Quartz OSL and K-feldspar post-IR IRSL dating of loess in the Huangshui river valley, northeastern Tibetan plateau

Aeolian Research 33 (2018) 23–32

Contents lists available at ScienceDirect

Aeolian Research journal homepage: www.elsevier.com/locate/aeolia

Quartz OSL and K-feldspar post-IR IRSL dating of loess in the Huangshui river valley, northeastern Tibetan plateau

T

⁎

Yixuan Wanga,b,c, , Tianyuan Chenc,d, Chongyi E.e, Fuyuan And, Zhongping Laif, Lin Zhaoa, ⁎ Xiang-Jun Liud, a

State Key Laboratory of Cryospheric Sciences, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China Salt Lake Chemistry Analysis and Test Center, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China c University of Chinese Academy of Sciences, Beijing 100049, China d Key Laboratory of Salt Lake Geology and Environment of Qinghai Province, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China e Qinghai Normal University, Xining 810000, China f School of Earth Sciences, China University of Geosciences, Wuhan 430074, China b

A R T I C LE I N FO

A B S T R A C T

Keywords: Northeastern Tibetan Plateau Loess Quartz OSL dating K-feldspar pIRIR dating

The northeastern Tibetan Plateau (NETP) is located in the climatically sensitive semiarid zone between the regions controlled by the East Asian monsoon and the Westerlies and loess deposits there may preserve a record of regional paleoenvironmental change. Establishing a robust loess chronology is critical for interpreting and correlating environmental records. In this study, quartz optical stimulated luminescence (OSL) and K-feldspar post-IR infrared (IR) stimulated luminescence (pIR-IRSL) dating methods have been used to date the Ledu loess section in the Huangshui river valley, on the NETP. In terms of quartz OSL dating, the results from both the 63–90 μm and 38–63 μm quartz fractions are consistent within errors. The reliability of the 63–90 μm K-feldspar pIRIR dating was confirmed by internal check using preheat plateau, dose recovery, anomalous fading, and residual dose tests. The results suggest that the K-feldspar pIRIR signals at stimulation temperatures of 170 and 225 °C were well bleached before deposition of Ledu loess. Comparison between quartz OSL and K-feldspar pIRIR dating indicates that quartz ages older than 50 ka (∼150 Gy) may be underestimated. In establishing the chronological framework for the study section, we selected quartz OSL results for ages < 50 ka and the Kfeldspar pIRIR170 and pIRIR225 results for ages > 50 ka. The results demonstrate that aeolian dust accumulated continuously between 67 and 25 ka, and there were two gaps in deposition, between 25 and 2 ka and from 80 to 67 ka.

1. Introduction The northeastern part of the Tibetan Plateau (TP) is the transition zone between the TP and the Chinese Loess Plateau (CLP); it lies in the monsoon marginal zone and is influenced by the westerlies, East Asian summer monsoon, and plateau monsoon (Liu et al., 2015; Lu et al., 2004). The area is regarded as an ideal region for research on uplift process of the TP, environmental changes, and evolution of the Asian monsoon (An et al., 2012; Lu et al., 2004). Research based on geomorphologic, stratigraphic, geochemical, and zircon U-Pb chronological analysis suggests the northern and northeastern TP forms an important source region for silts deposited in the CLP (Bird et al., 2015; Bowler et al., 1987; Kapp et al., 2011; Li et al., 2013; Licht et al., 2016; Nie et al., 2015; Pullen et al., 2011; Stevens et al., 2013; Liu et al.,

2017). During recent decades, the northeastern TP has become a key area for the reconstruction of the palaeoclimatic evolution of central Asia (Stauch et al., 2016). Loess deposits, which are widespread on the NETP, are highly sensitive to shifts in the Asian summer and winter monsoon and/or northern hemisphere westerly circulation (Liu & Ding, 1998; Lu et al. 2004). Loess deposits also preserve important information on Quaternary climate change and atmospheric dust flux, however, a robust chronological framework is critical for retrieving this environmental information (Roberts, 2008; Timar-Gabor et al., 2011). OSL dating of quartz using the single-aliquot regenerative-dose (SAR) dating protocol is now being widely applied to late Quaternary sediments (Murray and Olley, 2002; Wintle and Murray, 2006). Over the past decade, a considerable amount of research has been undertaken on luminescence dating of Chinese loess-paleosol sequences,

⁎ Corresponding authors at: State Key Laboratory of Cryospheric Sciences, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China (Y. Wang). E-mail addresses: [email protected] (Y. Wang), [email protected] (X.-J. Liu).

https://doi.org/10.1016/j.aeolia.2018.04.002 Received 6 December 2017; Received in revised form 13 April 2018; Accepted 17 April 2018 1875-9637/ © 2018 Elsevier B.V. All rights reserved.

Aeolian Research 33 (2018) 23–32

Y. Wang et al.

(38–63 μm) and coarse (63–90 μm) grain size fractions were obtained by wet sieving. Heavy liquids with densities of 2.62, 2.75, and 2.58 g/ cm3 were used to separate the quartz and K-feldspar fractions of each sample. The 38–63 μm quartz fraction was then treated with silica saturated fluorosilicic acid (H2SiF6) for about two weeks, while the 63–90 μm quartz fraction was etched with 40% HF for 60 min, and both were then treated with 10% HCl to remove any fluorides. The purity of the extracted quartz was checked by IR stimulation; where there were obvious IR signals, quartz grains were re-etched with H2SiF6 or HF to avoid age underestimation (Duller, 2003; Lai and Brückner, 2008; Roberts, 2007). The K-feldspar 63–90 μm fraction of separates were not HF etched as HF etching on K-feldspar tends to cause deep pitting and to preferentially attack the cleavage planes rather than removing a uniform shell from the grains (Duller, 1994; Long et al., 2014). Quartz and K-feldspar grains were then mounted as a mono-layer on the central part (∼0.7 cm diameter) of stainless steel discs (∼0.97 cm diameter) using silicone oil. The OSL signal was measured using an automated Risø TL/OSL-DA-20 reader. Laboratory irradiation was carried out using 90Sr/Y90 sources mounted within the reader, with a dose rate of 0.089 Gy/s. The OSL signal was obtained after passage through a U-340 filter and the IRSL signal was detected using a photomultiplier tube with the IRSL passing through BG-39 and coring-759 filters. The environmental dose rate was calculated from measurements of radioactive element concentrations of the surrounding sediment with a small contribution from cosmic rays. For all samples, U and Th concentration and K content was determined using neutron activation analysis at the Chinese Atomic Energy Institute. Calculation of the cosmic dose rate was based on Prescott and Hutton (1994). The measured water content of the loess samples from the section varied between 1 and 6%, however, considering that the section has been exposed by sand excavation for a long time, this is likely to be an underestimate. Based on data from previous loess studies (ChongYi et al., 2012; Lai, 2010; Li et al., 2016), a water content of 10 ± 5% was used in all dose rate calculations. The a-value for 38–63 μm was taken as 0.035 ± 0.003 (Lai et al., 2008). For K-feldspar dose rates, a K concentration of 12.5 ± 0.5% and Rb concentration of 400 ± 100 ppm was assumed (Huntley and Baril, 1997).

mainly based on quartz OSL (Buylaert et al., 2007, 2008; Lai, 2010; Stevens et al., 2006, 2008), and recently this has been applied to the NETP (Liu and Lai, 2013; Liu et al., 2015, 2016; Yu and Lai, 2014). Buylaert et al. (2008) conducted low stratigraphic resolution quartz OSL dating on loess from the NETP, and reported that the quartz ages saturated at ∼50 ka. In an analysis of 30 high resolution quartz OSL ages, Wang et al. (2015a) revealed episodic accumulation of loess from 30 to 0.2 ka. However, quartz OSL dating is generally limited to a saturation dose of 120–150 Gy, for loess deposits with a typical dose rate 3–4 Gy/ka, which restricts its use to the last 40–50 ka (Buylaert et al., 2007; Chapot et al. 2012; Li et al., 2016; Roberts, 2008; Timar-Gabor and Wintle, 2013; Yi et al., 2015, 2016). Feldspar luminescence provides an alternative sediment dating method that has a higher saturation dose compared to quartz (Huntley and Lamothe, 2001). However, most feldspar suffers anomalous fading, which results in underestimation of the true age (Spooner, 1994; Wintle, 1973). Recently, two new protocols have been developed, post-IR IRSL (pIRIR) and multielevated-temperature post-IR IRSL (MET-pIRIR), to obtain lower fading rates and improve the reliability of feldspar luminescence dating (Buylaert et al., 2009, 2012; Li and Li, 2011, 2012; Thiel et al., 2011; Thomsen et al., 2008). In this study, we used quartz OSL and K-feldspar pIRIR methods to date Ledu loess in the Huangshui river valley, NETP. We first explored the characteristics of quartz SAR OSL, then investigated the luminescence characteristics of the elevated temperature IRSL signals in a SAR post-IR IRSL protocol. The reliability of K-feldspar pIRIR age estimates was confirmed by internal checks of luminescence characteristics, a fading test, and by comparison of the quartz and K-feldspar ages. Finally, we used the luminescence ages to explore the continuity of loess deposition in the Huangshui river valley, to test recent suggestions of episodic loess deposition on the NETP (Liu et al., 2017; Wang et al., 2015a). 2. Study area and sampling The NETP is situated at the junction of areas controlled by the Asian summer monsoon and Westerlies (An et al., 2012). The annual mean precipitation and temperature are ∼340 mm and 7 °C, respectively. Loess deposits are widely distributed on the NETP, and are generally coarser and less compacted than those in the central CLP (Lu et al., 2004, 2011; Vriend and Prins, 2005). The Huangshui river valley contains loess accumulations that are commonly mantled on a series of river terraces within the Xining, Ledu, and Minhe basins (Fig. 1). For this study, we sampled an approximately 23-m thick loess section, which overlies the third terrace of the Huangshui river in the Ledu basin (termed the LD section). The top 10 m of the section comprises typical loess, with a median grain size of around 35 µm, overlying 13 m of light yellow loess alternating with thin reddish-yellow silt layers (Figs. 2 and 3). The loess grain size distribution curves show a typical distribution, with a modal size of ∼55 µm (Fig. 4), which is similar to the nearby loess section reported by Wang et al. (2015a). Paleosols are weakly developed and are difficult to identify in the field. Thirty-nine luminescence samples were collected at 50-cm intervals from the freshly excavated profile using light-tight steel cylinders (diameter 5 cm, length 20 cm) (Fig. 2).

4. Luminescence characteristics 4.1. Quartz OSL A combination of SAR protocol (Murray and Wintle, 2000) and standardized growth curves (SGCs) (Lai, 2006; Lai et al., 2007; Roberts and Duller, 2004), i.e., the SAR-SGC method, was used to determine 39 medium-grained (38–63 µm) and 8 coarse-grained (63–90 µm) quartz De. For each sample, 6–8 aliquots were measured by SAR to build a SGC, and then 12–24 additional aliquots were measured by SGC. The final De for each sample was derived from the mean of the SAR De and the SGC De. The net quartz OSL signal was calculated using the initial 0.64 s integral of the OSL decay curve minus the last 8 s integral. The suitability of the SAR procedure for De determination was tested using a dose recovery test (Murray and Wintle, 2003). The dose recovery test was performed on two samples, from the upper (LD-2, 38–63 μm) and a lower (LD-30, 38–63 μm) section. Twenty-four natural aliquots were stimulated twice by blue-light stimulation at 130 °C for 60 s. The bleached aliquots were then given a laboratory dose of 89 Gy (LD-2) and 160 Gy (LD-30), close to their natural De. Preheat temperatures ranged from 220 to 300 °C at 20 °C intervals for 10 s, using a heating rate of 5 °C/s, and the cut-heat temperature was fixed at 220 °C for all measurements. At each preheat temperature, four aliquots were measured for calculation of mean values. The ratio of measured to given De, and recycling and recuperations ratios for samples LD-2 and LD-30 are plotted in Fig. 5. For sample LD-2, a plateau was observed for temperatures from 220 to 280 °C. The recycling ratios for different

3. Materials and methods All laboratory pretreatments, sample preparation, and luminescence measurements were conducted under subdued red light in the luminescence laboratory at the Qinghai Institute of Salt Lakes, Chinese Academy of Science. Three cm of material at each end of sample tubes was removed and reserved for environment dose rate measurement. The unexposed part in the middle of the tube was used for equivalent dose (De) determination. All samples were treated with 10% HCl and 30% H2O2 to remove carbonates and organic matter. Medium 24

Aeolian Research 33 (2018) 23–32

Y. Wang et al.

Fig. 1. Location maps. (A) Location of the study area (red rectangle) in China. (B) DEM image of the study area. The study site in the Ledu basin is illustrated by a solid white star (the LD loess section), and the previously reported loess section of Wang et al. (2015a) is illustrated by a solid white circle (the HS loess section). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

importance to find a balance between sufficient signal stability and minimized contribution of residual doses (Kars et al., 2014). Previous studies have demonstrated that the residual dose increases as a function of preheat and/or stimulation temperature (Fu et al., 2012; Reimann et al., 2011; Zhang et al., 2015). To investigate the impact of residual doses due to increasing preheat and stimulation temperature, 24 aliquots of sample LD-2, LD-15, and LD-34 were bleached for 56 h under sunlight (8h per day for 7 days). The relationship between the residual dose of pIRIR and preheat temperature for the three samples is show in Fig. 8. The residual doses gradually increases with preheat and stimulation temperature, indicating that harder-to-bleach signals are stimulated at higher temperatures. Furthermore, the larger the De value, the larger the residual dose; this is consistent with previous studies (Buylaert et al., 2012; Sohbati et al., 2012; Zhang et al., 2015). For sample LD-2, the residual dose of the pIRIR signal ranges between 0.5 and 9.4 Gy, which is less than 7% of its De, and for sample LD-15, the residual dose ranges between 1.3 and 14.7 Gy, which is less than 10% of its De. These results indicate that it is safe to ignore the residual dose at any temperature for LD-2 and LD-15. However, for sample LD-34, the residual dose (which ranges between 4.5 and 37.7 Gy) is greater than 10% of the De when the preheat temperatures is above 280 °C, which can lead to age overestimation.

measurement temperatures all fall in the 0.9–1.1 range, varying between 0.99 and 1.06. Recuperations for different preheat temperatures are less than 3% of the natural signal, ranging from 0.95 to 2.88%. For sample LD-30, a plateau was observed for temperatures from 240 to 280 °C. The recycling ratios for different measurement temperatures all fall in the 0.9–1.1 range, varying between 0.99 and 1.02. Recuperations for different preheat temperatures are less than 2% of the natural signal, ranging from 1.10 to 1.80%. Based on these results the SAR sequence with a preheat temperature of 260 °C and a cut-heat of 220 °C was selected to measure the De of the quartz fraction. The OSL decay curves and reconstructed dose response curves for sample LD-8 are shown in Fig. 6. The blue-light stimulated OSL signals decrease quickly during the first second of stimulation, indicating that the signal is dominated by the fast component (Singarayer and Bailey, 2003). The De and calculated quartz OSL age for each sample are listed in Table 1. 4.2. K-feldspar pIRIR characteristics 4.2.1. Preheat plateau test A preheat plateau test for the pIRIR dating protocol was conducted to find the most suitable preheat and stimulation temperatures for De determination. Twenty-four aliquots of samples LD-2 and LD-34 were prepared for measurement under eight different temperature conditions. Preheat temperatures at 20 °C intervals from 180 to 320 °C were maintained for 60 s, with the first IR stimulation carried out at 50 °C for 200 s (IR50), followed by a second stimulation for 200 s at an elevated temperature (pIRIR) that tracked the preheat temperature by 30 °C. The preheat test results are shown in Fig. 7. For both samples, the pIRIR De shows a systematic increase with preheat temperatures between 180 and 320 °C, and a plateau between 200 and 260 °C. The recycling ratios for different preheat temperatures all fall in the range of 0.9–1.1, and the recuperation values for the different preheat temperatures are all less than 5% of the natural signal. In contrast to the pIRIR signals, the IR50 De systematically increases up to 220 °C for both samples, then decreases above 220 °C. Similar trends in De have been observed in previous studies (Roberts, 2012; Zhang et al., 2015).

4.2.3. Anomalous fading A fading test was carried out for sample LD-2 following the method of Auclair et al. (2003), with laboratory fading rates (g-values) determined for pIRIR170 and pIRIR225. The pIRIR170 and pIRIR225 g-values obtained for sample LD-2 were 0.78 ± 0.27%/decade and 0.66 ± 0.34%/decade, respectively, which represent less than 1%/ decade. This result underlines the suggestion that low fading rates may be a laboratory artifact, and that anomalous fading is negligible (Buylaert et al., 2012; Thiel et al., 2011). Hence, in this study we followed previous protocol (Buylaert et al., 2012; Li et al., 2015; Long et al., 2014) and did not correct the pIRIR170 and pIRIR225 ages for anomalous fading. 4.2.4. Dose recovery test In order to check the reliability of the pIRIR dating sequence, pIRIR170/pIRIR225 was checked with a dose recovery test on samples LD-2 and LD-34. A laboratory dose of ∼107 Gy (LD-2) and ∼235 Gy

4.2.2. Residual dose For pIRIR dating of sediments with different ages, it is of crucial 25

Aeolian Research 33 (2018) 23–32

Y. Wang et al.

Fig. 2. Ledu (LD) loess section and stratigraphic plot. The black dots denote OSL sample collection sites; orange bands represent the red colored flood silt deposits. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

5. Results and discussion

(LD-34), close to their average De values, was added to aliquots which had been bleached for 56 h under sunlight (8 h per day for 7 days). The ratios of measured/given dose were obtained after subtraction of the residual dose. For sample LD-2, the measured/given dose ratio was calculated as 0.96 ± 0.01 for pIRIR170 and 0.92 ± 0.01 for pIRIR225, and the equivalent ratios for LD-34 were 0.94 ± 0.01 and 0.99 ± 0.04. The dose recovery test results show that both pIRIR170 and pIRIR225 are reliable for De determination. Based on the above conditional experiment results, feldspar De values for Ledu loess were determined using stimulation temperatures of 170 °C (pIRIR170) and 225 °C (pIRIR225), measured using pIRIR protocols (Table 2) similar to those of Buylaert et al. (2009) and Li et al. (2015). The integrated signal for both pIRIR and IRSL50 was calculated from the first 2 s minus the background from the last 40 s. The stimulation time for pIRIR signals used in the current pIRIR SAR protocol is 200 s. We kept the test dose constant at ∼30% of the total measured dose. The pIRIR170 and pIRIR225 decay curves for sample LD-15 are illustrated in Fig. 9a and b, respectively. The IRSL 50 °C signal decreases more rapidly than the pIRIR170 and pIRIR225 signals, suggesting the latter bleach more slowly. The pIRIR170 and pIRIR225 growth curves for sample LD-15, as shown in Fig. 9a and b, can be readily fitted using a single saturation exponential.

5.1. Comparison of 38–63 μm and 63–90 μm quartz ages In principle, luminescence dating of sediments is applicable to a wide range of grain sizes, from silt to sand. Different loess grain size ranges have been investigated in previous studies, such as 4–11 μm (Kang et al., 2015; Roberts, 2008), 38–63 μm (Lai et al., 2007; Lai and Wintle, 2006), 63–90 μm (Buylaert et al., 2008; Wang et al., 2015a). The reliability of OSL dating results for a sample may be determined by comparison of ages derive from different particle size ranges. Here, we compare OSL ages derived from two different grain size fractions, coarse (63–90 μm) and medium (38–63 μm). OSL ages derived from coarse and medium quartz fractions for seven samples distributed from top to bottom of the LD section are shown in Fig. 10. The dating results of the 63–90 μm fraction are essentially consistent with the results of the 38–63 μm fraction within errors.

5.2. Comparison of pIRIR170 and pIRIR225 feldspar ages The pIRIR dating method has been tested by many researchers under various measurement conditions. Usually, a pIRIR dating 26

Aeolian Research 33 (2018) 23–32

Y. Wang et al.

Fig. 3. Photos of parts of the Ledu loess section. (a) 12.5 m depth and (b) 9.5–10 m depth.

bleached before burial or any residual signal must be quantifiable (Kars et al., 2014). Based on our preheat plateau and residual dose experiments, we found that although the residual dose varies for the different signals examined, it is not large enough to account for the dramatic variation in De values obtained using the elevated preheat temperature. The quartz age of sample LD-2 (∼26.1 ka) is the same as the pIRIR170 (∼26.9 ka) and pIRIR225 (∼27.2 ka) ages, but the pIRIR290 (∼32.0 ka) age is overestimated even with subtraction of the residual dose. These analyses indicate that stimulation temperatures of 170 and 225 °C provide reliable age estimates for K-feldspar samples. Comparison of the 21 pIRIR170 ages and 27 pIRIR225 ages from the LD section (Table 1) provides a cross-check of the reliability of the pIRIR protocols using elevated stimulation temperatures of 170 and 225 °C; the dating results for both are consistent within errors. Previous studies have also indicated that the K-feldspar pIRIR170 signal in loess of the NETP and the arid central Asia is stable. ChongYi et al. (Unpublished results) found that loess on the NETP can be well dated using a stimulation temperature of 170 °C rather than 290 °C for pIRIR K-feldspar dating. Li et al. (2015) also found that the pIRIR170 signal of loess in ACA is stable. These findings demonstrate that K-feldspar pIRIR170 provides an alternative method for obtaining a luminescence chronology when quartz OSL dating is unavailable or where there is incomplete bleaching of the pIRIR signal at higher stimulation temperatures.

Volume percentage (%)

8

6

4

2

0 0.01

0.1

1

10

100

1000

ȝm Fig. 4. Characteristic grain size distribution curves for loess at 3, 5, 7, and 9.5 m depth.

protocol using a high preheat temperature (e.g., 250 and 320 °C for 60 s) is applied to obtain a low fading rate of the pIRIR signal (Buylaert et al., 2009; Thiel et al., 2011). However, when a high preheat temperature is used, unbleachable residual doses of a few Gy to several tens of Gy can be observed (Buylaert et al., 2012), and a pIRIR signal obtained at higher stimulation temperature is harder to bleach (Buylaert et al., 2009; Thomsen et al., 2008). A lower preheat temperature has been shown to reduce the residual dose to a level at which it can be ignored (e.g., Li et al., 2015; Long et al., 2014; Madsen et al., 2011; Reimann and Tsukamoto, 2012). For dating sediment with different ages, the key is that either the samples must have been completely

5.3. Comparison of quartz and K-feldspar ages The 39 medium-grained quartz OSL ages, 21 pIRIR170 ages and 27 pIRIR225 coarse-grained K-feldspar pIRIR ages for the LD loess section are plotted against depth in Fig. 11. The quartz and feldspar ages are in 27

Aeolian Research 33 (2018) 23–32

Y. Wang et al.

Fig. 5. Dose recovery test results for 38–63 μm quartz in samples LD-2 and LD-30.

framework of the LD section, we selected the quartz OSL result for ages < 50 ka and the K-feldspar pIRIR result for ages > 50 ka. 5.4. Ledu loess chronology and palaeoclimatic implication The Ledu loess section we investigated lies on the third level river terrace of the Huangshui river; the sediments immediately below the loess deposit comprise laminated fluvial silts and mud, which are underlain by fluvial gravels of unknown depth (Fig. 2). Our dating results show that the river terrace formed before 80 ka, corresponding to the MIS 5e–5d stage river terrace, as reported in Wang et al. (2015b). Wang et al. (2015b) proposed that the lower fluvial gravels were deposited during cold stages (such as MIS 6 and MIS 5d), and that aggradation during cold periods was associated with floodplain widening. The coarse-grained cold phase deposits are covered by inter-bedded, horizontally-laminated silt and sand (representing flood sediments that often contain reworked soil material), during the (cold to warm) transitional phases (Wang et al., 2015b). The quartz and feldspar OSL ages we obtained indicate that loess accumulated continuously from approximately 67–25 ka, with gaps in deposition between 25–2 ka, and 80–67 ka. Wang et al. (2015a) previously reported rapid accumulation of loess in the Huangshui river valley at approximately 12.3, 16, 21–23, 25–28, and 30–33 ka, separated by hiatuses in accumulation. However, our aeolian section in the Ledu area lacks sediment dating to between the last glacial maximum and the early to mid-Holocene. Interestingly, Wang et al. (2015a) reported a low early and middle Holocene loess accumulation rate (only ∼50 cm loess deposited between 9.4 and 0.2 ka) in an aeolian section near Ledu. Furthermore, Wang et al.’s (2015a) identification of several deposition gaps between 33 and 12 ka contrasts with our finding of continuous loess deposition persisting during the last glacial, from 67 to 25 ka, and depositional gaps between 25 and 2 ka (Fig. 11). It seems that loess accumulation patterns in the Huangshui river valley are complex, and more loess sections need to be studied to provide a deeper understanding of loess deposition processes. Our dating results show that loess sediment accumulation is episodic, with greatest deposition of 17 m during MIS3, equivalent to a mass accumulation rate of ∼40.5 cm/ka. The importance of the northern and northeastern Qinghai-Tibetan Plateau as a major source region for the CLP has been

Fig. 6. Luminescence characteristics of 38–63 μm quartz for sample LD-8. A typical growth curve was fitted using an exponential plus linear function. Inset shows quartz OSL decay curves for the natural (N), test dose (TD), and regeneration dose (0 Gy).

good agreement back to ∼50 ka; this consistency provides confidence in the reliability of the pIRIR age. Beyond 50 ka (De > 150 Gy) the quartz OSL ages are systematically younger than the pIRIR170 and pIRIR225 ages. This suggests that the SAR protocol on medium(38–63 μm) and coarse-grained (63–90 μm) quartz should be restricted to ages not exceeding ∼150 Gy (∼50 ka). This observation is consistent with previous studies on the NETP (Buylaert et al., 2007, 2008; ChongYi et al., Unpublished results). Lai (2010) suggested that an upper dating limit of ∼70 ka for silt-sized quartz on the CLP, and that De larger than 230 Gy will provide age underestimates. Li et al. (2016) found quartz OSL age underestimation for samples in arid central Asia older than ∼40 ka. Inconsistency in the upper OSL dating limit may be due to variation in loess quartz OSL characteristics in different regions. Overall, the findings imply that when dating loess samples older than 40–50 ka, there needs to be comparison between quartz and K-feldspar ages to ensure the reliability of results. In establishing the chronological 28

LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD LD

OSL-1 OSL-2 OSL-3 OSL-4 OSL-5 OSL-6 OSL-7 OSL-8 OSL-9 OSL-10 OSL-11 OSL-12 OSL-13 OSL-14 OSL-15 OSL-16 OSL-17 OSL-18 OSL-19 OSL-20 OSL-21 OSL-22 OSL-23 OSL-24 OSL-25 OSL-26 OSL-27 OSL-28 OSL-29 OSL-30 OSL-31 OSL-32 OSL-33 OSL-34 OSL-35 OSL-36 OSL-37 OSL-38 OSL-39

Sample ID

0.1 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.8 11.3 11.8 12.3 12.8 13.3 13.8 14.3 14.7 15.2 15.6 16.3 16.8 17.3 17.9 18.4 18.9 19.5

(m)

Depth

1.78 1.82 1.96 1.86 1.98 1.99 2.04 1.86 1.93 1.94 1.98 1.97 1.95 1.90 2.00 1.99 1.89 1.93 1.93 1.88 1.87 1.74 1.88 1.84 1.86 1.93 1.83 1.91 1.75 1.95 1.83 1.92 1.89 1.88 2.02 1.92 2.06 1.88 1.90

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

K (%)

0.07 0.07 0.06 0.07 0.07 0.05 0.04 0.06 0.05 0.07 0.06 0.07 0.06 0.05 0.06 0.04 0.05 0.05 0.06 0.04 0.04 0.04 0.05 0.05 0.05 0.06 0.05 0.06 0.04 0.07 0.06 0.06 0.05 0.05 0.07 0.07 0.07 0.06 0.07

12.16 12.56 13.16 11.33 12.87 12.56 13.42 12.85 12.60 11.84 12.62 13.23 11.87 11.95 12.70 12.43 12.58 11.73 11.77 12.33 12.47 11.78 13.09 13.06 13.06 11.88 13.63 12.47 12.56 13.61 11.54 12.76 11.92 12.69 13.56 11.93 13.20 12.49 12.56

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

Th (ppm)

0.22 0.14 0.10 0.09 0.10 0.27 0.16 0.15 0.23 0.11 0.20 0.15 0.21 0.31 0.34 0.32 0.18 0.18 0.25 0.31 0.34 0.25 0.28 0.23 0.28 0.24 0.27 0.23 0.27 0.21 0.18 0.15 0.17 0.29 0.31 0.18 0.23 0.25 0.26

2.78 2.89 3.31 2.86 2.98 3.02 2.89 3.04 3.00 2.89 2.92 2.74 2.70 2.72 2.84 2.73 2.73 2.62 2.59 2.63 2.68 2.56 2.81 2.91 2.88 2.81 2.95 2.83 2.72 2.90 2.62 2.90 2.70 2.85 2.78 2.62 2.81 2.72 2.50

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

U (ppm)

0.05 0.04 0.04 0.04 0.06 0.08 0.06 0.06 0.07 0.06 0.06 0.05 0.08 0.08 0.12 0.06 0.06 0.07 0.06 0.07 0.06 0.07 0.07 0.06 0.06 0.07 0.08 0.09 0.08 0.08 0.07 0.08 0.10 0.06 0.07 0.06 0.10 0.09 0.05

10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

(%) 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

Water content

Table 1 Quartz OSL and K-feldspar pIRIR170 and pIRIR225 equivalent doses and ages.

3.36 3.36 3.58 3.26 3.44 3.46 3.52 3.33 3.36 3.29 3.37 3.36 3.24 3.20 3.36 3.30 3.21 3.17 3.16 3.15 3.16 2.97 3.22 3.20 3.21 3.18 3.23 3.20 3.04 3.31 3.02 3.23 3.11 3.18 3.35 3.11 3.36 3.13 3.11

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

(Gy/ka) 0.15 0.15 0.16 0.15 0.15 0.16 0.16 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.14 0.15 0.15 0.15 0.15 0.15 0.15 0.14 0.16 0.14 0.15 0.15 0.15 0.16 0.15 0.16 0.15 0.15

Q-Dose rate

3.75 3.75 3.97 3.65 3.83 3.85 3.92 3.74 3.77 3.69 3.77 3.76 3.64 3.60 3.76 3.70 3.61 3.57 3.56 3.55 3.57 3.37 3.62 3.60 3.61 3.58 3.63 3.60 3.44 3.72 3.42 3.63 3.51 3.58 3.75 3.51 3.76 3.53 3.51

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

(Gy/ka) 0.15 0.14 0.17 0.13 0.16 0.16 0.17 0.16 0.16 0.15 0.16 0.15 0.15 0.15 0.16 0.15 0.14 0.14 0.14 0.14 0.15 0.13 0.14 0.15 0.15 0.14 0.15 0.15 0.14 0.15 0.14 0.15 0.15 0.25 0.16 0.15 0.16 0.14 0.14

FK-Dose rate

4.9 ± 0.5 87.5 ± 2.8 93.1 ± 3.6 94.1 ± 4.7 96.0 ± 4.6 93.7 ± 2.2 116.1 ± 3.5 110.1 ± 3.5 121.5 ± 2.4 115.8 ± 3.5 123.8 ± 3.0 118.4 ± 3.4 136.7 ± 5.6 119.1 ± 4.6 139.4 ± 4.8 132.5 ± 2.7 135.3 ± 7.8 144.3 ± 5.2 137.6 ± 5.2 147.1 ± 5.9 149.4 ± 6.6 164.0 ± 7.3 143.3 ± 4.6 163.2 ± 5.8 137.4 ± 2.9 160.6 ± 6.2 177.7 ± 5.6 203.8 ± 23.2 179.5 ± 5.3 163.4 ± 5.8 148.4 ± 6.1 173.6 ± 6.1 185.8 ± 8.2 178.2 ± 4.7 176.3 ± 6.9 181.5 ± 8.6 183.3 ± 5.9 143.1 ± 4.3 169.6 ± 10.6

Quartz OSL

De (Gy)

29

218.9 210.0 216.5 216.0 215.1 221.4 241.5 233.1 266.0

± ± ± ± ± ± ± ± ±

3.8 3.0 3.7 4.5 3.2 5.3 4.8 2.5 2.8

185.4 ± 3.1 197.8 ± 4.8

186.8 ± 1.9

147.7 ± 0.6

129.6 ± 1.1 136.6 ± 3.7

116.2 ± 1.4

112.9 ± 1.2

8.4 ± 0.3 100.7 ± 0.7 102.6 ± 1.5 111.2 ± 0.8

pIRIR170

± ± ± ± ± ±

± ± ± ± ± ± ± ± ± ± ±

3.4 3.3 1.0 0.7 3.4 3.7

3.4 1.6 1.0 4.6 2.6 3.6 7.9 1.3 2.7 4.1 2.3

236.0 ± 3.3 286.0 ± 3.5

218.0 ± 4.6

213.8 ± 1.7 222.4 ± 2.7

192.1 194.8 198.9 212.0 218.7 219.3

147.1 159.3 147.8 156.5 162.3 176.4 172.0 180.1 180.6 190.0 191.8

127.0 ± 1.4 131.2 ± 1.0

104.9 ± 4.1 113.4 ± 2.1 120.6 ± 0.7

pIRIR225 1.5 ± 0.2 26.1 ± 1.5 26.0 ± 1.6 28.9 ± 2.0 27.9 ± 1.9 27.1 ± 1.5 33.0 ± 2.0 33.0 ± 2.0 36.1 ± 2.0 35.2 ± 2.1 36.7 ± 2.1 35.2 ± 2.0 42.2 ± 2.7 37.3 ± 2.4 41.5 ± 2.5 40.2 ± 2.2 42.1 ± 3.2 45.5 ± 2.8 43.6 ± 2.8 46.7 ± 3.0 47.2 ± 3.2 55.3 ± 3.8 44.5 ± 2.8 51.0 ± 3.2 42.8 ± 2.4 50.5 ± 3.3 55.0 ± 3.4 63.7 ± 8.0 59.1 ± 3.6 49.3 ± 3.1 49.1 ± 3.2 53.8 ± 3.4 59.7 ± 4.0 56.1 ± 3.2 52.6 ± 3.4 58.3 ± 4.1 54.5 ± 3.3 45.8 ± 2.8 54.6 ± 4.4

Quartz OSL

Age (ka)

64.0 57.9 61.6 60.4 57.4 63.0 64.2 66.1 75.8

± ± ± ± ± ± ± ± ±

3.3 2.9 3.2 3.2 2.9 3.4 3.3 3.2 3.7

51.5 ± 2.7 54.4 ± 2.9

51.9 ± 2.6

39.3 ± 1.9

34.4 ± 1.6 36.3 ± 2.0

31.1 ± 1.5

29.3 ± 1.4

2.2 ± 0.1 26.9 ± 1.3 25.9 ± 1.3 30.5 ± 1.4

pIRIR170

± ± ± ± ± ±

± ± ± ± ± ± ± ± ± ± ±

2.7 2.8 2.7 2.9 3.2 3.0

2.1 2.2 1.9 2.4 2.3 2.6 3.2 2.5 2.6 3.0 2.6

66.9 ± 3.4 80.5 ± 3.9

58.1 ± 3.1

58.9 ± 2.9 63.3 ± 3.2

53.2 54.4 54.8 58.9 63.6 59.0

40.4 44.3 39.3 42.3 44.9 49.4 48.3 50.7 50.6 56.4 53.0

33.7 ± 1.6 35.6 ± 1.7

27.4 ± 1.7 29.4 ± 1.5 30.8 ± 1.5

pIRIR225

Y. Wang et al.

Aeolian Research 33 (2018) 23–32

Aeolian Research 33 (2018) 23–32

Y. Wang et al.

Fig. 7. Preheat plateau test results for 63–90 μm K-feldspar in samples LD-2 and LD-34.

Fig. 9. Characteristics of K-feldspar luminescence growth curves for sample LD15. (a) pIRIR170 and (b) pIRIR225. Insets show the K-feldspar IRSL and (a) pIRIR170 and (b) pIRIR225 signals for sample LD-15.

Fig. 8. Residual doses of pIRIR signal measured after 56 h exposure in sunlight (8h per day for 7 days) plotted against preheat temperature. Table 2 Modified pIRIR SAR protocol (Buylaert et al., 2009; Li et al., 2015). Step

Treatment

1 2

Dose Preheat at 200 °C for 60 s IRSL measurement at 50 °C for 200 s IRSL measurement at 170 °C for 200 s Test dose Preheat at 200 °C for 60 s IRSL measurement at 50 °C for 200 s IRSL measurement at 170 °C for 200 s IRSL bleaching at 205 °C for 200 s Return to step 1

3 4 5 6 7 8 9 10

Observed

Lx1 Lx2

Tx1 Tx2

Treatment Dose Preheat at 250 °C for 60 s IRSL measurement at 50 °C for 200 s IRSL measurement at 225 °C for 200 s Test dose Preheat at 250 °C for 60 s IRSL measurement at 50 °C for 200 s IRSL measurement at 225 °C for 200 s IRSL bleaching at 255 °C for 200 s Return to step 1

Observed

Lx1 Lx2

Tx1 Tx2

Fig. 10. OSL ages of medium (38–63 μm) and coarse (63–90 μm) quartz fractions for seven samples from the LD section.

30

Aeolian Research 33 (2018) 23–32

Y. Wang et al.

0.0

6. Conclusions Quatrz OSL

This study has established a reliable chronology of the past 80 ka at the LD loess section on the NETP, based on quartz OSL and K-feldspar pIRIR ages of 39 samples. The 63–90 μm quartz dating results are essentially consistent with the results of 38–63 μm quartz dating within errors. In terms of pIRIR dating, luminescence characteristics, internal checking with a preheat test, and a dose recovery test demonstrated that at lower temperatures (pIRIR170 and pIRIR225) loess samples were well bleached before deposition and could provide reliable age for loess on the NETP. The constructed quartz and K-feldspar OSL chronology for LD loess reveals that dust accumulation was continuous from 67 to 25 ka, and there were two hiatuses in deposition between 25 and 2 ka and from 80 to 67 ka.

k-feldspar pIRIR170 k-feldspar pIRIR225

4.0

Depth(m)

8.0

12.0

16.0

Acknowledgments This work was jointly funded by the National Natural Science Foundation of China (Grant Number 41671006) and the Youth Innovation Promotion Association of Chinese Academy of Sciences (Grant Number 2015350).

20.0

0

20

40

60

80

100

Age(ka)

References

Fig. 11. Comparison of quartz OSL and K-feldspar pIRIR170 and pIRIR225 ages with depth in the LD section.

An, Z.S., Colman, S.M., Zhou, W.J., et al., 2012. Interplay between the Westerlies and Asian monsoon recorded in Lake Qinghai sediments since 32 ka. Sci. Rep. 2, 619. Auclair, M., Lamothe, M., Huot, S., 2003. Measurement of anomalous fading for feldspar IRSL using SAR. Radiat. Meas. 37, 487–492. Bird, A., Stevens, T., Rittner, M., et al., 2015. Quaternary dust source variation across the Chinese Loess Plateau. Palaeogeogr. Palaeoclimatol. Palaeoecol. 435, 254–264. Bowler, J.M., Chen, K.Z., Yuan, B.Y., 1987. In: Systematic variations in loess source areas: Evidence from Qaidam and Qinghai basins, western China. Aspects of Loess Research, China Ocean Press, Beijing, pp. 39–51. Buylaert, J.P., Vandenberghe, D., Murray, A.S., et al., 2007. Luminescence dating of old (> 70 ka) Chinese loess: a comparison of single-aliquot OSL and IRSL techniques. Quat. Geochronol. 2, 9–14. Buylaert, J.P., Murray, A.S., Vandenberghe, D., et al., 2008. Optical dating of Chinese loess using sand-sized quartz: establishing a time frame for Late Pleistocene climate changes in the western part of the Chinese Loess Plateau. Quat. Geochronol. 3, 99–113. Buylaert, J.P., Murray, A.S., Thomsen, K.J., et al., 2009. Testing the potential of an elevated temperature IRSL signal from K-feldspar. Radiat. Meas. 44, 560–565. Buylaert, J.P., Jain, M., Murray, A.S., et al., 2012. A robust feldspar luminescence dating method for Middle and Late Pleistocene sediments. Boreas 41, 435–451. Chapot, M.S., Roberts, H.M., Duller, G.A.T., et al., 2012. A comparison of natural- and laboratory-generated dose response curves for quartz optically stimulated luminescence signals from Chinese Loess. Radiat. Meas. 47, 1045–1052. ChongYi, E., Sohbati, R., Murray, A.S., et al. Hebei loess section: a high resolution luminescence chronology based on both quartz and feldspar. Boreas, Unpublished results. ChongYi, E., Lai, Z.P., Sun, Y.J., et al., 2012. A luminescence dating study of loess deposits from the Yili River basin in western China. Quat. Geochronol. 10, 50–55. Duller, G.A.T., 1994. Luminescence dating using feldspars: a test case from southern North Island, New Zealand. Quat. Sci. Rev. 13, 423–427. Duller, G.A.T., 2003. Distinguishing quartz and feldspar in single grain luminescence measurements. Radiat. Meas. 37, 161–165. Fu, X., Li, B., Li, S.H., 2012. Testing a multi-step post-IR IRSL dating method using polymineral fine grains from Chinese loess. Quat. Geochronol. 10, 8–15. Huntley, D.J., Baril, M.R., 1997. The K content of the K-feldspars being measured in optical dating or in thermoluminescence dating. Ancient Tl 15, 11–13. Huntley, D.J., Lamothe, M., 2001. Ubiquity of anomalous fading in K-feldspars and the measurement and correction for it in optical dating. Can. J. Earth Sci. 38, 1093–1106. Kang, S.G., Wang, X.L., Lu, Y.C., et al., 2015. A high-resolution quartz OSL chronology of the Talede loess over the past ∼ 30 ka and its implications for dust accumulation in the Ili Basin, Central Asia. Quat. Geochronol. 30, 181–187. Kapp, P., Pelletier, J.D., Rohrmann, A., et al., 2011. Wind erosion in the Qaidam Basin, central Asia: implications for tectonics, paleoclimate, and the source of the Loess Plateau. GSA Today 21, 4–10. Kars, R.H., Reimann, T., Ankjærgaard, C., et al., 2014. Bleaching of the post-IR IRSL signal: new insights for feldspar luminescence dating. Boreas 43, 780–791. Lai, Z.P., 2006. Testing the use of an OSL standardised growth curve (SGC) for De determination on quartz from the Chinese Loess Plateau. Radiat. Meas. 41, 9–16. Lai, Z.P., 2010. Chronology and the upper dating limit for loess samples from Luochuan section in the Chinese Loess Plateau using quartz OSL SAR protocol. J. Asian Earth Sci. 37, 176–185. Lai, Z.P., Brückner, H., Zöller, L., et al., 2007. Existence of a common growth curve for silt-sized quartz OSL of loess from different continents. Radiat. Meas. 42, 1432–1440. Lai, Z., Brückner, H., 2008. Effects of Feldspar contamination on equivalent dose and the

highlighted previously (Bowler et al., 1987; Kapp et al., 2011; Licht et al., 2016; Pullen et al., 2011). Liu et al. (2017) proposed that aeolian sediments accumulated on the NETP during interstadial or interglacial warm stages (such as MIS5, MIS3, and the Holocene), and were eroded away during stadial or glacial cold stages (such as MIS4 and MIS2). Our loess section in Huangshui river valley seems to be consistent with Liu et al.’s (2017) hypothesis for the last glacial stage. Anyhow, our dating results confirm the findings of previous studies that aeolian sediments on the NETP are not accumulated continuously (Buylaert et al., 2008; Liu et al., 2017; Wang et al., 2015a). The loess sequences contain gaps in deposition that are not easily identified by eye in field investigations and in proxy measurements. Hence, we advise caution when using loess in this area to explore paleoenvironmental changes, especially in interglacial stages such as the Holocene. Recently, Li et al. (2016) reported that loess accumulated in arid central Asia during MIS6, MIS4, MIS2, and MIS3 cold stages/stadials, and ceased to accumulate during the warm stages of MIS5, MIS3a, and MIS 1, and that depositional gaps can be as large as > 50 ka. Stevens et al. (2018) identified several depositional hiatuses of > 60 ka in the CLP Jingbian section during the past 250 ka using high resolution quartz SAR and feldspar pIRIR dating. It seems that loess near desert boundaries, or adjacent to source regions of the CLP, often accumulated episodically. These episodic loess deposition patterns are related to wetdry climate changes in source regions, variations in atmospheric circulation, and the status of vegetation status and coverage in loess accumulation areas. The rapid loess accumulation rate between 67 and 25 ka, along with the lack of paleosol formation in the LD section, suggests the climate of the NETP was relatively arid at this time and unsuitable for pedogenesis. Loess has been are widely deposited over the NETP since the last deglaciation (Liu et al., 2012, 2017; Lu et al., 2011, 2015; Wang et al., 2015a; Yu and Lai, 2012). The depositional hiatus between the last deglaciation and early to mid-Holocene found at the LD section is inconsistent with the regional aeolian sediment accumulation pattern. The deposition hiatus may have been caused by erosion events during the Holocene epoch and the lower accumulation rate during Holocene optimal stages.

31

Aeolian Research 33 (2018) 23–32

Y. Wang et al.

feldspars for optical dating of young coastal sediments – a test case from Darss-Zingst peninsula (southern Baltic Sea coast). Quat. Geochronol. 6, 207–222. Roberts, H.M., 2007. Assessing the effectiveness of the double-SAR protocol in isolating a luminescence signal dominated by quartz. Radiat. Meas. 42, 1627–1636. Roberts, H.M., 2008. The development and application of luminescence dating to loess deposits: a perspective on the past, present and future. Boreas 37, 483–507. Roberts, H.M., 2012. Testing Post-IR IRSL protocols for minimising fading in feldspars, using Alaskan loess with independent chronological control. Radiat. Meas. 47, 716–724. Roberts, H.M., Duller, G.A.T., 2004. Standardised growth curves for optical dating of sediment using multiple-grain aliquots. Radiat. Meas. 38, 241–252. Singarayer, J.S., Bailey, R.M., 2003. Further investigations of the quartz optically stimulated luminescence components using linear modulation. Radiat. Meas. 37, 451–458. Sohbati, R., Murray, A.S., Buylaert, J.P., et al., 2012. Optically stimulated luminescence (OSL) dating of quartzite cobbles from the Tapada do Montinho archaeological site (east-central Portugal). Boreas 41, 452–462. Spooner, N.A., 1994. The anomalous fading of infrared-stimulated luminescence from feldspars. Radiat. Meas. 23, 625–632. Stauch, G., Lai, Z.P., Lehmkuhl, F., et al., 2016. Environmental changes during the late Pleistocene and the Holocene in the Gonghe Basin, north-eastern Tibetan Plateau. Palaeogeogr. Palaeoclimatol. Palaeoecol. http://dx.doi.org/10.1016/j.palaeo.2016. 12.032. Stevens, T., Armitage, S.J., Lu, H.Y., et al., 2006. Sedimentation and diagenesis of Chinese loess: implications for the preservation of continuous, high-resolution climate records. Geography 34, 849. Stevens, T., Lu, H.Y., Thomas, D.S.G., et al., 2008. Optical dating of abrupt shifts in the late Pleistocene East Asian monsoon. Geology 36, 415–418. Stevens, T., Carter, A., Watson, T.P., et al., 2013. Genetic linkage between the Yellow River, the Mu Us desert and the Chinese Loess Plateau. Quat. Sci. Rev. 78, 355–368. Stevens, T., Buylaert, J.P., Thiel, C., et al., 2018. Ice-volume-forced erosion of the Chinese Loess Plateau global Quaternary stratotype site. Nat. Commun. 9, 1. Thiel, C., Buylaert, J.P., Murray, A.S., et al., 2011. Luminescence dating of the Stratzing loess profile (Austria) – testing the potential of an elevated temperature post-IR IRSL protocol. Quat. Int. 234, 23–31. Thomsen, K.J., Murray, A.S., Jain, M., et al., 2008. Laboratory fading rates of various luminescence signals from feldspar-rich sediment extracts. Radiat. Meas. 43, 1474–1486. Timar-Gabor, A., Vandenberghe, D.A.G., Vasiliniuc, S., et al., 2011. Optical dating of Romanian loess: a comparison between silt-sized and sand-sized quartz. Quat. Int. 240, 62–70. Timar-Gabor, A., Wintle, A.G., 2013. On natural and laboratory generated dose response curves for quartz of different grain sizes from Romanian loess. Quat. Geochronol. 18, 34–40. Vriend, M., Prins, M.A., 2005. Calibration of modelled mixing patterns in loess grain-size distributions: an example from the north-eastern margin of the Tibetan Plateau, china. Sedimentology 52, 1361–1374. Wang, X.Y., Vandenberghe, J., Yi, S.W., et al., 2015b. Climate-dependent fluvial architecture and processes on a suborbital timescale in areas of rapid tectonic uplift: an example from the NE Tibetan Plateau. Global Planet. Change 133, 318–329. Wang, X.Y., Yi, S.W., Lu, H.Y., et al., 2015a. Aeolian process and climatic changes in loess records from the northeastern Tibetan Plateau: response to global temperature forcing since 30 ka. Paleoceanography 30, 612–620. Wintle, A.G., 1973. Anomalous fading of thermo-luminescence in mineral samples. Nature 245, 143–144. Wintle, A.G., Murray, A.S., 2006. A review of quartz optically stimulated luminescence characteristics and their relevance in single-aliquot regeneration dating protocols. Radiat. Meas. 41, 369–391. Yi, S.W., Buylaert, J.P., Murray, A.S., et al., 2015. High resolution OSL and post-IR IRSL dating of the last interglacial–glacial cycle at the Sanbahuo loess site (northeastern China). Quat. Geochronol. 30, 200–206. Yi, S.W., Buylaert, J., Murray, A.S., et al., 2016. A detailed post-IR IRSL dating study of the Niuyangzigou loess site in northeastern China. Boreas 45, 644–657. Yu, L.P., Lai, Z.P., 2012. OSL chronology and palaeoclimatic implications of aeolian sediments in the eastern Qaidam Basin of the northeastern Qinghai-Tibetan Plateau. Palaeogeogr. Palaeoclimatol. Palaeoecol. 337–338, 120–129. Yu, L.P., Lai, Z.P., 2014. Holocene climate change inferred from stratigraphy and OSL chronology of aeolian sediments in the Qaidam Basin, northeastern Qinghai-Tibetan Plateau. Quat. Res. 81, 488–499. Zhang, J.R., Tsukamoto, S., Nottebaum, V., et al., 2015. De plateau and its implications for post-IR IRSL dating of polymineral fine grains. Quat. Geochronol. 30, 147–153.

shape of growth curve for OSL of Silt-Sized Quartz extracted from Chinese Loess. Geochronometria 30, 49–53. Lai, Z.P., Wintle, A.G., 2006. Locating the boundary between the Holocene and Pleistocene in Chinese loess using luminescence. Holocene 16, 893–899. Lai, Z.P., Zöller, L., Fuchs, M., et al., 2008. Alpha efficiency determination for OSL of quartz extracted from Chinese loess. Radiat. Meas. 43, 767–770. Li, G.J., Che, X.D., Xiao, G.Q., et al., 2013. Zircon ages of xining loess:implication for the provenance of the loess on chinese loess plateau. Q. Sci. 33, 345–350 (In Chinese with English Abstract). Li, B., Li, S.H., 2011. Luminescence dating of K-feldspar from sediments: a protocol without anomalous fading correction. Quat. Geochronol. 6, 468–479. Li, B., Li, S.H., 2012. Luminescence dating of Chinese loess beyond 130 ka using the nonfading signal from K-feldspar. Quat. Geochronol. 10, 24–31. Li, G.Q., Wen, L.J., Xia, D.S., et al., 2015. Quartz OSL and K-feldspar pIRIR dating of a loess/paleosol sequence from arid central Asia, Tianshan Mountains, NW China. Quat. Geochronol. 28, 40–53. Li, G.Q., Rao, Z.G., Duan, Y.W., et al., 2016. Paleoenvironmental changes recorded in a luminescence dated loess/paleosol sequence from the Tianshan Mountains, arid central Asia, since the Penultimate Glaciation. Earth Planet. Sci. Lett. 448, 1–12. Licht, A., Pullen, A., Kapp, P., et al., 2016. Eolian cannibalism: reworked loess and fluvial sediment as the main sources of the Chinese Loess Plateau. Geol. Soc. Am. Bull. 128, 944–956. Liu, T.S., Ding, Z.L., 1998. Chinese Loess and the Paleomonsoon. Annu. Rev. Earth Planet. Sci. 26, 111–145. Liu, X.J., Lai, Z.P., 2013. Optical dating of sand wedges and ice-wedge casts from Qinghai Lake area on the northeastern Qinghai-Tibetan Plateau and its palaeoenvironmental implications. Boreas 42, 333–341. Liu, X.J., Lai, Z.P., Yu, L.P., et al., 2012. Luminescence chronology of aeolian deposits from the Qinghai Lake area in the Northeastern Qinghai-Tibetan Plateau and its palaeoenvironmental implications. Quat. Geochronol. 10, 37–43. Liu, X.J., Lai, Z.P., Madsen, D., et al., 2015. Last deglacial and Holocene lake level variations of Qinghai Lake, north-eastern Qinghai-Tibetan Plateau. J. Quat. Sci. 30, 245–257. Liu, X.J., Madsen, D.B., Liu, R.Y., et al., 2016. Holocene lake level variations of Longmu Co, western Qinghai-Tibetan Plateau. Environ. Earth Sci. 75, 301. Liu, X.J., Xiao, G.Q., E C Y,, et al., 2017. Accumulation and erosion of aeolian sediments in the northeastern Qinghai-Tibetan Plateau and implications for provenance to the Chinese Loess Plateau. J. Asian Earth Sci. 135, 166–174. Long, H., Shen, J., Tsukamoto, S., et al., 2014. Dry early Holocene revealed by sand dune accumulation chronology in Bayanbulak Basin (Xinjiang, NW China). Holocene 24, 614–626. Lu, H.Y., Wang, X.Y., Ma, H.Z., et al., 2004. The Plateau Monsoon variations during the Past 130 Kyr revealed by loess deposit at northeast Qinghai-Tibet (China). Global Planet. Change 41, 207–214. Lu, H.Y., Zhao, C.F., Mason, J., et al., 2011. Holocene climatic changes revealed by aeolian deposits from the Qinghai Lake area (northeastern Qinghai-Tibetan Plateau) and possible forcing mechanisms. Holocene 21, 297–304. Lu, H.Y., Huissteden, K.V., An, Z.S., et al., 2015. East Asia winter monsoon variations on a millennial time-scale before the last glacial-interglacial cycle. J. Quat. Sci. 14, 101–110. Madsen, A.T., Buylaert, J.P., Murray, A.S., 2011. Luminescence dating of young coastal deposits from New Zealand using feldspar. Geochronometria 38, 379–390. Murray, A.S., Olley, J.M., 2002. Precision and accuracy in the optically stimulated luminescence dating of sedimentary quartz: a status review. Geochronometria 21, 1–16. Murray, A.S., Wintle, A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiat. Meas. 32, 57–73. Murray, A.S., Wintle, A.G., 2003. The single aliquot regenerative dose protocol: potential for improvements in reliability. Radiat. Meas. 37, 377–381. Nie, J.S., Stevens, T., Rittner, M., et al., 2015. Loess Plateau storage of Northeastern Tibetan Plateau-derived Yellow River sediment. Nat. Commun. 6, 8511. 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. Radiat. Meas. 23, 497–500. Pullen, A., Kapp, P., McCallister, A.T., et al., 2011. Qaidam Basin and northern Tibetan Plateau as dust sources for the Chinese Loess Plateau and paleoclimatic implications. Geology 39, 1031–1034. Reimann, T., Tsukamoto, S., 2012. Dating the recent past (< 500 years) by post-IR IRSL feldspar – examples from the North Sea and Baltic Sea coast. Quat. Geochronol. 10, 180–187. Reimann, T., Tsukamoto, S., Naumann, M., et al., 2011. The potential of using K-rich

32