Jurassic deposits. Jurassic system (period)

And Switzerland. The beginning of the Jurassic period is determined by the radiometric method at 185 ± 5 Ma, the end at 132 ± 5 Ma; the total duration of the period is about 53 million years (according to 1975 data).

Jurassic system in its modern volume, it was isolated in 1822 by the German scientist A. Humboldt under the name "Jurassic formation" in the mountains of the Jura (Switzerland), the Swabian and Franconian Alb (). In the territory Jurassic deposits were first established by the German geologist L. Buch (1840). The first scheme of their stratigraphy and division was developed by the Russian geologist K.F. Rul'e (1845-49) in the Moscow region.

Subdivisions. All the main subdivisions of the Jurassic system, which were subsequently included in the common stratigraphic scale, are identified in the territory of Central Europe and Great Britain. The division of the Jurassic system into divisions was proposed by L. Buch (1836). The foundations of the stage division of the Jura were laid by the French geologist A. d "Orbigny (1850-52). The German geologist A. Oppel was the first to produce (1856-58) a detailed (zonal) subdivision of the Jurassic deposits. See table.

Most foreign geologists attribute the Callovian stage to the middle section, motivating this by the priority of the three-term division of the Jurassic (black, brown, white) by L. Bukh (1839). The Tithonian stage is distinguished in the sediments of the Mediterranean biogeographic province (Oppel, 1865); for the northern (boreal) province, its equivalent is the Volgian Stage, first identified in the Volga region (Nikitin, 1881).

general characteristics. Jurassic deposits are widespread on the territory of all continents and are present in the periphery, parts of ocean basins, forming the base of their sedimentary layer. By the beginning of the Jurassic period, two large continental masses are separated in the structure of the earth's crust: Laurasia, which included platforms and Paleozoic folded regions of North America and Eurasia, and Gondwana, which united the platforms of the Southern Hemisphere. They were separated by the Mediterranean geosynclinal belt, which was the Tethys oceanic basin. The opposite hemisphere of the Earth was occupied by the Pacific Ocean basin, along the edges of which the geosynclinal regions of the Pacific geosynclinal belt developed.

In the Tethys oceanic basin, during the entire Jurassic period, deep-sea siliceous, clayey, and carbonate deposits accumulated, accompanied in places by manifestations of underwater tholeiite-basalt volcanism. The wide southern passive margin of the Tethys was an area of ​​accumulation of shallow water carbonate deposits. On the northern outskirts, which in different places and in different time had both an active and a passive character, the composition of the sediments is more varied: sandy-argillaceous, carbonate, in some places flysch, sometimes with manifestations of calc-alkaline volcanism. The geosynclinal regions of the Pacific belt developed in the regime of active margins. They are dominated by sandy-argillaceous deposits, a lot of siliceous ones, and volcanic activity was very actively manifested. The main part of Laurasia in the Early and Middle Jurassic was land. In the Early Jurassic, marine transgressions from geosynclinal belts captured only territories Western Europe, the northern part of Western Siberia, the eastern margin of the Siberian Platform, and in the Middle Jurassic and southern part East European. At the beginning of the Late Jurassic, the transgression reached its maximum, spreading to the western part of the North American platform, the East European, the entire Western Siberia, Ciscaucasia and Transcaspian. Gondwana remained dry land throughout the Jurassic. Marine transgressions from the southern margin of the Tethys captured only the northeastern part of the African and the northwestern part of the Hindustan platforms. The seas within Laurasia and Gondwana were vast, but shallow epicontinental basins, where thin sandy-argillaceous deposits accumulated, and in the Late Jurassic, in areas adjacent to the Tethys, carbonate and lagoonal (gypsum- and salt-bearing) deposits accumulated. In the rest of the territory, Jurassic deposits are either absent or represented by continental sandy-clayey, often coal-bearing strata that fill individual depressions. The Pacific Ocean in the Jurassic was a typical oceanic basin, where thin carbonate-siliceous sediments and covers of tholeiitic basalts, preserved in the western part of the basin, accumulated. At the end of the Middle - the beginning of the Late Jurassic, the formation of "young" oceans begins; there is an opening of the Central Atlantic, the Somali and North Australian basins of the Indian Ocean, the Amerasian basin of the Arctic Ocean, thereby beginning the process of dismemberment of Laurasia and Gondwana and the separation of modern continents and platforms.

The end of the Jurassic is the time of manifestation of the late Cimmerian phase of Mesozoic folding in geosynclinal belts. In the Mediterranean belt, folding movements manifested themselves in some places at the beginning of the Bajocian, in the pre-Callovian time (Crimea, Caucasus), at the end of the Jurassic (Alps, etc.). But they reached a special scope in the Pacific belt: in the Cordillera of North America (Nevadian folding), and the Verkhoyansk-Chukotka region (Verkhoyansk folding), where they were accompanied by the introduction of large granitoid intrusions, and completed the geosynclinal development of the regions.

The organic world of the Earth in the Jurassic period had a typical Mesozoic appearance. Among marine invertebrates reach their peak cephalopods(ammonites, belemnites), bivalves and gastropods, six-pointed corals, "wrong" sea ​​urchins. Among vertebrate animals in the Jurassic period, reptiles (lizards) sharply predominate, which reach giant size(up to 25-30 m) and a great variety. Terrestrial herbivores and carnivores (dinosaurs), sea swimmers (ichthyosaurs, plesiosaurs), flying pangolins (pterosaurs) are known. Fish are widespread in water basins, and the first (toothy) birds appear in the air in the Late Jurassic. Mammals, represented by small, still primitive forms, are not very common. The vegetation cover of the land of the Jurassic period is characterized by the maximum development of gymnosperms (cycads, bennetites, ginkgoes, conifers), as well as ferns.

Jurassic geological period, Jura, Jurassic system, middle period mesozoic. It began 206 million years ago and lasted 64 million years.

For the first time deposits of the Jurassic period were described in the Jura (mountains in Switzerland and France), hence the name of the period. The deposits of that time are quite diverse: limestones, clastic rocks, shales, igneous rocks, clays, sands, conglomerates formed in a variety of conditions.

190-145 million years ago in Jurassic period the single supercontinent Pangea began to disintegrate into separate continental blocks. Shallow seas formed between them.

Climate

The climate in the Jurassic period was humid and warm (and by the end of the period - arid in the equator).

In the Jurassic period, vast areas were covered with lush vegetation, primarily diverse forests. They mainly consisted of ferns and gymnosperms.

cycads- a class of gymnosperms that prevailed in the green cover of the Earth. Now they are found here and there in the tropics and subtropics. Dinosaurs roamed under the canopy of these trees. Outwardly, cycads are so similar to low (up to 10-18 m) palm trees that even Carl Linnaeus placed them among palm trees in his plant system.

During the Jurassic period, groves of ginkgo trees grew throughout the then temperate zone. Ginkgoes are deciduous (unusually for gymnosperms) trees with an oak-like crown and small, fan-shaped leaves. Only one species has survived to this day - ginkgo biloba. Very diverse were conifers, similar to modern pines and cypresses, which flourished at that time not only in the tropics, but had already mastered the temperate zone.

marine organisms

Compared with the Triassic, the population of the seabed has changed a lot. Bivalves displace brachiopods from shallow waters. Brachiopod shells are replaced by oysters. Bivalve molluscs fill all the vital niches of the seabed. Many stop collecting food from the ground and move on to pumping water with the help of gills. A new type of reef communities is emerging, approximately the same as it exists now. It is based on six-ray corals that appeared in the Triassic.

land animals

One of the fossil creatures of the Jurassic period, combining the features of birds and reptiles, is Archeopteryx, or the first bird. For the first time, his skeleton was discovered in the so-called lithographic slates in Germany. The discovery was made two years after the publication of Charles Darwin's On the Origin of Species and became a strong argument in favor of the theory of evolution. Archeopteryx still flew rather poorly (planned from tree to tree), and was about the size of a crow. Instead of a beak, he had a pair of toothy, although weak jaws. It had free fingers on its wings (of modern birds, they were preserved only in hoatzin chicks).

In the Jurassic period, small, woolly warm-blooded animals - mammals - live on Earth. They live next to dinosaurs and are almost invisible against their background.

Dinosaurs of the Jurassic period ("terrible lizards" from Greek) lived in ancient forests, lakes, swamps. The range of differences between them is so great that family ties between them are installed with great difficulty. They could be the size of a cat or a chicken, or they could reach the size of huge whales. Some of them moved on four limbs, while others ran on their hind legs. Among them were clever hunters and bloodthirsty predators, but there were also harmless herbivorous animals. The most important feature common to all their species is that they were land animals.

And was replaced by chalk, and had a duration of about 56 million years.

Geography and climate

During the Jurassic period, the supercontinent Pangea began to split into two separate continents:

• northern part known as Laurasia (which eventually split into North America and Eurasia, opening up basins to Atlantic Ocean, and the Gulf of Mexico)
• the southern part - Gondwana - drifted east (and eventually split into Antarctica, Madagascar, India and Australia, and its West Side, formed Africa, and South America).

This process of dividing Pangea, along with warmer global temperatures, allowed reptiles such as dinosaurs to diversify and dominate Earth for a long time.

plant life

During the Mesozoic era, plants developed the ability to lead a terrestrial lifestyle and not be limited only to the oceans. By the beginning of the Jurassic, life was from bryophytes, stunted bryophytes, and liverworts, which had no vascular tissue and were limited to wet swampy areas.

ginkgo trees

Ferns and gingkos, which have roots and vascular tissue for transporting water, and nutrients, as well as spore-reproducing, were the dominant plants of the early Jurassic. During the Jurassic period appeared new way plant reproduction. Gymnosperms such as coniferous trees, developed pollen, which, with the help of wind, is distributed over long distances and pollinates female cones. This method of reproduction made it possible to significantly increase the number of gymnosperms by the end of the Jurassic. Flowering plants did not evolve until the Cretaceous.

Age of dinosaurs

As shown in the movie Jurassic Park, reptiles were the dominant animal life form during the Jurassic period. They overcame evolutionary obstacles that limited . Reptiles had strong ossified skeletons with advanced muscular systems to support and move the body. Some of the largest animals that ever lived were Jurassic dinosaurs. Reptiles could also develop amniotic eggs that were incubated on land.

sauropods

Sauropods (lizard-footed dinosaurs) are herbivorous quadrupeds, with long necks and heavy tails. Many sauropods, such as brachiosaurs, were huge. Representatives of some genera had a body length of about 25 m, and the weight ranged from 50-100 tons, which makes them the largest land animals that have ever existed on Earth. Their skulls were relatively small, with nostrils set high towards their eyes. Such small skulls meant very small brains. Despite their small brains, this group of animals flourished during the Jurassic and had a wide geographic distribution. Sauropod fossils have been found on every continent, with the exception of Antarctica. Other famous dinosaurs the Jurassic includes stegosaurs and flying pterosaurs.

Carnosaurs were one of the main predators mesozoic era. The genus Allosaurus was one of the most widespread carnosaurs in North America. They are similar to later tyrannosaurs, although studies have shown that they have little in common. Allosaurus had strong hind limbs, heavy forelegs, and long jaws.

early mammals

Adelobasileus

Dinosaurs may have been the dominant land animals, but not the only fauna. Early mammals were mostly very small herbivores or insectivores, and did not compete with larger reptiles. Adelobasileus is the predatory ancestor of mammals. He had a special structure of the inner ear and jaws. This animal appeared at the end of the Triassic period.

In August 2011, scientists from China announced the discovery of Yuramaya. This tiny mid-Jurassic animal caused a stir among scientists because it was a clear ancestor placental mammals, indicating that mammals evolved much earlier than previously thought.

Sea life

Plesiosaur

The Jurassic period was also very diverse. the largest marine predators were plesiosaurs. These carnivorous marine reptiles usually had broad bodies and long necks with four flipper-shaped limbs.

Ichthyosaurus - a marine reptile, was most common in the early Jurassic period. Since some fossils have been found with smaller members of their species inside their bodies, it is suggested that these animals may have been among the first to have internal pregnancy and give birth to live young.

Cephalopods were also widespread during the Jurassic and included the ancestors of modern squid. Among the most beautiful fossils marine life spiral shells of ammonites can be distinguished.

For the first time, deposits of this period were found in the Jura (mountains in Switzerland and France), hence the name of the period. The Jurassic period is subdivided into three divisions: leyas, doger and malm.

The deposits of the Jurassic period are quite diverse: limestones, clastic rocks, shales, igneous rocks, clays, sands, conglomerates formed in a variety of conditions.

Sedimentary rocks containing many representatives of fauna and flora are widely distributed.

Intensive tectonic movements at the end of the Triassic and at the beginning of the Jurassic contributed to the deepening of the large bays that gradually separated Africa and Australia from Gondwana. The gulf between Africa and America deepened. Depressions formed in Eurasia: German, Anglo-Paris, West Siberian. The Arctic Sea flooded the northern coast of Laurasia.

Intense volcanism and mountain-building processes led to the formation of the Verkhoyansk fold system. The formation of the Andes and the Cordillera continued. Warm sea currents have reached the Arctic latitudes. The climate became warm and humid. This is evidenced by the significant distribution of coral limestones and the remains of thermophilic fauna and flora. There are very few deposits of a dry climate: lagoonal gypsum, anhydrites, salts and red sandstones. The cold season already existed, but it was characterized only by a decrease in temperature. There was no snow or ice.

The climate of the Jurassic period depended on more than just sunlight. Numerous volcanoes and outpourings of magma on the bottom of the oceans heated up the water and the atmosphere, saturating the air with the steam of water, which then fell as rain on land, flowing in stormy streams into lakes and oceans. Numerous freshwater deposits testify to this: white sandstones alternating with dark loams.

The warm and humid climate favored the flourishing of the plant world. Ferns, cicadas, and conifers formed extensive marshy forests. Araucaria, arborvitae, cicadas grew on the coast. Ferns and horsetails formed the undergrowth. In the Lower Jurassic, the vegetation throughout the northern hemisphere was fairly uniform. But already starting from the Middle Jurassic, two plant belts can be identified: the northern one, in which ginkgo and herbaceous ferns predominated, and the southern one, with bennetites, cicadas, araucaria, and tree ferns.

The characteristic ferns of the mountain period were matonii, which have survived to this day in the Malay

archipelago. Horsetails and club mosses almost did not differ from modern ones. The place of extinct seed ferns and cordaites is occupied by cycads, which still grow in tropical forests.

Ginkgoaceae were also widely distributed. Their leaves turned to the sun with an edge and resembled huge fans. From North America and New Zealand to Asia and Europe, dense forests of coniferous plants grew - araucaria and bennetites. The first cypress and, possibly, spruce trees appear.

The representatives of the Jurassic conifers also include sequoia - a modern giant California pine. Currently, sequoias remain only on the Pacific coast of North America. Separate forms have been preserved. even more ancient plants, such as glassopteris. But there are few such plants, since they were supplanted by more perfect ones.

The lush vegetation of the Jurassic period contributed to the widespread distribution of reptiles. Dinosaurs have greatly evolved. Among them are lizard and ornithischian. Lizards moved on four legs, had five toes on their feet, and ate plants. Most of them had long neck, small head and a long tail. They had two brains: one small, in the head; the second is much larger in size - at the base of the tail.

The largest of the Jurassic dinosaurs was the brachiosaurus, reaching a length of 26 m, weighing about 50 tons. It had columnar legs, a small head, and a thick long neck. Brachiosaurs lived on the shores of the Jurassic lakes, fed on aquatic vegetation. Every day, the brachiosaurus needed at least half a ton of green mass.

Diplodocus is the oldest reptile, its length was 28 m. It had a long thin neck and a long thick tail. Like a brachiosaurus, diplodocus moved on four legs, the hind legs were longer than the front ones. Diplodocus spent most of its life in swamps and lakes, where it grazed and escaped from predators.

Brontosaurus was comparatively tall, had a large hump on its back and a thick tail. Its length was 18 m. The vertebrae of the brontosaurus were hollow. Chisel-shaped small teeth were densely located on the jaws of a small head. The brontosaurus lived in swamps, on the shores of lakes.

Era. Continued for 56 million years. It began 201 million years ago and ended 145 million years ago. The geochronological scale of the history of the Earth of all eons, eras and periods is located.

The name "Jura" was named after the mountain range of the same name in Switzerland and France, where deposits of this period were first discovered. Later, geological formations of the Jurassic period were discovered in many other places on the planet.

In the Jurassic period, the Earth almost completely recovered from the largest in history. Various forms life - marine organisms, land plants, insects and many species of animals - begin to flourish and increase their species diversity. Dinosaurs reign in the Jurassic period - large, and sometimes just giant lizards. Dinosaurs existed almost everywhere and everywhere - in the seas, rivers and lakes, in swamps, forests, on open spaces. Dinosaurs received such a wide variety and distribution that over millions of years of evolution, some of them began to differ radically from each other. Dinosaurs included both herbivores and carnivores. Some of them were the size of a dog, while others reached a height of more than ten meters.

One of the species of lizards in the Jurassic period became the ancestor of birds. Archeopteryx, which existed just at this time, is considered an intermediate link between reptiles and birds. In addition to lizards and giant dinosaurs, warm-blooded mammals already lived on earth at that time. The mammals of the Jurassic period were mostly small size and occupied rather insignificant niches in the living space of the earth of those times. Against the background of the prevailing number and diversity of dinosaurs, they were almost invisible. This will continue throughout the Jurassic and all subsequent periods. Mammals will become full owners of the Earth only after the Cretaceous-Paleogene extinction, when all dinosaurs disappear from the face of the planet, opening the way for warm-blooded animals.

Jurassic period animals

Allosaurus

Apatosaurus

Archeopteryx

Barosaurus

Brachiosaurus

Diplodocus

Dryosaurs

Giraffatitan

Camarasaurus

Camptosaurus

Kentrosaurus

Liopleurodon

Megalosaurus

Pterodactyls

ramphorhynchus

Stegosaurus

Scelidosaurus

Ceratosaurus

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