Ordovician period - history - knowledge - catalog of articles - rose of the world. Ordovician period, Silurian period - geological eras Paleozoic Ordovician period

Ordovician period

Ordovician period - second period Paleozoic era(named after the Ordovician Celtic tribe that inhabited the territory of Wales). During this period, the continents again experienced subsidence, as a result of which geosynclines and low-lying basins turned into shallow seas. At the end of the Ordovician ca. 70% of the territory North America was flooded by the sea, in which powerful strata of limestone and shale were deposited. The sea also covered significant areas of Europe and Asia, partly - Australia and the central regions. South America.

All Cambrian invertebrates continued to evolve into the Ordovician. In addition, corals, pelecypods (bivalves), bryozoans, and the first vertebrates appeared. In Colorado, in Ordovician sandstones, fragments of the most primitive vertebrates, jawless (ostracoderms), were found, which lacked real jaws and paired limbs, and the front part of the body was covered with bone plates that formed a protective shell.

Based on the paleomagnetic study of the rocks, it was established that during most of the Paleozoic, North America was located in the equatorial zone. Fossil organisms and widespread limestones of this time testify to the predominance of warm shallow seas in the Ordovician. Australia was located near the South Pole, and northwestern Africa - in the region of the pole itself, which is confirmed by the signs of widespread glaciation imprinted in the Ordovician rocks of Africa.

At the end of the Ordovician period, as a result of tectonic movements, the uplift of the continents and marine regression occurred. In places, the original Cambrian and Ordovician rocks experienced a folding process that was accompanied by mountain growth. This oldest stage of orogeny is called the Caledonian folding.

Silurian

Silurian. For the first time, the rocks of this period were also studied in Wales (the name of the period comes from the Celtic Silur tribe that inhabited this region).

After the tectonic uplifts that marked the end of the Ordovician period, a denudation stage began, and then, at the beginning of the Silurian, the continents again experienced subsidence, and the seas flooded the low-lying areas. In North America, in the Early Silurian, the area of ​​the seas decreased significantly, but in the Middle Silurian, they occupied almost 60% of its territory. A thick layer of marine limestones of the Niagara Formation was formed, which got its name from the Niagara Falls, the threshold of which it forms. In the late Silurian, the areas of the seas were greatly reduced. In a strip stretching from the modern state of Michigan to the central part of the state of New York, thick salt-bearing layers accumulated.

In Europe and Asia, the Silurian seas were widespread and occupied almost the same territories as the Cambrian seas. The same isolated massifs remained unflooded as in the Cambrian, as well as large areas of northern China and Eastern Siberia. In Europe, thick limestone strata accumulated along the periphery of the southern tip of the Baltic Shield (at present they are partially flooded by the Baltic Sea). Small seas were common in eastern Australia, northern Africa and in the central regions of South America.

In the Silurian rocks, in general, the same main representatives of the organic world were found as in the Ordovician. Terrestrial plants did not yet appear in the Silurian. Among the invertebrates, corals have become much more abundant, as a result of which massive coral reefs have formed in many areas. Trilobites, so characteristic of the Cambrian and Ordovician rocks, are losing their dominant significance: they are becoming smaller both in quantitative and species terms. At the end of the Silurian, many large aquatic arthropods appeared, called eurypterids, or crustaceans.

The Silurian period in North America ended without major tectonic movements. However, in Western Europe at this time the Caledonian belt was formed. This mountain range stretched across Norway, Scotland and Ireland. Orogeny also took place in northern Siberia, as a result of which its territory was raised so high that it was never flooded again.

The Paleozoic era left its mark on the history of the Earth's development: turbulent geophysical processes, the formation of the main continents and seas, the birth of marine and land animals ... The Ordovician period - the second from the bottom of six periods in the historical geological system of separation - follows the Cambrian and precedes the Silurian.

History of study

History of geological and biological development The earth is traced through the study of radiological studies of the layers that were formed in each of the periods. The Paleozoic era is no exception. The Ordovician period is singled out and described by the English explorers Murchison and Lapworth, who suggested its name. The Ordovicians were an ancient tribe that lived in what is now Wales. It is in this place, in the area of ​​Areninga and Bala, that geological strata have been identified that correspond to the period that took place 500 million years ago, over a period of 60 million years.

At the 21st session of the International Geological Congress, the Ordovician period acquired the status of an independent system.

Subdivisions of the Ordovician

The Ordovician system is divided into three periods: lower, middle and upper. According to the accepted general international classification, they correspond to certain tiers:

• Lower Ordovician: Tremadocian, Floyian.
• Middle Ordovician: Dalingian, Darrivilian.
• Upper Ordovician: Sandbian, Katian, Hirnantian.

The geological history of the Ordovician period is studied in many countries, paleontologists put forward their own systems for dividing periods, somewhat different from the international version.

Continents and oceans

At the border of the Cambrian and Ordovician periods, the distribution of ocean and land looked like this: North America and Greenland made up a single mainland Laurentia. To the south of it was the mainland of Brazil. The African continent included Madagascar and Arabia. The north is the Russian continental platform, to the east of it is Angarida, the Chinese and Australian continents. Tectonic movements in the Ordovician period led to the convergence of the Russian, Siberian, Chinese and North American platforms and the formation of a single big mainland Laurasia. The southern platforms - Hindustan, African, Antarctic, South American, Australian - merged into the huge mainland Gondwana. The Tesis Sea separated two large continents - the place where the mountain systems of Europe, North Africa, Asia, and South America are located at present. High seismic activity is characteristic of these regions to this day.

Climate

Volcanoes continued to rage throughout the Ordovician period. The climate became warmer and wetter. The current hottest part of the world - Africa - in those days was under the very pole, as evidenced by traces of glaciation on its territory. The increase in the area of ​​the sea led to a decrease in the northern deserts and the complete disappearance of the southern dry zone. An active seismic environment leads to the accumulation of powerful volcanic rocks. Tufas and lava fill the sea trenches. On the seabed, which gradually descends, there is an accumulation of black volcanic ash and sand.

Minerals

Climatic conditions, tectonic and seismic activity of this period led to the formation of special accumulations characteristic only of the Ordovician in earth's crust. The Ordovician period is distinguished by deposits of rocks of marine origin: limestone, shale, sandstone. Volcanic lava, magmatic processes lead to the formation of phosphorites, oil shale, oil, iron and other ores, granite, marble, shell rock.

Ordovician period: flora

In the Ordovician, as in the previous Cambrian period, the class of plants is represented mainly by red and green algae. Plants that appeared on land are observed in the studied sections in very small numbers, obviously, these were the first samples of small tubular representatives of the flora, which were just beginning their continental development. For a more extensive conquest of the soil, the optimal conditions were formed only in the subsequent Devonian period, when the outbreaks of volcanic passions somewhat subsided and suitable humidity was established. The first algae are unicellular lower forms of plants, which, however, have survived to this day. Algae were adjacent to such plant forms like fungi and bacteria.

Animals of the Ordovician period

As you know, the origin of the animal world began in the ocean depths. In this regard, the Ordovician is characterized by explosive progress in the development of many new species and forms of major marine organisms.

Trilobites - a kind of marine arthropods that appeared in Cambrian times, experienced unprecedented progress. During the Ordovician period, the number of their genera increased to 77, they differed in size and lifestyle. Some species of trilobites were blind, but most of them had eyes with a number of facets from 10 to 1200. The body of these arthropods consisted of several segments (from 2 to 29) and was covered with spikes that protected from enemies and kept the trilobite on the surface of the water.

In the period under consideration (Ordovician) cephalopods received a surge in development. The ancestors of modern cuttlefish, squid and octopuses formed in those distant times many species and subspecies, ranging in size from a few centimeters to several meters.

In the sandy layers of the Ordovician period, remains of cores of foraminifera, radiolarians, and graptolites were found.

Bryozoans, echinoderms, tabulates, and corals have made significant progress in their development. The appearance of the most ancient vertebrates, the jawless fish agnates, is associated with the Ordovician. In their structure, the first cartilaginous fish resembled modern hagfish. It was a creature as flexible as a loach, with a cartilaginous spine along its slippery body. The first vertebrates still had a cover in the form of a hard shell that protected from external damage, but they were already more mobile than their predecessors, since the spine served as a support for developing muscles. At the very end of the period, the gills of some species turned into jaws, and the horny plates into teeth. First ferocious predators- placoderms - looked intimidating, reached three meters in length, moved quickly.

Ordovician catastrophe

Known to many historical fact about the mass extinction of dinosaurs on the planet, but few people know that the first significant catastrophe occurred about 200 years before the appearance of dinosaurs. Late Ordovician animal world lost about 60% of the species that existed at that time. Most living organisms belonged to primitive forms and existed mainly in an aquatic environment, however, in terms of the number of dead individuals, this event is the second in the list of such mass extinctions and the third in terms of the percentage of species and genera that disappeared forever from the face of the Earth.

Versions of the causes of the Ordovician catastrophe

As with the dinosaurs, the extinction of the Ordovician protozoa is a hotly debated issue among paleontologists. Discuss experts about the reasons that caused the tragedy. There are five main versions:

• First space: a powerful burst of gamma waves near the solar system.
• Second space: the fall of large meteorites or the collision of large asteroids.
• One of the reasons could be the intensive formation mountain systems, in particular the Appalachians, which leads to intense weathering, changes in the composition of soil and water.
• Climate version. The shift of Gondwana towards the South Pole led to a sharp cooling. The concentration of carbon dioxide decreased, the level of the World Ocean fell, followed by glaciation.
• Opponents of the version mentioned above are researchers chemical composition fossil microorganisms. They are sure that the reason lies in a sharp change in the ratio of carbon dioxide and oxygen in the air, the saturation of water with elements of iron, lead, copper, manganese. Living organisms underwent metamorphoses, and subsequently entire species and genera became completely extinct.

Main events of the Ordovician period

Summing up, we can single out several main and most important events of that era, which significantly influenced the course of the further history of the development of life on Earth.

• The area of ​​the seas has increased (compared to the previous period).
• The formation of the main platforms has been completed.
• There was an accumulation of thick layers of tuff, lava, sedimentary rocks, clastic deposits.
• Deposits of iron and manganese ores, gold, oil, building materials.
• The appearance of folded regions and mountain systems determined certain boundaries of the regions, which explains the difference in the development of vegetation in different parts the globe.
• Plants of the Ordovician period are represented by rapidly developing algae, the first of which appear on land, albeit in small quantities. Presumably, it was they who became the harbingers of the first land tubular plants - rhinophytes.
• Rapid development marine inhabitants: trilobites, echinoderms, mollusks, branchapods, bryozoans, corals.
• The most important and important event Ordovician was the appearance of the first vertebrates - cartilaginous jawless fish.

The Ordovician period (system) is the second layer of deposits of the Paleozoic group in our planet. The name comes from the ancient Ordovician tribe. They lived in Wales, Britain. This period was recognized as an independent system. It existed five hundred million years ago and lasted sixty million years. The period is distinguished on most of the modern islands and on all continents.

Geology of the Ordovician system

At the beginning of the period, North and South America were brought closer to Europe and Africa. Australia was next to Africa and was part of Asia. One of the poles was in northern Africa, the other in northern Africa. Pacific Ocean. At the very beginning of the Ordovician, most of the south of the Earth was occupied by the mainland Gondwana. It included what is now South America, the south Atlantic Ocean, Australia, Africa, northern Asia, and the Indian Ocean. Gradually, Europe and North America (Laurentia) began to move away from each other. The sea level was rising. Most of the land was in warm latitudes. Mountain and later continental glaciers appeared in Gondwana. In South America and in the northwestern part of Africa, sediments of bottom moraines have been preserved, which were left behind by

The Ordovician period on the Arabian Peninsula, in the south of France, Spain is characterized by icing. Traces of ice have also been found in Brazil and non-western Sahara. The expansion of maritime spaces took place in the middle of the Ordovician period. In the western part of North and South America, Britain, in the Ural-Mongolian belt, in the southeast of Australia, traces of Ordovician deposits reach up to ten thousand meters. There were many volcanoes in these places, lava strata were accumulated. Siliceous rocks are also found: jasper, ftanides. On the territory of Russia, the Ordovician period is clearly visible on the East European and Siberian platforms, in the Urals, on Novaya Zemlya, on the New Siberian Islands, on Taimyr, in Kazakhstan and Central Asia.

Climatic situation in the Ordovician system

During the Ordovician period, the climate was divided into four types: tropical, temperate, subtropical, and nival. Cooling occurred in the late Ordovician. In tropical regions, the temperature dropped by five degrees, in subtropical regions - by fifteen. It got very cold in high latitudes. The Middle Ordovician experienced a warmer climate than the previous era. This proves the distribution of limestone rocks.

Minerals in the Ordovician system

Among the fossils formed in this period, oil and gas are distinguished. There are especially many deposits of this period in North America. There are also deposits of phosphorites. These deposits are explained by geological processes in which magma was involved. For example, in Kazakhstan there are deposits of manganese ores, as well as barites.

Seas in the Ordovician period

In the Middle Ordovician, the expansion of marine spaces occurs. The bottom of the seas is getting lower. These changes greatly affected the accumulation of a large layer sedimentary rocks, which are represented by black silt. It is made up of volcanic ash and sand. Small seas were located on the territory of modern North America and Europe.

Ordovician flora and fauna

Algae in the Ordovician period did not change when compared with the previous period. The very first plants appear on earth. They are mainly represented by mosses.

Life in the water in this period is quite diverse. That is why it is considered very important in the history of the Earth. Formed the main species sea ​​creatures. The first fish appear. Only they are very small, about five centimeters. Sea creatures began to develop hard covers. This happened because living organisms began to rise above the sediments of the bottom and feed above the bottom of the sea. There are more and more animals that feed on sea ​​water. Some groups of vertebrates have already evolved, others have just begun to develop. At the end of the Ordovician, vertebrate organisms appear. Sea bladders, sea lilies appeared from echinoderms. Currently, organisms such as sea lilies and starfish also exist.

A flock of jellyfish floats above the sea lilies - this is a beautiful picture from ancient times. The owners of the shells also begin their livelihoods. Gastropods and laminabranchs are represented by a large number of species. In the Ordovician, the development of four-gill cephalopods takes place - these are primitive representatives of nautiloids. These organisms still live in the depths of the Indian Ocean. The shells of the ancient representatives of these living creatures were straight, unlike curved shells. modern species nautilus. These mollusks led a predatory lifestyle.

New animals in this period were graptolites. They reproduced by budding. Graptolites created colonies. Previously, they were classified as coelenterates, now they are classified as wing-gill invertebrates. AT given time graptolites do not live, but they exist distant relatives. One of them lives in the North Sea - this is Rhabdopleura normanni. A group of organisms is also emerging that helps corals build reefs. They also appeared at this time - these are bryozoans. They exist even now, these organisms look like beautiful lacy bushes. These were the aromorphoses of the Ordovician period in living organisms.

Sea dwellers

Fragments of jawless fish were found in the sandstones. Other remains of vertebrate creatures similar to sharks have also been recovered. Fossil evidence suggests that jawless Ordovician species are distinct from today's species.

The first animals to have teeth were conodonts. These creatures are like eels. Their jaws are different from the jaws of living beings. Scientists have counted six hundred species of living beings that lived in the seas during the period described above. Cooling has become one of the reasons for the extinction of many species. The shallow seas turned into plains, and the animals of these seas perished. The same result was also vegetable world of this period.

Cause of animal extinction

There are many versions of the mass extinction of creatures:

1. A burst of gamma rays within the solar system.
2. The fall of large bodies from space. Their fragments or meteorites are found to this day.
3. The result of the formation of mountain systems. Under the influence of wind, rocks are weathered and fall into the soil. As a result of these processes, little carbon remains, which contributes to warming.
4. The movement of Gondwana to the South Pole led to a cooling, and then glaciation, a decrease in the water level in the oceans.
5. Saturation of the oceans with metals. The studied plankton of that period contains an increased level of various metals. There was a poisoning of water with metals.

Which of these versions seems to be reliable, and why the animals of the Ordovician period became extinct, is currently not known for certain.

Ordovician or Ordovician system- the second period. The Ordovician lasted from 485 million years ago to 443 million years ago, that is, for 42 million years. In order not to get confused in eons, eras and periods, use the geochronological scale, which is located as a visual clue.

The name of this period was given according to the typical geological section, which clearly indicates the history of this period. The section is located in the area of ​​Wales, on the territory of which the Celtic tribe of the Ordovicians lived in ancient times.

In the Ordovician period, life continued to develop. During the study of the geological layer of the period, numerous discoveries were made regarding the Ordovician biota. It is noted that during this period great development and distribution of green and red algae. Moreover, in addition to marine plants, the first land plants appeared in this period. In the period from 485 to 443 million years ago, remains of spores of land plants were found, as well as imprints of stems, which, apparently, belong to vascular plants.

Concerning fauna, then, unlike plants, they had not yet reached land and lived only under water. The seas and oceans were inhabited by unicellular radiolarians, unicellular foraminifera, jawless vertebrates arandaspids (extinct), echinoderm sea buds (blastoids, extinct), echinoderm globules (sea bladders, cystodea, extinct), sea lilies, sea ​​stars. In addition, bivalves, gastropods and cephalopods, crustaceans, trilobites, brachiopods, bryozoans, sponges, graptolites, and horseshoe crabs lived in the Ordovician. The Ordovician is also characterized by such animals that lived only during this period, that is, they arose in the Ordovician and died out in the Ordovician. Scientists note that by the end of the Ordovician and the onset of the next period, unique groups of echinoderms, which are not observed in other periods, died out. In addition, by the beginning of the Silurian, many families of graptolites, brachiopods, corals, cephalopods, and trilobites became extinct, since on the border of the Ordovician and Silurian, mass extinction animals.

Ordovician-Silurian extinction is considered one of the five worst extinctions in history and the second largest loss among living organisms (the first is considered permian extinction, when 96% of all marine species and 70% of terrestrial vertebrate species became extinct). The main reason for the extinction of animals during this period is considered to be the movement of the Gondwana supercontinent, which was moving towards the region. south pole, which led to global cooling, glaciation and falling sea levels. In total, about 100 families of marine animals died out, or 49% of all animals on Earth.

Animals of the Ordovician period

Cincinnetina meeki

Platystrophy ponderosa

Rhynchotrema dentatum

Arandaspeeds

Blastoids

Graptolites

horseshoe crabs

Sea stars

sea ​​lilies

Orthoceras

radiolarians

Racoscorpions

Trilobites

foraminifera

Balloons

Endoceras

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ORDOVICAN PERIOD

Ordovician deposits were identified in England and described by the English geologist R. Murchison. - By decision of the XXI session of the International Geological Congress, the Ordovician was separated into an independent system.

Mainland Lawrence in the Ordovician period broke up into four large and a number of smaller islands. In place of the Russian mainland, two large islands were formed, separated by a narrow strait. Almost half of the territory of the Siberian and Chinese continents was flooded with shallow seas.

In the southern hemisphere, a huge continent was formed - Gondwana, which included modern South America, the southern part of the Atlantic Ocean, Africa, the Indian Ocean, Australia, and North Asia. The Northern Tien Shan, Altai, the Australian Cordillera, and the West Siberian ranges begin to form.

In the sea basins that existed on the territory of the Urals, Chukotka and the Cordillera, thousands of volcanoes were active, which produced thick deposits of volcanic rocks.

Among the rocks of the Ordovician, marine sediments predominate - sandstones, limestones, shales. Compared with the Cambrian deposits, there are fewer lagoonal formations - gypsum, salts, limestones, dolomites - among the Ordovician deposits. The climate in the Ordovician period becomes warmer and milder, as evidenced by the large distribution of limestones: stromatoporous, coral, crinoid, trilobite and cephalopod. The area of ​​the sea has increased significantly. The equatorial primary sea flooded vast areas of the Cambrian continents.

The southern dry zone completely disappears. The area of ​​northern deserts is shrinking. As a result of these changes, the animal and plant world is also changing. Mountain continents, wedged between sea basins, prevented the spread of animals and plants around the globe. That is why the fauna and flora of the European Ordovician differ from the Indian and East Asian ones.

At the end of the Cambrian period, volcanic eruptions fill the sea basins with tuffs and lavas. At the same time, the seabed drops significantly. All this led to the accumulation of thick strata of sedimentary rocks, in particular black silt, consisting of volcanic ash, sand, clastic rocks.

Algae almost did not change during this period. The marine fauna was characterized by such a wealth of forms that the Ordovician period seems to us the most important era in the entire history of the Earth. It was in the Ordovician that the main types of marine organisms formed. Compared with the Cambrian, the number of trilobites increases significantly. In the Ordovician, many large trilobites (up to 50-70 cm) also appear in Europe. This indicates that they felt good in the new conditions.

Due to the migration of fauna from west to east and adaptation to new conditions in the Ordovician seas, 77 new genera of trilobites appear. External structure body indicates that trilobites led a different way of life. Their eyes had from 10 to 1200 facets. There were also blind trilobites. The number of trunk segments (segments) varied in different species from 2 to 29. The body was covered with spines for protection from enemies or completely smooth, well adapted to crawling in mud. Sometimes the body was covered with long sharp spikes, which increased its surface, which allowed the animal to freely stay in the water.

All the most important groups of animals that lived in the seas at a later time were found in the Ordovician deposits. Loose green sandstones near Leningrad contain many foraminifera nuclei. Radiolarians are found in black shales. Quite numerous in the Ordovician deposits are sponges, in the skeleton of which there were silica needles: cyathophikas, up to 12 cm high, and brachiospondia, up to 30 cm high, with 12 root processes.

Sea sponges were four- and six-rayed. Particularly beautiful needles were distinguished by the four-beam eutax-sixadima six-beam receptaculitis. The body of the first, the size of a cherry, had a fibrous structure. Each of the fibers was a hexagonal tube, consisting of small four-beam needles, intertwined so closely that it is very difficult to separate at least one of them. Six-ray sponges appeared for the first time in the early Ordovician. The round, flat, pear-shaped or saucer-shaped body of this creature was covered with a shield of rhombic plates. Under each plate was an empty pointed column. The columns were connected to the inner plates. All this constituted the inner shell.

The first corals appeared, but they did not yet have much significance in nature. Of the mollusks, the most common were nautiloids and gastropods. Nautiloid shells were straight. The mollusk itself was placed in the living chamber, the remaining chambers were filled with gas. By filling these chambers with water, the mollusk could dive to considerable depths, and by displacing the water with gas, float to the surface. Graptolites appeared, which looked like branches, spirals, loops. They lived in colonies, attached to algae or swam freely with the help of a bubble.

In the Ordovician period, bryozoans and tabulates first appear, which spread especially in the Silurian period.

Brachiopods develop rapidly. If in the Cambrian there were 18 genera, then in the Ordovician there were already 41 genera of these animals.

Echinoderms in the Ordovician were represented by many types of cystoids, the body of which was covered with a calcareous shell. The round mouth opening was protected by a plate. A significant distribution of cystoid forms gives reason to consider them the ancestors of sea lilies, sea ​​urchins and starfish, since different cystoids had much in common in structure with these large groups of animals.

The Ordovician period lasted 60 million years. Its deposits contain polymetallic and iron ores, phosphorites, oil shale, building materials, and oil.