of southern Scandinavia, separate regions are distinguished, delimited by faults and grabens of submeridional strike. Particularly important tecto-orogenic importance is the fault zone of the lake. Vetter, stretching from the Baltic Sea to the borders of Norway and further north to Lake. Femunn. To the east of this zone lie: the Värmland granite massif, further to the southeast the Smaland granite massif and the Blekinge anticlinorium adjacent to it in the south, composed of gneisses. To the west of the Vetter Fault Zone extend almost in a meridional direction massifs of pre-Gothic and gray gneisses of southwestern Sweden. In the west, these structures are cut by the Oslo graben.
To the west of the Oslo graben there is a vast region of granite gneisses in southern Norway. In its eastern part, there is the Kontsberg-Bamblé massif, composed of sedimentary-metamorphic and igneous rocks. To the south-west of it is the equally complex Granit Telemark complex. In the northern part of the main region of the Precambrian of southern Norway, there is a sequence of folded sedimentary-metamorphic deposits about 4000 m thick.
In the structure of the tectonic relief of the crystalline basement of the Baltic Shield, the composition and structure of the ancient platform cover play an important role. Its remains have been preserved in some synclinal troughs, on different parts of the shield. Usually, the relics of the platform cover are composed of sedimentary, weakly metamorphosed rocks of iotnium and cambrosilur.
In the West Onega, Satakunta and other grabens, these deposits are represented by Potnian quartzite-sandstones, shales, siltstones, etc. the youngest deposits of the Precambrian are known in the graben of the lake. Vättern, where they are represented by arkosic sandstones and overlying shales. Cambrian-Ordovician deposits are common in the grabens of Västergötland and Ostergötland (the region of lakes Vänern and Vättern). They include sandstones, quartz shales, bituminous limestones, etc.
In the tectoorogeny of the Baltic Shield, the Oslo graben stands out as a separate structural complex. From the Oslofjord, the graben extends to the north, northeast of the quartzite cover of the Scandinavian mountains. The amplitude of the graben along the eastern coast of the Oslo Fjord is 2000-3000 m. It is made up of sandstones, shales and limestones of the Cambrian-Silurian age. In the northern part of the graben, these deposits form east-northeast folds; in the southern part, Paleozoic deposits contain intrusions of Permian alkaline rocks. Prior to this, the Paleozoic deposits were flattened, in the Early Permian they were overlain by continental deposits and basaltic sheets. Later, the intrusion of dikes and plutons of monzonite larvikites, syenite nordmarkites, etc., followed. Characteristic features of the structure of this graben are calderas that arose along ring faults and linearly elongated stepped faults.
scandinavian highlands. Caledonides. The Scandinavian, or Caledonian, mountains are the most ancient folded structure in the western part of the Eurasian massif of the continental crust. In the course of the history of geological development, the vast region of the Caledonides was divided into separate blocks, a significant part of which sank below the level of the Atlantic Ocean. The surviving areas of the Caledonides represent the border of the East European Platform on the eastern coast of the Atlantic Ocean and the Greenland and Canadian shields on the western coast. Significant isolated areas of the Caledonian structures are the islands of Svalbard, Jan Mayey, Bear, Faroe Islands, the tectonic connection of which with the marginal mountain structures of the Caledonides is still not clear enough.
The Caledonian border of the East European Platform is represented by the Scandinavian Mountains and the Caledonian Mountains (in the British Isles). Conventionally, this border also includes the Svalbard Caledonides, articulated with a fragment of the Precambrian island massif - part of the Baltic Shield or the hypothetical Baronets Sea Plate - the constituent elements of the Precambrian structure of the East European Platform. The mainland and insular parts of the Caledonian formations have similar features in the structure of the tectonic and climatic, in particular glaciogenic, relief.
The Scandinavian mountains are an integral part of the physical-geographical region of the Scandinavian highlands. To a large extent, they have lost their primary tectonic relief. General peneplenization in the Cretaceous - Paleogene time, fault tectonics and recent movements, together with superimposed surface forms, gave the landscapes of the Precambrian and Caledonian parts of Scandinavia a lot in common. Therefore, keeping in mind the difference in structures, age and history of development, we consider it expedient to jointly consider the tectoorogeny of the Baltic Shield and the mountains bordering it. The Caledonides of Scandinavia stretch along the outer edge of the peninsula from the Barents North Sea at a distance of over 1700 km. In the direction of the Atlantic Ocean, the abraded mountains form a shelf, in places reaching 250 km wide and plunging to a depth of 400 m.
Consider briefly geological structure Caledonid. The foundations of the mountains are made up of Precambrian rocks of the Baltic Crystalline Shield. In the folded zone, the foundation in some places protrudes in the form of windows or separate arrays. The platform cover is composed of strata of pre-Devonian terrigenous deposits. These include the sparagmite complex of coarse clastic rocks. In the eastern part of southern Norway, Finmarken and other places, the lower part of the complex is represented by sandstones and shales. In the upper part of it, strata of tillite, quartz sandstone and clayey rocks are distinguished, overlain by sediments containing Late Cambrian fossils.
In the northwest of the country and in the ancient geosynclinal zone, the Cambrian-Silurian deposits are represented by effusive and intrusive rocks. In the folded regions of southern Norway, the following are distinguished in the composition of sedimentary deposits: Oslo facies - knotty limestones, shales and sandstones of the Oldred type; marine deposits of the Trondheim region, including shales with sandstones, conglomerates and a thick basalt (underwater) sequence, as well as sequences of basic extrusive rocks; Norland facies - metamorphic rocks, mainly mica schists, crystalline limestones and dolomites.
In the Caledonides of Sweden, the following rocks lie on the crystalline Precambrian basement (Tectonics of Europe, 1963): Eocambrian - quartzites and slates; Ordovician - slates and shale, greywackes, crystalline limestones containing strata of volcanic rocks; Silurian - shales, limestones, quartzites, conglomerates and thick strata of basic volcanic rocks. These deposits are highly dislocated. The structure of the Caledonides of the Scandinavian Highlands is determined by complex folding, cover and fault tectonics. Numerous intrusions of igneous rocks are known in the intensely folded structure.
The main features of the Caledonian tectoorogeny create nappes. Their front stretches along the entire Scandinavian Peninsula. The hinterland of the mountains form a huge tectonic cover of Seva. Its frontal part stands out as an independent cover composed of granites and syenites. The middle part of the Seva cover, also independent, is composed of slates, dolomitic marbles, quartzites, and arkose sandstones. These rocks include dikes and sills of basalt, which formed in the pre-cover phase. The central part of the Seve cover is composed of garnet gneisses, highly metamorphosed rocks that arose from mudstones, limestones and amphibolites, which were part of the crystalline basement. These sequences are overlain by the Köli shale of the Cambrian-Silurian age. The entire rock mass of the Seva cover is intruded by granites, gabbro, basalts, etc. The Caledonide covers piled one on top of the other from west to east.
In the final phases of the Caledonian orogeny in the southern part of the mountainous country, horst, arched uplifts arose in the outer zone of overthrusts. Their eastern front parts are disturbed by normal faults and complicated by secondary overthrusts and overlying folds. These structures seem to be syntectoic for the younger nappes of southern Norway, thrust over older, similar Caledonian structures.
In the Caledonides of Scandinavia, separate tectonic regions are distinguished from north to south according to the structural features: the Varanger Peninsula, South Porsanger, Precambrian windows of the Porsanger Peninsula, Ofoten syncline, Lofotei eruptives, Rombak window, Nazafjell window, Quartzite cover, Sparagmite threshold, Trondheim anticlinorium , areas of sparagmites and gneisses, covers of Pot and. Each of the tectonic regions is distinguished by the peculiarities of the structure and composition of the strata that compose it, one way or another reflected in the relief.
On Svalbard, the Caledonides occupy the western part of the archipelago. They are articulated with the Precambrian basement of eastern Spitsbergen by a tectonic suture. The Svalbard Caledonides are composed of sedimentary deposits deposited on the island of North-Eastern Land on gneisses crumpled into latitudinal folds. These deposits coalesce into the Hekla Hook Formation. Shales, quartzites, dolomites, conglomerates, tillites predominate in its composition. In the western part of the archipelago, the thickness of the Gegla-Khuk stratum is about 16,000 m. It includes thick volcanogenic strata.
The rocks of the Hekla-Khuk series are collected in linearly elongated meridional folds overturned onto the platform and complicated by overthrusts. Large structures are the New Friesland anticlinorium, which stretches for 150 km, the Hinlopen Strait synclinorium, the Cross Fjord anticlinorium, and others. All of these deposits to the south of the archipelago are covered by a cover of Upper Paleozoic and Mesozoic deposits. In their composition, Lower Carboniferous deposits with interlayers of coal are known. In western Svalbard, they form a large trough (from southeast to northwest). In the center of the trough there is a depression filled with conglomerates, sandstones and clays of the Tertiary age with thick layers hard coal. The thickness of these deposits is about 2000 m. In the eastern part of the Svalbard archipelago, traps and traces of volcanic activity in the Mesozoic. The Caledonian folding on Svalbard ended in the Silurian. Intrusions of Caledonian granites are known on the island.
The Caledonides of the British Isles occupy the predominant part of them. Folded structures protrude to the surface here and are covered by a cover of Paleozoic and Cenozoic deposits. The Caledonides of the islands are squeezed into the frame of the Precambrian, in the northwest - by a fragment of the Erne platform, in central England - by the ledge of the East European platform. In the south of England and Ireland, the Caledonides border on the Variscides.
The crystalline basement of the Aria platform is exposed in the northwest of Scotland and the Outer Hebrides. The Precambrian basement of the East European Platform can be traced in the southeastern part of England north of the Hercynide zone. The frame of the Caledonides of Britannia was a single platform in the Precambrian, extending westward in the Atlantic Ocean to the continental slope. In the Late Precambrian, a ditch-shaped subgeosynclinal trough formed in the marginal part, in the modern structure it is occupied by folded Early Paleozoic formations.
Folded Caledonian formations are developed in most of the territory of the Scottish, Northern Irish and South Scottish Highlands, in the Pennines and Cambrian Mountains, and the Central Plain of Ireland.
Various sedimentary deposits of the Lower Paleozoic take part in the structure of the Caledonides of Britain. Their total thickness in the axial part of the British Caledonides, in the South Scottish Highlands, apparently reaches 20,000 m. Their most important feature is the large development of migmatites and granites. In the Caledonides of the British Isles at the present time (Tectonics of Europe, 1963), metamorphic and non-metamorphic zones are distinguished. The first occupies the northwestern part of the country. In the southeast, it is separated from the non-metamorphic zone by a deep fault, or lineament, with which the Great Boundary Fault is associated. The metamorphic zone is characterized by alpine-type tectonics with highly developed covers. Its structure is most pronounced in the Scottish Highlands and Northern Ireland. In the Scottish Highlands, the metamorphic zone is represented by argillite rocks of the Late Precambrian age, overlying shallow and deep water deposits with spilite lavas and greenstone intrusions. The age of these formations is from late Precambrian to late Cambrian.
The dislocations of the metamorphic zone took place in two phases: in the Early or Middle Ordovician and the Middle Silurian. The folds have undergone repeated crushing with the development of overlying folds and integuments. The movement was directed to the outer sides - to the northwest and southeast. In the northwest, the Moin cover is developed, southeast of which the large Grant Glen Fault passes. The foreland underthrust under the dislocated masses is 120 km. A large cover of Loch Tay is developed on the southeastern edge of the metamorphic zone. The recumbent wing of this nappe is exposed along the southern border of the Scottish Highlands. Extensive fields of migmatization and granite intrusions are developed in the Grampian Mountains.
In the southern part of the metamorphic zone, the large graben of the Midland Valley is filled with young sediments, under which the junction of metamorphic and non-metamorphic zones is hidden.
In the non-metamorphic zone of the Caledonides, three structural floors are distinguished. The lower one in the Midland graben, southwestern Scotland and northern Ireland is composed of a spilite complex. The middle structural stage forms the Southern Highlands. It includes the Upper Ordovician and Silurian. Its thickness is 10,000 m. It is characterized by early Devonian granodiorite intrusions. Their massifs are exposed in the western part of the South Scottish Highlands. The middle structural stage of the non-metamorphic zone also includes strata of ancient red sandstone. It was deposited in the ancient depressions of northern Scotland, the Midland graben and the Orkney Islands, accompanied by intense andesitic and basaltic volcanism.
Sedimentary sequences form a series of flexures separated by parallel normal faults. Their structure is complicated by isoclinal, overturned folds.
The complex structure and diverse lithological composition of the Caledonides determine the tectonic relief of the British Isles.
East European platform. Borders. Geological structure.
Borders
The problem of the position of the boundaries of the East European Platform has not yet been unambiguously resolved, and there are different points of view on it.
The map shows the top floor plan of the platform, which is reduced in area.
The nature of the borders is discordant (the platform was part of Pangea), in reality the border passes through the zones of tectonic faults.
The position of the eastern boundary of the platform is most definitely at present.
East platform frames the Ural fold belt 2200 km
(Permian marginal trough), the foundation penetrates part of the Urals, is cut off by a tectonic fault, i.e. in reality, this border is located 150 km east of what is on the map.
In the north-east the Timan-Pechora structure adjoins the platform - a rejuvenated basement (Baikal tectogenesis): it contains relics of an ancient basement - the boundary is drawn along the Urals to the coast; or we completely exclude this structure (according to Milanovsky).
In the north Atlantic Ocean - cont. / oceanic. bark, i.e. includes the shelf up to the Baltic Shield with the Caledonian structures of Scandinavia, which are pushed onto the platform with A = 150-120 km, than on the map to the northwest.
As western border the folded structure of the Carpathians is assumed - the Cis-Carpathian marginal foredeep, the boundary is not real, passes to the west than shown on the map. Moved to VEP. In this area, the super-young platform articulates with the super-old one and forms a giant shear sheet. The Carpathians are a skibian structure.
On South- the border is curvilinear, it passes through the region of the mountainous Crimea (short shelf), includes the Sea of \u200b\u200bAzov, then goes around the Caucasus, the Scythian Plate, reaches the Caspian depression. There is no crystalline basement crust in the axial part of the Caspian syneclise. Therefore, we take only half of the syneclise, one side, but this is not possible, therefore we take the entire structure. (the thickness of the sedimentary cover is 20-25 km, there is no II layer of granite-metal) includes ½; then it goes along the entire coast of the Northern Caspian, the Southern Caspian is not included, then the border reaches the Southern Urals.
Geol. Structure
The geological structure of the East European Platform began in the first half of the 19th century. During its study, for the first time such types of tectonic elements of ancient platforms were identified and named: shields, plates, anteclises, syneclises, aulacogens.
1. Shields - Baltic, Ukrainian.
Voronezh massif (without cover)
2. Cover - syneclises:
Moscow, Glazov, Black Sea, Caspian,
Polish-Lithuanian, Baltic
Anteclise:
Belarusian, Voronezh, Volga-Ural
3. Intermediate sheath - a series of aulacogens:
Moscow, Abdullinsky, Vyatsko-Kama, Lvov, Belomorsky (at the base of the syneclise)
Dnieper-Donetsk aulacogen - Pz structure of the sedimentary cover
It is located between the Voronezh and Ukrainian shields. Before D was a Sarman shield. Now they say that this is an intracratonic geosyncline or rift. According to its structure, it is not similar to syneclise and therefore we attribute it to aulacogen.
