Origin and Character 

of Loesslike Silt in the 

Southern Qinghai-Xizang 

(Tibet) Plateau, China

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1549
Cover. View south-southeast across Lhasa He (Lhasa River) flood plain from roof of Potala Palace, Lhasa, Xizang Autonomous Region, China. The Potala (see frontispiece), characteristic symbol of Tibet, nses 308 m above the valley floor on a bedrock hill and provides an excellent view 

of Mt. Guokalariju, 5,603 m elevation, and adjacent mountains 15 km to the southeast These 

mountains of flysch-like Triassic clastic and volcanic rocks and some Mesozoic granite characterize the southernmost part of Northern Xizang Structural Region (Gangdese-Nyainqentanglha Tectonic Zone), which lies just north of the Yarlung Zangbo east-west tectonic suture 50 km to the 

south (see figs. 2, 3). Mountains are part of the Gangdese Island Arc at south margin of Lhasa 

continental block. Light-tan areas on flanks of mountains adjacent to almost vegetation-free flood 

plain are modern and ancient climbing sand dunes that exhibit evidence of strong winds. From 

flood plain of Lhasa He, and from flood plain of much larger Yarlung Zangbo to the south (see 

figs. 2, 3, 13), large dust storms and sand storms originate today and are common in capitol city 

of Lhasa. Blowing silt from larger braided flood plains in Pleistocene time was source of much 

loesslike silt described in this report. Photograph PK 23,763 by Troy L. P6w6, June 4, 1980.
ORIGIN AND CHARACTER OF LOESSLIKE SILT IN THE SOUTHERN

QINGHAI-XIZANG (TIBET) PLATEAU, CHINA
Frontispiece. On a 130-meter-high bedrock hill of Mesozoic limestone and schist, the splendid 13-story Potala Palace rises 308 meters 

above flood plain of the Lhasa He (Lhasa River) in Lhasa, capitol 

city of Xizang Autonomous Region, China. Construction of this 

well-known symbol of Tibet started in the 7th century, and most 

work took place under the direction of the fifth Dalai Lama from 

1645 to 1693. The Potala served as home for the fifth and later Dalai

Lamas and about 1,000 monks. The striking 1,000-room structure 

today is a state historical museum with about 35 caretaker monks. 

Roof provides a spectacular view of terrain of the southern QinghaiXizang (Tibet) Plateau (cover photograph). North Mountain, in the 

distance, consists of coarse-grained biotite granite of the Gangdese 

batholith of late Cretaceous and Palaeogene age; view to northwest. 

Photograph PK 23,739 by Troy L. Pewe, June 3, 1980.
Origin and Character 

of Loesslike Silt in the 

Southern Qinghai-Xizang 

(Tibet) Plateau, China

By T.L. Pewe, Liu Tungsheng, Roger M. Slatt, and Li Bingyuan

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1549

Retransported, tan, loesslike silt is widespread in the southern 

Qinghai-Xizang (Tibet) Plateau. On low hilltops the silt is 

primary loess. On the lower slopes and in valley bottoms of the 

major river valleys, however, it is poorly to well-stratified 

retransported loesslike silt. The silt probably was originally 

deposited by winds blowing across broad vegetation-free flood 

plains.

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

For sale by

U.S. Geological Survey, Information Services

Box 25286, Federal Center

Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does 

not imply endorsement by the U.S. Government.

Text and illustrations edited by Mary Lou Callas

Line drawings by Susan M. Selkirk unless otherwise noted

Other graphics production by Susan M. Mayfield

Layout by Linnea Larsen

Library of Congress Cataloging-in-Publication Data

Origin and character of loesslike silt in the southern Qinghai-Xizang (Tibet) Plateau, China / by Troy L. Pewe ... [et al.].

p. cm. — (U.S. Geological Survey professional paper ; 1549) 

Includes bibliographical references.

1. Loess—China—Tibet, Plateau of. I. Pewe, Troy Lewis, 1918-. II. Series. 

QE579.075 1995 

552'.5—dc20

94-26508 

CIP
CONTENTS

Abstract........................................................................................................................ 1

Introduction................................................................................................................. 2

Acknowledgments....................................................................................................... 4

Physical setting............................................................................................................ 5

Physiography and general geology..................................................................... 5

Climate............................................................................................................... 8

Permafrost.......................................................................................................... 11

Geomorphology................................................................................................. 12

Loesslike silt deposits ................................................................................................. 15

Distribution and thickness.................................................................................. 15

Color and texture................................................................................................ 19

Mineral composition.......................................................................................... 24

Field relations..................................................................................................... 32

Fossils in loesslike silt................................................................................................ 32

Pollen................................................................................................................. 36

Methodology............................................................................................ 36

Results...................................................................................................... 36

Gastropods......................................................................................................... 37

Vertebrates.......................................................................................................... 39

Origin of loesslike silt................................................................................................. 39

Weathering hypothesis....................................................................................... 40

Lacustrine hypothesis......................................................................................... 40

Eolian hypothesis............................................................................................... 41

Field relations........................................................................................... 41

Topographic distribution ................................................................ 41

Independent lithologic character.................................................... 41

Absence of distinct stratification.................................................... 41

Color and texture............................................................................ 41

Association with other evidence of wind action............................ 41

Fossils of air-breathing animals..................................................... 43

Mechanical composition.......................................................................... 43

Petrographic character.............................................................................. 43

Summary............................................................................................................ 43

Retransported loess..................................................................................................... 43

Age and correlation of silt deposits............................................................................ 45

Summary...................................................................................................................... 46

References cited.......................................................................................................... 51

FRONTISPIECE

Frontispiece. Potala Palace and bedrock hills in Lhasa, Xizang Autonomous Region, China

FIGURES

1. Map showing distribution of loess in China and location of Qinghai-Xizang (Tibet) Plateau
VI CONTENTS

2. Landform and index maps of western China....................................................................................................... 6

3. Index map of south-central Qinghai-Xizang (Tibet) Plateau............................................................................... 8

4. Photograph of steam rising from wells in post-middle Pleistocene Yangbajain thermal field, 90 km

northwest of Lhasa................................................................................................................................................ 9

5. Map showing distribution of existing glaciers and snow-line elevations in China............................................. 10

6. Generalized precipitation and vegetation map of Xizang Autonomous Region................................................. 11

7-9. Climatic data for:

7. Lhasa (1951-1980) ........................................................................................................................... 12

8. Xigaze (1955-1980)...........................................................................................................TM 12

9. Tingri (1970-1980)..................................................................................................................................... 13

10. Map showing distribution of permafrost and seasonally frozen ground in China.............................................. 14

11-20. Photographs showing:

11. Eroded remnant of frost blister exposing part of an ice core.................................................................... 14

12. Broad flood plain of a north-flowing tributary of the Yarlung Zangbo about 40 km west of Xigaze...... 15

13. Broad flood plain of Yarlung Zangbo about 15 km downstream from Xigaze......................................... 16

14. View southeast (upstream) of west side of Nyang Qu valley.................................................................... 16

15. Active sand dunes on flood plain of Nyang Qu about 7 km southeast of Xigaze.................................... 17

16. Climbing sand dunes on lower flanks of hills along braided Lhasa He.................................................... 18

17. Sharply dissected fans of retransported loess at base of low west-facing mountains east of Tingri,

Xizang Autonomous Region....................................................................................................................... 19

18. Large dissected fan of retransported loess below site of Tibetan monastery and Xigar-Zhong

at Tingri, south-central Xizang Autonomous Region, 1980 and 1922 ...................................................... 20

19. Newly made bricks of loess and loess-brick walls 45 km southeast of Xigaze........................................ 21

20. Remnants of loess-brick walls of 13th century monastery about 10 km west of Xigaze......................... 23

21. Diagrammatic sketch of typical dissected loesslike silt with lenses and layers of fluvial sand and

gravel in valley bottoms....................................................................................................................................... 23

22-24. Photographs of:

22. Loess overlying bedrock on knob 15 m above Nyang Qu at Xigaze........................................................ 24

23. Deep, sharp-walled gully dissected into retransported loess fan at base of limestone knob east

of Xigaze..................................................................................................................................................... 26

24. Alluvial fan of retransported loess sharply dissected by steep-walled gullies east of Xigaze.................. 28

25. Physiographic diagram of Xigaze area at junction of Nyang Qu and Yarlung Zangbo...................................... 29

26. Photograph of flat-topped, steep-walled remnant of bedded, vertically jointed retransported loess in

Nyang Qu valley north of Xigaze........................................................................................................................ 29

27. Sketch map of flood plain and stratigraphic sections of retransported sandy loess on terrace on south side

of Xigaze........................................................................................................................................................" 30

28. Photograph of cliff-forming retransported tan loess exposed in road cut on south side of Xigaze .................. 31

29. Triangular diagram showing proportions of sand, silt, and clay in sediment samples from south-central

Qinghai-Xizang (Tibet) Plateau and a loess sample from Germany................................................................... 32

30-33. Graphs showing cumulative-frequency grain-size curves for:

30. Retransported loesslike silt in southern part of Qinghai-Xizang (Tibet) Plateau...................................... 33

31. Loess flanking or on top of bedrock knobs near Yarlung Zangbo and loesslike silt from Xizang

Autonomous Region ................................................................................................................................... 33

32. Clay-rich retransported loess, south-central Qinghai-Xizang (Tibet) Plateau........................................... 34

33. Eolian and fluvial sand, south-central Qinghai-Xizang (Tibet) Plateau .................................................... 34

34. Generalized geologic map of valley of Yarlung Zangbo and vicinity and weighted peak-percentage diagrams

of clay minerals and major minerals.................................................................................................................... 35

35. X-ray diffractograms of samples of loess and underlying volcaniclastic sandstone and lithic tuff................... 36

36. Diagram showing pollen composition of sediment samples from stratigraphic section on scarp of terrace of

Nyang Qu.............................................................................................................................................................. 37

37. Photograph of collecting fossils in loesslike silt at river-terrace exposure on south side of Xigaze................. 38

38. Photograph of fresh-water gastropods Radix auricularia (L.) from loesslike silt south of Xigaze................... 39
CONTENTS VH

39. Cumulative-frequency grain-size curves for loess and retransported silt from near Xigaze and for volcanic

ash and modern wind-blown dust from other parts of the world........................................................................ 44

40. Cumulative-frequency grain-size curves for loess and retransported silt from near Xigaze, from Beijing,

and from other parts of the world ........................................................................................................................ 45

41. Photograph of ruins of ancient city of Jiaohe near Turpan, Xinjiang Uygur Autonomous Region ................... 46

42. Block diagram showing retransported loess in valley beside ruins of Jiaohe..................................................... 47

43. Photograph of narrow steep-walled valley entrenched in retransported loess on west side of Jiaohe............... 48

44. Low oblique aerial photograph of mesa-like remnants of retransported loess at ruins of Jiaohe

near Turpan........................................................................................................................................................... 49

45. Cumulative-frequency grain-size curves for loess and retransported loess from Kuqa (Kucha), Jiaohe, and

Nilka, south and north flanks of Tian Shan, and from Xigaze area.................................................................... 50

46. Schematic block diagram of loess and retransported loess north of Nilka, in Hi He valley on north slope

of Tian Shan.......................................................................................................................................................... 50

TABLES

1. Data on Quaternary sediment samples collected in southern Qinghai-Xizang (Tibet) Plateau.............................. 22

2. Mechanical properties of sand and loesslike silt from southern Qinghai-Xizang (Tibet) Plateau.......................... 25

3. Percentage of sand, silt, and clay in sand and loesslike silt, southern Qinghai-Xizang (Tibet) Plateau ................ 27

4. Mineral compositions of >0.062-mm fraction of sand and loesslike silt, southern Qinghai-Xizang (Tibet)

Plateau ......................................................................... 27

5. Mineral composition of bulk samples of sand and loesslike silt, southern Qinghai-Xizang (Tibet) Plateau......... 28

6. Mineral composition by weighted peak-area percentages of <0.005-mm fraction of sand and loesslike silt,

southern Qinghai-Xizang (Tibet) Plateau................................................................................................................. 28

Origin and Character of Loesslike Silt in the 

Southern Qinghai-Xizang (Tibet) Plateau, China

By Troy L. Pewe, 1 Liu Tungsheng,2 Roger M. Slatt,3 and Li Bingyuan4

ABSTRACT

Tan loesslike silt of probable late Quaternary age is 

widespread in the southern Qinghai-Xizang (Tibet) Plateau of southwest China. Most of the silt has been retransported and occurs mainly in the lowlands and lower 

slopes; it is absent from steep slopes and active flood 

plains. This loesslike silt covers most alluvial fans and is 

interbedded with the sand and gravel of the fans. It is well 

exposed in the agricultural fields on low terraces in the 

valleys and in the steep-walled scarps of dissected valley 

fill. On low hilltops the silt is primary loess, probably deposited by winds that picked it up from broad vegetationfree flood plains and perhaps from dry lake basins to the 

north. In the lowlands, most of it is retransported loess 

that has been carried downslope and redeposited by water.

The primary loess is as thick as 6 m on hilltops or 

high flanks of hills and as thick as 10 to 15 m on the 

lower slopes. The thickest deposits are near the rivers in 

valley bottoms, where they develop vertical cliffs as high 

as 15 m.

The texture and mineral composition of the primary 

loess is relatively uniform; however, the retransported 

loess varies widely in texture. The silt is clay rich to sand 

rich, and some is even gravel rich, depending on how near 

the original loess source was, on the distance of retransportation, and on the amount of mixing with other sediments by fluvial action. The silt is massive, and erosion

1 Present address: Arizona State University, Box 871404, Tempe, 

AZ 85287-1404, U.S.A.

2 Institute of Geology, Academia Sinica, P.O. Box 634, Beijing, 

100029, People's Republic of China.

3 Colorado School of Mines, Golden, CO 80401, U.S.A.

4 Institute of Geography, Academia Sinica, P.O. Box 771, Beijing, 

100101, People's Republic of China.

5 The term for the Tibet Plateau that is approved by the U.S. Board 

on Geographic Names is "Qing Zang Gaoyuan". However, the term 

"Qinghai-Xizang (Tibet) Plateau" is most widely used in international 

scientific English-language publications and is used in this report.

Manuscript approved for publication May 18, 1994.

forms vertical cliffs and deep gullies. It has little or no 

stratification or jointing, except where it has been retransported to lower slopes and valley bottoms where it is well 

to poorly stratified.

The few fossils that have been found in the loesslike 

silt on the plateau include Quaternary pollen, ostracodes, 

gastropods, and vertebrate teeth and bones. They reflect a 

dry cold area with a few ponds or marshes.

Through the years, the origin of the loesslike silt on 

the plateau has been ascribed to in situ weathering of residual country rock as well as to lacustrine, fluvial, or eolian processes. The weathering or residual hypothesis has 

little support. The lacustrine hypothesis, either separately 

or in conjunction with fluvial processes, has been considered since the late 1970's and the 1980's. The eolian process was first proposed in the 1980's.

Since the early 1930's the loesslike silt has been described as a residual deposit formed by the breakdown by 

freezing and thawing of the underlying rocks. However, 

the silt bears no chemical, mineralogical, or textural relation to the underlying strata, and it is too thick to represent 

only a breakdown of rocks in place.

The most common explanation in the literature for 

the origin of these thick deposits of loesslike sediments, 

especially in valley bottoms, is by lacustrine processes. 

This origin is unlikely, however, because no shorelines, 

wave-cut beaches, deltas, mud cracks, or ripple marks have 

been found in the silt deposits. Neither lacustrine stratification nor an appreciable amount of clay exists in the silt. 

Moreover, the deposits have no definite upper boundary, as 

would be expected if they were lacustrine in origin.

The mantle of uniform loesslike silt on top of the 

bedrock hills is here considered to be primary loess, windblown and derived from the braided streams and broad 

plains, because (1) it occurs as a surficial mantle; (2) it is 

lithologically independent of the underlying material; (3) 

the fine silt is stratified indistinctly or not at all, except in 

retransported materials; (4) it is associated with sand 

dunes in a broad wind-blown area; (5) it contains fossils 

of land animals; (6) its sorting and texture on hilltops is 

similar to that of loess and windblown dust in many other

1
LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

places in the world; and (7) its grains are angular and relatively unweathered. The thick mantle of poorly to wellstratified loesslike silt on the lower slopes and along the 

bottoms of major river valleys, however, is retransported 

loess. It has been transported from a few meters to hundreds if not thousands of meters down slopes, primarily by 

processes involving water; consequently, it has become interlay ered with sand or with gravel. Almost all of the 

loesslike silt in the southern part of the Qinghai-Xizang 

(Tibet) Plateau is retransported loess.

it *K i

(1)

(2) (3)

(4) (5)

(6)

; (7)

INTRODUCTION

China is well known for some of the most extensive 

accumulations of loess in the world. Loess is one of the 

most extensive Quaternary deposits of the country, covering 

about 1,000,000 km2, or about 10 percent of China. Although most of the loess is in north-central China, it is also 

widespread in the northwestern and northeastern parts of the 

country (fig. 1). The earliest known description of Chinese

loess appears to be more than 2,300 years old (Liu and 

others, 1964, p. 10); the earliest known record of the ubiquitous dust storms from the deserts was a so-called "dust 

rain" that occurred in 1150 B.C. and is documented in the 

historical book, Zhu Shu, Ji Nian (Chronicles Recorded on 

Bamboo Slips) (see Liu, 1981). Characteristics of Chinese 

loess and diverse ideas of its origin have been known outside of China since the explorations of Raphael Pumpelly 

(1867, 1879), Baron Ferdinand Paul Wilhelm freiherrn von 

Richthofen (1877, 1882, 1886), and Bailey Willis, Eliot 

Blackwelder and R.H. Sargent (1907).

However, even on recent maps showing loess distribution in China (Wang and Zhang, 1980; Liu and Yuan, 

1982; Wang and Song, 1983; Liu and Ding, 1984; Liu 

and others, 1985, 1988; Liu, 1981, 1991), no loess is 

shown on the Qinghai-Xizang (Tibet) Plateau on a recent 

map of China (fig. 1). Lack of knowledge of detailed geologic reports of the plateau can be attributed to the geographical and political remoteness of this region, often 

called the "Roof of the World," that is rimmed by even 

higher mountains. This unique environment has an isolated civilization that was relatively unchanged until the 

1951 occupation by Chinese from the east. Since the 

1950's, China has organized seven multidisciplinary integrated surveys to the Qinghai-Xizang (Tibet) Plateau. 

More than 50 disciplines, represented by more than 1,600 

scientists and technicians from Academia Sinica have 

made very informative studies, and 32 volumes of reports 

have already been published. Yet much, if not most, of 

these efforts were unknown outside of China until the 

landmark international symposium on the geological and 

ecological studies of the Qinghai-Xizang (Tibet) Plateau 

was held in China in 1980 (Liu, 1981; Pewe, 1980a, b, 

1981; Reiter and Reiter, 1981; and Sengor, 1981). Academia Sinica arranged this historic symposium that included a field study trip to the Qinghai-Xizang (Tibet) 

Plateau. Of 79 scientists from 18 countries who initially 

met with 240 Chinese scientists in Beijing, 66 participated in a stimulating 2-week trip through the southern part 

of the plateau and traveled 1,000 km to Nepal.

This field trip followed and crossed broad, vegetation-free flood plains and sand dunes on the valley bottoms and low hillsides that are quite striking in the 

southern part of the Qinghai-Xizang (Tibet) Plateau. It 

soon became apparent to Liu and Pewe that the widespread yellowish loesslike sediment was undoubtedly retransported loess because (1) it covers some alluvial fans 

and is interbedded with the sand and gravel of the fans, 

(2) it is well exposed in agricultural fields in the valleys, 

and (3) it forms thick steep-walled terrace scarps in dissected valley fill. Winds probably blew it there originally 

from the sand and silt bars of the broad rivers and perhaps 

from dry lake basins to the north. The geologic guidebook 

of the area (Academia Sinica, 1980) does not mention 

loess but does mention thick lacustrine deposits.
INTRODUCTION

We saw small valleys as wide as 1 km that had 

slowly filled to a thickness of 30 m or more with retransported loess. These valley fills had subsequently been dissected by streams rejuvenated by uplift, probably in 

Holocene time. Slow aggradation and interlayering of retransported loess with some fluvial sand and locally fine 

gravel has created nearly flat surfaces on the old valley 

floors that now stand above valley flood plains as buttes or 

mesas, 15 to 30 m high, with almost vertical walls. These 

landforms are common at Xigaze and also at Turpan, 

1,500 km to the north, for example.

As silt accumulated locally in valley bottoms, remains 

of the extant flora and fauna were incorporated. Sandy primary loess accumulated on low hills next to the rivers and is 

interfingered downslope with coarse sediments. Pewe collected sediment samples and associated fossils in Yangbajain 

Basin north of Lhasa, in the vicinity of Lhasa, and southwestward through major valleys, high passes, and mountain ranges to Gyangze on the middle Nyang Qu and to Xigaze near 

the junction of the Nyang Qu and the Yarlung Zangbo (fig. 3, 

table 1). Detailed collections and observations were made 

near Xigaze. Sediments, topography, and geomorphology

70°E 80°E 90°E 100°E 110°E

•50°N

,70°E

XINJIANG UYGUR

AUTONOMOUS REGION

i^v\\\\\\\\\\\\\\\\\\\\j<\"\\\\x 

QINGHAI-XIZANG

(TIBET) PLATEAU

AUTONOMOUS^ 

REGION

.hasa

50°N'

40°N'

'30°N

30°N

130°E

80°E

EXPLANATION 

Loess

Retransported loess

RSSSJ Qinghai-Xizang 

fc^3 (Tibet) Plateau

•....-•'"' Boundary of Plateau

i'*--'' Boundary of adjacent Province or Region

/

20°N

250 0 500 1000 Km

SCALE

90°E 100°E 110°E 120°E

Figure 1. Distribution of loess in China and location of Qinghai-Xizang (Tibet) Plateau. Loess data from Liu (1981); Liu and 

others (1985). Retransported loess data from Wang and Song (1983), Mu Guijin (oral commun, 1986), and Pe"we (1987). 

From Pewe and others (1987) and reproduced with permission of China Ocean Press.
LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

were studied along the wide Yarlung Zangbo for about 60 km 

downstream from Xigaze and then westward to Lhaze and 

Tingri, where loesslike silt was seen. From Tingri, data were 

collected south to the Nepal-China border. Pewe left the 

group at Zham, exiting to Nepal. Liu and Li collected more 

samples at Xigaze and near Lhasa on their return trip to 

Beijing. For comparison with silt from the Qinghai-Xizang 

(Tibet) Plateau, typical loess deposits were examined and 

sampled by Pewe near Heidelberg, Germany (near the site 

where the term "loess" originated), and were analyzed in the 

same laboratory as samples from the plateau. To more fully 

understand the characteristics and distribution of the widespread retransported loess in China, Pewe also examined and 

collected samples of such deposits at Harbin (fig. 1) in 

northeast China in 1984 and 1986 and in Xinjiang Uygur 

Autonomous Region (fig. 1) from Turpan to Kuqa on the 

south side of the Tian Shan in 1986 (Pewe, 1987) and near 

Uriimqi in 1982. Li also made observations of the loesslike 

silt deposits in the southern part of the Qinghai-Xizang 

(Tibet) Plateau during the summers of 1974 and 1975.

In the summer of 1991, Pewe was a leader on a geologic field study trip of the International Union for Quaternary Research (INQUA) XIII International Congress, 

from Lanzhou across the Qinghai-Xizang (Tibet) Plateau 

through Qinghai Province and then south to Lhasa and to 

Nepal (fig. 1). The first week permitted observation of 

loess 1 to 2 m thick in the valleys of the northern part of 

the plateau. The last 5 days from Lhasa to the Himalayas 

allowed a reexamination of retransported loess along the 

same route of the 1980 geologic trip of Pewe, Liu, and Li.

Detailed examination was made of retransported 

loess by the international group of loess scientists at the 

south side of Xigaze, site of detailed observations and 

sample collections in 1980.

After discussions and collecting of silt and fossils by 

participants, it was the belief of the visiting loess experts 

that the loesslike silt was typical retransported loess.

ACKNOWLEDGMENTS

The authors deeply appreciate the cooperation and 

aid of many persons in several countries who made this 

study possible. Officials of the Academia Sinica Organizing Committee of the Symposium on the Qinghai-Xizang 

(Tibet) Plateau (Liu, 1981) and the government of the Xizang Autonomous Region provided the opportunity for 

Pewe, Liu, and Li to visit the area in 1980 and make the 

study. The U.S. National Academy of Sciences funded part 

of Pewe's 1980 visit to China while he was Chairman of 

the U.S. Organizing Committee of the Fourth International 

Conference on Permafrost. Part of Pewe's participation in 

the study was funded by a travel grant (No. EAR 8013759) 

from the National Science Foundation of the United States 

and a travel grant from Arizona State University.

Granulometric analyses of samples 1 to 10 and all 

mineralogical and chemical analyses were made at Exploration and Production Research of the Cities Service Company, Tulsa, Okla., under the direction of Roger M. Slatt, then 

Stratigraphy Research Manager. Granulometric analyses of 

samples 11 to 17 were made at the Geological Institute of 

the Academia Sinica, Beijing under the supervision of Liu 

Tungsheng. All analyses of loess sample 20 (tables 1-3), 

which was collected in 1973 near Beijing by Roger I.E. 

Brown, were made at the Centre de Geomorphologie, Caen, 

France, under the direction of Andre Journaux.

At the 15-m-high exposure of loesslike silt south of 

Xigaze, the authors were aided in collecting fossils by the 

late Anders Martinsson, University of Uppsala, Sweden, 

by Bruno Messerli, University of Bern, Switzerland, by 

Jack Ives, University of Colorado, U.S.A., and by Chinese 

and Tibetan assistants.

Fossils from the exposure near Xigaze were identified by experts in China and the United States. Li Yuanfang and Huang Cixuan, Geographical Institute, Beijing, 

Academia Sinica, examined the ostracodes and pollen, respectively. Charles E. Schweger, University of Alberta, 

Canada, supplied additional information on the interpretation of the pollen data. A.H. Clarke, Associate Curator of 

the Mollusca, U.S. Smithsonian Institution, Washington, 

D.C., identified the freshwater gastropods; and S.L. Olson, 

Division of Birds, U.S. National Museum of Natural History, Smithsonian Institution, Washington, D.C., identified 

the bird remains. Michael Carleton, Division of Mammals 

of the U.S. National Museum of Natural History identified 

the mammal bones. Radiocarbon analyses of gastropods 

collected by Pewe were made at the Smithsonian Institution Radiation Biology Laboratory, Washington, D.C., then 

under the direction of Dr. Robert Stuckenrath, and radiocarbon analyses of gastropods collected by Martinsson 

were made at the Institute of Physics, University of Uppsala, Sweden, under the direction of Ingred U. Olsson. 

Redford Ju helped translate some of the Chinese literature.

Mu Guijin, geologist with the Xinjiang Institute of 

Geography, Academia Sinica, Uriimqi, Xinjiang Uygur 

Autonomous Region, was especially valuable in researching some of the Chinese literature on the Quaternary geology of the Qinghai-Xizang (Tibet) Plateau, calculating 

statistical parameters of the sediment samples, drafting 

some illustrations, compiling tables 2 and 3, and making 

granulometric analyses of Chinese sediment samples 18 

and 19 while a visiting scholar at Arizona State University, 

1984-85. Hu Chang Kang kindly arranged meetings in 

1986 between Huang Wanpo (of the Institute of Vertebrate 

Paleontology and Paleoanthropology, Academia Sinica) 

and Pewe to discuss and examine the finds of vertebrate 

fossils in southern part of the Qinghai-Xizang (Tibet) Plateau. Wang Shuji (Director, Xinjiang Institute of Geography, Academia Sinica, Uriimqi) led Pewe on a 10-day field 

excursion in 1986 to examine retransported loess, gobi,
PHYSICAL SETTING

and sand dunes in the Turpan Depression, Tarim Basin, 

and Uriimqi area of the Xinjiang Uygur Autonomous 

Region.

The authors appreciate the time given to field discussions of the origin of loess deposits in Xizang Autonomous Region by participants of the 1991 field trip of the 

International Union for Quaternary Research (INQUA) to 

the plateau, especially N.W. Rutter, University of Alberta, 

Canada, and GJ. Kukla, Columbia University, U.S.A.

Special appreciation is extended to Margaret Fegtly 

Nichols, Tempe, Arizona, U.S.A., for aiding in literature 

search about exploration of southern Tibet by Europeans 

in the early part of the 20th Century; and to Susan Mary 

Selkirk, graphic artist, Arizona State University, for preparing most of the graphics in the report.

Helpful suggestions of the following people who reviewed all of the report are greatly appreciated: Mu 

Guijin, of the Xinjiang Institute of Geography, Academia 

Sinica, Uriimqi, China; George Gryc and Oscar J. Ferrians, Jr., of the U.S. Geological Survey; and Richard D. 

Reger of the Alaska Division of Geological and Geophysical Surveys, Fairbanks, Alaska, all of whom observed 

loess in eastern, central, and western (Lanzhou) China in 

1984.

PHYSICAL SETTING 

PHYSIOGRAPHY AND GENERAL GEOLOGY

The Qinghai-Xizang (Tibet) Plateau is a unique 

landform of the Earth, averaging more than 4,000 m in 

elevation and covering an area of 2,400,000 km2, almost 

one-quarter of China's territory. It is bounded by mountains on all sides: the Kunlun Shan on the north; the towering, glacier-clad Himalayas on the south; the Karakorum 

Shan on the west; and the Hengduan Shan on the east 

(fig. 2). Most of the plateau lies in the Xizang Autonomous Region (1,200,000 km2); one-quarter is in the Qinghai Province, and the rest is in adjacent provinces (fig. 1). 

The former political entity of Tibet coincides territorially 

with the present Xizang Autonomous Region, which constitutes part of southwestern People's Republic of China.

Most of the plateau is an arid, almost treeless, windswept landscape at elevations of 3,500 to 7,200 m. The 

complex of mountain ranges, broad valleys, and rocky 

plains is liberally strewn with shrinking lakes (Chen, 1986; 

Chinese Academy of Sciences, 1974, p. 80) of varying degrees of salinity containing as many as 46 kinds of salt 

minerals (Gao and Li, 1981). The area is sparsely occupied 

by Tibetan nomads. The populous cultivated valleys in the 

south and southeast part of the plateau lie below 4,000 m 

elevation. At the lower elevations and in local areas of alluvium and retransported loess, slightly greater precipitation 

permits a limited amount of agriculture.

The Yarlung Zangbo valley in the south (fig. 3), together with its tributary valleys, is the heartland of Xizang 

Autonomous Region. For centuries it was part of the 

major ancient trade routes from Europe, India, China, and 

central Asia. Lhasa, the capitol, formerly was also the residence (frontispiece) of the Dalai Lama, who headed the 

religious civil government of Tibet. Major centers of population, other than Lhasa, are Xigaze and Gyangze southwest of Lhasa (fig. 3).

The southern part of the plateau south of the Gangdese 

Shan (fig. 2) and Nyainqentanglha Shan (fig. 3), includes the 

Yarlung Zangbo, Pum Qu and Nyang Qu systems. Many 

major lakes exist, some without outlets (fig. 2). This part of 

the plateau is bisected from east to west by the Yarlung 

Zangbo valley; (fig. 3), which is dotted with as many as 600 

geothermal fields, such as the one in figure 4.

It has long been believed that the great elevation of 

the Qinghai-Xizang (Tibet) Plateau and the Himalayas is the 

result of shifting continental plates, as the northward-moving Indian plate from the south collides with and slides under 

the Eurasian plate to the north (Argand, 1924; Molnar, 

1989). An ophiolite belt along the Yarlung Zangbo, 3 to 

15 km wide, separates the two plates along this major tectonic suture (Academia Sinica, 1980; Kidd and others, 

1988). To the north the continental crust is about 70 km thick 

in what is termed the Gangdese-Nyainqentanglha Tectonic 

Zone (cover, fig. 3), or Northern Xizang Structural Area 

(Chang and Pan, 1981, fig. 2); to the south the crust is about 

50 km thick in what is called the northern part of the Himalayan Tectonic Zone (fig. 3). Uplift began in early Miocene 

time (Sorkhabi and Stump, 1993), was strongest near the end 

of the Pliocene, and extended into the Pleistocene. For the 

past 100,000 years, the average rate of uplift has been about 

10 mm per year (Liu, 1981, p. xix). Mt. Everest (Qomolangma Feng), the highest mountain in the world (8,848 m), 

straddles the crest of the Himalayas on the southern boundary of the Xizang Autonomous Region (figs. 2, 3).

North of the ophiolite belt, Cretaceous andesites, 

shales, and sandy conglomerates are more than 400 m 

thick. North of these rocks is a large, east-west belt of 

granodiorite and granite; the granite intrudes Triassic and 

Jurassic sandstones, shales and limestones. South of the 

Yarlung Zangbo, a wide belt of Triassic clastic rocks is 

predominantly turbidites. Near Xigaze an extensive eastwest belt of predominantly medial to distal Cretaceous turbidites includes some black shales and limestones. The 

lower Lhasa He flows through a granitic belt of the Northern Xizang Structural Region (cover photograph) that is in 

local contact with Triassic and Jurassic clastic rocks or 

limestones. Small hills rise about 100 m above the valley 

floor near Lhasa, and the magnificent monastery and former 

home of the Dalai Lama, Potala Palace (frontispiece), is 

built on one of Jurassic clastic rocks and limestone.

Mountains on the plateau and rimming it host most 

of the nearly 30,000 glaciers of China (Shi and others,
LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

Figure 2. Landform map (A) and index map (5) of western Index map by S.M. Mayfield. Names on landform map are EngChina showing location of Qinghai-Xizang (Tibet) Plateau and lish equivalents of those in use when map was prepared. Names

features of Xinjiang Uygur Autonomous Region, Xizang Autono- on index map include many used in this report. (U.S. Board on

mous Region, and parts of the Qinghai, Sichuan, and Gansu Geographic Names approved "Qing Zang Gaoyuan" as the name

Provinces. Landform map is part of "Landforms of China," for the Tibet Plateau; however, the term "Qinghai-Xizang (Tibet)

(copyright by Erwin Raisz, 1955, and reprinted with permission Plateau" is most widely used in international scientific Englishof Raisz Landform Maps, P.O. Box 773, Melrose, MA 02176). language publications and is used in this report.)
PHYSICAL SETTING

75° 80° 85 90° 100°

35

30

25
LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

Kunlun

Zone

'"yaa f

to»iczf.,

Hatchured area covered by geologic map (fig. 34 A)

\ 95°

. -s'o Maizhokunggar ~~"~ \Nyingchi J

x>

f. y Mainling / 

** •->

^5. 7-

\

Zham\o,-v

NEPAL

siKKlM

Y A S

BHUTAN

o 

Cona

\ "V

/ INDIA ,---?*

0 60 120 180 Kilometers

Figure 3. Index map of south-central Qinghai-Xizang (Tibet) Sinica, 1980) superposed on an outline map of Xizang AutonPlateau, China. Circled numbers are locations of sediment omous Region, China. Center rectangle is area covered by

samples (see table 1). Rectangle in upper left corner outlines geologic map (fig. 34A) and mineral distribution maps

the four major tectonic zones of the plateau (from Academia (figs. 345, C).

1980; Shi and Li, 1980, 1981; Shi, 1988). About 83 percent of the area covered by modern glaciers in China is in 

this region (fig. 5). Most are small cirque glaciers and 

winding alpine glaciers, although a few are nearly 30 km 

long. The high elevation, topography, and particularly the 

climate of the plateau influence the development and distribution of these glaciers (Kuhle, 1986). Two main types 

of glaciers are present on the plateau: Continental glaciers 

in the cold, dry parts of the plateau, and maritime glaciers 

in the southeastern part of the plateau, where monsoon 

precipitation is high. The snow line ranges from about 

4,400 m in the southeast to more than 6,200 m in the 

western part of the plateau (fig. 5). Snow-line variation is 

mainly due to the rapid decrease of precipitation in the 

higher mountains toward the inner parts of the plateau. 

The west-central part of the plateau receives the highest 

total solar radiation in China. Numerous mass-balance 

studies of glaciers have been made by Chinese scientists 

who found that solar radiation accounts for 80 to 90 percent of the heat sources in the majority of glaciers in the 

arid part of the plateau and decreases to about 60 percent 

in the humid southeastern plateau.

Natural vegetation of the southern part of the plateau 

is that of a montane shrubby steppe or locally an alpine

steppe (Zheng and others, 1981) of the semiarid region. 

Most common species are Sopora moorcroftiana, Trikeraia 

haekeri, Aristida triseta, and Artemisia. Common associates are Astragalus strictus, Poa patens, and Androsace 

graminofolia (Yang and others, 1983; Li and others 1983). 

This region is essentially unforested except for species locally growing near streams. Agriculture has been introduced in the broad valley lowland near the major villages. 

Conditions are suitable for growing barley, wheat, potatoes, peas, turnips, and apples.

CLIMATE

The climate of the Qinghai-Xizang (Tibet) Plateau is 

mainly characterized by strong winds, cold temperatures, 

and aridity, especially in the high western and central parts 

(fig. 6). Except for the southern major valleys (figs. 2, 3), 

the mean annual air temperature is colder than 0°C. On the 

higher plateau, the mean annual air temperature ranges 

from -6 to -10°C (Academia Sinica, 1980). Some of the 

earliest temperature records reported in English from the 

high plateau are from Hedin (1903), who recorded -32.5°C 

in January 1901. Climatic data have been collected since
PHYSICAL SETTING

« -i 53

3 >,»

HI S*S

2 oo -S 45 0\ 3 

-3^-3

« a f

3« « 

"M Pi rt

1

w

1W3 o"

Jscfl

1

p

tx

c/5

"S

mounl

«4-l

O

w

O

a.

_o

Cfl

w(11

«§Vl— 1 "8

_c

a. <u 

Pi

o

oo

ON

in

"s

o

<u

p

o -a ^> •? xi <u PH

2 O O T7 •*—»

— 00

« xi

'C 45
10 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

1957 along a road that runs northward from Lhasa to Qing- In the southern valleys, the mean air temperature durhai Province (Xie, 1982). At Fenghueo Shan Pass (eleva- ing the warmest month ranges from 10 to 16°C; during the 

tion 4,800 m), about 500 km north of Lhasa (fig. 2), for coldest month (January) it is -8°C. Mean annual air temperexample, the mean annual air temperature is -6.6°C (Wang ature ranges from 3 to 8°C. In Lhasa (elevation 3,658 m) the 

and French, 1994). mean annual air temperature is 7.5°C; the average for June

75 100°

EXPLANATION

• «*• Glacier

"~\ —4000— Snowline elevation

*\ in meters above

"I mean sea level

Approximate boundary of 

Peoples Republic of China

500 KILOMETERS

/CONTOUR INTERVAL 200 METERS /

30'

25

Figure 5. Distribution of existing glaciers and snow-line elevations in China (from Shi, 1980).
PHYSICAL SETTING 11

is 15.5°C and for January is -2.2°C (Academia Sinica, 1980, 

p. 5). The frost-free season is 140 days. As one goes west, 

the climate becomes colder and drier. Mean annual air temperatures of Lhasa, Xigaze, and Tingri are 6.3°C, 4.8°C, and 

2.7°C, respectively (figs. 7, 8, 9).

The western part of the plateau is arid, and most of it 

receives little more than 100 mm of precipitation annually 

(fig. 6). The southern valleys are in the semiarid zone (250- 

500 mm precipitation), and the far east is humid. The dry 

season extends from October to May and the wet season 

from June to September. Mean annual precipitation in 

Lhasa, Xigaze, Gyangze, and Tingri is 445, 431, 288, and 

318 mm respectively (Academia Sinica, 1980) (figs. 7, 8,9).

During winter, westerly winds prevail over the plateau, and from October through May there are clear skies 

and strong winds.

PERMAFROST

The Qinghai-Xizang (Tibet) Plateau lies in an area of 

widespread alpine permafrost. Permafrost, or perennially 

frozen ground, is a naturally occurring material that has 

been at a temperature of 0°C or colder continuously for 2 or 

more years. Permafrost is defined on the basis of temperature alone, notwithstanding the type of sediment or rock or 

the ice content. Most permafrost is consolidated by ice.

On the plateau, permafrost extends over an area of 

about 1,500,000 km2 and represents about 70 percent of

all the permafrost in China (fig. 10; Tong, 1981; Cheng, 

1983; Shi, 1988). Permafrost in the plateau exists at elevations higher than 4,100 to 4,200 m in the far north, where 

its minimum elevation rises by about 100 m per 1° latitude (Cheng and Wang, 1982); to the south it starts at 

about 5,200 to 5,400 m elevation on the northern slopes of 

the Himalayas. Tong (1981) estimates that the ground temperature may be as cold as -12°C at 6,000 m elevation in 

the northern part of the plateau and about -7.4°C underlying the north slope of the Himalayas. The temperature of 

permafrost underlying most of the plateau is considerably 

warmer, and much of it is near 0°C near the topographical 

lower limit of permafrost.

Permafrost thickness is estimated to be about 400 m 

at an elevation of 6,000 m and not more than 130 m in the 

valleys or basins at lower elevations. Generally there is no 

permafrost beneath large rivers and lakes on the plateau. Ice 

wedges have not been recorded in the Qinghai-Xizang 

(Tibet) Plateau, and only one or two are known in northeast 

China (Pewe, 1986a, b). However, they may have been 

widespread in the perennially frozen ground of China in late 

Pleistocene time, as indicated by the presence of ice-wedge 

casts (Lanzhou Institute of Glaciology and Cryopedology, 

1983; Sun and Li, 1986; Cheng and Liang, 1987).

A few pingos (large, ice-cored frost mounds in permafrost; Wang and Yao, 1981; Zheng and Jiao, 1991) and 

a multitude of high-altitude periglacial phenomena (Kuhle, 

1985) exist on the plateau. Palsas (elliptical frost mounds 

in peat in permafrost) reported in 1980 at an elevation of

80°E 85°E 90°E 95°E

35°N

30°N

EXPLANATION

Vegetation

•V'.-V'.-.V'.-.'J Conifers (with deciduous and broadleaf

-. _• -. .• •. _• -. i evergreens at lower elevations)

Alpine grass (some conifers and shrubs in 

____ sheltered locations)

[ | Alpine and drought-resistant plants

Precipitation

—250' ~ Annual precipitation in millimeters

Approximate boundary

of Xizang 

Autonomous Region

Approximate boundary % Xigaze

;;; t <• Gyangzc

of People's Republic 

of China

100 200 300 Kilometers

35°N

30°N

80°E 85°E 90°E 95°E

Figure 6. Generalized precipitation and natural vegetation map of Xizang Autonomous Region, China. Modified from Pradyumna 

(1976) and U.S. Government Printing Office (1971).
12 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

about 5,000 m above sea level southeast of Gyaco La Pass 

in the southern part of Xizang Autonomous Region (Pewe, 

1980a, b, 1981) are now thought to be frost blisters (low 

frost mounds in seasonal frost) (fig. 11). Because of the 

rigorous climate, perennially frozen ground and seasonally 

frozen ground are widespread, and a high number of 

freeze/thaw cycles per year favors mechanical breakdown 

of the rocks (Huang and others, 1981).

GEOMORPHOLOGY

The geomorphology of the broad, flat-floored valleys 

(fig. 12) and the adjacent slopes (Lhalungpa, 1983, p. 128- 

129) is of interest to this study. These areas exhibit sand 

dunes, sharply trenched terraces, and vertical silt cliffs. All 

the major rivers and many of the minor rivers in the 

southern part of the plateau seem to be braided and have

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC JAN JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC JAN

D 20

3

10

a o

I

-20

0° (freezing point)

MEAN TEMPERATURES

H 100

Z

HJ

U 50

C*

S o

Above Freezing

MEAN PERCENT OF DAYS WITH TEMPERATURE BELOW FREEZING 

201.8 mean annual number of days with temperature below freezing

OWr^ E""*

f—1 pJ

si r\ £~< 

U pJ

10

44.48 cm mean annual 

precipitation

MEAN PRECIPITATION

H 100

U 50

I o

MEAN PERCENT OF CLEAR, PARTLY CLOUDY, AND CLOUDY DAYS

87.8 mean annual 178.9 mean annual 98.3 mean annual 

clear days partly cloudy days cloudy days

SPEEE WIND IN METERS SECONI PER 

4

3 

2 

1 

0

i i i i i i i i i i i

- 2.2 meters per second mean monthly wind velocity

i i i i i i i i i i i

MEAN MONTHLY WIND VELOCITY

B 20

10

M. 0

-in

-20

H 100

Z

U 50 

C*

PQ n 

a. U

\ \

-1.4°C annual mean minimum temperature

MEAN TEMPERATURES

Above Freezing

MEAN PERCENT OF DAYS WITH TEMPERATURE BELOW FREEZING 

217.7 mean annual number of days with temperature below freezing

OPJ

U pj PJU

1 I T I I I

43.12 cm mean annual 

precipitation

MEAN PRECIPITATION

MEAN PERCENT OF CLEAR, PARTLY CLOUDY, AND CLOUDY DAYS

113.6 mean annual 172.7 mean annual 78.7 mean annual 

clear days partly cloudy days cloudy days

SPEEC WINDIN METERSSECONI PER 

4

3 

2 

1 

0

i i i i i i i i i i i 1 .8 meters per second

^ "~" ~~^~^___^ .mean monthly wind velocity

^-^^ _^

i i i i i i i i i i i

-

-X

MEAN MONTHLY WIND VELOCITY

0__i 

calm 25%

Lhasa(1951-1980) 

MEAN ANNUAL FREQUENCY OF WIND DIRECTION

Figure 7. Climatic data for Lhasa, Xizang Autonomous Region, 

China (1951-1980). From Meteorological Bureau, Xizang Autonomous Region (1983).

0__5% 

calm 46%

Xigaze(1955-1980) 

MEAN ANNUAL FREQUENCY OF WIND DIRECTION

Figure 8. Climatic data for Xigaze, Xizang Autonomous Region, 

China (1955-1980). From Meteorological Bureau, Xizang Autonomous Region (1983).
PHYSICAL SETTING 13

almost vegetation-free flood plains (cover, fig. 13). The 

Yarlung Zangbo in the vicinity of Xigaze is a heavily 

braided stream 8 to 10 km wide (Academia Sinica, 1980, 

p. 11). Large, low-angle alluvial fans form where major 

tributaries enter the wide valleys (fig. 14). Broad alluvial 

basins exist at Xigaze, Gyangze, Lhaze, Lhasa, Tingri, and 

many other places.

JAN FEE MAR APR MAY JUNE JULY AUG SEFf OCX NOV DEC JAN

-10

-20

1 1 I I I I I I I I

_.. _ _._—_an temperature

0° (freezing point)

-5.3°C annual mean 

minimum temperature

I I I

MEAN TEMPERATURES

100

-C/3

o w

50

MEAN PERCENT OF DAYS WITH TEMPERATURE BELOW FREEZING 

255.4 mean annual number of days with temperature below freezing

31.8 cm mean annual 

precipitation

MEAN PRECIPITATION

~i——i——i——r

MEAN PERCENT OF CLEAR, PARTLY CLOUDY, AND CLOUDY DAYS

143,6 mean annual 164.4 mean annual 57 mean annual 

clear days partly cloudy days cloudy days

igS3

t-1 2-LU n

"""""^ ^2.7 meters per second mean monthly wind velocity

i i i i i i

- .- — —— -~ — ———

^

\

MEAN MONTHLY WIND VELOCITY

0__5% 

calm 40%

Tingri (1970-1980) 

MEAN ANNUAL FREQUENCY OF WIND DIRECTION

Figure 9. Climatic data for Tingri, Xizang Autonomous Region, 

China (1970-1980). From Meteorological Bureau, Xizang Autonomous Region (1983).

Striking, active sand dunes and sand stringers have 

long been recorded in the broad valleys of the southern and 

central plateau (Rawling, 1905, p. 238). They are common 

on flood plains and on lower slopes of the bounding mountains (fig. 15) (Reiter and Reiter, 1981; Yang and others, 

1981, p. 1756; Zhao and others, 1976, p. 6; Wang and Li, 

1983, p. 4-5; Kreig and others, 1986; Wang and Fan, 1987). 

Most of them are conventional blow-out dunes or climbing 

dunes (cover, fig. 16), although an area of excellent barchan 

dune development was noted in the upper reaches of the 

Pum Qu valley near Tingri.

Lower slopes of foothills are characterized by fans 

of silt or fans of silt layers interbedded with sand or gravel 

layers that include silt. Most of the silt is well sorted, 

some of it is mixed with sand and gravel, and most is 

mineralogically different from the upslope bedrock. These 

fans are ubiquitously trenched by steep-walled V-shaped 

gullies (fig. 17), that radiate outward from the top of the 

fan and extend to the toe. These gullies were cut by 

streams in the easily erodible silt. At the village of Tingri 

(fig. 3), a gullied, low-angle fan of retransported loess sits 

at the base of a sharp-peaked hill of tilted sediments 

(fig. ISA). Because this site is along the road used by persons traveling south to Mt. Everest (Qomolangma Feng), 

numerous photographs show changing construction on the 

silt fan and at the adjoining Tibetan monastery (for example, fig. 18#) (Harvard, 1984, p. 77). Liu and Prof. Zhang 

Ronsu examined the sediments of the fan during the Academia Sinica scientific expedition to the Qinghai-Xizang 

(Tibet) Plateau of 1966-67, of which Liu was the leader. 

Zhang (now senior staff member at International Center 

for Integrated Mountain Development, Kathmandu, Nepal) 

observed then that the fan was a loesslike deposit. In 

1980, it was noted that small storage caves had been excavated in the loess, and, because of the ease in excavating 

loess, part of the fan was planed off in steps to make flat 

construction sites for more buildings (fig. ISA).

Locally, the distal parts of the silt fans have been 

eroded to form vertical cliffs as much as 15 m high. Like 

loess cliffs in central China, the Mississippi River valley 

and central Alaska, U.S.A., France, and elsewhere, these 

vertical silt cliffs in the southern plateau apparently stand 

for many years. The stability of these cliffs may be attributed to the angularity of the silt grains and to the strengthening effects of accretionary rods and tubes from earlier 

vegetation roots. Such cliffs are common south of Xigaze 

where they form the terrace scarps along the Nyang Qu 

(fig. 28).

The loesslike silt that water has transported from 

slopes to valley bottoms forms excellent agricultural land 

that locally supports large farms. The loesslike silt has 

been used to make bricks (fig. 19) for thousands of years, 

and some brick walls are still preserved in interesting archeological remnants (fig. 20) that remain along the busy 

trade routes of the past.
14 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

Figure 10. Distribution of permafrost 

and seasonally frozen ground in China. Map from Lanzhou Institute of 

Glaciology and Cryopedology (1983) 

and published with their permission.

Figure 11. Eroded remnant of frost 

blister exposing part of an ice core 

in shallow drainage way, elevation 

4,900 m, near Gyaco La Pass, near 

south border of Xizang Autonomous 

Region, China. Meter bar shows 

scale. Photograph 4583 by Troy L. 

Pewe, June 11, 1980; reprinted from 

Pewe (1981) and published with permission of "Geotimes."

80°E 90°E 110°E 120°E 130°E 140°E

100°E 120°E

50°N

40°N

30°N

130°E
LOESSLIKE SILT DEPOSITS 15

LOESSLIKE SILT DEPOSITS

DISTRIBUTION AND THICKNESS

In the mountainous Qinghai-Xizang (Tibet) Plateau, 

loesslike silt occurs in the lowlands and on gentle adjacent 

slopes; it is absent on the steep slopes and active flood 

plains (fig. 21). The silt is retransported loess that is thickest near major rivers and on parts of low fans, pediments, 

and river terraces. It lies in a belt between the major 

mountain ranges and the active flood plains, which are locally spotted with sand dunes or eolian sand blankets. This 

distribution of retransported loess is similar to that 1,400

km to the north in western Xinjiang Uygur Autonomous 

Region on the south and north sides of the Tian Shan 

(fig. 5; Pewe, 1987; Wang and Song, 1983).

Most of the loesslike silt has been slightly to 

considerably reworked and transported downslope by rill 

wash, sheet wash, stream action, and solifluction. As 

much as 1 to 2 m of silt still lies on a bedrock knob 

(fig. 22) 15 m above the Nyang Qu at Xigaze, and as 

much as 6 m of loesslike silt blankets the high flanks of 

a limestone knob 100 m above the south side of the 

Yarlung Zangbo 60 km downstream from Xigaze. The 

flanking silt is deeply dissected by deep, vertical-walled 

gullies (figs. 23, 24).

Figure 12. Broad flood plain of a north-flowing tributary of the 

Yarlung Zangbo about 40 km west of Xigaze, Xizang Autonomous Region, China. Area has barely enough vegetation to support a few herds of yak and dzo. Retransported loess occurs in

lower valleys at base of folded Cretaceous rocks which form the 

east-facing mountains in background. Photograph 4581 by Troy 

L. Pewe, June 1980; reprinted from Pewe (1981) and published 

with permission of "Geotimes."
16 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

Figure 13. Broad, almost vegetation-free flood plain of braided Yarlung Zangbo is a ready source of wind-blown silt about 15 km east 

of Xigaze, Xizang Autonomous Region, China. Late Mesozoic granodiorite forms south-facing mountains in background. Photograph 

PK 23,902 by Troy L. Pewe, June 9, 1980.

Figure 14. View southeast (upstream) of Nyang Qu valley from fortress 

on rock knob in valley at Gyangse, Xizang Autonomous Region, China. 

Fortress originally built by Tibetans as defense against Mongols. For

thousands of years, a braided stream wandered across this broad, almost 

vegetation-free flood plain, now spotted with sand dunes. Winds picked up 

silt and blew dust onto bounding hills. Broad valley is now irrigated and
LOESSLIKE SILT DEPOSITS 17

Figure 15. Active sand dunes on flood plain of Nyang Qu about 7 km southeast of Xigaze, Xizang Autonomous Region, China. View 

south. Photograph PK 23,871 by Troy L. Pewe, June 8, 1980.

supports crops for city of Gyangse, foreground, in center of valley. Note steep-sided gullies cut into 

fans of retransported loess along left edge of river valley. Surrounding hills composed of Jurassic and 

Cretaceous sandstone, limestone, and shale. Photographs 4572-4576 by Troy L. Pewe, June 8,1980.
18 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

About 10 to 20 m of loesslike silt covers the lower 

northwestern slope of a hill at Yangbajain at the southern 

foot of the Nyainqentanglha Shan (fig. 3; Academia Sinica, 1980, fig. n-2; Wang and Li, 1983, fig. 2-25, p. 52). 

Loesslike silt is most widely distributed where it spreads 

out as fans 1 to 2 m thick on or near the edges of flat, 

gently sloping valley floors. The fans are rarely all silt; 

they include layers of sand and fine gravel that permit 

higher angle fans than would be preserved if they were 

composed only of silt.

Narrow, steep-walled gullies in the loesslike silt are 

similar, but on a much smaller scale, to the spectacular 

results of loess erosion in north-central China (Wang and 

Zhang, 1980; Wang and Song, 1983). Except along terraces and valley-bottom deposits, thickness is difficult to 

measure; however, studies of gullies in the fans indicate 

that the loesslike silt is about 1 to 6 m thick.

Reports of loesslike silt on the plateau outside of the 

route of our 1980 investigation are not common. Zhao and 

others (1976, p. 20), on the basis of early expeditions to the

Himalayas in 1966-68, report a thin (1-m) loesslike silt 

overlying the first, second, and outwash terraces of Gyirong 

valley in the southwest part of the plateau (fig. 3). They 

also describe as much as 10 m of eolian loesslike silt and 

colluvium overlying the terrain near the bridge over the 

Pum Qu, 5 km south of Tingri (fig. 3). Also from the Himalayan expeditions in the 1970's, Wang and Li (1983) describe loesslike deposits on slopes in the southern Xizang 

Autonomous Region. Xu (1980, 1981) reports what he 

called extensive "periglacial" loess deposited in late Pleistocene time on the slopes of the Tanggula Shan (figs. 2, 5) 

in the central part of the Qinghai-Xizang (Tibet) Plateau. 

Derbyshire (1985) records local thin loess deposits in Qinghai Province northeast of the plateau (fig. 1).

Huang (1980) reports yellowish sandy soil at Tingri 

and as much as 9 m of loessic mud and sandy soil at Xiegal. At Yangbajain (fig. 3) he reports 19.8 m of yellowish 

clay over yellow silty sand with some gravel and mammalian fossils (Huang, 1980, p. 50). He believes both the silt 

here and the loesslike silt at Lingtse County (area to the

Figure 16. Climbing sand dunes on lower flanks of west-facing hills of Tertiary granite along braided Lhasa He 20 km southwest of 

Lhasa, Xizang Autonomous Region, China. Photograph 4547 by Troy L. Pewe, June 3, 1980; reprinted from Pewe (1981) and published with permission of "Geotimes."
LOESSLIKE SILT DEPOSITS 19

east around Nyingchi) are retransported loess (Huang 

Wanpo, oral commun., 1986). Yellowish silt is used for 

making brick and tile at Nyingchi.

The thickest deposits of loesslike silt are in valley 

bottoms and are commonly exposed in terrace scarps cut 

by streams (fig. 21). The deposits vary from relatively 

pure yellowish loess in vertical cliffs 10 m high to yellowish, fluvial, silty sand and silty clays that vary from less 

than a meter to 5 m thick.

The most striking and most extensive deposits of 

thick loesslike silt occur in the bottom of the Nyang Qu 

valley near its junction with the Yarlung Zangbo at Xigaze 

(fig. 25). There the Nyang Qu has cut down into a valleybottom deposit of retransported silt as thick as 15 m. The 

eroded edges of the terraces on each side of the valley are 

vertical walls 15 m high of bedded silt with some sandy 

layers. The most striking land forms are steep-sided flattopped buttes and mesas, the latter as much as 1 km in 

diameter, that remain in the valley bottom (fig. 26). These 

erosional remnants clearly exhibit the vertically jointed retransported silt. The tops of the erosional remnants are 

bare of vegetation, perhaps because they are well drained

and very dry. Similar land forms in retransported loess 

have developed on the south side of the Tian Shan in the 

Xinjiang Uygur Autonomous Region (Pewe, 1987).

Probably the most thoroughly studied section of retransported loess in the Qinghai-Xizang (Tibet) Plateau is 

along the main highway at the south edge of Xigaze 

(fig. 27). About 15 m of alternating beds of retransported 

loess, sandy loess, and sand are exposed, and the uppermost 6 m are easily accessible for collecting samples and 

fossils. Beds of relatively pure, cliff-forming, yellowish 

silt as thick as 3 m are quite impressive (fig. 28).

COLOR AND TEXTURE

The loesslike silt is commonly yellowish tan 

(fig. 28), although grayish-tan is not rare; when wet it is 

brown. In many localities thin, dark, carbonaceous and 

iron-stained bands or mottling are present.

Mechanical composition of the loesslike silt and associated sandy silt and sand was measured on 17 samples from 

the plateau and 3 samples of loess and retransported loess

Figure 17. Sharply dissected fans of retransported loess at base of low west-facing mountains east of Tingri, Xizang Autonomous 

Region, China. Photograph 4584 by Troy L. Pewe, June 11, 1980.
20 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

Figure 18. Large dissected fan of retransported loess below site of Tibetan monastery and fortifications of Xigar-Zhong, seat of district administration during Ching Dynasty, at Tingri in 

south-central Xizang Autonomous Region, China. Mountain of tilted shale and sandstone of 

Jurassic age. Note difference in use of fan for building sites in each picture. A, Early morning 

sun strikes remnants of once-splendid fortifications high on mountain. Loess is easily excavated, 

and small entrances to storage rooms can be seen in scarp at base of fan. Fan has been planed 

off in steps to accommodate modern buildings as city of Tingri expands. Photograph PK 23,950 

by Troy L. Pewe, June 12, 1980.

from elsewhere in China (table 1). Grain-size analyses of 

samples 1 through 10, and a sample of loess from near 

Heidelberg, Germany, were made by wet sieving to separate 

the >0.062 mm fraction, then pipetting that fraction at whole 

phi-size intervals according to the method of Folk (1974). 

Samples 11 through 17 were wet sieved, and calcium carbonate was removed before grain-size analyses were made 

by hydrometer. Samples 18 and 19 were wet sieved and 

further analyzed by the hydrometer method. Loess sample 

20 from near Beijing was analyzed by sedimentation in water. 

The powdery loesslike silty sediment is widespread 

in fans of different localities, shapes, and sizes and on
LOESSLIKE SILT DEPOSITS 21

Figure 18. B, View southeast toward intact monastery and fortifications on same hillside in 1922. Copyright photograph 092207-D525 

by T.G. Longstaff, MEE, while on reconnaissance expedition to Mount Everest. Published with permission of Royal Geographic 

Society, London.

Figure 19. Newly made bricks of loess in foreground, loess-brick walls around house in center. View west across valley of Nyang Qu 

near Bainang, about 45 km southeast of Xigaze, Xizang Autonomous Region, China. Photograph PK 23,878 by Troy L. Pewe, June 8, 

1980.
22 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

Table 1. Data on Quaternary sediment samples collected from southern Qinghai-Xizang (Tibet) Plateau, China, and from other parts of China. 

[Samples collected by T.L. Pewe except as noted. Mineralogy analysis includes clay minerals and rock fragments.]

Sample No. Material 

(figure)

1 Retransported 

(figs. 3, 34) sandy loess.

2 Silty sand..........

(figs. 3, 34)

3 Sandy loess....... 

(figs. 3, 22, 

25, 34)

4 Sandy loess ...... 

(figs. 3, 34)

Date Sample site 

collected

6/8/80 Bainang Agricultural Station, 

elevation 3,900 m, in Nyang 

Qu Valley, 40km NW of 

Gyangze. 

6/8/80 In Nyang Qu Valley, 22 km 

upstream from Xigaze.

6/9/80 On bedrock hill 60 m above 

river at junction of Nyang Qu 

and Yarlung Zangbo, north 

side of Xigaze. 

6/9/80 On flank of bedrock hill 1 5 m 

above and adjacent to

Position and stratigraphy at site

Surface sample in field at base 

of alluvial fan of silt with 

some gravel.

Surface sample in silty field at 

base of rock cliff on low 

terrace. 

At depth of 2.4 m in loess 

plastered on hill of volcani - 

clastic sandstone.

At depth of 2 m in gully of 

loess blanketing a bedrock

Analyses performed

Age 

Granule- Mineral- Pollen Ostra- Mol- Verte - 

metric ogy codes lusca brates

Holocene....... X

Holocene....... X

Late X 

Pleistocene.

Late X 

Pleistocene.

X

X 

X

X

5 Retransported 

(figs. 3, 27, loess (same

34) as sample No. 

15).

6 Retransported 

(figs. 3, 34) loess.

7 Retransported 

(figs. 3, 34) loess.

Yarlung Zangbo, 50 km 

downstream from Zigaze on 

south side of river.

6/9/80 On face of terraces of silt and 

sand (distal end of fans from 

hills), west side of Nyang Qu 

at south edge of Xigaze.

6/10/80 Agricultural field on

retransported loess at village 

of Netang, 14 km west of 

Xigaze.

6/10/80 1 km west of village of Jaling, 

75 km west of Xigaze.

hill of limestone.

Unit HI, 3.6 m below surface in Late 

bank of retransported fossilif - Pleistocene, 

erous loess and alluvial sand.

X X X X X

Near-surface sample on very 

gently sloping fan.

Holocene......

At depth of 3.0 m in broad fan Holocene......

of black gravel of angular 

clasts, 2-4 cm diam.; gravel 

2.5 m thick over 2.5-m layer 

of loess with 0.3-cm zone of 

red soil at base.

8 Retransported

(figs. 3, 34) loess.

9 Silty pebbly

(figs. 3, 34) retransported

loess.

10 Eolian sand ' ......

(figs. 3, 34)

1 1 Retransported

(figs. 3, 27) loessr.

12 Silty sand 1

(figs. 3, 27)

13 Retransported

(figs. 3, 27) loess 1 .

14 Retransported

(figs. 3, 27) loess 1 .

1 5 Retransported

(figs. 3, 27) loess (same

as sample No.

5) 1 .

1 6 Retransported

(figs. 3, 27) loess and

sandy loess ' .

17 Crossbedded

(figs. 3, 27) sand 1 .

1 8 Retransported

(figs. 5, 42, loess.

45

19 Retransported

(figs. 5, 45 gravely loess.

20 Loess 2

(fig- 1)

6/11/80

6/12/80

6/17/80

6/18/80

6/18/80

6/18/80

6/18/80

6/18/80

6/18/80

6/18/80

8/6/86

8/10/86

1973

Dissected alluvial fan of silt 15

km east of Lhaze.

70 km west of Tingri on south

side of Pum Qu valley.

45 km southwest of Lhasa

along west side of Lhasa He.

Terrace on west side of Nyang

Qu, south side of Xigaze.

Terrace on west side of Nyang

Qu, south side of Xigaze.

Terrace on west side of Nyang

Qu, south side of Xigaze.

Terrace on west side of Nyang

Qu, south side of Xigaze.

Terrace on west side of Nyang

Qu, south side of Xigaze.

Terrace on west side of Nyang

Qu, south side of Xigaze.

Terrace on west side of Nyang

Qu, south side of Xigaze.

Ancient city of Jiaohe, near

Turpan, Xinjiang Uygar

Autonomous Region.

West bank of Sigh He at Kuqa,

north of Tarim Basin,

Xinjiang Uygar Autonomous

Region.

Near Beijing... ..........................

Surface silt on fan... .................

Surface-sediment sample.........

Surface-sediment sample........

Unit VI, 0.9 m below surfaceUnit V, 1.4 m below surface..

Unit IV, 1.8 m below surface..

Unit IV, 2-3 m below surface.

Unit III, 3.6 m below surface....

Unit II, 4.8 m below surface.....

Unit I, 5.5 m below surface......

30-m vertical loess wall of

small creek valley. Sample

from 2.0 m below surface.

Alluvial loess and gravel

layers, 1-3 m thick. Sample

from 3 m below surface.

Surface sample..........................

Holocene......

Holocene......

Holocene......

Late

Pleistocene.

Late

Pleistocene.

Late

Pleistocene.

Late

Pleistocene.

Late

Pleistocene.

Late

Pleistocene.

Late

Pleistocene.

Late

Pleistocene.

Late

Pleistocene.

Late

Pleistocene.

X X

X X

X X

X XX

X XX

X XX

X XXX

X X X X X

X XXX

X XX

X

X

X •^y3 .A

Collected by Liu Tungsheng and Li Bingyuan. 

2Collected by Roger J.E. Brown. 

3 See Pewe and Journaux (1983) for mineral analyses.
LOESSLIKE SILT DEPOSITS 23

hills of different bedrock types. The silt varies widely in 

texture and sorting from clay-rich to sand-rich and even to 

gravel-rich, depending upon nearness to the original silt 

source and the various distances of retransportation and 

mixing with other sediments by fluvial and colluvial slope 

movement. Silt near the hills or mountain slopes is coarser 

and interbedded with more coarse beds than that at the toe

of low-angle silt fans near the center of the valleys. In 

great contrast to the uniform mechanical composition and 

texture of loess throughout the world (table 2; Pewe and 

Journaux, 1983, their figs. 28, 29), this retransported loess 

is less well sorted and generally has a lower percentage of 

silt-size particles (table 3, figs. 29, 30) than in situ loess. 

Percentages of grain sizes in silt samples vary: 8 to 55

Figure 20. Remnants of loess-brick walls of 13th century monastery about 10 km west of Xigaze, Xizang Autonomous Region, 

View west. Photograph PK 23,918 by Troy L. Pew<§, June 10, 1980.

China.

Figure 21. Diagrammatic sketch of typical dissected loesslike silt with lenses and layers of 

fluvial sand and gravel in valley bottoms along major streams in southern Qinghai-Xizang 

(Tibet) Plateau, China. Vertical exaggeration 33x. Diagram by S.M. Selkirk.
24 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

percent sand; 26 to 75 percent silt; and 2 to 67 percent 

clay (table 3).

However, loess on or flanking bedrock knobs or hilltops near the Yarlung Zangbo was retransported little or not 

at all; it is well sorted and has a relatively high sand content 

and a low clay content (fig. 31). The silt has the same texture 

throughout the section from the surface to the bedrock. Texture and cumulative-frequency grain-size curves of the sandy 

loess from near rivers (samples 3 and 4) are similar to those 

of sandy loess adjacent to braided streams in Alaska, Siberia, 

and elsewhere (Pewe and Holmes, 1964; Trainer, 1961; Pewe 

and Journaux, 1983). Samples 5, 7, 13, 14, 15, and 16 have 

more than 40 percent clay-size particles (figs. 30, 32) and 

are typical of silt deposits on fans. Huang (1980) refers to 

loessic mud at Tingri and yellowish clay at Yangbajain. 

Sample 6, which has the highest silt content (fig. 30) and is 

best sorted, is from an agricultural field on the toe of the 

slope far from the mountains. Some samples have fluvial 

silty sand and some have eolian sand (fig. 33). Fluvial sand 

is interbedded with the loesslike silt in many localities.

Silt grains in the loesslike silt are angular, and the 

sediment has little or no cementation. A few calcareous 

concretions (loess kindshen) are present locally. The presence 

of an expandable mixed-layer clay and stringers of calcite 

and small roots in some samples indicates that these sediments 

have been subject to soil-forming processes.

MINERAL COMPOSITION

Mineralogical analyses of 10 sediment samples from 

southern Qinghai-Xizang (Tibet) Plateau were compared 

with that of a control sample of loess from Germany. Mineral composition of the sand-size fraction of samples 1 

through 10 (table 4) was determined by impregnating the 

sand in epoxy resin, which allowed thin sections to be prepared, then using a petrographic microscope for point 

counting 200 grains. Petrographic examination reveals that 

the silt grains, although slightly iron stained, are angular 

and fresh.

Figure 22. Loess overlying bedrock on knob 15m above the Nyang Qu at Xigaze, Xizang Autonomous Region, China. Collection site 

of sample 3 (table 1). Photograph PK 23,896 by Troy L. Pewe, June 9, 1980.
LOESSLIKE SILT DEPOSITS 25

Table 2. Mechanical properties of sand and loesslike-silt samples from southern Qinghai-Xizang (Tibet) Plateau, China (Nos. 1-19), 

and loess and ash from other parts of the world.

[Sedimentological terms from Folk (1974). Compiled by Mu Guijin from cumulative-frequency curves (figs. 30-33). See table 1 for sampling 

information.]

Sediment 

sample

No.

Material

Graphic mean Median Inclusive graphic

standard deviation

(sorting) (01) <J>

Inclusive graphic Graphic kurtosis 

skewness (KG) 

(SKi)

1 Retransported sandy loess............................ 5.42 4.84

2 Silty sand....................................................... 4.82 3.82

3 Sandy loess.................................................... 4.58 4.58

4 Sandy loess.................................................... 4.35 4.13

5 Retransported loess....................................... 7.62 7.90

6 Retransported loess....................................... 5.32 5.35

7 Retransported loess....................................... 7.84 7.96

8 Retransported loess....................................... 7.45 7.48

9 Silty pebbly retransported loess.................... 6.76 6.72

10 Eolian sand.................................................... 3.18 3.12

11 Retransported loess....................................... 6.34 5.80

12 Silty No analyses available 

sand........................................................

13 Retransported loess....................................... 7.03 7.26

14 Retransported loess....................................... 6.57 6.65

15 Retransported loess....................................... 7.31 8.15

16 Retransported loess and sandy loess............ 6.2 6.50

17 Crossbedded sand......................................... No analyses available

18 Retransported loess....................................... 7.83 7.46

19 Retransported gravelly loess 1 ....................... 5.82 5.58

20 Loess, Beijing, China.................................... 7.94 7.65

Dust, Germany.............................................. 5.42 5.50

Volcanic ash, Fairbanks, Alaska, U.S.A...... 6.24 6.15

Dust, Kansas, U.S.A..................................... 6.84 5.90

Dust, Arizona, U.S.A.................................... 7.8 6.65

Loess, New Zealand..................................... 8.1 7.80

Loess, France................................................ 6.24 5.32

Loess, former Czechoslovakia..................... 7.37 5.95

Loess, Alaska, U.S.A.................................... 5.84 5.50

Loess, Uzbekistan......................................... 5.45 5.11

Loess, Illinois, U.S.A.................................... 6.07 5.95

Loess, Siberia, Russia................................... 5.58 5.27

Loess, Germany............................................ 5.40 5.38

2.00

2.65

1.08

2.15

2.10

1.46

1.79

1.49

2.02

1.80

2.24

1.92

2.99

2.35

3.18

2.07

2.55

2.84

0.95

1.28

2.41

2.87

2.83

1.91

2.96

1.36

1.48

1.23

1.87

.84

0.43 

.91 

.19

.23

-.27

-.05

-.16

-.04

-.01 

.26 

.31

.15 

.11

-.45 

.16

.23

.064

-.1

.17 

.03 

.44 

.46

.1

.63 

.56 

.26

.52 

.08 

.43 

.09

0.96

.91

1.14

1.50

.87

1.77

.77

.90

.84

2.13

.72

.63

.84 

.57

1.1 

1.51 

.83

1.02

1.23

1.26

1.47

.92

1.78

.98

1.12

1.7

1.64

1.86

1.59

Original sample included about 15 percent gravel larger than 2 mm, which was removed before this analysis.

Composition of bulk (not size-fraction) samples was 

determined by air drying, crushing to a uniform fine powder, 

then using X-ray diffraction analysis by using a Phillips 

APD-3500 instrument. Bulk samples consist mainly of 

quartz, feldspar, calcite, dolomite, micas, and clay minerals. 

Estimates of percentage abundance of the minerals (table 5) 

were made by measuring peak areas of the 4.25-A mica plus 

clay minerals, 3.36-A quartz, 3.25-A potassium feldspar, 

3.20-A plagioclase, 3.03-A calcite, and 2.88-A dolomite 

diffractogram peaks and by using the weighting factors of 

Schultz (1964). In order to correct for the 3.36-A illite peak 

that overlaps that of quartz, the 10-A illite peak was calculated and subtracted from that of the 3.36-A peak because 

10-A and 3.36-A illite peaks occur in roughly equal proportions (ASTM card 9-334).

Composition of the clay-size (<0.005-mm) fraction 

of samples, separated from bulk samples by centrifuging, 

was also determined by X-ray diffraction analysis of untreated and glycolated samples using a scanning speed of 

1° 20' per minute. To differentiate chlorite and kaolinite, 

slow scans (0.20°20' per minute) were run over the range 

24° to 26°20' (3.5-A peak) (Biscayne, 1965). This fraction 

consists of smectite, kaolinite, and chlorite with traces of 

quartz, feldspar, and calcite. X-ray patterns of some samples indicate the presence of a small amount of mixedlayer illite/smectite or smectite/vermiculite For comparative purposes, the relative abundances of the major clay 

minerals were determined by measuring and applying 

weighting factors to the following peak areas (peak height 

multiplied by peak width at half height) on the glycolated
26 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

pattern: The 17-A smectite peak; four times the 10-A illite 

peak; and twice the 7-A kaolinite plus chlorite peak (Biscayne, 1965) (table 6). The kaolinite/chlorite ratio was 

determined by measuring areas of the 3.54-A chlorite and 

3.58-A kaolinite peaks on the slow-scan diffractogram and 

apportioning the ratio to the 7-A peak area (Biscayne, 

1964). The four weighted peak areas were summed, and 

each is expressed as a percentage of the total, as 100 percent clay minerals.

In that part of southern Qinghai-Xizang (Tibet) Plateau (figs. 2 and 3) where samples 1 through 17 were collected, east-trending belts of Mesozoic sedimentary rocks 

make up the bulk of potential source rocks for sediment 

samples in the area. An east-trending belt of plutonic rocks 

occurs to the north, and a belt of ophiolitic rocks occurs 

close to many of the sampling sites in the center of the 

mapped area (fig. 34A).

Composition of the sand-size fraction of the sediments, particularly varieties of lithic fragments that were 

identified (table 4), can be used as a rough indicator of 

sediment sources. However, direct comparisons of sandfraction petrology cannot be made because the data also 

reflect variations in composition due to grain-size variations among the sand fractions analyzed (see Slatt and 

Eyles, 1981, for a discussion of variations in composition 

of glacially derived sands of different grain size; also see 

Pewe and Journaux, 1983, for a discussion of mineralogical differences that do not reflect size fractions of loess in 

Siberia). For example, samples 6 and 7 contain an abundance of igneous lithic fragments (table 4) that are of 

coarse-sand size. Most other samples contain only finesand-sized particles, which are enriched in quartz, shale, 

and carbonate lithic fragments. Although these sands may 

have had a plutonic or volcanic source, such fragments

Figure 23. Deep, sharp-walled gully 3 m wide at top, dissected into retransported loess fan at 

base of limestone knob 50 km downstream from Xigaze on the Yarlung Zangbo, Xizang Autonomous Region, China. View east of collection site 4 (table 1). Photograph PK 23,905 by Troy L. 

Pewe, June 9, 1980.
LOESSLIKE SILT DEPOSITS 27

Table 3. Percentage of sand, silt, and clay in sand and loesslikesilt samples from southern Qinghai-Xizang (Tibet) Plateau, China, 

and loess from Beijing, China.

[U.S. Department of Agriculture classification: sand, 1.0-0.05 mm; silt 

0.05-0.005 mm; clay, 0.005-0.002 mm. See table 1 for sampling information.]

Sample

No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

Material

Retransported sandy

loess.

Silty sand...................

Sandy loess................

Sandy loess................

Retransported loess...

Retransported loess...

Retransported loess...

Retransported loess...

Silty pebbly retransported loess.

Eolian sand.... ............

Retransported loess...

Silty

sand....................

Retransported loess...

Retransported loess...

Retransported loess...

Retransported loess

and sandy loess.

Crossbedded sand......

Retransported loess...

Retransported r »

gravelly loess .

Loess, Beijing,

China.

Sand

36.5

575

43.0

55.0

8.5

19.2

3.8

2.5

11.5

82.5

20.0

80.0

9.0

30.5

16.0

37.0

99.0

3.2

20.0

25.0

Silt

47.2

25.5

54.5

34.4

36.8

75.3

40.2

50.2

53.5

10.3

50.0

13.5

48.5

28.0

18.5

21.5

1.0

51.6

58.5

49.5

Clay

16.3

17.0

2.5

10.6

54.7

5.5

56.0

47.3

35.0

7.2

30.0

6.5

41.5

40.5

64.5

41.5

.0

21.5

21.5

25.5

Total

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

'Original sample included about 15 percent gravel larger than 2 mm, 

which was removed before this analysis.

would not be fine-sand-sized particles. To compare compositions of the ten sands accurately, only one sand-size 

fraction should have been studied petrographically: 

however, in most instances insufficient material was available to make such a fractionation. In addition, only a few 

sand samples contain any coarse sand, which is the most 

valuable fraction for recognizing lithic fragments.

Nevertheless, the data in table 4 show that a wide 

variety of rocks contributed to the sediments. Samples 6 

and 7 are rich in mafic plutonic and volcanic lithic fragments, probably derived from ophiolite terrane. Enrichment of sample 10 in felsic plutonic fragments, as well as 

in feldspar, indicates derivation from the nearby plutonic 

terrane. Samples 4, 5, and 8 are enriched in carbonate lithic fragments, which could have been derived from the 

same sequences. The lithic fragments in samples 1 to 10 

do not suggest a major plutonic source; however, much of 

the quartz could have such a derivation. Most quartz 

grains are angular, suggesting that they are first-cycle detritus; however, samples enriched in carbonate lithic fragments also contain a high proportion of multicycle 

rounded quartz grains. The high proportion of sand-size 

chlorite in samples 1, 2, and 7 probably reflects derivation 

from mafic ophiolitic rocks.

Composition of the clay-size fraction of the sediments (table 6) can be used to compare probable sediment 

sources. Relative proportions of the clay minerals are presented in figure 34B. Samples 1, 2, 7, and 10 contain the 

highest proportion of smectite, and samples 1 and 7 contain the highest proportions of chlorite; these proportions 

indicate at least partial derivation from mafic ophiolitic 

rocks. The site of sample 9, which has the lowest chlorite 

content, is farthest from the ophiolite terrane (fig. 34A).

Table 4. Mineral composition of sand-size (>0.062-mm) fraction of sand and loesslike silt from southern Qinghai-Xizang (Tibet) Plateau, China

[Calculations in weight percent. Heavy minerals include mainly amphiboles, pyroxenes, and opaque minerals. Tr, trace; -, not detected. Petrographic analyses by 

Cities Service Company, Tulsa, Okla. Samples collected by T.L. Pewe unless otherwise noted. See table 1 and figures 3, 27, and 34 for sampling sites.]

Lithic fragments

Sample

No.

1

2

3

4

5

6

7

8

9

10 1

Quartz

c

C3

Monocryst

35

43

57

43

21

15

26

33

40

47

e— i

Polycrysta

7

9

17

7

8

4

14

20

22

7

Feldspar

Orthoclasf

3

1

1

5

1

.

Tr

-

2

4

<D

Plagioclas

3

2

4

-

1

2

3

1

2

6

•e

<D

o.

.

Tr

2

-

2

Tr

Tr

-

-

3

o

0

plut Felsic 

.

-

-

-

-

2

1

-

-

9

Igneous

o "a

o

J3"o. 

o

1

.

-

-

-

-

22

4

-

-

•

o'e

~5 

o

1

Tr

Tr

-

-

-

37

29

7

Tr

Tr

Sandstone

1

-

-

2

5

_

Tr

-

1

Sedimentary

13

24

4

-

1

3

6

3

7

4

4

<D 

U

1

Tr

-

2

.

3

-

7

Tr

Carbonate minerals

3

2

-

36

53

1

Tr

14

2

-

Micas 

Metamorphic

$H *-• -S

* c/}gU

14

30

8

2

2

7

Tr 14

3

4 Tr

1 3

<u

Biotite ancmuscovi

5

2

2

2

2

Tr

1

3

6

8

Heavy

minerals

5

6

9

2

Tr

4

2

11

10

7

'Collected by Liu Tungsheng and Li Bingyuan.
28 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

Table 5. Mineral composition of bulk samples of sand and loesslike 

silt from southern Qinghai-Xizang (Tibet) Plateau, China (Nos. 1- 

10), and from Heidelberg, Germany.

[Calculations in weight percent; -, not detected. X-ray diffraction analyses 

by Cities Service Company, Tulsa, Okla. Samples collected by T.L Pewe 

unless otherwise noted. See table 1 and figures 3, 27, and 34 for sampling 

sites.]

Table 6. Mineral composition by weighted peak-area percentages of 

clay-size (<0.005-mm) fraction of sand and loesslike silt from southern 

Qinghai-Xizang (Tibet) Plateau, China.

[Calculations in weight percent. Tr, trace; -, not detected. X-ray diffraction 

analyses by Cities Service Company, Tulsa, Okla. Samples collected by T.L 

Pewe unless otherwise noted. See table 1 and figures 3, 27, and 34 for 

sampling sites.]

Sample Quartz Potassium Plagio- Calcite Dolomite Micas and 

No. feldspar clase clay minerals

1

2

3

4

5

6

7

8

9

10 1

Germany

33

44

32

29

31

35

30

34

18

33

29

9

1

6

6

10

.

1

2

22

3

11

8

9

25

-

13

8

5

8

29

6

2

5

7

7

17

6

2

4

53

-

27

3

3

11

1

1

_

-

1

.

-

32

51

31

40

32

45

36

60

55

19

16

14

Sample Smectite Illite Kaolinite Chlorite Quartz Feldspar Calcite 

No.

1

2

3

4

5

6

7

8

9

10 1

9

16

.

-

-

Tr

5

-

.

8

48

57

77

69

77

81

68

86

92

64

18

15

7

10

9

_

-

.

3

7

25

11

16

21

14

19

27

14

5

21

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

-

.

-

-

_

-

Tr

Tr

-

'Collected by Liu Tungsheng and Li Bingyuan.

Collected by Liu Tungsheng and Li Bingyuan.

Figure 24. Alluvial fan of retransported loess sharply dissected by steep-walled gullies as much as 6 m deep. Fans flank limestone 

bedrock knob 50 km downstream from Xigaze on the Yarlung Zangbo, Xizang Autonomous Region, China. Photograph PK 23,904 by 

Troy L. Pewe, June 9, 1980.
LOESSLIKE SILT DEPOSITS 29

200 400 600 800 1000m

Figure 25. Physiographic diagram of Xigaze area at junction of Nyang Qu and Yarlung 

Zangbo, Xizang Autonomous Region, China. Terrace remnants of loesslike silt are about 15 

m high. No. 3 is site of loess sample 3 (table 1; fig. 22), and "Fossil site" is a fossiliferous 

terrace (figs. 27, 37). Diagram by S.M. Selkirk from map prepared by Li Bingyuan.

Appreciable kaolinite is present in samples 1 to 5 and 

10 and is absent in samples 6 to 8 to the west. This distribution indicates at least two different types of source rocks. 

It is possible that the kaolinite is derived from weathered 

rocks of the northern plutonic terrain, but it may also be a 

second-cycle kaolinite derived from sedimentary rocks.

Some information on source terrains can be gained 

by comparing the compositions of bulk-sediment samples 

(fig. 34C, table 5), although, like the sand fraction, bulk 

compositions are also affected by variations in grain-size 

distribution among the samples (fig. 29). Sample 9 is rich 

in calcite, which possibly suggests a local limestone 

source (Jurassic sediments) quite unlike that of other samples. The feldspar content tends to diminish in sediments 

from east to west, generally in sampling sites that are farther from the plutonic terrain (fig. 34A). Samples 4 and 

10, located closest to the plutonic terrain, contain the most 

feldspar (plagioclase is greater than orthoclase). Variations 

in the feldspar content probably reflect a variable supply 

of plutonic detritus to the sediments.

Combining the above compositional data for sand, 

clay-mineral, and bulk samples allows some generalizations about sediment sources and the extent of sediment 

transport. Samples 1, 2, 7, and possibly 6 have a strong 

source component of ophiolitic rocks. Samples 3, 4, 5, and 

10 are at least partially derived from plutonic as well 

as Cretaceous sedimentary rocks (particularly carbonate

rocks), and samples 8 and 9 are probably derived mainly 

from Triassic and Jurassic sedimentary rocks, respectively. 

Thus, although the sediments were originally of windblown origin and have subsequently been reworked, they 

have not been transported far enough to lose the compositional imprint of a fairly local origin.

Figure 26. Flat-topped, steep-walled, 15-m-high remnant of 

bedded, vertically jointed retransported loess in bottom of Nyang 

Qu valley near its junction with Yarlung Zangbo on north side of 

Xigaze, Xizang Autonomous Region, China. View to southwest 

from bedrock knob near site of sample 3 (figs. 22, 25). Photograph PK 23,897 by Troy L. P6w6, June 9, 1980.
30

Q O O

£ 

w

CO

00

w

LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

89°15'

- •29°101

E 

A'

t

TERRACE

Area of detailed 

stratigraphic section (C)

100 METERS

I M '9I"|

i M • i I • . ' I '

• 150 METERS

Vli|>771T!.7TT'!7TTTirT7?.^/>7>ll

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8 9 10 11 12 13 14 15

Fine sand, silt and 

silty clay (retransported 

loess and sandy loess)

Silt, and silty clay 

(retransported loess)

Coarse sand

EXPLANATION

12 Sediment-sample site

II Stratigraphic unit

& Mollusca fossils

Bird and mammal fossils

Figure 27. Sketch map of flood plain and terraces side of Xigaze, Xizang Autonomous Region, China.

(A) and stratigraphic sections (B, Q of retransported Note collection sites of sediment samples 11 to 17

sandy loess, silty clay, and coarse sand cropping out (table 1) and of vertebrate and invertebrate fossils

on terrace scarp on west side of the Nyang Qu, south (see fig. 28).
LOESSLIKE SILT DEPOSITS 31

Figure 28. Cliff-forming retransported tan loess exposed in road 

cut near Army fuel station along Xigase-Lhasa Highway on south 

side of Xigaze, Xizang Autonomous Region, China. This classic 

section is site of bird fossils, thin layers of fresh-water mollusk 

shells near middle and lower part of the exposure, and numerous 

sediment and pollen samples (see figs. 27, 37). Note wall made

of bricks of loess in upper right. Inspecting scientists are members of International Union of Quaternary Research (INQUA) 

field excursion. View toward northeast. Hills of clastic rocks of 

Cretaceous age in distance lie east of the Nyang Qu and south of 

the Yarlung Zangbo (figs. 25, 34A). Photograph PK 29,937 by 

Troy L. Pewe, August 20, 1991.
32 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

SAND (>0.063mm)

SILT 

(0.063-0.004mm)

CLAY 

(<0.004mm)

Figure 29. Proportions of sand, silt, and clay in sediment samples 1 to 10 from south-central Qinghai-Xizang (Tibet) Plateau, 

China, and a loess sample from Germany (G). (See figs. 3 and 

34 for sampling sites.) Diagram by S.M. Selkirk.

In order to verify that sediment samples have indeed been transported and not derived by in situ weathering, a bedrock sample was collected from beneath 

loess sample 3 (figs. 22, 34A) on top of a 15-m-high 

bedrock knob at the junction of Yarlung Zangbo and 

Nyang Qu at Xigaze (fig. 3). Petrographic analysis indicates the rock is a volcaniclastic sandstone or lithic tuff 

of basaltic or andesitic provenance, which has undergone 

considerable alteration under either hydrothermal or lowgrade regional-metamorphic conditions that resulted in 

the authigenic mineral assemblage of subgreenschist 

fades. The rock consists mostly of altered mafic to 

intermediate volcanic-rock fragments and plagioclase. 

Volcanic glass fragments are altered to quartz and pumpellyite and lined with chlorite and sphene. Most of the 

quartz is authigenic, primary plagioclase is changed to 

albite, and chlorite and pumpellyite partially replace plagioclase. Results of X-ray-diffraction analyses of wholerock and clay-mineral fractions of sample 3 (figs. 35A, 

E) are compared with those of the underlying bedrock 

(fig 355, D). Analysis of sample 3 shows that the loess 

at that location is not derived from the underlying bedrock because (1) pumpellyite is present in the bedrock 

but absent in the sediment and (2) illite is present in the 

sediment but absent in the bedrock.

FIELD RELATIONS

Where the loesslike silt has been transported by fluvial or colluvial processes or is in an original position of 

deposition on top of a low hill next to a river (as in 

fig. 22), it overlies various substrates with a sharp contact.

Only on local hilltops is the silt massive, showing 

little or no stratification or jointing. Most of the loesslike 

silt has been retransported to lower slopes, alluvial fans, or 

valley bottoms, where it is thickest (figs. 21, 25, 26) and 

shows poorly to well-developed stratification. The stratification varies from iron-stained horizons, organic films, 

and color banding to well-developed sand-and-gravel layers 10 to 200 cm thick in sharp contact with the silt beds. 

Nowhere does the stratification resemble lacustrine bedding. No tephra layers are known in the loesslike silt, and 

no major soil horizons, such as are widely reported in central China (Liu and Chang, 1964; Liu and others, 1964, 

1966; Liu and Wang, 1965; Liu and others, 1985; Liu, 

1991; Rutter and others, 1991), were observed.

A conspicuous feature of the loesslike silt is its ability to stand in sheer cliffs (figs. 26, 27, 28). This characteristic is probably due to the angularity of the grains and 

to the strengthening by concretionary rods and tubes. This 

well-developed vertical cleavage of loess in China has 

been discussed from the beginning of the 20th century and 

attributed to vertical permeability by Willis (Willis and 

others, 1907) and to carbonate deposits around plant roots 

by Barbour (1925a, b). As in the loess elsewhere in China, 

vertical walls 10 to 15 m high in the valley-bottom facies 

of the loesslike silt at Xigaze have stood for many years. 

Jointing is not common, but vertical jointing typical of 

loess is well displayed in cliffs at Xigaze (fig. 28). Sharp, 

steep-walled gullies form in the loesslike silt and are most 

common on fans (figs. 17, 18, 23, 24).

FOSSILS IN LOESSLIKE SILT

Loess and retransported loess from many countries 

have long been known as excellent material for preserving 

Quaternary fossils: Vertebrates, mainly mammals, 

including frozen carcasses; invertebrates such as freshwater and pulmonate mollusca, insects; and flora, pollen 

and mega-specimens. Fossils in the classic loess areas of 

north-central and eastern China are widespread and include pollen, insects, ostracodes, mammals, birds (especially large ostrich eggs) and hominids. Fossils in the loess 

of China have been known to the western world since the 

days of von Richthofen's work in the 1870's and from 

later studies (von Richthofen, 1877, 1882; Andersson, 

1923; Barbour, 1925a, b, 1930; Liu and others, 1964, 

1966; Liu, 1985; Chen and others, 1985; Xue, 1984).

Reports of Quaternary fossils from the loesslike silt of 

the plateau are sparse, but observations are known from about 

the 1950's (Huang, 1980; Huang and Ji, 1981; Pewe, 1980a, 

b; Wang and Li, 1983). One of the most thoroughly studied 

fossil-bearing sections of loesslike silt in the plateau is a 6- 

m section exposed along the highway on the south side of 

Xigaze (figs. 27, 28). In 1980, Pewe, Liu, and Li, assisted 

by several scientists, collected sediment samples, fossils of
FOSSILS IN LOESSLIKE SILT 33

PERCENT IN

oo cn--JO 3C

>-

Ul

oUJ 

IT 

U.

UJ 40

loo

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0 ——————— ———— ———— ——— ————————————————————————————————————————————

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^^'",

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1.0 0.5 0.1 0.05 0.01 0.005 0.001 0.0005 0.0

DIAMETER, IN MILLIMETERS

Figure 30. Cumulative-frequency grain-size curves (short dashes where projected) for retransported loesslike silt in 

southern part of Qinghai-Xizang (Tibet) Plateau, China. Clay-size grains have been incorporated during retransportation, so curves are not typical of those for primary loess. (See figs. 3 and 34 for sampling sites.)

qn

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DIAMETER, IN MILLIMETERS

Figure 31. Cumulative-frequency grain-size curves 

(short dashed where projected) for samples of loess 

flanking or on top of bedrock knobs near the Yarlung 

Zangbo (Nos. 3, 4) and loesslike silt (No. 6) in agricultural field near toe of low-angle silt fan, Xizang Autonomous Region, China. Curves are similar to those of 

primary loess. Dots are data points. (See figs. 3 and 34 

for sampling sites.)
34 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

CUMULATIVE FREQUENCY, PERCENT IN 

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DIAMETER, IN MILLIMETERS

Figure 32. Cumulative-frequency grain-size curves (short dashed where projected) for clay-rich retransported 

loess, south-central Qinghai-Xizang (Tibet) Plateau, China. Many clay-sized grains have been incorporated during 

fluvial retransportation. (See figs. 3 and 34 for sampling sites.)

CUMULATIVE FREQUENCY, PERCENT IN 

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Figure 33. Cumulative-frequency grain-size curves for samples of eolian (No. 10) and fluvial (Nos. 2, 12) sand, 

south-central Qinghai-Xizang (Tibet) Plateau, China. Dots are data points. (See figs. 3 and 34 for sampling sites.)
FOSSILS IN LOESSLIKE SILT 35

mollusca, mammals, and birds, and samples for study of of the 13th Congress of International Union for Quaternary

pollen and ostracodes from this site. In 1991, Pewe led Research (INQUA) to this site, and many of the scientists

participants of the Qinghai-Xizang (Tibet) Plateau field trip collected mollusca fossils.

60 KILOMETERS 

I

^^| Quaternary fluvial and glacial sediments 

[•jijfc:';] Cretaceous sedimentary rocks 

Jurassic sedimentary rocks

Undivided Triassic and Jurassic sandstones, 

shales, and limestones

EXPLANATION

Triassic sedimentary rocks Contact

Paleozoic(?) sedimentary rocks o Sampling site and number

Ophiolite belt

Granite and granodiorite

B

S I K C

0 100

PERCENTAGE 

CLAY MINERALS

0 100

PERCENTAGE 

MAJOR MINERALS

Figure 34. Valley of Yarlung Zangbo and vicinity, south-central 

part of Qinghai-Xizang (Tibet) Plateau, China, from Lhasa to 

Tingri, showing sites of sediment samples 1 to 10 (white circles). (See fig. 3 for geographic details.) A. Generalized geologic 

map from Academia Sinica (1980). B, Weighted peak-area percentages of clay minerals in <0.005-mm fraction of sand and

loesslike silt samples. S, smectite; I, illite; K, kaolinite; C, chlorite. Quaternary sediments shown in black. C, Weight-percentage estimates of major minerals in sand and loesslike silt 

samples. Q, quartz; F, feldspar (orthoclase and plagioclase); C, 

carbonate minerals (calcite and lesser dolomite). Quaternary 

sediments shown in black.
36 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

POLLEN

Palynological research on loess of China began in 

the 1950's (Zhou and others, 1960) in the north-central 

part of the country and is now actively being pursued (Liu 

and others, 1985 p. 84-92). Pollen studies in the QinghaiXizang (Tibet) Plateau are not numerous, however. Huang 

and Ji (1981) and Wang and Fan (1987) report pollen in 

Holocene sediments near lakes in south Xizang Autonomous Region. Holocene peats have also been examined 

(Academia Sinica, 1980, p. 43-44; Wang and Fan, 1987, 

p. 50-52).

Huang Cixuan identified 25 types of pollen in seven 

sediment samples from the site above the highway on the 

south side of Xigaze in 1980. Her methods follow and her 

count and identifications are shown on figure 36.

METHODOLOGY

Samples of 100 to 200 grams were boiled for 1 to 3 

minutes in a 5-percent solution of sodium hydroxide. After

washing to neutral with distilled water, the samples were 

treated with dilute hydrochloric acid to dissolve the calcium carbonate. After again washing in distilled water, the 

samples were centrifuged in three different heavy liquids: 

Densities 2.3, 2.1, and 2.0. The remaining heavy material 

was diluted with three to five times its volume of acetic 

acid, then washed with distilled water. Next, the material 

was treated with a mixture of one part sulfuric acid and 

nine parts acetic acid and then washed with distilled water 

to neutral.

RESULTS

Analyses revealed few pollen, except in samples 12 

and 16 (figs. 27, 36). Woody species make up less than 10 

percent of the total pollen, and herbaceous species make 

up more than 90 percent; the latter are rich in Ranunculaceae and Artemisia (fig. 36).

These pollen, particularly Ephedra, Artemisia, Chenopodiaceae and Palygonaceae, suggest a dry-cold steppelike condition. However, several pollen types including

200

£160

£120

HI 

> 80

5

D: 40

10 20 

DEGREES 2-THETA

30

160

a 120

> 80

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a 40

40 10 20 30 

DEGREES 2-THETA

200

120

ui 

80

ui DC 40

B

0 10 20 30 

DEGREES 2-THETA 

BULK SAMPLE

Figure 35. X-ray diffractograms of bulk and <0.005-mm 

fractions of loess sample 3 (A, C) and sample of underlying 

bedrock of volcam'clastic sandstone and lithic tuff (B, D) 

from rock knob 15 m high at junction of Nyang Qu and

40 0 10 20 30 

DEGREES 2-THETA

<0.005-mm FRACTION OF SAMPLE

Yarlung Zangbo, Xizang Autonomous Region, China. Ca, 

calcite; Ch, chlorite; D, dolomite; I, illite; PI, plagioclase; 

Pu, pumpellyite; Q, quartz. (See figs. 22, 25 for sampling 

sites.)
FOSSILS IN LOESSLIKE SILT 37

Ranunculaceae, Cyperaceae, and Gentianaceae, indicate 

meadows and local moist substrate such as small ponds 

and wet ground. Myriophyllum is aquatic.

GASTROPODS

Fossil snails are common in Chinese loess and have 

been described over many years (Chen and others, 1985). 

However, most if not all of the work has been restricted to 

the study of land gastropods. Although pulmanate gastropods live today in southern Xizang (Chen and others, 

1985), we did not see any modern or fossil species in the 

loesslike silt. Pewe, Liu, Li, and associates collected many 

specimens of freshwater gastropods from two different 

zones in a 6-m-high exposure of loesslike silt on the south 

side of Xigaze (fig. 27, 37) in 1980. In both the upper and 

lower zones, the specimens were found in more or less 

horizontal layers a centimeter or two thick in relatively 

poorly stratified to almost unstratified silt containing some 

quartz and rock particles as much as 2 mm in diameter. 

The lower layer could be traced laterally for only about 10 

m and the upper layer for 3 or 4 m.

The lower of the two horizons has the highest concentrations of gastropods and is near the level of the road. 

The most common type and the largest species is Radix 

auricularia (L.) (fig. 38). The collection contains both juvenile and adult specimens that measure as large as 25 to

30 mm high and 20 to 30 mm wide. This is a white spiral 

gastropod; the last spiral is so large that it almost appears 

to form the entire shell. The larger specimens appear to 

be standard for this species (Zhadin, 1952, p. 118). The 

second most common species is a brownish or tan-colored, 

vertically coiled Fossari truncatula (Muller). It is much 

smaller than R. auricularia—only 5 to 7 mm high and 

only 3 or 4 mm wide. The least common gastropod is the 

small white Planorbidae, Gyraulus gredleri (Gredler). It is 

coiled in a rather flat horizontal plane, and these specimens are only about 1 to 3 mm in diameter.

The upper zone of gastropods is 3 to 5 m higher in 

the section (fig. 27), and contains fewer specimens than 

the lower zone. Only two different species were found. 

Most common by far was Fossari truncatula (Muller), and 

there were a few Gyraulus gredleri (Gredler).

Living specimens of these species are chiefly Eurasian in distribution, in areas of cold fresh water, and they 

have been reported from Quaternary deposits in the former 

Soviet Union, Alaska, and northwest Canada (Pewe and 

Journaux, 1983; Clarke and Harington, 1978). F. truncatula also lives in Newfoundland and British Columbia. Unfortunately, the terminology for these species is not always 

the same in different countries, and there has been a constant evolution of terminology over the years. This problem has been carefully pointed out by Zhadin (1952) and 

by Clarke (1973, p. 483). For example, Radix auricularia 

(L.) is also known as Lymnaea auricularia (L.).

Sample

No.

11

12

13

14

15

16 

17

Depth 

below 

surface 

(m)

Percentage (hachured) or 

number of pollen counted

Xerophyte

0 10 20

0.9

1.4 

1.8

2.0

3.6

4.8 

5.5

1

id 

14

17

17

M 

15

VI

§CJ 

rt•e

u

ffi

Pteridophyte

% 20 40 60 80% 0 10%

1 1 1 1 

1

y/////////////////////j(

2

1

6

'///////////////////A

35

i 

1

!

26

9

4

a 

5

Taxa

.8^S

^

+

+

+

+ 

+

1

SI

+

^ 

a 

c

SI

+

+

+

+

1

£

+

+

1-s;

£

+

+

+

-a

3

+

+ 

+

-S^

+

-2 

as 

tj CQ

+

+

+ 

+

to

a

£

*> a 

0)

Ranuculaceae

0 20 40 60 80%

+

^^M

Artemisia

<0

Chenopodiacea Polygonaceae Cyperaceae Gentianaceae Myriophyllum

20% 0 10%10%10%10%

+

•

+

+

+

1

•

+

+

1

1

+

1

+ +

Polypodiaceae

•Q '£.

•Si 

0,

10%

1

+

+

+ 

+

+

+

Onychium

+

+

+

Lycopodium

+

+

Concentricysts

+

+ 

+

Chlorophyta

+

+ 

+

+

+

+ 

+

Figure 36. Pollen composition of sediment samples from 

stratigraphic section (fig. 27) on scarp of terrace on west side 

of Nyang Qu, south of Xigaze, Xizang Autonomous Region, 

China. Hachured bar, percentage sum of individual taxa classified as Xerophytic (dry), Herbaceous (moist), or Pteridophytic (fern). Solid bar, percentage of individual taxa in 

assemblage. +, species present but not counted. Analyses by 

Huang Cixuan.
38 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

Radix auricularia (L.) lives in the marginal zones 

of large and small bodies of water such as rivers and 

brooks, and has been reported in Siberia (Zhadin, 1952, 

p. 118). Lozek (1964, p. 177) reports that the species is 

Paleoarctic and lives in plant-rich standing water. Pewe 

has collected it from cold-water ponds in central Alaska 

near Fairbanks and in western Alaska near Galena. 

Coworkers have found it in Quaternary sediments elsewhere in Alaska. The retransported loess of late 

Wisconsin age in central Alaska is rich in organic remains, including some fresh-water gastropods. Mertie 

(1937, p. 192-193), Taber (1943, p. 1491), and Pewe 

(1975a, p. 88-89) record Stagnicola and Gyraulus 

gredleri in the retransported loess of central Alaska. Zhadin (1952, p. 125) mentions that Fossari truncatula

(Muller) is widespread in the former U.S.S.R., is Paleoarctic, and has been found in Quaternary deposits in 

both east and west Siberia. He states that this species 

lives in silty biotopes and in cold or hot springs, as well 

as in swamps, pools, and rice fields; it occurs at elevations as high as 2,000 m above sea level. The gastropods 

at the Xigaze site, which is at 3,836 m, indicate that the 

ecological conditions under which they lived were mainly shallow ponds, probably on very gentle slopes, low 

terraces, and the flood plain of the Nyang Qu in late 

Quaternary time. As the fine-grained silt was carried by 

sheet wash and small rivulets across the gentle slopes 

from the hillsides to the terraces and flood plain, the 

ponds became filled, and adjacent land surfaces were aggraded as the sediment accumulated.

Figure 37. Collecting fossils in loesslike silt at river-terrace exposure south of Xigaze, Xizang Autonomous Region, China. Fresh-water mollusks from lower shell bed, 

right-center foreground; rodent and bird fossils from sediments beside collector at far upper left. Loess-brick wall 

in center background and a brick yard at upper far right. 

(Also see fig. 27, 28.) Photograph 4577 by Troy L. Pewe, 

June 9, 1980.
ORIGIN OF LOESSLIKE SILT 39

VERTEBRATES

Reports of Quaternary vertebrate fossils from 

Xizang Autonomous Region are not common. The few 

specimens collected in the 1970's during expeditions to 

the Qinghai-Xizang (Tibet) Plateau expeditions are reported by Huang (1980) and Huang and Ji (1981). Except for 

the Ovis sp. and Cervus reported from a cave in bedrock 

near Maizhokunggar (fig. 3), the remaining four localities 

reported by Huang (1980) are probably in loesslike silt.

An Equus sp. tooth was found in yellowish soil at 

Tingri (fig. 3), and two lower right jaw bones of Alticola 

sp. were in or near vertically jointed loesslike mud at Xiegal. Parts of Equus sp. and Bos sp. were recovered at 

Yangbajian from a 19-m-thick sediment layer believed by 

Huang (oral commun, 1986) to be retransported loess. A 

late Pleistocene metatarsal bone of Cervus sp. was recovered from a brick and tile plant at Nyingchi. Although described as from fluvial and lake deposits, the sediments are 

probably retransported loess because, as elsewhere in 

southern Xizang, it is used to make brick and tiles.

A unique collection of vertebrate fossils was recovered by Pewe, Liu, Li, and associates from loesslike silt in 

an exposure near the top of a terrace along the Nyang Qu 

at the south side of Xigaze (figs. 25, 27, 28, 37). In silt,

Figure 38. Fresh-water gastropods Radix auricularia (L.) from 

loesslike silt from stratigraphic section (fig. 28) on scarp of terrace, west side of Nyang Qu, south of Xigaze, Xizang Autonomous Region, China. Photograph PK 24,436 by Troy L. Pewe, 

Sept. 3, 1981.

about 3 m below the surface, Bruno Messerli noted small, 

delicate vertebrate bones of four different birds and two 

different rodents, identified below, and the remnants of a 

bird nest.

Asio flammeus, a short-eared owl. At least two very young 

individuals probably less than half grown and obviously still nestlings at the time of death, 

cf. Alauda arvensis, a skylark. At least three individuals. 

These specimens agree rather well with Alauda and 

do not seem to be similar to Eremophila, Galerita, 

or Lullula. The specimens are larger than available 

specimens of Alauda gulgula and therefore are most 

similar to A. arvensis.

Passer sp. (either montanus or rutilans), a sparrow. At 

least two individuals. Definitely too small for P. 

domesticus.

Passeriformes gen. et sp. indet, a song bird. One ulna and 

possibly two coracoids and two tarsometatarsi are 

from a passerine intermediate in size between Alauda and Passer.

Microtus (Pitimys) blythi, a Blyth's vole. At least 11 individuals.

Cricetulus katnensis, a Tibetan hamster. One 

individual.

The accumulation of vertebrate bones appears to be 

from a nest of the short-eared owl, and both nestlings and 

prey are represented. The species are all the same as those 

found in the southern plateau today. The owl and the lark 

are certain indicators of open country or grassland, and the 

owl may also indicate the presence of marshes. The area 

was probably one of a slowly aggrading flood-plain surface with small ponds and marshes. The bird and rodent 

bones in the old nest were covered by silt washed down 

from the slopes. Another interpretation is that the bones 

and the nest are much younger than the enclosing sediments and were deposited in a hole in the face of the silt 

cliff. Although small birds do live in holes in loess, the 

typical short-eared owl does not.

ORIGIN OF LOESSLIKE SILT

The origin of loess has been a controversial subject 

worldwide for about 100 years, and most of the discussions have centered on the loess in north-central China, 

central United States, and, later, Alaska and eastern Siberia. Less is known about the probable origin of the widespread loesslike silt in the valley bottoms and on flanks of 

the lower hills in the unglaciated southern part of the 

Qinghai-Xizang (Tibet) Plateau. Lacustrine, fluvial, weathering, and eolian processes have been invoked to explain 

the loesslike silt. The weathering or residual hypothesis 

has little support. The lacustrine hypothesis, either separately or with fluvial processes, has been held since the 

late 1970's and 1980's (Academia Sinica, 1980). The
40 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

eolian hypothesis has been strongly suggested since 1980 

(Pewe, 1980 a, b, 1981; and Pewe and others, 1981, 1985, 

1987). Whatever the origin, it is evident that most of the 

silt has been retransported downslope by sheet wash, rill 

wash, creep, solifluction, and (or) by small ephemeral 

streams or rivulets.

WEATHERING HYPOTHESIS

In the early part of this century, L.S. Berg proposed 

and expounded in many publications of the former 

U.S.S.R. that loess forms in place as the underlying rock 

breaks down (summarized in Berg, 1964 [I960]). His hypothesis exerted a profound influence over many Soviet 

scientists, but now it seems to have little support in the 

western part of the former Soviet Union. In the 1950's, 

Soviet scientists carried the concept of the origin of loess 

by residual weathering to China. For example, Pavlinov 

(1959) stated that loess formed from destruction of local 

underlying bedrock. Many scientists in eastern Siberia 

continued to hold the view that the loesslike silt is a product of rock material broken down by seasonal freezing and 

thawing. The eolian origin for the loess in eastern Siberia 

was demonstrated by Tomirdiaro (1972) and Pewe and 

Journaux (1983).

It has been suggested that the loesslike silt in the 

southern part of the Qinghai-Xizang (Tibet) Plateau formed 

in place by disintegration of local country rock. If the loesslike silts were formed in place by disintegration of the local 

country rock, three conditions would be expected.

(1) The mineralogy of the silt and the underlying 

rock would be similar, allowing for differential resistance 

to weathering. However, the loesslike silt in the area overlies many substrates, including alluvium, poorly consolidated sands, glacial outwash, limestone, and various other 

types of bedrock. In the vicinity of Xigaze, loesslike silt 

overlies a 15-m-high bedrock knob near the junction of 

the Nyang Qu and the Yarlung Zangbo. Mineralogical 

analyses show that the silt (sample 3; tables 1, 4, 6) could 

not have been derived from weathering, either chemical or 

mechanical, of the underlying rock, which is a volcaniclastic sandstone or lithic tuff that contains pumpellyite 

that is not present in the silt. Furthermore, the silt contains 

illite, which is not in the underlying rock.

On the south side of the Yarlung Zangbo, about 50 

km downstream from Xigaze, a thick deposit of loesslike 

silt (sample 4, table 1) blankets the upper flanks of the 

valley almost to the top of a small knob of limestone 

(figs. 23, 24). Although the loesslike silt includes grains of 

limestone, most of it is composed of multicycle quartz 

grains and abundant feldspar grains. The silt could not 

have resulted from weathering of the underlying bedrock.

(2) If silt accumulated on top of a hill or a flat-lying 

area through the disintegration of underlying bedrock, the

material at the surface should be finer and more weathered 

than that closer to bedrock. However, examination of the 

section of loesslike silt on the knob of rock near the Nyang 

Qu at Xigaze did not demonstrate this relation at all.

(3) The sediments produced by bedrock disintegration would undoubtedly contain some large bedrock particles, especially of the more resistant materials, and the 

contact with the bedrock would be gradational. No such 

particles were noted in the field, especially above the bedrock knob near Xigaze but also above other bedrock. The 

loesslike silt overlies the bedrock with a sharp contact, and 

coarse particles in the lower part of the section are scarce. 

The contact marks a striking change in textural and mineralogical composition.

In summary, a number of characteristics that would 

be expected in the loesslike silt if it were formed in place 

by disintegration of bedrock are not observed. The lack of 

all these conditions argues convincingly against the weathering hypothesis.

LACUSTRINE HYPOTHESIS

Only two publications suggest that thick deposits of 

loesslike sediments, especially in the bottoms of the valleys of Nyang Qu and elsewhere, may have been deposited in a now-drained Pleistocene lake at Xigaze (fig. 3) 

(Academia Sinica, 1980, p. 11; Zheng and Jiao, 1991). 

This idea was offered to explain the prominent silt terraces 

on the sides of the valley and the presence of fresh-water 

gastropods and ostracodes (figs. 25, 26, 27). The lacustrine 

hypothesis is improbable for several reasons:

(1) Barriers capable of damming water up the 

Yarlung Zangbo and Nyang Qu have not been proven to 

exist. Years ago, Ward (1926) examined the gorges for 

barriers of the Yarlung Zangbo without success. However, 

it is possible that the Yarlung Zangbo and its tributaries 

could have been flooded in the past.

(2) Evidence of shorelines, wave-cut benches, and 

deltas would be preserved in a lacustrine environment, but 

no such features are associated with the silt.

(3) Lacustrine deposits have a limited vertical extent, but the loesslike silt is found at various elevations, 

even on moraines in the Yangbajain valley.

(4) Lacustrine silt would be stratified and might 

even contain varves. This silt is poorly stratified, but some 

well-stratified sand-and-gravel beds occur locally. In no instance does the stratification resemble lacustrine bedding.

(5) An appreciable amount of clay could be expected 

in deposits of any large lake. Most of the sediment samples in the valley-bottom deposits are of silt or sand; however, locally the clay component is 30 to more than 40 

percent.

(6) Lacustrine deposits would bear little lithologic 

relation to the underlying rock. This characteristic, howev-
ORIGIN OF LOESSLIKE SILT 41

er, is typical of any transported sediment, including the 

loesslike silt.

(7) Some: forms of life would have existed in these 

lakes. So far as; we are aware, no lacustrine fossils such as 

fish have been found in the silt, although gastropods, ostracodes and pollen occur. Most of the pollen suggests an 

origin in meadows and small ponds, not in large deep 

lakes. The ostracodes indicate the same environment. The 

gastropods indicate mainly shallow ponds and marshes, 

probably on very gentle slopes, low terraces, and flood 

plains; they are not characteristic of large lakes.

(8) Land fossils would be absent or scarce in lacustrine deposits. The few mammal remains found in the silt 

indicate a land environment. In the thick loesslike silt deposits at Xigaze, the bones of four different birds and two 

different rodents that were found indicate an environment 

of small ponds and marshes, not a large lake.

(9) Mud cracks and ripple marks would be expected 

in lacustrine silt, but none have been observed in the 

loesslike silt.

All but one of these features that are characteristic 

of lacustrine deposits are contrary to the observed nature 

of the loesslike silt. The one feature (sample 6) that is 

consistent is typical of deposits transported by any mechanism. The observed characteristics of the silt in the southern part of the Qinghai-Xizang (Tibet) Plateau cannot be 

explained by the lacustrine hypothesis.

EOLIAN HYPOTHESIS

Scientists with the Qinghai-Xizang (Tibet) Plateau 

expeditions in the 1970's referred to some of the silt on 

and in the fans flanking the lower parts of the mountains 

and in valley bottoms in the southern part of the area as 

loesslike deposits (Zhao and others, 1976; Li and others, 

1983). The first published suggestions that the silt was retransported loess probably were by Pewe (1980 a, b, 1981) 

and Pewe and others (1981, 1985, 1987). This study of the 

silt in the southern part of the Qinghai-Xizang (Tibet) Plateau, and our comparison with similar deposits elsewhere 

in China and other parts of the world, supports the identification of the deposits as loess and retransported loess.

Features ;and characteristics of eolian-deposited silt 

fall into three groups: field relations, mechanical composition, and petrographic character (Smith and Fraser, 1935).

preloess topography, filling up the gullies, covering the 

minor elevations, lying deepest in the depressions and 

thinning-out up the flanking slopes of the higher ridges." 

The loesslike silt in the Qinghai-Xizang (Tibet) Plateau 

occurs as a surficial mantle and fits Barbour's description. 

It is thin on top of low hills, is thicker on the flanking 

fans, and reaches maximum thickness in the broad valley 

bottoms. A thin veneer of the silt remains on the rather flat 

passes or highlands where it has not been removed by 

down-slope processes.

INDEPENDENT LITHOLOGIC CHARACTER

Wind-deposited material usually differs mineralogically and texturally from the underlying material. In the 

southern part of the plateau, the loesslike silt covers sand 

and gravel, glacial till, and various types of bedrock. The 

fine texture of the silt contrasts strongly with the texture of 

the underlying material. Petrographic study of samples 

from the silt and bedrock at the knob at Xigaze, and at the 

limestone hill 50 km downstream from Xigaze, indicates 

mineralogical differences between the silt and the underlying bedrock.

ABSENCE OF DISTINCT STRATIFICATION

One characteristic of loess is the absence of distinct 

stratification in silt on top of hills. Within the study area, 

the loesslike silt on top of hills also lacks stratification. 

However, transportation of the silt from the slopes to the 

alluvial fans and to the valley bottoms produces poor to 

well-developed stratification, especially if interbedded 

with sand or gravel layers.

COLOR AND TEXTURE

Wind-deposited silt is generally light colored and 

stained by moving ground water or carbonaceous inclusions; the texture is generally uniform. In loess away from 

a river or not on slopes or valley bottoms, clay makes up 

no more than 10 to 15 percent of the sediment. The loesslike silt in the study area is comparable to loess elsewhere 

in the world, except that much of it is interbedded with 

sand and gravel.

FIELD RELATIONS

TOPOGRAPHIC DISTRIBUTION

As clearly stated by Barbour (1930, p. 468), in reference to the loess of central China, the mantle of loess

ASSOCIATION WITH OTHER EVIDENCE OF WIND ACTION

Smith and Fraser (1935, p. 19) state that sand dunes 

and ventifacts may be expected near the source of material. 

The plateau is conventionally referred to as a wind-swept

"conforms closely to the general contouring of the buried area and a land of blowing sand and dust. Inhabitants have
42 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

long been aware of these conditions, and early western explorers remarked about the "raving wind," "wind roaring 

over the sandbanks," "perpetual harassing blasts," and "ruthless winds" (Ward, 1926). Two French Vincentian missionaries to Lhasa in 1896 bitterly complained of the terrible 

north wind that lasted 15 days and menaced them with 

distraction (Hue and Gabet, 1928, v. 2, p. 147-148). A professor of Oriental language from London, entering Tibet in 

disguise in 1923, remarked of the effect of the wind on the 

Yarlung Zangbo "* * * so strong was the wind in the opposite 

direction [of the flow of the river] that its blasts on the river 

made it seem as if the water was flowing backward and 

uphill; in fact, so strong was the illusion that [the natives] 

thought it to be real and bowed down in worship of a supposed 

miracle." (McGovern, 1924, p. 285-286). Early western explorers also commented on the presence of immense sand 

dunes, especially in the Zangbo corridor (Rawling, 1905). 

Various types of dunes, especially climbing dunes (cover 

photograph, fig. 16), occur along the broad, gravel-floored 

valleys of major streams (Zhao and others, 1976, p. 6; Wang 

and Fan, 1987; Reiter and Reiter, 1981). David-Neel (1927, 

p. 299-300) commented about invading sand in 1923:

Quite near Lhasa, on the left bank of the Brahmaputra 

[Yarlung Zangbo], one finds a miniature Sahara whose extensive white dunes are invading the whole country* * *.

* * * In spite of a ridge which stood in their way, the sands 

have taken a firm footing in the Kyi Valley, and though still 

shallow on that side, their fine dust is beginning to accumulate along the hedges which border Norbu ling, the pleasure 

garden of the Dalai Lama. It may possibly be that in a few 

generations Lhasa will be reached. Who knows whether, in 

a still more distant future, some savant, excavating the entirely submerged city, may not discover the Potala and the 

Jo Khang, just as we now lay bare the palaces and temples 

which the sands of the great Gobi have overwhelmed* * *.

On our way * * * there were a few more villages whose fields 

are gradually disappearing beneath the mounting sands.

These dunes are evidence of eolian action still active 

on the almost vegetation-free flood plains (figs. 13, 15).

Bare sand-and-gravel bars of the braided streams 

(cover photograph and figs. 12-14) also provide an excellent source area for enormous clouds of blowing dust that 

are common in late winter, spring, and early summer. A rare 

photograph of clouds of dust beginning to form on the bare 

flood plain of the Lhasa He near Lhasa in 1954 is illustrated 

by Sis and Vanis (no date, pi. 50). The duststorms range 

from a "maze of dancing dust devils" (Ward, 1926, p. 43) 

to "huge black clouds approaching rapidly" (Harrer, 1953, 

p. 163). Harrer further states (1953, p. 163) that in Lhasa, 

"* * * the Potala Palace disappears and at once everyone 

rushes for home. Street life stops." and (p. 316) that the 

departure of the Dalai Lama from Lhasa to India on March 

19, 1959, occurred during a notorious sandstorm and duststorm that immobilized Lhasa in the early evening.

Commenting further in this vein, Alexandra DavidNeel (1927) reported that she became the first foreign 

woman in Lhasa in 1923 when an immense dust storm 

permitted her to enter the Forbidden City undetected as 

she states (p. 256-257):

All of a sudden a furious storm arose, lifting clouds of dust 

high into the sky. I have seen the simoon in the Sahara, but 

was it worse than this? No doubt it was. Yet, that terrible 

dry lashing rain of dust gave me the impression of being 

once more in the great desert.

Indistinct forms passed us, men bent in two, hiding their 

faces in the laps of their dresses, or whatever piece of cloth 

they might happen to have with them.

Who could see us coming? Who could know us? An immense yellow curtain of whirling sand was spread before 

the Potala, blinding its guests, hiding from them Lhasa, the 

roads leading to it, and those who walked upon them. I interpreted it as a symbol promising me complete security, 

and the future justified my interpretation. For two months, I 

was to wander freely in the lamaist Rome, with none to 

suspect that, for the first time in history, a foreign woman 

was beholding the Forbidden City.

"The gods threw a veil over the eyes of his adversaries and 

they did not recognise him." So went an old Thibet's tale 

which I had heard long ago.

Present day reports support these early views (Han, 

1979, p. 166):

The wind. A blinding, laceration blizzard of sand and stone, 

and the whole world destroyed by this maelstrom of small 

pebbles whirling in the choking air. Lips, hands and face 

are flayed. The turquoise sky, the white houses, even the 

Potala, are no longer, all swallowed in a yellow opaqueness 

which is the wind * * *. For three days the wind blew, and 

no planes came * * *. Then, relief. With the night the wind 

abates though an overhang of sand [dust] will remain in the 

air for another day or more. In the past, the lamas * * * 

blew long silver trumpets to compel the wind away.

In the absence of silver trumpets, similar or larger 

clouds of dust in late Pleistocene times undoubtedly deposited silt onto the slopes of the hills and mountains 

(cover photograph). Many workers have demonstrated that 

no more wind is necessary to blow that dust than is 

present today, as winds of 20 m/s are more than strong 

enough to bear quantities of dust in both periglacial areas 

and hot desert areas (Bryan, 1927, p. B39-B40; Pewe, 

1951; Warn, 1953; Pewe and others, 1976, 1981b). If there 

were larger source areas than today in late Pleistocene 

time, such as wider unvegetated flood plains of braided 

streams, from more extensive glaciated areas (Shi and others, 1993, fig. 3; Li and Li, 1991), wind-blown dust must 

have been abundant. In fact, Feng and Thompson (1989) 

and Zhang and others (1991) state that silt from the northern part of the Qinghai-Xizang (Tibet) Plateau may have
RETRANSPORTED LOESS 43

blown eastward to the great loess plateau of central China 

north of Xian (fig. 1) during Pleistocene time.

FOSSILS OF AIR-BREATHING ANIMALS

Fossils of air-breathing animals should logically be 

expected in the silt if the material is eolian. Late Pleistocene vertebrate fossils recorded in the loesslike silt in 

the southern part of the Qinghai-Xizang (Tibet) Plateau 

(Huang, 1980) include remains of horse, bison, and other 

mammals. Bones of two types of rodents and four types of 

birds were found in the loesslike silt near Xigaze. The 

preservation of many of the specimens shows very little 

evidence of transportation.

Although land gastropods are well known from loess 

in central China, none are reported in the loesslike silt in 

the southern part of the Qinghai-Xizang (Tibet) Plateau. 

Nevertheless, Succinea representatives live in the area 

today. Russell (1944, p. 34) regarded land gastropods as 

being characteristically present in loess. However, land 

gastropods have not been found in some U.S.A. loess in 

the upper Mississippi River valley or in most of the loess 

in Alaska (Pewe, 1955, p. 720-721).

MECHANICAL COMPOSITION

In loess, the grain-size and degree of sorting is similar to that of windblown dust or volcanic ash that has been 

transported a considerable distance (Udden, 1898, p. 31- 

60; Swineford and Frye, 1945, p. 252; Warn and Cox, 

1951, p. 559; Pewe, 1955, fig. 11; Pewe and others, 1976). 

Some of the material on the Qinghai-Xizang (Tibet) Plateau is similar to silt known to be loess. Cumulativefrequency grain-size curves of mechanical analyses of 

windblown dust from Arizona, Kansas, and Germany are 

similar to those of loesslike silt from the top of a bedrock 

knob (sample 3) and from other localities in the plateau, 

where the silt is near the river (sample 4) or is slightly 

retransported (sample 6; fig. 39).

Samples 3, 4, and 6 from the southern part of the 

plateau were compared with samples from deposits of 

silt of known eolian origin from elsewhere in the world 

(fig. 40). The great similarity of grain size and degree of 

sorting between the samples constitutes a strong argument for the eolian hypothesis. Cumulative-frequency 

grain-size curves of that loesslike silt from near Xigaze 

are compared with curves of known loess samples collected from Beijing, New Zealand, Alaska and Illinois in 

the U.S.A., France, the former Czechoslovakia, Siberia, 

and Uzbekistan. The sample of loesslike silt that has 

been retransported (sample 6) is mixed with different 

sediment sizes and bears less resemblance to primary 

loess.

PETROGRAPHIC CHARACTER

Angular grains have long been considered typical 

of loess (Barbour, 1925a, fig. 1; Twenhofel, 1932; Charlesworth, 1957), and scanning-electron-microscope analysis supports that assumption (Cegla and others, 1971; 

Pye, 1987). Silt grains from the Qinghai-Xizang (Tibet) 

Plateau are clearly angular, especially light minerals 

such as quartz. Loess grains probably should also be 

largely unweathered, and clay minerals among them 

should be largely unweathered (Smith and Fraser, 1935; 

Charlesworth, 1957), although the degree of weathering 

would depend on the age and rate of deposition of the 

sediment and the effects of diagenetic processes. The 

loesslike silt from the plateau, like upper Pleistocene 

loess from other parts of the world, is relatively fresh 

but shows some weathering under the scanning electron 

microscope.

SUMMARY

The characteristics of loesslike silt in the QinghaiXizang (Tibet) Plateau and the similarity between it and 

primary loess support the eolian hypothesis. In the light of 

this evidence, we conclude that the unstratified loesslike 

silt on top of bedrock hills of the plateau is primary loess, 

and that the poorly to well-stratified loesslike silt on the 

lower slopes and in valley bottoms of the major river valleys is retransported loess.

RETRANSPORTED LOESS

Very little of the loesslike silt in the southern part of 

the Qinghai-Xizang (Tibet) Plateau is primary loess; most 

of it is called "retransported loess" in this report. The retransported loess has been transported a few meters to 

hundreds, if not thousands of meters downslope, primarily 

by processes involving water. It is poorly to fairly well 

stratified and is intercalated with sand-and-gravel layers. 

With increasing distance from the hills and mountains, the 

sand, gravel, and other detritus became finer, and the numbers of layers of coarse sediments also decrease.

Retransported secondary loess is not unique to this 

area; it is widespread in the world, especially in areas of 

hills and mountains. Andersson (1923, p. 129) reported 

such deposits from central China many years ago and used 

the term "redeposited" loess:

In many valleys within the loess areas there are deposits of 

loess interstratified with gravel and occurring under such 

conditions that they must evidently be regarded as representing later depositions derived from the genuine loess. 

They are valley deposits of very limited extent with rapid 

and irregular changes of the stratification. Thick beds of
44 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

gravels suddenly appear, and the gravel component of these 

deposits is far more abundant than is the case in the genuine loess. Everything goes to show that in the formation of 

the secondary loess-gravel beds water action has been the 

dominant factor and the wind has played only a very subordinate role. I call these deposits Redeposited Loess in order 

to distinguish them from the genuine Primary Loess.

Such secondary loess deposits are known elsewhere 

in the world, and they have been described in various 

ways in different languages. Other terms include "alluvial 

loessial deposits" (Wang and Song, 1983), "loess-like 

slope deposits," "deluvial loess," "slope loess," a quite appropriate term "mountain loess" (Pecsi, 1965, 1967), and 

"colluvial silt" (Li and others, 1983). In Alaska, the term 

"retransported silt" has been used, and "muck" is used in 

the sub-Arctic and Arctic Alaska where the retransported 

material has a high organic content that has been frozen 

since the time it was deposited (Pewe, 1968, 1975a, b; 

Pewe and others, 1989). The frozen material has preserved 

an abundant number of mammal remains, including perennially frozen carcasses.

In some regions where thick loess is well studied, the 

primary loess deposits interfinger and are interleaved with

redeposited loess deposits. This interfingering indicates 

changes in climate and (or) the activity of erosional processes.

To more fully understand the characteristics of retransported loess in other parts of arid western China, and 

to compare such deposits with loesslike silt in the Qinghai-Xizang (Tibet) Plateau, Pewe examined retransported 

loess deposits and land forms on the south side of the Tian 

Shan in the Xinjiang Uygur Autonomous Region (fig. 1) 

in 1986 (Pewe, 1987) and discussed in detail with Mu 

Guijin in 1984 to 1986 the retransported loess deposits 

and landforms in the middle Hi He valley on the north 

slope of the Tian Shan. Mu is familiar in detail with the 

valley fills of loess in the Hi He valley and at Turpan (Mu, 

written commun., 1987; Yuan and others, 1983; and Wang 

and others, 1991). These deposits were classified as alluvial loessial deposits by Wang and Song (1983). It was immediately apparent to Pewe that this material in 

northwestern China exhibits the same characteristics as the 

loesslike silt in the southern part of the Qinghai-Xizang 

(Tibet) Plateau.

Turpan (figs. 1, 2, 5) lies in the hottest and lowest 

(154 m below sea level) part of China and is on the historical Silk Road. With irrigation from the mountains by the

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Figure 39. Cumulative-frequency grain-size curves for samples of loess (Nos. 3, 4) and retransported silt (No. 6) 

from near Xigaze, Xizang Autonomous Region, China, compared with those for volcanic ash (Ester Ash Bed) from 

near Fairbanks, Alaska (P6w6, 1955, fig. 11; pi. 2, fig. 1), and modern wind-deposited dust from roof of house at 

538 E. Fairmont Dr., Tempe, Ariz. (Pewe and others, 1981, fig. 5), the third floor outside window sill, Lakeway 

Hotel, Meade, Kan. (Swineford and Frye, 1945, p. 252), and from Breslau, Selesia, Germany (now Wroclaw, Poland) (Zeuner, 1949, p. 27). Samples from Alaska, Arizona, and China collected by T.L. P6w6. Alaskan sample 

analyzed by U.S. Army Corps of Engineers, Rock Island, 111.; Arizona sample analyzed by Andr6 Journaux at 

Centre de Geomorphologie du Centre National de la Recherche Scientifique, Caen, France; Chinese samples analyzed by R.M. Slatt at Cities Service Company, Tulsa, Okla.
AGE AND CORRELATION OF SILT DEPOSITS 45

method of underground canals (karez), the areas of retransported loess have become leading producers of excellent melons and grapes. Only 8 km west of Turpan, at the 

ruins of the ancient city of Jiaohe (figs. 41, 42), small 

streams are entrenched 30 m or more into the valley fill of 

retransported loess to produce vertical walls and mesas 

(figs. 43, 44) that are strikingly similar to the terraces and 

mesas cut into the poorly bedded loesslike silt at Xigaze 

(figs. 26, 27) in the Qinghai-Xizang (Tibet) Plateau. Granulometric analysis of the retransported loess at Jiaohe 

(sample 18) yields a cumulative-frequency grain-size 

curve similar to those of loesslike silt from near Xigaze 

(table 1, figs. 39, 45). The curves are not like those of 

primary loess. Retransported loesslike silt at Kuqa (figs. 1, 

2, 5; table 1, sample 19), 600 km west of Turpan, has interbedded gravel layers similar to those in fans in the 

Qinghai-Xizang (Tibet) Plateau. Cumulative-frequency 

grain-size curves show that the loesslike silt at Kuqa is 

coarser than that at Jiaohe and has a lower clay-size content (fig. 45).

Retransported loess along the middle Hi He valley 

on the north slope of the Tian Shan forms terraces similar

to those at Xigaze (fig. 46). The upper slopes of the valley 

walls are blanketed with primary loess of late Pleistocene 

age. A cumulative-frequency grain-size curve of clay-rich 

primary loess 15 km north of Nilka (sample M7, fig. 45; 

Mu Guijin, written commun., 1992) on the Hi He is similar to one for primary loess in the Qinghai-Xizang (Tibet) 

Plateau (sample 3). Poorly bedded retransported loess of 

late Pleistocene and Holocene age overlies sand-and-gravel alluvium of middle Pleistocene age (fig. 46) in the valley bottoms. At least two flat-topped terraces have been 

cut into the retransported loess by the river.

AGE AND CORRELATION 

OF SILT DEPOSITS

Although loess has been accumulating throughout 

Quaternary time in the areas of classic thick loess of 

north-central China (Burbank and Li, 1985; Heller and 

Liu, 1982, 1984; Heller and others, 1989; Liu and Yuan, 

1982; Liu, 1987; Rutter and others, 1991), loesslike silt of 

the southern part of the Qinghai-Xizang (Tibet) Plateau

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Figure 40. Cumulative-frequency grain-size curves for samples of loess (Nos. 3, 4) and retransported silt (No. 6) 

from near Xigaze, Xizang Autonomous Region, China, compared with those for loess from around the world: West 

side of Banks Peninsula, 40 km south of Christchurch, New Zealand; Brno, Czechoslovakia; 60 km northeast of 

Yakutsk, Yakutia (now Siberian Russia) (Pewe and Journaux, 1983, fig. 29, sample K); Fairbanks, Alaska (Pewe, 

1955, fig. 11); Beijing, China (sample 20); Rock Island, Illinois; 50 km south of Samarkand, Uzbekistan; and near 

Caen, Normandy, France. Sample from France collected by Andre Journaux; sample 20 collected by RJ.E. Brown; 

all others collected by T.L. Pewe. Illinois and Alaska samples analyzed at U.S. Army Corps of Engineers, Rock 

Island, 111.; samples 3, 4, and 6 analyzed by R.M. Slatt at Cities Service Company, Tulsa, Okla. Other samples 

analyzed at Centre de Geomorphologie du Centre National de la Research Scientifique, Caen, France, under direction of Andre Journaux.
46 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

seems to represent only late Quaternary time. Vertebrate 

remains in the retransported loess are late Quaternary, although Huang (1980) states that paleontological studies of 

loess in the southern Qinghai-Xizang (Tibet) Plateau are 

only just beginning and that middle Quaternary vertebrates 

may be recovered during further investigations.

Attempts to date gastropod shells from the 15-mhigh section of retransported loess at Xigaze (fig. 27) give 

interesting results. The shells were taken from the upper 

shell bed near the top of a section, which is thought to be 

of late Pleistocene age, where considerable subsequent 

downcutting has left high terraces on both sides of the 

Nyang Qu (figs. 25, 26, 27). The shells submitted by 

Anders Martinsson show a radiocarbon age of 2,010+85 yr 

B.P. (U. Olsson, written commun. to Liu Tungsheng, 

1981). Olsson also stated that the "sample was a little too 

small." Gastropod shells collected by Pewe show a radiocarbon age of 3,645±110 yr B.P. (Robert Stuckenrath, 

written commun., 1981, laboratory sample SI-4651). 

Stuckenrath found the date puzzling and concluded from 

his testing that the snails must have been heavily charged

with radon from their local microenvironment. Both laboratories, therefore, consider the ages questionable.

SUMMARY

Retransported loesslike silt occurs as fans and valley-bottom deposits in the southernmost part of the 

Qinghai-Xizang (Tibet) Plateau. The loesslike silt, reaching thicknesses of as much as 15 m, is well sorted, poorly 

stratified, and interbedded locally near the hills and mountains with layers and lenses of sand and gravel. It overlies 

all substrates with a sharp contact and contains minerals 

not present in the underlying bedrock. The loesslike silt is 

massive, stands in sheer cliffs, and is strikingly eroded by 

narrow steep-walled gullies. It contains a few land vertebrate fossils and fossil gastropods that lived in shallow 

fresh-water ponds.

Hypotheses to explain the origin of the loesslike silt 

have included residual, lacustrine, and eolian processes. 

The hypothesis that loesslike silt is a residual product of

Figure 41. Ruins of ancient city of Jiaohe 8 km west of Turpan, 

Xinjiang Uygur Autonomous Region, China (figs. 1, 2). City in 

this arid region existed about 2,000 years ago; walls of loess 

bricks were built on mesa of retransported loess 30 m high and 

bounded on three sides by two steep-walled narrow valleys.

View southeast toward flat aggradational surfaces of retransported loess beyond valley that crosses near top of photograph. (Also 

see figs. 42, 43, and 44 and compare with fig. 26 that shows 

mesa-like remnants of retransported loess at Xigaze, China.) 

Photograph 4900 by Troy L. Pewe, Aug. 5, 1986.
SUMMARY 47

breakdown in place of the underlying rocks, mainly by 

frost action, has little support. Evidence against this hypothesis includes (1) minerals in the silt are not everywhere similar to those in the underlying bedrock, (2) no 

large particles of more resistant minerals are present, and 

(3) the silt does not become progressively coarser toward 

bedrock.

The lacustrine hypothesis is strongly supported by 

scientists in some areas because of the prominent silt terraces along the sides of valleys and because of the presence of fresh-water gastropods and ostracodes. But several 

circumstances indicate this origin is unlikely. No shorelines, wave-cut beaches, or deltas are present; nor are ripple marks, mud cracks, and deep-water lake fossils found. 

Neither lacustrine stratification nor an appreciable amount 

of clay exists in the silt. No definite upper limit of the 

deposits, to be expected under a lacustrine hypothesis, is 

present.

Evidence for the eolian origin of the upland silt is 

abundant. (1) The silt blankets older topography. (2) It is 

lithologically independent of the underlying material. (3) 

Stratification is indistinct or absent on small hilltops where

the silt has not been retransported. (4) The silt is abundant 

in areas having sand dunes and active duststorms. (5) It 

contains fossils of air-breathing animals. (6) Sorting and 

texture of the loesslike silt on hilltops or near hilltops are 

similar to those of loess and windblown dust from many 

different areas in the world. (7) Individual silt grains are 

angular and relatively fresh.

The only glaciation in the southern part of the Qinghai-Xizang (Tibet) Plateau has been in the high areas of 

the Himalayas, the Nyainqentanglha Shan, and associated 

mountains in the upper reaches of the Yarlung Zangbo. 

Valley glaciers in these mountains were more extensive 

during glacial maxima, and unvegetated floodplains, characteristic of the modern major streams, were more widespread then. We believe the upland silt on the plateau is 

loess that was deposited against the hills and mountains by 

winds blowing across the unvegetated floodplains and the 

desert rocky plains to the north during late Quaternary 

time. Most of the loesslike silt on the plateau is silt retransported loess that has been moved downslope and redeposited by rillwash, sheetwash, stream action, and 

solifluction.

Retransported__]k ; 

loess -±i=:

Figure 42. Schematic block diagram of late Pleistocene retransported bedded loess (Wang and Song, 1983) in small valley at Jiaohe 8 km west of Turpan, Xinjiang Uygur 

Autonomous Region, China (fig. 1). Arrows on circled numbers show direction of view of photographs in figures 41 and 

43 (fig. 44 faces opposite direction of fig. 41 and also includes southeast end of mesa). Sketch by Mu Guijin, 1986; 

vertical exaggeration 7.5.x.
48 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

Figure 43. View upstream (northwest) of narrow, irrigated, steep-walled valley entrenched 30 m into retransported loess on west side 

of ruins of ancient city of Jiaohe near Turpan, Xinjiang Uygur Autonomous Region, China (figs. 1, 42). Photograph 4898 by Troy L. 

Pewe, August 5, 1986.
SUMMARY 49

Figure 44. Oblique northwest-facing aerial photograph of mesa-like remnants of retransported loess 8 km west 

of Turpan, Xinjiang Uygur Autonomous Region, China (figs. 1, 41, 42). Ruins of ancient city of Jiaohe on 

mesa outline house structures built of loess bricks. Photograph by Georg Gerster, Copyright National Geographic Society; taken September 5, 1987, at 9:30 a.m., and published with permission.
50 LOESSLIKE SILT IN THE SOUTHERN QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

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Figure 45. Cumulative-frequency grain-size curves for samples of primary loess and retransported loess from Xinjiang Uygur Autonomous Region in northwestern China (figs. 1, 2) and primary loess and retransported loess from 

southern Qinghai-Xizang (Tibet) Plateau (fig. 34). Sample 4 is sandy primary loess from east of Xigaze, Xizang 

Autonomous Region (fig. 34; table 1); M7 is clay-rich primary loess from 15 km north of Nilka in Hi He valley, 

Xinjiang Uygur Autonomous Region (figs. 1, 46); 18 and 19 are retransported loess from Xinjiang Uygur Autonomous Region (figs. 1, 2, 5; table 1); and 7 is retransported loess from west of Xigaze (table 1). Samples 4 and 7 

collected by T.L. Pewe and analyzed by R.M. Slatt at Cities Service Company, Tulsa, Okla.; samples 18 and 19 

collected by T.L. Pewe (Pewe, 1987) and analyzed by Mu Guijin at Arizona State University, Tempe, Ariz.; sample 

M7 collected and analyzed by Mu Guijin, Institute of Geography, Academia Sinica, Uriimqi, Xinjiang Uygur Autonomous Region, China. Dots are data points.

Sand and 

gravel alluvium

Figure 46. Schematic block diagram of loess and retransported 

loess 15 km north of Nilka, in Hi He valley, north slope of Tian 

Shan in Xinjiang Uygur Autonomous Region, China (200 km 

north of Kuqa) (fig. 1). Valley has three levels of terraces. Primary loess blankets high terrace and uplands, and retransported 

stratified loess of late Pleistocene to Holocene age is exposed on

two lower levels of terraces in valley, beside and over Middle 

Pleistocene sand-and-gravel alluvium. Retransported loess and 

terrace scarps are similar to those at Xigaze and elsewhere in the 

southern part of the Qinghai-Xizang (Tibet) Plateau (figs. 26, 

27). Tl, terrace number; M7, location of loess sample. Sketch 

by Mu Guijin in 1986; vertical exaggeration lOx.
REFERENCES CITED 51

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433.

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