Luminescence dating has been widely used to date late Quaternary deposits from different geographical areas of the world (Aitken, 1998). Traditionally, optically stimulated luminescence (OSL) dating of sedimentary quartz has been employed to date sediments from a range of depositional settings (Murray and Wintle, 2000). However, the quartz OSL signal generally saturates between ∼100 and 200 Gy, corresponding to 40–80 ka (for a dose rate of 2.5 Gy/ka) (Wintle, 2008) but is also insensitive in some regions of the world (Preusser
Lacustrine sediments are conventionally dated using radiocarbon methods, but this is not always possible particularly in previously glaciated settings where there may be contaminated by old carbon (Dodson and Zhou, 2000; Pessenda
As an alternative, dating of lacustrine sediments using pIRIR methods could be facilitated by selecting profiles containing sediments which were subjected to transport conditions optimal for inducing signal resetting. Important developments to the pIRIR protocol (Buylaert
Bosten Lake, located in the central Tian Shan, arid Central Asia (ACA), is the second-largest freshwater lake in China. In this study, different potential sources of sediments in the Bosten Lake Basin were collected to evaluate the bleachability of different pIRIR signals (e.g. pIR50IR170, pIR50IR290 and pIR200IR290). The collected samples include: (i) three samples from pluvial fans deposited along the northern margin of the lake; (ii) six samples from point bars at different locations along the Kaidu River; (iii) four eolian sand samples from dunes around Bosten Lake (
a) location map indicating position of Bosten Lake located on the southeastern side of the Yanqi basin on the southern slope of the Tian Shan Mountain; b) indicates the distribution of different modern depositional environments around the Bosten Lake Basin which were sampled. Four eolian sand samples (BST16S-1, BST16S-2, BST16S-3, and BST16S-14) were collected from the widespread sand dune field around the lake. Six samples BST16S-4, BST16S-5, BST16S-6, BST16S-7, BST16S-8 and BST16S-9 were collected from the over flooding deposit at different points of Kaidu River channel. Three samples BST16S-10, BST16S-11 and BST16S-12 were collected from the surface of the pluvial fan down the Elbin-Alagou Mountains. The red cycle with BST12B besides is the location of drill core BST12B from Li et al. (2016).
Bosten Lake (41°56′–42°14′N, 86°40′–87°26′E) is located on the southeastern side of the Yanqi basin on the southern slope of the Tian Shan, NW China, which is the second-largest inland freshwater lake in China. The Yanqi basin is 56,000 km2 (Cheng, 1993) and is flanked by the northern Tian Shan in the north and Horo-Kurnktag Mountains in the south (
The potential source materials of lake sediment from Bosten Lake mainly consist of fluvial sediments transported by the Kaidu River, and aeolian sand dunes and pluvial fans deposited around the lake. A total of thirteen modern samples were collected from different locations of the lake basin (
Locations of modern analogue samples collected from different potential sources of lake sediment at Bosten Lake Basin.
The location and sediment type of samples from Bosten lake Basin.
BST16S-1 | Eolian sand dunes | Around 0.05 km | 41.88N, 87.22E | 1061 |
BST16S-2 | Eolian sand dunes | Around 0.07 km | 41.93N, 87.13E | 1060 |
BST16S-3 | Eolian sand dunes | Around 0.10 km | 41.90N, 86.99E | 1055 |
BST16S-14 | Eolian sand dunes | Around 0.19 km | 42.08N, 87.02E | 1056 |
BST16S-4 | Fluvial sand from Kaidu river | Around 16.29 km | 41.97N, 86.64E | 1055 |
BST16S-5 | Fluvial sand from Kaidu river | 0 | 41.93N, 86.75E | 1051 |
BST16S-6 | Fluvial sand from Kaidu river | Around 3.33 km | 41.90N, 86.72E | 1050 |
BST16S-7 | Fluvial sand from Kaidu river | Around 36.14 km | 42.07N, 86.50E | 1061 |
BST16S-8 | Fluvial sand from Kaidu river | Around 48.54 km | 42.12N, 86.41E | 1067 |
BST16S-9 | Fluvial sand from Kaidu river | Around 78.92 km | 42.22N, 86.25E | 1078 |
BST16S-10 | Gravel sand from pluvial fans | Around 21.72 km | 42.31N, 86.91E | 1166 |
BST16S-11 | Gravel sand from pluvial fans | Around 20.45 km | 42.30N, 86.91E | 1140 |
BST16S-12 | Gravel sand from pluvial fans | Around 19.59 km | 42.25N, 87.06E | 1114 |
Sample pretreatments and luminescence measurements were conducted in a darkroom under subdued red light. Sample preparation followed the methods described by Aitken (1998). The preparation method comprises the following steps: firstly, soaking the samples in HCl (10%) and H2O2 (30%) for removal of CaCO3 and organic matter, respectively. Samples were then wet sieved to obtain the 90–125 μm fraction, from which K-rich feldspar was concentrated using sodium polytungstate liquid at a density of 2.58 g/cm3. The K-feldspar fraction was etched using 10% HF for 40 min to remove the outer layer irradiated by alpha particles. Finally, the samples were dissolved by using 1 mol/L HCl for 15 min to remove fluorides created during the HF etching. A total of thirteen K-feldspar samples were prepared for measurement. Etched grains were mounted on 5–6 mm aliquots using silkospray.
Luminescence signals were measured using an automated Risø TL/OSL-DA-20 reader (Bøtter-Jensen
The pIRIR dating protocol using: (i) the pIR50IR170 signal (Li et al., 2015b); (ii) the pIR50IR290 signal (Thiel et al., 2011); and (iii) the pIR200IR290 signal (Li and Li, 2012).
1 | Give dose Dia | Give dose Dia | Give dose Dia | |||
2 | Preheat at 200°C for 60 s | Preheat at 320°C for 60 s | Preheat at 320°C for 60 s | |||
3 | IRSL, 200 s at 50°C | Lx1 | IRSL, 200 s at 50°C | Lx1 | IRSL, 200 s at 200°C | Lx1 |
4 | pIRIR, 200 s at 170°C | Lx2 | pIRIR, 200 s at 290°C | Lx2 | pIRIR, 200 s at 290°C | Lx2 |
5 | Give test dose | Give test dose | Give test dose | |||
6 | Preheat at 200°C for 60 s | Preheat at 320°C for 60 s | Preheat at 320°C for 60 s | |||
7 | IRSL, 200 s at 50°C | Tx1 | IRSL, 200 s at 50°C | Tx1 | IRSL, 200 s at 200°C | Tx1 |
8 | pIRIR, 200 s at 170°C | Tx2 | pIRIR, 200 s at 290°C | Tx2 | pIRIR, 200 s at 290°C | Tx2 |
9 | IRSL, 200s bleaching at 325°C | IRSL, 200s bleaching at 325°C | ||||
10 | Return to 1 | Return to 1 | Return to 1 |
Dose recovery tests for the different pIRIR signals were conducted on sample BST16S-1 to check the suitability of the SAR protocol for the modern samples (Wallinga
Dose rate data based on Neutron Activation Analysis for samples from Bosten lake Basin.
BST16S-1 | 90–125 | 1.58 ± 0.07 | 4.9 ± 0.17 | 1.67 ± 0.06 | 0.20 | 1 ± 0.5 | 0.46 ± 0.03 | 0.33 | 3.21 ± 0.06 |
BST16S-2 | 90–125 | 1.08 ± 0.06 | 3.74 ± 0.14 | 2.29 ± 0.07 | 0.40 | 1 ± 0.5 | 0.46 ± 0.03 | 0.33 | 3.66 ± 0.06 |
BST16S-3 | 90–125 | 1.27 ± 0.06 | 5.18 ± 0.18 | 1.99 ± 0.06 | 0.05 | 1 ± 0.5 | 0.46 ± 0.03 | 0.33 | 3.50 ± 0.06 |
BST16S-14 | 90–125 | 1.44 ± 0.07 | 5.33 ± 0.18 | 1.62 ± 0.05 | 0.03 | 1 ± 0.5 | 0.46 ± 0.03 | 0.33 | 3.16 ± 0.06 |
BST16S-4 | 90–125 | 2.33 ± 0.09 | 11.8 ± 0.33 | 1.79 ± 0.06 | 4.5 | 6 ± 3 | 0.46 ± 0.03 | 0.33 | 3.83 ± 0.12 |
BST16S-5 | 90–125 | 1.33 ± 0.07 | 6.07 ± 0.20 | 1.94 ± 0.06 | 24.8 | 6 ± 3 | 0.46 ± 0.03 | 0.33 | 3.37 ± 0.10 |
BST16S-6 | 90–125 | 1.71 ± 0.08 | 6.33 ± 0.21 | 2.03 ± 0.06 | 32.5 | 6 ± 3 | 0.46 ± 0.03 | 0.33 | 3.72 ± 0.12 |
BST16S-7 | 90–125 | 1.74 ± 0.08 | 7.26 ± 0.23 | 2.13 ± 0.06 | 1.2 | 6 ± 3 | 0.46 ± 0.03 | 0.33 | 3.72 ± 0.11 |
BST16S-8 | 90–125 | 1.67 ± 0.08 | 8.56 ± 0.26 | 2.09 ± 0.06 | 2.7 | 6 ± 3 | 0.46 ± 0.03 | 0.33 | 3.76 ± 0.12 |
BST16S-9 | 90–125 | 1.84 ± 0.08 | 8.59 ± 0.26 | 2.13 ± 0.06 | 8.6 | 6 ± 3 | 0.46 ± 0.03 | 0.33 | 3.84 ± 0.12 |
BST16S-10 | 90–125 | 2.36 ± 0.09 | 12.9 ± 0.36 | 2.05 ± 0.06 | 2.1 | 1 ± 0.5 | 0.46 ± 0.03 | 0.34 | 4.37 ± 0.07 |
BST16S-11 | 90–125 | 1.86 ± 0.08 | 9.82 ± 0.28 | 2.32 ± 0.07 | 2.2 | 1 ± 0.5 | 0.46 ± 0.03 | 0.33 | 4.32 ± 0.07 |
BST16S-12 | 90–125 | 1.97 ± 0.08 | 12.6 ± 0.35 | 2.54 ± 0.07 | 0.2 | 1 ± 0.5 | 0.46 ± 0.03 | 0.33 | 4.77 ± 0.07 |
In order to check the bleachability of the pIRIR signals of samples from the Bosten lake area, all K-feldspar samples (three aliquots each sample) were exposed to sunlight for 112 h (8 h per day, 2 weeks, April, 2018, Lanzhou, China), and then the residual doses were measured using the three pIRIR dating protocols (
The dose rate of all samples was obtained by measuring the radioactive element concentrations of uranium (U) and thorium (Th) and potassium (K) content using Neutron Activation Analysis. For each sample, ∼5 g of each sample was ground to < 4 μm using an agate mortar. All results were converted to beta and gamma dose rates according to the conversion factors of Guérin
The dose recovery test results of sample BST16S-1 for pIR50IR170, pIR50IR290 and pIR200IR290 signals are illustrated in
a) b) c) show the dose recovery test results from sample BST16S-1. a is the measured dose/given (M/G) dose; b) and c) show the recycling ratios and recuperation values.
The growth curve and decay curves of pIR50IR170, pIR50IR290, and pIR200IR290 signals for a K-feldspar sample (BST16S-5) are illustrated in
Luminescence characteristics of K-feldspar pIRIR signal for samples: a), b) and c) show representative decay and growth curves from the pIR50IR170, IR50, pIR50IR290, IR50 and pIR200IR290, IR200 signals for K-feldspar sample BST16S-5. d), e) and f) show the recycling ratios and recuperation values of all aliquots for the pIR50IR170, pIR50IR290 and pIR200IR290 De measurements for all samples, respectively.
For the pIR50IR170 De measurements, the average recycling ratio for all 83 aliquots of the 13 K-feldspar samples is 0.99 ±0.003. The recuperation of the signals for almost all aliquots (77) is less than 10%, except for six aliquots (
Summary of K-feldspar pIRIR age data for samples from Bosten lake Basin.
BST16S-1 | 11/5/4 | 0.8±0.3 | 0.8±0.1 | 0.3±0.03 | 2.9±0.2 | 1.8±0.2 | 5.4±0.3 | 72±15 | 11±4 | 9±4 | 0.2±0.1 | 0.2±0.03 | 0.1±0.01 | 0.9±0.1 | 0.6±0.1 | 1.7±0.1 |
BST16S-2 | 4/8/4 | 4.6±0.1 | 7.4±0.3 | 3.3±0.3 | 9.3±0.7 | 5.1±0.6 | 13.0±0.3 | 5±2 | 23±6 | 4±2 | 1.3±0.04 | 2.0±0.1 | 0.9±0.1 | 2.5±0.2 | 1.4±0.2 | 3.5±0.1 |
BST16S-3 | 4/5/4 | 0.6±0.04 | 1.3±0.1 | 0.9±0.1 | 4.8±0.4 | 1.8±0.1 | 6.4±0.2 | 9±3 | 15±5 | 3±2 | 0.2±0.01 | 0.4±0.03 | 0.3±0.03 | 1.4±0.1 | 0.5±0.03 | 1.8±0.1 |
BST16S-14 | 11/5/4 | 0.2±0.1 | 0.4±0.1 | 0.4±0.1 | 3.0±0.2 | 1.0±0.02 | 4.0±0.2 | 53±11 | 12±4 | 7±3 | 0.1±0.03 | 0.1±0.03 | 0.1±0.03 | 0.9±0.1 | 0.3±0.01 | 1.3±0.1 |
BST16S-4 | 4/4/4 | 0.8±0.1 | 3.5±0.3 | 3.1±0.5 | 19.2±1.7 | 6.5±0.2 | 31.0±1.0 | 16±6 | 16±6 | 4±2 | 0.2±0.03 | 0.9±0.1 | 0.8±0.1 | 5.0±0.5 | 1.7±0.1 | 8.1±0.4 |
BST16S-5 | 4/4/5 | 1.2±0.1 | 3.4±0.04 | 1.6±0.2 | 9.8±0.4 | 3.9±0.3 | 15.1±0.7 | 0 | 7±3 | 7±3 | 0.4±0.03 | 1.0±0.03 | 0.5±0.1 | 2.9±0.1 | 1.2±0.1 | 4.5±0.2 |
BST16S-6 | 4/4/6 | 1.8±0.1 | 5.9±0.2 | 3.2±0.3 | 18.2±1.6 | 7.5±0.4 | 30.7±1.8 | 5±2 | 16±6 | 10±4 | 0.5±0.03 | 1.6±0.1 | 0.9±0.1 | 4.9±0.5 | 2.0±0.1 | 8.3±0.6 |
BST16S-7 | 8/4/4 | 1.7±0.1 | 6.0±0.6 | 2.9±0.1 | 22.3±1.9 | 7.9±1.0 | 33.7±2.6 | 24±6 | 15±6 | 13±5 | 0.5±0.03 | 1.6±0.2 | 0.8±0.04 | 6.0±0.5 | 2.1±0.3 | 9.1±0.8 |
BST16S-8 | 8/7/8 | 2.7±0.9 | 6.8±0.8 | 2.9±0.3 | 20.5±1.6 | 8.9±1.1 | 40.2±3.5 | 32±8 | 22±6 | 19±5 | 0.7±0.2 | 1.8±0.2 | 0.8±0.1 | 5.4±0.5 | 2.4±0.3 | 10.7±1 |
BST16S-9 | 8/7/9 | 2.2±0.2 | 10.9±1.1 | 4.1±0.6 | 23.0±1.1 | 10.2±0.8 | 38.5±2.9 | 31±8 | 14±4 | 21±5 | 0.6±0.1 | 2.8±0.3 | 1.1±0.2 | 6.0±0.3 | 2.7±0.2 | 10±0.8 |
BST16S-10 | 8/5/4 | 89.0±3.8 | 160.5±5.5 | 60.5±5.7 | 158.2±11.8 | 86.6±4.1 | 197.2±14.1 | 8±2 | 15±5 | 11±4 | 20.4±0.9 | 36.7±1.4 | 13.8±1.3 | 36.2±2.8 | 19.8±1 | 45.1±3.3 |
BST16S-11 | 4/9/4 | 3.7±0.2 | 20.8±2.1 | 7.6±0.5 | 46.7±2.8 | 19.8±1.8 | 84.9±4.6 | 17±6 | 18±4 | 9±3 | 0.9±0.05 | 4.8±0.5 | 1.8±0.1 | 10.8±0.7 | 4.6±0.4 | 19.7±1.1 |
BST16S-12 | 4/5/4 | 2.2±0.2 | 19.0±1.8 | 4.1±0.7 | 31.0±1.9 | 18.3±1.8 | 71.4±6.7 | 17±6 | 11±4 | 16±6 | 0.5±0.04 | 4.0±0.4 | 0.9±0.1 | 6.5±0.4 | 3.8±0.4 | 15±1.4 |
K-feldspar pIRIR residual Des for samples from different sources exhibit large differences (
The distribution of De (a) and age (b) values obtained using different pIRIR signals (pIR50IR170 De, pIR50IR290 De and pIR200IR290).
The average pIR50IR170, pIR50IR290 and pIR200IR290 ages for eolian sand samples are ∼ 0.7 ka, 1.5 ka and 2.5 ka, respectively (
a) and b) pIRIR ages from eolian and river sediments plotted as a function of distance from sampling sites from Bosten Lake, respectively.
Notably, the pIRIR residual ages of the fluvial samples decrease with proximity to the lake (from 4–1 ka) indicating improved bleaching with transport distance (Murray
The residual doses of pIR50IR170, pIR50IR290 and pIR200IR290 for all samples after 112 h sunlight bleaching during April in Lanzhou, China, are listed in
Plots of the residual doses of eolian samples (a), fluvial samples (b) and pluvial samples (c) obtained using different pIRIR signals after 112 h sunlight bleaching as a function of the associated De values.
Summary of the residual dose after 112 h bleaching under sunlight for all samples from Bosten lake Basin.
BST16S-1 | 0.53 ± 0.01 | 0.10 ± 0.005 | 0.34 ± 0.01 | 2.01 ± 0.05 | 0.76 ± 0.02 | 2.11 ± 0.08 |
BST16S-2 | 0.05 ± 0.001 | 0.33 ± 0.01 | 0.32 ± 0.01 | 2.06 ± 0.05 | 0.75 ± 0.02 | 2.26 ± 0.09 |
BST16S-3 | 0.07 ± 0.002 | 0.15 ± 0.005 | 0.32 ± 0.01 | 1.80 ± 0.05 | 0.78 ± 0.02 | 2.48 ± 0.11 |
BST16S-4 | 0.08 ± 0.002 | 1.02 ± 0.02 | 0.80 ± 0.02 | 4.74 ± 0.12 | 1.82 ± 0.04 | 6.01 ± 0.22 |
BST16S-5 | 0.06 ± 0.002 | 0.62 ± 0.02 | 0.65 ± 0.02 | 3.43 ± 0.09 | 1.57 ± 0.04 | 5.00 ± 0.19 |
BST16S-6 | 0.39 ± 0.01 | 1.02 ± 0.02 | 1.00 ± 0.03 | 4.93 ± 0.13 | 1.99 ± 0.04 | 6.85 ± 0.27 |
BST16S-7 | 0.26 ± 0.01 | 1.10 ± 0.03 | 0.95 ± 0.02 | 6.00 ± 0.17 | 1.66 ± 0.04 | 5.48 ± 0.18 |
BST16S-8 | 0.30 ± 0.01 | 1.34 ± 0.03 | 0.89 ± 0.02 | 5.11 ± 0.14 | 2.25 ± 0.05 | 7.53 ± 0.28 |
BST16S-9 | 0.42 ± 0.01 | 1.58 ± 0.04 | 1.04 ± 0.03 | 5.19 ± 0.14 | 2.21 ± 0.05 | 7.21 ± 0.26 |
BST16S-10 | 0.50 ± 0.01 | 3.47 ± 0.08 | 1.57 ± 0.04 | 10.69 ± 0.29 | 3.50 ± 0.08 | 14.32 ± 0.51 |
BST16S-11 | 0.56 ± 0.01 | 3.91 ± 0.09 | 1.77 ± 0.04 | 11.35 ± 0.29 | 3.82 ± 0.08 | 15.94 ± 0.55 |
BST16S-12 | 0.89 ± 0.02 | 1.80 ± 0.04 | 0.81 ± 0.02 | 7.70 ± 0.20 | 3.06 ± 0.07 | 10.24 ± 0.35 |
BST16S-14 | 1.14 ± 0.02 | 0.17 ± 0.01 | 0.33 ± 0.01 | 1.72 ± 0.05 | 0.80 ± 0.02 | 2.18 ± 0.09 |
For eolian samples from dunes around the lake, the hard-to-bleach dose of the pIR50IR170 signal ranged from ∼0.15 Gy to ∼0.33 Gy (∼0.03 to ∼0.09 ka), which is similar to previously reported hard-to-bleach dose values (< 0.5 Gy) from loess deposited in the Tian Shan (Li
a), b), c) and d) show the hard-to-bleach dose values for eolian, fluvial, and pluvial and lacustrine samples, respectively. pIR50IR170 residual dose of loess (red cycles) in a) and pIR50IR290 residual dose of lacustrine samples (square and triangle) in d) are cited from Li et al. (2015b) and Li et al. (2016), respectively.
The possibility of distinguishing fluvial and eolian source materials for age determination based on the depositional process of lake sediment is helpful for discussion of the reliability of the chronology. A key advantage of using a low stimulation temperature for pIRIR dating can substantially reduce significant contributions of a residual dose (Kars
A series of potential sediment source materials (sand dunes, river sediments and pluvial fan sediments) around Bosten Lake, arid central Asia were sampled to investigate the extent to which different pIRIR signals (pIR50IR170, pIR50IR290 and pIR200IR290) had been bleached. There is a significant difference in both the residual and hard-to-bleach doses from the different types of sources materials. When the sampling site is closer to the lake, its pIRIR residual dose is lower. Until the sampling point is located under the lake, the residual ages up to 4.5 ka can be considered well-bleached; but in contrast, the pluvial fan sediment is very poor-bleached. The residual doses of both fluvial and eolian samples were shown to be sensitive to pIRIR stimulation temperature. The evidence in this paper indicates that the pIR50IR170 signal is the most suitable for dating Holocene samples, but the pIR200IR290 or pIR50IR290 signals can be used to date older Pleistocene material at sections containing reworked fluvial or eolian material can be demonstrated. Efforts to date the sediments of Bosten Lake using pIRIR methods should take care to exclude sections likely to have been influenced by significant inputs of poorly bleached pluvial fan material. This study provides an important methodological basis for testing the suitability of pIRIR dating in lacustrine environments and would be an important step forward in constraining the chronology of lacustrine sedimentation, particularly in areas where radiocarbon dating methods are unsuitable.