Geology of the European North, U.S.S.R.: Encyclopedia Arctica Volume 1: Geology and Allied Subjects

CONTENTS

GEOLOGY OF THE EUROPEAN NORTH, U.S.S.R.

Geological Structure and Evolution of Relief

Diversified in its geological structure and relief, the northern Euro– pean territory of the Russian Soviet Federated Socialist Republic has undergone a very complicated evolution.

Eozoic Era . The oldest geological formations crop out in the northwestern part of the territory, which forms the eastern margin of the vast crystalline Baltic shield. In the central and eastern parts of the northern European R.S.F.S.R., they are deeply buried under a thick accumulation of younger sedi– mentary rocks, but they reappear at the surface in the uplifted regions of ancient folding to the east in the Timan Ridge and the Urals.

Even though fossil remains of animals and plants are not preserved in these rocks, detailed geological investigations during the past 15 or 20 years (prior to 1946) have made it possible to outline three great cycles in the formation of these ancient rocks, embracing the Archean and Proterozoic periods, with which a definite complex of mineral resources is associated. Each cycle breaks down into three periods: ( 1 ) a period of accumulation of sediments; ( 2 ) a period of warping of the sediments into mountain folds, often accompanied by manifestations of volcanic activity; and ( 3 ) a period of erosion and denudation of the mountain structures, and leveling of relief.

The garnet and mica gneisses and granites which compose consider– able areas of the Murmansk region are regarded as the oldest rocks (Archean) in the territory. According to Arthur Holmes, they were formed in the

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“Svionian” epoch, about 1,500 million years ago. In the ensuing “Saamian” epoch, they were warped into massive mountain folds trending for the most part northwest, and, less frequently, east and west, and north and south. In– trusions of molten magma were injected along fractures in the earth’s crust which formed at this time, altering the rocks with which they came into con– tact, and enriching them with mineral wealth (chiefly iron and copper ores, kyanites, etc.)

Toward the end of Archean time, a new series of sedimentary rocks, sub– sequently transformed into their metamorphic equivalents (schistose amphi– bolites with seams of iron) which have been given the name “Bothnian,” was laid down on the leveled surface of the former mountains.

In the ensuing “Svecofennian” epoch of mountain building, massive folded mountain ranges arose once more, trending north-northwest, and east and west; this was accompanied by large-scale intrusions of granitic magma in the form of tabular masses ^ great blocks^ and thick pegmatitic veins, rich in ceramic raw materials (feldspar and quartz) and in mica. These mountains were also reduced to a plain.

The third cycle belongs to the Proterozoic period, which followed the Archean and was current around 1,000 million years ago.

Sedimentary rocks deposited at this time (the so-called “Karelian forma– tion”) are found on Kola Peninsula in two broad parallel belts extending along the main axis of the peninsula. The northern belt makes up the ridge of hills known as the “Keivy,” which consists of various schists; the southern belt ex– tends from Lake Imandra to the upper reaches of the Varzuga River, and is com– posed of Quartzites, limestones, dolomites, and greenstones. The nature of the rocks in the Karelian formation indicates that they were laid down on the bottom of a shallow sea which covered the area. These sedimentary rocks were only later converted into crystalline schists (metasediments). Both belts are

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of great industrial importance, as they contain a whole series of valuable mineral resources (garnet, kyanite, magnetite, limestone, rare minerals, etc.).

The rocks of the Karelian formation were also warped into folded moun– tains trending northwest, and known in the literature as the “Karelids.” Vol– canic activity which accompanied the orogeny has left its traces in the form of lavas, tuffs, and granites, which make very beautiful and variegated struc– tural and facing material.

A long period of quiescence which followed the Karelian orogenic period led to the destruction of the “Karelids” and a new leveling of the surface. A thick sequence of rocks, named the “Jotnian” and referred to the upper Proterozoic, was laid down on the beveled surface of the crystalline shield in many places.

That the sea which covered Kola Peninsula did not attain great depths is evident from the coarse clastic nature of its sediments. Until recently these deposits, which are particularly widespread in the neighboring areas of the Karelo-Finnish Republic and of Finland, were believed to include the red sand– stones on the southern shore of Kola Peninsula, but the latest investigations compel us to regard the latter as considerably younger (Devonian).

The Jotnian rocks have suffered almost no dislocation, for they seem to lie relatively undisturbed, except for occasional recent faults. After they were uplifted, they were deeply eroded.

The geological events of this period in the more easterly parts of the northern territory are obscured by a thick accumulation of younger sediments. Recent gravimetric and magnetic observations indicate that here too the ancient crystalline rocks lie at comparatively shallow depths and have the same complexly folded structure as in the areas where they appear at the surface.

Paleozoic Era . At the beginning of the Paleozoic era, during the Cambrian period, the greater part of the northern European R.S.F.S.R. was dry land; but where presently the Urals rise above the lowlands there was a deep geosynclinal basin occupied by a sea. A Cambrian sea also covered considerable areas in the

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region of the Baltic crystalline shield, but, owing to the subsequent uplift and protracted erosion of that area, the sediments (or strata) remained in– tact only here and there in isolated depressions (grabens). At times the land surface to the west of the Urals was depressed below sea level, and at other times again rose slightly. These oscillations were accompanied by volcanism, traces of which have survived in the western foothills of the Urals. The forma– tion of mountain ranges at the site of the modern Timan Ridge began at this time.

In the Ordovician and Silurian periods, a thick series of limestones, dolomites, and sandstones was laid down in a sea which inundated the region of the Urals and the modern Pechora Basin. Similar deposits are encountered in the Timan Ridge and on Kanin Peninsula, as well as in the northernmost parts of the Murmansk r ^ R^ egion, where strata of this age, consisting of limestones, sandstones, and slates crop out on Rybachii Peninsula and on Kildin Island. Except in the areas mentioned, no Ordovician or Silurian deposits have been found in the northern European R.S.F.S.R., and the remainder of the territory was apparently dry land in process of erosion.

In northern Europe, as well as in many other places, widespread folding took place at the end of the Silurian and the beginning of the Devonian period, thus bringing about the formation of mountain ranges in the British Isles, Scandinavia, and Spitsbergen. Such folding apparently took place simultaneously in the regions of the Timan Ridge, Kanin Peninsula, the Ural Mountains, and the Pai-Khoi Range.

The greater part of the northern European R.S.F.S.R. was dry land at the beginning of the Devonian period, for only the region of the Ural foothills was depressed below sea level. Later on, however, a gradual sinking of the land led to an expansion of the sea. Advancing from the east, the shallow sea occupied almost the entire northern territory, and left strata of clays and sandstones,

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and in places (in the Timan region), limestones and shales. Owing to the fact that beds of petroleum and oil shales are associated with them, the Devonian deposits in the Timan have recently been studied with particular thoroughness.

Until recently it was assumed that the Devonian sea did not enter the region of the Baltic shield, but investigations in late years have shown that continental and also shall ^ ow^ -water marine deposits of upper Devonian age are wide- ^ ✓^ spread both in the central parts of Kola peninsula (the Khibin Mountains and the Lovozero tundras) and in the southern parts (Turii Peninsula dn ^ and^ the Varzuga area). ^ ✓^ It is very probable that the entire territory of Kola Peninsula was covered by a thick series of Devonian rocks, which were later eroded away with the remnants in– tact only in regions of subsidence.

Brown algae, subsequently altered to a peculiar coal of extremely high quality, was ^ were^ deposited in the shallow, water-filled depressions of the Ural foot– hills and the Timan at this time. The known reserves of this coal are not large, and as yet have no economic importance.

Various individual districts also underwent elevation and subsidence during the Carboniferous period. At times the northern territory was dry land, and at other times it was covered by a shallow sea. These oscillatory movements of the land influenced the crystalline Baltic massif with the result that the rigid body of the massif was broken by numerous cracks into separate blocks, some of which were upheaved, and some of which subsided. Along the deepest fractures molten magma rose, in part solidifying at depth, and in part breaking through to the surface. Apparently the formation of the great laccoliths of the Khibin and Lovozero tundras, with their rich deposits of phosphorous ore (apatite) and their whole complex of various rare minerals, dates from post-Devonian time. It is possible that the main massifs of the Monche tundra, with their copper-nickel and sulfide ores, were also formed at this same time. Volcanism also affected the region of Timan, the Pechora Basin, and the Urals.

In the region of the western foothills of the Urals, thick layers of plant remains, subsequently converted into beds of coal, were laid down on the bottom of large lakes and swamps, which were covered at that time by a luxurious tropical vegetation.

From the end of the c ^ C^ arboniferous period and existing into the Triassic ^ ✓^ period, a widespread mountain building revolution (Variscian and Herzynian) involving most of Europe also led to the uplift, which marked the beginning of the Urals and the Timan as independent mountain systems. During this same period of disturbance intensified tectonic and volcanic manifestations were felt in the Baltic shield as well.

The beginning of the Permian period is marked by a flooding of almost all the central and eastern parts of the northern territory which, however, thereafter gradually receded. Limestones, marls, and gypseous dolomites were deposited in vast lagoons and brackish lakes, which covered the areas left by the sea. As a result l ^ L^ arge deposits of gypsum ^ of this age^ are now being worked on the banks of the Severnaia Dvina. Simultaneously, an accumulation of coal-bearing argillaceous and arenaceo-argillaceous shales, sandstones, and conglomerates were laid down in the northern part of the Pechora Basin from which coal of varying quality is mined in great quantities on the Usa River and its tributaries (the Vorkuta, Kos-Iu, Adzva, Khalmer-Iu, etc.)

Later, a thick accumulation of clastic rocks (red-colored detritus, con– glomerates, sandstones, and clays) washed down from the neighboring mountains into the eastern Ural sections. Large brackish lakes, in which thick beds of potassium and sodium salts were deposited, formed at the foot of the mountains. The richest deposits of potassium salts in the work, located in the Solikamsk i ^ ✓^ district, as well as num b erous salt springs (the Seregovskie and Solikamskie in the basin of the B ^ V^ ychegda, on the Mezen River, etc.), are associated with the ^ ✓^ sediments of these bodies of water.

Mesozoic Era . At the beginning of the Triassic period, the territory was dry land; sediments deposited during this period consist of brightly colored red, blue, and yellow clays, sands, and conglomerates, and they are of continental origin. During the Jurassic and Cretaceous periods, only the region of the Pechora Basin was depressed below the level of the sea, and marine fossiliferous sands, clays, conglomerates, and shales were laid down.

Cenozoic Era . The northern European territory of the R.S.F.S.R. con– tains no Tertiary rocks except for isolated outliers which have survived erosion on the coast of Kanin Peninsula.

Orogenic processes which involved vast areas of the globe during the Tertiary epoch brought about a reactiv at ation of ancient fractures and fissures ^ ✓^ in the northern territory, which generally trend southeast or northeast; along these, vertical displacement of individual blocks occurred, causing some of the depressed localities to be flooded subsequently by sea waters (the White Sea and parts of the Barents Sea), and others to become lakes. The upheaved sections formed highlands, thus accounting for the present-day basic pattern of relief.

This relation of modern topography to the predominant tectonic lines is not confined to the crystalline shield, but also appears throughout the re– maining northern territory. The broad valleys of the great northern rivers (the Onega, Severnaia Dvina, Pinega, and Mezen), separating elevated regions, lie on the sites of the chief depressions in the crystalline shield. Thus, the valley of the Severnaia Dvina extends along a prolongation of the main depression of the White Sea; the valley of the Onega River, along a prolongation of the Gulf of Onega; and the depression that runs along the Murman coast extend southward in the form of the Vashka-Mezen lowlands. Apparently the system of fractures in the Baltic crystalline shield also pervaded the crystalline basement which underlies the strata of sedimentary rocks in the eastern districts.

The northern territory, which long had remained as a positive land area, underwent continuous erosion, especially intensive in the mountainous areas. Those areas which are compose of more resistant rocks have survived as elevated massifs (the Khibiny and the Chuna tundra on Kola Peninsula, and the hilltops of the Pai-Khoi); those underlain by softer rocks remain as lowlands.

Later — in the Quaternary — the Urals were upheaved a second time.

In the region of the Baltic crystalline shield, erosion is most marked along the tectonic fissures and fractures, where the rocks are weakened by such structural failures.

In the southern parts of the northern territory, the ridge of hard car– boniferous limestones which extends southwestward from the southern shore of Lake Onega, and the residual buttes in the region of the Kama-Vychegda water– shed also owe their topographic expressions to differential erosion.

Glacial Epoch . In northern Scandinavia, on Novaya Zemlya, and in the arctic Urals, the change in climatic conditions which began at the end of Tertiary time led to considerable accumulations of snow, which gradually turned into firn, and eventually the area was completely glaciated early in Pleistocene time.

The number of these glaciations is still not wholly clear. Numerous localities in the northern territory contain two moraini n ^ c^ layers interlayered ^ ✓^ with deposits of sand of marine or continental origin, indicating two glacial advances, whereas other areas show signs of another, earlier glaciations, whose traces may for the most part have been obliterated by later advances; but lack of evidence makes it impossible to reconstruct the complete picture of glaciations in this area. A maximum advance of glaciers moving from the north– west and northeast apparently coalesced in the Timan region, and, heading south, occupied more than half of the European part of the U.S.S.R. Skirting the central Russian uplands, and moving down in two tongues through the Dnepr and

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Don lowlands, the ice reached the latitudes of Dnepropetrovsk and Ust-Medveditskaia. The northern region, where ice accumulation reached its maximum thickness and velocity of movement, is extensively scoured, and the area is characterized by a thin veneer of unconsolidated drift.

Fragmental material was transported southward by the ice and deposited in the area of ablation, forming moraines and glaciofluviatile deposits.

Study of the distribution of erratic contained in these moraines indi– cates that the ice of the Novaya Zemlya-Ural center attained its greatest magnitude in this period of glaciations, pushing back the ice of the Scandinavian center west of the Timan Ridge.

Following this initial glacial stage, a change in climate, trending toward greater dryness and warmth, led to an excess of ablation over accumulation. The ice began to melt intensively and to diminish in thickness, and the glacier terminus began to retreat. Large quantities of meltwater rushed down the gradient of the region toward the north; forming large ice-dammed lakes in which stratified drift was deposited. Relics of these proglacial basins have survived in the shape of broad flat plains composed of sands and loams lying horizontally, and constituting watersheds for numerous rivers. When the coastal regions, which had been isostatically depressed under the weight of the ice, were freed by melting, they were inundated by the sea, which pene– trated far inland over the lowlands. The depositional proof, consisting of fossiliferous clays and sands of this marine transgression, which has been given the name “Boreal,” is found on Kola Peninsula at an elevation of 140 meters, in the basin of the Severnaia Dvina and the Onega at an elevation of 60 to 80 meters, and in the extreme northeast at 200 to 280 meters, above sea level.

Shells found in the marine deposits, and belonging to kinds of mollusks now living in the warmer waters of the Mediterranean and Black seas, indicate that, in the period of the transgression, the sea was warmer than at the present time. In the areas which were not inundated by the sea, interglacial deposits are represented by lake and river sands, clays, and gravels, contain– ing fossil remains of vegetation which is also indicative of warmer climate.

After the warm interglacial period, cooler climatic factors gave rise to a new and final glacial stage which was of comparatively small dimensions, and during which ice exceeded the boundaries of the region under consideration only in the west.

The extreme limit of spread of the glaciers advancing from the northwest was apparently on a line running from the mouth of the Mezon River, on the southeast, through the confluence of the Severnaia Dvina and Vaga rivers to Vologda and thence to the Upper Volga, on the southwest. This limit abruptly separates the pronounced and well-preserved morainic forms, prevalent in the northwest, from the blurred, eroded and smoothed-over forms of relief which have survived from the preceding glaciation in the southeast.

Owing to inadequate study of the terrain, it is much more difficult to determine the limit of the spread of glaciers from the Novaya Zemlya-Ural center of glaciation. Well-preserved morainic formations are found in the Kanin, Malozemelskaia, and Bolshezemelskaia tundras.

Numerous data point to the fact that in the epoch of the last glaciations the Scandinavian and Novaya Zemlya-Ural glaciers did not coalesce, and that an unglaciated belt existed between them.

At the end of this glaciations, the terrain at the glacial front was again overspread by proglacial lakes fed by glacial meltwater. Especially large

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lakes formed in the regions of the upper reaches of the Pechora River, and of the headwaters of the Mezen, the Severnaia Dvina, and the Onega. Vast plains composed of sands and clays are the residues of these bodies of water.

During the retreat of the glacier, at a time ^ when^ ice filling the narrow part (the “Gorlo,” or “Throat”) of the White Sea sealed off the waters of the Barents Sea, large deep freshwater lakes formed in the depressions, already partially freed of ice, in the central part of the White Sea.

The level of the lakes at this time was considerably higher than present sea level; the position of the former may be determined from the lacustrine depots (varved clays) found on the southern coast of Kola Peninsula, and on other shores of the White Sea as well.

At the end of the glacial period, sea waters flooded the littoral zone once more, but this neoglacial transgression did not attain the dimensions of its interglacial predecessor, and now occupies considerably smaller areas. This transgression attained its greatest development in the west, where its deposits are found as high as 100 to 150 meters at the present time. At that time the White Sea may have been connected both with the Kola Inlet of the Barents Sea (through Lake Imandra), and the Baltic Sea (through Lake Onega and Lake Ladoga). On the east, traces of the marine transgression have been recorded at height of 50 to 60 meters.

The final (postglacial) marine transgression, traces of which are found at heights of 18 to 20 meters along the shores of the White Sea, and at heights of 50 to 70 meters in the extreme northeast, was still weaker. No traces of this transgression have been found in the Timan region. After the main mass of ice had finally melted away, small local glaciers continued to exist over a long period on the highest summits. Evidence for this type of

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glaciations is found in the form of cirques, troughs, and terminal moraines, therefore bearing witness to the fact that these areas were freed by the glaciers quite recently.

When such glaciers move into the range of occurrence of the overwide crystalline rocks, they smoothed and polished the projecting crags, giving them gentle, rounded contours, particularly on the side facing toward the moving ice. Numerous scars and scratches, which have survived on the polished surface of the rocks, indicate the direction of movement of the ice. In the region of the crystalline shield, the moraine generally reaches no great thickness; only in places where the terminus of the retreating glaciers remained for a long time does the thickness of the debris increase. Esker ridges up to 20 meters in height, stretching for several kilometers, and drumlins, occur frequently here. Morainic ridges and hills occur more rarely.

Outside the borders of the crystalline shield, the thickness of moraines increases, and morainic hills acquire great importance, especially at the terminal limits and in the region of the ridge of Carboniferous limestones, where glacial crags are observed.

When the glacier encountered projections of rock in its path, it not only smoothed them over, but tore off large blocks and transported them sometimes over a great distance. Thus, large blocks of rock are found in the basin of the Severnaia Dvina which have been transported over a distance of approximately 200 kilometers. Evidently the large blocks of limestone of the Kazan stage which are found on the heights of Tsypina-Gora and Maura near the White Sea are of the same origin.

In places the rocks have buckled under the weight of the masses of ice, forming small folds (glacial deformation).

Outside the limits of the last glaciations, glacial meltwater played an important role in the process of washout and planning of the relief produced by old glaciations, and developed a network of broad valleys; thin loams covering the moraine were spread over the flat interfluves and gentle slopes.

The elevation and subsidence of individual areas of the land in the Quaternary period, due to isostatic adjustments under ice load, produced a renewal of old tectonic fissures and fractures, as well as development of new ones, in the crystalline massif. Fresh, gaping chasms — fissures which have not been filled by Quaternary deposits — are found both along the coasts and in the central massifs (the Khibiny) of Kola Peninsula. Upheaval of the crystalline shield is taking place at the present time, reaching its greatest intensity of the central parts, whereas the peripheral parts are rising more slowly or not at all. Some districts lying outside the shield (the littoral of Mezen Gulf, for example) are similarly undergoing adjustment. The uneven rising of different parts of the shield is expressed in alteration of the shore line of the sea and of the lakes on Kola Peninsula. The northwestern shores of many lakes are marked by a lowering of the water level and drying of the banks, while the opposite shores are being submerged, and tilting of shore line ^ s^ is the observed results. ^ ✓^

These adjustments in the earth’s crust are often accompanied by earth– quakes, which have been recorded repeatedly on Kola Peninsula (at Kola, Kandalaksha, and other places). Modern processes of denudation by running water have altered somewhat the glacial relief, and produced the existing surface features.

Geomorphological Regions.

As a result of the geological processes which have been described, the following geomorphological regions of the territory are now recognized:

The region of the crystalline Baltic shield embraces Kola Peninsula. The regions is composed of ancient crystalline rocks and metamorphic schists, with isolated inliers of metamorphosed Paleozoic rocks (Silurian and Devonian) which have escaped erosion.

The basic features of the relief result from fractures, block faulting, and differential erosion. Since the region is located close to a center of Quaternary glaciations, it contains abundant traces of glacial scour and roches moutonn e ^ é^ es . The thickness of the glacial till is thin and scattered, ^ ✓^ found chiefly in the form of ridges trending in the direction of movement of the glaciers, and at right angles to it.

The marginal area of the Russian platform lies between the border of the crystalline shield and the Timan-Kanin mountain system. The crystalline basement is deeply buried and concealed sedimentary Paleozoic and Mesozoic rocks, lying for the most part horizontally, and composing a struc– tural plateau. This is dissected by wide, deep valleys, the distribution of which is related to fractures in the underlying crystalline shield. During periods of submergence, the broad valleys served as channels for postglacial marine invasions, whereas during times of uplift the same channels served for the discharge of glacial meltwaters and normal runoff. In the northwestern part of the region, the part which falls within the area of the last glaciations, thick accumulations of moraine have been well preserved, forming the characteristically hilly topography, with lake-filled depressions which for the most part occur in clusters, and often united into chains. Intervening level areas are overlaid with fluvioglacial deposits. Beyond the limits of the last glaciations, the morainic accumulations of the maximal glaciations are much eroded, and often covered by glaciofluvial deposits.

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Gentle rolling divides, with a network of ancient glacial meltwater channels and rather extensive glacial lake flats, predominate.

The Timan-Kanin belt of residual folding is an area of ancient mountain uplift composed of folded Paleozoic sediments with isolated outcrops of igneous and metamorphic rocks, eroded to a stage of residual highlands. The highest ridges and hills are associated with the rocks yielding less readily to erosion. The depressions between the ridges and hills are filled with ancient alluvial, lacustrine, and (in part) marine deposits. The thickness of the drift is not great, the thickest moraines being those left by the last glacial stage.

The region of the Pachora Basin is characterized by a complicated geo– logical structure as yet inadequately studied, and is bordered by the ancient folded systems of the Timan, the Urals, and the Pai-Khoi. The Paleozoic rocks which make up the region are in places crumpled into folds and broken by faults, particularly in the vicinity of the Urals.

The northern part (the Bolshezemelskaia and Malo s ^ z^ emelskaia tundras) ^ ✓^ was glaciated, the ice having moved down from Novaya Zemlya and the Urals; this area is characterized by a very pronounced row of hills consisting of morainic topography. In the southern parts, plains composed of fluvioglacial deposits predominate. The low-lying seacoast and the broad valley of the Pechora River are covered with marine deposits.

The Ural and Pai-Khoi belt of folding is an area of ancient mountain uplift, the northern part consisting of chains of hills, composed of the harder rocks, which have survived erosion. The smoothed forms of relief typical of glaciated areas are prevalent here. In the parts of the Arctic and northern Urals which were considerably upheaved in Quaternary time, traces of local glaciation of the alpine type are very pronounced.

G. D. Rikhter. The Northern European Part of the U.S.S.R.: physicogeographical characteristics . Mosco s ^ w^ , 1946, p.17 ff. ^ ✓^ Translated by Ordway Southard

Geology of the European North, U.S.S.R.: Encyclopedia Arctica Volume 1: Geology and Allied Subjects