Late Quaternary palaeolake levels in Tengger Desert, NW Chinamyz.adrem.org.cn/pdf/21.pdf · Late Quaternary palaeolake levels in Tengger Desert, NW China H.C. Zhanga,b,*, J.L. Pengc,

www.elsevier.com/locate/palaeo

Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) 45–58

Late Quaternary palaeolake levels in Tengger Desert, NW China

H.C. Zhanga,b,*, J.L. Pengc, Y.Z. Maa, G.J. Chend, Z.-D. Fenga,e, B. Lia,H.F. Fana, F.Q. Changa, G.L. Leia, B. Wunnemannf

aKey Laboratory of Western China’s Environmental Systems (Lanzhou University), Ministry of Education;

College of Earth Sciences and Environments, Lanzhou University, Lanzhou 730000, ChinabNanjing Institute of Geography & Limnology, eAS, 73 East Beijing Road,Nanjing 21000, China

cNanjing Institute of Geology and Paleontology, Academia Sinica, Nanjing 210008, ChinadDepartment of Geography, Mary Immaculate College, University of Limerick, Limerick, Ireland

eDepartment of Earth and Environmental Studies, Montclair State University, Upper Montclair, NJ 07043, USAf Interdisciplinary Center for Ecosystem Dynamics in Central Asia, Free University of Berlin,

Malteserstr. 74-100, 12249 Berlin, Germany

Received 21 November 2002; received in revised form 4 November 2003; accepted 13 April 2004

Abstract

Comprehensive field investigations and laboratory analyses show that palaeolakes, including the Megalake Tengger, and

other semi-connected and isolated water bodies, during late Pleistocene covered an area of more than 20,000 km2. This is an

area more than half the size of the Tengger Desert in NW China. Stratigraphic correlations and chronological evidence indicate

that the palaeolakes started to develop around 42,000 14C year BP (uncalibrated, all throughout the paper) but their extent was

limited until 37,000 14C year BP. Based on the chronology of representative lacustrine deposits, it can be deduced that the

Megalake Tengger was established around 35,000 14C year BP and maintained until 22,000 14C year BP, leading to the

formation of the Baijian Hu terraces, which are regarded as firm evidence of the existence of palaeolakes. The formation

mechanism is unclear and the climate situation at the time is still an open question.

The Holocene palaeolakes started to develop around 12,000 14C year BP. The Baijian Hu terraces indicate that the high

water levels in the area occurred around 8500, 5400–5100, 3500, and 1860–1370 14C year BP. The extent of the Holocene

palaeolakes, primarily migratory lakes, was smaller than that of the Late Pleistocene palaeolakes.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Late Pleistocene; Lake level; Tengger Desert; NW China; 14C data

1. Introduction

Climate change during the late Pleistocene has

been a focus of recent studies to understand the

natural state of the Earth’s climatic systems. Although

0031-0182/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.palaeo.2004.04.006

* Corresponding author.

E-mail addresses: [email protected],

[email protected] (H.C. Zhang).

the astronomic forces have been well demonstrated to

modulate the general rhythms of long-term climatic

changes (Imbrie et al., 1984), the controlling mecha-

nisms of some major climatic variations remain un-

accounted for. For example, O–D oscillations

(Dansgaard et al., 1993), Heinrich Events (Heinrich,

1988), and abrupt climate events during the classical

Last Glaciation have been widely documented

throughout the world (Bender et al., 1994; McManus

H.C. Zhang et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) 45–5846

et al., 1994; Porter and An, 1995) yet their forcing

mechanisms remain controversial (Cane, 1998). Our

understanding of climatic stability and forcing mech-

anisms during the Holocene, the current interglacial, is

at least as blurred as our understanding of conditions

during the late Pleistocene (Overpeck, 1993; Rind and

Overpeck, 1993). Multiple lines of evidence show that

the climate and associated environments during the

marine isotope stage 3 (MIS 3) are unique in the

geological records and in climatic reconstructions

(Anderson and Lozhkin, 2001; Chen et al., 1990;

Pachur et al., 1995; Shi et al., 2001; Thompson et

al., 1997; Van Andel, 2002; Yao et al., 1997; Zhang et

al., 2001, 2002). In other words, the geological

record-based climatic reconstruction of MIS 3 cannot

Fig. 1. Study areas. (The study areas include arid–semiarid Tengger Dese

Sections and/or studied sites, stars mark the drilling sites).

be explained by means of our current understanding

of climatic change (Anderson and Lozhkin, 2001;

Dam et al., 2001; Shi et al., 2001; Van Andel, 2002;

Zhang et al., 2001, 2002).

During the last 10 years extensive, systematic and

detailed field investigations have been conducted in

NW China by both Chinese scientists and scientists

from a Sino-German bilateral cooperation group.

Geomorphological, sedimentological, palaeobiologi-

cal and chronological studies have led us to conclude

that there existed vast areas of lakes in the Tengger

Desert and its adjacent areas including the Qilian

Mountains and Badanjilin Desert (Fig. 1) in the period

between 35,000 and 22,000 year BP (Pachur et al.,

1995; Zhang and Wunnemann, 1997; Zhang et al.,

rt, hyper-arid Badanjilin Desert and cold-high Qilian Mountains. z:

H.C. Zhang et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) 45–58 47

2001, 2002; Wunnemann et al., 1998). Synchronous

high lake levels have also been found in northern

Xinjiang (Rhodes et al., 1996) and in the Tibetan

Plateau (Li et al., 1991; Li and Zhu, 2001). In

addition, multiple soil-forming events in the northern

Mongolian Plateau from approximately 40,000 to

22,000 year BP (Feng, 2001), and reducing-dominat-

ed environmental events in the western Chinese Loess

Plateau from approximately 40,000 to 20,000 year BP

(Feng et al., 1998) might also correspond to the

expansion of palaeolakes in the arid areas. Palaeolake

expansion during the later MIS 3 in the presently arid

and semiarid areas of the Old World Desert Belts

(OWDB) may have had global climatic significance.

Developing our earlier work (Pachur et al., 1995;

Zhang and Wunnemann, 1997), we extended our

research area and intensified our research effort on

several previously studied sections in order to re-

construct the spatial distribution of palaeolakes and

their lake-level history. This paper presents regional

evidence from these investigations in the Tengger

Desert that sheds new light on the nature of the later

MIS 3 environments. This study also provides re-

gional evidence of Holocene lake-level variations in

the Tengger Desert that may be useful for further

understanding the abrupt events of the classic last

glaciation and the feedback mechanisms of climatic

forcing.

2. Study area

Tengger Desert is located in the arid–semiarid area

of northwestern China and is a key component of the

OWDB (Fig. 1). With a total area of 36,000 km2, it is

the fourth largest desert in China (Zhu et al., 1986). The

desert is bounded by the Qilian Mountains in the

southwest and by the Yabulai Mountain in the north-

west. The Helan Mountain, a barrier for the East Asian

Monsoon, separates the Tengger Desert from the Mo

Us sandy land to the east. To the south, the desert

stretches as far as the Loess Plateau. Climatically, the

area is situated at the conjunction of the arid and hyper-

arid northwest, the arid–semiarid southeast and the

cold-high mountain-plateau regions in the southwest.

The strong seasonal influence of the East Asian Mon-

soon, coupled with the meandering of the Westerly-Jet

results in concentrated rainfalls during summer. Cold

and dry air masses originating in the Siberian–Mon-

golian High Pressure cell generally prevail during

winter. The mean annual temperature and precipitation

are 7.8 jC and 115 mm, respectively, while the mean

annual potential evaporation is about 2600 mm (Agri-

cultural Regional Commission, 1985). The Tengger

Desert is primarily covered with mobile sand dunes and

its elevation ranges from 1000 to 1500 m above sea

level (a.s.l.). The vegetation, predominantly grasses

and shrubs (e.g. Nitraria tangutorum, N. sphaero-

carpa, Haloxylon ammodendron, Aneurolepidium

dasystachys, Kalidium, Reaumuria soongorica, Ephe-

dra, Artemisia xerophytica, Brachanthemum, Ajania,

and Stipa breviflora), is concentrated in low flat areas

and in inter-dune depressions where the groundwater

level is near the surface.

3. Methods

The locations and elevations of previously stud-

ied sections (Pachur et al., 1995; Zhang and Wun-

nemann, 1997; Ma et al., 1998; Peng et al., 1998)

were systematically measured by GPS survey and

crosschecked with topographical map gridding. For

this study, we excavated and sampled several new

sections and refined the chronology and stratigraphy

of Baijian Hu terraces, which were first reported by

Pachur et al. (1995). We also re-excavated two of

the previously studied sections, Duantouliang (DTL,

39j37V21WN, 103j55V13WE) and Tudongcao (TDC,

39j32V53WN, 103j46V37WE), and re-sampled them at

denser intervals for various analyses.

Conventional 14C dating (Table 1) was conducted

in three different laboratories: Lanzhou University,

Lanzhou Desert Institute of China, and the Bunde-

sanstalt fur Geowissenschaften und Rohstoffe in

Hannover, Germany. AMS dating was carried out at

Beta Analytic, Miami, USA. The materials used for14C dating include organic carbon (bulk samples),

charcoal, and carbonate. When there was no alterna-

tive, fossil shells were used. To avoid inconsistencies,

we chose mollusk shells of the same species that did

not appear to be reworked. The samples were cleaned

with 5% HCl for 2 to 3 h and then washed with

distilled water. The pre-treated samples were treated

again in the laboratory before analysis to make sure

the samples were uncontaminated. At the same time,

Table 1

Radiocarbon dates in Tengger Desert and its adjacent areas

Locality North latitude East longitude Depth/height C-14 age Material/Lab.a Source/remarks

(cm) (year BP)

Jilantai Site 1 in Fig. 6 135 9360F 120 Carbonate/LDI Uncalibrated/

192 15770F 210 Carbonate/LDI Author

240 7130F 106 Organic/LDI

240 25230F 610 Carbonate/LDI

Yabulai 39j43V51W 103j07V09W 325 25390F 690 Organic/LDI Uncalibrated/

202 29430F 1090 Charcoal/LDI Author

DTL 39j37V21W 103j55V13W 37 18860F 340 Organic/LDI Uncalibrated/

77.5 20060F 410 Organic/LDI Author

116 21150F 420 Shell/LDI

172.5 22950F 530 Organic/LDI

214.5 24150F 600 Organic/LDI




319.5 35160F 1930 Organic/LDI

TDC 39j32V53W 103j46V37W 42 20420F 400 Organic/LDI Uncalibrated/

82.5 21910F 460 Organic/LDI Author


137.5 24480F 640 Organic/LDI


198.5 29780F 1150 Organic/LDI

226.5 32260F 1540 Organic/LDI


Baijian Hu 39j09V 104j10V T21 32520F 840 Shell/LZU Uncalibrated/

Terrace T22 31520F 840 Shell/LZU Author

31360F 1240 Shell/LDI

T23 29480F 560 Shell/LZU



22480F 590 Shell/LZU

22220F 180 Shell/LZU

T3 8450F 90 Snail/LZU


5100F 70 Snail/LZU


T6 1860F 60 Carbonate/Hv

1370F 60 Carbonate/LZU

Baijian Hu Core 39j01V17W 104j01V37W 638 31060F 220 Organic (AMS)/Beta Uncalibrated/

670 26990F 1060 Carbonate /Hv authors

820 27150F 620 Carbonate /Hv

936.5 35660F 420 Organic (AMS)/Beta

Baijian Hu 39j00V54W 104j00V54W 26 970F 60 Carbonate/LZU Uncalibrated/

Section 34 1910F 60 Carbonate/LZU authors

56.5 3320F 130 Carbonate/Hv

92 6420F 70 Carbonate/LZU

92 6670F 100 Carbonate/Hv

Alashanzuoqi Site 11 in Fig. 6 112.5 21020F 360 Organic/LDI Uncalibrated/

author

197.5 19900F 330 Uncalibrated/

212.5 15850F 220 author

312.5 9720F 120


Table 1 (continued)

Locality North latitude East longitude Depth/height C-14 age Material/Lab.a Source/remarks

(cm) (year BP)

Hongshui River 38j10V46W 102j45V53W 7.5 3160F 90 Organic/LDI

57.5 3620F 120

122.5 4410F 80

127.5 4520F 90

192.5 5060F 120

277.5 5840F 120

325 6550F 80

400 6920F 70

475 7290F 120

Hongshui River 38j10V44W 102j45V56W 95 9760F 130 Organic/LDI Uncalibrated/

(Lower) 175 10370F 130 Organic/LDI author



13220F 100 Carbonate/LDI

370 12030F 90 Organic/LZU

11760F 590 Organic/LDI


16520F 160 Organic/LDI


20690F 860 Organic/LZU

Shiquanzi 39j47V00W 99j09V17W 22.5 3360F 80 Organic/LDI Uncalibrated/

62.5 5430F 100 author

97.5 7080F 110

180 9390F 150

297 14500F 260

373.5 19240F 440

450 20490F 400

479 25250F 820

655 29360F 1240

719.5 31550F 1580

794 35500F 2610

Hala Lake 38j12V16W 97j44V06W 26190F 520 Carbonate/LDI Uncalibrated/

author

Qinghai Lake 36j46V14W 99j42V29W 33980F 1100 Snail/LDI Uncalibrated/

27210F 470 Carbonate/LDI author

a LDI =Lanzhou Desert Research Institute, Academia Sinica, Lanzhou, China; LZU=Geography Department, Lanzhou University,

Lanzhou, China; Hv =Bundesanstalt fur Geowissenchaften und Rohstoffe in Hannover, Germany; Beta =Beta Analytic, Miami, USA.


the shells used for dating were analyzed by X-ray

diffraction to ensure that they consisted only of

aragonite without any recrystallization, to ascertain

that carbonate exchange did not occur between the

ground waters and the shells. A half-life of 5568

years was used for the calculation and the results

have not yet been calibrated. No data is presented on

d13C for the organic matter here because: first some

of the data are missing and second our dates were

measured at different times in different laboratories.

Our test results show that there are few aquatic plants

in the organic component and we found great differ-

ences between the data from different laboratories.

The reliability of these radio carbon dates have been

and are being tested using independent methods (e.g.

Pa–Th–U; OSL , IRSL and TSL) and a separate

paper dealing with this issue is in preparation.

The dates listed in Table 1 appear to be acceptable

for three reasons. First, the dates of organic carbon

from different laboratories are stratigraphically com-

parable. Second, almost all of the dates of organic

carbon at the same section, e.g. DTL and TDC

sections, are stratigraphically in order. Third, dates

from the same stratigraphic layer but different sam-


pling sites are also stratigraphically comparable. For

example, samples from the Baijian Hu terrace T22

(obtained from the same layer at different times and

different sites and analyzed at two different laborato-

ries) were dated at 31,520F 840 and 31,360F 1240

year BP (Table 1). It should be noted here that dates on

inorganic carbon (CaCO3) are variable and are usually

older than the dates on organic carbon because of the

dead carbon effect. Thus, our discussions are primarily

based on the dates of organic carbon and mollusk

shells.

4. Palaeolake level records

4.1. Baijian Hu terraces and fossil assemblages

Complete and well-preserved lake terrace sequen-

ces and associated fossil assemblages are probably the

best evidence for reconstructing palaeolake levels.

Our investigations identified six terraces in Baijian

Hu (39j09VN, 104j10VE) (Fig. 2). The highest terrace

T1 is 30–31 m above the present Baijian Hu playa

surface. The second terrace T2, the Main Terrace, is

about 22 m above the playa surface. T2 can be divided

into three parts: a broken terrace T21 on the outer side

and two well preserved parallel terraces T22 and T23

on the inner side. The terrace T21 was partially eroded

by lake water during the formation of T22, suggesting

that the water level during T22 might have been higher

Fig. 2. Cross section of lake terraces

than during T21. On all three terraces, we found

abundant fresh water fossil mollusk shells (e.g. Cor-

bicula fluminea and Cubicula largillierti) and snail

(e.g. Gyraulus chinensis).

Other terraces (T3, T4, T5 and T6) occur at 15.7,

14, 7–8 and 4–4.5 m above the playa surface,

respectively. Their sediments are rich in fossil snails,

which sometimes occur as distinctive layers about 5

cm in thickness. T1 is not dated for lack of datable

matter. T21 was dated at 32,560F 1090 year 14C BP.

Two dates for T22 are 31,520F 840 and 31,360F1240 year BP. Five dates obtained for T23 range

from 30,000 to 22,000 year BP (29,480F 560,

26,430F 980, 22,710F 380, 22,480F 590 and

22,220F 180 year BP). T3 was dated at 8450F 90

year BP. T4 has two dates: 5360F 60 and 5100F 70

year BP. T5 was dated at 3560F 60 year BP and the

lacustrine deposits associated with T6 were dated at

1860F 60 and 1370F 60 year BP.

4.2. Jilantai section and its correlation with nearby

fluvial deposits

Lacustrine deposits are widely distributed in the

Tengger Desert and adjacent areas. Typical sections

that represent the Late Pleistocene Megalake Tengger

are shown in Fig. 3. Jilantai Section (number 1 in

Fig. 1) is 800 cm thick, with the portion from 240 to

687 cm being composed of fine clayey deposits (Fig.

3). Sedimentary and geochemical properties indicate

at Baijian Hu and their dates.

Fig. 3. Stratigraphical columns of the Late Pleistocene palaeolake deposits. (The numbers indicate localities of the sections and/or studied sites

shown in Fig. 6. At site 6, late Pleistocene stratigraphy is marked as core100 and Holocene stratigraphy is marked as BJH in Fig. 4).


that this portion was deposited under stable and

deep-water conditions. The top of the clayey deposit

was dated at 25,230F 610 year 14C BP using a

carbonate nodule. We disregarded the macrofossil

(root) date obtained from the same level (7130F110 year 14C BP) because the tree may have

become established later. The clayey silt deposit at

210–185 cm depth was dated at 15,770F 210 year


BP and a carbonate crust at depth 140–130 cm at

9360 year BP. These two carbonate-enriched layers

are widely distributed in the area, indicating a

widespread shallow water swamp or semi-lacustrine

environment.

Vast fluvial fan deposits occur to the northwest of

the Jilantai section associated with traceable terraces.

Fossil shells in the fluvial fan deposits include Cor-

bicula fluminea and Cubicula largillierti and snails

Gyraulus chinensis, similar to the species found in the

Baijian Hu terraces, implying that these fluvial-fan

associated terraces correlate with the main palaeolake

terraces at Baijian Hu. It can also be correlated with

the fan deposits dated between 30,350F 470 and

21,970F 160 year BP in the foothills of Helan Moun-

tain (Hofmann, 1994). Although there is no age

control at the bottom of the lacustrine deposit (240–

687 cm), regional stratigraphic correlation and radio-

carbon dates higher in this unit suggest that the

lacustrine deposit at the Jilantai section was deposited

synchronously with those at the TDC and DTL

sections. The date of 35,660F 420 year BP in the

middle of the lacustrine deposit of the Baijian Hu core

(number 6 in Fig. 6) is an anomaly in interpretation

that Megalake Tengger was at its maximum from

approximately 35,000 to 22,000 year BP. A possible

explanation is that the Baijian Hu core is located in the

central part of the Megalake Tengger, and the older

date at the bottom of the lacustrine deposit may

simply mean that Megalake Tengger evolved earlier

in its center. A regional correlation of these represen-

tative sections shows that the late Pleistocene palae-

olake deposits are thinner and coarser in the western

part of the Tengger Desert (e.g. Duantouliang and

Tudongcao) than in the eastern part (e.g. Jilantai). The

oldest date at the lower part of DTL section is

35,160F 1930 and 35,660F 420 year BP in the

Baijian Hu core. Using the sedimentation rates inter-

polated from age to depth relationships (Fig. 3), the

extrapolated date for the bottom of the lacustrine

deposit, i.e. the beginning of the palaeolake develop-

ment, is 42,000–40,000 year BP.

The Holocene lacustrine deposits are much more

variable in the Tengger Desert (Fig. 4). It is impos-

sible to establish regional stratigraphy of the Holo-

cene lacustrine deposits because the extent of the

Holocene palaeolakes was limited and their positions

were movable. The dates of the Hongshui River

section (13 L in Fig. 4 and number 13 in Fig. 6)

show that the Holocene lacustrine deposits were

deposited as early as 12,030F 90 14C year BP in

the Tengger Desert.

4.3. Yabulai section and its correlation with Baijian

Hu terraces

Drilling data from the Yabulai Basin in the western

part of the Tengger Desert revealed that the Quater-

nary deposits are more than 400 m thick and domi-

nated by lacustrine sediments. On the eastern slope of

the Yabulai Mountain, flat-topped fluvial fans, prob-

ably fluvial terraces, developed at elevations between

1300 and 1350 m (a.s.l., Fig. 5a). We investigated a 4-

m-thick section (Fig. 5b) exposed by river erosion and

observed six layers of fine silt-clay, marked as A, B,

C, D, E and F. Three samples, YBL1, YBL2 and

YBL3, were taken for pollen and microfossil analyses.

A charcoal sample in YBL1 and an organic matter

sample in YBL2 were dated at 29,430F 1090 and

25,390F 690 year BP, respectively. The species of

ostracod microfossils include Iiyocypris gibba, Heter-

ocypris salina, eucypris sp., Candona candida, Can-

dona compressa, Limnocythere inopinata and

Cyprideis torosa. These species indicate a fresh-water

deltaic-lacustrine environment (Peng et al., 1998),

suggesting that these six layers of fine silt-clay were

deposited in transitional environments between river

and paleaolake.

The sporo-pollen assemblages identified from three

samples (YBL1, YBL2 and YBL3. Table 2) indicate

that trees including needleleaf trees (mainly Cupres-

saseae, Picea and Larix) and broadleaf trees (mainly

Quercus and Populus) were dominant during the

Megalake Tengger period. Forests must have appeared

on the nearby Yabulai Mountains below 1800 m

(a.s.l.) since there are only a few peaks with limited

areas above this elevation.

Based on the E–W gradient of the lower limits of

the modern treeline from the Helan Mountain on the

east to the Qilian Mountains on the west, we infer that

the modern potential lower limit of treeline in the

Yabulai Mountain would be 2200–2400 m a.s.l. The

difference between the present potential lower limit of

treeline and the inferred lower limit of the Megalake

Tengger treeline suggests that the lower limit of the

treeline during the Magelake Tengger period was

Fig. 4. Stratigraphical columns of the Holocene paleaolake deposits of the Tengger Desert. (The numbers indicate localities of the sections and/

or studied sites showing in Fig. 6. At site 13, Hongshui River Section (HS) is composed by two parts: the upper part HSU and lower part HSL).


about 400–600 m lower than that of today. At the

present time, the Yabulai Mountain is almost bare and

free of vegetation and the vegetation in the lowland

area is dominated by desert types (e.g. Artemisia

sphaerocephala, Calligonum mongolicum and Halox-

ylon ammodendron).

5. Discussion and conclusion

Based on the elevation of the Baijian Hu terraces

and the distribution and elevation of lacustrine-fluvial

deposits in the Yabulai Mountain area, it can be

deduced that the high water level of the Megalake


Tengger during the Late Pleistocene was between

1310 and 1321 m above sea level. The palaeolake

area calculated along the 1310 m contour is 16,000

km2 (Pachur et al., 1995), which is almost four times

as big as Qinghai Lake, the biggest inland lake in

China. Later field investigations and C-14 dates

confirmed that the Main Terrace T2 was formed

between 22,000 and 32,000 year BP and is 2 m higher

than the 1310 m hypsometeric contour (Zhang and

Wunnemann, 1997). Therefore, instead of 1310 m

contour used by Pachur et al. (1995), we here used the

1312 m contour to recalculate the paleaolake area for

the western part of Tengger Desert where the Mega-

lake Tengger and other connected water bodies

existed. We added to the paleaolake area the palae-

olake areas in the eastern part of the Tengger Desert

where only isolated water bodies existed at the time.

The total area of the palaeolakes in the Tengger Desert

Fig. 5. Geomorphological map of Yabulai M

during the Megalake Tengger period was about

20,000 km2 (Fig. 6), or more than half of the total

area of Tengger Desert. The palaeolake area might

have been considerably larger during the Megalake

Tengger period if T1 was formed at the time. Based on

microfossil (Peng et al., 1998) and geochemical data

(Zhang et al., 2002), it is deduced that Megalake

Tengger was a fresh to mesohaline lake with a depth

ranging from 20 to 60 m.

Megalake Tengger started to develop around

42,000–40,000 year BP and maintained its highest

water level between 35,000 and 22,000 14C year BP.

The vast paleaolake area and high water level, as well

as biological (Ma et al., 1998; Peng et al., 1998) and

geochemical data (Zhang et al., 2002), indicate that

the climate was much moister than today. It is most

likely that the palaeolakes were sustained by the water

from the surrounding mountains and local rainfall.

ountain (a) and cross section A–B (b).

Fig. 5 (continued).


High lake-level during the Megalake Tengger pe-

riod (35,000–22,000 year BP) was not only a local

phenomenon. Synchronous palaeolakes with high

water levels have also been found in northwestern

Bandanjilin Desert (Wunnemann et al., 1998) and

north Xinjiang (Rhodes et al., 1996). Our recent

investigation and analyses show that the fresh-water

species of fossil snail found in a beach gravel layer of

the Qinghai Lake, situated about 140 m higher than

Table 2

Statistical data of pollen assemblages from Yabulai section

Sample Needleleaf trees Broa

YBL-1 41.29% 41.9

Cupressaseae (28.39%) Quer

Larix (10.32%) Popu

(+ Juniperus + Picea)

YBL-2 43.69% 14.2

Cupressaseae (33.61%) Popu

(+ Juniperus +Larix + Picea) (+Q

YBL-3 27.18% 55.8

Cupressaseae (23.30%) Betu

(+ Picea + Larix) Popu

Quer

(+U

the present lake level, date from 33,980F 1100 14C

year BP. A carbonate crust covering the gravel layer is

dated at 27,210F 470 year BP (Zhang et al., unpub-

lished data). Around the Hala Lake area (see Fig. 1), a

carbonate crust covering a beach gravel layer at an

elevation much higher than the present lake level is

dated at 26,190F 520 year BP. The carbonate crusts

both in the Qinghai and Hala lakes in the northeastern

Tibetan Plateau suggest a drastic decline of the lake

dleaf trees + shrubs Herbs + aquatic taxa

4% 16.78%

cus (29.68%) Artemisia (11.62%)

lus (12.25%) Chenopodiaceae (3.87%)

(+Gramisia)

8% 42.10%

lus (7.56%) Artemisia (30.25%)

uercus +Betula) Chenopodiaceae (6.72%)

(+ Typha + Polygum+Ephadra)

2% 16.99%

la (24.76%) Artemisia (6.80%)

lus (24.27%) Gramisia (4.37%)

cus (4.85%) Chenopodiaceae (2.91%)

lmus) (+ Lilium)

Fig. 6. Reconstructed extent of palaeolakes in the Tengger Desert and adjacent areas based on the distribution patterns of the palaeolake deposits

and morphological closure. Localities of the studied sections are designated by the circled numbers.

Fig. 7. Reconstructed water level fluctuations of palaeolakes in Tengger Desert (solid line indicates the measured height of the terraces and

dashed line shows the possible water level fluctuation processes).



levels. Towards the interior of the Tibetan Plateau,

high palaeolake levels have also been extensively

documented to have occurred around 20,000 to

40,000 14C year BP (Li et al., 1991; Li and Zhu,

2001). The climate conditions during this period

were unique to the area and have no modern

analogue. Geological evidence implies that the cli-

mate, especially the hydrological circulation, might

have been very different from that of today (Zhang

et al., 2001, 2002). However, the mechanisms con-

trolling how these Megalakes were formed remains

an open question.

The stratigraphic evidence shows that no lakes

existed in the Tengger Desert during the LGM cen-

tered around 18,000 14C year BP (Zhang et al., 2002).

Lacustrine deposits show that the palaeolakes reap-

peared as early as 12,000 year BP. In the Baijian Hu

area, high water levels indicated by Holocene terraces

occurred around 8500, 5400–5100, 3500, and 1860–

1370 year BP (Table 1), but the water levels were

considerably lower than that during the Megalake

Tengger period. The periodic appearances of the

Holocene palaeolakes and drastic fluctuations of the

lake levels (Fig. 7) might be attributable to the

alternating strengthening and weakening of the sum-

mer monsoon circulation (Kutzbach, 1981; Gasse et

al., 1991, 1996; Zhang et al., 2000).

Acknowledgements

This research was supported by NSFC (No.

49971015, 40001022 and 40371117). We sincerely

thank T.C. Johnson and J. Casanova for their kind and

patient reviewing of this paper and making valuable

suggestions for its improvement.

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Late Quaternary palaeolake levels in Tengger Desert, NW Chinamyz.adrem.org.cn/pdf/21.pdf · Late Quaternary palaeolake levels in Tengger Desert, NW China H.C. Zhanga,b,*, J.L. Pengc,