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Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages
Quaternary International xxx (2015) 1e8
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Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages SiWen Liu a, b, ZhongPing Lai c, *, YiXuan Wang d, XiaoLu Fan e, LuLin Wang e, MingZhong Tian e, **, YaDong Jiang f, Hua Zhao g a
National Research Center for Geoanalysis, Beijing 100037, China Key-laboratory of Eco-geochemistry, Ministry of Land and Resources, Beijing 100037, China School of Earth Sciences, China University of Geosciences, Wuhan 430074, China d Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China e School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China f Inner Mongolia Geological Environment Monitoring, Hohhot 010020, China g Institute of Hydrogeology and Environmental Geology, CAGS, Shijiazhuang 050061, China b c
a r t i c l e i n f o
a b s t r a c t
Article history: Available online xxx
Sand dunes up to 400 m high are common in the Badain Jaran Desert in China, but how and why megadunes grow remains unclear. Timing is the most critical to clarify this issue. The chronological data are still limited with only a few 14C ages from carbonate, not the direct age of the dune, and a few thermoluminescence (TL) ages whose unbleachable residual signals may result in uncertainty in age. Optically stimulated luminescence (OSL) dating uses quartz or feldspars and thus directly dates the sands. It could also be completely reset by daylight with no residual signals. We here report for the first time a batch of OSL ages, and discuss the pattern of the mega-dune growth. Field observation showed that wet sand layers could be exposed in the slope surface and could be easily seen due to its wetness and calcareous cement, causing stronger resistance to wind deflation relative to the adjacent sands. Wet sand layers are normally situated on the mega-dune windward slope, and sometimes could even be seen near the top of a mega-dune, with well-preserved original bedding layers, making them the ideal locations for collecting luminescence samples. Our four OSL samples collected from the Barunbaoritaolegai sand mountain (BSM) show that OSL ages are 4.4 ± 0.5, 5.6 ± 0.5, 11.9 ± 0.9, and 125 ± 11 ka, respectively, from top to bottom. These ages are concentrated in the early to middle Holocene and the Last Inter-glaciation (corresponding to MIS 5e). Based on field observation and OSL ages, we propose that the mega-dunes grow mostly during humid periods with water as cementing agents to build up the sands. The issues, such as the source of the water, how the water seeps into the high sand dunes, how the loose sands could build up to mega-height, etc., require further study. © 2015 Elsevier Ltd and INQUA. All rights reserved.
Keywords: Mega-dunes in the Badain Jaran Desert in China OSL dating Pattern of mega-dune growth
1. Introduction The tallest dunes (the sand mountains) in the earth are observed in the Badain Jaran Desert in China (Yang et al., 2003; Dong et al., 2013) (Fig. 1). Those issues that how and why mega-dunes grow have been discussed from different dimensions, such as geomorphology, wind regime (Dong et al., 2004), and under groundwater (Chen et al., 2004), but still remains unclear. Timing is the
* Corresponding author. ** Corresponding author. E-mail address: [email protected] (Z. Lai).
most critical to clarify these issues. However, the chronological data are still limited with only a few of 14C ages using carbonate of the calcareous roots (Yang and Williams, 2003; Yang et al., 2003; Hartmann and Wünnemann, 2009), and thermoluminescence (TL) ages (Yan et al., 2001). 14C ages using calcareous roots from the sand dune reflect the formation of the calcite rather than events of sand accumulation. TL signals have residuals even after exposure to sunshine for days, which may occupy a high percentage (e.g. 10e30%) of the total signals accumulated during burial for Holocene age samples and are also difficult to evaluate, leading to large uncertainty in age. Optically stimulated luminescence (OSL) could be reset completely by daylight, and uses quartz or feldspar. Thus OSL is an ideal technique to date directly sand dunes.
http://dx.doi.org/10.1016/j.quaint.2015.09.048 1040-6182/© 2015 Elsevier Ltd and INQUA. All rights reserved.
Please cite this article in press as: Liu, S.W., et al., Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.09.048
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S. Liu et al. / Quaternary International xxx (2015) 1e8
Fig. 1. Map of study area (background map plotted by DEM sourced from ArcGIS online). The triangle represents the Baoritaolrgai Sand Mountains (BSM). The filled black square represents profile Chalegebulu (Li et al., 2005). Dot represents the Core WEPD02 drilling site (Wang et al., 2015).
As mega-dunes are covered by drift sands and the knowledge of the structure inside the mega-dunes is limited, it is difficult to locate a position to collect OSL samples. Our field observations showed that wet sand layers (Li et al., 2009) could be exposed on the slope surface and could be easily seen due to the wetness and calcareous cement with stronger resistance to wind deflation relative to the adjacent sands. These layers are normally situated on the windward slopes of mega-dunes, and sometimes are exposed near the top of a mega-dune. The original bedding layers could be seen on the exposure surface of the layer, and thus these are ideal locations for collecting luminescence samples. Deposition structure (or bedding layers) observed in the exposed wet sand layers are similar to that of the mega dunes 10 m below the surface detected using Ground Penetrating Radar (GPR) (Li et al., 2009; Bai et al., 2011a). The wet sand layers (most of them in the form of calcareous cementation layers) were previously interpreted as representing a humid climate phase related to regional precipitation (Yang et al., 2003). This interpretation might have been trying to correlate the alternating wet sand layers and relative dry sand layers to the alternating paleosol and loess layers in the Chinese Loess Plateau. We investigated systemically the Barunbaoritaolegai sand mountains (BSM) and obtained four OSL samples in the Badain Jaran Desert. We report the dating results of these OSL samples and discuss the pattern of the mega-dunes growth.
transverse mega-dunes and compound star mega-dunes. The Bilutu Peak is the tallest mega-dune with a height of ~450 m, and is of a compound transverse type. The strike of a mega-dune main body is normally from northeast to southwest, in agreement with the prevailing northwest wind. The inclination of mega-dune leeward slop is southeast. The scales of the mega-dunes are normally 1e10 km long and 1e4 km wide. The highest point of a megadune occurs at the central ridge. The mega-dunes have steep leeward slops, and gentle windward slops where secondary smaller dunes are superposed. Artemisia scoparia and Psammochloa mongolica grow on the mega-dunes due to the existence of wet sand layers. 2.2. Profiles and samples The Barunbaoritaolegai Sand Mountain (BSM) (Fig. 1), the typical mega-dune in the southeast of the Badain Jaran Desert, was selected for study. The BSM is a giant compound star sand dune with three arms (Fig. 3a). Two of them run from northeast to
2. Study area, materials and methods 2.1. Study area The Badain Jaran Desert is located in the Mongolia Plateau (Fig. 1), northwest China, covering an area of 5.05 104 km2 (Zhong, 2003). It is known for the tallest mega-dunes in the world, which are distributed densely in the southeast of the Badain Jaran Desert (Fig. 2). The area of mega-dunes with a height of >100 m occupies 68% of the total area of the desert (Lu and Guo, 1995), and most of these dunes are higher than >200 m. The main types of mega-dunes described in Dong et al. (2004) are compound
Fig. 2. Locations of sampling sites of published ages in mega-dunes and lake sediments in the Badain Jaran Desert. See Fig. 1 for specific location within the desert.
Please cite this article in press as: Liu, S.W., et al., Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.09.048
S. Liu et al. / Quaternary International xxx (2015) 1e8
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Fig. 3. Studied dune, profiles, and OSL ages of the Barunbaoritaolegai sand mountain (BSM).
southwest, forming the central part of the main body of the BSM, with a length of 2 km and a width of 1.1 km. The third arm runs from northwest to southeast with a length of about 0.6 km. The maximum height of the central ridge is 150 m, 1420 m above sea level (a.s.l.). Sand wet layers occur on the windward slope at different elevations (Fig. 3a). OSL dating samples were collected at the BSM from the wet sand layers (Fig. 3a) using steel pipes with a diameter of 4 cm. Four profiles (BSM1, 2, 3, 4) were dug from the bottom to the top of the BSM, and one OSL sample was collected from each of the profiles (BRMS OSL 1, 2, 3 and 4) (Fig. 3). In addition, three samples were collected for X-ray diffraction (XRD) measurement. These samples are surface sand collected from the surface the BSM, caliche collected from profile BSM4, and paleo-lake sediments 500 m east of BSM developed in the last interglacial (Fan et al., 2014).
OSL measurement was performed on Daybreak-2200 equipped with blue light stimulation (470 nm, maximum power 60 Mw/cm2) and infrared stimulation (880 nm, maximum power 80 Mw/cm2) in the luminescence laboratory of Institute of Hydrogeology and Environmental Geology, China (CAGS). Preheating at 260 C for 10 s and cut-heat at 220 C for 10 s were applied before measuring OS. Fine quartz grains were measured using simplified multiple aliquot regenerative-dose (SMAR) (Lu et al., 2007). The contribution of cosmic rays was calculated according to Prescott and Hutton (1994). 10 ± 5% of sample water contents were used for dose rate calculation. Coarse quartz grain was measured using single-aliquot regenerative-dose procedure (SAR) (Murray and Wintle, 2000). XRD was measured using the X-ray diffractometer (D/max-rA) in the Micro Structure Analysing and Testing Lab, China.
2.3. Sample preparation and measurements
3.1. Stratigraphical characteristics
Samples in the steel pipes were taken out under red light (wave length 640 ± 10 nm) in the laboratory, and materials at the ends of the pipes were kept for measuring the water contents and the concentrations of U, Th, K using neutron activation analysis. The coarse quartz (90e125 mm, samples BRMS OSL 1 and 2) and fine grain fraction (4e11 mm, BRMS OSL 3 and 4) were used for De determination. The materials in the center part of a pipe were placed in the beaker and were added HCl (10%) and H2O2 (40%) for removing carbonates and organic matter, respectively. For extracting 4e11 mm quartz, the samples were then treated according to Stokes Law, and were further added H2SiF6 with concentration of 30% to etch for 3 days. To extract 90e125 mm quartz, HF (40%) etching for 60 min was performed. Chemically purified quartz grains were dried and then the magnetic minerals were removed to obtain pure quartz grains. The purity of quartz grains was monitored by the level of Infrared Stimulated Luminescence (IRSL) signals. Samples that showed obvious IRSL signals were retreated with H2SiF6 or HF again. Pure quartz samples were then mounted on stainless steel disks.
The profile BSM1 (Fig. 3b) is located at the top of the BSM, about 97 m above the modern lake level with an elevation of 1375 m a.s.l. It is near the plant growing region between two secondary dunes on the windward slop with a slope angle of 26e28 . The profile BSM1 was dug to a depth of about 90 cm with well-preserved sand bedding and water content of ~10%. Two kinds of sedimentation bedding, type A and type B, can be identified: (1) in thick bedding (Fig. 3b, type A bedding), grain size was dominated by well-sorted, rounded, pinky-grey, middle to fine sand, containing less melanocratic minerals (such as hornblende, pyroxene and magnetite), and the thickness varies from 0.6 cm to 16 cm. (2) In thin bedding (type B bedding), grain size was dominated by well sorted, rounded, grayish-black fine sand to silt, containing more dark minerals and carbonate, with thickness from 0.3 cm to 0.5 cm. Materials with type B bedding are dominant in caliche (Fig. 3e). Bedding on the top of profile BSM1, about 0e13 cm in depth, are dominated by type A with thicknesses of 3e5 mm. Bedding beneath the depth of 13 cm are dominated by alternating type A and type B layers. The thickness of type A bedding gradually increases from the top to the bottom. The maximum thickness of the type A bedding occurs at
3. Results
Please cite this article in press as: Liu, S.W., et al., Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.09.048
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the bottom of the profile where OSL sample BRMS OSL1 was collected. Profiles BSM2 and BSM3 are located in the exposed wet sand layers. Beddings of profiles BSM2, BSM3, and BSM1 are generally similar, although there are differences. For example, profile BSM3 (Fig. 3c) is at 1314 m a.s.l. with a height of 26 m above the modern lake level. The depth of the profile is 80 cm, with present water content about 10%. The upper part of the section is dominated by pink-grey middle to fine sands, while the lower part is dominated by gray-black fine sands. The boundary between the upper and lower parts is clear, where lithites occur with grain diameter varying from 0.5 to 1 cm. Multi-phase dune erosion and superimposition contact relation between type A and type B bedding, as well as crossbedding (Fig. 3c), can be seen in the newly-cleaned surface after air-drying for 15e20 min. The type B bedding became harder than when it was wet, and these air-dried layers are similar to paleo-caliche found in the dune. The crossbedding shown in Fig. 3b,c indicate sampling sites with no bioturbation. The OSL sample BRMS OSL3 was collected at the bottom of the profile BSM3. The profile BSM4, with an elevation of 1284 m a.s.l. at the bottom of the BSM, was 6 m above the modern lake level and near the rim of the lake basin (Fig. 3e). It was dug in a paleo-sand sub-dune to a depth of 60 cm. The upper part of the profile is composed of caliche with a thickness of about 10 cm and about 1e2 cm for each sublayer (Fig. 3d). The inclination of the caliche agrees with leeward slope inclination of the mega-dunes. The windward slope of the paleo-sand dune had been eroded completely, and coarse quartz sand remained between beds. The lower part of the profile BSM4 is pebbly pink-grey fine sand and gravels with diameters of ~1.5 mm, water content about 10%, and obvious bedding. The OSL sample BRMS OSL4 was collected from the lower part of the profile BSM4.
Fig. 4. Growth curves of the typica OSL sample BRMS OSL3.
period of increased climatic humidity. Their 14C ages of mega-dunes (39 280 N, 102 290 E), using calcareous plant roots from four calcareous layers on the windward slop with 10 m elevation intervals, dated at the C-14 and H-3 Laboratory in Hannover in Germany, are 31.75 ± 0.485 ka (Hv 15943), 19.1 ± 0.770 ka (Hv 15944), 9.44 ± 0.345 ka (Hv 15938), and 2.10 ± 0.1 ka (Hv 15937), respectively (Fig. 5). They also reported TL ages for samples from the highest mega-dune (39 52.50 N, 102 30.20 E), dated at Luminescence Laboratory at Wollongong University in Australia and the Luminescence Laboratory at the Guangzhou Institute of Geochemistry of the Chinese Academy of Sciences. They were 2.1 ± 0.170 ka (TGD602) and 18.500 ± 1.5 ka (TGD-601). TGD-602 was collected from the upper part of mega-dunes and beneath the surface of about 1 m, with an elevation difference of about 230 m. Sample TGD-601 was collected under a calcareous cementation layer in the middle of the slope, indicating that the age of the bottom of the dunes could be even much older than 19 ka. TL sample (W2804) reported by Yang et al. (2003) has an age of 1.300 ± 0.09 ka, and it was collected from a mega-dune south to the highest mega-dune from which
3.2. Dating results Dating results are listed in Table 1 and ages are labeled in Fig. 3. Ages of the four samples are 4.4 ± 0.5 (BRMS OSL1), 5.6 ± 0.5 (BRMS OSL2), 11.9 ± 0.9 (BRMS OSL3), and 125 ± 11 ka (BRMS OSL4), respectively. Table 1 Results of OSL dating for mega dune samples from the Badain Jaran Desert. Sample Lab ID
Sample field ID
Elevation (m)
Depth (cm)
Grain size (mm)
K (%)
11G-067 11G-068 11G-069 11G-070
BRMS BRMS BRMS BRMS
1375 1350 1314 1284
50 70 50 80
90e125 90e125 4e11 4e11
1.28 1.37 1.57 1.60
OSL1 OSL2 OSL3 OSL4
± ± ± ±
Th (ppm) 0.05 0.06 0.06 0.07
2.67 2.54 3.17 4.21
The recycling ratio in SAR protocol is a check method for sensitivity change correction (Murray and Wintle, 2000). Recycling ratios for most aliquots are in the range of 0.9e1.1, and those aliquots with recycling ratios that fall outside this range were rejected. The regeneration dose of zero Gy (R0) is to measure recuperation, which was calculated by comparing its sensitivitycorrected OSL signal to the sensitivity-corrected natural signal. Recuperation was in all cases less than <7%. Preheat plateau test and dose recovery test (BRMS OSL2) showed that the SAR protocol was suitable for De determination, which was typical for sand samples from China deserts. A growth curve is shown in Fig. 4. 4. Discussion Yang et al. (2003) found that the calcareous layer on the megadunes represents the old configuration of dunes and indicates a
± ± ± ±
0.20 0.17 0.18 0.20
U (ppm) 0.70 0.72 0.86 1.36
± ± ± ±
0.10 0.11 0.11 0.13
Water content （%） 10 10 10 10
± ± ± ±
5 5 5 5
De (Gy) 7.82 10.44 27.40 323
± ± ± ±
Dose rate (Gy/ka) 0.57 0.54 0.39 13
1.79 1.87 2.30 2.58
± ± ± ±
0.12 0.13 0.15 0.17
Age (ka) 4.4 5.6 11.9 125
± ± ± ±
0.5 0.5 0.9 11
samples TGD601 and TGD602 were collected, and was collected at 1 m in depth below the surface at a site 80 m lower than the crest of a 420 m high dune. The two TL ages (TGD-601 and W2804) from the upper parts of the two mega-dunes indicated that the height of the two dunes remained approximately constant during the last 1000e2000 years. Paleo-dunes and modern-dunes were distinguished by Yan et al. (2001) based on the extent of calcareous cementing on the mega-dune. Yan et al. (2001) had reported TL ages for Yikeer Aobo sand mountains (Fig. 2) with a relative elevation of about 180 m. Their five TL ages are 8 ± 2, 27 ± 6, 29 ± 6, 31 ± 6, and 68 ± 10 ka, respectively, indicating two phases of mega-dunes formation, i.e. the early-middle Holocene and the last glacial period. All the published ages, including our OSL ages, of mega-dunes, are compiled in Table 2 and their sampling sites in Fig. 2. Three out of four of our OSL ages fall into 4e11.9 ka, middle to early Holocene, with samples from middle to top of the mega-dunes.
Please cite this article in press as: Liu, S.W., et al., Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.09.048
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Table 2 Published ages of mega-dune and inter-dune lake sediments in the Badain Jaran Desert. Sediment type
Mega-dune
Inter-dune lake
Location
Dating materials and ages Materials
Age (ka BP)
See Fig. 2 ①
Calcareous plant roots (from top to bottom)
See Fig. 2 ②
Sand from mega-dune (from top to bottom)
See Fig. 2 ② See Fig. 2 ③
Sand from mega-dune (top) Sand from mega-dune (from top to bottom)
Badain
Ash, gasteropod fossils, organic matter, and calcareous root tube from lacustrine sediment
Kuhejilin Suminjilin Nuoertu Badain
Organic carbon from lacustrine sediment
Organic carbon from lacustrine sediment
Aomenjilin
Inorganic carbon from lacustrine sediment
East Shaobaijilang West Shaobaijilang
Organic carbon from lacustrine sediment
Sayinwusu Yindeertu Badain Zhalate See Fig. 2 ④
Inorganic carbon from lacustrine sediment Snail shells from lacustrine sediment Lacustrine sediment Lacustrine sedimentt Organic carbon from lacustrine sediment Lacustrine sediment (from top to bottom)
Barunbaoritaolegai (BAR.)
Lacustrine sediment (from top to bottom)
2.10 ± 0.100 9.44 ± 0.345 19.10 ± 0.770 31.75 ± 0.485 2.10 ± 0.170 18.5 ± 1.50 1.3 ± 0.09 8±2 27 ± 6 29 ± 6 31 ± 6 1 9.23 ± 0.154 1.09 ± 0.325 5.97 ± 0.218 7.71 ± 0.150 8.16 ± 0.320 2 7.41 ± 0.265 3 7.44 ± 0.151 679 ± 0.195 cal. 7.41 ± 0.135 cal. 6.18 ± 0.167 cal. 6.43 ± 1.66 cal. 4.94 ± 0.253 cal. 4.34 ± 0.318 cal. 9.04 ± 0.298 cal. 4.19 ± 0.304 cal. 5.63 ± 0.211cal. 7.14 ± 0.200cal. 4.76 ± 0.315 cal. 9.75 ± 0.206 cal. 7.42 ± 0.07cal. 11.88 ± 1.07 4.65 ± 0.191 cal. 2 ± 0.08 7 ± 0.40 101 ± 17 140 ± 19 74.4 ± 3.5 92.3 ± 4.2 10.5 ± 4.1
Four out of seven ages by Yang et al. (2003) and one out of five by Yan et al. (2001) also fell into this period. For older ages, the oldest age is our OSL age of 125 ± 8 ka, falling into the last interglaciation period (corresponding to marine isotope stage 5e, MIS 5e), and other ages were scattered between 15 and 73 ka falling into the last glacial period (Fig. 5). The OSL ages in this study show that mega-dunes have formed at two warm and humid phases, i.e. the Holocene and the last interglaciation. Similar results were reported recently that in the Badain Jaran Desert during the last inter-glacial period sand dunes tended to be active with enhanced aeolian activities indicated by OSL and ESR ages of a 230 m drill-core (WEDP02) (Wang et al., 2015). In other deserts in north China, the situation is the opposite. Sand dunes featured by stabilization in the Holocene and last interglaciation revealed by OSL ages of paleosols from Mu Us desert (He et al., 2010), Horqin dunefield (Yang et al., 2010a), Hunshandake and Hulun Buir deserts (Lu et al., 2013). Evidence also showed the Badain Jaran Desert expanded during the last glacial (Wang et al., 2015,Fan et al., submitted for publication). Thus, the land surface process in the Badain Jaran Desert during the warm and humid inter-glaciation periods seems to be unique from other deserts in north China. Ground water may be the reason, for this as it preserved the aeolian process records by stabilizing the drift sands. Ground water played an important role in the dune build-up in the Badain Jaran Desert (Chen et al., 2004). Water in the mega dune
Dating method
References
14
Yang et al., 2003
C
TL
cal. cal. cal. cal. cal. cal. cal.
TL
Yan et al., 2001
14
C
Li et al., 2010
14
C
Yang et al., 2003
14
C
Yang et al., 2010b
14 C TL 14 C OSL
Yang et al., 2003
OSL
Fan et al., 2014
Hofmann, 1999 Bai et al., 2011
may be recharged by rainfall (Li et al., 2009), or by underground water sourced from the precipitation and snowmelt water from the Qinghai-Tibetan Plateau passing through the fault zone (Chen et al., 2006). Previous studies show that underground water recharging the dunes or inter-dune lakes may contribute to regional atmospheric precipitation (Yang et al., 2010b) or deeper aquifers (Chen et al., 2004; Ma and Edmunds, 2005; Chen et al., 2006). Fitzsimmons et al. (2007a) also found that, in the Strzelecki Desert of Australia, the nature and initiation of dune activity is controlled not only by aridity, but also by local hydrology, such as underground water level changes reflected by inter-dune lake levels. They reported that dune activity is linked to playa conditions, and that relatively higher lake levels corresponded to pedogenesis within the dunes. Dune horizons containing clay pellets (corresponding to the type B layers on the mega dune in the Badain Jaran Desert, see Fig. 3b and text below) are interpreted as having been deposited close to a threshold of dune instability, while horizons devoid of clay pellets (corresponding to the type A layers on the mega dune in the Badain Jaran Desert) are interpreted as having occurred under more arid conditions (Fitzsimmons et al., 2007b). Our geophysical measurement in mega-dunes (unpublished data) also confirmed that aquifers with thickness about dozens to hundreds of meters developed under mega-dunes and normal faults. During our field trips, we found evidence indicating that moisture was recharged by the underground water. This evidence include
Please cite this article in press as: Liu, S.W., et al., Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.09.048
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S. Liu et al. / Quaternary International xxx (2015) 1e8
Fig. 5. Summary of published chronological data (including the OSL ages of the current study) of mega-dunes and comparison with regional climate records over the past 130 ka. These ages mainly cluster at two periods, i.e. the Holocene and last interglaciation.
springs and tufa, distributed from east to west in the Badain Jaran Desert. Inter-dune lakes, i.e. Lake Wuertabulage, Lake Bayinnuoer, Lake Hasatu (Fig. 2), are recharged by springs originating from mega-dunes at the east sides of these lakes. The formation of mega dunes in the Badain Jaran Desert is complicated and affected by multiple factors such as wind parameters, local geology, topography, and interactions between climate and aeolian/fluvial processes (Yang et al., 2011), as well as by the unique hydrogeological situations (Chen et al., 2004, 2006; Gates et al., 2008). OSL dating could be critical for understanding the formation of sand dunes (Telfer and Hesse, 2013). Our mega dune OSL ages indicates a moist and warm climate may be a prerequisite of mega dune growth. During our field trips, paleo-lake sediments were observed in inter-dune depressions. Evidence from other deserts shows that lake sediments (or lake floors) may be the main dust source for aeolian activity (Fitzsimmons et al., 2007b). 14C ages of the interdune paleo-lake sediments using carbonate and snail fossils (Yang and Williams, 2003; Yang et al., 2003; Hartmann and Wünnemann, 2009; Li et al., 2010; Yang et al., 2010b, 2011) suggested that high stand fresh water lakes once occurred during the Holocene in the study area. These 14C ages have been plotted in Fig. 5, and their sampling locations in Fig. 2. OSL ages of lake sediments by Bai et al. (2011b) and Fan et al. (2014) showed that high stand lakes also occurred during MIS5, during which the oldest dunes formed (125 ± 11 ka of sample BRMS OSL4). The recent drill core WED-02 dated by OSL and ESR from the Badain Jaran Desert reveals that during 15e0 ka the area was lake dominated, and during 130e70 ka was also lake dominated but with increased aeolian activity (Fig. 5). 14C ages (from 2.16 ± 0.07 ka to 29.61 ± 0.74 ka) and a TL age (147.8 ± 11.8 ka) of paleosol and lake sediments existed in profile Chalegebulu at the east edge of the Badain Jaran Desert (Fig. 5) (Li et al., 2005; Yang et al., 2008). High lake levels on the southeastern margin of the Badain Jaran and in the dunefields were dated mainly to ca 89 ka and the Early Holocene (Yang, 2004). The drill core from the Ulan Buh Desert northeast of the Badain Jaran Desert also show a paleolake developed during 155e87 ka (Li et al., 2014). Our four profiles all show well-bedding layers in dunes, indicating that during the middle Holocene and the last inter-glaciation aeolian processes were still active. The profile was characterized by alternations of type A and type B layers (Fig. 3b). The type A layers represent the coarse grain size fraction with high content of quartz,
and the sedimentary characteristics are close to that of the surface sand with nearly no carbonate. The XRD of surface sand suggests that no calcite is present (Fig. 6). Type A may be sourced from the aeolian sand of the lake basin or re-activated paleo-sand dunes, within which the fine grain fraction was deflated and thus only the coarse grain fraction remained. XRD results suggest that the caliche and the lake sediment contain similar minerals as shown in Fig. 6. The type B layer represents a fine grain fraction with high carbonate content, and these materials might have come from lake sediments nearby. Our XRD results show that only lake sediments could contain calcite content as high as 20%, and that the calcite could not be found in the surface drift sands (Fig. 6). The WED-02 drill core (Wang et al., 2015) suggests that during the periods of lake development the Badain Jaran lake sediments could contain carbonate up to 100%, while aeolian sands contain 10% carbonate at most. Low content of lithites (Fig. 6) between layers of mega-dunes indicates that carbonate leaching by rainfall from the upper layers is weak. Thus, most carbonate in the type B layer should have come from aeolian dust sourced from paleo-lake sediments near the megadunes instead of from leaching. Mineral kaolinite, an indicator of a wet and warm environment with strong chemical weathering, is rare in the surface sand and lake sediments (Fig. 6), and may be from weathered feldspars. Feldspars in dune sand are common (Fig. 6). Consequently, the type B layers may represent periods when the sand dune was relatively fixed with more moisture, while type A represents dry periods and sand dune re-activation. During the humid and warm periods in the Bdain Jaran Desert underground water was supplied to sand dunes, and local rainfall could be greater during the last 30 ka (Yang et al., 2003). The dunes formed during humid and warm periods may contain more water, which could adhere to loose sand grains (Chen et al., 2006). Calcium cementation in the form of pedogenic calcretes can enhance the process. Our XRD results of caliche collected from profile BSM4 show that the content of calcite is about 49%. Increasing rainfall and higher water table would promote the growth of mega-dunes when more carbonate would accumulate in dunes. The caliche could prevent mega-dunes from wind erosion. During the field investigation we observed that caliches could develop from the wet sand layers (type B layers) after exposure for more than 30 min under sunshine. We also found abundant Neolithic stone tools in many lacustrine sediment surfaces in the inter-dune depressions, indicating intensive human activities and much more friendly living conditions in
Please cite this article in press as: Liu, S.W., et al., Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.09.048
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Fig. 6. XRD results of three samples (surface sand, calcrete, and lake sediment) collected from the BSM and nearby.
the past in this nowadays hyper-arid and harsh natural environment, suggesting occurrence of dramatic climatic changes. Further work is required to address these issues. 5. Conclusions Based on systematic geomorphological observations and OSL dating of mega-dunes in the Badain Jaran Desert in China, we concluded that: (1) The best locations for OSL sample collection in the megadunes are the easy-seen exposed wet sand layers. Our field observation showed that wet sand layers could expose in the slope surface and could be easily seen due to its wetness and calcareous cementing with stronger resistance to wind deflation relative to the adjacent sands, with well-preserved original bedding layers. (2) Our OSL ages are 4.4 ± 0.5, 5.6 ± 0.5, 11.9 ± 0.9, and 125 ± 11 ka from the top to the bottom of the mega-dune. These ages indicate that there were two phases of dune development in the Holocene and last inter-glaciation, which were both warm and humid periods. Main growth period of mega-dunes occurred during the Holocene. Underground water supply and climatic changes play an important role in the mega dune growth, confirming the previous conclusions (e.g. Chen et al., 2004; Yang et al., 2010b). (3) In order to understand the mechanism of the mega-dunes formation and its relation to climate/environment, more systematic dating work is required for the dunes and the lacustrine sediments in the inter-dune depressions. Acknowledgments We wish to thank three anonymous reviewers for constructive suggestions. Thanks may extend to Xinqiang Chen for his assistance in field investigation. This work was funded by National Research Center for Geoanalysis (NRCGA) Basal Research Fund Special Funds (No. 2013CSJ02), the CAS Strategic Priority Research Program (Grant No. XDA05120501), and China NSF (41290252).
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monsoon drift on a large scale toward NW China during the Holocene Megathermal. Journal of Earth Environment 1 (2), 133e138 (in Chinese with English abstract). Li, G.Q., Jin, M., Wen, L.J., Zhao, H., Madsen, D., Liu, X.K., Wu, D., Chen, F.H., 2014. Quartz and K-feldspar optical dating chronology of eolian sand and lacustrine sequence from the southern Ulan Buh Desert, NW China: implications for reconstructing late Pleistocene environmental evolution. Palaeogeography, Palaeoclimatology, Palaeoecology 393, 111e121. Li, X.Z., Wang, Z.T., Chen, F.H., Lancaster, N., Li, Z.G., Li, G.Q., Ren, X.Z., Dong, G.R., 2009. Deposition of transverse dune mountains in Badain Jaran Desert of China by GPR-detection. Quaternary Sciences 29 (4), 797e805 (in Chinese with English abstract). Lu, H.Y., Yi, S.W., Xu, Z.W., Zhou, Y.L., Zeng, L., Zhu, F.Y., Feng, H., Dong, L.N., Zhuo, H.X., Yu, K.F., Mason, J., Wang, X.Y., Chen, Y.Y., Lu, Qi, Wu, B., Dong, Z.B., Qu, J.J., Wang, X.M., Guo, Z.T., 2013. Chinese deserts and sand fields in Last Glacial Maximum and Holocene Optimum. Chinese Science Bulletin 58 (23), 2775e2783. Lu, J.H., Guo, Y.S., 1995. Study on compilation of landscape map of typical area of high dunes in Badain Jaran Desert. Journal of desert research 15 (4), 385e391 (In Chinese with English abstract). Lu, Y.C., Wang, X.L., Wintle, A.G., 2007. A new OSL chronology for dust accumulation in the last 130,000 yr for the Chinese Loess Plateau. Quaternary Research 67, 152e160. Ma, J.Z., Edmunds, W.M., 2005. Groundwater and lake evolution in the Badain Jaran Desert ecosystem,Inner Mongolia. Hydrogeology Journal 14 (7), 1231e1243. Murray, A.S., Wintle, A.G., 2000. Luminescence dating of quartz using an improved single aliquot regenerative-dose protocol. Radiation Measurements 32 (1), 57e73. 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 (2), 497e500. Telfer, M.W., Hesse, P.P., 2013. Palaeoenvironmental reconstructions from linear dunefields: recent progress, current challenges and future directions. Quaternary Science Reviews 78, 1e21.
Wang, F., Sun, D.H., Chen, F.H., Bloemendal, J., Guo, F., Li, Z.J., Zhang, Y.B., Li, B.F., Wang, X., 2015. Formation and evolution of the Badain Jaran Desert, North China, as revealed by a drill core from the desert centre and by geological survey. Palaeogeography, Palaeoclimatology, Palaeoecology 426, 139e158. Yan, C.M., Wang, G.Q., Li, B.S., Dong, G.R., 2001. Formation and growth of high mega dunes in Badain Jaran Desert. Acta Geographica Sinica 56 (1), 83e91 (in Chinese with English abstract). Yang, L.H., Zhou, J., Lai, Z.P., Long, H., Zhang, J.R., 2010a. Lateglacial and Holocene dune evolution in the Horqin dunefield of northeastern China based on luminescence dating. Palaeogeography, Palaeoclimatology, Palaeoecology 296, 44e51. Yang, X.P., Liu, T., Xiao, H.L., 2003. Evolution of megadunes and lakes in the Badain Jaran Desert, Inner Mongolia, China during the last 31,000 years. Quaternary International 104 (1), 99e112. Yang, X.P., Ma, N.N., Dong, J.F., Zhu, B.Q., Xu, B., Ma, Z.B., Liu, J.Q., 2010b. Recharge to the inter-dune lakes and Holocene climatic changes in the Badain Jaran Desert, western China. Quaternary Research 73 (1), 10e19. Yang, X.P., Williams, M.A., 2003. The ion chemistry of lakes and late Holocene desiccation in the Badain Jaran Desert, Inner Mongolia, China. Catena 51 (1), 45e60. Yang, Y., Li, B.S., Qiu, S.F., Wu, Z., Gao, Q.Z., Li, Y.Z., 2008. Climatic changes indicated by trace elements in the Chagelebulu stratigraphic section, Badain Jaran Desert, China, since 150 kyr B.P. Geochemistry International 46, 96e103. Yang, X.P., 2004. Late Quaternary wetter epochs in the southeastern Badain Jaran Desert, Inner Mongolia, China. Zeitschrift für Geomorphologie Suppl.-Bd 133, 129e141. Yang, X.P., Scuderi, L., Paillou, P., Liu, Z.T., Li, H.W., Ren, X.Z., 2011. Quaternary environmental changes in the drylands of China - a critical review. Quaternary Science Reviews 30, 3219e3233. Zhong, D.C., 2003. Dynamical Change Map of Modern Sand Desert in China (1:4,000 000). Sinomap Press, Beijing.
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Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages SiWen Liu a, b, ZhongPing Lai c, *, YiXuan Wang d, XiaoLu Fan e, LuLin Wang e, MingZhong Tian e, **, YaDong Jiang f, Hua Zhao g a
National Research Center for Geoanalysis, Beijing 100037, China Key-laboratory of Eco-geochemistry, Ministry of Land and Resources, Beijing 100037, China School of Earth Sciences, China University of Geosciences, Wuhan 430074, China d Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China e School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China f Inner Mongolia Geological Environment Monitoring, Hohhot 010020, China g Institute of Hydrogeology and Environmental Geology, CAGS, Shijiazhuang 050061, China b c
a r t i c l e i n f o
a b s t r a c t
Article history: Available online xxx
Sand dunes up to 400 m high are common in the Badain Jaran Desert in China, but how and why megadunes grow remains unclear. Timing is the most critical to clarify this issue. The chronological data are still limited with only a few 14C ages from carbonate, not the direct age of the dune, and a few thermoluminescence (TL) ages whose unbleachable residual signals may result in uncertainty in age. Optically stimulated luminescence (OSL) dating uses quartz or feldspars and thus directly dates the sands. It could also be completely reset by daylight with no residual signals. We here report for the first time a batch of OSL ages, and discuss the pattern of the mega-dune growth. Field observation showed that wet sand layers could be exposed in the slope surface and could be easily seen due to its wetness and calcareous cement, causing stronger resistance to wind deflation relative to the adjacent sands. Wet sand layers are normally situated on the mega-dune windward slope, and sometimes could even be seen near the top of a mega-dune, with well-preserved original bedding layers, making them the ideal locations for collecting luminescence samples. Our four OSL samples collected from the Barunbaoritaolegai sand mountain (BSM) show that OSL ages are 4.4 ± 0.5, 5.6 ± 0.5, 11.9 ± 0.9, and 125 ± 11 ka, respectively, from top to bottom. These ages are concentrated in the early to middle Holocene and the Last Inter-glaciation (corresponding to MIS 5e). Based on field observation and OSL ages, we propose that the mega-dunes grow mostly during humid periods with water as cementing agents to build up the sands. The issues, such as the source of the water, how the water seeps into the high sand dunes, how the loose sands could build up to mega-height, etc., require further study. © 2015 Elsevier Ltd and INQUA. All rights reserved.
Keywords: Mega-dunes in the Badain Jaran Desert in China OSL dating Pattern of mega-dune growth
1. Introduction The tallest dunes (the sand mountains) in the earth are observed in the Badain Jaran Desert in China (Yang et al., 2003; Dong et al., 2013) (Fig. 1). Those issues that how and why mega-dunes grow have been discussed from different dimensions, such as geomorphology, wind regime (Dong et al., 2004), and under groundwater (Chen et al., 2004), but still remains unclear. Timing is the
* Corresponding author. ** Corresponding author. E-mail address: [email protected] (Z. Lai).
most critical to clarify these issues. However, the chronological data are still limited with only a few of 14C ages using carbonate of the calcareous roots (Yang and Williams, 2003; Yang et al., 2003; Hartmann and Wünnemann, 2009), and thermoluminescence (TL) ages (Yan et al., 2001). 14C ages using calcareous roots from the sand dune reflect the formation of the calcite rather than events of sand accumulation. TL signals have residuals even after exposure to sunshine for days, which may occupy a high percentage (e.g. 10e30%) of the total signals accumulated during burial for Holocene age samples and are also difficult to evaluate, leading to large uncertainty in age. Optically stimulated luminescence (OSL) could be reset completely by daylight, and uses quartz or feldspar. Thus OSL is an ideal technique to date directly sand dunes.
http://dx.doi.org/10.1016/j.quaint.2015.09.048 1040-6182/© 2015 Elsevier Ltd and INQUA. All rights reserved.
Please cite this article in press as: Liu, S.W., et al., Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.09.048
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Fig. 1. Map of study area (background map plotted by DEM sourced from ArcGIS online). The triangle represents the Baoritaolrgai Sand Mountains (BSM). The filled black square represents profile Chalegebulu (Li et al., 2005). Dot represents the Core WEPD02 drilling site (Wang et al., 2015).
As mega-dunes are covered by drift sands and the knowledge of the structure inside the mega-dunes is limited, it is difficult to locate a position to collect OSL samples. Our field observations showed that wet sand layers (Li et al., 2009) could be exposed on the slope surface and could be easily seen due to the wetness and calcareous cement with stronger resistance to wind deflation relative to the adjacent sands. These layers are normally situated on the windward slopes of mega-dunes, and sometimes are exposed near the top of a mega-dune. The original bedding layers could be seen on the exposure surface of the layer, and thus these are ideal locations for collecting luminescence samples. Deposition structure (or bedding layers) observed in the exposed wet sand layers are similar to that of the mega dunes 10 m below the surface detected using Ground Penetrating Radar (GPR) (Li et al., 2009; Bai et al., 2011a). The wet sand layers (most of them in the form of calcareous cementation layers) were previously interpreted as representing a humid climate phase related to regional precipitation (Yang et al., 2003). This interpretation might have been trying to correlate the alternating wet sand layers and relative dry sand layers to the alternating paleosol and loess layers in the Chinese Loess Plateau. We investigated systemically the Barunbaoritaolegai sand mountains (BSM) and obtained four OSL samples in the Badain Jaran Desert. We report the dating results of these OSL samples and discuss the pattern of the mega-dunes growth.
transverse mega-dunes and compound star mega-dunes. The Bilutu Peak is the tallest mega-dune with a height of ~450 m, and is of a compound transverse type. The strike of a mega-dune main body is normally from northeast to southwest, in agreement with the prevailing northwest wind. The inclination of mega-dune leeward slop is southeast. The scales of the mega-dunes are normally 1e10 km long and 1e4 km wide. The highest point of a megadune occurs at the central ridge. The mega-dunes have steep leeward slops, and gentle windward slops where secondary smaller dunes are superposed. Artemisia scoparia and Psammochloa mongolica grow on the mega-dunes due to the existence of wet sand layers. 2.2. Profiles and samples The Barunbaoritaolegai Sand Mountain (BSM) (Fig. 1), the typical mega-dune in the southeast of the Badain Jaran Desert, was selected for study. The BSM is a giant compound star sand dune with three arms (Fig. 3a). Two of them run from northeast to
2. Study area, materials and methods 2.1. Study area The Badain Jaran Desert is located in the Mongolia Plateau (Fig. 1), northwest China, covering an area of 5.05 104 km2 (Zhong, 2003). It is known for the tallest mega-dunes in the world, which are distributed densely in the southeast of the Badain Jaran Desert (Fig. 2). The area of mega-dunes with a height of >100 m occupies 68% of the total area of the desert (Lu and Guo, 1995), and most of these dunes are higher than >200 m. The main types of mega-dunes described in Dong et al. (2004) are compound
Fig. 2. Locations of sampling sites of published ages in mega-dunes and lake sediments in the Badain Jaran Desert. See Fig. 1 for specific location within the desert.
Please cite this article in press as: Liu, S.W., et al., Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.09.048
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Fig. 3. Studied dune, profiles, and OSL ages of the Barunbaoritaolegai sand mountain (BSM).
southwest, forming the central part of the main body of the BSM, with a length of 2 km and a width of 1.1 km. The third arm runs from northwest to southeast with a length of about 0.6 km. The maximum height of the central ridge is 150 m, 1420 m above sea level (a.s.l.). Sand wet layers occur on the windward slope at different elevations (Fig. 3a). OSL dating samples were collected at the BSM from the wet sand layers (Fig. 3a) using steel pipes with a diameter of 4 cm. Four profiles (BSM1, 2, 3, 4) were dug from the bottom to the top of the BSM, and one OSL sample was collected from each of the profiles (BRMS OSL 1, 2, 3 and 4) (Fig. 3). In addition, three samples were collected for X-ray diffraction (XRD) measurement. These samples are surface sand collected from the surface the BSM, caliche collected from profile BSM4, and paleo-lake sediments 500 m east of BSM developed in the last interglacial (Fan et al., 2014).
OSL measurement was performed on Daybreak-2200 equipped with blue light stimulation (470 nm, maximum power 60 Mw/cm2) and infrared stimulation (880 nm, maximum power 80 Mw/cm2) in the luminescence laboratory of Institute of Hydrogeology and Environmental Geology, China (CAGS). Preheating at 260 C for 10 s and cut-heat at 220 C for 10 s were applied before measuring OS. Fine quartz grains were measured using simplified multiple aliquot regenerative-dose (SMAR) (Lu et al., 2007). The contribution of cosmic rays was calculated according to Prescott and Hutton (1994). 10 ± 5% of sample water contents were used for dose rate calculation. Coarse quartz grain was measured using single-aliquot regenerative-dose procedure (SAR) (Murray and Wintle, 2000). XRD was measured using the X-ray diffractometer (D/max-rA) in the Micro Structure Analysing and Testing Lab, China.
2.3. Sample preparation and measurements
3.1. Stratigraphical characteristics
Samples in the steel pipes were taken out under red light (wave length 640 ± 10 nm) in the laboratory, and materials at the ends of the pipes were kept for measuring the water contents and the concentrations of U, Th, K using neutron activation analysis. The coarse quartz (90e125 mm, samples BRMS OSL 1 and 2) and fine grain fraction (4e11 mm, BRMS OSL 3 and 4) were used for De determination. The materials in the center part of a pipe were placed in the beaker and were added HCl (10%) and H2O2 (40%) for removing carbonates and organic matter, respectively. For extracting 4e11 mm quartz, the samples were then treated according to Stokes Law, and were further added H2SiF6 with concentration of 30% to etch for 3 days. To extract 90e125 mm quartz, HF (40%) etching for 60 min was performed. Chemically purified quartz grains were dried and then the magnetic minerals were removed to obtain pure quartz grains. The purity of quartz grains was monitored by the level of Infrared Stimulated Luminescence (IRSL) signals. Samples that showed obvious IRSL signals were retreated with H2SiF6 or HF again. Pure quartz samples were then mounted on stainless steel disks.
The profile BSM1 (Fig. 3b) is located at the top of the BSM, about 97 m above the modern lake level with an elevation of 1375 m a.s.l. It is near the plant growing region between two secondary dunes on the windward slop with a slope angle of 26e28 . The profile BSM1 was dug to a depth of about 90 cm with well-preserved sand bedding and water content of ~10%. Two kinds of sedimentation bedding, type A and type B, can be identified: (1) in thick bedding (Fig. 3b, type A bedding), grain size was dominated by well-sorted, rounded, pinky-grey, middle to fine sand, containing less melanocratic minerals (such as hornblende, pyroxene and magnetite), and the thickness varies from 0.6 cm to 16 cm. (2) In thin bedding (type B bedding), grain size was dominated by well sorted, rounded, grayish-black fine sand to silt, containing more dark minerals and carbonate, with thickness from 0.3 cm to 0.5 cm. Materials with type B bedding are dominant in caliche (Fig. 3e). Bedding on the top of profile BSM1, about 0e13 cm in depth, are dominated by type A with thicknesses of 3e5 mm. Bedding beneath the depth of 13 cm are dominated by alternating type A and type B layers. The thickness of type A bedding gradually increases from the top to the bottom. The maximum thickness of the type A bedding occurs at
3. Results
Please cite this article in press as: Liu, S.W., et al., Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.09.048
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the bottom of the profile where OSL sample BRMS OSL1 was collected. Profiles BSM2 and BSM3 are located in the exposed wet sand layers. Beddings of profiles BSM2, BSM3, and BSM1 are generally similar, although there are differences. For example, profile BSM3 (Fig. 3c) is at 1314 m a.s.l. with a height of 26 m above the modern lake level. The depth of the profile is 80 cm, with present water content about 10%. The upper part of the section is dominated by pink-grey middle to fine sands, while the lower part is dominated by gray-black fine sands. The boundary between the upper and lower parts is clear, where lithites occur with grain diameter varying from 0.5 to 1 cm. Multi-phase dune erosion and superimposition contact relation between type A and type B bedding, as well as crossbedding (Fig. 3c), can be seen in the newly-cleaned surface after air-drying for 15e20 min. The type B bedding became harder than when it was wet, and these air-dried layers are similar to paleo-caliche found in the dune. The crossbedding shown in Fig. 3b,c indicate sampling sites with no bioturbation. The OSL sample BRMS OSL3 was collected at the bottom of the profile BSM3. The profile BSM4, with an elevation of 1284 m a.s.l. at the bottom of the BSM, was 6 m above the modern lake level and near the rim of the lake basin (Fig. 3e). It was dug in a paleo-sand sub-dune to a depth of 60 cm. The upper part of the profile is composed of caliche with a thickness of about 10 cm and about 1e2 cm for each sublayer (Fig. 3d). The inclination of the caliche agrees with leeward slope inclination of the mega-dunes. The windward slope of the paleo-sand dune had been eroded completely, and coarse quartz sand remained between beds. The lower part of the profile BSM4 is pebbly pink-grey fine sand and gravels with diameters of ~1.5 mm, water content about 10%, and obvious bedding. The OSL sample BRMS OSL4 was collected from the lower part of the profile BSM4.
Fig. 4. Growth curves of the typica OSL sample BRMS OSL3.
period of increased climatic humidity. Their 14C ages of mega-dunes (39 280 N, 102 290 E), using calcareous plant roots from four calcareous layers on the windward slop with 10 m elevation intervals, dated at the C-14 and H-3 Laboratory in Hannover in Germany, are 31.75 ± 0.485 ka (Hv 15943), 19.1 ± 0.770 ka (Hv 15944), 9.44 ± 0.345 ka (Hv 15938), and 2.10 ± 0.1 ka (Hv 15937), respectively (Fig. 5). They also reported TL ages for samples from the highest mega-dune (39 52.50 N, 102 30.20 E), dated at Luminescence Laboratory at Wollongong University in Australia and the Luminescence Laboratory at the Guangzhou Institute of Geochemistry of the Chinese Academy of Sciences. They were 2.1 ± 0.170 ka (TGD602) and 18.500 ± 1.5 ka (TGD-601). TGD-602 was collected from the upper part of mega-dunes and beneath the surface of about 1 m, with an elevation difference of about 230 m. Sample TGD-601 was collected under a calcareous cementation layer in the middle of the slope, indicating that the age of the bottom of the dunes could be even much older than 19 ka. TL sample (W2804) reported by Yang et al. (2003) has an age of 1.300 ± 0.09 ka, and it was collected from a mega-dune south to the highest mega-dune from which
3.2. Dating results Dating results are listed in Table 1 and ages are labeled in Fig. 3. Ages of the four samples are 4.4 ± 0.5 (BRMS OSL1), 5.6 ± 0.5 (BRMS OSL2), 11.9 ± 0.9 (BRMS OSL3), and 125 ± 11 ka (BRMS OSL4), respectively. Table 1 Results of OSL dating for mega dune samples from the Badain Jaran Desert. Sample Lab ID
Sample field ID
Elevation (m)
Depth (cm)
Grain size (mm)
K (%)
11G-067 11G-068 11G-069 11G-070
BRMS BRMS BRMS BRMS
1375 1350 1314 1284
50 70 50 80
90e125 90e125 4e11 4e11
1.28 1.37 1.57 1.60
OSL1 OSL2 OSL3 OSL4
± ± ± ±
Th (ppm) 0.05 0.06 0.06 0.07
2.67 2.54 3.17 4.21
The recycling ratio in SAR protocol is a check method for sensitivity change correction (Murray and Wintle, 2000). Recycling ratios for most aliquots are in the range of 0.9e1.1, and those aliquots with recycling ratios that fall outside this range were rejected. The regeneration dose of zero Gy (R0) is to measure recuperation, which was calculated by comparing its sensitivitycorrected OSL signal to the sensitivity-corrected natural signal. Recuperation was in all cases less than <7%. Preheat plateau test and dose recovery test (BRMS OSL2) showed that the SAR protocol was suitable for De determination, which was typical for sand samples from China deserts. A growth curve is shown in Fig. 4. 4. Discussion Yang et al. (2003) found that the calcareous layer on the megadunes represents the old configuration of dunes and indicates a
± ± ± ±
0.20 0.17 0.18 0.20
U (ppm) 0.70 0.72 0.86 1.36
± ± ± ±
0.10 0.11 0.11 0.13
Water content （%） 10 10 10 10
± ± ± ±
5 5 5 5
De (Gy) 7.82 10.44 27.40 323
± ± ± ±
Dose rate (Gy/ka) 0.57 0.54 0.39 13
1.79 1.87 2.30 2.58
± ± ± ±
0.12 0.13 0.15 0.17
Age (ka) 4.4 5.6 11.9 125
± ± ± ±
0.5 0.5 0.9 11
samples TGD601 and TGD602 were collected, and was collected at 1 m in depth below the surface at a site 80 m lower than the crest of a 420 m high dune. The two TL ages (TGD-601 and W2804) from the upper parts of the two mega-dunes indicated that the height of the two dunes remained approximately constant during the last 1000e2000 years. Paleo-dunes and modern-dunes were distinguished by Yan et al. (2001) based on the extent of calcareous cementing on the mega-dune. Yan et al. (2001) had reported TL ages for Yikeer Aobo sand mountains (Fig. 2) with a relative elevation of about 180 m. Their five TL ages are 8 ± 2, 27 ± 6, 29 ± 6, 31 ± 6, and 68 ± 10 ka, respectively, indicating two phases of mega-dunes formation, i.e. the early-middle Holocene and the last glacial period. All the published ages, including our OSL ages, of mega-dunes, are compiled in Table 2 and their sampling sites in Fig. 2. Three out of four of our OSL ages fall into 4e11.9 ka, middle to early Holocene, with samples from middle to top of the mega-dunes.
Please cite this article in press as: Liu, S.W., et al., Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.09.048
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Table 2 Published ages of mega-dune and inter-dune lake sediments in the Badain Jaran Desert. Sediment type
Mega-dune
Inter-dune lake
Location
Dating materials and ages Materials
Age (ka BP)
See Fig. 2 ①
Calcareous plant roots (from top to bottom)
See Fig. 2 ②
Sand from mega-dune (from top to bottom)
See Fig. 2 ② See Fig. 2 ③
Sand from mega-dune (top) Sand from mega-dune (from top to bottom)
Badain
Ash, gasteropod fossils, organic matter, and calcareous root tube from lacustrine sediment
Kuhejilin Suminjilin Nuoertu Badain
Organic carbon from lacustrine sediment
Organic carbon from lacustrine sediment
Aomenjilin
Inorganic carbon from lacustrine sediment
East Shaobaijilang West Shaobaijilang
Organic carbon from lacustrine sediment
Sayinwusu Yindeertu Badain Zhalate See Fig. 2 ④
Inorganic carbon from lacustrine sediment Snail shells from lacustrine sediment Lacustrine sediment Lacustrine sedimentt Organic carbon from lacustrine sediment Lacustrine sediment (from top to bottom)
Barunbaoritaolegai (BAR.)
Lacustrine sediment (from top to bottom)
2.10 ± 0.100 9.44 ± 0.345 19.10 ± 0.770 31.75 ± 0.485 2.10 ± 0.170 18.5 ± 1.50 1.3 ± 0.09 8±2 27 ± 6 29 ± 6 31 ± 6 1 9.23 ± 0.154 1.09 ± 0.325 5.97 ± 0.218 7.71 ± 0.150 8.16 ± 0.320 2 7.41 ± 0.265 3 7.44 ± 0.151 679 ± 0.195 cal. 7.41 ± 0.135 cal. 6.18 ± 0.167 cal. 6.43 ± 1.66 cal. 4.94 ± 0.253 cal. 4.34 ± 0.318 cal. 9.04 ± 0.298 cal. 4.19 ± 0.304 cal. 5.63 ± 0.211cal. 7.14 ± 0.200cal. 4.76 ± 0.315 cal. 9.75 ± 0.206 cal. 7.42 ± 0.07cal. 11.88 ± 1.07 4.65 ± 0.191 cal. 2 ± 0.08 7 ± 0.40 101 ± 17 140 ± 19 74.4 ± 3.5 92.3 ± 4.2 10.5 ± 4.1
Four out of seven ages by Yang et al. (2003) and one out of five by Yan et al. (2001) also fell into this period. For older ages, the oldest age is our OSL age of 125 ± 8 ka, falling into the last interglaciation period (corresponding to marine isotope stage 5e, MIS 5e), and other ages were scattered between 15 and 73 ka falling into the last glacial period (Fig. 5). The OSL ages in this study show that mega-dunes have formed at two warm and humid phases, i.e. the Holocene and the last interglaciation. Similar results were reported recently that in the Badain Jaran Desert during the last inter-glacial period sand dunes tended to be active with enhanced aeolian activities indicated by OSL and ESR ages of a 230 m drill-core (WEDP02) (Wang et al., 2015). In other deserts in north China, the situation is the opposite. Sand dunes featured by stabilization in the Holocene and last interglaciation revealed by OSL ages of paleosols from Mu Us desert (He et al., 2010), Horqin dunefield (Yang et al., 2010a), Hunshandake and Hulun Buir deserts (Lu et al., 2013). Evidence also showed the Badain Jaran Desert expanded during the last glacial (Wang et al., 2015,Fan et al., submitted for publication). Thus, the land surface process in the Badain Jaran Desert during the warm and humid inter-glaciation periods seems to be unique from other deserts in north China. Ground water may be the reason, for this as it preserved the aeolian process records by stabilizing the drift sands. Ground water played an important role in the dune build-up in the Badain Jaran Desert (Chen et al., 2004). Water in the mega dune
Dating method
References
14
Yang et al., 2003
C
TL
cal. cal. cal. cal. cal. cal. cal.
TL
Yan et al., 2001
14
C
Li et al., 2010
14
C
Yang et al., 2003
14
C
Yang et al., 2010b
14 C TL 14 C OSL
Yang et al., 2003
OSL
Fan et al., 2014
Hofmann, 1999 Bai et al., 2011
may be recharged by rainfall (Li et al., 2009), or by underground water sourced from the precipitation and snowmelt water from the Qinghai-Tibetan Plateau passing through the fault zone (Chen et al., 2006). Previous studies show that underground water recharging the dunes or inter-dune lakes may contribute to regional atmospheric precipitation (Yang et al., 2010b) or deeper aquifers (Chen et al., 2004; Ma and Edmunds, 2005; Chen et al., 2006). Fitzsimmons et al. (2007a) also found that, in the Strzelecki Desert of Australia, the nature and initiation of dune activity is controlled not only by aridity, but also by local hydrology, such as underground water level changes reflected by inter-dune lake levels. They reported that dune activity is linked to playa conditions, and that relatively higher lake levels corresponded to pedogenesis within the dunes. Dune horizons containing clay pellets (corresponding to the type B layers on the mega dune in the Badain Jaran Desert, see Fig. 3b and text below) are interpreted as having been deposited close to a threshold of dune instability, while horizons devoid of clay pellets (corresponding to the type A layers on the mega dune in the Badain Jaran Desert) are interpreted as having occurred under more arid conditions (Fitzsimmons et al., 2007b). Our geophysical measurement in mega-dunes (unpublished data) also confirmed that aquifers with thickness about dozens to hundreds of meters developed under mega-dunes and normal faults. During our field trips, we found evidence indicating that moisture was recharged by the underground water. This evidence include
Please cite this article in press as: Liu, S.W., et al., Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.09.048
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S. Liu et al. / Quaternary International xxx (2015) 1e8
Fig. 5. Summary of published chronological data (including the OSL ages of the current study) of mega-dunes and comparison with regional climate records over the past 130 ka. These ages mainly cluster at two periods, i.e. the Holocene and last interglaciation.
springs and tufa, distributed from east to west in the Badain Jaran Desert. Inter-dune lakes, i.e. Lake Wuertabulage, Lake Bayinnuoer, Lake Hasatu (Fig. 2), are recharged by springs originating from mega-dunes at the east sides of these lakes. The formation of mega dunes in the Badain Jaran Desert is complicated and affected by multiple factors such as wind parameters, local geology, topography, and interactions between climate and aeolian/fluvial processes (Yang et al., 2011), as well as by the unique hydrogeological situations (Chen et al., 2004, 2006; Gates et al., 2008). OSL dating could be critical for understanding the formation of sand dunes (Telfer and Hesse, 2013). Our mega dune OSL ages indicates a moist and warm climate may be a prerequisite of mega dune growth. During our field trips, paleo-lake sediments were observed in inter-dune depressions. Evidence from other deserts shows that lake sediments (or lake floors) may be the main dust source for aeolian activity (Fitzsimmons et al., 2007b). 14C ages of the interdune paleo-lake sediments using carbonate and snail fossils (Yang and Williams, 2003; Yang et al., 2003; Hartmann and Wünnemann, 2009; Li et al., 2010; Yang et al., 2010b, 2011) suggested that high stand fresh water lakes once occurred during the Holocene in the study area. These 14C ages have been plotted in Fig. 5, and their sampling locations in Fig. 2. OSL ages of lake sediments by Bai et al. (2011b) and Fan et al. (2014) showed that high stand lakes also occurred during MIS5, during which the oldest dunes formed (125 ± 11 ka of sample BRMS OSL4). The recent drill core WED-02 dated by OSL and ESR from the Badain Jaran Desert reveals that during 15e0 ka the area was lake dominated, and during 130e70 ka was also lake dominated but with increased aeolian activity (Fig. 5). 14C ages (from 2.16 ± 0.07 ka to 29.61 ± 0.74 ka) and a TL age (147.8 ± 11.8 ka) of paleosol and lake sediments existed in profile Chalegebulu at the east edge of the Badain Jaran Desert (Fig. 5) (Li et al., 2005; Yang et al., 2008). High lake levels on the southeastern margin of the Badain Jaran and in the dunefields were dated mainly to ca 89 ka and the Early Holocene (Yang, 2004). The drill core from the Ulan Buh Desert northeast of the Badain Jaran Desert also show a paleolake developed during 155e87 ka (Li et al., 2014). Our four profiles all show well-bedding layers in dunes, indicating that during the middle Holocene and the last inter-glaciation aeolian processes were still active. The profile was characterized by alternations of type A and type B layers (Fig. 3b). The type A layers represent the coarse grain size fraction with high content of quartz,
and the sedimentary characteristics are close to that of the surface sand with nearly no carbonate. The XRD of surface sand suggests that no calcite is present (Fig. 6). Type A may be sourced from the aeolian sand of the lake basin or re-activated paleo-sand dunes, within which the fine grain fraction was deflated and thus only the coarse grain fraction remained. XRD results suggest that the caliche and the lake sediment contain similar minerals as shown in Fig. 6. The type B layer represents a fine grain fraction with high carbonate content, and these materials might have come from lake sediments nearby. Our XRD results show that only lake sediments could contain calcite content as high as 20%, and that the calcite could not be found in the surface drift sands (Fig. 6). The WED-02 drill core (Wang et al., 2015) suggests that during the periods of lake development the Badain Jaran lake sediments could contain carbonate up to 100%, while aeolian sands contain 10% carbonate at most. Low content of lithites (Fig. 6) between layers of mega-dunes indicates that carbonate leaching by rainfall from the upper layers is weak. Thus, most carbonate in the type B layer should have come from aeolian dust sourced from paleo-lake sediments near the megadunes instead of from leaching. Mineral kaolinite, an indicator of a wet and warm environment with strong chemical weathering, is rare in the surface sand and lake sediments (Fig. 6), and may be from weathered feldspars. Feldspars in dune sand are common (Fig. 6). Consequently, the type B layers may represent periods when the sand dune was relatively fixed with more moisture, while type A represents dry periods and sand dune re-activation. During the humid and warm periods in the Bdain Jaran Desert underground water was supplied to sand dunes, and local rainfall could be greater during the last 30 ka (Yang et al., 2003). The dunes formed during humid and warm periods may contain more water, which could adhere to loose sand grains (Chen et al., 2006). Calcium cementation in the form of pedogenic calcretes can enhance the process. Our XRD results of caliche collected from profile BSM4 show that the content of calcite is about 49%. Increasing rainfall and higher water table would promote the growth of mega-dunes when more carbonate would accumulate in dunes. The caliche could prevent mega-dunes from wind erosion. During the field investigation we observed that caliches could develop from the wet sand layers (type B layers) after exposure for more than 30 min under sunshine. We also found abundant Neolithic stone tools in many lacustrine sediment surfaces in the inter-dune depressions, indicating intensive human activities and much more friendly living conditions in
Please cite this article in press as: Liu, S.W., et al., Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.09.048
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Fig. 6. XRD results of three samples (surface sand, calcrete, and lake sediment) collected from the BSM and nearby.
the past in this nowadays hyper-arid and harsh natural environment, suggesting occurrence of dramatic climatic changes. Further work is required to address these issues. 5. Conclusions Based on systematic geomorphological observations and OSL dating of mega-dunes in the Badain Jaran Desert in China, we concluded that: (1) The best locations for OSL sample collection in the megadunes are the easy-seen exposed wet sand layers. Our field observation showed that wet sand layers could expose in the slope surface and could be easily seen due to its wetness and calcareous cementing with stronger resistance to wind deflation relative to the adjacent sands, with well-preserved original bedding layers. (2) Our OSL ages are 4.4 ± 0.5, 5.6 ± 0.5, 11.9 ± 0.9, and 125 ± 11 ka from the top to the bottom of the mega-dune. These ages indicate that there were two phases of dune development in the Holocene and last inter-glaciation, which were both warm and humid periods. Main growth period of mega-dunes occurred during the Holocene. Underground water supply and climatic changes play an important role in the mega dune growth, confirming the previous conclusions (e.g. Chen et al., 2004; Yang et al., 2010b). (3) In order to understand the mechanism of the mega-dunes formation and its relation to climate/environment, more systematic dating work is required for the dunes and the lacustrine sediments in the inter-dune depressions. Acknowledgments We wish to thank three anonymous reviewers for constructive suggestions. Thanks may extend to Xinqiang Chen for his assistance in field investigation. This work was funded by National Research Center for Geoanalysis (NRCGA) Basal Research Fund Special Funds (No. 2013CSJ02), the CAS Strategic Priority Research Program (Grant No. XDA05120501), and China NSF (41290252).
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Please cite this article in press as: Liu, S.W., et al., Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.09.048