J Paleolimnol (2014) 51:179–195 DOI 10.1007/s10933-012-9674-6
ORIGINAL PAPER
Re-assessment of the paleoclimate implications of the Shell Bar in the Qaidam Basin, China Steffen Mischke • Zhongping Lai Chengjun Zhang
•
Received: 3 February 2012 / Accepted: 12 December 2012 / Published online: 5 January 2013 Ó Springer Science+Business Media Dordrecht 2013
Abstract The Shell Bar in the Qaidam Basin, China, is a prominent geological feature composed of millions of densely packed Corbicula shells. Since the mid 1980s, it has been regarded as evidence for existence of a large lake during Marine Isotope Stage (MIS) 3 in the presently hyper-arid Qaidam Basin. Early studies suggested the bivalve shells accumulated at the shore of a large lake, whereas more recent work led to the conclusion that the Shell Bar was formed within a deeper water body. Based on our re-assessment of sediments and fossils from the Shell Bar, investigation of exposed fluvio-lacustrine sections upstream of the Shell Bar and study of nearby modern streams, we infer that the Shell Bar represents a stream deposit. Corbicula is a typical stream-dweller around the world. Preservation of Corbicula shells of different
sizes, as well as occurrence of many articulated shells, provide evidence against post-mortem transport and accumulation along a lake shore. Additionally, the SENW alignment of the Shell Bar is similar to modern intermittent stream beds in its vicinity and corresponds to the present-day slope towards the basin centre further NW, and furthermore, the predominantly sandy sediments also indicate that the Shell Bar was formed in a stream. Abundant ostracod shells in the Shell Bar sediments originated from stream-dwelling species that are abundant in modern streams in the vicinity of the Shell Bar, or in part from fluviolacustrine sediments exposed upstream of the Shell Bar, as a result of erosion and re-deposition. Deflation of alluvial fine-grained sediments in the Shell Bar region and protection of the stream deposits by the
S. Mischke (&) Institute of Earth and Environmental Science, Universita¨t Potsdam, Karl-Liebknecht-Str. 25/H27, 14476 Potsdam-Golm, Germany e-mail:
[email protected]
Z. Lai Key Laboratory of Qinghai-Tibetan Plateau Environment and Resource, MOE, School of Life and Geographic Science, Qinghai Normal University, Xining 810008, China
S. Mischke Institute of Geological Sciences, Freie Universita¨t Berlin, Malteserstr. 74-100, 12249 Berlin, Germany
C. Zhang Centre for Arid Environment and Paleoclimate Research, School of Resources and Environmental Sciences, Lanzhou University, 222 Tianshui South Road, Lanzhou 730000, China e-mail:
[email protected]
Z. Lai State Key Laboratory of Cryosphere Sciences, Cold and Arid Regions Environment and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China e-mail:
[email protected]
123
180
large and thick-walled Corbicula shells reversed the former channel relief and yielded the modern exposure, which is a prominent morphological feature. Occurrence of Corbicula shells in the Qaidam Basin indicates climate was apparently warmer than present during the formation of the Shell Bar because Corbicula does not live at similar or higher altitudes in the region today. Because the Shell Bar is no longer considered a deposit formed within a lake, its presence does not indicate paleoclimate conditions wetter than today. Keywords Qaidam Basin Tibetan Plateau Late Pleistocene Corbicula Ostracoda Taphonomy
Introduction The Quaternary environmental and climate history of western China prior to the Last Glacial Maximum is not well understood because of the rare preservation and exposure of geological archives and dating problems near or beyond the limit of 14C analysis (Li et al. 1991; Qi and Zheng 1995; Thompson et al. 1997; Mischke et al. 2010a). The Shell Bar in the Qaidam Basin represents a well-known exception, which has been studied since the mid 1980s (Chen and Bowler 1986; Chen et al. 1990; Zhang et al. 2007a, 2008a; Fig. 1). The Shell Bar is a 2.1-km-long, 100-m-wide and 2–3m-high ridge consisting of millions of densely packed bivalve shells of the genus Corbicula (Figs. 1, 2). Chen and Bowler (1985, 1986) and Chen et al. (1990) described the Shell Bar as a relict of a former shoreline and correlated the freshwater bivalve shells from the Shell Bar’s marginal position in the Qaidam Basin with shells of the freshwater ostracod Qinghaicypris recovered from 50 m depth below the present playa surface, near the basin’s centre. In contrast, Lei et al. (2007), Niu et al. (2007) and Zhang et al. (2007a, b, 2008a, b, c) regarded the Shell Bar as a typical lacustrine accumulation from considerable water depth, based on sedimentological structures, abundant and diverse ostracod shells and the well-preserved disarticulated and articulated Corbicula shells. Its age was assigned to MIS 3 and 2, specifically to the period between 40 and 17 ka, based on 36 radiocarbon and three uranium series dates (Zhang et al. 2007b, 2008a), or between 39 and 29 ka,
123
J Paleolimnol (2014) 51:179–195
based on five radiocarbon dates (Zheng et al. 2005). It served as evidence for much wetter conditions during MIS 3 in the presently hyper-arid Qaidam Basin (Fang 1991; Shi et al. 2001; Zhang et al. 2004; Yang et al. 2004, 2011). Other records from Tibetan Plateau lakes and ice cores, and from its northern and eastern foreland, also indicate that MIS 3 was a significantly wetter and warmer period, comparable or even exceeding Holocene moisture and temperature levels (Pachur et al. 1995; Thompson et al. 1997; Feng et al. 1998; Li 2000; Li and Zhu 2001; Zheng et al. 2005; Lu et al. 2007). Recently published data from Lake Qinghai and the Loess Plateau, however, show that the MIS 3 was not as wet and warm as the Holocene (Madsen et al. 2008; Rhode et al. 2010; Long et al. 2011). Here, we re-assess the fossils and sediments of the Shell Bar in the Qaidam Basin and demonstrate this prominent geological phenomenon does not represent deposition in a lake or at a lake shore. New chronological data for the Shell Bar (Lai et al. this issue) indicate its formation already during MIS 5. Study area The Qaidam Basin is an endorheic basin at the northern margin of the Tibetan Plateau and covers an area of *120,000 km2 (Fig. 1a). One quarter of the basin is occupied by playas and shallow, hypersaline lakes, located about 2,700 m above sea level (asl). Alluvial plains and fans, and yardangs (wind-shaped ridges of fluvio-lacustrine sediments) cover the regions above. The basin is bordered by the Kunlun Mountains to the south, the Altun Mountains to the west and the Qilian Mountains to the north and east, with peaks reaching above 5,000 m asl. Mean annual precipitation in the basin is low (\50 mm), mean annual temperature is *4 °C, mean January temperature is about -12 °C and mean July temperature *16 °C (Wang 1999; Zhu 1999). The surrounding mountain ranges receive significantly more precipitation. For example, a value of *400 mm/yr was estimated for the Dunde ice cap, in the southern branch of the Qilian Mountains (Thompson et al. 1989). The desert vegetation in the basin is dominated by Chenopodiaceae and Ephedra, Nitraria, and Compositae (Zhao et al. 2007). Salt deposits and fluvio-lacustrine and aeolian sediments of Holocene age are exposed in the central and eastern part of the Qaidam Basin (Zhang and Yang
J Paleolimnol (2014) 51:179–195
Fig. 1 The Shell Bar in the southeastern Qaidam Basin. a Location (black arrow) of the Shell Bar in the northeastern region of the Tibetan Plateau (grey shading for altitude [3,000 m asl). b Shell Bar (black) and its vicinity. Black star represents position of the SSB section. Position of transect A–A0 between the Shell Bar and SSB section marked by black line. c Transect A–A0 . Signatures for SSB section as in Fig. 5. d The western part of the Shell Bar and location of sediment and water sample sites. White star represents SB section. Legend for b and
181
d: A, extent of the Shell Bar; B, exposed fluvial and lacustrine sediments in the south of the Shell Bar; C, inferred extent of fluvial and lacustrine sediments; D, modern salt flats (playas); E, samples from the alluvial plain near the Shell Bar (samples 1–3 from 0.4 m below the surface) and from a dry stream bed (4); F, samples from 0.3 m below the Shell Bar surface; G, surface mud and water samples from modern water bodies (spring boils: 13, 16; streams: 14, 15, 17, 18)
123
182
J Paleolimnol (2014) 51:179–195
Fig. 2 a Dam-like structure of the Shell Bar, elevated *2–3 m above the alluvial plain. b Articulated Corbicula shells embedded in silty, fine sand. Note small juvenile shells in centre and at left upper margin in addition to large shells
2007; An et al. 2012; Yu and Lai 2012). Pleistocene alluvial, salt and other lacustrine deposits predominate in the western part. Neogene siltstones and sandstones of the Shizigou and Youshashan Formation occur in both regions (Zhang and Yang 2007). Surrounding mountain ranges are dominated by Permian and Triassic granitic rocks, with Precambrian gneisses in the south and Silurian and Triassic granitic rocks and Silurian clastic rocks (Balonggonggaer Formation) in the north (Zhang and Yang 2007).
Materials and methods Sediment samples were collected from the Shell Bar and its vicinity in August 2009 and September 2010. Unweathered sediments from the Shell Bar were sampled from an artificial section (SB section, a few metres from the SB1 section of Lai et al. [this issue]) and from 0.3-m depth along a NW–SE transect (Table 1; Fig. 1d). Samples from the surrounding salt-crust-covered alluvial plain were collected from 0.4-m depth. Exposed stratified sediments and a dry stream bed were sampled about
123
5 km SE of the Shell Bar (Table 1; Fig. 1b). In addition, water and the upper 1 cm of surface mud were collected from modern water bodies including the river in Nuomohongxiang (= Nomhon Town, 25 km further upstream in the southeast). Specific conductivity (SC) of the water, pH, dissolved oxygen (DO) concentration and percent saturation and water temperature were measured in the field with a portable field device (WTW Multi 340i). Alkalinity was measured using the Alkalinity AL 7 titration test kit of Macherey–Nagel. Water samples for cation and anion analyses were stored in separate polyethylene bottles without cooling for less than a week in the field and cation samples were acidified using HNO3. Water analyses were performed at the Institute of Geological Sciences, Freie Universita¨t Berlin. Grain-size analysis was performed on the sediment samples collected 0.3 m below the Shell Bar surface, the alluvial plain and dry stream bed samples, and samples from the SSB section. Analysis was done using a Malvern Co. Ltd. Mastersizer 2,000 laser diffraction particle size analyzer (size range 0.02–2,000 lm). Sample pretreatment included (1)
J Paleolimnol (2014) 51:179–195
183
Table 1 Types and locations of samples collected from the Shell Bar and its vicinity No.
Type
16
Water and sediment from modern spring
13 17
Water and sediment from modern stream
Latitude (°N)
Longitude (°E)
Altitude (m)
Deptha below surface (m)
36.51490
96.19940
2,699
0–0.01
36.51561
96.19772
2,699
0–0.01
36.51589
96.19944
2,698
0–0.01
18
36.51540
96.20006
2,698
0–0.01
15
36.51535
96.19778
2,698
0–0.01
14
36.51572
96.19677
2,698
0–0.01
38
36.43362
96.45003
2,791
0–0.01
36.51610
96.20364
2,698
0.40
2
36.51787
96.20198
2,698
0.40
3
36.51445
96.19648
2,698
0.40
1
Sediment from alluvial plain
4
Sediment from dry modern stream bed
36.48553
96.25090
2,714
0–0.01
12
Sediment from Shell Bar along NW–SE transect
36.51315
96.20405
2,700
0.30
11
36.51326
96.20316
2,700
0.30
10
36.51540
96.19995
2,699
0.30
9
36.51541
96.19860
2,699
0.30
8
36.51591
96.19749
2,699
0.30
7
36.51607
96.19668
2,699
0.30
6
36.51619
96.19637
2,699
0.30
5
36.51619
96.19637
2,699
0.30
36.51402
96.20220
2,700
0.75
21
a.a.
a.a.
a.a.
1.25
20
a.a.
a.a.
a.a.
1.75
22
Sediment from Shell Bar (SB) section, thickness 2.25 m
19
a.a.
a.a.
a.a.
2.10
36.48412
96.25110
2,725
0.20
36
a.a.
a.a.
a.a.
1.00
35
a.a.
a.a.
a.a.
1.40
34
36.48523
96.24986
2,723
2.00
33
a.a.
a.a.
a.a.
3.00
32
a.a.
a.a.
a.a.
3.70
31
a.a.
a.a.
a.a.
4.60
30
a.a.
a.a.
a.a.
5.40
29
a.a.
a.a.
a.a.
5.80
28
a.a.
a.a.
a.a.
6.70
27
a.a.
a.a.
a.a.
7.20
26
a.a.
a.a.
a.a.
7.90
25
a.a.
a.a.
a.a.
8.20
24
a.a.
a.a.
a.a.
8.60
23
a.a.
a.a.
a.a.
9.25
37
Sediment from SSB section, thickness 9.40 m
a.a. as above a
Depth below surface given for sediment samples. Water samples were collected 0.1 m below the water surface. Samples are ordered similar to arrangement in Fig. 7
adding H2O2 to remove organic matter and soluble salts, (2) using diluted 1 N HCl to remove carbonate, and (3) using Na-hexametaphosphate to disperse aggregates (Singer and Janitzky 1987). Mean grain
size and sorting were calculated according to Folk and Ward (1957). Total organic carbon (TOC) was determined for the samples from the alluvial plain, the dry stream bed,
123
184
and the SSB section using the antititration method, with concentrated sulfuric acid (H2SO4) and potassium dichromate (K2Cr2O7). The carbonate content was determined for the same samples by treatment with dilute 1 N HCl and measuring the generated CO2 volume. All above analyses were conducted in the National Laboratory of Western China’s Environmental Systems at Lanzhou University. Corbicula shells were extracted from sediments of the SB section and cleaned by washing 500 g of sediment through a 1-mm mesh. Length data for all obtained specimens were determined with a caliper. The length of Corbicula shells ranged from 1.8 to 23.1 mm, and five size classes (1.8–6.1, 6.2–10.3, 10.4–14.6, 14.7–18.8, 18.9–23.1 mm) were used to present the length distribution data as frequency diagrams (Fig. 3). Non-articulated and articulated shells were recorded separately. Ostracods from the samples collected 0.3 m below the Shell Bar surface, the SB section, the alluvial plain and dry stream bed, and the SSB section were separated by drying samples at 50 °C, treating with 3 % H2O2 solution, and washing through 0.25-mm meshes. Samples from modern water bodies were not treated with H2O2 prior to sieving. All ostracod shells were picked from the sieve residues under a lowpower binocular microscope. Species identification was supported using a Zeiss Supra 40 VP scanning electron microscope (SEM). So-called marginal ripplets on the inner lamella of the left valves of Ilyocypris were examined and different marginal ripplet patterns enabled assignment to three species, I. sebeiensis Yang & Sun, 2004, I. bradyi Sars, 1890 and I. decipiens Masi, 1905, according to the publications of Van Harten (1979), Janz (1994) and Mischke et al. (2006). SEM analysis showed that shells of I. decipiens from the Shell Bar and its vicinity are characterized by tubercles, enabling them to be distinguished from shells of I. sebeiensis and I. bradyi, which lack tubercles, under a low-power binocular microscope. Results Grain-size analysis of samples from 0.3 m below the Shell Bar surface provided mean grain sizes between 18 and 108 lm (Fig. 4). Six of eight samples have a mean grain size in the range of fine sand. Sorting is
123
J Paleolimnol (2014) 51:179–195
Fig. 3 Sketch of the Shell Bar section SB (grey shading represents cementation by rock salt). Rectangles at right of lithological column indicate positions of bivalve samples. Frequency diagram for size classes (1–5) of Corbicula shells. Black sections indicate portion of articulated shells
poor with two exceptions of moderately well sorted sediments. The sand fraction of the Shell Bar sediments exceeds 55 % for six samples. Samples 1–3 from the salt-crust-covered alluvial plain have a mean grain size between 9 and 26 lm. Sorting is poor, and silt is the dominating grain-size fraction. Sample 4 from the dry stream bed has a mean grain size of 46 lm and is very poorly sorted. The dominant fraction is the silt component.
J Paleolimnol (2014) 51:179–195
Fig. 4 Grain-size characteristics of samples collected from 0.4 m below the surface of the alluvial plain (AP) near the Shell Bar, the dry stream (DS) bed and from 0.3 m below the Shell Bar surface. Position of samples given in Fig. 1. (mod—moderately)
The samples from the SSB section in the SE of the Shell Bar have a mean grain-size range from 11 to 56 lm (Fig. 5). A relatively high mean grain size was determined for three samples from the cross- and ripple-bedded units. Sediments are poorly sorted, with the exception of the lowermost sample, and silt is the predominant constituent. Most sediment samples from the Shell Bar (samples 5–8, 10–11) have a primary modal peak between 100 and 150 lm in grain-size frequency distribution curves (GSFDCs; Fig. 6). The sediments from the SSB section mostly have a primary modal peak between 30 and 70 lm. The primary modal peak of sediments from the alluvial plain is between 5 and 40 lm and that of the dry stream bed at the SSB section site is 49 lm (Fig. 6). The TOC content is between 0.3 and 1.2 % for samples from the salt-crust-covered alluvial plain and 3.3 % for the sample from the dry stream bed. Samples from the SSB section have TOC contents between 0.1 and 0.8 %. CaCO3 content is between 4 and 24 % for alluvial plain samples, 31 % for the dry stream bed and between 11 and 26 % for samples from the SSB section (Fig. 5).
185
Corbicula shells were present in three of the four samples (19–22) from the SB section (Fig. 3). Sample 20 from 0.5 m above the section base, is dominated by shells of the two largest size classes. Articulated shells attain the highest frequency here (Fig. 3). Sample 21 from 1.0 m above the base has a bimodal size distribution, with maxima at the second smallest and the largest shell-size class. Articulated shells were not recorded in sample 21. Sample 22, from 1.5 m above the base, is dominated by shells of the smallest and a moderate size class. Articulated shells were recorded with frequencies of B2.2 % in individual size classes. Corbicula was not recorded from the SSB section. A total of 30 ostracod taxa were identified from the Shell Bar and its vicinity, and the SBB section (Figs. 6, 7, 8, 9, Appendix). Shells belonging to Ilyocypris bradyi and I. sebeiensis were recorded in high abundance from almost all samples containing ostracod remains. Additional frequently recorded species were Limnocythere inopinata (Baird 1843), Candona neglecta Sars 1887, Leucocythere dorsotuberosa Huang 1982, Fabaeformiscandona rawsoni (Tressler 1957) and Tonnacypris edlundi Van Der Meeren, Khand & Martens, 2009. Juvenile shells usually did not outnumber adult shells or shells of last instar stages. Samples 1 and 2 from the alluvial plain in the north of the Shell Bar and samples from the springs (13 and 16) did not contain ostracod shells (Figs. 1, 6). Of 14 taxa recorded, with at least 10 shells per sample, in Shell Bar or SSB section sediments, only three taxa were not recorded from SB and SSB sites. The river water sample from Nuomohong village had a SC of 0.72 mS cm-1 and a pH of 8.6, and was dominated, in order of abundance, by cations Ca2?, Na? and Mg2? and anions HCO3-, Cl- and SO42-. The two springs of the Shell Bar had SCs of 1.1 mS cm-1 and a pH of 9, and were dominated by the cation Na? and, in order of abundance, by anions HCO3-, Cl- and SO42-. Water temperatures were 12.5 °C for the larger and 11.0 °C for the smaller spring. DO saturation in waters of the larger and smaller springs was 0 and 8 %, respectively. Streams flowing from these springs have SCs in the range from 1.1 to 2.4 mS cm-1, pH values in a range from 9.1 to 10.1, and water composition similar to the springs. DO saturation of stream waters was in the range from 71 to 170 % and temperatures were between 16 and 23 °C in September 2010.
123
186
J Paleolimnol (2014) 51:179–195
Fig. 5 Lithology, TOC, carbonate content and grain-size characteristics of the SSB section. 1 homogenous carbonaterich silt; 2 horizontally layered silt, finely laminated; 3 silt and
fine sand with current ripples and cross stratification. Horizontal grey bars indicate sandy sediment units. (m.s—moderately sorted, p.s—poorly sorted)
Discussion
samples, indicating that the sediments of all sampled stratigraphic levels were accumulated in a water body. Cross- and ripple-bedding of the sandier units shows that these sediments were deposited from flowing waters in a stream. The GSFDCs for samples 23 and 24 from the lowermost sandier bed of the SSB section have a well-defined primary modal peak at a grain size of 56 lm and a significantly smaller secondary mode on the fine side at a grain size of *7 lm (Figs. 5, 6). This pattern resembles modern river sediments in northwestern China, with the finer and coarser-grained modes representing the suspension and saltation loads, respectively (Sun et al. 2002; Zhang et al. 2008d). In comparison, the primary modal peak for samples 23 and 24 is at a significantly finer grain size than that of the modern river samples discussed by Sun et al. (2002) and Zhang et al. (2008d). Sample 31 has a less well-defined primary modal peak, at a grain size of
The SSB section Sediments from the SSB section are dominated by the silt-sized fraction. Silt amounts to *70 % in the laminated sediments and comprises 50–64 % in the cross- and ripple-bedded, sandier units (Fig. 5). The TOC content of the SSB sediments is between 0.1 and 0.8 % and thus, similar or slightly higher than the *0.1 % TOC content determined for the sediments from the Shell Bar (Zhang et al. 2007b). The CaCO3 content of the SSB sediments, with values mainly between 11 and 15 % and a mean CaCO3 content of 13 %, is relatively similar to the CaCO3 contents of 5–15 % (mean CaCO3 content 13 %) determined for the Shell Bar by Niu et al. (2007). Ostracod shells belonging to 22 species were recorded in all SSB
123
J Paleolimnol (2014) 51:179–195
187
grain-size range from 8 to 16 lm and a GSFDC similar to sediments reported from lakes Lop Nur (Xinjiang) and Daihai (Inner Mongolia), in China’s arid regions (Sun et al. 2002; Zhang et al. 2008d). Therefore, samples 25, 30 and 37 represent lake sediments based on grain-size characteristics and higher carbonate content. The other laminated sandy silt samples from the SSB section probably represent sediments that are transitional between the fluvial and lake sediment endmembers, and were accumulated at varying distance from a river mouth in a lake. Relatively low water depth is inferred from the predominantly detrital character of the SSB sediments, the cross- and ripple-bedded intercalations and the relatively high diversity of ostracods, typical for the different micro-habitats in the shallower regions of a lake (Mischke et al. 2006, 2010b; Zhai et al. 2010). Dominance of adult and late-instar shells further points to shallow waters prone to sediment re-suspension by wave action and currents. The presence of Cyprideis torosa and Heterocypris salina in about half of the SSB samples shows that the lake was periodically at least slightly brackish, whereas most other species indicate freshwater to slightly oligohaline conditions (Mischke et al. 2007). Although detailed studies on the regional extent of the SSB sediments are still lacking, the sediments are apparently widely exposed in the south and southeast of the Shell Bar, implying that a relatively large shallow lake existed in this area (Fig. 1b). Fig. 6 Grain-size frequency distribution curves for sediments from the Shell Bar (SB), the nearby alluvial plain (AP) and a dry stream bed (DS), and the SSB section. Graphs sorted according to the grain size of the primary modal peak (a, b, c) and their relatively ‘flat’ shape (d)
*65 lm and more coarse- and fine-grained components than samples 23 and 24. The relatively low grain sizes of the primary modal peaks of the three samples indicate that relatively low current velocities existed during the deposition of the SSB sediments, with cross bedding and ripple structures. The finer-grained laminated sediments with relatively low carbonate content (samples 26–29, 32–34, and 37) have a less pronounced primary modal peak, mostly between 32 and 65 lm and significantly larger fine component, compared to samples 23 and 24 (Fig. 6). In contrast, samples 25, 30 and 37 from the finer-grained sediments with relatively high carbonate content, have an even lower primary modal peak in the
The Shell Bar In comparison to the sediments of the SSB section, the silty fine sands sampled from the Shell Bar are significantly coarser. The silt content is distinctly lower, with *20 % (Fig. 4). The clay-sized fraction of the Shell Bar sediments is mainly \10 %, whereas that of the SSB section is mainly [10 %. Similar results for sediments from the uppermost 1 m of the Shell Bar, were presented by Lei et al. (2007). The majority of the grain-size frequency distribution curves for the Shell Bar samples shows a welldefined primary modal peak in the grain-size range from 100 to 150 lm (Fig. 6). A secondary modal peak in grain-size ranges between 5 and 14 lm and is separated by a distinct minimum between the two modal peaks. The high primary modal peak, with values of *10 % and a grain size of[100 lm, a welldefined Gaussian distribution, a minimum between the
123
188
J Paleolimnol (2014) 51:179–195
primary and secondary modal peak and a significantly lower modal peak, with a grain size of *10 lm, resembles the GSFDCs of modern and pre-Quaternary Cenozoic fluvial sediments in northwestern China (Sun et al. 2002; Zhang et al. 2008d). Unlike the grain size of *330 lm for the primary modal peak of modern and pre-Quaternary Cenozoic river sediments from the Loess Plateau investigated by Sun et al. (2002), the grain size of the primary modal peak of the SB samples shown in Fig. 6a is significantly lower. Sample 12 from the Shell Bar shows a GSFDC similar to those of most samples from the laminated SSB sediments. Consequently, still-water conditions influenced by nearby flowing waters are inferred. The GSFDC of sample 9 shows four modal peaks in a wide grain-size range, similar to reworked loess (Sun et al. 2002). Considering the GSFDC-derived inference of fluvial conditions for most SB samples, a depositional setting of a crevasse splay or an oxbow lake is regarded as the likely scenario for formation of sediments in samples 9 and 12.
Fig. 8 Ostracod shells from the Shell Bar (marked with *) and c from the SSB section in its south. 1 Candona candida right valve (RV) external view (ev)*; 2 Candona weltneri left valve (LV) internal view (iv); 3–4 Candona neglecta, 3 female LV iv, 4 male LV iv; 5 Pseudocandona sp. RV ev*; 6 Leucocythere dorsotuberosa RV ev*; 7 Leucocythere sp. RV ev*; 8 Fabaeformiscandona rawsoni male RV iv; 9 Fabaeformiscandona danielopoli LV iv*; 10 Cyclocypris sp. RV iv; 11 Heterocypris salina RV iv; 12 Heterocypris incongruens RV iv; 13 Cypridopsis vidua LV iv*; 14 Paralimnocythere psammophila LV ev; 15 Eucypris dulcifons RV ev; 16 Eucypris mareotica RV ev*; 17 juvenile Cypris pubera LV ev*; 18 Limnocytherina cf. sanctipatricii male LV ev*; 19–20 Limnocythere inopinata, 19 female RV ev, 20 male LV ev; 21 Trajancypris laevis RV iv*; 22–23 Tonnacypris edlundi, 22 female LV iv, 23 male RV iv. All specimens housed at Institute of Geological Sciences, Freie Universita¨t Berlin
Fig. 7 Comparison of ostracod assemblage data from the SSB section, the Shell Bar (SB section and samples from 0.3m below its surface), samples from the alluvial plain (AP) next to the Shell Bar, a dry stream bed (DS), and modern streams and
springs. Semi-quantitative scale explained in lower right box. Ratio of male shells of Limnocythere inopinata to all shells of the species and number of total shells are given. Location of samples shown in Fig. 1
123
In comparison to the SB and SSB sediments, the GSFDCs of the samples 2–4 from the alluvial plain and the dry stream bed are significantly different, indicating distinct depositional environments. Four modal peaks over a wide grain-size range in these
J Paleolimnol (2014) 51:179–195
189
123
190
J Paleolimnol (2014) 51:179–195
Fig. 9 Ostracod shells of Ilyocypris from the Shell Bar (marked with *) and from the SSB section in its south. 1 I. sebeiensis RV ev*; 2 I. bradyi RV ev; 3 I. decipiens RV ev*; 4–5 I. sebeiensis, 4 LV iv, 5 enlargement of posteroventral area of specimen to the left showing numerous marginal ripplets close to the outer valve margin, drawing of marginal ripplets pattern at right; 6–9 Ilyocypris bradyi, 6 LV iv, 7 enlargement of posteroventral area of specimen to the left showing four larger marginal ripplets close to outer margin, a central list and smaller marginal ripplets above the list, drawing of this marginal ripplets pattern (subtype
A) at right, 8 LV iv*, 9 enlargement of posteroventral area of specimen to the left showing weakly developed four marginal ripplets close to the outer margin and list above*, drawing of this marginal ripplets pattern (subtype B) to the right; 10–11 I. decipiens, 10 LV iv*, 11 enlargement of posteroventral area of specimen to the left showing central list and numerous small marginal ripplets in central area of inner lamella*, drawing of this marginal ripplets pattern to the right. Scale bar only for shells at top and at left side. All specimens housed at Institute of Geological Sciences, Freie Universita¨t Berlin
samples indicate a mixture of sediments accumulated by different transport modes, probably including longdistance dust transport, local dust and aeolian sand,
and water-borne suspension, saltation and traction (bed-) load of streams. Only sample 1 from the alluvial plain shows a GSFDC relatively comparable to that of
123
J Paleolimnol (2014) 51:179–195
sample 28 from the SSB section. Accordingly, still water conditions are tentatively inferred for the formation of sediments at the site of sample 1. Shells of Corbicula from the Shell Bar do not show signs of transport and size sorting (Figs. 2, 3). Corbicula shells of small and large size occur next to one another (Fig. 2). Articulated shells are abundant, probably representing shells in life position. Zhang et al. (2007a, 2008b) also found no evidence for transport and re-deposition of Corbicula shells. Zhang et al. (2008b, c), Niu et al. (2007) and Lei et al. (2007) inferred a deep and stagnant water body from the mass occurrence of Corbicula shells in the Shell Bar, whereas accumulation at a former shoreline was suggested by the earlier studies of Chen and Bowler (1986) and Chen et al. (1990). According to identifications by Baoyu Huang, the Corbicula shells from the Shell Bar belong to C. largillierti and C. fluminea (Chen and Bowler 1986; Appendix). Both species generally thrive in the flowing waters of large streams and estuaries, which represent high-energy settings (Zhadin and Gerd 1963; Ituarte 1994; Beasley et al. 2003; Kotzian and Simo˜es 2006; Chen et al. 2009; Zhou et al. 2010). Fresh to slightly brackish waters are inhabited (Zhadin and Gerd 1963). Corbicula largillierti occurs in modern springs and streams in Yunnan Province and C. fluminea in rivers and estuaries in southern and eastern China (Morton 1977; Li et al. 2006; Chen et al. 2009; Zhou et al. 2010; Du et al. 2011). Pleistocene fossils of C. largillierti from China were recorded in fluvial sediments from China’s coastal region and in beach sands and gravels of paleolakes in the Ulah Buh Desert, Inner Mongolia (Lin et al. 2005; Chun et al. 2008). Preservation in life position and the large size range of Corbicula shells from the Shell Bar show that the specimens did not undergo post-mortem transport. This fact provides evidence against accumulation at the shore of a former lake, suggested by Chen and Bowler (1986); Chen et al. (1990). The common occurrence of Corbicula in modern rivers, the linear alignment of the Shell Bar and the sand-dominated sediments and their GSFDC patterns of the Shell Bar indicate it did not form from accumulation in a deep lake, as suggested by Zhang et al. (2008b, 2008c); Niu et al. (2007) and Lei et al. (2007). A larger, three-dimensional extension of sediments containing shells of Corbicula must be assumed if the Shell Bar is regarded to represent the remnant of a deeper lake. To the contrary, the Shell
191
Bar is the only geological structure of its kind in the Qaidam Basin (Zhang et al. 2007b, 2008a, b), and its elongated orientation requires a different explanation. The SE-NW alignment of the Shell Bar, similar to many modern intermittent stream beds (Fig. 1), the slight inclination of its surface, descending from its SE tip to its NW tip by *2 m (Zhang et al. 2007b, 2008a), the predominantly sandy sediments and their grainsize characteristics, and the mass occurrence of remains of the typical stream-dwelling Corbicula, all suggest that the Shell Bar represents a stream deposit, confirming the view of Lai et al. (2011, 2012). Deflation of sediments from the alluvial plain in the vicinity of the Shell Bar caused the reversal of the relief because Corbicula shells protected the stream deposits as a desert pavement. The abundant ostracod shells in the Shell Bar sediments may represent ostracods that lived in the stream during the formation of the Shell Bar. This assumption is supported by the presence of mainly large adult and late-instar shells in the sediments, and the presence of ostracods in the modern streams flowing from the springs on the Shell Bar (Fig. 7). Lack of the large species Tonnacypris edlundi in Shell Bar sediments and its frequent occurrence in the SSB sediments and modern water bodies on the one hand, and the otherwise comparable ostracod species assemblage from the SSB section and the Shell Bar on the other hand, suggest ostracod shells were eroded from the SSB sediments upstream and incorporated into the Shell Bar sediments. Large shells of T. edlundi were likely destroyed during the erosion and re-deposition process, whereas the more robust shells of smaller species apparently survived the short transport downstream. The comparable CaCO3 content of the SSB sediments and the Shell Bar also suggests that Shell Bar sediments at least partly derived from eroded and re-deposited SSB sediments. The TOC content of the upstream SSB sediments is slightly higher than those of the Shell Bar and the mean grain size significantly lower, further supporting this scenario. Organic matter from the SSB sediments was probably degraded during erosion and re-deposition. Eroded fine-grained sediments from the SSB were probably held in suspension for a longer time in comparison to the sandier sediments, and were consequently transported further downstream into the basin centre. However, ostracod shells in the Shell Bar sediments either originated from contemporary stream-dwelling
123
192
species during the formation of the Shell Bar or from the erosion and re-deposition of ostracod-rich sediments upstream of the Shell Bar. Paleoclimate implications Our re-assessment of the Shell Bar as a stream deposit does not support the previous inference for past existence of a large lake in the Qaidam Basin and related wetter conditions. Streams of various size exist in the presently hyperarid Qaidam Basin because of higher precipitation in the surrounding mountain ranges and the presence of water resources such as snow, ice and frozen ground at higher altitude. Thus, wetter conditions inferred by Chen and Bowler (1986), Chen et al. (1990); Zhang et al. (2007a, b, 2008a, b, c); Niu et al. (2007) and Lei et al. (2007) are not supported by our re-examination of the Shell Bar, nearby sediments and modern water bodies. The presence of Corbicula in the Qaidam Basin, however, has paleoclimate implications. Corbicula does not occur at similar or higher altitudes in the region today (Zhang et al. 2008a, b). Rather, Corbicula is abundant in the lower and warmer regions of southern and eastern China (Morton 1977; Li et al. 2006; Chen et al. 2009; Zhou et al. 2010; Du et al. 2011). Thus, the mass occurrence of Corbicula in the Qaidam Basin shows that climate conditions were probably warmer than today. Corbicula largillierti occurs up to an altitude of 2,073 m asl in the Muyang River, upstream of Dianchi Lake in Yunnan (Li–Na Du pers. commun.). The mean July air temperature in Kunming at 1,900 m asl and at Lake Dianchi’s shore, is 19.8 °C (WorldClimate: http:// www.worldclimate.com/). The highest Corbicula site in the Dianchi Lake catchment is 173 m higher. Based on a lapse rate of -0.5 °C/100 m on the southern Tibetan Plateau (Bo¨hner 2006), a mean July temperature of *18.9 °C is estimated for the highest Corbicula sites of Du et al. (2011). The Shell Bar lies *500 m lower than the meteorological station at Dulan, where a mean July temperature of 15.0 °C is recorded (WorldClimate: http://www.worldclimate. com/). Based on a lapse rate of -0.6 °C/100 m for the northern Tibetan Plateau (Bo¨hner 2006), a mean July temperature of about 18.0 °C is calculated for
123
J Paleolimnol (2014) 51:179–195
the Shell Bar position. Thus, summer temperatures *1 °C higher than at present were probably required for the establishment of the Corbicula population during the time of the Shell Bar formation. This is a tentative conclusion, and more detailed studies to confirm the Corbicula species identification for the specimens from the Shell Bar and to examine the highest (coldest) occurrences of living Corbicula populations in the Tibetan Plateau region are required for a more reliable inference of past temperatures, during the formation of the Shell Bar.
Conclusion Our re-assessment of the Shell Bar in the Qaidam Basin, China, shows how a detailed multi-proxy investigation of sediments and fossils from a wellknown paleoclimate archive may lead to a paradigm shift in comparison to many earlier studies. Our conclusion that the Shell Bar is a stream deposit, in contrast to earlier interpretations as a lake deposit, is based on sedimentological (grain size), paleoecological (bivalve, ostracods) and taphonomical (size measurements, records of articulated shells) data, as well as morphological and geological field observations in the wider vicinity of the Shell Bar. As a result, interpretation of the Shell Bar as a lake deposit, which has been generally accepted for almost three decades, now must be rejected. We hope our results will encourage others to critically assess paleoclimate data, even in cases where they are apparently well established and widely accepted. New paleoclimate studies will benefit from focusing on discrepancies with earlier data, and should avoid the tendency to find ‘supporting’ evidence for previously established paleoclimate inferences. Acknowledgments We thank Hailei Wang and Biao Zhang for help during fieldwork and Elke Heyde for analysis of water samples. Li–Na Du kindly provided information on the highestaltitude occurrences of living Corbicula in Muyang River, Yunnan Province. We are grateful to Peter Frenzel and an anonymous reviewer for constructive and thorough reviews, which helped to improve the original manuscript, and to Xiaozhong Huang and Mark Brenner for editorial assistance. Funding was provided by the Deutsche Forschungsgemeinschaft and China NSF (41121001, 41172168).
J Paleolimnol (2014) 51:179–195
Appendix Faunal list Ostracoda Darwinula stevensoni (Brady & Norman, 1870) Candona candida (O.F. Mu¨ller, 1776) Candona neglecta (Sars, 1887) Candona weltneri (Hartwig, 1899) Fabaeformiscandona caudata (Kaufmann, 1900) Fabaeformiscandona danielopoli (Yin & Martens, 1997) Fabaeformiscandona fabaeformis (Fischer, 1854) Fabaeformiscandona rawsoni (Tressler, 1957) Pseudocandona sp. Cyclocypris sp. Ilyocypris bradyi (Sars, 1890) Ilyocypris decipiens (Masi, 1905) Ilyocypris sebeiensis (Yang & Sun, 2004) Cypris pubera (O.F. Mu¨ller, 1776) Eucypris dulcifons (Diebel & Pietrzeniuk, 1969) Eucypris mareotica (Fischer, 1855) Prionocypris sp. Tonnacypris edlundi (Van der Meeren, Khand & Martens, 2009) Tonnacypris tonnensis (Diebel & Pietrzeniuk, 1975) Trajancypris laevis (G.W. Mu¨ller, 1900) Heterocypris incongruens (Ramdohr, 1808) Heterocypris salina (Brady, 1868) Cypridopsis vidua (O.F. Mu¨ller, 1776) Limnocythere inopinata (Baird, 1843) Limnocytherina cf. sanctipatricii (Brady & Robertson, 1869) Paralimnocythere psammophila (Flo¨ssner, 1965) Leucocythere dorsotuberosa (Huang, 1982) Leucocythere sp. Cytherissa lacustris (Sars, 1863) Cyprideis torosa (Jones, 1850) Bivalvia Corbicula fluminea (Mu¨ller, 1774) Corbicula largillierti (Philippi, 1844)
References An FY, Ma HZ, Wei HC, Lai ZP (2012) Distinguishing aeolian signature from lacustrine sediments of the Qaidam Basin in northeastern Qinghai-Tibetan Plateau and its palaeoclimatic implications. Aeolian Res 4:17–30 Beasley CR, Tagliaro CH, Figueiredo WB (2003) The occurrence of the Asian clam Corbicula fluminea in the lower Amazon Basin. Acta Amazonica 33:317–324
193 Bo¨hner J (2006) General climatic controls and topoclimatic variations in central and high Asia. Boreas 35:279–295 Chen K, Bowler JM (1985) Preliminary study of sedimentary characteristics and evolution of palaeoclimate of Qarhan Salt Lake in Qaidam Basin. Sci Sin (Ser B) 28:1218–1232 (in Chinese with English abstract) Chen K, Bowler JM (1986) Late Pleistocene evolution of salt lakes in the Qaidam Basin, Qinghai Province, China. Palaeogeogr Palaeoclimatol Palaeoecol 54:87–104 Chen K, Bowler JM, Kelts K (1990) Palaeoclimatic evolution within the Qinghai-Xizang (Tibet) Plateau in the last 40000 years. Quat Sci 3:21–31 (in Chinese with English abstract) Chen Z, Guo L, Jin B, Wu J, Zheng G (2009) Effect of the exotic plant Spartina alterniflora on macrobenthos communities in salt marshes of the Yangtze River Estuary, China. Estuar Coast Shelf Sci 82:265–272 Chun X, Chen F, Fan Y, Xia D, Zhao H (2008) Formation of Ulan Buh desert and its environmental changes during the Holocene. Front Earth Sci China 2:327–332 Du L-N, Chen X-Y, Yang J-X (2011) Effect of eutrophication on molluscan community composition in the Lake Dianchi (China, Yunnan). Limnologica 41:213–219 Fang J (1991) Lake evolution during the past 30.000 years in China, and its implication for environmental change. Quat Res 36:37–60 Feng Z-D, Chen F-H, Tang L-Y, Kang J-C (1998) East Asian monsoon climates and Gobi dynamics in marine isotope stages 4 and 3. Catena 33:29–46 Folk RL, Ward WC (1957) Brazos River bar: a study in the significance of grain size parameters. J Sediment Petrol 27:3–26 Ituarte CF (1994) Corbicula and Neocorbicula (Bivalvia: Corbiculidae) in the Parana´, Uruguay and Rı´o de la Plata Basins. The Nautilus 107:12–135 Janz H (1994) Zur Bedeutung des Schalenmerkmals, Marginalrippen’ der Gattung Ilyocypris (Ostracoda, Crustacea). Stuttgarter Beitra¨ge zur Naturkunde, Serie B 206:1–19 (in German with English abstract) Kotzian CB, Simo˜es MG (2006) Taphonomy of recent freshwater molluscan death assemblages, Touro Passo stream, southern Brazil. Rev Bras Paleontol 9:243–260 Lai ZP, Liu XJ, Long H, Madsen D (2011) Was late Marine Isotope Stage (MIS) 3 warm and humid in nowadays arid northwestern China? Abstract of XVIII INQUA Congress, Bern, pp 21–27 Lai Z, Mischke S, Madsen D (2012) MIS 5 OSL ages for the Shell Bar in the Qaidam Basin, northeastern QinghaiTibetan Plateau, and the palaeoenvironmental implications. J Paleolimnol (this issue) Lei G, Zhang H, Zhang W, Chang F, Fan H, Yang M, Chen Y, Niu J (2007) Characteristics of grain size and sedimentation of Shell Bar section in salt lake Qarhan Qaidam Basin. Acta Sediment Sin 25:274–282 (in Chinese with English abstract) Li B (2000) The last greatest lakes on the Xizang (Tibetan) Plateau. Acta Geogr Sin 55:174–182 (in Chinese with English abstract) Li B, Zhu L (2001) ‘‘Greatest lake period’’ and its palaeoenvironment on the Tibetan Plateau. J Geogr Sci 11:34–42 Li S, Zheng B, Jiao K (1991) Preliminary research on lacustrine deposits and lake evolution on the south slope of the west
123
194 Kunlun Mountains. Sci Geogr Sin 11:306–314 (in Chinese with English abstract) Li L, Chen Z, Xu S, Hou J, Bi C, Shi G (2006) Temporal and spatial distribution characteristics and indicator effects of Corbicula fluminea in coastal flat of Changjiang estuary. Ying Yong Sheng Tai Xue Bao = J Appl Ecol 17:883–886 (in Chinese) Lin C-M, Zhuo H-C, Shu G (2005) Sedimentary facies and evolution in the Qiantang River incised valley, eastern China. Mar Geol 219:235–259 Long H, Lai Z, Fuchs M, Zhang J, Yang L (2011) Palaeodunes intercalated in loess strata from the western Chinese Loess Plateau: timing and palaeoclimatic implications. Quat Int 263:37–45 Lu HY, Wu NQ, Liu KB, Jiang H, Liu TS (2007) Phytoliths as quantitative indicators for the reconstruction of past environmental conditions in China II: palaeoenvironmental reconstruction in the Loess Plateau. Quat Sci Rev 26:759–772 Madsen DB, Ma H, Rhode D, Brantingham PJ, Forman SL (2008) Age constraints on the late Quaternary evolution of Qinghai Lake, Tibetan Plateau. Quat Res 69:316–325 Mischke S, Herzschuh U, Sun Z, Qiao Z, Sun N, Zander AM (2006) Middle Pleistocene Ostracoda from a large freshwater lake in the presently dry Qaidam Basin (NW China). J Micropal 25:57–64 Mischke S, Herzschuh U, Massmann G, Zhang C (2007) An ostracod-conductivity transfer function for Tibetan lakes. J Paleolimnol 38:509–524 Mischke S, Bo¨ßneck U, Diekmann B, Herzschuh U, Jin H, Kramer A, Wu¨nnemann B, Zhang C (2010a) Quantitative relationship between water-depth and sub-fossil ostracod assemblages in Lake Donggi Cona, Qinghai Province, China. J Paleolimnol 43:589–609 Mischke S, Sun Z, Herzschuh U, Qiao Z, Sun N (2010b) An ostracod-inferred large Middle Pleistocene freshwater lake in the presently hyper-arid Qaidam Basin (NW China). Quat Int 218:74–85 Morton B (1977) The population dynamics of Corbicula fluminea (Bivalvia: Corbiculacea) in Plover Cove Reservoir, Hong Kong. J Zool 181:21–42 Niu J, Zhang H, Chang F, Chen Y, Fan H, Zhang W, Yang M, Lei G (2007) The 87Sr/86Sr ratios of Shell Bar section at Charhan Lake, Qaidam Basin and its paleoenvironmental significance. Geol J China Univ 13:14–22 (in Chinese with English abstract) Pachur H-J, Wu¨nnemann B, Zhang H (1995) Lake evolution in the Tengger Desert, Northwestern China, during the last 40,000 years. Quat Res 44:171–180 Qi W, Zheng M (1995) Sedimentary characteristics of ZK91-2 core and climate-environment evolution of Zabuye Lake Tibet Plateau. J Lake Sci 7:133–140 (in Chinese with English abstract) Rhode D, Ma H, Madsen DB, Brantingham PJ, Forman SL, Olsen JW (2010) Paleoenvironmental and archaeological investigations at Qinghai Lake, western China: geomorphic and chronometric evidence of lake level history. Quat Int 218:29–44 Shi Y, Yu G, Liu X, Li B, Yao T (2001) Reconstruction of the 30–40 ka BP enhanced Indian monsoon climate based on geological records from the Tibetan Plateau. Palaeogeogr Palaeoclimatol Palaeoecol 169:69–83
123
J Paleolimnol (2014) 51:179–195 Singer M, Janitzky P (1987) Field and laboratory procedures used in soil chronosequence study. USGS Bull, p 1648 Sun D, Bloemendal J, Rea DK, Vandenberghe J, Jiang F, An Z, Su R (2002) Grain-size distribution function of polymodal sediments in hydraulic and aeolian environments, and numerical partitioning of the sedimentary components. Sediment Geol 152:263–277 Thompson LG, Mosley-Thompson E, Davis ME, Bolzan J, Dai J, Yao T, Gundestrup N, Wu X, Klein L, Xie Z (1989) Holocene-late Pleistocene climatic ice core records from Qinghai-Tibetan Plateau. Science 246:474–477 Thompson LG, Yao T, Davis ME, Henderson KA, MosleyThompson E, Lin P-N, Beer J, Synal H-A, Cole-Dai J, Bolzan JF (1997) Tropical Climate Instability: the Last Glacial Cycle from a Qinghai-Tibetan Ice Core. Science 276:1821–1825 Van Harten D (1979) Some new shell characters to diagnose the species of the Ilyocypris gibba-biplicata-bradyi group and their ecological significance. In: Serbian Geological Society (ed) Taxonomy, biostratigraphy and distribution of ostracodes. Proceedings of the 7th International Symposium on Ostracodes. Serbian Geological Society, Belgrade, pp 71–76 Wang D (1999) Mean Temperature. In: Sun H (ed) The National Atlas of China. China Cartographic Publishing House, Beijing, pp 75–76 Yang B, Shi Y, Braeuning A, Wang J (2004) Evidence for a warm-humid climate in arid northwestern China during 40–30 ka BP. Quat Sci Rev 23:2537–2548 Yang X, Scuderi L, Paillou P, Liu Z, Li H, Ren X (2011) Quaternary environmental changes in the drylands of China—a critical review. Quat Sci Rev 30:3219–3233 Yu LP, Lai ZP (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 Zhadin VI, Gerd SV (1963) Fauna and flora of the rivers, lakes and reservoirs of the U.S.S.R. (Translated from Russian) Smithonian Institution and National Science Foundation. Israel Program for Scientific Translations, Washington, p 626 Zhai D, Xiao J, Zhou L, Wen R, Chang Z, Pang Q (2010) Similar distribution pattern of different phenotypes of Limnocythere inopinata (Baird) in a brackish-water lake in Inner Mongolia. Hydrobiologia 651:185–197 Zhang X, Yang S (2007) Qinghaisheng Quyu Dizhi Gailun/The regional geology of Qinghai province—a guide to the geological map of Qinghai province 1:1,000,000. Geological Publishing House, Beijing Zhang HC, Peng JL, Ma YZ, Chen GJ, Feng ZD, Li B, Fan HF, Chang FQ, Lei GL, Wu¨nnemann B (2004) Late Quaternary palaeolake levels in Tengger Desert, NW China. Palaeogeogr Palaeoclimatol Palaeoecol 211:45–58 Zhang H, Chang F, Li B, Lei G, Chen Y, Zhang W, Niu J, Fan H, Yang M (2007a) Branched aliphatic alkanes of Shell Bar section in Qarhan Lake, Qaidam Basin and their paleoclimatic significance. Chin Sci Bull 52:1248–1256 Zhang H, Lei G, Chang F, Fan H, Yang M, Zhang W (2007b) Age determination of Shell Bar section in salt lake Qarhan Qaidam Basin. Quat Sci 27:511–521 (in Chinese with English abstract)
J Paleolimnol (2014) 51:179–195 Zhang H, Lei G, Chang F, Pu Y, Fan H, Lei Y, Yang M, Zhang W, Yang L (2008a) Chronology of the shell bar section and a discussion on the ages of the Late Pleistocene lacustrine deposits in the paleolake Qarhan, Qaidam basin. Front Earth Sci China 2:225–235 Zhang H, Wang Q, Peng J, Chen G (2008b) Ostracod assemblages and their paleoenvironmental significance from Shell Bar section of palaeolake Qarhan Qaidam Basin. Quat Sci 28:103–111 (in Chinese with English abstract) Zhang P, Song C, Yang Y, Gao H, Zhang H, Liu W, Pan M, Liu P, Hu S, Xia W (2008c) The significance and establishment of discriminant function with grain size of stable lacustrine sediment and eolian loess. Acta Sediment Sin 26:501–507 Zhang W, Zhang H, Lei G, Yang L, Niu J, Chang F, Yang M, Fan H (2008d) Elemental geochemistry and paleoenvironment evolution of Shell Bar section at Qarhan in the
195 Qaidam Basin. Quat Sci 28:917–928 (in Chinese with English abstract) Zhao Y, Yu Z, Chen F, Ito E, Zhao C (2007) Holocene vegetation and climate history at Hurleg Lake in the Qaidam Basin, northwest China. Rev Palaeobot Palynol 145:275–288 Zheng M, Yuan H, Zhao X, Liu X (2005) The Quaternary panlake (Overflow) period and paleoclimate on the QinghaiTibet Plateau. Acta Geol Sin 79:821–834 (in Chinese with English abstract) Zhou H, Liu CQ, Jiang Q, Jiang W, Zhao YL, Ding WC, Yan H (2010) Stable carbon isotopes in the shell of Corbicula fluminea (Mu¨ller 1774): implications for understanding environmental changes in drainage basins. Chin Sci Bull 55:4162–4167 Zhu R (1999) Precipitation. In: Sun H (ed) The National Atlas of China. China Cartographic Publishing House, Beijing, p 83
123
