Tethys is an ancient ocean that existed in the Mesozoic era between the ancient continents of Gondwana and Laurasia. The relics of this ocean are the modern Mediterranean, Black and Caspian Seas.
The systematic finds of fossils of marine animals from the Alps and Carpathians in Europe to the Himalayas in Asia since ancient times have been explained by the biblical story of the Great Flood.
Advances in geology have made it possible to date marine remains, casting doubt on this explanation.
IN 1893 year the Austrian geologist Eduard Suess in his work "Face of the Earth" suggested the existence of an ancient ocean on this place, which he called Tethys (the Greek goddess of the sea of \u200b\u200bTephis - Greek Τηθύς, Tethys).
Nevertheless, based on the theory of geosynclines up to the seventies XX century, when the theory of plate tectonics was established, it was believed that the Tethys was only a geosyncline, and not an ocean. Therefore, for a long time, Tethys was called in geography "the system of reservoirs", the terms Sarmatian Sea or Pontic Sea were also used.
Tethys existed for about a billion years ( 850 before 5 million years ago), dividing the ancient continents of Gondwana and Laurasia, as well as their derivatives. Since during this time continental drift was observed, the Tethys constantly changed its configuration. From the wide equatorial ocean of the Old World, it turned into the western bay of the Pacific Ocean, then into the Atlanto-Indian channel, until it broke up into a series of seas. In this regard, it is appropriate to talk about several Tethys oceans:
According to scientists, Prototethis formed 850 million years ago as a result of the split of Rodinia, it was located in the equatorial zone of the Old World and had a width of 6 -10 thousand km
Paleotethis 320 -260 million years ago (Paleozoic): from the Alps to Qinling. The western part of the Paleotethis was known as Reikum. At the end of the Paleozoic, after the formation of Pangea, the Paleotethis was an ocean-bay of the Pacific Ocean.
Mesotethis 200 -66,5 million years ago (Mesozoic): from the Caribbean basin in the west to Tibet in the east.
Neotethis (Paratethys) 66 -13 million years ago (Cenozoic).
After the split of Gondwana, Africa (with Arabia) and Hindustan began to move northward, compressing Tethys to the size of the Indo-Atlantic Sea.
50 millions of years ago, Hindustan wedged into Eurasia, taking the modern position. Closed with Eurasia and the Afro-Arabian continent (in the region of Spain and Oman). The convergence of the continents caused the rise of the Alpine-Himalayan mountain complex (Pyrenees, Alps, Carpathians, Caucasus, Zagros, Hindu Kush, Pamir, Himalayas), which separated the northern part from Tethys - Paratethys (sea "from Paris to Altai").
Sarmatian Sea (from the Pannonian Sea to the Aral Sea) with islands and the Caucasus 13 -10 million years ago. The Sarmatian Sea is characterized by isolation from the world's oceans and progressive desalination.
Near 10 million years ago, the Sarmatian Sea is reestablishing communication with the world's oceans in the Bosphorus Strait. This period was called the Meotic Sea, which was the Black and Caspian Sea, connected by the North Caucasian channel.
6 million years ago, the Black and Caspian seas separated. The disintegration of the seas is partly attributed to the uplifting of the Caucasus, partly to a decrease in the level of the Mediterranean Sea.
5 -4 mln years ago, the level of the Black Sea rose again and it again merged with the Caspian into the Akchagyl Sea, which evolves into the Absheron Sea and covers the Black Sea, Caspian, Aral and floods the territory of Turkmenistan and the lower Volga region.
The final "closure" of the Tethys Ocean is associated with the Miocene epoch ( 5 million years ago). For example, the modern Pamir for some time was an archipelago in the Tethys Ocean.
The waves of the huge ocean stretched from the Isthmus of Panama across the Atlantic Ocean, the southern half of Europe, the Mediterranean region, flooding the northern shores of Africa, the Black and Caspian Seas, the territory now occupied by the Pamir, Tien Shan, Himalayas, and further through India to the Pacific islands.
The Tethys has existed for most of the history of the globe. Numerous peculiar representatives of the organic world lived in its waters.
The globe had only two huge continents: Laurasia, located on the site of modern North America, Greenland, Europe and Asia, and Gondwana, which united South America, Africa, Hindustan and Australia. These continents were separated by the Tethys Ocean.
Mountain building processes took place on the territory of the continents, erecting mountain ranges in Europe, in Asia (Himalayas), in the southern part of North America (Appalachians). The Urals and Altai appeared on the territory of our country.
Huge volcanic eruptions flooded the plains that were on the site of the modern Alps, Central Germany, England, and Central Asia with lava. Lava rose from the depths, melted rocks and solidified in huge masses. So, between the Yenisei and Lena, Siberian traps were formed, which have a large capacity and occupy an area of \u200b\u200bmore 300 000 sq. km.
The flora and fauna underwent great changes. On the shores of oceans, seas and lakes, inside the continents, giant plants inherited from the Carboniferous period grew - lepidodendrons, sigillaria, calamites. In the second half of the period, conifers appeared: walchia, ulmania, voltzia, cicada palms. In their thickets lived armor-headed amphibians, huge reptiles - pareiasaurs, otherotrances, and tuataras. The descendant of the latter still lives in our time in New Zealand.
The population of the seas is characterized by an abundance of protozoan foraminifera (fusulin ishwagerin). Large bryozoan reefs grew in the shallow zone of the Permian seas.
The sea, leaving, left vast shallow lagoons, at the bottom of which salt and gypsum settled, as in our modern Sivash. Huge areas of lakes covered continents. The sea pools were teeming with rays and sharks. Shark helicopryon, which had a dental apparatus in the form of a needle with large teeth. Armored fish give way to ganoid, lung-breathing fish.
The climate had distinct zones. Glaciers, accompanied by a cold climate, occupied the poles, which were then located differently than in our time. The North Pole was in the North Pacific Ocean, and the South Pole was near the Cape of Good Hope in South Africa. The desert belt occupied Central Europe; the deserts lay between Moscow and Leningrad. The temperate climate was in Siberia.
Crimea - Sudak - New Light
The edge of the ocean was in place, and corals grew in the shallow water warmed by the sun. They formed a huge barrier reef, separated from the coast by a wide strip of sea. This reef was not a continuous strip of land; rather, it was a series of coral islands and shoals separated by straits.
Tiny coral polyps, sponges, bryozoans, and algae lived in the warm, sunlit sea, extracting calcium from the water and surrounding themselves with a strong skeleton. Over time, they died away, and a new generation developed on them, and then died, giving life to the next - and so on for hundreds of thousands of years. This is how islands and rocky uplifts and shallows appeared in shallow waters. Later, the coral reefs were covered with clay.
Ocean Tethys disappeared from the face of the Earth, breaking up into a number of seas - Black, Caspian, Mediterranean.
The coral reefs were petrified, the clays eroded over time, and the coral limestone massifs appeared on the surface in the form of isolated mountains.
The links of the fossil coral reef are found near Balaklava, on and Chatyrdag, on Karabi-yayla and on Babugan-yayla.
But only reefs can boast of such expressiveness and such "concentration" in such a limited area. This section of the Black Sea coast can even be called a “reserve of fossil reefs”.
A squat cape and a giant crowned with medieval towers Fortress and Sugarloaf adjacent to it, powerful Koba-kaya and a long narrow Cape Kapchik, rounded Bald Mountain and jagged peak Karaul-oba, Delikli-kaya and Parsuk-Kaya - all these are fossil reefs of the Jurassic period ...
Even without a magnifying glass on the slopes of these mountains, you can see the remains of fossil organisms that were firmly attached to the rocky seabed during life. But these are not loose remains of corals and algae - these are hard marbled limestones.
In the porous reef, constantly washed by water, calcium carbonate of the reef-builders' skeletons dissolved, and remained here in the voids, strengthening the coral structure.
That is why the strong limestones of the reef are so durable, easily polished to a mirror shine, and the bizarre forms of fossils and intergrowths of calcite crystals in the former cavities of the reef are used as a beautiful decorative stone. You will not see strata in any of the reef massifs.
Generations of corals were changing continuously, and the limestone massif formed as a whole. Reefs are hundreds of meters thick, while corals cannot live below 50 m.
This suggests that the bottom was slowly sinking, with the rate of sinking of the seabed being about the same as the rate of rise of the barrier reef.
If the bottom sinks faster than the reef grows, there are “dead reefs” at great depths. If the rate of reef growth exceeds the rate of bottom sinking, the reef structure is destroyed by waves. Modern coral reefs grow at an average rate of 15 -20 mm per year.
Any of the mountains of the Sudak environs is interesting in its own way, picturesque and not like the neighboring ones. This is a one of a kind "collection" of fossil reefs.
Groves of the rarest and tree-like junipers grow in the Novy Svet, giving the area a peculiar beauty and special value.
For this reason, part of the Novosvetsky coast is protected and has the status of a landscape-botanical state reserve.
The Neotethis Sea in the Paleogene era (40-26 million years ago)
Ocean Tethys existed for about a billion years (850 to 5 million years ago)
Relict pine of Stankevich in the Novosvetsky Botanical Reserve
460 million years ago - At the end of the Ordovician period (Ordovician), one of the ancient oceans, Iapetus, began to close and another ocean appeared - Rhea. These oceans were located on either side of a narrow strip of land that was near the South Pole and today forms the east coast of North America. Small fragments chipped off the supercontinent of Gondwana. The rest of Gondwana moved south, so that what is now North Africa was right at the South Pole. The area of \u200b\u200bmany continents increased; high volcanic activity added new land areas to the east coast of Australia, to Antarctica and South America.
In Ordovician, ancient oceans separated 4 barren continents - Lorentia, Baltica, Siberia and Gondwana. The end of the Ordovician was one of the coldest periods in Earth's history. Ice covered most of southern Gondwana. In the Ordovician period, as well as in the Cambrian, bacteria prevailed. Blue-green algae continued to develop. Calcareous green and red algae that lived in warm seas at a depth of up to 50 m reach lush development. Remains of spores and rare finds of stem prints, probably belonging to vascular plants, testify to the existence of terrestrial vegetation in the Ordovician period. Of the animals of the Ordovician period, only the inhabitants of the seas, oceans, and also some representatives of fresh and brackish waters are well known. There were representatives of almost all types and most classes of marine invertebrates. At the same time, jawless fish-like fish appeared - the first vertebrates.
IN THE ORDOVIK PERIOD, LIFE BECOMED EVERYTHING RICHER, BUT THEN CLIMATIC CHANGE HAS DESTRUCTED THE ENVIRONMENT OF MANY SPECIES.
During the Ordovician period, the rate of global tectonic changes increased. During the 50 million years that the Ordovician lasted, from 495 to 443 million years ago, Siberia and the Baltic moved to the north, the Iapetus ocean began to close, and the Rhea ocean gradually opened in the south. The southern hemisphere was still dominated by the supercontinent Gondwana, while North Africa was located at the South Pole.
Almost all of our knowledge about the changes in the Ordovician climate and the position of the continents is based on the fossil remains of creatures that lived in the seas and oceans. In the Ordovician period, primitive plants, along with some small arthropods, had already begun to populate the land, but the bulk of life was still concentrated in the ocean.
In the Ordovician period, the first fish appeared, but most of the inhabitants of the sea remained small - few of them grew to a length of more than 4-5 cm. The most common owners of shells were oyster-like brachiopods, reaching a size of 2 - 3 cm. and more than 12,000 brachiopod fossils have been described. The shape of their shells changed with environmental conditions, so fossil remains of brachiopods are helping to reconstruct the climate of ancient times.
The Ordovician period represented a turning point in the evolution of marine life. Many organisms have grown in size and have learned to move faster. Of particular importance were the jawless creatures called conodonts, extinct today, but widespread in the seas of the Ordovician period. They were close relatives of the first vertebrates. The appearance of the first fish-like jawless vertebrates was followed by the rapid evolution of the first shark-like vertebrates with jaws and teeth. This happened over 450 million years ago. It was during this period that animals first began to go out onto land.
In the Ordovician period, animals made their first attempts to go to land, but not directly from the sea, but through an intermediate stage - fresh water. These footprints in parallel centimeter-wide lines have been found in Ordovician sedimentary rocks of freshwater lakes in northern England. Their age is 450 million years. Probably, they were left by an ancient arthropod - a creature with a segmented body, numerous articulated legs and an exoske in summer. It looked like modern centipedes. However, so far no fossil remains of this creature have been found.
The Ordovician seas were inhabited by numerous animals that differed sharply from the inhabitants of the ancient Cambrian seas. The formation of hard covers in many animals meant that they acquired the ability to rise above the sediments and feed in the food-rich waters above the seabed. During the Ordovician and Silurian periods, more and more animals appeared to extract food from the sea water. Among the most attractive are sea lilies, which look like hard-shelled starfish on slender stalks swaying in streams. With long flexible beams covered with a sticky substance, sea lilies caught food particles from the water. Some species had up to 200 such rays. Sea lilies, like their stemless cousins \u200b\u200b- sea stars - have happily survived to this day.
SECTION 5
PALAEOZOIC
SILURIAN
(approximately 443 million to 410 million years ago)
Silurian: collapse of continents
420 million years ago - If you look at our earth from the side of the poles, it becomes clear that in the Silurian period (Silurian), almost all continents lay in the Southern Hemisphere. The giant continent of Gondwana, which included modern South America, Africa, Australia and India, was located at the South Pole. Avalonia, a continental fragment that represented most of America's east coast, approached Laurentia, from which modern North America would later emerge, and closed off the Iapetus Ocean along the way. South of Avalonia, the Rhea Ocean appeared. Greenland and Alaska, now located at the North Pole, were near the equator during the Silurian period.
The boundary between the Ordovician and Silurian periods of the ancient history of the Earth was determined by the geological strata near Dobslinna in Scotland. In the Silurian, this area was located at the very edge of the Baltic, a large island that also included Scandinavia and part of Northern Europe. The transition from earlier - Ordovician to later - Silurian strata corresponds to the boundary between layers of sandstone and shale formed on the seabed.
During the Silurian period, Lorentia collides with the Baltic with the closure of the northern branch of the Iapetus ocean and the formation of the "New Red Sandstone" continent. Coral reefs are expanding and plants begin to colonize barren continents. The lower boundary of the Silurian is determined by a major extinction, as a result of which about 60% of the species of marine organisms that existed in the Ordovician disappeared, the so-called Ordovician-Silurian extinction.
Our planet is not a monolith. On the contrary, it stands out for its constant geological activity. This activity causes earthquakes, volcanic eruptions, tsunamis, tectonic splits and the formation of the earth's crust.
Once upon a time, six modern continents were united into one supercontinent called Pangea. Many geologists assume that now they are moving towards each other. Probably, in the next 750 million years, another supercontinent will appear on the Planet - New Pangea or Pangea Proxima.
The oldest piece of the earth's crust
Unsurprisingly, most of the earth's crust is relatively fresh. Geological processes constantly change the surface of the ocean floor, and given that this bottom is covered with sediments tens of meters thick, it is difficult to determine which section of the seabed is new and which is not.
However, a geologist from Israel's Ben-Gurion University claims to have found the oldest section of the ocean floor to date. Roy Grano discovered in the Mediterranean a section of the earth's crust with an area slightly exceeding 150 thousand square kilometers, the age of which, according to his calculations, reaches 340 million years. The scientist admits an error of 30 million years, but not more. According to the find, this area of \u200b\u200bthe Mediterranean Sea witnessed that very Pangea.
Ancient ocean
In addition, this section of the seabed is at least 70% older than other known sections, including the explored areas of the Indian and Atlantic Oceans. Grano even ventured to suggest that the piece of the earth's crust he found could be part of the legendary Tethys, an ancient ocean of the Mesozoic period. Tethys washed two ancient supercontinent - Gondwana and Laurasia, which existed about 750-500 million years ago. If this is true, then the newly discovered site formed even before Pangea formed. In the scientific community, it is believed that the Mediterranean, Black and Caspian Seas are divided parts of the Tethys.
Long research
This popular theory was the reason that for two years Grano explored the bottom of the Mediterranean Sea using sonar and magnetic sensors.
According to him, this part of the earth's crust has not yet been discovered because it was hidden under an almost 20-kilometer layer of bottom sediments.
Research team Grano dragged two sensors behind their boat, taking magnetic data from the seabed. Scientists hoped to discover anomalies pointing to ancient magnetic rocks. The general picture of the anomalies could indicate to geologists the presence of an ancient plate hidden under the silt.
After deciphering the data collected over two years, Grano found exactly what he was looking for. The find of the year turned out to be the oldest piece of the Mediterranean Sea floor located between Turkey and Egypt, which is the oldest to date.
If this plate was part of the Tethys ocean floor, it means that the ocean was formed 50 million years earlier than geologists thought. Grano, however, does not insist that the site was part of ancient Tethys. It is possible that this plate was part of another body of water, but ended up in the Mediterranean Sea due to those very geological processes. After all, 340 million years is a long period.
There are places on Earth that have remained unchanged for millions of years. When you find yourself in such places, you involuntarily become imbued with awe for the time and feel like just a grain of sand.
This review contains the oldest geological antiquities of our planet, many of which are still a mystery to scientists today.
1. The oldest surface
1.8 million years
In Israel, one of the local desert areas looks the same as it did almost two million years ago. Scientists believe that this plain remained dry and extremely flat for such a long time due to the fact that the climate did not change here and there was no geological activity. According to those who have been here, you can look at the endless barren plain almost forever ... if you tolerate the wild heat well.
2. The oldest ice
15 million years
At first glance, the McMurdo Dry Valleys in Antarctica are ice-free. Their eerie "Martian" landscapes are composed of bare rocks and thick layers of dust. There are also remnants of ice that are about 15 million years old. Moreover, a mystery is connected with this most ancient ice on the planet. For millions of years the valleys have remained stable and unchanged, but in recent years they have begun to thaw. For unknown reasons, unusually hot weather for Antarctica was established in the Garwood Valley. One of the glaciers began to melt vigorously for at least 7000 years. Since then, it has already lost a huge amount of ice and there are no signs that this will stop.
3. Desert
55 million years
The Namib Desert in Africa is officially the world's oldest "pile of sand". Among its dunes one can find mysterious “magic circles” and desert plants of velvichia, some of which are 2500 years old. This desert has not seen surface water for 55 million years. However, its origins go back to the continental split of Western Gondwana, which occurred 145 million years ago.
4. Oceanic crust
340 million years
The Indian and Atlantic oceans were far from the first. Scientists believe they have found traces of the primitive Tethys Ocean in the Mediterranean Sea. It is very rare that the crust of the seabed can be dated more than 200 million years ago, as it is in constant motion and new layers are rising to the surface. The site in the Mediterranean escaped normal geological recirculation, and a scan revealed its record age (340 million years ago). If this is indeed a part of Tethys, then this is the first evidence that the ancient ocean existed earlier than previously thought.
5. Reefs created by animals
548 million years
The oldest reef is not just one or two coral branches. It is a massive petrified “net” that stretches for 7 km. And he is in Africa. This miracle of nature was created in Namibia by the claudins - the first creatures to have skeletons. The extinct rod-shaped animals produced their own calcium carbonate cement, like modern corals, and used it to stick together. Although very little is known about them today, scientists believe that claudins have banded together to defend against predators.
6. Mount Roraima
2 billion years
Three countries border this mountain: Guyana, Brazil and Venezuela. Its huge flat top is a popular tourist attraction, and when rainfall is high, the water from the mountain falls in waterfalls onto the plateau below. The sight of Roraima inspired Sir Arthur Conan Doyle so much that he wrote his famous classic The Lost World. At the same time, few tourists know that Mount Roraima is one of the most ancient formations in the world.
7. Water
2.64 billion years
At a depth of 3 kilometers in a Canadian mine is what used to be a prehistoric ocean floor. After the scientists took samples from the "pocket" of water found in the mine, they were shocked when this liquid turned out to be the oldest H2O on the planet. This water is older than even the first multicellular life.
8. Impact crater
3 billion years
A huge meteorite could have “knocked out” a significant chunk from Greenland a long time ago. If proven, the Greenland crater will “move off the throne” of the current champion - the 2 billion-year-old Vredefort crater in South Africa. Initially, the crater diameter was up to 500 kilometers. To this day, there is evidence of impact, such as shattered rocks at the crater's edges and molten mineral formations. There is also ample evidence that seawater poured into the newly formed crater and that huge amounts of steam altered the chemistry of the environment. If such a whopper hits the Earth today, the human race will face the threat of extinction.
9. Tectonic plates
3.8 billion years
The outer layer of the earth is made up of several “plates” that are stacked together like puzzle pieces. Their movements shape the outward appearance of the world, and these "plates" are known as tectonic plates. Traces of ancient tectonic activity have been found on the southwestern coast of Greenland. 3.8 billion years ago, the colliding plates "squeezed" out the "pillow" of lava.
10. Earth
4.5 billion years
Scientists believe that part of the Earth, which the planet was at birth, may have fallen into their hands. Volcanic rocks have been found in Baffin Land in the Canadian Arctic, which formed even before the earth's crust formed. This discovery may finally reveal what happened to the globe before it became solid. These rocks contained a previously unseen combination of chemical elements - lead, neodymium and extremely rare helium-3.
Even Leonardo da Vinci found fossilized shells of marine organisms on the peaks of the Alps and came to the conclusion that there used to be a sea on the site of the highest ridges of the Alps. Later, marine fossils were found not only in the Alps, but also in the Carpathians, the Caucasus, the Pamirs, and the Himalayas. Indeed, the main mountain system of our time - the Alpine-Himalayan belt - was born from the ancient sea. At the end of the last century, the contour of the area covered by this sea became clear: it stretched between the Eurasian continent in the north and Africa and Hindustan in the south. E. Suess, one of the greatest geologists at the end of the last century, called this space the Tethys Sea (in honor of Thetis, or Thetis - the sea goddess).
A new turn in the concept of Tethys came at the beginning of the current century, when A. Wegener, the founder of the modern theory of continental drift, made the first reconstruction of the Late Paleozoic supercontinent Pangea. As you know, he pushed Eurasia and Africa to North and South America, combining their coasts and completely closing the Atlantic Ocean. At the same time, it was found that, covering the Atlantic Ocean, Eurasia and Africa (together with Hindustan) diverge to the sides and between them, as it were, a void appears, a gaping several thousand kilometers wide. Of course, A. Wegener immediately noticed that the gaping corresponds to the Tethys Sea, but its dimensions corresponded to the oceanic ones, and one should speak of the Tethys Ocean. The conclusion was obvious: as the continents drifted, as Eurasia and Africa moved away from America, a new ocean, the Atlantic Ocean, was opened and at the same time the old ocean, the Tethys, was closed (Fig. 1). Consequently, the Tethys Sea is a lost ocean.
This schematic picture, which emerged 70 years ago, has been confirmed and detailed over the past 20 years on the basis of a new geological concept, which is now widely used in the study of the structure and history of the Earth, - plate tectonics. Let us recall its main provisions.
The upper solid shell of the Earth, or the lithosphere, is broken by seismic belts (95% of earthquakes are concentrated in them) into large blocks or plates. They cover continents and oceanic spaces (there are 11 large plates in total today). The lithosphere has a thickness of 50-100 km (under the ocean) to 200-300 km (under the continents) and rests on a heated and softened layer - the asthenosphere, along which plates can move in a horizontal direction. In some active zones - in the mid-oceanic ridges - lithospheric plates diverge to the sides at a speed of 2 to 18 cm / year, making room for basalts - volcanic rocks melted from the mantle - to rise upward. When basalts solidify, they increase the diverging edges of the slabs. The process of plate spreading is called spreading. In other active zones - in deep-water trenches - lithospheric plates approach each other, one of them "dives" under the other, going down to depths of 600-650 km. This process of sinking plates and absorbing them into the Earth's mantle is called subduction. Long belts of active volcanoes of specific composition (with a lower content of silica than in basalts) arise above the subduction zones. The famous Pacific Ring of Fire is located directly above the subduction zones. Catastrophic earthquakes registered here are caused by the stresses necessary for the lithosphere to pull the plate down. Where the plates approaching each other carry continents that are not able to sink into the mantle due to their lightness (or buoyancy), continents collide and mountain ranges arise. The Himalayas, for example, were formed during the collision of the continental block of Hindustan with the Eurasian continent. The rate of convergence of these two continental plates is now 4 cm / year.
Since lithospheric plates are rigid in the first approximation and do not undergo significant internal deformations during their movement, a mathematical apparatus can be applied to describe their movements along the earth's sphere. It is not complicated and is based on L. Euler's theorem, according to which any movement along a sphere can be described as rotation around an axis passing through the center of the sphere and crossing its surface at two points or poles. Therefore, in order to determine the movement of one lithospheric plate relative to another, it is enough to know the coordinates of the poles of their rotation relative to each other and the angular velocity. These parameters are calculated from the values \u200b\u200bof directions (azimuths) and linear velocities of plate movements at specific points. As a result, for the first time it was possible to introduce a quantitative factor into geology, and it began to move from a speculative and descriptive science to the category of exact sciences.
The above remarks are necessary in order for the reader to become clear in the future the essence of the work done jointly by Soviet and French scientists on the Tethys project, which was carried out within the framework of an agreement on Soviet-French cooperation in the study of the oceans. The main goal of the project was to restore the history of the disappeared Tethys Ocean. On the Soviet side, the Institute of Oceanology named after V.I. P.P. Shirshova of the USSR Academy of Sciences. Corresponding members of the Academy of Sciences of the USSR A.S. Monin and A.P. Lisitsyn, V.G. Kazmin, I.M.Sbolshchikov, L.A. Savostia, O. G. Sorokhtin and the author of this article took part in the research. Employees of other academic institutes were involved: D. M. Pechersky (O. Yu. Schmidt Institute of Physics of the Earth), A. L. Knipper and M. L. Bazhenov (Geological Institute). Great assistance in the work was provided by employees of the Geological Institute of the Academy of Sciences of the GSSR (Academician of the Academy of Sciences of the GSSR G.A. and M.I.Satian), the Geological Faculty of Moscow State University (Academician of the USSR Academy of Sciences V.: E. Khain, N.V. Koronovsky, N.A. Bozhko and O. A. | Mazarovich).
On the French side, the project was led by one of the founders of the theory of plate tectonics C. Le Pichon (University of Pierre and Marie Curie in Paris). Experts in the geological structure and tectonics of the Tethys belt took part in the research: J. Dercourt, L.-E. Rikou, J. Le Privière and J. Jeysan (Pierre and Marie Curie University), J.-C. Cie-Bouet (Center for Oceanographic Research in Brest), M. Westphal and J.P. Lauer (University of Strasbourg), J. Boulen (University of Marseille), B. Bijou-Duval (State Oil Company).
The research included joint expeditions to the Alps and Pyrenees, and then to the Crimea and the Caucasus, laboratory processing and synthesis of materials at the University. Pierre and Marie Curie and at the Institute of Oceanology of the USSR Academy of Sciences. The work was started in 1982 and completed in 1985. Preliminary results were reported at the XXVII session of the International Geological Congress, held in Moscow in 1984. The results of the joint work were summarized in a special issue of the international journal "Tectonophysics" in 1986. Abridged version of the report at published in French in 1985 in the Bulletin societe de France, in Russian the History of the Tethys Ocean was published.
The Soviet-French Tethys project was not the first attempt to reconstruct the history of this ocean. It differed from the previous ones by the use of new, better data, a much greater extent of the studied region - from Gibraltar to the Pamirs (and not from Gibraltar to the Caucasus, as it was before), and most importantly, by attracting and comparing materials from various sources independent from each other. Three main groups of data were analyzed and taken into account during the reconstruction of the Tethys Ocean: kinematic, paleomagnetic, and geological.
Kinematic data relate to mutual displacements of the main lithospheric plates of the Earth. They are entirely related to plate tectonics. Penetrating into the depths of geological time and consistently moving Eurasia and Africa to North America, we obtain the relative positions of Eurasia and Africa and identify the contour of the Tethys Ocean for each specific moment in time. Here a situation arises that seems paradoxical to a geologist who does not recognize mobilism and plate tectonics: in order to represent events, for example, in the Caucasus or in the Alps, it is necessary to know what was happening thousands of kilometers from these regions in the Atlantic Ocean.
In the ocean, we can reliably determine the age of the basalt basement. If we combine the same-age bottom strips, which are symmetrically on opposite sides of the axis of the mid-oceanic ridges, we will obtain the parameters of plate movement, that is, the coordinates of the rotation pole and the angle of rotation. The procedure for searching for parameters for the best alignment of the same-age bottom bands is now well developed and is carried out on a computer (a series of programs is available at the Institute of Oceanology). The accuracy of determining the parameters is very high (usually fractions of a degree of the great-circle arc, that is, the error is less than 100 km), and the accuracy of reconstructions of the former position of Africa relative to Eurasia is just as high. This reconstruction serves as a rigid framework for each moment of geological time, which should be taken as a basis for reconstructing the history of the Tethys Ocean.
The history of plate movement in the North Atlantic and the opening of the ocean in this place can be divided into two periods. In the first period, 190-80 million years ago, Africa was separated from the united North America and Eurasia, the so-called Laurasia. Prior to this split, the Tethys Ocean had a wedge-shaped outline, widening with a bell to the east. Its width in the Caucasus region was 2500 km, and on the traverse of the Pamirs, at least 4500 km. During this period, Africa moved eastward relative to Laurasia, covering a total of about 2,200 km. The second period, which began about 80 million years ago and continues to this day, was associated with the division of Laurasia into Eurasia and North America. As a result, the northern edge of Africa along its entire length began to draw closer to Eurasia, which ultimately led to the closure of the Tethys Ocean.
The directions and speeds of movement of Africa relative to Eurasia did not remain unchanged throughout the Mesozoic and Cenozoic eras (Fig. 2). In the first period, in the western segment (west of the Black Sea), Africa moved (albeit at a low speed of 0.8-0.3 cm / year) to the southeast, making it possible to open up a young oceanic basin between Africa and Eurasia.
80 million years ago, in the western segment, Africa began to move northward, and in recent times it is moving northwestward in relation to Eurasia at a speed of about 1 cm / year. The fold deformations and growth of mountains in the Alps, Carpathians, and Apennines are in full accordance with this. In the eastern segment (in the Caucasus region), Africa 140 million years ago began to converge with Eurasia, and the speed of convergence fluctuated noticeably. The accelerated approach (2.5-3 cm / year) refers to the intervals of 110-80 and 54-35 million years ago. It was in these intervals that intense volcanism was noted in the volcanic arcs of the Eurasian margin. The slowdown of movement (up to 1.2-11.0 cm / year) falls on the intervals of 140-110 and 80-54 million years ago, when stretching occurred in the rear of the volcanic arcs of the Eurasian margin and the deep-sea basins of the Black Sea were formed. The minimum approach speed (1 cm / year) refers to 35-10 million years ago. Over the past 10 million years, in the Caucasus region, the rate of convergence of plates has increased to 2.5 cm / year due to the opening of the Red Sea, the Arabian Peninsula broke away from Africa and began to move northward, pressing its ledge into the edge of Eurasia. It is no coincidence that the mountain ranges of the Caucasus have grown on the top of the Arabian ledge. The paleomagnetic data used in the reconstruction of the Tethys Ocean have as their source measurements of the remanent magnetization of rocks. The fact is that many rocks, both igneous and sedimentary, at the time of their formation were magnetized in accordance with the orientation of the magnetic field that existed at that time. There are methods that allow you to remove the layers of later magnetization and establish what the primary magnetic vector was. It should be pointed towards the paleomagnetic pole. If the continents are not drifting, then all vectors will be oriented in the same way.
Back in the 50s of our century, it was firmly established that within each, separately taken continent, paleomagnetic vectors are indeed oriented parallel and, although they are not elongated along modern meridians, are still directed to one point - the paleomagnetic pole. But it turned out that different continents, even nearby ones, are characterized by completely different orientations of vectors, that is, the continents have different paleomagnetic poles. This alone has in itself served as the basis for the assumption of large-scale continental drift.
In the Tethys belt, the paleomagnetic poles of Eurasia, Africa, and North America also do not coincide. For example, for the Jurassic period, the paleomagnetic poles have the following coordinates: in Eurasia - 71 ° N. w „150 ° h. (Chukotka region), in Africa - 60 ° N. w, 108 ° W (region of Central Canada), near North America - 70 ° N. w., 132 ° E (the area of \u200b\u200bthe Lena estuary). If we take the parameters of plate rotation relative to each other and, say, move the paleomagnetic poles of Africa and North America along with these continents to Eurasia, then we will find an amazing coincidence of these poles. Accordingly, the paleomagnetic vectors of all three continents will be oriented subparallel and directed to one point - the common paleomagnetic pole. This kind of comparison of kinematic and paleomagnetic data was carried out for all time intervals, from 190 Ma to the present. There was always a good match; by the way, it is a reliable evidence of the reliability and accuracy of paleogeographic reconstructions.
The main continental plates - Eurasia and Africa - fringed the Tethys Ocean. However, inside the ocean, undoubtedly, there were smaller continental or other blocks, as now, for example, inside the Indian Ocean is the microcontinent of Madagascar or a small continental block of the Seychelles. Thus, inside the Tethys there were, for example, the Transcaucasian massif (the territory of the Rion and Kura depressions and the mountain bar between them), the Daralagez (South Armenian) block, the Rhodope massif in the Balkans, the Apulian massif (covering most of the Apennine Peninsula and the Adriatic Sea). Paleomagnetic measurements within these blocks are the only quantitative data that allow us to judge their position in the Tethys Ocean. Thus, the Transcaucasian massif was located near the Eurasian margin. The small Daralagez block is, as it turns out, of southern origin and was previously annexed to Gondwana. The Apulian massif did not move much in latitude relative to Africa and Eurasia, but in the Cenozoic it was turned counterclockwise by almost 30 °.
The geological group of data is the most abundant, since geologists have been studying the mountain belt from the Alps to the Caucasus for a good one and a half hundred years. This group of data is also the most controversial, since a quantitative approach can least of all be applied to it. At the same time, geological data are in many cases decisive: it is the geological objects - rocks and tectonic structures - that were formed as a result of the movement and interaction of lithospheric plates. In the Tethys belt, geological materials made it possible to establish a number of significant features of the Tethys paleoocean.
Let's start with the fact that only by the distribution of marine Mesozoic (and Cenozoic) deposits in the Alpine-Himalayan belt, it became obvious that the sea or the Tethys ocean here in the past. Tracing different geological complexes on the area, it is possible to determine the position of the seam of the Tethys ocean, that is, the zone along which the continents that framed Tethys converged on their edges. Of key importance are the outcrops of the so-called ophiolite complex (from the Greek ocpir \u200b\u200b- snake, some of these rocks are called serpentines). Ophiolites are composed of heavy rocks of mantle origin, depleted in silica and rich in magnesium and iron: peridotite, gabbro and basalt. Such rocks make up the bedrock of modern oceans. With this in mind, geologists came to the conclusion 20 years ago that ophiolites are remnants of the crust of ancient oceans.
Ophiolites of the Alpine-Himalayan belt mark the Tethys ocean floor. Their outcrops form a winding strip along the strike of the entire belt. They are known in the south of Spain, on the island of Corsica, stretching in a narrow strip along the central zone of the Alps, continuing into the Carpathians. Large tectonic ophiolite scales have been found in the Dealer Alps in Yugoslavia and Albania, in the mountain ranges of Greece, including the famous Mount Olympus. Outcrops of ophiolites, forming an arc facing south, between the Balkan Peninsula and Asia Minor, and then traced in southern Turkey. Ophiolites are beautifully exposed in our country in the Lesser Caucasus, on the northern shore of Lake Sevan. From here, they stretch to the Zagros ridge and the mountains of Oman, where ophiolite plates are thrust over the shallow sediments of the Arabian Peninsula outskirts. But even here the ophiolite zone does not end, it turns to the east and, following parallel to the coast of the Indian Ocean, goes further northeast into the Hindu Kush, Pamir and Himalayas. Ophiolites are of different ages - from Jurassic to Cretaceous, but everywhere they are relics of the earth's crust of the Mesozoic ocean Tethys. The width of the ophiolite zones is measured in several tens of kilometers, while the initial width of the Tethys Ocean was several thousand kilometers. Consequently, when the continents approached, almost all of the oceanic crust of the Tethys went into the mantle in the zone (or zones) of subduction along the edge of the ocean.
Despite the small width, the ophiolite, or main, seam of the Tethys separates two provinces sharply different in geological structure.
For example, among the Upper Paleozoic sediments that accumulated 300-240 million years ago, to the north of the seam, continental sediments predominate, some of which were deposited in desert conditions; while south of the seam, thick strata of limestone, often reef, are widespread, marking a vast shelf sea in the equatorial region. Equally striking is the change in Jurassic rocks: clastic, often coal-bearing, deposits north of the seam again oppose limestones south of the seam. The seam separates, as geologists say, different facies (conditions for the formation of precipitation): the Eurasian temperate climate from the Gondwana equatorial 'climate. Crossing the ophiolite seam, we find ourselves, as it were, from one geological province to another. To the north of it, we meet large granite massifs surrounded by crystalline schists and series of folds that arose at the end of the Carboniferous period (about 300 million years ago), to the south - layers of sedimentary rocks of the same age lie consistently and without any signs of deformation and metamorphism ... It is clear that the two margins of the Tethys Ocean - Eurasian and Gondwana - were sharply different from each other both in their position on the earth's sphere and in their geological history.
Finally, we note one of the most significant differences in the areas lying north and south of the ophiolite suture. To the north of it there are belts of volcanic rocks of the Mesozoic and Early Cenozoic age, formed over 150 million years: from 190 to 35-40 million years ago. Volcanic complexes in the Lesser Caucasus are especially well traced: they stretch in a continuous strip along the entire ridge, going west to Turkey and further to the Balkans, and east to the Zagros and Elburs ranges. The composition of the lavas has been studied in great detail by Georgian petrologists. They found that the lavas are practically indistinguishable from the lavas of modern volcanoes, island arcs and active margins that make up the ring of fire of the Pacific Ocean. Let us recall that the volcanism of the Pacific Ocean framing is associated with the subduction of the oceanic crust under the continent and is confined to the boundaries of convergence of lithospheric plates. This means that in the Tethys belt, volcanism, similar in composition, marks the former boundary of the convergence of plates, on which the subduction of the oceanic crust took place. At the same time, to the south of the ophiolite suture there are no volcanic manifestations of the same age; throughout the Mesozoic era and during most of the Cenozoic era, shallow-water shelf sediments, mainly limestones, were deposited here. Consequently, the geological data provide solid evidence that the margins of the Tethys Ocean were fundamentally different in tectonic nature. The northern, Eurasian margin with volcanic belts constantly forming at the border of the convergence of lithospheric plates was, as geologists say, active. The southern, Gondwana margin, devoid of volcanism and occupied by a vast shelf, quietly passed into the deep basins of the Tethys Ocean and was passive. Geological data, and above all materials on volcanism, make it possible, as we see, to reconstruct the position of the former boundaries of lithospheric plates and to outline ancient subduction zones.
The above does not exhaust all the factual material that must be analyzed to reconstruct the disappeared Tethys Ocean, but I hope this is enough for the reader, especially far from geology, to understand the basis of the constructions done by Soviet and French scientists. As a result, color paleogeographic maps were compiled for nine points in geological time from 190 to 10 million years ago. On these maps, using kinematic data, the position of the main continental plates - the Eurasian and African (as parts of Gondwana) was restored, the position of the microcontinent inside the Tethys Ocean was determined, the boundary of the continental and oceanic crust was outlined, the distribution of land and sea was shown, paleolatitudes were calculated (based on paleomagnetic data )4 ... Particular attention is paid to the reconstruction of the boundaries of lithospheric plates - spreading zones and subduction zones. The vectors of displacement of the main plates for each moment of time are also calculated. In fig. 4 shows the diagrams compiled from color maps. To make the prehistory of Tethys clear, a diagram of the arrangement of continental plates at the end of the Paleozoic (Late Permian epoch, 250 million years ago) was also added to them.
In the Late Paleozoic (see Fig. 4, a), the Paleo-Tethys Ocean stretched between Eurasia and Gondwana. Already at this time, the main tendency of tectonic history was determined - the existence of an active margin in the north of Paleo-Tethys and a passive margin in the south. At the beginning of the Permian period, comparatively large continental massifs - Iranian, Afghani, Pamirian, were split off from the passive margin, which began to move, crossing the Paleo-Tethys, to the north, to the active Eurasian margin. The oceanic bed of the Paleo-Tethys in the front of drifting micro-continents was gradually absorbed in the subduction zone near the Eurasian margin, and in the rear of the micro-continents, between them and the Gondwana passive margin, a new ocean opened up - the Mesozoic Tethys proper, or Neo-Tethys.
In the Early Jurassic (see Fig. 4, b), the Iranian microcountry adjoined the Eurasian margin. When they collided, a folded zone (the so-called Cimmerian folding) arose. In the Late Jurassic, 155 million years ago, the opposition of the Eurasian active and Gondwana passive margins was clearly defined. At that time, the width of the Tethys Ocean was 2500-3000 km, that is, it was the same as the width of the modern Atlantic Ocean. The spread of Mesozoic ophiolites made it possible to outline a spreading axis in the central part of the Tethys Ocean.
In the Early Cretaceous (see Fig. 4, c) the African Plate - the successor to the disintegrated Gondwana by this time - moved towards Eurasia in such a way that in the west of the Tethys the continents diverged somewhat and a new oceanic basin arose there, while in the eastern part the continents approached and the ocean floor Tethys was absorbed under the Lesser Caucasian volcanic arc.
At the end of the Early Cretaceous (see Fig. 4, d), the oceanic basin in the west of Tethys (it is sometimes called Mesogea, and its remains are the modern deep-sea basins of the Eastern Mediterranean), ceased to open, and in the east of Tethys, judging by the dates of the ophiolites of Cyprus and Oman , the active stage of spreading ended. In general, the width of the eastern part of the Tethys Ocean by the middle of the Cretaceous period decreased to 1500 km abeam the Caucasus.
The Late Cretaceous, 80 million years ago, includes the rapid reduction in the size of the Tethys Ocean: the width of the strip with the oceanic crust at that time was no more than 1000 km. In places, as in the Lesser Caucasus, collisions of microcontinents with an active margin began, and the rocks underwent deformation, accompanied by significant displacements of tectonic covers.
At the Cretaceous – Paleogene boundary (see Fig. 4, e), at least three important events took place. Firstly, ophiolite plates, which cut off the oceanic crust of Tethys, were thrust on the passive margin of Africa by a wide front.