6 : S 7 L ( d 1 /2, T 1 /2 ) m [ 45 ], 715cm - T 1 /2 1, 1, -, B lake [ ], Laschamp [ ], Santa Rosa [ 40, 42 ], Punaruu [ 4

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1 QUATERNARY SC IENCES Vol. 27, No. 6 November, (2007) S 7 L 8 3 M. Toshiaki H. M asayuki (, ; Research Center for Inland Seas, Kobe University, Kobe , Japan;, ;, ) S 7 L 8,,, - (M 2B), S 7 L , S 7 L 8 5 8cm P318, S15 A 1 -, [ 1 7 ], - [ 7 10 ], [ 11 ], - (M 2B) M 2B 19 (M IS 19), -, [ L ] 8, S 8 [ ] L 8 M IS 20 [ ], M 2B [ ] [ 17 ] 6 L 8 S 8, M 2B [ 1, 9, ], -, Spassov [ 30 ] - : ( PDRM ),, (CRM ), - ( lock2in) (, [ ] ), - M2B,, M 2B, - [ ] m [ 35, 36 ], : 36 E2mail: yangtsh@ itpcas1ac1cn 3 ( : ) ( : KZCX3 - SW - 143) ,

2 6 : S 7 L ( d 1 /2, T 1 /2 ) m [ 45 ], 715cm - T 1 /2 1, 1, -, B lake [ ], Laschamp [ ], Santa Rosa [ 40, 42 ], Punaruu [ 40, 43 ], R union [ 14, 15, 44 ], 2000 Mono Lake [ 45, 46 ] [ ] [ 37, 39, 47, 48 ],, W ang [ 49 ] S 8 19 (M IS 19), S 7 18 (M IS 18), - M 2B M 2B, M 2B, -, -, - L 7 S 8 -,, S 7 L 8 2 ( 3414 N, E) 9km, 160m, 37 -, 30m L 7 S 8 40cm, 3 20cm, 2cm 2cm 2cm, 215cm MMTD600 ASC2TD48, ; 2G , 95%, 200 ( 1a 1c),, S 7 L 8 ( 1 d 1f) 300 ( 1g 1h), ( ), ( ) 312, 2 4 ( IRM ), IRM IRM 200mT, 200mT IRM ( SIRM ) 90%, ; 217T, 2 4, ( 3) IRM, 3 580,, [ ],,, ( 1) 4

3 Fig. 1 O rthogonal vector p rojections of the rep resentative specimens. Solid and open symbols rep resent the p rojections onto the horizontal and vertical p lanes, respectively, M 2B 3. 3 (AM S ) AMS [ 53 ], Zhu [ 54 ], KLY - 3 (AMS) AMS ( K 1 2Inc) 20 ( 5g),, S 7 L 8 5 K 1 2Inc (VGP) 45, S 7 L 8, m m Zhu [ 38 ] 5 : 1)

4 6 : S 7 L ( a), ( b), ( c) ( d)m2b Fig. 2 Acquisition curves of isothermal remanent magnetization ( IRM ). Specimens in graphs ( a), ( b), ( c), and ( d) are from intervals of the normal polarity, reversed polarity, geomagnetic excursion, and M 2B transition, respectively 3 016T ( a), ( b), ( c) ( d) M2B Fig. 3 Thermomagnetic curves obtained in air and in a magnetic field of 016T. Specimens in graphs( a), ( b), ( c), and ( d) are from intervals of the normal polarity, reversed polarity, geomagnetic excursion, and M 2B transition, respectively

5 (7162cm /ka) L 7, 751ka 759ka, M 2B 775ka 785ka ( 5h) 755ka, 8ka, M 2B 10ka S 7 L 8 4 Fig. 4 Suscep tibility changes during p rogressive thermal demagnetization ; 2) ; 3) AMS, K 1 ; 4) ; 5) S 7 ( m ) L 8 ( m),, S 7, L 8 M 2B 4 M 2B - [ 26, 27, 29 ] S 7 S 8 19 [ 49, 56 ], L 7 S 8 M 2B Yang [ 42 ] M 2B L 8 /S 8 111m, Jaram illo L 8 /S m, M 2B L 8 /S 8 019m ( 5) 210ka [ 57 ] 16m -,, 1600cm /210ka = 7162cm /ka -, [ 58 ] 5b S 7 L 8, L 8, m 3 /kg, L 9 [ 42 ], L iu [ 59 ] Spassov [ 60 ] L iu [ 61 ],,, ( 1) ( 3) S 7 L 8,, PDRM ( 1a 1f), M 2B, ( 1g h) M 2B,,, 50cm /ka [ 62 ] ( ) (10 50mT) [ 63 ] M 2B,, ( pyrrhotite) ( greigite), Hyodo PDRM,

6 6 : S 7 L ( a) ( b) ( c) ( d) ( e) ( f) ( g) ( h), 1; 0 215m, Yang [ 55 ] Fig. 5 Stratigraphic p lots of lithology( a), mass2specific low2field magnetic suscep tibility( b), declination ( c), inclination ( d), virtual geomagnetic pole (VGP) latitude ( e), relative geomagnetic intensity( f), maximum inclination of the anisotropy of low2field magnetic suscep tibility( g), and magnetostratigraphy( h). For specimenswith open circles, thermal demagnetization diagram s are shown in Figure 1. The data in the dep th of 0 215m were already reported by Yang et al. [ 55 ] [ 63 ], - PDRM, S 7 L M 2B 6 -, S 7 ( 5 6), VGP 6 45, 5,, VGP 7214,, 755ka, Hyodo [ 63 ] 38916m, SPECMAP 18 O,

7 , 1 Fig. 6 Inclination comparison between Baoji loess2paleosol and O saka Bay marine sediments 759ka,, S 7 ( 6) M 2B,, [ 17, 30, 64 ] :, M 2B 30 60cm, 5 9 [ 16, 17 ] 0, M 2B 7 (N1 N7) 7 (R1 R7) 14 ( 6), N1 1ka, 6 7 1ka, M 2B 5 (N2 N6) R5 R ka,,, M2B (, ) Spassov [ 30 ] M 2B 7, - -, Spassov [ 30 ] -, PDRM, M 2B ( ) L 8, -, [ 63 ], M 2B 4 4 ( 6), c d R6 R7, a N1 N1 N2, 5 (N2 N6), ( 6), 3, Hyodo [ 63 ] 8 VGP,

8 6 : S 7 L M 2B, M 2B ( 5 6) ( 1) S 7 L ( / 7162cm /ka), [ 63 ] [ 31 ],,, S 7 L 8 500, 7162cm /ka, S 7 L 8 8cm ChRM, :, ;,,,,,, ;, ( ) 215cm, S 7 L 8 5cm ( 5cm) (JSPS),! (R efe rence s) 1 Heller F, Evans M E. Loess magnetism. R eviews of Geophysics, 1995, 33: EvansM E, Heller F. Magnetism of loess/paleosol sequences: Recent developments. Earth2Science Review s, 2001, 54: ,,.., 2007, 27 (2) : Deng Chenglong, L iu Q ingsong, Pan Yongxin et al. Environmental magnetism of Chinese loess2paleosol sequences. Q uaternary Sciences, 2007, 27 (2) : ,,.., 1995, (2) : Zhu Rixiang, Yue Leping, Bai L ixin. Progress of Quaternary paleomagnetism in China. Q ua terna ry Sciences, 1995, (2) : ,,.., 1997, (3) : Han Jiamao, Jiang W enying, Chu Jun. Grain size distribution of magnetic m inerals in loess and paleosol. Q uaternary Sciences, 1997, (3) : ,. -., 2005, 25 (4) : Huang Xiaogang, Sun Jimin. Study of the magnetic fabrics in Chinese loess2paleosols since the last interglacial: Implication of the paleowind direction. Quaternary Sciences, 2005, 25 (4) : :, L iu Tungsheng et al. Loess and the Environment. Beijing: Science Press, Heller F, L iu T S. Magnetism of Chinese loess deposits. Geophysical Journal of the R oyal Astronom ical Society, 1984, 77: Kukla G, Heller F, L iu X M et al. Pleistocene climates in China dated by magnetic suscep tibility. Geology, 1988, 16: ,,. -., 2006, 26 (5) : An Zhisheng, Zhang Peizhen, W ang Eechie et al. Changes of the monsoon2arid environment in China and growth of the Tibetan Plateau since the M iocene. Q uaternary Sciences, 2006, 26 ( 5 ) : Tauxe L, Herbert T, Shackleton N J et al. Astronomical calibration of the Matuyama2Brunhes boundary: Consequences for magnetic remanence acquisition in marine carbonates and the Asian loess sequences. Earth and Planetary Science Letters, 1996, 140: ,.., 1984, (2) : L iu Tungsheng, An Zhisheng. A prelim inary magnetostratigraphic study of the Baihanzhai loess section. Geochim ica, 1984, ( 2 ) : , 1995, 38 (3) : Yue Leping. Palaeomagnetic polarity boundary were recorded in Chinese loess and red clay, and geological significance. Acta Geophysica S inica, 1995, 38 (3) : Zheng H B, An Z S, Shaw J. New contributions to Chinese Plio2 Pleistocene magnetostratigraphy. Physics of the Earth and Planetary Interiors, 1992, 70 (3 4) : L iu X M, L iu T S, Xu T C et al. The Chinese loess in Xifeng, I. The p relimary study on magnetostratigraphy of a loess profile in Xifeng area, Gansu Province. Geophysical Journal International, 1988, 92: Zhu R X, Laj C, Mazaud A. The Matuyama2B runhes and Upper Jaram illo transitions recorded in a loess section at W einan, North2 central China. Earth and Planetary Science Letters, 1994, 125: ,,. : -., 1998, 43 (11) : Zhu R ixiang, Pan Yongxin, Guo B in et al. A recording phase lag between ocean and continent climate changes: Constrained by the Matuyama /B runhes polarity boundary. Chinese Science B ulletin, 1998, 43 (19) :

9 Rutter N, D ing Z L, Evans M E et al. Magnetostratigraphy of the Baoji loess2paleosol section in the north2central China Loess Plateau. Q uaternary International, 1990, 7 /8: Sun D H, Shaw J, An Z S et al. Magnetostratigraphy and paleoclimatic interpretation of a continuous 712Ma Late Cenozoic eolian sediments from the Chinese Loess Plateau. Geophysical Research Letters, 1998, 25 (1) : D ing Z L, Sun J M, Yang S L et al. Prelim inary magneto2 stratigraphy of a thick eolian red clay2loess sequence at L ingtai, the Chinese Loess Plateau. Geophysical Research Letters, 1998, 25 (8) : D ing Z L, Rutter N, L iu T S. Pedostratigraphy of Chinese loess deposits and climatic cycles in the last 215 Myr. Catena, 1993, 20 (1 2) : Heller F, L iu T S. Magnetostratigraphical dating of loess deposits in China. N ature, 1982, 300: ,,.., 1999, 19 (1) : Jiang Fuchu, Wu Xihao, Xiao Huaguo et al. Mangshan loess in China central plains and the coupling effect between tectonics and climate. M arine Geology & Quaternary Geology, 1999, 19 (1) : ,, Lgvlie R. L 9., 2005, 25 (4) : W ang Xisheng, Yang Zhenyu, Lgvlie R et al. Remagnetization of L 9 in the Sanmenxia area and p relim inary analysis of remagnetization mechanism s. Q uaternary Sciences, 2005, 25 (4) : Forster Th, Heller F. Loess deposits from the Tajik dep ression (Central A sia) : Magnetic properties and paleoclimate. Planetary Science Letters, 1994, 128 (3 4) : Earth and 26 D ing Z L, Derbyshire E, Yang S L et al. Stacked 2162Ma grain size record from the Chinese loess based on five sections and correlation with the deep2sea 18 O record. Paleoceanography, 2002, 17 ( 3 ) : doi: /2001PA Sun Y B, Clemens S C, An Z S et al. A stronom ical timescale and palaeoclimatic imp lication of stacked 3162Myr monsoon records from the Chinese Loess Plateau. Quaternary Science Reviews, 2006, 25: Zhou L P, Shackleton N J. 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W hy are geomagnetic excursions not always recorded in sediments? Constraints from post2depositional remanent magnetization lock2in modeling. Earth and P lanetary Science Letters, 2004, 227 (3 4) : Zhu R X, Zhou L P, Laj C et al. The B lake geomagnetic polarity ep isode recorded in Chinese loess. Geophysical Research Letters, 1994, 21: Zheng H B, Rolph T, Shaw J et al. A detailed palaeomagnetic record for the last interglacial period. Earth and Planetary Science Letters, 1995, 133 (3 4) : Fang X M, L i J J, van der Voo R et al. A record of the B lake event during the last interglacial paleosol in the western Loess Plateau of China. Earth and Planetary Science Letters, 1997, 146 ( 1 2 ) : ,,. Cobb Mountain. (D ), 1998, 28 (4) : Guo B in, Zhu R ixiang, Yue Leping et al. Cobb Mountain event recorded in Chinese loess. Science in China ( Series D ), 1998, 28 (4) : Zhu R X, Pan Y X, L iu Q S. Geomagnetic excursions recorded in Chinese loess in the last 70, 000 years. Geophysical Research Letters, 1999, 26 (4) : ,,.. ( D ), 2000, 30 ( 3 ) : Zhu R ixiang, Guo B in, Pan Yongxin et al. Reliability of geomag2 netic secular variations recorded in a loess section at L ingtai, North2 central China. Science in China ( Series D), 2000, 43 (1) : Pan Y X, Zhu R X, L iu Q S et al. Geomagnetic ep isodes of the last 112 Myr recorded in Chinese loess. Geophysical Research Letters, 2002, 29 (8) : doi: /2001GL Guo B, Zhu R X, Florindo F et al. A short, reverse polarity interval within the Jaram illo subchron: Evidence from the Jingbian section, Northern Chinese Loess Plateau. Journal of Geophysical Research, 2002, 107 (B6) : 2124, doi: /2001JB Yang T S, Hyodo M, Yang Z Y et al. Evidence for the Kam ikatsura and Santa Rosa excursions recorded in eolian deposits from the southern Chinese Loess Plateau. Journal of Geophysical Research, 2004, 109: B12105, doi: /2004JB Yang T S, Hyodo M, Yang Z Y et al. A first paleomagnetic and rock magnetic investigation of calcareous nodules from the Chinese Loess Plateau. Earth Planetary and Space, 2005, 57 (1) : Yang T S, Hyodo M, Yang Z Y et al. Early and m iddle Matuyama geomagnetic excursions recorded in the Chinese loess2paleosol sediments. Earth P lanetary and Space, 2007, 59: Lund S P, L iddicoat J C, Lajoie K R et al. Paleomagnetic evidence for long2term (10 4 year) memory and periodic behavior in the earthπs core dynamo p rocess. Geophysical Research Letters, 1988, 15: Coe R S, L iddicoat J C. Overp rinting of naturalmagnetic remanence in lake sediments by a subsequent high2intensity field. N ature, 1994, 367: Heslop D, Shaw J, B loemendal J et al. Sub2m illennial scale variations in East A sian monsoon system s recorded by dust deposits from the North2W estern Chinese Loess Plateau. Physics and Chem istry of the Earth (A), 1999, 24: L iu Q S, Banerjee S K, Jackson M J et al. Inter2p rofile correlation of the Chinese loess/paleosol sequences during Marine Oxygen

10 6 : S 7 L Isotope Stage 5 and indications of pedogenesis. Q uaternary Science Reviews, 2005, 24: W ang X S, Yang Z Y, Lgvlie R et al. A magnetostratigraphic reassessment of correlation between Chinese loess and marine oxygen isotope records over the last 111Ma. Physics of the Earth and Planetary Interiors, 2006, 159: ,, Laj C. Upper Jaram illo., 1995, 38 (1) : Zhu R ixiang, W u Hanning, Laj C et al. Upper Jaramillo sub2 polarity transition obtained from a loess section at W einan, North2 central China. Acta Geophysica S inica, 1995, 38 (1) : L iu X M, Hesse P, Rolph T. O rigin of maghaem ite in Chinese loess deposits: Aeolian or pedogenic? Physics of the Earth and Planetary Interiors, 1999, 112: EvansM E, Heller F. Magnetic enhancement and palaeoclimate: A study of a loess/paleosol coup let across the Loess Plateau of China. Geophysical Journal International, 1994, 117: Zhu R X, L iu Q S, Pan Y X et al. Identifying the origin of the magnetic directional anomalies recorded in the Datong loess p rofile, Northeastern Chinese Loess Plateau. Geophysical Journal International, 2006, 164: Zhu R X, L iu Q S, JacksonM J. Paleoenvironmental significance of the magnetic fabrics in Chinese loess2paleosols since the last interglacial( < 130ka). Earth and Planetary Science Letters, 2004, 221 (1 4) : Yang T S, Hyodo M, Yang Z Y et al. Two geomagnetic excursions during the B runhes chron recorded in Chinese loess2palaeosol sediments. Geophysical Journal International, 2007, 171: L iu Q S, Roberts A P, Rohling E J et al. W here is the Matuyama2 B runhes geomagnetic reversal boundary in marine sediments and Chinese loess/paleosol sequences? Geophysical Research Abstracts, 2006, 8: Cande S C, Kent D V. Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic. Journal of Geophysical R esearch, 1995, 100 (B4) : L iu Q S, Deng C L, Torrent J et al. Review of recent developments in m ineral magnetism of the Chinese loess. Q uaternary Science Review s, 2007, 26: L iu Q S, Banerjee S K, Jackson M J et al. Grain sizes of susceptibility and anhysteretic remanent magnetization carriers in Chinese loess/paleosol sequences. Journal of Geophysical Research, 2004, 109: B03101, doi: /2003JB Spassov S, Heller F, Kretzschmar R et al. Detrital and pedogenic magnetic m ineral phases in the loess/palaeosol sequence at L ingtai ( Central Chinese Loess Plateau ). Physics of the Earth and Planetary Interiors, 2003, 140: L iu Q S, Banerjee S K, Jackson M J et al. An integrated study of the grain2size2dependent magnetic m ineralogy of the Chinese loess/ paleosol and its environmental significance. Journal of Geophysical Research, 2003, 108: 2437, doi: /2002JB B iswas D K, Hyodo M, Taniguchi Y et al. Magnetostratigraphy of Plio2Pleistocene sediments in a 17002m core from O saka Bay, Southwestern Japan and short geomagnetic events in the m iddle Matuyama and early B runhes Chrons. Palaeogeography, Palaeo2 clim atology, Palaeoecology, 1999, 148: Hyodo M, B iswas D K, Noda T et al. M illennial to subm illennial2 scale features of the Matuyama2B runhes geomagnetic polarity transition from O saka Bay, Southwestern Japan. Journal of Geo2 physical Research, 2006, 111: B02103, doi: /2004JB Sun D H, Shaw J, An Z S et al. Matuyama /B runhes ( M /B ) transition recorded in Chinese loess. Journal of Geom agnetism Geoelectricity, 1993, 45: INVEST IGAT IO N O N THE LOCK2I N D EPTH O F PAL EO SOL L 7 AND LO ESS L 8 I N BAO J I Yang Tianshui L i Huidi Fu J ianli M. Toshiaki Yang Zhenyu H. Masayuki ( Institute of Tibetan Plateau Research, Chinese Academ y of Sciences, B eijing ; R esearch Center for Inland Seas, Kobe U niversity, Kobe , Japan; Institute of Geom echanics, Chinese Academ y of Geological Sciences, B eijing ; D epartm ent of Earth Sciences, N anjing U niversity, N anjing ) Abstract Detailed paleomagnetic and rock2magnetic investigations have been carried out in paleosol S 7 and loess L 8 from the B aoji section, southern Loess Plateau. M ass2specific low2filed suscep tibility revealed that the degree of pedogenesis of these two units is rather weak. Acquisition of isotherm al remanent magnetization ( IRM ), thermal demagnetization of three2axis IRM, and thermomagnetic analyses showed that detrital magnetite and hem atite are dom inant magnetic carriers in the studied loess2paleosol sedim ent. M easuring results of magnetic suscep tibilities after each p rogressive therm al demagnetization step disp layed no significant change. Progressive thermal demagnetization results showed that a few specimens from the geomagnetic excursion and the M atuyama2b runhes transition have two clearly high temperature components(htc) above 250, while those from the fully normal and reverse polarity intervals have only a single HTC. H igh2resolution m agnetostratigraphy indicated a geomagnetic excursion, which is mainly characterized by short2lived departures in declination, in the paleosol S 7, and the

11 Matuyama2B runhes(m 2B) transition, which is characterized by 14 short2lived reversal ep isodes, in the loess L 8. M ultip le rock2m agnetic experiments demonstrated that the specimens from the excursion and M 2B transition intervals have uniform magnetic p roperties as those from the B runhes normal or M atuyama reversed polarity intervals. By extrapolating a mean accumulation rate of the late Matuyama chron, the geomagnetic excursion in the paleosol S 7 is estimated to occur from 759ka to 751ka, and the M 2B transition in loess L 8 is dated to occur from 785ka to 775ka. Comparison with a high2resolution paleomagnetic record from the O saka core sediment revealed that the paleosol S 7 and loess L 8 have potential to record the short2lived reversal ep isodes lasting for years, which, combined with many reversal ep isodes occurring during them2b transition, imp lies that their lock2in dep th is less than 5 8cm. Key words paleosol, loess, geomagnetic polarity transition, geomagnetic excursion, lock2in

QUATERNARY SC IENCES Vol. 27, No. 2 March, (2007) (, ; National Oceanography Centre, University of Sout

27 2 2007 3 QUATERNARY SC IENCES Vol. 27, No. 2 March, 2007 1001-7410 (2007) 02-193 - 17 3 (, 100029; National Oceanography Centre, University of Southamp ton, Southamp ton SO14 3ZH UK) - -,, P318. 41,