Historical geology. Historical geology and the past of the earth What does historical geology study

23.12.2020

- (a. historic geology; n. historische Geologie; f. geologie historique; and. geology histurica) is a science that studies the history and patterns of geol. development of the earth. The tasks of I. g. are the reconstruction and systematization of natures. stages of development... Geological Encyclopedia

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historical geology- A branch of geology that studies the history of the development of the Earth from the formation of the earth's crust to its current state ... Geography Dictionary

historical geology- HISTORICAL GEOLOGY, studies the history and patterns of the development of the Earth from the moment the earth's crust was formed to its current state. The main branch of historical geology is stratigraphy. The tasks of historical geology are the restoration of the evolution of the face ... ... Illustrated Encyclopedic Dictionary

historical geology- a branch of geology that studies the history and patterns of development of the earth's crust and the earth as a whole. Its main tasks are the restoration and theoretical interpretation of the evolution of the face of the earth's surface and the organic world inhabiting it, as well as ... ... Great Soviet Encyclopedia

historical geology- a branch of geology that studies the history and patterns of development of the earth's crust and the earth as a whole. The main branch of historical geology is stratigraphy. The tasks of historical geology are the restoration and theoretical interpretation of the evolution of the face of the earth ... ... encyclopedic Dictionary

HISTORICAL GEOLOGY- a branch of geology that studies the history and patterns of development of the earth's crust and the earth as a whole. Main branch of I. g. stratigraphy. Tasks I. g. restoration and theoretical. interpretation of the evolution of the face of the earth's surface and organic. peace, as well as clarifying ... ... Natural science. encyclopedic Dictionary

GEOLOGY- (Greek, from ge earth, and logos word). The science of the composition and structure of the globe and of the changes that have taken place and are taking place in it. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. GEOLOGY Greek, from ge, earth, and logos ... Dictionary of foreign words of the Russian language

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Historical geology , D. I. Panov , E. V. Yakovishina , I. V. Shalimov , L. F. Kopaevich , A guide to practical exercises is intended for students of geological specialties of universities studying the discipline `Historical geology`. This guide consists of two parts. First… Category: Miscellaneous Publisher:

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Abstract "Historical geology"

Chapter. 1 Precambrian

1.1 Organic world

1.2 Platforms

1.3 Geosynclines

1.4 Epochs of folding

1.6 Minerals

Section 2. Paleozoic era

2.2.1 Organic world

2.2.2 Platforms

2.2.3 Geosynclinal belts

2.2.4 Epochs of folding

2.2.6 Minerals

Section 3. Late Paleozoic

3.1 Organic world

3.2 Platforms

3.3 Geosynclinal belts

3.4 Epochs of folding

3.5 Physical and geographical conditions

3.6 Minerals

Section 4. Mesozoic era

4.1 Organic world

4.2 Platforms

4.3 Geosynclinal belts

4.4 Epochs of folding

4.5 Physical and geographical conditions

4.6 Minerals

5.1 Organic world

5.2 Platforms

5.3 Geosynclinal belts

5.6 Minerals

Bibliography

Chapter 1. Historical geology - as a science

precambrian paleozoic fossil geosynclinal

Historical geology includes a number of sections. Stratigraphy deals with the study of the composition, place and time of formation of rock layers and their correlation. Paleogeography considers climate, relief, development of ancient seas, rivers, lakes, etc. in past geological epochs. Geotectonics is engaged in determining the time, nature, and magnitude of tectonic movements. Time and conditions of formation of igneous rocks are restored by petrology. Thus, historical geology is closely connected with almost all areas of geological knowledge.

One of the most important problems in geology is the problem of determining the geological time of formation of sedimentary rocks. The formation of geological rocks in the Phanerozoic was accompanied by increasing biological activity, so paleobiology is of great importance in geological research. For geologists, an important point is that evolutionary changes in organisms and the emergence of new species occur in a certain period of geological time. The principle of final succession postulates that the same organisms are distributed in the ocean at the same time. It follows from this that a geologist, having determined a set of fossil remains in a rock, can find simultaneously formed rocks.

The boundaries of evolutionary transformations are the boundaries of the geological time of formation of sedimentary horizons. The faster or shorter this interval, the more opportunities for more fractional stratigraphic divisions of strata. Thus, the problem of determining the age of sedimentary strata is solved. Another important task is the determination of habitat conditions. Therefore, it is so important to determine the changes that the habitat has imposed on organisms, knowing which we can determine the conditions for the formation of precipitation.

Chapter 2. Geological history of the Earth

Chapter. 1 Precambrian

The Precambrian is the oldest stage of the geological development of the Earth, covering the Archean and Proterozoic eras. During this stage, all the rocks that lie below the Cambrian deposits were formed, which is why it is called the Precambrian. The Precambrian stage is very different from all later stages - the Paleozoic, Mesozoic and Cenozoic. The main features of the Precambrian are the following:

1.1 Organic world

In the Precambrian, there were organisms devoid of skeletal formations. Most of these soft-bodied organisms have not been preserved in the fossil state, which does not allow paleontologists to restore the organic world of the Precambrian. Based on rare finds, it has been indisputably established that the simplest unicellular plant organisms already existed in the Archaean, and representatives of most types of animals lived at the end of the Proterozoic. This indicates a long and complex process of evolution of the organic world in the Precambrian, which scientists are not yet able to trace.

The latest data obtained from the study of Archean rocks under a microscope showed that the "line of life" has dropped to almost 3.5 billion years. Extremely few paleontological finds from Archean rocks, which are still difficult to decipher, are known from Africa, North America, Australia, and the European part of Russia. The most ancient of them (3.2-3.4 billion years) come from South Africa, where the smallest spherical bodies were found, apparently belonging to the simplest unicellular plant organisms. In the younger Archean rocks of South Africa (3 billion years), the most ancient stromatolites, the waste products of blue-green algae, were found in the form of calcareous crusts. In the oldest rocks in Ukraine (3.1 billion years), microscopic rounded formations, possibly of organic origin, were found. Life originated in the Archean in an oxygen-free atmosphere.

In the early Proterozoic (2.6-1.6 billion years), the protozoan unicellular animals and blue-green algae continued their development. Few organic remains are known from the deposits of this time. Organic remains with a well-preserved cellular structure are known from Lower Proterozoic deposits, but all cells were still non-nuclear.

The organic world reached diversity in the late Proterozoic and especially at its end - the Vendian. The Upper Proterozoic limestones contain a variety of stromatolites in large quantities, with the help of which the stratigraphy of the Riphean and Vendian is developed.

The Vendian deposits (680-570 million years) are richest in paleontological remains. Not only numerous unicellular organisms were found in them, but also indisputable imprints of soft-bodied multicellular organisms: coelenterates - jellyfish, worms, arthropods, echinoderms, etc. Their findings are known from the Vendian deposits of Russia, Ukraine, England, USA, Africa, Australia.

Findings of multicellular organisms from South Australia (Ediacara, Flinders Ridge) are very interesting. Here, in the Vendian deposits, more than 1500 imprints of various marine jellyfish, worms, arthropods and other well-preserved non-skeletal animals were found.

Apparently, they lived in shallow lagoons, where they were buried. Jellyfish swam in shallow water. Getting on the sand, they died and left clear casts. Obviously, there were still no predators: the animals had no teeth and no bite marks were found on any organism. Numerous imprints of various soft-bodied animals and traces of their vital activity (minks, traces of crawling, feeding, etc.) were found in the Vendian deposits on the coast of the White Sea.

The Wend represents an important initial stage in the evolution of invertebrate metazoans.

1.2 Platforms

Precambrian metamorphic rocks are exposed in separate areas that have experienced a long uplift. The most extensive areas of Precambrian rocks are shields - places where a folded base comes to the surface - the foundation of ancient platforms. Within the shields, the study of Precambrian rocks is mainly carried out, developing the stratigraphy of the Precambrian.

Precambrian rocks and Precambrian history are well studied on the East European and North American ancient platforms, within the Baltic and Canadian shields. Here the Precambrian rocks are exposed over large areas. The huge glaciers that covered these territories during the recent Quaternary glaciation, in their movement to the south, removed from the surface of the Precambrian rocks a powerful weathering crust, which is widely developed on all shields of other ancient platforms and greatly hinders the study of the Precambrian.

The East European Platform covers the European part of Russia and Ukraine (excluding Crimea, the Caucasus and the Carpathians), as well as most of Poland, the eastern part of Germany and the countries of the Scandinavian Peninsula. On the platform, the Baltic and Ukrainian shields are distinguished, between which there is an extensive Russian plate.

The Baltic Shield occupies a significant northwestern part of the platform. In Russia, it includes Karelia and the Kola Peninsula, outside - Finland, Sweden and a small southern part of Norway.

The entire Baltic Shield is composed of Archean and Proterozoic rocks, which are overlain in places by Quaternary glacial and other continental deposits.

The Archean group consists of two complexes: the Kola and the Belomorsky, composed of deeply metamorphosed rocks. The oldest Kola complex has been preserved in very small areas. These are gneisses that occurred due to deep metamorphism (ultrametamorphism) of volcanic rocks of the basic composition. The age of the rocks of the Kola complex is more than 3000 million years.

The Belomorian complex is more widely distributed, the rocks are exposed along the shores of the White Sea and form the Archean Belomorian massif. These are various gneisses and crystalline schists, which occurred due to deep metamorphism of both igneous and sedimentary rocks. Marbles are also found among them. All rocks are very strongly folded into complex folds, their thickness is several kilometers. The age of the rocks of the White Sea complex is determined in the range of 2900–2600 Ma.

The rocks of the Belomorian complex occur in relatively simple flattened depressions, which differ from true geosynclines. Therefore, they are called "protogeosynclines" (i.e., the precursors of geosynclines). As a result of the White Sea folding, which manifested itself at the end of the Archean era, the protogeosynclines turned into Archean folded massifs.

The Proterozoic rocks are more widespread than the Archean ones; they form folded systems in a northwestern direction. Three complexes have been identified in the Proterozoic on the Baltic Shield: Lower Karelian, Upper Karelian, and Yatulian.

The Lower Karelian complex consists of various crystalline schists, quartzites, marbles and gneisses with a thickness of 2000-3500 m in Karelia, and up to 8000-12000 m in Finland. Most of these rocks were of marine origin; Initially, they were clayey, sandy and carbonate sediments, which alternated with products of underwater volcanism - lavas, tuffs. Later, they all underwent metamorphism and turned into these metamorphic rocks. The Nizhnekarelian complex is cut through by various intrusions (granites, gabbro, etc.), all rocks are crumpled into complex linear folds. The composition, thickness, and occurrence conditions of the rocks of the Lower Karelian Complex indicate that they were already formed under present geosynclinal conditions. The age of the Lower Karelian complex corresponds to most of the Early Proterozoic (the rocks were formed in the interval 2600--1900 million years) and at the end of this boundary all the rocks were covered by the Karelian folding.

The Upper Karelian complex is very different from the Lower Karelian one both in composition and in the conditions of rock occurrence. It consists mainly of clastic rocks - metamorphosed conglomerates, quartzites, quartzite-like sandstones with interlayers of volcanic formations. All these rocks are thinner, less metamorphosed, and form simpler folded structures than the Lower Karelian ones. By their nature, they resemble the molasse formation, which is formed at the orogenic, final stage of geosynclinal development. The Upper Karelian complex was formed in the interval 1900-1800 Ma.

The Yatuli complex is represented by weakly metamorphosed sedimentary rocks: quartzite-like sandstones, argillaceous and siliceous shales, marbled dolomites, occurring almost horizontally and having a thickness of up to 700-1200 m. Volcanic rocks are rare. In terms of sediment composition, thickness, and occurrence conditions, the Yatuli complex already corresponds to the platform stage of development. The age of the Yatuli complex is the end of the Early Proterozoic (1800-1650 million years interval); at that time, the platform cover of the East European platform began to form.

After the formation of the Yatulian complex, the introduction of peculiar rapakivi granites (in Finnish means “rotten stone”) took place. These dark red granites have very large feldspar crystals, they were intruded and solidified in platform conditions and did not undergo further deformation and metamorphism. In Karelia, Finland and Sweden, large massifs are composed of these granites; they have long been developed as a valuable building material. In St. Petersburg, the Alexandria Column and the columns of St. Isaac's Cathedral were carved from these granites.

The Precambrian of the Ukrainian shield differs in composition and structure of the rocks. Almost the entire shield is composed of Archean gneisses and granite-gneisses. The Lower Proterozoic rocks fill narrow meridional depressions extending northward beyond the Ukrainian shield into the Kursk and Voronezh regions. These rocks are associated with deposits of iron-rich ores of Krivoy Rog and colossal deposits of the Kursk magnetic anomaly. In Krivoy Rog, the Lower Proterozoic deposits are part of the Krivoy Rog complex, which consists of alternating thin layers of shale and ferruginous quartzites. The latter are fine-grained quartzites with interlayers of iron oxide - hematite. The extent of these thin layers over long distances indicates that the ferruginous quartzites were formed under marine conditions. The Krivoy Rog complex has a thickness of more than 4000 m and corresponds in age to most of the Early Proterozoic (radiometric methods determined the interval of its formation - 2600-1900 million years). During the late Proterozoic, the Baltic and Ukrainian shields were uplifted areas - demolition areas. Clastic rocks of the platform cover accumulated between them over a vast area of the Russian Plate. Riphean coarse clastic rocks occur in deep troughs - aulacogenes, while Vendian sandy and clayey deposits are more widespread, they lie at the base of the platform cover of the East European Platform.

Other ancient platforms

On other ancient platforms, the structure of the Precambrian and the Precambrian history in general terms show similarities with the East European platform. In the Early Archean, the formation of volcanic rocks of basalt composition and an insignificant amount of sedimentary rocks was noted on all ancient platforms, and in the Late Archean, rather thick sedimentary and volcanic formations accumulated in protogeosynclinal troughs. In contrast to the East European Platform, in the Early Proterozoic, both geosynclinal and platform deposits were formed on the territories of the Siberian, North American, and South African platforms. In contrast to the platform deposits of the cover of ancient platforms, these ancient Lower Proterozoic platform deposits are called protoplatform deposits. On the Siberian Platform, protoplatform deposits of the most ancient Lower Proterozoic cover are known in Transbaikalia in the western part of the Aldan Shield, north of the Stanovoi Ridge. Here, in a large trough, very gently thick sedimentary deposits (up to 10-12 km) occur, consisting of weakly metamorphosed sandstones and shales. The thickest deposits of the most ancient protoplatform cover are found in the south of the African-Arabian platform. In the Transvaal, weakly metamorphosed detrital and volcanic rocks are exposed over a large area, reaching a colossal thickness of 20 km. Deposits of gold and uranium are confined to conglomerates. On all the ancient platforms, as well as on the East European one, intensive folding processes appeared in the second half of the Early Proterozoic, as a result of which, at the end of the Early Proterozoic, a folded basement of ancient platforms was formed and the accumulation of sedimentary rocks of the platform cover began. The process of accumulation of cover rocks was especially intense in the Late Proterozoic.

1.3 Geosynclines

Geosynclinal belts arose in the Proterozoic era. Small belts - Intra-African and Brazilian - existed from the beginning of the Proterozoic era and completed their geosynclinal development at its end. Their structure and geological history are very poorly studied. Large belts began their geosynclinal development from the Late Proterozoic. Upper Proterozoic rocks are widely distributed in them, but they come to the surface only in certain areas that have experienced prolonged uplift. Everywhere these rocks are metamorphosed to one degree or another and have enormous thicknesses. Until now, the Upper Proterozoic rocks in different belts have been studied extremely unevenly. They have been studied in more detail within the Ural-Mongolian belt.

This belt covers a vast territory located between the East European, Siberian, Tarim and Sino-Korean ancient platforms. It has a complex geological structure, the study of which (except for the territory of the Urals) began almost during the years of Soviet power.

The Upper Proterozoic rocks are very widely distributed within the belt, but they are well studied in the Urals, Kazakhstan, Altai, the Tien Shan, and the Baikal folded region.

On the western slope of the Urals there is a complete section of Riphean and Vendian deposits of great thickness (up to 15 km). Here, Soviet geologists first identified Riphean deposits. The entire section is divided into 4 complexes, which consist of metamorphic marine sedimentary deposits crumpled into folds: sandstones, shales and limestones with rare interlayers of volcanic rocks. Various stromatolites are found in limestones, according to which the stratigraphy of the Riphean is developed.

To the east, in Kazakhstan, on the Tien Shan and in the Altai-Sayan mountainous region, the role of volcanic rocks among the Upper Proterozoic deposits sharply increases. In some areas, these deposits reach a colossal thickness - over 20 km. All rocks are intensely folded and strongly metamorphosed.

Vast areas are composed of Upper Proterozoic rocks in the Baikal and Transbaikal regions, where they form a complexly constructed folded area. Very thick, highly metamorphosed Riphean marine sedimentary and volcanic formations, which were undoubtedly formed at the main geosynclinal stage, are especially widespread here. All these Riphean deposits are intruded by numerous granite intrusions. The Riphean folded rocks are overlain by Vendian coarse clastic rocks (up to 6 km), which formed during the orogenic stage.

The study of the Upper Proterozoic deposits in the Baikal folded region allowed Soviet geologists to establish the largest epoch of mountain building in the Precambrian, which manifested itself at the end of the Proterozoic in all geosynclinal belts and was called the Baikal folding.

1.4 Epochs of folding

Precambrian epochs of folding, epochs of increased tectono-magmatic activity, which manifested themselves during the Precambrian history of the Earth. They covered the time interval from 570 to 3500 million years ago. They are established on the basis of a number of geological data - changes in the structural plan, manifestations of breaks and disagreements in the bedding of rocks, abrupt changes in the degree of metamorphism. The absolute age of D. e. With. and their interregional correlation are established on the basis of determining the time of metamorphism and the age of igneous rocks using radiological methods. Methods for determining the age of ancient rocks allow for the possibility of errors (about 50 million years for the late and 100 million years for the early Precambrian). Therefore, the establishment of the time D. e. With. much less certain than the dating of the Phanerozoic folding epochs. The data of radiometric determinations testify to the existence in the Precambrian of a number of epochs of tectonic-magmatic activity, which manifested themselves approximately simultaneously throughout the globe. On different continents D. e. With. received different names.

The most ancient of them - the Kola (Saami; Baltic Shield), or Transvaal (South Africa), manifested itself at the turn of about 3000 million years ago and was expressed in the formation of the most ancient cores of the continents. Relics of these cores have been found on all ancient platforms (so far, except for the Sino-Korean and South China). Even more widespread are manifestations of the next epoch, which is called White Sea on the Baltic Shield, Kenoran in Canada, and Rhodesian in Africa; it manifested itself 2500 million years ago, the formation of large cores of shields of ancient platforms is associated with it. Of great importance was the Early Karelian (Baltic Shield) or Eburnean (West Africa) epoch (about 2000 million years ago), which, together with the subsequent Late Karelian epoch (Hudson for the Canadian Shield and Mayomb for Africa), which took place about 1700 million years ago , played a decisive role in the formation of the foundations of all ancient platforms. Tectonic-magmatic epochs in the interval of 1700-1400 million years (for example, the Luxford in Scotland - about 1550 million years) have been established only on individual continents.

Of planetary significance is the Gothic (Baltic Shield) or Elsonian (Canadian Shield) epoch - about 1400 million years ago, but it was expressed not so much in the folding of geosynclinal formations, but in repeated metamorphism and granitization of individual zones within the foundation of ancient platforms. The next epoch, the Dalslandian (Baltic Shield), Grenville (Canadian Shield), or Satpur (Indostan), which took place about 1000 million years ago, was the first major epoch of folding of the Neogean geosynclinal belts. Final from D. e. With. - Baikal (Assintskaya in Scotland, Kadomskaya in Normandy and Katangese in Africa) - very widely manifested itself on all continents, including Antarctica, and led to the consolidation of significant areas within the neogean geosynclinal belts. The Baikal movements began about 800 million years ago, their main impulse occurred about 680 million years ago (before the deposition of the Vendian complex), the final impulse occurred at the beginning or in the middle of the Cambrian.

The Baikal fold systems on the territory of the USSR include the systems of Timan, the Yenisei Ridge, parts of the Eastern Sayan, and the Patom Highlands; Baikal folded systems of this age are widespread in Africa (Katangides, Western Congolids, Atakor and Mauritanian-Senegal zones, etc.), in South America (Brazilides), in Antarctica, Australia, and on other continents. A common feature of D. e. With. -- a significant development of regional metamorphism and granitization, decreasing in intensity from ancient to later eras; on the contrary, the scale of mountain building and folding itself, apparently, were weaker than the Phanerozoic; characteristic structural forms, especially for the Early Precambrian, were granite-gneiss domes.

1.5 Physical and geographical conditions

The physical and geographical situation in the Precambrian differed not only from the modern one, but also from that which existed in the Mesozoic and Paleozoic. In the Archean era, the hydrosphere already existed and sedimentation processes were underway, but the Earth’s atmosphere did not yet have oxygen, its accumulation was associated with the vital activity of algae, which only in the Proterozoic conquered more and more expanses of the ocean floor, gradually enriching the atmosphere with oxygen. The processes of sedimentation are directly dependent on physical and geographical conditions; in the Precambrian, these conditions had their own specific features, in many respects different from modern ones. Thus, for example, among the Precambrian rocks, ferruginous quartzites, siliceous rocks, and manganese ores are often found, and, conversely, phosphorites, bauxites, salt-bearing, coal-bearing, and some other sedimentary deposits are completely absent.

All these features of the Precambrian greatly complicate the reconstruction of its geological history. Significant difficulties also arise in determining the age of rocks. For this purpose, non-paleontological methods for determining the relative age of rocks and methods for determining their absolute age are used.

For the Precambrian, unified international geochronological and stratigraphic divisions have not yet been developed. It is customary to distinguish two eras (groups) - Archean and Proterozoic, the boundary between which is often difficult to draw. With the help of radiometric methods, it was established that this boundary passes at the turn of 2600 Ma. The Proterozoic era (group) is usually subdivided into 2 sub-eras (subgroups), smaller divisions are local regional.

The following division of the Precambrian is accepted

Eras (groups)	Subdivisions of the Proterozoic	Main boundaries
Proterozoic PR (more than 2 billion years)	Late (upper) Proterozoic, or Riphean, PR2 (1030 Ma)	Late (Upper) Riphean R3 Middle Riphean R2 Early Riphean (lower) R1	End 570 million 1600 million years
	Early (lower) Proterozoic, or Karelia, PR1 (1000 Ma)	2600 Ma start over 4000 Ma
Archean AR (approximately 1.5 billion years)	There are no generally accepted subdivisions, the lower limit has not been established

1.6 Minerals

A diverse complex of minerals is associated with the Precambrian strata: over 70% of iron ore reserves, 63% of manganese, 73% of chromium, 61% of copper, 72% of sulfide nickel, 93% of cobalt, 66% of - uranium ores. The Precambrian contains the richest deposits of iron ores - ferruginous quartzites and jaspilites (the Kursk magnetic anomaly, the Karsakpai deposit of Kazakhstan, etc.). Also associated with the Precambrian are deposits of aluminum raw materials (kyanite and sillimanite, bauxites, for example, the Bokson deposit in Russia), manganese (numerous deposits of India). The Witwatersrand Precambrian conglomerates contain the largest deposits of uranium and gold, and numerous intrusions of basic and ultrabasic rocks in many areas of the world contain deposits of ores of copper, nickel and cobalt. Lead-zinc deposits are confined to the carbonate rocks of the Precambrian, and oil deposits are associated with the very tops of the Precambrian of eastern Siberia (the Markovskoye deposit in the Irkutsk region).

Section 2. Paleozoic era

Paleozomy emra, Paleozomy, PZ (Greek r?lbyt - ancient, Greek zhshchYu - life) - the geological era of the ancient life of the planet Earth. The oldest era in the Phanerozoic eon follows the Neoproterozoic era, followed by the Mesozoic era. The Paleozoic began 542 million years ago and lasted about 290 million years. Consists of the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian periods. The Paleozoic group was first identified in 1837 by English geologist Adam Sedgwick. At the beginning of the era, the southern continents were united into a single supercontinent Gondwana, and by the end other continents joined it and the supercontinent Pangea was formed. The era began with the Cambrian explosion of the taxonomic diversity of living organisms, and ended with the mass Permian extinction.

2.1 Organic world

In the Cambrian period, the main life was concentrated in the seas. Organisms have colonized all the variety of available habitats, down to coastal shallow waters and, possibly, fresh water bodies. The aquatic flora was represented by a wide variety of algae, the main groups of which arose as early as the Proterozoic era. Starting from the late Cambrian, the distribution of stromatolites gradually decreases. This is due to the possible appearance of herbivorous animals (possibly some forms of worms) eating stromatolite-forming algae.

The bottom fauna of shallow warm seas, coastal shoals, bays and lagoons was represented by a variety of attached animals: sponges, archaeocyates, coelenterates (various groups of polyps), stalked echinoderms (sea lilies), brachiopods (lingula) and others. Most of them fed on various microorganisms (protozoa, unicellular algae, and so on), which they filtered out of the water. Some colonial organisms (stromatopores, tabulates, bryozoans, archaeocyates), possessing a calcareous skeleton, built reefs on the bottom of the sea, like modern coral polyps. Various worms, including hemichordates, have adapted to burrowing life in the thickness of the bottom sediments. Inactive echinoderms (starfish, brittle stars, sea cucumbers, and others) and mollusks with shells crawled along the seabed among algae and corals. In the Cambrian, the first free-swimming cephalopod mollusk appears - the nautiloid or boat. In the Devonian, more perfect groups of cephalopods (ammonites) appeared, and in the Lower Carboniferous, the first representatives of higher cephalopods (belemnites) arose, in which the shell gradually reduced and turned out to be enclosed by the soft tissues of the body. In the thickness and on the surface of the water in the seas lived animals that drifted with the current and kept on the surface with the help of special swim bladders or “floats” filled with gas (intestinal siphonophores, hemichordal graptolites). Highly organized animals also lived in the Cambrian seas - arthropods: gill-breathers, chelicerae and trilobites. Trilobites flourished in the early Cambrian, at that time accounting for up to 60% of the entire fauna, and finally died out in the Permian. At the same time, the first large (up to 2 meters in length) predatory arthropod eurypterids appeared, which reached their peak in the Silurian and the first half of the Devonian and disappeared in the early Permian, when they were replaced by predatory fish.

Beginning with the Lower Ordovician, the first vertebrates appeared in the seas. The oldest vertebrates were fish-like animals, devoid of jaws, with a body protected by a shell (armored jawless). In the Upper Silurian and Devonian deposits, the remains of the most ancient ostracoderms begin to be found, devoid of a heavy bone shell, but covered with scales. The oldest representatives of fish appeared in the seas and fresh waters of the early and middle Devonian and were dressed in a more or less strongly developed bone shell (armored fish). By the end of the Devonian, the armored invertebrates die out, replaced by more progressive groups of jawed. In the first half of the Devonian, there already existed diverse groups of all classes of fish (ray-finned, lung-finned, and lobe-finned), which had a developed jaw, true paired limbs, and an improved gill apparatus. The subgroup of ray-finned fish in the Paleozoic was small. The "golden age" of the other two subgroups fell on the Devonian and the first half of the Carboniferous. They formed in intracontinental fresh water bodies, well warmed by the sun, abundantly overgrown with aquatic vegetation and partly swampy. In such conditions of lack of oxygen in the water, an additional respiratory organ (lungs) arose, allowing the use of oxygen from the air.

2.2.2 Platforms

The geological development of the ancient platforms proceeded in calmer conditions than the development of geosynclinal belts. At the beginning of the early Paleozoic, the platforms of the northern hemisphere experienced subsidence and were covered by sea waters over large areas. The subsidence gave way to slow uplifts, which at the end of the early Paleozoic led to the almost complete drying of all ancient platforms. The huge Gondwana platform massif that existed in the southern hemisphere was uplifted and only its individual marginal parts were periodically covered with small shallow seas.

East European ancient platform

Most of the territory of this platform during the early Paleozoic was dry land. To the south of the Baltic Shield was a vast sea bay, which was located in the so-called Baltic trough. The sea entered this trough from the west and in the Early Cambrian reached the platform boundary near the mountainous area of the Timan-Pechora Baikalids. Sands and clays of small thickness accumulated in the shallow marine basin in the Cambrian. In St. Petersburg, the thickness of the Cambrian deposits reaches 140 m, the greatest thickness is observed in the Northern Dvina basin - more than 500 m. Compared with the thicknesses in geosynclinal areas, these thicknesses seem small.

In the Ordovician, the area of the sea basin decreased. Sands accumulated in its coastal parts, and carbonate silts accumulated over a larger area, from which limestones and marls were later formed. Clay sediments were formed in the extreme west. Among the Ordovician limestones there are oil shales, which were formed from blue-green algae. They have long been developed in a number of fields in Estonia. The Ordovician deposits are thickest in the west, where the subsidence was more intense; in the vicinity of Oslo, the thickness reaches 350-500 m, and in Russia, in the Vologda region, it somewhat exceeds 250 m.

In the Silurian, the area of the marine basin continued to shrink, but the deposits differed little from the Ordovician in their composition and thickness; limestones and clays predominate among them, while oil shales are absent. The regression of the sea continued throughout the Silurian, it led first to the establishment of lagoonal conditions, and at the end of the period to the complete drying of the platform.

Siberian ancient platform

During the early Paleozoic, the Siberian Platform was dominated by marine conditions and its geological history differed from that of the East European Platform. Particularly strong subsidence occurred in the Cambrian period, when almost the entire territory of the platform (except for the Aldan and Anabar shields) was covered by the sea. Among the Cambrian rocks, limestones and dolomites sharply predominate; they formed almost everywhere. Only at the beginning of the period in the south, in lagoonal conditions, there was an accumulation of salt-bearing deposits - gypsum, anhydrites and rock salt, together with carbonate and detrital. The thickness of the Cambrian rocks on the Siberian platform is much greater than on the East European one, it reaches 2.5-3 km, and in the southwest it even exceeds 5 km.

In the Ordovician, the area of the sea basin decreased. It continued to accumulate carbonate sediments, and as it moved southwest, the role of clastic material increased.

The thickness of the Ordovician deposits is less than that of the Cambrian, it does not exceed 2 km and is usually 500–700 m.

In the Silurian, the sea basin continued to shrink, and at the beginning of the period it occupied about half of the platform. It was a huge sea bay, located in the northwestern part of the platform, in which carbonate sediments continued to accumulate. Only in the southwest of this basin, as in the Ordovician, did conglomerates, sandstones, and clays form. At the end of the Silurian, the regression of the sea reached its climax and almost the entire territory of the Siberian Platform turned into lowland land. The thickness of the Silurian deposits is less than the Ordovician, it does not exceed 500 m.

gondwana

Starting from the Cambrian period, Gondwana was a huge platform massif, which during the entire early Paleozoic was in continental conditions and only its marginal parts were covered with shallow seas. Erosion processes took place on the territory of Gondwana, in some places continental sediments accumulated in the depressions.

2.2.3 Geosynclinal belts

During the early Paleozoic, the geosynclinal regime dominated over vast areas of all geosynclinal belts. The exceptions are those parts of the belts that have turned into Baikalids; they developed as young platforms.

The Early Paleozoic geological history of geosynclinal belts is complex and has been studied unevenly in different belts. It has been more fully restored in the Atlantic and Ural-Mongolian belts.

Atlantic geosynclinal belt

This belt covers the coastal areas of Europe and North America. In Europe, the belt includes its northwestern part and a small section of the northeast of Greenland, in North America - a narrow strip of the east coast of Canada, the USA and Mexico. The central part of the belt is currently occupied by the northern basin of the Atlantic Ocean, which did not yet exist in the Paleozoic. As an example, consider the Early Paleozoic history of Northwestern Europe, where the Grampian geosynclinal system was located.

The Grampian geosynclinal system covers Ireland, England and Norway. It consists of rocks of the Lower Paleozoic, crumpled into complex folds, elongated in a northeasterly direction. In the western part of England - Wales - there are complete and well-studied sections of the Cambrian, Ordovician and Silurian; here, back in the 30s of the last century, the corresponding systems were identified.

The section of Wales begins with Cambrian deposits, consisting mainly of sandstones and shales of great thickness (up to 4.5 km). These marine sediments accumulated in deep geosynclinal troughs separated by geoanticlinal uplifts, the main sources of drift. Geosynclinal troughs continued to descend intensively in the Ordovician, during this period a thick sequence (5 km) of clayey and volcanic rocks of basic composition was formed. The presence of thick effusive rocks indicates that during the Ordovician period, strong subsidence in geosynclinal troughs and uplifts in geoanticlines led to the formation of deep faults, along which igneous material erupted onto the surface of the seabed. Similar conditions existed at the beginning of the Silurian, but volcanic activity ceased, so clayey and sandy sediments accumulated. Up the section of the Silurian deposits, the role of clastic material increases, it becomes more and more coarse. Clayey rocks are less and less common, and sandstones and conglomerates sharply predominate. Such a change in the rocks in the section indicates the process of general uplift in the Silurian, which led to an increase in the drift from the land and the influx of a mass of clastic material into the troughs. By the end of the period, all geosynclinal troughs in Wales were filled with coarse clastic sediments, which in some areas reached a very thick thickness (up to 7 km). The Lower Paleozoic deposits at the end of the Silurian period turned out to be intensively folded and uplifted above sea level. Geosynclinal troughs ceased to exist.

Analysis of the geological section of Wales makes it possible to construct a paleogeographic curve that reflects tectonic movements in the early Paleozoic in the area of the Grampian geosynclinal system under consideration. The maximum subsidence and manifestation of volcanic activity occurred in the first half of the Ordovician. Then uplifts began, which continuously increased and led to a general uplift. Characteristically, other parts of this system experienced a similar development in the Early Paleozoic. The mountain-building processes that engulfed the Grampian system and led to a general uplift were called the Caledonian folding (from the old name of Scotland - Caledonia), and the resulting structures are called the Caledonides. As a result of this folding, at the end of the Early Paleozoic, the main geosynclinal stage of development in the Grampian system ended. Instead of a system of geosynclinal troughs and geoanticlinal uplifts, a mountain folded system arose. Completion of the main geosynclinal stage was accompanied by intrusive activity - the intrusion of granitic magma. The considered geological history of Wales in the early Paleozoic is typical for the development of geosynclinal regions at the main geosynclinal stage.

Caledonian folding manifested itself in other geosynclinal systems of the Atlantic belt, but it did not lead everywhere to the completion of the main geosynclinal stage and the creation of Caledonian fold systems. The Caledonids originated in northeastern Greenland, Svalbard, Newfoundland, and the northern Appalachian Mountains. As for the Southern Appalachians and the coast of the Gulf of Mexico, in these areas of the Atlantic belt the main geosynclinal stage continued into the Late Paleozoic.

Ural-Mongolian geosynclinal belt

The vast territory of this belt has a complex structure. In its modern structure, there are several areas of folding of different age. Baikalids are located along the edges of ancient platforms (Timan-Pechora and Baikal-Yenisei regions of the Baikalids); Caledonides - in the center of the belt (Kokchetav-Kyrgyz region) and to the south of the Siberian Baikalids (Altai-Sayan region); Hercynides cover most of the belt (Ural-Tien Shan and Kazakhstan-Mongolian regions). In the early Paleozoic, these areas developed differently. The areas of the Baikal folding completed the geosynclinal development, all the rest were at the main geosynclinal stage.

Altai-Sayan geosynclinal region. This area covers the Mountainous and Mongolian Altai, the Western Sayan, the Tannu-Ola Range and Central Mongolia. Its early Paleozoic history was similar to the history of the Grampian system - the Caledonian folding also manifested itself here, the Caledonides formed, and at the end of the Silurian the main geosynclinal stage ended. Rocks of volcanogenic-sedimentary, terrigenous and carbonate formations are widely distributed. In contrast to the Grampian system, the thickness of the Lower Paleozoic deposits here is much greater (Cambrian - 8-14 km, Ordovician - up to 8 km, Silurian - 4.5--7.5 km).

Kokchetav-Kyrgyz geosynclinal region. This region, located in the middle part of the Ural-Mongolian belt, stretches in a wide arcuate strip from Central Kazakhstan to the Northern Tien Shan. Thick (up to 15 km) marine Cambrian and Ordovician deposits are widespread here, while Silurian deposits are slightly developed and are represented by red-colored continental rocks of the molasse formation.

An analysis of the composition of rocks and their distribution indicates that mountain-building processes in the Kokchetav-Kyrgyz region appeared at the end of the Ordovician. At the turn of the Ordovician and Silurian, the main geosynclinal stage ended, and the orogenic stage began in the Silurian.

Ural-Tien-Shan geosynclinal region. Within this area, located in the western part of the Ural-Mongolian belt, two geosynclinal systems are distinguished: the Ural and the South Tien Shan. The geological structure and geological history of the Ural system are well studied.

The Ural geosynclinal system includes the Urals and Novaya Zemlya. Being a natural pantry of huge mineral wealth, the Urals is still the main mining region of our country. In its bowels are stored large reserves of a wide variety of minerals.

Cambrian rocks in the Ural system are slightly distributed in the south, in the far north of the Urals and on Novaya Zemlya. The small distribution area and the predominance of clastic rocks indicate that in the Cambrian the Urals were a mountainous country that arose as a result of Baikal folding. The sea existed only in the south and north.

Baikal folding, which manifested itself in the Urals, did not lead to the end of the geosynclinal regime, as happened in the adjacent Timan-Pechora region. The processes of subsidence, which began at the end of the Cambrian, covered the entire territory of the Urals in the Ordovician and led to the emergence of the Ural geosynclinal system - a series of meridional geosynclinal troughs separated by geoanticlinal uplifts. This is evidenced by the wide distribution of thick Ordovician deposits. In the central part of the Ural system in the Ordovician, the Uraltau geoanticlinal uplift arose, which was expressed in the relief as a chain of meridionally elongated islands. This uplift divided the Urals into two parts - western and eastern, the development of which proceeded in different ways. Sandy-argillaceous and carbonate deposits accumulated in the western troughs in the Ordovician, while thick volcanic-sedimentary rocks accumulated in the eastern ones. The same distribution of deposits was preserved in the Silurian, when the processes of subsidence were especially intensive, as evidenced by the large thickness of the deposits. In the east, the Silurian rocks reach 5 km, and in the west they do not exceed 2 km. The greater thickness of the deposits and the presence of volcanic rocks in the east are evidence of a stronger subsidence and sharp differentiated movements of the eastern part of the Ural geosynclinal system. The formation of deep faults was accompanied by underwater volcanism. In the west, sedimentation took place in calmer conditions.

The noted regularity in the development of geosynclinal troughs is also inherent in other geosynclinal systems: troughs located near the platforms experienced a smoother subsidence than troughs located far from the platforms. This explains the lower thickness of the deposits and the absence of volcanic material in near-platform troughs.

The main difference between the Early Paleozoic history of the Ural geosynclinal system and the Grampian one is the absence of traces of the Caledonian orogeny in the Urals. The limestones of the Upper Silurian are replaced by the limestones of the Lower Devonian without any trace of a break and differ from each other only in the composition of the fossil marine fauna. Caledonian folding did not appear in the Urals, the main geosynclinal stage continued in the Late Paleozoic.

Even a brief review of the Early Paleozoic history of the three geosynclinal regions of the Ural-Mongolian belt shows that they developed differently. Caledonian folding manifested itself in the Altai-Sayan and Kokchetav-Kyrgyz regions, but at different times. In the Kokchetav-Kyrgyz region, it ended at the border of the Ordovician and Silurian, and in the Altai-Sayan region, at the end of the Silurian. Therefore, the final stage of geosynclinal development in these areas began at different times. In the Ural-Tien Shan region, the Caledonian folding did not manifest itself, and the main geosynclinal stage continued in the Late Paleozoic.

The individual phases of the Caledonian folding that appeared during the Early Paleozoic significantly influenced paleogeography, which is well reflected in paleogeographic maps.

2.2.4 Epochs of folding

Tectonic movements, magmatism and sedimentation. During the early Paleozoic, the earth's crust experienced strong tectonic movements, called the Caledonian folding. These movements did not manifest themselves simultaneously in the geosynclinal belts and reached their maximum at the end of the Silurian period. The most widespread Caledonian folding manifested itself in the Atlantic belt, a large northern part of which turned into a folded area of the Caledonides. The Caledonian orogeny was accompanied by the emplacement of various intrusions.

In the tectonic movements of the early Paleozoic, a certain regularity is observed: in the Cambrian and the beginning of the Ordovician, subsidence processes prevailed, and at the end of the Ordovician and in the Silurian, uplift processes prevailed. These processes in the first half of the Early Paleozoic caused intensive sedimentation in geosynclinal belts and on ancient platforms, and then led to the creation of Caledonian mountain ranges in a number of areas of geosynclinal belts and to a general regression of the sea from the territory of ancient platforms.

The main areas of sedimentation were geosynclinal belts, where the accumulation of very thick, many kilometers long volcanogenic-sedimentary, terrigenous and carbonate formations took place. Carbonate and terrigenous sediments were formed on the ancient platforms of the northern hemisphere. Vast areas of sedimentation were located on the Siberian and Chinese-Korean platforms, and on the East European and North American platforms, sedimentation occurred in limited areas. Gondwana was predominantly an area of erosion, and marine sedimentation occurred in minor marginal areas.

2.2.5 Physical and geographical conditions

According to the theory of lithospheric plate tectonics, the position and outlines of the continents and oceans in the Paleozoic differed from the modern one. By the beginning of the era and throughout the Cambrian, the ancient platforms (South American, African, Arabian, Australian, Antarctic, Hindustan), rotated by 180 °, were united into a single supercontinent called Gondwana. This supercontinent was located mainly in the southern hemisphere, from the south pole to the equator, and covered a total area of more than 100 million km². Gondwana contained a variety of high and low plains and mountain ranges. The sea periodically invaded only the marginal parts of the supercontinent. The remaining smaller continents were located mainly in the equatorial zone: North American, East European and Siberian.

There were also microcontinents:

Central European, Kazakhstan and others. In the marginal seas there were numerous islands bordered by low-lying coasts with a large number of lagoons and river deltas. Between Gondwana and other continents there was an ocean, in the central part of which there were mid-ocean ridges. There were two largest plates in the Cambrian: the entirely oceanic Proto-Kula and the predominantly continental Gondwana plate.

In the Ordovician, Gondwana, moving south, entered the region of the South Geographic Pole (now it is the northwestern part of Africa). The Proto-Farallon oceanic lithospheric plate (and probably the Proto-Pacific plate) was subducted under the northern margin of the Gondwana plate. The reduction of the Proto-Atlantic basin, located between the Baltic Shield, on the one hand, and the single Canadian-Grenland Shield, on the other hand, began, as well as the reduction of oceanic space. During the entire Ordovician, there is a reduction in oceanic spaces and the closure of the marginal seas between the continental fragments: Siberian, Proto-Kazakhstan and China. In the Paleozoic (up to the Silurian - the beginning of the Devonian), the Caledonian folding continued. Typical Caledonides have survived in the British Isles, Scandinavia, North and East Greenland, Central Kazakhstan and the North Tien Shan, Southeast China, Eastern Australia, the Cordillera, South America, the Northern Appalachians, the Middle Tien Shan and other areas. As a result, the relief of the earth's surface at the end of the Silurian period became elevated and contrasting, especially on the continents located in the northern hemisphere. In the early Devonian, the closing of the Proto-Atlantic basin and the formation of the Euro-American mainland took place, as a result of the collision of the Pro-European mainland with the Pro-North American one in the region of present-day Scandinavia and Western Greenland. In the Devonian, the displacement of Gondwana continues, as a result, the South Pole is in the southern region of modern Africa, and possibly present-day South America. During this period, the Tethys ocean depression was formed between Gondwana and the continents along the equatorial zone, three entirely oceanic plates were formed: Kula, Farallon and Pacific (which sank under the Australo-Antarctic margin of Gondwana).

In the Middle Carboniferous, Gondwana and Euroamerica collided. The western edge of the current North American continent collided with the northeastern margin of the South American, and the northwestern edge of Africa collided with the southern edge of present-day Central and Eastern Europe. As a result, a new supercontinent, Pangea, was formed. In the late Carboniferous - early Permian, the Euro-American continent collided with the Siberian continent, and the Siberian continent with the Kazakhstan continent. At the end of the Devonian, the grandiose era of the Hercynian folding began with the most intense manifestation during the formation of the mountain systems of the Alps in Europe, accompanied by intense magmatic activity. In places where the platforms collided, mountain systems arose (with a height of up to 2000-3000 m), some of them have existed to this day, for example, the Urals or the Appalachians. Outside Pangea was only the Chinese block. By the end of the Paleozoic in the Persmian period, Pangea stretched from the South Pole to the North. The geographic South Pole at that time was within the boundaries of present-day East Antarctica. The Siberian continent, which was part of Pangea, which was the northern outskirts, approached the North Geographic Pole, not reaching it by 10--15 ° in latitude. The North Pole was in the ocean throughout the Paleozoic. At the same time, a single oceanic basin was formed with the main Proto-Pacific Basin and the Tethys Ocean Basin, which is the same with it.

See what "Historical Geology" is in other dictionaries:

He studies the patterns of development of the earth's crust in time and space from the moment of its formation to the present day. Historical geology studies: the age of rocks, that is, the chronological sequence of their formation and position in the context ... ... Wikipedia

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historical geology- - Topics oil and gas industry EN historical geology ... Technical Translator's Handbook

historical geology- A branch of geology that studies the history of the development of the Earth from the formation of the earth's crust to its current state ... Geography Dictionary

Branch of geology that studies the history and patterns of development of the earth's crust and the earth as a whole. The main branch of historical geology is stratigraphy. The tasks of historical geology are the restoration and theoretical interpretation of the evolution of the face of the earth ... ... encyclopedic Dictionary

Branch of geology that studies the history and patterns of development of the earth's crust and the earth as a whole. Main branch of I. g. stratigraphy. Tasks I. g. restoration and theoretical. interpretation of the evolution of the face of the earth's surface and organic. peace, as well as clarifying ... ... Natural science. encyclopedic Dictionary

- (Greek, from ge earth, and logos word). The science of the composition and structure of the globe and of the changes that have taken place and are taking place in it. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. GEOLOGY Greek, from ge, earth, and logos ... Dictionary of foreign words of the Russian language

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Historical geology , N. V. Koronovsky , V. E. Khain , N. A. Yasamanov , The textbook was created in accordance with the Federal State Educational Standard in the field of Geology (bachelor's qualification). The textbook outlines modern ... Category: Textbooks for universities Series: Higher professional education. Undergraduate Publisher:

HISTORICAL GEOLOGY, a science that studies the history and regularities of the geological development of the Earth from the moment of its formation. The global tasks of historical geology are the identification and systematization of the natural stages in the development of the earth's crust, the earth as a whole and the organic world of the geological past, the elucidation of the general patterns of the geological development of the earth and the processes that transform it. Among the particular tasks: determining the age of rocks, reconstructing the physiographic (landscape-climatic) conditions of the earth's surface of the past, paleotectonic and paleogeodynamic conditions, studying the history of geological processes (volcanism, plutonism and metamorphism), tectonic movements and deformations, patterns of development of the structure of the earth's crust and the lithosphere in general. To solve these problems, data and methods of stratigraphy and geochronology, paleogeography, historical geotectonics and historical geodynamics are used. In addition, historical geology is also associated with regional geology, paleontology, lithology, mineralogy, petrology, geochemistry, geophysics and other sciences and uses their methods. Among the main ones: methods for determining the relative and isotopic (absolute) geological age of rocks, the actualistic method in combination with facies analysis, methods for analyzing facies, thickness and volume of deposits, formational and lithodynamic complexes, breaks and unconformities; paleomagnetic, seismostratigraphic, etc.

As a complex science, covering all aspects of the geological history of the Earth, historical geology developed in the process of formation of stratigraphy, paleogeography, geotectonics and geology in general (see historical essays of the relevant articles). Modern historical geology, along with the solution of retrospective problems of restoring the geological past of the Earth, sets the task of predicting its future changes. The applied significance of historical geology is determined by the use of established patterns in the history of the formation of the earth's crust to create a theoretical basis for the rational search for mineral deposits contained in it.

The most important problems of historical geology are regularly discussed at the sessions of the International Geological Congress, in Russia - at the annual tectonic, stratigraphic and lithological meetings.

Lit .: Leonov G.P. Historical geology: Fundamentals and methods: Precambrian. M., 1980; Reed G., Watson J. History of the Earth. L., 1981. [T. 1-2]; Windley B. F. The evolving continents. 3rd ed. Chichester; N.Y., 1995; Koponovsky N. V., Khain V. E., Yasamanov N. A. Historical geology. 2nd ed. M., 2006.

The hypothesis of continental drift had a great influence on the development of many branches of geology, including historical geology. I would like to consider this section of geological science in more detail, due to its great importance not only for reconstructing the picture of the Earth's past, but, to a large extent, for predicting its future. Historical geology is one of the major divisions of the geological sciences, in which the geological past of the Earth is considered in chronological order. Since the earth's crust is still accessible to geological observations, consideration of various natural phenomena and processes extends to the earth's crust. The formation of the Earth's crust is determined by various factors, of which the leading ones are time, physical and geographical conditions and tectonics. Therefore, to restore the history of the earth's crust, the following tasks are solved:

1. Determining the age of rocks.

2. Restoration of the physical and geographical conditions of the earth's surface of the past.

3. Restoration of tectonic movements and various tectonic structures.

Even at the beginning of the last century, all the main conclusions about relative geochronology were based mainly on the study of more or less large and relatively highly organized animals, such as molluscs, corals, trilobites, some crustaceans, brachiopods, and vertebrates. Based on these organisms, the main stages in the development of the animal world of the planet were also established. The remains of protozoa and other microscopic organisms were usually not paid serious attention by geologists, because in the light of the then prevailing evolutionary views, it was assumed that these animals change very little over time and cannot be used as indicators of the age of deposits.

However, when drilling wells, it is often completely impossible to detect any signs of a “traditional” fauna in a thin column (core) of the rock raised to the surface. And if the remains of such animals are found, these are often fragments cut by a drill, which are far from always possible to determine. Therefore, it was necessary to pay attention to those organisms that were previously considered unpromising for stratigraphy.

One of the first new groups of particular interest to stratigraphic geologists was the foraminifera. These are small protozoan animals from the class of rhizopods that now inhabit thousands of square kilometers of the seabed. Some of them are spherical in shape, others are star-shaped, and others are lenticular. Even before biologists discovered these creatures in modern seas, their fossils were known to people.

Twenty centuries ago, the ancient Greek geographer Strabo noted that in Egypt there are a large number of small flat stones, which the Egyptians consider to be petrified lentils. Subsequently, it was found that imaginary lentils are animal shells. But only in the 20th century foraminifers took their rightful place in the geochronological scale.

In both the Paleozoic and Mesozoic eras, foraminifera played a huge role in the accumulation of seabed sediments. An even greater number of their skeletons are found in the deposits of the Cenozoic age. A comparative study of the morphological structure of these protozoa showed their rapid evolution over time. Having determined the species and genera of foraminifera encountered in the borehole core, the geologist can confidently judge the relative age of the host rocks. Thanks to the study of ancient foraminifers, serious clarifications were made to the stratigraphic schemes of many areas.

Sometimes the shells of these animals accumulated at the bottom of the seas so much that they formed powerful layers up to several hundred meters thick. Such rocks, almost entirely composed of foraminiferal skeletons, are even named after the predominant forms of these organisms. Limestones of similar origin, called alveolian, are found in the west of France and east of the Adriatic Sea. Another limestone - nummulite - can be traced in a wide band stretching from the Alps and the Southern Mediterranean to the Himalayas. In the countries of the former USSR, nummulite limestones stretch along the northern slopes of the Crimean Range from Sevastopol to Feodosia, and beyond the Caspian Sea they are found in the Paleogene deposits of Ustyurt and Mangyshlak.

Over the years, methods for studying microscopic fossils have improved, become more accurate and versatile. Nowadays, micropaleontology, a branch of paleontology that studies the remains of small organisms, has become an equal participant in stratigraphic research.

The study of primitive crustaceans - ostracods and phyllopods - is now becoming increasingly important. These small crustaceans, whose structure can only be seen under a microscope, are interesting because they live in pools of varying salinity. This makes it possible to compare sediments of different origin, and, knowing the signs by which the inhabitants of marine and freshwater reservoirs are distinguished, one can also judge the conditions under which these sediments were deposited.

In recent years, the attention of many researchers has been attracted by scolecodonts, fossil serrated jaws of annelids, and conodonts, small lamellar formations consisting of crystalline apatite, the origin of which has not yet been sufficiently elucidated. Many also appear to be the jaws of predatory worms, and some are likely body parts of cyclostomes.

In recent decades, another method has appeared in the arsenal of science about the relative age of the Earth, called the spore-pollen method. In spore-pollen analysis, fossil remains of pollen from seed plants and spores belonging to ancient spores, such as mosses, club mosses, and ferns, are examined. Wind and water currents carry myriads of these particles across the surface of the Earth. The dense outer integument of the spores is excellently preserved in the fossil state. The spore-pollen method, first used to clarify the history of modern forests and peatlands, has now taken a prominent place in a number of studies that make it possible to establish the age of sedimentary rocks.

Sometimes, most often in marine sediments, microscopic organisms of peridinea and acritarchs are found along with spores and pollen of plants. It has been established that the Peridineans are fossil remains of dinoflagellates (or flagellates). What is akritarchs is not yet fully understood. Some researchers consider them to be small colonial animals, others to be crustacean eggs, algae, or even dinoflagellates, clothed in a cyst (a shell that some organisms surround themselves with when they find themselves in adverse conditions). But although the nature of these microfossils still remains unclear, their abundance and wide distribution forced scientists to take this group into service, which also helps to solve the problem of the age of the rocks and the conditions for their formation. Together with acritarchs and dinoflagellates, diatoms and golden algae became the subject of stratigraphic studies. All these four groups of paleontological objects are united under the general name "nanoplankton".

In a number of new areas of research, the importance of paleocarpology (from the Latin "carpus" seed) is growing, a branch of paleontology that studies fossil fruits, seeds and megaspores of ferns. Judging by the progress achieved in determining the age of Cenozoic deposits, one can hope that paleocarpological methods will also be useful for the stratigraphy of older formations.

Representatives of this or that extinct species can be found in the intervals of the sedimentary section of different lengths, which indirectly indicates the duration of the existence of this species. Comparing the patterns of distribution of various organisms in time, it is possible to establish the stratigraphic value of each of them and justify the accuracy with which the duration of geological events can be measured. Through the work of many generations of paleontologists, the Phanerozoic geological calendar has been created on a relative time scale.

The fossil remains of ancient plants and animals make it possible to determine the sequence of occurrence of the earth's layers and quite accurately compare the layers containing the fossils. They can be used to judge whether one or another layer is older or younger than another. The remains of organisms will indicate at what stage in the history of the Earth the studied deposits were formed, and will allow them to be correlated with a certain line of the geochronological scale. But if the rocks are "silent", that is, do not contain fossil organisms, this issue cannot be resolved. Meanwhile, many kilometers of Precambrian formations are devoid of fossils. Therefore, in order to determine the age of the most ancient layers of the Earth, some other methods are needed that are fundamentally different from the traditional methods adopted by paleontology.

To accomplish this task, a number of simple and intuitive signs of the temporal relationships of rocks have been developed since ancient times. Intrusive relationships are represented by contacts between intrusive rocks and their enclosing strata. The discovery of signs of such relationships (hardening zones, dikes, etc.) unequivocally indicates that the intrusion was formed later than the host rocks.

Sexual relationships also allow you to determine relative age. If a fault tears rocks, then it was formed later than they. Xenoliths and clasts enter the rocks as a result of the destruction of their source, respectively, they were formed earlier than the host rocks, and can be used to determine the relative age.

The principle of actualism postulates that the geological forces acting in our time worked similarly in former times. James Hutton formulated the principle of actualism with the phrase "The present is the key to the future." The principle of primary horizontality states that marine sediments are deposited horizontally when formed. The principle of superposition lies in the fact that the rocks located in the occurrence not disturbed by folding and faults follow in the order of formation, the rocks lying above are younger, and those that are lower along the section are older.

Historical geology. Historical geology and the past of the earth What does historical geology study

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