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Silurian period (system) (Silurian, also Silurian period) - geological period, the third period of the Paleozoic, after the Ordovician, before the Devonian. It began 443 million years ago and lasted 27 million years. The lower boundary of the Silurian is determined by major extinction, as a result of which about 60% of the species that existed in the Ordovician disappeared marine organisms, the so-called Ordovician-Silurian extinction. During the time of Charles Lyell (mid-19th century), the Silurian was considered the oldest geological epoch.
Animal world of the Silurian
Acanthodes, or prickly-toothed (lat. Acanthodii, before - Acanthodei) is a class of extinct fish. They existed from the late Silurian to the early Permian. Jaw-mouthed fish also appear - bone-shelled and shellless. The rise of graptolites. The rise of straight-shelled nautiloids. The diversity of brachiopods has increased markedly.
In the Late Silurian, cartilaginous ray-finned fish from the order Palaeonisciformes appear.
Flora of the Silurian
Cooksonia, oldest vascular plant, Middle Silurian
At the end of the Silurian, another group of plants appeared on land - vascular (Tracheophyta). Their imprints have been found in the Upper Silurian deposits in Great Britain, the Czech Republic, Ukraine, and Kazakhstan. The appearance of vascular plants is one of the key events in the history of the biosphere.
sedimentation
In the Silurian, the East Siberian Platform was covered by a shallow (10–20 m deep) sea, the level of which was very constant, in other words, at that time both the sea level and the East Siberian Platform were stable and did not fluctuate.
Minerals
Silurian deposits contain copper pyrite ores (Urals and Norway). With siliceous strata Southern Urals and Central Asia deposits of manganese and phosphorites are connected. In the United States (states of New York and Alabama) iron ore deposits and gypsum deposits (central New York State) have been discovered and are under development. The main minerals of the Silurian period: iron ore, gold, copper, oil shale, phosphorites and barite.
Geography and climate
For Silurian period characterized by gradual development of arid climate.
The Silurian only lasted about 25 Ma, but this period of geological history witnessed at least three major events in prehistoric life: the appearance of the first land plants, the subsequent colonization of land by land plants, and the evolution of jawed fish. The Silurian was the third period (542-252 million years ago). It was preceded by and , and then changed to , and .
Climate and geography
In the first half of the Silurian, most of the earth's continents were covered with glaciers, and global temperatures rose to about 25 ° C by the end of the period. The giant supercontinent Gondwana (which was destined to split hundreds of millions of years later into Antarctica, Australia, Africa and South America) gradually moved to the far southern hemisphere, while the smaller continent of Laurentia (future North America) occupied the equator.
Sea life
Invertebrates
The Silurian period followed the first major global extinction of living organisms, at the end of the Ordovician, during which about 75% of the species became extinct.
Within a few million years, most life forms recovered to a large extent, especially cephalopods and tiny organisms known as graptolites. One of the major achievements of the Silurian period was the spread of reefs, which thrived at the edges of the Earth's evolving continents and hosted a wide variety of corals, crinoids, and other tiny animals.
Giant sea scorpions such as Eurypterus(see photo above) up to 25 cm long, also lived during the Silurian and were the largest arthropods of their time.
Vertebrates
The Silurian period was marked by the evolution of jawless fish (such as the Birkenia), which improved significantly compared to the predecessors of the Ordovician period (such as Arandaspis). The evolution of the jaws and their accompanying teeth allowed the prehistoric fishes of the Silurian period to pursue more diverse prey as well as defend themselves against predators, and was the main driver of subsequent evolution.
Vegetable world
The Silurian is the first period when scientists have convincing evidence of the life of land plants. These were tiny, fossil spores from genera such as Cooksonia and Baragvanatia. These early plants were no more than 5 centimeters in height and, therefore, had only rudimentary (underdeveloped) internal organs for water exchange. Some botanists suggest that Silurian plants actually evolved from freshwater algae (which grew on the surfaces of small puddles and lakes).
land animals
As a rule, wherever terrestrial plants grew, some species of animals can be found. Paleontologists have found direct fossil evidence of the first and scorpions of the Silurian period, as well as other relatively primitive terrestrial arthropod species. However, large land animals have not yet appeared, as vertebrates gradually began to colonize the land.
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Silurian
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Information about Silure
Silurian period - geological period in the history of the Earth, the third period Paleozoic era, following after the Ordovician before the Devonian. It began - 443 million years ago, continued - 27 million years. The lower limit of the Silurian is determined by a major extinction, which resulted in the disappearance of about 60% of the species of marine organisms that existed in the Ordovician (the so-called Ordovician-Silurian extinction). The Silurian system as a statistic unit is subdivided into 2 divisions, 4 subdivisions and 8 tiers. The Silurian period is named after the ancient Celtic (Irish) tribe of the Silures. It is subdivided into two sections: lower and upper Silurian. In the Silurian, the continent of Laurentia re-formed in the northern hemisphere. The sea advancing from the south to the territory of Gondwana formed a large shallow bay, almost dividing Gondwana into two parts. Other continents and islands have little changed their outlines, acquired in the Cambrian period.
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Silurian statistic unit
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Silurian tectonics
In the Silurian period, the land gradually subsided under water; at the beginning of the Silurian, after a relatively small Ordovician regression, a transgression of the sea again occurs, almost equal in scale to the Ordovician, and approximately in the same areas. The sea eroded many previously formed mountain ranges and flooded vast areas. The slow sinking of the land and the lowering of the ocean floor led to the accumulation of sedimentary rocks - marls, sandstones, clays, dolomites, chalk, with the completion of the Caledonian stage of development, extensive uplifts occur both in geosynclinal belts and on platforms. As a result, regressions develop, and many platform territories not only dry up, but for a long time, for whole periods, acquire a continental development mode. It was a period of violent volcanic activity and intense orogeny - the period was famous for very frequent and strong earthquakes. At the end of the Silurian, mountain building processes take place, thanks to which the Scandinavian, Cambrian mountains, Khibiny, Sudetenland, Apennines, as well as the mountains of Iceland, South Scotland and East Greenland were formed. In place of Siberia and East China formed big mainland Angarida, the American Cordilleras and the volcanoes of Kamchatka and the Kuriles were partially formed. The end of the Silurian period was marked by the completion of the Caledonian folding. Areas of Caledonian consolidated structures are most clearly defined in the Atlantic geosynclinal belt, especially within the Grampian geosynclinal region (Scandinavian Mountains, Northern part British Isles, the western part of the Svalbard Islands, the eastern tip of Greenland), partly in the Appalachian geosynclinal region, in the form of vast territories - in the Ural-Mongolian geosynclinal belt (Sayans, Central Kazakhstan, Northern Tien Shan, Severnaya Zemlya) and in the West Pacific geosynclinal belt (Katazian geosynclinal region - east of the South China platform, Australian geosynclinal region - west of the arc of the Australian Cordillera). The formation of vast consolidated areas in the Grampian geosynclinal region caused the reunification of the East European and North American platforms into one vast continent, called the North Atlantic. Under the influence of the Caledonian tectogenesis in the basement of a number of platforms (Siberian, Caspian, Iranian-Indian, etc.), deep faults (Gissaro-Kokshaal, Merv-Jalalabad in Central Asia) and depressions (Karagie and Balkhash in Kazakhstan) occur, the deepening of syneclises and the initiation of depressions.
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Silurian Climate
The climate of the Silurian period at its beginning was warm, humid, similar to subtropical, and only at the end of the Silurian in the south did it become cold and frosty, and in the north, on the contrary, it became dry and hot; on the whole, the Silurian period is characterized by a gradual development of aridity of the climate - the frequency of droughts was high, dust storms and hot winds. Precipitation was negligible, no rain fell, but there were frosts. The sun in the Silurian period reached a very high activity, which caused the aridity of the climate.
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Living organisms of the Silurian: Flora
In the Silurian period, life penetrates the land. The first land plants, the remains of which were found in the Silurian deposits of the Cordillera, were called psilophytes, which means leafless, naked and seedless plants. They were no more than half a meter high, but appearance resembled modern sphagnum mosses, but had a simpler organization. In their structure, psilophytes are similar to brown algae from which they appear to have originated. Psilophytes grew in moist places or in shallow water bodies. Branching in psilophytes was dichotomous, that is, each branch was divided into two. Their body has not yet been clearly divided into root and stem parts. Instead of roots, they had processes - rhizoids, with which they were attached to the soil. The role of leaves was performed by scales. At the ends of psilophyte branches, there were reproductive organs - sporangia, in which spores developed. Among the Silurian plants water basins green, blue-green, red, and siphon algae predominated. Brown, almost did not differ in their structure from modern algae. This similarity prompted some researchers to the idea that in some parts of modern oceans the temperature, salinity, and other features of the water remained the same as they were at that distant time. At the end of the Silurian, another group of plants appeared on land - vascular (Tracheophyta). The appearance of vascular plants is one of the key events in the history of the biosphere and period.
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Living organisms Silurian: Fauna
The fauna of the Silurian period is represented mainly by the same types of invertebrates that lived in the Ordovician. Trilobites (over 80 species), molluscs (over 760 species), brachiopods (over 290 species) and sea lilies were quite common, the cups of which had rhombic pores characteristic of cystoids. Numerous representatives appear in the Late Silurian starfish, sea sponges and sea urchins. Among Silurian bivalves great importance acquire taxodonts, heterodonts, desmodoites. characteristic feature some of these animals was that their valves were bent in opposite directions. Brackish-water bays and lagoons were inhabited by many thin-shelled forms. Silurian gastropods were distinguished by very curious features. The vast majority of the shell was wrapped to the right. In addition, some of them had a spherical shell with a cut in the middle, gradually overgrown or turned into a series of holes. Cephalopods spread significantly in the seas of the Silurian period. Representatives of a small genus - volbortella - with a horn shell, who lived in the Cambrian and Ordovician periods, gave numerous descendants (large and small) with rounded and smooth calcareous shells. In the Silurian period, all the main classes of invertebrate organisms that exist to this day were formed, including the first primitive vertebrates (jawless and fish).
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Minerals of Silurian times
Silurian deposits contain sedimentary rocks that are widespread in the world and copper ores (the Urals, Ukraine, the Apennines, the Chilean Andes, Poland and Norway). In the middle of the Silurian, the formation of gold deposits began in the earth (Yakutia, the Caucasus, Alaska, Manchuria, Sakhalin, Iran and the Arabian-Somali platform). Deposits of manganese, tektites and phosphorites are associated with the siliceous strata of the Southern Urals, Kyrgyzstan, Mongolia and Central Asia. In Canada and the USA (states of New York and Alabama) iron ore deposits, as well as deposits of gypsum, barite and asbestos (central Georgia) have been discovered and are under development. High-quality hematites of the Silurian period are mined in the Czech Republic, Spain and Iran. The main minerals of the Silurian period: sedimentary rocks, iron ores, hematites, tektites, gold, copper, oil shale, asbestos, phosphorites and barite.
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Interesting…!
Scientists from Poland have found the victim of the first forest fire on Earth Polish scientists have discovered a petrified tree - evidence of the very first known forest fires on the planet, according to the international English TV channel "BBC News" with reference to the journal "Geology". Discovered near the military town of Dombrovnin-Gurnicza on the Polish-Ukrainian border, the fossil is a small piece of coal (presumably brown), which before the fire was a tree that grew in these places during the hot Silurian period - about 430 million years ago, archaeologists and historians told reporters from Poznań University. Then the planet was covered mainly by small trees (only a few centimeters in height), which burned well. And they burned down as a result of the arid climate, which was common in the Silure. Scientists from Poland managed to establish that the first forest fire on the planet quickly ended, and the combustion temperature was minimal, which is consistent with the atmosphere of that period when there was less than 18 percent oxygen in the air, against today's 21. It was the low oxygen content that made the fires of those times sluggish . After them, there was very little coal left that would have allowed scientists to make this discovery earlier. In addition, during the study of petrified wood, scientists were able to find traces of the vital activity of a living creature, presumably a centipede, on it. It is possible that she died in the fire.
The mutual arrangement of continents and seas remained approximately the same as in the Ordovician. The largest land mass - the mainland Gondwana - covered most of the modern territory of Africa (south of the Sahara), Arabia, Hindustan, Antarctica and Brazil. The continents were distinguished by a flat, slightly dissected relief; mountain ranges and chains, apparently, were absent. The end of the Silurian is the end of mountain building. Actual climate data are scarce. The wide distribution of rich shell fauna and the abundance of reefs in the seas suggest that they were formed in a warm mild climate.
organic world
By the beginning of the period, all the main classes of invertebrate organisms had formed and the first primitive vertebrates appeared. In the Silurian period, two groups of vertebrates appeared: jawless and fish. Among the jawless, there are bone-shelled and shellless, and among fish - acanthodes.
In the Silurian period, plants finally made their way to land. To do this, they needed to develop a waterproof outer cover - a cuticle pierced by tiny pores, or stomata. Through them, gas exchange was carried out during photosynthesis. To transport water from roots to shoots, plants developed a system of tubules, or vessels, and the stem began to lengthen further. Wood fabric began to be produced in it, which served as an additional support for it.
SILURIAN SYSTEM (PERIOD), Silurian from lat. Silures - Silures, the name of an ancient Celtic tribe that inhabited Wales * a. Silurian system(period); n. Silur; f. silurien, systeme (periode) silurien, Gothlandien; and. sistema (period) silurica, sistema (period) siluriana, - the third system from the bottom of the Paleozoic erathemacorresponding to the third period of the era of the geological history of the Earth. In the stratigraphic scale, it follows the Ordovician and precedes the Devonian system. The duration of the period is determined by radiometric methods at 30 million years (from 435 + 10 to 400 + 10 million years from the present). It was isolated in 1835 by the English geologist R. Murchison, but was initially combined with Ordovician system in Gotland. In 1960, at the 21st session of the International Geological Congress, it received an independent status.
In Russia ( European part, Siberia and Middle) Silurian system from the middle of the 19th century. was studied by the Russian geologists F. B. Schmidt, A. Kaiserling, E. Eichwald, I. V. Mushketov, and N. I. Lebedev; after the October Revolution of 1917, by V. N. Weber, A. N. Ryabinin, and D. V. Nalivkin, B. B. Chernyshev, B. S. Sokolov, O. I. Nikiforova, A. M. Obut, D. L. Kal’o, and others. , J. Hall, C. Schuchert, A. Cooper, O. M. Bulman, A. Martinsson and A. Buko.
Subdivisions. The general stratigraphic scale of the Silurian system includes the Llandoverian, Wenlockian, Ludlovian, and Przhidolian stages; all but the last one are subdivided into 2nd and 3rd (Llandovery) substages. It is accepted that the Silurian system is divided into lower and upper sections with a boundary at the base of the Ludlovian stage. The basis of the Silurian system is determined at the base of the Parakidograptus acuminatus graptolitic zone with a stratotype in South Scotland; the boundaries of all subdivisions of the scale also coincide with the graptolitic zones. The latter are the most fractional units of planetary correlation of deposits of the Silurian system (table).
general characteristics. Deposits of the Silurian system are known on all continents, with the exception of Antarctica, most of whose territory is hidden under ice. They are represented by 2 main facies types: shallow shelf, predominantly carbonate, strata with benthic fauna and organogenic structures and deep-water basin sediments of terrigenous composition with planktonic fauna (graptolites, conodonts, etc.). The former are distributed on the East European and Siberian platforms, in Central and South China, on the North American Midcontinent and in North Africa; the latter are characteristic of the marginal zones of the listed platforms and are widely distributed within many folded systems: Grampian, Paleo-Tethys, Ural-Tien Shan, Cordillera, Appalachian, and others. , in the European part of the CCCP (Baltic, Podolia), in the Urals, in the Southern Tien Shan, in southeast Australia, in the Appalachians and Morocco.
The largest Silurian continent was Gondwana, located in the Southern Hemisphere. Smaller land masses are also known: Lawrence (North America, Greenland), Baltosarmatia, Angarida, etc. The continents were distinguished by a slightly dissected flat relief, large mountain ranges and chains, apparently, were absent. The Silurian period is characterized by a wide distribution of epicontinental seas, which during periods of maximum transgressions went inland for more than 2000 km (Gondwana).
The beginning of the Silurian period is preceded by a major global event - a sheet glaciation, traces of which (tillites) are recognized in South America and North Africa (, Bolivia, Mauritania). It is associated with the maximum regression and breaks in some platform sections at the Ordovician–Silurian boundary. The latter begins with a powerful Llandoverian transgression, which is maximally manifested in Gondwana, on the North American and Siberian platforms. As a result, strata of evaporites, carbonates, incl. and reef, rocks; carbonate-detrital, as well as pelagic clayey and siliceous sediments accumulated on the outer shelf and in the open basin. From the end of the Early Wenlock, a regressive sedimentation cycle begins, which continues until the middle of the Early Devonian. In some shelf sections, short-term transgressive periods are recorded at the beginning of the Ludlovian and in the Przhidolian time (margins of the East European Platform). Geosynclinal zones are characterized by differentiated tectonic movements and variegated rainfall. At the geosynclinal stage of development, fine-grained terrigenous deposits accumulated in variscides (Urals, Central Europe, North Africa, Andes). For internal parts(eugeosynclines) were characterized by underwater volcanic eruptions: lavas, volcanic breccias and tuffs of ophiolite and andesite formations. Sedimentary-volcanogenic strata rich in siliceous matter are characteristic of many folded belts (, Ural-Tien Shan, Paleotethys). In the Caledonides during the orogenic stage coarse clastic sediments of the molasse type were deposited (Kazakhstan, Appalachians). At the end of the Silurian period, the Caledonian cycle (the Grampian geosyncline) ends and, as a result of regression, the vast epicontinental seas ( and ) become shallow. The isolation of some basins leads to the formation of red-colored deposits, salts, gypsum ( and ). A few lithological indicators of paleoclimate indicate the predominance of humid conditions in the Llandoverian and gradual warming and aridization of the climate from the beginning of the Wenlock to the Late Silurian. Reconstruction of paleolatitudes based on paleomagnetic, sedimentological, and biogeographic data indicates the possibility of the existence of 3 climatic zones: equatorial (0°-10° north and south latitude) with clastic, reef and carbonate sedimentation, tropical (10°-30° north and south latitude) with evaporites, carbonates and clay silts and temperate (30°-60° north and south latitude) with a predominance of clastic sediments. Judging by the position of the paleoequator, most of the known outcrops of the Silurian system were located within the tropical and low latitudes of the temperate zone.
organic world. By the beginning of the Silurian, all the main classes of invertebrate organisms had formed and the first vertebrates appeared. Shallow epicontinental seas and shelf zones of geosynclinal basins are characterized by shell-coral fauna. Among the inhabitants of the bottom, brachiopods and mollusks (gastropods, bivalves, first tentaculites) are especially numerous. Ostracods, trilobites and crustacean scorpions (eurypterids) led a mobile lifestyle or inhabited the soft bottom in lagoon zones and on the open shelf. The main biomass of the shallow and shallow zones were corals and hydroid polyps(tabulates, rugoses, stromatoporates), sea lilies, as well as algae. A variety of jawless animals are known (armorless, thelodonts, etc.). At the end of the Silurian, the first true fish appeared - acanthodes. In the late Silurian, in the coastal flood plains, the first higher plants(psilophytes). The inhabitants of the pelagial were graptolites, nautiloids and conodonts. A characteristic feature of the fauna is its cosmopolitan distribution. The exception is the endemic fauna of the brachiopods Clarkeia (Malvinokaffra province) and Tuvaella (south of the Asian part of the CCCP,
