Quaternary International, Vol

http://www.paper.edu.cn Quaternary International, Vol. 45/46, pp. 135-142, 1998. ~ i Pergamon Copyright © 1997 INQUA/Elsevier Science Ltd Printed in Great Britain. All rights reserved. PII: S 1040-6182(97)00011--6 1040-6182/98 $19.00

THE SEQUENCE OF QUATERNARY GLACIATION IN THE BAYAN HAR MOUNTAINS

Zhou Shangzhe and Li Jijun Quaternary Glacial and Environmental Research Center of China, Lanzhou University, Lanzhou 730000, China

Four periods of Quaternary glaciation in the Pleistocene have been found in the area of the Bayan Har Mountains. They represent, respectively, the two stages of the Last Glacial age; the penultimate ice age, and an earlier ice age. During the late stage of the Last Glacial age, glaciers developed only near the mountain ridges of the Bayan Har. In the earlier stage, glaciers expanded down to the piedmont of the Bayan Har Mountains and were as much as 40 km long. In the penultimate ice age, an extensive ice cover developed, depositing an areally widespread till sheet. Erratics were transported 60 km from Bayan Har peak to Qingshuihe town to the south, and to Yematan land to the north. Granitic erratics are also distributed over elevated geomorphological positions, such as Chalaping Ridge. The area of ice cover encompassed up to 50,000 km2. Furthermore, evidence including glacial landforms and sediments shows that a larger glaciation existed in this area in an earlier time, possibly during the third most recent (ante-penultimate) glaciation. The scale of this glaciated area is greater than those of the more recent events in the Qinghai-Xizang Plateau, extending over 80,000 km2. This glaciation covered the source area of the Yellow River from Xingsuhai in the west to Duogerangtan in the east, including the areas of Gyaring and Ngoring lakes. Based on the extent and locations of the glaciations, the Bayan Har Stage and Galalahai Stage of the Last Glacial age; the Yematan Ice Age; and the Huanghe Glacial Age can be recognized. © 1997 INQUA/Elsevier Science Ltd

INTRODUCTION Mountains is 5268 m a.s.1, and is located at 34°15'N, 97°30'E. The Bayan Har Mountains also represent the The Qinghai-Xizang (Tibet) Plateau, termed 'the roof initial watershed between the Changjiang (Yangtze River) of the world', is the focus of more and more attention and the Hwanghe (Yellow River) (see Fig. 1). because of its important position in global change The orientation of the Bayan Har Mountains is research. The problem of Quaternary glaciation on this controlled by two fault groups, with a north-northwest plateau is always one of the focal points. Whether the alignment. The mountains are composed of gray-green entire Qinghai-Xizang Plateau was covered by a large ice feldspathic sandstone, slate, and limestone of the Bayan sheet in the Pleistocene, or alternatively if a model of Har Group. Near the summit is an exposure of granite. limited glaciation is more realistic, has been disputed The Bayan Har area is one of the two lowest heatedly in recent years. Some geographers did their temperature centers in the Qinghai-Xizang Plateau (the utmost to propose the viewpoint that the plateau was other is the HoH Xil area), because temperature is covered completely by a large ice sheet during the Last controlled by the Mongolian High pressure system in Glacial Maximum (Kuhle, 1987). However, most scien- winter and by the establishment of the Southeast Asian tists suggest that the viewpoint of Kuhle is not convin- Monsoon system in summer. Precipitation during the cingly documented, because only evidence for montane latter period makes this area the most humid center in the glaciers and ice caps has been found on the plateau (Shi inland plateau region. For example, the annual precipita- Yafeng et al., 1991; Derbyshire et al., 1991). Recent work tion is 300-400 mm in Madoi, four times more than in the in the Bayan Har Mountains (Fig. 1) is significant for the HoH Xil area in the interior of the plateau. resultion of this dispute.

BAYAN HAR IN THE LAST GLACIAL AGE BAYAN HAR MOUNTAINS Many big rivers diverge from the summit section of the As the source area of the Yellow River, the Bayan Har Bayan Har to Changjiang and Huanghe. The valleys Mountains are known worldwide. The mountains lie in display typical glacial U-shaped cross-sections, and well- the eastern part (33o-35 ° N, 95°-101°E) of the Qunghai- defined moraines are preserved. The Galala River Xizang Plateau, oriented northwest-southeast, and a originates between Bayan Har summit and Bayan Har relative relief of about 1000 m above the plateau surface Pass, and flows initially to the northeast, then to the north. (4300 m a.s.l.). They extend discontinuously approxi- It is a great glaciated valley. The valley mouth and the mately 600 km, from east of Kunlun Pass to the western area directly below are flanked by large moraines along edge of the Zoige Basin. The summit of the Bayan Har both sides. The moraines extend downwards to 4400 m IThe project was aided financially by National Natural Science elevation, where Galala Lake, with an area of 24 km 2, is Foundation of China. impounded by the moraines. The Heihe River, which

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flows out of the lake, is a tributary of Huanghe. The these valleys at 4406 m elevation. The end moraine is moraines have heights of 100--200 m, with distances of 120 m high. The distances from the moraine to the 8-10 krn between the two sides. The terminus of the headwaters of the three branches are 56 km, 46 kin, and moraines is 44 km from the headwaters, indicating that a 50 km, respectively, indicating the occurence of large, huge valley glacier developed in the past. At the mouth of coalescing mountain glaciers. These glacial valleys and the valley, at 4507 m a.s.l., there is another end moraine. sediments demonstrate the northeastern part of the which has been eroded by the river, and above the glaciation affecting Bayan Har during the last glacial moraine there are numerous small lakes. The upper age. Above 4580 m elevation, where the three branches moraine is 21 km from the headwaters, showing that the join, smaller moraines are evident from topographic glacier also stopped here for a long time, and thus maps. Similar situations are found in the north and the represents another glacial event. southeast. West of Galala River are other rivers, including Across Bayan Har Pass along the Qingkang Highway, Gaerlawang, Lelahewang, and Lela rivers, which also the headwater region of the Zhaqu River, the upper flow in glaciated valleys. The Lela River, flowing to segment of Yalongjiang, is located. This river also flows Nyoring Lake, is the largest of these streams. As in the through a large glaciated valley, and till deposits can be Galala valley, moraines are present in these glaciated seen everywhere. The terminus of the last glaciation troughs. Together, these troughs and moraines, including appears to have been near Zhalagou. those of the Galala valley, constitute the glaciation system In addition to the main peak of Bayan Har Mountain, of the north slope of the summit section of Bayan Har. there exist other relics of the last glaciation in the area. Laqu Mr. (5175 m a.s.1.) and Zengbugongmazha Mt. For example, 75 km south of the Bayan Har summit, is (5226 m a.s.1.) are located 60 km southeast of the summit. Sexichayima (5131 m a.s.1.), around which very typical The Baeangchun River, a tributary of Yalongjiang, flows valleys and moraines are distributed. At the west bank of southward from this area. In this valley, thick till deposits Zhaqu, near Sexichayima, a large glacial deposit is are well preserved. The lateral moraine is up to 200 m in present, and glacially striated stones are extremely height. The Baeangchun consists of two branches. The common in this till. The moraines are tens of metres in glacier responsible was a composite feature, and the height, and the deposits originated from the mountains moraine formed from the confluence is approximately along the north bank of the Tongtian River. The glacial 300 m high. It is 33 km from the end moraine, situated at valleys are more than 20 km long. 4400 m a.s.l., to the headwater area. Relatively smaller In the west section of the Bayan Har is another moraines can be found at 4600 m in the two tributary important center of glaciation. In this area, where valleys, and above these moraines are many small lakes. elevations exceed 5000 m and the highest peak, Gong- These glacial relics represent the glaciation system of the malongzangu, reaches 5336 m a.s.l., many glaciated southest slope of the Bayan Har summit section during valleys are distributed normal to the northwest-southeast the last glacial age. topographic divide. These glaciated troughs extend l0 to Another large branch of Huanghe in this area is Requ, 15 km from the plateau summits. In addition, between which flows to Huanghe to the east of Yematan after Gyaring Lake and Qumarleb County, mountainous areas meeting the Heihe. Its upper section is named Chaqu, and higher than 5000 m a.s.1, display glaciated valleys, originates from three tributary streams which rise undoubtably the products of the last glaciation. respectively to the east of Bayan Har Pass, and from The evidence from these well-preserved topographic two other summits at 5249 m and 5175 m a.s.l. These features and glacial deposits in the Bayan Har Mountains valleys were also glaciated. Preserved moraines remain in indicates that: 中国科技论文在线 http://www.paper.edu.cn The sequence of quaternary glaciation in the Bayan Har mountains 137 all of the mountains which contain evidence of the last Highway from Bayan Har Pass to Qingshuihe (4400 m). glaciation have summits in excess of 5000 m a.s.l.; during Qinshuihe is a small town built on till. Granite erratics the last glaciation, the glaciers of the Bayan Har formed present were transported from near Bayan Har summit, confined alpine valley ice; and more than 60 km away. Along the highway are splendid in the largest mountain areas (such as the Bayan Har till sections, such as that at milestone 552. Undoubtedly, summit), evidence for two distinctive glacial phases these erratics and till deposits are the products of the during the last glaciation can be found. These undoubt- Yematan glacial age. About 20-40 km south of Qing- edly represent the two stages of the Last Glacial age, shuihe is Sexichayima Mountain and the north bank of the separated by an interstadial. As the early stage is Tongtian River, discussed above. Thus, large glaciers represented in the Galala Lake area, it is here termed must have developed during the Yematan Glacial age and the Galala Stage. As the glaciers of the second stage formed a large ice cover in coalescence with those of appear to have developed only adjacent to the ridge of the Bayan Har, as is apparent from many geomorphologic summit of Bayan Har, this is termed the Bayan Har Stage. phenomena (Zhou Shangzhe et al., 1994). The snowlines for the two stages are located at 4650 m Analysis of remotely sensed images indicates that the a.s.l, and 4750 m a.s.l., respectively. northern border of the Yematan glaciation extends from Yematan westward to the south shores of Ngoring and Gyaring lakes. Shiqu County, in Sichuan Province, was YEMATAN GLACIAL AGE also covered by a large ice cap at this time. The total area was approximately 50,000 square kilometers. Thus, South of four smaller lakes near Madoi, the Heihe during the Yematan glacial age, extensive ice cover flows out of Galala Lake and formed the Heihe Valley. existed in the Bayan Hat area. This valley is also called Yematan ('wild horse grass- The age of the Yematan glaciation was most probably land'). Yematan was formed by aggradation of fluvial- associated with Marine Oxygen Isotope Stage 6. A lacustrine sediments throughout the late Quaternary. Drill sample from the fluvio-lacustrine sediments overlying hole data indicate that the sediment thickness exceeds the Yematan till and erratics, obtained from 132 m depth, 200 m (Wang Shaoling, 1991). Some small lakes remain was 14C dated at 50,000 BP. As the deposit is thicker than in the valley, with Jiangmeng being the largest in area at 200 m, and the sedimentation rate was higher in the basal 6 km 2. A large number of erratics are distributed along layers (Wang Shaoling, 1991), the underlying erratics and the southern marginal foothills of the basin, at 4260 m till were deposited at least 10,000 years prior to 50,000 a.s.1. Till deposits, and glacially striated clasts, are also BP. At Yeniu River bank, 6 km south of Yematan, a large present. The position of the till deposits indicates that section 13 m high contains alternating gravel and silt-clay continued aggradation by modern geomorphic processes beds. The gravels contain flatiron, facetted, and striated will eventually result in their burial, and it can therefore erratics. The geomorphology and stratigraphy suggest that be assumed that the glacial sediments are present in the the gravels are ice-contact deposits, as the units are valley floor, extending beneath the fluvial-lacustrine adjacent to till deposits and granite erratics of Yematan deposits (Fig. 2). The erratics are mainly composed of age. Thermoluminescence dating of the uppermost silt granite from near the Bayan Har summit, 60 km distant layer in this section yielded an age of 133±23 ka BP. from Yematan. The granite erratics are distributed from Therefore, these data suggest that the Yematan glacial age higher elevations, such as Chalaping (4650 m a.s.1.) to was the penultimate ice age, corresponding to Oxygen Yematan. Between the Yematan and the Bayan Har Isotope Stage 6 of the deep sea record. summit are undulating glacial hills. In the northern part of Yematan, including Madoi, glacial deposits are not present. Thus, the Yematan glacial HUANGHE GLACIAL AGE deposits appear to represent the margin of a glaciation, and hence the episode responsible is termed the Yematan Prior to the Yematan, a previous glacial event glacial age. appears to have involved a larger extent of ice cover. Along the south slope of Bayan Har, erratics and till Although no glacial sedimentologic evidence is present deposits can be found everywhere along the Qingkang in the Madoi area, glacial landforms are faintly

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12 BuerhanbudaMtns. Glaciatedland ~'~ River http://www.paper.edu.cn 13 BuqingMtn. Shiqu EndMoraine A Peak 14 Laqu Mtn. AAA Erratics 15 NyoringLake 16 GyaringLake ~A Tilldeposit [] County 17 Chalaping 0 20 40 60 km. Pingo 18 Qumarleb I I I I 19 Xingsuhai 20 Duogerongtan

FIG. 3. Sketch map of glacial landformsand deposits in Bayan Har area. 中国科技论文在线 http://www.paper.edu.cn The sequence of quaternary glaciation in the Bayan Har mountains 139

apparent. The four lakes south of Madoi are elongated Sediments with granitic clasts are also present on in a north-south orientation. They are oriented normal mountain summits west of Xingsuhai. These data thus to east-west trending faults, and thus were not tectoni- indicate the existence of the Huanghe glacial age cally influenced. These lakes, short, wide, shallow, (Fig. 3). and straight, may be explained as glacial trough The reconstructed area of Huanghe glacial ice is features. Along the north shore of Gyaring Lake, there 80,000 km 2, according to the distribution of glacial are additional valleys similar to those of the Madoi features and erratics. It was a relatively small ice sheet, area, although they are much larger. Streamlined land- and the largest Quaternary glaciation noted in the forms of glacial origin differ from those formed by Qinghai-Xizang Plateau. Its north-south profile is shown fluvial erosion around the source area of Huanghe. in Fig. 4. Similar landforms are distributed over the south pied- Although there is no chronological data for the mont of Buqing Mountain, including all of the drainage Huanghe glacial age, previous investigations have basin of the uppermost reaches of Huanghe, from indicated that the Nieniexunla ice age represented the Yueguzonglie in the west to Duogerongtan in the east, largest glaciation in the Qinghai-Xizang Plateau (Li Jijun including the Gyaring and Nyoring lakes. In the south- et al., 1986). Thus, the Huanghe glacial age should east, these features extend to Shiqu County of Sichuan, correspond to the Nieniexunla ice age, correlated with and cover all the areas where the penultimate glaciation Marine Oxygen Isotope Stage 12. occurred. The earlier event exceeded the Yematan glaciatiuon to the north, and covered the area west of 99°E longitude in the valley of Huanghe. Thus, this glaciation is termed the 'Huanghe glacial age'. CONCLUSION The Huanghe glacial age is suggested by sedimento- logic as well as geomorphologic evidence. Near mile- Four glaciations are recognized in the Bayan Har stone 439 km of the Qingkang highway, between area: the Bayan Har and Galala stages of the Last Huashixia and Madoi, a 4 m thick section composed of Glacial; the Yematan ice age; and the Huanghe ice gravels and rock flour derived from sandstone of the age. Their extents are shown in Fig. 5. It seems that Bayan Har Group was excavated. The uppermost 1 m the Bayan Har area was most advantageous for the of the section has weathered to brown-yellow, whereas development of glaciation in the Qinghai-Xizang Pla- the basal part remains grey. Glacial erratics are present teau during the Quaternary. within the deposit, and the sedimentology and geomor- The mean altitude of the plateau surface adjacent to phology suggests that the unit can be interpreted as Bayan Har is approximately 4300 m. It increases in a lodgement till. Other till deposits are present near elevation from this area to the west, reaching approxi- Huashixia, marked by numerous striated clasts. This mately 5000 m in the hinterland of the plateau. So far as section is 150 km from the summit of Bayan Har, altitude is concerned, the hinterland of the plateau would 75 km from Anyemaqen Mountain and 60 km from seem to be more advantageous for developing Quaternary Buerhanbuda Mountain. The till deposits at Huashixia ice sheets. However, Kunlun Pass, 375 km west of were thus undoubtably formed by an extensive glacia- Madoi, shows only limited glaciation. Thus, the extent tion. Granite erratics were scattered on the western of the ice sheet during the Huanghe glacial age depended shores of Gyaring and Ngoring lakes, and at Xingsuhai. on the Bayan Har source area, and ice did not extend Albert Tafel noted in 1906 that till boulders had existed across the entire Qinghai-Xizang Plateau. between Huanghe and Shuga Rivers, along the upper Study of the modern climate of the Qinghai-Xizang section of the Colmud River (Xu Jinzhi, 1948). Plateau reveals that the Bayan Har area differs from

S 50 °w ------N 500 E Bayan Har Yellow River Tongtian River | / Ela Mt.

< 100 200 360 400 Distance (km) ~Bay~ Hat group (Sandstone slate) [~ Sandstone ~ Granite ~ BasicRock

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FIG. 4. Diagram showing the geological structure in SN direction across Bayan Har and the ice sheet profile. 中国科技论文在线

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~ Huanghe http://www.paper.edu.cn 12 Buerhanbuda Mtns. --] Lake 13 Buqing Mtn. me age 14 Laqu Mtn. 15 Nyoring Lake --~ River --] Town 16 Gyaring Lake 17 Chalaping ) 20 40 60km. 18 Qumadeb I I I I 19 Xingsuhai 20 Duogerongtan

qG. 5. The approximate scales of the glaciations in Bayan Har Area. 中国科技论文在线 http://www.paper.edu.cn The sequence of quaternary glaciation in the Bayan Hat mountains t41 other regions. In Bayan Har, air temperature is lower rain into this area, causing four times as much precipita- due to the influence of a cold air current from the north tion here in comparision to the inland plateau regions. As (Qing Tian, 1987). In winter, this area is controlled a result, the modern snowline increases from east to west by the Mongolian High Pressure system. In summer, on the plateau. It is 5000 m in elevation in the the hinterland of Qinghai-Xizang is more strongly Anyemaqen Mountains, 5400 m a.s.1, in Kunlun Pass affected by plateau effects than its marginal areas, (35°40'N, 90°00'E), and 5800 m a.s.1, in the HoH Xil inducing thermal modification. The source area of region within the plateau hinterland. Huanghe is always colder throughout the year than is Although the Qinghai-Xizang Plateau has been the hinterland (Fig. 6). extensively uplifted through the Late Quaternary (Li Precipitation (30(000 mm) in the Huanghe source Jijun et al., 1979), the monsoonal pattern was estab- area also exceeds values in the inland areas of the plateau. lished earlier, in the Middle Pleistocene (Li Jijun, This is due to the influence of the southwest monsoon. 1991). Thus, atmospheric circulation has apparently not Tropical air masses from the Bay of Bengal bring much exchanged since the Huanghe glacial age until the

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FIG. 6. Air temperature distribution (°C) on the northern part of the Qinghai-Tibet Plateau Bayan Hat region: A, mean summer temperature; B, mean winter temperature; C, deviation from model annual temperature. Value for the Bayan Hat region and the headwaters of the Huang He is 4°C below the regional mode. 中国科技论文在线 http://www.paper.edu.cn

142 Z. Shangzhe et aL present. During the last glaciation, the snowline stood REFERENCES at 4600 m a.s.1, in the Anyemaqen Mountains, Derbyshire, E. (1991). Quaternary glaciation of Tibet: the geological 5000 m a.s.l, at Kunlun Pass, and 5500 m a.s.1, in HoH evidence. Quaternary Science Reviews, 10, 485-510. Xil (Li Bingyuan et al., 1991). All of these facts Kuhle, M. (1987). Subtropical mountain and highland glaciation as ice indicate that the headwater area of Huanghe was the age triggers and the waning of the glacial periods in Pleistocenc. Geo- most favorable for the development of large-scale Joural, 131(6). Li Bingyuan et al. (1991). Quaternary Glacial Distribution Map of glaciers on the Qinghai-Xizang Plateau during the Qinghai-Xizang Plateau. Science Press, Beijing, China. Pleistocene, and also explain why the entire plateau was Jijun, Li (1991). The environmental effects of the uplift of the Qinghai- Xizang Plateau. Quaternary Science Reviews, 10, 479-483. not covered by a successively larger ice sheet during Jijun, Li (1992). Glacial relics of monsoonal Asia in the Last Glaciation. subsequent glaciations. Quaternary Sciences, 4, 332-340. Thus, in China as well as in Japan, the early stage of the Li Jijun et al. (1986). Glaciers in Tibet. Science Press, Beijing, China. Jijun, Li (1979). On the time,amplitude and form of uplift of Qinghai- Last Glacial was more favorable to glaciation than was the Xizang Plateau. Scientia Sinica, 6, 608--616. latest stage (Minato, 1972; Li Jijun, 1992). This pattern Minato M. (1972). Late Quaternary geology in Northern Japan. differs from that of North America and Europe, where the Radiocarbon Chronology, 24th I.G.C., Section 12, pp. 55--61. Qing Tian (1987). Climate and Weather of Qinghai-Tibet, pp. 92-104. scale of glaciation was larger during the latest stage (the Qinghai People's Press, Xining, China. LGM). In monsoonal Asia, the earlier stage is more Shi Yafeng et al. (1991). A controversy to M. Kuhle's ice sheet appropriately regarded as the Last Glacial Maximum. hypothesis. The Geomorph. N.F. Suppl. Bd, pp. 19-35. Berlin. Shaoling, Wang (1991). Schematic profile and stratigraphic meanings of Bore No. 4 at bank of Heihe River nearby Qing-Kang highway. Arid Land Geography, 14, 1-8. ACKNOWLEDGEMENTS Jinzhi, Xu (1948). The source section of the Yellow River. Acta Geographica Sinica, 15, 31-40. The authors are thankful to Prof. Nat Rutter for his working Shangzhe, Zhou (1994). A preliminary study on the local ice sheet of encouragement and English correction, to Prof. Cui Zhijiu, Prof. Nat Pleistocene in the source area of Yellow River. Acta Geographica Rutter, Prof. E. Derbyshire, Prof. Yugo Ono, Prof. Rein Valkae and Prof. Sinica, 49, 64-72. M. Kuhle for an academic excursion and discussion in the yellow River source area, to Prof. Shi Yafeng for his long concern with our work, and to Prof. Mark Talbot for the text editing and correction.