Did the Tethys Ocean exist? Ancient oceans Primordial ocean.
There are places on Earth that have remained unchanged for millions of years. When you get to such places, you willy-nilly imbued with reverence for 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 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 can stand the wild heat well.
2. The oldest ice
15 million years
At first glance, the McMurdo Dry Valleys in Antarctica appear to be ice-free. Their eerie "Martian" landscapes are made up of bare rocks and a thick layer of dust. There are also remnants of ice 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 reasons unknown, the Garwood Valley experienced unusually hot weather for Antarctica. One of the glaciers began to melt intensively for at least 7000 years. Since then, it has already lost a huge amount of ice and there is no sign that this will stop.
3. Desert
55 million years
The Namib Desert in Africa is officially the oldest "pile of sand" in the world. Among its dunes, you can find mysterious “fairy circles” and desert velvichia plants, some of which are 2,500 years old. This desert has not seen surface water for 55 million years. However, its origins go back to the Western Gondwana continental break that 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 primordial Tethys Ocean in the Mediterranean Sea. It is very rare that the seafloor crust can be dated to more than 200 million years, as it is in constant motion and new layers are being brought to the surface. A site in the Mediterranean has escaped normal geological recycling and has been scanned for a record age of 340 million years ago. If this is indeed 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 sprigs of corals. This is a massive petrified “network” that stretches for 7 km. And it is in Africa. This miracle of nature was created in Namibia by claudins - the first creatures with skeletons. Extinct rod-shaped animals made their own cement from calcium carbonate, like modern corals, and used it to stick together. Although very little is known about them today, scientists believe that claudins combined to protect themselves from 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 there is a lot of rainfall, the water from the mountain flows down in waterfalls to 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 lies what used to be the prehistoric ocean floor. After scientists took samples from a “pocket” of water found in a 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 piece of Greenland a long time ago. If this is proven, then the Greenland crater will “move off the throne” the current champion - the 2 billion year old Vredefort crater in South Africa. Initially, the diameter of the crater was up to 500 kilometers. To this day, evidence of impact is observed in it, such as eroded rocks at the rims of the crater and molten mineral formations. There is also ample evidence that sea water gushed into the freshly formed crater and that gigantic amounts of steam changed the chemistry of the environment. If such a behemoth 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 form the appearance of the world, and these “plates” are known as tectonic plates. On the southwestern coast of Greenland, traces of ancient tectonic activity have been found. 3.8 billion years ago, colliding plates “squeezed out” a “cushion” of lava.
10. Earth
4.5 billion years
Scientists believe that a part of the Earth, which the planet was at birth, may have fallen into their hands. In Baffin Island in the Canadian Arctic, volcanic rocks have been found that formed 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.
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 both sides of a narrow strip of land that was near the South Pole and today forms the east coast of North America. Small fragments were breaking off from the supercontinent Gondwana. The rest of Gondwana moved south, so that what is now North Africa was right at the South Pole. The area of many 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 - Laurentia, Baltica, Siberia and Gondwana. The end of Ordovician was one of the coldest periods in the history of the Earth. Ice covered much of southern Gondwana. In the Ordovician period, as well as in the Cambrian, bacteria dominated. Blue-green algae continued to develop. Calcareous green and red algae, which lived in warm seas at depths of up to 50 m, reach lush development. The existence of terrestrial vegetation in the Ordovician period is evidenced by the remains of spores and rare finds of imprints of stems, probably belonging to vascular plants. Of the animals of the Ordovician period, only the inhabitants of the seas, oceans, as well as 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.
DURING THE ORDOVICAN PERIOD, LIFE WAS INCREASINGLY RICHER, BUT THEN CLIMATE CHANGE DESTROYED THE HABITATS OF MANY SPECIES OF LIVING THINGS.
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 northward, the Iapetus Ocean began to close, and the Rhea Ocean gradually opened in the south. The Southern Hemisphere was still dominated by the Gondwana supercontinent, with North Africa located at the South Pole.
Almost all of our knowledge of the Ordovician climate changes 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 brachiopods similar to oysters, reaching a size of 2 - 3 cm. and over 12,000 fossil brachiopod species have been described. The shape of their shells changed depending on environmental conditions, so the fossil remains of brachiopods help to reconstruct the climate of ancient times.
The Ordovician period represented a turning point in the evolution of marine life. Many organisms have increased in size and learned to move faster. Of particular importance were 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 land on land.
In the Ordovician period, animals made their first attempts to reach land, but not directly from the sea, but through an intermediate stage - fresh water. These centimeter-wide parallel 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 jointed legs and exoske in the summer. It looked like modern centipedes. However, no fossil remains of this creature have been found so far.
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 bottom sediments and feed in food-rich waters above the seabed. During the Ordovician and Silurian periods, more animals appeared that extract food from sea water. Among the most attractive are the sea lilies, which look like hard-shelled starfish on thin stalks, swaying in water currents. With long flexible rays covered with a sticky substance, sea lilies caught food particles from the water. Some species of such rays had up to 200. Sea lilies, like their stemless relatives - starfish, have successfully survived to this day.
SECTION 5
PALAEOZOIC
SILURIAN
(approximately from 443 million to 410 million years ago)
Silurian: the collapse of the continents
420 million years ago- If you look at our land from the poles, it becomes clear that in the Silurian period (Silur), almost all the continents lay in the Southern Hemisphere. The giant continent of Gondwana, which included present-day South America, Africa, Australia and India, was located at the South Pole. Avalonia - a continental fragment that represented most of the east coast of America - approached Laurentia, from which modern North America was later formed, and along the way closed the Iapetus Ocean. South of Avalonia, the Rhea Ocean appeared. Greenland and Alaska, today located near 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 geological strata near Dobslinn in Scotland. In the Silurian, this area was located on 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 layers corresponds to the boundary between the layers of sandstone and shale formed on the seabed.
During the Silurian period, Laurentia 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 are beginning to colonize barren continents. The lower boundary of the Silurian is defined by a major extinction, which resulted in the disappearance of about 60% of the species of marine organisms that existed in the Ordovician, the so-called Ordovician-Silurian extinction.
Tethys is an ancient ocean that existed during the Mesozoic era between the ancient continents of Gondwana and Laurasia. The relics of this ocean are the modern Mediterranean, Black and Caspian Seas.
Systematic finds of fossils of marine animals from the Alps and Carpathians in Europe to the Himalayas in Asia have been explained since ancient times by the biblical story of the Great Flood.
The development of geology allowed the dating of marine remains, which cast doubt on such an explanation.
IN 1893 In 1994, the Austrian geologist Eduard Suess in his work The Face of the Earth suggested the existence of an ancient ocean at this place, which he called Tethys (the Greek goddess of the sea Tethys - Greek Τηθύς, Tethys).
However, based on the theory of geosynclines up to the seventies XX century, when the theory of plate tectonics was established, it was believed that Tethys was only a geosyncline, and not an ocean. Therefore, for a long time, Tethys was called in geography a "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), separating the ancient continents Gondwana and Laurasia, as well as their derivatives. Since the drift of the continents was observed during this time, Tethys was constantly changing its configuration. From the wide equatorial ocean of the Old World, it turned now 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, Prototethys 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.
paleotethys 320 -260 million years ago (Paleozoic): from the Alps to Qinling. The western part of Paleo-Tethys was known as Reikum. At the end of the Paleozoic, after the formation of Pangea, Paleotethys was an ocean-gulf of the Pacific Ocean.
Mesotethys 200 -66,5 million years ago (Mesozoic): from the Caribbean basin in the west to Tibet in the east.
neotethys(Paratethys) 66 -13 million years ago (Cenozoic).
After the split of Gondwana, Africa (with Arabia) and Hindustan began to move north, compressing Tethys to the size of the Indo-Atlantic Sea.
50 million years ago, Hindustan wedged itself into Eurasia, occupying its present 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 (the 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 restores its connection with the oceans in the area of the Bosphorus. 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 collapse of the seas is partly associated with the rise of the Caucasus, partly with a decrease in the level of the Mediterranean Sea.
5 -4 million 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 Apsheron Sea and covers the Black Sea, Caspian, Aral and floods the territories 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 vast 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 Pamirs, the Tien Shan, the Himalayas, and further through India to the islands of the Pacific Ocean.
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, uniting South America, Africa, Hindustan and Australia. These continents were separated by the Tethys Ocean.
On the territory of the continents, mountain-building processes took place, 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 through the rocks and solidified in huge masses. So, between the Yenisei and the Lena, Siberian traps were formed, which have a large capacity and occupy an area of more than 300 000 sq. km.
The animal and plant world experienced great changes. Along the shores of the 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: Walhia, Ulmania, Voltsia, cicada palms. In their thickets lived armor-headed amphibians, huge reptiles - pareiasaurs, foreigners, tuatara. A descendant of the latter still lives in our time in New Zealand.
The population of the seas is characterized by an abundance of protozoan foraminifers (fusulin ischvagerin). 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 the continents. Sea pools abounded with stingrays and sharks. Shark Helicoprion, which had a dental apparatus in the form of a needle with large teeth. Armored fish give way to ganoid, lungfish.
The climate had clearly defined zones. Glaciations, accompanied by a cold climate, occupied the poles, which then were 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 belt of deserts occupied Central Europe; deserts lay between Moscow and Leningrad. The temperate climate was in Siberia.
Crimea - Sudak - New World
In place was the outskirts of the ocean, and corals grew in the shallow water warmed by the sun. They formed a huge barrier reef, separated from the shore 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, algae lived in the warm, sunlight-filled sea, extracting calcium from the water and surrounding themselves with a strong skeleton. Over time, they died off, and a new generation developed on them, and then died, giving life to the next one - and so on for hundreds of thousands of years. So islands and rocky uplifts-shoals arose in shallow water. Later coral reefs were covered with clays.
The Tethys Ocean disappeared from the face of the Earth, breaking up into a number of seas - the Black, Caspian, Mediterranean.
Coral reefs petrified, clays eroded over time, and coral limestone massifs appeared on the surface in the form of isolated mountains.
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 Sugar Loaf adjacent to it, powerful Koba-kaya and long narrow cape Kapchik, rounded Bald Mountain and jagged peak of Karaul-both, 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, one can see the remains of fossil organisms, firmly attached to the rocky seabed during life. But these are not loose remains of corals and algae - these are strong marbled limestones.
In the porous reef, constantly washed with water, the calcium carbonate of the skeletons of reef builders dissolved, and remained here in the voids, strengthening the coral structure.
That is why the strong limestones of the reefs are so durable, easily polished to a mirror shine, and the bizarre fossils and intergrowths of calcite crystals in the former voids of the reef are used as a beautiful decorative stone. You will not see layers in any of the reef massifs.
Generations of corals changed 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 seafloor subsidence being about the same as the growth rate of the barrier reef.
If the bottom sinks faster than the reef grows, "dead reefs" are found at great depths. If the rate of reef growth exceeds the rate of bottom subsidence, the reef structure is destroyed by waves. Modern coral reefs are growing at an average rate of 15 -20 mm per year.
Any of the mountains of the Sudak environs is interesting, picturesque in its own way and does not look 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 New World as well, giving the area a peculiar picturesqueness and special value.
For this reason, part of the Novosvetsky coast is protected and has the status of a landscape and botanical state reserve.
The Neotethys Sea in the Paleogene Epoch (40-26 million years ago)
The Tethys Ocean existed for about a billion years (850 to 5 million years ago)
Relic pine of Stankevich in the Novosvetsky botanical reserve
Our planet is not a monolith. On the contrary, it is distinguished by 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 even 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 section of the earth's crust
Not surprisingly, most of the earth's crust is relatively fresh. Geological processes are constantly changing 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 segment 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 Sea an area of \u200b\u200bthe earth's crust with an area slightly exceeding 150 thousand square kilometers, whose age, according to his calculations, reaches 340 million years. The scientist allows an error of 30 million years, but no more. According to the find, this section of the Mediterranean Sea was a witness to the same Pangea.
ancient ocean
In addition, this section of the seabed is older than other known segments by at least 70%, this includes the explored sections of the Indian and Atlantic Oceans. Grano even ventured to suggest that the segment of the earth's crust he had found could be part of the legendary Tethys, the ancient ocean of the Mesozoic period. Tethys washed two ancient supercontinents - Gondwana and Laurasia, which existed about 750-500 million years ago. If this is true, then the newly discovered site formed before Pangea formed. The scientific community believes that the Mediterranean, Black and Caspian Seas are the separated parts of the Tethys.
Long study
This popular theory was the reason that for two years Grano explored the bottom of the Mediterranean Sea with the help of sonars and magnetic sensors.
According to him, this part of the earth's crust has not been discovered so far because it was hidden under an almost 20-kilometer layer of bottom sediments.
Grano's research team lugged two sensors behind their boat that took magnetic data from the seafloor. Scientists hoped to find anomalies pointing to ancient magnetic rocks. The overall picture of the anomalies could indicate to geologists the presence of an ancient slab 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 a section of the bottom of the Mediterranean Sea, located between Turkey and Egypt, which is the oldest to date.
If this plate was part of the Tethys ocean floor, then the ocean was formed 50 million years earlier than geologists thought. However, Grano does not insist that the found site was part of the ancient Tethys. It is quite possible that this plate was part of another body of water, but ended up in the Mediterranean Sea due to those same geological processes. After all, 340 million years is a long time.
Even Leonardo da Vinci found fossilized shells of marine organisms on the tops 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 of the end of the last century, called this space the Tethys Sea (in honor of Thetis, or Tethys, the sea goddess).
A new turn in the idea of Tethys came at the beginning of this 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, closing 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 gap corresponds to the Tethys Sea, but its dimensions corresponded to those of the ocean, and one should have spoken of the Tethys Ocean. The conclusion was obvious: as the continents drifted, as Eurasia and Africa moved away from America, a new ocean opened up - the Atlantic and at the same time the old ocean - Tethys closed (Fig. 1). Therefore, the Tethys Sea is a vanished ocean.
This schematic picture, which emerged 70 years ago, has been confirmed and detailed in the last 20 years on the basis of a new geological concept that is now widely used in studying the structure and history of the Earth - lithospheric plate tectonics. Let us recall its main provisions.
The upper solid shell of the Earth, or the lithosphere, is divided by seismic belts (95% of earthquakes are concentrated in them) into large blocks or plates. They cover the continents and oceanic spaces (today there are 11 large plates in total). 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-ocean ridges - lithospheric plates diverge to the sides at a speed of 2 to 18 cm / year, making room for the uplift of basalts - volcanic rocks melted from the mantle. Basalts, solidifying, build up the divergent edges of the plates. The process of spreading the plates is called spreading. In other active zones - in deep-sea trenches - lithospheric plates approach each other, one of them "dives" under the other, going down to depths of 600-650 km. This process of submerging plates and absorbing them into the Earth's mantle is called subduction. Above the subduction zones, extended belts of active volcanoes of a specific composition (with a lower content of silica than in basalts) arise. The famous ring of fire of the Pacific Ocean is located strictly above the subduction zones. Catastrophic earthquakes recorded here are caused by the stresses necessary to pull the lithospheric plate down. Where plates approaching each other carry continents that are not capable of sinking into the mantle due to their lightness (or buoyancy), a collision of continents occurs 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 on the earth's sphere. It is not complicated and is based on L. Euler's theorem, according to which any movement along the sphere can be described as rotation around an axis passing through the center of the sphere and intersecting its surface at two points or poles. Therefore, in order to determine the movement of one lithospheric plate relative to another, it is sufficient 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 of directions (azimuths) and linear velocities of plate movements at specific points. As a result, for the first time, a quantitative factor was introduced into geology, and it began to move from a speculative and descriptive science into the category of exact sciences.
The above remarks are necessary in order for the reader to further understand 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 A.I. P. P. Shirshov Academy of Sciences of the USSR. Corresponding members of the USSR Academy of Sciences A. S. Monin and A. P. Lisitsyn, V. G. Kazmin, I. M. Sborshchikov, L. A. Savostii, O. G. Sorokhtin and the author of this article took part in the research. Employees of other academic institutions 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. Tvalchrelidze, Sh. and M. I. Satian), Faculty of Geology, Moscow State University (Academician of the Academy of Sciences of the USSR V.: E. Khain, N. V. Koronovsky, N. A. Bozhko and O. A. | Mazarovich).
From the French side, the project was headed by one of the founders of the theory of plate tectonics, K. Le Pichon (University named after Pierre and Marie Curie in Paris). Experts in the geological structure and tectonics of the Tethys belt took part in the research: J. Derkur, L.-E. Ricou, J. Le Priviere and J. Jeyssan (University named after Pierre and Marie Curie), J.-C. Cibuet (Center for Oceanographic Research in Brest), M. Westphal and J.P. Lauer (University of Strasbourg), J. Boulin (University of Marseille), B. Bijou-Duval (State Oil Company).
The research included joint expeditions to the Alps and the 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 summed up in a special issue of the international journal "Tectonophysics" in 1986. An abbreviated version of the report on published in French in 1985 in the Bulletin societe de France, in Russian was published The History of the Tethys Ocean.
The Soviet-French project "Tethys" was not the first attempt to restore the history of this ocean. It differed from the previous ones in the use of new, better-quality data, in the significantly greater extent of the region under study - from Gibraltar to the Pamirs (and not from Gibraltar to the Caucasus, as it was before), and most importantly, in the involvement and comparison of materials from various independent sources. 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 the mutual movements of the main lithospheric plates of the Earth. They are entirely related to plate tectonics. Penetrating into the depths of geological time and successively moving Eurasia and Africa closer to North America, we obtain the relative positions of Eurasia and Africa and reveal 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 plate mobilism and tectonics: in order to represent events, for example, in the Caucasus or in the Alps, it is necessary to know what happened thousands of kilometers from these areas in the Atlantic Ocean.
In the ocean, we can reliably determine the age of the basalt base. If we combine coeval bottom bands located symmetrically on opposite sides of the axis of the mid-ocean ridges, we will obtain the parameters of plate movement, that is, the coordinates of the pole of rotation and the angle of rotation. The procedure for searching for parameters for the best combination of coeval 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 a 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 for each moment of geological time as a rigid frame, 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 separated from the united North America and Eurasia, the so-called Laurasia. Prior to this split, the Tethys Ocean had a wedge-shaped outline, expanding with a bell to the east. Its width in the region of the Caucasus was 2500 km, and on the traverse of the Pamirs it was at least 4500 km. During this period, Africa shifted to the east relative to Laurasia, covering a total of about 2200 km. The second period, which began about 80 million years ago and continues to the present 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 converge with Eurasia, which ultimately led to the closure of the Tethys Ocean.
The directions and speeds of Africa's movement 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, allowing the young ocean basin between Africa and Eurasia to open up.
80 million years ago, in the western segment, Africa began to move northward, and in recent times it has been moving northwest with respect to Eurasia at a rate of about 1 cm/year. In full accordance with this are folded deformations and the growth of mountains in the Alps, Carpathians, Apennines. In the eastern segment (in the region of the Caucasus), Africa began to approach Eurasia 140 million years ago, and the rate of approach fluctuated noticeably. Accelerated approach (2.5-3 cm/year) refers to the intervals 110-80 and 54-35 million years ago. It was during 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 deep-water basins of the Black Sea were formed. The minimum approach rate (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 fact that the Red Sea began to open, the Arabian Peninsula broke away from Africa and began to move north, pressing its protrusion into the edge of Eurasia. It is no coincidence that the mountain ranges of the Caucasus grew on the top of the Arabian ledge. The paleomagnetic data used in the reconstruction of the Tethys Ocean are based on 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 layers of later magnetization and establish what the primary magnetic vector was. It should be directed to the paleomagnetic pole. If the continents do not drift, then all vectors will be oriented in the same way.
Back in the 50s of our century, it was firmly established that within each individual continent, paleomagnetic vectors are indeed oriented in 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 orientation of the vectors, that is, the continents have different paleomagnetic poles. This alone has given rise to 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: near Eurasia - 71 ° N. w „ 150 ° in. d. (region of Chukotka), near Africa - 60 ° N. latitude, 108° W (region of Central Canada), near North America - 70 ° N. latitude, 132° E (the area of the mouth of the Lena). If we take the parameters of plate rotation relative to each other and, say, move the paleomagnetic poles of Africa and North America together with these continents to Eurasia, then a striking coincidence of these poles will be revealed. Accordingly, the paleomagnetic vectors of all three continents will be oriented subparallel and directed to one point - a common paleomagnetic pole. This kind of comparison of kinematic and paleomagnetic data was made for all time intervals from 190 million years ago 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 - bordered the Tethys Ocean. However, there were undoubtedly smaller continental or other blocks inside the ocean, as now, for example, inside the Indian Ocean there is a 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 bridge between them), the Daralagez (South Armenian) block, the Rhodope massif in the Balkans, the Apulia 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 appears to be of southern origin and was previously annexed to Gondwana. The Apulian massif did not shift much in latitude relative to Africa and Eurasia, but in the Cenozoic it was rotated 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 hundred and fifty years. This group of data is also the most controversial, since it can be least of all applied to a quantitative approach. At the same time, geological data in many cases are decisive: it is 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 have made it possible to establish a number of essential features of the Tethys paleoocean.
Let's start with the fact that it was only by the distribution of marine Mesozoic (and Cenozoic) deposits in the Alpine-Himalayan belt that the existence of the Tethys sea or ocean in the past became obvious. Tracing different geological complexes over 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 at their edges. Of key importance are the outcrops of rocks of the so-called ophiolite complex (from the Greek ocpir - a snake, some of these rocks are called serpentines). Ophiolites consist of heavy rocks of mantle origin, depleted in silica and rich in magnesium and iron: peridotites, gabbro and basalts. Such rocks form the bedrock of modern oceans. Given this, 20 years ago, geologists came to the conclusion that ophiolites are the remains of the crust of ancient oceans.
Ophiolites of the Alpine-Himalayan belt mark the bed of the Tethys Ocean. 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 scales of ophiolites were found in the Dealer Alps in Yugoslavia and Albania, in the mountain ranges of Greece, including the famous Mount Olympus. The outcrops of ophiolites form an arc facing south between the Balkan Peninsula and Asia Minor, and then are 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 extend to the Zagros Range and into the mountains of Oman, where ophiolite plates are pushed over the shallow sediments of the margin of the Arabian Peninsula. 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 to the Hindu Kush, the Pamirs and the Himalayas. Ophiolites have different ages - from Jurassic to Cretaceous, but everywhere they are relics of the earth's crust of the Mesozoic Tethys Ocean. The width of the ophiolite zones is measured by several tens of kilometers, while the original width of the Tethys Ocean was several thousand kilometers. Consequently, during the approach of the continents, almost the entire oceanic crust of 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, suture of the Tethys separates two provinces that are sharply different in geological structure.
For example, among the Upper Paleozoic deposits accumulated 300-240 million years ago, north of the suture, continental sediments predominate, some of which was deposited in desert conditions; while to the south of the suture, thick strata of limestones, often reefs, are widespread, marking a vast shelf sea in the equator region. The change of Jurassic rocks is just as striking: detrital, often coal-bearing, deposits north of the seam again oppose limestone south of the seam. The seam separates, as geologists say, different facies (conditions for the formation of sediments): the Eurasian temperate climate from the Gondwanan equatorial climate. Crossing the ophiolite seam, we get, as it were, from one geological province to another. To the north of it we find large granite massifs surrounded by crystalline schists and a 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 occur consistently and without any signs of deformation and metamorphism . It is clear that the two margins of the Tethys Ocean - the Eurasian and the Gondwana - differed sharply 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 between the areas north and south of the ophiolite suture. To the north of it 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. The 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 almost indistinguishable from the lavas of modern island arc volcanoes and active margins that make up the ring of fire of the Pacific Ocean. Recall that the volcanism of the rim of the Pacific Ocean is associated with the subduction of the oceanic crust under the continent and is confined to the boundaries of the convergence of lithospheric plates. This means that in the Tethys belt, volcanism similar in composition marks the former boundary of convergence of plates, on which subduction of the oceanic crust took place. At the same time, south of the ophiolite suture, there are no coeval volcanic manifestations; throughout the Mesozoic era and during most of the Cenozoic era, shallow-water shelf sediments, mainly limestone, 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 boundary of the convergence of lithospheric plates, was, as geologists say, active. The southern, Gondwana margin, devoid of volcanism and occupied by a vast shelf, calmly passed into the deep basins of the Tethys Ocean and was passive. Geological data, and primarily materials on volcanism, make it possible, as we see, to restore the position of the former boundaries of the lithospheric plates and outline ancient subduction zones.
The above does not exhaust all the factual material that must be analyzed for the reconstruction of the disappeared Tethys Ocean, but I hope this is enough for the reader, especially far from geology, to understand the basis of the constructions made by Soviet and French scientists. As a result, color paleogeographic maps were compiled for nine moments of geological time from 190 to 10 million years ago. On these maps, according to kinematic data, the position of the main continental plates - the Eurasian and African (as parts of Gondwana) was restored, the position of the microcontinents inside the Tethys Ocean was determined, the boundary of the continental and oceanic crust was outlined, the distribution of land and sea was shown, and paleolatitudes were calculated (from paleomagnetic data)4 . Particular attention is paid to the reconstruction of the boundaries of lithospheric plates - spreading zones and subduction zones. The displacement vectors of the main plates are also calculated for each moment of time. On fig. 4 shows diagrams compiled from color maps. To make clear the prehistory of Tethys, they also added a diagram of the location of continental plates at the end of the Paleozoic (Late Permian era, 250 million years ago).
In the Late Paleozoic (see Fig. 4, a), the Paleo-Tethys ocean extended between Eurasia and Gondwana. Already at that time, the main trend of tectonic history was determined - the existence of an active margin in the north of the Paleo-Tethys and a passive one in the south. From the passive margin at the beginning of the Permian, relatively large continental masses were split off - Iranian, Afghan, Pamir, which began to move, crossing the Paleo-Tethys, to the north, to the active Eurasian margin. The Paleo-Tethys oceanic bed in the front of drifting microcontinents was gradually absorbed in the subduction zone near the Eurasian margin, and in the rear of the microcontinents, between them and the Gondwana passive margin, a new ocean opened - the Mesozoic Tethys proper, or Neo-Tethys.
In the Early Jurassic (see Fig. 4b), the Iranian microcotinent joined the Eurasian margin. When they collided, a folded zone arose (the so-called Cimmerian folding). In the Late Jurassic, 155 million years ago, the opposition of the Eurasian active and Gondwana passive margins was clearly marked. 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 distribution of Mesozoic ophiolites made it possible to mark the 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 Gondwana that had disintegrated by that time - moved towards Eurasia in such a way that in the west of the Tethys the continents parted somewhat and a new ocean basin arose there, while in the eastern part of the continents they converged and the bed of the Tethys ocean 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 the Tethys (it is sometimes called the Mesogea, and its remains are the modern deep-water basins of the Eastern Mediterranean) ceased to open up, and in the east of the Tethys, judging by the dating of the ophiolites of Cyprus and Oman , the active stage of spreading was completed. In general, the width of the eastern part of the Tethys Ocean decreased to 1500 km by the middle of the Cretaceous at the traverse of the Caucasus.
By the Late Cretaceous, 80 million years ago, there was a rapid reduction in the size of the Tethys Ocean: the width of the strip with 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 sheets.
At the turn of the Cretaceous and Paleogene (see Fig. 4, e), at least three important events took place. First, ophiolite plates, torn off the oceanic crust of Tethys, were pushed over the passive margin of Africa by a wide front.
