Aeolian sediments evolution controlled by fluvial processes, climate change and human activities since LGM in the Qaidam Basin, Qinghai-Tibetan Plateau

Quaternary International 372 (2015) 23e32

Contents lists available at ScienceDirect

Quaternary International journal homepage: www.elsevier.com/locate/quaint

Aeolian sediments evolution controlled by fluvial processes, climate change and human activities since LGM in the Qaidam Basin, Qinghai-Tibetan Plateau LuPeng Yu a, b, c, *, ZhongPing Lai d, c, **, Ping An b, Tong Pan b, QiuFang Chang e, f a

College of Resources and Environment, Linyi University, Linyi 276000, China Key Laboratory of Geological Processes and Mineral Resources of Northern Qinghai-Tibetan Plateau, Qinghai Geological Survey Institute, Xining 810012, China c State Key Laboratory of Cryospheric Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China d School of Earth Sciences, China University of Geosciences, Wuhan 430074, China e Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, 810012, China f University of Chinese Academy of Sciences, 100049, China b

a r t i c l e i n f o

a b s t r a c t

Article history: Available online 13 October 2014

Aeolian sediments are widely distributed in the eastern Qaidam Basin (QB), the main habitats for human in the hyper-arid basin during the Holocene, especially since 3 ka. The evolution of aeolian sediments is an important factor for the environmental change, and influence human activities and migration. However, many questions, e.g., when the aeolian sediments start to accumulate, what controls their initiation and how their evolution responds to climate change and human activities, still need further studies. In this study, we present a detailed Optically Stimulated Luminescence (OSL) chronology for both aeolian and underlying fluvial sediments from the Tiekui Desert in the eastern QB to discuss aeolian and fluvial processes, climatic changes, desert evolution, and human activities. Dating results show that: (1) underlying fluvial sediments were formed during ~23.9e12.1 ka, and the erosion caused by the fluvial process may provide an explanation for the absence of aeolian sediments during and before this period; (2) aeolian sediments accumulated from ca. 9e8 ka to modern times, with loess development from 9 e8 ka to 1.6 ka and 1.4e0.7 ka, and dune sand accumulation at 1.6e1.4 ka and 0.7e0 ka. Through the comparison with the local and global palaeoclimatic records, we suggest that desert evolution in this region was sensitive to climatic changes induced by the Asian summer monsoon. Detailed local historical records of the past 2000 years suggest that desert evolution was also influenced by human activities. © 2014 Elsevier Ltd and INQUA. All rights reserved.

Keywords: OSL dating Desert evolution Palaeoenvironmental change Human activity Deglaciation and Holocene Qinghai-Tibetan plateau

1. Introduction The climate in the Qaidam Basin (QB, Fig. 1A and B), northeastern Qinghai-Tibetan Plateau (QTP), is windy, cold and hyperarid, making it a major source area for modern Asian mineral dust (Chen et al., 2007), and for Quaternary loess deposits on the Chinese Loess Plateau (Kapp et al., 2011; Pullen et al., 2011; An et al.,

* Corresponding author. College of Resources and Environment, Linyi University, Linyi 276000, China. ** Corresponding author. School of Earth Sciences, China University of Geosciences, Wuhan 430074, China. E-mail addresses: [email protected], [email protected] (L.P. Yu), zplai@ lzb.ac.cn, [email protected] (Z.P. Lai). http://dx.doi.org/10.1016/j.quaint.2014.09.043 1040-6182/© 2014 Elsevier Ltd and INQUA. All rights reserved.

2012a; Lai et al., 2014). Aeolian sediments are direct records of the aeolian activities and palaeoclimatic change in the QB. However, aeolian sediments evolution and their relevance to river and alluvial fan evolutions, palaeoclimatic changes, and human activities in the QB are still poorly understood. The age when the aeolian sediments in the QB started to accumulate is crucial for the depositional process and climatic change studies. Hao et al. (1998) dated the paleosol in the eastern QB by thermoluminescence (TL) dating, and showed paleosols accumulated before 50.2 ka and since the last interglaciation (ca. 130e70 ka). Zeng et al. (1999, 2003) obtained four TL ages from the dune sands in the eastern QB and pointed out that the dune sands were deposited during the Last Glacial Maximum (LGM) and Younger Dryas (YD) events. However, newly published

24

L. Yu et al. / Quaternary International 372 (2015) 23e32

Fig. 1. Geomorphology of the study region and location of the sections. (A), map showing the location of the Qaidam Basin and the dominant circulation systems of the Westerlies, the Indian Summer Monsoon, the East Asian Summer Monsoon and East Asia winter monsoon. The yellow square denotes the location of the Qaidam Basin; the red dotted line marks the modern Asian Summer Monsoon (ASM) limit (modified from Gao, 1962). (B), the DEM map revealing the geomorphology of the Qaidam Basin, the sites mentioned in former studies (white squares), and cities and towns (white dots with red margin). The yellow square indicates the study area of Tiekui Desert shown in (C), which displays the locations of the sections in this region, i.e., WLS1, BDB, and XXT sections in Yu and Lai (2012), SYK1 and XRH sections in Yu and Lai (2014a), and HSZ sections (unpublished data, their location is the same with the Xiaxitai sections mentioned in Niu et al. (2010)). (D) shows the locations of sections in the Hebeicun (HBC) region. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Optically Stimulated Luminescence (OSL) dates indicated much younger onset ages of aeolian sediments. Owen et al. (2006) reported the earliest OSL age of 14.9 ka for aeolian sediments from a sand wedge at Lenghu in the northern QB. Loess on the Golmud River terraces in the Kunlun Mountains to the south of the QB were reported to be formed since 8 ka (Owen et al., 2006) and 13.9 ka (Chen et al., 2011) based on OSL dating. Yu and Lai (2012, 2014) provided 89 OSL ages in all for aeolian sand-loess-paleosol sections in the eastern QB, and the oldest age for aeolian sediment was 12.4 ± 0.7 ka during the deglaciation. Yu et al. (2013) studied paleodunes in the middle and southwestern QB, and their OSL dating results showed these paleodunes mainly formed since ca. 4e3 ka. Zhou et al. (2012) proposed that the linear dunes in the middle QB were also accumulated since 3.2 ka, using OSL dating. The phenomenon of aeolian sediment accumulating from the deglaciation (ca. 15 ka) has also been found in the Qinghai Lake Basin (Lu et al., 2011; Liu et al., 2012) and in the interior Tibet (Sun et al., 2007). This is either due to the minimal vegetation cover with resultant limited dust-retention ability during the cold, dry LGM, or due to erosion by glaciofluvial outwash during the beginning of each interglaciation period (Sun et al., 2007). This mechanism seems plausible in the QB, taking into account that aeolian sediments are mainly located over the fluvial or alluvial

sediments, to be confirmed by the dating of the underlying fluvial/ alluvial sediments. The climate change during the Holocene in the eastern QB has been reconstructed as humid in early Holocene (11.6e8.3 ka), relatively humid in mid-Holocene (8.3e3.5 ka), becoming arid in late Holocene (Yu and Lai, 2012, 2014). However, due to the sampling requirements of OSL dating (~30 cm from the boundary), relatively lower depositional rate, and incomplete sedimentary records caused by surface erosion, the climate changes and desert evolution during the late Holocene are difficult to be reconstructed in detail (Yu and Lai, 2012, 2014). To resolve this question, sections with higher depositional rate and stratigraphic changes are essential. In the eastern QB, frequent alternation between loess and dune sand can be found in the upper parts of many sections around the modern desert margin, which might demonstrate the desert evolution during the late Holocene. Both climatic and environmental changes could affect human activities. Zeng (2006) found two layers of human activity remains (3229 ± 82 and 3477 ± 63 cala BP) in Nuomuhong, southern QB, and both cultural layers started on the silt layers and terminated with the occurrence of aeolian sand, displaying a direct connection between environmental changes and human activities. Moreover, even some dynasty changes in Chinese history probably resulted

L. Yu et al. / Quaternary International 372 (2015) 23e32

from the cold/dry events (Zhang et al., 2008; Liu et al., 2009). In turn, human activities can also affect the environment, for example, desert expansion was caused by large scale farming or overgrazing during the past 2000 years in the Horqin sand-fields (Zhao et al., 2007; Yang et al., 2012a), Mu Us Desert (Sun et al., 2000; Huang et al., 2009) and Otindag sand-fields (Han and Sun, 2004). Human activities in the northeastern QTP can be traced to 15 ka BP (Madsen et al., 2006; Sun et al., 2012a). The eastern QB has been controlled by nomads or by the Central China government alternatively during the past 2000 years according to historic records (Cui et al., 1999). We have found numerous human activity remains from the aeolian sediments in the QB. However, relationships among human activities, climatic changes, and desert evolution have not been investigated. In this study, we present a detailed OSL chronology for both the aeolian and fluvial sediments from the eastern QB in order to address these issues. 2. Study area The QB in northeastern QTP, with an area of 1.2
105 km2 and a catchment of about 2.5
105 km2, is one of the largest hyper-arid

25

intermontane basins on Earth (Fig. 1A). It has an mean elevation of 2800 m asl at the playa floor, and is surrounded by the over 5000 m Qilian, Kunlun, and Altun Mountains (Fig. 1B). The annual mean precipitation and evaporation of the hyper-arid central basin are about 26 mm and 3000e3200 mm, respectively. The precipitation is mainly concentrated in summer, and the moisture is mainly from the Asian summer monsoon (ASM, Yu and Lai, 2014). The westerlies are the major circulation over the basin, with prevailing strong north and northwesterly winds in winter and spring (Wu et al., 1985). Severe wind erosion is demonstrated in the western QB by the presence of extensive fields of yardangs (Kapp et al., 2011). A portion of the wind-eroded material from the yardangs in the western basin, playas in the central basin, and alluvial fans around the basin was redistributed to, and stored within the eastern QB (Kapp et al., 2011; Yu and Lai, 2012), where the Tiekui Desert is located (Fig. 1B and C). The Tiekui Desert, the largest desert in the QB, is at 2800e3300 m asl, with playas below 2800 m to the west and mountains over 4000 m to the east (Fig. 1B). Mobile dunes are widely distributed inside the desert, and the loess/paleosol deposits are distributed around the desert margin. The region

Fig. 2. (A) Aeolian sections and (B) human activity remains, e.g., pottery fractions (B1e5), a horse tooth (B6), bones (B7), sheep dungs (B8), and hearths (B9e11) in aeolian sediments (B) in the HBC region.

26

L. Yu et al. / Quaternary International 372 (2015) 23e32

beyond the eastern margin of the Tiekui Desert (Fig. 1C and D) is the most humid region in the QB, e.g., the average annual precipitation of the Xiariha Town is 240.8 mm (Chorographic Committee of Dulan County, 2001), and is one of the major habitats for humans in the QB. The climate changes in late Holocene in the northeastern QTP (An et al., 2012b; Yu and Lai, 2014) were relatively smaller-scale compared to those of the whole Holocene; as a result the changes of desert area should also be smaller-scale. This is why desert shrink/expansion was not well recorded inside (SYK1 section) and beyond (WLS, BDB, XXT, and XRH sections) the Tiekui desert (Fig. 1C, Yu and Lai, 2012, 2014). However, the Hebeicun (HBC) region is located on the northeastern margin of the Tiekui Desert (Fig. 1C and D), and as a result is sensitive to even slight changes of the desert margin. Alternation between dune sand and loess layers could be found in the upper parts of the sections in this region (Figs. 2A and 3A), which might demonstrate the desert shrink and expansion during the late Holocene. There are many gullies with depth of 3e5 m along the Xiariha River, a branch of the Chahan Us River. Most of these gullies are very young and caused by runoff erosion, and stratigraphy could be clearly displayed by these gullies. The aeolian sediments in the HBC regions are mainly composed of two layers of loess and two layers of sand overlying the fluvial sediments (Figs. 2A and 3A). Grain-size distributions of dune sand samples HBC2 and HBC3, which are different from those of the loess samples HBC4 and HBC5 (Fig. 3B), show that these aeolian sands are well sorted and are dune sand. The dunes on the surface were originally mobile, and some have been semi-fixed by artificially vegetation to protect the farmland in the down wind direction during the past decades (Figs. 1D and 2A). The lower dune sand layer intercalated into the two loess layers is a marker layer and can be found in most of the sections in this region (Figs. 2A and 3A), revealing the onset of desert in this region.

3. Sections and samples To reconstruct the desert evolution on the desert margin region, seven sections were investigated to confirm the existence of the possible smaller-scale desert shrink/expansion events during the late Holocene in the HBC region (Figs. 1D, 2A and 3A). In the HBC1 section, a semi-fixed dune with a thickness of 1.60 m is exposed on the top of this section, and the loess occurs at 1.60e4.70 m with intercalated aeolian sand at 2.25e3.00 m Fluvial sediments underlying the aeolian sediments at 4.70e6.40 m (Fig. 2A) demonstrate that the aeolian sediments were deposited after the termination of the fluvial processes. The HBC2, HBC3, HBC5, and HBC7 sections have the same stratigraphic composition of two dune sand layers and two loess layers (Figs. 2A and 3A). The HBC4 and HBC6 sections are composed of only one dune sand layer in the upper part and one loess layer in the lower part (Fig. 3A). The sediments at the depth of 0e0.40 m and 2.00e2.05 m in the HBC4 section were modified by water, which might cause the differing sedimentary compositions from the other sections. Stratigraphic compositions in this region are similar, but the thickness of each layer varies in different sections. Moreover, human activity remains, e.g., pottery fractions, hearths, charcoals, bones, and sheep dung, were frequently found within the aeolian sediments, especially in the lower loess layer (Figs. 2B and 3A), demonstrating this region has been important habitation for humans in history. And long-term human activities might have affected the evolution of the desert. Charcoals and bones were found at 3.20e3.30 m in the HBC1 section, i.e., upper part of the lower loess layer, where human activity remains are found frequently in the whole region. One piece of pottery and many pieces of bones were found in the loess deposits in HBC2 section. A hearth ~0.80 m long and 0.05 m thick was found at the depth of 2.0 m in the loess deposits in HBC3 section. There were

Fig. 3. (A) Stratigraphy and ages of the HBC sections and (B) Grain-size distribution curves of dune sand (HBC1-2 and HBC1-3) and loess (HBC1-4 and HBC1-5) samples.

L. Yu et al. / Quaternary International 372 (2015) 23e32

many charcoals distributed in mainly three different depths in the loess deposits of HBC4. A horse tooth was found in the overlying sand layer at the depth of 1.07 m, and a large charcoal, a piece of bone, a piece of pottery fraction, and a few sheep dungs were found at the depth of 1.53 m, 1.68 m, and 2.50 m, respectively, in the loess deposits in HBC6. In the HBC7 section, to the east of HBC1 section, a hearth (0.60 m long and 0.05e0.08 m thick) was found at the depth of 1.30 m, and a pottery fraction, a bone and a few charcoals (taken for AMS 14C dating) were found around the depth of ~1.50 m, and another hearth (1.60 m long and 0.08e0.10 m thick), was found at the depth of 2.90 m of the bottom of the loess deposits (Figs. 2B and 3A). Taking into account that the sections in this region are mainly the same, e.g., HBC1, HBC2, HBC3, HBC5, HBC6, and HBC7, and that the HBC1 section is much thicker and with more underlying fluvial sediments exposed, which can offer higher resolution depositional records and chronological control, only the HBC1 section was systemically sampled to offer a chronological frame for the fluvial and desert evolution. Nine OSL samples were collected from the HBC1 section. The HBC4 section is different from the others, and was apparently modified by water (Fig. 3A), so four OSL samples were taken from this section to demonstrate whether different desert evolution information was recorded. All luminescence samples were collected by hammering steel tubes (~22 cm long cylinder with a diameter of ~5 cm) into freshly cleaned vertical sections. The ends of tubes were then wrapped to avoid light exposure. Bulk samples were also collected in each sample location for dose rate and water content analysis.

27

purify quartz of 38e63 mm and 90e125 mm, the sieved mix samples were etched with 35% H2SiF6 for about two weeks to dissolve feldspars (Roberts, 2007; Lai et al., 2007a; Lai, 2010) and with 40% HF for 40 min to dissolve feldspars and the alpha-irradiated outer layer (~10 mm), respectively, and then with 10% HCl to remove fluoride precipitates. The purity of quartz grains was checked by IR (l ¼ 830 nm) stimulation, and any samples with obvious IRSL signals were treated with H2SiF6 again to avoid De underestimation (Lai and Brückner, 2008). The well pretreated grains were then mounted on the center part (with a diameter of ~0.5 cm) of stainless steel discs (with a diameter of 1 cm) using silicone oil. The luminescence was stimulated by blue LEDs (l ¼ 470 ± 20 nm) at 130  C for 40 s, or by IR at 125  C for 100 s using a Risø TL/OSL-DA20 reader with 90% diode power, and detected using a 7.5 mm thick U-340 filter (detection window 275e390 nm) in front of the photomultiplier tube. Irradiations were carried out using a 90Sr/90Y beta source in the reader. A preheat plateau test was conducted on sample HBC1-4, and the preheat temperatures of 220, 240, 260, 280 and 300  C were tested. The result shows a De plateau at 240e280  C. So preheat at 260  C for 10 s for natural and regenerative doses, and cut-heat at 220  C for 10 s for test doses was chosen for quartz. Signals of the first 0.64 s stimulation were integrated for growth curve construction after background (last 10 s) subtraction. The concentrations of U, Th and K were measured by neutron activation analysis. For the 38e63 mm quartz grains, the alpha efficiency value was taken as 0.035 ± 0.003 (Lai et al., 2008). The cosmic-ray dose rate was estimated for each sample as a function of depth, altitude, and geomagnetic latitude (Prescott and Hutton, 1994). The dose rates are shown in Table 1.

Table 1 Environmental radioactivity and OSL dating results. Sample ID

Depth (m)

K (%)

HBC1-1* HBC1-2* HBC1-A HBC1eB HBC1-3# HBC1-4 HBC1-5 HBC1-6 HBC1-7 HBC4-1# HBC4-2 HBC4-3 HBC4-4

0.55 1.30 1.70 2.00 2.60 3.30 4.35 4.95 5.80 0.95 1.35 2.50 4.60

1.58 1.51 1.94 1.84 1.81 1.60 1.58 1.64 1.67 1.70 2.05 2.23 1.90

± ± ± ± ± ± ± ± ± ± ± ± ±

Th (ppm) 0.09 0.08 0.04 0.04 0.09 0.09 0.09 0.09 0.09 0.04 0.04 0.06 0.04

5.48 6.71 8.54 9.05 5.21 8.00 7.83 6.47 5.46 6.11 8.81 11.10 11.66

± ± ± ± ± ± ± ± ± ± ± ± ±

0.30 0.37 0.60 0.60 0.27 0.43 0.42 0.35 0.30 0.50 0.60 0.70 0.70

U (ppm) 1.35 1.74 2.52 2.52 1.50 2.22 2.51 1.65 1.22 1.70 2.66 3.10 2.58

± ± ± ± ± ± ± ± ± ± ± ± ±

0.18 0.20 0.40 0.40 0.18 0.21 0.22 0.19 0.17 0.30 0.40 0.40 0.40

Water content (%) 3 3 5 5 3 5 5 3 3 3 5 5 5

± ± ± ± ± ± ± ± ± ± ± ± ±

2 2 2 2 2 2 2 2 2 2 2 2 2

Dose rate (Gy/ka) 2.92 3.08 3.43 3.21 2.85 2.97 3.00 2.75 2.56 2.75 3.66 4.09 3.62

± ± ± ± ± ± ± ± ± ± ± ± ±

0.17 0.17 0.19 0.17 0.18 0.17 0.17 0.16 0.16 0.14 0.20 0.22 0.20

Aliquot number

De (Gy)

12a þ 6b 12a þ 6b 6a þ 12b 6a þ 12b 6a þ 12b 6a þ 12b 6a þ 12b 6a þ 12b 6a þ 12b 6a þ 12b 6a þ 12b 6a þ 12b 6a þ 12b

0.16 1.61 2.43 1.42 4.19 4.68 20.3 33.2 61.3 1.94 4.23 8.30 20.9

± ± ± ± ± ± ± ± ± ± ± ± ±

0.01 0.02 0.09 0.10 0.18 0.12 0.6 0.8 1.9 1.14 0.15 2.20 0.5

OSL age (ka) 0.06 0.52 0.71 1.4 1.5 1.6 6.8 12.1 23.9 0.70 1.2 2.0 5.8

± ± ± ± ± ± ± ± ± ± ± ± ±

0.01 0.03 0.05 0.1 0.1 0.1 0.4 0.8 1.7 0.06 0.1 0.1 0.4

The sample ID marked with “*” means measured by IRSL. The sample ID marked with “#” means measured with 90e125 mm fraction, and the others are measured with 38e63 mm fraction. a Aliquot number used for SAR. b Aliquot number used for SGC.

4. OSL dating

4.2. Equivalent dose determination

4.1. OSL sample preparation and measurement techniques

In the current study, the combination of the Single Aliquot Regeneration (SAR) protocol (Murray and Wintle, 2000) and the Standard Growth Curve (SGC) method (Roberts and Duller, 2004; Lai, 2006; Lai et al., 2007b; Yu and Lai, 2012, 2014), i.e., the SARSGC method (Lai and Ou, 2013), was employed for De determination. In this method, for each sample, 6e12 aliquots were measured using SAR protocol to get 6e12 growth curves, which were then averaged to construct a SGC for this individual sample, e.g., the SGC of sample HBC1-5 (Fig. 4A); then more aliquots were measured to obtain the values of test-dose corrected natural signals (Ln/Tx) only, and each of the values were matched in the SGC to obtain a De. For each sample, the final De is average of the SAR Des and SGC Des. A

In the luminescence dating laboratory of Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, the unexposed middle part of the tube was used to extract minerals for equivalent dose (De) determination. The samples were treated first with 10% HCl and 30% H2O2 to remove carbonates and organic matter, respectively. The fractions of 38e63 mm and 90e125 mm were then extracted by wet sieving. Most of the samples were dated with OSL signals from quartz, while for the very young samples, e.g., HBC1-A and HBC1-B, the quartz OSL signal was too dim to be detected, so the Infrared Stimulated Luminescence (IRSL) signals from feldspar was used. To

28

L. Yu et al. / Quaternary International 372 (2015) 23e32

“dose recovery test” (Murray and Wintle, 2003) was conducted on 6 aliquots of sample HBC1-D, and the ratio of the measured (4.9 ± 0.45 Gy) to the given (5.0 Gy) dose was 0.980 ± 0.090, suggesting the SAR protocol is suitable for De determination of samples from this region. Fig. 4B shows typical OSL decay curves of HBC1-5, and the signals decayed to the level of the background within 1e2 s, demonstrating that these signals were mainly from the fast components. Fig. 4C displays the near normal De distribution of HBC1-2. Fig. 4D shows the comparison between SAR Des and SGC Des, which are in agreement within 10% error, suggesting the SARSGC method is suitable for the aeolian and fluvial samples in the eastern QB. 5. Dating results and desert expansion events OSL dating results are listed in Table 1, and are also shown in Fig. 3A. All OSL ages are in stratigraphic order, and the youngest age of 0.06 ± 0.01 ka demonstrates that OSL signals were well bleached before burial. The underlying fluvial sediments accumulated at 23.9 ± 1.7e12.1 ± 0.8 ka, i.e., from the LGM to deglaciation. According to the depositional rate (0.202 m/ky) revealed by OSL ages from the lower loess layer (6.8 ± 0.4 ka and 1.6 ± 0.1 ka), the base of the aeolian sediments might formed at ca. 8.5 ± 0.4 ka, so the estimation of ca. 8e9 ka is reasonable. As a result, there might be a hiatus of ca. 3e4 ky during the early Holocene between the fluvial and aeolian sediments, which might be caused by fluvial erosion. The age of the lower aeolian sand is 1.5 ± 0.1 ka. Taking into account its error and age of its underlying (1.6 ± 0.1 ka) and overlying (1.4 ± 0.1 ka) loess layer, this lower sand layer was deposited at 1.6e1.4 ka, and the lower loess deposits should end at ~1.6 ka.

The upper dune sand layer in HBC1 section started to accumulate after 0.71 ± 0.05 ka and the sand layer in the HBC4 section started to accumulate before 0.70 ± 0.06 ka, consequently, the upper dune sand layer should have started to accumulate at ca. 0.70 ka. Accordingly, the upper loess layer was deposited at 1.4e0.70 ka. The youngest age of aeolian sand at 0.5 m was 0.06 ± 0.01 ka, demonstrating that the dune activities might have lasted from 0.70 ka until modern times. Although the stratigraphy of HBC4 section is different from those of the other sections, the OSL ages of its dune sand layer (0.70 ± 0.06 ka), the upper loess layer (1.2 ± 0.1 ka), and the lower loess layer (2.0 ± 0.1 ka) could be compared with the HBC1 section. The waterlain sand in the HBC4 section should correspond to the lower dune sand layer in the other sections (Fig. 3A), and demonstrates that the absence of the lower dune sand layer might be caused by water erosion. Consequently, the aeolian records of HBC4 section are similar with the other sections, with some records eroded. The 14C age (1802 ± 28 14C a BP, 1701e1741 cal a BP) of a charcoal in the HBC7 section imply that these human activity remains from the upper part of the second loess layer in these sections might be of the same time, i.e., 2.0e1.5 ka, offering a marker layer for these sections (Fig. 3A). According to the dating results, two desert expansion events at 1.6e1.4 ka and 0.70e0 ka were reconstructed on the desert margin in the HBC region (Figs. 3A and 4A). These two events were also recorded in the loess deposits beyond the Tiekui Desert, although aeolian sand layers were not directly observed in sections. In XXT region (HSZ site in Fig. 1C), 16 km from HBC1 section to the northeast and 17 km away from the modern Tiekui Desert to the west, the grain-size and SiO2/TiO2 of loess deposits increased during1.7e1.4 ka and after 0.8 ka, caused by intensive winter monsoon and Tiekui Desert expansion (Niu et al., 2010). This shows

Fig. 4. OSL Standard Growth curve (A), decay curves (B), De distributions (C), and comparison between SGC Des and SAR Des (D).

L. Yu et al. / Quaternary International 372 (2015) 23e32

that, although of smaller-scale, the two desert expansion events should be common in the desert margin region. 6. Discussion 6.1. Fluvial processes influence the starting age of the aeolian sediments Aeolian sediments accumulated during the Holocene are widely distributed in the QB (Niu et al., 2010; Yu and Lai, 2012, 2014; Zhou et al., 2012; Yu et al., 2013), so aeolian activities must be more intensive during the last glaciation, especially in the LGM, when climate was much colder, arid, and windy. Aeolian sediments deposited during or before the LGM have been found in the Lhasa area (Lai et al., 2009), in the Qinghai Lake Basin (Liu et al., 2012), and in the Gonghe Basin (Qiang et al., 2013) on the QTP. Therefore, aeolian sediments should have accumulated during and before the LGM in the QB. However, based on the OSL chronology, the aeolian sediments in the QB were mainly deposited since the deglaciation or Holocene (Owen et al., 2006; Niu et al., 2010; Chen et al., 2011; Yu and Lai, 2012, 2014; Zhou et al., 2012; Yu et al., 2013). Aeolian sediments in most areas of the Qinghai Lake Basin (Porter et al., 2001; Lu et al., 2011; Liu et al., 2012) and in the valley of Yarlung Zangbo River (Sun et al., 2007) were also formed since deglaciation. According to Sun et al. (2007), the lack of full glacial loess deposition is either due to the minimal vegetation cover with resultant limited dust-retention ability or due to erosion by glaciofluvial outwash during the beginning of each interglaciation period, but not due to the lack of silt availability. Differing from deserts in northern China, aeolian sediments in the QB are mainly located over the fluvial or alluvial sediments around the basin, and the onset of aeolian sediments could be largely affected by the fluvial/alluvial processes. The underlying fluvial sediments deposited during the late LGM and early Holocene have been found in this region (Yu and Lai, 2012). In this study, the OSL chronology of the underlying fluvial sediments in the HBC1 section further confirms the existence of fluvial processes during the LGM and deglaciation (23.9 ± 1.7 to 12.1 ± 0.8 ka). These sections are from the higher terraces of the river. As a result, the underlying fluvial sediments in this region were mainly deposited since the LGM. Additionally, alluvial fans around the basin should be also formed since the deglaciation due to the increased glacier ablation and increased precipitation during the Holocene. Consequently, the underlying fluvial and alluvial sediments controlled the starting age of the overlying aeolian sediments, which offers explanation and evidence for the absence of aeolian sediments during/before the LGM in the QB. The following phenomenon in the HBC1 section imply the possible erosion caused by fluvial process: (1) occurrence of the water-transported loess-like deposit (silt) intercalated with fine gravels within the fluvial sediments at the depth of 5.15e5.55 m, (2) the hiatus from ~12.1 ka to ca. 9e8 ka between fluvial and aeolian sediments, and (3) only 1 m-thick fluvial sediments were preserved during 23.9e12.1 ka. Consequently, the absence of aeolian sediments accumulated during and before the LGM should be mainly due to the erosion caused by fluvial and alluvial processes during the LGM and deglaciation. Additionally, the other important process is the wind. The absence of aeolian sediments during the LGM might be caused by: (1) for loess deposits, deposition of dust might be hindered due to the limited vegetation (Sun et al., 2007; Yu and Lai, 2014); and (2) for dune sand, if the dunes kept moving during the LGM, the aeolian activities could not be recorded by OSL ages (e.g., Roskin et al., 2011; Yu et al., 2013, 2014) until the desert mobility decreased during the deglaciation and Holocene. For the absence of aeolian sediments formed before the LGM, they might have been

29

eroded by the strong wind during the LGM, because wind-erosion is an important geomorphologic process in the QB, e.g., the formation of the yardangs in the western QB (Kapp et al., 2011; Rohrmann et al., 2013) and the absence of surface sediments during the late Pleistocene (Han et al., 2014; Lai et al., 2014). 6.2. Impact of climatic changes and human activities on desert evolution 6.2.1. Impact of palaeoclimatic changes on desert evolution Although desert activity is related to effective moisture, transport capacity of the wind (Lancaster, 1988) and sand supply (Cohen et al., 2010), generally speaking, the formation of sand sea is a response to arid climate, with the occurrence of sandy layers in sedimentary sequences from both the deserts (Zhu et al., 1980) and the desert-loess margins (Liu, 1985), and is commonly used as a proxy for changes in aridity (Yang et al., 2012b). The sand supply in the QB is mainly from the yardangs in the northwestern QB, alluvial fans around the basin, and the adjacent river bed, so the sand supply in the QB is consistent during such a relevant short period (Yu et al., 2014). The changing effective moisture would affect vegetation density, known to have dramatic effects on sand mobility (Liu et al., 2005). In the northeastern QTP, the westerlies, the main wind regime for aeolian activities in the QB, strengthened with the shrinking of the ASM, i.e., the increase of the aridity (An et al., 2012b). Consequently, the evolution of the desert is mainly controlled by the aridity, and alternate deposition of aeolian sediments were used to reconstruct the palaeoclimatic changes in the Qinghai Lake Basin (Lu et al., 2011; Liu et al., 2012), the Gonghe Basin (Qiang et al., 2013), and the QB (Yu and Lai, 2012, 2014) in the northeastern QTP. In order to study the relationships between desert evolution (Figs. 3 and 5A) and climatic changes, a few regional and global palaeoclimatic records with precise chronology were chosen to compare with desert evolution records in this study. In the northeastern QB, tree-rings offered important palaeoclimatic records, and most were from Dulan County. As a result, the tree-ring records from the Qilian Mountains (Fig. 5B, Yang et al., 2014) and from Dulan region (Fig. 5C, Liu et al., 2009) are treated as local records. The d18O records of stalagmite from the Dongge Cave (Fig. 5D, Wang et al., 2005) are regarded as regional records of ASM changes. Surface hydrographic changes in North Atlantic served as an important trigger for millennial global climatic changes during the Holocene (Fig. 5E, Bond et al., 2001), which have been demonstrated by the studies from the Chinese Loess Plateau (Sun et al., 2012b) and QTP (An et al., 2012b). As a result, the ice-rafted debris (IRD) records in North Atlantic (Fig. 5E, Bond et al., 2001) were chosen as global climatic change records. Loess accumulated from 9 to 8 ka to 1.6 ka. Climate of the midHolocene (8.3e3.5 ka in the eastern QB according to Yu and Lai (2014)) was optimal, and it was also a main stage for the loess and paleosol accumulation in the eastern QB (Yu and Lai, 2012, 2014). After 3.5 ka, effective moisture decreased gradually (Yu and Lai, 2014). Consequently, many lakes, e.g., Chaka Salt Lake in the eastern QB (Liu et al., 2008), Da Qaidam Lake, and Bieletan Salt Lake in the middle QB (Huang et al., 1981), became salt lakes and formed saline deposits. Lake level of Xiao Qaidam Lake in the northern QB shrank sharply at ca. 3 ka (Sun et al., 2010). Paleodunes in the middle and southwestern QB also accumulated since ca. 4e3 ka (Yu et al., 2013). Linear dunes in the central QB formed since 3.2 ka (Zhou et al., 2012). All these records showed that the climate became arid since ca. 4e3 ka in the QB. However, aeolian sand was not found during this period in the HBC1 section, because the eastward desert expansion had not reached the HBC region, the modern desert margin, at that time.

30

L. Yu et al. / Quaternary International 372 (2015) 23e32

Fig. 5. Comparisons among aeolian records, paleoclimatic records and historical records. (A) Aeolian records in this study, (B) Tree-ring reconstructed precipitation in the Qilian Mountains region (Yang et al., 2014), (C) Tree-ring reconstructed paleotemperature in Dulan (Liu et al., 2009), (D) Stalagmite records from Dongge Cave (Wang et al., 2005), (E) IRD records from the Northern Atlantic (Bond et al., 2001) and (F) Historical records from Dulan County: (F-1) Dulan was the pasturing land of Qiang people, an ancient ethnic minority living on hunting and grazing, and was only shortly controlled by Han Dynasty at 4e23 AD; (F-2) “Southern Silk Road” passed across Dulan, and capital of Tuyuhun Kingdom was built in Dulan, which increase the population largely and deforestation; (F-3) Dulan was alternatively controlled by the Tuyuhun, Tubo, Yuan and Ming Dynasties, and frequent wars triggered the emigration and decrease the impact to environment; (F-4) Nomads from East Mongolia immigrated to the QB, and population of Mongolian increased greatly; (F-5) Chief of Mongolian recruited the Han people to reclaim on the grassland and teach the Mongolian nomads farming techniques in Dulan; and (F-6) 2000 defending solders of Qing Dynasty reclaimed and farmed on the grassland in Dulan (Cui et al., 1999). In (F), the red records mean harmful to the environment, while the green ones mean beneficial for the environment. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

With the desert expanding eastward gradually, sand deposits occurred at 1.6e1.4 ka in this region. The reconstructed precipitation based on tree-ring records from the Qilian Mountains, northeastern QTP, displays arid climate during 1.6e1.4 ka (Yang et al., 2014). Liu et al. (2009) reconstructed palaeotemperature based on the tree-ring records in Dulan County, northeastern QB, and showed that the period from the East Jin Dynasty to the Northern and Southern Dynasties (~1.7e1.4 ka) was very cold, during which 348e366 AD (~1.65 ka) was the coldest period in the past 2485 years. This unprecedented cold period might be a trigger for the demise of the East Jin Dynasty, as the cold climate caused the grassland to expand southward, accompanied by invasion of the northern nomads (Liu et al., 2009). The stalagmite of the Dongge Cave recorded a weak event of the ASM at 1.6e1.4 ka (Fig. 5D, Wang et al., 2005), and an IRD event (Bond 1) was found in the North Atlantic at the same time (Fig. 5E, Bond et al., 2001). These records demonstrated that this was a global cold event, and this desert expansion event in the eastern QB might be a response. Loess of 0.6 m thick accumulated during1.4e0.7 ka, corresponding to the relevant warm and humid climate recorded by the tree-ring records in the northeastern QTP (Fig. 5B and C, Yang et al., 2014; Liu er al., 2009), stalagmite in the Dongge Cave (Fig. 5D, Wang et al., 2005) and IRD record in the North Atlantic (Fig. 5E, Bond et al., 2001). This period spanned the medieval warm period (1.2e0.7 ka), and the palaeotemperature recorded by the tree-rings in the Dulan County implied temperature increase during this period, and warmer/wetter climate was also detected from the peat record on the eastern QTP (Hong et al., 2003). As a result, the retreat of desert and development of loess during this period could be a response to the increased ASM.

Modern mobile deserts in this region mainly formed during 0.70e0 ka, corresponding to the Little Ice Age (LIA), with ASM weakening event at 0.70e0.16 ka (Fig. 5C, Wang et al., 2005), and Bond-0 cold event in the North Atlantic (Fig. 5D, Bond et al., 2001). According to the tree-ring record from the Qilian Mountains, northeastern QTP, notable historical dry periods occurred in the second half of the 15th century AD (Fig. 5B, Yang et al., 2014). Treering records from the Dulan County showed that the longest cold period occurred at 0.45e0.25 ka during the past 2485 years, synchronous with the collapse of the Ming Dynasty and the establishment of the Qing Dynasty (Fig. 5C, Liu et al., 2009). Palaeoprecipitation reconstructed by the tree-ring records from adjacent Wulan and Delingha regions demonstrated that the longest dry events happened at ca. 0.5e0.3 ka, according to extremely weak perturbations in the solar output (Shao et al., 2006). Comparisons between desert evolution and palaeoclimatic records show that loess developed when the climate was warm and humid, while aeolian sand accumulated when the climate was cold and dry. As a result, desert evolution in this region was sensitive to climatic changes.

6.2.2. Impact of human activities on desert evolution Historic records in the Dulan County (Fig. 5F, Cui et al., 1999) were referred to assess human activity records during the past 2 ka. During ~8e1.6 ka, human activities were still rare. This region was mainly controlled by the Qiang people, an ancient ethnic minority living on hunting and grazing, and was only shortly controlled by Han Dynasty during 4e23 AD (Fig. 5F-1, Cui et al., 1999). Influence

L. Yu et al. / Quaternary International 372 (2015) 23e32

of human activities on the environment could be ignored during this period. According to the historical records, frequent wars blockaded the traditional Silk Road from the Hexi Corridor to the Tarim Basin during the 4the6th centuries (1.6e1.4 ka). Alternatively, the so called “southern Silk Road” was opened through the QB, which made Dulan County a prosperous traffic center (Fig. 5F-2, Cui et al., 1999). Meanwhile, the capital of the Tuyuhun Kingdom was settled in Dulan County at 4the8th centuries AD (1.6e1.2 ka). Thousands of ancient tombs of that period, each of which was made of tens to thousands of Sabina przewalskii with tree-ages of 200 to over 1000 years, have been found in this region, and the timbers were progressively thinner in the later tombs (Qian and Li, 2004). Sabina przewalskii grows slowly, and it needs ca. 200 years to get a DBH (diameter at breast height) of 20 cm (Qian and Li, 2004). Consequently, the over-exploitation might have affected the restoration of vegetation and caused soil erosion and desertification. Dulan County was controlled by the Tuyuhun, Tubo, Yuan and Ming Dynasties successively during 1.4e0.7 ka (Fig. 5F-3, Cui et al., 1999) and frequent wars could have triggered emigration, reducing the impact of human activity on the ecological environment. No farming record was found during this period (Cui et al., 1999). During the Ming Dynasty (~0.65e0.35 ka), with the decrease of wars, more and more nomads migrated to the Dulan region, increasing the impact on the environment. Yibuci and Aertusi, chiefs of eastern Mongolia, led their nomadic tribes to the QB and the Qinghai Lake Basin at 1512 AD (0.5 ka). Aletan, another Mongolian chief, led his tribe to the Qinghai Lake region at 1559 AD (0.45 ka), and soon after thousands of Mongolians followed him (Fig. 5F-4, Cui et al., 1999). During the Qing Dynasty (0.35e0.1 ka), the Han people came to assart and farm in this region. In 1723 AD, a Mongolian chief of the Balong Banner (Banner is a Mongolian administrative unit like “County”) in the Xiangride region (Fig. 1C) recruited the Han people from the eastern Qinghai to farm in Dulan region and to teach the local nomads farming techniques (Fig. 5F5). After that, 2000 defending solders of the Qing Dynasty in the Xiariha region, where the HBC sections located, tried to farm, and the harvested grains was used as army provisions for the Mongolian solders (Fig. 5F-6, Cui et al., 1999). Farming was a governmental policy in the Qing Dynasty, and this might have made great impact on the ecological environment. Desert expansion was caused by large scale farming or overgrazing during the past 2000 years in the Horqin sand-fields (Zhao et al., 2007; Yang et al., 2012a,b), Mu Us Desert (Sun et al., 2000; Huang et al., 2009) and Otindag sand-fields (Han and Sun, 2004). Consequently, the increasing population and productive activities, e.g., increasing husbandry since the Ming Dynasty and occurrence of farming since the Qing Dynasty, might have promoted the desertification. 7. Conclusions The fluvial sediments formed at 23.9e12.1 ka offer evidence for the existence of consistent fluvial/alluvial processes during the LGM and deglaciation, and also provide an explanation for absence of aeolian sediments before/during this period. Accumulation of aeolian sediments started at ca. 9e8 ka and lasted until modern times. The aeolian sediments recorded two desert expansion events represented by dune sand accumulation at 1.6e1.4 ka and 0.7e0 ka. The desert shrinking stages correspond to warm and humid periods, while the desert expansion stages correspond to cold and dry periods. As a result, desert evolution in this region was sensitive to climatic changes. Meanwhile human activities might also played an important role in the past 2 ka, e.g., deserts expanded when the

31

population was larger, cities and large tombs were massively built, and farming policy was practiced.

Acknowledgments This study was supported by NSFC (41462006), SKLLQG (SKLLQG1217), CAS (XDA05120501), Qinghai Science & Technology Department (2013-Z-928Q), China Postdoctoral Science Foundation (2013T60902, 2012M521822). We thank Zheng Sun, Yuwei Ma and Xiaohua Guo for their help in the field, and two anonymous reviewers for helpful comments.

References An, F.Y., Ma, H.Z., Wei, H.C., Lai, Z.P., 2012a. Distinguishing aeolian signature from lacustrine sediments of the Qaidam Basin in northeastern Qinghai-Tibetan Plateau and its palaeoclimatic implications. Aeolian Research 4, 17e30. An, Z.S., Colman, S.M., Zhou, W.J., Li, X.Q., Brown, E.T., Jull, A.J.T., Cai, Y.J., Huang, Y.S., Lu, X.F., Chang, H., Song, Y.G., Sun, Y.B., Xu, H., Liu, W.G., Jin, Z.D., Liu, X.D., Cheng, P., Liu, Y., Ai, L., Li, X.Z., Liu, X.J., Yan, L.B., Shi, Z.G., Wang, X.L., Wu, F., Qiang, X.K., Dong, J.B., Lu, F.Y., Xu, X.W., 2012b. Interplay between the Westerlies and Asian monsoon recorded in Lake Qinghai sediments since 32 ka. Nature Scientific Reports 2 (619), 1e7. Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Bond, R.L., Hajdas, I., Bonani, G., 2001. Persistent solar influence on North Atlantic climate during the holocene. Science 294, 2130e2136. Chen, J., Li, G., Yang, J., Rao, W., Lu, H., Balsam, W., Sun, Y., Ji, J., 2007. Nd and Sr isotopic characteristics of Chinese deserts: implications for the provenances of Asian dust. Geochimica et Cosmochimica Acta 71, 3904e3914. Chen, Y.X., Li, Y.K., Zhang, Y., Zhang, M., Zhang, J.C., Yi, C.L., Liu, G.N., 2011. Late Quaternary deposition and incision sequences of the Golmud River and their environmental implications. Quaternary International 236, 48e56. Chorographic Committee of Dulan County, 2001. Annals of Dulan County. Shaanxi People's Publishing House, Xi'an, pp. 79e89 (in Chinese). Cohen, T.J., Nanson, G.C., Larsen, J.R., Jones, B.G., Price, D.M., Coleman, M., Pietsch, T.J., 2010. Late Quaternary aeolian and fluvial interactions on the Cooper Creek Fan and the association between linear and source-bordering dunes, Strzelecki Desert, Australia. Quaternary Science Reviews 29, 455e471. Cui, Y.H., Zhang, D.Z., Du, C.S., 1999. General History of Qinghai Provence. Qinghai People's Publishing House, Xining (in Chinese). Gao, Y.X., 1962. On some problems of Asian monsoon. In: Gao, Y.X. (Ed.), Some Questions about the East Asian Monsoon. Science Press, Beijing, pp. 1e49 (in Chinese). Han, P., Sun, J.M., 2004. OSL dating of the Otindag desert. Quaternary Science 24 (7), 480 (in Chinese). Han, W.X., Ma, Z.B., Lai, Z.P., Appel, E., Fang, X.M., Yu, L.P., 2014. Wind erosion on the north-eastern Tibetan Plateau: constraints from OSL and U-Th dating of playa salt crust in the Qaidam Basin. Earth Surface Processes and Landforms 39, 779e789. Hao, Y.P., Fang, X.M., Xi, X.X., HU, S.X., Guan, D.H., 1998. The characteristic of climatic fluctuation recorded by soil formation since late Pleistocene in east region of Qaidam Basin. Scientia Geographica Sinica 18, 249e254 (in Chinese). Huang, Q., Cai, B.Q., Yu, J.Q., 1981. The 14C age and cycle of sedimentation of some saline lakes on the Qinghai-Xizang Plateau. Chinese Science Bulletin 26, 66e70. Huang, Y.Z., Wang, N.A., He, T.H., Chen, H.Y., Zhao, L.Q., 2009. Historical desertification of the mu Us desert, northern China: a multidisciplinary study. Geomorphology 110, 108e117. Hong, Y.T., Hong, B., Lin, Q.H., Zhu, Y.X., Shibata, Y., Hirota, M., Uchida, M., Leng, X.T., Jiang, H.B., Xu, H., Wang, H., Yi, L., 2003. Correlation between Indian Ocean summer monsoon and North Atlantic climate during the Holocene. Earth and Planetary Science Letters 211, 371e380. Kapp, P., Pelletier, J.D., Rohrmann, A., Heermance, R., Russell, J., Ding, L., 2011. Wind erosion in the Qaidam basin, central Asia: implications for tectonics, paleoclimate, and the source of the Loess Plateau. GSA Today 21 (4/5), 4e10. Lai, Z.P., 2006. Testing the use of an OSL standardized growth curve (SGC) for De determination on quartz from the Chinese Loess Plateau. Radiation Measurements 41, 9e16. Lai, Z.P., 2010. Chronology and the upper dating limit for loess samples from Luochuan section in Chinese Loess Plateau using quartz OSL SAR protocol. Journal of Asian Earth Sciences 37, 176e185. Lai, Z.P., Wintle, A.G., Thomas, D.S.G., 2007a. Rates of dust deposition between 50 ka and 20 ka revealed by OSL dating at Yuanbao on the Chinese Loess Plateau. Palaeogeography, Palaeoclimatology, Palaeoecology 248, 431e439. €ller, L., Fülling, A., 2007b. Existence of a common growth Lai, Z.P., Brückner, H., Zo curve for siltesized quartz OSL of loess from different continents. Radiation Measurements 42, 1432e1440. Lai, Z.P., Brückner, H., 2008. Effects of feldspar contamination on equivalent dose and the shape of growth curve for OSL of silt-sized quartz extracted from Chinese loess. Geochronometria 30, 49e53.

32

L. Yu et al. / Quaternary International 372 (2015) 23e32

€ ller, L., Fuchs, M., Brückner, H., 2008. Alpha efficiency determination for Lai, Z.P., Zo OSL of quartz extracted from Chinese loess. Radiation Measurements 43, 767e770. Lai, Z.P., Kaiser, K., Brückner, H., 2009. Luminescence-dated aeolian deposits of late Quaternary age in the southern Tibetan Plateau and their implications for landscape history. Quaternary Research 72, 421e430. Lai, Z.P., Mischke, S., Medsen, D., 2014. Paleoenvironmental implications of new OSL dates on the formation of the “Shell Bar” in the Qaidam Basin, northeastern Qinghai-Tibetan Plateau. Journal of Paleolimnology 51 (2), 197e210. Lai, Z.P., Ou, X.J., 2013. Basic procedures of optically stimulated luminescence (OSL) dating. Progress in Geography 32 (5), 683e693 (in Chinese with English abstract). Lancaster, N., 1988. Development of linear dunes in the southwestern Kalahari, Southern-Africa. Journal of Arid Environments 14, 233e244. Liu, L.Y., Skidmore, E., Hasi, E., Wagner, L., Tatarko, J., 2005. Dune sand transport as influenced by wind directions, speed and frequencies in the Ordos Plateau, China. Geomorphology 67, 283e297. Liu, T.S., 1985. Loess and the Environment. China Ocean Press, Beijing. Liu, X.J., Lai, Z.P., Yu, L.P., Sun, Y.J., Madsen, D., 2012. Luminescence chronology of aeolian deposits from the Qinghai Lake area in the Northeastern QinghaiTibetan Plateau and its palaeoenvironmental implications. Quaternary Geochronology 10, 37e43. Liu, X.Q., Dong, H.L., Rech, J.A., Matsumoto, R., Yang, B., Wang, Y.B., 2008. Evolution of Chaka Salt Lake in NW China in response to climatic change during the Latest PleistoceneeHolocene. Quaternary Science Reviews 27, 867e879. Liu, Y., An, Z.S., Linderholm, H.W., Chen, D.L., Song, H.M., Cai, Q.F., Sun, J.Y., Tian, H., 2009. Annual temperatures during the last 2485 years in the mid-eastern Tibetan Plateau inferred from tree rings. Science in China (Series D: Earth Sciences) 52 (3), 348e359. Lu, H.Y., Zhao, C.F., Mason, J., Yi, S.W., Zhao, H., Zhou, Y.L., Ji, J.F., Swinehart, J., Wang, C.M., 2011. Holocene climate changes revealed by Aeolian deposits from the Qinghai Lake area (northeastern Qinghai-Tibetan Plateau) and possible forcing mechanisms. The Holocene 21, 297e304. Madsen, D.B., Ma, H.Z., Brantingham, P.J., Xing, G., Rhode, D., Zhang, X.Y., Olsen, J.W., 2006. The Late Paleolithic occupation of the northern Tibetan Plateau margin. Journal of Archaeological Science 33, 1433e1444. Murray, A.S., Wintle, A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurement 32, 57e73. Murray, A.S., Wintle, A.G., 2003. The single aliquot regenerative dose protocol: potential for improvements in reliability. Radiation Measurements 37, 377e381. Niu, G.M., Qiang, M.R., Song, L., Lang, L.L., Wang, L.Q., 2010. Change of eastern Asian winter monsoon recorded by aeolian deposits over the past 5000 years at the southeastern margin of Qaidam Basin. Journal of Desert Research 30, 1031e1039 (in Chinese with English abstract). Owen, L.A., Finkel, R.C., Ma, H.Z., Barnard, P.L., 2006. Late Quaternary landscape evolution in the Kunlun Mountains and Qaidam Basin, Northern Tibet: a framework for examining the links between glaciation, lake level changes and alluvial fan formation. Quaternary International 154-155, 73e86. Porter, S.C., Singhvi, A., An, Z.S., Lai, Z.P., 2001. Luminescence age and palaeoenvironmental implications of a Late Pleistocene ground wedge on the Northeastern Tibetan Plateau. Permafrost and Periglacial Processes 12, 203e210. Prescott, J.R., Hutton, J.T., 1994. Cosmic ray contributions to dose rates for luminescence and ESR dating: large depths and long-term time variations. Radiation Measurements 23, 497e500. Pullen, A., Kapp, P., McCallister, A.T., Chang, H., Gehrels, G.E., Garzione, C.N., Heermance, R.V., Ding, L., 2011. Qaidam Basin and northern Tibetan Plateau as dust sources for the Chinese Loess Plateau nad palaeoclimatic implications. Geology 39, 1031e1034. Qian, R., Li, T., 2004-10-18. Ancient Tombs in Dulan County Qinghai Provence: Treasures Interpreting Historical Mystery. Xinhuanet. http://news.xinhuanet. com/expo/2004-10/18/content_2103684.htm (in Chinese). Qiang, M.R., Chen, F.H., Song, L., Liu, X.X., Li, M.Z., Wang, Q., 2013. Late quaternary aeolian activity in gonghe Basin, northeastern Qinghai-Tibetan plateau, China. Quaternary Research 79, 403e412. Roberts, H.M., Duller, G.A.T., 2004. Standardised growth curves for optical dating of sediment using multipleegrain aliquots. Radiation Measurements 38, 241e252. Roberts, H.M., 2007. Assessing the effectiveness of the double-SAR protocol in isolating a luminescence signal dominated by quartz. Radiation Measurements 42, 1627e1636. Rohrmann, A., Heermance, R., Kapp, P., Cai, F.L., 2013. Wind as the primary driver of erosion in the Qaidam Basin, China. Earth and Planetary Science Letters 373, 1e10.

Roskin, J., Tsoar, H., Porat, N., Blumberg, D.G., 2011. Palaeoclimate interpretations of Late Pleistocene vegetated linear dune mobilization episodes: evidence from the northwestern Negev dunefield, Israel. Quaternary Science Reviews 30, 3364e3380. Shao, X.M., Liang, E.Y., Huang, L., Wang, L.L., 2006. A reconstructed precipitation series over the past Millennium in the northeastern Qaidam Basin. Advances in Climate Change Research 2 (3), 122e126 (in Chinese). Sun, J.M., 2000. Origin of eolian sand mobilization during the past 2300 years in the Mu Us Desert, China. Quaternary Research 53, 73e88. Sun, J.M., Li, S.H., Muhs, D.R., Li, B., 2007. Loess sedimentation in Tibet: provenance, processes, and link with Quaternary glaciations. Quaternary Science Reviews 26, 2265e2280. Sun, Y.B., Clemens, S.C., Morrill, C., Lin, X.P., Wang, X.L., An, Z.S., 2012b. Influence of Atlantic meridional overturning circulation on the East Asian winter monsoon. Nature Geoscience 5, 46e49. Sun, Y.J., Lai, Z.P., Long, H., Liu, X.J., Fan, Q.S., 2010. Quartz OSL dating of archaeological sites in Xiao Qaidam Lake of the NE Qinghai-Tibetan Plateau and its implications for palaeoenvironmental changes. Quaternary Geochronology 5, 360e364. Sun, Y.J., Lai, Z.P., Madsen, D., Hou, G.L., 2012a. Luminescence dating of a hearth from the archaeological site of Jiangxigou in the Qinghai Lake area of the northeastern Qinghai-Tibetan Plateau. Quaternary Geochronology 12, 107e110. Wang, Y.J., Cheng, H., Edwards, R.L., He, Y.Q., Kong, X.G., An, Z.S., Wu, J.Y., Kelly, M.J., Dykoski, C.A., Li, X.D., 2005. The holocene asian monsoon: links to solar changes and North Atlantic climate. Science 308, 854e857. Wu, G.H., Hu, S.X., Zhang, Z.L., Zhao, H., Fang, X., 1985. The Qaidam Basin. Journal of Lanzhou University 21, 35e52 (in Chinese). Yang, B., Qin, C., Wang, J.L., He, M.H., Melvin, T.M., Osborn, T.J., Briffa, K.R., 2014. A 3,500 year tree-ring record of annual precipitation on the northeastern Tibetan Plateau. Proceedings, National Academy of Sciences 111, 2903e2908. Yang, L.H., Wang, T., Zhou, J., Lai, Z.P., Long, H., 2012a. OSL chronology and possible forcing mechanisms of dune evolution in the Horqin dunefield in northern China since the Last Glacial Maximum. Quaternary Research 78 (2), 185e196. Yang, X.P., Scuderi, L., Paillou, P., Liu, Z.T., Li, H.W., Ren, X.Z., 2012b. Quaternary environmental changes in the drylands of China e a critical review. Quaternary Science Reviews 30, 3219e3233. Yu, L.P., Lai, Z.P., 2012. OSL chronology and palaeoclimatic implications of aeolian sediments in the Qaidam Basin of the northeastern Qinghai-Tibetan Plateau. Palaeogeography, Palaeoclimatology, Palaeoecology 337-338, 120e129. Yu, L.P., Lai, Z.P., 2014. Holocene Climate changes based on OSL chronology and stratigraphy of the aeolian sediments in the eastern Qaidam Basin, northeastern Qinghai-Tibetan Plateau. Quaternary Research 81, 488e499. Yu, L.P., Lai, Z.P., An, P., 2013. OSL chronology and paleoclimatic implications of paleodunes in the middle and southwestern Qaidam Basin, Qinghai-Tibetan Plateau. Sciences in Cold and Arid Regions 5 (2), 211e219. Yu, L.P., Lai, Z.P., Dong, Z.B., Qian, G.Q., Pan, T., 2014. Origin and lateral migration of linear dunes in the Qaidam Basin of NW China revealed by dune sediments, internal structures, and optically stimulated luminescence ages, with implications for linear dunes on Titan: comment and discussion. GSA Bulletin. http:// dx.doi.org/10.1130/B31041.1 (in press). Zeng, Y.F., 2006. Environmental changes and cultural transition at Late Holocene in Qaidam Basin. Journal of Arid Land resources and Environment 20, 61e64 (in Chinese). Zeng, Y.N., Feng, Z.D., Cao, G.C., 2003. Desert formation and evolution in Qaidam Basin since the Last Glacial epoch. Acta Geographica Sinica 58, 452e457 (in Chinese). Zeng, Y.N., Ma, H.Z., Sha, Z.J., Li, L.Q., Li, Z., Cao, G.C., 1999. The record of Younger Drays event in eolian sand deposit in Qaidam Basin. Chinese Geographical Science 9, 92e95. Zhang, P.Z., Cheng, H., Edwards, R.L., Chen, F.H., Wang, Y.J., Yang, X.L., Liu, J., Tan, M., Wang, X.F., Liu, J.H., An, C.L., Dai, Z.B., Zhou, J., Zhang, D.Z., Jia, J.H., Jin, L.Y., Johnson, K.R., 2008. A test of climate, sun, and culture relationships from an 1810-year Chinese cave record. Science 322, 940e942. Zhao, H., Lu, Y.C., Yin, J.H., 2007. Optical dating of Holocene sand dune activities in the Horqin sand-fields in Inner Mongolia, China, using the SAR protocol. Quaternary Geochronology 2, 29e33. Zhou, J.X., Zhu, Y., Yuan, C.Q., 2012. Origin and lateral migration of linear dunes in the Qaidam Basin of NW China revealed by dune sediments, internal structures, and optically stimulated luminescence ages, with implications for linera dunes on Titan. Geological Society of America Bulletin 124 (7/8), 1147e1154. Zhu, Z., Wu, Z., Liu, S., Di, X., 1980. An Outline of Chinese Deserts. Science Press, Beijing (in Chinese).