Cretaceous period 1. Cretaceous period. Key Features. The division of the Cretaceous period, geographical features and climatic changes

Starting 145 million years ago, it lasted about 79 million years and ended 66 million years ago. Its name comes from the abundance of writing chalk, formed from dying invertebrate organisms, in its deposits. The Cretaceous period is significant for the second largest (after the Permian) worldwide extinction of species.

In 2016, the International Union of Geological Sciences adopted the following division of the Cretaceous:

Periods, geography and climate of the Cretaceous period

In the Cretaceous period, the division of Laurasia into the North American continent and the European-Asian continent continued. Gondwana finally broke up into the South American continent, the African, Indian segment, Antarctica and Australia. Throughout the Cretaceous, these gigantic land areas diverged more and more from each other, the southern and northern parts of the Atlantic Ocean were no longer connected by narrow straits, but acquired an integral oceanic structure. But, despite this, a tangible part of Europe, the Middle East, the Caucasus and the northern part of Africa, until the very end of the Cretaceous period, were still under water.

The climate of the Cretaceous period in comparison with the previous Jurassic became noticeably colder. At the beginning of it average temperature across the planet fell by 5 degrees, which led to the formation of polar ice caps, but after a while the climate warmed up again, and in general it was relatively warm all over the planet, winter temperatures even in the coldest zones the globe on average fluctuated within +4°C. By the end of the period, the greenhouse effect caused by side factors served to increase the temperature even more and sharply.

sedimentation

The Cretaceous period is characterized by the maximum flysch accumulation in geosyncal areas in the entire history of the Earth. As a result of violent magmatism caused by the split of continental areas, siliceous and split-dibasic formations were formed, granitoid ejections were extensive and grandiose. In general, the accumulation of trigenic and volcanogenic strata was widespread during the Cretaceous. Such rift zones arose in Africa and Brazil. IN sea ​​depths huge thicknesses of writing chalk accumulate.

Cretaceous Animals

The most significant in the Cretaceous period among marine invertebrates were cephalopods. In the Upper Cretaceous, the role of the outer-shell (ammonoids) slightly decreased, but the inner-shell (belemnites) were fundamental until the very end of the period. Closer to the middle, some ammonoids, for example, such as ammotoceras, reached 2 meters in size.

Such mollusks as pelecypods (bivalves) and gastropods (gastropods) have also received wide development. Most bivalves will die out completely by the end of the Cretaceous. Irregular sea urchins also developed along with large foraminifers.

The insects of the Cretaceous period, which adapted to the existing flowering plants, also felt great. Due to biological changes in vegetation, they also progressed in their development. All kinds of worms also felt great. The first lobsters and other predatory crustaceans, such as crabs and shrimp, appeared in coastal seas and oceanic zones.

Dinosaurs

The vertebrate animals of the Cretaceous period, dinosaurs, were distinguished by the fact that among them, as in the Jurassic period, reptiles reigned supreme (Fig. 1). Among them were crawling, and walking on four limbs, and moving only on two hind limbs, and waterfowl and, of course, flying hymenoptera. The richness of their diversity and forms was truly amazing. All this large army of reptiles incessantly devoured both huge masses of green spaces and themselves, meanwhile, increasing in number more and more, until, in an incomprehensible way, in the upper Maastrichtian stage of the Cretaceous period, it almost completely and everywhere died out.

Rice. 1 - Cretaceous Dinosaurs

The first snakes appeared (Fig. 2). Some grew to truly gigantic sizes and hunted mainly in aquatic environment, in coastal or river basins. It was not difficult for some of them to wrap around and crush or strangle a gaping one and a half meter raptor.

Rice. 2 - Cretaceous Snake

The variety of flying dinosaurs was also great. The real giant was the pteradon, whose wingspan reached an average of 8 meters. These giant reptiles hunted mainly over the sea, diving with ease in the air currents and now and then, snatching fish and other representatives of the marine fauna from the water.

Birds also developed widely, the first varieties of which appeared in the Jurassic period. In the Cretaceous, highly organized and specialized formations appeared among them.

And in the depths of the sea, fish with a hard-bone skeleton received further development. The ray-finned offspring of the Triassic and Jurassically multiplied, a huge number of new varieties appeared both among the inhabitants of freshwater and inland basins, and among salty marine and oceanic varieties (Fig. 3).

Rice. 3 - Marine animals of the Cretaceous period

Despite the undivided dominance of reptiles, mammals still advanced in their evolutionary development in the Cretaceous period. Having appeared on the threshold of the Mesozoic, these animal-like animals (synapsids) slowly but surely waited in the wings throughout the epoch, more and more adapting to a difficult life in the background. Synapsids often settled in cold areas of the continents, where predatory, but heat-loving reptiles were rare guests. Those who were forced to live among reptiles in hot areas went out to hunt mainly at night. All this greatly contributed to their adaptation to difficult conditions, which determined the survival of mammals in the difficult conditions of the asteroid winter that hit the Earth at the end of the Cretaceous.

All synapsids were divided into three main varieties - dicynodonts, cynodonts and allotheria. Dicyodonts and cynodonts almost completely died out during the Cretaceous period, and allodonts developed into mammals. During the late Jurassic and the subsequent Cretaceous period, they clearly divided into three branches - oviparous, marsupial and placental. Oviparous, unable to withstand competition with marsupials and placentals, soon also disappeared, marsupials today have survived only in Australia, namely, all subsequent species of modern mammals have developed from placentals. Placentals at that time were divided into Laurasiatherians and Gondwanatherians. It was Gondwanotheres that were the ancestors of modern rodents and primates.

From the marsupial branch, opossum-like ones originated, and only platypuses are currently left from the egg-laying ones. The ancient mammal purgatorius is considered the ancestor of primates.

In the main, mammals of the Cretaceous period (Fig. 4) weighed no more than half a kilogram and rarely exceeded the modern rat in size. Of course, there were also such rare specimens as meter and fourteen kilogram repenomams, but they were too few.

Rice. 4 - Cretaceous Mammals

For the most part, reptiles owe their extinction to these small creatures, which, having multiplied unusually by the end of the Cretaceous period, fed mainly on insects, but did not disdain reptile eggs.

Despite the fact that the first flowering plants began to appear long before the Cretaceous, it was at this time that the formation of flowering vegetation entered the stage of a real boom. It is no coincidence that half of all the currently known plants that exist are flowering plants. And this is connected with this.

By dispersing spores in the wind, primitive plants took great risks. And not in vain, since the bulk of the disputes did not reach the set goal. And many plants of that era have not yet acquired at least some kind of spore spraying mechanisms. Their spores were forced to fall to the ground, right in the same place where the plants themselves grew. It is clear that with such reproduction it was not possible to achieve a more or less reliable result. Hence, there was a vital need to develop new, more efficient methods of pollen distribution. And insects came to the aid of plants.

A kind of union began to develop and grow stronger between the flower groups. While the insects carried the pollen of the plants, the plants produced nectar for them, so that they worked more intensively on pollination. In the process of evolution, it turned out that many insects simply could no longer do without flowering plants, since their entire life and body biology was inextricably linked and aimed at life associated with such plants. And plants, with the help of their helper insects, began to multiply many times faster, and soon dense vegetation spread even to those parts of the land where it had never been before. This kind of partnership between plants and insects continues to this day.

Rice. 5 - Cretaceous Plants

The underwater plants of the Cretaceous period were in many respects similar to the plants of the previous periods of the Mesozoic. The only difference was that such microscopic algae as nanoplankton (for example, golden coccolithophores) and diatoms multiplied unusually. It is nanoplankton and small foramnifers that are responsible for the formation of such thick layers of writing chalk.

By the end of the Mesozoic era, the flora of the land has undergone a number of significant changes. From the middle of the Cretaceous, the first angiosperms began to appear, which, towards the end of the Cretaceous, already constituted the overwhelming majority among land plants. The first varieties of plants with foliage of increased juiciness began to appear. This is most true of places where the climate began to acquire a more arid and hot character.

Cretaceous extinction

Happened at the turn of the Mesozoic and Cenozoic, or rather, in the Maastrichtian final stage of the Upper Division, the Cretaceous extinction of species was the second largest after the Permian. Overnight, coccolithophorids ceased to exist, there were no Cretaceous planktonic foramonifers, ammonites, belemnites, coral-like bivalve mollusks - rudists. Dinosaurs and many other species of reptiles disappeared from the face of the earth. Many species of birds and insects, both surface and underwater world. In particular, the total number of all kinds of raliolaria decreased by 50%, 75% of all brachiopods died out, from 30 to 75% of bivalves and gastropods, sea lilies and hedgehogs. Of the total number of sharks, only 25% remained. Over 100 different families of marine invertebrates have ceased to exist. In general, the damage suffered by the flora and fauna was truly enormous.

What caused such a mass extinction of species in the Cretaceous period is still not known. Scholars are divided on this issue. Opinions were also expressed about the fact that powerful cosmic radiation formed as a result of a supernova explosion reached the Earth. Someone is talking about a strong greenhouse effect associated with extremely aggravated volcanic activity. But most are in favor of the version, which is based on the fall of a giant asteroid to the earth (Fig. 6). This version is confirmed by the presence of inclusions of iridium in the layers of this era, which is constantly found in places where meteorites fall.

Rice. 6 - Asteroid impact

It is alleged that an asteroid measuring from 10 to 15 km, entering the earth's atmosphere at great speed, split into several segments, which collided with the earth's surface. Explosive energy, amounting to approximately 10 30 erg, lifted a lot of pollutant from the earth's crust, which for a long time closed access to plants and animals. sunlight. Thus, as a result of the created kind of "asteroid winter", the majority of terrestrial animals died out. Apparently, this did not affect the plant world so much because the atmosphere cleared up in a relatively short period of time. And if the seeds of plants were safely able to survive this catastrophe in the soil and soon simply sprouted as if nothing had happened, then animal world Cretaceous period could not endure this global catastrophe with such ease. And as a result, only the most adapted and more tenacious species survived, such as, for example, mammals.

Minerals of the Cretaceous period

The Cretaceous period is unusually prolific different kinds minerals, most of which arose as a result of intrusive magmatism and volcanism, which accompanied the worldwide division of Pangea into smaller components. About 20% of coal deposits were accumulated during this time. The largest coal basins of this period are the Lena and Zyryansk coal basins, as well as a number of North American coal basins.

Most of the Russian, French and Spanish bauxite deposits, West Siberian oil and gas fields, oil and gas fields of Kuwait and Canada are also associated with the Cretaceous period. Vast deposits of oolitic iron ores were discovered on the territory of Western Siberia. Phosphate deposits are also numerous in the territories of Russia, Morocco, and Syria. Extensive salt deposits have been found on the territory of Turkmenistan and in some North American regions. In the northeast of Russia, on the territory North America found deposits of tin, lead and gold. The famous Indian and South African diamond deposits also belong to the Cretaceous period.

Writing chalk has been found almost everywhere in Cretaceous deposits.

Geology

During the Cretaceous period, the split of the continents continued. Laurasia and Gondwana fell apart. South America and Africa moved away from each other, and Atlantic Ocean got wider and wider. Africa, India and Australia also began to diverge in different sides, and giant islands eventually formed south of the equator.

Climate

70 million years ago, the Earth was cooling. Ice caps have formed at the poles. Winters were getting harsher. The temperature dropped in some places below +4 degrees. For dinosaurs of the Cretaceous period, this difference was sharp and very noticeable. Such fluctuations in temperature were caused by the split of Pangea, and then Gondwana and Laurasia. The sea level rose and fell. The jet streams in the atmosphere have changed, as a result of which the currents in the ocean have also changed.

At the end of the Cretaceous period, the temperature began to rise sharply. There is a hypothesis that the oceans were the cause of these changes: instead of absorbing heat, they may have reflected it back into the atmosphere. In doing so, they caused the greenhouse effect.

Vegetation

In the Cretaceous period, angiosperms appeared - flowering plants. This entailed an increase in the diversity of insects that became pollinators of the flowers. As temperatures increased during the late Cretaceous period, plants with more luscious foliage developed.

Animal world

Among terrestrial animals, various large reptiles reigned. This was the heyday of giant lizards - many dinosaurs reached 5-8 meters in height and 20 meters in length. Winged reptiles - pterodactyls - occupied almost all niches of aerial predators, although real birds have already appeared. Thus, in parallel there were flying lizards, lizard-tailed birds of the Archeopteryx type and real fan-tailed birds.

There were no mammals in the seas, but a niche large predators occupied by reptiles - ichthyosaurs, plesiosaurs, mosasaurs, sometimes reaching 20 meters in length.

The diversity of marine invertebrates was very great. As in the Jurassic, ammonites and belemnites, brachiopods, bivalves, and sea urchins were very common. Among bivalve mollusks, rudists, which appeared at the end of the Jura, played a large role in marine ecosystems - mollusks that looked like solitary corals, in which one valve looked like a goblet, and the second covered it like a kind of lid.

By the end of the Cretaceous, a lot of heteromorphs appeared among the ammonites. Heteromorphs arose earlier, in the Triassic, but the end of the Cretaceous became the time of their mass appearance. The shells of heteromorphs were not similar to the classical spiral-twisted shells of monomorphic ammonites. These could be spirals with a hook at the end, various balls, knots, unfolded spirals. Paleontologists have not yet come to a unified explanation of the causes of the emergence of such forms and their way of life.

In the seas, orthoceras were still found - relics of the bygone Paleozoic era. Small shells of these straight-shelled cephalopods are found in the Caucasus.

Cretaceous disaster

At the end of the Cretaceous period, the most famous and very large extinction of many groups of plants and animals occurred. Many gymnosperms, aquatic reptiles, pterosaurs, all dinosaurs died out (but birds survived). Ammonites disappeared, many brachiopods, almost all belemnites. In the surviving groups, 30-50% of the species became extinct. The causes of the Cretaceous catastrophe are not fully understood.

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Notes

Literature

• Jordan N. N. development of life on earth. - M .: Enlightenment, 1981.
• Koronovsky N.V., Khain V.E., Yasamanov N.A. Historical Geology: Textbook. - M .: Academy, 2006.
• Ushakov S.A., Yasamanov N.A. Continental drift and climates of the Earth. - M .: Thought, 1984.
• Yasamanov N.A. Ancient climates of the Earth. - L.: Gidrometeoizdat, 1985.
• Yasamanov N.A. Popular paleogeography. - M .: Thought, 1985.

Links

• - Site with information about the state of research in the field of Cretaceous stratigraphy and paleogeography in Russia. Library of scientific publications related to the study of Cretaceous deposits.

An excerpt characterizing the Cretaceous period

The Cretaceous period is a geological period. Cretaceous - the last period of the Mesozoic era, began 145 million years ago and ended 65 million years ago. It lasted about 80 million years.

In the Cretaceous period, angiosperms appeared - flowering plants. This entailed an increase in the diversity of insects that became pollinators of flowers. So the vegetation cover of the Earth in the Cretaceous period would no longer surprise modern man. What can not be said about the animal world of that time.

Among the land animals reigned a variety of dinosaurs. Dinosaurs are divided into two groups - lizards, among which were both predators and herbivorous forms, and ornithischians, exclusively herbivores. The most famous lizard dinosaurs are tyrannosaurs, tarbosaurus, brontosaurs. Among ornithischian lizards, ceratopsians, iguanodons, and stegosaurus are known. This was the heyday of giant lizards - many dinosaurs reached 5-8 meters in height and 20 meters in length. Winged reptiles - pterodactyls occupied almost all niches of aerial predators, although real birds have already appeared. Thus, in parallel there were flying lizards, lizard-tailed birds of the Archeopteryx type and real fan-tailed birds.

Modern lizards and snakes emerged, so snakes are a relatively young group.

There were no mammals in the seas, and the niche of large predators was occupied by reptiles - ichthyosaurs, plesiosaurs, mososaurs, sometimes reaching 20 meters in length.

The variety of marine invertebrates was very great. As in the Jurassic, ammonites and belemnites, brachiopods, bivalves and sea urchins were very common. Among bivalve mollusks, rudists, which appeared at the end of the Jura, played an important role in marine ecosystems - mollusks that look like single corals, in which one valve looked like a goblet, and the second covered it like a kind of lid.

During the Cretaceous period, the split of the continents continued. Laurasia and Gondwana fell apart. South America and Africa were moving away from each other, and the Atlantic Ocean was getting wider and wider. Africa, India and Australia also began to move apart, and giant islands eventually formed south of the equator.

The causes of the Cretaceous catastrophe are not fully understood. Now the asteroid theory has become the most popular theory - explaining the extinction of dinosaurs and other organisms by the fall of a giant asteroid and the “asteroid winter” that followed. On the surface of the Earth, there really is a crater from a meteorite fall, formed about 65 million years ago at the end of the Cretaceous period as a result of a meteorite impact with a diameter of about 10 km - this is the Chicxulub crater. But the asteroid theory cannot explain why certain organisms survived when others died. In addition, many groups of animals clearly began to die out long before the end of the Cretaceous. The transition of the same ammonites to heteromorphic forms also clearly indicates some kind of instability. It may very well be that many species have already been undermined by some long-term processes and stood in the way of extinction, and the catastrophe - an asteroid, increased volcanism or climate change due to the movement of the continents - simply accelerated the process.

144 million years ago, the Cretaceous period began, it lasted 80 million years and was the link between the early Mesozoic and the Cenozoic era, the era of mammals.
By the beginning of the Cretaceous period, the Earth began to acquire many features known to us. Animals and plants began to characterize regional features as the division of continents continued. The division of the continents also had an impact on the climate. During the Cretaceous period, the world's climate became more and more seasonal, with annual fluctuations in precipitation and air temperature becoming more pronounced.
The Cretaceous period got its name because powerful chalk deposits are associated with it. It is divided into two sections: lower and upper.
The Cretaceous period is the final part of the Mesozoic era. He is known for his tragic travels of the continents, the explosion of life, the one that ended in a tragic and disastrous high sea level.

The Cretaceous period comes after the Jurassic and began about 144 million years ago. During this period, the supercontinent - Pangea - split into two large parts, one - Laurasia, and the second - Gondwana. Laurasia went to the north, and Gondwana, respectively, to the south. But these continents also did not last long in this state and began to divide, in turn, into smaller parts. This is how the continents on which humanity now lives were formed.
These changes caused very strong changes in the Earth's climate, this was reflected in the water level in the ocean, at that time it was 200 meters higher than now. The name of this period was formed due to the fact that shells in shallow water covered the bottom of shallow water in several layers, and as a result turned into chalk.

In the Cretaceous period, the first angiosperms appeared - flowering plants.

Cretaceous period, or Cretaceous (145-66 million years ago)

This entailed an increase in the diversity of insects that became pollinators of flowers. Evolution flora gave impetus to the rapid development of the animal world, including dinosaurs. The diversity of dinosaur species in the Cretaceous period reached its peak.

Tyrannosaurus. Photo: Martin Belam

Dinosaurs are divided into two groups - lizards, among which were both predators and herbivorous forms, and ornithischians, exclusively herbivores. The most famous lizard dinosaurs are tyrannosaurs, tarbosaurus, brontosaurs. Among ornithischian lizards, ceratopsians, iguanodons, and stegosaurus are known. It was the heyday of giant lizards - many dinosaurs reached 5-8 meters in height and 20 meters in length. Winged reptiles - pterodactyls occupied almost all niches of aerial predators, although real birds had already appeared. Thus, in parallel there were flying lizards, lizard-tailed birds of the Archeopteryx type and real fan-tailed birds.

In the Cretaceous period, the first placental mammals appeared, and groups of ungulates, insectivores, predators and primates have already been distinguished.
Modern lizards and snakes evolved, so snakes are a relatively young group.
There were no mammals in the seas, and the niche of large predators was occupied by reptiles - ichthyosaurs, plesiosaurs, mososaurs, sometimes reaching 20 meters in length.

The variety of marine invertebrates was very great. As in the Jurassic, ammonites and belemnites, brachiopods, bivalves and sea urchins were very common. Among bivalve mollusks, rudists, which appeared at the end of the Jura, played an important role in marine ecosystems - mollusks that look like single corals, in which one valve looked like a goblet, and the second covered it like a kind of lid.

By the end of the Cretaceous, a lot of heteromorphic forms appeared among ammonites. Heteromorphs arose earlier, in the Triassic, but the end of the Cretaceous became the time of their mass appearance. The shells of heteromorphs were not similar to the classical spiral-twisted shells of monomorphic ammonites. It could be a spiral with a hook at the end, various coils, knots, unfolded spirals. Paleontologists have not yet come to a unified explanation of the causes of the emergence of such forms and their way of life.
Oddly enough, in the seas extremely rare, but still came across orthoceratids - relics of the bygone Paleozoic era. Small shells of these straight-shelled cephalopods are found in the Caucasus.

The Cretaceous system occupies one of the first places among the subdivisions of the Phanerozoic in terms of the diversity and quantity of minerals. One of the most significant ore formations in the history of the Earth is associated with the powerful magmatism of the Cretaceous period. The predominant part of ore minerals tends to the Pacific mobile belt, within which there are deposits of non-ferrous metal ores. IN East Asia the largest tin-bearing province stretches from north to south. Since the end of the Late Cretaceous around Pacific Ocean porphyry copper deposits are formed, most of which are confined to the eastern branch of the belt from Alaska in the north to Chile in the south. Copper and accompanying molybdenum ore occurrences are also known in the western branch in Chukotka, Kamchatka, and Primorsky Krai. In the Mediterranean belt, porphyry copper deposits of the Late Cretaceous - Paleogene age are found in Yugoslavia and Bulgaria. In the Caucasus, sulphurous and copper-sulfide ores of the Somkheto-Karabakh zone are associated with volcanogenic rocks of the Upper Cretaceous, skarns with iron and cobalt of Dashkesan, as well as copper-molybdenum deposits of the Miskhan-Zangezur zone are confined to the pre-Cenomanian magmatic series. In the Cretaceous deposits in Ukraine and Siberia there are zirconilmenite coastal-marine placers, they also contain gold placers of Zeya, Khingan, Kuznetsk Alatau and eastern Transbaikalia.

The Cretaceous system contains rich deposits of combustible minerals. In terms of total oil reserves, they are in 2nd place after the Cenozoic, about 1/2 of the gas reserves of the world's main fields are confined to them. The main oil and gas basins and provinces associated with the Cretaceous system are located along the Rocky Mountains of North America, in Alaska and California, in the Gulf of Mexico region, in many countries of South America, in West Africa, on the northern and northeastern framing of the African-Arabian platform from Libya to the Persian Gulf Central Asia, in Western Siberia and other regions.

One of the largest in the world - the Persian Gulf oil and gas basin, in which 1/3 of the oil reserves are confined to Cretaceous reservoirs. Lower Cretaceous sandstones in the basin of Lake Athabasca (Canada) contain large accumulations of semi-solid bitumen. On the territory of the former CCCP, Cretaceous deposits occupy the 1st place in terms of oil and gas reserves. The largest concentration of deposits is found on the West Siberian plate, where the main deposits of oil are concentrated in the Neocomian and partially Aptian rocks, and natural gas - in the Aptesenomanian. Many deposits belong to the Lower and Upper Cretaceous North Caucasus and Central Asia. The Cretaceous period, and especially its late epoch, was a time favorable for the deposition of phosphates.

At the end of the Cretaceous period, the most famous and very large extinction of many groups of plants and animals occurred. Many gymnosperms, all dinosaurs, pterosaurs, aquatic reptiles died out. Ammonites disappeared, many brachiopods, almost all belemnites. In the surviving groups, 30-50% of the species became extinct.

The causes of the Cretaceous catastrophe are not fully understood. Now the asteroid theory has become the most popular theory - explaining the extinction of dinosaurs and other organisms by the fall of a giant asteroid and the “asteroid winter” that followed. On the surface of the Earth, there really is a crater from a meteorite fall, formed about 65 million years ago at the end of the Cretaceous period as a result of a meteorite impact with a diameter of about 10 km - this is the Chicxulub crater. But the asteroid theory cannot explain why certain organisms survived when others died. In addition, many groups of animals clearly began to die out long before the end of the Cretaceous. The transition of the same ammonites to heteromorphic forms also clearly indicates some kind of instability. It may very well be that many species have already been undermined by some long-term processes and stood in the way of extinction, and the catastrophe - an asteroid, increased volcanism or climate change due to the movement of the continents - simply accelerated the process.

V.V. Arkadiev. Russian Geological Encyclopedia, 2011.

Cretaceous system / period(eng. Cretaceous System)- the upper system of the Mesozoic erathem. The exact position of the lower boundary of the system is debatable. The system was identified in 1822 by the Belgian geologist J.B. d'Omalius d'Allois in the Anglo-Paris basin. The name of the system comes from the strata of writing chalk, widespread in Europe, Western Asia and North America, which make up its upper part. It is divided into lower and upper sections, which unite six tiers each (see table).

The four lower tiers were sometimes combined into an overtier neocom, and the top four - in the overtier senon.

There was a variant of the three-membered division of the Cretaceous, in which the Albian, Cenomanian, Turonian and Cognac were usually assigned to the middle section. The tiered scale was developed in Western Europe. Stratotypes of Valanginian and Hauterive are in Switzerland, Maastrichtian - in the Netherlands, other stages - in France. The zonal division of the Cretaceous deposits is based on the distribution of ammonites, and in a number of areas - bivalves (inocerams and buchians). In addition, for the Upper Cretaceous stratigraphy importance have belemnites, sea urchins and foraminifers, for continental deposits - reptiles.

The Cretaceous period is the last period of the Mesozoic era lasting 80 million years. It began 145.5 million years ago and ended 65.5 million years ago. The Cretaceous system is second only to the Quaternary in distribution. Cretaceous marine facies are fully and diversely represented in the folded structures of the Alpine (Pyrenees, Alps, Atlas, Crimea, Caucasus, Kopetdag, Central Iran, Himalayas) and Pacific ( Far East and northeast Russia, Alaska and the Cordillera) belts. Various continental deposits are widespread on the platforms - red-colored, gypsum-bearing and salt-bearing, freshwater lacustrine-deltaic and coal-bearing sediments. On the East European Platform in the Early Cretaceous, there was a meridionally elongated marine basin connecting the northern seas with the seas of the Mediterranean belt. In it, in the conditions of a shallow cold sea, with currents and calm bays, small sandy-argillaceous sediments accumulated. Marine sedimentation conditions persisted throughout the Cretaceous in the West Siberian depression. Here, Cretaceous deposits are represented by a thick (several km) stratum of sandy-argillaceous rocks with remains of marine fauna. On the territory of North America, the Cretaceous system corresponded Comanche(lower section) and gulfian(upper section) of the system.

In the Cretaceous period, the process of opening oceanic depressions continues. In the Early Cretaceous, the South Atlantic was formed, the Caribbean and the Tethys Ocean continued to expand, and the ocean depth increased (black clays and turbidites accumulated in the Central and South Atlantic). Indian Ocean passed initial stage spreading (clay deposits were formed here) (Fig. 1).

In the early Cretaceous, the Cimmerian (Mesozoic) tectogenesis ends. Hyperborea collides with the northeastern margin of Eurasia, where the Verkhoyansk-Chukotka folded region is formed. At the end of the Early - the beginning of the Late Cretaceous, in the space from Chukotka to Kalimantan, as a result of the collision of microcontinents with the margin of Eurasia, a powerful East Asian (Chukotka-Katazian) volcanic-plutonic belt is formed.

In the Late Cretaceous, the separation of Australia from Antarctica began, and in the north of the Atlantic, Greenland, together with Eurasia, from North America (the formation of the North Atlantic) (Fig. 2).

As a result of the expansion of the Indian Ocean, Africa and Hindustan are shifting to the north. The pressure of Africa on the western part of the Mediterranean belt is associated with the deformations of the Alpine tectogenesis in the Late Cretaceous, which manifested itself in the Eastern Alps, Carpathians, Balkanides, Crimea, the Caucasus, Iran and Southern Afghanistan. On the Pacific active margin of both Americas, intense folding and the formation of thrusts (Laramian orogeny) also occur. In all collision zones of the Cretaceous, folding was accompanied by powerful granitoid magmatism. Colossal outpourings of basalts at the bottom of the oceans and on the surface of the continents are dated for the Cretaceous period. hemispheres (Hindostan, South America).

Starting from the Albian, one of the largest transgressions in the history of the Earth takes place.

Cretaceous system (PERIOD)

A significant part of the territory of Eurasia, from England to Western Asia, at that time was covered by a relatively shallow sea, in which carbonates accumulated (writing chalk formation). The Late Cretaceous transgression was widely manifested in Africa and on the North American Platform.

The Cretaceous period is characterized by the flourishing of the two most important groups of invertebrates - ammonites and belemnites. Large coral-like bivalve mollusks, rudists and nerineids (gastropods), were widespread in tropical seas. Irregular sea urchins, sea lilies, and inoceramides and sponges in the Late Cretaceous reached considerable diversity. The main reef-building organisms were scleractinians and bryozoans. Among marine algae, golden ones are very characteristic - coccolithophores and diatoms. Together with small foraminifers, they participated in the formation of white writing chalk in the Late Cretaceous. Of the vertebrates, reptiles dominated, conquering land, water and air space. There were a variety of herbivores and huge carnivorous dinosaurs(tyrannosaurs, tarbosaurs) (Fig. 3, 4). The Cretaceous period is characterized by the appearance of snakes. Bony fish evolved significantly, toothy birds spread, and placental mammals appear. The plant world of the Early Cretaceous is characterized by the predominance of gymnosperms and ferns, but starting from the Albian, angiosperms sharply predominate (the beginning of the cainophyte stage in the development of vegetation). By the end of the Cretaceous, at the turn of the Maastrichtian and Denmark, coccolithophorids, planktonic foraminifers, ammonites, belemnites, inoceramides, rudists, dinosaurs, and a number of other groups disappeared. 50% of the families of radiolarians disappeared, 75% of the families of brachiopods, the number of sea ​​urchins and sea lilies, sharks decreased by 75%. In general, more than 100 families of marine invertebrates became extinct, and about the same among land animals and plants. This decline in fauna and flora is often referred to as the "great Mesozoic extinction event". One of the most widely held ideas about the causes of this extinction is the collision of the Earth with an asteroid, the diameter of which could be 10-15 km. Traces of such a collision were recorded in the form of an “iridium anomaly” in the boundary layers of the Cretaceous and Paleogene in a number of sections in the Zap. Europe. The Chicxulub crater on the Yucatan Peninsula in Mexico is currently considered the most likely candidate for large craters formed on Earth from the fall of an asteroid at the turn of the Cretaceous and Paleogene. The "asteroid winter" that came after the explosion could cause a number of processes negative for the life of organisms - a reduction in food resources, a violation of food ties, a decrease in temperature, etc.

In the Cretaceous period, climatic zonality was clearly expressed. In particular, the Boreal, Mediterranean (Tethyan), Southern, and Pacific paleobiogeographical regions were distinctly distinguished, differing in the nature of precipitation and the development of groups of the organic world.

The Cretaceous system is rich in various minerals. More than 20% of the world's coal reserves are associated with continental deposits (the Lena and Zyryansk coal basins in Russia, coal basins in the west of North America). Large bauxite deposits are known in the Turgai Trough, the Yenisei Ridge, the Southern Urals, the Ukrainian Shield, and the Mediterranean. A belt rich in phosphorites stretches from Morocco to Syria; deposits of phosphorites are known on the East European Platform. There are salt deposits confined to lagoon deposits in Turkmenistan and North America. Large reserves of writing chalk and raw materials for the cement industry are associated with the Upper Cretaceous on the territory of the North American and East European platforms. Cretaceous age have many oil and gas fields in Western Siberia, in the west Central Asia, in Libya, Kuwait, Nigeria, Gabon, Canada and the Gulf of Mexico.

Tin, lead, and gold deposits associated with Cretaceous acid intrusions are known in northeastern Russia and western North America. The largest tin belt can be traced on the territory. Malaysia, Thailand and Indonesia. Large deposits of tin, tungsten, antimony and mercury are known in southeast China and in South Korea. Diamond deposits in Cretaceous kimberlite pipes are being developed in South Africa and India.

Bibliography::

Biske Yu.S., Prozorovsky V.A. General stratigraphic scale of the Phanerozoic. Vendian, Paleozoic and Mesozoic. Ucheb. allowance. St. Petersburg: Publishing house of St. Petersburg State University, 2001.

Fedorov P.V. History of the earth's crust. Atlas of illustrations for the course of historical geology: Tutorial. - St. Petersburg State University, 2006, 16.

Khain V.E., Koronovsky N.V., Yasamanov N.A. Historical geology. M.: Publishing House of Moscow State University, 1997.

Not everywhere the coastline is sandy beaches, gradually descending to the sea. In some places, rocky cliffs rise along the coast, and sometimes they are not brown, but white.

The White Cliffs rise along the coast near Dover on the southwest coast of England, as well as around Calais in northeast France.

There are no beaches in these parts of the coast.

Cretaceous period

It is very difficult to land on the rocky shore. All this makes navigation here very dangerous.

Why are these rocks white?

The rocks are made of chalk - the fossilized remains of single-celled animals that once lived in the sea. They were very small, and today the remains of animals can only be seen under a microscope.

Many centuries ago, they died, their remains sank to the bottom, and chalk formed from them.

His White color due to the fact that the calcium contained in fossil animals eventually turned into limestone. And limestone, as you know, is a white mineral.

The stone that borders these coasts can be white, gray or bluish. The more chalk is contained in the stone, the lighter it is.

Chalk is a very fragile mineral, so the rocks consisting of it are gradually washed away by the sea and destroyed by the wind. Floods have a no less devastating effect on the chalk cliffs.

You can see this for yourself if you just put a piece of chalk in water. You will see how it is saturated with water and becomes very soft.

When water constantly rolls over the same place, huge caves form in the rock.

If the cave becomes too large, the upper layers of chalk collapse and water flows into the cave. Such a cave is called a grotto. The noise of waves and wind fills the grottoes with bizarre sounds. Therefore, folk fantasy populated them with underwater inhabitants - mermaids and morgans.

Era. The Cretaceous period lasted for 79 million years, starting from 145 million years ago and ending 66 million years ago. In order not to get confused in the eras and periods of the history of the Earth, use the geochronological scale, which is located.

Chalk got its name from the rich deposits of chalk that are found in the geological strata of this period. It is worth knowing that the same chalk used to write in school is fossil invertebrate marine organisms that lived tens of millions of years ago.

Chalk is divided into two sections - and. The beginning and end of the period differ radically. If the lower and part of the Upper Cretaceous is the active development of life, the emergence of new species, the kingdom and diversity of dinosaurs, then the end of the Upper Cretaceous is a real tragedy for the animal kingdom of that period. In the Upper Cretaceous, a catastrophe of a planetary scale occurred, as a result of which all dinosaurs, as well as many species of plants and animals, died.

In the Cretaceous period, the split of the continents continued. There is no mention of the former supercontinent Pangea. The continents moved further and further away from each other. Many scientists believe that due to the separation of the continents, the increase in the Atlantic Ocean, changes in air currents in the atmosphere and currents in the ocean, the Earth began to cool in the first period of the Cretaceous period. However, at the end of the Cretaceous, temperatures began to rise. Judging by some hypotheses, the reason for the increase in temperature was the increase in the area of ​​​​the world's oceans.

Cretaceous Animals

The Cretaceous period is an active development of life of almost all species. The first flowering plants appeared in the Cretaceous period. This led to the fact that there was an increase in the diversity of insects that began to pollinate flowers. Such large predators as ichthyosaurs, plesiosaurs, and mososaurs lived in the seas.

Marine animals sometimes reached colossal sizes, for example, ichthyosaurs grew up to 24 meters in length, plesiosaurs - up to 20 meters, mososaurs - up to 14 meters. It is worth noting that they were still not as huge as, for example, the modern Blue whale, reaching a length of 33 meters, however, the Blue whale is a peaceful creature that feeds on plankton, but predators that reached 20 meters posed a real threat to their victims in the seas.

Giant animals, dinosaurs, existed on land. A large species diversity is observed already in the period, and in the Cretaceous their diversity became even greater. Some dinosaurs were over 10 meters tall and over 20 meters long. Such sizes are record for terrestrial animals.

In addition to large lizards, this period is also noticeable by a large variety of flying animals. If in our time only birds mastered the air environment, then in the Cretaceous period there were flying pangolins (pterosaurs), lizard-tailed birds and ordinary birds (fan-tailed). The largest flying creature in those days was a representative of the pterosaur order Quetzalcoatl, whose wingspan reached from 12 to 15 meters.

In the same period, the first snakes appeared. Reptiles without legs and limbs, snakes, are considered the youngest group of reptiles. Also, this species of animals, along with some others, was able to survive the upcoming catastrophe and survive to this day.

In the Cretaceous period, a variety of mammals is also observed. If in the Jurassic period there were only small species of warm-blooded mammals, then in the Cretaceous period ungulates, insectivores, predators, as well as the very first primates, which, as everyone knows, became the ancestors of modern people, appeared.

Cretaceous-Paleogene extinction event

The Cretaceous period and the entire Mesozoic era ended with the mass extinction of animals. The causes of the Cretaceous-Paleogene catastrophe have not yet been reliably elucidated. The most likely cause was the fall of a large asteroid or even several asteroids. In addition, there are also such versions as: increased volcanic activity, change weather conditions, an excess of oxygen in the atmosphere, a mass epidemic, excessive development of flowering plants and many others. One way or another, as a result of the mass extinction, all the dinosaurs that developed over many tens of millions of years disappeared. In layers later than the time of the Cretaceous-Paleogene extinction, archaeologists no longer find the remains of any dinosaurs, which suggests that none of the dinosaurs could survive. In addition, many aquatic reptiles, flying pterosaurs, ammonites, and brachiopods became extinct. In total, 16% of families of marine animals and 18% of families of terrestrial vertebrates died. Many small reptiles, birds, warm-blooded survived. After the global extinction of animals, mammals began to reign on Earth.

Cretaceous Dinosaurs

Velociraptor

Gainosaurus

ichthyosaurs

carnotaurus

Quetzalcoatl

Majungasaurus

Mosasaurus

Parasaurolophus

Plesiosaurs

Pteranodon

Styracosaurus

Tarbosaurus

tyrannosaurus rex

torosaurus

Triceratops

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Cretaceous period tectonics:

During Cretaceous the movement of the continents continued. Laurasia and Gondwana fell apart. Africa, India and Australia also began to move apart, and giant islands eventually formed south of the equator. South America and Africa were moving away from each other, and the Atlantic Ocean was getting wider and wider. Some obvious catastrophes in Cretaceous was not, so the process of evolution went naturally. The earth acquired outlines very close to those known to us.

Climate Cretaceous:

The climate has changed since the Jurassic. Due to the changing position of the continents, the change of seasons became more and more noticeable. Snow began to fall near the poles, although there were no such ice caps as now on Earth. On different continents the climate was different. This caused differences in the development of flora and fauna in different parts of the world.

Flora Cretaceous:

Flora Cretaceous was rich and varied. In addition to the plant species transferred from the Jurassic period, a new, revolutionary branch of flowering plants appears. Flowering plants, having concluded an "alliance" with insects, had advantages over their predecessors. Through this partnership, flowering plants spread much faster. Gradually populating the land, new groups of plants began to form vast forests. There, at the service of land animals, there were a wide variety of leaves and other edible vegetation. Due to the appearance of flowering plants in Cretaceous the amount of plant biomass has increased.
The reverse process took place at sea. This was again facilitated by the development of flowering plants. Dense roots prevented soil erosion and therefore fewer minerals entered the sea. The amount of phytoplankton has decreased.

Fauna Cretaceous:

Insects:

Growth of flowering plants Cretaceous contributed to an increase in insect species that feed on nectar and carry pollen. Exactly at Cretaceous period. Insects appeared, the life of which is completely dependent on flowering plants. These are bees and butterflies. Insects collected pollen and delivered it to its destination. The brightly colored petals and the attractive fragrance of the flowers became bait for insects. In turn, the sweet sugary nectar and the pollen itself provided the insects with all the nutrients they needed. Cretaceous period marked the beginning of an era of close interaction between plants and insects.

Dinosaurs:

Among the land animals reigned a variety of dinosaurs. During the Cretaceous period the diversity of dinosaur species was especially great. The development of the plant world and the increase in plant biomass gave impetus to the emergence of new species of herbivorous dinosaurs.
Of the lizard dinosaurs, the most famous of which was tyrannosaur, were widespread tarbosaurus, spinosaurus, deinonychus and others.
The variety of ornithischian dinosaurs was especially great in the Cretaceous period. Widely known in Jurassic period, stegosaurs disappear from the face of the planet. Their place will be taken by such famous herbivorous dinosaurs as iguanodons, triceratops, ankylosaurs, pachycephalosaurs and many other types.

First mammals:

The first animal-like animals appeared in the Triassic period, about 220 million years ago. These animals belong to the so-called synapsid group.
In the first half Cretaceous, among these inconspicuous, against the backdrop of dinosaurs, mammals, serious evolutionary processes began to occur. As a result, these processes resulted in the appearance of single-pass marsupial and placental mammals. It is to these groups of animals at the end Cretaceous and the beginning of the Cenozoic era was destined to become the successors of the dinosaurs.

The vast majority of Cretaceous synapsids are mammals. Primitive dicynodonts and cynodonts are not yet extinct, but are already close to that. Almost all mammals Cretaceous belonged to the primitive subclass of allotheria and differed little from the Jurassic predecessors. These were small creatures weighing 20-500 g similar to mice. There were also among them repenomamas reaching a length of 1 m and weighing up to 14 kg, but most were as small as other mammals of the Cretaceous period.

At first Cretaceous true animals, the ancestors of modern mammals, separated from allotheriums. They rather quickly divided into three main branches: oviparous, marsupial and placental mammals, and the placental ones were already divided into laurasiatherians, gondwanatherians, and the latter were divided into rodents and primates. The marsupial branch gave birth to almost modern opossums, and the oviparous branch gave birth to almost modern platypuses. Purgatorius was the first known primate-like mammal.

Flying:

Winged reptiles - pterodactyls occupied almost all niches of aerial predators. Cretaceous period gave rise to the largest flying creatures that have ever lived on Earth. These are giant Orcheopteryx and Quetzatcoatl. To date, the question of which of them was larger has not been finally resolved.

But in the Cretaceous period, the pterosaurs had competitors - birds. And although the first birds appeared in the Jurassic period, in Cretaceous their species diversity has increased. A transitional species between pterosaurs and birds, the Archiopteryx became extinct. Thus, flying lizards and birds existed in parallel.
Some Cretaceous birds are the ancestors of modern birds. Already in Cretaceous ducks, semi-fingered geese, loons and plovers appeared, almost no different from modern versions of these birds. Many of the birds Cretaceous were a dead end branch of evolution and subsequently died out. Bird classification Cretaceous very vague and inconsistent.
The size of Cretaceous birds ranged from 4 cm to 1.5 m in length, and weight - from a few grams to several kilograms.

Marine fauna:

There were no mammals in the seas, and the niche of large predators was occupied by reptiles - ichthyosaurs, plesiosaurs, mososaurs, sometimes reaching 20 meters in length.
Among the inhabitants of the Cretaceous seas, the majority were plesiosaurs with long necks and small heads, feeding on small fish and shellfish. They could not swim fast, but they were very maneuverable, and their small head on a very long neck made it difficult for them to timely detect a school of prey - the fish saw only a small head, and a huge body was lost in the distance. A prominent representative of this species was Elasmosaurus, up to 20 m long and weighing 14 tons.

Another species that lived in the seas Cretaceous were mosasaurs. Mosasaurs are very large predatory, marine lizards that reigned in the Cretaceous seas. They replaced the saltwater crocodiles of the Jurassic period. These were very aggressive animals - in many mosasaurs, traces of healed fractures and bites are found on the bones, obviously received in fights with their own kind.

Turtles Cretaceous practically indistinguishable from modern ones. The size of Cretaceous turtles varied from 20 cm to 4.6 m, weight reached 2 tons. Most species were aquatic.

Other reptiles:

IN Cretaceous the first lizards and snakes arose, so that snakes. They have survived to this day almost unchanged. This is a relatively young group of animals.

All Cretaceous Dinosaurs

Herbivorous dinosaurs:

Sauropods: abydosaurus ... agustinia ... alamosaurus ... amargosaurus ...

ampelosaurus ... aragosaurus ... argentinosaurus ... egyptosaurus ... laplatasaurus ...

maxcalisaurus ... nigersaurus ... paralithitan ... saltasaurus ... seismosaurus ...

Thierophores, ankylosaurids: acanthopholis ... aletopelta ... ankylosaurus ...

minmi ... nodosaurus ... scolosaurus ... styracosaurus ... talarurus ... evoplacecephalus

Ceropods: avaceratops ... agathamus ... adasaurus ... adamanthisaurus ...

ankyceratops ... barylium... hypselospin ... hypselophodon ... zalmoxis ...

iguanodon ... Zuniceratops ... coahuilaceratops ... leptoceratops ...

medusaceratops ... monoclone ... muttaburrasaurus ... ochoceratops ...

pachyrhinosaurus ... protoceratops ... psitaccosaurus ...stegoceras ... torosaurus ...

treceratops ... chasmosaurus ...

Hadrosaurs: anatotitan (anatosaurus)... brachylophosaurus ... hadrosaur ...

saurolophus ... corythosaurus ... lambeosaurus ... mayasaur ... parasaurolophus ...

probactosaurus ... tenodontosaurus ... ouranosaurus ... edmontosaurus ...

Pachycephalosaurs: dracorex ... pachycephalosaurus ... stegoceras ... techacephalus

Carnivorous Dinosaurs:

Theropods: abelisaurus ... avimim ... Australovenator ...