BAIKAL-AMUR MAINLINE (BAM) (RU: Байкало-Амурская магистраль) is the railway track within the Eastern Siberia and at the Far East, the second mainline railway access of the USSR to the Pacific ocean. It lays on the territory of the northern districts of the Irkutsk province (pre-Baikalian part), Buryat ASSR, Chita province (trans-Baikalian part), Amur province and Khabarovsk territory (Far Eastern part). The total length of the track from the Taishet town to the Sovetskaya Gavan town is 4300 kilometres, of them the length of the part, which is under construction since the 1974, namely, from the Ust-Kut town (on the Lena river) to the Komsomolsk-on-Amur city, is 3100 kilometres; there adjoin to it two previously built parts: from the Tayshet town to the Ust-Kut town (733 kilometres, has been commissioned during the 1958), and from the Komsomolsk-on-Amur city to the Sovetskaya Gavan town (434 kilometres, has been commissioned during the 1947). Three connecting lines join the BAM with the Trans-Siberian railway: from the BAM to the Tynda town, from the Izvestkovaya town to the Urgal town, and from the Volochaevka town to the Komsomolsk-on-Amur city. The territory, which belongs to the zone of influence of the BAM (1.5 million square kilometres) is distinguished by the very complicated natural conditions, geological structure and relief, development of the permafrost rocks, strong seismicity, significant swamping, which are determining the large amount of the geological researches, engineering-geological and hydrogeological searches, which are associated with the laying of the track, construction of the near-station and other towns and cities, mastering of the mineral raw material resources.
Relief. The pre-Baikalian part occupies the Prilenskoe (Angara-Lena) plateau with the prevalence of the mild forms of the relief, namely, wide flat watersheds, small depressions and plains. The absolute heights range within the limits of 400-1000 metres. The track has been laid mainly through the valleys of the Lena, Tayura, Kirenga, Kunerma rivers. The trans-Baikalian part is situated entirely within the limits of the Baikalian mountainous country. There are located within its western part the Baikalskiy, Akitkanskiy, Synnyrskiy, and Barguzinskiy ridges with the heights of up to 2600 metres. There are characteristic for the Baikalskiy ridge the alpine forms of relief, namely, the trough valleys, limestone pavements, circuses, stony placers (kurums), and others; the ridges have the features of the bare rocky plateaus. The eastern part occupies the vast and complicately built Stanovoe highland, where are alternating themselves the high ridges and deep basins, which are stretched from the west or south-west to the east or north-east. The latter ones divide this highland into the two chains: the northern one, which includes the Verkhneangarskiy, Delyun-Uranskiy, North-Muiskiy, Muyakanskiy, and Kodarskiy ridges, and the southern one, which includes the South-Muiskiy, Kalarskiy, and Udokanskiy ridges. The absolute heights reach 2800 metres (the Skalistyi Golets within the Kalarskiy ridge).
All the ridges represent the systems of the dome-shaped or flat-topped bare rocky mountain peaks, which are covered by the placers of the coarse clastic depositions, and within the axial parts of the ridges they represent the alpine forms of the relief; there exist the traces of the ancient, and within the Kodar ridge also of the modern glaciation (circuses, limestone pavements, moraine ridges, glacial lakes). The large part of the track within this part of the mainline traverses the largest basins, namely, the Verkhneangarskaya, Muysko-Kuandinskaya, and Verkhnecharskaya, which are having the absolute heights of 500-700 metres and the hilly-plain relief. There belong to the trans-Baikalian part of the mainline all the tunnels of the BAM, the total length of which is 26 kilometres, including the 15.3 kilometres of the North-Muyskiy one, 6.7 kilometres of the Baikalian one. There exist together within the Far Eastern part of the mainline the medium-height and low-height mountains with extensive accumulation-denudation plains. The track passes here along the southern spurs of the Stanovoy ridge, traverses the Tukuringra-Dzhagdy, Turana, Bureinskiy, Dusse Alinskiy, Badjalskiy, Sikhote-Alin ridges, and exits to the coast. Approximately 1/3 of the Far Eastern part of the track passes through the Upper Zeya and Amur-Zeya-Bureya fluvial plains, which are having the low-ridged and very swampy relief. Within the mountainous regions, the track passes mainly on the slopes of the mountains and the valleys of the rivers (the left tributaries of the Amur river).
Geological structure. The territory, which is adjacent to the BAM, covers the fragments of several largest tectonic structures, namely, of the Siberian tectonic plate, Baikalskaya and Stanovaya mountainous provinces, Mongol-Okhotsk and Sikhote-Alin folded systems (see the map). These structures are limited by the thick extended zones of the faults; the numerous ruptured disturbances cause their mosaical blocky structure. The long and complex history of the geological development has predetermined the wide distribution of the sedimentary, volcanogenic, intrusive, metasomatic, and metamorphic complexes of the different ages (from the Archaean to the Cenozoic) and extremely diverse composition, and also of the useful minerals, which are associated with them. The western part of the territory (the drainage basins of the Angara and Lower Tunguska rivers, the headwaters of the Lena river) belongs to the south-eastern periphery of the Siberian tectonic plate. Here are developed the carbonatic-terrigenous depositions of the Paleozoic and Mesozoic, which are embedded with the slight inclination, and are saturated with the sills of the diabases. Within the Western near-Baikalian territory, the thickness of the Paleozoic and underlying Proterozoic depositions sharply increases, as well as the degree of their dislocatedness (the Angara-Lena downfold).
There are widely distributed within the Baikalian mountainous country the metamorphosed and dislocated sedimentary and volcanogenic strata of the Upper Archean, Proterozoic, and Lower Paleozoic, which are riddled by the intrusions of the different composition. There exist the outcrops of the most ancient crystalline basement (Baikalian, North-Muyskaya blocks, and others). There are noted within the certain places the Mesozoic sedimentary, volcanogenic, and intrusive formations. The large depressions of the Baikalian type are formed by the stratum of the loose Cenozoic depositions (see the "Baikalian system of the rifts" article). Within the limits of the Aldan shield, there are developed the metamorphic strata of the Lower Archean, among which are mapped the numerous sutural downfolds (troughs) with the greenstone sedimentary-volcanogenic-siliceous formations. They are overlain within the Kodar-Udokan region by the thick stratum of the Lower Proterozoic terrigenous depositions, and within the drainage basins of the Zhuya, Aldan, Uchur rivers by the terrigenous and carbonatic depositions of the Proterozoic, Vendian, Paleozoic, and Mesozoic, which are embedded with slight inclination. Along the southern periphery of the shield, there extends the series of the depressions with the Jurassic and Cretaceous coal-bearing depositions (Chulmanskaya, Tokiyskaya, and others). The intrusive formations include the ancient granites, gabbro and ultrabasites, Paleozoic granitoids, small Mesozoic intrusions of the alkaline composition, Proterozoic intrusions of the alkaline ultrabasic rocks. The Stanovaya mountainous province is characterized by the wide distribution of the Archean metamorphic rocks and granite-gneisses, Mesozoic granitoids. There exist the troughs with the greenstone complexes of the pre-Cambrian. There are noted everywhere the disunited Mesozoic volcanic structures, small intrusions of the diverse composition, and also the grabens, which are formed by the Jurassic and Cretaceous coal-bearing depositions.
Within the Mongol-Okhotsk folded system, there are developed the metamorphosed and dislocated sedimentary and volcanogenic strata of the Proterozoic, Paleozoic, and Mesozoic, which have been breached by the intrusions of various ages. Within the drainage basin of the Zeya river and its tributaries, there are known the Mesozoic volcanic structures and depressions, which are filled by the coal-bearing depositions. Within the limits of the Bureinskiy massif, there prevail the ancient granitoids, which are breaching the pre-Cambrian crystalline schists. At the east of the region, there are developed the sedimentary-volcanogenic formations of the Mesozoic and Paleozoic, which are forming the Sikhote-Alin folded system. There are very numerous the volcanic structures and belts (Primorskiy, Yam-Alin), in the forming of which take part the Mesozoic and Paleogene - Early Quaternary volcanic rocks. Among the intrusive formations, there prevail the granitoids of the Late Mesozoic. The series of the large riftogenic depressions and extensive downfolds is filled by the Cenozoic sediments (Tugurskiy graben, Khabarovsk depression, and others).
Seismicity. The part of the zone of the BAM is highly seismic. The pre-Baikalian part of the mainline, which passes on the Siberian tectonic plate, is aseismic, but sometimes the "in-transit" earthquakes with magnitude of up to 5 points also arrive here from the side of the Baikalian seismic belt. The trans-Baikalian part of the mainline is most seismic. It has been determined, that the epicentres of the earthquakes group themselves into the relatively narrow strip along the chain of the rift depressions; at the same time, there are characterized by the increased seismicity the inter-rift mountain connections (Verkhneangarskaya-Muyskaya, Muyskaya-Charskaya). The seismic situation at the Far Eastern part of the mainline is very varying. The increased seismicity from the Udokanskiy ridge to the east and within the region of the middle flow of the Olekma river is associated with the system of the ruptures of the Stanovoy fault. The seismicity weakens from the Olekma river to the east, but increases again within the region of the Tukuringra-Dzhagdy ridge; it is associated with the Mongol-Okhotsk fault. Further to the East, the earthquakes occur less frequently, and are of the less strength, though even here exist the seismic focuses (Zeyskiy, Amgunskiy, and others) with the magnitude of the earthquakes of up to 7 points. Thus, the zone of the BAM is situated within the complex engineering-seismological conditions; during the designing of the built structures, there is provided the anti-seismic strengthening of the constructions.
Permafrost. The extreme western part of the mainline belongs to the non-frozen zone; on the remaining territory, the permafrost is distributed either everywhere, or in the form of the islands. From the Angara river to the east, to the Baikalskiy ridge, the permafrost occupies small areas, it may be found in the form of the isolated massifs within the swamped river valleys and on the northern slopes. Within the large rift depressions of the Baikalian mountain province, the permafrost is developed only on the flood plains and first terraces of the rivers, on the diluvial plumes and cones of the outflow, which are usually swamped. The thickness of the permafrost rocks may reach, apparently, the values from 150 to 500-600 metres. The most severe permafrost conditions exist within the mountainous framing of the depressions with the heights of the ridges of 2000-2800 metres. The permafrost strata are characterized by the almost continuous distribution, being interrupted by the taliks only at the bottoms of the deeply incised large valleys, and within the zones of the flooded faults. Their thicknesses reach, apparently, more than 1 kilometre. On the Aldan shield, the continuity and thickness of the permafrost increases with the height. The most mild permafrost conditions exist within the range of the heights of 800-1000 metres, where the watersheds are usually melted. Such watersheds are developed mainly within the limits of the Mesozoic coal-bearing depressions. Below this height, permafrost again gets prevalently continuous distribution, being interrupted by the taliks only within the valleys of the large rivers.
The watershed spaces of the most high ridges (Stanovoy, Yankan, Tukuringra), are, as a rule, frozen, the thickness of permafrost reaches 200 metres. On the southern slopes, and on the low (500-1000 metres) watersheds, the thickness of the permafrost rocks sharply decreases, the taliks are extensively developed; the swamped bottoms of the valleys and the diluvial plumes at the foot of the slopes are permanently frozen. Within the middle mountain ridges of the near-Amur region (Soktakhan, Dzhagdy, Ezop, Dusse-Alin, Bureinskiy, and others), the regularities of the structure of the permafrost are similar. The permafrost conditions of the intermountain depressions are more differentiated. Within the most northern of them, namely, Verkhnezeyskaya, the permafrost rocks have almost continuous distribution. Within the limits of the Zeya-Bureya fluvial plain, they cover the bottoms of the broad swamped intermountain valleys, measured low ridges, watersheds, which are formed at the surface by the finely dispersed depositions.
Underground waters. Depending on the natural conditions, there exist the great differences of the conditions for the forming of the resources and composition of the underground waters. Under the tectonic plate conditions of the Angara-Lena plateau, there prevail the stratified and stratified-karstic waters within the terrigenous-carbonatic rocks of the Ordovician and Lower Cambrian, to the lesser degree within the alluvial and glacial depositions. The large focuses of the discharge of the underground waters form themselves sometimes at the places of contact of the highly permeable carbonatic rocks with the slightly permeable terrigenous ones, which are forming the lithological barriers. Within the Baikalian mountainous country, the significant resources of the underground waters are concentrated within the alluvial and lacustrine-alluvial depositions, within the massifs of the carbonatic rocks within the zones of the faults (talik waters). On the Aldan shield and within the Stanovoy ridge, the underground waters are also associated mainly with the continuous taliks within the alluvial depositions; there exist the cracked sub-permafrost and fractured-veinous waters within the zones of the faults. Within the Zeya and Zeya-Bureya fluvial depressions, the abundant horizons of the pressurized waters (often sub-permafrost) are associated with the Jurassic and Cretaceous sandstones and lacustrine- alluvial depositions. Within the Bureinskiy ridge and Sikhote-Alin province, there exist the significant accumulations of the layered and fractured waters; there are most suitable for the practical usage the underground waters of the alluvial depositions within the fluvial valleys.
The permafrost rocks have the important significance for the forming of the hydrogeological conditions on the large part of the territory of the zone of the BAM. In certain cases they exclude from the active water exchange the huge massifs, in other cases they serve as the regional aquitard, which is separating the waters into the sub-permafrost ones and supra-permafrost ones. The underground waters of the zone are extremely diverse in their chemical composition, which is determined by the chemical composition of the water-bearing rocks. There also varies within the very wide limits the degree of the mineralization of the waters (from 0.1 to 630 grams per litre). The sources of the mineral waters are quite numerous. There are distinguished the Eastern-Siberian hydromineral province of the nitrogenous and methane chloridic and sulfatic salt waters and brines, Baikalian province of the nitrogenous and methane thermal waters, lower-Amur province of the cold waters with carbon dioxide, Amur-Primorskaya province of the nitrogenous and methane thermal waters. The mineral waters may be used here for the medicinal, thermo-energetical, industrial purposes, as the source for the extraction of the table salt, and so on.
Engineering-geological conditions. The most common feature of the engineering-geological structure of the zone is the prevalent development of the hard rocks, which are overlain by the non-significant cover of the loose Quaternary depositions of the eluvial, diluvial, alluvial, and glacial genesis. The thickness of this cover is 2-3 metres, in rare cases more than 10-15 metres. This stratum is the object for the engineering-geological mastering; it fills the over-deepened valleys, includes certain fields of the development of the glacial and water-glacial depositions, large diluvial plumes. There occupy the substantially smaller area the regions, where all the engineering-geological cross-section is formed by the loose Cenozoic depositions. These regions are the rift depressions of the Baikalian province, and the large depressions of the near-Amur region.
The most important factor for the forming of the engineering-geological conditions is the modern geological processes and phenomena. There are distributed everywhere within the zone of the BAM the slope processes (diluvial wash, solifluction, and especially the stone rivers), which represent the special danger during the construction on the surface of the ground. There are widely distributed on the ridges of the alpine type the avalanches, mudslides, and the forms (focuses, troughs, plumes), which are associated with them. The zone of the BAM is covered by the aufeis of the underground and ground waters, which are having the varying dimensions and dynamics. The significant part of the aufeis has developed the well-expressed aufeis glades. There are common such cryogenic phenomena, as the thermokarst, polygonal formations (repeated-veinous ices, ground veins, and similar ones), structural soils (stone rings, spots-lockets, and others), which are associated mainly with the bottoms of the valleys, wide watershed spaces, plains. As a whole, the conditions for the engineered mastering of the zone of the BAM are difficult, especially within the limits of the Baikalian folded province, where combine themselves the high seismicity, most severe permafrost, and high mountainous relief.
Mineral raw material resources. The zone of the BAM is the relatively little studied, but promising region at the east of the country: the known large deposits and ore manifestations permit to hope for the possibility of the discovery of the new industrial deposits of the diverse useful minerals. There are known on the Siberian tectonic plate the fields of the gas condensate (Markovskoe, Yaraktinskoe, and others), thick layers of the rock and potassium salts (Nepa-Gazhenskiy basin), there have been uncovered the small deposits and manifestations of the phosphorites, coals, copper sandstones. From the Ust-Kut to the west, there have been identified and explored the deposits of the iron ores of the Angara-Ilim and Angara-Kata regions. Within the Baikalian mountainous country, there have the importance of the first degree the deposits of the pyrite-polymetallic ores within the greenstone strata of the Proterozoic (Kholodninskoe), muscovite (Mama district), chrysotile asbestos (Molodezhnoe), gold (placer deposits and small ore deposits), and diverse ornamental stones. There are known also the fluorite-polymetallic deposits within the carbonatic strata (Barvinskoe, Tabornoe, and others), the manifestations of the nickel, molybdenum, tungsten, rare elements, and also of the mineral and brown coals. For the Aldan shield, there are the most important the gold, mineral coal, copper, and iron. Besides the ore deposits of gold (Aldan region), there are known the numerous placer deposits. The deposits of coal have been explored within the Chulmanskaya depression; there are significant the prospects of the Tokkinskaya depression and other Mesozoic depressions, which are forming the South Yakutia coal basin. The depositions of the copper sandstones are known at the west of the Aldan shield (the Udokan deposit). Within the Chara-Tokko region, there have been determined the significant reserves of iron (magnetitic quartzites within the ancient strata), within the South Aldan region, there have been explored the deposits of the iron ores of the metasomatic type (Taezhnoe, Desovskoe, Pionerskoe, and others). There are being developed the deposits of phlogopite (Aldan region), there have been discovered the deposits of the apatite (Seligdarskoe), copper-cobalt ores with platinoids (Chineyskoe), rare elements, and also of the corundum, graphite, charoite (the single deposit within the world), rock crystal, and so on.
Within the Stanovaya province, there has the industrial significance the extraction of gold; there have been identified the ore manifestations of the molybdenum, copper sandstones, polymetallic ores, mercury, rare elements, apatite, magnetitic ores, ornamental stones, building materials. The Mongol-Okhotsk system and the Bureinskiy massif are characterized by the numerous placer deposits and small deposits of the ores of gold, iron (Garinskoe), coal (Bureinskiy coal basin), by the manifestations of the tin-polymetallic ores, molybdenum, manganese, phosphorites. Within the Sikhote-Alin system, the leading role belongs to the extraction of tin (Komsomolskiy, Badzhalskiy, and other regions), there are known also the deposits of the ores of gold and tungsten.
There are enclosed within the Neogene-Quaternary depressions the mineral and brown coals (the Lianskoe deposit). Within all parts of the zone of the mastering of the BAM, there are numerous the deposits of the various building materials, the reserves of which provide the construction of the track itself, industrial and dwelling-servicing facilities.
The mastering of the mineral raw material resources, together with the forest developments, will give the impetus for the development of the productive forces of the zone of the BAM. The large reserves of the valuable useful minerals assist to the forming on their basis of the territorial-industrial complexes, such as within the South Yakutia, where develops the large-scale extraction of coal, and there is possible in the future the extraction of the iron ores, apatite, and so on.
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