Comparative study on the Late Cenozoic red clay deposits from China and Central Europe (Hungary)

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Com par a tive study on the Late Ce no zoic red clay deposits from China and Cen tral Eu rope (Hun gary)

JánosKOVÁCS, György VARGA and József DEZSŐ

Kovács J., Varga G. and Dezső J. (2008) — Com par a tive study on the Late Ce no zoic red clay sed i ments from China and Cen tral Eu rope (Hun gary). Geol. Quart., 52 (4): 369–382. Warszawa.

In the east ern Loess Pla teau re gion of North ern China, the Qua ter nary loess-palaeosol se quences of the last 2.6 Ma are un der lain by the Hipparion Red-Earth For ma tion (namely the “Red Clay”). The red clay is also a sig nif i cant de posit in Hun gary, the or i gin of which is con tro ver sial. This pa per is a com par a tive study of the Cen tral Eu ro pean (Hun garian) red clay suc ces sion and the Xifeng Red Clay pro - file, the type sec tion for this de pos its in the east ern Loess Pla teau re gion. Op ti cal mi cro scopic and SEM anal y sis were used for grain-size mea sure ments, and both ma jor- and trace-el e ment geo chem i cal prop er ties were ana lysed to ad dress the ques tion of the or i gin of Hun gar - ian red clay as well as its en vi ron men tal im pli ca tion. We com pare the Xifeng Up per Red-Earth (age: ~3.6 to 2.6 Ma BP) with the Hun gar - ian, Tengelic Red Clay For ma tion (age: ~3.5 to 1.0 Ma BP); both are ae olian de pos its ge net i cally re lated to the Qua ter nary loess -palaeosol se quence.

János Kovács, György Varga, De part ment of Ge ol ogy, Uni ver sity of Pécs, Ifjúság u. 6, H-7624 Pécs, Hun gary; e-mails:

jones@gamma.ttk.pte.hu, gyoker@gamma.ttk.pte.hu; József Dezső,In sti tute of En vi ron men tal Sci ences, Uni ver sity of Pécs, Ifjúság u. 6, H-7624 Pécs, Hun gary; e-mail: dejozsi@gamma.ttk.pte.hu (re ceived: Feb ru ary 05, 2008; ac cepted: Sep tem ber 29, 2008).

Key words: Hun gary, China, Plio cene, red clay, palaeoenvironment, ae olian de pos its.

INTRODUCTION

On the Chi nese Loess Pla teau, the Qua ter nary loess- palaeosol se quences are un der lain by Ter tiary red silty clay (Liu, 1985), termed the Hipparion Red-Earth (namely the “Red Clay”). The red clay in Hun gary is also over lain by loess palaeosol se quences (Sümeghy, 1944; Jámbor, 1980, 1997;

Halmai et al., 1982; Fekete et al., 1997; Schweitzer and Szöőr, 1997; Viczián, 2002; Kovács, 2003, 2008). The thick ness of the red clay ranges from 10 to more than 100 m in China (Ding et al., 1998a, 1999; Sun et al., 1998; Guo et al., 2001; Lu et al., 2001; Hao and Guo, 2004, 2007; Li et al., 2006; Xue et al., 2006) and from 4 to 90 m in Hun gary (Jámbor, 1980, 1997;

Halmai et al., 1982; Fekete et al., 1997; Schweitzer and Szöőr, 1997; Fekete, 2002; Földvári and Kovács-Pálffy, 2002;

Viczián, 2002; Kovács, 2003, 2008). The Chi nese de posit has been in ves ti gated for over 80 years (An der son, 1923). The Hun gar ian red clays had been rec og nized ear lier (Lóczy, 1886), but re search on them was sub se quently in ter mit tent.

The re mark able prog ress made on red clay re search world - wide show that the sedimentology, geo chem is try, geo mor phol - ogy and field re la tions all dem on strate a wind-blown or i gin for

the Chi nese red clay (Ding et al., 1998a,b; Lu et al., 2001;

Xiong et al., 2002; Sun et al., 2002; Miao et al., 2004; Yang and Ding, 2004; Sun et al., 2006), sim i lar to that for the over ly - ing Pleis to cene and Ho lo cene loess.

In Hun gary, lit tle at ten tion has been paid to the red clay over the last cen tury. Dif fer ent views on the for ma tion, prop er ties and dis tri bu tion of red clays in Hun gary have been pub lished. Early sci en tists de scribed the red clay as a va ri ety of loess, sed i ment formed by the de po si tion of wind-blown silt (Lóczy, 1886;

Sümeghy, 1944), while in the last de cade there have been geo - log i cal, min er al og i cal and pedological stud ies (Jámbor, 1997;

Schweitzer and Szöőr, 1997; Fekete, 2002; Földvári and Kovács-Pálffy, 2002; Viczián, 2002). Stud ies of the ge ol ogy, geo mor phol ogy, min er al ogy and geo chem is try have been car - ried out by only a few au thors (Schweitzer and Szöőr, 1997;

Kovács, 2003, 2007). Re cent in ves ti ga tions also dem on strate an ae olian or i gin for the red clay in Hun gary (Kovács, 2006, 2008).

This pa per pres ents re sults of grain-size, min eral and chem i cal anal y ses and their im por tance for the in ter pre ta tion of the or i gin of the Qua ter nary de pos its in Hun gary and China. The aim of this study is to dem on strate the ex tent of sim i lar i ties be tween the Chi nese and Hun gar ian de pos its, as well as show their im por - tance in palaeoenvironmental re search.

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GEOLOGICAL SETTING

The Plio cene Up per Red-Earth For ma tion at Xifeng (Fig. 1) is well known from sev eral re search pro jects (Ding et al., 1998a,b; Sun et al., 1998, 2002; Lu et al., 2001; Xiong et al., 2002; Vandenberghe et al., 2004; Yang and Ding, 2004;

Liu et al., 2006; Xue et al., 2006; Wang et al., 2006). De tailed geo log i cal and strati graphi cal de scrip tions of the Up per Red-Earth at Xifeng can be found in Guo et al. (2001, 2004). In the east ern Loess Pla teau re gion, the Red-Earth se quences gen - er ally have a silty-clay or clayey-silt tex ture, a hue vary ing from 7.5 to 5 YR, and con tain abun dant car bon ate-rich lay ers (Guo et al., 2001). The Xifeng sec tion (107°58’E, 35°53’N) is lo cated in the cen tral part of the Loess Pla teau; the en tire Red-Earth For ma tion in the re gion is gen er ally 50–60 m thick and is a type se quence for the east ern Loess Pla teau re gion (Liu, 1985; Sun et al., 1998; Guo et al., 2001; Lu et al., 2001).

The Late Mio cene–Plio cene Red Clay For ma tion of the Xifeng sec tion over lies lac us trine strata and is over lain by Qua ter nary loess of the past 2.5 Ma. This unit of the Red-Earth sec tion con - sists of al ter nat ing red dish lay ers (5 YR 5/6–8) and yel low ish to brown ish lay ers (7.5 YR 5/6–8). Each of the red dish lay ers are un der lain by a car bon ate-rich ho ri zon. The red dish lay ers are

char ac ter ized by dis sem i nated, rel a tively soft cal car e ous nod - ules (10–20 cm in di am e ter).

The red clay de pos its of the Carpathian Ba sin are known from both ex po sures and bore holes. The sec tions in ves ti gated in this study are lo cated mainly in the foot hills of the Hun gar ian moun tains ex cept for the cen tral part (Fig. 2). The age of the Tengelic Red Clay For ma tion is ~3.5–1.0 Ma (Gyalog and Budai, 2004). For cor re la tion with the neigh bour ing area see Ta ble 1.

The un der ly ing (Mio cene–Lower Plio cene) strata are gen - er ally com posed of thick grey ish-yel low, mica-rich, cross-bed - ded sand and sandy clay or lo cally lime stone (in South ern Hun - gary). In the north ern part of the coun try, the lower part of the sand unit con tains a va ri ety of fos sils (an i mals, plants), some - times be tween sand stone benches. Many bone frag ments, such as teeth, jaws, ribs of Hipparion sp., Mast odon sp., Rhi noc eros sp. and Sus sp. can be found in the up per part of the sand bed (Kovács, 2003; Fábián et al., 2008). The age of the re cov ered ver te brate fos sils is ~6 Ma (Fábián et al., 2008). The cross-bed - ded sand or sandy clay is over lain by a 3–20 m thick red clay unit (Fig. 3). The thick ness of this unit is about 3 to 6 m in the north ern and south ern parts of the coun try (Fig. 3A, B). In the cen tral part (es pe cially in bore holes) this thick ness is much greater (10–20 m or more). The red clay (5 YR 5/6) dis plays a

China

L O E S S P L A T E A U Xifeng

km

Fig. 1. Sketch map show ing the lo ca tion of the Xifeng pro file in the Loess Pla teau of China

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Fig. 2. Sche matic map show ing the study ar eas of the red clay de pos its in Hun gary (mod i fied af ter Horváth and Bada, 2005)

T a b l e 1 Cor re la tion of the Pannonian Ba sin lithostratigraphy with neigh bour ing ar eas

(af ter Piller et al., 2004; Kováč et al., 2006)

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pris matic struc ture with slick en sides, stress sur faces and brown and yel low ish spots. CaCO3 nod ules, 3–5 cm in di am e ter, oc - cur in the lower part of the red clay. Gen er ally, the col our of the lower part is lighter than that of the up per part. Black Fe-Mn stains are gen er ally abun dant through out the en tire red clay unit, which is cov ered by the Qua ter nary loess-palaeosol suc - ces sion (Fig. 3C).

MATERIALS AND METHODS

Red clay sam ples from the Pannonian Ba sin were col lected dur ing the field work. A to tal of 50 sam ples were taken from the north ern, south ern and cen tral parts of Hun gary. The se quences were con tin u ously sam pled at 10–20 cm in ter vals. All sam ples were trans ferred to the lab o ra tory for granulometric, chem i cal and min er al og i cal anal y ses. The grain-size dis tri bu tion of all sam ples was mea sured by la ser dif frac tion (Fritsch Analysette 22) meth ods ac cord ing to the ap proach de scribed by Konert and Vandenberghe (1997).

Subsamples for geo chem i cal anal y sis were finely ground in an ag ate mill. Sed i ment pow ders (for AAS — Atomic Ab sorp - tion Spetroscopy) of 1 g were then di gested with 55 ml of con -

cen trated nitrohydrochloric acid (aqua regia) and 10 ml 0.1 N HCl in an air tight Tef lon cru ci ble (Kovács, 2007). Con cen tra - tions of trace el e ments in the di gested so lu tions were de ter - mined by a Perkin Elmer AAnalyst 600. Con cen tra tions of ma - jor and trace el e ments were de ter mined by a Fisons In stru ments ARL 8410 type se quen tial, wave length-dispersive XRF spec - trom e ter (equipped with a Rh-an ode, 3-kW end-win dow X-ray tube) as de scribed by Kovács (2007). Pre ci sion and ac cu racy were con firmed by rep li cate anal y ses of na tional stan dards (GSD-2 and GSD-6) and the use of blanks. An a lyt i cal un cer - tain ties are gen er ally less than 5%. Loss on ig ni tion (LOI) was ob tained by weigh ing af ter 1 hour of cal ci na tion at 950°C.

X-ray dif frac tion and ther mal anal y sis (DTA) were ap plied to de ter mine the min eral com po si tion. Sam ples were mea sured with a Philips X-ray Diffractometer (PW 1730 se ries), us ing CuKa ra di a tion and a Paulik-Paulik-Erdey type derivatograph.

The monomineralic quartz frac tion of 50 sam ples from Hun gary was ex tracted us ing the so dium pyro sul fate fu - sion–hydrofluorosilicic acid method (Xiao et al., 1995). Scan - ning elec tronic mi cros copy (SEM) anal y ses were per formed on the sam ples with a JEOL JCM 5800.

The av er age val ues of 50 Hun gar ian sam ples are rep re - sented by five points in Fig ures 4, 5 and 9 be cause of the cor re - la tion of five pub lished Xifeng Up per Red-Earth data.

Fig. 3A — study site in North ern Hun gary (Atkár); B — close-up pro file of the red clay (Atkár);

C — over ly ing loess se quence in Cen tral Hun gary (Szekszárd)

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MICROMORPHOLOGY AND GRAIN-SIZE OF THE RED CLAY

Grain-size dis tri bu tions of de tri tal de pos its are usu ally re - garded as use ful pa ram e ters in char ac ter iz ing sed i men tary en - vi ron ments and dy nam ics. Grain-size dis tri bu tions of the red clay were ana lysed and com pared with those of typ i cal ae olian loess and of the palaeosols de vel oped on loess (Guo et al., 2001; Lu et al., 2001; Kovács, 2006, 2008). Lu et al. (2001) sedimentological data were used to pres ent the grain-size pa - ram e ters of the red clays. The granulometric re sults are pre - sented in Ta ble 2. The grain-size dis tri bu tion curves of the Hun gar ian sam ples dem on strate a pre dom i nantly bi modal char ac ter (Fig. 4). The >63 mm (4j) frac tion is al most in sig nif i - cant in the de pos its. The fine frac tion is clay or very fine silt, while the coarser frac tion is me dium to coarse silt. The modal size of the coarse frac tion grad u ally coars ens from the Xifeng de pos its (ca. 6–9j) to the Hun gar ian red clay (5–7j). Both red clay de pos its show a bi modal char ac ter. In the Hun gar ian red clay, the coarser frac tion is lo cated be tween 4 and 6j and the finer frac tion be tween 7 and 9; in the Chi nese red clay, these val ues are 4.5–6.5 and 8–10j. The red clays are mod er ately sorted. Both de pos its types show pos i tively skewed to sym met - ric grain-size dis tri bu tion. The pos i tively skewed dis tri bu tion in di cates that the finer frac tion is in cluded in the grain-size dis - tri bu tion. We com pare the sta tis ti cal grain-size pa ram e ters of the Xifeng Red-Earth with the Tengelic Red Clay in Fig ure 5.

Grain-size pa ram e ters vary a lit tle, the char ac ter is tics of the Tengelic For ma tion be ing very sim i lar to those of the Xifeng Red-Earth. Only the mean and skew ness pa ram e ters are dif fer - ent, the mean square de vi a tion (MSD) and kurtosis be ing al - most iden ti cal.

SEM ob ser va tions showed that the ma jor ity of the quartz grains from the Hun gar ian sites are finer than 100 mm in di am e - ter, mostly rang ing from 10 to 40 mm. Grains >60 mm rep re sent a very small frac tion. Most of the quartz grains have ir reg u lar and an gu lar shapes (Fig. 6) and many are char ac ter ized by sharp edges, breaks and stepped sur faces (Fig. 6B, D), as well as conchoidal frac tures (Fig. 6C). These grain-mor phol ogy fea -

Fig. 4. Grain-size dis tri bu tion curves of the Plio cene red clay and Qua ter nary loess sam ples from Hun gary

Fig. 5. Mean grain-size vs. sort ing and skew ness vs.

kurtosis for fine grain sam ples in the Xifeng sec tion and the Tengelic Red Clay

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tures are very sim i lar to those of the Xifeng ae olian sam ples (cf.

fig. 1 in Liu et al., 2006; Guo et al., 2001, 2004), and also to those of Qua ter nary and Plio cene ae olian de pos its else where (Liu, 1985; Lu et al., 2001; Vandenberghe et al., 2004; Łącka et al., 2007; Kenig, 2008). They are con sid ered char ac ter is tic of ae olian dust de pos its (Pye and Sperling, 1983; Pye, 1995;

Wright, 2001). The an gu lar grains re sulted from me chan i cal col li sions, salt dis in te gra tion and freeze-thaw weath er ing in desert re gions (Pye and Sperling, 1983; Wright, 2001, 2007;

Smith et al., 2002), as ae olian dust in North ern China was mainly de flated from the north west ern desert lands (Liu, 1985;

Ding et al., 1999). Be cause the dust grains were trans ported by wind in sus pen sion, their sharp edges were not abraded. Ac - cord ing to Pye and Sperling (1983), this kind of an gu lar grain-mor phol ogy (Figs. 6 and 7C) is only char ac ter is tic of ae - olian dust par ti cles.

The struc ture of the red clay seen by op ti cal mi cros copy are: an over all clayey tex ture (Fig. 7A), with few par ti cles coarser than coarse silt (Fig. 7C); no ori ented coat ings are de - vel oped, but there are some weakly-ar ranged clay ag gre gates (Fig. 7B, D) and strips in chan nels and voids. De tri tal cal cium car bon ate is rare, but there is a small quan tity of weakly ori - ented micritic car bon ate in chan nels and voids (Fig. 7D). There are a few scat tered unoriented black-brown Fe-Mn stains (Fig. 7A). These char ac ter is tics show that the red clay is a type of palaeosol which de vel oped in a semiarid en vi ron ment (see later in Dis cus sion and con clu sions).

These sedimentological data are there fore highly con sis tent with the mor pho log i cal fea tures that sup port an ae olian or i gin for the Up per Red-Earth at Xifeng and for the red clay in the Carpathian Basin.

T a b l e 2 Sta tis ti cal pa ram e ters of grain-size dis tri bu tion of the red clay

de pos its from Hun gary and China

Sam ple Mean MSD Skew ness Kurtosis

Hun-1 5.59 1.45 1.51 2.64

Hun-2 5.49 1.35 1.46 2.68

Hun-3 5.51 1.43 1.49 2.82

Hun-4 5.88 1.63 1.66 2.81

Hun-5 6.67 1.71 1.48 2.68

Xif-1 7.31 1.65 0.16 2.54

Xif-2 7.20 1.72 0.08 2.70

Xif-3 7.35 1.53 0.18 2.56

Xif-4 7.38 1.59 0.25 2.58

Xif-5 7.27 1.65 0.13 2.50

Hun-1 to Hun-5 — red clay sam ples from Hun gary; Xif-1 to Xif-5 — red cley sam ples from China (data from Lu et al., 2001)

Fig. 6. Scan ning elec tron mi cro scopic pho to graphs of <60 mm quartz grains from the Tengelic Red Clay (Hun gary)

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MINERALOGY

Thin-sec tion ob ser va tions (Fig. 7C) show that (at both the Chi nese and Hun gar ian sites) the coarse frac tion (>10 mm) mainly con sists of quartz (50–60%) and feld spar and micas (>30%). Pyroxene, hornblende, goethite and he ma tite were also ob served. The min er al ogy of the red clay was de ter mined for the <2 mm size frac tion (x-ray dif frac tion — XRD and dif - fer en tial ther mal anal y sis — DTA). The ma jor com po nents are illite, kaolinite, quartz, plagioclase, smectite and chlorite with a high amount of amor phous mat ter (Schweitzer and Szöőr, 1997; Földvári and Kovács-Pálffy, 2002; Viczián, 2002;

Kovács, 2007).

GEOCHEMICAL PROPERTIES OF THE RED CLAY DEPOSITS

MAJOR ELEMENTS

The chem i cal com po si tion of the red clay de pos its in Hun - gary is dom i nated by SiO2, Al2O3, Fe2O3, CaO, MgO and K2O, sim i lar to that of the Xifeng Red-Earth (Ta ble 3 and Fig. 8A).

There are clear dif fer ences in loss on ig ni tion (LOI) be tween the Hun gar ian and the Chi nese de pos its, which may re sult from dif fer ences in the con tent of car bon ate, or ganic mat ter and hy - drous phases (Ta ble 3). Af ter re cal cu la tion on a vol a tile-free ba sis, there is a high cor re la tion (R²= 0.98) of ma jor el e ment con cen tra tion be tween the two red clay de pos its (Fig. 8A).

The chem i cal in dex of al ter ation (CIA) for the sam ples var - ies from 67 to 80 (Fig. 9). In the (A–CN–K) tri an gu lar di a gram (Fig. 9), in sol u ble res i dues lie close to the area of illite and smectite. The ter nary di a gram shows that all of the de pos its lie par al lel to the A–CN line. This pat tern sug gests that chem i cal weath er ing of the sed i ments re sulted in re moval of Ca and Na (pri mar ily plagioclase) from the source rocks and less leach ing of K, whereas in the sed i ments it caused con sid er able dis so lu - tion of Ca–Na host min er als and even K-bear ing min er als (mainly K-feld spar) as well. The Chi nese CIA val ues are around 70; those of the Hun gar ian de pos its are closer to 80.

These re sults show that chem i cal weath er ing was more in ten - sive in Cen tral Eu rope than in China.

TRACE ELEMENTS

We re cal cu lated the trace el e ment con cen tra tions on a vol a - tile-free ba sis (Ta ble 4). Com par i sons of the av er age con cen -

Fig. 7. Micromorphological fea tures of the Tengelic Red Clay

A — black-brown Fe-Mn stains (nat u ral light — NL); B — soil frag ments in the red clay (NL);

C — an gu lar mor phol ogy of the coarse grains in the red clay (po lar ized light — PL);

D — pedogenic car bon ate and clay ag gre ga tions (NL)

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tra tions of trace el e ments be tween the two red clay de pos its are shown in Fig ure 8B. The strong sim i lar ity be tween the Chi nese Red-Earth de posit and the Hun gar ian red clay again sup ports the con clu sion that the Mio cene Red-Earth de posit is of wind- blown or i gin, and that the Mio cene Red-Earth de posit has a sim i lar source prov e nance to that of the late Qua ter nary loess- soil in this re gion (Guo et al., 2001, 2004; Kovács, 2007, 2008). While the quan tity of most of the trace el e ments in the Red-Earth de posit is com pa ra ble to those in the loess-soil units, some el e ments (e.g., Sr, Zr, Hf) are slightly de pleted in the Red-Earth de posit (Ding et al., 2001; Guo et al., 2001, 2004;

Kovács, 2007). This may be due to stron ger chem i cal weath er - ing, which is in agree ment with field pedogenic ob ser va tions, sug gest ing that the cli mate of the Mid dle Mio cene in the north - east ern Ti betan Pla teau area and the Mid dle Plio cene in the Carpathian Ba sin were warmer and wet ter than dur ing the Late Pleis to cene.

An av er age up per con ti nen tal crust (UCC)-nor mal ized spiderdiagram for the sam ples from the Plio cene red clay se - quences is shown in Fig ure 10. In the Hun gar ian sam ples, the in -

T a b l e 3 Ma jor el e ment com po si tion of red clay sam ples from Hun gary and China [wt.%]

Sam ples SiO2 TiO2 Al2O3 Fe2O3 MnO CaO MgO K2O Na2O P2O5 LOI

Hun-1 56.60 1.02 18.80 7.20 0.12 1.61 2.49 2.29 0.26 0.15 9.21

Hun-2 57.40 0.76 18.20 6.90 0.11 1.94 2.25 2.83 0.48 0.09 8.70

Hun-3 55.00 0.93 19.00 6.80 0.09 1.68 1.66 1.86 0.25 0.08 12.50

Hun-4 57.90 1.05 18.70 6.70 0.13 0.95 2.33 2.13 0.39 0.09 9.40

Hun-5 56.10 0.95 18.90 6.70 0.08 1.21 3.23 2.18 0.64 0.08 9.70

Xif-1 52.90 0.63 11.65 3.89 0.09 1.03 2.44 2.24 0.74 0.12 14.00

Xif-2 49.61 0.60 11.38 3.81 0.08 1.26 2.43 2.11 0.55 0.09 16.00

Xif-3 52.43 0.64 12.13 4.08 0.06 0.98 3.00 2.34 0.64 0.12 13.86

Xif-4 51.74 0.64 12.03 3.96 0.09 1.02 3.00 2.31 0.63 0.12 14.35

Xif-1 to Xif-4 — red clay sam ples from China (data from Guo et al., 2001, 2004); LOI — loss on ig ni tion; for other ex pla na tions see Ta ble 2

Fig. 8. El e men tal com po si tion of the red clay de pos its from Hun gary and China A — com par i son of ma jor el e ment com po si tion be tween the red clay de pos its;

B — com par i son of trace el e ment com po si tion be tween the red clay de pos its

Fig. 9. The ter nary di a grams show ing the weath er ing trend of red clays (all in mo lar pro por tions); ba sic Al2O3–CaO+Na2O–K2O (A–CN–K) ter nary di a gram with CIA (chem i cal in dex of al ter - ation) val ues

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sol u ble res i dues are char ac ter ized by re mark able de ple tion in Sr, Nb, Ba and en rich ment in Cr and Co rel a tive to UCC. Some el e - ments (e.g., Cr, Co, Sr, Ba, Hf) are slightly de pleted in the Xifeng sam ples. Com par ing with the two red clay ar eas, only Cr, Co and Hf are dif fer ent, the other el e ments be ing al most iden ti - cal. De ple tion of Sr is more re lated to feld spar weath er ing than to CaCO3 dis so lu tion. In sed i men tary pro cesses, the dis tri bu tion of Sr is af fected by strong ad sorp tion on to clay min er als. Stron tium is eas ily mo bi lized dur ing weath er ing, es pe cially in oxi dis ing acid en vi ron ments, and is in cor po rated into clay min er als.

DISCUSSION AND CONCLUSIONS

Sed i ment ac cu mu la tion rates in creased on or near con ti - nents in Late Ce no zoic time, near 2–4 Ma. Ob vi ously, such in - creases in sed i men ta tion sug gest in creased rates of ero sion of nearby ter rain. Sources of sed i ment can be high or low ter rain and tec toni cally ac tive or in ac tive re gions (Molnar, 2004). One of the pre con di tions for the for ma tion of the ae olian se quences in China and Hun gary is the ex is tence of arid lands. Arid i fi ca - tion in the dust source ar eas leads to veg e ta tion de gen er a tion, shrink ing rivers and lakes, as well as to ex ten sive ar eas of bare sur face, which causes in ten si fi ca tion of phys i cal weath er ing and of wind abra sion. This will pro duce large quan ti ties of silt (Wright, 2007).

CHINA

Two main fac tors may be in voked to ex plain de ser ti fi ca tion in the in te rior of Asia in the Late Mio cene–Plio cene time. Cli - mate mod els sug gest that the up lift of the Ti betan Pla teau may have played an im por tant role in Asian aridification through mod u lat ing the at mo spheric cir cu la tion and its bar rier ef fect to mois ture (Ruddiman and Kutzbach, 1989; Manabe and Broc - coli, 1990; An et al., 2001; Guo et al., 2002; Zhang et al., 2007). An other fac tor was the on go ing global cool ing and the ex pan sion of the Arc tic ice-sheet, which is likely to have had a ma jor im pact on the in ten sity of the win ter Si be rian high pres - sure cell, re sult ing in higher con ti nen tal arid ity in Asia (Ruddiman and Kutzbach, 1989; Zhang et al., 2007).

CENTRAL EUROPE (CARPATHIAN BASIN)

Late Neo gene changes in the palaeo ge ogra phy and palaeotopography of Eu rope are mainly re lated to the Af ri - can–Eur asian col li sion. These changes in clude the up lift of moun tain ranges such as the Alps, Pyr e nees, Carpathians and Cau ca sus, as well as the shrink ing of the Paratethys Sea (Van Dam, 2006). Up lift within Eu rope ex plains fur ther re gional aridification and sharp en ing gra di ents, es pe cially dur ing the Plio cene. But the gen eral con sen sus is that high to pog ra phies were not at tained be fore Plio-Pleis to cene times, im ply ing that up lift might at least be held partly re spon si ble for the on go ing aridification of parts of Cen tral and East ern Eu rope dur ing the Plio cene. The shrink ing of the East ern Paratethys dur ing the Early Plio cene (Dacian) to what are now the Cas pian and Black Sea might ad di tion ally have ex plained aridification in that area (Popov et al., 2006; van Dam, 2006).

The par ti cle-size char ac ter is tics of the Neo gene red clay de - pos its are very sim i lar to those of the Pleis to cene loess de pos its (Fig. 4), sug gest ing an ae olian or i gin for the red clay (Kovács, 2006, 2007). It ap pears from the sedimentological data that the main part of the red clay is of wind-blown or i gins. What was the source of the red clay? Smith et al. (1991) has pro posed lo - cal sources for loess and palaeosols in the Carpathian Ba sin.

The Late Mio cene de pos its within the Carpathian Ba sin are loosely con sol i dated and un der lie the Great Hun gar ian Plain.

The Late Mio cene de pos its con sist of ma rine and shal low lac - us trine con glom er ates, marls, sand stones, clays, and sands which were mainly eroded from the East ern Alps (Mag yar et al., 1999; Kuhlemann et al., 2002). Un der suit ably arid–semiarid con di tions and/or lim ited veg e ta tion cover, these sed i ments would pro vide a source of loose gran u lar ma te rial, which could be en trained by ae olian pro cesses (Kovács, 2003, 2008; Wright, 2007). The cli mate of the Early Plio cene was a tran si tion be tween semi desert and sa van nah (Schweitzer and Szöőr, 1997; Kovács, 2003, 2008). Lab o ra tory ex per i ments have dem on strated the pos si bil ity that ae olian re work ing of the Messinian sands and other sim i lar de pos its could the o ret i cally have con trib uted ma te rial to the red clay, loess and loess-like de pos its of the Carpathian Ba sin (Smith et al., 1991, 2002;

Kovács, 2008). As a re sult, the red clay was trans ported by weak west erly winds and was then mod i fied by post- depositional al ter ation (Fig. 11). This means that silty (loess- like) ma te rial was orig i nally de pos ited and later it was weath - ered to red clay. The palaeoclimate of the Mid dle Plio cene (ca.

3 Ma) was gen er ally warmer than at pres ent, par tic u larly at mid dle to high lat i tudes. The pre cip i ta tion in crease around 3 Ma, which just pre ceded the on set of the Late Plio cene–Pleis - to cene gla cial–inter gla cial al ter na tions, could be a re flec tion of the glob ally rec og nized “Mid-Plio cene warmth” (Van Dam, 2006). The ef fects of trans gres sion ac com pa ny ing the Plio cene op ti mum can ex plain the re turn to wet ter con di tions in East ern Eu rope around 3 Ma. Far ther con ti nent-in ward trans port of At - lan tic mois ture as pos tu lated by Haywood et al. (2000) could also have played a role. Ac cord ing to Haywood et al. (2000), in the Eu ro pean and Med i ter ra nean re gion the cli mate was warmer (by 5°C), wet ter (by 400–1000 mm/yr), and less sea - sonal than at pres ent. The weath er ing val ues sug gest that the Neo gene palaeoclimate in the Carpathian Ba sin was more hu -

Fig. 10. UCC-nor mal ized spiderdiagrams for sam ples from the red clay pro files of China and Hun gary

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mid and hot ter (thus fa vour ing in tense chem i cal weath er ing) com pared to the pres ent cli mate re gime with an av er age an nual tem per a ture of 10°C and pre cip i ta tion of 500–700 mm. In the Plio cene (~3 Ma) the Carpathian Ba sin was sit u ated in a warm and hu mid subtropic-kind zone with an nual tem per a ture and pre cip i ta tion av er ag ing 13–17°C and 800–1000 mm, or more (Jánossy, 1971; Montuire et al., 2006). Sim i lar de pos its (namely “red beds” or “Rote Lehm?” or “rubefied palaeo - sols?”) to the Tengelic Red Clay can be found in the neigh bour - ing area in the Vi enna Ba sin and in Slovakia (e.g., Lukáčovce Mem ber, Kováč et al., 2006) as well as in the north ern fore land of the Carpathians (Grabowski, 2004; Ber, 2005; Lindner et al., 2006). At pres ent the or i gin of such “red” soils need con di tions with av er age sum mer tem per a tures in the in ter val from 21 to 30°C and sea sonal hu mid ity only for a few months (ca. 4 months) in the year (Kováč et al., 2006).

The Neo gene red clay ac cu mu lated un der per sis tent weak winds and a rather steady warm-arid cli mate. The red clay, as well as the loess, thick ens from west to east in the Carpathian Ba sin. There fore, we in fer that the clay-trans port ing wind came from the west, maybe from Cen tral Eu rope, and we in ter pret these winds as driven by the wes ter lies. Mod ern dust ob ser va - tions and sim u la tion ex per i ments have sug gested the coarse grain pop u la tion or silt frac tions in ae olian sed i ments, with an av er age grain-size range of >20 mm, could only be sus pended for short in ter vals at low al ti tudes, even if en trained by strong winds. Thus, the >20 mm par ti cles in red clay should have been trans ported by low-level winds (Guo et al., 2002; Wen et al., 2005). The up per wes ter lies have been ac tive as a plan e tary cir -

cu la tion sys tem in the mid dle lat i tudes of the north ern hemi - sphere and gen er ally trans port the fine pop u la tions (grain-size less than 10 mm) or clay frac tion in long-dis tance sus pen sion, de pos it ing dust in down wind ar eas far from the source re gions.

More de tailed anal y ses of the spa tial vari a tion of grain-size dis - tri bu tion could help re solve the im pli ca tions for depositional en vi ron ment and palaeowind di rec tions.

The red clay was mod i fied by post-depositional weath er ing un der warm-hu mid cli mate. These en vi ron men tal char ac ter is - tics ac com pa ny ing the de po si tion and weath er ing of red clay are re spon si ble par tic u larly for the finer grain-size dis tri bu tions and a lower dustfall rate than for the over ly ing loess. The red clay is an ae olian de posit that has been sub jected to strong pedogenesis dur ing a warm and moist cli mate punc tu ated by small-am pli tude os cil la tions of cold and dry cli mate in ferred from field in ves ti ga tions in Hun gary (col our vari a tions, abun - dance of clay coat ings and car bon ate nod ules) as well as in China (Ding et al., 1999, 2001). Red clay formed dur ing pe ri - ods of warmer and moister cli mate is red der, con tains more clay coat ings and fewer car bon ate nod ules. Ac cord ing to Kováč et al. (2006), the de vel op ment of “rubefied palaeosols”

(or red clays) is a re sult of sea sonal vari a tion in hu mid ity. Its de vel op ment needed chem i cal weath er ing and a warm cli mate with sea sonal hu mid ity changes for some 100 thou sand to some mil lion years. A most strik ing fea ture of the red clay se quences is the ex is tence of many hor i zon tal car bon ate nod ule ho ri zons at both lo ca tions (Hun gar ian, Chi nese). The thick ness of these ho ri zons ranges from 10 to over 100 cm (Ding et al., 1999, 2001; Kovács, 2003, 2008). Most of the nod ules are less than

Fig. 11. Il lus tra tion of the hy poth e sized depositional pro cesses of the red clay in the Carpathian Ba sin (Late Mio cene and Plio cene)

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10 cm in di am e ter. In gen eral, red clays show a red der col our than that of the soils in the over ly ing Pleis to cene loess. The ma - te ri als have been sub jected to rel a tively strong pedogenic pro - cesses, as in di cated by the rel a tive abun dance of clay and Fe-Mn skins (Ding et al., 1999, 2001; Guo et al., 2001, 2004;

Liu et al., 2006). Ob vi ously, these are pedological B ho ri zons.

A re mark able dif fer ence be tween the soil ho ri zons of the red clay and loess se quences is that the pedogenic A ho ri zons are gen er ally lack ing in the red clay se quence, whereas a com plete A–B–C se quence is readily rec og nized in some of the palaeosols in the Pleis to cene loess de pos its (Ding et al., 1999).

Be sides, the up per and lower bound aries of the B ho ri zons in the red clay se quence are in dis tinct. In a pedological sense, the en tire red clay se quence may be re garded as an ex tremely thick soil com plex (Ding et al., 1999). No lami na tions are seen in the en tire red clay se quence. There fore, the char ac ter is tics of the

red clay men tioned above may be best ex plained by accretionary pro cesses as so ci ated with the ac cu mu la tion of wind-blown dust.

We con clude that the red clay in the Carpathian Ba sin is of wind-blown or i gin, and that it was subsequently af fected by weath er ing pro cesses in the Plio cene–Early Pleis to cene.

Ac knowl edge ments. Thanks are ex tended to Prof. Z. T.

Guo (In sti tute of Ge ol ogy and Geo phys ics, Chi nese Acad emy of Sci ences) for help ful dis cus sions and the pro vi sion data on the Chi nese red clay, to Drs. S. Á. Fábián and G. Varga (De - part ment of Phys i cal Ge og ra phy, Uni ver sity of Pécs) for field as sis tance. Two anon y mous re view ers are thanked for their con struc tive com ments and sug ges tions. The au thors are also grate ful to F. Csirkés (Uni ver sity of Chi cago) for lan guage im - prove ment.

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T a b l e 4 Trace el e ment com po si tion of red clay sam ples from Hun gary and China [ppm]

Sam ples Hun-1 Hun-2 Hun-3 Hun-4 Hun-5 Xif-1 Xif-2 Xif-3 Xif-4 Xif-5

Sc 17.0 11.0 15.0 16.0 12.0 13.0 10.0 12.0 13.0 10.0

Cr 170.0 130.0 160.0 140.0 150.0 46.0 42.0 54.0 42.0 46.0

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Zn 108.0 79.0 84.0 88.0 77.0 64.0 68.0 105.0 65.0 75.0

Ga 19.0 16.0 19.0 21.0 13.0 17.0 13.0 17.0 17.0 14.0

Rb 120.0 130.0 110.0 110.0 120.0 85.0 78.0 84.0 74.0 76.0

Sr 90.0 103.0 68.0 94.0 110.0 196.0 194.0 171.0 206.0 206.0

Y 39.0 25.0 32.0 42.0 42.0 16.0 16.0 17.0 14.0 14.0

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Ta 1.0 1.0 1.0 1.0 1.0 0.7 0.7 0.8 0.5 0.7

Pb 30.0 39.0 31.0 26.0 40.0 19.0 23.0 21.0 19.0 20.0

Th 17.0 15.0 18.0 15.0 15.0 11.0 11.0 12.0 10.0 11.0

Xif-1 to Xif-5 — red clay sam ples from China (data from Guo et al., 2001, 2004); for other ex pla na tions see Ta ble 2

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