Darhad paleolake and Darhad glacial Megafloods in the context of Catafluvial events in North Asia in the late Pleistocene

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Аннотация

A set of geomorphological and geochronological studies was carried out aimed at determining the reasons for the formation of the periglacial Darhad paleolake and the age of the Darhad megafloods (glacial superflood). The main landforms and sedimentary strata from the Darhad Basin to the Western Sayan Ridge, formed in the zone of dynamic influence of the glacial superflood, are characterized. Based on analysis, satellite images, digital elevation model, mapping and reconstruction, new data were obtained on the conditions for the formation of the glacier dam in the valley of the Shishkhid-Gol. The confluence of the large glaciers Khara-Byarangiin-Gol and Ikh-Dzhams-Gol below the mouth of the Tengisiin-Gol formed a backwater of the Shishkhid-Gol with a height of 300 m. The presence of ancient coastlines up to an altitude of 1713 m in the immediate vicinity of the newly identified glacial dam indicates its dominant role in the formation of the Darhad paleolake. Within the Darhad Basin, as a result of an analysis of the absolute heights of the highest coastline of the Darhad paleolake, downward tectonic deformations were revealed over the last 18–23 ka with an amplitude of 27 m. As a result of field research and cosmogenic dating (¹⁰Be), the first dates were obtained for the exposure of boulders within four fields of gravel dunes, as well as an erratic boulder exposed within a bar in the valley of the Kaa-Khem. The age distribution of 14 samples showed a scatter of dates within the range of 38–18 ka, which have three peaks. Two of them correspond to two megafloods of 38–36 ka and 23–18 ka and one, intermediate, associated with intermittent exposure resulting from the impact of a second megaflood on boulder exposure within gravel dunes.

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Авторлар туралы

S. Arzhannikov

Institute of the Earth’s Crust SB RAS

Хат алмасуға жауапты Автор.
Email: sarzhan@crust.irk.ru
Ресей, Irkutsk

A. Arzhannikova

Institute of the Earth’s Crust SB RAS

Email: sarzhan@crust.irk.ru
Ресей, Irkutsk

R. Braucher

French National Centre for Scientific Research (CNRS); Centre européen de recherche et d’enseignement de géosciences de l’environnement (CEREGE)

Email: sarzhan@crust.irk.ru
Франция, Aix-en-Provence; Aix-en-Provence

Әдебиет тізімі

  1. Arzhannikov S.G., Arzhannikova A.V. (2011). The Late Quaternary Geodynamics of the Hyargas Nuur Basin and Bordering Scarps (western Mongolia). Russian Geology and Geophysics. V. 52. № 2. P. 220–229. https://doi.org/10.1016/j.rgg.2010.12.016
  2. Arzhannikov S., Arzhannikova A., Braucher R. (2023). Darhad megaflood (southern Siberia): Сause, age and consequence. Quat. Int. № 643. P. 1–21. https://doi.org/10.1016/j.quaint.2022.10.002
  3. Arzhannikov S.G., Braucher R., Jolivet M. et al. (2012). History of late Pleistocene glaciations in the central Sayan-Tuva Upland (southern Siberia). Quat. Sci. Rev. V. 49. P. 16–32. ttps://doi.org/10.1016/j.quascirev.2012.06.005
  4. Arzhannikov S.G., Braucher R., Jolivet M. et al. (2015). Late Pleistocene glaciations in southern East Sayan and detection of MIS 2 terminal moraines based on beryllium (¹⁰Be) dating of glacier complexes. Russian Geology and Geophysics. V. 56. № 11. P. 1509–1521. https://doi.org/10.1016/j.rgg.2015.10.001
  5. Arzhannikova A.V., Arzhannikov S.G., Akulova V.V. et al. (2014). The Origin of Sand Deposits in the South Minusa Basin. Russian Geology and Geophysics. V. 55. № 10. P. 1183–1194. https://doi.org/10.1016/j.rgg.2014.09.004
  6. Arzhannikova A.V., Arzhannikov S.G., Chebotarev A.A. (2024). Morphotectonics and paleoseismology of the North Darhad fault (SW Baikal Rift, Mongolia). J. of Asian Earth Sci. V. 259. 105882. https://doi.org/10.1016/j.jseaes.2023.105882
  7. Bacon S.N., Bayasgalan A., Gillespie A.R. et al. (2003). Paleoseismic displacement measurements from landforms subjected to periglacial processes: observations along the Jarai Gol fault near the Tamyn Am Hills, Darhad Depression, northern Mongolia. XVI Inqua Congress, Abstract with Programs. P. 103.
  8. Baker V.R. (1973). Paleohydrology and sedimentology of Lake Missoula flooding in Eastern Washington. Geological Society of America. Special Paper. V. 144. P. 1–79. https://doi.org/10.1130/SPE144-p1
  9. Baker V.R., Benito G., Rudoy A.N. (1993). Paleohydrology of Late Pleistocene superflooding, Altay Mountains, Siberia. Science. V. 259. № 5093. P. 348–350.
  10. Baker V.R., Bunker R.C. (1985). Cataclysmic late Pleistocene flooding from Glacial Lake Missoula: a review. Quat. Sci. Rev. V. 4. P. 1–41. https://doi.org/10.1016/0277-3791(85)90027-7
  11. Baryshnikov G.Ya. (1979). On the issue of the formation of large boulder alluvium of the Biy river. In: Materialy Regional’noi nauchno-prakticheskoi konferentsii “Geologiya i poleznye iskopaemye Altaiskogo kraya”. Barnaul. P. 117–119. (in Russ.)
  12. Batbaatar J., Gillespie A.R. (2016a). Outburst floods of the Maly Yenisei. Part I. Int. Geology Rev. V. 58. Iss. 14. P. 1723–1752. https://doi.org/10.1080/00206814.2015.1114908
  13. Batbaatar J., Gillespie A.R. (2016b). Outburst floods of the Maly Yenisei. Part II – new age constraints from Darhad basin. Int. Geology Rev. V. 58. Iss. 14. P. 1753-1779. https://doi.org/10.1080/00206814.2016.1193452
  14. Benito G., Thorndycraft V. (2020). Catastrophic glacial lake outburst flooding of the Patagonian Ice Sheet. Earth-Science Rev. V. 200. 102996. https://doi.org/10.1016/j.earscirev.2019.102996
  15. Borisov B.A., Minina E.A. (1982). Features of the formation of ribbed main moraines in mountainous countries and their significance for paleoglaciology. Materialy glyatsiologicheskikh issledovanii. V. 44. P. 129–133. (in Russ.)
  16. Bricheva S. S., Gonikov T. V., Panin A. V. et al. (2022). The origin of giant dunes in the Kuray Basin (Southeastern Gorny Altai) based on morphometric analysis and GPR studies. Geomorfologiya. V. 53. No. 4. P. 25-41. (in Russ.) https://doi.org/10.31857/S0435428122040034
  17. Chmeleff J., von Blanckenburg F., Kossert K. et al. (2010). Determination of the ¹⁰Be half-life by multicollector ICP-MS and liquid scintillation counting. Nucl. Instrum. Methods Phys. Res. Sect. B 268. P. 192–199. https://doi.org/10.1016/j.nimb.2009.09.012
  18. Clark P., Marshall S., Clarke G. (2001). Freshwater Forcing of Abrupt Climate Change During the Last Glaciation. Science. V. 293. Iss. 5528. P. 283–287. https://www.science.org/doi/epdf/10.1126/science.1062517
  19. Clarke G., Leverington D., Teller J. et al. (2004). Paleohydraulics of the last outburst flood from glacial Lake Agassiz and the 8200 BP cold event. Quat. Sci. Rev. V. 23. Iss. 3-4. P. 389–407. https://doi.org/10.1016/j.quascirev.2003.06.004
  20. Enikeev F.I. (2009). Pleistocene glaciations of eastern Transbaikalia and south-east of Middle Siberia. Geomorfologiya. № 2. P. 33–49. https://doi.org/10.15356/0435-4281-2009-2-33-49
  21. Gillespie A.R., Burke R.M., Komatsu G. et al. (2008). Late Pleistocene glaciers in Darhad Basin, northern Mongolia. Quat. Res. V. 69. Iss. 2. P. 169–187. https://doi.org/10.1016/j.yqres.2008.01.001
  22. Gosse J.C., Phillips F.M. (2001). Terrestrial in situ cosmogenic nuclides: theory and application. Quat. Sci. Rev. V. 20. P. 1475–1560. https://doi.org/10.1016/S0277-3791(00)00171-2
  23. Grosswald M.G., Rudoy A.N. (1996). Quaternary glacial-dammed lakes in the Siberian Mountains. Izvestiya Rossiiskoi Akademii nauk. Seriya geograficheskaya. № 6. P. 112–126. (in Russ.)
  24. Kleiven H., Kissel C., Laj C. et al. (2008). Reduced North Atlantic Deep-Water Coeval with the Glacial Lake Agassiz Freshwater Outburst. Science. V. 319. № 5859. P. 60–64. https://doi.org/10.1126/science.1148924
  25. Komatsu G., Arzhannikov S.G., Gillespie A. et al. (2009). Quaternary paleolake formation and cataclysmic flooding along the upper Yenisei River. Geomorphology. V. 104. Iss. 3-4. P. 143–164. https://doi.org/10.1016/j.geomorph.2008.08.009
  26. Komatsu G., Baker V., Arzhannikov S. (2016). Catastrophic flooding, palaeolakes, and late Quaternary drainage reorganization in northern Eurasia. Int. Geology Rev. V. 58. Iss. 14. P. 1693–1722.https://doi.org/10.1080/00206814.2015.1048314
  27. Korschinek G., Bergmaier A., Faestermann T. (2010). A new value for the half-life of ¹⁰Be by heavy-ion elastic recoil detection and liquid scintillation counting. Nucl. Instrum. Methods Phys. Res. Sect. B 268. P. 187–191. https://doi.org/10.1016/j.nimb.2009.09.020
  28. Kotlyakov V.M., Grosswald M.G. (Eds.). (1987). Vzaimodeistvie oledeneniya s atmosferoi i okeanom. (Interaction of glaciation with the atmosphere and ocean). Moscow: Nauka (Publ.). 250 p. (in Russ.)
  29. Krivonogov S.K., Sheinkman V.S., Mistryukov A.A. (2005). Stages in the development of the Darhad dammed lake (Northern Mongolia) during the Late Pleistocene and Holocene. Quat. Int. V. 136. Iss. 1. P. 83–94. https://doi.org/10.1016/j.quaint.2004.11.010
  30. Krivonogov S.K., Yi S., Kashiwaya K., Kim J.C. (2012). Solved and unsolved problems of sedimentation, glaciation and palaeolakes of the Darhad Basin, Northern Mongolia. Quat. Sci. Rev. V. 56. P. 142–163. https://doi.org/10.1016/j.quascirev.2012.08.013
  31. Kudryavtseva G.A. (Ed). (1964). Geologicheskaya karta SSSR M-46-V, m-ba 1:200 000 (Geological map of the USSR M-46-V, scale 200 000). Leningrad: Fabrika № 9 (Publ.). 1 p.
  32. Logachev N.A. (Eds.). (1993). Seismotektonika i seismichnost’ Prihubsugul’ya (Seismotectonics and seismicity of the Khubsugul region). Novosibirsk: Nauka (Publ.). 182 p. (in Russ.)
  33. Margold M., Jannson K., Stroeven A. et al. (2011). Glacial Lake Vitim, a 3000-km3 outburst flood from Siberia to the Arctic Ocean. Quat. Res. V. 73. Iss. 3. P. 393–396. https://doi.org/10.1016/j.yqres.2011.06.009
  34. Margold M., Jansen J., Codilean A. et al. (2018). Repeated megafloods from Lake Vitim, Siberia, to the Arctic Jcean over the past 60000 years. Quat. Sci. Rev. V. 187. P. 41–61. https://doi.org/10.1016/j.quascirev.2018.03.005
  35. Martini I.P., Baker V.R., Garzon G. (Eds.). (2002). Flood and Megaflood Processes and Deposits: Recent and Ancient Examples. Int. Association of Sedimentologists. Special Publication. V. 32. Blackwell Science. London. 320 p.
  36. Norris S.L., Garcia-Castellanos D., Jansen J. D. et al. (2021). Catastrophic drainage from the northwestern outlet of glacial Lake Agassiz during the Younger Dryas. Geophysical Res. Letters. V. 48. Iss. 15. e2021GL093919. https://doi.org/10.1029/2021GL093919
  37. O’Connor J.E., Costa J.E. (2004). The world’s largest floods, Past and Present: Their causes and magnitudes. U.S. Geological Survey Circular 1254: Reston. VA. U.S. Geological Survey. 13 p.
  38. Parnachev S.G. (1999). Geologiya vysokikh altaiskikh terras (Yalomano-Katunskaya zona) (Geology of high Altai terraces (Yalomano-Katun zone)). Tomsk: IAP TPU (Publ.). 137 p. (in Russ.)
  39. Perepelov A.B., Kuzmin M.I., Tsypukova S.S. et al. (2017). Eclogite trace in evolution of late Cenozoic alkaline basalt volcanism on the southwestern flank of the Baikal Rift Zone: geochemical features and geodynamic consequences. Dokl. Earth Sci. V. 476. № 2. P. 1187–1192.https://doi.org/10.1134/S1028334X1710018X
  40. Rudoy A.N. (1984). The giant current ripples are proof of the catastrophic outbursts of the glacial lakes of the Altay Mountains. In: Sovremennye geomorfologicheskie protsessy na territorii Altaiskogo kraya. Biysk. P. 60–64. (in Russ.)
  41. Rudoy A.N. (2002). Glacier-dammed lakes and geological work of glacial superfloods in the Late Pleistocene, Southern Siberia, Altai Mountains. Quat. Int. V. 87. Iss 1. P. 119–140. https://doi.org/10.1016/S1040-6182(01)00066-0
  42. Rudoy A.N., Baker V.R. (1993). Sedimentary effects of cataclysmic late Pleistocene glacial outburst flooding, Altay Mountains, Siberia. Sediment. Geol. V. 85. Iss. 1-4. P. 53–62. https://doi.org/10.1016/0037-0738(93)90075-G
  43. Selivanov E.I. (1967). Neogene-Quaternary giant lakes in Transbaikalia and Northern Mongolia. Doklady Akademii nauk SSSR. V. 177. № 1. P. 175–178. (in Russ.)
  44. Selivanov E.I. (1968). Drained lakes. Priroda. № 3. P. 81–82. (in Russ.)
  45. Spirkin A.I. (1970). On the ancient lakes of the Darhad Basin. In: Geology of the Mesozoic and Cenozoic of Western Mongolia. Moscow: Nauka (Publ.). P. 143–150. (in Russ.)
  46. Stolz C., Hülle D., Hilgers A. et al. (2012). Reconstructing fluvial, lacustrine and aeolian process dynamics in Western Mongolia. Zeitschrift für Geomorphologie. V. 56. Iss. 3. P. 267–300. https://doi.org/10.1127/0372-8854/2012/0078
  47. Stone J.O. (2000). Air pressure and cosmogenic isotope production. J. of Geophysical Res. V. 105. Iss. B10. P. 23753–23759. https://doi.org/10.1029/2000JB900181
  48. Sugorakova A.M., Yarmolyuk V.V., Lebedev V.I. (2003). Kainozoiskii vulkanizm Tuvy (Cenozoic volcanism of Tuva). Kyzyl: TuvKOPR SO RAN (Publ.). 92 p. (in Russ.)
  49. Tsypukova S.S., Perepelov A.B., Demonterova E.I. et al. (2022). Two stages of the cenozoic alkaline-basalt volcanism in the Darhad depression (Northern Mongolia) – geochronology, geochemistry, and geodynamic consequences. Geodinamika i tektonofizika. V. 13. № 3. P. 1–15. (in Russ.). https://doi.org/10.5800/GT-2022-13-3-0613
  50. Uflyand A.K., Ilyin A.V., Spirkin A.I. (1969). Baikal-type depressions in Northern Mongolia. Byulleten' MOIP. Otdel geologicheskii. V. 44. № 6. P. 5–22. (in Russ.)
  51. Uflyand A.K., Ilyin A.V., Spirkin A.I. et al. (1971). Main features of stratigraphy and conditions for the formation of Cenozoic formations in the Kosogol region (MPR). Byulleten' MOIP. Otdel geologicheskii. V. 46. № 1. P. 54–69. (in Russ.)
  52. Wagner G.A. (1998). Age determination of young rock and artifacts. Springer. 466 p.
  53. Zolnikov I.D., Deev E.V. (2013). Glacial superfloods on the territory of the Altai Mountains in the Quaternary period: formation conditions and geological features. Earth’s cryosphere. V. 17. № 4. P. 74–82.
  54. Zolnikov I.D., Deev E.V., Kurbanov R.N. et al. (2023). Age of glacial and fluvioglacial deposits of the Chibitsky glaciocomplex and its dammed lake (Gorny Altai). Geomorfologiya i Paleogeogragiya. V. 54. № 1. P. 90–98. (in Russ.) https://doi.org/10.31857/S0435428123010133
  55. Zolnikov I.D., Mistryukov A.A. (2008). Chetvertichnye otlozheniya i rel’ef dolin Chui i Katuni (Quaternary sediments and relief of the Chuya and Katun valleys). Novosibirsk: Parallel (Publ.). 180 c.
  56. Zolnikov I.D., Novikov I.S., Deev E.V. et al. (2021). Facies composition and stratigraphic position of the quaternary Upper Yenisei sequence in the Tuva and Minusa depression. Geologiya i geofizika. V. 62. № 10. 1127-1138. https://doi.org/10.2113/RGG20204183
  57. Zolnikov I.D., Novikov I.C., Deev E.V. et al. (2023). The Last Glaciation and Ice-Dammed Lakes in the South-East Altai. Led i Sneg. V. 63. № 4. P. 639-651. (in Russ.) https://doi.org/10.31857/S207667342304018X

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2. Fig. 1. Location of the three largest paleolakes (Chuya-Kurai, Darhad, Vitim) and the associated megafloods of Eastern Siberia: Altai, Darhad and Vitim.

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3. Fig. 2. Interpretation by various authors of the glacial dam location in the Shishkhid-Gol valley. The map and profiles were produced using SRTM data V4.

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4. Fig. 3. Levels of terraces, giant current ripples and bars. On the background is the TanDEM-X. Red dots show the location of samples taken for cosmogenic (¹⁰Be) dating (а, б, в, г). Examples of boulders from which the samples were taken (д, е).

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5. Fig. 4. Position of a series of ancient coastlines (black arrows) that record the level of the paleolake below of the Tengisiin-Gol mouth. On the background are Google Earth satellite images. The yellow dotted line indicates the 1713 m asl contour line. All satellite images show the right side of the Shishkhid-Gol valley.

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6.

Fig. 5. Overview map of the Late Quaternary glaciation of the mountain frame of the Darhad Basin and the location of key research points within the Darhad paleolake and the Shishkhid-Gol valley, discussed in the text. SRTM V4 data was used to produce the map.

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7. Fig. 6. Satellite images (Google Earth) show paleo shoreline. See Fig. 5 for the location of each image. The altitudes are shown for the highest coastlines. The presented data indicate intense tectonic deformations of the lake terraces.

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8. Fig. 7. The digital elevation model (SRTM v4), satellite images (а, б) (Google Earth) and aerial photographs (в) show lines of tectonic and seismogenic deformations located in the northern and eastern parts of the Darhad Basin.

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9. Fig. 8. Reconstruction of the glacier boundary at the mouth of the Tengisiin-Gol, which existed during the LGM (MIS 2). (а) – spillway (erosive incision of melted glacial waters), located on the right bank of the Tengisiin-Gol; (б) – spillway, located on the left bank of the Tengisiin-Gol; (в) – left bank of the Shishkhid-Gol (the mouth of the Ikh-Sarig-Gol river) and elements of glacial relief (a slope abraded by a glacier and a fragment of the terminal moraine of the Tengisiingol glacier); (г, д) – reconstruction of the level of the Tengisiingol glacier (the left side of the mouth of the Tengisiin-Gol) in the first phase of the Sartan glaciation (LGM).

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10. Fig. 9. On the digital elevation model, the camera symbol (а, б, в, г) shows the directions to the location of the photographs located in Fig. 10 and the strike of profiles АБ, ВГ. The profiles show the parameters of the reconstructed Tengisiingol glacier and reflect its role in the formation of the backwater of the Darhad paleolake. The figure uses SRTM v4 data and Google Earth satellite images.

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11. Fig. 10. Reconstruction of glacial backwater at the mouth of the Tengisiin-Gol for the period 20–18 ka. Profiles show glacier levels and the surface of the Darhad paleolake.

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12. Fig. 11. Reconstruction of glaciers of two tributaries of the Shishkhid-Gol (Khara-Byarangiin-Gol and Ikh-Zhams-Gol), which formed the glacial backwater of the Darhad paleolake. The digital elevation model (a, б) shows the valleys of the Khara-Byarangiin-Gol and Ikh-Zhams-Gol rivers, respectively. The numbers indicate the altitude of the lateral moraines. The inset (в) shows the area of confluence of glaciers in the Shishkhid-Gol valley and the formation of a glacier dam. Satellite image (г) shows a series of melt water channels formed along the edge of the glacier.

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13. Fig. 12. Results of interpretation of TanDEM-X data, showing the nature of the accumulative-erosive activity of the Darhad megaflood in the Yenisei valley in the Tuva Basin (а, б). Red squares indicate the spatial location of sampling points for cosmogenic (¹⁰Be) dating of exposed boulders within the gravel dunes. The yellow square indicates the location of a complex of high erosion levels, reflecting the maximum level of the Darhad megaflood in the Tuva Basin (for details, see Fig. 18).

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14. Fig. 13. The satellite image (Google Earth) shows a 55 km section of the Bii-Khem with the location of giant current ripples (green circles) formed under the influence of the Darhad megaflood (a); (б, в) – reconstruction of the direction of currents in the paleoflow of the Darhad megaflood in the mouth part of the Bii-Khem (Google Earth). FGCRs I, II, III – fields of giant current ripples formed in currents of different directions and time during the Darhad megaflood.

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15. Fig. 14. Satellite image (Google Earth) shows the location of giant current ripples I and II in the northwestern part of the Darhad Basin (a). The morphology and substrate composing the giant current ripples: (б, г) – GCRs I, (в, д) – GCRs II.

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16. Fig. 15. The photographs and satellite image (Google Earth) reflect the morphology of giant current ripples located in the of Yenisei valley (Kaa-Khem, Ulug-Khem) (а, б, в).

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17. Fig. 16. Sedimentary complex of various fractions, formed in the Yenisei valley (Kaa-Khem, Ulug-Khem) as a result of the erosion-accumulation activity of the Darhad megaflood and aeolian processes.

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18. Fig. 17. Widespread aeolian sand massifs (а, б, в, г) in the Tuva Basin have a primary alluvial genesis and are associated with the Darhad megaflood. (а) – scheme of the location of sand massifs and their main orientation, according to the prevailing winds; (б, в, г) – details of the surface structure of aeolian sand massifs; (а, б, г) – fragments of satellite images (Google Earth).

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19. Fig. 18. Photographs (a, б) show a complex of terraces up to 100 m high, formed as a result of erosion of the Kaa-Khem valley slopes by Darhad megaflood. Location of high erosion terraces in the Kaa-Khem valley (в) and their relationship with FGCRs (г). The blue outline in diagram (в) shows the maximum level of the Darhad megaflood in this part of the river valley.

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20. Fig. 19. Morphology and structure of the terrace complex of the Bii-Khem valley in the Begreda Area. (а) – general view of the Bii-Khem valley in the Begreda Area (ALOS digital elevation model). Blue circles and numbers indicate the altitude of the area. Red circles indicate observation points, letter indices in squares correspond to the photographs below; (б) – the photograph shows a hill (745 m above sea level), covered with pebbles, boulders and unrounded blocks of bedrock. The yellow outline indicates the visible position of the alluvial sediment cover. The red ellipse represents a person for scale. The black solid arrow shows the current direction of the Bii-Khem flow. The black dotted arrow shows the reconstructed, temporary direction of the Bii-Khem flow, modified by the Darhad megaflood; (в) – complex of terraces in the Bii-Khem valley (Begreda Area). The numbers reflect the height of the terrace. The upper part of the hill with a relative height of 83 m is composed of pebbles and unrounded blocks. The terrace level of 19 m is represented by giant carrent repples; (г, д) – The photographs show the nature of the distribution and occurrence of alluvial deposits with the inclusion of unrounded blocks of bedrock; (е) – the thickness of the mudflow facies (lower part) formed in the front of the Darhad megaflood; (ж) – mudflow facies, represented by boulders.

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21. Fig. 20. Graph of distribution of cosmogenic (¹⁰Be) ages obtained from exposed boulders within GCRs in the Kaa-Khem valley.

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22. Fig. 21. Graph (a) displays the exposed age of the moraine of the Eastern Sayan Ridge and Northern Mongolia. Plot (б) shows three peaks in exposed ages (¹⁰Be) associated with two Darhad megafloods and one with the loss of beryllium atoms due to changes in boulder exposure during the second Darhad megaflood. The black five-pointed star marks the age of a significant change in the fraction in the sedimentary complex of the Darhad paleolake. The black multi-rayed star shows the exposed age of the maximum extension of the Tengisiingol glacier (high level). The black pentagon shows the age of formation of the meltwater drainage channel of the low-level Tengisiingol glacier.

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