OSL Ages Revealing the Glacier Retreat in the Dangzi Valley in the Eastern Tibetan Plateau During the Last Glacial Maximum

Quaternary Geochronology 10 (2012) 244e249 Contents lists available at SciVerse ScienceDirect Quaternary Geochronology journal homepage: www.elsevier.com/locate/quageo Research paper OSL ages revealing the glacier retreat in the Dangzi valley in the eastern Tibetan Plateau during the Last Glacial Maximum Biao Zhang a,b,d, XianJiao Ou b,c, ZhongPing Lai a,b,* a Luminescence Dating Group, Qinghai Institute of Salt Lakes, CAS, 18 XinNing Rd, Xining 810008, China b State Key laboratory of Cryospheric Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China c School of Geography and Tourism, Jiaying University, Meizhou 514015, China d Graduate University of Chinese Academy of Sciences, Beijing 100049, China article info abstract Article history: Mountain glaciers are highly sensitive to temperature and precipitation fluctuations and, thus, the Received 14 October 2011 deposits of glacier growth and retreat constrain climatic variables. The Dangzi valley, located on the Received in revised form northern slope of Queer Shan Mountain, eastern Tibetan Plateau, is influenced by Indian monsoon and 19 January 2012 has preserved four integrated sets of moraines and associated glacial sediments. Numerical ages are Accepted 21 January 2012 scarce in this area, even though the moraines have been investigated for decades. In this study, dating of Available online 30 January 2012 the glacial tills and glaciofluvial deposits was undertaken using quartz optically stimulated luminescence (OSL). We conclude that: (1) OSL ages show good agreement with geomorphological features. The Keywords: OSL dating samples should have been well-bleached before deposition, otherwise it is rather impossibly that all the Moraines ages in the former three sets are overestimated to a similar degree due to poor beaching as the spatial Last Glacial Maximum (LGM) and temporal dynamics vary within glaciated valley. (2) Mountain glaciers have reached the maximum Dangzi valley extent at about 25e22 ka in Dangzi valley during the Last Glacial Maximum (LGM). Then the glaciers Eastern Tibetan Plateau retreated several times and formed the last terminal moraine at about 16.5 ka, which may indicate the termination of LGM on the eastern Tibetan Plateau. (3) The age of DZ307 (54.0 Æ 4.7 ka) demonstrates that the glacial advance also occurred at Marine Isotope Stage (MIS) 3, and that the glacial advance was larger in MIS 3 than in LGM, which is in agreement with previous results in the adjacent Yingpu valley. (4) The glacial evolution during the LGM in the study area was possibly controlled by the temperature changes, which could response to the summer solar insolation in northern hemisphere. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction on the range of glaciation on the Tibetan Plateau due to poor http://ir.isl.ac.cnchronological data (Kuhle, 1988, 1995; Zheng, 1989; Zheng and The Tibetan Plateau and the bordering mountains contain many Rutter, 1998). Within the last decade, two new techniques have glaciers outside of the Polar Regions, and extensive glacial sedi- promised to remedy this situation. The application of optically ments for past glaciations are still well preserved. These glacial stimulated luminescence (OSL) and terrestrial cosmogenic radio- deposits are particularly helpful for reconstructing palaeoclimate nuclide (TCN) methods has expanded the number of chronologies because mountain glaciers are dependent on regional climate as throughout the Tibetan Plateau and determined the timing and well as global condition and extremely sensitive to environmental style of glaciation in some key areas on the Tibetan Plateau and change (Derbyshire et al., 1991; Shi, 1992; Gillespie and Molnar, adjacent areas (Richards et al., 2000; Spencer and Owen, 2004; 1995; Owen et al., 2009). The use of glacial sediments as palae- Owen et al., 2008; Schäfer et al., 2008; Lai et al., 2009; Zhao oenvironmental proxy requires a temporal framework. During the et al., 2009; Xu et al., 2009, 2010; Ou et al., 2010). past several decades, relative dating methods, such as the use of As an important component of a broad scientificefforttounder- morphostratigraphy and relative weathering have been widely stand the Earth’s surface during the Last Glacial Maximum (LGM) used (Li and Su, 1996; Shi, 2006). Nevertheless, different views exist (CLIMAP Project Members,1981), the timing and style duringthe LGM glaciation on the Tibetan Plateau is still poorly defined (Lehmkuhl et al., 1998; Schäfer et al., 2002; Owen et al., 2002). Owen et al. * Corresponding author. Luminescence Dating Group, Qinghai Institute of Salt (2008) have recently assessed that the glacial advances in MIS 2 Lakes, CAS, 18 XinNing Rd, Xining 810008, China. Tel.: þ86 (0) 971 6330670; were less extensive than those in MIS 3. Schäfer et al. (2006) sug- fax: þ86 (0) 971 6336002. E-mail address: [email protected] (ZhongPing Lai). gested that large-scale retreats of mid-latitude LGM glaciers 1871-1014/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.quageo.2012.01.013 B. Zhang et al. / Quaternary Geochronology 10 (2012) 244e249 245 commenced at about the same time in both hemispheres. However, defined sets of terminal moraines are preserved with an average the evolution of any history of the mountain glaciers on the Tibetan height of 3e7 m in the outer and inner parts of the Dangzi valley at Plateau during the LGM is still an open question. Moreover, the an altitude of 3985e3866 m asl (Fig. 2). Boulders, some of which are responses of glacial activity to climate change at the LGM have extremely large, scattered widely across the surface of these remained perplexing. The key point to solve this question is to find out moraines and between the four sets. Evidence for the first set suitable terminal moraine sequences that document high frequency comprises only a single prominent terminal moraine that are glacial fluctuation at the LGM. In this study, we obtained new data closely linked and located near the outlet of Dangzi Lake. This about glacial history at the LGM using OSL for the eastern margin of moraine was influenced by river incising, so that it can be clearly the Tibetan Plateau. Our discussion is based on the combination of seen that glaciofluvial sediments were deposited near the terminal geomorphological relationship, OSL chronologyand reconstruction of moraine. Moraines of the second set occur within 1e1.5 km of the former ice extents from well-preserved terminal moraines. lake outlet including three arc-like end moraines. The tills of the third set are w4 km down away from the lake outlet and display 2. Study area closely clustered moraines containing a set of four prominent ridges. The outer most terminal moraine set, which includes two The study area, the Dangzi valley, is situated in the northern moraines, marks the maximum extent of the Dangzi valley glaciers, margin of Queer Shan Mountain, which belongs to the Hengduan about 8 km far from the cliff closed to the Dangzi Lake. The fourth Mountains on the eastern margin of the Tibetan Plateau (Fig. 1a and set was covered by loess, and tills and boulders in this set show b). In the northern slope of the Queer Shan, modern glaciers have much greater degree of weathering than that of the former three developed at the high altitude with the equilibrium-line altitude sets, suggesting that it is possibly older. (ELA) at about 5200 m asl. The Dangzi valley is adjacent to the The climate of the region is relatively warm and humid, strongly Yingpu and Langlong valley. It reaches the southern margin of the influenced by the south Asia monsoon in the summer, which Zhuqing basin from the northern slope of the Queer Shan (Fig. 1c). provides most of the annual precipitation of typically more than The Dangzi valley is an NNWeSSE trending U-shaped valley with 600 mm, and the mid-latitude westerlies in the winter (Shi, 2006). a length of 8 km and is between 3900 and 4200 m asl. The Dangzi An early survey and mapping of the area was carried by Li and Su River originates from the northern slopes of Queer Shan and flows (1996). Li and Su (1996) assessed the past glacial advances along northwards through the Duoji lake and Dangzi lake eventually into Dangzi valley into the two stages, using the relative dating methods the Yalongjiang River. From the upper part of the valley, Dangzi based on morphostratigraphy and relative weathering criteria. The Lake, with a distance about 6.5 km from the headwall, was eroded three sets in the head part were assigned to be the last ice age, and by glacial advance and then glacier melt water was accumulated the tail set was attributed to the penultimate glaciation. Glacial due to terminal moraines damming. advances during the last glacial period in the Dangzi valley were The valley is flat and wide, which implies that this valley could supported by a TL age (24.7 Æ 2 ka) obtained from the most outside be the ideal area for the preservation of glacial evolution. Four well- set of moraine in the Dangzi valley (Lehmkuhl et al., 1998). http://ir.isl.ac.cn Fig. 1. (a) Shuttle Radar Topography Mission (SRTM) DEM image of the Tibetan Plateau. (b) Main mountains and rivers in the Hengduanshan region. (c) The location of Dangzi valley in the Zhuqing basin. 246 B. Zhang et al. / Quaternary Geochronology 10 (2012) 244e249 Fig. 2. The geomorphic map of Dangzi valley and the sampling sites. The OSL ages are showed in each site. Bold lines of different colours across the Dangzi valley are remnant of end moraine. According to several OSL and ESR results from the moraines in determined using a combination of the single aliquot regenerative- Yingpu valley, Xu et al.

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