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Quaternary Science Reviews 24 (2005) 1391–1411

Climatic and topographic controls on the style and timing of Late Quaternary glaciation throughout Tibet and the Himalaya deﬁned by 10Be cosmogenic radionuclide surface exposure dating

Lewis A. Owena,Ã, Robert C. Finkelb, Patrick L. Barnardc, Ma Haizhoud, Katsuhiko Asahie, Marc W. Caffeef, Edward Derbyshireg

aDepartment of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, USA bLawrence Livermore National Laboratory, Center for Accelerator Mass Spectrometry, Livermore, CA 94550, USA cUnited States Geological Survey, Paciﬁc Science Center, 400 Natural Bridges Drive, Santa Cruz, CA 95060, USA dInstitute of Saline Lakes, Chinese Academy of Sciences, Xining, Qinghai, PR China eDepartment of Geography, Tokyo Metropolitan University, Tokyo, 192-0397, Japan fDepartment of Physics/PRIME Lab., Purdue University, West Lafayette, IN 47907, USA gCentre for Quaternary Research, Department of Geography, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, UK

Received 25 June 2003; accepted 24 October 2004

Abstract

Temporal and spatial changes in glacier cover throughout the Late Quaternary in Tibet and the bordering mountains are poorly defined because of the inaccessibility and vastness of the region, and the lack of numerical dating. To help reconstruct the timing and extent of glaciation throughout Tibet and the bordering mountains, we use geomorphic mapping and 10Be cosmogenic radionuclide (CRN) surface dating in study areas in southeastern (Gonga Shan), southern (Karola Pass) and central (Western Nyainqentanggulha Shan and Tanggula Shan) Tibet, and we compare these with recently determined numerical chronologies in other parts of the plateau and its borderlands. Each of the study regions receives its precipitation mainly during the south Asian summer monsoon when it falls as snow at high altitudes. Gonga Shan receives the most precipitation (42000 mm a1) while, near the margins of monsoon influence, the Karola Pass receives moderate amounts of precipitation (500–600 mm a1) and, in the interior of the plateau, little precipitation falls on the western Nyainqentanggulha Shan (300 mm a1) and the Tanggula Shan (400–700 mm a1). The higher precipitation values for the Tanggula Shan are due to strong orographic effects. In each region, at least three sets of moraines and associated landforms are preserved, providingevidence for multiple glaciations. The 10Be CRN surface exposure datingshows that the formation of moraines in Gonga Shan occurred during the early–mid Holocene, Neoglacial and Little Ice Age, on the Karola Pass during the Lateglacial, Early Holocene and Neoglacial, in the Nyainqentanggulha Shan date during the early part of the last glacial cycle, global Last Glacial Maximum and Lateglacial, and on the Tanggula Shan during the penultimate glacial cycle and the early part of the last glacial cycle. The oldest moraine succession in each of these regions varies from the early Holocene (Gonga Shan), Lateglacial (Karola Pass), early Last Glacial (western Nyainqentanggulha Shan), and penultimate glacial cycle (Tanggula Shan). We believe that the regional patterns and timing of glaciation reflect temporal and spatial variability in the south Asian monsoon and, in particular, in regional precipitation gradients. In zones of greater aridity, the extent of glaciation has become increasingly restricted throughout the Late Quaternary leading to the preservation of old (b100 ka) glacial landforms. In contrast, in regions that are very strongly influenced by the monsoon (b1600 mm a1), the preservation potential of pre-Lateglacial moraine successions is generally extremely poor. This is possibly because Lateglacial and Holocene glacial advances may have been more extensive than early glaciations and hence may have destroyed any landform or sedimentary evidence of earlier glaciations. Furthermore, the intense denudation, mainly by fluvial and mass movement processes, which characterize these wetter environments, results in rapid erosion and re-sedimentation of glacial and associated landforms, which also contributes to their poor preservation potential. r 2004 Elsevier Ltd. All rights reserved.

ÃCorrespondingauthor. Tel.: +1 512 556 3732; fax: +1 513 556 6931. E-mail address: [email protected] (L.A. Owen).

1. Introduction highlighted the importance of these climatic systems on glacier formation both regionally and on local scales, The timingand extent of late Quaternary glaciation and suggested that the relative importance of each throughout the high mountains of Tibet and the Himalaya climatic system varied throughout the Quaternary, in has attracted much attention duringrecent years ( Owen turn influencingthe style and timingof glaciation and Lehmkuhl, 2000; Owen and Zhou, 2002; Owen et al., throughout the region. They noted that the affect of 2002d; Bo¨ se et al., 2003). The Tibetan Plateau has a the monsoon is greatest on the eastern and southern profound influence on regional and global atmospheric slopes of the Himalaya and in eastern Tibet, all of which circulation and is therefore important for understanding experience a pronounced summer maximum in precipi- the dynamics of global environmental change (Ruddiman tation that falls as snow at high altitudes as the result of and Kutzbach, 1989; Molnar and England, 1990; Prell moisture advection northwards from the Indian Ocean. and Kutzbach, 1992; Owen et al., 2002d). In particular, it This summer precipitation, however, declines sharply is becoming increasingly apparent that changes in from south to north across the main Himalayan chain glaciation and snow cover on both short (years to and is also much higher at the eastern end of the decades) and long(thousands of years) timescales have a mountain belt than in the west. In contrast, the more profound affect on the regional climate, glaciation and northern and western ranges, such as the Karakoram hydrological regimes (Hahn and Shukla, 1976; Dey and Mountains and the western Kunlun, in NW Tibet, Bhanu Khumar, 1982; Dey et al., 1985; Dickson, 1984; receive heavy snowfall duringthe winter supplied by Sirocko et al., 1991; Prell and Kutzbach, 1992; Soman and the mid-latitude westerlies that draw moisture from Slingo, 1997; Bush, 2000, 2002; Zhao and Moore, 2004). the Mediterranean, Black and Caspian Seas. In the Two major climatic systems, the mid-latitude wester- extreme west this effect leads to a winter precipitation lies and the south Asian monsoon, dominate the maximum. Changing lapse rates, related to a reduc- climatology of the Tibetan Plateau and the Himalaya tion in the moisture content of air masses as they are (Figs. 1 and 2). In addition, the El Nin˜ o Southern forced over the Himalaya, are also important in deter- Oscillation (ENSO) produces significant inter-annual miningthe variability of snow and ice accumulation climatic variability in the region. Benn and Owen (1998) across the Himalaya and Tibet. There are also strong

Fig. 1. Digital elevation model of Tibet and the bordering mountains showing the locations of the main study areas. ARTICLE IN PRESS L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411 1393

JAN. the age of previously undateable glacial and associated landforms to be assessed. This has led to the emergence ° WESTERLIEWES 40 TER LIES of a framework for the timing of glaciation throughout selected areas of the Himalaya and Tibet (Shiraiwa,

Lee ne 1993; Sharma and Owen, 1996; Phillips et al., 2000; tan e zo TibetanTibe Leencec zone verg convergencon Richards et al., 2000a,b; Owen et al., 2001, 2002a,c, 2003a,b,c, submitted; Scha¨ fer et al., 2001; Tsukamoto ES RLIE WESTE et al., 2002; Finkel et al., 2003; Zech et al., 2003; Barnard 20° et al., 2004a,b, submitted). These studies are providinga basis for testing Benn and Owen’s (1998) hypothesis, and

DES indicate that precipitation changes related to oscillations TRADESTRA in the South Asian monsoon were important in controllingglacier ﬂuctuations over at least the last E EQUATO 0° RIAL WESTERLIES glacial cycle (Richards et al., 2000a,b; Owen et al., 2001,

(A) 80° 100° 120° 2002a,b,c, 2003a,b,c; Finkel et al., 2003; Barnard et al., 2004a,b). Furthermore, these results indicate that, JULY although glaciation throughout these regions was W ESTERLIES broadly synchronous, it was out of phase with fluctua- 40° tions of the Northern Hemisphere ice sheets and changes in oceanic circulation that predominantly control global climate (Owen et al., 2002a,b; Finkel et al., 2003). The studies mentioned above mainly pertain to regions in which glaciation is sustained by monsoonal moisture. Much of Tibet, however, is beyond the 20° influence of the monsoon and is classified as semi-arid to arid; glaciers here are largely influenced by the mid- latitude westerlies. Recent work by Scha¨ fer et al. (2001),

S L I E Yi et al. (2002) and Owen et al. (submitted), in the A S T E R E Q U A T O R I A L E Tanggula Shan, Puruogangri and Ladakh, at the

0° extreme margins of monsoon inﬂuence, suggests that

80° 100° 120° in these arid regions glaciation during most of the last 0 2000 km Air flow at 500 m glacial cycle (since 60 ka) was very limited in extent. It (B) Scale for A & B Air flow at 3000 m is therefore likely that glaciers beyond the margins of the Fig. 2. Summary maps showing the main air flows associated with (A) monsoon influence behaved differently from the mon- the south Asian winter and summer (B) monsoons in central Asia. soon-affected glaciers throughout the Late Quaternary. Adapted from Benn and Owen (1998). In order to investigate the regional pattern of glaciation and to look for correlations between distant microclimatic variations within individual watersheds regions within the Himalaya–Tibet region, we have and also regionally as a result of orographic effects. As undertaken studies of the Quaternary glacial geology of climate changed throughout the Quaternary, the relative selected areas of southern, southeastern and central importance of these climatic systems changed. Benn and Tibet. UsingCRN surface exposure dating,we have Owen (1998) hypothesized that, as a result, Quaternary defined the timingof glaciation as a means of testingthe glaciation may have been asynchronous between differ- relative importance of different climatic systems in ent regions of Tibet and the Himalaya. The limited determining the timing and extent of glaciation through- numerical dating control on glacial successions throughout the region as a whole. These newly defined out the Himalayan and Tibet did not, however, allow chronologies and their correlation with adjacent regions this hypothesis to be tested. are presented in this paper, and used to examine the The scarcity of numerical dates is the direct result of various climatic processes that might control glaciation. the low abundance of organic matter within sediments in these high mountain environments that provided few opportunities for radiocarbon dating. Furthermore, 2. Methods most organic matter present is only of Holocene age (Lehmkuhl, 1997). The development of cosmogenic 2.1. Field methods and sampling for CRN dating radionuclide (CRN) and cosmogenic stable nuclides (CSN) surface exposure, and optically stimulated lumi- The glacial geologic evidence was examined on either nescence (OSL) dating, however, has recently allowed side of the Tanggula Pass (Tanggula Mountains), south ARTICLE IN PRESS 1394 L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411 of the Samdainkangsang Mountain along the eastern trations were then converted to zero-erosion exposure slopes of the western Nyainqentanggulha Mountains, on ages using sea level high latitude (SLHL) 10Be produc- the eastern side of Karola Pass in southernmost Tibet, tion rate of 5.2 at/g-quartz/y (Stone, 2000). The Be and on the eastern slopes of Gonga Shan in the Daxue production rate used is based on a number of indepen- Shan of SE Tibet (Fig. 1). Standard geomorphic and dent measurements as discussed by Owen et al. (2001, sedimentological field techniques (cf. Benn and Owen, 2002a). Production rates were scaled to the latitude and 2002) were used to determine the genesis of landforms elevation of the samplingsites usingthe star scaling and to help identify a succession of morphostratigra- factors of Lal and Peters (1967) and Lal (1991) and an phically distinct moraines within each region. In this assumed 3% SLHL muon contribution, and were way, appropriate sites for CRN datingwere identified further corrected for changes in the geomagnetic field within each study area. over time. Details of the calculation are given in Owen Zreda and Phillips (1995), Gosse et al. (1995a,b), et al. (2001, 2002a). Gosse and Phillips (2001), Owen et al. (2001, 2002a), Benn and Owen (2002) and Easterbrook et al. (2003) highlighted some of the limitations of dating moraines 3. Study areas usingCRN and CSN techniques, and cautioned that local records may be fragmented. Nevertheless, many of 3.1. Gonga Shan these problems can be overcome by obtainingnumerous CRN and CSN dates on individual moraines, the At 7514 m asl, Gonga Shan (Minya Gongkar in approach adopted here in datingthe moraine succession Tibetan) is the highest mountain in China, outside of the in each of the study areas (cf. Putkonen and Swanson, Himalaya. It is located on the easternmost edge of the 2003; Easterbrook et al., 2003). Samples for CRN dating Tibetan Plateau in Sichuan Province (Fig. 1). Thomas were collected by chiselingoff 500 gof rock from the (1997) states that the maximum precipitation upper surfaces of quartz-rich boulders alongmoraine (41900 mm a1) alongthe east slopes occurs at 2900 crests. Locations were chosen where there was no to 3200 m asl, at far lower altitudes than in other apparent evidence of exhumation or slope instability. Tibetan mountain ranges. However, other studies The largest boulders were chosen to help reduce the suggest that the mean annual precipitation is signifi- possibility that boulders may have been covered with cantly higher (Kodrau, 1981; Pu et al., 1998). Most of snow for significant periods (several months) of the year. this precipitation falls between May and September To provide a check on the reproducibility of the dating duringthe monsoon season. The mean annual tempera- and to check for the possibility of inheritance of CRNs, ture and temperature ranges on the eastern slopes of where possible, several boulders were sampled from Gonga Shan at 3000 m asl are 3.9 and 17.2 1C (January each moraine ridge. The degree of weathering and the to July ¼4.5–12.7 1C), respectively (Thomas, 1997). site conditions for each boulder were recorded. Topo- The glaciers are of monsoon maritime type with the graphic shielding was determined by measuring the basal ice temperature around 0 1C(Derbyshire, 1981; inclination from the boulder site to the top of the Zheng, 1997; Su and Shi, 2002). These are high activity surroundingmountain ridgesand peaks. glaciers with terminal positions extending into forest zones at 2940 m asl. Pu et al. (1998) note that the mean 2.2. Laboratory methods for CRN dating annual air temperature at the equilibrium-line (at 4970 m asl) on the Hailuoguo glacier is 4.4 1C with First, the samples were crushed and sieved. Quartz an annual precipitation of 3357 mm, and basal ice was then separated from the 250–500 mm size fraction temperatures between 1.0 and 0 1C. usingthe method of Kohl and Nishiizumi (1992). After Zheng(1997) summarizes the glacial geomorphologi- addition of Be carrier, Be was separated and purified by cal work undertaken by Chinese scientists duringthe ion exchange chromatography and precipitation at latter part of the last century. These studies include pH47. The hydroxides were oxidized by ignition in geomorphic mapping, monitoring of recent glacial quartz crucibles. BeO was then mixed with Nb metal retreat and radiocarbon dating of the Hailuoguo glacier prior to determination of the 10Be/9Be ratios by on the eastern slopes of Gonga Shan (Fig. 3). A four- accelerator mass spectrometry at the Center for Accel- fold glacial succession is recognized, which Zheng(1997) erator Mass Spectrometry in the Lawrence Livermore believes represents the global Last Glacial Maximum National Laboratory. Isotope ratios were compared to (LGM), early to middle Holocene, Neoglacial and Little ICN 10Be standards prepared by K. Nishiizumi (pers. Ice Age glacial advances. A moraine platform, comm. 1995). 60–120 m above the present river, considered to The measured isotope ratios were converted to CRN represent the LGM advance, extends to 1850 m in concentrations in quartz usingthe total Be in the the Hailuoguo valley where it forms a cross-valley ridge samples and the sample weights. Radionuclide concen- (Fig. 4). Zheng(1997) cites radiocarbon dates of ARTICLE IN PRESS L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411 1395

er Settlement (A) N Rivers

Contemporary glaciers Moxi Riv Moxi Little Ice Age moraines Neoglacial moraines Xinxing Glaciers of the Last Glacial GS10-13 Post-last glacial glacio-fluvial l. o terraces

29 40'N Sampling sites for CRN dating Moxi Radiocarbon sampling site Yanzigou G GS17-20 and dates from Zheng (1997) Mozigong Gl. 7514 m H Radiocarbon 1580 + 60 yr BP a GS14 & 15 (B) Mt. Gonga i ages lu GS1-4 540 + 70 yr BP o Hailuogou B gu 150 + 60 yr BP ig Gonga G o River Gl . 3080 + 80 yr BP & GS8-9 ~2430 + 80 yr BP Dadu River

Gonggigou Riv part B 1550 + 70 yr BP 940 + 50 yr BP er GS5-7 o Hailuoguo Glacier 102 E 10 km 1 km

Fig. 3. The Gonga Shan massif showing the main moraines and a reconstruction of the maximum extent of glaciers (A) and the moraines around the Hailuoguo Glacier (B) adapted from Zheng(1997) and the locations for cosmogenic samples. The radiocarbon dates shown in part B are from Zheng (1997).

24,3907750 years BP in silts intercalated within (Fig. 3B). He refers to this advance as the Guanjingtai the moraines and 19,7007300 years BP on sinter on glacial advance. These moraines extend to within a few the upper moraines. However, no specific details of the kilometres of the present ice margins. datingprocedures are provided. Beyond the ice limit, the The Little Ice Age moraines form a series of end valley shape changes from broad, typically glacial forms moraines that rise to several tens of metres above the to steep gorge sections. Impressive glaciofluvial terraces present river and are inset within the Neoglacial (450 m thick) are present beyond the limit of Zheng’s moraines. These extend a few kilometres beyond the (1997) LGM moraines and these are considered to be present ice margin. A radiocarbon age of 150760 years post-last glacial in age (Fig. 5). Zhengexpresses the is provided for a ‘rotten wood’ sample from a lateral opinion that a lower step in the moraine platform of moraine in front of the Hailuoguo Glacier (Fig. 3). LGM age represents an early to middle Holocene To test the chronology presented by Zheng(1997) ,we advance. This is most evident where a ridge dams a collected samples from the moraines in the Hailuoguo small lake at 2720 m asl on the north side of the valley and from the post-Last Glacial glaciofluvial Hailuoguo valley 5 km down valley from the Hailuo- terrace in the Moxi valley (Figs. 3–5). Samples (GS17- guo glacier. He also suggests that this glacial advance is 20) were collected from Zheng’s (1997) terminal position represented by a small end moraine in the upper Moxi of the LGM in the Hailuoguo valley at 1860 m asl, valley and in the Gonggigou valley near the confluence while samples GS14 and 15 where collected from the of the Ginggigou and Gonga rivers. However, this lake dammed by Zheng’s (1997) early to middle advance is not marked on the glacial map presented in Holocene moraines at 2720 m asl (Fig. 3). We also Zheng(1997) . Rather, it is inferred as beingwithin the sampled the Neoglacial and Little Ice Age moraines in reconstructed ice extent of the LGM and down valley of front of the Hailuoguo Glacier (Figs. 3 and 4). the Neoglacial moraines (Fig. 3). The Neoglacial moraines comprise ridges that rise 3.2. Karola Pass many tens of metres above the present river level (Fig. 4). Zheng(1997) provides radiocarbon dates of The Karola Pass (sometimes spelt Karila or Karela) several thousand years for material he describes as at 5042 m asl is the highest road pass on the ‘rotten wood’ within the upper parts of the moraines Lhasa–YadongHighway.To the north and south lie ARTICLE IN PRESS 1396 L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411

Fig. 5. Exposures within post-Last Glacial glacioﬂuvial terraces (A) and a typical surface boulder (B) at Xinxingin the Moxi valley east of Gonga Shan. The building in part A and the sampling bag in part B provides a scale. The boulder in part B had large lichens on its surface and was clearly not moved duringthe construction of the adjacent track.

moraines are sharp crested and rise several tens of meters above the valley floor. These are typical of Benn and Owen’s (2002) latero-frontal moraines that form on high-altitude debris covered glaciers (Fig. 6B). The Fig. 4. Views illustrating the characteristics of the geomorphology in oldest moraine, however, comprises denuded till benches the Hailuoguo valley on the eastern slopes of Gonga Shan. (A) that terminate in an end moraine at 4770 m asl. This is Looking west up the Hailuoguo Glacier from the top of Neoglacial moraines. (B) Lookingwest from the Little Ice Ageat the snout of the well preserved on the north side of the valley and Hailuoguo Glacier and its historical moraines. (C) View west of a fluvially cut exposures show that it comprises a well- samplinglocation on the end moraine that marks the maximum extent indurated and sheared deformation till with bullet- of glaciation on the eastern slopes of Gonga Shan. shaped clasts in the lower third of the exposure, overlain by a bouldery supraglacial till unit with a more open Mount Lingjing Kangsha (7191 m asl) and Mount fabric. Below this moraine, however, the valley retains Kaluxung(6475 m asl) that are part of southernmost its broad glaciated form, suggesting an earlier, more Tibet. The annual precipitation on the pass is extensive glaciation. Zheng(1989) describes till deposits 500–600 mm, most fallingas snow duringthe summer on the north side of the KaluxungRiver and west of the monsoon season. The glaciers in this region are Karola Pass as older deposits of the Nieniexongla glacia- transitional in type between monsoonal and continental tion. However, we were unable to find the Nieniexongla (Derbyshire, 1981; Su and Shi, 2002). glacial deposits, described by Zheng(1997) , on the east Zheng(1989) describes the glacial geomorphology side of the Karola Pass. On the basis of relative and provides a map of the landforms (Fig. 6). The best weatheringcriteria, Zheng(1989) believed the moraines succession of moraines is preserved on the west side of to represent glacial advances during the Neoglacial the pass, down valley of the Qiangrong glacier. Here the (which they call ‘New Glaciation’), Early Holocene ARTICLE IN PRESS L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411 1397

o Peaks (A) 7191 m 090 15'E Kaluxung Glacier Streams Glaciers

Karola Glaciated valleys Pass Cirque basins Watershed 28o 55'N PR39-42 Kaluxung Riv er PR35-38 PR31-34

rong G

Qiang Mt. Kaluxung 6679 m

5 km N Neoglacial moraines Early Holocene moraines LGM-Late glacial moraines

Terminal moraine (B) PR31-34 of New Glaciation 6679 m asl PR35-38 Neoglacial Qiangrong PR39-42 Early Terminal Glacier LGM- Lateglacial Holocene moraine of Late Moraines of Terminal Last Glaciation Penultimate moraine of Glaciation Early Last Glacial at 4720 m asl

lake

ly Last Glaciation

Ter minal moraine of Ear

Fig.6. Geomorphic map (A) and field sketch (B) showingthe moraine succession on the Karola Pass showingthe samplinglocations for CRN dating. The field map is modified from Zheng(1989) and we define the ages of the moraines based on our CRN dating. The field sketch, adapted from Zheng(1989) , shows our new interpretation of the moraine ages (in bold text) and Zheng’s (1989) interpretation of the moraine ages (in plain text). ARTICLE IN PRESS 1398 L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411

Advance, early Last Glacial and penultimate Glacial front. These comprise diamictons containingmeter-size (Fig. 6B). Samples for CRN datingwere collected from boulders (Fig. 8). each of these moraines (Fig. 6). For our study area, we chose a valley 15 km south of Samdainkangsang Peak (6532 m asl), that contained 3.3. Nyainqentanggulha Shan some of the best-preserved moraines, and associated hummocky moraine on the foreland (Figs. 7 and 8). The Nyaingentangulha Shan forms an extensive Samples for CRN datingwere collected from the east–west mountain range in southern Tibet to the hummocky moraine (Fig. 8; samples PR43–47) and north of the Tsangpo valley (Fig. 1). This lies on the from two sets of moraines within the range (Fig. 7; extreme margin of the present inﬂuence of the monsoon, samples PR52–55 and PR48–51). receiving o400 mm precipitation per annum. The glaciers in this region are of cold continental type 3.4. Tanggula Shan (Derbyshire, 1981; Su and Shi, 2002). Lehmkuhl et al. (2002) examined Late Quaternary The Tanggula Shan is an east–west trending mountain glacier advances, lake level ﬂuctuations and aeolian range in central Tibet (Fig. 1). The surrounding sedimentation on the northwestern side of the western lowlands are semi-arid (5400 mm a1), while the higher Nyainqentanggulha Shan, and suggested evidence for peaks of the Tanngula Shan receive up to 5700 mm a1 multiple glaciations that spanned the last two glacial due to orographic effects during the summer monsoon cycles. However, they were not able to date the moraines season. The contemporary glaciers in this region are of directly in this region. The glacial succession on the cold continental type (Derbyshire, 1981; Pu et al., 1998; more accessible (eastern) side of the western Nyainqen- Su and Shi, 2002). Pu et al. (1998) showed that, for tanggulha has not been previously described, despite the the Xiao Dongkemadi Glacier in the vicinity of the presence of well-preserved multiple successions of Tanggula Pass, the mean annual temperature and moraines. At least two major sets of incised latero- precipitation at the equilibrium line is 9.8 1Cand frontal moraines are present within the u-shaped valleys 560 mm (at 5600 m asl), respectively, and the basal ice on the eastern side of the western Nyainqentanggulha temperature is 7.5 1C. Shan. Hummocky moraines are present in the forelands The glacial geology of the region was originally of the mountains as much as 5 km from the mountain described by Zhengand Jiao (1991) who produced a

Samdainkangsang N u-shape (6532 m) d valley

u-shaped valley

u-shaped v Meltwater alley cut gorge

PR52 to 55

Hummocky PR48 to 51 moraine

o PR43-47 30 45'N o 2 km Highway 091 36'N Golmud-Lhasa

Fig. 7. Geomorphic map of the moraines and associated landforms south of Samdainkangsang Peak on the eastern slopes of the Nyainqentanggulha Shan. The moraines and samplinglocations are mapped on a Landsat image. ARTICLE IN PRESS L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411 1399

dates in Table 1 and Fig. 10, however, have not been corrected for the possibility of weathering. For weath- eringrates of 1–5 m Ma 1, an exposure age of 10 ka, calculated on the assumption of zero erosion, would underestimate the true age by 1–4%; an age of 20 ka, by 2–9%; an age of 50 ka, by 4–20%; an age of 100 ka, by 10–36%; and an age of 200 ka, by 15–54%. We do not make a correction for shieldingdue to snow cover because we do not believe it has a significant effect on the ages of our samples. This is because present day snow cover is generally sparse and usually o1 m thick, lastingonly a few weeks/months at the elevations from Fig. 8. View looking southwest at the oldest moraine on the eastern where we collected the samples for dating. Of course slopes of the Nyainqentanggulha. The boulder in the foreground snow cover may have been greater during glacial time. illustrates a typical samplinglocation. However, if snow cover was an important shielding factor in our study areas we would expect to see older map of the Tanggula Pass showing evidence for at least ages on the higher boulders on each dated landform. three major glaciations (Fig. 9). They referred to these as This is because the taller boulders would have had less the Tanggula Ice Age, the Zhajiazangbo Ice Age and the snow on them than the shorter ones. There is no such Bashico Ice Age and regarded them as representing relationship between boulder height and age in our data ‘extremely old’, penultimate, and last glacial cycles, (Table 1) and we therefore conclude that snow cover respectively. Duringthe first two of these glaciations, shieldingis not a significant shieldingfactor in our study glaciers and ice caps expanded into the forelands from areas. the Tanggula Shan to form a continuous ice cap that, in For each of the study areas, the CRN ages on sampled the area around the Tanggula Pass, was 90 km and moraines confirm the morphostratigraphy; that is, the 25 km wide during the Tanggula and Zhajiazangbo Ice sets of ages are progressively younger for morphostrati- ages, respectively (Derbyshire et al., 1991; Zhengand graphically younger moraines. Furthermore, the dates Jiao, 1991). This produced extensive sheets of till and from most moraines cluster reasonably well. The most subdued terminal moraines. The extent of the glacial notable exceptions are for the Tanggula Shan where advance duringthe Bashico Ice Agewas restricted to the boulder ages are the oldest of all the study areas only several kilometres beyond the present ice margins. (Fig. 10D). For example, the moraines of the Zhajia- Scha¨ fer et al. (2001) dated four glacial boulders on the zangbo glacial are well bracketed between the Tanggula Tanggula Pass using 10Be, 26Al, and 21Ne surface and Bashico Glacial Stages at 148736 ka (mean age exposure dating( Fig. 9). They showed that three and the errors are quoted as 1s for all the samples dated boulders within the Tanggula glacial limit had ages of of the same glacial stage) and 68726 ka, yet the CRN 181.3715.7, 89.378.0 and 172.9713.8 ka, while a ages range from 4210 too50 ka (118773 ka). The boulder within the limit of the Bashico Ice Age had a youngagesmay be attributed to extreme weathering surface exposure age of 72.176.2 ka. We collected (although care was taken to avoid any boulder that samples from boulders within the same regions as these showed signs of significant weathering) or recent authors, as well as from moraines datingfrom the exhumation by erosion and/or frost heaving. The old Zhajiazangbo Ice Age. This provides a test of the ages may be boulders derived from older glacial events validity of the glacial ages based on the samples dated by and/or ones that were not adequately eroded by glacial Scha¨ fer et al. (2001), as well as a means of examiningthe processes and therefore have inherited CRNs from prior age of the previously undated intermediate glaciation, exposure on hill slopes. Despite the scatter of ages, the the Zhajiazangbo. data show that the Zhajiazangbo glaciation must have occurred duringthe early part of the last glacial cycle, the Tanggula Glacial prior to the last interglacial (the 5. CRN dating results younger dates for samples PR58 and PR77 may well be the results of weatheringor exhumation) and the The 10Be CRN ages determined in this study are listed Bashico Glacial probably duringmarine isotope stage in Table 1. The 10Be ages are plotted by moraine and (MIS) 4 or the latter part of MIS 5. These data compare relative age in Fig. 10 to show the range and clustering well with the CRN dates determined by Scha¨ fer et al. of ages. Such plots provide a qualitative assessment of (2001) for the five boulders in his study (Fig. 9). the potential likelihood of spurious ages due to weath- The dated successions in the Gonga Shan clearly ering, exhumation and/or toppling of boulders, and/or show that the moraines considered by Zheng(1997) to derivation of CRN from derived boulders. The CRN be equivalent to the global LGM, on the basis of ARTICLE IN PRESS 1400 L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411

(A) N Highway Stream Unglaciated Glacier

Lake

Moraines formed during Bashico Glacial Stage

Maximum limit of ice ver during the Zhajiazangbo PR80-82 Glacial Stage

Bu Qu Ri Maximum limit of ice during the Tanggula PR78-79 Glacial Stage

Sampling site and sample number/s for CRN dating PR77 6140

PR77 PR76

PR71-75 6022

(B) Bashico

PR62-65 Tanggula Pass (5231)

5830

PR66-70

(C)

Zhajiazangbo(72.1 +/- 6.2ka) (89.3 +/- 8.0 ka & 172.9 +/- 13.8 ka)

PR59 & 61 PR57 & 58 (181.3 +/- 15.7 ka) Unglaciated 10 km (D)

Fig. 9. The glacial geology in the area around the Tanggula Pass. (A) Simpliﬁed geomorphic map of the Tanggula Pass showing the sites where we have obtained CRN dates on moraines (modiﬁed from Benxingand Keqin, 1991). The dates in parenthesis were undertaken by Scha¨ fer et al. (2001). (B) View of end moraines of the Bashico Glacial Stage south of the Tanggula Pass. (C, D) Typical glacial boulders on surface of moraines deposited during the Zhajiazangbo (C: boulder PR76) and Tanggula Glaciations and (D: boulder PR77). ARTICLE IN PRESS L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411 1401

Table 1 Cosmogenic radionuclide data for Gonga Shan, Karola Pass, Nyainqentanggulha Shan and Tanggula Shan. Samples are grouped per landform in stratigraphic order within each study area

Relative age Sample Location Altitude Latitude & Boulder height/ 10610Be atoms/ 10Be exposure latitude/ (m asl) altitude maximum gof quartz age (ka) longitude correction width (m)

Gonga Shan Youngest GS5 29134.2770N/ 3010 6.63 1.5/4.5 0.010370.0030 0.3170.09 moraine 101159.9420E GS6 29134.2990N/ 2988 6.54 1.5/3.5 0.078470.0295 2.4070.90 101159.9350E GS7 29134.2160N/ 2979 6.51 1.2/1.0 0.012170.0013 0.3770.04 101159.9350E GS1 29134.1910N/ 3174 7.29 2.0/2.0 0.031170.0039 0.8670.11 101159.1320E GS2 29134.1910N/ 3160 7.23 1.4/1.0 0.047970.0061 1.3370.17 101159.1320E GS3 29134.5450N/ 3056 6.81 1.0/0.7 0.024670.0032 0.7270.10 102100.2200E GS4 29134.5450N/ 3056 6.81 1.0/1.0 0.082070.0140 2.4270.41 102100.2200E GS8 29134.6070N/ 2972 6.48 0.8/1.2 0.021470.0101 0.6670.31 102100.1860E GS9 29134.6110N/ 2959 6.43 1.2/1.5 0.027170.0029 0.8570.09 102100.1850E Outwash GS10 29141.2390N/ 2043 3.63 1.1/2.2 0.112970.0095 6.2570.52 terrace 102104.5950E GS11 29141.2330N/ 2110 3.8 1.1/2.5 0.065570.0085 3.4670.45 102104.5970E GS12 29141.2380N/ 2039 3.62 1.8/4.0 0.101470.0083 5.6070.46 102104.6170E GS13 29141.2550N/ 2045 3.64 1.8/2.0 0.059270.0078 3.2770.43 102104.6560E GS14 29134.1450N/ 1670 2.82 0.4/1.2 0.088070.0066 6.2770.47 102101.4870E GS15 29135.2750N/ 1670 2.82 0.4/1.5 0.051370.0079 3.6570.56 102101.2670E Oldest moraine GS17 29136.7290N/ 1858 3.21 1.2/1.8 0.145970.0080 9.1570.50 102106.2080E GS19 29136.7070N/ 1864 3.22 0.5/1.4 0.135270.0090 8.4370.56 102106.2900E GS20 29136.7070N/ 1884 3.26 1.0/1.4 0.128670.0110 7.9470.68 102106.3070E GS19R 29136.7070N/ 1864 3.22 0.5/1.4 0.128570.0102 7.9970.64 102106.2900E GS20R 29136.6900N/ 1884 3.26 1.0/1.4 0.122770.0118 7.5770.73 102106.3070E Karola Pass Youngest PR31 28153.4390N/ 4980 18.08 0.9/1.2 0.25970.0238 3.4870.32 moraine 090113.6850E PR33 28153.3510N/ 4994 18.19 0.3/0.5 0.18570.0101 2.5370.13 090113.7080E PR34 28153.3320N/ 4989 18.15 0.6/1.0 0.16770.0109 2.0970.14 090113.7110E PR35 28153.6800N/ 4914 17.54 0.6/1.0 0.81970.0247 9.9173.4 090113.7910E PR36 28153.7410N/ 4897 17.41 1.7/1.6 0.74870.0247 9.3170.31 090113.7630E PR37 28153.7490N/ 4891 17.36 1.7/2.2 0.85670.0211 10.6370.26 090113.7560E PR38 28153.7580N/ 4878 17.26 0.6/0.6 0.73270.0177 9.1770.22 090113.7540E ARTICLE IN PRESS 1402 L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411

Table 1 (continued )

Relative age Sample Location Altitude Latitude & Boulder height/ 10610Be atoms/ 10Be exposure latitude/ (m asl) altitude maximum gof quartz age (ka) longitude correction width (m)

Oldest moraine PR39 28153.4900N/ 4774 16.45 1.4/2.0 1.1670.0421 15.6570.57 090114.9850E PR40 28153.4980N/ 4781 16.5 0.6/0.7 1.2870.0465 17.1570.62 090114.9830E PR41 28153.5030N/ 4778 16.48 0.3/0.5 1.4570.0453 19.3870.61 090114.9870E PR42 28153.5060N/ 4764 16.37 0.4/0.5 1.1770.0470 15.8370.64 090115.0140E Nyainqentanggulha Youngest PR48 28146.9280N/ 4916 18.45 1.5/4.8 1.4470.0479 16.7970.56 moraine 091135.3870E PR49 28146.9270N/ 4919 18.48 1.3/3.8 1.2670.0366 15.0870.43 091131.3810E PR50 28146.9300N/ 4923 18.51 no data 1.2470.0399 15.6770.47 091131.3830E PR51 28146.9280N/ 4922 18.5 0.9/3.0 1.3770.0417 16.0070.49 091131.3950E PR52 28146.5290N/ 4724 16.88 1.1/3.2 1.6370.0597 20.6770.76 091132.5580E PR53 28146.5300N/ 4721 16.85 0.6/2.3 3.53770.114 41.3271.33 091132.5580E PR54 28146.5320N/ 4717 16.82 0.8/2.5 1.5470.0445 19.6070.57 091132.5710E PR55 28146.5230N/ 4712 16.78 1.1/2.1 1.4870.0408 18.8870.52 091132.5850E Oldest moraine PR43 28146.5670N/ 4667 16.43 0.7/1.2 4.3170.0804 52.6270.99 091135.9170E PR44 28146.5380N/ 4669 16.44 0.7/1.5 5.8070.0929 71.4771.15 091135.9360E PR45 28146.3980N/ 4687 16.58 0.6/2.3 8.9870.219 108.6072.65 091135.9180E PR46 28146.3260N/ 4712 16.78 1.4/3.2 4.5170.102 54.2271.23 091135.9800E PR47 28146.2450N/ 4717 16.82 0.5/1.1 4.7870.107 57.7071.29 091136.0320E

Tanggula Shan Youngest PR62 32149.6590N/ 5113 20.7 0.4/0.7 5.2470.135 49.2271.27 moraine 091154.4230E PR63 32149.6350N/ 5114 21.36 0.4/0.9 5.3470.0797 50.3070.75 091154.3920E PR64 32149.6320N/ 5116 21.37 0.5/0.9 4.8870.155 45.4371.44 091154.3940E PR65 32149.6360N/ 5122 21.39 0.4/0.6 6.4870.0873 61.8570.83 091154.3900E PR66 32149.2200N/ 5067 20.92 0.3/0.8 11.770.335 112.7173.24 091153.3520E PR67 32149.2400N/ 5071 20.95 0.4/0.7 12.070.364 115.8073.51 091153.3660E PR68 32149.2450N/ 5068 20.93 0.3/0.5 10.870.345 104.7073.36 091153.3700E PR69 32149.2030N/ 5099 21.22 0.3/0.5 3.4670.131 33.8571.28 091153.7580E PR70 32149.2070N/ 5100 21.23 0.3/.07 4.9470.185 46.4271.74 091153.7590E PR71 32156.0.660N/ 5216 22.42 0.3/1.0 5.4070.227 48.2072.02 091158.4320E PR72 32156.0690N/ 5215 22.41 0.2/0.8 7.3670.240 67.0272.19 091158.4450E PR73 32156.1330N/ 5206 22.32 0.8/2.4 7.4770.186 68.3471.71 091158.3730E ARTICLE IN PRESS L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411 1403

Table 1 (continued )

Relative age Sample Location Altitude Latitude & Boulder height/ 10610Be atoms/ 10Be exposure latitude/ (m asl) altitude maximum gof quartz age (ka) longitude correction width (m)

PR74 32156.1170N/ 5222 22.48 0.4/1.0 6.9570.319 63.2272.91 091158.4480E PR75 32156.1190N/ 5206 22.32 1.0/2.2 8.6170.471 79.2874.34 091158.5260E PR78 33106.9030N/ 4958 20.07 0.7/1.4 2.0570.267 215.3772.81 091150.5300E PR79 33106.9040N/ 4964 20.12 0.3/0.6 12.470.376 124.7673.78 091150.5260E PR80 33107.0440N/ 4963 20.12 0.6/1.0 4.6870.242 46.4772.40 091150.4400E PR81 33107.0570N/ 4967 20.15 0.7/0.9 4.7570.211 47.1372.09 091150.4600E PR82 33107.1880N/ 4966 20.14 0.4/0.6 15.370.732 157.0877.54 091150.5240E Oldest moraine PR57 32138.5210N/ 5061 20.76 0.5/1.5 18.070.241 181.0372.43 091151.5630E PR58 32138.6500N/ 5052 20.68 0.5/1.7 11.070.281 107.5472.76 091151.7280E PR59 32138.6450N/ 5052 20.68 0.5/1.2 17.770.263 178.8872.66 091151.7390E PR61 32138.6710N/ 5054 20.69 0.4/1.4 13.970.169 136.5471.66 091151.7140E PR76 33100.9180N/ 5082 21.17 1.0/3.4 17.770.496 175.6274.91 091158.0590E PR77 33101.5160N/ 5078 21.14 1.6/3.6 11.070.256 105.7174.39 091157.6980E

Atoms of 10Be per gram of quartz before application of shielding correction factor.

radiocarbon dating, have CRN surface exposure ages dated moraines formed at 2.670.6, 9.870.7 and that are early Holocene (Fig. 10A). The recessional 17.071.7 ka (Fig. 10B). These dates contrast with the moraine and postglacial glaciofluvial outwash terrace chronology suggested by Zheng(1989) , which is based has CRN surface exposure ages indicating that these on morphostratigraphy and relative weathering criteria. landforms formed duringthe middle Holocene The new data presented here show that the moraine ages (3–6 ka). Our datingof the Neoglacial and Little should be assigned to the Neoglacial, early Holocene Ice Age moraines of Zheng(1997) confirms their and the global LGM, and not to late Last Glacial, early Neoglacial (1–2 ka) and Little Ice Age (a few hundred Last Glacial and the penultimate Glacial as suggested by years) ages. Zheng(1989; Fig.6B) . The difference between the CRN and radiocarbon ages The three sets of moraines on the eastern slopes of for material indicatingthe maximum extent of glaciation the western Nyainqentanggulha Shan have ages that is difficult to reconcile. The tight clustering of CRN ages cluster around 69.777.8 ka (sample PR45 rejected), suggests that exhumation and weathering of the boulders 19.770.9 ka (sample PR45 rejected) and 15.970.9 ka. is unlikely to be the cause of the problem, and that our Samples PR45 and P53 have significantly older ages dates are realistic. It is difficult to assess the validity of than the rest of the population and we believe these may the radiocarbon dates because of the lack of specific be due to inherited CRNs. details presented in Zheng(1997) . However, the radiocarbon dates may represent an older moraine that was overridden duringan early Holocene glacial advance. 6. Discussion Richards et al. (2000a) and Benn and Owen (2002) describe such composite moraines in the Himalaya and The four research areas considered in this study help provide dates showingthat they may form over many illustrate the complexity of the glacial record throughout millennia and through multiple glacial cycles. Tibet. Each of the study areas has a relatively well- The CRN surface exposure dates for the Karola Pass preserved succession of moraines representingmultiple study area are tightly clustered, showing that the three glaciations. In addition, the extent of glaciation in the ARTICLE IN PRESS 1404 L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411

0 0 (A) Gonga Shan (B) Karola Pass GS6 GS5

2 GS8 GS9 4 PR31 PR32 PR33 PR34 Mean GS1 GS2 GS3 GS4

4 GS7 Neoglacial moraines Little Ice Age 8 moraine 6 12 Mean PR35 PR36 PR37 PR38 Mean CRN Age (ka) CRN Age (ka) GS14 GS15 GS11 GS10 GS12 8 GS13 Local LGM Post-glacial PR39 PR40 PR41 PR42 Mean 'Recessional' outwash moraine 16 10 terrace

GS17 GS19 GS19R GS20 GS20R No formal names Local LGM moraine 20

0 0 (C) Western Nyainqentangulha Shan (D) Tanggula Shan Zhajiazangbo Bashico Glacial Stage Glacial Stage 20 M1b 50 PR48 PR49 PR50 PR51 Mean 40 unnamed PR43 PR44 PR45 PR46 PR47 Mean 100 PR62 PR63 PR64 PR65 PR71 PR72 PR73 PR74 PR75 PR55 PR52 PR53 PR54 Mean 60 Mean M1a

150 PR66 PR67 PR68 PR69 PR70 80 CRN Age (ka) CRN Age (ka) PR81 PR82 200 PR80 PR57 PR61 PR77 PR76 PR58 PR59 100 Mean Mean Tanggula Glacial Stage

120 250 PR78 PR79

Fig. 10. CRN 10Be surface exposure dates for the moraines dated from each of the study areas. In part A, 10Be CRN surface exposure dates are also presented for the glacioﬂuvial terraces that were dated in the Moxi valley on the eastern slopes of Gonga Shan. The boxes enclose sets of CRN dates that were collected from the same moraine ridge. The mean values that are shown refer to the mean of the data in the adjacent box and the error bar is expressed as 1s: Samples GS19R and GS20R are repeat dates of samples GS19 and GS20 from the same boulder.

Gonga Shan, Karola Pass and western Nyainqentang- The Karola Pass is in a transitional zone between the gulha Shan is very similar for each successively older set monsoon-influenced and the semi-arid interior. This is of moraines. Nevertheless, the ages obtained from these reflected in the fact that the oldest moraines in this moraines are remarkably different. Furthermore, the region are intermediate in age between the other regions. moraines in the Tanggula Shan show markedly more The difference in the ages of the moraines between extensive glaciations than in the other three study these study areas suggests that preservation and/or style regions and are far older than those in other regions. of glacial advance differs markedly throughout Tibet. These observations lead unavoidably to the conclusion For example, moraines in monsoon-influenced regions that morphostratigraphy and relative dating techniques are more likely to be eroded by intense fluvial and mass should only be used with extreme caution when movement processes, while those in semi-arid regions reconstructingregional correlations in the Himalayan– appear to have been subjected to only minor geo- Tibet region. It is understandable, therefore, that morphic modification, mainly consistingof weathering moraines such as those on the Karola Pass have been processes. assigned to the wrong glacial ages. Our results highlight The fact that usually only 3–5 sets of moraines are the need for intensive numerical datingstudies in any generally present within our study areas might be a new research area within the Himalayan–Tibetan region result of randomness and obliterative overlap as because of the demonstrably strongregional variability. suggested in Gibbons et al.’s (1984) probability model The new chronologies presented here show that the for the survival of moraines in a succession of glacial ages of the deposits of the oldest preserved glacial advances. However, the regional pattern we describe advance become progressively older as one moves from and illustrate in Fig. 11, suggests that successions of monsoon-influenced to semi-arid regions of Tibet. Thus, moraines within the Himalaya and Tibet are not the only Holocene moraines are preserved in the wettest result of random preservation. Moreover, preservation regions (Gonga Shan), while the oldest moraine succes- potential by itself does not adequately explain the sions occur in the semi-arid regions of central Tibet, observed pattern because if it did, some evidence of namely the Nyainqentanggulha and Tanggula Shan. earlier glacial advances, such as valley form and/or ARTICLE IN PRESS L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411 1405

MIS 4 MIS MIS 5 MIS MIS 3 MIS MIS2 MIS1 2400 Qilian Shan 10 mm 50 mm 500 mm 100 mm unnamed 800 mm unnamed i ). The color bars in (C) unnamed La J Mountains + NE Tibet Halong Anye- maqen Anye- maqen Qiemuqu + Owen et al., 2001, 2002a,c, 2003a,b,c Jiukehe and glacial chronologies that have been Nianbo- yeze ; Ximencuo + + lar colors to the bars. Meriaux et al., 2004 200 * M1 M2 No numerical dating to confirm age of glacial stage + Duration of glacial stage is poorly defined h name indicates that no numerical datinghas >110 ka Sulamu N Tibet unnamed unnamed + + + * * Puruo- gangri Moraine Moraine V Moraine Moraine IV Moraine Moraine III * + + + Mean January Precipitation Mean July Precipitation han Bashico Tanggula Tanggula S unnamed ~160 to 200 ka Tanggula Central Tibet (B) + + Moraines I & II Moraines + Richards et al., 2000a,b 2 , unpublished data; H1 0 1a 1b ; M M M M M 50 ainqen- 400 700 500 200 100 300 600 800 > 132 ka 2000 1000 2800 1400 2400 1200 1600 4000 3200 Ny tanggulha 10870 H2 10000 M Gonga Litang unnamed precipitation precipitation (mm) Mean annual o o o o Gonga Shan * unnamed S and SE Tibet 25 N 40 N 35 N 30 N Phillips et al., 2000 Nianboyeze Barnard et al., 2004a ; o ; Karola Pass unnamed unnamed unnamed Y. Dhaulagiri Y. 105 E ampu Litang Nauri Ghasa

Kanchen- junga Himal undefined Tandung Tandung Dhaulagiri & D o I Thyangboche E Transhimalaya 100 E Thyang- boche II Thuklha I Periche Periche II Periche Chhukung Khumbu Himal + Zech et al., 2003 Lobuche & historical Lobuche ; Anyemaqen Langtang Himal Gora Gora & Tabela Lama undefined Lirung Langtang + o + Yala I & II Yala Sharma and Owen, 1996 95 E Gorkha Himal unnamed unnamed unnamed unnamed * Kulti o Batal Finkel et al., 2003 Lahul Himalaya undefined Chandra 90 E ; Sonapani I & II

Nanda Devi unnamed unnamed unnamed o Bhagirathi + 85 E Kedar Shivling Garhwal Himalaya Western and central Himalaya Nyainqentanggulha Yi et al., 2002 ; Kalam 1 Gabral 2 Gabral Swat Himalaya + + + o + + + + + 80 E arbat) Kar Leh Middle Indus Valley (Nanga P Gangotri & Bhujbas Indus Valley MIS-6 MIS-8 unnamed unnamed unnamed unnamed + ar Kar Leh 'Kulti' Indus Valley 'Batal' MIS-6 MIS-8 Ladakh Zansk o + + + + + 75 E 'Kulti' Tsukamoto et al., 2002 'Batal' Middle Indus Valley Zanskar unnamed unnamed unnamed ; unnamed + * Karola Pass Puruogangri Tanggula o Borit Jheel tages unz & Batura Hunza Valley 70 E Ghulkin II Ghulkin I Ghulkin Y Shanoz S undefined Pasu I & II Pasu Western Transhimalaya * * + + Pr e t Drosh Barum Chitral Shandur fer et al., 2001 ¨

90 40 50 70 80 10 20 30 60 Age (k Age a) (A) (C) Qilian Sulamu Hunza Chitral Swat Nanga Parbat Ladakh Zanskar Lahul Garhwal Nanda Devi Gorkha Langtang Khumbu La Ji Kanchenjunga Scha represents the likely duration ofbeen each undertaken glacial advance to and confirm the an name age of each and glacial the stage duration has of been the inserted into glacial the is box. poorly An defined, asterisk and respectively. cross A after tentative eac correlation is suggested by applying simi submitted; numerically dated throughout the Himalaya and Tibet (data from Shiraiwa, 1993; Fig. 11. The contemporary mean annual (A) and mean January and July (B) precipitation across Tibet and the bordering regions showing (C) the locations ARTICLE IN PRESS 1406 L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411 buried tills, should still persist beyond the maximum As highlighted by Finkel et al. (2003), glacial extent of younger surviving moraines. In Gonga Shan, advances can be broadly regionally correlated through- for example, the valley form changes abruptly from a out the Himalaya. Our new data presented here, and the broad u-shape to a gorged box-shape beyond the early data compilation summarized in Fig. 11, suggests this Holocene moraines. This strongly suggests that the early broad regional correlation can be extended across Tibet. Holocene glacial advances in the monsoon-influenced It is apparent that glacial advances occurred during the regions may have been at least as extensive as the Little Ice Age, Neoglacial, Middle Holocene, early Pleistocene glacial advances. This conclusion is consis- Holocene, Lateglacial Interstadial, 15 ka (Heinrich tent with Zheng’s (1997) 20 ka radiocarbon dates from Event 1), global LGM, one/two advances during MIS 3, within the moraines dated in this study to the early early Last Glacial and an in earlier glacial cycles. Holocene if the moraines are composite, produced However, each of these glaciations is not represented in through the effects of several glacial advances. every region. In the wettest regions only the Holocene Glaciation in the strongly monsoon-influenced Hima- moraines survive. Multiple glaciations on sub-Milanko- laya shows similar patterns to those found in the Gonga vitch timescales are supported by the ice core work on Shan. In the wettest monsoon-influenced regions the Dunde and Guiliya ice caps in NW Tibet (Thomp- (42400 mm a1), such as Nanda Devi and Langtang, son et al., 1989, 1997). Fig. 12 plots all published 10Be for example, only Holocene and Lateglacial moraines CRN dates for boulders on moraines, includingthose in are present (Barnard et al., 2004b and submitted). In this study and compares them with the January and contrast, the driest regions of the Himalaya and June insolation curves for the last 400 ka. This compila- Transhimalaya, such as Ladakh, preserve extremely tion clearly reveals the greater abundance of young ages old moraines (4300 ka; Owen et al., submitted). In (Holocene and particularly late Holocene) that probably regions such as the Hunza valley and Khumbu Himal, reflects the greater preservation of younger moraines. which are close to the limits of monsoon influence, with Nevertheless, distinct clusters of 10Be CRN ages are annual precipitation in the range of 500–1000 mm, evident, such as duringthe Neoglacial, Early Holocene evidence for at least eight glacial advances during the and Heinrich Event 1. Clusteringof 10Be CRN dates for last glacial cycle is preserved, and the maximum extent the global LGM and MIS 3 is less evident, and dates of glaciation occurred during the early part of the last prior to MIS 4 are sparse. glacial cycle (Owen et al., 2002a; Finkel et al., 2003). The Our new data supports the views of Owen et al. Karola Pass, which is in a similar transitional zone, is (2002a, 2003c) and Finkel et al. (2003) that glaciation somewhat unusual because it preserves evidence for only throughout the Himalaya and Eastern Tibet is strongly four glacial advances (including the Little Ice Age controlled by precipitation changes related to oscilla- moraines that were not dated in this study) datingback tions in the South Asian monsoonal system combined to the global LGM. However, Zheng(1997) cites with coolingthat is broadly associated with Heinrich evidence of older moraines that we were unable to find events. Beyond the heavily monsoon-influenced regions on the eastern side of the pass. In the Macha Khola (with annual precipitation 52000 mm), the local last valley (Gorkha Himal, Nepal), Zech et al. (2003) glacial maximum occurred early in the last glacial cycle. showed that moraines formed duringMIS 3–4 (or This observation supports the views of Gillespie and earlier), MIS 2, Lateglacial, mid-Holocene and Late Molnar (1995) and Benn and Owen (1998) who Holocene. The local last glacial maximum occurred suggested that glaciation in the Himalaya and Tibet duringMIS 3–4 (or earlier), but the Macho Khola was asynchronous with the maximum extent of the glacier during MIS 2 was almost the same thickness as it Northern Hemisphere ice sheets. In particular, it was duringMIS 3–4 (or earlier). Zech et al.’s (2003) appears that in many regions, such as the Hunza valley, study adds complexity to our proposed pattern of Khumbu Himal and NE Tibet, glaciers reached their glaciation because the Gorkha Himal is close to the maximum extent duringthe insolation maximum of strongly monsoon-influenced Langtang Himal where MIS 3 (cf. Figs. 11 and 12). Usingother proxy data, only Holocene moraines are preserved. The pattern of includinglake records and palynology, Shi et al. (2001) moraines in the Macha Khola valley might reflect emphasized the fact that MIS 3 was a time of enhanced preservation, but it might also indicate that the climatic monsoon moisture supply to Tibet. Hence, at high conditions in the valley are transitional between the altitudes, snowfall would have increased and glaciers wetter regions of the Langtang and the drier Transhi- expanded. However, a glacial advance during MIS 3 is malaya where evidence for older glaciations is preserved. not recognized in the data for the new study areas Given such complexity, we stress the need for more discussed here. Rather, the CRN ages cluster at about extensive studies of the glacial geology of other areas 70 ka, albeit not very tightly, in the case of the throughout Tibet and the bordering mountains to test Nyainqentanggulha and Tanggula Shan, suggesting that the apparent regional variability in timing and extent of glaciers may have advanced during the latter part of glaciation. MIS 5 or even MIS 4. Unfortunately, CRN datingis ARTICLE IN PRESS L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411 1407 n = 304 n = 334 , submitted). The duration of 10 Be CRN sample per 5 ka 10 Number of Be CRN sample perNumber 1 ka Barnard et al., 2004a,b ; 0 5 10 15 20 25 30

Be CRN dates on moraine boulders that have been published

0 5 Number of 10 10 15 20 25 30 35 40 45 50 55 60 65 70 Time (ka) Time n = 412 0 102030405060 Finkel et al., 2003 ; 0 50

100 150 200 250 300 350 400 June Insolation January Insolation Insolation difference between January and June Time (ka) Time ) compared with the fer et al., 2001 ¨ Scha o 5d N Berger and Loutre, 1991 , submitted; o MIS-9c MIS-7e MIS-5e MIS-5a t Holocene MIS-4 30 MIS-3 MIS-2 . Insolation (W/square m) 175 225 275 325 375 425 475 525 575 0

20 40 60 80

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 June Insolation January Insolation Insolation difference between January and June Time (ka) Time Winograd et al. (1997) Owen et al., 2001, 2002a, 2003a,b,c June Insolation Difference between January and June Insolation ; N for the last 400,000 years (data taken from 1 o N and 30 MIS-9c MIS-7e 1 MIS-5e 60 N MIS-5a to 5d Holocene MIS-4 MIS-2 MIS-3 Phillips et al., 2000 Insolation (W/square m) January Insolation 0 50 100 150 200 250 300 350 400 450 500 550 0

20 40 60 80

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 Time (ka) Time Fig. 12. Insolation curves for 60 interglacials that are colored light brown are taken from for the Himalaya (data from ARTICLE IN PRESS 1408 L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411 presently not precise enough to allow us to determine insolation values for MIS 8 were not unlike those of whether glaciers advanced in response to increased the last glacial cycle, yet more extensive glaciations insolation duringMIS 5c or 5a or to coolingduringMIS occurred in Ladakh (Owen et al., unpublished data). 4, synchronously with the Northern Hemisphere ice Therefore, the different patterns of insolation between sheets. These regions are on the distal margins of glacial cycles cannot simply explain the changing styles monsoon influence and might have responded more of glaciation during the last few hundreds of thousands readily to changes in the Northern Hemipshere ice years. sheets and oceans. As Scha¨ fer et al. (2001) pointed out, the presence of Throughout all the regions of the Transhimalaya and moraines that antedate the last glacial cycle in the Tibet, glacial advances during the global LGM appear Tanggula Shan provides evidence that an extensive ice to have been very restricted in extent, generally having sheet, as proposed by Kuhle (e.g. 1985, 1988, 1991, and been limited to o10 km beyond the present ice margins 1995), could not possibility have existed on the Tibetan (cf. Owen et al., 2002b). In the Nyainqentanggulha Plateau duringthe last glacialcycle. Had such an ice Shan, the LGM advance limit lay within only a few sheet developed, the glacial landforms and associ- kilometers of the present ice margins, while in the ated boulders from earlier glaciations would have Tanggula Shan it must have been significantly less than been eroded away. Furthermore, Kuhle used the the extent of the Bashico Glacial moraines that lie presence of moraines at low altitudes alongthe margins 10 km from the present ice margin and date from of the Tibetan Plateau and in the borderingmountains 70 ka. The restricted advance duringthis time may to support his ice sheet proposal. However, many of have been a consequence of reduced monsoon precipita- the moraines used in Kuhle’s ice sheet reconstructions tion duringthis insolation minimum. Duringsuch times, occur in the monsoon-influenced regions; many of snowfall at high altitudes would be reduced and would these are Holocene in age and are a consequence severely restrict the ability of glaciers to persist at lower of high moisture flux delivered by the south Asian altitudes. On the other hand, temperatures on the summer monsoon to the high mountains that border Tibetan Plateau lowered by 8–9 1C compared to the the Tibetan Plateau. present (Shi, 2002) would have made possible some In summary, there is a general synchroneity in the glacier advance to lower altitudes, albeit of limited timing of glaciation in the monsoon-influenced regions extent. of the Himalaya and Tibet, but within the semi-arid The extensive early Holocene advance in the wettest regions beyond monsoon influence, glacial advances regions and evidence of its presence, albeit moderated, may be asynchronous, movingin synchrony with the in most of the other study regions through the Himalaya Northern hemisphere ice sheets, possibly under the and Tibet (Fig. 11) further support the case for strong influence the mid-latitude westerlies. Strongregional monsoonal control. Duringthis insolation maximum variations in the extent of glaciation occur throughout (Fig. 12), increased precipitation fallingas snow at high the region. Such variations in extent have yet to be altitudes would have produced positive glacier mass systematically quantified by such techniques as recon- balances resultingin glacieradvance. The reduced struction of equilibrium-line altitudes (ELAs). How- insolation duringthe winter would have also contrib- ever, as Benn and Lehmkuhl (2000), Owen and Benn uted to the positive glacier mass balance. (2005) and Benn et al. (2005) emphasize, reconstruc- Glaciation in the Tanggula Shan was more extensive tions of former ELAs in high altitude environments in the penultimate glacial cycle than during the last are rife with problems owingto thick supraglacial glacial cycle. This situation is similar to that observed in debris cover, and extreme microclimatic and topo- other semi-arid regions such as Ladakh and the graphic variability within individual regions. Regional westernmost Nyainqentangguhla Shan (Owen et al., correlations can be adequately achieved only by detailed submitted; Lehmkuhl et al., 2002). Progressive diminu- numerical datingstudies within individual areas be- tion of glacial extent over several glacial cycles is cause, given the strong topographic and climatic difficult to explain, but might indicate progressive gradients, severe errors can arise if only morphostrati- reduction in moisture supply as continued mountain graphic correlation and relative weathering studies uplift reduced the influence of moisture sources such as are relied on. Furthermore, the precision and accu- the south Asian monsoon and/or the mid-latitude racy of CRN and CSN surface exposure datingis westerlies. Alternatively, this pattern might reflect subtle not good enough at present to test the synchronuity changes in insolation over individual glacial cycles. For of glacial events on sub-millennial scales for the example, summer and winter insolation were higher and Holocene and Lateglacial, and on sub-Milankovitch lower, respectively, duringthe penultimate glacialcycle scales for pre-LGM times. Improvements in methodo- compared to the last glacial cycle at 301N(Fig. 12). This logies and further dating studies promise to refine pattern might have driven more extensive glaciation the hypotheses and conclusions presented in our duringthe penultimate glacialcycle. However, the study. ARTICLE IN PRESS L.A. Owen et al. / Quaternary Science Reviews 24 (2005) 1391–1411 1409

Reconstructions of the timingand extent of Late Himalaya. We therefore believe that glaciation through- Pleistocene glaciers in Tibet and the Himalaya are out Tibet and the Himalaya is strongly influenced by fundamental for improved understandingof the links orography that, in turn, strongly influences climate. between climate change, glaciation and hydrology. Recent model results suggest that anthropogenic forcing (e.g. greenhouse gas, land-cover change) is important in Acknowledgements controllingvariations in the Asian monsoon ( Wake et al., 2001), which, in turn, affects glaciation and We would like to thank the Pacific Rim Program of surface hydrology, changes which could have profound the University of California for fundingour fieldwork. affects on large human populations. While, the variation This work was performed under the auspices of the US in glacial style shown in this study adds to the Department of Energy by the University of California, complexity involved in modelingand predictingfuture Lawrence Livermore National Laboratory, under glacial and hydrological change, it does provide a Contract No. W-7405-Eng-48 as part of an IGPP/ workingframework with which to beginthe process of LLNL research grant. Particular thanks to Douglas examiningmore closely the connections between atmo- Benn and John Gosse for their constructive and helpful sphere, cryosphere and hydrosphere in the high moun- reviews of our paper. tains of central Asia. References

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