The area is located in the central part of the Moscow syneclise. Its geological structure includes heavily deformed crystalline rocks of the Archean and Proterozoic age, as well as a sedimentary complex represented by deposits of the Riphean, Vendian, Devonian, Carboniferous, Jurassic, Cretaceous, Neogene and deposits of the Quaternary system.

Due to the fact that the description of this territory is carried out according to the available hydrogeological map at a scale of 1: 200,000, the geological structure of the region is given only up to the Moscow stage of the Carboniferous system.

Stratigraphy and lithology

The modern erosion network has exposed Quaternary, Cretaceous, Jurassic deposits and rocks of the upper and middle sections of the Carboniferous system (Appendix 1).

Paleozoic erathema.

Carboniferous system.

The middle section is the Moscow Stage.

Lower Moscow Substage.

Deposits of the Moscow Stage of the Middle Carboniferous are developed everywhere. Their total thickness is 120-125 m. Among the deposits of the Moscow stage, the Vereya, Kashirsky, Podolsky and Myachkovsky horizons stand out.

Vereisky horizon () is ubiquitous. Represented by a pack of oily and silty clays of cherry-red or brick-red color. There are interlayers of limestone, dolomite and flint up to 1m thick. The Vereisky horizon is divided into three strata: Shatsky layers (clays are red with ocher spots); Alyutovskie sequences (fine-grained red sandstone, brick-red clay, clay with silt interlayers); Horde layers (red clays with brachiopods, greenish dolomites, white dolomites with traces of worms). The total thickness of the Vereian horizon in the south is 15-19 m. Determined: Choristites aliutovensis Elvan.

The Kashirsky horizon () is composed of light gray (to white) and variegated dolomites, limestones, marls and clays with a total thickness of 50-65 m. According to lithological features, the Kashirsky stratum is divided into four strata, comparable with the Narskaya (16 m), Lopasninskaya (14 m ), Rostislavl (11 m) and Smedvinskaya strata (13 m) of the southern flank of the syneclise. Rostislavl variegated clays with thin interlayers of limestones and marls with a total thickness of 4-10 m occur in the roof of the Kashirsky horizon. The Rostislavl stratum is absent in the central part of the territory. Kashir deposits contain fauna: Choristites sowerbyi Fisch., Marginifera kaschirica Ivan., Eostafella kaschirika Rails., Parastafella keltmensis Raus.

The Upper Moscow substage is developed everywhere and is subdivided into the Podolsk and Myachkov horizons.

The deposits of the Podolsky horizon () within the pre-Jurassic erosion valley lie directly under the Mesozoic and Quaternary deposits. In the rest of the territory, they are covered by deposits of the Myachkovo horizon, forming a single stratum with it, represented by gray fractured limestones with clay interlayers. On the deposits of the Kashirsky horizon, the Podolsky stratum overlies with a stratigraphic unconformity. The Podolsky horizon is represented by white, yellowish and greenish-gray fine- and fine-grained organogenic limestones with subordinate interlayers of dolomites, marls and greenish clays with chert concretions, with a total thickness of 40-60 m. Choristites trauscholdi stuck., Ch. jisulensis Stuck., Ch. mosquensis Fisch., Archaeocidaris mosquensis Ivan.

The Myachkovsky horizon () in the southern part of the territory under consideration lies directly under the Mesozoic and Quaternary deposits, in the northern and northeastern parts it is overlain by Upper Carboniferous deposits. In the area of ​​the village of V. Myachkovo and near the village. The Kamenno-Tyazhino deposits of the Myachkovian age come to the surface. In the river valley Pakhra and its tributaries have no Myachkovo deposits. The Myachkovsky horizon lies with a stratigraphic unconformity on the deposits of the Podolsky horizon.

The horizon is represented mainly by pure organogenic limestones, sometimes dolomitized with rare interlayers of marls, clays and dolomites. The total thickness of deposits does not exceed 40 m. Myachkovo deposits contain abundant fauna: brachiopods Choristites mosquensis Fish., Teguliferinamjatschkowensis Ivan.

Upper department.

Upper Carboniferous deposits are developed in the northern and northeastern parts of the area under consideration. They are exposed under the Quaternary and Mesozoic formations, and in the area of ​​the city of Gzhel they come to the surface. The Upper Carboniferous is represented by deposits of the Kasimov and Gzhel stages.

Kasimovian stage.

Deposits of the Kasimovian stage are distributed in the northeastern part of the territory. They lie on the Myakkov deposits with erosion.

The Krevyakinsky, Khamovnichesky, Dorogomilovsky and Yauzsky horizons are distinguished in the Kasimovian stage.

The Krevyakinsky horizon in the lower part is composed of limestones and dolomites, in the upper part - variegated clays and marls, which are a regional aquiclude. Horizon thickness up to 18 m.

The Khamovniki horizon is composed of carbonate rocks in the lower part, and clay-marl rocks in the upper part. The total thickness of the deposits is 9-15 m.

The Dorogomilovsky horizon is represented in the lower part of the section by limestone strata, in the upper part by clay and marls. Triticites acutus Dunb are common. Et Condra, Choristites cinctiformis Stuck. The thickness of the deposits is 13-15 m.

The Yauz layers are composed of dolomitic limestones and yellowish, often porous and cavernous dolomites with interlayers of red and bluish carbonate clays. Thickness is 15.5-16.5 m. Triticites arcticus Schellw appears here, Chonetes jigulensis Stuck, Neospirifer tegulatus Trd., Buxtonia subpunctata Nic. The full thickness reaches 40-60 m.

The Gzhel tier () is usually very thin.

The deposits of the Gzhelian stage within the area under consideration are represented by Shchelkovo layers - light gray and brownish-yellow fine-grained or organogenic-clastic, sometimes dolomitic limestones and fine-grained dolomites, in the lower part red clays with limestone interlayers. The total capacity is 10-15m.

Among the Mesozoic deposits in the area described, there are formations of the Jurassic and lower parts of the Cretaceous system.

Jurassic system.

Sediments of the Jurassic system are ubiquitous, except in places of high occurrence of Carboniferous deposits, as well as in ancient and partly modern Quaternary valleys, where they are eroded.

Among the Jurassic deposits, continental and marine sediments stand out. The former include undivided deposits of the Bathonian and lower part of the Callovian stages of the middle section. The second group includes deposits of the Callovian stage of the middle section and the Oxfordian stage of the upper section, as well as deposits of the Volgian regional stage.

The Jurassic deposits rest with angular unconformity on deposits of the Carboniferous system.

Middle department.

The Bathonian and the lower part of the Callovian are combined ()

Continental sediments of the Batian-Callovian age are represented by a sequence of sandy-clayey sediments, gray fine-grained, in some places inequigranular sands with gravel and black clays containing charred plant remains and carbonaceous interlayers. The thickness of these sediments varies from 10 to 35 m, increasing in the lower parts of the pre-Jurassic erosion valley and decreasing on its slopes. They usually lie quite deep under marine sediments of the Upper Jurassic. The output of continental Jurassic deposits on the day surface is observed on the river. Pakhra. The age of the sequence is determined from the remains of the Middle Jurassic flora in similar clays. Identified: Phlebis whitbiensis Brongn., Coniopteris sp., Nilssonia sp., Equisetites sp.

Callovian stage ()

In the territory under consideration, the Callovian stage is represented by the middle and upper Callovian.

The Middle Callovian overlies transgressively on the eroded surface of the Upper and Middle Carboniferous or on continental Batian-Callovian deposits. On the territory under consideration, it has been preserved in the form of separate islands within the Main Moscow Hollow. Usually the deposits are brown-yellow and gray sandy-clay strata with ferruginous oolites with concretions of oolitic marl. Middle Callovian fauna: Erymnoceras banksii Sow., Pseudoperisphinctes mosquensis Fisch. ., Ostrea hemideltoidea Lah., Exogyra alata Geras., Pleurotomaria thouetensis Heb. Et Desl., Rhynchonella acuticosta Ziet, Rh. alemancia Roll, etc.

The thickness of the middle Callovian ranges from 2 to 11; in a buried pre-Jurassic hollow, it reaches 14.5 m. The maximum thickness is 28.5 m.

The Upper Callovian overlies the middle Callovian with erosion and is represented by gray clays, often sandy, with phosphorite and marsh nodules containing ferruginous oolites. The Upper Callovian is characterized by Quenstedticeras lamberti Sow. In connection with their erosion in the Oxfordian time, the Upper Callovian deposits have an insignificant thickness (1-3 m) or are completely absent.

Upper department.

Oxford Tier ()

The deposits of the Oxfordian stage lie with stratigraphic unconformity on the rocks of the Callovian stage and are represented in the study area by the Lower and Upper Oxford.

Lower Oxford is composed of gray, rarely black, sometimes greenish clays with occasional nodules of oolitic marl. The clays are oily, plastic, sometimes shaly, slightly sandy and slightly micaceous. Phosphorites are dense, black inside. The fauna of Lower Oxford is often abundant: Cardioceras cordatom Sow., C. ilovaiskyi M. Sok., Astarta deprassoides Lah., Pleurotomaria munsteri Roem.

The thickness of the lower Oxford is very insignificant (from 0.7 to several meters).

The upper Oxford differs from the lower in a darker, almost black, color of clays, greater grit content, micacity, and an increase in the admixture of glauconite. There are traces of erosion or shallowing at the boundary between upper and lower Oxford. At the contact with Lower Oxford, an abundance of pebbles from the underlying clays, the presence of rounded fragments of belemnite rostra, and bivalve shells are noted.

Upper Oxford is characterized by ammonites of the Amoeboceras alternans Buch group. Here are found: Desmosphinctes gladiolus Eichw., Astarta cordata Trd. and others. The average thickness of the Upper Oxfordian ranges from 8 to 11 m, the maximum reaches 22 m. The total thickness of the Oxfordian stage ranges from 10 to 20 m.

Kimmeridgian ()

The deposits of the Kimmeridgian stage lie with a stratigraphic unconformity on the thickness of the rocks of the Oxfordian stage. The deposits are represented by dark gray clays with interlayers of rare phosphorites and pebbles at the base of the sequence. Identified: Amoeboceras litchini Salt, Desmosphinctes pralairei Favre. and others. The layer thickness is about 10 m.

Volga region.

Lower subtier ()

Occurs with erosion on Oxford. The deposits of the lower Volgian stage come to the surface along the banks of the Moscow, Pakhra, and Mocha rivers.

Dorsoplanites panderi Zone. At the base of the lower Volgian stage there is a thin layer of clay-glauconite sand with rounded and thinned phosphorite concretions. The phosphorite layer is rich in fauna: Dorsoplanites panderi Orb., D. dorsoplanus Visch., Pavlovia pavlovi Mich. The thickness of the lower zone in outcrops does not exceed 0.5 m.

The Virgatites virgatus zone consists of three members. The lower member is represented by thin gray-green glauconite clayey sands, sometimes cemented into sandstone, with rare disseminated phosphorites of the clayey-glauconite type and phosphorite pebbles. Here, for the first time, ammonites of the Virgatites yirgatus Buck group were found. The thickness of the member is 0.3-0.4 m. The upper member is composed of black glauconite clayey sands and sandy clays. The thickness of the pack is about 7 m. The total thickness of the zone is 12.5 m.

The Epivirgatites nikitini Zone is represented by greenish-gray or dark green fine-grained glauconite sands, sometimes clayey, cemented into loose sandstone; nodules of sandy phosphorite are scattered in the sands. The fauna includes Rhynchonella oxyoptycha Fisck, Epivirgatites bipliccisormis Nik., E. nikitini Mich. The thickness of the zone is 0.5–3.0 m. The total thickness of the Lower Volgian stage varies from 7–15 m.

Upper substage ()

The Upper Volgian substage was exposed by boreholes and comes to the surface near the Pakhra River.

It consists of three zones.

The Kachpurites fulgens Zone is represented by dark green and brownish green fine-grained, slightly clayey glauconite sands with fine sandy phosphorites. Here are found: Kachpurites fulgens Trd., K. subfulgens Nik., Craspedites fragilis Trd., Pachyteuthis russiensis Orb., Protocardia concirma Buch., remains of Inoceramus., sponges. The thickness of the zone is less than 1 meter.

The Garniericicaras catenulatum zone is represented by greenish-gray, weakly clayey, glauconite sands with sandy phosphorites, rare at the bottom and numerous in the upper part of the sequence. The sandstones contain abundant fauna: Craspedites subditus Trd. Zone thickness up to 0.7 m.

The Craspedites nodiger Zone is represented by sands of two fapial types. The lower part of the sequence (0.4 m) is composed of glauconite sand or sandstone with intergrowths of phosphorite. The thickness of this sequence does not exceed 3 m, but sometimes it reaches 18 m. Fauna is typical: Craspedites nodiger Eichw., C. kaschpuricus Trd., C. milkovensis Strem., C. mosquensis Geras. The zone reaches a considerable thickness from 3-4 m to 18 m, and in the Lytkarino quarries up to 34 m.

The total thickness of the Upper Volga substage is 5-15 m.

Cretaceous system

Lower section.

Valanginian stage ()

The deposits of the Valanginian stage overlie with stratigraphic unconformity on the rocks of the Volgian regional stage.

At the base of the Valanginian Stage, there is the Riasanites rjazanensis zone - the Ryazan Horizon" - preserved as small islands in the basin of the 30th Moskva River. It is represented by a thin (up to 1 m) layer of sand with sandy phosphorite nodules, with Riasanites rjasanensis (Venez) Nik., R. subrjasanensis Nik., etc.

Barremian ()

The deposits of the lower Valanginian are overlain by the Barremian sandy-argillaceous sequence composed of intercalation of yellow, brown, dark sands, sandy clays, and strongly micaceous argillaceous sandstones with siderite concretions with Simbirskites decheni Roem. The lower part of the Barremian stage, represented by light gray sands 3–5 m thick, is observed in many deposits on the Moskva, Mocha, and Pakhra rivers. At the top, they gradually pass into the Aptian sands. The total thickness of the Barrem deposits reaches 20-25 m; however, due to Quaternary erosion, it does not exceed 5-10 m.

Aptian stage ()

The deposits are represented by light (to white), fine-grained micaceous sands, sometimes cemented into sandstones, with interlayers of dark micaceous clays, in places with plant remains. The total thickness of the Aptian deposits reaches 25 m; the minimum thickness is 3-5 m. Gleichenia delicata Bolch is characteristic.

Albian ()

The deposits of the Albian Stage have been preserved only on the Teplostan Upland. The Aptian deposits lie with stratigraphic unconformity. Under the rough boulders, a 31 m thick sandy-argillaceous deposit was exposed, lying on the gray sands of the Aptian.

Neogene system (N)

Deposits of the Neogene system rest with angular unconformity on Cretaceous deposits.

On the territory under consideration, an alluvial sandy stratum was found. The most complete outcrops of sands of this type are located on the river. Pakhra. These deposits are represented by white and gray 31 fine-grained quartz sands, interbedded with coarse-grained and gravel sands, with flint pebbles at the base, and in some places with interlayers of clays. The sands are diagonally layered, containing pebbles and boulders of local rocks - sandstone, chert and limestone. The total thickness of the Neogene does not exceed 8 m.

Quaternary system (O)

Quaternary deposits (Q) are developed everywhere, overlapping an uneven bed of bedrocks. Therefore, the modern terrain to a large extent repeats the buried relief, which was formed by the beginning of the Quaternary period. Quaternary sediments are represented by glacial formations, which are represented by three moraines (Setun, Don and Moscow) and fluvioglacial deposits separating them, as well as alluvial sediments of ancient Quaternary and modern river terraces.

Lower-Middle Quaternary deposits of the Oka-Dnieper interglacial () are opened by wells and come to the day surface along the tributaries of the river. Pakhry. Water-bearing rocks are represented by sands with interlayers of loams and clays. Their thickness varies from a few meters to 20 m.

Moraine of the Dnieper glaciation (). Has a wide circulation. Represented by loams with pebbles and boulders. The thickness varies from 20 to 25 m.

Alluvial-fluvioglacial deposits occurring between the moraines of the Moscow and Dnieper glaciations (). Distributed in vast spaces between the rivers and along the valleys of the river. Moscow and r. Pakhra, as well as in the southwest, northwest and southeast of the territory. The deposits are represented by loams, sandy loams and sands, with a thickness of 1 to 20 m, sometimes up to 50 m.

Moscow glaciation moraine and cover loams (). Distributed everywhere. The deposits are represented by red-brown boulder loam or sandy loam. The thickness is small 1-2 m.

Water-glacial deposits of the time of the retreat of the Moscow glacier () are common in the northwestern part of the territory and are represented by moraine loams. The thickness of the deposits reaches 2 m.

Valdai-Moscow alluvial-fluvioglacial deposits () are distributed in the southeast of this territory. The deposits are represented by fine-grained sands, about 5 m thick.

Middle-Upper Quaternary alluvial-fluvioglacial deposits () are distributed within three floodplain terraces in the valleys of the Moscow, Pakhra and their tributaries. The deposits are represented by sands, in places with interlayers of loams and clays. The thickness of the deposits varies from 1.0 to 15.0 m.

Modern alluvial lake-marsh deposits () are distributed mainly in the northern part of the territory, on watersheds. The deposits are represented by sapropel (gyttia), gray gleyed lacustrine clays or sands. The thickness varies from 1 to 7 m.

Modern alluvial deposits () are developed within the floodplain terraces of rivers and streams, in the bottoms of ravines. The deposits are represented by fine-grained sands, sometimes silty, in the upper part with interlayers of sandy loams, loams and clays. The total thickness is 6-15 m, on small rivers and in the bottoms of ravines 5-8 m.

Ukraine

Geological structure of Ukraine.

The earth's crust within the territory of Ukraine is of continental type and has a thickness of 25-25 km. It consists of basalt, granite and sedimentary layers. The greatest thickness in Ukraine the earth's crust reaches on the Ukrainian shield and in the Carpathians, and the smallest - in Transcarpathia and under the Black Sea.

Earth's crust

Between the earth's crust and upper mantle is Mohorovichic surface , where the speed of passage of seismic waves changes rapidly. In 1909, its existence was established by the Yugoslav geophysicist Andrei Mohorovichich (1857-1936). In Ukraine, the surface of Mohorovichich lies mainly at a depth of 40-50 km with fluctuations from 30 to 60 km.

The formation of the earth's crust took place over a long geological history - the basalt layer was formed 3.8-4.2 billion years ago. The oldest rocks in Ukraine were found on the Ukrainian Shield (near the city of Zaporozhye) - they are represented by Archean crystalline rocks, whose age is estimated at 3.7 billion years. The age of the Precambrian rocks of the Krivoy Rog ore-bearing series is 2-2.5 billion years, and that of the Kirovograd and Zhitomir granites is 1.9 billion years. The Paleozoic deposits of the Donbass were formed 250-440 million years ago, the Mesozoic deposits of the Crimean mountains - 70-240 million years, and the Cenozoic (Paleogene and Neogene) of the Ukrainian Carpathians - 10-65 million years.

1 - Ukrainian shield; 2 – slopes of the Ukrainian shield and the Voronezh massif; 3 - shield framing: Volyn-Podolsk and Scythian plates, Dnieper-Donetsk depression and Pripyat trough; 4 – southeastern margin of the West European Platform; 5 - Black Sea depression; 6 - Donetsk folded area; 7 - fold systems of the Carpathians, Dobruja and Crimea; 8 - Carpathian and Predobrudzha troughs.

The Earth's crust and mantle surface together make up the Earth's lithosphere. Due to the interaction of the lithosphere, hydrosphere, atmosphere and biosphere, modern landscapes of the earth's surface were formed. An important role in their formation belongs to rocks and the nature of their occurrence.

Ukraine has a number of tectonic regions of different ages, with redi which are the Precambrian East European, Paleozoic Scythian and West European platforms, Cimmerian and Alpine folded structures with a complex geological history and structure.

Ukrainian shield - one of the oldest geological structures of the Earth. It stretches across the entire territory of the country from the northwest (the village of Klyosov, Rivne region) to the southeast almost to the Sea of ​​Azov. The area of ​​the shield is about 180,000 km 2 , the length is more than 1000 km, and the maximum width is 250 km.

Ukrainian shield

The East European platform enters Ukraine with its southwestern and southern parts and occupies a significant area of ​​flat Ukraine. Depending on the depth of the sedimentary strata, crystalline shields and massifs, plateaus, depressions and troughs are distinguished within the platform.

The foundation of the Ukrainian part of the East European Platform is formed by the Ukrainian shield, consisting of solid crystalline Precambrian rocks - granites, gneisses, labradorites, amphibolites, etc. They come to the surface in river valleys on the territory of Rivne, Zhytomyr, Cherkasy, Dnepropetrovsk, Zaporozhye and some other regions .

In the western direction, the rocks of the Ukrainian Shield submerge to a depth of 4-6 km. Here they are covered with a thick layer of Paleozoic, Mesozoic and Cenozoic deposits that form the Volyn-Podolsk plate.

Volyn-Podolsk plate

The Volyn-Podolsk plate is a marginal structure bounded in the southwest by the Carpathian foredeep. The Precambrian basement within the Volyn-Podolsk plate is located at a depth of 2000-2500 m. On its uneven surface, disturbed by tectonic faults, Paleozoic deposits occur. Cambrian rocks are exposed in the river valley. Goryn and Mogilev Transnistria. Deposits of the Ordovician and Silurian systems (represented by carbonate sandstones and limestones) are most common near the city of Kamenetz-Podolsky, where they form the slopes of the Dniester valley and its tributaries (Smotrych, Zbruch and Zhvanchik). Devonian deposits (shales, sandstones and dolomites) are exposed in the Dniester valley near the town of Zalishchyky.

Jurassic deposits and Cretaceous deposits unconformably overlie the uneven surface of Paleozoic rocks. They are represented mainly by chalk and marl, the total thickness of Mesozoic rocks increases from the east (20-30 m) to the west (600-800 m).

Paleogene sands, clays and sandstones are exposed only in the northeast of Volyn Polesie. Significant areas (mainly in the south) are occupied by Neogene limestones, sands, clays and gypsums. Anthropogenic deposits have an almost continuous distribution and are represented mainly by loess-like loams, and in Volyn Polissya - by glacial, water-glacial, alluvial and lacustrine deposits.

Slopes of the Voronezh massif

The northeastern part of Ukraine is occupied by the southwestern slope of the Voronezh crystalline massif. Precambrian rocks occur here at a depth of 150 m (Znob-Novgorodskoye) to 970 m (Putivl) and are overlain by sedimentary Meso-Cenozoic deposits of the Permian, Jurassic, Cretaceous and Paleogene age. Marls, limestones, chalk, glauconite sands, sandstones and clays are exposed in many places in the Sumy, Kharkiv and Lugansk regions (especially on the slopes of river valleys). Anthropogen deposits take part in the structure of the modern relief.

Dnieper-Donetsk depression

Between the Ukrainian shield and the Voronezh crystalline massif is located Dnieper-Donetsk depression - one of the deepest depressions on the East European platform. In its axial part, the Precambrian basement is located at a depth of 12-20 km.

The Dnieper-Donetsk depression is filled mainly with Devonian (over 4000 m thick) sedimentary deposits, Carboniferous (3700 m), Permian (1900 m), Triassic (450 m), Jurassic (650 m), Cretaceous (650 m), Paleogene (250 m ) and Neogene (30 m) rocks. Oil and gas fields are associated with Devonian and Carboniferous rocks in the Dnieper-Donetsk depression. Permian deposits are represented by variegated clays, limestones, dolomites and gypsums. Part of the gas fields are located in the thickness of the Triassic rocks (clays, sands, sandstones and marls). From the Meso-Cenozoic deposits within the Dnieper-Donetsk depression, Jurassic (on the southwestern slope), Cretaceous, Paleogene and Neogene rocks are exposed. The most common Paleogene sands, sandstones, marls and clays. Paleogene and Neogene deposits are overlain by Anthropogenic alluvial and fluvioglacial sands, moraine clays, and loess-like loams.

Donetsk folded region

Dislocated Devonian, Carboniferous and Permian deposits take part in the geological structure of the Donetsk folded region. The most ancient, Devonian, deposits are common in the river basin. Wet Volnovakha and are represented by limestones, shales, sandstones, basalts and tuffs. Particularly important is the carbon deposits, the thickness of which is 10-12 km. These are shales, limestones, sandstones, among which there are numerous (more than 200) layers of coal - for more than two centuries the main mineral resource of Donbass. Permian, Triassic, and Jurassic sandy-argillaceous rocks occur in the northwestern part of the Donets Basin. Cretaceous deposits (marls, chalk) are exposed on the slopes of the hills, and Paleogene clays, sands, marls are found on the periphery of the Donbass, and Neogene sands and clays are found in the southeast.

Granulites are preserved as relict 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.

The formations of the later (Early Proterozoic) time 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.

The 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.
The 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 the 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 Proteroeoic 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
- noe diversity and high degree of 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) the Anginskaya series of the early Proterozoic - amphibolites formed as a result of metamorphism after ancient basaltic 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-basaltic tuffs;
d) the rocks of the Primorsky deep fault zone are represented by Early Proterozoic granites, pre-Riphean dike mafic rocks, metamorphic rocks of the Precambrian series and analogs 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 rocks of the Upper Proterozoic Teptorginsky series developed from 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 suites: 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). The sediments of the Kachergat suite 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 Motskeya 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 erode 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 interlayers of siltstones and sandstones, then quartz and carbonate sandstones with interlayers of marls and siltstones, and at the very top lie 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 partly 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. Upper Psleozoic 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 topography 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 is composed, like the Tutonchanskaya suite, 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, in some places, the pre-Jurassic weathering crust has been preserved in the depressions, represented by siliceous-kaolin, sandy-siliceous breccias and kaolin clays of various colors - white, blue, red, etc. 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, 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 of the 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 on 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 magmatic 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, Sharyzhalgai, 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.
The following tectonic structures can be distinguished by the nature of the Jurassic deposits within the areas of its distribution: 1) the Irkutsk basin and the Rybinsk depression - parts of the foothill 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 blocky 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 bringing to the surface of the Archean rocks of the basement of the ancient platform (Sharyzhalgay, Biryusinsky and Charsky ledges) 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?

GEOLOGICAL STRUCTURE AND HISTORY OF THE DEVELOPMENT OF THE TERRITORY

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 warm seas formed, 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

Questions and tasks.