Devonian deposits were first described in the English county of Devonshire. The Devonian period is subdivided into three divisions: lower, middle and upper. In the Devonian, the northern continents formed a single large continent, Atlantia, to the east of which was Asia. Gondwana continues to exist. Huge continents were blocked by mountain ranges, which, collapsing, filled the hollows between the mountains with fragments. The climate became dry and hot. Lakes and lagoons dried up, and the salts and gypsum that were part of their waters precipitated, forming saline and gypsum-bearing strata. Volcanic activity is intensifying.

In the middle Devonian, the sea again advances on land. There are numerous depressions. They are gradually flooded by the sea. The climate becomes warm and humid. In the Upper Devonian, the seas become shallow again, small mountains appear, which were later almost completely destroyed. The most characteristic deposits of the Devonian period are continental red sandstones, shales, gypsum, salt, limestones.

Physical and geographical conditions have changed significantly, leading to a change in flora and fauna.

Numerous algae lived in the waters of the Devonian seas and oceans: siphon, blue-green, red, in the lagoons - char.

The psilophytes that appeared in the Silurian period in the early Devonian already had a more complex organization. Their body was quite clearly divided into root, stem and branches. Primitive ferns originated from them in the Middle Devonian. Psilophytes already had a woody stem. The branches of these plants begin to perform various functions, and their end parts gradually turn into dissected leaves, with the help of which photosynthesis is carried out. Other descendants of psilophytes also grow:
lycopsform and arthropods, with a more complex organization than psilophytes. They gradually displace their ancestors, seizing their places and settling in wet areas, in shallow lagoons and swamps. In the Upper Devonian, psilophytes disappear. The first seed ferns, cordaites and true ferns appear.

Spore psilophytes, primitive ferns, club mosses, and arthropods grew in humid and swampy places, forming dense thickets. They reached 30 m in height and one meter in thickness. Plants reproduced by spores that germinated into sprouts only in a humid environment.

The first seed plants had seed primordia at the tops of specialized leaves lying openly on the leaves. Therefore, plants are called gymnosperms. They were already real trees with real leaves and reproductive organs in the form of cones. Gymnosperms could reproduce directly on land, since an aquatic environment is not needed for seed germination. In addition, seeds are a multicellular organ with a significant amount of reserve nutrients that provide the embryo with everything necessary at the beginning of its life, and the seed coat protects it well from adverse conditions. All this made it possible for gymnosperms to spread widely on land. And although spore plants continued to exist, gymnosperms gradually occupy a dominant position among plants.

The dry, hot climate on the continents has led to the drying up of many rivers, lakes, marshes, lagoons, and shallow inland seas. Of the aquatic animals, only those survived that, in addition to the gills that allowed them to live in water, also possessed lungs. When the reservoirs dried up, they could breathe atmospheric air. These include primarily lungfish, which had horny teeth and sharp ribs. In 1870, living specimens of lungfish were found in two small rivers in Australia, the structure of which strongly resembled their fossil ancestors. Subsequently, live lungfish have also been found in Africa and South America. In addition to them, in the drying reservoirs of the Devonian period, lobe-finned fish were found. With the help of fins resembling a brush, the lobe-finned fish were able to crawl. swim bladder they were enriched with blood vessels and played the role of lungs. Thus, lobe-finned fish could breathe air and crawl from lagoon to lagoon in search of food and water. The lobe-finned skeleton is almost completely ossified. The skull consisted of bones present in the skulls of higher vertebrates. Consequently, the lobe-finned fishes were the ancestors of all terrestrial vertebrates, including amphibians, which appeared in the Upper Devonian. These were already real land animals. They lived on land, although they still had much in common with fish - the shape of the skull, scales, gill covers.

In 1938, in the waters of the Indian Ocean off the southeastern coast of Africa, living fossil lobe-finned fish were found. They are called coelacanthus, or coelacanths. Coelacanthus live at considerable depths. They are predators. Of particular interest are fossilized paw prints found in Pennsylvania. Three of the five fingers had claws. The trace of the tail, which stretched behind the body of the animal, is clearly visible. Probably, this footprint belongs to a lobe-finned fish moving in search of water bodies along the Devonian land.

The Devonian period is often referred to as the "Age of the Fishes". The most diverse forms of life abounded in rivers, inland seas and freshwater lakes.
The period was named after the county, which is located in the southwestern part of England. It was in this area that new geological rocks were formed. It is assumed that it was here that the first rocks appeared. 10 million years before the end of the period, a global paleogeographic reform took place on Earth.

The Devonian period lasted from 417 to 354 million years ago. In this period, the Iapetus Ocean finally closed, North America and Greenland (Laurentia) collided with the southern part of the British Isles (Avalonia) and Scandinavia (Baltic), forming a single continental mass. From Scandinavia through Britain to Newfoundland and Canada, the central mountain belt. And the supercontinent Gondwana was shifting from the South Pole to the north. In the Devonian period, the climate on Earth remained warm. The formation of new land masses led to the emergence of vast dry inland plains, which turned into huge deserts. Mighty rivers crossed the continents, flowing into inland seas and lakes. The first numerous freshwater fauna found shelter in them. During the mid-Devonian period, the polar ice caps began to melt and sea levels rose, allowing coral reefs to grow off the coasts of Laurentia and Australia.

In the process of evolution of the animal world, the same adaptation was often "invented" several times. This is what happened in the Devonian period with a group of fish known as placoderms.
Placoderms had powerful jaws - blade-like plates with tooth-like protrusions. But since placoderms were not direct descendants of the first jawed fish, most experts believe that this valuable adaptation developed independently in different fish. Along with the jaws, these fish had two hard shields - one covered the head, and the other the front of the body. The shields were connected by a pair of "loops" that allowed the overhead shield to rise when the fish bit the prey.

Some placoderms lived on seabed, where they ate mollusks and other shell animals, but by the end of the Devonian, some of them began to hunt in the open sea. Here they were the largest predatory fish. One of the species - dunkleosteus - reached almost 4 meters in length and could bite any other fish in half with its mouth plates.

Dunkleosteus. Photo: Ryan Somma

The giant armored fish dunkleosteus is approaching the cladoselachia, the primordial shark. In Dunkleosteus, the dental plates did not change during life, and in Cladoselachia, like in today's sharks, dozens of triangular teeth continued to grow on the inner edge of the jaws. Both of these primitive fish swam by undulating tails; their fins were stiff and stabilized her position in the water, helping her stay on course.
During the Devonian period, placoderms shared the seas with several other groups of jawed and jawless fish. There were jawless species with bizarrely armored bodies, but there were also unarmored species that resembled modern ones in many ways. Shellless fish were divided into two groups: in some, the skeleton consisted of cartilage, and in others, of real bones.

Cartilaginous fish were the ancestors of modern sharks and rays. Their bodies were covered with small, coarse scales called skin denticles, and in their mouths those same denticles enlarged and became an endless row of sharp teeth. From the very beginning of their existence, many of these fish resembled modern sharks, and by the end of the Devonian, representatives of one of the groups, cladoselachia, had already grown up to two meters. Bony fish were usually small, and the scales that covered them became thinner and lighter. These fish developed a gas-filled swim bladder that gave them buoyancy and movable fins to help them maneuver.

One group of bony fish, called lobe-finned or sarcopterygians, developed fleshy fins. These fish are of particular interest to scientists, because it is from them that four-legged vertebrates descend. Not all lobe-finned animals could leave the water: several species, including lungfish and coelacanths, lived in fresh and salt waters, where they live to this day.

Feel great in the Devonian seas cephalopods. In the Devonian period, the first ammonites appeared - mollusks with a shell twisted into a flat spiral. They acquired an amazing device - an outer shell, divided by partitions into isolated chambers. The mollusk filled these empty cavities with gas or water and, changing its buoyancy, could rise to the sea surface or sink into the water column.

Ammonites were very active predators. Pushing water out of the body cavity and using a jet propulsion method, they made fast swimming movements. Other mollusks and small fish became prey for ammonites.

Ammonite shells were twisted in 5-7 turns. The body of the mollusk was placed only in the outer - living chamber, the rest of the shell was used as a float. Ammonites had several tentacles surrounding a mouth, which was armed with a sharp beak and a pair of eyes. Their "finest hour" came in a later, compared with the Devonian, Mesozoic, when ammonites reached an unprecedented variety of shapes and sizes, and then disappeared from the face of the Earth.

In the Devonian period, hitherto lifeless land was gradually covered with a carpet of green vegetation, creeping up on it from the sea. At the beginning of the Devonian, the land was a collection of bare barren continents, bordered by warm, shallow seas and marshes, and towards the end, vast areas were already overgrown with dense virgin forests.
Scientists obtained the most important information about the plant world of that era from the Early Devonian deposits near the city of Rynie in Scotland, where many fossil plants were found. They grew in a marshy area at the edge of a small lake. Their remains were found in the thickness of the flint and preserved down to the smallest detail.

In those days, several groups of vascular plants already existed. The most common were ripia - so they were named after the city of Raini. In the thickness of the silt there was a creeping root of rhinia, from which several short stems branched off, each not higher than 17 cm. There were no leaves on the stems, but at their tips there were round sporangia with spores. This group of plants - the so-called rhinophytes - is the forerunner of ferns, horsetails and flowering plants.

Another group of early plants gave rise to the mosquito plants from which modern club mosses originated. Their stems were covered with thin, intertwining green scales. During the Devonian period, they became larger and more numerous, until they finally turned into huge trees of coal marshes up to 38 m high. skin.

Gradually, land areas along the shores of lakes and waterways were covered with increasingly dense thickets of plants. It was getting darker and darker there. Plants, in order to receive more light, had to reach up, overtaking their neighbors in growth. There was a need for a solid foundation. Over time, plants began to produce woody tissue, and the first trees arose. An advantage over neighbors was the ability to more rapid growth. The plants needed even more light and developed broader, flatter leaves as a result. Ancient forests looked very different from today's. The trees rested on roots that branched above the soil layer. Their trunks were covered not with bark, but with shiny scales, like those of reptiles.

Associated with Devonian deposits a large number of minerals: oil, rock salt, oil shale, bauxite, iron ore, copper, gold, manganese ores, phosphorites, gypsum, limestone.



General characteristics, stratigraphic divisions and stratotypes

The Devonian system was established in 1839 by the famous English geologists A. Sedgwick and R. Murchison in England in Devonshire, after whom it was named.

The duration of the Devonian period is 48 million years, its beginning is 408 million years, and its end is 360 million years ago.

The sections of the Devonian of Great Britain are composed of continental facies and can be subdivided into stratotypes to distinguish stages. Therefore, the dismemberment of the Devonian system was carried out in the Ardennes on the territory of Belgium, France and in the Rhine Slate Mountains on the territory of Germany. The Devonian system is subdivided into three divisions.

In the 1960s, Czechoslovak researchers suggested that instead of the Zhedino and Siegen stages, the Lochkovian and Pragian stages should be distinguished, which were established in the marine sections of the Barrandov trough in the Bohemian massif not far from Prague, which are well characterized by fauna. There is also a recognized border between the Silurian and the Devonian, drawn between the Przhidolsky and Lochkovian stages. In 1985, the International Subcommittee on Devonian Stratigraphy recommended the Lochkovian and Pragian stages of the Czech Republic as typical for the Lower Devonian. Since then, geologists have been using precisely these stages, although the former Zhedinsky and Siegen stages roughly corresponding to them have not been formally abolished. This explains the "dual power" in the lower part of the tiered scale of the Devonian system. Characteristic sections of the Devonian system are shown in schemes IV and V, col. incl.

organic world

The organic world of the Devonian period was rich and varied. Terrestrial vegetation has made significant progress. The beginning of the Devonian period was characterized by the wide distribution of "psilaphites" (rhinophytes), which reached their peak at that time. Their dominance is observed in swampy landscapes. At the beginning of the Middle Devonian, rhinophytes died out, they were replaced by great ferns, in which leaf-like forms began to form. The Late Devonian flora was named Archeopteris, after the widespread heterosporous fern Archaeopteris. At the end of the Devonian, forests already existed on the planet, consisting of the plants listed above.

Conodonts have the greatest biostratigraphic importance in the Devonian. These representatives of the primitive chordates, which appeared in the middle Cambrian, already gained a dominant position in the Ordovician. In the late Devonian, the second peak of their heyday is observed. The conodonts changed so rapidly in the Devonian that they make it possible to distinguish more than 50 standard zones in the Devonian deposits with a duration of the Devonian period of about 50 million years. This is a prime example of using the remains of rapidly evolving organisms to create ultra-detailed stratigraphy. w Graptolites (one rare genus Monograptus in the Lower Devonian) and cystoids survive in the Devonian; the variety of forms of trilobites and nautiloids is sharply reduced. Castle brachiopods (brachiopods) from the spiriferid family with the main genus Spirifer and pentamerids (genus Pentamerus), four-beam corals, and tabulates are widespread.

Cephalopod mollusks are significant in their significance: the orders of goniatites, agonyatites and climenia. They have a simple septal line with solid pointed lobes and solid rounded saddles (goniatite), or with rounded lobes and saddles (agoniatite). Clymenia is a specific group of ancient ammonoids, in which the siphon was located closer to the dorsal side, and not to the ventral side, as in most representatives of the ammonoid subclass. Clymenia were characteristic only of the Late Devonian.

For the first time in the history of the Earth, bivalves and some lower crustaceans began to play an important role, which is associated with the existence of numerous basins of abnormal salinity in the Devonian. It should be noted the abundance of the smallest crustaceans - ostracods and phyllopods.

For the stratigraphy of marine sediments, the most important are conodonts, ammonoids, brachiopods, corals, tentaculites, and ostracods. Vertebrates began to acquire ever-increasing importance. Jawless and especially fish are widespread: lungfish, armored, lobe-finned, cartilaginous (sharks, rays). In freshwater and brackish-water basins, fish, apparently, were already numerous. Since the Devonian, the first amphibians are known - stegocephals.

The development of land by plants and animals continued. Among the latter, there are scorpions and centipedes, which appeared in the Silurian, as well as wingless insects.

Crustal structures and paleogeography v

Does not occur during the Devonian significant changes in the distribution and outline of the main structural elements of the earth's crust, created by the beginning of the Devonian (platforms, geosynclinal belts and Caledonides). This is explained by the weak development of fold processes in the Devonian, which are characterized by low intensity. Only at the end of the period, in some geosynclinal areas, the Breton phase of folding appeared - the beginning of the Hercynian era of tectonogenesis. The Breton phase of folding is established in the northwest of the Mediterranean (European) geosynclinal region (Brittany Peninsula) and in the South Appalachian geosynclinal region. The Caledonian folding led to uplifts not only of the Caledonian regions, but also of many platforms. In the Early Devonian, the regression, which began at the end of the Silurian, reached its maximum. The areas of destruction and demolition were the Caledonides and vast expanses of platforms. Sedimentation on the platforms was sharply reduced, it continued only in areas bordering the Caledonides. This stage is characterized by inland water bodies with abnormal salinity. The marine regime has been preserved in geosynclines.

From the middle of the Devonian, in many parts of the world, ascending movements gave way to subsidence, and a new transgression developed. The sea advanced on the platforms and penetrated the limits of the Caledonides.

At the end of the Late Devonian, in the Famennian, the rise of the platforms began again (the Breton phase) and, in connection with this, some regression of the sea.

; characteristic feature Devonian is the formation of intermountain depressions, in which continental terrigenous, mainly red-colored deposits and volcanic rocks with a thickness of several thousand meters accumulated. The deposits of intermountain depressions are collected in folds or lie flat. In some depressions, they are cut through by intrusions and metamorphosed to varying degrees. The appearance of depressions is associated with the emergence and activation of faults, with block movements characteristic of the Devonian. The formation of such depressions occurred during the final - orogenic - stage of the development of geosynclines.

The beginning of the Devonian period (Early Devonian epoch) fully deserves the name of the geocratic epoch in the life of the Earth, that is, the epoch with the predominance of the continental regime. Since the Middle Devonian, the areas occupied by the seas have increased both on platforms and in geosynclinal areas. The land area is shrinking. At the same time, there is a general alignment, a gradual peneplanization of the continents, as well as insular land areas scattered over the area of ​​geosynclinal regions. This is evidenced by the almost ubiquitous change of terrigenous sedimentation characteristic of the Early Devonian to carbonate. Until the end of the Devonian period, the mountainous relief remained most stable in the Caledonian regions, but even there, by the end of the period, it turned out to be significantly smoothed in places, as evidenced by the relative fine-grained upper layers of the "ancient red sandstone" of the British Isles, the Minusinsk depressions, etc.

The late Devonian epoch, in contrast to the early Devonian, especially its first half (the Frasnian age), was a time of widespread development of marine transgressions, a time of predominant dominance of the sea over land. Similar epochs in the life of the Earth are called thalassocratic.

Restoring the position of the climatic zones of the Devonian is difficult, since the ground vegetation is sparse. Only character traits A number of continental and lagoonal facies of the Devonian make it possible to draw some paleoclimatic conclusions, which, however, are insufficient for reconstructing the general picture of climatic zonality in the Devonian period.

When considering the conditions for the formation of "ancient red sandstone", many facts point to the arid climate of the intermountain depressions in which these sediments accumulated. In the Devonian, the middle part of the Russian Plate was apparently characterized by a dry and hot climate, as evidenced by the widespread development of lagoonal chemogenic sediments (dolomites, gypsum, etc.) here. The same precipitation outlines within Europe a zone of arid climate, stretching from the northwest to the southeast. Other evidence of the Devonian climate is the tillites of the Cape Mountains of South Africa (30 m thick), 500 km long. It is not clear whether the moraine accumulations associated with this glaciation have continental or mountain genesis. Other manifestations of glacial activity in the Devonian are unknown.

North Atlantic Platform (Lawrence)

This superplatform unites the North American platform, the Caledonides of the Grampian Hersyncline and the East European (Russian) platform. This huge continent was called the "Ancient Red Continent" by the distribution of Devonian red-colored sandy deposits.

The American part of the North Atlantic Platform was dry land in the Early Devonian. From the second half of the Devonian, the transgression began, reaching a maximum at the beginning of the Late Devonian. Under conditions of a warm, shallow sea, carbonate silts were deposited, and reef masses were located in the west. Clastic material began to flow from the uplifts rising in the Appalachian geosyncline. Red-colored sand deposits spread to the west, the sea gradually shrinks, leaving behind a desert continent by the end of the period.

Continental conditions prevailed in the territory of the British Caledonides in the Devonian. The thicknesses of the continental deposits of England and Ireland are known under the name of "ancient red sandstone" (Old Red sandstone). The ancient red sandstone is subdivided into lower, middle and upper, which corresponds to the three divisions of the Devonian.

The classic area of ​​development of "ancient red sandstone" is Scotland. In the Lower Devonian, the bright red, brown color of the lower red sandstone and the presence of feldspar sandstones indicate arid climate. Debris from the surrounding mountain structures was carried into the depressions of Scotland. Sometimes shallow lakes arose in the depressions, in which finer sediments were deposited, crustaceans, fish, and lower crustaceans lived. There are volcanic rocks.

In the Middle Devonian, the deposits of the lower red sandstone were subjected to rather intense folding and the intrusion of granite intrusions. The Upper Red Sandstone (Upper Devonian) unconformably overlies the underlying one. The deposits become less coarse-grained, volcanic rocks almost disappear, and the thickness decreases (the total thickness of the "ancient red sandstone" in Scotland is 8 km). The most important fossils in the Devonian of Scotland are the remains of armored and cross-finned fishes and fish-like jawless fishes.

In the Caledonides of eastern Greenland, Scandinavia and about. Svalbard also formed red-colored molasses up to 5-7 km thick.

On the East European (Russian) platform, Devonian deposits are distributed over almost the entire territory, except for the Baltic and Ukrainian shields and areas of small outcrops of Lower Paleozoic rocks. However, the Devonian is exposed in limited areas: in the west of Eastern Europe- Russian plate (Main Devonian field), in the central part of the Russian plate along the river valleys (Central Devonian field), as well as in the Dniester river basin and on the Timan. The Lower Devonian is known only in the Baltic states and in the basin of the river. The Dniester, middle and upper sections are developed throughout the Russian plate.

In the eastern part of the Russian Plate, the Devonian is similar in lithology, cyclicity, and paleontological characteristics to the Western Uralian. Here, the Lower Devonian is absent, while the Middle Devonian lies transgressively on the basement or on the Upper Proterozoic deposits and marks the beginning of the transgression from the Ural geosyncline. The deposits are distinctly cyclic: up to four stages of transgression followed by short-term regressions. Freshwater and brackish-water basins with the remains of plants, fish, lower crustaceans (esteria), and linguls developed. These deposits were replaced by clay-carbonate with the remains of marine fauna: corals, stromatoporates, brachiopods.

The transgression continued in the Frankish century. The basal layers of the new cycle - the Pashian horizon of sandstones occupy large areas in the east of the plate. This is an important productive oil horizon. The Frasnian stage is characterized by limestones with a rich complex of marine fauna and Domanic rocks enriched in organic matter. Devonian terrigenous packs form the main productive horizons of the Volga-Ural and Timan-Pechora oil and gas provinces. On the Timan, bauxites have Devonian age.

In the west, within the Main Devonian field, sediments of the upper half of the Devonian are distributed with a thickness of several hundred meters to 1 km. Only in the westernmost regions - in Lithuania and Latvia - are Lower Devonian deposits known - variegated clays with interlayers of marls and remains of ichthyofauna with gypsum inclusions and drying cracks on the bedding surface. These are deposits of a continental drying basin, which replaced the Silurian sea-bay.

In the Middle Devonian, intense subsidence began, covering vast areas. Variegated and red-colored sandy-argillaceous deposits predominate, often with oblique bedding. In the Frasnian, the sea intruded into the Main Devonian field from the east. Different facies were deposited: from clays with sand to carbonate sediments. In places, lagoons appeared with dolomites, clay silts with gypsum. The thickness of marine sediments is variable - from 0 to 90 m. In the fauna of the Frasnian Sea of ​​the Main Devonian field, pelecypods and brachiopods are widespread (one species in huge quantities). At the end of the Frasnian age, within the Main Devonian field, again

In the southwest of the East European platform, in the Pripyat trough, variegated sandy-argillaceous deposits of the Middle Devonian (150-200 m) lie on the basement and are replaced higher by the Upper Devonian salt-bearing complex (3-3.5 km).

The large thickness of the rocks of this complex, the presence of volcanic rocks in some places in its composition indicate that the complex under consideration was formed in a rift vpv-dyne - aulacogene (Pripyat-Donetsk aulacogen).

There are two stages in the geological history of the eastern part of the North Atlantic Platform. At the beginning of the Devonian (the first stage), the East European Platform was subjected to drainage, only in the west there were still residual basins. In the middle of the Devonian, the second - transgressive - stage began. New deep faults appeared and old ones revived, which was accompanied by magmatism and led to the emergence and activation of aulacogens. Various ups and downs were formed. It is assumed that the modern structural plan of the platform was mainly laid down in the Devonian. During the transgression, the Baltic and Ukrainian shields acted as uplifts, but the eastern and central parts of the East European platform, the Pripyat-Donetsk aulacogen, and the Baltic regions subsided.

Siberian platform

Small outcrops of the Devonian are noted on the Siberian platform.

The Lower Devonian can be traced in the extreme northwest; the middle and upper are more widely distributed. The Devonian system on the Siberian platform is represented by variegated clayey-carbonate, often gypsum-bearing, rarely saline deposits with rare organic remains. Gray-colored clayey and carbonate strata with marine fossils are much less common. In the southwest of the platform, depressions accumulated sediments similar to coeval formations of intermountain depressions.

In the Early Devonian, almost the entire Siberian Platform was land. The transgression began "In the Middle Devonian, reached its maximum in the Frasnian and ended in the Early Carboniferous. The Siberian Platform is characterized by sea-bays of abnormal salinity. The presence of rock salt, gypsum, anhydrite, the red color of the deposits indicates an arid climate. , lava erupted in places, small intrusions were introduced.Probably, some kimberlite pipes have Devonian age.

Chinese platform

During the early Devonian, most of the Chinese Platform was a denudation area. In the Middle and Late Devonian, an extensive transgression captured the southern and western parts of the platform. Initially, the marine regime was unstable; therefore, in the sections, alternation of continental and marine sands is observed, later replaced by clayey sediments.

The territory of the platform at the beginning of the Devonian was characterized by an orogenic type of development. Here, the Lower Devonian continental quartz sandstones, quartz conglomerates and red-colored shale (total thickness 1-1.5 km) with structural unconformity lie on the underlying formations. Transgression developed in the Middle and Late Devonian; deposits of this time, which often occur on Devonian rocks, are represented by sandstones and siltstones, and their thickness does not exceed hundreds of meters. This shows that by the Middle Devonian, the orogenic development of this territory was replaced by platform development.

gondwana

A significant part of Gondwana retained an elevated position in the Devonian and was subjected to intense denudation. Terrigenous material - a product of land destruction - accumulated in shallow marine basins, which occupied limited areas everywhere, with the exception of South America. Only in South America did a major transgression occur in the Early Devonian. The Devonian Sea penetrated the western margin of Australia, as evidenced by terrigenous deposits alternating with carbonate deposits, reef structures arose in places.

The location of the continents in the Middle Devonian in accordance with the concept of plate tectonics is shown in scheme XVIII, col. incl.

History of the development of geosynclinal belts

As a result of the past Caledonian folding, the Grampian geosynclinal region ceased to exist, the Caledonides reduced the area of ​​other geosynclines, divided the geosynclinal belts, and influenced further geological processes.

Ural-Mongolian geosynclinal belt

In the Devonian, the Ural-Mongolian belt is divided into two parts by the Caledonides of the Kazakh macroisthmus. One of them includes the Ural and Tien Shan geosynclines. Another part of the belt - Central Asian - is located between the Caledonides of the Kazakh macroisthmus in the west, the Caledonides of southern Siberia and Northern Mongolia in the north, and the Chinese platform on the lore.

Ural geosyncline. Devonian outcrops are observed on the western and eastern slopes of the Urals from Pai-Khoi in the north to Mugodzhar in the south. At the base of the Devonian section of the western slope of the Urals, massive, often reef limestones occur (see Scheme V, color incl.). In limestones - algae structures, stromatoporates, corals, sea lilies, brachiopods. In the early Devonian, it was a barrier reef in the tropical sea of ​​the Ural geosyncline.

The Middle and Upper Devonian consists of cycles, each with erosion rests on the underlying rocks and is represented by limestones with a thin unit of sandstones and clays at the base. Basal sandstone members often contain iron ores and bauxites. In the upper part of the lower cycle there is a peculiar horizon - infradomanic, composed of often interbedded thin-layered dark gray bituminous limestones, marls, shales with shells of bivalves, ostracods, and less often goniatites. In the uppermost part of the Lower Frasnian cycle, there is a domanic horizon of highly bituminous black, dark gray limestones, marls, shale with nodules and flint lenses. Small skeletal elements (tentaculites) were found in clayey rocks, conodonts, goniatite shells, brachiopods, and pelecypods were found in limestones. The total thickness of the Middle and Upper Devonian in the Western Urals is 1.2 km.

The Devonian of the western slope of the Urals is represented by all three sections, according to it lies on the Silurian and overlaps according to the Carboniferous deposits. The section is subdivided into two parts corresponding to two stages of development. The first stage corresponds to the Middle Paleozoic regression. In the Urals at that time there was a tropical sea with reefs, and to the west stretched a huge continent - the Ancient Red Continent. The second stage began in the Middle Devonian. The sea from the Ural geosyncline advanced on the North Atlantic platform. The maximum transgression occurred in the Frankish century. The cyclicity of deposits, characteristic of the Middle - Upper Devonian, indicates that the transgression developed against the background of oscillatory movements. The slowing down of subsidence and intensification of uplifts led to the erosion of previous deposits and to the accumulation of terrigenous formations.

The sections of the Devonian of the Urals are well characterized paleontologically and have become reference points for the whole world. They are characteristic of the miogeosyncline, since they do not contain volcanic rocks, are not cut through by intrusions, are collected in simple folds, and are weakly metamorphosed.

The Devonian deposits of the eastern slope of the Urals formed typical eugeosynclinal formations. These are predominantly volcanic formations, sedimentary rocks play a subordinate role and are represented by sandstones, clay and siliceous shales, jaspers, limestones (thickness - 7-8 km). They are collected in complex systems of folds, disturbed by numerous ruptures, cut through by intrusions, and strongly metamorphosed. These deposits form part of the so-called greenstone strip of the Urals, bounded in the west by the Main Ural Fault.

Southern and eastern parts of the Ural-Mongolian geosynclinal belt. Devonian deposits dominate among the Paleozoic formations of Kazakhstan. In the Devonian period, a significant part of this territory belonged to the Caledonides of the Kazakh macroisthmus, within which sedimentation took place in intermountain depressions under continental conditions. To the east of the macroisthmus there was a geosyncline, where thick sequences of sediments of marine origin were formed. Numerous faults arose along the boundary, which experienced the sinking of the geosyncline and the uplifting Caledonides, along which magma erupted and ejections of pyroclastic material occurred. They formed the Kazakhstan marginal volcanic belt. Thus, three types of sections are distinguished within Central Kazakhstan. One of them - a section of the Balkhash region - characterizes geosynclinal conditions. It is dominated by sandstones and siltstones intercalated with limestones with a rich and diverse marine fauna. A significant admixture of volcanic material is evidence of volcanism in adjacent areas. The presence of coarse-grained sandstones, conglomerates, the irregularity of individual layers along the strike, traces of erosion, finds of plant remains - all this indicates fluctuations in the level of the seabed, the existence of islands that have been subjected to erosion. The abundance of various organic remains, the presence of marine forms, and the often large sizes of brachiopod and pelecypod shells are evidence of a warm, shallow sea of ​​normal salinity. The thickness of the section deposits reaches 5 km.

Caledonides of the Altai-Sayan folded region. Most of the Caledonian zone in southern Siberia and Mongolia is characterized by the accumulation of thick strata of Devonian rocks in intermountain troughs superimposed on a folded pre-Devonian basement and bounded by faults. Continental red-colored sediments and volcanogenic formations predominate.

Sediments of marine origin are represented by thin members of gray-colored sandy-clayey and carbonate rocks with remains of brachiopods, corals, bryozoans, sea ​​lilies. This is the result of ingressions (penetration of the sea into the lower areas of the nearest land) that took place in the Middle and Late Devonian. Also rarely, in a subordinate amount, there are deposits of internal basins of abnormal salinity (carbonate-argillaceous rocks with remains of bivalves, gastropods, linguls, conodonts, ostracods, phyllopods, fish).

The Devonian deposits of the intermountain basins are of great thickness, weakly metamorphosed, collected in simple folds, cut through by small intrusions. An example of such a section is the Devonian of the Minusinsk depressions, reaching a thickness of 3-9 km. These are predominantly red-colored sandstones and siltstones with drying cracks, glyptomorphoses after rock salt, and gypsum lenses. The section is characterized by a clear cyclicity: the lower (thick) part of each cycle is composed of red-colored continental sediments, and the upper (thin) part is composed of gray-colored lagoonal-marine sediments. Terrestrial volcanic formations are widespread in the Lower and Middle Devonian.

The Devonian formations of the northeastern slope of the Salair Ridge have a different character. By the beginning of the Devonian, the territory of Kuzbass, according to M.A. Rzhonsnitskaya, was the marginal part of the geosynclinal region, which was limited by Caledonian mountain structures from the south and east. In the early and early Middle Devonian, the open marine basin occupied the southwestern part of this territory and freely communicated with the Ural-Tien Shan and Altai geosynclinal seas. The large thickness of the sediments of the relatively deep sea of ​​this time (about 4.5 km) indicates a significant subsidence of the bottom of the sea basin. The Lower and Middle Devonian deposits of the northeastern Salair are mainly represented by gray and dark gray limestones with the richest marine fauna of brachiopods, corals, stromatoporates, crinoids, conodonts, tentaculites, cephalopods, bivalves, bryozoans, fish, ostracods, etc. marls, mudstones, siltstones, sandstones. The composition of the fauna, the presence of large reef structures testify to warm climatic conditions. By the end of the Middle Devonian, the sea basin becomes shallower, and terrigenous sediments begin to predominate. On the outskirts of Kuzbass in the Givetian Age, volcanic activity begins in the form of both underwater and terrestrial outpourings. At the end of the Middle Devonian, there was a general uplift of the Salair Ridge and a significant subsidence of the territory between it and the Kuznetsk Alatau, followed by the formation of the Kuznetsk depression. In the Late Devonian, marine conditions are restored on the northern and northwestern margins of Kuzbass; on the southwestern margin (Salair), sedimentation at the end of the Middle - Late Devonian no longer occurs.

This belt experienced a significant intensive subsidence in the Devonian. In the central part of Western Europe, the middle massif remained - the Franco-Czech or Moldanub uplift (block). The name comes from the rivers Moldova and Danub - the ancient name of the Danube. This median massif arose as a result of Baikal folding. To the north and south of this uplift, the Devonian contains a significant role of volcanic rocks. In the north, sandy-argillaceous deposits are traced, in the south - carbonate.

The largest outcrops of the Devonian are known in the Ardennes and the Rhine shale mountains, where stratotypes of a number of stages of the Devonian system have been identified.

In the Ardennes, Devonian deposits rest with a clear structural unconformity caused by Caledonian folding on Cambrian rocks. Here, the Lower Devonian is composed of erosion products of the Brabant massif - conglomerates and arkose sandstones, rapidly changing up the section with a thick layer of alternating polymictic sandstones and red shales. Based on the study of brachiopods, the Zhedinsky, Siegen, and Ems stages are distinguished. Above lies a sequence of shales with limestone lenses, which Belgian geologists attribute to the Couvenian regional stage. The Givetian and Frasnian stages are represented by limestones with remains of tabulates, rugoses, brachiopods, goniatites, and conodonts. The Famennian Stage is composed of shales with climenia. The total thickness of the Devonian is at least 7 km.

The bay of the Middle Paleozoic sea existed in the east of the Moldanub uplift (block) in the region of Prague. Here in the Barrand trough, named after the outstanding paleontologist I. Barrand, the Devonian sediments conformably overlie the Silurian rocks. The section of the deposits of the Barrand trough does not exceed 450-500 m in thickness, which is explained by the accumulation of sediments on the rigid base of the middle massif. The section is composed of limestones with interlayers of calcareous shales and is characterized by a rich and diverse marine fauna. In the lower part of the section, there are stratotypes of the Przhidolian, Lochkovian, and Pragian stages.

In the West Pacific geosynclinal region, three types of sections were formed in the Devonian: eugeosynclinal, miogeosynclinal, and typical for median massifs.

In the eugeosynclinal zone of the Pacific coast in northeast Asia, strata of spilite-diabase composition, siliceous, sandy, and carbonate sediments accumulated. The same type of section can be traced in the Japanese Islands, where the Devonian is represented by keratophyres, mafic lavas, their tuffs, shales, and limestones with a total thickness of up to 3 km. Everywhere the Devonian deposits conform to the Silurian.

In the middle massifs (Omolonsky, Khankaisky and Bureinsky) in terrestrial or shallow marine conditions, relatively thin strata of sandy-argillaceous and carbonate sediments, as well as lavas of acidic and intermediate composition, were formed. They lie with a sharp angular unconformity on the underlying formations.

The geological history of the Australian part of the Western Pacific geosynclinal region is more complex. Two zones are distinguished here: eastern - eugeosynclinal and western - mio-geosynclinal. In the western zone in the Middle Devonian, sedimentation was interrupted by a folding phase and the intrusion of granitoid intrusions. In the Late Devonian, orogenic depressions formed here, in which red- and variegated terrigenous, sometimes volcanogenic, sequences accumulated. In the eastern zone, the eugeosynclinal regime was preserved.

In the East Pacific geosynclinal region in the Devonian, as well as in the Ordovician and Silurian, miogeosynclinal and eugeosinclinal types of sections were formed, and the second of them is developed to a limited extent - in the west of the Cordillera. The Caledonian folding led here to the fallout from the Lower Devonian sections. Middle-Upper Devonian volcanics, siliceous and sandy rocks (3 km) unconformably lie on older formations. Miogeosynclinal marine sandy-argillaceous deposits (3-4.5 km) are characteristic of South America. Undoubtedly, the manifestation of the Caledonian folding in the north of the Andes, where the introduction of acidic intrusions is associated with it.

Minerals

Despite the poverty of terrestrial vegetation, its development led to the formation in the Devonian period of the first industrial deposits in the history of the Earth. hard coal.

It should be noted that a binary division of the Carboniferous (lower and upper sections) is currently being discussed and, apparently, will be established, corresponding to the marine and continental facies of this system in Western Europe, America and Asia. Only within the East European Platform, the maritime regime was preserved throughout the entire period. Therefore, in this region, the system was subdivided into three sections and almost all tiers were installed here (with the exception of the two lower ones). Due to the lack of a newly proposed Carboniferous stratigraphy approved at the International Geological Congress, the authors present a previously known scheme.

The Carboniferous flora is called "anthracophyte". Carboniferous vegetation, dying and being buried, formed the largest accumulations of coal in the history of the Earth.

The seas of the Carboniferous are characterized by the rapid development of foraminifers, which sometimes played the role of rock-forming organisms (fusulin limestones). It should be noted the order Fusulinida - large foraminifers, especially significant accumulations of which are observed in the Volga region.

Of the other invertebrates in the Carboniferous, great importance some four-pointed corals - Lonsdaleia, Caninia and tabulates - Chaetetes, Syringopora, Michelinia. Some groups of brachiopods reached their peak in the Carboniferous. Particularly typical are the productids - Productidae and spiriferids - Spiriferidae. Numerous sea ​​urchins. Quite often, thickets of crinoids appeared on the seabed.

Of great stratigraphic importance, especially for the Lower Carboniferous, are conodonts, among which many new genera arose in the Carboniferous. The most preferred level of drawing the boundary between the Devonian and the Carboniferous is the base of the Siphonodella sulcata conodont zone. o Of the cephalopods, mention should be made of the detachment of ammonoids with a simple structure of partitions - goniatites and agoniatites. The lobed line and sculpture of goniatite shells become more complex. Bivalves and gastropods were abundant. Bivalves inhabited not only the seas, but also freshwater basins. The smallest crustaceans - ostracods - had a similar distribution.

Favorable climatic conditions and lush vegetation determined the abundance of terrestrial arthropods: spiders, scorpions, cockroaches, dragonflies (sometimes with a wingspan of up to 1 m). Numerous fish lived in the seas of the Carboniferous. A variety of amphibians (stegocephals) inhabited the shores of lakes, thickets of forests.

At the end of the Carboniferous, stegocephals gave rise to the first reptiles - reptiles. The progressive features of reptiles (horny cover that protects the body from moisture loss; reproduction by eggs laid on land) allowed them to penetrate deep into the continents.

For the stratigraphy of marine deposits of the Carboniferous, the most important are conodonts, foraminifers (fusulinids), goniatites, and brachiopods. Determination of the age of continental deposits is based on the study of plant remains, as well as complexes of spores and freshwater bivalves.

Crustal structures and paleogeography

In the Carboniferous, Laurentia, the Siberian and Chinese platforms, and the Gondwana superplatform continued to exist within the modern continents. Between them were the Appalachian geosyncline, the Mediterranean, Ural-Mongolian and Pacific geosynclinal belts.

After a lull in the Devonian, the earth's crust is covered by a new wave of tectonic movements that make up the Hercynian era of tectonogenesis or Hercynian folding (from the ancient name of Hercynia - the Harz mountains in Germany). The following phases of the Hercynian folding are usually distinguished. The first of them (D3-C]) Breton phase manifested itself limitedly at the end of the Devonian. She closed the Innuit geosyncline. The Sudetstya phase is traced to the end of the Early Carboniferous. It manifested itself most significantly in the north of the Mediterranean geosynclinal belt, on the territory of the Appalachian geosyncline and the Ural-Mongolian belt. Therefore, in these regions and adjacent parts of the platforms, the Middle and Upper Carboniferous are represented by molasses, often continental and coal-bearing, filling marginal and intermountain troughs. The Asturian phase appeared at the end of the Middle Carboniferous; Uralic - at the beginning of the Early Permian; Za-Alskaya - at the end of the Early - the beginning of the Late Permian and the Palatinate - at the end of the Permian - the beginning of the Triassic.

The Hercynian folding closed a number of geosynclinal regions and almost completely the Ural-Mongolian belt. Significantly reduced after the Hercynian folding, the Mediterranean geosynclinal belt is usually called the Tethys geosynclinal region.

All platforms of the Northern Hemisphere, together with the Hercynides that joined them, merged into one huge platform (superplatform) Laurasia. The Hercynian folding led to an increase in the size of Gondwana as a result of the extinction of the geosynclinal regime in the south of the Atlas Mountains and in the mountains of eastern Australia.

The Hercynian folding was accompanied by intense effusive and intrusive magmatism, which, in turn, is associated with the formation of mineral deposits. Tectonic movements were revived in areas of more ancient folding. In parts of the Caledonides adjacent to the Hercynides, these movements were accompanied by the outpouring of effusives and the emplacement of intrusions. For areas of Hercynian folding, marginal troughs are very characteristic, which formed during the orogenic stage of development of geosynclines along their border with platforms. Due to the fact that the first phases of the Hercynian folding were very strong and the phenomena of compression of the earth's crust prevailed on the planet, rifting for the Carboniferous and the very beginning of the Early Permian is not typical. An exception in this respect is the Pripyat-Donetsk aulacogen.

The regression, which began at the end of the Devonian, was long and stable within Gondwana, where the continental setting persisted throughout the Early Carboniferous. On the northern continents, at the beginning of the Carboniferous, transgression began again, which, in addition to the pre-Cambrian platforms, covered some areas of the Caledonides, which were significantly leveled by denudation. The seas occupied part of the Caledonides on the territory of England, the eastern most of the East European, the western part of the North American (Canadian) platforms and a small section of the Siberian platform adjacent to the Yenisei. Starting from the end of the Early Carboniferous, with the development of folding and mountain building, vast areas in geosynclines were freed from the sea. At the same time, all the platforms of the Northern Hemisphere were gradually freed from the sea. An exception is the East European Platform, where the sea remained until the end of the period, only slightly reduced in size. On the Siberian, Chinese and Canadian platforms, by the end of the Carboniferous, land dominated. In Gondwana, on the contrary, the area of ​​the sea expands and sea waters penetrate into the Amazon River basin, into northern Africa and southwestern Australia.

In the Early Carboniferous, there is still no sharp differentiation into climatic zones. The wide development of moisture and heat-loving lepidodendron flora testifies to the uniform and humid climate of most of the Earth's surface. In the second half of the Carboniferous, distinct differences are found between the lepidodendron flora of the Westphalian (near equatorial) floristic region, on the one hand, and the Tunguska (northern temperate) and glossopterian (southern temperate) floras, on the other.

In the Westphalian region, the climate was humid and warm, while in the Tunguska and glossopterian regions it was temperate and cold. The processes of mountain building and regression led to such climate differentiation. At the end of the Carboniferous and the beginning of the Permian, extensive glaciation took place in Gondwana.

The arrangement of the continents in the Late Carboniferous, compiled in accordance with the concept of a new global tectonics, is shown in scheme XIX, col. incl.

History of platform development North Atlantic platform (Lawrence)

At the beginning of the Carboniferous period, the conditions that existed in the Late Devonian were generally preserved on the North Atlantic Platform. The deposits of the Lower Carboniferous (Tournai and Vise) are mainly represented by carbonate rocks of marine origin. At the end of the early-beginning of the Middle Carboniferous, due to the development of the Hercynian folding, which manifested itself in the Mediterranean geosynclinal belt adjacent to the platform and the Appalachian geosyncline, the nature of sedimentation in Laurentia changed dramatically. Therefore, in the west, within the North American part of the platform, the Pennsylvania deposits are represented by a coal-bearing sequence of paralytic origin. In the British Caledonides, the coal-bearing sequence of the same age in its upper part accumulated partly already under limnic conditions.

A marine basin continued to exist in the east of the Lavrentia platform in the Carboniferous, as follows from the analysis of the section near Moscow. It is characterized by the predominance of carbonate rocks with numerous remains of foraminifers, brachiopods, corals, bivalves (pelecypods), gastropods, echinoderms, and sometimes goniatites. This section is an example of typical platform deposits accumulated in a warm marine basin. The marine regime was disturbed twice: during the accumulation of coal-bearing strata in the Visean and at the beginning of the Middle Carboniferous, which resulted in the absence of deposits of the Bashkirian stage (see Scheme VI, col. incl.). In the east, the terrigenous rocks of the Vise - an analogue of the coal-bearing strata of the Moscow region - are one of the most important productive horizons of the Volga-Ural oil-bearing province.

Siberian platform

During the Carboniferous, most of the Siberian Platform was dominated by continental conditions. At the beginning of the Early Carboniferous, the sea penetrated only the northwestern and northeastern margins of the platform. The accumulation of carbonate sediments with a thickness of several hundred meters took place here. In the Middle and Upper Carboniferous, most of the platform was involved in subsidence, with the exception of its southern margin and the Anabar massif. Sands, silts, clays and peat bogs accumulated in oxbows, lakes, swamps, on floodplain terraces and marshy spaces between the rivers, where lush vegetation dominated with a predominance of cordaites, which subsequently formed interlayers of coal. The Late Paleozoic flora of Siberia is better studied in the Kuznetsk Basin, therefore, the age of the host deposits is determined by comparison with the Kuzbass section.

Chinese platform

During the Carboniferous, the southern part of the Chinese platform was dominated by the sea. The accumulation of carbonate sediments prevailed here. In the Middle Carboniferous, the north of the platform experienced transgression. When the sea attacked this territory, as a result of washing of the weathering crust formed during the Early Carboniferous, deposits of bauxite and iron ore. Above lies a paralytic coal-bearing formation with a thickness of hundreds of meters.

The territory of the platform in the Early Carboniferous was a demolition area. In the Middle and Late Carboniferous, carbonate strata accumulated here with interlayers of continental sandy-argillaceous and coal-bearing deposits with a total thickness of several hundred meters.

gondwana

Most of Gondwana in the Carboniferous, as well as in the Devonian, retained an elevated position. Only in the Early Carboniferous did the marginal parts of the supercontinent experience subsidence.

At that time, the sea existed in the north of the African part of Gondwana, where it penetrated from the Mediterranean geosynclinal belt. Here there was an accumulation of sands, clays and carbonate sediments, in some places - the formation of reefs. The sea also occupied the west of the Australian part of Gondwana. Predominantly carbonate sediments accumulated in the west, and terrigenous sediments accumulated in the southeast.

The continental and lagoonal rocks of the Lower Carboniferous are even more limitedly distributed in Gondwana. In northern Africa, they formed along the periphery of the sea basin and are represented by sandy-clayey sediments with plant remains. In the east of Brazil, a terrigenous sequence containing coal interlayers has the same age. In the Middle Carboniferous, the sea penetrated into the northeast of Brazil and into the Amazon basin. In the northeast of Brazil, a sequence of sandstones, siltstones, siliceous rocks and limestones up to 250 m thick was formed. In the north of the African part of Gondwana, a regression took place in the Middle Carboniferous, and a coal-bearing stratum formed here.

The Late Carboniferous was marked by an extensive glaciation of Gondwana. Tillites are known in Africa, Madagascar, Hindustan, Australia, South America and Antarctica, where they are part of the Gondwanan series of continental deposits (Upper Carboniferous - Lower Cretaceous). in the south, Central Africa and in Madagascar, tillites (400 m) are formed by unsorted, to varying degrees rounded pebbles and blocks (up to 2 m in diameter) of Precambrian rocks, which are covered with glacial shading and cemented by sandy-clayey material. Remains of fish, mollusks and crinoids are found in the clay layers - evidence of a short-term penetration of the sea. The tillites rest on uneven, glacially polished and scarred surfaces.

The wide distribution of tillites is an undoubted confirmation of the general cooling in Gondwana in the Late Carboniferous. Warm climate, judging by the finds of Upper Carboniferous red-colored deposits, existed only in northern Africa.

The unity of the Gondwana continent, in addition to climatic conditions, is also proved by the common complex of Late Paleozoic flora and reptile remains.

History of development of geosynclinal belts Ural-Mongolian geosynclinal belt

Within the Ural-Mongolian belt in the early Carboniferous, there were the Ural, Tien Shan, Dzhungar-Balkhash, Zaisan and Mongolian geosynclines, separated from each other by areas of Caledonian and more ancient folding.

The geological history of these geosynclines, starting from the Middle Carboniferous, is different due to the different manifestations of the first phases of Hercynian folding in them.

Ural geosyncline. Carboniferous deposits are widespread both on the western and eastern slopes of the Urals.

The Carboniferous section of the western margin of the Urals is continuous, represented by all three sections. The section is dominated by limestones with diverse fauna. Deposits of this type were formed under conditions of a warm sea basin extending further westward into the East European Platform. The total thickness is 0.5-1.3 km. This is a typical miogeosynclinal section (there are no volcanic rocks, no intrusions, weak metamorphism, rocks are collected in simple folds).

The section located to the east (eastern slope of the Urals) also contains all three sections of the Carboniferous (see Scheme VII, col. inc.). The section is composed of terrigenous rocks: sandstones, clayey shales; interlayers of coarse-grained rocks and conglomerates appear in the Middle and Upper Carboniferous. The rocks are often rhythmically layered, contain interlayers of siliceous, carbonate, and tuffaceous deposits. Thickness 2.7-3.7 km. Sediments of this type accumulated in the more actively subducting part of the geosyncline.

The Lower Carboniferous of the eastern sections is characterized by the presence of powerful volcanic formations. The thickness of the Lower Carboniferous reaches 3.5 km. This is a eugeosynclinal type of section, which characterizes the most actively developing part of the geosyncline. The Middle Carboniferous is represented by clastic deposits up to 1 km thick, with interlayers of carbonate rocks Often there are thick interlayers of conglomerates and accumulations plant residues. All this testifies to the Hercynian uplifts in the east of the Ural geosyncline, which supplied clastic material to the sea located to the west. The carboniferous of the eastern slope is assembled into complex folds disturbed by numerous ruptures, melted through and penetrated by intrusions, and strongly metamorphosed.

Dzhungaro-Balkhash geosyncline. In the first half of the Early Carboniferous, the Dzhungar-Balkhash geosyncline was occupied by a shallow marine basin, in which siliceous-argillaceous and siliceous sediments and tuffaceous material brought from the islands accumulated.

In connection with the manifestation of the Middle Visean folding phase in the second half of the Early Carboniferous, the sea was preserved in the southeast of the geosyncline; Numerous volcanoes arose in its northwest. The next - pre-Middle Carboniferous - phase of folding led to the extinction of geosynclinal conditions in this area, so the Middle and Upper Carboniferous are mainly represented by continental volcanogenic strata. The sea existed in the extreme southeast, where terrigenous sediments were formed with a significant admixture of volcanic material.

In the Kuznetsk Basin, the Carboniferous section is complete, well paleontologically characterized, and is a reference for Central Siberia and adjacent areas.

The Tournaisian and Visean stages in Kuzbass are composed of marine carbonate and terrigenous deposits up to 1 km thick. They are characterized by a variety of organic remains, which made it possible to correlate these deposits with the stratotype units of the Tournaisian and Visean stages of Western Europe.

Above lies a coal-bearing formation (up to 5-8 km thick), in which gray sandstones and siltstones are repeatedly interbedded, coal beds are of subordinate importance. The age of this coal-bearing formation is from the Serpukhovian to the late Permian inclusive. The coal-bearing formation is characterized by a rich complex of fossil flora, in which cordaites predominate, as well as remains of bivalves (pelecypods), barnacles, fish, and insects. In the lower part of the formation, at the boundary of the Lower and Middle Carboniferous, there is a horizon of calcareous sandstones with marine fauna.

The coal-bearing formation is subdivided into series, sub-series and suites. This subdivision is based on lithological data and cross-sectional changes in plant assemblages and freshwater bivalves. However, due to the uniqueness of the fauna and flora, the comparison of different parts of the coal-bearing formation with stages and even divisions of the general scale is conditional. The coal-bearing formation contains about 300 coal seams with a total thickness of 5-8 km. After a shallow warm bay in the Early Carboniferous, in which carbonate and terrigenous sediments accumulated, from the Middle Carboniferous this bay became swampy and coal accumulated.

Appalachian geosynclinal region

In the northern part of the Appalachian geosyncline, the Acadian phase of folding was strongly manifested, so the Carboniferous history of the northern and southern parts of the geosyncline is different. In the north, thick (more than 6 km) deposits of the molasse type, largely coal-bearing, accumulated in intermountain depressions. The accumulation of thick sandy-argillaceous strata in the southern part of the geosyncline at the end of the Mississippian time was interrupted by the Hercynian folding. In the area bordering the North American Platform, a marginal trough developed in the Pennsylvanian time, which was filled with coal-bearing molasse.

Mediterranean geosynclinal belt

The section of the Carboniferous of the West European Hercynides was studied earlier than in other regions, and therefore became the standard in the development of the stratigraphic scheme of the Carboniferous system. Dinant (Tournay, Vise) is represented by typical geosynclinal formations (see Scheme VII, color inc.). In some areas, this is a thick layer of monotonous clay shales with interlayers of sandstones, siliceous shales, and in some places effusives. In areas close to the border with the North Atlantic Platform, these are limestones containing numerous remains of corals and brachiopods, on which the division of the dinant into the Tournaisian and Visean stages is based (after the names of the cities of Tournai and Wiese in Belgium).

After the Sudetenian phase of folding, which was accompanied by the introduction of intrusions, a mountainous country arose on the northern margin of the Mediterranean geosynclinal belt. Sedimentation took place in intermontane depressions, where limnic coal-bearing strata were formed.

In the Namurian and Westphalian centuries, the sea remained only on the border of the mountain structure and the Laurentian platform. A typical foredeep was formed here, stretching from southern England through northern France, Belgium, Germany, southern Poland and northern Czechoslovakia, and a paralytic coal-bearing molasse was formed. Its accumulation ceased in the Stephanian, when, as a result of the Asturian phase of folding, this area was involved in uplift.

Pacific geosynclinal belt

In the West Pacific geosynclinal region, the same three types of sections are distinguished in the Carboniferous as in the Devonian. The eugeosynclinal type of the section is characteristic of the inner part of the geosyncline gravitating towards the Pacific coast. In Kamchatka, in the Koryak Highlands and Japan, thick volcanic-siliceous, in some places flysch strata were formed in the Carboniferous. Much wider in the outer zone of the geosyncline, the miogeosynclinal type of the section is developed, well represented in Verkhoyansk and in the basin of the river. Kolyma. Here, limestones accumulated in the tour, and from the Visean age, the formation of the terrigenous Verkhoyansk complex began, which continued until the end jurassic. The thickness of the Carboniferous deposits in these areas reaches 3-4 km. The third type of the Carboniferous section, relatively thin (up to 700 m), is distributed within the middle massifs; it is composed of carbonate-terrigenous and andesite-basalt formations.

In the East Pacific geosynclinal region, the eugeosynclinal zone is distinguished only in the north as a narrow strip along the Pacific coast from Alaska to Mexico. Here, siliceous and clayey sediments, limestones, lavas, and tuffs of predominantly andesitic composition were formed in the Carboniferous. In the miogeosynclinal zone, due to the manifestation of the Breton phase of folding, the Mississippian deposits everywhere lie sharply unconformably on older formations. In the Cordillera of North America, they are represented by marine terrigenous sediments, along the border with the platform - by carbonate rocks. Due to the strong manifestation of the Sudetenian phase of folding, the Pennsylvania deposits are limited in distribution, lie unconformably on the underlying rocks and are represented by conglomerates and coarse-grained sandstones.

In the South American part of the considered geosynclinal region, the Breton phase of folding was accompanied by the emplacement of granite intrusions; it led to the uplift of the Central Andes, which continued throughout the Early Carboniferous, and to mountain glaciation. At that time, variegated molasse with interlayers of coals, lavas, and felsic tuffs accumulated in intermountain depressions; in some places this molasse is replaced by sands, clays and limestones formed under marine conditions. In Pennsylvania, limestones with interlayers of clays were formed, which were replaced along the border with the platform by continental red-colored sediments.

Devonian - fourth period Paleozoic era in the geological history of our planet. This is a time of rapid development of the biological system and serious cataclysms. The events that took place in those days had an extraordinary impact on the development of subsequent earthly life. This is the period of the formation of the soil, the development of new forms and types of living beings, the dynamic conquest of land by them, the beginning of the formation of humus and mineral deposits.

Devonian system

For the first time this term was singled out by scientists - the Englishmen Adam Sedgwick and Roderick Murchison - in 1839 in Devonshire, hence the name of the period. With the help of radiological studies, the times (420-350 million years ago) and the duration of the Devonian period were established, which becomes about 60 million years. In 1845, the German scientists, the Zanberger brothers, having dissected the tiers in the Ardennes and the Rhine mountains, formed the first division of the system. At the moment, Devon is divided into three periods and seven tiers, which have undergone some changes since the first experiments.

Fossils - indicators of the era

Paleontology is the science of vegetation, fauna, geology of past periods. The remains extracted from the rock layers of their time serve as an indicator of their era. Make a correct idea of ​​the climate, the conditions for the existence of organisms, their evolution and adaptation to natural environment, which constantly changed under the influence of cataclysms, fossil fossils help. The Devonian period is the time of the first ferns, the first land animals, spore plants, bivalves, trilobites, fish, corals, the first terrestrial insects and amphibians.

Start

The geological period of the Devonian is characterized as an era of land dominance, which rose due to the regression of the sea. After a series of earthquakes and volcanic eruptions of the early period, the seas in the folds of the Ural-Tien Shan, Cordillera and Tasman geosynclines were significantly reduced, the troughs in which were gradually filled with sand and pebbles, which were formed in the process of land erosion. As a result, vast areas of red sandstone were formed. Numerous rivers carrying sediments to the seas have formed swampy deltas, very convenient for life and development of various forms and types of living beings. The territories of the East European platform, the Western Sayan and Central Kazakhstan became dry. As a result of the collision of Eastern Europe and North America, the mainland Lavrussia was formed.

Time of cataclysms

During the Middle Devonian period, the sea again began its offensive. This was facilitated by the activation of volcanoes. The land again began to sink into the water. The Ural-Tien Shan geosyncline has become wider. Large parts of the East European and Siberian platforms were flooded, the sea also filled some areas of the North American and Australian platforms. In parallel, the African and South American platforms remained dry.

The geological period of Devon ended with the fact that the Siberian platform completely passed into the land and formed the continent of Angara, in Africa the area of ​​the sea decreased, and South America was completely freed from the sea.

Climatic conditions

The Devonian period of the Paleozoic era is characterized by arid and hot climatic conditions, which contributed to the evaporation of moisture and a decrease in the territory of water bodies. An arid desert climate is established on most of the continents. Deserts and semi-deserts formed on land, and the concentration of salt in the seas increased. Climatic zoning was established, which was more pronounced than at the beginning of the era.

Chemical analysis of the remains of that period made it possible to establish an approximate scale of temperatures characteristic of that time. The territory of modern Eastern Europe and the Urals was in equatorial belt, and Transcaucasia - in the tropics.

The Devonian period in the final phase is characterized by a milder and more humid climate, the weakening of volcanic processes. The established conditions became suitable for the development of land by living organisms.

Jawless and armored

Volcanic activity, the redistribution of land and sea, cosmic and atmospheric phenomena led in the Devonian period to mass extinction living beings that appeared in previous geological periods. There has been a revolution of species on land and at sea. But the biggest renaissance has come in the world of fish. Scientists call this part of the Paleozoic era the era of fish.

Agnate fish did not have jaws and teeth, the front part of their body was covered with a bone skeleton, which was a huge advantage in the struggle for survival. One of the armored fossil fish, diniztis, had a terrible head with a stone "bag" about a meter long. Fish lived in reservoirs, moving along the bottom with the help of sharp fins - spikes. Subsequently, armored jawless fish died out, giving way to bone and lobe-finned relatives, but some of them have survived to this day. These are ocean lampreys and hagfishes. These ancient predators, of course, got rid of the heavy shell, and in terms of the rest of the structure and way of life they are very similar to their ancient ancestors.

bony fish

Heavy armored fish gave way to lighter mobile descendants, with a flexible tail and powerful fins. They had powerful developed jaws and thin scales. First bony fish- Osteichthia and are the ancestors of most modern fish. Light osteichthia with bone skeletons instead of cartilaginous ones were equipped with a new important organ - an air bladder. The ancestors of modern sharks and rays also appeared in the Devonian period. Fish gradually divided into ray-finned (most modern fish) and lobe-finned.

In an era when land and water bodies constantly replaced each other, the lobe-finned fish managed to maintain an enviable vitality. Their fins were reborn in the likeness of a brush, with the help of which the fish easily crawled from a dry place to another body of water. In addition, these amphibians had the ability to breathe both on land and in water, and acquired the name lungfish. Currently, some species of lungfish are found in South America and Africa - places that are subject to frequent droughts. AT Indian Ocean not so long ago they discovered an ancient species of fish - the cross-finned coelacanth.

land conquest

At the beginning of the Devonian, the surface of the earth was a collection of bare rocky continents in the vicinity of small swamps and seas. Gradually, the warm, humid climate had a beneficial effect on the development of vegetation. Animals and plants began to massively conquer new space. Numerous remains of arthropod invertebrates have been found in the shales of the Devonian system. Primitive insects settled on the first plants, miniature mites fed on green leaves with plant juice. These insects and mites were hunted by the same miniature spider ancestors. Life was in full swing!

New inhabitants of the seas

More changes have been made undersea world. In addition to numerous species of fish, invertebrate mollusks were developed during the Devonian period. Only bivalves, born in those days, there are 56 genera, in addition to them, 24 genera of corals and 28 genera of cephalopods. At the bottom of the sea, trilobites, tabulates, echinoderms and various gastropods led an active lifestyle. Brachiopods reached their maximum flourishing, especially such species as spiriferids and atripids.

Ancestors of amphibians

It was the Devonian period that prepared all the prerequisites for the transition of the inhabitants of reservoirs to land. The characteristics of new species of marine predators, as well as the active development of lobe-finned bipedal fish, is a confirmation of this. An imposing inhabitant of the Devonian is the racoscorpion, the ancestor of modern scorpions. These predators had a long body that ended in a tail with a long spike, oar-shaped limbs for swimming, and legs for raids on the coast, where one could hunt for small insects. It is believed that these creatures wore spiral-shaped shells on their backs, which served as gills for them. The end of the Devonian period is the time of the appearance of the first amphibians, which were called stegocephals.

Stegocephals are a kind of prefabricated type from amphibians, reptiles and fish. Outwardly, they resembled modern lizards or salamanders, but with a hard shell. The sizes of the first amphibians are very diverse - from small, a few centimeters, to huge four-meter individuals.

Vegetable world

The first algae that adapted to life on the shores of water bodies appeared back in Silurian period and continued into the early Devonian. Rhiniophytes did not have a root system and deciduous shoots. Gradually, the warm and humid climate of the Devonian allowed them to be reborn into clubs, the thickets of which became more and more dense. To ensure life processes, plants reached for the sun, and became higher and higher. To provide high support, a dense tree-like trunk was required. Soft stems began to stiffen and turn into the first shrubs and trees. During the late Devonian period, already dense and tall forests were noisy on the earth, which in places reached up to 38 meters. Plant species also became more diverse, horsetails and ferns coexisted along with club mosses. The Rinias lost their advantage and died out by the end of the period.

Animals and plants in the Devonian period successfully mastered the land, but still, their existence was significantly dependent on water, and the active development of new territories took place a short distance from the shores of water bodies. Places far from the seas remained bare and uninhabited. And only at the end of the period did seed ferns appear, which became the progenitors of seed plants. An increasingly complex plant world was born, lived and died. A lot of fallen leaves and wood were processed by microorganisms. With the evolution of flora and fauna, the first soil layer was formed.

Minerals of the Devonian period

The Paleozoic era is the time of the birth of many mineral deposits that are so important for humanity in the modern period. In the Devonian, in places with high humidity, manganese oxides and iron hydroxides were formed. The regions of Eastern Siberia turned out to be rich in these elements. The territories of modern Uruguay, Argentina, Australia, as well as some places in the northeast and south of Asia, were filled with reef limestones. The oldest coal deposits on the planet, oil and gas reservoirs in the Ural region of Russia, in the oil regions of the USA, Canada, and the Middle East also belong to the Devonian period.

In places high humidity deposits of potassium salts were formed. Active volcanic processes led to the accumulation of ores of copper pyrite, lead and zinc, iron manganese. So the rich deposits of the Urals were formed, North Caucasus, Tatarstan and central Kazakhstan. Flashes of magmatism led to the formation of kimberlite pipes with diamonds.

Devonian period: main events

Summing up, we can highlight the main events of the Devonian, which significantly influenced the development of the world in the future:

• The main continental land masses have been identified
• Formation of land cover.
• The evolution of plants, the emergence of new forms and species.
• Metamorphoses in the world of fish.
• The origin of the lungs, the appearance of lungfish, and the first amphibians.
• Formation of the first soil layer.
• The origin of arrays of minerals.

Devonian

Already many hundreds of millions of years have elapsed since life arose on Earth in the form of microscopic lumps of protein matter. Countless generations of living beings have succeeded each other.

A rich and diverse world of plants and animals inhabits the waters of the seas. Invertebrates have reached their peak. Life has come ashore. Psilophyte greens enliven the rugged, rocky landscape.

In what ways will the further evolution of life on Earth go? In what forms will it manifest itself in the coming millennia?

We are on the threshold of the Devonian period of the Paleozoic era.

The name of this period comes from the name "Devonshire" - a county in southwestern England, where the system of Devonian layers was first identified by scientists in 1839.

... Geologists are walking around the country. They climb the gentle slopes of the Ural Mountains, pass through the plains of the Leningrad Region, explore rock formations in Kazakhstan, Central Asia, and Siberia. And in all these places, their keen eye detects layers of Devonian limestones, red sandstones, volcanic tuffs, clays. The layers of these sedimentary rocks contain many remains of plants and animals, telling about great changes in the flora and fauna in the Devonian time.

The warm waters of the Devonian seas were abundantly inhabited by cephalopods, corals and brachiopods - animals that had a bivalve shell. The remains of marine animals formed layers of Devonian shell limestones.

In the rivers and desalinated lagoons lived armored fish - coccosteus. Remains of coccosteus are often overfilled with layers of red sandstone deposited in the vast Devonian lagoons. Along with the remains of armored fish, we find the remains of their enemies - giant crustacean scorpions. Despite their bone protection, the clumsy, slow carapaces easily fell prey to these predators. Therefore, over time, the number of armored fish in lagoons and rivers has greatly decreased: they began to die out.

Giant shell scorpion.

But at the end of the Devonian, some types of shells moved to live in the open sea. Here they found favorable conditions for development. The descendants of many of them reached enormous proportions. So, for example, the marine predatory carapace dinichthys reached 10 meters in length.

Dinichthys hunting sharks.

In the layers of the early Devonian, scientists also found the remains of bony fish. The structure of their body was more perfect than that of fish-like shells. These ancient fish had fins that allowed them to swim quickly; they had jaws with which they actively captured food.

Vegetation took over the land more and more. The earth was no longer covered only by moss-like psilophytes. Primitive ferns and ancestors of marsh horsetails grew along the sea and river banks. These plants already had real stems and leaves.

All plants of the early Devonian were spores, that is, they reproduced by scattering microscopic cells - spores. But in the middle of the Devonian, seed ferns also appeared, reaching our trees in size. On the branches they developed not spores, but large seeds, the size of a hazelnut. Devonian seed ferns were the ancestors of all seed plants.

Wingless insects, centipedes, scorpions crawled across the damp soil, hunting each other. The descendants of some species of these invertebrates - for example, scorpions - almost unchanged, have survived to this day.

The Devonian period lasted about 55 million years. Important changes took place during this time in the animal world of the Earth.

Devon landscape.

High mountain ranges, rising along the coasts of the continents, retained moist sea air, prevented it from penetrating deep into the continents. Therefore, the climate of the continents in the Devonian was dry, sharply continental.

Sea bays and numerous lakes dried up. They developed fish that gradually adapted to a more or less prolonged stay out of the water. Scientists call these fish lobe-finned - according to the structural features of their fins: unlike the fins of ordinary, ray-finned fish, the paired fins of the lobe-finned fish were narrow and sat on an axis covered with scales.

The swim bladder in lobe-finned fish began to do the work of the lungs: it helped to breathe atmospheric air. Thanks to this, the fish could live for some time without water, when the shallow creeks and lakes where they lived dried up under the scorching rays of the sun. Moving with the help of fins, fish could crawl into other water bodies.

So, in the struggle for existence, new forms of the animal world were developed from fish - amphibians, which over time adapted to life on land.

Cross-finned Devonian fish.

And now there are fish that can be out of the water for some time - for example, the periophthalmus, which lives on the coasts of the Indian Ocean.

Periophthalmus is one of the most interesting modern fish. In length, it reaches 15 centimeters. Large eyes sit on a large head, almost protruding from the surface of the body. The pectoral fins are very strong, muscular, similar to the paws of amphibians. Periophthalmus often comes out of the water, especially at low tide, and, quickly flipping its fins, crawls along soft silt, climbs onto the roots and trunks of mangrove trees, hunting for insects. On land, the periophthalmus feels as good and free as in the water. It is very difficult to catch him - he makes such energetic and unexpected jumps when trying to grab him with his hands ...

Creeper fish (periophthalmus) on the shore.

At the end of the Devonian, the first amphibians appeared - stegocephals ("covered heads"). They were descendants of lobe-finned fish. Scientists called them covered-headed because the upper part of their skull was a solid bone shell, in which there were five holes: a pair of nasal, a pair of ocular and one for the third parietal eye.

Stegocephalians were sedentary animals, they lived in marshy places, but they already breathed with lungs. If the swamp dried up, they crawled into neighboring water bodies, moving slowly on five-fingered paws.

The first land animal is a stegocephalus.

But not only museum fossils have been left to us by the long-extinct Devonian life.

From the remains of the organic world of the Devonian period, accumulations of oil were formed. This oily liquid formed as a result of the decomposition of animal and plant residues is the most valuable and important raw material for our industry. The richest deposits of Devonian oil are located between the Volga and the Urals. This huge oil-bearing region is called the "Second Baku".

Of all combustible materials - coal, firewood, oil shale - oil gives the greatest amount of heat during combustion: almost one and a half times more than the best grade of coal - anthracite, three times more than firewood, seven times more than oil shale.

It is difficult to enumerate the branches of industry in which oil or products derived from it are used.

The main petroleum products - gasoline, naphtha, kerosene, fuel oil and lubricating oils - are needed for aircraft, cars, tractors, tanks, and agricultural machines. Fuel oil, which gives much more heat than coal, is now the main fuel for sea and rail transport.

Vanillin, saccharin, aspirin, petroleum jelly, explosives are produced from petroleum products ...

Resins and rose oil are obtained from petroleum gas.

Resins are used to make artificial leather, replacing the real one, and synthetic rubber, and rose oil is used to manufacture the best varieties spirits.

Varnishes, paints, safety glass and many other valuable products are produced from oil - this precious gift of the earth ...

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