What is the center of ancient glaciation? Glaciation of the earth

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It is difficult for residents of Europe and North America to imagine that only 200–14 thousand years ago (from a geological point of view, very recently) powerful ice sheets, similar to the Antarctic ones, repeatedly covered vast territories. Individual blades of ice sheets descended in Eastern Europe to 49° N. latitude, and in North America - up to 38° N. w. On the site of Moscow or Chicago there were glaciers up to 1–3 km thick. It is not surprising that in the middle of the nineteenth century. the discovery of traces of these glaciations, dating back to the late Quaternary era and the time of the appearance of modern man, became a great scientific sensation. Some researchers believed 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 the boulder loams, believed 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 the 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 externally similar non-glacial deposits. The most important features of tillites are (erratic) boulders brought from afar, faceted and streaked by glaciers; rocks of glacier beds streaked or crumpled into complex folds (glaciodislocations); frost wedges and polygonal soils; stones melted from icebergs (dropstones), fragments of moraines, etc.

In the second half of the 19th century. and at the beginning of the 20th century. Traces of significantly older glaciations were discovered: Late Paleozoic (now dated in the range of 300–250 million years ago) and then Precambrian (750–550 and 2400–2200 million years ago). These discoveries refuted the Kant-Laplace theory of the gradual cooling (up to Quaternary glaciation) of the initially hot Earth. In the 20th and early 19th 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 geosciences 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, regulating internal and partially external heat and mass transfer. Glaciations are some of the most extreme climate events. They are associated with many catastrophic changes on Earth, which caused dramatically 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 21st 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 last 3 billion years of geological history, there has been an alternation of long intervals with frequent glaciations (glaciers) and intervals in which there are no traces of them (thermoeras) [,]. Glaciers consist of alternating glacial periods (glacioperiods), and glacial periods, in turn, consist of glacial and interglacial epochs (Fig. 1). Some researchers call glacial eras glacial ( icehouses), and thermoeras are greenhouse ( greenhouses) cycles, or cold and warm climate modes.

To date, in observable geological history, five glacial eras and four thermoeras separating them have been established.

Kaapval Glacioera(about 2950–2900 million years ago). Its traces were found in the Upper Archean of South Africa, on the Kaapvaal craton. They are recorded in the Gaverment subgroup in the Witwatersrand trough and in the Mozaan group in the Pongola trough. The Governorment Subgroup of the Coronation Formation describes two horizons of tillites about 30 m thick, separated by a sequence of sandstones and shales about 180 m thick. The tillites contain scattered faceted and streaked stones. Their age ranges from 2914–2970 million years. To the east, in the upper part of the Mozaan Group, four layers of tillites ranging in thickness from 20 to 80 m are observed in the Odvaleni Formation. They contain stones of varying sizes, roundness and composition. Some of them bear characteristic traces of glacial abrasion, and the dropstones scattered in the shales are surrounded by syngenetic deformations such as splash structures.

Late Archean Thermal Era(2900–2400 million years ago). In this interval of geological history, no glacial deposits have yet been discovered, which allows us to conditionally consider it as a thermal era.

Huronian Glacioera(2400–2200 million years ago). Traces of glaciations 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, three glacial formations are established (from bottom to top): Ramsay Lake, Bruce and Gowganda. They are separated by thick non-glacial deposits. The Huronian Ice Complex is younger than 2450 million years old and older than 2220 million years. In the state of Wyoming, 2000 km southwest of the lake. Huron, glacial deposits similar to the Huronian, are known in the Snow Pass Supergroup. It is likely that analogues of the Huronian tillites are also present in the Shibugamo area, northeast of Lake. Huron and west of Hudson Bay. The widespread occurrence in North America of glacial deposits aged 2200–2450 Ma indicates that at the beginning of the Early Proterozoic, a significant part of the ancient Archean core of this continent was repeatedly subjected to glaciations.

In Europe, deposits similar to glacial ones are known in the upper part of the Sariolia series, which lies on the Archean Karelo-Finnish massif of the Baltic shield. Their age is estimated at 2300–2430 million years.

In Africa, in the Griqualand Trough, the Makganyene glacial formation (previously called the Griquatown Tillites) is described as younger than 2415 million years old and older than 2220 million years. It is composed of coarse-bedded tillites up to 500 m thick, which contain erratic and glacially processed stones. A glacial bed is observed at the base of the tillites. Analogues of the Makganyene formation are also found in the Transvaal trough.

Glacial deposits from Meteorite Bore are common in Western Australia. Their age lies in the range of 2200–2450 million years.

Thus, in the period between 2400 and 2200 million years ago, large glaciations, often of a cover nature, occurred repeatedly on the four modern continents of the Earth. 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 Early Proterozoic glacial horizons with each other is difficult, and it is still difficult to establish the exact number of glaciations in the Early Proterozoic and their rank. It is suggested that there were at least three ice ages in the Huronian Glacioera, and each of them contains traces of several subordinate discrete events that qualify as ice ages.

Great Ice Break. Following the Huronian glacioera, a long thermal era 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 glaciations 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 of gypsum, anhydrite, and rock salt. In Australia, Russia (Karelia) and the USA, similar rocks were found in sediments 2100–2250 million years old. 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. Higher up, in the Tulomozero Formation, about 2100 million years old, a well uncovered a rock salt layer 194 m thick. It is overlain by a three-hundred-meter-thick pack of anhydrites and magnesites. Numerous traces of arid sedimentation are also recorded in younger Proterozoic sediments, up to the middle of the Upper Riphean (about 770 million years).

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

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

Glacieriod Kaigas. The first glaciation of the African glacioera, the 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 ice age, leaving behind the traditional name Kaigas. Its rocks are represented by marine-glacial and glacial fluvial (fluvioglacial) deposits, in which iron ore horizons are found in places. It was assumed that the Kaigas glaciation was regional in nature. However, now traces of approximately coeval glaciation have been established in Central Africa (Great Katanga Conglomerate, 735–765 million years old). The significant distribution area and presence of marine-glacial deposits indicate that the glaciers of this period were not local, but advanced in a wide front onto the continental shelf.

In Brazil, carbonate sediments at the base of the Bambui Series are dated to 740 Ma, and the underlying glacial sediments of the Macaubas Formation can also be attributed to the Caigas glaciation period.

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

Glacieriod Sturt represented by the Yudnamontana subseries in South Australia. At least two glacial episodes are distinguished in it. The first is associated with the Tillite Pualko, separated from the second glacial episode of the Vilierpa by an unconformity and a sequence of terrigenous, sometimes iron-ore rocks and a dolomite member. In Australia, the Sturt deposits are directly overlain by 660 Ma dolomites and black shales. Marine-glacial deposits have been preserved from the Sturt glaciations, which indicate their cover nature. 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 glaciation period. In Kyrgyzstan, very large deposits of iron ore are associated with it.

Marino glaciation period includes a group of glaciations that occurred about 640–630 million years 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 - by 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 suddenly (635 million years ago) is unfounded. This conclusion is based on hypothetical ideas about continuous total glaciations of the Earth, covering all continents and oceans (hypothesis snowball earth). This hypothesis contradicts the nature of the type sections of Marino, Sturt, Rapiten and other comparable deposits, as well as evidence of the preservation of the general water cycle on Earth at that time.

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

Gasquier glaciation period. Its glacial deposits, 584–582 million years old, were found on the Newfoundland Peninsula. In North America, their probable analogues are the deposits of the Squantum and Fakir formations.

In the Middle Urals, the age interval of 567–598 million years has been determined for glacial formations that correlate with the Gaskier deposits. Some other glacial strata are attributed to this glaciperiod on the basis of distant stratigraphic correlations (Mortensnes Formation in northern Norway, etc.) or completely unsubstantiated, only by 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 glacial horizon.

Glacier period Baikonur. This glaciation occurred immediately before the Nemakit-Daldynian age, which completed the Vendian period of the late Precambrian (547–542 million years ago). Its deposits include the Baikonur Formation of Central Asia, the basal part of the Zabit Formation of the Eastern Sayan, the Khankalchoug Formation of the Kurugtag Range, Hongtiegou Tsaidam, Zhengmuguang of the Helan Shan Mountains, Lochuan and its analogues in China. The Baikonur glaciation period also includes tillites of the Precambrian massifs of Central Europe (younger than 570 and older than 540 Ma), the triad of the Purpur de Ahnet Ahaggar series (535–560 Ma), the Vingerbrick subformation (545–595 Ma) and the lower part of the Nomtsas formation of the group Nama of Namibia (539–543 Ma).

The main glacial episode of this glaciperiod occurred near the lower boundary of the Nemakit-Daldynian age, about 542 million years ago. Its significance is emphasized by the stratigraphic break and the large negative excursion of δ 13 C at the base of the Nemakit-Daldyn stage sediments. The Baikonur episode itself and the probably similar Nomtsas glaciation in Namibia were preceded by the Vingerbrick glacial episode (545 million years ago), as well as the recently described Hongtiegou episode in Tsaidam. Fossils found below and above the Hong Tiegou Formation indicate that its age is close to the Middle Vendian.

Early Paleozoic Thermal Era(540–440 million years ago). Throughout the Cambrian and most of the Ordovician, no traces of glaciations were found. This time interval, despite the fact that large tracts of Gondwanan landmass 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. Red-colored carbonate rocks and kaolinite clays were often encountered. Then (with the exception of the Cambrian) the faunal diversity of marine biota grew rapidly, especially in the Middle Ordovician and the beginning of the 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 to be a thermoera, which lasted about 100 million years.

Gondwanan Glacioera(440–260 million years ago). These glaciations are mainly associated with the Gondwana megacontinent. Five glacial periods are distinguished here.

Early Paleozoic glaciation period. The first relatively small glaciations in the Early Paleozoic apparently occurred at the beginning or middle of the Catian Age (Caradocian), and the last reliably established traces of glaciations of this glaciation period date back to the Late Landoverian - Early Wenlockian 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-Wenlockian.

Katian Glacioepoch. Evidence that the Ordovician glaciations began in the Caradocian has appeared repeatedly. In eastern North America (in Nova Scotia), near the top of the Halifax Formation, a member of metatillites with erratic, faceted, streaked and iceberg stones is known. The overlying White Rock Formation contains some Caradocian or perhaps somewhat younger fauna. A more confident age is established for the Gander Bay marine-glacial deposits of northeastern Newfoundland, which are directly overlain by the Caradocian graptolite shales. In southern Africa, in the Table Mountain group, two glacial horizons are known in the Pakhuis Formation, the nature of which is confirmed by the presence of streaked and faceted stones, an glacial bed, glacial dislocations, frost wedges and polygonal soils. Their age is most likely Katian. Fauna characteristic of the later Hirnantian is found in the sediments covering the tillites. The older Hangklin tillite was discovered in the rocks underlying the Pakhuis Formation. Its age, based on rare fauna and indirectly, based on the rate of sedimentation, is estimated as Caradocian. Some researchers believe that at least three glaciations occurred in the Catian Stage.

Hirnantian Glacioepoch. During this era, the Early Paleozoic glaciation reached its maximum extent (Fig. 4). Its nature and age are particularly well established in North Africa and Arabia, the classic areas of its development. Here, in the most complete Hirnantian sections, at least five glacial episodes are recorded, the total duration of which is estimated at 1.4 ± 1.4 million years. According to some estimates made from glacioeustatic fluctuations (fluctuations in sea level caused by the formation and melting of glaciers), the Hirnantian cover covered all of Africa, Arabia, Turkey, as well as a large area of ​​​​central South America. In the foothills of the Andes, Lower Paleozoic glacial deposits stretch in an almost continuous belt from Ecuador to Argentina. The fauna of the upper Hirnantian zone was discovered directly above the tillites.

Llandoverian-Wenlockian glacioepoch. 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 assigned to the Lower Silurian, beginning with Llandovery. In the southwestern part of Bolivia and in a large area of ​​​​adjacent regions of Peru and Argentina, the marine-glacial formation of Kankaniri (Tillites Zapla) is widespread. It is composed of massive, layered or gradation-layered tillites, which contain erratic and streaked stones and boulders up to 150 cm in diameter. Middle and Late Landoverian and Early Wenlockian fossils were found in them.

Late Devonian - Early Carboniferous glaciperiod began at the end of the Famennian. In northern Brazil, traces of three glacial episodes are preserved in the Famennian and Lower Carboniferous. Traces of the Upper Famennian glaciation were also 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 piedmont nature. However, the fact that basinal and fluvioglacial facies are present in the sediments indicates the spread of glaciers into the plains, and sometimes onto the coasts of large basins, which is possible only with very significant glaciation. This is also evidenced by glacial deposits of Late Devonian - Early Carboniferous age in the north of Brazil, which accumulated in vast platform basins of mid-latitudes.

Middle Carboniferous glaciation period. Its deposits are much more widespread and are found in the western, eastern and northern parts of Gondwana. Judging by well-studied sections of eastern 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 Moscovian. 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 million years, in which there are no traces of glaciations. All these episodes can be classified as glacial and interglacial epochs.

Early Permian glaciation period - maximum in the Gondwanan Glacioera. It apparently began at the end of the Gzhel century, and ended at the beginning of the Artinsky. It highlights two glacial episodes. Outside of Australia, deposits of the Early Permian Ice Age are distributed over a vast area - from the western to eastern parts of Gondwana (Fig. 5).

Late Permian glaciperiod ended the Gondwanan Glacioera. Its deposits are of limited distribution. In the eastern regions of Australia it includes two glacial episodes. The first, covering the end of the Kungurian and part of the Kazanian, is represented by distal iceberg glacial facies. The second, covering the upper part of the Wardian stage and the Capitanian stage (the middle part of the Tatarian stage), is also composed of iceberg deposits. The Late Permian glaciation also appeared in northeast Asia. In the Verkhoyansk folded zone, Upper Permian tilloids (tillite-like unsorted and non-layered 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 disturbances of the Gondwanan glaciation era gave way to the warm Mesozoic climate.

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

During the Mesozoic, quite significant changes in climatic zonation sometimes occurred, but all these changes were limited to the region of positive temperatures. No direct evidence of Mesozoic glaciations has been found, with the exception of one case in South Australia, where a Tillite Livingstone up to 2 m thick was found in a single outcrop of Berriasian-Valanginian rocks. Judging by its limited distribution, this is a purely local formation. Conglomerates, breccias, and unsorted pebble shales were sometimes considered “possible tillites,” and seasonal freezing of reservoirs and rivers was considered glacial conditions.

Despite the lack of direct evidence of the existence of Mesozoic glaciations, in recent years a hypothesis has emerged cold snabs. It suggests repeated repetitions of very short glacial episodes in the Mesozoic, which manifested themselves only at high latitudes and led to small polar glaciations, accounting for about one-third of the modern polar ice caps.

This hypothesis is entirely based on indirect evidence. Firstly, on rapid fluctuations in sea level 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 Middle Jurassic and Cretaceous deposits is considered to confirm this hypothesis. In the Mesozoic, they are distributed mainly in high paleolatitudes and have different origins. Most often encountered and mentioned are stones carried away by seasonal ice. Now they regularly form in the seas, lakes and rivers of the temperate climate zone, up to 45° N. w. These latitudes are characterized by positive average annual temperatures. There are no glaciations (except in the mountains) 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- widespread in Mesozoic deposits of glendonites - White Sea flyer (CaCO 3 6H 2 O). However, now these formations are constantly found in cold basins of high and middle latitudes. Their presence indicates a cold-temperate climate rather than glaciation.

Apart from the mentioned tillite outcrop in Australia, no traces of Mesozoic glacial deposits have been found on any of the Earth’s continents or on the Arctic islands. It is often assumed that the centers of glaciations are hidden under the modern Antarctic ice sheet. But such conclusions are not confirmed 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 primarily of year-round green broadleaf conifers, and was similar to modern moist temperate forests of southern New Zealand.

Mesozoic temperatures of deep waters in the southern high latitudes, obtained (δ 13 O-method) from benthic foraminifera, in the Jurassic and Cretaceous ranged from 5 to 11 ° C, which allows us to conclude that in the Mesozoic there was no psychrosphere (a layer of water on the ocean floor with a temperature about 4°C, several hundred meters thick). Let us recall that now the temperature of deep waters in high southern latitudes is −1.5 - +0.5°C. The data presented indicate that Antarctica was not subject to glaciations in the Mesozoic. This conclusion is consistent with the results of the most realistic computer models. The latter show that if any Mesozoic glaciations occurred in Antarctica, 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 there are widespread, 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, compiled a paleoclimatic reconstruction for the Middle-Upper Jurassic boundary interval of the Northern Hemisphere. They reconstructed a huge ice sheet, only slightly smaller in size than Antarctica. Its thickness exceeded 5 km and it stretched for 4000 km - from Chukotka to the western edge of the Siberian Platform. The supposed shield should have left traces of its existence in many large troughs filled with continental and marine Jurassic sediments (including sediments of the middle and upper sections of the Jurassic system). However, no traces of Jurassic glacial deposits have yet been discovered there. In some sections there are glendonites and rare fragments - traces of dispersal by seasonal ice. No wonder. According to paleomagnetic data, the region was located at high polar latitudes at that time. 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 reconstruction 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 will limit ourselves to only a brief listing of the main events of the Antarctic glacioera.

At the beginning of the Cenozoic, in the Paleocene and Eocene, the Earth's climate (as in the Mesozoic) remained ice-free. The end of the Paleocene and the beginning of the Eocene were especially warm. During this interval, several temperature maxima were observed on Earth. Among them, the early and middle Eocene optimums stand out. 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 drift in the Arctic has intensified. Apparently, in the highlands of Antarctica at that time, mountain glaciers were born, the tongues of which in places (for example, in Prudhos Bay) reached the sea. A continental ice sheet comparable to that of today 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. Modeling estimates that the volume of the East Antarctic Ice Sheet at that time was sometimes reduced to 25% of its present size. Most likely, this is when the Rhone and Ross ice shelves arose. In the late Miocene, severe cooling occurred again. The ice sheet has again reached continental proportions. A short-term warming similar to the modern one occurred in the middle Pliocene 3.3–3.15 million years ago. The almost complete disappearance of the West Antarctic Shield may have been associated with it.

The late Pliocene and Quaternary periods were characterized by rapid progressive cooling. At the same time, continental glaciation began in the Northern Hemisphere. Ice sheets arose 2.74–2.54 million years ago in northern Eurasia and Alaska. Seasonal ice transport of terrigenous material in the Arctic Ocean has increased. This cooling led to the growth of the Antarctic ice sheet, which 20–11 thousand years ago reached the edge of the shelf and the continental slope of the continent. During glacial maxima, glaciers in Eurasia and North America extended to mid-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 amplitude and sign. They are sometimes (very conventionally) called glacial and interglacial. Judging by the periodicity, the cause of glacial oscillations was fluctuations in solar insolation. The latter were caused by the superposition of oscillations of different durations associated with variations in the eccentricity of the Earth's orbit, the angle of inclination of the Earth's axis and its precession. In total, these variations gave a complex picture with groups of cycles prevailing in amplitude in the intervals of 19–24 thousand years (precessional), 39–41 thousand years (due to the tilt of the Earth’s axis), 95–131 and 405 thousand years (orbital). The shortest of these cycles (approximately corresponding to the Milankovitch cycles) determined the alternation of glacial and interglacial periods in the late Pliocene and Pleistocene. In sediments drilled on the Ross Ice Shelf over 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, associated with changes in the inclination of the Earth’s axis and orbit, began to dominate.

General nature of glaciations

The first thing that attracts attention when looking at Fig. 1, this is a clear increase in the number and density of glaciations over the past 3 billion years. This fact is difficult to explain by the poorer knowledge of ancient deposits. In the second half of the twentieth century, especially during the Cold War, in connection with the pursuit of strategic raw materials, geological mapping of almost all areas of our planet (even underdeveloped countries and inaccessible 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, moreover, attract the attention of geologists with their extraordinary appearance and origin. In addition, an increase in the frequency of glaciations is observed throughout the thoroughly studied Late Precambrian and the entire Phanerozoic. It can be assumed that such an increase over time is associated with a weakening of mantle volcanism and the progressive development of the biosphere.

Glacioera of different ages have certain similarities. Firstly, those glacioeras that can be dated are close in duration (Huronian - about 200 million years, African - 210 million years, Gondwanan - 190 million years). Secondly, they are similar in structure. All glacioeras consist of 3–6 discrete ice ages lasting from several million to several tens of millions of years.

There have been at least 20 ice ages in the observable history of the Earth. All of these, in turn, consisted of discrete glacial events that can be classified as glacial epochs. A detailed study of oxygen isotopes in the Late Cenozoic and partially Paleozoic showed that the glacial eras were complicated by significant climatic fluctuations with periods from 400–500 thousand to 20 thousand years.

Glacioera 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 maximum (usually intercontinental) scales in the second half of the glacioera, spreading to middle and sometimes, possibly, low latitudes. Then the glaciations quickly degraded. Pleistocene glaciation was apparently maximum in the Late Cenozoic Glacioera. It can be assumed that the Holocene warming (if humans do not intervene) should be followed by a new small glaciation.

Between the Precambrian and Phanerozoic glaciations, not only similarities are noted, but also certain differences. Firstly, individual Precambrian glaciations were apparently more widespread than the most extensive Phanerozoic ones. Secondly, the Precambrian and Phanerozoic glaciations are associated with δ13Ccarb anomalies of opposite sign (negative in the Precambrian and positive in the Phanerozoic). Finally, many Neoproterozoic glaciations were followed by the deposition of units of characteristic thin-bedded dolomites. The listed differences between the Precambrian and Phanerozoic glaciations are very significant for elucidating the reasons for their onset. However, a convincing explanation for these facts has not yet been found.

Possible causes of glaciations

The causes of glaciations are still the subject of numerous competing and mutually exclusive hypotheses, which relate to a wide range of processes - from intergalactic to microbiotic. Now many researchers are inclined to believe 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 glacioeras) 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. Enhanced absorption of CO 2 by phototrophic organisms, with its subsequent 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 into the ocean and precipitation of carbon in the form of carbonates could also cause warming. At the same time, there was an increase in oxygen content in the atmosphere and methane oxidation. 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 with associated calc-alkaline explosive volcanism, then further cooling of the Earth occurred as a result of additional removal of carbon from the biosphere and its burial in the mantle. Clogging of the stratosphere with products of explosive volcanism reduced the transparency of the atmosphere. As a result of the superposition of these processes, the heat balance of the biosphere decreased and cold snaps and glaciations occurred. The astronomical cycles mentioned above were superimposed on these main climatic cycles, determined by geodynamic processes and the nature of volcanism.

The role of glaciations in the biosphere

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

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

Ice shelves and perennial ice sheets appeared in the hydrosphere, and the temperature and sea level dropped. This led to the emergence of a psychrosphere, temperature geochemical and gas stratification of water masses and a change in the circulation system in the ocean. On the continents, shelves and epicontinental basins outside glaciation zones dried up, the nature of climatic, biogeographic and soil zones changed and shifted, the erosion base decreased, solid runoff increased and soluble runoff from land weakened. Repeated glacioeustatic and isostatic subsidence and uplift were noted in the earth's crust.

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 liberation of a significant part of the old and the emergence of new ecological niches led to the diversification of surviving organisms. Continuous and severe stress during a cascade of environmental crises caused hypermutations in organisms and, as a consequence, the formation of new forms. The selection of resistant organisms from them led to the emergence of bionovations. The emergence of new and diversification of forms that survived crises, in turn, gave rise to irreversible ecological and more general biosphere restructuring. They contributed to evolutionary processes in the biosphere in general and in the biota in particular. Thus, a close connection arose between the rates of abiotic and biotic processes.

With the Huronian Glacioera, the widespread distribution of cyanophytes and the primary oxygenation of the ocean and atmosphere began. During the early Proterozoic and most of the Riphean, evolutionary processes occurred primarily at the molecular and cellular level. They ended in the Late Riphean with the mass eukaryotization of biota, which became the prerequisite for the stormy biosphere and biotic events of the African glacioera.

Due to repeated repetitions of glaciations of different scales and associated ecological crises, the African glaciation era was characterized by a number of evolutionary impulses that accelerated biological evolution as a whole. At that time, as a result of a series of glaciations, a new Phanerozoic biota and biosphere of the Earth was formed. Rare remains of annelidomorphs and armored amoebae appeared in the section of Upper Riphean sediments after the first three Neoproterozoic glaciations. The sediments covering the Vendian Nantou tillites (a stratigraphic analogue of the Marino tillites) yielded the first macroscopic algae, sponge biomarkers, and possibly metazoan embryos.

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

Thus, after each glaciation of the African glaciation era, the emergence of new groups of organisms, the flourishing of some previously existing ones, and the change of dominant ones are noted. As a result of these processes, at the end of the African glacioera, a Phanerozoic-type biosphere was formed on Earth. The acceleration culminated in the unusually rapid development of multicellular askeletal and skeletal organisms in the Nemakitdaldinian Vendian and early Cambrian. It is no coincidence that the moment of 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 Glacial Era is especially noticeable against the backdrop of long-term evolutionary processes that characterized the Great Ice Pause.

The Gondwanan Glacioera was accompanied by a massive conquest of new ecological spaces by organisms: the pelagic zone (graptolites, endoceratids, actinoceratoids, fish, lizards, etc.), land (a variety of plants, forests, amphibians, reptiles) and the 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 glacial era was the formation of humanity. Rapid hominid divergence occurred in parallel with major glaciations. The first representatives of the suborder Hominidae appeared in the Oligocene, and the first three species from the hominid family were discovered in the Upper Miocene, which was characterized by a sharp cooling. In the deposits of the even colder Pliocene, 13 species of hominids have already been discovered, including the remains of australopithecines. In the first half of the Pleistocene (about 2.4–1.9 million years ago), the first primitive species of the genus Homo ( H. habiles etc.) and the simplest tools. The remains belong to the second half of the Pleistocene (about 0.6–0.5 million years ago) 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 appeared H. sapiens.

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

Palaeogeogr., Palaeoclimat., Palaeoecol. . Fedonkin M. A. Eukaryotisation of the Early Biosphere: a biogeochemical aspect // Geochem. Int. 2009. V. 47. P. 1265–1333.
. Catt J. A., Maslin M. A. Human time scale // The geologic time scale 2012 / Eds. F. Gradstein, J. G. Ogg, M. Schmitz, G. Ogg. Amsterdam, 2012, pp. 1011–1032.

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

Let us recall that the expected several times smaller increase in the average temperature of the Earth is considered as a serious catastrophe for humanity.

GLACIATION CENTER - the area of ​​the greatest accumulation and greatest power. ice, where it begins to spread. Usually C. o. associated with elevated, often mountainous centers. So, Ts. o. The Fennoscandian ice sheet were Scandinavian. On the territory of northern Sweden it reached power. at least 2-2.5 km. From here it spread across the Russian Plain for several thousand km to the Dnepropetrovsk region. During the Pleistocene ice ages, there were many color systems on all continents, for example, in Europe - Alpine, Iberian, Caucasian, Ural, Novaya Zemlya; in Asia - Taimyr. Putoransky, Verkhoyansky, etc.

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

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One of the mysteries of the Earth, along with the emergence of Life on it and the extinction of dinosaurs at the end of the Cretaceous period, is - Great Glaciations.

It is believed that glaciations repeat on Earth regularly every 180-200 million years. Traces of glaciations are known in sediments that are billions and hundreds of millions of years old - in the Cambrian, Carboniferous, Triassic-Permian. That they could be is “said” by the so-called tillites, breeds very similar to moraine the latter, more precisely last glaciations. These are the remains of ancient glacial deposits, consisting of a clayey mass with inclusions of large and small boulders scratched by movement (hatched).

Separate layers tillites, found even in equatorial Africa, can reach thickness of tens and even hundreds of meters!

Signs of glaciations were found on different continents - in Australia, South America, Africa and India, which is used by scientists for reconstruction of paleocontinents and is often cited as confirmation plate tectonics theories.

Traces of ancient glaciations indicate that glaciations on a continental scale– this is not a random phenomenon at all, it is a natural natural phenomenon that occurs under certain conditions.

The last of the ice ages began almost million years ago, in Quaternary time, or the Quaternary period, the Pleistocene and was marked by the extensive spread of glaciers - The Great Glaciation of the Earth.

Under thick, many-kilometer-long covers of ice were the northern part of the North American continent - the North American Ice Sheet, which reached a thickness of up to 3.5 km and extended to approximately 38° north latitude and a significant part of Europe, on which (an ice sheet with a thickness of up to 2.5-3 km) . On the territory of Russia, the glacier descended in two huge tongues along the ancient valleys of the Dnieper and Don.

Partial glaciation also covered Siberia - there was mainly the so-called “mountain-valley glaciation”, when glaciers did not cover the entire area with a thick cover, but were only in the mountains and foothill valleys, which is associated with the sharply continental climate and low temperatures in Eastern Siberia . But almost all of Western Siberia, due to the fact that the rivers were dammed and their flow into the Arctic Ocean stopped, found itself under water, and was a huge sea-lake.

In the Southern Hemisphere, the entire Antarctic continent was under ice, as it is now.

During the period of maximum expansion of the Quaternary glaciation, glaciers covered over 40 million km 2–about a quarter of the entire surface of the continents.

Having reached their greatest development about 250 thousand years ago, the Quaternary glaciers of the Northern Hemisphere began to gradually shrink as the glaciation period was not continuous throughout the Quaternary period.

There is geological, paleobotanical and other evidence that glaciers disappeared several times, giving way to epochs interglacial when the climate was even warmer than today. However, the warm eras were replaced by cold snaps again, and the glaciers spread again.

We now live, apparently, at the end of the fourth epoch of the Quaternary glaciation.

But in Antarctica, glaciation arose millions of years before the time when glaciers appeared in North America and Europe. In addition to the climatic conditions, this was facilitated by the high continent that had existed here for a long time. By the way, now, due to the fact that the thickness of the Antarctic glacier is enormous, the continental bed of the “ice continent” is in some places below sea level...

Unlike the ancient ice sheets of the Northern Hemisphere, which disappeared and then reappeared, the Antarctic ice sheet changed little in its size. The maximum glaciation of Antarctica was only one and a half times larger than the modern one in volume, and not much larger in area.

Now about the hypotheses... There are hundreds, if not thousands, of hypotheses about why glaciations occur, and whether there were any at all!

The following main ones are usually put forward: scientific hypotheses:

• Volcanic eruptions leading to a decrease in the transparency of the atmosphere and cooling throughout the Earth;
• Epochs of orogenesis (mountain building);
• Reducing the amount of carbon dioxide in the atmosphere, which reduces the “greenhouse effect” and leads to cooling;
• Cyclicity of solar activity;
• Changes in the position of the Earth relative to the Sun.

But, nevertheless, the causes of glaciations have not been fully elucidated!

It is assumed, for example, that glaciation begins when, with an increase in the distance between the Earth and the Sun, around which it rotates in a slightly elongated orbit, the amount of solar heat received by our planet decreases, i.e. glaciation occurs when the Earth passes the point of its orbit that is farthest from the Sun.

However, astronomers believe that changes in the amount of solar radiation hitting the Earth alone are not enough to trigger an ice age. Apparently, fluctuations in the activity of the Sun itself also matter, which is a periodic, cyclical process, and changes every 11-12 years, with a cyclicity of 2-3 years and 5-6 years. And the largest cycles of activity, as established by the Soviet geographer A.V. Shnitnikov - approximately 1800-2000 years old.

There is also a hypothesis that the emergence of glaciers is associated with certain areas of the Universe through which our Solar System passes, moving with the entire Galaxy, either filled with gas or “clouds” of cosmic dust. And it is likely that “cosmic winter” on Earth occurs when the globe is at the point furthest from the center of our Galaxy, where there are accumulations of “cosmic dust” and gas.

It should be noted that usually before epochs of cooling there are always epochs of warming, and there is, for example, a hypothesis that the Arctic Ocean, due to warming, at times is completely freed from ice (by the way, this is still happening), and there is increased evaporation from the surface of the ocean , streams of moist air are directed to the polar regions of America and Eurasia, and snow falls over the cold surface of the Earth, which does not have time to melt during the short and cold summer. This is how ice sheets appear on continents.

But when, as a result of the transformation of part of the water into ice, the level of the World Ocean drops by tens of meters, the warm Atlantic Ocean ceases to communicate with the Arctic Ocean, and it gradually becomes covered with ice again, evaporation from its surface abruptly stops, less and less snow falls on the continents and less, the “feeding” of the glaciers deteriorates, and the ice sheets begin to melt, and the level of the World Ocean rises again. And again the Arctic Ocean connects with the Atlantic, and again the ice cover began to gradually disappear, i.e. the development cycle of the next glaciation begins anew.

Yes, all these hypotheses quite possible, but so far none of them can be confirmed by serious scientific facts.

Therefore, one of the main, fundamental hypotheses is climate change on the Earth itself, which is associated with the above-mentioned hypotheses.

But it is quite possible that glaciation processes are associated with combined influence of various natural factors, which could act together and replace each other, and the important thing is that, having begun, glaciations, like a “wound clock,” already develop independently, according to their own laws, sometimes even “ignoring” some climatic conditions and patterns.

And the ice age that began in the Northern Hemisphere about 1 million years back, not finished yet, and we, as already mentioned, live in a warmer period of time, in interglacial.

Throughout the era of the Great Glaciations of the Earth, the ice either retreated or advanced again. On the territory of both America and Europe there were, apparently, four global ice ages, between which there were relatively warm periods.

But the complete retreat of the ice occurred only about 20 - 25 thousand years ago, but in some areas the ice lingered even longer. The glacier retreated from the area of ​​modern St. Petersburg only 16 thousand years ago, and in some places in the North small remnants of ancient glaciation have survived to this day.

Let us note that modern glaciers cannot be compared with the ancient glaciation of our planet - they occupy only about 15 million square meters. km, i.e. less than one-thirtieth of the earth's surface.

How can one determine whether there was glaciation in a given place on Earth or not? This is usually quite easy to determine by the peculiar forms of geographical relief and rocks.

In the fields and forests of Russia there are often large accumulations of huge boulders, pebbles, blocks, sands and clays. They usually lie directly on the surface, but they can also be seen in the cliffs of ravines and on the slopes of river valleys.

By the way, one of the first who tried to explain how these deposits were formed was the outstanding geographer and anarchist theorist, Prince Peter Alekseevich Kropotkin. In his work “Research on the Ice Age” (1876), he argued that the territory of Russia was once covered by huge ice fields.

If we look at the physical-geographical map of European Russia, then we can notice some patterns in the location of hills, hills, basins and valleys of large rivers. So, for example, the Leningrad and Novgorod regions from the south and east are, as it were, limited Valdai Upland shaped like an arc. This is exactly the line where in the distant past a huge glacier, advancing from the north, stopped.

To the southeast of the Valdai Upland is the slightly winding Smolensk-Moscow Upland, stretching from Smolensk to Pereslavl-Zalessky. This is another of the boundaries of the distribution of cover glaciers.

Numerous hilly, winding hills are also visible on the West Siberian Plain - "manes" also evidence of the activity of ancient glaciers, or rather glacial waters. Many traces of stopping moving glaciers flowing down the mountain slopes into large basins were discovered in Central and Eastern Siberia.

It is difficult to imagine ice several kilometers thick on the site of current cities, rivers and lakes, but, nevertheless, the glacial plateaus were not inferior in height to the Urals, the Carpathians or the Scandinavian mountains. These gigantic and, moreover, moving masses of ice influenced the entire natural environment - topography, landscapes, river flow, soils, vegetation and wildlife.

It should be noted that on the territory of Europe and the European part of Russia, practically no rocks have been preserved from the geological eras preceding the Quaternary period - Paleogene (66-25 million years) and Neogene (25-1.8 million years), they were completely eroded and redeposited during the Quaternary period, or as it is often called, Pleistocene.

Glaciers originated and moved from Scandinavia, the Kola Peninsula, the Polar Urals (Pai-Khoi) and the islands of the Arctic Ocean. And almost all the geological deposits that we see on the territory of Moscow - moraine, more precisely moraine loams, sands of various origins (aquaglacial, lake, river), huge boulders, as well as cover loams - all this is evidence of the powerful influence of the glacier.

On the territory of Moscow, traces of three glaciations can be identified (although there are many more of them - different researchers identify from 5 to several dozen periods of ice advances and retreats):

• Oka (about 1 million years ago),
• Dnieper (about 300 thousand years ago),
• Moscow (about 150 thousand years ago).

Valdai the glacier (disappeared only 10 - 12 thousand years ago) “did not reach Moscow”, and the deposits of this period are characterized by hydroglacial (fluvio-glacial) deposits - mainly the sands of the Meshchera Lowland.

And the names of the glaciers themselves correspond to the names of those places to which the glaciers reached - the Oka, Dnieper and Don, the Moscow River, Valdai, etc.

Since the thickness of the glaciers reached almost 3 km, one can imagine what colossal work he performed! Some hills and hills on the territory of Moscow and the Moscow region are thick (up to 100 meters!) deposits that were “brought” by the glacier.

The best known are, for example Klinsko-Dmitrovskaya moraine ridge, individual hills on the territory of Moscow ( Sparrow Hills and Teplostanskaya Upland). Huge boulders weighing up to several tons (for example, the Maiden Stone in Kolomenskoye) are also the result of the glacier.

Glaciers smoothed out the unevenness of the relief: they destroyed hills and ridges, and with the resulting rock fragments they filled depressions - river valleys and lake basins, transporting huge masses of stone fragments over a distance of more than 2 thousand km.

However, huge masses of ice (given its colossal thickness) put so much pressure on the underlying rocks that even the strongest of them could not stand it and collapsed.

Their fragments were frozen into the body of the moving glacier and, like sandpaper, for tens of thousands of years they scratched rocks composed of granites, gneisses, sandstones and other rocks, creating depressions in them. Numerous glacial grooves, “scars” and glacial polishing on granite rocks, as well as long hollows in the earth’s crust, subsequently occupied by lakes and swamps, are still preserved. An example is the countless depressions of the lakes of Karelia and the Kola Peninsula.

But the glaciers did not plow up all the rocks on their way. The destruction was mainly carried out in those areas where the ice sheets originated, grew, reached a thickness of more than 3 km and from where they began their movement. The main center of glaciation in Europe was Fennoscandia, which included the Scandinavian mountains, the plateaus of the Kola Peninsula, as well as the plateaus and plains of Finland and Karelia.

Along the way, the ice became saturated with fragments of destroyed rocks, and they gradually accumulated both inside the glacier and under it. When the ice melted, masses of debris, sand and clay remained on the surface. This process was especially active when the movement of the glacier stopped and the melting of its fragments began.

At the edge of glaciers, as a rule, water flows arose, moving along the surface of the ice, in the body of the glacier and under the ice thickness. Gradually they merged, forming entire rivers, which over thousands of years formed narrow valleys and washed away a lot of debris.

As already mentioned, the forms of glacial relief are very diverse. For moraine plains characterized by many ridges and shafts, marking places where moving ice stops, and the main form of relief among them is shafts of terminal moraines, usually these are low arched ridges composed of sand and clay mixed with boulders and pebbles. The depressions between the ridges are often occupied by lakes. Sometimes among the moraine plains you can see outcasts- blocks hundreds of meters in size and weighing tens of tons, giant pieces of the glacier bed, transported by it over enormous distances.

Glaciers often blocked river flows and near such “dams” huge lakes arose, filling depressions in river valleys and depressions, which often changed the direction of river flow. And although such lakes existed for a relatively short time (from a thousand to three thousand years), at their bottom they managed to accumulate lacustrine clays, layered sediments, by counting the layers of which, one can clearly distinguish the periods of winter and summer, as well as how many years these sediments have accumulated.

In the era of the last Valdai glaciation arose Upper Volga periglacial lakes(Mologo-Sheksninskoye, Tverskoye, Verkhne-Molozhskoye, etc.). At first their waters flowed to the southwest, but with the retreat of the glacier they were able to flow to the north. Traces of Mologo-Sheksninsky Lake remain in the form of terraces and shorelines at an altitude of about 100 m.

There are very numerous traces of ancient glaciers in the mountains of Siberia, the Urals, and the Far East. As a result of ancient glaciation, 135-280 thousand years ago, sharp mountain peaks - “gendarmes” - appeared in Altai, the Sayans, the Baikal region and Transbaikalia, on the Stanovoi Highlands. The so-called “net type of glaciation” prevailed here, i.e. If you could look from a bird's eye view, you could see how ice-free plateaus and mountain peaks rise against the background of glaciers.

It should be noted that during the ice ages, quite large ice massifs were located on part of the territory of Siberia, for example on archipelago Severnaya Zemlya, in the Byrranga mountains (Taimyr Peninsula), as well as on the Putorana plateau in northern Siberia.

Extensive mountain-valley glaciation was 270-310 thousand years ago Verkhoyansk Range, Okhotsk-Kolyma Plateau and Chukotka Mountains. These areas are considered centers of glaciations in Siberia.

Traces of these glaciations are numerous bowl-shaped depressions of mountain peaks - circuses or punishments, huge moraine ridges and lake plains in place of melted ice.

In the mountains, as well as on the plains, lakes arose near ice dams, periodically the lakes overflowed, and gigantic masses of water through low watersheds rushed with incredible speed into neighboring valleys, crashing into them and forming huge canyons and gorges. For example, in Altai, in the Chuya-Kurai depression, “giant ripples”, “drilling boilers”, gorges and canyons, huge outlier boulders, “dry waterfalls” and other traces of water flows escaping from ancient lakes “only” are still preserved. just” 12-14 thousand years ago.

“Invading” the plains of Northern Eurasia from the north, the ice sheets either penetrated far to the south along relief depressions, or stopped at some obstacles, for example, hills.

It is probably not yet possible to accurately determine which of the glaciations was the “greatest,” however, it is known, for example, that the Valdai glacier was sharply smaller in area than the Dnieper glacier.

The landscapes at the boundaries of the cover glaciers also differed. Thus, during the Oka glaciation era (500-400 thousand years ago), to the south of them there was a strip of Arctic deserts about 700 km wide - from the Carpathians in the west to the Verkhoyansk Range in the east. Even further, 400-450 km to the south, stretched cold forest-steppe, where only such unpretentious trees as larches, birches and pines could grow. And only at the latitude of the Northern Black Sea region and Eastern Kazakhstan did comparatively warm steppes and semi-deserts begin.

During the era of the Dnieper glaciation, glaciers were significantly larger. Along the edge of the ice sheet stretched the tundra-steppe (dry tundra) with a very harsh climate. The average annual temperature was approaching minus 6°C (for comparison: in the Moscow region the average annual temperature is currently about +2.5°C).

The open space of the tundra, where there was little snow in winter and there were severe frosts, cracked, forming the so-called “permafrost polygons,” which in plan resemble a wedge in shape. They are called “ice wedges,” and in Siberia they often reach a height of ten meters! Traces of these “ice wedges” in ancient glacial deposits “speak” of a harsh climate. Traces of permafrost, or cryogenic effects, are also noticeable in sands; these are often disturbed, as if “torn” layers, often with a high content of iron minerals.

Fluvio-glacial deposits with traces of cryogenic impact

The last “Great Glaciation” has been studied for more than 100 years. Many decades of hard work by outstanding researchers went into collecting data on its distribution on the plains and in the mountains, mapping end-moraine complexes and traces of glacial-dammed lakes, glacial scars, drumlins, and areas of “hilly moraine.”

True, there are also researchers who generally deny ancient glaciations and consider the glacial theory to be erroneous. In their opinion, there was no glaciation at all, but there was a “cold sea on which icebergs floated,” and all glacial deposits are just bottom sediments of this shallow sea!

Other researchers, “recognizing the general validity of the theory of glaciations,” nevertheless doubt the correctness of the conclusion about the grandiose scale of glaciations of the past, and they are especially distrustful of the conclusion about ice sheets that overlapped the polar continental shelves; they believe that there were “small ice caps of the Arctic archipelagos”, “bare tundra” or “cold seas”, and in North America, where the largest “Laurentian ice sheet” in the Northern Hemisphere has long been restored, there were only “groups of glaciers merged at the bases of the domes”.

For Northern Eurasia, these researchers recognize only the Scandinavian ice sheet and isolated “ice caps” of the Polar Urals, Taimyr and the Putorana Plateau, and in the mountains of temperate latitudes and Siberia - only valley glaciers.

And some scientists, on the contrary, are “reconstructing” “giant ice sheets” in Siberia, which are not inferior in size and structure to the Antarctic.

As we have already noted, in the Southern Hemisphere, the Antarctic ice sheet extended over the entire continent, including its underwater margins, in particular the areas of the Ross and Weddell seas.

The maximum height of the Antarctic ice sheet was 4 km, i.e. was close to modern (now about 3.5 km), the ice area increased to almost 17 million square kilometers, and the total volume of ice reached 35-36 million cubic kilometers.

Two more large ice sheets were in South America and New Zealand.

The Patagonian Ice Sheet was located in the Patagonian Andes, their foothills and on the adjacent continental shelf. Today it is reminded of by the picturesque fjord topography of the Chilean coast and the residual ice sheets of the Andes.

"South Alpine complex" of New Zealand– was a smaller copy of Patagonian. It had the same shape and extended onto the shelf in the same way; on the coast it developed a system of similar fjords.

In the Northern Hemisphere, during periods of maximum glaciation, we would see huge Arctic ice sheet resulting from the merger North American and Eurasian covers into a single glacial system, Moreover, an important role was played by floating ice shelves, especially the Central Arctic, which covered the entire deep-water part of the Arctic Ocean.

The largest elements of the Arctic ice sheet were the Laurentian Shield of North America and the Kara Shield of Arctic Eurasia, they were shaped like giant flat-convex domes. The center of the first of them was located over the southwestern part of Hudson Bay, the peak rose to a height of more than 3 km, and its eastern edge extended to the outer edge of the continental shelf.

The Kara ice sheet occupied the entire area of ​​the modern Barents and Kara seas, its center lay over the Kara Sea, and the southern marginal zone covered the entire north of the Russian Plain, Western and Central Siberia.

Of the other elements of the Arctic cover, it deserves special attention East Siberian Ice Sheet, which spread on the shelves of the Laptev, East Siberian and Chukchi seas and was larger than the Greenland ice sheet. He left traces in the form of large glaciodislocations New Siberian Islands and Tiksi region, are also associated with it grandiose glacial-erosive forms of Wrangel Island and the Chukotka Peninsula.

So, the last ice sheet of the Northern Hemisphere consisted of more than a dozen large ice sheets and many smaller ones, as well as the ice shelves that united them, floating in the deep ocean.

The periods of time during which glaciers disappeared, or were reduced by 80-90%, are called interglacials. Landscapes freed from ice in a relatively warm climate were transformed: the tundra retreated to the northern coast of Eurasia, and the taiga and deciduous forests, forest-steppes and steppes occupied a position close to the modern one.

Thus, over the past million years, the nature of Northern Eurasia and North America has repeatedly changed its appearance.

Boulders, crushed stone and sand, frozen into the bottom layers of a moving glacier, acting as a giant “file”, smoothed, polished, scratched granites and gneisses, and under the ice, peculiar layers of boulder loams and sands were formed, characterized by high density associated with the influence of glacial load - main, or bottom moraine.

Since the size of the glacier is determined balance between the amount of snow that falls on it annually, which turns into firn, and then into ice, and what does not have time to melt and evaporate during the warm seasons, then with climate warming, the edges of the glaciers retreat to new, “equilibrium boundaries.” The end parts of the glacial tongues stop moving and gradually melt, and boulders, sand and loam included in the ice are released, forming a shaft that follows the contours of the glacier - terminal moraine; the other part of the clastic material (mainly sand and clay particles) is carried away by meltwater flows and deposited around in the form fluvioglacial sandy plains (Zandrov).

Similar flows also operate deep in glaciers, filling cracks and intraglacial caverns with fluvioglacial material. After the melting of glacial tongues with such filled voids on the earth's surface, chaotic piles of hills of various shapes and composition remain on top of the melted bottom moraine: ovoid (when viewed from above) drumlins, elongated, like railway embankments (along the axis of the glacier and perpendicular to the terminal moraines) oz and irregular shape kama.

All these forms of glacial landscape are very clearly represented in North America: the boundary of ancient glaciation here is marked by a terminal moraine ridge with heights of up to fifty meters, stretching across the entire continent from its eastern coast to the western. To the north of this “Great Glacial Wall” the glacial deposits are represented mainly by moraine, and to the south of it they are represented by a “cloak” of fluvioglacial sands and pebbles.

Just as four glacial epochs have been identified for the territory of the European part of Russia, four glacial epochs have also been identified for Central Europe, named after the corresponding Alpine rivers - Günz, Mindel, Riess and Würm, and in North America - Nebraska, Kansas, Illinois and Wisconsin glaciations.

Climate periglacial The areas (surrounding the glacier) were cold and dry, which is fully confirmed by paleontological data. In these landscapes a very specific fauna appears with a combination cryophilic (cold-loving) and xerophilic (dry-loving) plants – tundra-steppe.

Now similar natural zones, similar to periglacial ones, have been preserved in the form of so-called relict steppes– islands among the taiga and forest-tundra landscapes, for example, the so-called alasy Yakutia, the southern slopes of the mountains of northeastern Siberia and Alaska, as well as the cold, dry highlands of Central Asia.

Tundra-steppe was different in that her the herbaceous layer was formed mainly not by mosses (as in the tundra), but by grasses, and it was here that it took shape cryophilic option herbaceous vegetation with a very high biomass of grazing ungulates and predators – the so-called “mammoth fauna”.

In its composition, various types of animals were intricately mixed, both characteristic of tundra – reindeer, caribou, muskox, lemmings, For steppes - saiga, horse, camel, bison, gophers, and mammoths and woolly rhinoceroses, saber-toothed tiger - Smilodon, and giant hyena.

It should be noted that many climate changes have been repeated, as it were, “in miniature” within the memory of mankind. These are the so-called “Little Ice Ages” and “Interglacials”.

For example, during the so-called “Little Ice Age” from 1450 to 1850, glaciers advanced everywhere, and their sizes exceeded modern ones (snow cover appeared, for example, in the mountains of Ethiopia, where there is none now).

And in the period preceding the Little Ice Age Atlantic optimum(900-1300) glaciers, on the contrary, shrank, and the climate was noticeably milder than the present one. Let us remember that it was during these times that the Vikings called Greenland the “Green Land”, and even settled it, and also reached the coast of North America and the island of Newfoundland in their boats. And the Novgorod Ushkuin merchants traveled along the “Northern Sea Route” to the Gulf of Ob, founding the city of Mangazeya there.

And the last retreat of glaciers, which began over 10 thousand years ago, is well remembered by people, hence the legends about the Great Flood, as a huge amount of meltwater rushed down to the south, rains and floods became frequent.

In the distant past, the growth of glaciers occurred in eras with lower air temperatures and increased humidity; the same conditions developed in the last centuries of the last era, and in the middle of the last millennium.

And about 2.5 thousand years ago, a significant cooling of the climate began, the Arctic islands were covered with glaciers, in the Mediterranean and Black Sea countries at the turn of the era the climate was colder and wetter than now.

In the Alps in the 1st millennium BC. e. glaciers moved to lower levels, blocked mountain passes with ice and destroyed some high-lying villages. It was during this era that glaciers in the Caucasus sharply intensified and grew.

But by the end of the 1st millennium, climate warming began again, and mountain glaciers in the Alps, Caucasus, Scandinavia and Iceland retreated.

The climate began to change seriously again only in the 14th century; glaciers began to grow rapidly in Greenland, summer thawing of the soil became increasingly short-lived, and by the end of the century permafrost was firmly established here.

From the end of the 15th century, glaciers began to grow in many mountainous countries and polar regions, and after the relatively warm 16th century, harsh centuries began, which were called the “Little Ice Age”. In the south of Europe, severe and long winters often recurred; in 1621 and 1669, the Bosporus Strait froze, and in 1709, the Adriatic Sea froze off the coast. But the “Little Ice Age” ended in the second half of the 19th century and a relatively warm era began, which continues to this day.

Note that the warming of the 20th century is especially pronounced in the polar latitudes of the Northern Hemisphere, and fluctuations in glacial systems are characterized by the percentage of advancing, stationary and retreating glaciers.

For example, for the Alps there is data covering the entire past century. If the share of advancing alpine glaciers in the 40-50s of the 20th century was close to zero, then in the mid-60s of the 20th century about 30%, and at the end of the 70s of the 20th century, 65-70% of the surveyed glaciers were advancing here.

Their similar state indicates that the anthropogenic (technogenic) increase in the content of carbon dioxide, methane and other gases and aerosols in the atmosphere in the 20th century did not in any way affect the normal course of global atmospheric and glacial processes. However, at the end of the last, twentieth century, glaciers began to retreat everywhere in the mountains, and the ice of Greenland began to melt, which is associated with climate warming, and which especially intensified in the 1990s.

It is known that the currently increased man-made emissions of carbon dioxide, methane, freon and various aerosols into the atmosphere seem to help reduce solar radiation. In this regard, “voices” appeared, first from journalists, then from politicians, and then from scientists about the beginning of a “new ice age.” Environmentalists have “sounded the alarm”, fearing “the coming anthropogenic warming” due to the constant increase in carbon dioxide and other impurities in the atmosphere.

Yes, it is well known that an increase in CO 2 leads to an increase in the amount of retained heat and thereby increases the air temperature at the Earth’s surface, forming the notorious “greenhouse effect”.

Some other gases of technogenic origin have the same effect: freons, nitrogen oxides and sulfur oxides, methane, ammonia. But, nevertheless, not all carbon dioxide remains in the atmosphere: 50-60% of industrial CO 2 emissions end up in the ocean, where they are quickly absorbed by animals (corals in the first place), and of course they are also absorbed by plants–Let's remember the process of photosynthesis: plants absorb carbon dioxide and release oxygen! Those. the more carbon dioxide, the better, the higher the percentage of oxygen in the atmosphere! By the way, this already happened in the history of the Earth, in the Carboniferous period... Therefore, even a multiple increase in the concentration of CO 2 in the atmosphere cannot lead to the same multiple increase in temperature, since there is a certain natural regulation mechanism that sharply slows down the greenhouse effect at high concentrations of CO 2.

So all the numerous “scientific hypotheses” about the “greenhouse effect”, “rising sea levels”, “changes in the Gulf Stream”, and naturally the “coming Apocalypse” are mostly imposed on us “from above”, by politicians, incompetent scientists, illiterate journalists or simply science scammers. The more you intimidate the population, the easier it is to sell goods and manage...

But in fact, an ordinary natural process is taking place - one stage, one climatic epoch gives way to another, and there is nothing strange about it... But the fact that natural disasters occur, and that there are supposedly more of them - tornadoes, floods, etc. - is another 100-200 years ago, vast areas of the Earth were simply uninhabited! And now there are more than 7 billion people, and they often live where floods and tornadoes are possible - along the banks of rivers and oceans, in the deserts of America! Moreover, let us remember that natural disasters have always existed, and even destroyed entire civilizations!

As for the opinions of scientists, which both politicians and journalists love to refer to... Back in 1983, American sociologists Randall Collins and Sal Restivo, in their famous article “Pirates and Politicians in Mathematics,” wrote openly: “...There is no immutable set of norms that guide the behavior of scientists. What remains constant is the activity of scientists (and related other types of intellectuals), aimed at acquiring wealth and fame, as well as gaining the ability to control the flow of ideas and impose their own ideas on others... The ideals of science do not predetermine scientific behavior, but arise from the struggle for individual success under various competition conditions...”

And a little more about science... Various large companies often provide grants for so-called “scientific research” in certain areas, but the question arises - how competent is the person conducting the research in this area? Why was he chosen out of hundreds of scientists?

And if a certain scientist, “a certain organization” orders, for example, “a certain research on the safety of nuclear energy,” then, it goes without saying that this scientist will be forced to “listen” to the customer, since he has “well-defined interests,” and it is understandable , that he will most likely “adjust” “his conclusions” to the customer, since the main question is already not a question of scientific research–and what does the customer want to receive, what is the result?. And if the customer's result won't suit, then this scientist won't invite you anymore, and not in any “serious project”, i.e. “monetary”, he will no longer participate, since they will invite another scientist, more “amenable”... Much, of course, depends on his civic position, professionalism, and reputation as a scientist... But let’s not forget how much they “get” in Russia scientists... Yes, in the world, in Europe and the USA, a scientist lives mainly on grants... And any scientist also “wants to eat.”

In addition, the data and opinions of one scientist, albeit a major specialist in his field, are not a fact! But if the research is confirmed by some scientific groups, institutes, laboratories, etc. o only then can research be worthy of serious attention.

Unless, of course, these “groups”, “institutes” or “laboratories” were funded by the customer of this research or project...

A.A. Kazdym,
Candidate of Geological and Mineralogical Sciences, member of MOIP

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Dnieper glaciation
was maximum in the Middle Pleistocene (250-170 or 110 thousand years ago). It consisted of two or three stages.

Sometimes the last stage of the Dnieper glaciation is distinguished as an independent Moscow glaciation (170-125 or 110 thousand years ago), and the period of relatively warm time separating them is considered as the Odintsovo interglacial.

At the maximum stage of this glaciation, a significant part of the Russian Plain was occupied by an ice sheet that penetrated southward in a narrow tongue along the Dnieper valley to the mouth of the river. Aurelie. In most of this territory there was permafrost, and the average annual air temperature was then no higher than -5-6°C.
In the southeast of the Russian Plain, in the Middle Pleistocene, the so-called “Early Khazar” rise in the level of the Caspian Sea by 40-50 m occurred, which consisted of several phases. Their exact dating is unknown.

Mikulin interglacial
The Dnieper glaciation followed (125 or 110-70 thousand years ago). At this time, in the central regions of the Russian Plain, winter was much milder than now. If currently the average January temperatures are close to -10°C, then during the Mikulino interglacial they did not fall below -3°C.
The Mikulin time corresponded to the so-called “late Khazar” rise in the level of the Caspian Sea. In the north of the Russian Plain, there was a synchronous rise in the level of the Baltic Sea, which was then connected to Lakes Ladoga and Onega and, possibly, the White Sea, as well as the Arctic Ocean. The total fluctuation in the level of the world's oceans between the eras of glaciation and melting of ice was 130-150 m.

Valdai glaciation
After the Mikulino interglacial there came, consisting of the Early Valdai or Tver (70-55 thousand years ago) and Late Valdai or Ostashkovo (24-12:-10 thousand years ago) glaciations, separated by the Middle Valdai period of repeated (up to 5) temperature fluctuations, during which the climate was much colder modern (55-24 thousand years ago).
In the south of the Russian Platform, the early Valdai is associated with a significant “Attelian” decrease - by 100-120 meters - in the level of the Caspian Sea. This was followed by the “early Khvalynian” rise in sea level by about 200 m (80 m above the original level). According to calculations by A.P. Chepalyga (Chepalyga, t. 1984), the supply of moisture to the Caspian basin of the Upper Khvalynian period exceeded its losses by approximately 12 cubic meters. km per year.
After the “early Khvalynian” rise in sea level, there followed the “Enotaevsky” decrease in sea level, and then again the “late Khvalynian” increase in sea level by about 30 m relative to its original position. The maximum of the Late Khvalynian transgression occurred, according to G.I. Rychagov, at the end of the Late Pleistocene (16 thousand years ago). The Late Khvalynian basin was characterized by temperatures of the water column slightly lower than modern ones.
The new drop in sea level occurred quite quickly. It reached a maximum (50 m) at the very beginning of the Holocene (0.01-0 million years ago), about 10 thousand years ago, and was replaced by the last - “New Caspian” sea level rise of about 70 m about 8 thousand years ago.
Approximately the same fluctuations in the water surface occurred in the Baltic Sea and the Arctic Ocean. The general fluctuation in the level of the world's oceans between the eras of glaciation and melting of ice was then 80-100 m.

According to radioisotope analysis of more than 500 different geological and biological samples taken in southern Chile, mid-latitudes in the western Southern Hemisphere experienced warming and cooling at the same time as mid-latitudes in the western Northern Hemisphere.

Chapter " The world in the Pleistocene. The Great Glaciations and the Exodus from Hyperborea" / Eleven Quaternary glaciationsperiod and nuclear wars

© A.V. Koltypin, 2010