GENETIC TYPES OF THE HOLOCENE SOIL AND THE PLEISTOCENE PALEUSOLS IN THE XIPENG

LOESS SECTION IN CENTRAL CHINA

Gun 2hengtmg1 Fedoroff ~ i c o l a s ~ and An zhisheng3

\ 1ns:irute of Geofogy. Chinese Academy of Sciences. P. 0 Box 634. Dn~jlnf

IOO029, Chl113

2 Service des Sc~ences du Sol et d'Hydrologie, INA.PG, 78850 Gr~gnc~n . Fra~rcc

J X I ' A ~ I Lboiatory of tocss and Quaternary Geology, Chlr~ere Acadcmj of Scierlccs Xl'an 7 1006 1 . China

Abstract

Ttic Xilcng locss section in' the ccnrra! part of the Loess Y!atesl? is a conrinuous acc~~mulation of the last 2. 5 Ma., containing 3 8 palcosols wi[h inlerbcridcd loess. The Holocene soil and the Pleistocene paleosoIs are sW01rd by using micromclrphologicai methods combined with chemical and mineralog~cal anaryscs

? h e modern soil has strongly disturbed hy human actjvilies and rhe nlajur pan of the iop soil (chemozem) was fanned dur@g the Mid-Hcloccnc under :I slightly more humid chrnate Otan h a t of the present-day.

Slcppc vegetation was dominant for all of rhe Pleisrocenc paleosols. I t was replaced rempornrily,by forest during thc formation of the paieosols SI , S5-I and 55- 3. Strong biologic,al activity, rubification, decalciticarion and sccandory csrbonale accumulation represent h e , major sail-fortning process. The palcosols 54 arid 55 were also aflcckd by alkalizatian during the last soil-fornling stagc and acolia~l dukt

dcposhon scerns to be the only possibility [or 1h;Eia' source. The Brun i~csaged pnIeosols are rnostly well developed Kastarlozems. pnsscsslng at once calcic and chromic charactcrs. The paleaclimates they wyre subjected to were scasor.nlly cr>ntrastcd, charactcrized by cold, dry winter and hat, humid sunnmrr with strong evapnlranspiration. In contrast. U1e Matuyama aged palcosols arc weakiy tieveloped

Kasinnozems and significant dust dcpsitiOn cor~tinued contemporancousljr with pcdogencsis

Introduction

The loess-palensol successio~~ in central China (L.oes.s Picltc:3~) pntcrttially

0 3

pi-oviiics one of the best concnuous records of pasf climates for the last 2 . 5 Ma. (l.,it~ T. S. rt a]., 1385; 1,iu T. S. and Yuan £3. Y., 1987). The pcllcosuls i.nterbedded in locss cover more than half of the Quaterrlary according a) the magnetic susceptibility tirrlc scale (I-iu X. M. et a]., 1987; Kulkl~t, 1987). Nurnerolls str.,dies were carricd out, especially d~~r ing the last decade with a mrnrnon airn of rcconstnlcti,r~g tl?e pLzlcroctimatic history. A great arnaunt of reJiahIc irlfurnistion was acquircii. Howeve;, knowledge of pa~eosols, in cunuast tu that of othcr topics ( e . g. loess stratigraphy.) seems much more lirnited.

J. Throp (1936) was probably the first pedologist who rioted the esiater~ce of palcc?sols i.n Chinese loess. The paleosols; however, were rczrely mc~ltioiied until the 1950's, when Zhu X. M. (19581, Ma Y. 2. (19581, Sh Y. C. (1958) and I.,iu T. S. ( 1 0 9 ) , brlscd on field investigations, confirmed that the so-called red bands interbedded in loess are buried soils. Lii~ T . S. et al. (1964) and ZIlu .X. hi . ( 1965) considsrcd thc locss to have bcen deposited under dry-cold cLilnatic co~lditions whcrcas tiic pal~u~sols forined during watm-slightly humid clinlatic periods. The authors c1:tssifred thc top soii and palcosols into two basic group : bhck lanm and c i r~namor~ scrils, respectively. Elemental chemical analyses were also rnadc c)n sornc paleosols (Wa11g 2. Q. ct a!., 1958; Zhu X. M., l 965). A primitive description of the micr.of:~br.ics, calcitic and illuvial features was given by Zhu H. Z. (1063) trsirig petrographic 111-inciples. The author paid special attention ~ C I the iiistribution panern of skclcolr and plasma, and tcrrned die iUuvial features as 01-ierzted clap.

Reiativeiy intcnsivc studies on paleosols have been effectuated since the I'i,YCi's, rnair~ly on the Luochuan loess sections. An 2. S. and Wci 1,. Y . (19SO), and Tang K . I-. (1981) were among the first who applied s ~ i l m i c r o r n a r ~ ~ h ~ l o ~ i c a l mcthotls to tilese studies. Tlley focused on the paleosol S5 which wns inrcl-prctcd as brown cinnamon soil {in I,uod~uan), (An Z. S. and Wei I... Y., 1980) or brown foresr soil (iri Wugong) (Tang K. L., 198 1 ). A classification of the ~>aleosols was also -proposed by Kyurnn. et a1 ( 1 985), based on field ohscrvntions cornhirled with sornc ~I iemical analyses. Bronger and Hcinkele (1989) contributed a micrilmorphological study on thc Luochuan loess section. However, only very gcr~cral wnclusions werc publisl~cd about lFIc paIcosols in h e WricIleng loess nf the Early Pleistoccnc.

h.tc?re syritlictic srudics on the paleosols werc carricd out by Liu 'I'. S . et d. (1SF;Sj . -l-he autlrors classified the Holocene soil in Luochua~l as b1ac.k lorn aid h e p:ileosi>ls irlto forir groups: carbonate cirmamon soil, cinnamon soils, leached cirlnamon soils and brown cinriarnon soils. Annual mean tcn1per;lture and precipitation tluring fhc soil forri~atiori were also estimated by contparir~g thc palcosols with kodcrn soils.

I n spitc of thc wealth of infornlation revealed by the above wc>r-ks, I~owever, some t'undamuntal problc~ns, rnerltioned hcllow, remain to be addressed.

( 1 i ?'hc palcoclintatic interprctnrjon of The palcoso]s is usually based on the c(.lrnj.>:in.;on walh kloloccne soil. The question which ariscs is whcihcr. thc t-iolocene sniJs cnn bc rc!at.~d directly to the clunate prevailing t o d q ~n the Loess P]atc.a~i, and i low to distingrlish the impact of hurnan activities on the Holocene soil.

( 2 ) Sod-forming processes have not been systcrnatically invcstig;itcd u p to date. The classificatiorls of palcosols in rhe light of modern soil clnss;fication

sysrerns ;ire usually approximative and not always sufficient tcl nbtaln vnluablc p a l e o d u ~ \ a ~ c information, because past climates under wfiicfi a palcosol formed could be considerably chfferent from modern climatic t y ~ x s . In this case, it is thflicult, even impossible, to find an exact position for pdcoa>ls iu thc existing soil classittcation systems. For a reliable paleocli~~iatic irlterpret;ition, or:c has to identify all the sirlgle soil-forming processes and interpret comprehcnsivclq~ the cnvironmcnM conditions under which the processes opcratc.

(3) Tho paleosols in the Wucheng loess have riot k e n studied accurately. As a result, the cm~tinuity of the Wucheng loess and its przleoclunauc ~rnphcations are in dwbt (Pecsi, 1985). The aim of this study is to clarify these z~spects.

Materials and Methods

'The Xllcng loess sectlon is located on the cenrral part of tile I.mss Plateau (Flg. I ) . It a a continuous accurn~ilatic~n of the entire Quaternary, conlaming 38 p.fleosc>ls with interbedded lmss. ?be total thicknes? of thc section IS ,tborit 163 In.

Recc;lt pdeumagt~etic investigations have given a reliable chrorlostratigra~>llic scale (1 iu X. M. c? al., 1087; Kukla, 1987). Traditioxlaldy, the locss sequence in China is subciividcd into threc major straugraphic units (Liu et a]., 1985), fi on1 hotwrn to top rhcse :ire Wucheng Loess (Lower Plcistuccnc;), Lishl I,oess (M~ddle Pleiswcene) snd Malan Loess (Upper Pleistocene). The FIoltxxne sill1 (labeled SO) c/verGcs Ule Malm loess. The 14 palcasols in the Lishi loess were lsbcled fron~ lop to hottom as SI, S2, ..., S14. The paleosols in the Wucheng loess were not respccrively designated in thc Xifeng section It should be mentioned that in China, t l ~ c Pleisrncc~le/Pljocerie boutldm-y (lower boundary of the Wucheng locss) IS dated :it ( i b ~ ~ ~ t 2 . 4 Ma RP., and that the boundary between the 1,lshi Loess and the CC'uchcng 1,ocss Ls considered to be the Middle Pleistoccnc/I_owcr Pleistocene bounciary, dated at about 1.1 Ma. BP. (Liu et al., 198.5). A stratigraphic summary IS shown in Fig 2. The modern climatic data is given in Flg 3

fig I . Loc3Elon of X~feng loess section (Ktlk!:~, 1987)

Fi g. 2. Strarigraphic summary of Lhe W e n g section,

One I~uncired a r ~ d ten soil and loess samples for micromorp1lalogicaI siudy were systematically taken. Thin sections ( 5 x 12 cm in size) were made according to the mcthod of Guillore (19 85) and described according to BuUock ct al. (1 985).

Fig 3 Climatic data for Xireng Mp Annual precipitatron; MI: Annual mean ternpcran>re, d: AItitudc; P: Precipitation curve: T: Temperature curve

Carlxx~ate nodules were studied with SEM equipped with a dispersion energy niicroprohc. Determination of pH and exchangeable cations were done, using the rnethods described in Bonneau and Souchier (1979). Ions in the solution were deterniined by using the 1/5 extraction method. The clay fraction was analyzed as orientcd s,mples using a Philips PW 1710 XRD unit after Mg-ethylene-glycol and glycerol treatments as well as after K-sahiration and heating to 20, 120, 400 and 550 "C:

Holocene Soil

I t is well known that the Loess Plateau is the cradle of Chinese civilization. Agriculhlral activities make it impossible to find original soil protiles with climatic vcgctqbon

Our fiejd obscrvstions show that soil profiles are composed of two uqxrposed unkrs wiBl very clear boundary between them. The upper part, Ap horizon (70 crn, light grey brown, 10 YR 6/3, dry) is very hamogeneous with a weak nlcdiurn granular structure. In thin sections, they have a fragmented rnicrostructurc. The groundninss contains about 10% primary carbonates. Same bnck pieces, charcoals

a d b r o w reddish clay coamg fragments are distributed randornly throughout the entire horizon The ahove features suggest that the Ap horizon is derived from a partly ~ntl~ropogenetical depasir. In fact, on the Loess Plateau for a long tirue, Ole drject~oru usually mixed with loess and ash are brought every year to d ~ i . fields as soil fclzili.zcr.

The lov.7cr part of the profile is thought to bc thc original soil fcrnned before human actlvltlcs began on thc Loess Plateau. An Ah-AC-Ck horizon scqucnce was recogn17cd. ?hey have a silt texture with fme granular structure. The color become progrcssiveljj lighter from top (Ah, brown black 10 YR 3/J) to bottom (AC, grey brownish hl:ick 10 YR 412). Abundant pseudornycelia was observed at thc top and at thc bottorn of the lower part. All of them have a well developed sp0n-w microstn~cturc (Fig. Gc), resulting from strong biological activity, whirli is charactenstic for steppe soil (Pawluk and Bal, 1985) The perfect conservation of this structure irnplies a relatively dry soil water rkgirne, under which the profile is rarely water saturated (Courty and Fedoroff, 1985). The fine fraction with dark brown color contaming many charcoal particles (1-2 in), shows a relatively high humus conrent, and this is particularly evident in the Ah horizon. Decalcification W ~ S toully achieved in the A h horizon, and partly in the AC horizon ( 2 4 % pnmary carbonates), which is responsible for the abundant pseudornycclia in the Ck horizon. The pseudomycelia in the Ah horizon can be interpreted as a result of the dccaI(:~ficafion nf the overlying Ap horizon.

All of the soil horizons as yell as the mlderlying loess (Matan loess) show a very similar clay mincralogial association. They contain illites, kaolinite and chlorites in thc order of abundance estimated according to the X-R diagrams Smectiles arid intcrsQalifxcd minerals are in small amounts. These irnply that the clay minerals were mainly inherited from the aeolian dusts.

For a reasonable classification, the mtlxopic horizon and the original so11 must be corlsldcred separately. An accurate classification for the modem soil is nearly impossible due U> Zhe persurbatiot~ of the human activities, but the touI C X C ~ C I T I C T I ~ : ~

microstnichlre suggests a szeppe envirorment. Thc clrissification of the lower soiI according to the existing systerns is

unsahsfacto~g.. Strong biological activity and hurnifiestion show that the pedogeneses are similar to those of chcrnozem according to the F A 0 systcm (FAO- Unesco, 1974) and of Mo'ihsol to Soil Taxonomy (Soil Survey staff, 1975). However, the hl~rtius accumulation is so weak that it can not be considered as typical In mrnpnsir~g with tile tYpicaI chemozem in the Russian Plain, the soil water regime should be Q e r .

The above arguments show orat the major body ( the lower part) of the Holocene sol1 ~ v a s formed during the Mid-Holocene, probably contemporaneous with the Atlantic period, because agriculture in Xifeng has a history of more than 3000 years Adorcover, slightly more humid conditions can be suggested.

Paleosols S I to S8 in the tishi Loess

I . Pedtrlogical processes

T h ~ s seqccnce contams 12 paleosols. In tact, the sot1 S5 consists <)f three superpc;:,cd soils, labeled here as S5-1, S5-2 and S5-3 from top to bott~xn They are scparatcd by two thin loess layers. In addition, two other weakly developed soils (52-2 and 50-2) interbcddcd respectively in the loess units 1-3 ;ukd 1 7 were fou:~il (F1g 2)

These sulls are very similar, yet different from itze Holocene so11 The A tiorizot~ hZ5 been truncated for all the profiles. The pedons consist of e light hrnwn B 1 with mc~liurn granular structure overlying a redclish.brn.n B2 with subacgular blocky strmcture Abundant pseudnmycelia is frequerltly observeti in thc upper part sf tile E2 horizons. All- of the paleosols possess a calcareous hortzon at bott~rn ( 30-50 crri in thickness), which can be classified into three types according to the norphnlogy of thc calcareous nodules: soft nodules (S2-2 and SG-2) , h:lrrl nodtllus S 2, S 3 , S 4 : Sf) and SX ) and scoiious nodtlles (S 1 and S 5 ) .

'Ille p;?.lcosols, even the best developed S1 and S5 have a sbn11:ir dLty mnlcral ssoclat~orl vath underlying loess (Fig 4) indicating a very weak wearhering lrocess The clay rIlinernls are dominated by illitcs, kaolinite, chloritcs and :nechtes. Vern~tculites are in a negligibIe amount. It was observeci i r ~ the L~~ochuan -.caon that the crystallinity of illites decreases considerably m pdcosills due to edogena~s (1,iu et al., 1985) This phenomenon is scarcely visible I r l t11c Xifeng ecbon.

These paleusols were affected by very si~rular pedogenetic processes The sscntinl wdogenew can bc interpreted as follows :

( f ) Decalcification and accumulation of secondary carbonate Dccalciricatiort represents probably the first soil-forming suge. It was totidy

iclu~.ved in the paleosols SI, S2, S I , S5, S6 arid S8 whereas clasnc carbonate is 3boiit I -2% in 53 and S'J, 3-494 in S2-2 and S6-2 .

It was shown thai the calcareous horizons underlying the B h ~ r i ~ o r i s of the soils are of pcdofogical origin (Guo Z. T. and Fedoroff, 1990) All the nodules result from micritic impregnation in a loessial groundn~ass T h e ~ r morphology is related to the degree of soil evolution. The soft nodules are assoc~atcd wt11 the w~nlily decalcified soils (52-2 <and S 6 - 2 ) , while the hsrcl nodnles are fo t~nd under the totCiil!: or near-totally decalcified soils (S2, S3, 54, S5-2, Sh , S7 and Sh) Tt~eir intcrna! strlicni:e is similar to that of the hard nodules (Fig. 6a), but t l~e jmiphcry is strongly dissolved (Fig. 6h). These features suggest that the scnrious nodules result from dissolution of the hard nodules, and that the lower bound:uy of the R horizon had dczpcned Into the calcareous horizon during soil forn~nuon whtc-h can hc regarded as a function of increasing humidity.

The above results allows us to propose a model of the evolution of pcdological cakaseous hunzons, shown in Fig 5. -

It is coraeitfcred that pedological calcareo~rs horizons are typ~c:il for step@ cnvironr:lel~ts under arid and semi-arid cliniates (Duchaufour, 1977, Biskelmcf , 1984) '[fie fact that all the pdeosols have a calcareous 'norizorl suggests that the paleochlatcs during their formations were never humid enough for cstabl~shrnent of a typical forest vegetation. Moreover, the cIinlates sho~ild bc seast)~lally cclntrsstecl with strong evapotranspiration, heavy rains and relatively high tcmpcralurcs in sununer

1 ig. 4 X-Roy diffraction panem a i the clay fraction from rhe paleosols S5-3 (Icft, Dr hoructn) and ~e uncterly~ng loess (right). Mg-nature: samples saturared by

M g t + vi~rllout other treatrnenl; Mg-EG: Samples sawrated by Mgt" wth Ethylene glycol treatment; Mg-GL: samples saturated by ME*' wkth

Glycerol treatment: K-ZO°C: samples saturated by K' without h e a t

treatnlenr; K- 120 *C: samples saturated by K t and heated to I20 "T; K-

4 0 0 v samples saturated by Kt and Heated to 400 T.

Fig 5 . Mcaci of t'le ei.oluBon of a pedologicat calcireous horizon. I . Loess accumuia.tion: 2. Eeginniiig of the decalcification, very soCt calcareous nodules are toi;::ct!;

3. ar~d 4 More advanced smge, the ccxi~~les became harder and h;irdi.r;

5. Tile profile is lo&lly c!ecalciil~l, hard nodules are forrncd; 6 . Tile Lower boundary of the decalcific.tCon deepens sn lhnt the periphcr;: c:

the hard nodules is dissolved and tnnsformed into scorious nod1t1i.s

(2) RiologicaI activity All the paleosols were affccted by srrong bioiogical activity, as can br

dcrnor~st:atcd in tJlz field by aburldarlt bioporrs, even in the r:lost cievc.lop&d S5 . In d1ir.i sections (Fig. 6d), they have a total excremen&l niicrostrtic:ure (Courty and Fedoroil', 1985) or spongy rr~icrostruciure (Bulicck et al., 1985).

l l ie spongy rnicrostiucture is considered typical only for the rnollic: epipedans of st?ppo soils (Pawluk an3 Bal, 1985). Moreover, the conscrv::rion of rhis structtlre suggcsh that soils water regimes during the soil development were dry enolzgh ti121 water-saicrated states rarely occurred (Courty and Fedoroff, 1!lP,5). These features eGmina'ie the possibility (sf qpical forest cover, evcn fo r Ihc most dct*cloped psleos~l S5.

111 spite of strong 'ninlogical activity, hurrdficatiori is relatively W C R ~ PI most of i he pa!co~::l:j exrppt th:: sZ-2 and 56-2 soils in which h imus i-ontc~lt is tiigher. T h s plieriomc.non i:iciiczitcs tf1a.t the soi!s had g o d oxidizing cnnciitions, :ind that tile S I I I T ~ ~ ~ I ~ I - turrlpi.raturc WL. ttoo Itig11 ?'or humus itccumulrttion. li shotjiii bi. stressed th3t the lower ~ L I ~ I I U S coniecl% irl Uie paleoso~s are unlikely tc! be cxplairicd only by 11un:us cicwr:~position as tLie goes on, bccausc the paleosols 52-2 2nd S6-2 have higher i:ll!nus corltent?.

(133 Kecidering P ~ ~ ~ C C S S It1 zhe field, except for the weakly developed 52-2 ar~ci 56-2 . : i ;c ps!cosols

PCL"SCC'I~ a reddish color. T h e huc ranges from 7 . 5 YR to 5 YR (dry). T h e rc:tldrr?irig prwess i s ir!tc:~sive for ?he palecsols S4, S5-I and 55-3 (yellow red; 5 Y R 4/6),

an~l car; bc rcg:udcd as typical nnbiflcation. It is moderate for S 1, 52, S 3 , S5-2, S6, S7 2nd SS (reddish brown, 7. 5 YR 5/4).

Micrornurpl~ological investigations show that the redhsh color is closely relared to tlic fine fraction, ~+~iucii contains n great anlount of red iron oxihydroxide

parti<lcs (2- I Oprnf. X-R determination corlfirms that hematite represents a sigrllficant proportion of the clay fraction. Our results are in agreement ~ 7 t h those of Gfl~dricr and Pye (1981) and Schwerunanri er d (1982) ~ 1 1 o considered t h x the red colr~r is related mai:dy to hematite whereas gocthitc and hydrox~des give :I yellow tvowrl mlor.

Intensity of the rubification depends upon the quantity and the size of dlese iron ox~de particles Tile raore fine and abundant the particles are, llle more thc soil is red In the most-nlbificated p~deosol S5- I , these p,uticles constinltr about 5 % of the

fine tr:irt~on and most of them are less than 3 pm in size. From tIik point of view, the less ~l;t,erlsive rcddenmg process in the paleosol S1, 52, 53, 55-2, S b , S7 and SX, h:iving a sm~ilnr' ~ncchanism as for S4, S5-I and S5-3, can be regarded as the heginning of rubifllwhon.

Thc ecological condioons reqllired for rubifir~tion n r e cantroversial l t was tho~lghr that rela~veiy high hurru&ty is necessary for mblficatrorl ((3ardricr and Pye, 19h 1 ) whcrcas S c h v x ~ t m a n n (197 1) cnnsidered that in the desert env~roi~rrients, the lug11 tcmpcranires, the oxidiang conditions and absence of organic rnatlers arc ideal for the cxmserrration of hematite, thus favorable to rubiticatiort. FIowever, it is unanlrnously agreed that a relatively hot pedoclimale is indispensab!e for ruhif~catiorx. The most typicsl rubificatiort is located in Medtterranean cnviranments. 1 7 ~ clunare 1s seasonally COl3ti astcd, characterized by alterrlation of fresh winters 2 n d hot sumrncrs wiTh strong evapotranspiration (Duchaufour, 1976, 1377)

Irl summary, the most favorable conditions for rubificat~on seem to b e a) prcclplt:l?lcn necessary for rhc decalcification which is the precursor condition (Duchaufour, 1977) ; b) a hot pedoclimatc, and c ) an accentuated cituiccatlo~~ with strong cvnpotransp~ration. In gcneral, strons n~bification is rclatccl to thc polyphase dcvclopmrn t (for telrrk see Fedoroff, 1 gX6) of the soils (Duchaufour, 1977). However, the studled palcosols are inostly monophase, but s~gnik~cantly I-~t)~ii&lIed, ~l~Il~:-itLng that rfle paleoclirnatcs during &LC formallon of the paleosols vicrc corripnrable to the monsoon climatcs preva~llng at present on the Loess Plateau, but htgher summer ternperattires and stronger evnpotranspil-arkon are su ggcsted.

(4j Clay ~liuv~ation lllcvial fcatures are scarcely visible 1n the f1e1d because they exst l_n vcry sr~lall

amounts the surface horlzons of the paleusols wcsc all truncated Under :illrrc>sl-cq>o, :hey al-e obscnrcd only in S1 (1-2%), S 5 - I (2-3%) md Si -3 (1-2%) l't:c tcxrur31 fcanlrcs in thcsc so~ls are comparable, cha ra~ te r i z~d by limpid rnoderetcly nlicrolamir~ated brow11 reddish clay coatu~gs witit st~ofig b~refnngcnce (Fig be). Thcir linlpldiry and m~crolarnir-tarlon indlcatc a rypic~l illuvirll pi-occss, corrcspondlng to II corir~nuous forest cover (Fedoroff and Goldbrrg, 19821 Fedoroff and Courty, 1987). The absence of humus, even of the ck~arconl particles usually inhcritccl due to tlic decomposition of organlc matter, indicates a broc(!lcavcd I'orcst. Moreover, rclativdy abundant and rcgular prcclpllauons s h ~ i ~ l d

I 0 !

F I ~ 6 a Inknlal swcture of a hard nodule (S1, 2000 x); b, deplenon feature at Lhe

periphery of a scorious nodule (S1, 2000 x); c. Spongy micrustrucrure of the

Holocene soil (30 x): d. Microstructure of the paleosoi S1 (30 x), e. Clay coating in the paleosol S5- 1 (300 x); f . Water-reworked loess (Lw-2, 100 x)

bt: suggcst.cd. l a should be srrcssed that irl the studied soils, thesc clay coatings, typical for a

forcsr vcgctittion, arc developed in a grourldrnass with a spongj rrr~icrostructurc, characteris'cic for steppe soils. These features suggested that a steppe covcr w;ls donrinnn: durLng ~!;c soil formation, but it was replaced temporarily by forest during a s h o ~ ~ clixlatic optimum. Thus the pclleosols S 1, 55- 1 and 55-3 can be inrcrprcred :is st.cppc soils uith short forest cover whereas the other pdcosols wcrc always dcvclopcd uadcr steppe vegetation.

(5:) Alkalization Alkaline propertics of rhe paleosols were never found in earlier works. Our

chcn~ic -1 nnalyses show that the paleosols S4, S5-1, S5-2 and 55-3 wcre affct::cd by alkalization. I t is expressed by high pH values and concentration of ~xchangcable Nay Na2C03 is &o detected in the soil solution (Tab. I ) .

i t should be mentioned that the chemical characters for pdeosols are generally considercri to be unstzible (Yaalon, 1951). However, the following fats sue,gest rhzt d ~ o s e in the studied soits are cer-tainly inherited from the moment before trle soils w r i . bcr-ied, but wcre produced in the last stage of soil development.

a) S:i1h~-nlkali properties are only detected in S4, S5- 1, S5-2 ar:c? SS-3. '171c.y wcss ahscrit ever1 in tlre underlying loess.

b j These properties are cl~sely associated kith morphological features. In 54

and S 5 , the original spongy microstructure slightly collapsed due to the Nxi in soil. C ) S O J I I ~ of the textural featurcs i r ~ S5-1 and S5-3 are irltcrcillatcd in thc

ground~n:ls. Such pheriomenon is considered typical for natnc horizons (Fetforoff and Courty, 1986). Moreover, thc hnpidity of the illuvial feamres Lqdicates that the alkalirlc propcrries wcrc produced after the illuvial stage.

Ac01i:lri clusr seems tu be the only possibility for the Na' source. Firstiy, cl;ly rnitlcra1ogic:ii analyses show that the ureaBicring was too wkak to release cno~igh

Nni f~,otn K:l-bearing mincrnls. Secondly, no trace of paleo-phrcatic lcvel was iounii in tile field. Mor+covor, all the nbovc paleosols have a less wcat1lert:d f3 l horizcin con:1:1:4recl wi~h B2 horizon, wiiich implics that dust dupositiorl was :~clive

dl1ri11g the I:st periodof soil gcncsis. In any w e , the conservation of N 3 ' in I'ricse soils indii:etcs titat very humid climatic conditions ncvcr cxistcd in the Xifcng arc:,.

2. C;cfic:ic types of rhe paleosols As r:lc existirig soil classifications a r e usually based on tJ-~e rni)cicrii cult.ivatcd

soils, the c1:tssification of palcosols acc~rdi,ng to these systems is alwjys d i l t i c ~ i l t arid r?ppr.osimati-fe. + f i e paleosols UI the 1,uociluan locss section wcre cl~!iificd ns 1-letu (chinose classification), corresponding xpproxirnatcly to cinnanlon snils (I..lu

cc al . . l ' ~85) . I r i fact, the type prufilcs of Hctu cover a vcry lr?rgo area f!-orn Ijcijing

in rhc no141 lo Xi'an i :~ d ~ e sourl~. 7hc Itlrarl annual tcnlpcrarurc vru-fcs fi-otn 9 OC to

1 5 O C and dlc rncnn annual prcci;litation t ron 400m.m to 700'rnm {Zhv H . J. , 1985). Cli~n,ltic: vcgcbii(>n is difficult to infer duc to thti agricultural cxploital.ion. Acl:orriil:g to %hi1 11. J ( 1 S i S S ) , a fcrcst or stcl:pc-forcst vcgctablc covcr car1 bc s~~ggcstcd. The cxacr pii:;i\1011 of Hctu in the diagnostic classification systems is not very clear.

rable 1.. Exckangeab!c cations asd i o t s in the solution of the

paleosols and locss (meg/ I OOg)

------- p...--......-----4".-

C B i Bscbar~.caticrs 100s in the sal~tioa C a t t ngtt Baf K t

---- -------- 1 6 . 2 0 13.78 2.15 8.10 0.25 12.10 9.60 2.15 8.15 0.20 9.10 4.95 2.58 0.15 0.20 9.50 3.65 3.35 Ball 4.30

13.58 3.55 9.40 6.20 0.35 13.90 4.70 1.63 0.10 8.35

6 . 9 5 1.15 5.35 8.15 0.20 16.65 1.58 8.60 0.40 8.25 11.50 6.25 5.00 0.12 0.13 15.95 1.35 6.?0 0.10 4.20 16.28 9.70 7.64 0.75 0.15 14.19 5.85 7.90 0.20 0.15

12.63 2.15 8.35 1.85 1.30

10.30 6.63 3.20 U.20 0.25 9.55 6.95 2.15 8.20 0.25

15.30 5 .40 9.00 0 .60 9.30 9.98 1.75 7.78 0.10 0.15

13.40 6.70 5.45 0.98 0.35

14.25 3.78 8.80 1.45 8.30 13.90 4.65 1.90 1.15 0.20

11.65 1.15 1.35 1.95 0.20 10.18 B.DO9.#OB.O08.30 1 . 5 0 0 . l B 0 . 0 0 2 .2B9 .550 .581 .29 1.25 13.15 5 . 9 0 5 . I D i . 6 5 0 . 4 0 0 . 6 5 1 . 0 5 0 . 0 B 1 . 7 0 0 . Z O 8 . 0 0 1 . 2 5 1.15 11.48 5.75 4.10 1 .60 0.35 0.85 0.40 0.00 1.25 0.35 0.01 1.10 1.43 11.45 8.15 4.35 1.10 0.40 0.85 0.65 0.30 1.10 0.15 t racel .38 1.45 13.25 7.68 4.38 1.00 8.35 0.85 0.40 0.25 1.50 0.15 0,BB 1.20 1.35 13.55 8.15 4.50 9.55 0.35 0.70 0 , 2 5 0.15 1.10 0.15 0.00 1.M 1.15

12.48 6.95l .bB8.558.30 0 . 8 5 8 . 7 5 b . O Q 1 . 6 0 0 . 1 8 8 . 0 0 1 . 3 0 1.10 13,IO 6.19 5.35 2.15 0.30

9.10 5 . 0 0 l . I 5 8 ~ 1 5 0 . 2 0 0 . 8 5 P . 3 0 0 . 0 0 1 . 1 5 0 . 0 5 0 . 0 0 l . l J l . t 5 13-65 5.48 7.55 b.30 8.40

,15,25 1.15 6.95 0 , l b 6.35 11.611 4.10 7.6j 0.25 0.25

, 7.95 3.15 6.IQ'Q.JO 0.20 15.90 7.55 7.20 8.60 8.55

113.20 5 . 2 8 5.85 0.15 9.40 13.45 5.95 1.35 0.75 t.40

111.50 5.15 5.05 0.35 9.25 15.30 10.45 3.65 8.50 t.50

)15 ,55 6.75 5.48 0.65 0.35

Au-ordlng to Zhu H. J. (1 985), it mrresponds to arthic luvisols or chromic 1uvix)ls UI the F A 0 system and l3aploxerolls, Agrixcrolls md part of X e r ~ l u c p t s 111 the Amencan classification (soil survey staff, 1975).

Thc pedogenet;,~ processes discussed ahovc converge to show dlat the palrosols in the Xife~lg section were deveIoped under steppe cnvironrnents except the shun forest sugcs for the pdeosols Sl, S5-1 and 55-3. The paleochnarcs wcre senn-arid type, characterized by prominently contrasted seasons, high temperature and strong evapotrarlspiration in summer. Thcsc paleosols can be classified as kastanozem according to the FAQ system (FAO-Unesco, 19741, because a) the strongly developed excremental microstructure suggests a rnollic A l~orizon even though the surface horizons wcre tru~rcated; b) all of then1 show a chroma > 2; and c) all of them have a well developed calcareous horizon.

This classification is, however, very general. The difficulty arises f ron~ the facts that ( 1) the depth of the calcareous horizons for most of the paleosols is more than 1.5 rrl, largely in excess of that in the definition (120 cm, FAO-Unesco, 1'374), and (2) thls cor~cepltian covers sods under very different climates, such as the contiilcnbl climate in the Russian Plain, the Mediterranean clirrlate anci the arid tropi~al clirnate (FAO-Unesco, 1974, Boulaine, 19 82).

The paleosols in Xifeng are cerlainly different from tlrc kastsnozorn in the Russian Plain because the later has generally a hue 10 YR (Duchauftair, 1976) whereas the hue of the studied paleosols ranges from 7. 5 Y R to 5 YK. On the contrary, the rubification and the calcareous horizons of the psleosols art. closer to those of North Africa although the studied paleosols were less rubificated. Frorn this point of vicw, the Xifeng paleosols associates calcic and chromic characters, similar to thosc of the sols ma r ro r~ of the French classification (Duchat~four, 197 7) Palcud~matic conditions should be car~siderably warmer than the present- day climate, but h~ i~n id~ ty was not enough for a forest vegetation. The position in the diagnostic cl.lssificatinn systems is not clear. Roulaine(f982) proposed to put h s type of soils into a special fftufiily. In the light of this proposition, the paleosols S 1 to 58 in the Xifeng section can be tentatively classified as folIows accord~ng to Urcir n13jor sod-fornling processes.

( I ) Chronljc iuvic kastanozem- This group includes the palco%>ls S 5 - I arid S5- I . The profiles were strongly rubificated (hue = 5 YR) and totally decalcified, cont:iu-&lg :it once some illilvial features. The climate was much wamicr than that of today A rlcnsc stcppo was domincmt during the soil formation, bur it w s replaced dunng a short hurnid climatic optirrllim by forest cover.

(2) L,nvic kastanozenl. The S1 sol can be classified as ttlis type. 7 hc proftle was ~ntxlerntrzly rubificatcd and totally decalcified. Sirmlar clinlatic vegetatton to the above grotlp can be suggested and less strong rubification was probably relnred to lowcr silnlJner temperatures.

( 3 ) Chrorrlic dccalcLficd k~~tartozern: Tlte S4 sol, strongly rubif~catcd :ad torally decalcified, can be placed in this type. A dense steppe cover was don~irlarit dunng the soil development. The paleoclrmate was hot, but not lnlrrud criougf? for a forest vcgetatinn, cvcn during the clirnatic optimum.

(4) Ilecalcified k;istanozctn This group mcludes the palzosols SZ, SS-2, SG anrl SY soi;s 'The profdes were rnoderately rublficated arid totally decalcified. The

clunaric con&tiom wcre comparable to those for the S1 soil, but the h t~n~i : i iv w,u not sufficient for a forest cover. A steppe vegetation was ciurnirlent duri~ig the so2 formation.

( 5 ) Partly d c c ~ f ~ e d kastanozern: The S3 and 57 can be classifiocl as iyp, formed under steppe covers. The less developed profdes irt cornparisorl w t h grijup (4) can be regarded as a function of shorter time duration ~ad 'o r drjc:. clinmti:: corlchbons.

( 6 ) Intergrade knstanozern-chernazem: The weakly developed pr~ieusols S2-2 and S6-2 car1 be classified as this type. The weakly rubificated protiles and the calcareous horizons are characteristic for kastanozem whereas the humus ~ccnmulation is more similar to that of chernozem. I.,ess w m e r and prolinbly also dryer clin~atjc conditions can he suggested.

Paleosols From S9 to S15 and in the Wuchcng 1,oess

Magnetostratigraphic studies (Liu T. S. et a]., 1985; L.iu X M e! a1 , 1987; Kukla, 1087) show that rhc paleasol S9 is about 0.85 Ma in age. The Manly m4G:wss (2.5 Ma. BP. ) boundary is located near the boun<i:iry hetween Wucheng Ivess and the underlqulg Pliocene red day (J>iu T. S. ct d , 1985, I,iu X. M. et a1 , 1987) 111 earlier works, 6 paleosols were noted for the scqi!t.nr.o from S9 to 1.15 (9.85-1.15 Ma. BP.), and were labelled as SS9, 510 ,..., S14. 'The Ilfucheng loess (GO ni In thickness) was generally divided into three soil groups (WSI to WS1) and t'uee loess members labelled as WLI, W 2 and WL3 (Liu T. S. ct al.. 1985)

Although the sequence from S9 to LI 5 was placcd in thc I.ishi I,oess, corresponding to the Middle Pleistocene (Liu T. S. et al., 19851, our study shows that the paleosols arc cxtrcmcly similar to those in the Wuchcng L,oess The palensnls S9 and S 1 4 are both composed of two supeqoscd soils (S9- 1 and S9- 2, S14- 1 and S14-2). One soil interbedded in the loess unit L15 was also found (S 15). The Wucheng loess formation contains 17 paleosols and only 7 loess layers. In o r c l ~ r ta tacilitatc the disc~lssions in tlis study, they are labelled respcctivcly as Sw- 1 to Sw- 17 and Lsv- 1 to Lw-7 (Fig. 2). It should be stressed that rhese 111bcl.; do not possess ar,y stratigraphic impliaation.

In thc field, the loess layers seem typicd and the paleosols appear forined MI srn~ Mlcromorphological investigations show that sever;il loess arid 1);ile17501~ wcre rotally or parfly cilsrurbed. The loess L14 and Lw-2 were pa t iy I eworked by wakr, prohnbly dug to the trickling process. The gro~~ndrriass contains so;;le fine slit tcxti~ral feait~rcs (5 -8%) [of sefdimentary origin (Fig. 6 f ) A srr~all q u , i ~ ~ t l t y o f similar features are also observed in the paleosols Sw-6, Sw-8, Sw-9 anci S V J - ~ 5 in which rlie B horizons were largely disturbed. They consisr of 3 greai arnount of soil fragrncnfs (40-60°/o) rrlived $1 a loess matrix. It should be stressed however ttlar the underlying calcareous horizons of the paleosols zre always u1 sitil cxolur-fing a signi tican t dlsci~ntlt~uity of the stratigraphy.

A very remarkable phenomenon of this sequerlcc 1s that the palcosols superpose one anod~er without interbebedded laess layers (Fig. 2) This suggests that

c lunr i~c fluc~uatiorns for tr?e early Queternary were ?lore frequent and most of the dust deposixion sbges were very 5hoi.t and during these stages, t l lc chlares were m~lch less severe so ti~ai &tire aeolian dust deposit was totally sffecred by peciogcnesis.

Among tiic 25 paieosols, orliy the 512 wid Sw-17 were mblly dccdclilcd and strong!^ mblficat~d (ye',low re6 5 YX 5!6). They are comparable to thc yourrger chiorruc k:btanozerns. Ail the oaer paieoscls were we&!y developed kstanozenls, corlta~rting about 3 4 % primary carbonate. The differentiation of pedologrcal hc?r~-rons IS so we& tlislt their profiles show a surprising hornvgenei!y. The n ~ h l l ? ~ a b ~ ! l 1s largely less iniensive (gerierally 7. 5 k% S/6 ) than m the younger palcosols. The rclahvc quantity of smectites is notably k~creased iz: cornpririsnn with uppor scqucnces, but it ca;l not be explained by pedogenetic transformation b-?~st> the minernlogicz! csn~positions of the soil profiles arid ~nder lymg loess are very si~nilnr.

Dunng the devoloprncnts of theso paleomls, dust deposition bras tertainly i r npom~t a n d probabl) r-ever interrupted. Following featiires crin be regarded as d i :~gt i ( -s~c .

( 1 ) [3espte th, vrry weak weat.liericg process, most of th paicasols snow a great ;'licl;nms (Fig. 2j, generally > l .5 m and sometines near 3 tn (e g. Sw-9).

ixplres tl:at d:rst deposition played a s i a f i w t role in the rejuvenat~on P: so11 protilcs.

(2) '171e cr-llcareous horizons of the paleosols usually consist of a redd~sii grouncirriass weakly-impregnated by micritic carbonate. Micromorphologicai invcstgatium show thct the goun&nass had been strongly affected by pedogenesls before ciuF.onate mli>rugr~ztion. Moreover, the horizons are very tldck (generally >1 n; 1.5 rn for Sw-9 and 3 m for Sw- 1 I ) , Mfering greatly fron normal soil profiles (FIE 2) ' 'rhc~c i'ca:.urcs car. be explained by the following 11lodel : in the wake of dust deposiQcm on the sail surface, the upper b0unda.y of the calcarkous horizon rose progressively up into the 8 horizon. Thus the B h o r i z ~ n was rccalcificd and the cdcareous horizon became incressingly thicker.

In $urnln:lry, th6se paleosols can be regarded as a resuit of interactiori bctweur: pedogeriesls 2nd intensive dust sedimentation. The sigdicmt dust deposition dunng tiic soil development suggests thai clim3tcs were colder and rlayer t h a ~ ~ those for thc you:lgt'r palt'oso!~. The water reworked loess and soils :?re probably related to tile pdtoto~mgaph;r in the kxd area.

General Conciusions

77-le fnodr~ i ~ 1 1 s iz ;he X5feng area are considersbly retvorked by agriz:~:;ural acnvities 21irlti the mxjor part of the top so3 wzs forrncd duriag tile Mid-lloivccne T11e facc th:ir dejccuons mixed with loess has been brought to the field for rhe past t.*o or three tEsocs;tnds ygars makes it impossible to estilnrtte t h ~ quantily of' kIolocene dust cfcpc~sibor,. This phe~oxnenon was probably conunon on ,the whole Locss Plateau. However, tke morphogenetic chairzckrs of the soil. does not support the notior, of greiit cEmntic difference between the present-day and the Mid-

f ioir:cer:e %mi-sr:tl climates and steppe vegetatiorz. were d~mixliFrlt f o r all P'tcistocenc

pdcosols. Short forest stzga, rejxesentiqg cljmahc optr?li7als, are ordy idt-nufied ]:I t!\e pa;c:>sols S1 , S5- I and 55-3. The Br~:nhes/Mat'uynn!a bo~~nciary tail be 1cg artlrc: : ~ s a remtvkzble iimit for the Pl'leistoccnc pdeo-pcdogencsis Tfic Rmtlhcs cpocil is character~zed hqr well devt!oped kastmozelns that were formccl under c!ii-nates seasonally conwasted with hi@ temperatures and strong cvaputi anspiranor! 111 summer. The summer temperatures wcre much higher t h x i today. On the contr:iry, rrxtxt cf t'ne Maruyaiia pleosols were weakly dcQeloped kasLmozcnls and aco!lan &dst deposition continued contemp?raiieously urith pedogenesis This leacis 1;oi oi:!y to t h e hcnogencity of the sc i l profiles but also the rcjuvenz?ion of the s,lils 111 these cases, cautions is necessary for the paleoctlmatic jriterpretations based on thc cclmpar-ison of the weathcri? degree betwecr, sol1 profiles a1l.d the ur;durlying laess.

D i ~ s t depositmn d~iri[fg the forination of the paleosols m the Wucheng loess w:t\ prubzhly intensive only at the north western part of the Loess Pla~eau. In the ezst, the n~ilch nlrlse humid palemlimntes were certainly fztvorahle to pedogenesis, and x!:it'~vorablc t:) dlist sedinenGtion. These ~paleosols should be more de:trly ex!):cssed m,d better developed than in the me-eng section, as de~crihed hy Xi~tter et :11 (19'11)

Ackrrowledgcmet~t The autllors t h a n k Prof. Lit1 Tungshetig for his support and suggestions to this

work, Dr. M. A. Co~~rfy and Dr. 2. L. Ding for helpful discussiorss. We are also grntef~ll to J. Bcrrier, P. Guillorc, C. Lucet, D. M. Sun, J, i.. Xian ant1 Y . 7.. Zhu Sol. lakorritory and field assismce.

References

An. Z.. S., arrd Wei, I+. Y. (1980). The fifth layer paleo.wl in the l ~ s h i Imss and ia paleocliinatic

sig11iiic;ln::e. Acfa f ecr'ological Suzica 17, 1 - 12.

Hir'keIand, P. Vr'. (1 984). S0i1.s anand Geon~orpho!oogy New York, Oxiorrd. Oxfor.d Urljversily Press, 372 p!?.

Bo:~r.eau, bl , and Saucnier, i3. (1979). Pedologie Tome II . .Cons!.%?snLr er Proprirtfc.~ dij So!. I'tl;~.son ?:iris-Ncw York-Earcelorke-Mila&.- 459' pp. .

13cot1l%~,lne, J . (1982) Typologic d?s Sols. Tome I. .Sol. 1, Instirut National Agroclonlique Rirn- Crrig.ric-,n, France, 1'39 pp.

3rc:cgcr A., aid Memkek, Ih. (1989). ~tcromorphoko~~ and genesis of paleoscls i i ~ rk1.e Luwt~iian !ocss scction, Chmn: Pedostratigraphic and cnvirormental implicatioris. Gc~dcrrrzn45, 123-

I 4 :3 .

?3tiUo~k, P , Fedoroff, N., jongerius, A., Stoops, G , and Tursine, T (I"3tSj. 19,~ndbr.wk 1F;c.r Soil . 7

Inin kcl ion i'lcsc,+priorr W&qe Research Pubticaticn, 152 pp. C c ~ r t y , M. A., and Fedoroff. N. (1985): hlicromorpho!ogy of recent and burkc": xxl3 ir: a semi-arid

region of Nordiwcs; India. Gcodznna3 5, 287-332.

Dnchaufour, Ph. (1976). Arlas Ecoiogjque der Sois du Monde. M:t.sson Paris-New York- Harcelone-Milan, I 7 8 pp.

Duchnufour, Ph. (1977). Pedolngic, 'Tame 1 , Pcdogencse ef CIassiffca?icm. Masson. Paris-New York-Barcelone-Milcun, 477 pp.

F A 0 -Unesco (1974). &if Map orthe World Vol. 1. Legend. Paris. FedoroIf, N . , .and Goidberg. P. (1982). Comparative nicromorphology of two late I'leistocene

paIeomls ( in the Paris Basin). Cofena 9 ' 227-251. Fctiilrolf, N. (1'386). Un plidoyer en faveur lie la pafeopedologie, Builtin de 1;lrsociation

Franwise pour 1 'Ehrde du ~ u 3 f e m s f n 3-4: 135-204. Fcdoroff, N., and Courty, M. A. (1986). h4icromorphology of naltic hC~riZ0nS. in: Transactions

XI11 Congress of ISSS, pp. 1551-1552, Hamburg.

Fedoroff, N. , artd Courty. M. A. (1987). Morphdagy and distribution of iexrural ieaturcs in arid and semi-arik regions. In: Micrornorphogie dcs Sob (N. Fedoroff, L. M. Brm~on and M A.

Crx~r ty , Eds.), pp. 21 3-220. A F B , PaIaisir, France. Gardncr, R . and Pye, K. (1981). Nature, origin and paleoenvironmenc~l signiI<flc?s,ce of red coast11

and desert dune sandrj. Progres5 in Physical Geography 5, 5 14-534. Guiflore, P. (198 53. Methode de Fabrication Mecanique ef en Sene des L.arnes Minces. INA-P.

G. Grignon. France, 22 pp. Guo 2. T., wd FcdorofI, N. (1989). Genesis of calcium carbonate in loess and in paleosols in

central China. in: Soil Micrornorphology: a Basic and Applied Science. f l ... A. Uougla~, Ed) F3sevier. Amskrdam-Oxford-New York-Tokyo, pp. 355-359.

KuUa, G. (1 987). b s s stratigraphy in central China. Quaternary Science Revie~s 6 , 19 1-2 19.

Kyum3. K., Wang, Y. Y., Tulaphiuk, T., Yue, L. P., Araki, S., and hliao, J . Y (1985).

Paleosols in the Luochuan loess section. I. Field occurrence and general chnrac tcristics. Soil Scc. Plant. 1~13rr.2, 263-286.

LIU, T. S. (1959). Younger loess andolder loess. J. f 3 i . 5 . 22-25. (in Chinese). L-lu, 7'. S . e l 31. (1964). The loess along tiit middle reaches of the Yeilow River Science Press,

Beijing. (in Chinese). l i l t , T. S . et al. (1985). I ~ m s and Environmenf China Ocean Press, Beijing, 751 pp.

Litl, T. S . , and Yuan, B. Y. (1987). Paleoclimatic cycles i n northern China: l..unchian loess section atld i t s environmental implications. In: Aspects oC Lues Rcscnrch. (T. S Liu, Ed.), pp. 3-26. China Ocean Press, Bcijing.

Liu, X. hf.. L.iu, T. S., Xu, T. C., Liu, C., and Cheng, M . Y. (1987). A preluninary study dn nlagnetcstratigraphy of a loess profile in Xtfeng area, G a r ~ u provmce. In: Aspecrs or Loess Hesearch. IT. S. Liu, Eti.), pp. 164-174, China Ocean Press, Beijing. '\

Ma, Y Z . (1958) . Some suggestion on the origin and the paleogtogiaphic imphcaLion of Quatenlay strata. Quaremary Sinicrc l(1): 70-73. (in Chinese).

P x ~ l u k , S., and Bal, S. (1985). Micromorphology of selecred ntollic epiprdons. In: Soil

hlicronorlpholog and Soil Classification (L. A. Douglas and hf. L. Thompson, Fds), pp 63-84. SSSA Special Pubkcation NQ 15, Madison.

Pecsi, M. (1987). Interpretation des loess et des formation lcessiques, paleosols cr arg~l-s ru~lges d:tns les recherches du loess. Symposium international du loess cn Chinc. I n Loess and

Perigscial Phtnomena (M. Pecsi and H. M. Franch. Eds.), pp. 63-86" Akademjaikiado-

W~dapesr. Kurter, N., Ding, 2.. Evans, M. E., and Liu, T. (1991). Haoji-type pcdusira:igrrtphic srchon,

l..oess Plateau, nor~h-central China. Quaternary Science Reviews 1 0, 1-22.

.Clhwcilmann, U (197 1). Transformation of hcmatitr lo goeLIutc in soils. h'ittvro2 12 , 645.646.

.C;:hwcr~inar~n, IJ. , Murad, E, anc! Schulze, D. 6. (1982). Is thcrc Holoccne reddcaing (hematite formrzrion) in soik of axeric Wmperdtc areas? Geodcma27, 209-223.

Shi, Y . C. (l(j58). I.aess and irs origin in western Skvtvi Province. Qtrsrernatia Si,rli~? 1 ( 1) .

252-25.3 (in Cininese). Soil Su wey Staff, ( I 975). ,Soil Taxommy: A Basic Systena o f Sni! C7I&ssification fcr .M;rkng

and Inlerprelii~g Soil Surveys. USDA-SCS Agric. Hsndb. 436. 13.. S. GaverrL~cn: Printing Office, Washington. EX, 754 pp.

Tang. K. 1.. (I ' iSt) . Micromorphology and'geaesis of fhe paleosols in lixss, Wugoiig, Shasnxi.

Kcsur Tungbao26.177- 179. (in C h i r C e ~ ) . 'Thorp, J . (1336). C;coqaphy of the soil of China. Geol. Surrr China. W m g , Z. Q , , and Feng, X. hl . (1958). Prelinlinary study on the elernsnrril propcrrics of ttre

culljvatcd crnnarnon soil and pdeosois:Special Publication of Pedology No 1 5 ( in Chinese). Yaalnn. 0. ii. [ I P ? l ) . Soil-fonning processes in time and space. In: Palenpedology. Origi~i.

Natnrc and Dating o l Pateosols. (D. H. Yaalon, Ed). pp. 29-30. Hehrew Umversity, Jcnrsalem

Zhu, H . J ( 1985) ,k>jl Geography of rhe World China Higher Ed~lcaticin Press. Brijing .177 pp

mu, I f . Z. (116;) Sornc characLerisdcs of rh~ .~r r r in size and texrtrre of hlalan loess in 12ie nliddlc re;~ches of rhe Yellow Ricer. Scienria @ologica Sinica2, 88-102. ( i n Chinese)

Zilri. X. M . (1958) Discus;ion on the problcm of red layers intercalated in thc loess section.

Quaremaria S j n h l(1): 74-82. fin Chinese). Zhk~. X. M . (i065). Psleosols in loessic sedimenrs of China, Quaternaria S~?lcn4(1). 9 I 9 fin

Chinese).