6 500 ka BP A CTA GEO GRA PH ICA S IN ICA. M ay, Fe2O 3 CaCO 3. E2m ail: L snnu1edu1cn

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1 A CTA GEO GRA PH ICA S IN ICA V o l156, N o13 M ay, 2001 : (2001) ka BP (, ) :, 5 CaCO 3 Fe2O 3, 5 B ts2c s2c l2 Bk2C B ts2cf2c s2c l2bk2c Fe2O 3, Fe2O 3CaCO ka BP,,, : ; ; ; ; : P467; : A, 30 [1, 2 ], 500 ka BP [35 ] 5 (S5), , S5 [6 ], [7 ],,, S5 15, : ; : : ( IGCP379), ( SNU 27) ( ) [Foundation Item: International Geo logical Co rrelation P rogram, N o1igcp 379, key p ro ject of Shaanxi N o rm al U niversity, N o1 SNU 27 and the key p ro ject of M inistry of L and and Resources, N o ] : (19532),,,,,, 60 E2m ail: L hy@ snnu1edu1cn

2 , S5, 34 (1a, 2a) 1 (B ts), 3, 115 m 2 (C s), 0125m 3 (C l), 0135 m 4 CaCO 3 (Bk), 012 m 5 (C)3,, CaCO 3, 11 ; 21 ; 31 ; 41 ; 51 ; 61CaCO 3 ; 71 ; 15 (% ) F ig11t he w eathered sections of 5th paleo so l in loess and the content change of chem ical compo sition (% ), 3 : CaCO 3, ; ; Fe2O 3 (1a, 2a) 3 CaCO 3, Fe2O 3,, B ts (B t) C sc lbkc, C s C sc lbk C,

3 3 : 500 ka BP 325 B ts1 5 ; Cf1 ; C s1 ; C l1 ; Bk1 CaCO 3 ; C1 ; 25 F ig12t he w eathered sections of 5th paleo so l in Changw u and X i an 1125 [8 ],,, S5 3 (1b, 2b), (B ts), 415 m 2 (Cf), 12 mm, 015 m 3 (C s), 112 m 4 (C l), 016 m 5 CaCO 3 (Bk), 012 m 6 (C), 3 (Cf) CfC s C s S5, S5 3, (Cf) Fe2O 3,,,, (Cf), S5 B tscfc sc lbkc, S5 B ts,

4 , S5 15cm, 65 CaCO 3, 62 Fe2O 3A l2o 3 (1, 1) 1 5 Tab11The chem ical composition and magnetic susceptibility in weathered section of 5th paleosol Fe2O 3g% A l2o 3g% g10 26 S I CaCO 3, S5 CaCO 3, 1%212%, 015% ; CaCO 3, 015% ; CaCO 3, 40% ; CaCO 3 8%16% (1) CaCO 3, S5 CaCO 3, CaCO 3 S5 31 (1, 1a), Fe2O 3A l2o %5178% 12164%14112%, 2, 3 3,,,, Fe2O 3 A l2o 3 (1),, Fe2O 3 A l2o 3 Fe2O 3 A l2o 3,, S5 Fe2O 3 A l2o 3, Fe2O 3 [9 ] [8, 10 ], S5 Fe2O 3 A l2o 3,,

5 3 : 500 ka BP 327 (1a, 2a),, Fe2O 3, Fe2O Fe2O 3 ( 2) F ig13t he content difference of Fe2O 3 among layers in w eathered section of 5th paleo so l a1 ; 31, b1 ; Fe2O 3 A l2o %6174% 13162%15181% ; 2 (1b)Fe2O 3 6%, 6%, 1%116% A l2o 3 14%, 15%, 2% Fe2O 3 A l2o 3, Fe2O 3 (1, 3b),, CaCO 3, Fe2O 3A l2o 3,, S5 (1),, CaCO 3, S5 CaCO 3, Fe2O 3 A l2o 3 S5 500 ka BP S5, S5 1 Fe2O 3 A l2o % 21145%, 2 [11 ], S5 62 (4), S53218%4118% ; S5 3814%4913%,,, (C) ; S5, CaCO 3,,

6 (< mm ) ( 2) a1 ; b1 F ig14t he content change of clay grains (< mm ) among layers in w eathered section of 5th paleo so l 3 5 S5, S5 2 X2,,, (2), [11 ] S5 8%9%, 25 (% ) Tab12M ineral composition of clay f ilm in 5th paleosol at L iuj iapo section in X i an S5B S5B S5, S5 3, ,, (A rtem isia)(compo sitae)(chenopodiaceae), (Q uercu s)(a lnu s)(ju lan s) (Co rylu s), (L iqu idam bar) (Castanopo sis) (Castanea) (P istacia) (Gleichen ia),,,

7 3 : 500 ka BP ka B P S5,, [12, 13 ] S5,,,,, S5, S5 500 ka BP,,,,, 3 CaCO 3 Fe2O 3, 500 ka BP mm, mm,,,,, 3 Tab13Climatic indexes under so il bottom and mean annual ra infall S 1 5 S5 2 S5 3 S5 3 (m ) CaCO 3 (m ) a Fe2O 3 (m ) b (mm ) : a CaCO 3, b, 650 mm 600 mm,, 850 mm, 500 ka BP 850 mm, 500 ka BP mm, S5,,

8 ,, 100 ka BP 1 [8 ] S5 100 ka BP,,,,! (References) : [ 1 ]Zhao J ingbo1 T he cycles and periods of the Q uaternary clim ate change[j ]1 J ou rnal of G laciology and Geocry ology, 1988, 10 (2): ( In Ch inese) [1 [J ]1, 1988, 10 (2): ] [2 ]D ing Zhongli, L iu Dongsheng, L iu X ium ing, et al137 cycles since 215M a BP [J ]1 Ch inese S cience B u lletin, 1989, 34 (19): ( In Ch inese) [,,. 250 ka BP 37 [J ]., 1989, 34 (19): ] [3 ]L iu Dongsheng1 L oess and Environm ent[m ]1 Beijing: Science P ress, 1985, ( In Ch inese) [. [M ]. :, 1985, ] [4 ]Kuk la G, H eller F, L iu X M, et al1p leistocene clim ates in Ch ina dated by m agnetic suscep tibility [J ]1 Geology, 1988, 16: [5 ]D ing Z1L, Yu ZW, R utter N, et al1tow ards an o rbital tim e scale fo r Ch inese loess depo sits[j ]1Q uaternary S cience R ev iew, 1994, 13: [6 ]A n Zh isheng, W eil angying, L u Yanchou1 A p rim ary study on so il stratigraphy in L uochuan loess section[j ]1 Q uaternary S ciences, 1985, 6 (1): ( In Ch inese) [,, 1 [J ]1, 1985, 6 (1): ] [ 7 ]T ang Keli1 A discussion about the m icro structure of buried paeo so ls in loess depo sit and its o rigin in W ugong [J ]1 Ch inese S cience B u lletin, 1981, 26 (3): ( In Ch inese) [. [J ]1, 1981, 26 (3): ] [8 ]Zhao J ingbo1 Illuvial dep th of CaCO 3 of the paleo so ls in the loess of Guanzhong P lain[j ]1 Ch inese S cience B u lletin, 1992, 37 (5): [ 9 ]Chen Jun, J i Junfeng, Q iu Gang et al1 Geochem ical study on w eathering degree of loess in L uochuan of Shaanxi[J ]1 S cience in Ch ina, series D, 1997, 27 (6): ( In Ch inese) [,, 1 [J ].,D, 1997, 27 (6): ] [10 ]Zhao J ingbo1 N ew geo logical theo ry about w eathering and eluvial zone2illuvial theo ry on dep th of CaCO 3[J ]1 A cta S ed im entolog ical S inica, 35 ] 2000, 18 (1): ( In Ch inese) [. CaCO 3 [J ]., 2000, 18 (1): 292 [11 ]N anjing Institute of So ils, CA S1 So ils in Ch ina (M ) 1Beijing: Science P ress, ( In Ch inese) [ 1 [M ]1 :, 1980, ] [12 ]Fedo roff N, Go ldberg P1 Comparative m icromo rpho logy of two L ate P leistocene paleo so ls in the Paris Basin [J ]1 Catena, 1982, 9: [ 13 ]Guo Zhengtang, Fedo roff N 1 P rim ary study on saline2alkali paleo so l and its clim atic significance in loess in X ifeng and X i an [J ] 1Q uaternary S ciences, 1992, [J ]1, 1992, (2): ] (2): ( In Ch inese) [, Fedo roff N 1

9 3 : 500 ka BP 331 The Paleosol and the M igration of Climatic Zone about 500 ka BP in L oess Plateau, Shaanx i Prov ince ZHAO J ing2bo (D ep artm ent of Geog rap hy, S haanx i N orm al U niversity, X i an710062, Ch ina) Abstract: It is discovered th rough field investigation s that the illuvium of CaCO 3 in the 5th layer of paleo so l in Changw u and X i an does no t get in touch w ith the bo ttom of clay grou ting layer bu t lies in loess w h ich is m deep under the bo ttom of clay grou ting layer, and the red ferruginou s clay film also m igrated to the mo ther loess1 It is indicated that CaCO 3 and Fe2O 3 m igrated ou t of the paleo so l, the paleo so l has the character of acid elevation and at least the w eathering had already been in the m iddle of the chem ical w eath2 ering p rocess at that tim e1 T he w eathered loess layer (C s) w ith ferruginou s film and w eathered loess layer (C l) w ithou t ferruginou s film w ere discovered under the bo ttom of the 5th layer of paleo so l in Changw u and X i an, and the ligh t red2b row n w eathered loess layer (Cf) w ith ferruginou s concretion w as discovered under the bo ttom of 5th paleo so l in X i an1 Generally, the con2 ten t of CaCO 3 is less than 015% in w eathered loess layers, and the con ten t of clay grain s, Fe2O 3 and A l2o 3 is h igher in w eathered loess layers than in the unw eathered loess layer, w h ich indicates that each of the w eathered loess layer had experienced chem ical w eathering to a certain ex ten t1 T he m aterial show s that the 5th layer of paleo so l in Changw u and X i an has the character of sub trop ical so il and its p rofile con struction is B ts2c s2c l2bk2c in Changw u and is B ts2cf2c s2bk2c in X i an1 T he con ten t of sm alite takes 8% 29% in the clay film of the 5th layer of paleo so l in X i an, the spo ro2po llen of som e sub trop ical L iq2 u idam bar and Castanopo sis appear in the paleo so l in Changw u, w h ich po in ts ou t that the 5th paleo so l developed in sub trop ical clim ate1 Six indexes, rem oved dep th of Fe2O 3 and CaCO 3, deep w ea thered loess layers and spo ro2po llen and so on, indicate that the sub trop ical clim ate m igrated to the m iddle area of L oess P lateau at abou t 500 ka BP, m ean annual p recip itation w as mm in Chang2 w u area and w as abou t mm in X i an area1 A cco rding to the obviou s increase of the p recip itation at abou t 500 ka BP and 100 ka BP ascertained by the au tho r, after elim inating the effect of the new tectogenesis, it can be draw n that in in terglacials w h ich w as obviou s2 ly w arm er than today, Q in ling M oun tain s w as no t the dem arcation line betw een the Sou th and N o rth Ch ina and the eco logical environm en t of the L oess P lateau w as getting m uch better at the tim e1 Key words: L oess P lateau; character of paleo so l; m igration of chem ical compo sition; deep w eathered layers; m igration of clim atic zone