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Tasks of historical geology and the main stages of its development. Historical geology and the earth's past Education and work

10.12.2023

Existed at different times in geological history.

tectonic situation and the nature of the past, the development of the earth's crust, the history of the origin and development - uplifts, troughs, folds, faults and other tectonic elements.

Historical geology is one of the major branches of geological sciences, which examines the geological past of the Earth 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 a variety of factors, the leading ones being time, physiographic conditions and tectonics. Therefore, to restore the history of the earth’s crust, the following tasks are solved:

Determining the age of rocks.

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

Reconstruction of tectonic movements and various tectonic structures

Determination of the structure and patterns of development of the earth's crust

1. Includes the study of the composition, place and time of formation of rock layers and their correlation. It is solved by the branch of historical geology - stratigraphy.

2. Considers climate, relief, development of ancient seas, rivers, lakes, etc. in past geological epochs. All these questions are considered by paleogeography.

3. Tectonic movements change the primary occurrence of rocks. They occur as a result of horizontal or vertical movements of individual blocks of the earth's crust. Geotectonics deals with determining the time, nature, and magnitude of tectonic movements. Tectonic movements are accompanied by the manifestation of magmatic activity. Petrology reconstructs the time and conditions for the formation of igneous rocks.

4. Solved on the basis of analysis and synthesis of the results of solving the first three problems.

All main tasks are closely interconnected and are solved in parallel using various methods.

As a science, historical geology began to take shape at the turn of the 18th-19th centuries, when W. Smith in England, and J. Cuvier and A. Brongniard in France came to the same conclusions about the successive change of layers and the remains of fossil organisms located in them. Based on the biostratigraphic method, the first stratigraphic columns, sections reflecting the vertical sequence of sedimentary rocks, were compiled. The discovery of this method marked the beginning of the stratigraphic stage in the development of historical geology. During the first half of the 19th century, almost all the main divisions of the stratigraphic scale were established, the geological material was systematized in chronological sequence, and a stratigraphic column was developed for all of Europe. During this period, the idea of catastrophism dominated in geology, which connected all the changes occurring on Earth (changes in the occurrence of strata, the formation of mountains, the extinction of some types of organisms and the emergence of new ones, etc.) with major disasters.

The idea of catastrophes is replaced by the doctrine of evolution, which considers all changes on Earth as the result of very slow and long-term geological processes. The founders of the doctrine are J. Lamarck, C. Lyell, C. Darwin.

By the middle of the 19th century. These include the first attempts to reconstruct physical and geographical conditions for individual geological epochs for large land areas. These works, carried out by scientists J. Dana, V.O. Kovalevsky and others, laid the foundation for the paleogeographical stage in the development of historical geology. The introduction of the concept of facies by the scientist A. Gressley in 1838 played a major role in the development of paleogeography. Its essence lies in the fact that rocks of the same age can have different compositions, reflecting the conditions of their formation.

In the second half of the 19th century. The idea of geosynclines as extended troughs filled with thick layers of sedimentary rocks is emerging. And by the end of the century A.P. Karpinsky lays the foundations of the doctrine of platforms.

The idea of platforms and geosynclines as the main elements of the structure of the Earth's crust gives rise to the third “tectonic” stage in the development of historical geology. It was first outlined in the works of the scientist E. Og “Geosynclines and Continental Areas.” In Russia, the concept of geosynclines was introduced by F.Yu. Levinson-Lessing at the beginning of the 20th century.

Thus, we see that until the mid-20th century. historical geology developed with the predominance of one scientific direction. At the present stage, historical geology is developing in two directions. The first direction is a detailed study of the geological history of the Earth in the field of stratigraphy, paleogeography and tectonics. At the same time, old research methods are being improved and new ones are being used, such as: deep and ultra-deep drilling, geophysical, paleomagnetic; space sensing, absolute geochronology, etc.

The second direction is work to create a holistic picture of the geological history of the earth’s crust, identify patterns of development and establish a causal relationship between them.

1. The method of ribbon clays is based on the phenomenon of changes in the composition of sediments that are deposited in a calm water basin during seasonal climate change. In 1 year, 2 layers are formed. In the autumn-winter season, a layer of clayey rocks is deposited, and in the spring-summer season, a layer of sandy rocks is formed. Knowing the number of such pairs of layers, one can determine how many years it took for the entire thickness to form.

2.Methods of nuclear geochronology

These methods rely on the phenomenon of radioactive decay of elements. The rate of this decay is constant and does not depend on any conditions occurring on Earth. During radioactive decay, the mass of radioactive isotopes changes and the decay products - radiogenic stable isotopes - accumulate. Knowing the half-life of a radioactive isotope, you can determine the age of the mineral containing it. To do this, you need to determine the relationship between the content of the radioactive substance and its decay product in the mineral.

In nuclear geochronology the main ones are:

Lead method - the process of decay of 235U, 238U, 232Th into isotopes 207Pb and 206Pb, 208Pb is used. The minerals used are monazite, orthite, zircon and uraninite. Half-life ~4.5 billion years.

Potassium-argon - during the decay of K, the isotopes 40K (11%) turn into argon 40Ar, and the rest into the isotope 40Ca. Since K is present in rock-forming minerals (feldspars, micas, pyroxenes and amphiboles), the method is widely used. Half-life ~1.3 billion. years.

Rubidium-strontium - the isotope of rubidium 87Rb is used to form the isotope of strontium 87Sr (the minerals used are mica containing rubidium). Due to its long half-life (49.9 billion years), it is used for the most ancient rocks of the earth's crust.

Radiocarbon - used in archaeology, anthropology and the youngest sediments of the Earth's crust. The radioactive carbon isotope 14C is formed by the reaction of cosmic particles with nitrogen 14N and accumulates in plants. After their death, carbon 14C decays, and the rate of decay determines the time of death of the organisms and the age of the host rocks (half-life 5.7 thousand years).

The disadvantages of all these methods include:

low accuracy of determinations (an error of 3-5% gives a deviation of 10-15 million years, which does not allow the development of fractional stratification).

distortion of results due to metamorphism, when a new mineral is formed, similar to the mineral of the parent rock. For example, sericite-muscovite.

Nevertheless, nuclear methods have a great future, since equipment is constantly being improved, allowing more reliable results to be obtained. Thanks to these methods, it was established that the age of the Earth's crust exceeds 4.6 billion years, whereas before the use of these methods it was estimated only at tens and hundreds of millions of years.

Relative geochronology determines the age of rocks and the sequence of their formation by stratigraphic methods, and the section of geology that studies the relationships of rocks in time and space is called stratigraphy (from Latin stratum-layer + Greek grapho).

biostratigraphic or paleontological,

not paleontological.

Paleontological methods (biostratigraphy)

The method is based on determining the species composition of fossil remains of ancient organisms and the idea of the evolutionary development of the organic world, according to which ancient deposits contain the remains of simple organisms, and younger ones contain organisms of complex structure. This feature is used to determine the age of rocks.

For geologists, an important point is that evolutionary changes in organisms and the emergence of new species occur over a certain period of time. The boundaries of evolutionary transformations are the boundaries of the geological time of accumulation of sedimentary layers and horizons.

The method of determining the relative age of layers using leading fossils is called the leading fossil method. According to this method, layers that contain similar guiding forms are coeval. This method became the first paleontological method for determining the age of rocks. On its basis, the stratigraphy of many regions was developed.

To avoid mistakes, along with this method, the method of paleontological complexes is used. In this case, the entire complex of extinct organisms found in the studied strata is used. In this case, the following can be distinguished:

1-fossil forms that lived in only one layer; 2-forms that first appeared in the layer under study and pass into the overlying one (the lower boundary of the layer is drawn); 3-forms passing from the lower layer and ending their existence in the studied layer (surviving forms); 4-forms that lived in the lower or upper layer, but were not found in the studied layer (upper and lower boundaries of the layer).

Non-paleontological methods

The main ones are divided into:

lithological

structural-tectonic

geophysical

Lithological methods for separating strata are based on differences in individual layers that make up the strata under study in color, material composition (mineralogical and petrographic), and textural features. Among the layers and units in the section, there are those that differ sharply in these properties. Such layers and units are easily identified in adjacent outcrops and can be traced over long distances. They are called the marking horizon. The method of dividing sedimentary strata into individual units and layers is called the marking horizon method. For certain regions or age intervals, the marker horizon can be interlayers of limestone, siliceous shales, conglomerates, etc.

The mineralogical-petrographic method is used when there is no marker horizon and the sedimentary strata is quite uniform in lithological composition; then, to compare individual layers in the section and their relative age, they rely on the mineralogical-petrographic features of individual layers. For example, minerals such as rutile, garnet, zircon were identified in several layers of sandstone and their % content was determined. Based on the quantitative ratio of these minerals, the thickness is divided into separate layers or horizons. The same operation is carried out in an adjacent section, and then the results are compared with each other and the layers in the section are correlated. The method is labor-intensive - it is necessary to select and analyze a large number of samples. At the same time, the method is applicable for small areas.

Structural-tectonic method - it is based on the idea of the existence of breaks in sedimentation in large areas of the earth's crust. Breaks in sedimentation occur when the area of the sea basin where sediment accumulated becomes elevated and the formation of sediments stops there for this period. In subsequent geological times, this area may begin to sink again, again becoming a sea basin in which new sedimentary strata accumulate. The boundary between the strata is a surface of unconformity. Using such surfaces, the sedimentary sequence is divided into units and compared in adjacent sections. Sequences contained between identical unconformity surfaces are considered to be of the same age. In contrast to the lithological method, the structural-tectonic method is used to compare large stratigraphic units in strata.

A special case of the structural-tectonic method is the method of rhythmostratigraphy. In this case, the sedimentary section is divided into units that were formed in the basin during alternating subsidence and uplift of the sedimentation surface, which was accompanied by the advance and retreat of the sea. This alternation was reflected in the sedimentary strata as a sequential change of horizons of deep-water rocks to shallow-water ones and vice versa. If such a sequential change of horizons is observed repeatedly in a section, then each of them is distinguished into a rhythm. And according to such rhythms, stratigraphic sections within one sedimentation basin are compared. This method is widely used to correlate sections of thick coal-bearing strata.

The process of formation of igneous bodies is accompanied by their intrusion into the sedimentary strata of rocks. Therefore, the basis for determining their age is the study of the relationships between the igneous and vein bodies and the sedimentary rock units that they intersected and whose age is established.

Geophysical methods are based on comparing rocks by physical properties. In their geological essence, geophysical methods are close to the mineralogical-petrographic method, since in this case, individual horizons are identified, their physical parameters are compared, and sections are correlated using them. Geophysical methods are not independent in nature, but are used in combination with other methods.

The considered methods of absolute and relative geochronology made it possible to determine the age and sequence of formation of rocks, as well as to establish the periodicity of geological phenomena and identify stages in the long history of the Earth. During each stage, rock strata accumulated successively, and this accumulation occurred over a certain period of time. Therefore, any geochronological classification contains double information and combines two scales - stratigraphic and geochronological. The stratigraphic scale reflects the sequence of accumulation of strata, and the geochronological scale reflects the time period corresponding to this process.

Based on a large amount of data from various regions and continents, the International Geochronological Scale, common to the earth’s crust, was created, reflecting the sequence of time divisions during which certain complexes of sediments were formed and the evolution of the organic world.

In stratigraphy, units are considered from large to small:

eonothema - group - system - department - tier. They correspond

eon - era - period - epoch - century

The main tasks of historical geology 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 elucidation of the history of the transformation of the internal structure of the earth's crust and the development of endogenous processes associated with this. Historical geology also studies the history of the formation of the structure of the earth's crust (historical geotectonics), since movements and tectonic deformations of the earth's crust are the most important factors in most of the changes that have occurred on Earth.

Historical geology is based on the conclusions of special geological sciences. Its basis is stratigraphy, which establishes the sequence of formation of rocks in time and develops a system of chronology of the geological past. One of the main sections of stratigraphy is Biostratigraphy, which uses the remains of extinct animals and plants as indicators of the relative age of rocks and is closely related to paleontology.

Of particular importance to historical geology is the doctrine of the formations of historically determined natural associations (parageneses) of rocks, which reflect in their composition and structure the complex interaction of various processes that took place in the past.

Main part

By the middle of the 19th century. These include the first attempts to reconstruct physical and geographical conditions for individual geological epochs for large land areas. These works, carried out by scientists J. Dan, V.O. Kovalevsky and others, marked the beginning of the paleogeographical stage in the development of historical geology. The introduction of the concept of facies by the scientist A. Gressley in 1838 played a major role in the development of paleogeography. Its essence lies in the fact that rocks of the same age can have different compositions, reflecting the conditions of their formation.

In the second half of the 19th century. the idea of geosynclines as extended troughs filled with thick layers of sedimentary rocks is emerging. And by the end of the century, A.P. Karpinsky laid the foundations of the doctrine of platforms.

The second direction is work to create a holistic picture of the geological history of the earth’s crust, identify patterns of development and establish a causal relationship between them.

The lithosphere is in continuous interaction with other geospheres. The formation of sedimentary rocks occurs as a result of the interaction of the water or air environment, climate and landscape conditions. Climatic conditions, physical and chemical characteristics of sea basins, which determine their salinity, temperature, gas regime, as well as bottom topography and hydrodynamic regime, the nature of continental denudation and accumulation, are always reflected in the textures and material composition of sedimentary rocks. Therefore, sediments formed in a marine or continental setting represent documentary evidence of physical and geographical conditions that existed in the geological past, and rock strata reflect the sequence of their changes. The study of the chemical and mineral composition and structural and textural features of igneous rocks and the shape of the bodies they compose reveals a number of features of their formation and makes it possible to judge the specific features of deep-seated igneous melts. The composition, occurrence conditions, physico-chemical and structural-textural features of volcanogenic and volcanogenic-sedimentary rocks make it possible to establish the types of volcanic apparatuses and other features of terrestrial and underwater volcanism.

The remains of animals and plants buried in rocks provide documentary evidence of the past life of our planet and allow us to consider the history of the Earth and the development of life on it as a single whole.

Historical geology is a complex scientific discipline in which the problem of the geological development of the planet, individual geospheres and the evolution of the organic world are considered as the final results obtained after conducting research within various geological disciplines. Different aspects of this problem are studied by special branches of geology and individual scientific areas. Historical geology uses the results of stratigraphy and paleontology, lithology and petrology, regional geology and geotectonics. In contrast to the listed scientific disciplines and areas, which directly or indirectly address the problem of the historical development of a particular geological object, the goal of historical geology is to generalize the entire set of historical and geological data. After its emergence, historical geology, from a science that dealt with the systematization of geological events and the consideration of historical and geological data in chronological order, gradually began to acquire a synthesizing character. In connection with the differentiation of scientific knowledge, such areas as stratigraphy, geochronology, paleogeography, the study of facies, the study of formations, paleovolcanology, historical geotectonics, etc. were separated from it.

Historical geology equips geologists with the necessary and most important theoretical knowledge. By applying the methods of historical and geological research in practice, geologists learn the patterns of formation of geological bodies; reconstruct the natural conditions that existed on the earth's surface and the physical and chemical conditions in the bowels of the earth; reveal the general genetic and chronological patterns of the occurrence and placement of minerals in the earth's crust; identify evolutionary and catastrophic changes in the atmosphere, hydrosphere, lithosphere and biosphere. All this helps to master the entire cycle of geological sciences and conduct targeted searches and exploration of mineral deposits. Along with this, knowledge about changes in the natural environment over the entire existence of our planet makes it possible to predict the state of the geological environment and the development paths of the biosphere.

Even ancient naturalists and philosophers paid attention to the long history of our planet and the changes that it underwent. Many interesting ideas about the emergence and development of the World were expressed by Thales, Empedocles, Aristotle, Anaximander, Strabo and others. The Middle Ages, with long internecine wars, with the decline of scientific thinking and production, did not know any other history of the creation and development of the earthly face other than the biblical one. During the Renaissance, a turning point occurred in the knowledge of the Earth, as well as in other areas of science and technology. Leonardo da Vinci (1452-1519), studying layers of sedimentary rocks in Lombardy (Northern Italy) in the process of carrying out engineering work, understood the significance of fossil shells as remnants of extinct life.

In 1669, the Danish naturalist Niels Steno (1638-1686), who worked in Italy (Tuscany) and known in scientific circles as Nikolaus Steno, formulated six basic principles of stratigraphy:

the layers of the Earth are the result of sedimentation in water;
the layer containing fragments of another layer was formed after it;
each layer was deposited later than the layer on which it lies, and earlier than the one that overlies it;
a layer containing sea shells or sea salt formed in the sea; if it contains plants, then it came from a river flood or the appearance of an influx of water;
the layer must have an indefinite extent and can be traced across any valley;
the layer was first deposited horizontally; the inclined layer indicates that it has experienced some kind of upheaval. If the next layer rests on inclined layers, then the overturn occurred before the deposition of this layer.

In these correct provisions of N. Stenon we see the beginnings of stratigraphy and tectonics.

In the middle of the 18th century. the great Russian scientist M.V. Lomonosov (1711 -1765) noted the length of geological time, repeated changes in the earth's surface by various geological processes, significant changes in climate and landscape during the history of the Earth.

Historical geology arose in the second half of the 18th century. and was reduced mainly to stratigraphy. A great contribution to the development of this science was made by the Italian scientist D. Arduino, who in 1760 created the first scheme for dividing rocks by age. Thanks to the research of German geologists, especially A. G. Werner (1750-1817), a regional stratigraphic scheme of Central Germany was developed, and on its basis an attempt was made to reconstruct the geological history of the development of Europe.

The French naturalist J. de Buffon (1707-1788), in his work “The Theory of the Earth” (1749), made the first attempt to identify certain stages in the development of the Earth. He divided all sedimentary strata into primary, secondary, and tertiary. The latter term has survived in literature to this day.

The emergence of the paleontological method was of outstanding importance for the development of historical geology. The founders of this method are the English researcher W. Smith (1769-1839) and the French scientists J. Cuvier (1769 - 1832) and A. Brongniard (1801 - 1876). Carrying out geological research at the same time, but independently of each other, they came to the same conclusions related to the sequence of occurrence of the layers and the remains of fossil fauna and flora contained in them, which made it possible to compile the first stratigraphic columns, geological maps and sections of the series regions of England and France. Based on the paleontological method in the first half of the 19th century. Most of the currently known geological systems were identified and the first geological maps were compiled.

The major French scientist J. Cuvier was not only one of the founders of the paleontological method, but also the author of the theory of catastrophes, which at one time enjoyed wide popularity. Based on geological observations, he showed that some groups of organisms died out over geological time, but new ones took their place. His followers J. Agassiz (1807 - 1873), A. d'Orbigny (1802-1857), L. Elie de Beaumont (1798-1874) and others began to explain not only the extinction of organisms, but also many other events occurring in the world as catastrophes. earth's surface. In their opinion, any changes in the occurrence of rocks, relief, changes in landscapes or habitat conditions, as well as the extinction of organisms were the results of various scale catastrophic phenomena that occurred on the earth's surface. Later, the theory of catastrophes was sharply criticized by prominent scientists of the 19th century. - J. Lamarck (1744-1829), C. Lyell (1797 - 1875), C. Darwin (1809 - 1882).The French naturalist J. Lamarck created the doctrine of the evolution of the organic world (Lamarckism) and for the first time proclaimed it a universal law of living nature The English geologist Charles Lyell, in his work “Fundamentals of Geology,” argued that major changes on the Earth occurred not as a result of destructive catastrophes, but as a result of slow, long-term geological processes.Knowledge of the history of the Earth Charles Lyell suggests starting with the study of modern geological processes, considering that they are “the key to understanding the geological processes of the past.” This position of Charles Lyell was subsequently called the principle of actualism. The appearance of the works of Ch. Darwin provided great support to the teachings of evolutionists, since they proved that the organic world is transformed through slow evolutionary changes.

By the middle of the 19th century. These include the first attempts to reconstruct the physical-geographical conditions of certain geological epochs both for individual regions (studies by G. A. Trautschold, J. Dahn, V. O. Kovalevsky) and for the entire globe (J. Marcoux). These works laid the foundations of the paleogeographical direction in historical geology. The introduction of the concept of facies in 1838 by A. Gresley (1814-1865) was of great importance for the development of paleogeography.

During the second half of the 19th century. Expanding geological work is providing more and more information about the structure and history of development of individual regions. By the beginning of the 80s, a colossal amount of material had been collected that needed generalization. This was undertaken by the Austrian geologist E. Suess (1831 - 1914). Information on stratigraphy, the history of the development of the earth's crust, and the activity of geological processes, collected in many parts of the globe, was systematized by E. Suess in the three-volume work “The Face of the Earth” (1883-1909). Geological science after his work acquired a completely different character: scientists began to engage not only in searching for ways to subdivide sedimentary strata and their correlation, but also mainly tried to find explanations for the changing appearance of the earth’s surface, identify patterns in the location of land and sea, explain the localization of minerals, establish the origin of certain rocks, etc.

By the second half of the 19th century. refers to the emergence of the doctrine of facies (German scientist J. Walter, 1893) and a new direction in historical geology - paleogeography (German geologists).

At the turn of the 19th and 20th centuries. A major event in the history of natural science occurred - the discovery of natural radioactivity, which made it possible to establish the true age of our planet, which had previously been estimated by indirect methods that gave significantly underestimated values, and to develop an absolute geochronology. Both meant revolutionary changes in the development of historical and geological knowledge.

The end of the 19th and the beginning of the 20th centuries. were also marked by major discoveries in the field of biostratigraphy and elucidation of the geological history of regions. In Western Europe, North America and Russia, based on the application of the paleontological method, rock strata have been dissected and monographs have been published on fossil remains of various periods of the Paleozoic, Mesozoic and Cenozoic.

Many scientists have contributed to the development of historical geology, and among them it is necessary to note the outstanding role of A.P. Karpinsky (1847 - 1936), the first elected president of the Russian Academy of Sciences. Back at the end of the 19th century. he summarized data on the geological history of the European part of Russia and for the first time compiled paleogeographic maps of this territory.

At the same time, based on the application of the paleontological method, the most prominent domestic geologists S.N. Nikitin (1851 - 1909), F.N. Chernyshev (1856 - 1914) and A.P. Karpinsky published monographs on Paleozoic and Mesozoic deposits of the European part of Russia and the Urals.

At the beginning of the 20th century. the largest French geologist G. E. Og (1861 - 1927) in a multi-volume work described the activity of modern geological processes and tried to decipher the geological history of the Earth. Being a supporter of the doctrine of geosynclines, the idea of which was developed in North America in 1859 by the works of J. Hall and J. Dan, G. E. Og was the first to clearly contrast geosynclines with platforms (the latter he called contrasting areas).

Meanwhile, in the works of Russian scientists A.P. Pavlov (1854-1929) and A.P. Karpinsky, the foundations of the doctrine of platforms were laid, later developed in the works of A.D. Arkhangelsky and N.S. Shatsky.

In Russia, the concept of geosynclines was introduced at the beginning of the 20th century. F.Yu.Levinson-Lessing (1861 - 1939), and A.A. Borisyak (1872 - 1944), following G.E. Og, began to consider historical geology as the history of the development of geosynclines and platforms. In the 1920s, D.V. Nalivkin (1889–1982) developed the fundamentals of the study of facies, and somewhat later, in the works of R.F. Hecker, B.P. Markovsky and other scientists, a paleoecological direction in the study of the geological past began to take shape.

In the first quarter of the 20th century. German geophysicist A. Wegener (1880-1930) first formulated the theory of continental drift - the first hypothesis of mobilism. Despite all its attractiveness, this hypothesis did not gain general acceptance, and soon after the death of its author it was almost completely rejected. However, systematic studies of the ocean floor, begun in the 50s, as well as new geophysical data, brought a large amount of new factual material confirming this hypothesis, and on a different basis, Wegener’s hypothesis was revived and in the 60s it turned into a coherent doctrine - a theory tectonics of lithospheric plates.

20-40s of the XX century. were a time of widespread development of geological research in different regions of the Earth. On their basis, large generalizing works were created on the geological structure and history of the development of Europe (S.N. Bubnov, 1888 - 1957), Siberia (V.A. Obruchev, 1863 - 1956), the European part of Russia (A.D. Arkhangelsky) , North America and other regions. The development of regional studies was facilitated by a generalization of the patterns of development of the earth's crust thanks to the ideas about orogenic phases, substantiated by the largest German tectonist G. Stille (1876-1966) in the second half of the 20th century. as a result of studying enormous factual material on stratigraphy, paleogeography, magmatism, and tectonics.

A big impetus and further development of historical geology was given by deep-sea drilling at the bottom of the World Ocean, which began to be systematically carried out in the mid-60s. As a result of these works, invaluable information was obtained for the first time about the structure and development of the earth's crust not only within the continents, but also within the oceans. Opening in the 50s of the twentieth century. paleomagnetism and the phenomenon of periodic inversion of the Earth's magnetic field led to the emergence of a new physical method in stratigraphy - magnetostratigraphy.

The progress of radiogeochronometry was of great importance for historical geology. For the first time, it made it possible to decipher the Precambrian history of our planet, which was more than six times longer in duration than the Phanerozoic and encrypted mainly in the strata of deeply metamorphosed rocks. Previously, their age was determined mainly by the degree of metamorphism, which sometimes led to gross errors, since on the Canadian Shield Archean formations were considered younger and more strongly metamorphosed than the Middle Proterozoic ones.

Some progress was also achieved in the field of biostratigraphy of the Late Precambrian and, in particular, the Late Proterozoic fauna of invertebrates was discovered.

The concepts put forward in the second half of the 20th century contributed to the discovery of new large mineral deposits, which were preceded by careful and comprehensive historical and geological studies. As a result of historical and geological research, unique oil and gas deposits were discovered in the Volga-Ural region and Western Siberia, in Central Asia, the largest deposits of diamonds, coal, iron ores, non-ferrous and rare metal ores, uranium deposits, precious metals and stones and etc.

Having completed a brief description of the emergence and development of historical geology, let us dwell on the main tasks of this discipline. The main documents by which the geological history of the development of the region is reconstructed are the rocks, the minerals that compose them and the fossil organic remains contained in them, collected by geologists in the process of field work. These materials contain information about geological phenomena and events that occurred in the geological past. A comprehensive study of rock samples in laboratories, restoration of the appearance of animals and plants, their way of life and interaction with the environment make it possible to decipher the geological events that took place and reconstruct the physical and geographical conditions that existed on the earth's surface in the past.

Conclusion

Historical geology studies the geological history of the Earth from the time of its origin, establishes the causes of formation and development of the lithosphere, atmosphere, hydrosphere, cryosphere and biosphere, characterizes landscape-climatic and geodynamic conditions, determines the time of occurrence and studies the conditions for the formation of rocks and associated minerals .

The long history of the Earth is full of many different geological events, phenomena and processes. Considering the geological past in chronological order, historical geology makes it possible to outline both the general patterns of development of our planet and the earth's crust, and the features of individual stages of geological history.

Historical geology is one of the most important courses in geological education. The history of the development of continents and oceans, the evolution of climate, landscapes and the organic world, various catastrophic natural phenomena considered by historical geology, provide a complete scientific understanding of the general patterns of the historical development of geospheres and the Earth as a whole.

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Nemkov G.I., Levitsky E.S., Grechishnikova I.A. et al. Historical geology. - M.: Nedra, 2006.
Podobina V. M., Rodygin S. A. Historical geology. - Tomsk: NTL Publishing House, 2000.

The continental drift hypothesis 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 restoring a picture of the Earth’s past, but, to a large extent, for predicting its future. Historical geology is one of the major branches of geological sciences, which examines the geological past of the Earth 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 a variety of factors, the leading ones being time, physiographic 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. Reconstruction of tectonic movements and various tectonic structures.

Historical geology includes a number of sections. Stratigraphy is the study of the composition, location and time of formation of rock layers and their correlation. Paleogeography examines climate, topography, the development of ancient seas, rivers, lakes, etc. in past geological epochs. Geotectonics deals with determining the time, nature, and magnitude of tectonic movements. Petrology reconstructs the time and conditions for the formation of igneous rocks. Thus, historical geology is closely related to almost all areas of geological knowledge.

One of the most important problems of 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 within a certain period of geological time. The principle of final succession postulates that the same organisms are common 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 rocks that formed at the same time.

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

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 mollusks, 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 established. Geologists usually did not pay serious attention to the remains of protozoa and other microscopic organisms, because in the light of the then prevailing evolutionary views it was assumed that these animals changed very little over time and could not be used as indicators of the age of sediments.

However, when drilling wells, it is often completely impossible to detect any signs of “traditional” fauna in a thin column (core) of rock raised to the surface. And if the remains of such animals are found, they are often fragments cut with a drill, which are not always possible to identify. Therefore, we had to pay attention to those organisms that were previously considered unpromising for stratigraphy.

One of the first new groups that stratigraphic geologists became particularly interested in were foraminifera. These are small protozoan animals from the class of rhizomes, now inhabiting thousands of square kilometers of the seabed. Some of them are spherical, others are star-shaped, and others are lenticular. Even before biologists discovered these creatures in modern seas, people knew their fossil remains.

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

In both the Paleozoic and Mesozoic eras, foraminifera played a huge role in the accumulation of sediments on the seafloor. An even larger number of their skeletons are contained in sediments of Cenozoic age. A comparative study of the morphological structure of these protozoa showed their rapid evolution over time. By identifying 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 foraminifera, serious refinements were made to the stratigraphic schemes of many areas.

Sometimes so many shells of these animals accumulated on the bottom of the seas that they formed thick layers up to several hundred meters thick. Such rocks, almost entirely consisting of foraminiferal skeletons, were 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 - nummulitic - 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, nummulitic 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, becoming more precise 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, the structure of which 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 origins, and, knowing the characteristics by which the inhabitants of marine and freshwater bodies are distinguished, one can also judge the conditions in which these sediments were deposited.

In recent years, the attention of many researchers has been attracted by scolecodonts, fossil serrated jaws of annelid annelids, and conodonts, small, plate-like formations consisting of crystalline apatite, the origin of which is still not well understood. Many of them also appear to be the jaws of predatory worms, and some are probably 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 of seed plants and spores belonging to ancient spores, such as mosses, mosses, and ferns, are examined. Wind and water currents carry myriads of these particles across the surface of the Earth. The dense outer covers of the spores are excellently preserved in fossil form. 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 peridinea are fossil remains of dinoflagellates (or flagellates). What acritarchs are is not yet completely clear. Some researchers consider them small colonial animals, others consider them to be crustacean eggs, algae, or even dinoflagellates encased in a cyst (a membrane with which some organisms surround themselves when exposed to unfavorable conditions). But although the nature of these microfossils continues to remain unclear, their abundance and wide distribution have forced scientists to take this group into account, which also helps solve the question of the age of the rocks and the conditions of their formation. Along with acritarchs and dinoflagellates, diatoms and golden algae became the subject of stratigraphic research. All these four groups of paleontological objects are united under the general name “nanoplankton”.

Among the new areas of research, the importance of paleocarpology (from the Latin “carpus” seed), a branch of paleontology that studies the fossil fruits, seeds and megaspores of pteridophytes, is growing. Judging by the successes achieved in determining the age of Cenozoic deposits, one can hope that paleocarpological methods will also be useful for the stratigraphy of more ancient formations.

Representatives of one or another extinct species can be found in intervals of sedimentary sections of different lengths, which indirectly indicates the duration of existence of this species. By comparing the patterns of distribution of various organisms over 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, a relative time scale, the geological calendar of the Phanerozoic, is being created.

Fossil remains of ancient plants and animals make it possible to determine the sequence of occurrence of the earth's layers and fairly accurately compare the strata containing fossils. From them one can judge whether one or another layer is older or younger than another. The remains of organisms will indicate at what stage of the Earth's history the sediments being studied 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 oldest layers of the Earth, some other methods are needed, fundamentally different from the traditional methods adopted by paleontology.

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

Cross-sectional relationships also allow one to determine relative age. If a fault breaks rocks, it means it formed later than they did. Xenoliths and fragments enter rocks as a result of the destruction of their source, respectively, they formed before their host rocks, and can be used to determine relative ages.

The principle of actualism postulates that the geological forces operating in our time also acted similarly in earlier 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 occur horizontally when formed. The principle of superposition is that rocks that are not disturbed by folds and faults follow in the order of formation, the rocks that lie higher are younger, and those that are lower in the section are older.

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 elucidation of the history of the transformation of the internal structure of the earth's crust and the development of endogenous processes associated with this.

I. geological research is based on the conclusions of particular geological sciences. Its basis is Stratigraphy, which establishes the sequence of formation of rocks in time and develops a system of chronology of the geological past. One of the main sections of stratigraphy is Biostratigraphy, which uses the remains of extinct animals and plants as indicators of the relative age of rocks and is closely related to paleontology. Along with relative geochronology, absolute geochronology is developing, making it possible to directly determine the absolute age of rocks (see Geochronology).

The construction of a system of geological chronology is only a necessary prerequisite for historical and geological research proper, the main content of which is to reconstruct the chronicle of diverse exogenous and endogenous processes that occurred in past times on the surface and in the interior of the Earth.

Restoring these processes and the physical and geographical conditions in which they occurred, including the distribution of land and sea, the depth and characteristics of the hydrological regime of marine reservoirs, relief and climate, the distribution of organisms and their communities, is the task of paleogeography (See Paleogeography).

Ig also studies the history of the formation of the structure of the earth's crust (historical geotectonics), since movements and tectonic deformations of the earth's crust are the most important factors in most of the changes that have occurred on the earth. In matters of the development of deep-seated magmatism, volcanism, and metamorphism, which are naturally related to deformations of the earth’s crust, geological studies are closely related to genetic petrography. Of particular importance to historical geology is the doctrine of the formations of historically determined natural associations (parageneses) of rocks, which reflect in their composition and structure the complex interaction of various processes that took place in the past.

Stratigraphy developed earlier than other branches of biogeography, which became an independent discipline at the beginning of the 19th century, when W. Smith in Great Britain and J. Cuvier and A. Brongniard in France laid the foundations of the biostratigraphic method. This made it possible by the middle of the 19th century. develop in its main outlines a scale of relative geochronology. J. Cuvier developed the concept of catastrophism (see. Catastrophe theory). In the middle of the 19th century. As a result of the triumph of the uniformitarian ideas of Charles Lyell (See Lyell), the catastrophic concept was abandoned in I. and ideas about the continuous and gradual transformation of the face of the Earth were established. In the 2nd half of the 19th century, after the appearance of the works of Charles Darwin, evolutionary teaching penetrated into geology. The formation of modern geological studies as a science also dates back to this period.

I. g. the main patterns of development of geological processes were identified (the emergence and transformation of geosynclines (See Geosyncline) and platforms (See Platform), the formation of continents, changes in the nature of magmatism in the history of the Earth, etc.), and a general direction in the development was outlined the earth's crust and the planet as a whole. see also Geology.

Lit.: Pavlov A.P., Essay on the history of geological knowledge, M., 1921; Borisyak A. A., Course of Historical Geology, 4th ed., L.-M., 1935; Mirchink G.F., Historical Geology, part 1, M.-L., 1935; Mazarovich A.N., Historical Geology, 3rd ed., M.-L., 1938; Korovin M.K., Historical Geology, M., 1941; Strakhov N.M., Fundamentals of Historical Geology, parts 1-2, M.-L., 1948; Leonov G.P., Historical Geology, M., 1956; Bubnov S.N., Basic problems of geology, M., 1960.

E. V. Schanzer.

Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

See what “Historical Geology” is in other dictionaries:

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 section... ... Wikipedia

- (a. historic geology; n. historische Geologie; f. geologie historique; i. geologia histurica) a science that studies the history and patterns of geology. development of the Earth. The tasks of historical geology are the reconstruction and systematization of natural history. stages of development... ... Geological encyclopedia

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

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 present state... Dictionary of Geography

Historical geology- HISTORICAL GEOLOGY, studies the history and patterns of development of the Earth from the moment of formation of the earth's crust to its present 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

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

A branch of geology that studies the history and patterns of development of the earth's crust and the Earth as a whole. Basic branch I. g. stratigraphy. Problems of 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 the changes that have occurred and are occurring 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 preparation Geology (Bachelor qualification). The textbook outlines modern... Category: Textbooks for universities Series: Higher professional education. Bachelor's degree 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 Physiographic 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 Physiographic 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

The boundaries of evolutionary transformations are the boundaries of the geological time of formation of sedimentary horizons. The faster or shorter this interval, the greater the opportunity for more detailed stratigraphic divisions of strata. Thus, the problem of determining the age of sedimentary strata is solved. Another important task is to determine living conditions. Therefore, it is so important to determine the changes that the habitat 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 in the geological development of the Earth, spanning the Archean and Proterozoic eras. During this stage, all the rocks underlying the Cambrian deposits were formed, which is why it is called the Precambrian. The Precambrian stage is very different from all later stages - Paleozoic, Mesozoic and Cenozoic. The main features of the Precambrian are the following:

1.1 Organic world

In the Precambrian there were organisms lacking skeletal structures. Most of these soft-bodied organisms are not preserved in fossil form, which prevents paleontologists from reconstructing the organic world of the Precambrian. Based on rare finds, it has been indisputably established that the simplest single-celled plant organisms already existed in the Archean, and at the end of the Proterozoic, representatives of most types of animals lived. This indicates a long and complex process of evolution of the organic world in the Precambrian, which scientists are not yet able to trace.

Recent data obtained from studying Archean rocks under a microscope have shown that the “frontier of life” has dropped to almost 3.5 billion years. Very 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 discovered, apparently belonging to the simplest unicellular plant organisms. In the younger Archean rocks of South Africa (3 billion years old), the most ancient stromatolites were found in the form of calcareous crusts - waste products of blue-green algae. In the oldest rocks in Ukraine (3.1 billion years old), microscopic rounded formations were discovered, possibly of organic origin. Life originated in the Archean under conditions of an oxygen-free atmosphere.

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

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

The Vendian sediments (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 finds are known from the Vendian deposits of Russia, Ukraine, England, the USA, Africa, Australia.

The finds of metazoans from South Australia (Ediacaran, Flinders Range) are very interesting. Here, in Vendian sediments, more than 1,500 well-preserved prints of various marine jellyfish, worms, arthropods and other non-skeletal animals were found.

Apparently, they lived in shallow lagoons, where they were buried. Jellyfish swam into shallow water. When they fell 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. On the shores of the White Sea, in Vendian deposits, numerous prints of various soft-bodied animals and traces of their vital activity (burrows, traces of crawling, feeding, etc.) were discovered.

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

1.2 Platforms

Precambrian metamorphic rocks are exposed in isolated areas that have experienced long-term uplift. The most extensive areas of Precambrian rocks are shields - places where the folded base - the foundation of ancient platforms - comes to the surface. Within the shields, Precambrian rocks are mainly studied, developing Precambrian stratigraphy.

Precambrian rocks and Precambrian history are well studied on the East European and North American ancient platforms, within the Baltic and Canadian shields. Here, Precambrian rocks are exposed over large areas. The huge glaciers that covered these territories during the recent Quaternary glaciation, during their movement to the south, removed a thick weathering crust from the surface of Precambrian rocks, 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 a vast Russian plate.

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

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

The Archean group consists of two complexes: the Kola and the White Sea, 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 basic composition. The age of the rocks of the Kola complex is more than 3000 million years.

The White Sea complex is more widespread; rocks are exposed along the shores of the White Sea and form the Archean White Sea 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 crushed 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 million years.

The rocks of the Belomorsky complex occur in relatively simply constructed flattened depressions that differ from true geosynclines. Therefore, they are called “protogeosynclines” (i.e., predecessors of geosynclines). As a result of the White Sea folding, which manifested itself at the end of the Archean era, protogeosynclines turned into Archean folded massifs.

Proterozoic rocks are more widespread than Archean rocks; they form folded systems in a northwestern direction. Three complexes have been identified as part of 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 consisted of clayey, sandy and carbonate sediments, which alternated with products of underwater volcanism - lavas, tuffs. Later, they all underwent metamorphism and turned into the indicated metamorphic rocks. The Lower Karelian complex is broken through by various intrusions (granite, gabbro, etc.), all rocks are crushed into complex linear folds. The composition, thickness and conditions of occurrence of the rocks of the Lower Karelian complex indicate that they were already formed under real geosynclinal conditions. The age of the Lower Karelian complex corresponds to most of the Early Proterozoic (the rocks were formed in the range of 2600-1900 million years) and at the end of this period all the rocks were covered by the Karelian folding.

The Upper Karelian complex is very different from the Lower Karelian complex both in composition and in the conditions of occurrence of rocks. 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 million years.

The Yatulian complex is represented by weakly metamorphosed sedimentary rocks: quartzite-like sandstones, clayey and siliceous shales, marbled dolomites, lying almost horizontally and having a thickness of up to 700-1200 m. Volcanic rocks are rare. In terms of the composition of sediments, thickness and conditions of occurrence, the Yatulian complex corresponds to the platform stage of development. The age of the Yatulian complex is the end of the Early Proterozoic (interval 1800-1650 million years); At this 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 (meaning “rotten stone” in Finnish) occurred. These dark red granites have very large feldspar crystals and were intruded and solidified under platform conditions and did not undergo further deformation or 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 the composition and structure of the rocks. Almost the entire shield is composed of Archean gneisses and granite gneisses. Lower Proterozoic rocks fill narrow meridionally elongated depressions that extend north beyond the Ukrainian shield into the Kursk and Voronezh regions. Deposits of Krivoy Rog ores rich in iron content and colossal deposits of the Kursk Magnetic Anomaly are confined to these rocks. In Krivoy Rog, Lower Proterozoic deposits are part of the Krivoy Rog complex, consisting of alternating thin layers of clayey shales and ferruginous quartzites. The latter are fine-grained quartzites with layers of iron oxide - hematite. The extension of these thin layers over long distances indicates that the ferruginous quartzites 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 (the interval of its formation was determined by radiometric methods to be 2600-1900 million years). During the late Proterozoic, the Baltic and Ukrainian shields were uplifted areas - areas of demolition. Clastic rocks of the platform cover accumulated between them on the vast territory of the Russian Plate. Deep troughs - aulacogens - contain Riphean coarse clastic rocks, and Vendian sand and clay 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 Precambrian structure and Precambrian history are broadly similar to the East European Platform. In the Early Archean, on all ancient platforms, the formation of volcanic rocks of basaltic composition and a small amount of sedimentary rocks was noted, and in the Late Archean, fairly 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 in 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. On the Siberian Platform, protoplatform deposits of the ancient Lower Proterozoic cover are known in Transbaikalia in the western part of the Aldan Shield, north of the Stanovoy Range. Here, in a large trough, very gently sloping thick sedimentary deposits (up to 10-12 km) lie, consisting of weakly metamorphosed sandstones and shales. The thickest deposits of the ancient protoplatform cover are found in the south of the African-Arabian Platform. In the Transvaal, weakly metamorphosed clastic and volcanic rocks are exposed over a large area, reaching a colossal thickness of 20 km. Deposits of gold and uranium are confined to the conglomerates. On all ancient platforms, as well as on the East European one, in the second half of the Early Proterozoic, intense folding processes appeared, as a result of which, at the end of the Early Proterozoic, the folded foundation of ancient platforms was formed and the accumulation of sedimentary rocks of the platform cover began. The process of accumulation of cover rocks occurred especially intensively 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 in the Late Proterozoic. Upper Proterozoic rocks are widespread in them, but come to the surface only in isolated areas that have experienced prolonged uplift. Everywhere these rocks are metamorphosed to one degree or another and have enormous thicknesses. Until now, Upper Proterozoic rocks in different zones 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.

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

On the western slope of the Urals there is a complete section of Riphean and Vendian sediments 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 folded metamorphic marine sedimentary deposits: sandstones, shales and limestones with rare interlayers of volcanic rocks. Limestones contain various stromatolites, from which Riphean stratigraphy has been developed.

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

Vast areas are composed of Upper Proterozoic rocks in the Baikal region and Transbaikalia, where they form a complex folded region. Particularly widespread here are very thick, folded into complex folds and highly metamorphosed Riphean marine sedimentary and volcanic formations, which undoubtedly formed at the main geosynclinal stage. 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), the formation of which occurred during the orogenic stage.

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

1.4 Epochs of folding

Precambrian eras of folding, eras of increased tectono-magmatic activity that appeared 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, the manifestation of breaks and unconformities in the bedding of rocks, sudden changes in the degree of metamorphism. Absolute age of D. e. With. and their interregional correlation is established based on 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 Precambrian and 100 million years for the Early Precambrian). Therefore, setting the time of D. e. With. much less certain than the dating of the Phanerozoic folding eras. Data from radiometric determinations indicate the existence of a number of epochs of tectonic-magmatic activity in the Precambrian, which manifested themselves approximately simultaneously throughout the entire globe. On different continents D. e. With. received different names.

The most ancient of them, the Kola (Sami; Baltic Shield), or Transvaal (South Africa), appeared 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 nuclei have been found on all ancient platforms (so far except the Chinese-Korean and South Chinese ones). Even more widespread are manifestations of the next era, called the White Sea on the Baltic shield, the Kenoran on the Canadian shield, and the Rhodesian in Africa; it appeared 2500 million years ago, and the formation of large shield cores of ancient platforms is associated with it. Of great importance was the Early Karelian (Baltic Shield) or Eburnian (West Africa) era (about 2000 million years ago), which, together with the subsequent Late Karelian era (Hudsonian for the Canadian Shield and Mayombian for Africa), which took place about 1700 million years ago , played a decisive role in the formation of the foundations of all ancient platforms. Tectono-magmatic epochs in the range of 1700-1400 million years (for example, the Laxford era in Scotland - about 1550 million years) are established only on individual continents.

The Gothic (Baltic Shield) or Elsonian (Canadian Shield) era is of planetary significance - 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 era - Dalsland (Baltic Shield), Grenville (Canadian Shield), or Satpur (Hindustan), which occurred about 1000 million years ago, was the first major era of folding of the Neogean geosynclinal belts. The final one from D. e. With. - Baikal (Assyntian in Scotland, Cadomian in Normandy and Katangian in Africa) - manifested itself very widely 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 fold systems of this age are widespread in Africa (Katangida, Western Congolides, Atakor and Mauritanian-Senegalese zones, etc.), South America (Brazilians), Antarctica, Australia and other continents. General feature of D. e. With. - 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 was apparently weaker than the Phanerozoic; Characteristic structural forms, especially for the Early Precambrian, were granite-gneiss domes.

1.5 Physiographic 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 larger and larger spaces of the ocean floor, gradually enriching the atmosphere with oxygen. Sedimentation processes are directly dependent on physical and geographical conditions; in the Precambrian, these conditions had their own specific features, largely different from modern ones. For example, among Precambrian rocks there are often ferruginous quartzites, siliceous rocks, manganese ores and, conversely, phosphorites, bauxites, salt-bearing, coal-bearing and some other sedimentary deposits are completely absent.

All of these features of the Precambrian greatly complicate the restoration of its geological history. Significant difficulties arise when 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. Using radiometric methods, it was established that this boundary passes at the turn of 2600 million years. The Proterozoic era (group) is usually divided into 2 sub-eras (subgroups), the smaller divisions being local regional.

The following division of the Precambrian is accepted

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

1.6 Minerals

A diverse complex of mineral resources is associated with the Precambrian strata: over 70% of iron ore reserves, 63% of manganese, 73% of chromium, 61% of copper, 72% of nickel sulfide, 93% of cobalt, 66% of - uranium ores. The Precambrian contains the richest deposits of iron ores - ferruginous quartzites and jaspilites (Kursk magnetic anomaly, Karsakpai deposit in Kazakhstan, etc.). The Precambrian is also associated with deposits of aluminum raw materials (kyanite and sillimanite, bauxite, for example the Boksonskoye deposit in Russia), and manganese (numerous deposits in India). The Precambrian conglomerates of the Witwatersrand contain major deposits of uranium and gold, and numerous intrusions of mafic and ultramafic rocks in many areas of the world contain deposits of copper, nickel and cobalt ores. Lead-zinc deposits are associated with the carbonate rocks of the Precambrian, and oil deposits are associated with the very tops of the Precambrian in eastern Siberia (Markovskoye field 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 planet Earth. The most ancient era in the Phanerozoic eon, follows the Neoproterozoic era, after it comes 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 the 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 taxonomic diversity of living organisms and ended with the Permian mass extinction.

2.1 Organic world

During the Cambrian period, most life was concentrated in the seas. The organisms colonized the full range of available habitats, down to shallow coastal waters and possibly freshwater bodies. The aquatic flora was represented by a wide variety of algae, the main groups of which arose in the Proterozoic era. Beginning in the Late Cambrian, the distribution of stromatolites gradually decreased. This is due to the possible appearance of herbivorous animals (possibly some form of worms) eating the stromatolite-forming algae.

The bottom fauna of shallow warm seas, coastal shallows, bays and lagoons was represented by a variety of attached animals: sponges, archaeocyaths, coelenterates (various groups of polyps), stalked echinoderms (crinoids), brachiopods (lingula) and others. Most of them fed on various microorganisms (protozoa, unicellular algae, etc.), which they strained from the water. Some colonial organisms (stromatopores, tabulates, bryozoans, archaeocyaths), with a calcareous skeleton, built reefs on the seabed, like modern coral polyps. Various worms, including hemichordates, have adapted to burrowing life in the thickness of bottom sediments. Sedentary 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 - a nautiloid or boat - appears. In the Devonian, more advanced groups of cephalopods (ammonites) appeared, and in the Lower Carboniferous, the first representatives of higher cephalopods (belemnites) arose, in which the shell was gradually reduced and became enclosed in 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 stayed on the surface with the help of special swim bladders or “floats” filled with gas (coelenterate siphonophores, hemichordate graptolites). The Cambrian seas were also inhabited by highly organized animals - arthropods: gill-breathing animals, chelicerates and trilobites. Trilobites flourished in the early Cambrian, making up 60% of the total fauna at that time, and finally became extinct in the Permian period. At the same time, the first large (up to 2 meters in length) predatory eurypterid arthropods appeared, which reached their greatest prosperity in the Silurian and the first half of the Devonian and disappeared in the early Permian, when they were replaced by predatory fish.

Starting from the Lower Ordovician, the first vertebrates appeared in the seas. The most ancient 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 most ancient representatives of fish appeared in the seas and fresh water bodies of the Early and Middle Devonian and were dressed in a more or less highly developed bony shell (armored fish). By the end of the Devonian, armored invertebrates died out, replaced by more advanced groups of gnathostomes. In the first half of the Devonian, various groups of all classes of fish (ray-finned, lungfish and lobe-finned fish) already existed, having a developed jaw, true paired limbs and an improved gill apparatus. The subgroup of ray-finned fish was small in the Paleozoic. The “golden age” of the other two subgroups occurred in the Devonian and the first half of the Carboniferous. They formed in inland fresh water bodies, well heated 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 ancient platforms proceeded under 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 with sea water 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 some of its marginal parts were periodically covered by 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 there 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 border of the platform near the mountainous region of the Timan-Pechora Baikalids. In the shallow sea basin in the Cambrian, sands and clays of small thickness accumulated. In St. Petersburg, the thickness of Cambrian sediments reaches 140 m, the greatest thickness is observed in the Northern Dvina basin - more than 500 m. Compared with the thickness 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 subsequently formed. Clay sediments formed in the far west. Among the Ordovician limestones there are oil shales, which were formed from blue-green algae. They have been developed for a long time in a number of deposits in Estonia. The Ordovician deposits are thickest in the west, where subsidence was more intense; in the vicinity of Oslo the thickness reaches 350-500 m, and in Russia in the Vologda region it slightly exceeds 250 m.

In the Silurian, the area of the sea basin continued to shrink, but the sediments differed little in composition and thickness from the Ordovician; Limestones and clays predominate among them, and oil shale is 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 predominate; they were formed almost everywhere. Only at the beginning of the period in the south, in lagoonal conditions, was the accumulation of salt-bearing deposits - gypsum, anhydrites and rock salt, together with carbonate and clastic deposits. The thickness of Cambrian rocks on the Siberian platform is much greater than on the East European platform, 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. Carbonate sediments continued to accumulate in it, and as it moved southwest, the role of clastic material increased.

The thickness of Ordovician deposits is less than Cambrian, it does not exceed 2 km and is usually equal to 500-700 m.

In the Silurian, the sea basin continued to shrink and at the beginning of the period it occupied approximately 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, were conglomerates, sandstones and clays formed. At the end of the Silurian, the regression of the sea reached its apogee and almost the entire territory of the Siberian Platform turned into low-lying 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 throughout the early Paleozoic was in continental conditions and only its marginal parts were covered by shallow seas. Erosion processes took place on the territory of Gondwana, and continental sediments accumulated in some depressions.

2.2.3 Geosynclinal belts

During the Early Paleozoic, the geosynclinal regime dominated over vast areas of all geosynclinal belts. The exception is those sections of the belts that turned into baikalides; 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 northeastern Greenland; in North America, it includes a narrow strip of the eastern coast of Canada, the United States 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 Lower Paleozoic rocks, folded into complex folds elongated in a northeast 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 demolition. Geosynclinal troughs continued to sink intensively in the Ordovician; during this period, a thick layer (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 uplift in geoanticlines led to the emergence of deep faults along which magmatic material flowed onto the surface of the seafloor. Similar conditions existed at the beginning of the Silurian period, but volcanic activity ceased, so clayey and sandy sediments accumulated. Up the section of Silurian deposits, the role of clastic material increases and it becomes increasingly coarse. Clay rocks are becoming less and less common, while sandstones and conglomerates predominate. Such a change in the rocks in the section indicates a process of general uplift in the Silurian, which led to an increase in the removal from land and the entry of a mass of clastic material into the troughs. By the end of the period, all geosynclinal troughs of Wales were filled with coarse sediments, reaching very large thicknesses in some areas (up to 7 km). Lower Paleozoic sediments at the end of the Silurian period turned out to be intensively crushed and raised above sea level. Geosynclinal troughs ceased to exist.

Analysis of the geological section of Wales allows us to construct a paleogeographical curve that displays tectonic movements in the Early Paleozoic in the considered area of the Grampian geosynclinal system. The maximum subsidence and manifestation of volcanic activity occurred in the first half of the Ordovician. Then uprisings began, which continually increased and led to a general uprising. It is characteristic that other parts of this system experienced similar development in the Early Paleozoic. The mountain-building processes that engulfed the Grampian system and led to general uplift were called the Caledonian folding (from the old name of Scotland - Caledonia), and the resulting structures are called Caledonides. As a result of this folding, at the end of the Early Paleozoic in the Grampian system, the main geosynclinal stage of development ended. Instead of a system of geosynclinal troughs and geoanticlinal uplifts, a mountain fold system arose. The completion of the main geosynclinal stage was accompanied by intrusive activity - the introduction of magma of granitic composition. The geological history of Wales in the Early Paleozoic considered is typical of the development of geosynclinal areas during the main geosynclinal stage.

The Caledonian folding also manifested itself in other geosynclinal systems of the Atlantic belt, but not everywhere it led to the completion of the main geosynclinal stage and the creation of folded systems of the Caledonides. The Caledonides originated in northeastern Greenland, Spitsbergen, Newfoundland and the northern Appalachian Mountains. As for the Southern Appalachians and the Gulf Coast, in these parts 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, several areas of folding of different ages are distinguished. The 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 south of the Siberian Baikalids (Altai - Sayan region); the Hercynides cover most of the belt (Ural-Tien Shan and Kazakhstan-Mongolian regions). In the early Paleozoic, these areas developed differently. The areas of Baikal folding completed geosynclinal development, all others were at the main geosynclinal stage.

Altai-Sayan geosynclinal region. This region covers the Mountain and Mongolian Altai, Western Sayan, Tannu-Ola Range and Central Mongolia. Its Early Paleozoic history was similar to the history of the Grampian system - the Caledonian folding also appeared here, the Caledonides were formed, and the main geosynclinal stage ended at the end of the Silurian. Rocks of volcanic-sedimentary, terrigenous and carbonate formations are widespread. 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 arc-shaped 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 insignificantly developed and are represented by red-colored continental rocks of the molasse formation.

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 Ordovician-Silurian boundary, the main geosynclinal stage ended, and the orogenic one began in the Silurian.

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

The Ural geosynclinal system includes the Urals and Novaya Zemlya. Being a natural storehouse of enormous mineral wealth, the Urals are still the main mining region of our country. Its depths contain large reserves of a wide variety of minerals.

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

The Baikal folding, which appeared in the Urals, did not lead to the completion of the geosynclinal regime, as happened in the nearby Timan-Pechora region. The subsidence processes that 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 relief by a chain of meridionally elongated islands. This uplift divided the Urals into two parts - western and eastern, the development of which proceeded differently. In the western troughs, sandy-clayey and carbonate deposits accumulated in the Ordovician, and thick volcanic-sedimentary rocks accumulated in the eastern troughs. The same distribution of sediments was preserved in the Silurian, when subsidence processes were especially intense, as evidenced by the large thickness of sediments. In the east, Silurian rocks reach 5 km, and in the west they do not exceed 2 km. The greater thickness of sediments and the presence of volcanic rocks in the east are evidence of 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 occurred under calmer conditions.

The noted pattern of development of geosynclinal troughs is also inherent in other geosynclinal systems: troughs located near the platforms experienced a more gradual subsidence than troughs located far from the platforms. This explains the lower thickness of sediments 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 Upper Silurian limestones are replaced by the Lower Devonian limestones without any traces of interruption and differ from each other only in the composition of fossil marine fauna. The Caledonian folding did not appear in the Urals; the main geosynclinal stage continued in the late Paleozoic.

Even a brief examination of the Early Paleozoic history of the three geosynclinal regions of the Ural-Mongolian belt shows that they developed differently. The Caledonian folding appeared 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 in geosynclinal belts simultaneously and reached their maximum at the end of the Silurian period. The Caledonian folding manifested itself most widely in the Atlantic belt, the large northern part of which turned into the Caledonides folded region. The Caledonian orogeny was accompanied by the introduction of various intrusions.

A certain pattern is observed in the tectonic movements of the Early Paleozoic: subsidence processes predominated in the Cambrian and early Ordovician, and uplift processes predominated at the end of the Ordovician and Silurian. 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 the Caledonides mountain chains in a number of areas of geosynclinal belts and to the general regression of the sea from the territory of ancient platforms.

The main areas of sedimentation were geosynclinal belts, where very thick, many kilometers long volcanic-sedimentary, terrigenous and carbonate formations accumulated. On the ancient platforms of the northern hemisphere, the formation of carbonate and terrigenous sediments took place. Vast areas of sedimentation were located on the Siberian and Sino-Korean platforms, while 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 Physiographic conditions

According to the theory of lithospheric plate tectonics, the position and outlines of continents and oceans in the Paleozoic were different from modern ones. By the beginning of the era and throughout the Cambrian, the ancient platforms (South American, African, Arabian, Australian, Antarctic, Hindu), 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 occupied 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 outlying parts of the supercontinent. The remaining smaller continents were located mainly in the equatorial zone: North American, Eastern European and Siberian.

There were also microcontinents there:

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. In the Cambrian, there were two largest plates: the entirely oceanic Proto-Kula plate and the predominantly continental Gondwana plate.

In the Ordovician, Gondwana moved south and reached the region of the South Geographic Pole (now the northwestern part of Africa). The oceanic lithospheric plate Proto-Farallon (and probably the Proto-Pacific plate) was being pushed under the northern margin of the Gondwana plate. The reduction of the Proto-Atlantic depression, located between the Baltic shield, on the one hand, and the single Canadian-Greenland shield, on the other hand, began, as well as the reduction of oceanic space. Throughout the Ordovician, there was a reduction in oceanic spaces and the closure of marginal seas between continental fragments: Siberian, Proto-Kazakhstan and Chinese. In the Paleozoic (up to the Silurian-early Devonian) the Caledonian folding continued. Typical Caledonides are preserved in the British Isles, Scandinavia, Northern and Eastern Greenland, Central Kazakhstan and Northern Tien Shan, Southeast China, Eastern Australia, the Cordillera, South America, Northern Appalachians, 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 Proto-Atlantic Trench closed and the Euro-American continent formed, as a result of the collision of the Pro-European continent with the Pro-North American continent in the area of present-day Scandinavia and Western Greenland. In the Devonian, the displacement of Gondwana continues, as a result, the South Pole ends up in the southern region of modern Africa, and possibly present-day South America. During this period, a depression of the Tethys Ocean formed between Gondwana and the continents along the equatorial zone, and three entirely oceanic plates were formed: Kula, Farallon and Pacific (which sank under the Australasian-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 edge of South America, and the northwestern edge of Africa collided with the southern edge of what is now Central and Eastern Europe. As a result, the new supercontinent Pangea was formed. In the late Carboniferous - early Permian there was a collision of the Euro-American continent 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 its most intense manifestation during the formation of the Alpine mountain systems in Europe, accompanied by intense magmatic activity. In places where platforms collided, mountain systems arose (with heights of up to 2000-3000 m), some of them have existed to this day, for example the Urals or the Appalachians. Outside Pangea there was only the Chinese block. By the end of the Paleozoic in the Persian period, Pangea stretched from the South Pole to the North Pole. The geographic South Pole at that time was located within modern East Antarctica. The Siberian continent, which was part of Pangea and was the northern outskirts, approached the North Geographic Pole, not reaching it by 10-15° in latitude. The North Pole was located 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, united with it.

Tasks of historical geology and the main stages of its development. Historical geology and the earth's past Education and work

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