Problematic ice sheets

Quaternary Intermttiomd. Vol. 2g pp. Iq 37. I~I~ Copyright (~ 19t~5 INOUA/Elsevicr Science Ltd Printed in Great Britain. All rights reserved 11141)-6182/95 $29 IMI

Pergamon

1040-6182(95)00045-5

P R O B L E M A T I C ICE SHEETS Nat R u t t e r

Department of Geology, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada

has been studied more extensively for a longer period than the more remote Laptevs Sea area where few investigations have been made, and only in the last few years.

INTRODUCTION Working Group One (Problematic Ice Sheets) of IGCP Project 253 was initiated during discussions with participants on the 1991 INQUA field trip across Tibet. It Occurred to a number of us how uncertain we are on the past ice cover over large areas of the globe, specifically Tibet and parts of Siberia. If we are to truly understand paleoclimatic systems during the Quaternary period and aid in the development and testing of various climate models, it is necessary to have a better understanding of worldwide distribution and timing of large ice sheets, especially during the last glacial cycle - - the concern of IGCP Project 253. The debate among scientists centers on the timing and maximum extent of ice over northern Siberia and the Tibetan (Qinghai-Xizang) Plateau. Most agree that there was limited ice, confined to local mountains or uplands, and in some cases minor ice sheets, but few agree on the presence or absence of major ice sheets. The objective of Working Group One was to organize and bring workers together in workshops and symposia in order to evaluate what we know, and what has to be done. The Working Group was organized at an opportune time because the opening of China and Russia politically has steadily increased the number of foreign workers collaborating with local scientists, resulting in more data and more diverse interpretation. However, the remoteness of both areas will continue to limit field investigations even though these areas are critical in understanding earth system processes during the Quaternary. This summary report is intended to review and evaluate the evidence for the various ice cover scenarios over northern Siberia and the Tibetan Plateau.

Eurasian Ice Sheet The best known advocate of a Late Weichselian Eurasian ice sheet is Grosswald (1977). Although Grosswald wrote on the subject in the late 1960s and 1970s, mostly in Russian, Grosswald's paper in English in Quaternary Research in 1980 brought worldwide attention to his concept (Grosswald, 1977, 1980, 1983, 1988, 1993). He infers an ice sheet that extended continuously from southern Ireland to northeastern Taimyr Peninsula, a distance of 6000 km and reaching as far south as 52°N in Western Europe whereas on the Taimyr Peninsula, some 4500 km farther east, it reached as far north as 75°N (Fig. 2). This latitudinal difference reflects the east-west increase in continentality and therefore less precipitation. Therefore, the ice sheet in Siberia did not extend as far south as the European component. The major components of this ice sheet were the British, Scandinavian, Barents and Kara ice domes reaching altitudes in the order of 3 km and an area of 8,370,000 kmL Grosswald discussed mechanisms of the inception and decay of the marine portion of the Eurasian ice sheet, by arguing for 'instantaneous glacierization' based upon a low glaciation threshold and relatively flat topography. He suggests rapid ice accretion over the whole shelf surface from a marine-based ice dome as opposed to 'conventional' glacierization through gradually transgression of glaciers from mountain sources. Therefore, the Barents and Kara ice domes originated by the formation of a floating ice shelf, gradually by thickening and grounding on continental shelves, eventually attaining equilibrium profiles. In time, the ice domes reached mean thicknesses of 1900 and 1500 m, respectively, including some 700-900 m of ice below sea level. Break-up of ice shelves that existed in conjunction with the domes, did not begin before 9000 BP. In addition, the ice sheet impounded north flowing rivers, and causing several ice-dammed lakes in west Siberia to divert water south into the Black Sea. When ice disappeared from the continent, rivers re-established their northward flow. Today, most workers agree that there was ice over the Kara and Barents seas, but there is controversy

SIBERIA In Siberia there are actually two areas under controversy - - one in western Siberia or Eurasia that includes the Barents and Kara seas (Kola Peninsula, Novaya Zemlya, northern Ural (Polar Urai) Mountains, Putorana Plateau, Yamal and Taimyr Peninsulas), and the other in eastern Siberia, east of the Taimyr Peninsula in the Laptevs Sea - - New Siberian Islands area (Figs 1 and 3). The former has sparked more controversy than the latter because the Eurasian area 19

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Problematic Ice Sheets

21

FIG. 2. Last Eurasian Ice Sheet and related proglacial drainage system (Grosswald, 1977). (1) Glacier-free deep sea: (2)ice-dammed and other inland freshwater basins; (3) ice-free land; (4) boundz~ries of ice sheets and mountain glacier complexes; (5) lines of ice Ilow on (a) terrestrial and grounded marinc parts, and (b) floating parts of the ice sheet: (6) surface of inland basins, m: (7) directions of stream flow in channels of the drainage system. (M) Mylva Channel, (K) Kcltma Channel. Ice domes and mountain glacier complexes: (Br) British; (Sc) Scandinavian; (B) Barents; (Sv) Svalbard; (K) Kara; (U) Uralian; (Pt) Putorana Plateau; (V) Verkhoyansk Mountains; (T) Tuva-Sayan Mountains; (A) Altai Mountains. Modiified from Grosswald (1980).

over the extent of ice during the Late Weichselian and whether or not the ice sheet developed from marine-based domes or from mountains and highlands. The credibility of Grosswald's concept depends on the correct interpretation of several lines of field evidence distributed over a wide area of the Arctic and Subarctic. In the E u r o p e a n Arctic, widespread glaciation is inferred from such evidence as the ' a b n o r m a l l y ' great depth of the continental shelf and concave shape of its surface, submarine troughs, boulder trains and sea bed diamictons. The diamictons are correlated to end moraines and proglaciai lacustrine deposits in the coastal lowlands of Eurasia. Grosswald (1980) has analysed and c o m p a r e d striae data on land, and sea-bed flow data, from widely spaced regions near where he places the margins of the Barents ice dome. H e concludes that ice radiated in all directions from the central part of the Barents Sea. The thinness of the drift, less than 6 m, present after such a long period of time that glacial sedimentation was possible ( + 3.3 Ma) suggests to Grosswald that the Barents sea floor was an area of mostly glacial scouring. Bottom topographic surveys have identified several parallel moraine belts that extend continuously along the margin of the Barents Sea. The outermost belt may be

an extension of the Egga moraine from the Norwegian shelf, suggesting no gaps between the ice sheets of the Barents Sea and Scandinavia (Grosswald, 1980). Uplift curves from Svalbard and Franz Josef Land have also been used to support the presence of a Late Weichselian ice sheet over the Barents Sea (Grosswald, 1967; Schytt et al., 1968; H o p p e , 1970). Isobase ntaps show that during the second half of Holocene time, the Barents Sea area experienced a dome-like up warping near the center of the shelf decreasing toward its edges. This up-doming coincided with the center of ice dispersion inferred from striae and sea-bed landforms. Dating the Barents Sea ice sheet as Late Weichselian is based upon a few finite post-glacial ~4C dates from unglaciated marine terraces and raised beaches in various marginal locations. In the Pechora and Mezen basins, peat and trees from alluvial and lacustrine deposits below till have been radiocarbon dated from 22,000 to 45,000 BP (Grosswald, 1981); Fig. 1). In addition, the surface morphology of the glacial deposits is fresh, and terraces that cut across these deposits are Holocene in age. The several morainal belts that are present on the northwesterq Russian plains have been dated between 20,000 and about 9000 BP suggesting that deglaciation was not complete for the Arctic

22 Continental

n. Ruttcr shelf until after 9000 BP (Grosswald,

198{)). Grosswald (1980) suggests that a dome developed over the Kara Sea area and was connected to the Barents Sea ice (Fig. 1). The basis for this connection stems from the presence of roche mounton4es, erratic boulders and stony clays on various islands as well as morphology of submarine troughs and the presence of sea-floor diamictons interpreted to be of glacial origin. The Taimyr Peninsula displays a variety of glacial features that include striae, erratics and U-shaped trough valleys indicating the ice moved towards the southeast from the Kara Sea right across the Peninsula. Other ice flow indicators show that ice flowed southwest from the Kara Sea parallel to the Polar Urals. It would be difficult to explain these flow indicators by local Polar Ural montane ice. Other evidence for Kara Sea ice is the trend and position of end moraines, and erratics data in the area of the Polar Urals and the Yamal and Taimyr Peninsulas. Radiocarbon dates from below till from the Ob River and Taimyr Peninsula range between about 25,000 and 45,000 BP, similar to those from below till of the Barents ice sheet, supporting a Late Weichselian

age for the Kara Ice Sheet (Grosswald, 1980, Fig. 1). Also supporting a Late Weichselian age are Holoccnc isostatic rebound data derived from heights and position of shorelines and end moraines, effectively bracketing the age of the Kara ice sheet. Later, Grosswaid (1988, 1993) dropped the Barents ice sheet suggesting that the entire Barents Sea was occupied by ice streams from united Scandinavian, Kara and Svalbard ice sheets (Fig. 3). The movement of these streams can better explain the geography of certain submarine features. Grosswald (1988) extended the Kara ice sheet limits further south in the vicinity of the Pechora lowlands (see Fig. 3). (In later papers Grosswald used the term Kara ice dome.) This was conceived in light of new geomorphic information (i.e. drumlins, crratics) by a number of workers including Arslanov et al. (1983, 1987). Observations in the middle Yenisei River basin where traces of a local ice d a m m e d lake was found suggested the maximum limit of the Kara ice sheet was further south by about 400 km (Goncharov, 1982; Arslanov et al., 1983; Fig. 3). Dates on underlying peat suggest that this lake and therefore the ice lobe, was about 18,000-20,000 years old. Additional evidence such as the alignment of moraines and drumlins, and glacial erratics in the Kotuy Plateau

FIG. 3. "l'~acc~,~1 the lasl glaciation in the Russian Northern Eurasia according to Grosswald (1988), end moraines and traces o1: ice movement: (I) continental slope; (2) genendized positions of ice margins at maximum and regressiomd stage (end moraines); (3) yedoma ridges separating a/as depressions: (4) indications of ice movement (glacial striae, boulder trains); (5) major submarine valleys (U-shaped Iroughs) on the contiulcntal shelf. Modified from Grosswald (1988).

Problematic Ice Sheets

(Dyatlova 1986; Andreyeva and Isayeva 1988) suggests that the Kara ice sheet flowed about 600 km further to the southeast than previously thought (Fig. 3).

Proglacial Drainage System Grosswald's (1980) reconstruction of ice-sheet glaciation of the Eurasian continental shelf forces damming of several major north flowing river systems including, among others, the Ob, Yenisei and Mezen (Fig. 2). The lakes formed a radial pattern as indicated by the distribution of lacustrine sediments, and drained eventually into the Black Sea. Upon ice break up, the system became marginal and discharged proglacial water mainly into the Norwegian Sea. Although the proglacial lake scenario supports Grosswald's ice-sheet concept, it is, at best, indirect evidence. As will be discussed below, other interpretations on both the origin and age of the sediments are possible. East Siberian Ice Sheet Grosswald (1988) expanded his Eurasian ice sheet concept to include a large area covering the Laptevs,

23

East Siberian and Chukchi Seas which he called the East Siberian ice sheet (Fig. 4). This was brought about by Grosswald's expansion of the Kara ice sheet and new information on the geomorphology of the New Siberian Islands and continental shelf. Specifically the trends of arcuate glaciotectonic ridges suggest that an ice sheet extended across the Laptevs Sea, 2500-3000 km farther east, thus merging the Kara ice sheet (Eurasian) with the newly named East Siberian ice sheet. Extending the ice further east is also based upon extending the equilibrium line altitude (ELA) from mountain glaciers in eastern Siberia which, as Grosswald (1988) says, fit nicely with the theory as do the estimated rates of glacioisostatic uplift. And finally, there are lacustrine sediments interpreted to have formed by glacial damming supporting widescale glaciation in the area. In a paper in 1992, Grosswald et al. presented results of recent fieldwork that suggested the East Siberian ice sheet reached as far as Tiksi Bay, near the mouth of the Lena River (Fig. 2). This was evidenced by fresh looking U-shaped valleys, giant flutes, rock drumlins,

FIG. 4. Unified terrestrial and marine ice sheets, main mountain glacier complexes and proglacial drainage systems in the northern hemisphere during the height of the last glaciation 17.(XXJ-20,(XX) years BP according to Grosswald (1989), (1) glacier-free ocean: (2) emerged continental shelves: (3) ice sheets and mountain-glacier complexes: (4) floating ice shelves: (5) freshwater basins; (6) grounding lines of ice shelves: (7) major spillways: (8) Urstromt~iler and direction of water flow. After Grosswald (1988).

24

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glacio-tectonic ridgcs, and other ice-erosional features indicating that the ice flowed off the shelf to the southwest. Chronological control was established by radiocarbon dates on moss from bottom sediments of two lakes joined by glaciotectonic ridges. Dates of 6450 + 110, 6870 _+ 80, and 8500 + 160 BP were obtained and are interpreted to date the minimum time of deglaciation. Grosswald (1993) now concludes that there were three major ice sheets that made up the massive Eurasian ice cap. These are the Scandinavian, Kara (he previously included the Barents ice sheet) and the East Siberian. Two second order ice caps over Britain and Svalbard are also recognized (Fig. 4).

that ice must have originated in uplands or mountains and coalesced into an ice sheet over the Kara Sea. Most criticism, however, is based upon interpretation of new field data, which will be discussed below, such as radiocarbon dates, glacial and periglacial landforms and the origin of sedimentary units. This has brought about new scenarios of the timing, number and extent of glacial advances during the last glacial cycle. Recent fieldwork in Russia has taken place in coastal areas of northwest Siberia, including the northern Yenisei River basin, the Yamal Peninsula, the Polar Urals and the Pechora Basin. In addition, more information is being accumulated by workers in Scandinavia, Finland, Svalbard, and the adjacent seas. One of the most active workers in the region is Astakhov. Although Astakhov earlier accepted Grosswald's L G M model, recent fieldwork in the upper Yenisei Valley (Fig. 5) has changed his opinion (Astakhov and Isayeva, 1988; Astakhov, 1992; Astakhov, this volume). Astakhov's acceptance of Grosswald's ice sheet concept was based on the lack of good evidence for large scale Late Weichselian mountain glaciation, large volumes of ground ice in west Siberia lowlands being glacial in origin (Toil, 1897) and that southmoving ice masses (flow indicators) invaded the area

Discussion

Controversy and criticism has erupted over several aspects of Grosswald's concept of the Kara ice sheet during the Last Glacial Maximum. This has come about because of a number of detailed studies, principally by Russian workers, in various areas affected by Kara ice. To Grosswald's credit, most workers agree that there was ice over the Kara Sea during the Last Glacial Maximum. Criticism has centered around the mechanism needed to form large ice sheets over continental shelves. Arkhipov et al. (1986a, b) believes

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Problematic Ice Sheets

25

(Astakhov, 1976; Kaplyanskaya and Tarnogradsky, of the Polar Urals and the Arctic coast. Astakhov (in 1976). However, he now thinks that late glacial ice prep.) places his Late Weichselian limit well north of did not reach as far south as Grosswald advocated Grosswald's, but more extensive than that of Biryukov during the Late Weichselian. This is based upon et al. (1988), and Faustova and Velichko (1992). The the reinterpretation of landforms, radiocarbon dates latter authors consider that highland ice domes such and proglacial lake deposits (Fig. 5). He believes as the Polar Urals, were the source of ice that only that 'fresh-looking' glacial topography is a result of partly coalesced in Late Weichselian time and left great 'retarded deglaciation', typical of permafrost areas expanses of lowlands and shelves ice-free. However, where differential melting of ice, controlled by climate Astakhov (in prep.) suggests that the latest ice flowed and latitude may continually alter topography for from the Kara ice sheet (Fig. 5). This is evidenced thousands of years. In ot.her words, 'fresh-looking' by fresh glacial tectonic features indicating southern topography interpreted as Late Weichselian glacial flow observed west of the Yamal Peninsula and along deposits could be older. In addition, Astakhov empha- the western part of the Arctic coast. Ice flowed up sizes that grea t care must be used in interpreting the slope parallel to the Polar Ural Mountain front as many radiocarbon dates that are available from below, indicated by such features as till fabrics, striations and within and above basal till and remnant ice. They are arcuate morainal ridges transverse to the mountain of little help if taken indiscriminately because infinite ranges (Sopkay moraine). Mountain ice contributed and finite dates can be found above and below till. very little during the final glaciation, although the Astakhov (1992) believes that there has been wide- Urals may have supported more extensive ice during spread redeposition by glacial processes (retarded de- at least two earlier periods. This is attributed to colder glaciation) and contamination by younger carbon. and drier periods in the Late Weichsclian in contrast to This was particularly evident in the 'Ice Hill' area earlier times when conditions may have been wetter in in the Yenisei River area just west of the Putorana the west (Scandinavian ice sheet) before the ice shelf Plateau (Astakhov and Isayeva, 1988). Astakhov only developed into an ice dome that eventually intercepted chose dates that show consistent ages in a succession moisture before reaching the mountains. and/or were derived from apparently local, preferably According to Astakhov (1992), there are no signs of perennially frozen material. He also eliminates ques- great proglacial lakes within the range of radiocarbon tionable dating material such as shells. This has dating found south of the last glacial limit. Instead, resulted in a more reliable interpretation of infinite there is a thick subaerial formation of loess, paleosols, and 'old' finite radiocarbon dates found in sands ice-wedge casts and remnants of terrestrial mammals and silts above the basal till and fossil glacial ice, spread widely over the Ycnisei lowlands. Among other and from the underlying marine sands and clay. The things, 20 m of silt, with no sand or clay seams, is underlying marine sands and clays are considered to most likely loess, and not a lacustrine deposit. The be Eemian equivalent. The last glaciation took place complexity of features observed, and the relatively long after deposition of these marine sediments. Astakhov time necessary for the formation of soils, paleosols, and (1992) suggests that final deglaciation in the Upper ice-wedge casts, rule out proglacial lakes. Additional Yenisei River area took place around 50,000 years ago, indirect evidence for the absence of proglacial lakes thereafter the cold and dry Weichselian climate resulted includes the lack of raised Holoccne shorelines in in 'retarded deglaciation' and active glacial karst the Kara Sea lowhmds, and the presence of two inversion. A marine transgression followed deglaciation pre-Holoccnc alluvial terraces in river valleys (i.e. depositing marine clays; then sands containing peat the Ob) of the glaciated area (Astakhov, 1992). lenses. Radiocarbon dates for this peat vary between Other workers in the Yenisei area such as Arkhipov 25 and 40 ka BP. This indicates that the marine et al. (1986a, b; Yakovlev. 1939), believe in a mountain transgression is Early to Middle Weichselian age. source for all glaciations and do not include the Kara Therefore, the Last Glacial Maximum was before Sea shelf as a dominant ice center in western Siberia. the Late Weichselian probably in Early to Middle Highland areas such as the Putorana Plateau, Taimyr Weichselian time. He places the southern limit in Peninsula, Novaya Zcmlya and Pohtr Urals mountains this region at about 66°N latitude between the Polar are thc major sources of ice. This is supported by Urals and Putorana Plateau (Fig. 5). This LGM limit pebble lithologies of tills. However, Astakhov (1992) is about 500 km further north than Grosswald's LGM does not believe highland pebbles in till is evidence for limit (Grosswald, 1988). Astakhov (1992) restricts a highland ice center, rather Kara ice could have picked Late Weichselian ice to the Putorana Plateau area, up pebbles scattered around the highland source. At and to west and northwest of the Yamal Peninsula any rate, Arkhipov et al. (1986a, b) have presented (Fig. 5). The precise limits are difficult to discern but a maximum and minimum extent of Late Weichselian interpretation of radiocarbon dates and geomorphology ice (Fig. 6). The two scenarios result from problems suggest limited ice. Although Astakhov agrees with interpreting ]4C dates and the geomorphology of the Grosswaid's concept of a Kara ice sheet, he indicates area. The extent of the maximum scenario is further that the climate was too dry to have ice sheets forming north than Grosswald's (1993) but about the same as to the east. Astakhov's Middle to Early Weichselian limit (Fig. 6). Working west of the Yenisei River Valley, in the area The minimum scenario is very close to Astakhov's limit,

26

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Late Weichselian- max. concept (Arkhipov el a1.1986) Late Weichselian-min. concept (Arkhipov et a1.1986) Glacial lake 500 km .I

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but with a different interpretation on the source of ice. In a later paper, Arkhipov et al. (in press) appears to favor the maximum concept of the Late Weichselian glaciation (Fig. 6). He disagrees with Astakhov's minimum scenario based principally on the interpretation of radiocarbon dates and reinterprets landforms thus criticizing Astakhov's theory of 'retarded deglaciation' and "glaciokarst f o r m a t i o n ' . Further, Arkhipov interprets the sediments south of the glacier limit of the maximum Late Weichselian concept as being deposited by ice-dammed lakes and that terraces along the Ob River are probably of glacioisostatic origin. West of the Polar Urals, in the vicinity of the Usa and Pechora River Basins, the Late Weichselian limit is based principally on the interpretation of radiocarbon dates and to a lesser extent on morainal ridges (Astakhov, in prep., Fig. 5). Lavrov (1977) placed the Late Weichselian maximum south of the

Laya-Adzva Push moraine and north of the Usa River, but later moved the limit further south to Grosswald's position (Lavrov, 1981). This is based on 14C dates of 44-47 ka BP in sediments underlying the surficial till in the Usa River Area. In contrast Astakhov (in prep.) places the Late Weichselian limit north of the LayaAdzva Push Moraine and along the Markhida Moraine. Astakhov's (in prep.) interpretation is based principally on the presence of two alluvial terraces along the Usa River with the upper one dated at 31-32 ka BP and the lower one at 11-14.5 ka BP. These are south of his Late Weichselian limits, whereas in the lower Pechora River valley there is only one alluvial terrace evident with dates ranging from 10,000 + 100 to 12,740 + 100 BP. One unanswered question is why did the latest advance move upslope on the western Yamal Peninsula and did not fill the lower area to the east. Perhaps as Astakhov (in prep.) suggests, older stagnant ice from the earlier advance was present and blocked flowage. Astakhov (in prep.) also suggests that Late Weichselian

Prohlematic Ice Sheets

and Mid-Early Weichselian ice had their own dispersal centers and that there was probably a shift of ice centers west (more moisture) during the last glaciation. Recent evidence such as sea bottom cores with glacial diamictons and sea level elevations have provided data for the reconstruction of the growth and decay of a Late Weichselian Barents Sea ice sheet (Vorren et al., 1988; Elverhoi, et al., 1990; Mangerud et al., 1992; Gatauilin et al., 1993; Hebbeln et al., 1994; Jones, pers. commun. , 1994; Forman et al., 1995). Evidence suggests that there was a two-step ice advance. At 22 ka BP the shallow shelf was covered and by 18 ka the entire shelf was covered. During recession, there was deep shelf calving and shallow shelf calving and melting, from about 14.5 to 13 ka BP. A minor readvance occurred from 13 to 12 ka BP. Thus, it appears that there was an ice build up over the Barents Sea, most likely connected to the Kara ice sheet, that in part flowed south onto the continents. Recent work by Mangerud et al. (1994, and pers. commun.) on the extent of Barents ice in the Markhida-Pechora Basin area has resulted in revisions of Grosswald and co-worker's (1992), Grosswald's (1993) and Lavrov's (1981) Late Weichselian limit. Mangerud's interpretation of ke~ stratigraphic sections and radiocarbon age interpretations, have led him to place the limit of Weichselian ice (either middle or late) at the Markhida moraine and not further south (Fig. 5). Grosswald (1993) and Lavrov (1981) consider the Markhida moraine as being late glacial, about 8500 BP based on radiocarbon dates. Tveranger et al. (pers. commun.) demonstrated that the Markhida moraine is older than 10,000 BP. Further, Mangerud (pers. commun.) considers the underlying marine sediments below the Markhida moraine as Eemian, and the till below as pre-Eemian, implying no Early to Mid Weichselian glaciation. This is in contrast to Astakhov (in prep.) who considers till south of his Late Weichselian limit as Early-Middle Weichselian (Fig. 5). Although controversy has risen over Grosswald's (1988) concept of an East Siberian Ice Sheet, very little published evidence against it is available. As mentioned earlier, Grosswald (1988) has interpreted geomorphic features in the New Siberian Islands and the area near the mouth of the Lena River on the northeast continental coast as glacial tectonic in origin and Late Weichselian in age (Figs 3 and 4). Hughes and Hughes (in press) mathematical modelling supports an East Siberian ice sheet. However, the dating control is poor. If the features interpreted as glacial are correct, there are essentially no convincing dates available as to what age the glaciation is or indeed if all glacial features are the same age. According to Velichko's (Arkhipov et al., 1986a) climate model cooling and precipitation forming glaciers in the west would cause eastern and northern Siberia to come under the influence of dry anticyclonic conditions, restricting glaciers to mountains. Probably the most compelling evidence for no Late Weichselian ice sheet in northern Siberia, are the large numbers of reliable, finite dates of

27

Late Weichselian age from mammoth bones from several sites, including the New Siberian Islands, that would have been covered by ice in Grosswald's model (Tomirdiaro et al., 1984; Sher, this volume). Younger Dryas Although this summary deals with ice cover during the Last Glacial Maximum, some mention of the Younger Dryas is warranted as the Younger Dryas has been one of the major focusses of IGCP 253. However, very little detailed and uncontroversial information is available for the Kara ice sheet and none, to the writer's knowledge for the questionable East Siberian ice sheet. The Keiva moraines, 250-300 km long, that run from west to east and north-northeast in the southern part of the Kola Peninsula are believed to be Younger Dryas moraines by Grosswald (1993, Fig. 7; Rainio et al., this volume). Lavrova (1932) believe the Keiva ridges are end moraines marking marginal positions of the Kola Peninsula's residual ice cap (Ponoy glacier), whereas Apukhtin and Ekman (1967) believe they are lateral moraines of a large ice stream that moved northeastward along the White Sea depression. Most believe (Lavrova, 1960; llyin et al., 1978) that they are the continuation or at least correlative with the 'Finnish Salpausselkas' (Younger Dryas) moraines, and so are a fragment of an ice marginal belt belonging to the Scandinavian end-moraine system. However, Grosswaid (1993) believes that the Keiva moraine is a signature of an ice-lobe from the northeast, from the Barents Sea and thus belongs to the Kara ice dome system. He concludes this principally by Landsat image interpretations. Others disagree that the age of the Keiva moraines are Younger Dryas. These moraines have been included in the ice-marginal formations of the Luga (13,000-14,000 BP) and Neva (11,900-12,400 BP) glacial stages (Apukhtin and Ekman, 1967) (Fig. 7). Accordingly, they are older than the Salpausselk~is (Younger Dryas). These researchers maintain that the Ponoy glacier did not exist during the Luga-Neva stages (Ekman and Ilyin, 1991). Strelkov (1976) is of the opinion that the Keiva moraines are somewhat older than the Salpausselk~is and were deposited mainly between the active White Sea lobe and the Ponoy glacier. Yevzerov (1990) agrees with Strelkov in the genesis of the Keiva moraines and the existence of the Ponoy glacier. From paleomagnetic determinations and pollen analyses, he and his fellow workers have concluded that Keiva I was deposited during the Neva stage and the northernmost Keiva II during the Luga stage (Ekman and Ilyin, 1991). Current opinion hold that the Marine Keiva (Kevia I) is an interlobate formation of Neva age between Ponoy ice cap and the White Sea lobe of the Scandinavian ice sheet (Ekman and Ilyin, 1991; Yevzerov and Kolka, 1993). The age of the Keiva II moraine is open. Ekman and Ilyin (1991) think that it is older than Kevia I whereas Yevzerov and Kolka (1993) do not clearly indicate their opinion.

28

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There is still a school of scientists with entirely different opinions of the origin of Keiva moraines and the deglaciation history of the White Sea basin, the Kola Peninsula, and the Barents Sea. As mentioned above, according to Grosswald (1983, 1993) the Keiva moraines are Younger Dryas lateral moraines deposited by a glacier which was fed from the northeast by the Barents Sea ice sheet. According to Grosswald the latest ice advance to reach the White Sea basin from the north was early Holocenc in age, i.e. ca. 9000 BP. The same advance would have penetrated from the north to the interior of the Kola Peninsula and east of the White Sea basin to the Markhida moraine to the south. This is in conflict with available data. The deglaciation of the Barents Sea was a much earlier event dated back to 14.5 BP (ElverhOi et al., 1990). The last (and only) ice movement direction found by Saarnisto (pers. c o m m u n . , 1994) in the Varsina and nearby Drosdovka Bay areas on the north coast of the Kola Peninsula was towards the north, which is in harmony with old evidence based on transport of indicator boulders (Ramsay, 1898) and also with the observations made during the IGCP 253 trip 1993 in the western part of the peninsula. The crystalline indicators from the Kola

Peninsula have been found some 100 km outside the present coast where a deep east-west trench possibly indicates the boundary between the Scandinavian and Barents Sea ice sheets (Gataullin et al., 1993, and pers. c o m m u n . , 1994). Thus it is likely that the Barents Sea ice sheet did not penetrate to the White Sea basin in Younger Dryas and early Holocene times. Grosswald (1993) continues his Younger Dryas limit eastward on the northern Eurasia across the Russian Plain, West Sibera, the Putorana Plateau and the Taimyr Peninsula by delineation of moraines, established and presumed, based on moraine morphology, flowline lengths and their possible orientations relative to the Kara Sea centre (Fig. 1). As mentioned above however, Mangerud (pers. c o m m u n . , 1994) suggests that the Markhida moraine is the Weichselian limit, which is north of Grosswald's Younger Dryas limit. However, on the Putorana Plateau, Astakhov (in prep.) states that the last advance of the Putorana glacier occurred before the deposition of nearby varved clays that are dated at 10,700 + 200 BP. This cold phase is called the Norilsk stade and corresponds to the Younger Dryas. Also, this must have occurred prior to the deposition of peats on Novaya Zemlya

Problematic Ice Sheets (10,550 + 160 BP) and southern Yamal Peninsula (10,700 + 140 BP). Therefore, the Younger Dryas limits that Grosswald suggested from dates from peats on the northern coast of western Siberia is in line with the thinking of Astakhov on the Putorana Plateau. It is obvious that as with the limits of the Late Weichselian and the Last Glacial Maximum in the Kara Sea area, the Younger Dryas is far from understood.

TIBET

Introduction There is little doubt of the importance in determining the extent and timing of glacial activity on the Tibetan Plateau. Not only is the uplift of the Plateau a major factor in past and present Asian climatic systems but no accurate climatic model during Quaternary cold periods can be developed without this knowledge. The Plateau is over 2.4 million km 2 consisting of series of roughly east-west and southeast trending mountain ranges separated by broad uplands (Fig. 8). The most prominent ranges are along the southern boundary where mountains reach over 8800 m a.s.I. (Mt Everest), whereas the average elevation for the Plateau is 5000 m a.s.l. Although the Plateau continues to rise, it is estimated that it reached an elevation of 2000 m by the early Pleistocene and > 4500 m by the upper Pleistocene (Li et al., 1979). However, Coleman and Hodges (1995) suggest that at least in north-central Nepal, the Tibetan Plateau reached its high mean elevation before Late Miocene time. This is based on 4°Ar/39Ar age of ~14 Myr from mica taken from an extensional fracture that is regarded as being related to gravitational collapse of the Plateau. In general, the Plateau is dry with broad areas of the interior receiving less than 200 mm of precipitation per year. Most precipitation falls along the southern and north-east mountain ranges where precipitation reaches over 3000 mm per year. Glaciers are present in the higher regions, but concentrated along the southern and western mountain ranges. Needless to say, the remoteness of the Tibetan Plateau has been an obstacle in answering the fundamental question of the extent of glaciation during the Quaternary. However, there have been, and are, dedicated Chinese and foreign scientists who are actively seeking the answer. The situation in Tibet is not unlike the situation in Siberia in that there is an advocate of a widespread ice sheet over the area during the late glacial maximum (Weichselian age) and a host of workers who believe that ice was very much restricted during the late glacial. Tibetan Ice Sheet The major advocate of widespread ice cover over Tibet during the late glacial is Kuhle who has worked in many parts of this Plateau for over 10 years (1987, 1988a, 1991, in press). His ice cover theory is based upon a combination of climatic theory and field

29

evidence, principally the position of the equilibrium line altitude. The evidence, according to Kuhle, points to large-scale glacial cover over the Tibetan Highland. Kuhle believes the marginal areas have been glaciated down to 2000-890 m a.s.l. This provides evidence of an ELA depression of 1160-1660 m to about 4720-3250 m a.s.i., roughly 1200-2700 m below the present ELA (5900 m) and about 280-1650 m below the average altitude of the Plateau (5000 m) at the Last Glacial Maximum (Kuhle, 1988a). This is the principal evidence for a unified ice sheet with an area of approximately 2.4 x 106 km 2 and ice thicknesses of 700-2000 m, possibly up to 2700 m (Fig. 9). In this model, climatic and topographic parameters act as a true feedback system, overriding the widespread aridity that extends over most of the Plateau. In particular, an increase of the catchment area evoked by an initial lowering of the ELA, produces an effect where topography can influence climate. An ELA depression would intersect the Plateau allowing piedmont glacier lobes to coalesce into an ice sheet. An increasing ice-surface would in turn adjust the amount of reflected energy into the atmosphere. Kuhle (1991) suggests that prior to glaciation, 80% of the sun's energy was absorbed, thus heating the Plateau's local atmosphere, whereas 95% is reflected during ~laciation, resulting in a lowering of temperatures and hence the ELA - - a self-boosting process. There are many problems in reconstructing ELA's in central Asia due to micro-climatic and topographic controls on the mass balance (Sharma and Owen, submitted; Kulharni, 1992). Using standard techniques, Kuhle calculated the present day ELA at 5900 m. In calculating prehistoric ELA's, he commonly halved the altitudinal difference between a catchment area and the toe of former glaciers (Kuhle 1987, 1988a; Fig. 9). At the present time and apparently in the past, the southern slopes of the Himalayas and the eastern portion of the Plateau received high rainfall during the monsoon season resulting in lower terminal positions and cirque elevation. According to Kuhle (1988a) ice margins on the southern slope extend to elevations in the order of 1200 m a.s.l, and to 2500 m a.s.l, north of the main Himalayan crest. On this north side, ice marginal ramps are used to delineate terminal positions for the last glaciation. These landforms suggest a drop in the ELA by 1110 m to an altitude of 3770 m a.s.i. Kuhle (1988b) calculated an ELA depression of only 200-300 m at Shisha Pangma, north of Kathmandu, vastly different from nearby values in the range of 1250 m. Kuhle suggests glacio-isostatic uplift from a massive ice load explains the small ELA depression, but offers no evidence. This variation he claims is attributed to post-glacial uplift, raising the terminal moraines a phenomenal 600 m in 15 ka! Further, he points out that only minor amounts of tectonic uplift are probably involved. Within and near mountain fronts Kuhle cites traditional, field evidence such as till and diamicton deposits, and morainal systems for the presence of

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former glaciers. Outside the mountainous regions, there is a lack of geomorphic features and deposits related to glaciation. Kuhle (1987) explains this on the basis of physiography and climate. High altitude mountain regions of the Plateau are less likely to preserve features such as moraines, due to erosion, frequent freeze-thaw mechanisms and mass wasting, as well as the presence of former cold based glaciers. In addition, Kuhle assumes a rapid decline m ice cover during deglaciation, allowing incomplete moraines to form. Therefore, other evidence to support ice altitude, thickness, and cover over plateau areas between mountain ranges is commonly indirect or incomplete and open to other interpretations. For example, granite erratics on mountain ridges 5800 m a.s.I, originating from Tanggula Shan (mountains) are used to explain plateau ice 5000-3000 m a.s.l, exceeding 500--600 m in thickness (Kuhle 1987), if Kuhle's estimate of the E L A is considered. Landform features that resemble roche mounton6es at elevations up to 440(0-4600 m a.s.I, are used as evidence for plateau ice. Glacial scouring at 6000 m a.s.l, in the Nyaingentanglha Mountains, where valley floors are 4200--4600 m a.s.l., provide evidence of inbound ice because the ice stream thickness would be at least 1400-1800 m and therefore would flow great distances. Trough-shaped valleys, without distinct striated or polished surfaces, in northern and southern Tibet are considered glacial evidence because they are of 'appropriate character' to prove the existence of what was probably a more than 2000 m thick inland ice cover. Kuhle (1987) explains V-shaped valleys as glacially-

derived landforms, a result of steeper gradient curves which do not allow high rates of erosion. Bedrock knobs considered to be glacially rounded, can be found at elevations up to 5250 m a.s.l suggesting inland ice cover. The knobs are covered in weathered material which Kuhle interprets as post-glacial frost action and were probably never polished because ice was firmly attached to the frozen ground. Finally, so-called ice marginal ramps (Kuhlc 1988a) have been interpreted as terminal landforms characteristic of piedmont glaciations that form between glacier tongues. They develop from sediments washed down the glacier's surface to the edge of the ice in the accumulation zone, similar to alluvial fans (Kuhle, 1987, 1990). Kuhle used these extensively to define the limit of glaciation and to support a lowering of the E L A by 1110 m during the last glaciation. However, some 'ice marginal ramps' are actually tilted fault blocks with overlying gravel (Owen, pers. c o m m u n . , 1995). In summary, then, it appears that uncontroversial evidence for glaciation, such as till, erratics, scouring and morainal systems are almost always near or within mountain ranges, suggesting that ice was locally derived and can be explained without assuming an ice sheet. Much of the glacial evidence for an extensive ice cover outside mountain areas can be interpreted in other ways. These include such features as bedrock knobs, trough valleys, marginal ramps, and V-shaped valleys. A major problem is the age of Kuhle's proposed ice sheet. There is very little dating control within

32

,, b~ulAc i

the entire Tibetan Phttcau so that dating c~cnts, no matter what the reconstruction, is difficult. Kuhlc bases much of his evidence for a late glacial (Weichselian)ice sheet on the elevation of the Plateau. Hc recognizes old glaciations by the prcserwnion of moraines with intensive tropical w'cathcrmg down to about 6(11)In a.s.l, within the present warm sub-tropical climate. This indicates that the Tibetan Plateau was alrcady highly uplifted in order for ice to reach this Imv elevation. He cstimatcs that the [il,A must have bccn 3()1)--4()(1 m lower p,ior to thc lasl 5.,~ icram ' " n. This would mean then that the area for ice supply (height of plateau) must have been much greater during earlier ice accumulation than during the last glacial period. Kuhlc (1987) bclie\cs thal the uplift ol l i b c t canlc to its 'early Pleistocene" end as a result of the burden of inland ice, although hc presents no substantiating evidence. ]'his ensured the deglaciation of the Platcau during the interglacial period as a continuation of wasting begun by lowland ice. Therefore, the prescnl uplift in Tibet is considered primarily glacio-isostatic. Ice margins and terminal moraines arc found in many locations but are approximately 15(1-30() m Ioucr than that of the last glaciation (Weichsclian). This is compatible with the 10(I-201)m difference between ELA lines in other, less active tectonic areas. Thb indicates that primary uplift essentially stopped during the late Pleistocene because the older moraines haxe not been destroyed by Weichselian glaciation. As mentioned above, absolute dates arc scarce. In Muztagh valley' at 3940 m a.s.l, m the forclicld of

the 43 kin long Skamri glacier an age from peat is 12,870 _+ 180 BP. This indicates that deglaciation to the approximate position of the present glacier had taken place before this (Kuhle, 1988a). In the Qaidam depression (Fig. 8), interlocking ice age lacustrine deposits and outwash are present. Dates from a 10-180 m bore hole yielded ages of 35,12(b-47,270 BP. These ages. Kuhle believes, gives an estimate of the time of thc LGM. Kuhlc also quotes radiocarbon dates or 2< 1()() _+ 6()() to 32,390 _+ 1780 BP from the base of a glacio-lacustrinc terrace in the Chu Valley (Tien Shan) and therefore are post-glacial (Fig. 8). Chinese and other workers (e.g. Burbank and Kang, 1991: Derbyshire etal., 1991; Lehmkuhl and Liu, 1994; ()smaston. 1989) have studied evidence for glaciation in the Tibetan Plateau for over four decades. Their rcsearch supports limited glacial activity. They believe that extensive ice caps developed during the Pleistocene but argue that the}' were not interconnected to form a unified ice sheet. Lately, however, there have been some revisions of the original concept. Zhou and Li (m press) cite evidence for a relatively large local ice sheet that developed from mountain ice in the Bavan Har Mountain area (Fig. 8) in the east-central plateau arc~,. in general, most workers depend upon direct, more conventional (or uncontroversial) glacial evidence in reconstructing glaciations. S h i e t al. (1992) reconstructed E[,A's for the last glaciation from preserved cirque ttoors and terminal moraines, and arrived at snowlinc values ranging between 300--1200 m lower

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Problematic ice Sheets

33

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in mountainous areas and 500 m lower in the inland parts of the Plateau (Figs 10 and 11). These values are about half of what Kuhle calculated. The distribution of LGM snowline elevations over all of eastern Asia, on the basis of cirque floors and terminal moraines also illustrates a steep snowline gradient around the eastern margin of the Tibetan Plateau, where the snowline elevation attained 4000-4400 m (Ono, 1991). The distribution of snowline elevations across the Plateau are about 1000 m in the south-east margins and south slope of the Himalayas, 500-800 m in the Qilian Mountains and in the north-eastern margins, 200-300 m on the north slope of the middle Himalayas, and 500 m in the hinterland of the Plateau. These values differ markedly from Kuhle's interpretation and suggest a completely different style and extent of glaciation for the last glaciation. The interpretation of moraines bordering or relatively close to present day glacial termini represent the key to understanding past glaciation for the region. In many localities there is evidence of successive morainal arcs, a few kilometres down valley of the present glacial terminous. The controls on whether all moraines are present in an area are based upon interpreting plaeo-elevation and precipitation. Most workers believe that the glacial maximum was reached during the late-middle Pleistocene (Shi et al., 1992). This is based upon glacial morphology and the degree of preservation and weathering of glacial features in many high peak areas. The age of a feature is established from when the Plateau was at a lower elevation (3000 m) and was influenced by moist, monsoonal air from the south. They (Shi et al., 1992) believe as further uplift took place this climate became progressively drier, diminishing the extent of glaciers during the late

Pleistocene. Therefore, the snowline controlled by the variation of precipitation throughout the Plateau was about 4000 m a.s.l, along the southeast and northeast edges of the Plateau, and ascended to 5500 m a.s.I, in the northwest during the latter Pleistocene. Several examples of late Pleistocene glacial activity can be cited. Recent work includes Sharma and Owen ( s u b m i t t e d ) in northwest Garhwal, Li Shijie and Shi Yafeng (1992) in the west Kunlun Mountains, Burbank and Kang (1991) in the Rongbuk Valley, Mt Everest, H6vermann et al. (1993) and Zheng Benxing (1989) in eastern and central Tibet. Depending upon the area, there are generally, two or three phases of glacial activity recognized in the late Pleistocene. The furthest extent of the late Pleistocene (LGM) event is marked by prominent lateral moraines left by a glaciation (Qomolangma I) that was stimulated by mountain uplift during the Middle and Upper Pleistocene. This was followed by a late stage of the LGM (Qomolangma II) evidenced by end and lateral moraines. Following this event are less extensive moraines believed to be neoglacial in age and a younger set, near the terminus area of present day glaciers, believed to be 'Little Ice Age' moraines. Dating the Last Glacial Maximum and succeeding events is a problem. Kuhle would assign the moraines of the LGM (Weichselian), as younger or a similar age, but would consider them a part of the waning stages of a much more extensive glaciation. Successive, younger moraines are assigned ages according to what he considers late glaciations. What absolute dating do we have? Recent work by Sharma and Owen (submitted) in northwest Garhwal, central Himalayas, has evidence that the Last Glacial Maximum occurred ca. 62 ka BP, based upon optical simulation dates. The ELA depression was 640 m and

34

N. Ruttcr

glaciers flowed about 40 km from the snout of the present day Gangatri Glacier. Shi et al. (1992) cored a lake in the west Kunlun Mountains at 5300 m, 6.5 km beyond the present Chongce glacier terminus and within what is considered to be the terminal moraine of the Last Glacial Maximum. The core yielded organic material, radiocarbon dated at 14,930 _+ 320 BP, This is good evidence that the terminal moraine was deposited sometime before 15,000 BP. Another 14C date of 30,935 + 1700 BP was obtained from organic material from a lacustrine deposit below the terminal moraine. This means that an E L A was lowered only 200-3(t0 m below the present E L A for the LGM. A 14C date of 8287 + 160 B P from organic material derived from a second moraine above the moraines of the LGM was obtained from the Keriya glacier area forty miles to the east of Chongce glacier (Li and Shi, 1992). This corresponds with a cold period in the early Holocene suggested by Denton and Karl6n (1973). The third and fourth moraines of the Chongce glacier are Neoglacial deposits located 1.2 km from the end of the glacier. Radiocarbon ages of 3922 + 120 BP and 3522 + 117 BP are derived from soils on the moraines. Other dates from other areas could be cited for neoglacial moraines. Nearer the glacier are three 'Little Ice Age" moraines.

Li (pers. c o m m u n . ) reports dates from fossil ice wedges between 15 and 20,000 BP in the source area of the Yellow River. He suggests they are beyond the limits of the LGM and therefore the land was bare and free from ice cover during the LGM. Indirect dating of the LGM is provided from the Charham Salt Lake deposits in the Qaidam Basin (Fig. 8). Chen et al. (1985) established that before 24,000 BP, a relatively wet period, resulted in a large freshwater lake (isotope stage 3), that was succeeded by an arid and salt-forming period during 24,000--9000 BP. The appearance of KCI, KCI, MgC12.6HzO indicates that the arid condition was intensive. The salt lake may have dried up at about 16,000 BP. After 9000 BP, the climate became wet again, a new salt lake developed along the south margin of the Qaidam Basin where a freshwater supply was abundant. This contradicts Kuhle's conjecture that the Qaidam Basin was a large lake filled with glacier meltwater during the LGM (Kuhle, 1988a). Kuhle's idea that the lowering of the E L A provides the climate for glaciers to expand and create a feedback system enhancing glacial activity, does not adequately explain the extreme aridity in many parts of the Plateau during the Weichselian. There is little

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35

Problematic Ice Sheets

reason to believe that the LGM climate was much different from today. The big question is, how does his feedback system override the presence of aridity? Kuhle suggests a temperature reduction of 10°C from pre-glacial conditions (Kuhle, 1987). Actually, a lower temperature would influence precipitation negatively because of the atmosphere's lower moisture carrying capacity. Today there is an average of four times more evaporation than precipitation occurring on the Plateau (Songqias, 1986). A new development in the past year or so is the recognition by some Chinese workers that indeed an ice sheet did cover parts of the Tibetan Plateau, not nearly to the extent envisioned by Kuhle and, not during the LGM. Zhou and Li (pers. commun.) suggest that an ice sheet, tens of thousands of square kilometres, covered the north central part of the Tibetan Plateau in the source area of the Yellow River (4300 m). This area is surrounded by marginal mountains, including Burhan Budai Range (5536 m) along the north, Bayan Har Range (5267 m) stretching along the south, and Anyemaqen Mountain (6282 m) on the east, which supports modern glaciers (Fig. 12). The authors indicate that ice covered all mountains to around 5000 m. The mountain glaciers gradually coalesced toward the basin center. The central ice sheet thickness is estimated at 1.3 km, covering mountains as high as 1000 m above the plateau. Evidence for this ice sheet is: (1) streamlined landforms, such as rounded top mountains, whalebacks, drumlins and roche mounton~es observed in the source area of the Yellow River (no striated surfaces observed); (2) prominent troughs in the mountains extending to lower altitudes near Gating Lake; and (3) erratics that are widely distributed in the source area of the Yellow River. Granodiorite en'atics originating in Bayan Har Mountains extend for about 60 km from the source area, as does till. Dating of this event is provided by ice wedge casts in the source area of the Yellow River suggesting that during the Last Glacial Maximum and the Penultimate ice age, glaciers advanced on the northern pediments but would not have connected to form an ice sheet. This created a periglacial environment for ice wedges to form beyond the glacial limits. Dating of the wedges of the Last Glacial Maximum is provided by a 14C date of 24,490 + 350 BP on unspecified material. The Penultimate ice wedge casts were dated by TL methods yielding a date of 135,000 _+ 10,500 BP, which would have to be suspect. Limited ice extent during the two most recent glaciations suggests that an ice sheet must have formed during the third or earlier glaciation (Li Jijun et al., 1991). Why this ice sheet developed here is that even though the altitude of the source area of the Yellow River is 4300 m, as opposed to 5000 m to the west in the hinterland of the Plateau, temperatures in winter on the average are lower around the source area of the Yellow River because of cold currents from the north (Mongolian High Pressure). In addition the Yellow

River area has an annual precipitation of 300-400 mm, higher than most of the Plateau. However, some workers recognize that the evidence for an ice cap is commonly indirect or open to other interpretations. Yugo Ono (pers. commun., 1994) suggests that all the truly glacial features can be explained by extensive mountain glaciers forming valley and piedmont glaciers far from the mountain front. Therefore, the ice from the Bayan Har and Anyemaqen mountains did not necessarily join. However, he argues that the evidence for glaciation far from the mountains indicates older glaciations which surely antedate isotope stage 5, (and possibly stages 7 or 9) based on the well developed nature of paleosols over several tills. In conclusion then, we find less resistance by Chinese workers to ice cap cover over parts of the Plateau than we did a very few years ago, although not nearly as extensive as what is proposed by Kuhle, but more extensive than traditional Chinese thinking. In addition, we need to examine landforms and sediments in various parts of the Plateau more critically before we label them glacial in origin. We are somewhat closer to dating the various moraine systems but still much is based upon relative ages and little on absolute dates. As reviewed earlier in this paper, the same kinds of problems remain in Eurasia and eastern Siberia, that is poorly dated glacial events and questions on the extent of ice during different time intervals, and indeed did glaciers exist at all in parts of Siberia.

ACKNOWLEDGEMENTS The author acknowledges with thanks the numerous discussions in the field and at workshops with many colleagues, especially those from Russia and China. This review is not intended on my part to take any particular side on the controversial issues, but rather to present the arguments and facts as the author sees them. The author also appreciate the efforts of Dean Rokosh and Jeffrey Bond (University of Alberta), Li Jijun (Lanzhou University), Lewis Owen (Royal Holloway, University of London), Jan Lundqvist (University of Stockholm), Jan Mangerud (University of Bergen), Yugo Ono (Hokkaido University), and Matti Saarnisto (Finland Geological Survey), for reviewing and improving the present manuscript. Aid for travel to and from workshops and the field were provided from time to time by the Swedish Academy of Sciences, Chinese Academy of Sciences, IGCP 253, and the' Natural Sciences and Engineering Research Council of Canada (NSERC). This was greatly appreciated.

REFERENCES Andreyeva, S.M. and Isayeva, L.L. (1988). The dynamics of the ice sheet on the northeastern part of the Central Siberian Plateau in the Late Pleistocene. Polar GeographicalGeology, 12(3), 212-220. Apukhtin, N.I. and Elunan, T.M. (1967). Strafigrafiya: Murmanskaya oblast, Kareliya, zapad Arkhangelskov, sever~zapad Vologodskoy i sever Leningradskoy oblasti. Geologiya chetvertnikh otiozheniy Severo-Zapada Evropeyskoy chasti SSSR, pp. 48-110. Leningrad, Nedra. Arkhipov, S.A., Bespaly, V.G., Faustova, M.A., Glushkova, O. Yu., Isaeva L.L. and Velichko, A.A. (1986a). Ice-sheet reconstructions. Quaternary Science Reviews, $, 475-483. Arkhipov, S.A., Isayeva, L.L., Bespaly, V.G. and Glushkova, O. (1986b). Glaciation of Siberia and North-east USSR. Quaternary Science Reveiews, 5, 463-474.

36

N. Rutter

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