Journal of Southeast Asian Earth Sciences, Vol. 6, No. 2, pp. 75 82, 1991 0743-9547/91 $3.00 + 0.00 Printed in Great Britain Pergamon Press plc

Extractable Fe-A! and geochemistry of Late Pleistocene paleosols in the Dalijia Shan, western China

WILLIAM C. MAHANEY,* R. G . V. HANCOCK'~ and KANDIAH SANMUGADAS*

*Geomorphology and Pedology Laboratory, Atkinson College, York University, 4700 Keele Street, North York, Ontario, Canada M3J 1P3; and "t'SLOWPOKE Reactor Facility and Department of Chemical Engineering and

Applied Chemistry, University of Toronto, Toronto, Ontario, Canada M5S IA4

(Received 16 October 1990; accepted 16 May 1991)

Abstract--Surface paleosols in two tills and a diamicton were analyzed for extractable Fe and A1 and to determine if elemental distributions would assist in the interpretation of past and present soil-forming environments. Extractable Fe and A1 distributions indicate that leaching (based on movement of Fep) is pronounced in paleosols dating from the last glaciation. Moreover, analysis of oxalate extractable Fe and dithionite extractable Fe (Feo/Fed) shows that amorphous Fe increases with depth in all three paleosola with similar rates of conversion to crystalline Fe. Data for extractable forms of Al-oxides show somewhat higher values of pyrophosphate extractable AI with time. Because the climate in the field area is dry (precipitation < 760 mm) the amounts of crystalline Fe (Fed) in paleosols dating from early and late stades of the last glaciation are not high. Using values in the paleosol sola the difference amounts to 0.4%. Pyrophosphate extractable Fe shows a pronounced increase in the two older paleosols that may result from interstadial paleoclimates of the last glaciation. The geochemistry of the glacial and aeolian sediments (paleosols) indicates differences that they are probably related to the source areas of the different parent materials.

INTRODUCTION

SURFACE ALPINE PALEOSOLS undergo changes in the con- centrations of extractable Fe and Al that have proved useful in relative age determination as well as in assess- ment of past and present soil-forming environments (Mahaney and Fahey 1988). Also, extractable Fe and Al have been utilized to separate surface soils and place them taxonomically (Blume and Schwertmann 1969, Lutwick and Dormaar 1973, Mahaney and Fahey 1988). In this study, we sought to determine whether ex- tractable Fe and Al, and geochemical data might (a) assist in the interpretation of the genesis of three surface paleosols (relict types; see Ruhe, 1965), (b) be used for age determination, and (c) prove useful in determining downward translocation of fine-grained material in the three paleosols.

FIELD AREA

The Dalijia Mountains lie on the border between Gansu and Qinghai provinces (Fig. 1A) of western China. From the summit area of 4636 to ~3100 m.a.s.1. moraines, dating from the last glaciation, cover the valley bottoms forming prominent end-moraine arcs (Fig. 1B). These end-moraine arcs join prominent valley train deposits in the lower valleys. End-moraine deposits are located both to the east (in Gansu Province) and to the west (in Qinghai Province) of the Dalijia interfluve which is covered with a diamicton that may have either a mass wasted or glacial origin. Because the age of the diamicton is subject to considerable controversy, we consider that percent extractable Fe (especially Fed) might provide some new information on time since deposition (after comparison with the deposits emplaced presumably during two stades of the last glaciation).

Present-day climatic parameters in the Dalijia Shan are not known with precision but the mean annual temperature is estimated (from lapse rate) at -1.6°C. Extreme temperatures range from 24 to -29°C. Precipi- tation is probably less than ~ 760 mm. While evapotran- spiration is unknown, low vegetation density in the field area gives the impression of a dry climate. Precipitation on the eastern side of the Dalijia Pass (Fig. 1A) is higher than on the western side as a result of the monsoonal effect. Because of the higher elevation of DLJ10 relative to the other sites (difference = 240 m), and its position on a ridge crest open to the influence of the wind, it might be possible to argue that a slower weathering rate would retard soil development. However, the altitude difference only gives a 1.2°C temperature difference (using a lapse rate of 0.5°C/100 m). The wind effect on evapotranspiration rates is unknown but might reduce the available soil moisture during the summer months. Because the local inhabitants have removed much of the cover vegetation of woody shrubs dominated by witch hazel (Hamamelis kobresia) it may be that the dry present-day climate is the result of devegetation by human impact (see Mahaney and Zhang 1991). This is compounded somewhat by overgrazing by horses and yaks which are important elements in the local economy.

The paleosols are divided into three groups: (1) DLJ6--the youngest paleosol formed in till of the

late stade of the last glaciation. (Dehi-Shuigou Stade equivalent to the Wiirm Glaciation in the Alps; Li and Pan 1989.)

(2) DLJl-- the older paleosol formed in till of the early stade of the last glaciation (Qingshuihe Stade considered equivalent to the Riss Glaciation in the Alps; Li and Pan 1989).

(3) DLJ10--paleosol formed in a diamicton that may have been emplaced during the last glaciation. However, this deposit is also considered by some workers to be

75

76 WILLIAM C. MAHANEY et al.

A ( IOZ;,15'E QINGHAI ~; \ ~ ' , ' ~ ' \ -" ~ H O U

%%"~. " ' . f ~ f a r m i n g ~-TillsoftheLoslG ~otton] ," GANSU /~ ] "°" ~ o ' ~ < ~ C am m u nit , / ~ ,, (:Wurm, J /" I ' '

" ~ / / [ ' T I ~ I o I ~ ~ Oiamictons ~ " ,, t (: M nde ) I~o,oi., of Qingshuihe stode [ x ' K ~ / / : , ~ ~ End moraines I of DolijiolceAge l I \ " ~ \ l l ~.. l , ~ . • , ~ \~,no,/,,~6o, t ~ \ \ Administrative I ( - " " r h ' G ~ _ . ~ "// X X - - - - boundary

) ) ' ~ r ~ ° / ~ " ~ ~ . . . . . . Road 3s '~5 ' . ~ , P ' DALIJIA PASS ~ ~s'~s'.

-~ , . - . / / ~ ~ T T .... ~ ",~--'--.-" / / / (" I

' ~ . . , ?~'4~'~ ~ . _ N B

metres a,s.I, - 3900

L , ~ r - - D L J I O CRYSTALLINE ROCKS including ,7/'.-'l.~"~,.~__~ / granite of early F:~aleozoic age "L~'J'~) ~",,~ ' ~ L , ~ ' ~ '~1 and metamor p hie rocks L/.~. ~ . ~ , ? , ~ . (including schist.slate and marbl~ ','~'2)_ 7 .~-~S,~,_',~ of Triassic age.

,>, '?.' '-;". P- ~.~, '~'~'E ,~c "~-' '-,' ',;. -;' . ~ L J 6

• ,.,,- ~.'. ,' ~., .., - :.',- .~.W'..~.,.~;'.. ;.~ ..... ,, .'.." ,.~(,~.~.q.,_,

3150

Fig. 1. (A) Location of moraines and diamictons in the Dalijia Shan, western China; (B) topographic profile showing the distribution of moraines and sites referred to in the text.

equivalent to the Mindel Glaciation of the European Alps (Li and Pan 1989).

METHODS

Soil descriptions follow the Soil Survey Staff (1951, 1975) and Birkeland (1984). Particle size determinations are based on procedures established by Day (1965) and particle size divisions follow the Wentworth Scale (Folk 1968) with the exception of clay/silt at 2/xm. Sites were selected on representative moraine and diamicton crests. To avoid dissolution effects, no acid pretreatment was used in preparing the samples for laboratory study (Dormaar and Lutwick 1983). Extractable Fe and AI were obtained from 5 g subsamples of whole-soil ma- terial (less than 2 mm in average grain diameter) using sodium citrate, dithionite, and bicarbonate and follow-

ing established procedures (Coffin 1963, McKeague and Day 1966). All extracts were analyzed in duplicate using a Perkin Elmer 373 atomic absorption spectropho- tometer.

Extraction with sodium dithionite removes finely dis- seminated hematite, goethite, amorphous AI and Fe, and organically complexed AI and Fe. Acid ammonium oxalate removes only amorphous Fe and A1 plus organ- ically complexed Fe and A1. Sodium pyrophosphate extracts only organically complexed Fe and AI (McKeague and Day 1966).

The pH was measured from a soil water suspension with a ratio of 1:5. Total salts were determined by conductivity using the procedures of Bower and Wilcox (1965).

Samples comprising the < 2 mm fractions of the tills and the diamicton were subsampled for chemical analy- sis by neutron activation. They were chosen to range in

Late Pleistocene paleosols, western China

mass from 700 to 850 mg in an attempt to guarantee representative samples. The analytical samples were stored and analyzed in Olympic Plastics Co. flip-top polyvials.

For elements such as U, Dy, Ba, Ti, Mg, Na, V, AI, Mn, Ca, and K, which produce short-lived radioiso- topes, the samples were irradiated serially for 1 min at a neutron flux of 1.0 x 10 II n/cm 2 s -I in the SLOWPOKE nuclear reactor at the University of Toronto. After a delay of approximately 19 min to allow the very short lived 28A1 to decay to acceptable levels, each sample was assayed using 5min counts with on-site gamma-ray spectrometers, as described by Hancock (1978). Appro- priate gamma-ray peak areas were measured and the chemical concentrations calculated using the comparator method.

The samples were then batch irradiated for 16 hr at a neutron flux of 2.5 x 10 ~j n/cm2/s -~ and after a delay of approximately 7 days the concentrations of Sm, U, Yb, La, As, Sb, Br, Sc, Fe, and Na were similarly deter- mined, with the Na giving a cross-check with the first analysis. After a 2 week delay, the samples were re- counted and the concentrations of Nd, Ce, Lu, Ba, Th, Cr, Hf, Sr, Cs, Ni, Tb, Sc, Rb, Fe, Co, Ta, and Eu were measured. Once again, the Sc and Fe were used to cross-check the second phase of the analysis.

DLJ6 ; l , . k ~ . I

• ........,:.; .. : :I2 . . . . . . . . . ,

,;....::.:..:::" . . . ~

60

RESULTS AND DISCUSSION

Profiles

The three paleosols, formed in tills (DLJ1 and DLJ6) and in a diamicton (DLJ10) (Fig. 1A), are considered to have relative ages ranging from before the last glaciation (DLJ10) to the beginning (DLJ1) and end (DLJ6) of the last glaciation (Li and Pan 1989). However, field charac- teristics and paleosol morphology indicate that all soil profiles probably date from the early and late stades of the last glaciation (Mahaney unpublished). While these paleosols vary somewhat in thickness (Fig. 2), they cover fresh unweathered sediments. The paleosols are all Cry- ochrepts (Soil Survey Staff 1975).

The DLJ6 profile (elevation 3370m.a.s.l.) is the youngest in the group with an estimated age of

15,000 yr BP (Fig. 2). This profile contains a 30 cm thick soil solum with grayish yellow brown (10YR 4/2) colors in the A horizon grading to dull yellow brown (10YR 5/4) in the B horizon (12cm thick). The AB horizon contact is clear and distinct, but wavy with a range of ___6 cm. The older DLJ1 paleosol, at approxi- mately the same elevation, is located in an end moraine surface that is 0.3 km down valley from the younger end moraines. This older end moraine complex has fiat- topped deposits with gentle slopes < 15 ° (compared with steeper slopes of > 15 ° on the flanks of the younger deposits). Stone frequencies also decline with age although no counts were taken in the field. The DLJI profile (Fig. 2) is an Inceptisol (Cryochrept) with a considerably thicker AB (solum complex). The Bw hor-

77

70

80

• SLOPEWASH

~ LOESS

~ TILL

DLI1 . - 7 1 ,

AB

, . . . ,.....

~ 8 :l l;:lll

DLI1O

:i!. i.-.):: : .!~~

. A ; . . : tL

?Cox ii::;~!:~

A

AB

2Bw!

2cg

Fig. 2. Till and diamicton sequences on the Dalijia Shan, western China. DLJ6 = late WOrm, DLJI = early WOrm, and DLJ10 = early

WOrm.

izon, in particular, because of its brown (10YR 4/4) color, greater thickness, and blocky structure, is con- sidered to have a greater age. The color alone argues for higher contents of organic matter and of liberated oxides.

The DLJ10 profile (elevation 3610 m), formed in a diamicton covering a prominent interfluve between the east and west Dalijia end moraines, contains an Incepti- sol (Cryochrept) that is remarkably similar to the DLJI profile (Fig. 2). Colors and structure are similar with depth indicating a probable close correspondence in age. Pebble weathering with depth is similar to the DLJ1 profile where maximum alteration occurs in the 2Bwl/ 2Bw2 horizons. This deposit is considered to have been emplaced during an earlier and more extensive glacia- t ion-Pass Ice Age--which may be equivalent to the Mindel in the Alps of Western Europe (Li and Pan 1989). However, this deposit could have a mass wasting origin that occurred during either the early or late stades of the last glaciation (see Mahaney et al. 1984, Der- byshire and Mahaney 1989, for discussion of the origin of diamictons).

Particle size

Particle size depth distributions (Fig. 3) were studied to determine the degree of clay translocation in the profiles and to separate till from aeolian components. In the youngest profile (DLJ6), there is no evidence for downward translocation of clay. However, in the older group of soils, pronounced movement occurs in DLJI;

78 WILLIAM C. MAHANEY et al.

I0.

2 0

30,

P.

z 5 0

¢:1 60-

70-

80-

9 0 -

I00

DLJ6 PERCENTAGE

I0 20 30 40 50 60 70 i i i

i i

I I

CLAY (<2#rn) SILT (63-2~m)

A

B w

2 C

DLI1 PERCENTAGE

0 10 20 30 40 50 60 70 i i J i i i i r I

l ' ~A ~ r J j, !

I I

1 A 8 I I

I

I . - 1 i

1 1 I B w i 1 I

1 . . . . . . . . . . . j

2Cox

0 10 20

DLI10 PERCENTAGE

30 40 50 60 70 i i i

i i

: A i i

i i i

' A B i

1 i i

r - J I

I 1 , 2 B w / I i i i L - . 1

28w2

f-J

2 ~

Fig. 3. Depth distribution of silt and clay, Dalijia Shan late Quaternary chronosequence, western China.

but no translocation occurs in DLJ10. The downward clay trends within these two older profiles may be attributed to the higher elevation of DLJ10 relative to DLJI or to the steeper surface slope of DLJ10, which may lead to higher surface runoff and lower percolation through the pedon.

All three soils show the effects of aeolian influx of silt. The greatest increases in silt occur in DLJ1 (40%) and in DLJ6 (30%), with the lowest in DLJI0 (15%) relative to the till units. Most of the silt increase across the sequence is attributed to age and length of time for aeolian processes to continue transporting sediment. The increase of silt in the surfaces of these pedons is similar to trends reported in the Rocky Mountains of the U.S.A. (Birkeland 1984, Mahaney 1974, Mahaney et al. 1984).

Extractable Fe and AI

As shown in Table 1, there are a few age-dependent trends among the three paleosols. Crystalline Fe (Fed) increases from DLJ6 to DLJI; the values in DLJI0 indicate that it may have an age similar to or slightly younger than the DLJI profile. The ratios of Fed/Fet across the sequence (Table 1) show rather similar trends in profiles DLJ6 and DLJ10 with a slight increase in the solum of profile DLJ1. Analysis of the Feo/Fed ratios indicate that both DLJ6 and DLJ1 have similar amounts of amorphous Fe; values for DLJ10 show higher quan- tities of amorphous Fe which usually suggest a younger age (Alexander 1974, Mahaney and Fahey 1988, Mahaney and Sanmugadas 1985). Organically-com-

Table 1. Extractable Fe and AI in profiles DLJ1, DLJ6 and DLJI0, Dalijia Shan, western China

Extractable Fe (%) Extractable AI (%) Depth Fep + Alp

Site Horizon (cm) F% Fe o Fed Alp AI o Aid Feo/Feo Fed + Alo

DLJ6

DLJ1

DLJ10

A 0-18 0.29 0.47 1.22 0.27 0.19 0.24 0.39 0.38 Bw 18-30 0.33 0.48 1.36 0.33 0.13 0.17 0.35 0.43 2C 30-76 0.13 0.27 0.51 0.15 0.02 0.06 0.53 0.49 2D 76 + A 0-7 0.22 0.33 0.94 0.24 0.13 0.20 0.35 0.40

AB 7-28 0.40 0.59 1.69 0.29 0.20 0.26 0.35 0.35 Bw 28-55 0.46 0.63 1.40 0.48 0.20 0.19 0.45 0.59

2Cox 55-106 0.10 0.37 0.51 0.16 0.09 0.08 0.73 0.44 2D 106+ A 0-10 0.40 0.69 1.10 0.31 0.22 0.20 0.63 0.55

AB 10-26 0.46 0.92 1.40 0.30 0.28 0.24 0.66 0.46 2Bwl 26-43 0.50 0.69 1.32 0.78 0.20 0.27 0.52 0.62 2Bw2 43~0 0.51 1.07 1.34 0.39 0.37 0.30 0.80 0.53 2Cg 60-112 0.20 0.49 0.82 0.25 0.19 0.14 0.60 0.47 2D 112+

Late Pleistocene paleosols, western China 79

plexed Fe (F%) increases slightly and then decreases with depth in the younger (DLJ6) profile. The same extract increases to a greater extent from the A to the B horizons in the older profiles (DLJ1 and DLJI0) suggesting different leaching histories. From the soluble Fe data we believe DLJI0 and DLJ1 formed under a wetter climate, that allowed pronounced downward translocation, compared with profile DLJ6, which did not. Even though the geochemical data (discussed in a later section) showed enriched Fe in the paleosol sola of DLJ1 and DLJ10, relative to the parent material, it is relatively uniformly distributed in the A/B horizons of DLJ6. Thus, these data probably indicate some differ- ences in climate during the interstade (wetter?) of the last glaciation and a drier late glacial and postglacial soil- forming interval.

The data for extractable AI (Table 1) show overall lower amounts compared with Fe, but indicate that higher amounts of A1 are organically complexed. In general, the values for pyrophosphate-extractable A1 increase downward in the profiles peaking in the B horizons (lower solum) and decreasing into the subsoil (C horizons). Also, Alp increases across the geological sequence from 0.33 in the B horizon of DLJ6, and 0.48 in the Bw horizon of DLJI, to 0.78 in the 2Bwl horizon of DLJ 10. Moreover, amorphous (Alo) tends to increase across the B horizon sequence along with crystalline AI (Aid). As noted by other workers (Birkeland et al. 1989), AId is often lower than values for Alo and so Ald probably does not represent total pedogenic AI. Using the ex- tractable A1 data, it is possible to differentiate two groups of paleosols with DLJI and DLJI0 having more advanced ages, and DLJ6 a younger age. The close similarity between AI o and AId values suggests a slow rate of conversion to crystalline forms, and is similar to data reported in the Rocky Mountains (Mahaney and Fahey 1988).

Iron crystallization in paleosols is considered to provide important criteria about relative age in soil morphogenesis and the activity ratio (Feo/Fed) is utilized often to assess the degree of aging (Blume and Schwertmann 1969, Mahaney 1974, Dormaar and Lutwick 1983, Mahaney and Sanmugadas 1985, Mahaney and Fahey 1988). In the soil sola of DLJ1 and DLJ6 the Feo/F% ratios are similar; in the C horizons Feo/Fed is higher in the older profile suggesting that overall less amorphous Fe might have been converted during the soil forming process in the older profile. The activity ratio in DLJ10 gives even higher values in the 2Bw/2Cg horizon complex suggesting less conversion to crystalline Fe. Using this ratio alone, and ignoring the subsoil horizons (C horizons), one is forced to conclude that profiles DLJ6 and DLJI have similar ages and DLJ10 is younger. However, because Feo concentrations are affected by ground water (Mahaney and Fahey 1988) it may be that high values in DLJ1 and DLJ10 reflect periodically high water tables.

To determine evidence for downward translocation of Fe and A1, the U.S. Soil Taxonomy (Soil Survey Staff 1975) uses the ratio (Fep + AIp)/(F% +Ald) as a means

of determining the presence of a spodic horizon in a profile. The values of (F% + Alp)/(Fed + Aid) shown in Table 1 provide evidence of movement of Fe and Ai from the A horizon complexes to the B horizon com- plexes in all three profiles. The trends show increases from DLJ6 to the DLJI and DLJ10 groups giving the impression that there is little difference between profile DLJ1 and DLJ10. Because the soil colors described in a previous section indicate higher organic matter in the B horizons of the DLJ1 and DLJI0 profiles, it is likely that the two older profiles come close to meeting the chemical requirements of a spodic horizon (higher secondary illuvial humus and F% + Alp in the Bw horizons). Using the same requirement for the B horizon in the DLJ6 profile, it is unlikely that it would meet the illuvial humus content (even though the Fep + Alp values are adequate).

Geochem&try

The analytical data for the elemental concentrations of the <2 mm fractions of the Dalijia Shan paleosol sequence are presented in Table 2. The inter-correlations among the elements were determined by calculations of Pearson correlation coefficients. These correlation coefficients show that a minimum of four different source materials are present in the samples. The first material is enriched in Na, K, Rb, Ta, Th, AI, Sr, Ba, Hf, and U, which are all positively correlated. All of these elements are negatively correlated with elements such as Fe, Br, Sb, Sc, As, Co, Cr, Cs, Ti, Mn, the heavy rare earth elements, and Mg, which are enriched in the second material. Of this second group, all elements are posi- tively correlated with the exception of Br, implying that the primary source of Br is different to that of the other elements in the second source, and therefore requiring a separate source material for Br. All of the major elements analyzed are weakly negatively correlated with Ca, which in turn is positively correlated with Sr, and may correspond to the presence of small amounts of a fourth source material such as limestone.

Since Na and K correlate highly with other major, minor, and trace elements, there is minimal evidence of selective Na and/or K leaching in these paleosols.

To add to data interpretation problems, it appears that the A horizons of DLJ1 are either organic material (and/or silica) diluted to different extents, since many of the elemental concentrations for these two samples are lower than their underlying counterparts. DLJ1 data should be corrected for an excess of 25 30% diluent and DLJ10 data might profitably be corrected for an excess of 15-20% diluent. This effect may correlate with the relative ages of the sequences since DLJ1 and DLJ10 are early Wfirm while DLJ6 is late W/irm.

Apart from this effect, the other observable variations in the geochemical data of Table 2 appear to be explain- able by variable combinations of the first two source materials (till vs loess), with the high Fe etc. material being more abundant in the paleosol sola (A and B horizons) relative to the C parent material, and the high Na, K, etc. material being less abundant in the paleosol

Tab

le 2

. G

eoch

emis

try

* o

f th

e <

2m

m

frac

tio

ns

in t

he D

alij

ia S

han

pal

eoso

l se

quen

ce,

wes

tern

Ch

ina

Dep

th

Mg

A

I K

C

a Si

te

Ho

rizo

n

(cm

) N

a (%

) (%

) C

1 (%

) (%

) S

c T

i V

C

r M

n

Co

F

e A

s B

r R

b

DL

J6

A

0-1

8

13,6

00

1.1

7.6

< 2

80

2. I

1.2

11.0

36

50

81

74

659

12.8

3.

43

15.2

2.

5 12

2 B

w

18-3

0 14

,800

1.

1 7.

5 <

140

2.

0 0.

9 10

.8

4460

92

74

63

0 13

.5

3.47

16

.0

1.7

115

2C

30~7

6 24

,600

0.

9 7.

7 <

320

3.

1 1.

2 5.

6 20

60

42

31

472

6.1

2.09

4.

6 0.

9 16

7 D

LJI

A

0

-7

8100

1.

0 4.

8 _<

180

1.

6 1.

8 8.

6 28

10

59

58

612

I0.1

2.

56

14.5

6.

3 96

A

B

7-28

12

,100

1.

1 7.

2 <

150

1.

9 1.

0 12

.4

3920

92

86

70

5 14

.5

3.85

21

.0

3.7

123

Bw

28

-55

13,3

00

1.2

7.7

<2

70

2.

0 0.

9 12

.2

4440

89

86

79

4 15

.9

3.88

19

.2

1.4

117

2Cox

55

-106

23

,100

0.

7 7.

3 <

160

2.

9 1.

3 5.

6 26

50

93

31

489

6.4

2.20

4.

2 <

0.7

18

3 D

LJI

0

A

I~I0

93

70

0.9

5.6

<1

50

1.

9 1.

3 10

.5

3180

72

68

52

0 10

.8

3.05

14

.5

5.1

114

AB

10

-26

14,3

00

0.7

7.0

<2

20

2.

4 0.

9 11

.4

3660

78

73

72

7 12

.8

3.54

14

.7

3.3

147

2Bw

l 26

-43

14,8

00

1.4

7.9

<1

70

2.

1 0.

8 11

.9

3940

86

74

95

3 13

.2

3.64

17

.4

3.4

150

2Bw

2 4

3~

0

13,7

00

1.2

7.2

<2

10

2.

7 0.

7 11

.4

4230

83

72

56

6 11

.3

3.43

15

.3

3.3

136

2Cg

60-1

12

16,5

00

1.0

7.2

< 1

80

2.2

0.6

8.8

3270

70

56

64

8 9.

8 2.

73

10.8

1.

7 14

3 ~

r O

Dep

th

Site

H

ori

zon

(c

m)

Sr

Sb

Cs

Ba

La

Ce

Nd

S

m

Eu

T

b

Dy

Y

b

Lu

Hf

Ta

Th

U

DL

J6

A

0-18

18

0 1.

19

10.1

44

0 31

.6

65.5

31

5.

01

0.98

0.

84

3.6

2.45

0.

36

5.81

1.

20

13.9

3.

2 B

w

18

30

140

1.20

9.

4 45

0 34

.8

75.8

37

6.

65

1.25

0.

96

4.0

2.88

0.

39

6.11

2.

34

14.4

3.

3 2C

30

-76

230

0.27

6.

5 52

0 30

.5

61.7

27

4.

23

0.83

0.

54

2.2

1.64

0.

21

5.64

2.

04

20.2

3.

1 D

LJI

A

0

-7

180

1.18

8.

5 41

0 26

.0

48.3

26

4.

47

0.83

0.

66

3.1

2.32

0.

28

3.81

0.

85

9.6

2.6

AB

7-

28

170

1.54

12

.0

530

36.6

68

.8

33

5.96

1.

05

0.98

3.

2 3.

14

0.41

5.

81

1.32

13

.6

3.4

Bw

28

-55

130

1.36

11

.I

510

33.9

68

.9

30

5.32

1.

03

0.89

3.

2 2.

97

0.39

6.

21

1.31

13

.1

3.1

2Cox

55

10

6 23

0 0.

26

7.7

520

30.4

63

.3

31

5.37

0.

95

0.68

2.

2 1.

85

0.25

6.

63

2.95

18

.5

4.2

DL

JI0

A

0

-10

13

0 1.

27

9.5

410

34.6

57

.3

28

5.03

0.

95

0.76

3.

1 2.

46

0.32

4.

62

1.05

12

.0

3.0

AB

10

-26

160

0.96

11

.2

580

38.9

72

.2

33

5.64

1.

19

0.88

3.

8 2.

77

0.38

5.

99

1.45

17

.6

3.7

2Bw

l 26

-43

150

1.08

11

.6

490

39.8

69

.9

31

5.51

1.

01

0.92

3.

2 2.

76

0.33

5.

50

1.34

20

.4

3.8

2Bw

2 4

3~

0

150

1.09

11

.7

490

37.7

66

.8

33

5.88

1.

11

0.84

4.

2 2.

78

0.36

5.

79

1.59

15

.8

3.6

2Cg

6~

11

2

120

0.71

7.

8 47

0 35

.1

63.6

31

5.

67

1.02

0.

69

3.4

2.51

0.

30

5.52

1.

94

15.4

3.

0

*D

ata

are

give

n in

pp

m u

nles

s o

ther

wis

e in

dica

ted.

Late Pleistocene paleosols, western China

Table 3. Geochemical ratios of mobile to immobile elements in the Dalijia Shan paleosol sequence, western China

81

Site

Depth N a * x 100 C a x 100 S b x l 0 0 N a * × 100 C a x 100 B r x 10

Horizon (cm) AI A1 As/Sc Sc Sc Sc Sc

DLJ6 A (~18 18 16 1.4 9.2 12.4 11 2.3 Bw 18 30 20 12 1.5 11.0 13.7 9 1.6 2C 30-76 32 16 0.8 4.8 43.9 22 1.6

DLJ1 A 0 7 17 39 1.7 13.7 9.4 21 7.3 AB 7 28 17 15 1.7 12.4 9.4 9 3.0 Bw 28 55 17 12 1.6 l I . l 10.9 8 1.1

2Cox 55-106 32 18 0.8 4.6 41.3 23 < 1.2 DLJI0 A 0 10 17 22 1.4 12.1 9.0 12 4.9

AB 10-26 20 13 1.3 8.4 12.5 8 2.9 2Bwl 26-43 19 10 1.5 9.1 12.4 6 2.9 2Bw2 43-60 19 10 1.3 9.6 I 1.4 6 2.9 2Cg 60-112 23 9 1.2 8.1 18.8 7 1.9

Pearson correlation coefficient + 0.60 - 0.69 + 0.96 + 0.89 - 0.71 - 0.43 + 0.36

*Na converted to % for this ratio.

sola (A and B horizons) relative to the C parent material. Note that the chemistry of the Cg horizon of DLJI0 indicates that it is probably a 50-50 mixture of the two major source materials, so the effects noted in the C horizons of DLJ1 and DLJ6 are not readily observable in the DLJI0 profile. The chemistry also indicates that DLJI0 comprises a mixture of sediments. This latter finding is compatible with DLJ 10 originating from mass- wasting and/or glacial deposition followed by emplace- ment of aeolian sediments.

Although the Ca concentrations are low and relatively uniform, it might be proposed that the surface paleosols are enriched relative to the lower horizons. This higher surface Ca may be a result of plant recycling or aeolian influx of fine-grained materials.

Ratios of potentially, geologically, mobile and im- mobile elements are presented in Table 3. Caxl00/A1 and Caxl00/Sc confirm relative Ca enrichments in the sur- face paleosols of DLJI and DLJ10 (and possibly DLJ6). Relative Ca enrichments also appear in the C horizons of DLJI and DLJ6.

The ratios Naxl00/Al, Naxl00/Sc, As/Sc, and Sb/Sc show the effects of the mixing of the two major source materials, with the ratios for the A and B horizons either consistently higher or consistently lower than those for the corresponding C horizons, depending on the element in the numerator. Therefore, Naxl00/A1, and Naxl00/Sc generate relative enrichments in the C horizons, while As/Sc and Sb/Sc generate relative depletions in the C horizons.

Table 4. Total salts and pH in late Quaternary soils of the Dalijia Shan, western China

Depth pH (mmhos/cm Site Horizon (cm) (1: 5) 2 5 C )

DLJ6 A 0-18 7.0 0.07 Bw 18-30 6.7 0.03 2C 30-76 6.8 0.02

DLJ 1 A 0-7 6.6 0.14 AB 7 28 6.7 0.05 Bw 28-55 6.8 0.03

2Cox 55-106 6.8 0.02 DLJI0 A 0-10 6.1 0.09

AB 10-26 6.2 0.04 2Bwl 26-43 5.9 0.02 2Bw2 4 3 ~ 0 5.7 0.03 2Cg 60 112 6.2 0.02

For Brxl0/Sc the ratio data is different. Relative Br enrichments occur only in the surface horizons, possibly relating to the organic material (silica) diluent material proposed to be present there, especially since the A horizon of DLJ 1 exhibits the greatest Br content and the A horizon of DLJ10 exhibits the second greatest Br content.

Soil chemistry

The pHs of the soil (Table 4) indicate neutral soils with no variation down each profile. The total salt contents (Table 4) are low with the expected exception of the A horizons of each profile. Overall, the pH and total salt distributions do not indicate any appreciable differences in movement of soluble materials over time.

CONCLUSIONS

Paleosols often provide enormously useful infor- mation on relative ages of deposits and on past and present soil-forming environments. In this study, the relative age criteria suggest that there are two groups of paleosols that appear to have formed during the early (DLJl and DLJ10) and late (DLJ6) stades of the last glaciation. Both crystalline Fe and A1 support the hy- pothesis of different ages for the two groups of paleosols, while the activity ratio Feo/F% is not so useful, possibly because it is compounded by different amounts of amor- phous Fe in the subsoils of the three paleosols.

The geochemical data indicate the presence of at least four different source materials. The Ca-rich source is derived locally from limestone outcrops while the other Fe-rich, and Fe-poor source materials have unknown provenances. Various ratios of mobile to immobile elements show the effects of mixing of major source materials and some movement of mobile elements in the paleosol sola.

Extractable forms of Fe and Al yield data on relative movement and indicate that the older group of paleosols (DLJ1 and DLJI0) may have been subjected to a stronger (wetter) climate, or to somewhat longer time to achieve greater movements of Fep + Alp downward in the two systems. Because the present-day climate is

82 WILLIAM C. MAHANEY et al.

considered to be dry, it may be that the paleoclimate was indeed wetter at least during Pleistocene interstadial time. It is likewise possible that human impact on the environment, connected with removal of woody veg- etation, actually changed the microclimate to a signifi- cant extent.

Acknowledgements--We thank the Natural Sciences and Engineering Research Council of Canada for support of the SLOWPOKE Reactor Facility at the University of Toronto. Travel funds (to W.C.M.) from the U.N. Development Program in China are gratefully acknowledged. Laboratory analyses were completed at the SLOWPOKE Reactor Facility (funded by NSERC) of the University of Toronto and in the Geomorphology and Pedology Laboratory at York University. Pro- fessor L. Zhang (Lanzhou University, People's Republic of China) introduced W.C.M. to the field area. Several graduate students at Lanzhou University assisted with the field program. Dave Hinbest assisted with the laboratory analyses at York University. Janet Allin drafted the illustrations.

REFERENCES

Alexander, E. B. 1974. Extractable iron in relation to soil age on terraces along the Truckee River, Nevada. Soil Sci. Soc. Am. Proc. 38, 121-124.

Birkeland, P. W. 1984. Soils and Geomorphology, 372pp. Oxford University Press, New York.

Birkeland, P. W., Burke, R. M. and Benedict, J. B. 1989. Pedogenic gradients for iron and aluminium accumulation and phosphorus depletion in arctic and alpine soils as a function of time and climate. Quaternary Res. 32, 193-204.

Blume, H. P. and Schwertmann, U. 1969. Genetic evaluation of profile distribution of aluminum, iron and manganese oxides. Soil Sci. Soc. Am. Proc. 33, 438-444.

Bower, C. A. and Wilcox, L. V. 1965. Soluble salts. In: Methods of Soil Analysis (Edited by Black, C. A.), pp. 933-951. American Soc. Agronomy, Madison, Wisconsin.

Coffin, D. E. 1963. A method for the determination of free iron in soils and clays. Canadian J. Soil Sci. 43, 7-17.

Day, P. 1965. Particle fractionation and particle size analysis. In: Methods of Soil Analysis (Edited by Black, C. A.), pp. 545-567. American Soc. Agronomy, Madison, Wisconsin.

Derbyshire, E. and Mahaney, W. C. 1989. A preliminary scanning electron microscope study of five diamictons from Mount Kenya. In: Quaternary and Environmental Research on East African Mountains (Edited by Mahaney, W. C.), pp. 155-164. Balkema, Rotterdam.

Dormaar, J. F. and Lutwick, L. E. 1983. Extractable Fe and AI as an indicator for buried soil horizons. Catena 10, 167-173.

Folk, R. L. 1968. Petrology of Sedimentary Rocks, 170pp. Hemphill Press, Austin, Texas.

Hancock, R. G. V. 1978. Some aspects of the analysis of ancient artifacts by neutron activation. J. Int. Inst. Conservation--Canadian Group 3, 21 27.

Li, J. and Pan, B. 1989. Quaternary glaciation in the Dalijia Mountains on the northeast border of Qinghai-Xizang Plateau. International Field Workshop on Loess Geomorphologieal Processes and Hazards, May 23-June 5 1989, pp. 105-108.

Lutwick, L. E. and Dormaar, J. F. 1973. Fe status of Brunisolic and related soil profiles. Canadian J. Soil Sci. 53, 185-197.

McKeague, A. and Day, J. 1966. Dithionite- and oxalate extractable Fe and Al as aids in differentiating various classes of soils. Canadian J. Soil Sci. 46, 13-22.

Mahaney, W. C. 1974. Soil stratigraphy and genesis of Neoglacial deposits in the Arapaho and Henderson cirques, central Colorado Front Range. In: Quaternary Environments: Proceedings of a Sym- posium; Toronto, Geographical Mongraphs, No. 5, York Univ. Series in Geog. (Edited by Mahaney, W. C.), pp. 197-240.

Mahaney, W. C. and Fahey, B. D. 1988. Extractable Fe and AI in late Pleistocene and Holocene paleosols on Niwot Ridge, Colorado Front Range, Catena 15, 17-26.

Mahaney, W. C., Halvorson, D., Piegat, J. and Sanmugadas, K. 1984. Glacial chronology of the Rocky Mountains: some problems from western Wyoming. In: Correlations of Quaternary Chronologies (Edited by Mahaney, W. C.), pp. 255-241. Geo Books, Norwich.

Mahaney, W. C. and Hancock, R. G. V. 1989. Effect of industrial pollutants on soils in glacial deposits in the Western Alps. J. Radioanalyt. Nucl. Chem. 131(2), 289-298.

Mahaney, W. C. and Sanmugadas, K. 1985. Notes on the use of extractable iron and clay minerals for determination of soil age. Geografisk Tidsskrift 85, 14-20.

Mahaney, W. C. and Zhang, L. 1991. Removal of local alpine vegetation (Hamalelis kobresia) and overgrazing in the Dalijia Shan, northwest China. Mountain Res. Dev. (in press).

Ruhe, R. V. 1965. Quaternary paleopedology. In: The Quaternary of the U.S. (Edited by Wright, H. E. Jr and Frey, D. G.), pp. 755 764. Princeton University Press, Princeton.

Soil Survey Staff 1951. Soil Survey Manual, Washington U.S. Govern- ment Printing Office, 503pp.

Soil Survey Staff 1975. Soil Taxonomy, Agriculture Handbook 436, U.S.D.A., Washington, 754pp.