Quaternary glaciations in the Verkhoyansk Mountains, Northeast Siberia

Quaternary Research 74 (2010) 145–155

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Quaternary Research j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / y q r e s

Quaternary glaciations in the Verkhoyansk Mountains, Northeast Siberia Georg Stauch ⁎, Frank Lehmkuhl RWTH Aachen University, Templergraben 55, 52056 Aachen, Germany

a r t i c l e

i n f o

Article history: Received 20 August 2008 Available online 26 May 2010 Keywords: Siberia Paleoclimate Quaternary Geomorphology Glacier Dating

a b s t r a c t Geomorphological mapping revealed five terminal moraines in the central Verkhoyansk Mountains. The youngest terminal moraine (I) was formed at least 50 ka ago according to new IRSL (infrared optically stimulated luminescence) dates. Older terminal moraines in the western foreland of the mountains are much more extensive in size. Although the smallest of these older moraines, moraine II, has not been dated, moraine III is 80 to 90 ka, moraine IV is 100 to 120 ka, and the outermost moraine V was deposited around 135 ka. This glaciation history is comparable to that of the Barents and Kara ice sheet and partly to that of the Polar Ural Mountains regarding the timing of the glaciations. However, no glaciation occurred during the global last glacial maximum (MIS 2). Based on cirque orientation and different glacier extent on the eastern and western flanks of the Verkhoyansk Mountains, local glaciations are mainly controlled by moisture transport from the west across the Eurasian continent. Thus glaciations in the Verkhoyansk Mountains not only express local climate changes but also are strongly influenced by the extent of the Eurasian ice sheets. © 2010 University of Washington. Published by Elsevier Inc. All rights reserved.

Introduction Quaternary glaciations in the northern hemisphere are a major consequence of global climate change during the Quaternary. While the large northern hemispheric ice sheets are primary controlled by global climate changes, mountain glaciations also strongly reflect regional and local climate. Reconstruction of the timing and style of mountain glaciations is an important proxy for the reconstruction of Quaternary climate development. While a wealth of information has been published about glacial and periglacial paleoenvironments in other high-latitude areas in Eurasia recently (e.g., Glushkova, 2001; Schirrmeister et al., 2002, 2008; Brigham-Grette et al., 2003; Svendsen et al., 2004; Astakhov and Mangerud, 2007; Mangerud et al., 2008a,b; Möller et al., 2008) only sparse information is available about northeastern Siberia. The Verkhoyansk Mountains (Fig. 1) are of particular interest in reconstructing high-latitude northern hemisphere glaciations. They are the easternmost mountains on the Eurasian continent, which receive their precipitation mainly from the west and therefore from the Atlantic Ocean. The extent of late Pleistocene glaciations in the Verkhoyansk Mountains has been debated for a long time (Arkhipov et al., 1986). Figure 2 shows three maps reflecting different opinions on the maximum extent of glaciations in the last glacial cycle (Weichselian). Grosswald and Hughes (2002) suggested the largest glaciation in the area, with an ice cap up to 2000 m high, was centered in the Yana Highlands during the late Weichselian. The ice cap was part of a large

⁎ Corresponding author. Fax: + 49 241 8092460. E-mail address: [email protected] (G. Stauch).

pan-Arctic ice sheet (see also Grosswald et al., 1992; Grosswald and Spektor, 1993; Grosswald, 1998). However, the hypothesis of such a large arctic ice sheet has been seriously challenged in recent years (e.g., Sher, 1995; Svendsen et al., 1999, 2004; Karhu et al., 2001; Spielhagen, 2001; Gualtieri et al., 2000, 2003). The map of Arkhipov et al. (1986) shows a much smaller mountain glaciation, with glaciers restricted to the Verkhoyansk Mountains. On the western side, valley glaciers nearly reached the banks of the Lena River. An even smaller glaciation has been reconstructed by Zamoruyev (2004). During the late Weichselian, valley glaciers existed in the area while glaciations in the early last glacial cycle were larger, reaching an area comparable to the one mapped by Arkhipov et al. (1986). The chronostratigraphy in the area was mainly based on radiocarbon dating from the 1960s and 1970s and correlation with type sections in Central and West Siberia. Major work in the area has been done by Kind et al. (1971), Kind (1975) and Kolpakov (1979). According to these authors, up to ten different glacial advances can be distinguished. However, only three of them form major terminal moraines at the surface. The oldest glaciation has been attributed to the previous glacial cycle and is only preserved as ground moraines. The glaciation was less extensive than the later advances, which is different from the rest of Siberia where the so-called Samarov glaciation was the largest one (Kind, 1967, 1975; Astakhov, 2004; see also Astakhov, 2001 for a discussion on the Russian stratigraphy). The Zyryan glaciation was the maximum one during the last 120 ka but is also only preserved as ground moraines. The following Karginsk glaciation (Kind, 1975; Kolpakov, 1979; Kolpakov and Belova, 1980; Arkhipov et al., 1986; Laukhin, 1994; Zamoruyev, 2004) is unique in the Verkhoyansk Mountains. Radiocarbon dates above and below glacial sediments point to a glacial advance between

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Figure 1. The Verkhoyansk Mountains. The white box indicates the study area.

33,000 and 30,000 14C yr BP (Kind, 1975). The term Karginsk was originally applied for interstadial sediments dated to 22–50 ka at the mouth of the Yenissey River and has been widely used in the literature of northern Siberia. Recent investigation showed that these sediments belong to the Eemian period (Astakhov, 2001, 2007). Three large terminal moraines were formed in the western foreland during the late Weichselian. Radiocarbon ages supported a formation between 29,000 and 15,000 14C yr BP (Kind, 1975; Kolpakov, 1979; Kolpakov and Belova, 1980). Spielhagen et al. (2005) suggest a younger age for a large glaciation on the basis of a strong freshwater peak in the Laptev Sea. They assumed that a freshwater peak at 13 ka was caused by the collapse of an ice dam blocking the Lena River. Several small terminal moraines have been identified upstream of these three large moraines in the western foreland. They have been attributed to the retreat of the late Weichselian glaciers and early Holocene advances (Flint, 1971; Kind, 1975). In this paper we will describe the geomorphological setting of the moraines in the central Verkhoyansk Mountains, present a new chronology of glaciations in the area, and discuss paleoclimatic implications for northern Asia. Study area The Verkhoyansk Mountains are a mountain range 1200 km long and 200 to 300 km wide located in northeastern Siberia at about 125°

to 145°E. To the north the mountains are bound by the Laptev Sea coast at 72°N, while the southern margin is at 59°N. The geographical margins to the east and west are formed by the Lena River valley and the Jana Highlands, respectively. Maximum elevations of the summits increase from the north to the south. In the northernmost part, the summits reach an elevation of about 1400 m asl in the area of the Charaulach, while the central parts are between 2000 and 2200 m in elevation. The highest summit (2959 m asl) is located in the Suntar Chajata, a southern branch of the mountain system (Fig. 1). The Verkhoyansk Mountains are the westernmost part of the Verkhoyansk–Chukotka orogenic zone. They are mainly build up by Mesozoic sand and siltstones, which have been folded at the eastern flank of the Angara craton. A few granitic intrusions reach the surface (Parfenov and Natal'in, 1986; Parfenov, 1991; Layer et al., 2001; Oxman, 2003; Popp et al., 2007). The climatic conditions in the area are extremely continental. Mean monthly air temperatures vary between −40°C in January and +20°C in July. The mean annual air temperature is at most stations well below − 10°C (Lydolph, 1977). Due to orographic effects, precipitation on the western and eastern side of the mountains varies considerably. Climatic stations in the Lena valley and in central Yakutia show an annual precipitation above 200 mm/a. On the western flank, precipitation of up to 700 mm/a and more is assumed while on the eastern side only 130 mm/a and less occurs (Lydolph, 1977; Shahgadenova et al., 2002; Murzin, 2003). Recent glaciation in the Verkhoyansk Mountains is limited. In the northern part of the

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Figure 2. Extent of Weichselian glaciations according to Grosswald and Hughes (2002-left), Arkhipov et al. (1986-center) and Zamoruyev (2004-right).

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mountains only small glaciers with a maximum length of up to 3.5 km are preserved. In the Suntar Chajata, glaciers cover an area of more than 200 km² (Krenke and Chernova, 1980; Koreisha, 1991; Murzin, 2003; Ananicheva and Krenke, 2005; Ananicheva et al., 2008). In this study, we focused on the central Verkhoyansk Mountains (Fig. 3), at about 65°N/129°E. The study area comprises an area of 150,000 km². The size of the catchments on the western side is between 9000 and 13,000 km² while the one on the eastern side is between 2700 and 6500 km². Three major geomorphological regions can be distinguished (Stauch, 2006). On the western side a broad, gently inclining foreland stretches with a width of about 80 km between the mountains and the Lena River. These forelands mainly consist of fluvial gravels of Pleistocene age (Alekseev and Drouchits, 2004). In the central part of the study area, the Verkhoyansk Mountains are located, which comprise several N–S and E–W trending mountain ridges. The mountainous area has a width of 200 to 250 km. Maximum elevations are 2120 m in the eastern part of the Tumara catchment. The Yana Highlands in the northeast of the study area are characterized by undulating hills and generally low relief. Methods Geomorphological mapping in the area was done by fieldwork and by the use of satellite images and digital terrain models (DTM). Fieldwork was carried out in two catchment areas in the central Verkhoyansk Mountains (Tumara and Djanushka Rivers, A and B in Fig. 3), where about 100 sections have been studied. Selected exposures were sampled for sedimentological analysis and dating. Mapping concentrated on glacial landforms and related sediments, as well as on aeolian deposits. To extend the study area in the adjacent catchments we utilized Landsat7 and Corona satellite images with a

resolution of 15 m and up to 2 m, respectively. Landsat7 data were the main source for mapping, while the Corona images were used as a control set for assessing the accuracy of the Landsat images (Stauch, 2006). Medium and large geomorphological features were identified by visual image interpretation. In the western foreland, morphological landforms typically have a low relief, which complicates identification of landforms. Therefore, in these areas DTMs were created from topographical maps with a scale of 1:200,000. Combination of DTMs and satellite images improved the identification of geomorphological features due to artificial hill shading. In the mountain system, detection of glacigenic forms was more complicated. Weathering of rock layers can produce landforms that resemble the shape of lateral moraines. Therefore, identification of lateral moraines that were not connected to terminal moraines was not possible within the targeted accuracy by the use of remote sensing data. Furthermore, periglacial slope processes, especially in connection with fault lines, result in landforms that are similar to U-shaped valleys (Stauch, 2006). These facts prevented the estimation of the former glaciated area. However, as it was possible to detect terminal moraines quite clearly, the maximum extent of the different valley glaciers could be established. A relative chronology was achieved by correlating the geomorphological appearance of the moraines. Three simple parameters were used: i) the position of the moraine in comparison to the source area of the glacier, ii) the size of the glacial deposits, namely their height and width, and iii) the appearance of the surfaces. Younger moraines, generally speaking, have a rough surface with many small ridges and depressions, while older landforms have a more undulating surface. Lakes on the moraines in the upper part of the catchment are generally smaller than lakes on older moraines. Periglacial processes lead to lateral erosion at the banks of the lake and their progressive aggregation through time. A correlation of the different terminal

Figure 3. Study area with geomorphological regions and selected terminal. White dots are cirques, Black star in the south indicates location of Figure 5.

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moraines by the use of the mineral composition of the sediments has not been successful (Popp et al., 2007). Dating was based on the IRSL (infrared optically stimulated luminescence) method in two catchment areas (Tumara River and Djanushka River). We used aeolian cover sediments to obtain minimum ages of the underlying glacial material. At selected sites, glaciofluvial material was used. For a discussion of the dating method and the results see Stauch et al. (2007). Results According to the field mapping, the analysis of the satellite images, and the DTM, as many as five terminal moraines can be identified in the different catchments of the study area. These moraines are named by their relative downglacier position, moraine I for the youngest to moraine V for the oldest in the sequence. Moraine I In all studied catchment areas on the western mountainside, deposits forming moraine I have been deposited within the mountain valleys (see In I, Dj I, Tu I and Ke I in Fig. 3). Terminal moraines form concentric arches with a diameter of up to 10 km. Several small ridges are imposed on the surface. A large number of kettle lakes are typical, which were interpreted as landforms of decaying ice. An exception is the moraine at the Kele River in the southeast of the study area (Ke I), which is only partly preserved due to subsequent fluvial processes. In two tributaries of the Indyulyung River, some ambiguous landforms may be interpreted as small terminals moraines upstream of moraine I (In I). However, if these are true glacial landforms they might be formed as remnants of a retreating glacier rather than a younger advance, as no comparable features have been preserved in any other studied catchments. At the Tumara River, two sections were studied about 100 and 600 m downstream of the terminal moraine (Tu I) in 380 m asl. At both sites, aeolian sediments cover fluvioglacial gravels of the glacial outwash fan. At the base of the aeolian sediments at one of the profiles, sediments have an IRSL age estimate of 52.8 ± 4.1 ka (V09, Table 1) giving a minimum age for the underlying fluvioglacial sediments. At the other profile, aeolian sediments have been dated to 29.5 ± 2.8 ka (V08). The terminal moraine at the Djanushka River (Dj I) consists of two large lobes on the valley floor at about 200 m asl, which are divided by a small hill. The glacial sediments reach heights of 100 m and more above the present river. The moraine mainly consists of rounded blocks, up to 1 m in diameter, in a clayey matrix. The blocks show common glacial features like glacial striae, crescentic fractures and chatter marks, with no signs of weathering. The moraine is nearly completely covered by aeolian sediments of up to several tens of centimeters (Fig. 4). Table 1 IRSL ages (from Stauch et al., 2007). Nr.

Moraine

Origin

IRSL Age in ka

V08 V09 Dj01 V10 V17 V23 V25 Dj22 V27 V28 V29 V30 Dj30 Dj31

Tu I Tu I Dj I Tu II Tu II Tu III Tu III Dj III Tu IV Tu IV Tu IV Tu IV Dj V Dj V

Aeolian Aeolian Aeolian Aeolian Aeolian Aeolian Fluvioglacial Fluvial Aeolian Aeolian Fluvioglacial Aeolian Fluvioglacial Fluvioglacial

29.5 ± 2.8 52.8 ± 4.1 39.7 ± 3.1 19.2 ± 2.1 46.8 ± 3.7 48.5 ± 3.9 86.9 ± 6.8 92.3 ± 6.5 107 ± 10 123 ± 10 97.6 ± 6.8 110 ± 8 135 ± 9.0 141 ± 10

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Upstream of the moraine in section P51, glacial sediments are covered by 1 m of limnic clays. These are remnants of a lake, which might have been formed during an initial phase of the glacier retreat. Above the lake sediments, a further 1 m in the section is build up of alternating layers of clays and sands, indicating changes in flow conditions. These sediments are topped by aeolian silts and sands, which were dated to 39.7 ± 3.1 ka (Dj01). The thin aeolian cover on top of the moraine consists mostly of sand-size particles (see P52, P57, P59, and P60 in Fig. 4). At the base of one of the aeolian sections (P57) several ventifacts have been preserved. Downstream of the moraine on the right side of the valley, a large fluvioglacial fan is located (P62). Only a few km downstream of the glacially eroded water divide, on the eastern flank of the Verkhoyansk Mountains, several small terminal moraines have been preserved in the uppermost part of the Otto-Sala, Dulgalakh and Echly catchments (Fig. 3). They have been deposited at elevations of about 1000 m asl and are heavily eroded. For all valley systems, the proposed centers of the different glaciations have been located some tens of km west of the water divide. Moraine II On the western side of the mountains, moraine II has been deposited mainly in the foreland (Fig. 3). These moraines are much larger than the ones upstream. At the Tumara River they have a relative elevation of up to 370 m and a diameter of up to 20 km. The surface is marked by several lines of small kettle lakes (Fig. 5). Up to four marked ridges have been imposed on the surface, indicating oscillations of the glacier. Directly downstream of the moraine, a 43m-high section has been studied in detail. The section consists of three major units, of which the two lower ones are build up by fluvial gravels. The lower unit has a height of 15 m and a matrix with a yellowish color. Scanning electron microscope (SEM) images of the sandy matrix show reformation quartz crystals, indicating an old formation age. The second unit consists of 20 m of gray gravels with a sandy matrix. These sediments have been interpreted as fluvioglacial deposits of the Tu II moraine due to common glacial marks on the surface of the gravels. On top of the gravels we found 8 m of aeolian sediments. Aeolian sediments also form a continuous cover on top of the moraine. Aeolian sediments on top of the moraine have been dated to 19.2 ± 2.1 ka (V10) and 46.8 ± 3.7 ka (V17). As these ages are minimum ages, the deposition of the underlying till must have occurred before 47 ka. However, its relative position suggests that it must be older than moraine I. On the eastern mountainside, small moraines are preserved in elevations between 800 and 950 m asl. According to their position and shape, they might be formed at the same time as moraine II at the western side. However, due to the deposition of the sediments in small valleys, preservation of the moraines is generally poor, even with lower amounts of precipitation, in comparison to the western side. Moraine III Moraine III is the largest in the study area, based on the relative height of the preserved morainic sediments of up to 380 m. Lakes and small ridges are also present at the surface but have been partly destroyed by meltwater channels of the younger glacial advance (Fig. 5). The ridges on the surface are much more eroded and are smoother than moraine II. A typical moraine sequence is shown in Figure 6 from the Djanushka catchment. In the two northernmost catchments, the Djanushka and Indyulyung, the glacial sediments have been deposited at elevations of 70 m and 80 m asl, respectively. In the Tumara and Kele forelands, the moraines are located at elevations of 150 m and 200 m asl.

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Figure 4. Cross section of Moraine Dj I (Stauch, 2006).

The glacial sediments at the Tumara River consist of two different types of till. At their base, well rounded blocks with glacial striae and chatter marks rest in a clayey/silty matrix and form a highly compacted ground moraine. The matrix of the till near the surface has a much higher sand content and incorporates a layer of fluvial sands, indicating a glacial terminus environment of deposition. SEM images of the matrix of the upper till shows signs of glacial transport on the quartz grains. The fluvial sands provide an IRSL age of 86.9 ± 6.8 ka (V25). Above the till, fluvioglacial gravels are present. These gravels are covered by 25 cm of presumably aeolian sediments with an IRSL age of 48.5 ± 3.9 ka (V23), which is comparable to the aeolian sediments covering moraine I and II. In the Djanushka River catchment, bright yellow fluvial sands covering morainic sediments have been IRSL dated to 92.3 ± 6.5 ka (Dj22).

On the eastern side, the third moraine also formed the largest landforms. In many catchment areas, two distinct ridges with a length of several tens of km can be observed. They are located at elevations between 700 and 900 m asl in the three studied catchments. Moraine IV Complete arcs of moraine IV are seldom preserved. Lakes and subdued ridges are only visible at few locations. Erosion by younger meltwater channels as well as by the Lena and Aldan rivers has been strong (Fig. 6). Sections of this moraine have been studied at the Tumara River. Similar to the Tu III moraine, the base consists of compact dark gray ground moraine that is covered by a moraine with a sandier matrix. At the top of the moraine, fluvioglacial gravels were found. In the uppermost part of the gravels, a 5-cm-thick layer of fluvial sands is incorporated. The gravels are covered by about 110 cm of aeolian sediments. These sediments are sandier in the lower part and have high silt content in the upper part. The uppermost 80 cm of the section consist of relocated slope material. The fluvial sands in between the fluvioglacial gravels give an IRSL age of 97.6 ± 6.8 ka (V29). However, the aeolian sediments above the gravel have been dated to 123 ± 10 ka (V28) in the lower part of the profile and 107 ± 10 ka (V27) in the upper part. Farther downstream of the section, fluvioglacial gravels are covered by sands that have been dated to 110 ± 8 ka (V30). On the eastern side of the Verkhoyansk Mountains, moraines at elevations between 600 and 700 m have been mapped as corresponding terminal position of the glaciers. Like the one in the western foreland they are heavily eroded by later fluvial processes. Moraine V

Figure 5. Terminal moraines at the Tumara River (Corona Image). Bold lines indicate the main terminal moraines, dashed lines retreat stages (modified from Stauch, 2006). The white box marks a possible fault line.

The outermost moraine (V) is only preserved at the two northernmost catchments on the western side of the mountain range, in the Djanushka River and the Indyulyung River valleys. The moraine is located about 70 km west of the mountain front. Maximum heights of the deposits are a few tens of meters. The moraine has been studied at a long section at the Djanushka River, where the moraine has been incorporated in a Lena terrace with a table-like surface. Both glacial and fluvioglacial sediments were identified in this section (Fig. 7). Two thin layers of morainic sediments are the main component of the profile. These layers are very compact and have high clay content. Between the till sediments, a layer of fluvioglacial sand is preserved. Below the layers, sandy and clayey sediments are again present. On top of the upper till layer, coarse fluvioglacial sand has been deposited. The top of the section consist of about 10 cm of aeolian silt. The glacial deformed sand below the lower till gives an IRSL age of 141 ± 10 ka (Dj31) while the sand above the till has been dated to 135 ± 9 ka

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Figure 6. Terminal moraines at the Djanushka River. Combination of Landsat7 satellite image and a DTM.

(Dj30). According to these IRSL ages, the formation of the moraine took place in the penultimate glacial cycle. Several hundreds of meters downstream, a similar section was studied. Here the till is covered by fluvioglacial sands and aeolian silts. However, the silty sediments are much thicker. Close to the base of the aeolian sediments at depths of 130 cm and 45 cm, two layers of ventifacts have been found. The ventifacts reach a size of up to 20 cm. Below the till up to 4 m of fluvial sands have been deposited and which overlie about 8 m of fluvial gravels with diameters of up to 30 cm. The sand has most probably been deposited by the Lena River, while the size of the gravels indicates an origin from the Verkhoyansk Mountains. No corresponding terminal moraines have been detected on the eastern side of the Verkhoyansk Mountains. They might either been completely eroded by fluvial activity or the glacial advance was smaller than the later ones.

No clear terminal moraines have been found in the southwest of the study area. In the upper part several well-developed cirques have been mapped and valleys are at least partly shaped by glaciers. Therefore, both valleys have been glaciated during some time but moraines are not preserved. Cirques Further information concerning the distribution of Pleistocene ice can be derived from the existence of cirques in the Verkhoyansk Mountains. 498 cirques have been mapped (Fig. 3), which vary in altitude between 680 and 1800 m. The average altitude is 1382 m asl. 75% of the cirques are facing NW, N or NE (Fig. 8). It was not possible to distinguish between ages of cirque formation. However, cirques situated on the western side of the Verkhoyansk Mountains are generally at lower elevations than those in the inner part of the

Figure 7. Glacial sediments of moraine V at the Djanushka River.

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Figure 8. Cirque orientation (left) and elevation (right).

mountains and especially on the eastern side, demonstrating the influence of the moisture fluxes from the west. Cirque elevations are only low in the inner part close to the large W–E trending valleys, where precipitation can penetrate into the mountains. Snowlines Several methods have been used for estimating the possible elevation of the equilibrium line altitude (ELA), such as the balance ratio (BR) or the accumulation area ratio (AAR) (see Benn and Lehmkuhl, 2000 for details). However, none of the methods can be used in the area due to the unknown extent of the glaciated area. Using the toe-to-summit altitude ratio (TSAR), which only requires the elevation of the glacier marginal position indicated by the terminal moraine and the elevation of the highest summit in the source area of the glacier, it is possible to give an estimate of the ELA position (Louis, 1954; Lehmkuhl, 1998). For the western side of the mountains this method indicates an elevation of the Pleistocene snowline of 1250 m asl for the uppermost terminal moraine in the Kele R. catchment and 1050 m asl for the lowest terminal moraine at the Indyulyung River. However, differences between the valleys were larger than between the moraines in a single catchment. These values are therefore only rough estimations for possible Pleistocene ELAs. Using the same method for the moraines on the eastern flank of the mountains results in a ELA roughly 400 m higher. An often-used indicator for the ELA is the altitudinal position of cirque floors. According to Trenhaile (1975) the average altitude of all cirques is the maximum elevation of the snowline. This would yield a value of 1300 to 1400 m for the central Verkhoyansk Mountains. Meierding (1982) proposed the lowest cirque elevation as the most reasonable approximation, resulting in an ELA of around 700 m asl. However, excluding the lowermost 2% would result in an ELA of 1000 m asl. Nearly the same elevation results from using only the north- and northeast-facing cirques, as suggested by Flint (1971) for the northern hemisphere. Discussion According to our results, glacial advances in the Verkhoyansk Mountains are older than previously assumed. Aeolian sediments covering moraine I yield ages between 52.8 ± 4.1 and 29.5 ± 2.8 ka, providing minimum ages of the underlying glacial sediments. The results are comparable to the outcome of studies from the Charaulach Mountains, the northernmost branch of the Verkhoyansk Range, which have been free of ice at least since the last 60 ka (Schirrmeister

et al., 2002; Hubberten et al., 2004). Previous studies in the area indicated a Holocene age of deposition (e.g., Flint, 1971; Kind, 1975). Moraine III was deposited at 85 to 90 ka, based on fluvial sediments in and above the upper part of the moraine. Moraine II, which has been identified according to geomorphological criteria, formed sometime between 50 ka and moraine III. Aeolian cover sediments on top of moraine II are more of less the same age as the ones covering moraine I and are much younger than the underlying glacial material. Moraine IV has been previously dated to 33 ka (Kolpakov, 1979; Kolpakov and Belova, 1980). The herein presented IRSL ages indicate a much older age of formation. However, the dates in one of the profiles are inverted, with fluvial sands in the lower part having a younger IRSL age estimate than the covering aeolian sand (Stauch et al., 2007). We cannot explain this inversion up to now. Taking all four ages into account, a deposition between 100 and 120 ka is most likely, and despite the inconsistencies this moraine is older than the previously assumed interstadial age. Ten IRSL ages from aeolian sediments upstream of moraine IV give ages of older than 33 ka (Stauch et al., 2007). Kind (1975) and Kolpakov and Belova (1980) described a buried moraine on both banks of the Lena River. This moraine might be the moraine V described above. However, according to these authors, formation of the sediments took place in the early part of the last glacial cycle, while new IRSL ages (N130 ka) indicate a deposition in the previous glacial cycle. At the Djanushka River, fluvial gravels from the Verkhoyansk Mountains have been deposited below sands of the Lena River and glacial deposits of the stage V glacier advance. Due to the relatively low relief in the western foreland we suppose a nearglacial environment of deposition. Therefore, this section indicates an older advance than documented in moraine V. It remains speculative how far glaciers in the Verkhoyansk Mountains retreated during the glacial phases, or if they disappeared completely. The different sizes of the glaciers west and east of the mountains and the orientation of the cirques indicate a primary moisture source to the west during the late Quaternary. Reconstructions of former ELAs yield similar results. On the western side of the mountains, values of 1000 to 1250 m asl seem most likely while on the eastern side the ELA has been about 400 m higher. For the same area Vaskovskiy (1964) and Galabala (1997) proposed a late Pleistocene ELA of around 1300 m asl, while Kotljakov et al. (1997) suggested elevations of 800 m on the western and 1200 m asl on the eastern side of the central Verkhoyansk Mountains. These values are comparable to the assumptions presented in this study. Moisture-bearing winds crossed the whole Eurasian continent, as they are doing today.

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As assumed before, glaciations in the Verkhoyansk Mountains are also influenced by glaciations west of the mountain system. Svendsen et al. (2004) reconstructed the extent of the Eurasian ice sheets for four different time periods from the Late Saalian (N140 ka) until the Late Weichselian (25 to 15 ka). During these periods the Scandinavian ice sheet became larger during every glaciation, while glaciations in the eastern sector of the Eurasian ice sheets, the Barents-Kara ice sheet, were getting smaller in extent until the Late Weichselian due to reduced precipitation (see also Felzer, 2001; Hubberten et al., 2004). The timing and extent of glaciations in the Verkhoyansk Mountains is comparable to the development of the eastern sector of the Eurasian ice sheets (Fig. 9). Similar results have been obtained from the Polar Urals (Mangerud et al., 2008a) and the Putorana Plateau (Astakhov and Mangerud, 2007). In the Polar Urals, Late Weichselian glaciers were only slightly larger than today, while a second set of moraines might have an age of 50 to 60 ka which corresponds to MIS 4. From studies of the Yenisei River terraces farther to the east, Astakhov and Mangerud (2007) concluded that the last glaciers originating in the Putorana Plateau reached the Yenisei River during MIS 4. During the early part of the last glacial cycle, enough precipitation could cross the Eurasian continent to support the development of large glaciers in the Verkhoyansk Mountains, especially on the western flank. In phase with the progressive growth of the Scandinavian ice sheet, the precipitation was shielded from the eastern part of the Eurasian continent. An extremely dry environment in eastern Siberia at least during MIS 2 is consistent with results presented previously (see summary in Astakhov, 2008). East of the Verkhoyansk Mountains, the timing of mountain glaciations show a different pattern (Fig. 9). Glushkova (2001) presented results from the Chersky Mountains. The largest glaciation occurred during the early part of the last glacial cycle but there is also a smaller glaciation during MIS 2. Only few dating results from the area are available. Studies from the Anadyr Mountains, as well as from the Koryak Mountains in the eastern part of the Eurasian continent, described several well-developed moraine sequences that have been dated to the Late Weichselian (Gualtieri et al., 2000; Glushkova, 2001; Brigham-Grette et al., 2001, 2003; Heiser and Roush, 2001). Another glacial advance has been attributed to the MIS 4/MIS 3 transition and probably MIS 5b or 5d (Brigham-Grette, 2001; Brigham-Grette et al., 2001). A sediment core from Lake Elgygytgen, spanning the last 250 ka, shows several cold and dry as well as cold and wet periods

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during the last 120 ka (Melles et al., 2007; Nowaczyk et al., 2007). These periods can at least partly be correlated to the glaciations in the Verkhoyansk Mountains and in the eastern part of the Eurasian continent (Stauch and Gualtieri, 2008). However, while in the Anadyr and the Koryak mountains (and maybe in the Chersky Mountains) glacial advances took place during the Late Weichselian, in the Verkhoyansk Mountains no glaciation occurred. This can be attributed to the different moisture sources of the two regions. In the easternmost part of the Eurasian continent, precipitation from the east (Pacific Ocean) supported the build-up of large glaciers, while the Verkhoyansk Mountains in the western part were dry (Stauch and Gualtieri, 2008).

Conclusions Five different terminal moraines have been preserved in the central Verkhoyansk Mountains. These moraines can be distinguished on the base of their morphological appearance and their distance to the center of the glaciation. During MIS 2, no glaciers evolved due to extremely dry conditions in the area. The uppermost terminal moraine (I) has been dated to N50 ka. The moraines of this glacial advance have been deposited within the mountainous area and are much smaller than the older ones. Four farther outlying large moraines have been deposited in the western foreland. While no dating results are available for moraine II, the third moraine has been dated to 85 to 90 ka, which is much older than previously assumed. Moraine IV was deposited in an early phase of the last glacial cycle at 100 to 120 ka. One moraine has been dated to the previous glacial cycle with an age 135 to 140 ka. However, there are indications for an even older glacial advance, but no terminal moraines are preserved at the surface. The extent of Pleistocene glacial advances in the Verkhoyansk Mountains in general, reflects the aridization of eastern Siberia in particular during the last glacial cycle. This aridization was presumably caused by the growth of the Scandinavian ice sheet and prevented the growth of glaciers in the Verkhoyansk Mountains. East of the study area, glaciations occurred during MIS 2 due to precipitation from the Pacific Ocean. However, large parts of the interior of NE Russia lack a robust chronology of glacial advances, and further research will be necessary to establish the paleoclimatic development of the area.

Figure 9. Glacial advances during the last glacial cycle in northern Asia: A–C: Svendsen et al. (2004), D: Stauch et al. (2007); this study, E: Arkhipov et al. (1986); Glushkova (2001), F: Stauch and Gualtieri (2008), Stars: Brigham-Grette (2001) and cold phases (G: dots) according to Melles et al. (2007); modified from Stauch and Lehmkuhl (2008).

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Acknowledgments This study was funded by the German Research Foundation (DFG) with grant Le 730/10-1,2. We thank all the Russian and German colleges who worked together in the field (I. Belolyubsky, A.V. Prokopiev and V. Spektor). Special thanks are attributed to C. Siegert for scientific and logistic assistance. M. Frechen from the GGA Institute Hannover (Germany) measured the IRSL samples.

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