Regional Problems of Earth's Cryology The
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EARTH’S CRYOSPHERE SCIENTIFIC JOURNAL Kriosfera Zemli, 2018, vol. XXII, No. 3, pp. 3–15 http://www.izdatgeo.ru REGIONAL PROBLEMS OF EARTH’S CRYOLOGY DOI: 10.21782/EC2541-9994-2018-3(3-15) THE PHENOMENON OF GEOCRYOLOGICAL CONDITIONS IN THE EASTERN PART OF THE OLEKMACHARA PLATEAU S.N. Buldovich, E.N. Ospennikov, V.Z. Khilimonyuk Lomonosov Moscow State University, Faculty of Geology, 1, Leninskie Gory, Moscow, 119991, Russia; [email protected] The paper discusses results of the study of geocryological (permafrost) conditions in the eastern part of the Olekma-Chara Plateau at the watershed divide of the Tokko River and its tributary, the Choruoda River, carried out within the fi eld study of the sites of mineral showings (deposits), whose permafrost conditions are extremely contrasting. The combined impact of hydrogeological factors acting in the middle altitude environ- ment is found to be largely responsible for the unique permafrost conditions in the study area. Olekma-Chara Plateau, geocryological conditions, hydrological conditions, permafrost, annual average soil temperatures, geocryological processes INTRODUCTION The study area, located in the southwest of the Moscow State University, which conducted a compre- Republic of Sakha (Yakutia) and subsumed into the hensive permafrost-hydrogeological and permafrost- eastern part of the Olekma-Chara Plateau, is under- engineering geological survey within the Aldan-Timp- lain by permafrost which had been largely underex- ton interfl uve area. Later, in 1973–1985, this expedi- plored until the middle of the twentieth century, with tion conducted medium-scale surveys (1:50 000 and the information about it ranging from sketchy (i.e. 1:200 000) in the areas of coal deposits within the derived from results of comprehensive geological- Chulman Plateau, southern Yakutia [Kudryavtsev, geophysical expeditions) to unavailable. The system- 1975]. Results of the exogenous geological processes atic geocryological study began in the 1930s and and phenomena surveys (1:200 000 and 1:500 000 1940s and gained traction in the decades to follow. In scales) in the territory of the Aldan-Timpton inter- southern areas of permafrost distribution the studies fl uve in the late 70s–early 80s of the last century were were conducted by the Aldan permafrost research analyzed and discussed in [Ospennikov et al., 1980]. station (PRS) staff of the Permafrost Institute of the It is noteworthy that the Olekma-Chara Plateau USSR Academy of Sciences (V.M. Ponomarev, area has been hitherto least studied in southern Yaku- S.E. Su khodolskii, S.M. Fotiev, N.A. Vel’mina, tia, specifi cally, its part adjacent to the Tokko river G.N. Fi losofov, V.R. Alekseev and others). The 1951– valley [Ershov, 1989]. With regard to permafrost as- 1954 regional survey works as part of permafrost-hy- pects, the studies, in themselves, were reduced to the drogeological studies of the Aldan-Timpton inter- information about ground temperature regime in per- fl uve area were conducted by the Yakutia Complex mafrost zones obtained by M.N. Zheleznyak and Expedition (A.I. Efimov, P.I. Melnikov, I.D. Belo- others [Dorofeev et al., 1981; Zheleznyak, 1998, 2005; krylov and others) of the USSR Academy of Sciences Semenov and Zheleznyak, 2013]. Proceeding from Council for the study of Russian natural productive these, the average annual temperature of rocks in- forces. In the 1960s, these endeavors were continued creases in the direction from the watershed divides to by the Udokan Expedition of the Permafrost Insti- the river valley bottoms, where the rocks for the most tute of the USSR Academy of Sciences, during which part remain in the unfrozen state. a team of researchers headed by I.A. Nekrasov inves- During the 2009 Expedition, the researchers tigated geocryological conditions of the Udokan from the Department of Geocryology, Moscow State Ridge along with the Chara, Verkhne-Kalar and University conducted geocryological surveys along Nizhny Ingamatkit intermountain basins. with the 1:25 000 mapping of one of the sites located More complete data and materials on the forma- within the Verkhe-Tokkin area. The results allowed tion of permafrost and its regional variability in south- the fi rst ever comprehensive permafrost characteris- ern Yakutia were obtained during the works of the tics of the study area and provided new insights into 1961–1964 Expedition of the Faculty of Geology of its entire geocryological situation. Copyright © 2018 S.N. Buldovich, Е.N. Ospennikov, V.Z. Khilimonyuk, All rights reserved. 3 S.N. BULDOVICH ET AL. BRIEF CHARACTERIZATION vers, the tributaries to the Olekma river. All streams OF THE GEOEVIRONMENTAL SETTING are fi lled with water only during the spring snowmelt The study area is located in the watershed area and prolonged spells of summer rains. Otherwise, of the Tokko River and its tributary, the Charuoda most of the time the stream-beds remain dry. Their River (Fig. 1). thalweg marks range between 1100 and 1180 m. The area topography (relief) is medium-moun- The climate of the area, which is defi ned as sharp- tain, characterized by 1200–1400 m absolute eleva- ly continental, is largely controlled by the mountain- tions on the watershed surfaces and deeply embedded ous terrain, as well as by the band of air masses trans- (to 200–300 m) bottoms of the river valleys, with the fer shift from western to eastern direction, i.e. to the slope steepness reaching 25–30°. The river network East Pacifi c [Karausheva, 1977]. This area is charac- of the area, composed by small watercourses, is sub- terized by long cold winters and short summers with sumed into the basins of the Tokko and Charuodo ri- the avera ge values described as: the mean annual tem- Fig. 1. Location map of the inves- tigated area of the eastern part of the Olekma-Chara Plateau, on the watershed divide of the Tokko Rv. and its tributary Chorouda (South- ern Yakutia). 4 THE PHENOMENON OF GEOCRYOLOGICAL CONDITIONS IN THE EASTERN PART OF THE OLEKMACHARA PLATEAU perature is –7.8 °C; the annual amplitude of the mean tions. As is the case with watersheds and slopes oc- monthly temperature fl uctuations reaches 57 °C; the cupying most of the study area and underlain by per- annual precipitation ranges between 330 and 680 mm, mafrost to significant depths, the feeding of generally increasing with height. groundwaters by infi ltration waters is precluded. At Most of the precipitation falls during the sum- this, subsurface waters are recharged dominantly mer season (50–70 %), while only 7–15 % accounts from surface runoff during the warm season. In the for winter. The snow cover exists from September bottoms of river valleys, where the groundwater feed- through May, with its depth reaching 0.7–0.9 m or ing sources are amassed, groundwaters are widely de- greater, at the foot of slopes, particularly in their veloped in alluvial and fl uvioglacial sediments. Judg- wooded areas. The snow cover density varies from ing from the nature of circulation, these are porous 0.12 to 0.18 g/cm3, averaging 0.13 g/cm3. Due to in- phreatic waters, which discharge through the fault tensive snowdrift transport at the watersheds, the zones into the underlying aquifer complex of lower snow cover depth (average density: 0.145 g/cm3) Proterozoic sediments. According to drilling data does not exceed 0.2–0.4 m there. (depth range: up to 150 m), the rocks are either in the Soils and vegetation developed in the area belong permafrost state to a depth of hundreds of meters, or to the mountain-tundra, mountain-shrub-tundra, drained in most of the investigated area. As such, the mountain-sparse woodland, and mountain-valley situation is typical of the interfl uve and slope areas types. The area is differentiated by sparse marshy and of the valley bottoms. Locally, in eastern part of landscapes, observed in some segments of the Levy the study area, the position of water table of the con- Usu Creek valley bottom. Judging from the regional sidered aquifer is found to be close to the surface, vegetation cover pattern, the territory is labeled as though. the light coniferous taiga province of the middle taiga The deposits’ deep drainage within the study subzone. The presence of permafrost and seasonally area is, undoubtedly, exerted by the proximity of a frozen rocks slows down the biochemical reactions major regional drain, the Tokko river (∼7–8 km to fl ow in the soil horizon during a short vegetative sea- the west from the investigated site) with absolute el- son, along with the formation of soil profi le, causing evations of the valley tahlweg of about 650 m within thereby the dominance of thin, primitive and skeletal the considered intercept along the course of the river. soils across the area. With the spot elevations ranging between 1000 and Geological structure. In the geological framework 1400 m, the investigated site (as part of Tabornoe de- of the area, the most ancient structural stage is com- posit) represents a topographically elevated area and posed by Archean rocks: crystalline shales, gneisses, therefore the sedimentary rocks here are expected to amphibolites, quartzites. The upper structural stage have drained to signifi cant depths. The thickness of is represented by folded and metamorphosed lower the zone of aeration, even beneath the bottoms of the Proterozoic sediments, dominated by the metamor- valleys can reach 200–300 m, and signifi cantly deeper phosed terrigenous deposits, mainly sandstones and in the watershed areas (400–500 m). At this, the frac- siltstones. The intrusive Archean, early Proterozoic, tured solid rock mass is ubiquitously and completely late Proterozoic and late Jurassic rocks are made up saturated with water below the Tokko river stream- by amphibolites, gabbroids, pyroxenes, diabases and bed occurrence level.