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International Geology Review Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tigr20 Geochronology of the late Pleistocene catastrophic debris flow and the formation, Altai Region, Southern Gennady Baryshnikova, Andrei Paninb & Grzegorz Adamiecc a Geography Faculty, Altai State University, Barnaul, b Geography Faculty, Lomonosov Moscow State University, Moscow, Russia c GADAM Centre, Institute of Physics, Silesian University of Technology, Gliwice, Poland Published online: 06 Jul 2015.

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To cite this article: Gennady Baryshnikov, Andrei Panin & Grzegorz Adamiec (2015): Geochronology of the late Pleistocene catastrophic Biya debris flow and the Lake Teletskoye formation, Altai Region, Southern Siberia, International Geology Review, DOI: 10.1080/00206814.2015.1062733 To link to this article: http://dx.doi.org/10.1080/00206814.2015.1062733

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Geochronology of the late Pleistocene catastrophic Biya debris flow and the Lake Teletskoye formation, Altai Region, Southern Siberia Gennady Baryshnikova, Andrei Paninb and Grzegorz Adamiecc aGeography Faculty, Altai State University, Barnaul, Russia; bGeography Faculty, Lomonosov Moscow State University, Moscow, Russia; cGADAM Centre, Institute of Physics, Silesian University of Technology, Gliwice, Poland

ABSTRACT ARTICLE HISTORY In the Biya River valley flowing from Lake Teletskoye, geomorphic and sedimentological evidence Received 1 March 2015 of a catastrophic debris flow has been found and assigned to glacier retreat after the last glacial Accepted 11 June 2015 maximum. Here, we report the results of lithological analysis of three sedimentary sections along KEYWORDS – Lake Teletskoye the Biya River valley system and optically stimulated luminescence dating of key megaflood; outburst stratigraphic units that led to a revised model for the geomorphic history of the region. Maximal flood; debris flow; glacier advance is suggested to have occurred during MIS 4–early MIS 3. It was accompanied by moraine-dammed lake; OSL the damming of tributary valleys by ice, by terminal and side moraines, and by the accelerated dating; valley incision and aggradation of the trunk valley below the glacier front. Formation of Lake Teletskoye, which aggradation; deglaciation followed the glacier retreat, occurred between 35 and 40 ka BP, most probably around 37.5 ka BP. Lake formation was shortly followed by a break in the moraine dam, catastrophic debris flow, rapid valley incision, and reduction in the lake level by ~100 m. Subsequently, incision has proceeded at a much lower rate and produced valley deepening and lake lowering of 30–35 m in the last 35–40 ka, or 0.8–0.9 m per thousand years on average.

Introduction Numerous studies of megafloods in the Altai have focused on outflows from ancient lakes dammed in the In the Russian Altai, evidence has been recognized of Chuya and Kurai basins in southeast Altai, through the past megafloods – massive freshwater floods with dis- ‒ Chuya and river valleys (Baker et al. 1993; Rudoy, charges that exceeded 1 million m3 s 1,or1Sv(Baker, Baker, 1993; Rudoy 2002; Herget 2005; Carling et al. 2013). More than three decades ago, giant current 2009; Carling 2013; etc.; see review of publications ear- ripples were found in Altai in the valleys of the lier 1991 in Baryshnikov (1992)). Much less attention has , Chuya, and Katun rivers and in the Kurai been paid to the development of the other headwater Basin (Butvilovskiy 1982, 1985;Okishev1982;Rudoy of the River system – the Biya River valley.

Downloaded by [95.215.86.12] at 05:32 07 July 2015 1984), as well as in the Biya River valley (Baryshnikov Baryshnikov (1992) proposed that outburst floods in 1976, Baryshnikov, 1992). A number of workers the Biya valley had a different mechanism to that in hypothesized that these features are glacial till the Katun–Chuya system, where megafloods originated (Borisov and Minina 1979;Okishev1982, 2011). from breaks in dams formed by glaciers descending However, the majority of scholars interpret them as from tributary valleys. In the Biya valley, glaciers occu- evidence of catastrophic outburst floods that resulted pied the main valley itself and a large lake formed after from water flowing from big lakes formed due to glacier retreat due to damming by terminal moraines. blockage of rivers by glaciers. Later, other evidence of Destruction of the moraine dam was followed by a huge outbursts from glacial lakes was recognized, such as debris flow that spread for many tens of kilometres spillways and distant transportation of giant rocks torn downstream and probably extended out to the lowland from valley sides. Palaeohydraulic assessments (Baker section of the valley and to the Ob River. This event was et al. 1993;Herget2005;Carlinget al. 2010) indicate attributed to the late Pleniglacial shortly after the Last that the Altai outburst floods were up to 400 m deep, Glacial Maximum (LGM) (Baryshnikov 1992). The release flowed at 20–25 m s‒1, and discharged 10–20 million ‒ of a large amount of water initiated the Biya River m3 s 1, similar to the well-known Missoula flooding in incision and the formation of a series of fluvial terraces. the western USA (Baker 2009).

CONTACT Andrei Panin [email protected] © 2015 Taylor & Francis 2 G. BARYSHNIKOV ET AL.

The post-LGM age estimate for the drainage of the Regional settings: northeast Altai and the moraine-dammed lake in the Biya valley gave rise to the upper Biya valley late Pleniglacial dating of the maximal glacier advance Altai is a mountain terrain in southern Siberia, at the and to post-LGM dating of Lake Teletskoye. However, Russian political boundary with Mongolia, China, and this timing is still not completely clear because it is Kazakhstan (Figure 1). The modern basin-and-range based on indirect data – relatively few radiocarbon dates structure was developed during the late Cenozoic, in the range 15–16 ka (uncal) derived from fine-grained mostly during the late Pliocene–early Quaternary. At sediments in tributary valleys that were interpreted as that time, the Teletsky rift valley was formed and filled deposits of lakes dammed by side levees produced by by the ancient Lake Teletskoye. Tectonic restructuring the giant mudflow in the main valley (Baryshnikov 1992). led to large-scale transformation of the drainage net- Previously, no data were collected on the absolute geo- work, which is evident in the finds of alluvial gravels on chronology of the Biya River and tributary valley terraces watersheds far from the trunk river valleys. According to that could give direct estimation of the timing of the Baryshnikov (1984), in the early middle Pleistocene the outburst flood and subsequent valley deepening. Our ancient Biya was a small river whose upper course did goal in this study was to obtain numerical ages for the not reach Turachak village (Figure 2(a)). In this manner it alluvial fills in the Biya River–Lake Teletskoye system and is distinguished from the Katun, which totally inherited to use these as time constraints for the catastrophic drai- its valley from initial fluvial systems. In the late middle nage of the dammed lake and formation of the modern Pleistocene, outflow from Lake Teletskoye began and Lake Teletskoye. Downloaded by [95.215.86.12] at 05:32 07 July 2015

Figure 1. Location map. (a) Russian Altai; (b) Lake Teletskoye region. Open squares with numerals denote study sites: (1) Chechenek River at Yaylyu; (2) Yogach River at Artybash; 3: Turochak River at Kebezen’. INTERNATIONAL GEOLOGY REVIEW 3

Figure 2. Evolution of the drainage net in northeast Altai (after Baryshnikov 1992).

the Biya valley reach between the lake and Turachak At the source of the Biya the described lacustrine/ village was formed (Figure 2(c)). Therefore, the modern alluvial sequence is buried under glacial till (Figure 3). Biya valley is a combination of two parts with different An end moraine ridge is located here that marks the ages. The reach downstream from Turachak village is an maximal glacier advance in the Teletskoye–Biya valley ancient, probably pre-Quaternary, well-developed val- (Figure 4). The glacier moved from the Korbu Ridge ley. The reach upstream of Turachak village to Lake (Figure 1) northwards through the meridional section Teletskoe is young, late middle Quaternary. The latter of Lake Teletskoye. At the latitudinal section of the lake is the least developed and the narrowest section of the trough the glacier split into two branches, one crossing the watershed at Yaylyu while the other advanced Downloaded by [95.215.86.12] at 05:32 07 July 2015 whole valley. The present study was located within the latter section of the valley. through the lake trough. The end moraine of the latter Before the last glacial advance, the lake in its north- is significantly eroded and therefore not clearly pre- ernmost latitudinal reach extended downstream of its served in the topography. Baryshnikov (1992) located present position. This supposition is supported by a the end moraine using a mineralogical technique: the borehole 2.7 km downstream from Artybash that moraine was indicated by the presence of scheelite, a reveals buried lacustrine sediments (Bublichenko fragile mineral that is well preserved in moraine but 1939). This borehole is shown in geological profile II easily destroyed by water transport. The age of the (Figure 3) along with other borehole data within the terminal moraine and, consequently, of the maximal Biya valley. The upper 20 m of the section are repre- glacial advance was assigned to LGM based on few sented by alluvia coarsening upwards from fine sand indirect data (Baryshnikov 1992). (depth 14.8–20.8 m) to cobbles and boulders (upper After the glacier retreat, valley deepening started and 9.9 m). Below lie lacustrine deposits >40 m thick a staircase of terraces was formed (Figure 4). The upper (depth 20.8–62.7 m). The latter are clays and loams Biya valley terraces have been studied by a number of with abundant wood fragments intercalated with researchers (see the review in Baryshnikov 1992). sands. The basal 6 m of the section is alluvial gravel Terrace composition was considered unusual even for and cobble in a sandy matrix, interlayered with clays. alpine valley terrace composition – with the occurrence Bedrock is reached at a depth of 68.8 m. of large (3 m diameter), well-rounded boulders within 4 G. BARYSHNIKOV ET AL.

alluvial gravels. Accumulations of these boulders were often considered as markers for glacial boundaries within the valley. Therefore, in many papers, terraces were related to action of a valley glacier. Baryshnikov (1976), Baryshnikov (1992) and Baryshnikov and Panychev (1987) arrived at another con- clusion on the origin of the large blocks of rocks in the upper Biya valley. These authors proposed that these blocks represent a former moraine transported by a giant debris flow (termed below as the Biya Debris Flow (BDF)), which was formed due to the breach of the end moraine that dammed Lake Teletskoye at the sources of the Biya River (Figure 5). Velocities of the BDF were estimated at 7–7.5 m s‒1. Eroded material from the mor- aine dam was redeposited downstream and formed the 90–120 m terrace (‘BDF terrace’), which stretches out over >10 km downstream from the former dam as far as the Pyzha River (Figure 4). The terrace is composed of angular blocks and rounded boulders up to 3–4min diameter in a gravelly matrix. In re-entrants in the valley sides or downstream of isolated rock remnants, the ter- race is composed of sandy gravels with parallel bedding. The terrace staircase that formed after the dam failure consists of five terraces and a floodplain (Figure 4). The relative elevation of each terrace increases in the direc- tion upstream to the river outflow from Lake Teletskoye Figure 3. Geological profiles at the Biya River outflow from (Table 1), which illustrates higher rates of river incision in Lake Teletskoye (after Baryshnikov 1992). See location of pro- the vicinity of the former dam and consistent decrease of files in Figure 4. river slope due to incision. The route of the BDF can be Downloaded by [95.215.86.12] at 05:32 07 July 2015

Figure 4. Geomorphological map of the upper Biya valley downstream from Lake Teletskoye (after Baryshnikov 1992). INTERNATIONAL GEOLOGY REVIEW 5

Figure 5. Reconstruction of the catastrophic Biya Debris Flow (BDF) caused by failure of the moraine dam and outburst of Lake Teletskoye (after Baryshnikov 1992).

Table 1. Height of fluvial terraces at different locations in the (3) Tuloi River valley in the middle course at Ederbes Upper Biya valley (in metres above the river). village – 13,220 ± 100 BP (SOAN-3368) and Location 12,465 ± 75 BP (SOAN-3369); Terrace Dmitrievka village Turachak village Kebezen’ village (4) Turachak River valley 1.1 km upstream from its – – Floodplain 3 1 414 mouth at Kebezen’ village – 14,980 ± 70 BP I3–55–810–13 II 12–15 13–17 20–25 (SOAN-1863); III 20–25 25–30 30 (5) Pyzha River valley 10 km upstream from its IV – 35–40 40 V – 55 60–80 mouth at Novo-Troitskoye village – 16,120 ± 80 BP (SOAN-1864) and from this location 1 km upstream of Tomozhu creek (the right-hand tri- traced from local accumulations of large blocks formerly butary of Pyzha) – 15,270 ± 60 BP (SOAN-2017). transported by the catastrophic current. As such blocks could not be transported by normal river flow, they have When calibrated, these dates place the period of accumulated due to river incision and lateral migration. lacustrine sedimentation in tributary valleys within the – Now large blocks can be found at various elevations on interval 14.5 19.5 ka BP (cal). Baryshnikov (2012) used a different terraces and in the modern river channel and, slightly shorter series of dates and suggested constrain- – taken together, they outline the BDF axis (Figure 5). ing the BDF within 16 20 ka BP. However no direct Downloaded by [95.215.86.12] at 05:32 07 July 2015 Locations where the route of the catastrophic flow is dates from debris flow and alluvial terraces have pre- intersected by the modern river are marked by riffles viously been obtained to test this estimation. composed of large boulders that were previously inter- preted as terminal moraines (Schukina 1960) or ice-rafted Methods debris (Ostroumov 1963). In tributary valleys, clayey deposits are widespread We examined natural and artificial exposures to study and were considered to have been accumulated due to alluvial and lacustrine deposits in different geomorpho- damming of tributaries by products of BDF accumulated logical positions. Description of exposures and numera- in the trunk valley (Baryshnikov 1992, 2012). A number of tion of stratigraphic units in the text are from top to radiocarbon dates were obtained for these lacustrine bottom (in each section Unit 1 is the youngest). clays (Baryshnikov 1992, 2012;RusanovandOrlova To determine the numerical ages of deposits we 2013; see location of rivers and villages in Figure 1;all applied the optically stimulated luminescence (OSL) tech- dates uncalibrated): nique. During fieldwork, samples were taken in opaque plastic tubes from vertical sections that were preliminarily (1) Uchurga River at Saidyp village – 16,190 ± 90 BP cleaned to avoid contamination and to allow determina- (SOAN-3851); tion of the natural moisture content. In the laboratory, all (2) Lebed River valley 13 km upstream from its mouth samples were dried and high-resolution gamma spectro- at Turochak village – 13,750 ± 70 BP (SOAN-576); metry was carried out in order to determine the content of 6 G. BARYSHNIKOV ET AL.

Table 2. OSL dates from the studied sites in the Biya valley and Lake Teletskoye region. ‒1 No. Sample index D (m) Da (m) WCa (%) DR (Gy ka ) ED (Gy) NA Age (ka BP) Index GdTL Yaylyu site 1 Bi-1 16 5.0 15 2.280 ± 0.092 91.9 ± 2.6 16/16 37.7 ± 2.0 1712 2 Bi-2 10 5.0 18 1.849 ± 0.072 86.2 ± 6.0 11/11 46.6 ± 3.8 1713 3 Bi-3 5 5.0 19 1.868 ± 0.073 70.2 ± 3.3 12/12 37.5 ± 2.3 1714 Yogach site 4 Iog-1 55 60 7 1.770 ± 0.082 177 ± 13 10/10 82.6 ± 7.0 1715 5 Iog-2 5 20 7 1.914 ± 0.088 112.9 ± 6.0 13/13 50.2 ± 3.3 1716 Turochak site 6 Tur-1 14.1 7.0 15 1.933 ± 0.081 156.3 ± 7.9 14/14 73.1 ± 4.7 1718 7 Tur-2 4.0 4.0 7 1.849 ± 0.084 137 ± 16 13/13 63.7 ± 8.0 1719 8 Tur-3 1.1 1.1 7 1.791 ± 0.068 76 ± 11 10/10 37.4 ± 5.6 1720

Note: D, depth in geological section; Da, average lifetime depth used in DR calculations; WCa, average lifetime water content; DR, dose rate; ED, equivalent dose; NA, number of aliquots measured for ED determination/used for CAM (central age model) age calculation.

U, Th, and K in the samples. A HPGe detector manufac- above the GWL; therefore, none was assigned the

tured by Canberra was used for this purpose. To ensure WCa = SWC value. The cosmic ray dose–rate contribu- equilibrium between gaseous 222Rn and 226Ra in the 238U tion for the site was estimated as described by Prescott decay chain prior to measurement, the samples were and Hutton (1994). Based on these data, the average stored for ~3 weeks. Each measurement lasted for at dose rates for grain sizes of 90–125 µm were calculated least 24 hours. The activities of the isotopes present in (Table 2). the sediment were determined against IAEA standards For equivalent dose estimation, coarse grains of quartz RGU, RGTh, and RGK after subtraction of the detector (90–125 μm) were extracted from the sediment samples background. Dose rates were calculated using the conver- by routine treatment. Initially, the sediment was treated sion factors of Adamiec and Aitken (1998). with 20% hydrochloric acid (HCl) and 20% hydrogen per-

An important parameter for OSL age processing of oxide (H2O2). Quartz grains were separated by density samples is the lifetime-average water content (WCa). separation using sodium polytungstate solutions, leaving Past changes in local geomorphological status due to grains of densities between 2.62 and 2.75 g cm‒3.Inorder both natural and anthropogenic factors must have pro- to eliminate any feldspar grains not completely dissolved, vided significant local drainage and reduction in ground the grains were sieved twice, before and after the 60 min water level (GWL) over the last tens of thousands years etching, with concentrated hydrofluoric acid (HF). (due to the detection for each site turn from aggrada- All OSL measurements were performed using an tion to incision) and then again in recent decades (due automated Daybreak 2200 TL/OSL reader (Bortolot to the excavation of studied pits). The supposed 2000) on multi-grain aliquots. To prepare the aliquots, changes in water content in the past do not allow the 10 mm-diameter stainless steel discs were sprayed with

use of measurable in situ water content as the WCa silicone oil through a mask with holes of a diameter of

Downloaded by [95.215.86.12] at 05:32 07 July 2015 parameter. The somewhat dry climate of the region ~6 mm; the grains were attached to the oil-covered combined with the different positions of individual sam- areas. Blue light stimulation was carried out by the ples relative to local drainage must have produced a inbuilt array of blue LEDs (470 ± 4 nm) delivering wide range in the water content of sediments in differ- about 60 mW cm‒2 at sampling position. Laboratory ent parts of sections, from saturation water content irradiations were performed using a calibrated 90Sr/ (SWC) values (typically 30–40%) to low values. The pre- 90Y beta source integrated to the reader delivering a ‒1 sumptive high range of WCa within each section did not dose rate of 5.27 Gy min . permit adequate exploitation of the approach accepted Equivalent doses were determined using the single- in humid regions when all samples above GWL were aliquot regenerative-dose (SAR) protocol (Murray and

assigned equal WCa values, typically 0.75–0.8 SWC Wintle 2000) involving the following steps: (Vandenberghe 2004). In our case this approach would have led to a distortion of age sequences in high ver- (1) Irradiation with the regenerative beta dose Di;

tical sections. Therefore, we assigned WCa values on the (2) Preheating at 260°C for 10 s; basis of laboratory measurements of SWC and sample (3) Blue light stimulation at 125°C for 100 s; position in the section using a three-step scale: 0.75 × (4) Irradiation with the test dose Dt (10% of the SWC, 0.5 × SWC, and 0.25 × SWC. The higher a particular natural dose, but not less than 5 Gy); sample lies relative to the groundwater level, the lower (5) Cut-heating at 220°C;

WCa the value it was assigned. All samples were located (6) Blue light stimulation at 125°C for 100 s. INTERNATIONAL GEOLOGY REVIEW 7

Results Three sedimentary sections were examined in different positions along Lake Teletskoye–Buya River valley in order to characterize the variety of geomorphological conditions before and after BDF (see Figure 1 for site locations). The Yaylyu site is situated 26 km upstream of the former moraine dam (at the Yogach River mouth) on the northern bank of Lake Teletskoye, the Yogach site is at the dam, and the Kebezen’ site is located in the Biya valley 21 km downstream of the former dam (the Yogach River mouth).

Yaylyu site Lake Teletskoye (level 435 m a.s.l.) is bordered mostly by high rocky banks. One of the few exceptions represent- ing depositional environments is the terrace at Yaylyu village (see location in Figure 1). The Yaylyu terrace occupies an arcuate segment, 1 km wide and 4 km long, at the northern bank of the lake. It has a gently sloping (5°–7°) surface that starts 0.9–1.1 km north of the lake at an elevation of 560–580 m a.s.l. (up to 150 m above lake level), descends lake-wards down to alti- tudes 475–480 m a.s.l. (some 40 m above the lake), and falls at angles 15°–25º down to the modern lake beach. At the edge of the terrace, in elevation range 475–490 m, at various sites its surface becomes more – gentle and is dipping at 2° 3° only, making a clear step Figure 6. The Chechenek section (Yaylyu site): (a) general view; which breaks into a steep slope facing the lake. A (b) fragment of Unit Ch1; (c) fragment of Unit Ch2; (d) fragment number of small creeks flow onto the terrace from the of Unit Ch3. Ch1a . . . Ch3: stratigraphic units. north, from the Torot Range. The terrace is enveloped by alluvial/lacustrine deposits. Terrace composition was studied in a natural exposure at the western edge of exposed sedimentary sequence can be subdivided into Yaylyu village, near the edge of the terrace. three stratigraphic units, Ch1–3(Figure 6(a)). Downloaded by [95.215.86.12] at 05:32 07 July 2015 The Chechenek section (51.77004° N, 87.59908° E) is a Unit Ch1: full lens with maximum thickness of 6 m a 50 m-long natural exposure on the right side of the little to the right of the centre of the exposure. The unit is Chechenek valley (Figure 6(a)). Chechenek is a small composed of two rhythmic pairs consisting of a mixed (6 km long) creek flowing from the south slope of the sand lower sub-layer (subunits Ch1b, Ch1d) and gravel- Torot ridge through the Yaylyu terrace. The studied cobble (up to 15–20 cm in diameter) upper sub-layer exposure exhibits a 21 m-thick sedimentary section of (subunits Ch1a, Ch1c). Sandy subunits exhibit interbed- the Yaylyu terrace not far from the terrace edge where ding of laminated coarse sands (layers 5–10 mm) with the terrace slope becomes more gentle and makes a inclusions of fine gravel (up to 1 cm), and massive fine to 400–500 m-wide step with average slope of 2°–3°. The medium sands with unclear planar stratification at several top of the exposure at its middle part is at 471 m a.s.l., places. Cobble subunits have no clear bedding. The lower or 36 m above Lake Teletskoye. The exposure did not pair makes a lens conformal to the entire Unit 1, with include the near surface of the terrace, whose elevation erosive lower boundary (Figure 6(b)). Maximum thickness above the lake is about 40 m at this site. The upper of sandy subunit Ch1d is 1.1 m, gravelly subunit 1c – 1.8 m. 4–5 m of the terrace deposits were not exposed and The upper pair represents a half-exposed lens shifted to could not be cleaned, but their composition seems to the right. Sandy subunit Ch1b is an inclined layer be similar to the upper unit of the exposed section. The 0.5–0.6 m thick dipping upstream (i.e. opposite to the bottom of the section is at the level of the Chechenek lake). The uppermost gravelly subunit Ch1a has its max- creek (450 m a.s.l., 15 m above Lake Teletskoye). The imum thickness of ~4 m at the right edge of the exposure. 8 G. BARYSHNIKOV ET AL.

Unit Ch2: half-lens undercut by the terrace edge outflows from Lake Teletskoye (see location in Figure 1 where it has its maximum thickness of 7 m, and taper- (b)). In the lower course, the Yogach cuts through a ing out to the centre of the exposure. The uppermost terrace with a sub-horizontal surface lying 130 m above subunit Ch2a is composed of coarse gravel (3–5 cm) Lake Teletskoye (565 m a.s.l.) and 80–90 m above Yogach with an admixture of cobbles (5–10 cm) and no clear creek. It can be correlated to the BDF terrace of the Biya bedding. The lower 1.1–1.3 m of subunit Ch2a are com- valley. This terrace stretches along the right side of the posed of well-rounded cobbles (5–15 cm) with cross- Yogach valley for a distance of 0.7–0.8 km immediately bedding at places dipping upstream into the before its opening into the Biya valley. It is not recog- Chechenek valley (i.e. away from Lake Teletskoye). A nized anywhere upstream and seems to have been com- single rounded boulder (50 × 80 cm) was found at the pletely eroded within the rest of the valley. bed of subunit Ch2a. Subunit Ch2b is 50–70 cm-thick The Yogach exposure (51.77392° N, 87.25516° E) is a mixed sand with an erosive lower boundary (Figure 6 sand pit that undercuts the described terrace at its (c)). In the lower part it contains small lenses composed northwestern corner, immediately before the opening of unrounded fine gravel derived from the underlying into the Biya valley. The exposure base was at an alti- subunit Ch2c. The lowermost subunit, Ch2c, is a lens up tude of 487 m a.s.l. (12 m above Yogach creek, 52 m to 1 m thick in the left side of the exposure composed above Lake Teletskoye). The total height of the exposure of unsorted, mostly sub-rounded fine gravel (5–10 mm). was 55 m, with the top located at an altitude of 537 m a. Unit Ch3: a rather uniform deposit that stretches s.l. (62 m above Yogach creek, 102 m above Lake downwards below the valley bottom (depth 21 m). Teletskoye). The exposure top was 30 m below the sur- Due to subsequent erosion, elevation of the upper face of the terrace. The upper 30 m of the terrace sedi- boundary is not uniform: it rises from a depth of 13 m mentary sequence were unexposed and therefore were in the left to 8 m in the right corner of the exposure. In not studied. The terrace is composed of an upward- most parts, deposits are represented by parallel inter- coarsening, horizontally bedded sequence of loams, bedding of loam and silt layers 5–10 cm thick, with sands, and gravels that may be subdivided into three gradual boundaries, dipping lake-wards (SW) at an units that gradually merge into one another (Figure 7(a)). angle of 15° (Figure 6(a), (d)). Loam layers contain abun- Unit Y1, depth 0–18 m: horizontally bedded coarse dant, well-rounded gravel (up to 5 cm in diameter), gravels with inclusion of boulders up to 50 cm in dia- while silts contain solitary inclusions of coarse sand meter, with a few lenses of horizontally laminated mixed (up to a few millimetres in size). Several large (up to sand 0.5–1 m thick at an interval of 3–4m(Figure 7(b)). 1 m) angular and sub-rounded clasts lie in the upper half of the unit. All OSL dates were obtained from each of the three units (Table 2). Composition of the section provided the following facies interpretation of described units. Unit Ch3 represents relatively deep-water lacustrine sedi- Downloaded by [95.215.86.12] at 05:32 07 July 2015 ments with seasonal lamination: loams represent winter layers with a coarse fraction transported by ice rafting, and silts are summer layers. Inclination of lamination results most probably from the initial slope of the sub- merged surface that was covered by sediments yielded to the lake by small rivers from coastal ridges. Sandy silts of Unit Ch3 at depth 16 m provided OSL age 37.7 ± 2.0 ka BP (GdTL-1712) (Figure 6(d)). Units Ch2 and Ch1 are fluvial deposits. In each unit, basal sandy sub-layers were OSL dated. Subunit Ch2b (25 cm above its lower boundary) was dated at 46.6 ± 3.8 ka (GdTL-1713) (Figure 6(c)) and subunit Ch1d at 37.5 ± 2.3 ka (GdTL-1714) (Figure 6(b)).

Yogach site Figure 7. The Yogach section (Yogach site): (a) general view; (b) The Yogach is a small (35 km long) river flowing to Biya fragment of Unit Y1; (c) fragment of Unit Y3. See Figure 6 for from the left at Yogach and Artybash villages where Biya legend. Y1 . . . Y3: stratigraphic units. INTERNATIONAL GEOLOGY REVIEW 9

Unit Y2, depth 18–42 m: planar horizontal interbed- above the creek increases twice, from 9–10 m at the ding of sands (various sizes) and sandy gravels. Layers beginning of the terrace to 19–20 m at the valley end. are 0.5–3.0 m thick, with second-order fine horizontal The Turachak section (51.93103° N, 87.08705° E) is lamination. located in a sandpit cutting into the fourth (40 m) Biya Unit Y3, depth 42–55 m (the base of the exposure): terrace in the Turachak valley 370 m upstream from its planar horizontal interbedding of loams, fine sands, and inflow into the Biya, or some 200 m from the Turachak coarse sands (Figure 7(c)). Layers are 5–30 cm thick, valley end (i.e. in the middle of the 400 m terrace microlaminated. From a depth of 50 m upwards, layers segment). This section is 14.5 m thick, with its base of coarse sand contain inclusions of well-rounded fine standing at 414 m a.s.l. (18 m above the Biya) and top to medium gravel up to 2–3 cm in diameter. Loam at 428.5 m a.s.l. (32.5 m above the Biya). The exposure layers are disturbed by loading structures. reaches the surface of the terrace. Terrace deposits were The entire sequence was interpreted as lacustrine divided into two stratigraphic units (Figure 8(a)). deposits that filled a dammed lake in the Yogach valley. Unit T1, depth 03.7 m (Figure 8(b)): planar cross-bed- Sediments were transported from upstream into the val- ding of well-rounded coarse gravel (3–5cm)andfine ley. Two OSL dates were obtained from sand layers in the cobble (5–10 cm, up to 15 cm) with sandy–gravelly matrix; bottom and upper parts of the exposure (Table 2, Figure 7 beds dipping at 12°–15° to SE (i.e. across the terrace from (b), (c)). Unit Y3 at depth ~55 m (0.5 m above the base of the right side of the valley to the Turachak creek). the exposure) was dated at 82.6 ± 7.0 ka (GdTL-1715) and Unit T2, depth 3.7–14.5 m: horizontally bedded sands Unit Y1 at depth 5 m was dated at 50.2 ± 3.3 ka and gravels. Four subunits were distinguished based on (GdTL-1716). proportions of fine and coarse fractions: Subunit T2a, 3.7–6.4 m (Figure 8(c)): horizontally lami- nated fine to medium sand with sub-layers of small to Kebezen’ site medium gravel (20–30 cm thick); erosive upper boundary. Kebezen’ is a large village on the right bank of the River Subunit T2b, 6.4–9.9 m: interbedding of fine sands Biya 19 km downstream from the Yogach River and the with thin horizontal lamination (layer thickness Biya outflow from Lake Teletskoye (see location in 0.5–0.6 m) and coarse sands (up to 1 m). Figure 1(b)). It is located on the downstream edge of a Subunit T2c, 9.9–12.3 m: coarse gravel with fine valley widening occupied by the fifth (60–80 m) terrace gravel/sand matrix and rare cobbles (5–10 cm), with of the Biya (Figure 4). No natural or artificial exposures unclear thick horizontal bedding. on this terrace were suitable for study of terrace com- position. Further downstream the valley narrows and the river flows along the right valley side dissected by a few small valleys. One of these valleys is the Turachak, a 3 km-long creek that flows into the Biya at the north- ern end of Kebezen’. In its lower reach the valley is Downloaded by [95.215.86.12] at 05:32 07 July 2015 400 m wide. It is occupied by the present-day stream and its floodplain (50–70 m) and a 250 m-wide terrace 32–40 m above Biya, which corresponds to the 4th Biya terrace (Figure 4). Similar to the Yogach site, this terrace was designated only at the Turachak valley opening into the Biya valley and is not found anywhere upstream. In the lower course, the terrace forms a seg- ment on the right side of the valley 400 m long (along Turachak) and 200 m wide (across the valley). The ter- race surface dips notably across the valley with altitudes of 438 m a.s.l. (42 m above the Biya) at the valley side and 428 m a.s.l. (32 m above the Biya) at the terrace edge that rises above the Turachak floodplain. At the same time, no significant dipping of the terrace can be recognized downstream along the Turachak valley, Figure 8. The Turachak section (Kebezen’ site): (a) general view; though the present-day creek has a steep gradient of (b) fragment of Unit T1; (c) fragment of the top of Unit T2; (d) ‒1 35 m km . Along the 400 m terrace segment the fragment of the base of Unit T2. See Figure 6 for legend. T1 . . . relative height measured as the terrace edge elevation T3: stratigraphic units. 10 G. BARYSHNIKOV ET AL.

Subunit T2d, 12.3–14.5 m (Figure 8(d)): horizontally collected a number of creeks now flowing into Lake laminated sand, fine with silt layers in the lower 0.9 m Teletskoye. However, even if this was the case, the and coarse with fine gravel in the upper 1.3 m; erosional modern creeks could not yield enough water to fill the boundary between the two sand sub-subunits. palaeochannels, especially if they represent only a Three OSL dates were obtained from the section portion of a braided channel system. The large palaeo- (Table 2; Figure 8(b)–(d)). Unit T2 was interpreted as channel size indicates probably higher specific runoff lacustrine sediments filling a lake within the Turchak values (more humid climate?) than today. valley. At the base of the section (subunit T2d, depth Conformal bedding, the presence of sand layers with 14.1 m) they were dated at 73.1 ± 4.7 ka (GdTL-1718) microlamination within palaeochannel infills, as well as and at the top of the unit (subunit T2a, depth 4.0 m) the occurrence of a succession of palaeochannels may they were dated at 63.7 ± 8.0 ka (GdTL-1719). Sandy serve as arguments for a normal, non-catastrophic for- matrix from Unit T1 at depth 1.1 m provided OSL age of mation regime of both the palaeochannels and their 37.4 ± 5.6 ka (GdTL-1720). alluvial fills. The palaeostream flowed in a rather wide alluvial plain along the lake shore, which is expressed now as a 300–400 m-wide step at the edge of the Discussion Yaylyu terrace in the elevation range 475–490 m. Clearly, this alluvial plain was shortened by bank erosion Yaylyu site from the lake side as is evident from undercutting of The sedimentary sequence in the Chechenek section Unit Ch2 (Figure 6(a)). To prevent this stream from provides evidence for evolution from a deep lake (Unit eroding to the lake, the lake must have stayed at the Ch3) to a terrestrial environment (Units Ch2 and Ch1). same level (~470 m), and the present-day steep slope of Unit Ch3 provides a conclusion that in the interval the Yaylyu terrace must not have been in existence at 35–40 ka BP the lake had already existed and its level that time. The terrace edge was formed due to subse- was much higher than that today. Based on the eleva- quent reduction in lake level down to its modern posi- tion of Unit Ch3, the lake level could not be less than tion accompanied by retreat of the base of the slope 465 m a.s.l., or 30 m above the present-day level. caused by bank erosion. However, taking into account the facies interpretation The OSL dates collected from the Chechenek section (deep lake), one can assume that the lake level was are evidence that the switch to terrestrial conditions much higher, probably at or above the upper edge of occurred very quickly. In the series of three OSL ages, the Yaylyu terrace (560–580 m a.s.l., or ~130–140 m the date 46.6 ± 3.8 ka from Unit Ch2 makes an inver- above the modern lake). In this case the Chechenek sion: most probably this date overestimates the age of section should have been characterized by a water alluvium. This supposition is supported by the data from depth of ~100 m at a distance from the shore of the Yogach section where lacustrine sedimentation had about 1 km, which corresponds well to lithological fea- still not finished at ~50 ka BP. Given that lacustrine tures of accumulated sediments (Unit Ch3). sediments in Yogach (Unit Y1) were dated at an eleva- Downloaded by [95.215.86.12] at 05:32 07 July 2015 Alluvial Units Ch2 and Ch1 may be interpreted as tion ~70 m higher than the alluvial Unit Ch2, it appears alluvial fills of palaeochannels, probably branches of impossible that these alluvia can be of similar age, and braided or anastomosed palaeostreams. As the younger must be noticeably younger. These discrepancies pro- Unit Ch1 not only undercuts but also overlies Unit Ch2, vide the basis to reject the date 46.6 ka as overestimat- with the thalweg of the former lying 3–4 m higher than ing the real age. The remaining two dates are that of the latter, the entire sequence may be regarded surprisingly similar though obtained from quite differ- as having been formed by an aggrading stream. This ent facies – deep-water lacustrine (Unit Ch3) and alluvial fluvial aggradation could have not been a long-term (Unit Ch1). It may be interpreted as the result of a very tendency, but rather an episode within an overall fluvial fast transformation from a lacustrine to a terrestrial incision caused by the lowering of lake level. environment within the interval 35–40 ka BP. At this Orientation of alluvial troughs (i.e. cross sections of time the lake level must have dropped significantly palaeochannels) indicates the palaeostream direction and within a short time period. from NE to SW, along or diagonal to the lake shore. Dimensions of alluvial troughs provide an estimation of Yogach site palaeochannel width of 30–40 m and depth of 5–6m. These dimensions are much larger than the modern The Yogach section demonstrates continuous filling of a Chechenek creek, which is not more than 5–6 m wide lake that occupied the Yogach valley. This section did and 1–1.5 m deep at high water. Probably this stream not uncover the base of lacustrine sediment. Based on INTERNATIONAL GEOLOGY REVIEW 11

the OSL age of Unit Y3, one can only say that lake Accumulation of a 50 m deposit between the two formation occurred and lacustrine sedimentation dated samples at elevations 487 and 537 m a.s.l. took started before 80–85 ka BP. The most probable mechan- roughly 33 ka, which implies an average sedimentation ism of lake formation was moraine damming at the rate of 1.5 m ka‒1. As the terrace top is elevated at valley opening into the Biya valley. This could have 560–570 m, the remainder of the 30 m must have been provided by a valley glacier that moved down taken some 20 ka and sedimentation must have been the Biya valley at the end of MIS 5 (early Zyryanian, or completed not later than 30 ka BP. In fact this is an early Wurmian, glacial epoch) or at the end of MIS 6 overestimation of the residual time of terrace formation, (Samarian, or late Saalian, epoch). because in the late stages of lake filling sedimentation To choose between the two scenarios one must have rates must have increased. Therefore, terrace formation reliable ages of alluvial–lacustrine sediments from the must have been completed before 30 ka BP. valley buried 60 m deep as determined by boring in the Interruption of terrace aggradation may be considered vicinity of the Biya outflow from Lake Teletskoye. These to have resulted from the start of the Yogach River lacustrine sediments are covered by glacial deposits incision, which led to the formation of the present-day that form the morainic dam in the Biya outflow – the canyon in the valley lower course. The start of incision Yogach valley area (Figures 3 and 4), which puts a before 30 ka BP corresponds satisfactorily with the constraint on the age of maximal glacial advance and 35–40 ka BP age estimate for the sharp lake level drop formation of the morainic dam. Abundance of organic at the Yaylyu site. remains in the buried valley fill supports indirectly a Kazantsevian (MIS 5e, Eemian) age of the valley. Then Kebezen’ site the morainic dam and lake formation in the Yogach valley should be constrained to the end of MIS 5 (early The lower part of the sedimentary sequence in the Zyryanian glaciation). Turachak section (Unit T2) represents relatively deep- Whatever the scenario, the glacial advance to the water lacustrine deposits – sedimentary filling of a lake sources of the Biya and damming of the Yogach River which occupied the lower reaches of the Turachak val- and Lake Teletskoye cannot be dated to the LGM as was ley. It is similar to Unit Y3 in the Yogach section. The considered previously (Baryshnikov 1992). It must have upper, coarse-grained part of lacustrine sequence accu- occurred much earlier, and in the LGM the glacial mulated at the final stages of lake filling is not exposed boundary must have been far away from the latitudinal in the section as it was probably eroded out by the section of Lake Teletskoye and the Biya outflow from Turachak stream when it was incising into the lacustrine that. The other evidence in favour of this conclusion is terrace. The alluvial part of the section (Unit T1) repre- provided by the occurrence of alluvial and lacustrine sents an intermediate stage of this incision that began deposits in the Yaylyu terrace dated to MIS 3 and not at higher altitudes on the right side of the valley and covered by younger glacial deposits. This interpretation ceased close to the present-day elevation of the supports the findings of Okishev (2011) that the largest Turachak creek. During the incision, the stream was Downloaded by [95.215.86.12] at 05:32 07 July 2015 late Pleistocene glaciation in Altai occurred before the shifting to the left side of the valley, which provided LGM and had retreated before the middle of MIS 3. LGM dipping of the terrace by about 10 m between its was not the period of maximal glacial advance in Altai. coupling with the valley side and its edge where the The sedimentary sequence in the Yogach section studied exposure is located. demonstrates gradual filling of a lake. The lower, fine- The maximum elevation of the terrace in the mod- grained Unit Y3 exhibits conditions of a deep lake and a ern topography may not reflect the highest level of considerable distance from river inflow. Unit Y2, with lacustrine accumulation, as the terrace could have intercalation of fine- and coarse-grained layers, repre- been eroded at the very beginning of incision. This sents more shallow conditions and an approaching river former level can be roughly estimated from sedimen- mouth. Unit Y1, in which coarse-grained components tation rates. The two OSL ages from Unit T2 demon- prevail, indicates the sedimentary environment of a strate a 10 m aggradation in a roughly 10 ka interval, semi-filled lake. No alluvial facies were documented in which provides an aggradation rate of 1 m ka‒1. the section that must have been formed after the com- Aggradation rates are lower compared with those in plete filling of the lake. Most probably this is because the Yogach palaeolake, probably due to the smaller the upper part of the terrace that might contain such size of the river. If aggradation is assumed to have evidence was not exposed. finished between 35 and 40 ka BP based on estimations A rough estimation can be made of the time by for the Yaylyu and Yogach sites, then this section lacks which the terrace had been aggraded to its top. sediments from the last 25–30 ka, or the upper 25–30 m 12 G. BARYSHNIKOV ET AL.

of sediments. Given that the top of lacustrine sediments Late Pleistocene geomorphic history of the Lake in the Turachak section lies at 425 m a.s.l., the maximal Teletskoye–Biya valley system level of lacustrine sedimentation may be considered at The data and their interpretation given above are the 450–455 m a.s.l., or 60–65 m above the Biya. basis for outlining the following concept of the Lake This estimation corresponds well to the elevation of Teletskoye–Biya valley system development. the highest level of accumulation in the Biya valley, The last glacial advance to the end of Lake Teletskoye which demonstrates clear dipping at a 20 km section was preceded by the Biya valley over-deepening by of the valley from 120–130 m above the river at the about 60 m below the present-day channel (Figure 3). source of the Biya to 50–60 m at the Sarakoksha River, This large-scale valley incision occurred most probably at which is a left-bank tributary to the Biya 2 km down- the end of MIS 6, after or in the course of the retreat of stream from the Turachak creek. This dipping of the the Pleistocene maximal (according to Okishev 2011) highest Biya terrace gives a full impression of the glaciation in Altai. Alluvial aggradation in the valley was occurrence of a significant sediment supply at the occurring in the first half of the late Pleistocene and was modern source of the Biya that produced abundant accelerated by the approach of a valley glacier in the sediment which was transported down the valley and next cold epoch (middle–end of MIS 5–MIS 4). The valley formed an in-valley alluvial fan with maximum heights glacier occupied the whole of Lake Teletskoye, with its at the modern Biya sources and noticeably dipping front at the present-day source of the Biya. The glacier downstream. The role of such sediment source could and its front and side moraines dammed the tributary be played by a valley glacier whose front was located valleys, including Yogach. The glacier provided a consid- in the Yogach valley. Glacial and then morainic dam- erable increase in sediment production. Downstream ming is a reliable explanation for the palaeolake in the sediment transport caused the Biya valley aggradation Yogach valley, but it cannot explain the lakes in tri- below the glacier front and formation of the highest and butary valleys downstream of the ice front, such as widest terrace level. This terrace, whose height decreases Turachak. Lakes in these valleys can be reasonably rapidly from 120–130 m at Yogach–Artybash (source of explained by damming following rapid aggradation the Biya) to 50–60 m at the Sarakoksha and Turachak in the main valley caused by excessive sediment rivers 21–22 km downstream, may be regarded as an in- yield from the glacier. valley alluvial/glaciofluvial fan. Large-scale bedding in alluvial Unit T1 in the A rapid rise in the bottom of the Biya valley caused Turachak section must have been formed by a rather by aggradation of this fan resulted in damming of powerful stream. Cross-beds in Unit T1 most probably tributary valleys, such as the Turachak, and the forma- represent lateral accretion of a channel point bar in a tion of valley lakes in their lower courses. Similar phe- meandering or laterally shifting straight channel nomena of tributary valley damming may well be (Figure 8(a)). The direction of palaeochannel shift is recognized worldwide in similar mountainous terrains, in agreement with the general dipping of the terrace past or present, where valley glaciers descend deep into from the right side of the valley to the present-day Downloaded by [95.215.86.12] at 05:32 07 July 2015 lower altitudes. Frontal parts of glaciers serve as sedi- position of the Turachak creek (from left to right in ment sources to produce downstream aggradation in Figure 8). Each bed in the cross-bedding series repre- their hosting valleys. At the same time, climate- sents a former surface of palaeochannel bottom. As governed regional rates of sediment production are each bed can be recognized from the top to the too low to facilitate comparable rates of aggradation bottom of the alluvial layer (Unit T1), the palaeo- in tributary valleys and other parts of drainage net not stream must have been >4 m deep (thickness of occupied by glaciers. Unit T1 around 3.7 m). Palaeochannel width can be Based on OSL dating, aggradation of lacustrine estimated from the ‘two-thirds rule’, which states that deposits in the Biya tributary valleys started before point bars occupy two-thirds of a channel width (Allen 80 ka BP, was still in progress at 50–60 ka BP, and may 1965;EthridgeandSchumm1978). Based on the hor- be supposed to have continued further as the upper- izontal width of cross-beds of ~10 m, palaeochannel most parts of the alluvial/lacustrine terraces were not width could not be less than 15 m. The former stream dated in our study. Age constraint for the termination of appears to have been several times larger than the occurrence of valley lakes and the start of the Biya and present-day Turachak creek, which is only 2–3mwide tributary valley incision is provided by a number of and 0.5 m deep. This provides evidence, similar to that dates around 37.5 ka BP derived from lacustrine depos- in the Chechehek section, of a considerable increase its of Lake Teletskoye and alluvia overlying lacustrine in specific runoff at the time of river incision into the deposits (nos 1, 3, and 8 in Table 2). lacustrine terrace, between 35 and 40 ka BP. INTERNATIONAL GEOLOGY REVIEW 13

Close grouping of final lacustrine and initial alluvial accumulated under water depth of >100 m. Shortly dates around 37.5 ka BP lends credence to the sugges- after that the lake level dropped by about 100 m to tion that rapid changes in valley development had <470 m a.s.l. occurred around this time and definitely within Fluvial deposits formed in the vicinity of the ancient 35–40 ka BP. Before this date the latitudinal section of lake shoreline were dated to the same age, around the modern Lake Teletskoye had apparently been occu- 37.5 ka BP, as the deep-water lacustrine sediments in pied by a valley glacier which dammed some tributary the same location, which supports the sharp, probably valleys, including the Yogach, and resulted in the Biya momentary, drop in water level. This drop in level was valley aggradation which further resulted in damming probably caused by rapid discharge of the lake resulting of tributaries downstream of the Yogach. Retreat of the from rupture of the moraine dam at the present-day glacier must have occurred no later than 37.5 ka BP. This source of the Biya. This event is the most probable age estimate derived from local sedimentary chronol- candidate for the catastrophic BDF established by ogy does not contradict the findings of Okishev (2011), Baryshnikov (1992, 2012). The age of BDF provided by who recognized two phases of glacial advance in this author is significantly older than that suggested Russian Altai in the late Pleistocene and attributed the previously (Baryshnikov 1992). Assignment of BDF to maximal advance to the first of these. This maximal the LGM was suggested in that study based on a set phase was constrained between 32 and 58 ka BP based of radiocarbon dates from lacustrine clays in a number on radio-thermoluminescence dating of glacial till and of tributary valleys that were considered to have lacustrine sediments of glacial-dammed lakes in the resulted from their damming by the BDF. The existence Chuya Basin in southeast Altai. Moraines of the second of these clays dated in the range 12–16 ka BP (14 C glacial stadial correlated to MIS 2 are found now within uncal) reveals a wide occurrence of lacustrine sedimen- the post-maximal glacial complexes. Similar glacial his- tation in tributary valleys in post-LGM time that requires tory was detected in the mountain terrain in the Baikal reassessment and reinterpretation in the light of a much Region: Krivonogov et al.(2004) dated the maximal gla- younger age of this phenomenon relative to the BDF. cial advance to the early Zyryanian (early Wurmian) Rapid deepening of the Biya downstream from the epoch with numerical ages >39 ka BP. former dam after the BDF resulted in incision of tribu- Okishev (2011) overviewed published data and con- tary valleys and draining of residual lakes into these. cluded that typical for alpine regions of Eurasia in the Alluvial sequences formed during this rapid incision temperate zone was the occurrence of two glacial sta- demonstrate flow dimensions much larger than do the dials in the late Pleistocene, of which the earlier (pre- present-day streams in the same valleys. Larger stream LGM phase) was characterized by maximal glacial channels support the occurrence of runoff much higher advance and the second (LGM) phase was marked by than today, not only due to glacial melt water (in the both less glacial advance and less lowering of snowline. Biya valley), but also due to higher atmospheric preci- Krivonogov (2010) explains the wider extent of glacia- pitation (in small tributary valleys) around 37.5 ka BP. tion in the south of East Siberia in the late MIS 5–MIS 4 After the rapid phase of incision, valley deepening Downloaded by [95.215.86.12] at 05:32 07 July 2015 compared with that in the LGM by a changing atmo- slowed down. This inference is indicated by the dynamics spheric circulation over Eurasia in the late Pleistocene. of the level of Lake Teletskoye. After a rapid drop around According to this worker, moisture transport into the 37.5 ka BP, lake level lowering slowed considerably. This interior of the Eurasian continent was higher in MIS provided conditions for creation of the alluvial plain in the 4–MIS 5d and was reduced considerably in the LGM. lake coastal area where streams flowed alongside the Glacier retreat around 37.5 ka BP resulted in forma- lake. Further lowering of the lake had been generating tion of Lake Teletskoye, at least its northern latitudinal constantly increasing relief, which forced local streams to segment. We consider this date as the age of formation abandon the 37.5 ka alluvial plain and turn directly of the modern Lake Teletskoye. It is surprisingly close to towards the lake. The total amplitude of lake lowering the suggestion by Bublichenko (1939) of a lake age of since 37.5 ka BP to the present may be assessed at 36 ka, derived from simple sedimentological reasoning. 30–35 m. This value may also serve as an estimation of The initial post-glacial level of the lake was constrained the Biya River incision at its outflow from the lake during by the elevation of the terminal moraine that consti- the same period, which consequently occurred at an tuted the dam at the Yogach–Artybash location – 570 m average rate of 0.8–0.9 m ka‒1. Incision and the respective a.s.l. This level corresponds well to the maximal eleva- lowering of the lake continued in the late Holocene, tion of the Yaylyu terrace (560–580 m a.s.l.). Sediments which may be deduced from a stepwise morphology of of the initial stage of Lake Teletskoye are represented by low terraces recognized at the Yurtok River confluence Unit Ch3 in the Chechenek section (Figure 6(a), (d)) 2 km downstream from Lake Teletskoye. 14 G. BARYSHNIKOV ET AL.

Conclusion References Our study revealed a notably older age of the maximal Adamiec, G., and Aitken, M.J., 1998, Dose-rate conversion late Pleistocene glacial advance in the Lake Teletskoye– factors: Update: Ancient TL, v. 16, p. 37–50. Biya River system and the catastrophic BDF and forma- Allen, J.R.L., 1965, The sedimentology and paleogeography of the Old Red Sandstone of Anglesey, North Wales: Proceedings tion of the modern Lake Teletskoye associated with of the Yorkshire Geological Society, v. 35, no. 2, p. 139–185. glacial retreat. In previous studies, all these events Baker, V.R., 2009, Megafloods and global paleoenvironmental were assigned to the LGM. We studied three sedimen- change on mars and earth, in Chapman, M.G., and Kesthelyi, tary sections and produced luminescence dates from L. eds., Preservation of random mega-scale events on mars different sedimentary facies: (1) lacustrine deposits in and earth: Influence on geologic history: Geological Society of America Special Paper 453, p. 25–36. small valleys originated from glacially induced damming Baker, V.R., 2013, Global late Quaternary fluvial paleohydrol- prior to BDF; (2) lacustrine deposits of Lake Teletskoye ogy: With special emphasis on paleofloods and megafloods, at the initial phase of its formation shortly before the in Shroder, J. (Editor in Chief), and Wohl, E., eds., Treatise on BDF; and (3) alluvial deposits of the post-BDF incision geomorphology, Vol. 9, Fluvial geomorphology: San Diego, phase. CA, Academic Press, p. 511–527. The aggregation of data suggests that major geo- Baker, V.R., Benito, G., and Rudoy, A.N., 1993, Paleohydrology of late Pleistocene superflooding, Altay Mountains, Siberia: morphic events occurred in a short time span, within Science, v. 259, p. 348–350. doi: 10.1126/science. 35–40 ka BP. Glacial retreat occurred some time before 259.5093.348 and formed Lake Teletskoye dammed by terminal and Baryshnikov, G.Y., 1976, Morphology and deposits of the Biya side moraines. The initial lake water level stood some valley, in Baryshnikov, G., Luzgin, B., and Tsekhanovskaya, 130–140 m above its present-day level. Breaching of the N., eds., Problems of geomorphology of : Leningrad, LGU Press, p. 14–17. [in Russian] moraine dam around 37.5 ka BP caused the BDF and Baryshnikov, G.Y., editor, 1984, Aeolian sediments in the Altai rapid incision of the Biya valley by ~100 m, accompa- foothills and their links with paleoclimates, in Contemporary nied by an equivalent drop in the lake level. geomorphological processes in the Altai Krai: Biysk, Subsequently, Biya incision and lowering of Lake Pedagogical Institute Press, p. 6–9. [in Russian] Teletskoye slowed down and have continued till now Baryshnikov, G.Y., 1992, Landscape development in transi- at an average rate of 0.8–0.9 m ka‒1, producing total tional zones of orogens in the Cenozoic: Tomsk, Tomsk – University Press, p. 181. [in Russian] lowering of 30 35 m in the last 37.5 ka. However, the Baryshnikov, G.Y., 2012, Landscapes of transitional zones of Biya valley is still far from its pre-glacial depth of ~60 m orogens: Barnaul, Altai University Press, p. 498. [in Russian] below the modern valley bottom. Baryshnikov, G.Y., and Panychev, V.A., 1987, Formation of These results confirm the conclusion of other workers terrace assemblages in the upper Biya valley: Questions of – that the maximal glacial advance in alpine Southern Geography in Siberia, v. 17, p. 41 52. [in Russian] Borisov, B.A., and Minina, E.A., 1979, Rugged and cellular bottom Siberia occurred much earlier than the global LGM – in moraines in Eastern Pamir and Russian Altai: Geomorfologia, the late MIS 4 or early MIS 3. A phenomenon was also v. 1, no. 1979, p. 69–74. [in Russian with English summary] detected of the damming of tributary valleys and the Bortolot, V.J., 2000, A new modular high capacity OSL reader Downloaded by [95.215.86.12] at 05:32 07 July 2015 formation of in-valley lakes due to rapid aggradation in system: Radiation Measurements, v. 32, p. 751–757. doi: the trunk (Biya) valley caused by excessive sediment 10.1016/S1350-4487(00)00038-X production in front of the valley glacier. Bublichenko, N.L., 1939, Origin of the Teletskoye Lake: Bulletin of the West Siberian Geological Survey, v. 3, p. 42–58. [in Russian] Butvilovskiy, V.V., 1982, On the evidences of catastrophic releases of glacial-dammed lakes in the Eastern Altai, in Acknowledgements Baryshnikov, G., ed., Evolution of fluvial systems in the Altai – This study contributes to the joint Russian Foundation of Basic Region: Barnaul, Altai University Press, p. 12 16. [in Russian] Research and Russian Geographic Society (RFBR-RGS) Project Butvilovskiy, V.V., 1985, Catastrophic water releases from gla- 13-05-41070, ‘Extreme natural phenomena in alpine environ- cial-dammed lakes in the South-Eastern Altai and their ments in the past and present, with the focus on Russian geomorphological evidences: Geomorfologia, v. 1, no. – Altai’. The authors are grateful to Vic Baker (University of 1985, p. 65 74. [in Russian with English summary] Arizona) and to the anonymous reviewer for valuable com- Carling, P., Villanueva, I., Herget, J., Wright, N., Borodavko, P., ments on the paper draft and polishing the English. and Morvan, H., 2010, Unsteady 1D and 2D hydraulic models with ice dam break for Quaternary megaflood, , Southern Siberia: Global and Planetary Change, v. 70, p. 24–34. doi: 10.1016/j.gloplacha.2009.11.005 fl Disclosure statement Carling, P.A., 2013, Freshwater mega ood sedimentation: What Can We Learn about Generic Processes? Earth- – No potential conflict of interest was reported by the authors. Science Reviews, v. 125, p. 87 113. INTERNATIONAL GEOLOGY REVIEW 15

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