monitoring cenozoic climate evolution of northeastern tibet: stable isotope constraints from the...

ORIGINAL PAPER

Monitoring Cenozoic climate evolution of northeastern Tibet:stable isotope constraints from the western Qaidam Basin, China

Andrea B. Rieser Æ Ana-Voica Bojar ÆFranz Neubauer Æ Johann Genser Æ Yongjiang Liu ÆXiao-Hong Ge Æ Gertrude Friedl

Received: 14 March 2006 / Accepted: 16 February 2008 / Published online: 7 March 2008

� Springer-Verlag 2008

Abstract Carbon and oxygen stable isotopic composition

of Cenozoic lacustrine carbonates from the intramontane

Qaidam Basin yields cycles of variable length and shows

several distinct events driven by tectonics and climate

changes. From Eocene to Oligocene, the over-all trend in

the d13C composition of lacustrine carbonates shows a shift

toward higher values, possibly related to higher proportions

of dissolved inorganic carbon transported to the lake or

lower input of soil derived CO2. At the same time, the d18O

composition of lacustrine carbonates is decreasing in

accordance with the global cooling trend and northwards

drifting of the whole region. During the Miocene, distinct

isotopic events can be recognized, although their inter-

pretation and linkage to a certain tectonic event remains

difficult. These events may be related to uplift in the

Himalayas, to the strongest phase of uplift in the Altyn

Mountains, to pronounced subsidence of the Qaidam Basin

or to the expansion of C4 plants on land. Generally cold,

highly evaporative conditions can be deduced from

enrichment of d18O isotopic compositions during Pliocene

and Quaternary times.

Keywords Stable isotopes � Intracontinental basin �Climate change � Evaporation � Lacustrine carbonate

Introduction

It is widely accepted that the surface uplift of the Hima-

layas and the Tibetan plateau changed the regional climate

(e.g., Ramstein et al. 1997). But how, when and to what

extent is still highly debated. Raymo and Ruddiman (1992)

claim the Tibetan uplift to be the main driving force behind

Cenozoic climate change. Uplift of the southern Tibetan

plateau has strengthened summer monsoon and has brought

wetter climates to the south of the Himalayas (Burbank

et al. 2003; Sun and Wang 2005). With the Himalayan

range blocking the moisture, Central Asia becomes drier as

uplift proceeds (Guo et al. 2002). Palaeoelevations are

constructed based on the palaeoflora or stable isotope

studies (DeCelles et al. 2006; Currie et al. 2005 and

references therein). There are detailed stable isotope stud-

ies on fluvial and lacustrine carbonates from the Linxia

Basin (Dettman et al. 2003; Garzione et al. 2004), northern

Qaidam Basin as well as from the southern Tarim Basin

(Sun et al. 1999; Graham et al. 2005).

The impact of Himalayan and Tibetan uplift on global

circulation and climate has been the focus of several

numerical climate models. For example, Kutzbach et al.

(1997) showed that topography significantly influences

Earth’s climate, with considerable effect of uplift on global

and regional hydrology. Results of atmospheric general

circulation models show the importance of the shrinkage of

the Paratethys, which stretched E–W through Eurasia

A. B. Rieser � F. Neubauer � J. Genser � G. Friedl

Division General Geology and Geodynamics,

University of Salzburg, Hellbrunnerstr. 34,

5020 Salzburg, Austria

A.-V. Bojar

Institute of Earth Sciences, University of Graz,

Heinrichstr. 26, 8010 Graz, Austria

Y. Liu � X.-H. Ge

College of Earth Sciences, Jilin University,

Jianshe Str. 2199, 130061 Changchun, China

Present Address:A. B. Rieser (&)

Nagra, Hardstrasse 73, 5430 Wettingen, Switzerland

e-mail: [email protected]

123

Int J Earth Sci (Geol Rundsch) (2009) 98:1063–1075

DOI 10.1007/s00531-008-0304-5

during the Palaeogene and terminated to the north of the

future Tibetan plateau, for the climate evolution of central

Asia (Ramstein et al. 1997). The Paratethys shrinkage

resulted in a shift toward more continental climate and

aridity. Several models argue for significant elevation of

the Tibetan plateau already at 15–12 Ma (e.g., Dettman

et al. 2003; Rowley and Currie 2006). Further climate

studies and field proxies have shown the importance of

uplift of the Tibetan plateau at ca. 10–8 and 2.6 Ma,

resulting in enhanced aridity and strengthening of the

winter monsoon (e.g., Harrison et al. 1992; An et al. 2001).

The shift to a monsoon-dominated climate at 8 Ma is

reflected in the isotopic composition of palaeosol concre-

tions from the Siwalik Group in southern Nepal (Quade

et al. 1995). Within the last 8 Ma, monsoon intensity

changed several times. Strengthening at 3.5 and 2.6 Ma

(Qiang et al. 2001) is related to rapid uplift of the north-

western part of Tibet (Wang et al. 1999). What the Tibetan

plateau is for the northern hemisphere, the Andes are for

the southern hemisphere, a barrier to the main winds. Thus

the plateau is significantly influencing the regional wind

pattern.

The general Cenozoic climate of the Tibetan plateau is

considered arid with intervals of more humid conditions,

especially in the Miocene (Wang et al. 1999). These

reconstructions are based on palaeoflora observations from

Namling in southern Tibet (Spicer et al. 2003), pollen

sequences (Wang et al. 1999) or distribution of sedimen-

tary facies (Huang and Shao 1993).

In this paper, we present a pilot study on a Cenozoic

stable isotope record from the northwestern Qaidam Basin.

The scope is set on a regional scale. We attempt to reveal

the basic climatic developments in the early basin history

and its further evolution in Pliocene/Quaternary times. The

data are corroborative with field evidence and already

existing regional literature.

Geology and climate of the Qaidam Basin

The Qaidam Basin is a large intramontane sedimentary

basin at the northwestern margin of the Tibetan plateau

(Fig. 1). The basin center has an average elevation of

2,800 m while the surrounding mountains (Altyn, Kunlun/

Qimantagh and Qilian) reach heights in excess of 5,000 m.

It has a surface basin area of ca. 120,000 km2 and a

Cenozoic sedimentary sequence of 3–10 km thickness. The

Cenozoic terrestrial sedimentary sequence is made up of

fluvial sandstones and conglomerates and subordinate

lacustrine carbonates and mudstones. Lake sediments are

exposed in central sectors of the basin and are divided into

near-shore and deep-lake sediments, the latter including

many thin carbonate layers. During the Palaeocene time,

the lacustrine environment was limited to the western

sector of the Qaidam Basin (Duan and Hu 2001; Liu et al.

1998). During the Eocene, after the collision of India with

Eurasia (Fig. 2; Gradstein et al. 2004; Li 1996; Qiu 2002;

Zheng et al. 2000), the palaeo-lake depocentre started to

migrate from the west to the east (Liu et al. 1998). In the

Miocene, the lake expanded about 300 km eastwards

(Duan and Hu 2001) and possibly reached its maximum

extension as the climate became more humid (Wang et al.

1999). At that time climate was characterized by a south-

east–northwest trending arid climate belt that covered a

large part of China and withdrew to the northwestern part

until late Miocene (Wang et al. 1999; Sun and Wang 2005).

The Plio/Pleistocene Late Himalayan orogeny (e.g., Meyer

et al. 1998; Song and Wang 1993) initiated a phase of uplift

in the whole northwestern part of the Tibetan plateau (Sun

et al. 1999; Bojar et al. 2005a). In the western and central

Qaidam Basin fold structures resulted, nowadays offering

access to older formations. Together with increasingly drier

conditions, the tectonic processes caused the large palaeo-

lake to shrink and to break into several smaller lakes (Duan

and Hu 2001), of which only few salt-lakes in the southeast

remained.

The depositional environments of various Tertiary

stages are summarized in many papers and include alluvial

fans with coarse-grained clastics and fluvial deposits with

conglomerates and sandstones along basin margins, adja-

cent shore and shallow-lake deposits with mostly

sandstones, and deep-lake facies with mainly mudstone,

marls and rare carbonate layers (e.g., Huang et al. 1997;

Hanson et al. 2001; Xia et al. 2001 and references therein).

Carbonates and marls occur predominantly together with

mudstone and are therefore considered to represent the

deep-lake facies. Hydrocarbon source rocks, mostly marls

and shales, are common in the deep-lake facies during the

Oligocene (Hanson et al. 2001).

Fig. 1 Sketch map of the Himalaya-Tibet system of Central Asia and

location of the Qaidam Basin at the northeastern margin of the Tibet

plateau (redrawn after Tapponnier et al. 2001). The rectangleindicates the outline of Fig. 3

1064 Int J Earth Sci (Geol Rundsch) (2009) 98:1063–1075

123

Time correlations in the Qaidam Basin are based on

magnetostratigraphy (e.g., Sun et al. 2005; Yang et al.

1992), seismic stratigraphy (Xia et al. 2001) and micro-

fossils, especially ostracods (Sun et al. 1999). Nevertheless

the data for a good, basin wide stratigraphy are still

missing.

The present climate in the Qaidam Basin is highly arid,

with annual precipitation less than 50 mm/year (Lehmkuhl

and Haselein 2000) and potential evaporation of about

3,000 mm/year (e.g., Wang et al. 1999; Duan and Hu

2001). Freshwater is mainly provided as melt water to the

southern basin from the Kunlun and the Qilian Mountains.

The Altyn Mountains have been below the snowline during

the Cenozoic, therefore no melt water was provided to the

basin from north. Differences in the water quality are

shown by different ostracod assemblages (Sun et al. 1999).

In the northern part of the basin, there are exclusively

hypersaline species while in the southern and eastern parts,

in the mountain foreland, melt waters lead to small lakes

with brackish-freshwater conditions.

Sampling and methodology

Samples

Carbonate samples for whole-rock stable isotope analysis

have been collected mainly along three sections: two

sections in the Hongsanhan and one in the Ganchaigou

Valley (Fig. 3). We collected about 60 carbonate samples

for whole-rock stable isotope analysis along two sections in

the Hongsanhan (Fig. 4), an anticline situated at the

Holocene

Pleistocene

Pliocene

Miocene (Messinian)

Miocene (Tortonian-Langhian)

Lower Miocene

Oligocene (Chattian-Rupelian)

Eocene (Priabon)

Eocene (Bartonian-Ypresian)

EpochTime

Eocene (Ypresian)

1.8

23.5

37.0

46.0

7.3

15.8

33.7

Ma

5.3

Tectonics Reference

- 2000 m uplift of Himalaya

Elevation

present elevation

1500m

- Uplift of southern Tibet

- Small scale uplift in southern Tibet

- Collision of India and Asia

- Closure of Neotethys

- Tarim/Kunlun at sealevel

present elevationin S Tibet

- Continental extrusion of Indochina

- Rapid uplift of southern Tibet

- Uplift of NW Tibet and Qaidam Basin

- Himalaya: stage of rise and erosion relative calm tectonic activity

- Large-amplitude uplift in mountains around Tibet-Qinghai plateau

- Change in stress field in southern Tibet from N-S compression to E-W extension

- Onset of intracontinental convergence

- Crustal layering thickening

- Isostatic adjustment3000-->5000m

- Late Himalayan orogeny (stages 2 and 3)

- Himalayan movement stage 1

between India and Asia

[Lehmkuhl &Haselein, 2000]

[Harrison et al., 1992]




[Searle, 1995]

[Spicer et al., 2003]

[Guo et al., 2002]

[Dettman et al., 2003]

[Dettman et al., 2003]

[Wang et al., 1999]

[Sun et al., 1999]

[Spicer et al., 2003]

[Li, 1996]

[Li, 1996]

[Li, 1996]

[Li, 1996]

[Li, 1996]

[Li, 1996]

[Qiu, 2002]

[Zheng et al., 2000]

T0

T1

T'2

T2

T3

T5

Fig. 2 Major tectonic events

during the Cenozoic on the

Tibetan plateau with

significance for the Qaidam

Basin. Ages refer to the

International Geologic Time

Scale (Gradstein et al. 2004).

T0–T5 are the seismic reflectors

in the Qaidam Basin used for

correlation

Fig. 3 Simplified sketch map of the northwestern Qaidam Basin with

sample localities: (1) Hongsanhan Third Valley, (2) Hongsanhan Fifth

Valley, (3) Ganchaigou Valley, (4) Youshashan, (5) southern side of

Youshashan, (6) Dafeng Shan, (7) Qigequan, (8) Ahati, (9) Kaitemi-

like, (10) Youshashan, (11) Youquanzi, (12) Hongsanhan, (13)

Xiaoliangshan

Int J Earth Sci (Geol Rundsch) (2009) 98:1063–1075 1065

123

northern margin of the Qaidam Basin: 44 samples from the

Hongsanhan Third High Peak Valley and 15 samples from

the Hongsanhan Fifth High Peak Valley. The Pliocene

Hongsanhan anticlinal structure is incised by three large

parallel valleys, which run more or less perpendicular to

the anticline axis. Sedimentary rocks in this area range

from the Lower Eocene Lulehe Formation up to the Lower

Xiayoushashan Formation of Oligocene age. In the Eocene

Xiaganchaigou Formation, marls are abundant in the

Hongsanhan Third Valley. Some of the micritic-micro-

sparitic carbonates contain few fossils, such as ostracods,

charophytes and singular gastropods. Middle Eocene car-

bonates from the Hongsanhan Fifth Valley are extremely

hard, dark-gray or grayish-brown and when freshly sam-

pled they yield a strong smell of oil. They bear more fossils

(mainly charophytes and up to 2 cm large gastropods) than

the softer, greenish-bluish or beige and often marly car-

bonates in the Third Valley. Limestones are dominating in

Oligocene time and in the Hongsanhan Fifth Valley. The

Hongsanhan valleys offer good and continuous exposures

of the stratigraphic record. The section in the Third Valley

is about 1,000 m thick and the core of the anticline lies at

2,935 m elevation while the southern end of the section is

at 2,880 m. Recent magnetostratigraphy (Fig. 5; Sun et al.

2005) allows good time control. The Third and Fifth Valley

are about 8 km apart, the latter being situated further to the

east. Within the stratigraphic column (Fig. 5) of the Third

Valley, which shows a general coarsening upward trend,

several fining upward cycles can be distinguished, starting

with coarse sandstones or pebble conglomerates and

grading into fine mudstones and marls. The carbonates

often occur at the top of such fining upward cycles. The

thickness of individual carbonate layers is usually varying,

between a few and 20 cm with some layers reaching even

1.5 m. Within a section, the vertical distance between the

samples ranges from 10 cm up to 100 m. This constrains

Fig. 4 Detailed sketch map of the Hongsanhan anticline at the

northern margin of the Qaidam Basin showing the location of the two

sampled sections in the Third and Fifth Valley

Fig. 5 Sample distribution within the lithostratigraphic column of the

Hongsanhan Third Valley section (based on Ma, pers. comm. 2003)

together with the magnetostratigraphy after Sun et al. (2005). T3 marks

a seismic reflector defining the formation boundary. al Alluvial facies,

fl fluvial facies, sl shallow lake facies, dl deep lake facies, cl clay, s silt,

f fine sand, m medium grained sand, c coarse grained sand, cg gravel


123

the temporal resolution. In the Eocene Xiaganchaigou

Formation, mudstones, fine sandstones and carbonates are

more abundant than above in the Eocene–Oligocene

Shangganchaigou Formation. In the latter formation, the

carbonates are associated with coarser sediments such as

sandstones and conglomerates.

In order to cover the entire Eocene to Quaternary

succession, further samples were collected from the basin

center (Dafeng Shan, (6) in Fig. 3), Ganchaigou Valley

[(3) in Fig. 3] north of Huatugou, along the Youshashan

anticline [(4), (5), (9), (10) and (11) in Fig. 3] and from

the Xiaoliangshan anticline [(13) in Fig. 3]. All outcrops

are bound to Pliocene and Pleistocene fold structures

(Song and Wang 1993) and represent isolated carbonate

layers in between fine sandstones. Sampling intervals are

highly variable, depending on the abundance of suitable

material such as limestones and marls. It has to be

emphasized, that during the Neogene times, conditions for

carbonate formation were not favorable because of the

increasing coarse-grained clastic sediments due to ongo-

ing tectonism. Calcium carbonate formation requires low-

energetic environments. Times with higher terrigenous

input yield abundant marls. In the Hongsanhan section,

marls occur particularly in those horizons where abundant

hydrocarbon source rocks have formed. Fine-grained

carbonate rocks were deposited as a result of lake high-

stands (Huang and Shao 1993). Weak hydrodynamic

conditions enabled fine-grained carbonate rocks to deposit

in the center of the lake, which was little affected by the

sediment supply from the land. If fine-grained carbonate

rocks represent an expansion of the lake area and a

deepening of the lake water, it follows that significant

changes in the water level of the lake took place once

every several thousand to more than 2 million years

(Huang and Shao 1993).

Methods

Isotopic analyses were performed on well-homogenized

whole rock samples using an automatic Kiel II preparation

line and a Finnigan MAT Delta Plus Mass Spectrometer at

the Institute of Geology and Palaeontology at the Univer-

sity of Graz, Austria. NBS-19 and an internal laboratory

standard were analyzed continuously for accuracy control.

The standard deviation is ±0.1% for d18O and ±0.06% for

d13C. All isotopic results are reported in the d-notation in

per mil (%) relative to the Peedee belemnite standard

(PDB).

Six selected samples have been analyzed with a LEICA

Stereoscan 430 scanning electron microscope, equipped

with an Oxford MiniCL detector, in order to determine the

diagenetic overprint, which may have influenced the iso-

topic compositions.

Results

Stable isotope data are summarized in Table 1 and Figs. 6,

7, 8 and 9. A total of 100 analyses were made, some in

duplicate. They represent the whole-rock mean values of

well-homogenized samples. For the discussion, we also

include data from the Quaternary Qigequan Formation of

the Dafeng Shan locality (Bojar et al. 2005b).

To verify the whole-rock data, four hand specimens

were additionally microsampled (Table 2). The resulting

values vary within 0.8 per mil, often even within 0.5 per

mil and are close to the respective whole-rock values.

Carbon isotopes

The d13C data from the northwestern part of the Qaidam

Basin show a general trend towards heavier isotopic

composition through Cenozoic times. In the Hongsanhan

area, the values from marls and few limestones in the

Middle Eocene Xiaganchaigou Formation vary largely

between -5.5 and -0.3% (Fig. 6), showing several rapid

positive excursions. In the Upper Eocene–Lower Oligo-

cene Shangganchaigou Formation, carbon isotopic

composition shows less variation, that is, between -2.7

and -1.6%. Within the Xiaganchaigou and Shanggan-

chaigou Formations, the general trend is toward heavier

d13C values. The samples from the Hongsanhan Fifth

Valley section are characterized by lighter isotopic values

between -5.5 and -3.7% with one excursion to -1.4%.

Two additional samples (QA-130) from the Hongsanhan

area plot in the same range between -3.6 and -4.4% (see

Fig. 8).

The Ganchaigou section (Fig. 7) shows large variations

of the carbon isotope composition within the Xiaganchai-

gou Formation, then a positive excursion in the

Shangganchaigou Formation and a sharp negative excur-

sion of 3% at the boundary between the Shangganchaigou

and Xiayoushashan Formation. At the top of the Shang-

ganchaigou Formation, the d13C composition is 1.1% and

at the base of the Xiayoushashan Formation -1.4%. Note

that the differing interpretation of the palaeomagnetical

sections for the Hongsanhan and Ganchaigou section leads

to different ages for the formation boundaries. In the

summary figure (Fig. 8), the Ganchaigou samples are

plotted relative to their position within the formation. The

remaining samples (Fig. 8) show a wide scatter, partly due

to the very low abundance of late Miocene and Pliocene

carbonates. Within a suite of four samples across the

Shangyoushashan/Shizigou Formation boundary from the

southeast of the Youshashan anticline [(5) in Fig. 3], car-

bon isotopic values are continuously increasing from -3.8

to -1.1%. In the Quaternary Qigequan Formation values

of -1.5% and even 2.3% are reached.


123

Table 1 Stable isotope results from the northwestern Qaidam Basin

Sample # Formation d13C

%(VPDB)

d18O

%(VPDB)

d18O

%(SMOW)

Hongsanhan Third Valley (1)a

QA-190D-02 Xiayoushashan -3.60 -7.07 23.62

QA-189E-02 Shangganchaigou -3.39 -6.95 23.74

QA-189B-02 Shangganchaigou -2.47 -7.26 23.43

QA-306A-03 Shangganchaigou -2.66 -7.71 22.96

QA-186O-02 Shangganchaigou -2.16 -7.96 22.71

QA-305E-03 Shangganchaigou -2.54 -7.83 22.84

QA-305D-03 Shangganchaigou -2.11 -7.55 23.13

QA-305C-03 Shangganchaigou -2.05 -6.72 23.99

QA-186L-02 Shangganchaigou -2.67 -7.28 23.40

QA-186F-02 Shangganchaigou -2.57 -7.05 23.64


QA-304C-03 Shangganchaigou -2.44 -6.63 24.07

QA-304B-03 Shangganchaigou -4.45 -7.77 22.90


QA-303B-03 Xiaganchaigou -1.78 -5.21 25.54

QA-303A-03 Xiaganchaigou -2.17 -6.72 23.98



QA-301E-03 Xiaganchaigou -3.44 -6.87 23.83

QA-301D-03 Xiaganchaigou -1.97 -7.44 23.24

QA-301C-03 Xiaganchaigou -1.16 -1.14 29.73


QA-184Q-02 Xiaganchaigou -3.31 -7.33 23.35

QA-184P-02 Xiaganchaigou -4.49 -5.53 25.21

QA-184N-02 Xiaganchaigou -3.06 -5.41 25.33

QA-184L-02 Xiaganchaigou -3.57 -6.10 24.62


QA-300G-03 Xiaganchaigou -3.37 -2.65 28.18

QA-300F-03 Xiaganchaigou -1.65 -5.74 25.00

QA-300E-03 Xiaganchaigou -3.41 -6.72 23.99






QA-184J-02 Xiaganchaigou -2.77 -7.60 23.08

QA-184I-02 Xiaganchaigou -4.02 -7.40 23.28



QA-184G-02 Xiaganchaigou -3.20 -6.85 23.85

QA-184F-02 Xiaganchaigou -4.12 -7.30 23.38




Table 1 continued


%(VPDB)

d18O

%(VPDB)

d18O

%(SMOW)

Hongsanhan Fifth Valley (2)

LH5-8 Xiaganchaigou -3.69 -5.14 25.61

















Ganchaigou (3)

QA-286A-03 Xiayoushashan -4.36 -7.00 23.69

QA-285B-03 Xiayoushashan -2.30 -6.46 24.25



QA-283C-03 Xiayoushashan -1.71 -7.33 23.35

QA-283B-03 Xiayoushashan -1.76 -7.06 23.63

QA-283A-03 Xiayoushashan 1.43 -6.92 23.78

QA-93Af-01 Xiayoushashan -1.36 -7.57 23.11

QA-93Ac-01 Xiayoushashan -1.46 -7.54 23.14

QA-92B-01 Shangganchaigou 1.13 -6.42 24.30

QA-282A-03 Shangganchaigou 1.20 -3.15 27.66

QA-281B-03 Shangganchaigou 0.27 -5.92 24.81

QA-281A-03 Shangganchaigou 0.04 -6.42 24.29









Youshashan (4)






123

Oxygen isotopes

For the Hongsanhan sections (Fig. 6), the d18O data range

between -8.4 and -5.2% with several positive excursions

in the lower part. All excursion peak values originate from

marls. The upper, limestone-dominated part of the

Shangganchaigou Formation shows values within a range

of two per mil, that is, between -8.4 and -6.6%. In the

Hongsanhan Fifth Valley, the samples plot between -3.9

and -6.4% with a negative excursion to -7.5%. Samples

representing the same time interval in the Ganchaigou

section (Fig. 7) show constant values within one per mil

between -6.4 and -5.7%. Below the formation boundary,

the isotope composition shows higher values up to -3.1%and a much lower value of -7.6% across the boundary.

The Shangyoushashan/Shizigou Formation boundary is

characterized by decreasing values from -7.3 to -8.6% in

the Youshashan area, directly opposed to the carbon trend.

While one Quaternary sample from Qigequan yields a

value of -4.3%, the samples from Dafeng Shan yield

extremely high d18O values of up to +8.6% for matrix

material. This represents the most positive d18O value ever

measured on carbonates. This value and further measure-

ments of Quaternary material are reported and discussed in

Bojar et al. (2005b).

Discussion and conclusions

The carbon isotopic signature of lacustrine deposits is

mainly influenced by the following factors: (1) photosyn-

thesis and respiration within lake water. Planctonic biota

preferentially builds in the light 12C isotope, and therefore

the d13C of dissolved inorganic carbon (DIC) are shifted

toward more positive values; (2) CO2 exchange between

atmosphere and water; (3) isotopic composition of water

feeding the lake and type of vegetation surrounding the

lake; (4) CO2 released during oxidation of organic matter,

including, for example oxidation of methane. The Qaidam

Basin contains both oil and huge gas reservoirs (e.g., Wang

and Coward 1990). From gas reservoirs, methane is leaking

to the surface and partially oxidized. The resulting CO2

could drive the DIC toward more depleted carbon isotopic

compositions. However, in this study the carbon isotopic

compositions do not show unusually negative values, so

gas leakage is unlikely.

The oxygen isotopic signature of lacustrine carbonates is

dependent on water temperature and isotopic composition

of lake water, mainly controlled by the isotopic composi-

tion of precipitation, inflow waters and the rate of

evaporation. Several factors influence the oxygen isotopic

composition of precipitation: local temperature, seasonali-

ty, elevation, latitude and source of moisture. In areas

unaffected by the summer monsoon, d18O of precipitation

exhibits a strong relationship with air temperature (Johnson

and Ingram 2004). This is also shown in a study with

monthly resolution (Tian et al. 2003) where northern

Tibetan sites with continental moisture sources show

typical seasonal d18O variations, that is, heavier d18O

values during the warm summer months.

Diagenesis may affect the isotope composition of

lacustrine carbonates. The carbon isotopic composition is

less sensitive to diagenesis because meteoric fluids,

involved during diagenesis, generally have low carbon

contents. For example, most limestone samples have

proved conservation of their primary carbon isotopic

composition even during the dolomitization process

(Talbot 1994). Diagenetic dolomitization or synsedimen-

tary dolomitization cannot be excluded in a shallow-water

and evaporitic setting as the Qaidam lake. Primary

lacustrine dolomite is known from a variety of almost

exclusively saline or hypersaline lakes (Last 1990).

Potential existence of primary lacustrine dolomite in the

Qaidam Basin is supported by the composition of mud-

stones from the upper Xiaganchaigou Formation, which

yielded relatively high Mg contents (Rieser et al. 2005).

In order to determine the extent of diagenetic overprint,

we performed cathodoluminescence studies on a number

of samples. Cathodoluminescence analysis did not show

any significant differences in matrix composition or

Table 1 continued


%(VPDB)

d18O

%(VPDB)

d18O

%(SMOW)


Southern side of Youshashan (5)

QA-289A-03 Shizigou -1.10 -8.60 22.05

QA-294A-03 Shizigou -2.38 -8.39 22.26

QA-293A-03 Shizigou -2.69 -7.56 23.11

QA-290B-03 Shangyoushashan -3.78 -7.33 23.35

Various single samples

QA-141C-01b (6) Qigequan -1.50 8.70 39.88

QA-141C-01b Qigequan -1.63 8.68 39.86

QA-97A-01b (7) Qigequan 2.39 -4.14 26.64

QA-97A-01b Qigequan 2.24 -4.41 26.37

QA-295B-03 (8) Shizigou 0.72 -4.74 26.03

QA-155A-02 (10) Shangyoushashan -4.14 -9.14 21.49

QA-153A-02 (10) Xiayoushashan -2.35 -8.25 22.41

QA-162A-02b

(11)

Xiayoushashan 0.14 0.00 30.91

QA-162A-02b Xiayoushashan 0.24 0.07 30.98

QA-130A-01 (12) Xiaganchaigou -4.28 -5.62 25.12

QA-130D-01 (12) Xiaganchaigou -3.62 -6.23 24.49

a Numbers in brackets indicate locality on Fig. 3

* Two measurements of different portions of the same sample


123

multiple cement generations, the presence of secondary

sparite being only sporadic. Some samples revealed fossil

remains, completely recrystallized and filled with coarse

sparitic calcite within fine micrite. As the content of

biogenic shells is only a few percent, changes during

recrystallization will not significantly affect the bulk

composition of the rock. For the investigated carbonates,

diagenesis and reduction of the porosity took part soon

after deposition. The fluids involved during these pro-

cesses did not induce significant recrystallization or

dissolution of the primary carbonates.

High values for the isotopic composition of carbon and

oxygen are conventionally attributed to arid regions with

closed lakes (e.g., Talbot 1994). Evaporative drawdown of

lake volume drives the oxygen isotopic composition of lake

water to 18O enrichment. Concomitantly, the long resi-

dence time of waters favors equilibration between stable

isotope composition of DIC and atmospheric CO2, result-

ing in 13C-enriched carbonate minerals. For the Qaidam

Basin, such enrichment in 13C and 18O isotopes is recorded

in Quaternary samples (Bojar et al. 2005b). Figures 8 and 9

show the individual values for each formation.

Fig. 6 a Stable isotope data for

the Hongsanhan area. Stable

isotope results for the

Hongsanhan Third Valley are

shown together with a recent

magnetostratigraphy proposed

by Sun et al. (2005) and a

simplified stratigraphic column

(Ma, pers. comm. 2003). b The

lower part shows the data from

the Fifth Valley, which is

believed to represent a

downward continuation of the

Third Valley section, but with a

small missing interval


123

It is not possible to exactly correlate the sections from

the Third and Fifth Valley in the Hongsanhan area (Fig. 6).

As described above, the carbonate lithology in the two

sections is very different, which could be explained by a

difference in the depositional milieu, with an anoxic local

depression in the Fifth Valley region. A salinity gradient

Fig. 7 Stable isotope data for the Ganchaigou section. Stable isotope results are shown together with a magnetostratigraphy and a simplified

stratigraphic column, both based on Yang et al. (1992)

Fig. 8 Integrative stable isotope curves from the Qaidam Basin

together with global oxygen curves (Zachos et al. 2001; Lear et al.

2000). Chronology in the Xiaganchaigou and Lower

Shangganchaigou Formation is based on magnetostratigrapy (Sun

et al. 2005). Dotted lines connect samples that have been sampled in

sequence


123

could also cause the differences (Zhang et al. 2003). We

sampled the southern limb of the anticline in the Third

Valley and the northern limb in the Fifth Valley, which

represents a ‘‘downward’’ extension of the Third Valley

section (Fig. 6) with a probable, but small hiatus. This

downward extension further underlines the trend towards

heavier carbon composition in the Xiaganchaigou Forma-

tion. Within the Hongsanhan Fifth Valley section, one

small negative isotopic excursion occurs where oxygen

values drop to -7.5% due to, for example cooler condi-

tions. A positive excursion is observed for both carbon and

oxygen isotopes to -1.4 and -3.9%, respectively. As we

have no further age constraint for this event or a compar-

ative section within the Qaidam Basin, further

interpretation of these data remains open. In the Hong-

sanhan section that is characterized by synchronous

positive d13C and d18O peaks, a cyclic pattern of 1–3 Ma

duration can be distinguished. The exact length of these

and probably much shorter cycles are difficult to estimate

because of incomplete records and the availability of car-

bonate occurrences. These excursions may be related to

arid to semi-arid conditions, which are also supported by

the presence of anhydrite matrix in sandstones of the

Eocene Xiaganchaigou Formation (Rieser et al. 2005). The

general dry phase was interrupted by short events of

increased precipitation, either directly in the basin or in the

adjacent mountains, indicated by repeated thin layers of

coarse sands within the carbonates. The Interfingering of

these various deposits shows that the lake in the Qaidam

Basin was not in a steady state but had a diversified history

with many shrinking and growing phases.

For both the sections, the Hongsanhan and the Gan-

chaigou, the oxygen compositions show variable but

progressively decreasing values from Eocene to Early

Oligocene, that is, from the Xiaganchaigou to Shang-

ganchaigou Formation (Fig. 8). As there were no major

changes in the sedimentological record for this period, we

conclude that rather environmental changes were respon-

sible for the observed shift. We interpret the stable isotopic

composition trend to indicate cooler and/or wetter condi-

tions, both factors causing lowering of the oxygen isotopic

composition of carbonates. During Eocene to Oligocene,

beside the global cooling trend (Lear et al. 2000; Zachos

et al. 2001) the basin was characterized by northward drift

(Wang et al. 1999). Therefore, the decreasing values of the

oxygen isotopic composition are presumably related to

cooling associated to these trends. Continental carbonates,

in contrast to the marine ones, show generally lower iso-

topic values as temperature decreases (Hays and Grossman

1991).

As the Eocene carbonates have a higher organic con-

tent than the Oligocene carbonates, the shift towards

higher isotopic composition observed for this interval

cannot be related to increasing productivity. The sedi-

mentary facies show increasing terrigenous input from the

Xiaganchaigou to the Shangganchaigou Formation, which

is also indicated by the change from limestone- to marl-

dominated lithology (Fig. 5). A better explanation for the

observed trend, with higher d13C within the Oligocene,

would be an increasing proportion of the dissolved inor-

ganic carbon transported by the inflow waters or

increasing aridity in the surroundings of the lake and thus

a decreased contribution of the soil derived CO2 (Leng

and Marshall 2004; Bade et al. 2004).

Table 2 Stable isotope results from microsampling of hand speci-

mens from the northwestern Qaidam Basin

Sample # Formation d13C %(PDB)

d18O %(PDB)

d18O %(SMOW)

Hongsanhan Third Valley (1)a

QA-186L-02 Shangganchaigou -3.1 -7.36 23.32

-2.5 -7.03 23.66


-0.66 -1.13 29.75

-1.17 -0.32 30.58


-3.94 -5.73 25.00

-3.78 -6.28 24.44

-3.74 -5.83 24.90

Ganchaigou (3)


-3.64 -2.84 27.98

-4.89 -3.11 27.70

a Numbers in brackets indicate locality on Fig. 3

-8

-7

-6

-5

-4

-3

-2

1

2

-9 -8 -7 -6 -5 -4 -3 -2 -1 1 2 3 4 5 6 7 8 9

QigequanShizigouShangyoushashanXiayoushashanShangganchaigouXiaganchaigou

-1

add. Qigequan

δ18O (‰ PDB)

δ13C

(‰ P

DB)

Fig. 9 Cross-plot of stable isotope whole-rock composition of

lacustrine carbonates from the Qaidam Basin


123

For the Ganchaigou section (Figs. 7, 8), at the upper

formation boundary, the big step over almost 3% to even 5

% in d13C indicates a distinct change in environment

coinciding with the pronounced onset of Himalayan uplift

(Harrison et al. 1992). As the Himalayas have acted as a

barrier for the precipitation since the latest Oligocene (Sun

and Wang 2005), this trend may be interpreted as a shift

towards more arid conditions. However, this step is much

more obvious in the d13C than in d18O record. There are no

additional data about variation in the level of productivity.

Therefore, further investigations are necessary in order to

determine whether the observed positive trend in the

isotopic composition of carbonates was also driven by

variations in lake-productivity.

It can be seen in the summary graph (Fig. 8) that the

values in the Xiaganchaigou Formation show the same

range of variation in all sampled sections. The strongest

uplift of Himalayas, Tibet was associated with a climate

change (An et al. 2001), reflected in extremely variable

d13C values starting with a positive excursion followed by

a negative one at ca. 24 Ma. The Oligocene and Miocene

show similar d18O values, beside several events charac-

terized by more enriched isotopic compositions. Uplift of

the Altyn Mountains at around 16 Ma resulted in topo-

graphic separation of the Qaidam and Tarim basins. Both

carbon and oxygen isotopic compositions show a shift

toward more positive values at ca. 18–16 Ma ago, a shift,

which may be related to this uplift phase. This shift is

limited to one carbonate sample and further sedimento-

logical investigations would be needed for a reliable

interpretation. Further uplift leads to several changes in the

lake-level (Lehmkuhl and Haselein 2000) and finally to a

shrinking of the lake-area (Huang and Shao 1993).

Between 15 and 10 Ma the lake reached its maximum

extension (Sun et al. 1999), backed up by negative isotopic

trends for both d13C and d18O. The enhancement of relief

and the pronounced subsidence of the Qaidam Basin lead

to cooler/wetter conditions and catching of melt water from

the mountains. This event is temporally ill defined in stable

isotope analysis because of the scarcity of limestones and

marls during this interval, but seems to be reflected in the

pollen curves (Fig. 10; Wang et al. 1999) by a maximum in

the abundance of Pinus and a minimum in the abundance

of xerophytes at ca. 15 Ma. The associated negative trend

for the carbon isotopic composition may be related to

changing d13C values of DIC of the inflow waters, which

are related to changes in surrounding C3 vegetation

towards species adapted to more humid conditions (Far-

quhar et al. 1988) or to increasing in the soil CO2

production. It is towards the end of the Miocene that the

increasing abundance of xerophytes indicates a highly arid

episode following the maximum subsidence period. The

positive excursion in carbon, from 7 to 5 Ma (Fig. 8) may

be related to the expansion of C4 plants on land (Cerling

et al. 1993). Changing of the flora in the surrounding of the

lake, that is the appearance of C4 plants, changes the car-

bon isotopic composition of soil CO2 and thus the

composition of the DIC of the inflow waters.

Both the d13C and d18O isotopic compositions show a

trend towards dry and warmer climate in more recent time.

In accordance with previous lithological and other envi-

ronmental data (Duan and Hu 2001; Wang et al. 1999), the

isotopic compositions indicate the driest conditions in the

lifetime of the Qaidam Basin for the Quaternary. This may

be correlated with a strong phase of surface uplift in both

Himalaya and northern Tibet, and synchronous folding

induced segmentation of the Qaidam Basin, which already

had started during the Late Pliocene (Song and Wang

1993). The outstanding high d18O values of the Quaternary

samples from Dafeng Shan (Bojar et al. 2005b) represent

generally cold, extreme evaporative conditions and a

closed lake environment. This is supported with other

proxies like, for example the widespread salt-deposits

(Lehmkuhl and Haselein 2000) and crystallization of

celestine.

Acknowledgments We gratefully acknowledge the permission by

Ma Lixiang (Department of Petroleum, China University of Geo-

sciences, Wuhan) to use the lithostratigraphic section of Hongsanhan

Third High Peak Valley. We acknowledge continuous support for

fieldwork in the Qaidam Basin by both NSF of China and Qinghai Oil

Company. Ana-Voica Bojar acknowledges partial financial support by

FWF project P16258-N06. This manuscript has profited from a review

of an earlier version by Frederic Fluteau and consequent review by

two anonymous reviewers.

References

An ZS, Kutzbach JE, Prell WL, Porter SC (2001) Evolution of Asian

monsoons and phased uplift of the Himalaya Tibetan plateau

since late Miocene times. Nature 411:62–66

Bade DB, Carpenter SR, Cole JJ, Hanson PC, Hesslein RH (2004)

Controls of d13C-DIC in lakes: geochemistry, lake metabolism,

and morphometry. Limnol Oceanogr 49/4:1160–1172

Fig. 10 Cenozoic pollen sequence of the Qaidam Basin (redrawn and

adapted from Wang et al. 1999)


123

Bojar A-V, Fritz H, Nicolescu S, Bregar M, Gupta RP (2005a) Timing

and mechanisms of Central Himalayan exhumation: discrimi-

nating between tectonic and erosion processes. Terra Nova

17:427–433

Bojar A-V, Rieser AB, Neubauer F, Bojar H-P, Genser J, Liu Y, Ge X

(2005b) Stable isotopic and mineralogical investigations of an

arid Quaternary lacustrine paleoenvironment, Western Qaidam

basin, China. Geol Q 49/2:173–184

Burbank DW, Blythe AE, Putkonen J, Pratt-Sitaula B, Gabet E, Oskin

M, Barros A, Ojha TP (2003) Decoupling of erosion and

precipitation in the Himalayas. Nature 426:652–655

Cerling TE, Wang Y, Quade J (1993) Expansion of C4 ecosystems as

an indicator of global ecological change in the late Miocene.

Nature 361:344–345

Currie BS, Rowley DB, Tabor NJ (2005) Middle Miocene paleoal-

timetry of southern Tibet: Implications for the role of mantle

thickening and delamination in the Himalayan orogen. Geology

33:181–184

DeCelles PG, Quade J, Kapp P, Fan M, Dettman DL, Ding L (2006)

High and dry in central Tibet during the Late Oligocene. Earth

Planet Sci Lett: doi:10.1016/j.epsl.2006.11.001

Dettman DL, Fang X, Garzione CN, Li J (2003) Uplift-driven climate

change at 12 Ma: a long d18O record from the NE margin of the

Tibetan plateau. Earth Planet Sci Lett 214:267–277

Duan Z, Hu W (2001) The accumulation of potash in a continental

basin: the example of the Qarhan Saline Lake, Qaidam Basin,

West China. Eur J Minerol 13:1223–1233

Farquhar GD, Hubick KT, Condon AG, Richards RA (1988) Carbon

isotope fractionation and plant water-use efficiency. In: Rundel

PW, Ehleringer JR, Nagy KA (eds) Stable isotopes in ecological

research. Springer, Heidelberg, pp 21–40

Garzione CN, Dettman DL, Horton BK (2004) Carbonate oxygen

isotope paleoaltimetry: evaluating the effect of diagenesis on

paleoelevation estimates for the Tibetan plateau. Palaeogeogr

Palaeoclimatol Palaeoecol 212:119–140

Gradstein FM, Ogg JG, Smith A et al (2004) A Geologic time scale

2004. Cambridge University Press, Cambridge, pp 610

Graham SA, Chamberlain CP, Yue Y, Ritts BD, Hanson AD, Horton

TW, Waldbauer JR, Poage MA, Feng X (2005) Stable isotope

records of Cenozoic climate and topography, Tibetan Plateau

and Tarim Basin. Am J Sci 305:101–118

Guo ZT, Ruddiman WF, Hao QZ, Wu HB, Qiao YS, Zhu RX, Peng

SZ, Wel JJ, Yuan BY, Liu TS (2002) Onset of Asian

desertification by 22Myr ago inferred from loess deposits in

China. Nature 416:159–163

Hanson AD, Ritts BD, Zinniker D, Moldowan JM, Biffi U (2001)

Upper Oligocene lacustrine source rocks and petroleum systems

of the northern Qaidam basin, northwest China. Am Assoc Pet

Geol Bull 85(4): 601–619

Harrison TM, Copeland P, Kidd WSF, Yin A (1992) Raising Tibet.

Science 255:1663–1670

Hays PD, Grossman EL (1991) Oxygen isotopes in meteoric calcite

cements as indicators of continental paleoclimate. Geology

19:441–444

Huang X, Shao H (1993) Sedimentary characteristics and types of

hydrocarbon source rocks in the Tertiary semiarid to arid lake

basins of northwest China. Palaeogeogr Palaeoclimatol Palaeo-

ecol 103:33–43

Huang Q, Huang H, Ma Y (1997) Geology of Qaidam basin and its

petroleum prediction. Geological Publishing House, Beijing,

158 pp

Johnson KR, Ingram BL (2004) Spatial and temporal variability in the

stable isotope systematics of modern precipitation in China:

implications for paleoclimate reconstructions. Earth Planet Sci

Lett 220:365–377

Kutzbach JE, Ruddiman WF, Prell WL (1997) Possible effects of

Cenozoic uplift and CO2 lowering on global and regional

hydrology. In: Ruddiman WF (ed) Tectonic uplift and climate

change. Plenum Press, new York, pp 150–170

Last WM (1990) Lacustrine dolomite—an overview of modern,

Holocene, and Pleistocene occurrences. Earth Sci Rev 27:221–263

Lear CH, Elderfield H, Wilson PA (2000) Cenozoic deep-sea

temperatures and global ice volumes from Mg/Ca in benthic

foraminiferal calcite. Science 287:269–272

Lehmkuhl F, Haselein F (2000) Quaternary paleoenvironmental

change on the Tibetan Plateau and adjacent areas (Western

China and Western Mongolia). Quat Int 65/66:121–145

Leng MJ, Marshall JD (2004) Palaeoclimate interpretation of stable

isotope data from the lake sediment archives. Quat Sci Rev

23(7–8):811–831

Li T (1996) The process and mechanism of the rise of the Qinghai-

Tibet Plateau. Tectonophysics 260:45–53

Liu Z, Wang Y, Ye C, Li X, Li Q (1998) Magnetostratigraphy and

sedimentologically derived geochronology of the Quaternary

lacustrine deposits of a 3,000 m thick sequence in the central

Qaidam basin, western China. Palaeogeogr Palaeoclimatol

Palaeoecol 140:459–473

Meyer B, Tapponnier P, Bourjot L, Metivier F, Gaudemer Y,

Peltzer G, Shunmin G, Zhitai C (1998) Crustal thickening in

Gansu-Qinghai, lithosperic mantle subduction, and oblique,

strike-slip controlled growth of the Tibet plateau. Geophys

J Int 135:1–47

Qiang XK, Li ZX, Powell CM, Zheng HB (2001) Magnetostrati-

graphic record of the Late Miocene onset of the East Asian

monsoon, and Pliocene uplift of northern Tibet. Earth Planet Sci

Lett 187:83–93

Qiu N (2002) Tectono-thermal evolution of the Qaidam Basin, China:

evidence from Ro and apatite fission track data. Pet Geosci

8:279–285

Quade J, Cater JML, Ojha TP, Adam J, Harrison M (1995) Late

Miocene environmental change in Nepal and the northern Indian

subcontinent: stable isotope evidence from paleosols. Geol Soc

Am Bull 107:1381–1397

Ramstein G, Fluteau F, Besse J, Joussaume S (1997) Effect on

orogeny, plate motion and land-sea distribution on Eurasian

climate change over the past 30 million years. Nature 386:788–

795

Raymo ME, Ruddiman WF (1992) Tectonic forcing of late Cenozoic

climate. Nature 359:117–122

Rieser AB, Neubauer F, Liu Y, Ge X (2005) Sandstone provenance of

north-western sectors of the intracontinental Cenozoic Qaidam

Basin, western China: tectonic vs. climatic control. Sed Geol

177:1–18, doi:10.1016/j.sedgeo.2005.01.012

Rowley DB, Currie BS (2006) Palaeo-altimetry of the late Eocene to

Miocene Lunpola basin, central Tibet. Nature 439:677–681

Searle M (1995) The rise and fall of Tibet. Nature 374:17–18

Song T, Wang X (1993) Structural styles and stratigraphic patterns of

syndepositional faults in a contradictional setting: Examples

from Qaidam Basin, NW China. Am Assoc Pet Geol Bull

77:102–117

Spicer RA, Harris NBW, Widdowson M, Herman AB, Guo S, Valdes

PJ, Wolfe JA, Kelley S (2003) Constant elevation of southern

Tibet over the past 15 million years. Nature 421:622–624

Sun X, Wang P (2005) How old is the Asian monsoon system?—

Palaeobotanical records from China. Palaeogeogr Palaeoclimatol

Palaeoecol 222:181–222

Sun Z, Feng X, Li D, Yang F, Qu Y, Wang H (1999) Cenozoic

Ostracoda and palaeoenvironments of the northeastern Tarim

Basin, western China. Palaeogeogr Palaeoclimatol Palaeoecol

148:37–50


123

http://dx.doi.org/doi:10.1016/j.epsl.2006.11.001

http://dx.doi.org/10.1016/j.sedgeo.2005.01.012

Sun Z, Yang Z, Pei J, Ge X, Wang X, Yang T, Li W, Yuan S (2005)

Magnetostratigraphy of Paleogene sediments from northern

Qaidam Basin, China: implications for tectonic uplift and block

rotation in northern Tibetan plateau. Earth Planet Sci Lett

237:635–646

Talbot MR (1994) Paleohydrology of the late Miocene Ridge basin

lake, California. Geol Soc Am Bull 106:1121–1129

Tapponnier P, Ryerson FJ, Van der Woerd J, Meriaux A-S, Lasserre

C (2001) Long-term slip rates and characteristic slip: keys to

active fault behaviour and earthquake hazard. C R Acad Sci Paris

II A 333(9):483–494

Tian L, Yao T, Schuster PF, White JWC, Ichiyanagi K, Pendall E, Pu

J, Yu W (2003) Oxygen-18 concentrations in recent precipitation

and ice cores on the Tibetan Plateau. J Geophys Res 108:4293,

doi:10.1029/2002JD002173

Wang Q, Coward MP (1990) The Chaidam basin (NW China):

formation and hydrocarbon potential. J Pet Geol 13:93–112

Wang J, Wang JY, Liu ZC, Li JQ, Xi P (1999) Cenozoic

environmental evolution of the Qaidam Basin and its

implications for the uplift of the Tibetan Plateau and the drying

of central Asia. Palaeogeogr Palaeoclimatol Palaeoecol 152:37–

47

Xia W, Zhang N, Yuan X, Fan L, Zhang B (2001) Cenozoic Qaidam

basin, China: A stronger tectonic inversed, extensional rifted

basin. Am Assoc Petrol Geol Bull 85:715–736

Yang F, Ma Z, Xu T, Ye S (1992) A Tertiary paleomagnetic

stratigraphic profile in Qaidam Basin. Acta Petrolei Sinica

13:97–101

Zachos J, Pagani M, Sloan L, Thomas E, Billups K (2001) Trends,

Rhythms, and Aberrations in Global Climate 65 Ma to Present.

Science 292:686–693

Zhang X, Hu Y, Ma L, Meng Z, Duan Y, Zhou S, Peng D (2003)

Carbon isotope characteristics, origin and distribution of the

natural gases from the Tertiary salty lacustrine facies in the west

depression region in the Qaidam Basin. Sci China (Ser D)

46:694–707

Zheng HB, Powell CM, An Z, Zhou J, Dong G (2000) Pliocene uplift

of the northern Tibetan Plateau. Geology 28:715–718


123

http://dx.doi.org/10.1029/2002JD002173

monitoring cenozoic climate evolution of northeastern tibet: stable isotope constraints from the...

Documents