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GLACIATION CENTER - district of the largest clusters and the greatest power. ice from where it spreads. Usually C. about. associated with elevated, often mountainous centers. So, C. o. Fennoscandinavian ice sheet were Scandinavian. On the territory of S. Sweden reached a power. at least 2-2.5 km. From here it spread across the Russian Plain for several thousand kilometers to the Dnepropetrovsk region. During the Pleistocene glacial epochs, many central lakes existed on all continents, for example, in Europe - the Alpine, Pyrenean, Caucasian, Ural, and Novaya Zemlya; in Asia - Taimyr. Putoransky, Verkhoyansky and others.

Geological dictionary: in 2 volumes. - M.: Nedra. Edited by K. N. Paffengolts et al.. 1978 .

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Karakorum (Turk. - black stone mountains), a mountain system in Central Asia. It is located between Kunlun in the north and Gandishishan in the south. The length is about 500 km, along with the eastern continuation of K. - the Changchenmo and Pangong ridges, passing into the Tibetan ... ... Great Soviet Encyclopedia

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Accumulations of ice that slowly move across the earth's surface. In some cases, ice movement stops and dead ice forms. Many glaciers advance some distance into the oceans or large lakes, and then form a front ... ... Geographic Encyclopedia

Mikhail Grigoryevich Grosvald Date of birth: October 5, 1921 (1921 10 05) Place of birth: Grozny, Gorskaya ASSR Date of death: December 16, 2007 (2007 12 16) ... Wikipedia

They embrace in the life of the Earth the interval of time from the end of the Tertiary period to the moment we are experiencing. Most scientists divide the Ch. period into two epochs: the oldest glacial, deluvial, Pleistocene or post-Pliocene, and the latest, which include ... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron

Kunlun- Scheme of the Kunlun ranges. Rivers are marked with blue numbers: 1 Yarkand, 2 Karakash, 3 Yurunkash, 4 Keriya, 5 Karamuran, 6 Cherchen, 7 Huanghe. The ridges are marked with pink numbers, see Table 1 Kunlun, (Kuen Lun) one of the largest mountain systems in Asia, ... ... Tourist Encyclopedia

Altai (republic) The Republic of Altai is a republic of Russian Federation(see Russia), located in the south Western Siberia. The area of ​​the republic is 92.6 thousand square meters. km, the population is 205.6 thousand people, 26% of the population lives in cities (2001). AT … Geographic Encyclopedia

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Katunsky ridge- Katunskiye Belki Geography The ridge is located at the southern borders of the Altai Republic. This is the highest ridge of Altai, the central part of which does not fall below 4000 m for 15 kilometers, and the average height varies around 3200-3500 meters above … Tourist Encyclopedia

residents of Europe and North America it is hard to imagine that only 200-14 thousand years ago (from a geological point of view - quite recently) powerful ice sheets, similar to the Antarctic ones, repeatedly covered vast territories. Separate lobes of ice sheets descended in Eastern Europe to 49°N. sh., and in North America - up to 38 ° N. sh. In place of Moscow or Chicago, there were glaciers up to 1–3 km thick. Not surprisingly, in the middle of the nineteenth century. the discovery of traces of these glaciations dating back to the late Quaternary era and to the time of the appearance modern man became a great scientific sensation. Some researchers considered that these glaciations were the first episodes of the process of general freezing of the Earth, declared by the Kant-Laplace theory. Others doubted that boulder loams, thought to be glacial, were actually deposited by glaciers. However, a detailed study of these deposits and their comparison with deposits of modern glaciers confirmed the glacial genesis of boulder loams (moraines) that covered the northern parts of Europe and North America. A set of diagnostic criteria has been identified that make it possible to distinguish fossil moraines (tillites) from outwardly similar non-glacial deposits. The most important signs of tillites are (erratic) boulders brought from afar, faceted and hatched by glaciers; striated or crumpled into complex folds of the rock bed of glaciers (glaciodislocations); frost wedges and polygonal soils; stones melted from icebergs (dropstones), fragments of moraines, etc.

In the second half of the XIX century. and at the beginning of the 20th century. traces of much older glaciations were discovered: the Late Paleozoic (now dated in the range of 300–250 million years ago) and then the Precambrian (750–550 and 2400–2200 million years ago). These discoveries refuted the Kant-Laplace theory of gradual cooling (up to Quaternary glaciation) of the originally hot Earth. In the XX and early XIX centuries, glaciations were identified and studied in the Lower Paleozoic (about 450 million years ago) and the most ancient - in the late Archean (about 2900 million years ago). The causes, nature and consequences of glaciations have become a popular subject of scientific discussions and forecasts.

The great interest in glaciations in the Earth sciences is not accidental. Climate is an important factor in the evolution of the outer shells of our planet, especially the biosphere. It determines its thermodynamic state by regulating internal and, in part, external heat and mass transfer. Glaciations are one of the most extreme climatic events. They are associated with many catastrophic changes on Earth, which caused dramatic rapid quantitative and qualitative changes in the biosphere and biota of the planet.

History of glaciations

Conducted in the second half of the twentieth century. and the beginning of the XXI century. intensive geological research on all continents, as well as the achievements of radioisotope, paleontological and chemostratigraphic methods for determining the age of rocks, made it possible to significantly detail the history and distribution areas of ancient glaciations on Earth. Over the past 3 billion geological history there was an alternation of long intervals with frequent glaciations (glacioer) and intervals in which there are no traces of them (thermoer) [ , ]. Glacioera consist of alternating glacial periods (glacio periods), and glacial periods, in turn, consist of glacial and interglacial epochs (Fig. 1). Some researchers refer to glacial eras as glacial ( icehouses), and thermoeras - greenhouse ( greenhouses) cycles , or cold and warm climatic modes .

To date, five glacial eras and four thermal eras separating them have been established in the visible geological history.

Kaapval glacioera(about 2950–2900 Ma). Its traces were found in the upper Archean of South Africa, on the Kaapvaal craton. They are recorded in the Governmentment subgroup in the Witwatersrand trough and in the Mozaan group in the Pongola trough. The Governmentment subgroup of the Coronation Formation describes two horizons of tillites about 30 m thick, separated by a sandstone and shale sequence about 180 m thick. The tillites contain scattered faceted and hatched stones. Their age lies within 2914–2970 Ma. To the east, in the upper part of the Mozaan Group, in the Odvaleni Formation, four layers of tillites with a thickness of 20 to 80 m are observed. They contain stones of various sizes, roundness and composition. Some of them bear characteristic traces of glacial abrasion, and dropstones scattered in shales are surrounded by syngenetic deformations such as surge structures.

Late Archean thermoera(2900–2400 million years ago). No glacial deposits have yet been found in this interval of geological history, which allows us to conditionally consider it as a thermoera.

Huronian glacioera(2400–2200 million years ago). Traces of glaciation of this time are known in the south of Canada, on the northern coast of Lake. Huron. There, in the middle part of the Huron supergroup, there are three glacial formations (from bottom to top): Ramsay Lake, Bruce and Gauganda. They are separated by thick non-glacial deposits. The Huron glacial complex is younger than 2450 Ma and older than 2220 Ma. In Wyoming, 2000 km southwest of Lake. Huron, glacial deposits close to Huron, are known in the Snow Pass supergroup. Probably, analogues of the Huronian tillites are also present in the Shibugamo region, to the northeast of the lake. Huron and west of Hudson Bay. The wide distribution of 2200–2450 Ma glacial deposits in North America indicates that at the beginning of the Early Proterozoic, a significant part of the ancient Archean core of this continent was repeatedly subjected to ice sheets.

In Europe, deposits similar to glacial deposits are known in the upper part of the Sariolian series, which overlies the Archean Karelo-Finnish massif of the Baltic Shield. Their age is estimated at 2300–2430 Ma.

In Africa, in the Griqualand trough, the McGanyene glacial formation (previously called the Griquatown Tillites) is described younger than 2415 Ma and older than 2220 Ma. It is composed of coarsely bedded tillites up to 500 m thick, which contain erratic and glacier-cut stones. An ice bed is observed at the base of the tillites. Analogues of the Makganyene formation are also found in the Transvaal trough.

In Western Australia, glacial deposits of Meteorite Bore are common. Their age lies in the range of 2200–2450 Ma.

Thus, in the period between 2400 and 2200 million years ago, large glaciations repeatedly occurred on the four modern continents of the Earth, often of a cover character. This is evidenced not only by the wide distribution of glacial rocks, but also by the presence of marine-glacial (iceberg) deposits. The correlation of the Early Proterozoic glacial horizons is difficult, and it is still difficult to establish the exact number of glaciations in the Early Proterozoic and their rank. It is assumed that at least three ice ages existed in the Huronian glacioera, and in each of them there are traces of several subordinate discrete events that can be qualified as ice ages.

Great Ice Break. Following the Huronian glacioera, a long thermoera began. It lasted almost 1450 million years (2200–750 million years ago). Significant warming on Earth occurred immediately after the end of the Huronian glacioera. Even in those areas where traces of glaciation were recorded, the climate quickly changed to warm and arid. In a number of regions, carbonate, often red-colored and stromatolite deposits began to accumulate with numerous inclusions of pseudomorphs after gypsum, anhydrite, and rock salt. In Australia, Russia (Karelia), and the United States, similar rocks have been found in deposits aged 2100–2250 Ma. In Karelia, red-colored carbonate rocks and crusts such as caliche, calcrete and silcrete, characteristic of a hot climate, appear, as well as voids from the leaching of gypsum crystals. Above, in the Tulomozero suite, about 2100 Ma old, a rock salt stratum 194 m thick was recovered by a borehole. It is overlain by a 300 m anhydrite and magnesite member. Numerous traces of arid sedimentation are also recorded in younger Proterozoic deposits, up to the middle of the Upper Riphean (about 770 Ma).

Publications about traces of glaciation during the Great Glacial Pause are rare and raise doubts, since they do not contain typical, and even more so, direct signs of glacial rocks and have a purely local distribution.

African glacioera(750–540 million years ago). Its deposits have been preserved in many regions of the Earth, but are especially well represented in Africa. They have been studied in sufficient detail, which makes it possible to distinguish six glacial periods in its composition.

Glacioperiod Kaigas. The first glaciation of the African glacioera - Kaigas - occurred about 754 million years ago in South Africa. Somewhat later, 746 million years ago, the Chuos glaciation began. These two glacial episodes close in age and location should, apparently, be included in one glacial period, leaving behind the traditional name Kaigas. Its rocks are represented by marine-glacial and glacial fluvial (fluvioglacial) deposits, in which iron ore horizons occur in places. It was assumed that the Kaigas glaciation had a regional character. However, now traces of approximately the same age glaciation have also been established in Central Africa (the Great Katanga Conglomerate, 735–765 Ma). A significant area of ​​distribution and the presence of marino-glacial deposits suggests that the glaciers of this period were not local, but advanced in a wide front onto the continental shelf.

In Brazil, carbonate deposits at the base of the Bambui Series have been dated to 740 Ma, and the underlying glacial deposits of the Macaubas Formation can also be attributed to the Kaigas glacio period.

Glacioperiod Rapiten consists of deposits of the Rapiten groups in the Mackenzie (Canada) and Ghubrah (Oman) mountains, the lower tillite of the Pocatello Formation (USA, Idaho) and, possibly, also the Chucheng-Changan Formation (South China), formed 723–710 Ma ago. Large deposits of iron ore are associated with the deposits of this glacial period in Canada and some other regions.

Glacioperiod Sturt represented by the Yudnamontana subseries in South Australia. It distinguishes at least two glacial episodes. The first one is associated with Tillit Pualko, separated from the second Vilierpa glacial episode by an unconformity and a sequence of terrigenous, sometimes iron ore rocks and a dolomite unit. In Australia, the Sturtian deposits are directly overlain by 660 Ma dolomites and black shales. Marino-glacial deposits have survived from the Sturtov glaciations, which testify to their integumentary character. It is possible that some of the insufficiently studied rocks of the Ballaganakh Series of the Patom Highlands, similar to glacial deposits, also belong to this glacial period. In Kyrgyzstan, very large deposits of iron ores are associated with it.

Glacioperiod Marino includes a group of glaciations that occurred about 640–630 Ma ago (at the beginning of the Vendian system). In the type section of South Australia, it is represented by the Ierelina subseries, the structure of which indicates a threefold change in glacial and interglacial settings in the open basin. The Marino glaciation period began and ended gradually - with ice rafting, as evidenced by shales containing scattered pebbles. The assumption that the Marino glaciation began almost suddenly (about 650 million years ago), was continuous and ended abruptly (635 million years ago) is unfounded. This conclusion is based on hypothetical ideas about continuous total glaciation of the Earth, covering all continents and oceans (hypothesis snowball Earth). This hypothesis contradicts the nature of the type sections Marino, Sturt, Rapiten and other deposits comparable to them, as well as evidence of the conservation of the general water exchange cycle on Earth at that time.

Glacial deposits of the Marino glaciation period are known in many regions of the Earth: in the Patom Highlands (Fig. 2) and the Aldan Shield (Fig. 3) of Central Siberia, in Kyrgyzstan, China, Oman, the Mackenzie Mountains in Canada, in North Africa and South America. Several episodes are distinguished in their sections, which can be considered as glacial epochs.

Glacio period of Gasquier. Its glacial deposits aged 584–582 Ma have been established on the Newfoundland Peninsula. In North America, their likely counterparts are the deposits of the Squantum and Fakir formations.

In the Middle Urals, for glacial formations that correlate with the Gasquier deposits, an age range of 567–598 Ma has been determined. Some other glacial strata are attributed to this glacioperiod based on distant stratigraphic correlations (Mortensnes formation in northern Norway, etc.) or completely unproven, only according to their stratigraphic position in sections located above the Marino deposits (for example, the Halkanchoug and Lochuan formations in China and Sera Azul in Brazil). In fact, as will be shown below, many of them belong to the younger Baikonur glaciohorizon.

Glacio period Baikonur. This glaciation took place immediately before the Nemakit-Daldynian, which ended the Vendian period of the Late Precambrian (547–542 Ma). Its deposits include the Baikonur Formation of Central Asia, the basal part of the Zabit Formation of the East Sayan, the Khankalchog Formation of the Kurugtag Ridge, Hongtiegou Tsaidam, the Zhengmuguang Formation of the Helan Shan Mountains, Lochuan, and its analogues in China. The tillites of the Precambrian massifs can also be attributed to the Baikonur glaciation period. Central Europe(younger than 570 and older than 540 Ma), the Purple de Ahnet Ahaggara Triad (535–560 Ma), the Wingerbrick Subformation (545–595 Ma), and the lower part of the Nomtsas Formation of the Nama Group of Namibia (539–543 Ma).

The main glacial episode of this glaciation period occurred near the lower boundary of the Nemakit-Daldynian, about 542 Ma ago. Its significance is emphasized by the stratigraphic break and large negative excursion of δ 13 С at the base of the Nemakit-Daldynian deposits. The Baikonur episode proper and, probably, the Nomtsas glaciation in Namibia, which is close in age, was preceded by the Wingerbrik glacial episode (545 Ma), as well as the recently described Hongtiegou episode in Tsaidam. Fossils found below and above the Hongtiegou Formation testify to the proximity of its age to the middle part of the Vendian.

Early Paleozoic thermoera(540–440 million years ago). During the Cambrian and most of the Ordovician, no traces of glaciation have been found. This time interval, despite the fact that large massifs of the Gondwana land were located in high southern latitudes, was characterized by numerous signs of a warm and arid climate. At that time, carbonate deposits (including reefs) and salt basins were widespread. Often there were red-colored carbonate rocks and kaolinite clays. Then (with the exception of the Cambrian) the faunistic diversity of the marine biota grew rapidly, especially in the Middle Ordovician and early Late. This time is often referred to as the Great Ordovician biodiversification event. Thus, the segment of geological history from the beginning of the Cambrian to the beginning of the Late Ordovician is considered a thermoera, which lasted about 100 million years.

Gondwanan glacioera(440–260 million years ago). Glaciation data is mainly associated with the Gondwanan megacontinent. Five glacial periods are distinguished here.

Early Paleozoic glacioperiod. The first relatively small glaciations in the Early Paleozoic apparently occurred at the beginning or middle of the Catian Age (Caradoc), and the last reliably established traces of glaciations of this glaciation period date back to the Late Nellandoverian - Early Venlockian time. Thus, the Early Paleozoic ice age lasted about 20 million years. It is divided into three glacial epochs: the initial - Catian, the main - Hirnantian and the final - Llandoverian-Wenlock.

Katian Glacio Epoch. Evidence that the Ordovician glaciations began as early as Caradoca has appeared repeatedly. In the east of North America (in Nova Scotia), near the top of the Halifax Formation, a member of metatillites with erratic, faceted, hatched, and iceberg stones is known. The overlying White Rock Formation contains some Caradocian or possibly somewhat younger fauna. A more confident age is established for the Gander Bay marinoglacial deposits of northeastern Newfoundland, which are directly overlain by the Caradocian graptolite schists. In southern Africa, in the Table Mountain group, two glacial horizons are known in the Packhuis Formation, the nature of which is confirmed by the presence of hatched and faceted stones, an ice bed, glaciodislocations, frost wedges and polygonal soils. Their age, most likely, is Katian. Fauna characteristic of the later Hirnantian was found in the sediments overlying the tillites. The older tillite Hangklin was found in the rocks underlying the Packhuis Formation. Based on rare fauna and indirectly, on the basis of sedimentation rate, its age is estimated as Caradokian. Some researchers believe that at least three glaciations occurred in the Catian Stage.

Hirnantian Glacio Epoch. During this epoch, the Early Paleozoic glaciation reached maximum dimensions(Fig. 4). Its nature and age are especially well established in North Africa and Arabia, the classical regions of its development. Here, in the most complete sections of the Hirnantian, at least five glacial episodes are recorded, the total duration of which is estimated at 1.4 ± 1.4 Ma. According to some estimates made from glacioeustatic fluctuations (fluctuations in the level of the world's oceans caused by the formation and melting of glaciers), the Hirnant cover covered all of Africa, Arabia, Turkey, as well as a large area of ​​central South America. In the foothills of the Andes, the Lower Paleozoic glacial deposits stretch in an almost continuous belt from Ecuador to Argentina. The fauna of the upper Hirnantium zone was found directly above the tillites.

Llandoverian-Wenlock glacial epoch. Lower Paleozoic glacial deposits are known in the Amazon Basin, in the middle part they contain early Llandoverian fauna (including graptolites). The upper part of this section should therefore be attributed to the Lower Silurian, starting from Llandovery. In the southwestern part of Bolivia and in a large area of ​​the adjacent regions of Peru and Argentina, the marino-glacial suite of Kancaniri (Tillites Zapla) is widespread. It is composed of massive, layered or gradation-layered tillites, which contain erratic and hatched stones and boulders up to 150 cm across. They contain Middle and Late Nlandoverian and Early Wenlock fossils.

Late Devonian - Early Carboniferous glacial period began at the end of the famenn. In the north of Brazil, in the Famennian and Lower Carboniferous, traces of three glacial episodes have been preserved. Traces of the Upper Famennian glaciation have also been found in the USA, in the northeast of the Appalachian belt.

Most researchers are inclined to believe that the Late Devonian - Early Carboniferous glaciations were mainly of a foothill character. However, the fact that basin and fluvioglacial facies are present in the sediments indicates the spread of glaciers to the plains and sometimes to the coasts. major basins, which is possible only with a very significant glaciation. This is also evidenced by glacial deposits of the Late Devonian - Early Carboniferous age in the north of Brazil, which accumulated in the vast platform basins of the middle latitudes.

Middle Carboniferous glacial period. Its deposits are distributed much more widely and are established in the western, eastern and northern parts of Gondwana. Judging by the well-studied sections of the eastern part of Australia, which are dated by radioisotope and biostratigraphic methods, the Middle Carboniferous Ice Age began in the middle of the Serpukhovian and ended at the end of the Moscow. Four episodes are set here. The duration of each of them is from 1 to 5 million years. The episodes are separated by intervals of approximately 2–3 Ma, in which there are no traces of glaciations. All these episodes can be qualified as glacial and interglacial epochs.

Early Permian glacial period - maximum in the Gondwanan glacioera. It began, apparently, at the end of the Gzhel century, and ended at the beginning of the Artinsk. It has two glacial episodes. Outside of Australia, deposits of the Early Permian Ice Age are distributed over a vast territory - from the western to the eastern part of Gondwana (Fig. 5).

Late Permian glacial period completed the Gondwanan glacioera. Its deposits are of limited distribution. AT eastern regions Australia, it includes two glacial episodes. The first one, covering the end of the Kungurian and part of the Kazanian, is represented by distal iceberg glacial facies. The second one, covering the upper part of the Wardian Stage and the Capitanian Stage (the middle part of the Tatar Stage), is also composed of iceberg deposits. Late Permian glaciation also manifested itself in northeast Asia. In the Verkhoyansk folded zone, Upper Permian tilloids (tillite-like unsorted and unstratified coarse clastic rocks) are widespread. In a number of sections, they contain signs of glacial origin: dropstones, till pellets, faceted and hatched stones.

Mesozoic-Paleogene thermoera(250–35 million years ago). Long-term climatic perturbations of the Gondwanan glacioera gave way to a warm Mesozoic climate.

Global climate reconstructions based on a set of indicators have shown that all the high and middle latitudes of both hemispheres of the Earth in the Mesozoic were in temperate and warm humid climatic zones. Occasionally, seasonal ice has formed at high latitudes, as evidenced by the rare finds of dropstones. But, since both the territorial and stratigraphic distribution of ice was insignificant, it can be assumed that the average annual temperatures in high latitudes were significantly higher than now. An arid climate prevailed at low latitudes, and humid equatorial zones appeared only in the second half of the Cretaceous.

During the Mesozoic, quite significant rearrangements of climatic zonality sometimes occurred, but all these changes were limited to the area of ​​positive temperatures. No direct evidence of Mesozoic glaciations has been found, with the exception of one case in South Australia, where Tillit Livingston, up to 2 m thick, was found in a single outcrop of Berriasian-Valanginian rocks. Judging by the limited distribution, this is a purely local formation. Conglomerates, breccias, and unsorted pebble shales were sometimes classified as "possible tillites", and seasonal freezing of reservoirs and rivers was attributed to glacial conditions.

Despite the lack of direct evidence for the existence of Mesozoic glaciations, in last years a hypothesis arose cold snabs. It suggests repeated repetition in the Mesozoic of very short glacial episodes, which manifested themselves only in high latitudes and led to small polar glaciations, which accounted for about one third of modern polar caps.

This hypothesis is based entirely on circumstantial evidence. First, on rapid sea level fluctuations of the "second and third orders", which are attributed to a glacioeustatic nature, if they were accompanied by an increase in δ 18 O in sediments. However, a decrease in sea level of any origin due to an increase in the planet's albedo leads to some cooling and an increase in δ 18 O in precipitation.

Secondly, the presence of dropstones in some sediments of the Middle Jurassic and Cretaceous is considered to be a confirmation of this hypothesis. In the Mesozoic, they are distributed mainly in high paleolatitudes and have a different origin. Most often, stones are found and mentioned that are separated by seasonal ice. Now they regularly form in the seas, lakes and rivers of temperate climate zone, up to 45° N. sh. These latitudes are characterized by positive mean annual temperatures. There are no glaciations (with the exception of mountainous ones) there. In addition, dropstones may be of biogenic origin and should not serve as evidence of glaciations.

The third argument in favor of the hypothesis cold snabs- wide distribution in the Mesozoic deposits of glendonites - the White Sea flyer (CaCO 3 6H 2 O). However, now these formations are constantly found in the cold basins of high and middle latitudes. Their presence indicates a cold temperate climate, not a glaciation.

Except for the mentioned outcrop of tillites in Australia, no traces of Mesozoic glacial deposits have been found on any of the Earth's continents or on the islands of the Arctic. It is often assumed that the centers of glaciation are hidden under the modern Antarctic ice sheet. But such conclusions are not supported by detailed studies of fossil vegetation on the coast of Antarctica. For example, a study of the late Albian forest near the base of the Antarctic Peninsula showed that the forest there was of medium density, consisted mainly of year-round green broad-leaved conifers and resembled modern humid temperate forests of southern New Zealand.

The Mesozoic temperatures of deep waters in the southern high latitudes, obtained (by the δ 13 O-method) from benthic foraminifers, in the Jurassic and Cretaceous ranged from 5 to 11 around 4°C, several hundred meters thick). Recall that now the temperature of deep waters in the high southern latitudes is −1.5 - +0.5°С. These data indicate that Antarctica in the Mesozoic was not subjected to glaciation. This conclusion is consistent with the results of the most realistic computer models. The latter show that if any Mesozoic glaciations in Antarctica did occur, they were of a mountainous or very ephemeral nature.

It is even more controversial to assume the presence of Mesozoic ice sheets in the high latitudes of the Northern Hemisphere. Mesozoic deposits are widespread there, well studied and do not contain any traces of glacial deposits. However, based on the hypothesis cold snabs, some authors, relying only on abstract geochemical and climatic modeling, have compiled a paleoclimatic reconstruction for the Middle-Upper Jurassic boundary interval of the Northern Hemisphere. They reconstructed a huge ice sheet only slightly smaller than Antarctica. Its thickness exceeded 5 km and it stretched for 4000 km - from Chukotka to the western edge of the Siberian platform. The proposed shield should have left traces of its existence in many large troughs filled with continental and marine Jurassic deposits (including deposits of the middle and upper parts of the Jurassic system). However, no traces of Jurassic glacial deposits have been found there so far. In some sections, glendonites and rare fragments are found - traces of drift by seasonal ice. This is not surprising. According to paleomagnetic data, the region was located at that time in high polar latitudes. The reconstruction of a huge ice sheet in northeast Asia is also refuted by geological facts. The results of the mentioned simulation are completely absurd. Its authors were guided exclusively by abstract considerations and calculations, completely ignoring the available geological data. This approach is an example of turning a valuable method of paleoclimatic reconstructions into computer games. Unfortunately, it significantly discredits paleoclimate modeling methods in general.

Antarctic Glacioera(35 million years ago - now), in which we live, began in the late Cenozoic. Its history and, of course, the history of the current Quaternary period have been intensively studied over the past decades. A huge literature is devoted to this topic [,]. Here we restrict ourselves to a brief enumeration of the main events of the Antarctic glacioera.

At the beginning of the Cenozoic, in the Paleocene and Eocene, the climate of the Earth (as in the Mesozoic) remained ice-free. The end of the Paleocene and the beginning of the Eocene were especially warm. In this interval, several temperature maxima were noted on the Earth. Early and middle Eocene optima stand out among them. In the second half of the Eocene, cooling began, and the first traces of ice or glacial rafting appeared in the Southern Ocean. At the same time, seasonal ice rafting in the Arctic increased. Apparently, in the highlands of Antarctica at that time, mountain glaciers were born, the tongues of which in places (for example, in the Pryudos Bay) reached the sea. A continental ice sheet commensurate with the modern one formed in East Antarctica at the very beginning of the Oligocene, about 34 million years ago. Soon the glaciers reached the edge of the shelf. At the very end of the Oligocene and the beginning of the Miocene, some warming occurred, accompanied by significant fluctuations in climate and the volume of the ice sheet. Simulations have shown that the volume of the East Antarctic Ice Sheet at that time was sometimes reduced to 25% of its present size. Most likely, then the Rhone and Ross ice shelves arose. In the late Miocene, a strong cooling again occurred. The ice sheet has again reached continental dimensions. A short-term warming, similar to the modern one, occurred in the Middle Pliocene 3.3–3.15 million years ago. It may have been associated with the almost complete disappearance of the West Antarctic Shield.

The late Pliocene and Quaternary period were characterized by rapid progressive cooling. At the same time, continental glaciation began in the Northern Hemisphere. Ice sheets 2.74–2.54 million years ago arose in northern Eurasia and Alaska. The seasonal ice rafting of terrigenous material in the Arctic Ocean has intensified. This cooling led to the growth of the ice sheet of Antarctica, which 20–11 thousand years ago reached the edge of the shelf and the continental slope of the mainland. During the glacial maxima, the glaciers of Eurasia and North America extended to the middle latitudes.

In general, during the late Cenozoic, three main glacial maxima can be identified: in the Oligocene, at the end of the Miocene, and at the end of the Pliocene - Quaternary. Perhaps they should be considered as separate glacial glacial periods.

All glacial events of the Late Cenozoic both in Antarctica and in the Northern Hemisphere were complicated by a whole spectrum of shorter quasi-periodic climatic fluctuations of different amplitudes and signs. They are sometimes (very conditionally) referred to as glacial and interglacial. Judging by the periodicity, solar insolation fluctuations became the cause of glacial oscillations. The latter were due to the superimposition of oscillations of different duration associated with variations in the eccentricity of the Earth's orbit, the angle of inclination of the Earth's axis and its precession. In sum, these variations gave a complex picture with groups of cycles prevailing in amplitude in the intervals of 19–24 kyr (precessional), 39–41 kyr (due to the tilt of the Earth’s axis), 95–131, and 405 kyr (orbital). The shortest of these cycles (approximately corresponding to the Milankovitch cycles) determined the alternation in the late Pliocene and Pleistocene of glacial and interglacial periods. In the deposits drilled on the Ross Ice Shelf, in the last 4 million years, there are 32 glacial-interglacial cycles with an average duration of 125 thousand years. In Eastern Europe, 15 glacial episodes were recorded from the beginning of the Pleistocene to the beginning of the Holocene.

In the Miocene, climatic fluctuations of a predominantly precessional nature prevailed, with periods of 19–21 thousand years, and with the onset of glaciations in the Northern Hemisphere, fluctuations lasting 41 and 125 thousand years began to dominate, associated with changes in the tilt of the axis and orbit of the Earth.

General character of glaciations

The first thing that attracts attention when looking at Fig. 1, this is a distinct increase in the number and density of glaciations over the past 3 billion years. This fact can hardly be explained by the weaker knowledge of ancient deposits. In the second half of the 20th century, especially during the Cold War, in connection with the pursuit of strategic raw materials, geological mapping of almost all parts of our planet (even poorly developed countries and hard-to-reach regions) composed of ancient rocks was carried out. Subsequently, numerous deposits of various minerals were discovered in them. In such studies, it would be difficult to miss glacial deposits, which usually form large bodies, serve as stratigraphic markers, have a regional distribution, and also attract the attention of geologists with their extraordinary appearance and origin. In addition, an increase in the frequency of glaciations is also observed throughout the late Precambrian and the entire Phanerozoic, which has been studied in detail. It can be assumed that such an increase over time is associated with the weakening of mantle volcanism and the progressive development of the biosphere.

Glacioeras of different ages have a certain similarity. First, those glacioeras that can be dated are close to each other in duration (the Huronian is about 200 Ma, the African is 210 Ma, and the Gondwana is 190 Ma). Secondly, they are similar in structure. All glacial eras consist of 3–6 discrete ice ages lasting from several million to several tens of millions of years.

AT visible history The earth has at least 20 ice ages. All of them, in turn, consisted of discrete glacial events that can be qualified as ice ages. A detailed study of oxygen isotopes in the late Cenozoic and partially Paleozoic showed that glacial epochs were complicated by significant climatic fluctuations with periods from 400–500 thousand to 20 thousand years.

Glacioeras were similar not only in structure, but also in their general dynamics. They, as a rule, began with short regional ice ages, which, increasing in size and intensity, reached their maximum (usually intercontinental) scale in the second half of the glacioera, spreading to middle, and sometimes, possibly, to low latitudes. Then the glaciations rapidly degraded. The Pleistocene glaciation was apparently at its maximum in the late Cenozoic glacioera. It can be assumed that after the Holocene warming (if man does not intervene) a new small glaciation should come.

Between the Precambrian and Phanerozoic glaciations, there are not only similarities, but also certain differences. First, individual Precambrian glaciations were apparently more widespread than the most extensive Phanerozoic ones. Second, the Precambrian and Phanerozoic glaciations are associated with δ 13 C carb anomalies opposite in sign (negative in the Precambrian and positive in the Phanerozoic). Finally, many Neoproterozoic glaciations were replaced by the deposition of packs of characteristic thin-layered dolomites. These differences between the Precambrian and Phanerozoic glaciations are very important for clarifying the causes of their onset. However, a convincing explanation for these facts has not yet been found.

Possible causes of glaciations

The causes of glaciation are still the subject of numerous competing and mutually exclusive hypotheses that relate to a wide range of processes - from intergalactic to microbiotic. Now many researchers are inclined to think that glaciations were caused by the interaction of several geodynamic, geochemical and biotic processes. The Late Archean and Early Proterozoic glaciations are apparently associated with the appearance of phototrophic organisms and with the primary oxygenation of the atmosphere. In the Neoproterozoic and Phanerozoic, the leading cause of large climatic fluctuations (including the appearance of glacioera) were most likely geodynamic processes and the special nature of volcanism. Judging by the well-studied last segment of geological history, during the peaks of mantle-plume volcanism, the content of greenhouse gases in the atmosphere increased, which led to warming. Increased absorption of CO 2 by phototrophic organisms, followed by its burial in the form of coal, soils, carbonate and organic-rich silts, and, in addition, intensive absorption of CO 2 during the weathering of silicates, its removal to the ocean and carbon precipitation in the form of carbonates could also cause warming. Simultaneously, there was an increase in the oxygen content in the atmosphere and the oxidation of methane. These processes, which reduced the content of greenhouse gases in the atmosphere, led to cooling. If they coincided with the intense subsidence of the Earth's crust into the mantle in subduction zones and associated calc-alkaline explosive volcanism, then the Earth continued to cool as a result of additional removal of carbon from the biosphere and its burial in the mantle. Clogging of the stratosphere with the products of explosive volcanism reduced the transparency of the atmosphere. As a result of the superimposition of these processes, the thermal balance of the biosphere decreased and cooling and glaciation occurred. These main climatic cycles, determined by geodynamic processes and the nature of volcanism, were superimposed by the astronomical cycles mentioned above.

The role of glaciations in the biosphere

Climate has long been considered one of the engines of evolutionary processes. In particular, it was noted that the growth of biodiversity and the relative taxonomic stability of biota are associated with thermoeras, and, on the contrary, with glaciations, extinction and subsequent renewal of biota. However, the mechanisms for such updating have not been considered in detail. Modern data on glaciations allow us to draw some conclusions on this problem. The multi-stage hierarchy of glacial events (glacioera → glacio periods → glacio epochs → shorter oscillations of different frequencies) created a continuous series of biospheric crises. Climatic processes, characterized by high speed and different frequency, caused rearrangements of different scales in all subsystems of the biosphere (Fig. 6).

In the troposphere, glaciations caused a decrease in temperature, a reduction in moisture transfer, a restructuring and strengthening of circulation systems. During glaciations, the average temperature of the Earth decreased (by at least 5°C).

In the hydrosphere, ice shelves and perennial ice covers arose, the temperature and ocean level decreased. This led to the emergence of the psychosphere, temperature geochemical and gas stratification of water masses, and changes in the circulation system in the ocean. On the continents, the shelves and epicontinental basins were drained outside the glaciation zones, the character changed and the climatic, biogeographical and soil belts shifted, the basis of erosion decreased, the solid runoff from the land increased and the soluble runoff weakened. AT earth's crust repeated glacioeustatic and isostatic subsidence and uplift were noted.

Ecological and biotic crises associated with all these changes led to the extinction and migration of organisms. A certain number of species resistant to new conditions remained, and the emergence of new ones in crisis conditions slowed down. There was a kind of stagnation of the biota. At the same time, the release of a significant part of the old and the emergence of new ecological niches led to the diversification of the preserved organisms. Continuous and strong stresses during the cascade of ecological crises caused hypermutations in organisms and, as a result, the formation of new forms. The selection of resistant organisms from them led to the emergence of bionovations. The emergence of new forms and the diversification of forms that survived the crises, in turn, gave rise to irreversible ecological and more general biospheric changes. They contributed to the evolutionary processes in the biosphere in general and in the biota in particular. Thus, a close relationship arose between the rate of abiotic and biotic processes.

The wide distribution of cyanophytes and the primary oxygenation of the ocean and atmosphere began with the Huronian glacioera. During the early Proterozoic and most of the Riphean, evolutionary processes took place mainly at the molecular and cellular level. They ended in the Late Riphean with the mass eukaryotization of the biota, which became a prerequisite for the turbulent biospheric and biotic events of the African glacioera.

Due to the repeated repetition of glaciations of various scales and the associated environmental crises, the African glacioera was characterized by a number of evolutionary impulses that accelerated biological evolution generally. At that time, as a result of a series of glaciations, the formation of a new Phanerozoic biota and the biosphere of the Earth took place. Rare remains of annelidomorphs and armored amoebas appeared in the Upper Riphean section after the first three Neoproterozoic glaciations. Sediments covering the Vendian tillites of Nantou (a stratigraphic analogue of the Marino tillites) contain the first macroscopic algae, sponge biomarkers, and possibly metazoan embryos.

After the Gasquier glaciation, Vendian multicellular organisms flourished: large acanthomorphic acritarchs appeared, various multicellular algae(vendotenids, eocholinidae, etc.), animals of the Ediacaran type, and then bilaterians and the first animals with a carbonate (claudins) and agglutinated (sabellitids) skeleton. Following the Baikonur glaciation, a variety of small skeletal organisms arose - small-shell fauna.

Thus, after each glaciation of the African glacioera, the emergence of new groups of organisms, the flowering of some pre-existing ones, and the change of dominant ones are noted. As a result of these processes, at the end of the African glacioera, a biosphere of the Phanerozoic type was formed on Earth. The acceleration culminated in the unusually rapid development of multicellular non-skeletal and skeletal organisms in the non-Makitdaldyn Age of the Vendian and at the beginning of the Cambrian. It is no coincidence that the moment sharp acceleration of these processes, its extremum, coincided with the end of the last event of the African glacioera - the Baikonur glacioperiod. The acceleration of evolution during the African Glacioera is especially noticeable against the background of the long evolutionary processes that characterized the Great Glacial Pause.

The Gondwana glacioera was accompanied by a mass conquest of new ecological spaces by organisms: pelagials (graptolites, endoceratids, actinoceratoids, fish, pangolins, etc.), land (various plants, forests, amphibians, reptiles) and troposphere (flying insects). The Late Ordovician mass extinction was not a sudden and short-lived catastrophe, as it is usually presented. It was prepared by a series of previous glaciations and biotic events. The immediate impetus for extinction was the Great Hirnantian glaciation.

The main biotic event of the Antarctic glacioera was the formation of mankind. The rapid divergence of hominids took place in parallel with the main glaciations. The first representatives of the anthropoid suborder appeared in the Oligocene, and the first three species from the hominid family were found in the Upper Miocene, which was characterized by a sharp cooling. In deposits of an even colder Pliocene, 13 species of hominids have already been found, including the remains of Australopithecus. In the first half of the Pleistocene (about 2.4–1.9 million years ago), the first primitive species of the genus Homo appeared ( H. habiles etc.) and the simplest tools. The remains of H. heidelbergensis and traces of the systematic use of fire. At the end of the Pleistocene (about 0.2 million years ago, immediately before or during the Moscow-Dnieper glaciation), the species H. sapiens.

In conclusion, a few more words about the significance of glaciations. They played an important role in the development of the biosphere and biota of the Earth. Glacioera were critical intervals in the history of the biosphere, during which the processes of evolution accelerated and the formation of biospheres and biota of new types took place. In the Huronian glacioera and after, cyanobacteria became especially widespread, and the first oxygen appeared in the atmosphere. During the African glacioera, the biosphere and biota of the Phanerozoic type were formed. During the Gondwanan glacioera, terrestrial biota arose. Plants and animals have completely conquered the land. Of course, it is no coincidence that the formation of mankind occurred during the Antarctic glacioera.

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From the end of the Precambrian to the beginning of the Mesozoic, the Gondwana megacontinent united Africa, South America, India, Australia and Antarctica.

Recall that the expected several times lower increase in the average temperature of the Earth is regarded as a serious catastrophe for mankind.