Mineral magnetic investigation of the Talede loess–palaeosol sequence since the last interglacial in the Yili Basin in the Asian interior

Geophysical Journal InternationalGeophys. J. Int. (2012) 190, 267–277 doi: 10.1111/j.1365-246X.2012.05527.x

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Mineral magnetic investigation of the Talede loess–palaeosolsequence since the last interglacial in the Yili Basin in the Asianinterior

Yong Liu,1,2 Zhengtao Shi,1 Chenglong Deng,3 Huai Su1 and Wenxiang Zhang1

1College of Tourism and Geographical Sciences, Yunnan Normal University, Kunming, China. E-mail: [email protected] of Geography, Beijing Normal University, Beijing, China3State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

Accepted 2012 April 19. Received 2012 April 19; in original form 2010 November 22

S U M M A R YThe loess–palaeosol deposit in the Asian interior is sensitive to the evolution of the Westerlies,thus providing a good opportunity to investigate regional palaeoenvironmental evolution andits relationship with global climatic changes. Multiparameter mineral magnetic investigationshave been conducted on the Talede section in the Yili Basin, Asian interior. Our study finds that:(1) loess samples have higher concentration magnetic minerals than palaeosols, though themagnetic mineral composition is similar (ferrimagnetic magnetite, antiferromagnetic hematiteand lepidocrocite). (2) Large pseudo-single domain (PSD) and multidomain (MD)-like grainsdominate both in loess and palaeosols. However, magnetic mineral grains in loess are muchcoarser than those in the palaeosols. (3) Palaeosols contain approx 30 per cent more amountof hematite than the loess samples. The frequency-dependent susceptibility of both loess andpalaeosols is very low, indicating the small amount of super-paramagnetic grains. And thehigher χ fd per cent values of palaeosols also reveal that palaeosols have more amounts ofultrafine magnetic grains than loess. The magnetic variations in part (1) and (2) can be wellexplained by the wind vigour model, but the observed enrichment of hematite and ultrafinemagnetic grains in palaeosols also reveals the first onset of pedogenic enhancement. Therefore,the Talede section could be seen as an end-member of the classic Chinese Loess Plateau (CLP)magnetic enhancement model.

Key words: Environmental magnetism; Rock and mineral magnetism; Asia.

1 I N T RO D U C T I O N

The loess-palaeosol deposits of the Chinese Loess Plateau (CLP)could record the most complete terrestrial palaeoclimate variationssince the Miocene (e.g. Liu & Ding 1998; Guo et al. 2002; Ding et al.2002a). The good correspondence between palaeoclimate proxies ofChinese loess–palaeosol sequence and the marine oxygen isotoperecords suggests a close relationship between the Chinese eoliandeposits and global climate (Heller & Liu 1984; Kukla et al. 1988;Ding et al. 1995; Deng et al. 2006). Especially, the low-field mag-netic susceptibility was considered to be a sensitive palaeoclimateproxy for classic Chinese loess (Kukla et al. 1988; Heller et al.1991). For a characteristic loess profile on the CLP, palaeosols al-ways have higher susceptibility than the interbedded loess units. Ithas been widely accepted that ultrafine magnetite/maghemite grainsproduced during in situ pedogenesis are responsible for the magneticsusceptibility enhancement of the palaeosols in the CLP (Verosubet al. 1993; Liu et al. 2004a, 2005a, 2007a; Chen et al. 2005). Sincethe hallmark work of Heller & Liu (1984), magnetic susceptibility

has been used to investigate problems, such as the links betweenthe marine and the terrestrial climatic records (Hovan et al. 1989;An et al. 1990; Petit et al. 1990; Heller et al. 1991; Porter & An1995; Ding et al. 2002a), East Asian palaeomonsoon evolution (Anet al. 1991, 2001; Fang et al. 1999; An 2000), quantitative palaeo-climate (palaeorainfall) reconstruction (Maher et al. 1990; Helleret al. 1993; Liu et al. 1995; Han et al. 1996), Asia interior aridifi-cation and past global climate changes (Rea et al. 1998; Guo et al.2002; Deng et al. 2006).

The phenomenon of magnetic susceptibility enhancement dueto pedogenesis has been reported from loess–palaeosol recordsof some Central Europe countries, such as the Czech Republic(Forster et al. 1996; Zhu et al. 2001), Poland (Nawrocki et al.1996), Ukraine (Nawrocki et al. 1996; Tsatskin et al. 1998) andsome Central Asian countries, such as Kazakhstan and Tajikistan(Forster & Heller 1994; Dodonova et al. 1999; Ding et al. 2002b),as well as loess deposits from the Midwestern United States (Geiss& Zanner 2007). In contrast, magnetic susceptibility variationsof Alaskan loess (Beget & Hawkins 1989; Beget et al. 1990;

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Westgate et al. 1990; Liu et al. 1999a) and Siberian loess (Zhuet al. 2000; Matasova et al. 2001; Chlachula 2003) are differentfrom the CLP: the glacial loess has higher susceptibility valueswhile the interglacial palaeosol has lower susceptibility. Thus, awind vigour model has been proposed to explain the enhancementmechanisms for the Alaskan loess (Beget et al. 1990). The ‘windvigour’ model is based on strong and more frequent glacial windscarrying dense magnetic minerals in the loess material, whereasdecreased wind strength and increased moisture during interglacialperiods diminishes the concentration of magnetic minerals (Evans1999; Heil et al. 2010). However, both the wind vigour model andthe pedogenesis model have been invoked to explain the magneticsusceptibility enhancement of the Siberia loess (Matasova et al.2001; Chlachula 2003; Liu et al. 2007b).

The Yili Basin, located in west Xinjiang in the Asian interior,is an intermontane basin in the Tianshan Mountains. It is affectedby westerly circulation all year round. Thick loess–palaeosol se-quences are developed in the basin. Former studies found that theformation and evolution of these loess deposits are closely relatedto the evolution of the Central Asia deserts (Fang et al. 2002a; Shiet al. 2006a; Machalett et al. 2008; Zan et al. 2010) and aridificationof the Asian interior (Fang et al. 2002b; Shi et al. 2006b). The loessdeposits of the Asian interior differ from the classic CLP depositsin terms of dust sources, sedimentary conditions and climatic en-vironments. However, little is known about the magnetic propertiesof these loess deposits and their palaeoclimatic implications.

Recent studies on loess stratigraphy and palaeoclimate in the YiliBasin found that some loess layers have higher susceptibility thanthe corresponding palaeosol layers (Ye 2001; Shi et al. 2007; Songet al. 2008). The magnetic variations are similar to variations ob-served in Alaskan and Siberia loess. Correlation between magneticsusceptibility of modern soil and mean annual temperature (MAT)or mean annual precipitation (MAP) in the Xinjiang area is verycomplicated, and there are no obvious relationships between suscep-tibility and MAT/MAP (Han et al. 1996). And then many importantquestions arose: what causes the magnetic variations between theloess and palaeosols? Is the magnetic enhancement mechanism ofXinjiang loess similar to that of the Alaskan and Siberian loess? Canmagnetic parameters be used as proxies for past environmental con-ditions? Therefore, additional studies are necessary to understandthe relationship between the loess magnetic property and palaeocli-mate in the Asian interior. In our study we carried out multiparam-eter rock magnetic investigations on a suite of loess and palaeosolsamples selected from the upper part of a 96-m-long loess coredrilled from the seventh terrace of the Gongnaisi River in TaledeCounty, and then discussed the magnetic enhancement mechanismsof the Talede loess. This study could contribute to a better under-standing of the links between magnetic properties of the wind-blownsediments and palaeoenvironments in the Asian interior.

2 S E T T I N G A N D S A M P L I N G

The geomorphology of the Yili Basin looks like a westward opentrumpet, and the basin is divided into two sub-basins by Tianshanmountains (Fig. 1b; Ye 1999). During the winter months, the climateof this area is controlled by the Mongolia High and affected by thenorthern branch of the Westerlies. In the summer, the climate iscontrolled by the Indian Low and affected by the southern branchof the Westerlies. The average annual temperature is 9.2◦C. Underthe impact of airflow direction and topography, the distribution ofaverage annual precipitation is uneven: 200−500 mm in the plain,

and up to 800 mm in the mountainous area (Ye 1999). However,seasonal distribution of precipitation is relatively even (Ye 2000).

The loess deposits in the Yili Basin, varying from a few metresto 100 m in thickness, are distributed in the low mountains, the hillyareas and the terraces of the Yili, Kashi and Gongnaisi Rivers. Thehighest loess deposits are found at approximately 1900–2100 m,which coincides with the upper tree line. A 96-m-long core wasobtained from the seventh terrace of the Gongnaisi River at analtitude of approximately 1040 m at Talede. The MAP of Talede isabout 460 mm, while the mean annual evaporation is up to 1470 mm.We have sampled the upper 15.8 m of the core at 5 cm intervals,which consists of the Holocene soil S0, the last glacial loess L1and the last interglacial soil S1. The lithological units are describedfrom top to bottom: (1) the Holocene soil S0 with plant residue (0–1.5 m); (2) the last glacial loess L1 (1.5–12.5 m) intercalated with aweakly developed palaeosol Sm at the depth interval of 5.5–6.6 mand (3) the last interglacial soil S1 (12.5–15.8 m) interbedded withone subloess unit. The age frame of the studied loess–palaeosolsequence has been established based on 14C and optically stimulatedluminescence (OSL) dating (Fig. 2; Shi 2005).

3 M E T H O D O L O G Y

Magnetic susceptibility of all samples was measured with a Bart-ington MS2 meter (Witney, Oxfordshire, UK) at frequencies of 470Hz and 4700 Hz. Two measures of frequency-dependent magneticsusceptibility [χ fd, defined as χ lf − χ hf , and χ fd per cent, definedas (χ lf − χ hf )/χ lf × 100 per cent] were calculated from these mea-surements. Then 21 typical samples, including 10 loess samples and11 palaeosol samples were selected for detailed mineral magneticanalysis.

High-temperature magnetic susceptibilities (χ−T curves) weremeasured using a KLY-3 Kappabridge with a CS3 high-temperaturefurnace (Agico Ltd., Brno, Czech Republic). To minimize the possi-bility of oxidation, the samples were heated and cooled in an argonatmosphere. The contributions of the sample holder and thermo-couple to magnetic susceptibility were subtracted.

High-temperature magnetization measurements (J−T curves)were performed in air using a Variable Field Translation Balance(VFTB; Peterson Corp., Germany). Hysteresis parameters were alsoobtained using the VFTB, with the magnetic field being cycled be-tween ±1.0 T for each sample. Saturation magnetization (M s), sat-uration remanence (M rs) and coercivity (Bc) were determined afterthe correction for the paramagnetic contribution identified from theslope at high fields. Isothermal remanent magnetization (IRM) wasimparted from 0 to 1.0 T also using the VFTB. Subsequently theIRM at 1.0 T was stepwise demagnetized in backfields from 0 to0.3 T to obtain coercivity of remanence (Bcr).

Low-temperature thermal demagnetization of SIRM was car-ried out with a XP-5 Magnetic Properties Measurement System(Quantum Design Inc., San Diego, CA, USA). Samples were firstcooled to 20 K then a field of 5 T was applied, and then the rema-nence was measured as they recovered to room temperature. Thelow temperature susceptibility was measured from 80 to 300 K at afrequency of 976 Hz.

Grain-size distributions were analysed using a Malvern Master-sizer 2000 (Malvern, Worcestershire, UK), with a size detectionrange of 0.02–2000 µm. Organic matter was removed by boilingthe sample in 10 ml of 10 per cent H2O2 for 10 min. Carbonateswere then removed by gradual addition of 10 ml of 10 per cent HCl,digestion for another 10 min. Finally, the sample containers were

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Talede loess–palaeosol sequence 269

Figure 1. Schematic map showing the loess distribution in China (a) and in the Yili Basin (b) [modified from Maher et al. (2009) and Ye et al. (2005)] as wellas the location of studied Talede section.

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Figure 2. Stratigraphy (a), 14C (stars) and OSL (triangle) dating (Shi 2005), χ lf (b), χ fd per cent (c), median grain size (Md) (d), <2 µm content (e) and>63 µm content (f) for the Talede loess section. Arrows in subpart(b) indicate the position of samples selected for mineral magnetic experiments.

filled with distilled H2O and samples were allowed to settle for 12hr. After removing the supernatant, samples were then dispersedwith 10 ml of 0.05 N (NaPO3)6 solutions and ultrasonicated for 10min before measurement.

4 R E S U LT S

4.1 Magnetic susceptibility (χ lf ) and its frequencydependency (χ fd per cent) and median grain size (Md)

The stratigraphic variations of magnetic susceptibility (χ lf ) and itsfrequency dependency (χ fd per cent) and median grain size (Md) ofthe Talede section are shown in Fig. 2. χ lf values range from 46 ×10−8 m3 kg−1 to 98 × 10−8 m3 kg−1 with a mean of 73 × 10−8

m3 kg−1. The mean magnetic susceptibility of the last interglacialsoil S1 (59 × 10−8 m3 kg−1) is generally lower than that of the lastglacial loess L1 (75 × 10−8 m3 kg−1). χ fd per cent is generally low,ranging from 0 and 3.9 per cent with an average of 1.2 per cent. Themean χ fd per cent values of S0, L1 and S1 are 2.1, 1 and 1.5 per cent,respectively. The palaeosols have higher χ fd per cent values thanloess. The median grain size ranges from 14.76 µm to 31.86 µmwith an average of 22.15 µm. The correlation coefficients betweenχ lf and Md, <2 µm content, >63 µm content, are 0.51, −0.52and 0.45, respectively. These correlations are significant at the 0.01level (n = 312). The correlation coefficients indicate that magneticsusceptibilities are positively correlated with the coarse grain sizefractions (Fig. 3).

χ lf and χ fd per cent variations observed in the Talede section aresignificantly different from those of the loess sections in the central

CLP, for example, the Xifeng section. Both loess units at Taledeand Xifeng have similar magnetic susceptibility values (Talede =75 × 10−8 m3 kg−1, Xifeng = 80 × 10−8 m3 kg−1), however,susceptibility of S1 at Talede is only half as much as at Xifeng(Talede = 59 × 10−8 m3 kg−1, Xifeng = 121 × 10−8 m3 kg−1). Thedifference in χ lf between loess and palaeosol in the Talede sectionis minor, while the magnetic susceptibility of the CLP palaeosolis generally two times of that of the loess. χ fd per cent of Taledesection (χ fd per cent = 1.2 per cent) is far lower than that of theCLP loess, for example, the Xifeng loess (χ fd per cent = 8.9 percent; Sun et al. 2009).

Figure 3. Correlation between χ lf and the >63 µm content of Talede loessand palaeosol samples.

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Figure 4. High-temperature magnetic susceptibility (χ−T curves) of typical samples from the loess–palaeosol sequence at Talede. All the samples wereheated and cooled in an argon atmosphere. Solid (dotted) lines represent heating (cooling) curves.

4.2 High-temperature magnetic susceptibility(χ−T curves)

χ−T curves are highly sensitive to mineralogical changes duringthermal treatment and can provide information about magnetic min-eral composition and magnetic grain size (Deng et al. 2000, 2001;Liu et al. 2005b). All the χ−T curves for selected samples of theTalede section are characterized by a major decrease in suscepti-bility at about 580◦C (Fig. 4), the Curie point of magnetite. Thisbehaviour indicates that magnetite is the major contributor to themagnetic susceptibility.

The normalized heating curves record the specific informationof magnetic minerals transition during the heating process. Theheating curves (Fig. 5a) of most samples display a slight increase

in magnetic susceptibility from room temperature to about 260◦C,probably being due to the production of maghemite (γ Fe2O3) fromsome less magnetic Fe-hydroxides (e.g. lepidocrocite, γ FeOOH;Oches & Banerjee 1996). The following decrease in susceptibilitybetween 260 and 500◦C probably results from thermally inducedconversion of metastable ferrimagnetic maghemite to weakly mag-netic hematite (αFe2O3; Florindo et al. 1999; Deng et al. 2000).The increase in susceptibility from room temperature to 260◦C isnearly reversed from 260 to 500◦C, which indicates that there is noin situ maghemite in the samples. The loess and palaeosol samplesfrom Kurtak section in Siberia have the same property (Fig. 5b; Zhuet al. 2000).

The heating and cooling curves of all the samples are irreversible,with the cooling curves being far higher than the heating curves

Figure 5. Normalized heating curves of the temperature-dependent magnetic susceptibilities (χ−T curves) of selected samples from the Talede section (a),and from the Kurtak section in Siberia (b) (modified from Zhu et al. 2000).

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(Fig. 4). Susceptibility values of the heated sample are about threetimes higher than those of the original sample. The cooling curves ofall samples show an increase in susceptibility below 580◦C. All thebehaviours indicate that the antiferromagnetic hematite has beenconverted to ferrimagnetic magnetite during the cooling processdue to the reducing condition during heating and cooling. All theheated samples changed to black, which is indicative of magnetite orcharcoal organic matter. The mean �χ (defined as χfinal − χ original)of the loess samples (114 × 10−8 m3 kg−1) is lower than that ofthe palaeosol samples (149 × 10−8 m3 kg−1), and this reveals thatthere is approximately (149 – 114)/114 = 30 per cent more anti-ferromagnetic hematite in the palaeosol samples than in the loesssamples. The nearly identical heating curves of loess and palaeosols(Fig. 5a) confirm that the difference between loess and palaeosolsis characteristic of the original samples.

4.3 High-temperature magnetization measurements(J−T curves)

J−T curves are useful for the identification of the magnetic min-eralogy (Dunlop & Ozdemir 1997). The J−T curves of selectedsamples of the Talede loess deposits are shown in Fig. 6. All curvesshow a Curie temperature of 580◦C (Fig. 6), indicating the pres-ence of magnetite. All the cooling curves are lower than the heatingcurves, due to the production of weakly magnetic hematite result-ing in a loss of magnetization (Liu et al. 1999b; Zhu et al. 2003).The almost same mean �J (defined as J original − Jfinal) values ofloess samples (16.5 × 10−5Am2 kg−1) and palaeosol samples (14 ×10−5Am2 kg−1) indicate that there are about the same amount of un-stable magnetic minerals converted to hematite both in loess andpalaeosol samples. In other words, loess and palaeosols contain thesame amount of precursor mineral.

4.4 Low-temperature magnetic measurements

At low temperature, we can use the special magnetic mineral phasetransformation point to determine the presence of certain mag-netic minerals, such as the Verwey transition of magnetite at 120 K(Nagata et al. 1964), and the Morin transition of hematite at 260K (Ozdemir et al. 2008). All the samples show an obvious Verweytransition around 120 K indicating the presence of coarser-grainedmagnetite (Fig. 7a).

The low-temperature thermal demagnetization of SIRM curvesof loess and palaeosol samples show a high degree of consistency(Fig. 7b). The pronounced transition of all curves at about 120 Kvalidates the presence of abundant magnetite. The obvious Verweytransition of both loess and soil samples also show that there isnegligible maghemite produced by oxidation of magnetite (Ozdemiret al. 1993). The result coincides with that of the χ−T curves.

4.5 IRM acquisition curves and remanentcoercivity spectra

The characteristics of IRM acquisition and dc field demagnetizationof the SIRM are further used to assess the magnetic mineralogy. TheIRM acquisition curves from loess and palaeosol samples displaysimilar behaviour (Fig. 8a). Both loess and palaeosol samples ac-quired 90 per cent or more of their SIRM intensity under a fieldof 0.3 T (Fig. 8a), indicating that magnetically soft components,such as magnetite, are the major carriers of magnetic remanence.The rest 10 per cent SIRM intensity may be contributed by theantiferromagnetic components (hematite/goethite), which meansthat the loess and palaeosol samples containing a little amount ofhematite/goethite by volume or by mass.

Values of the remanence coercivity (Bcr) for the selected loessand palaeosol samples range from 54 mT to 66 mT (Fig. 8b andTable 1). The mean Bcr values of palaeosols and loess are 58 mT

Figure 6. High-temperature magnetization (J−T curves) of typical samples from the loess–palaeosol sequence at Talede. The measurements were performedin air. Solid (dotted) lines represent heating (cooling) curves. The applied field is 0.5 T.

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Figure 7. Low-temperature magnetic susceptibility curves (a) and low-temperature thermal demagnetization of SIRM curves (b) of selected samples from theTalede section.

Figure 8. IRM acquisition curves and backfield curves of IRM for selected samples of Talede loess and palaeosol samples.

and 60 mT, respectively, which is pretty much the same within theerrors of the averages.

Average Bc values of loess and palaeosols are 13 mT and 16 mT,palaeosols have higher Bc values than loess, and the difference isconfirmed by independent samples T test (p = 0.00 < 0.05).

4.6 Hysteresis parameters

The values of M rs/M s versus Bcr/Bc are plotted in a Day plot (Dayet al. 1977), which indicates that the magnetic component is domi-nated by larger pseudo-single domain (PSD) and multidomain (MD)grains (Fig. 9). Moreover, in the Day plot, the loess samples showevidently coarser mean magnetic grain size than palaeosols.

The magnetite grains in both the loess and palaeosol samplesdisplay a coarse-grained MD-like behaviour, as further suggestedby the nearly temperature-independent nature of low-field suscep-tibility below 585 ◦C (Fig. 4) and by the low values of average χ fd

per cent (1.22 per cent). This coarse-grained magnetite makes sig-nificant contributions to the magnetic susceptibility of the Taledesection.

5 D I S C U S S I O N

5.1 Magnetic mineralogy

High-temperature magnetic measurements (χ−T and J−T curves;Figs 4 and 6) and low-temperature magnetic measurements (Fig. 7)reveal that the predominant magnetic minerals in Talede loess andpalaeosols is magnetite, as well as approximately 15 per cent oflepidocrocite by mass. The variations of IRM acquisition curvesalso reveal the presence of hematite/goethite in the Talede loessand palaeosols. Heavy mineral analysis of the Yili loess furtherconfirmed the presence of magnetite, limonite (mixture of goethite,lepidocrocite, hematite, etc.), as well as ilmenite (Ye 2000). And theloess and palaeosols have the same magnetic mineral composition.

From the χ−T experiments, we can see that palaeosols have ap-proximately 30 per cent higher amount of hematite than loess. Thisresult could be confirmed by the soil colour experiment, the meanredness values of S0, Sm and S1 are 5.8, 5.3 and 5.2, respectively,while the mean redness value of L1 is only 4.7 (Shi 2005). And thehigher Bc values of palaeosols also reveal the palaeosols have moreamount of hard magnetic materials (e.g. hematite) than loess.

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Table 1. Magnetic parameters for the selected loess and palaeosol samples of the Talede section.

Sample Depth Loess/ χ lf χ fd Bc Bcr M rs M s

(m) palaeosol (10−8 m3 kg−1) (per cent) (mT) (mT) (10−4 Am2 kg−1) (10−4 Am2 kg−1)

TLDZ60 0.6 Loess 77.6 2.00 12 54 0.31 1.91TLDZ270 2.7 Loess 83.55 1.26 13 58 0.52 3.26TLDZ285 2.85 Loess 87.1 1.49 13 58 0.39 2.52TLDZ310 3.1 Loess 82.35 1.82 13 56 0.53 3.26TLDZ405 4.05 Loess 74.5 0.34 14 59 0.34 2.06TLDZ735 7.35 Loess 80.25 0.25 13 59 0.36 2.38TLDZ860 8.6 Loess 60.2 1.83 14 60 0.26 1.57TLDZ920 9.2 Loess 81.4 1.23 13 55 0.39 2.47TLDJ1060 10.6 Loess 79.95 0.06 14 61 0.42 2.51TLDJ1230 12.3 Loess 66.7 1.42 14 60 0.33 1.9TLDJ1285 12.85 Palaeosol 50.9 1.38 15 60 0.35 1.89TLDJ1295 12.95 Palaeosol 48.5 0.31 16 61 0.32 1.61TLDJ1305 13.05 Palaeosol 46.85 1.17 16 66 0.34 1.62TLDJ1335 13.35 Palaeosol 52.35 1.62 17 60 0.4 1.96TLDJ1345 13.45 Palaeosol 56.8 1.32 16 61 0.44 2.14TLDJ1395 13.95 Palaeosol 80.2 1.00 16 58 0.46 2.43TLDJ1440 14.4 Palaeosol 56.85 1.93 15 58 0.3 1.53TLDJ1485 14.85 Palaeosol 46.2 2.06 16 59 0.35 1.62TLDJ1495 14.95 Palaeosol 48.35 1.65 16 59 0.32 1.52TLDJ1515 15.15 Palaeosol 61.95 1.78 16 60 0.46 2.24TLDJ1565 15.65 Palaeosol 62.4 0.96 16 57 0.37 1.77

Figure 9. Hysteresis parameter ratios plotted on a Day diagram (Day et al.1977) of the loess (open symbols) and palaeosol (solid symbols) samplesof the Talede section. SD, single-domain; PSD, pseudo-single domain; MD,multidomain.

The low χ fd per cent values reveal that the concentration of ultra-fine magnetic grains both in loess and palaeosols is extremely low.However, the slightly higher χ fd per cent values of palaeosols alsoindicate that palaeosols have more amounts of ultrafine magneticgrains than loess.

5.2 Magnetic susceptibility enhancement mechanismof Talede loess

The magnetic properties of Talede loess are dominated by coarseeolian magnetite, and the loess samples have evidently coarser mean

magnetic grain size than palaeosols. The observed magnetic varia-tions can be well explained by the wind vigour model invoked byBeget et al. (1990) in Alaska. The higher magnetic susceptibilityof glacial loess is attributed to stronger and more frequent stormsduring the glacial period.

The magnetic properties of Talede loess are dominated by theeolian coarse-grained magnetite. The eolian magnetic signals canbe estimated by fitting a linear regression to χ fd versus χ lf (Fig. 10).The y-axis intercepts χ 0 represent the initial eolian inputs withoutpedogenic overprints (Liu et al. 2004b). As shown in Fig. 10, the χ0

of Talede loess is 67.5 × 10−8 m3 kg−1, which is about 90 per centof the whole magnetic susceptibility (mean magnetic susceptibilityis 73 × 10−8 m3 kg−1). The value is far higher than that of the CLPloess, for example, χ 0 of Baicaoyuan loess (Deng 2008), Jiaodaoloess (Deng et al. 2005) and Luochuan loess (Bloemendal & Liu2005) are 27.1 × 10−8 m3 kg−1, 27.5 × 10−8 m3 kg−1 and 32.9 ×10−8 m3 kg−1, respectively.

However, the wind vigour model cannot explain all the observedmagnetic variations. The observed enrichment of hematite and ul-trafine magnetic grains in palaeosols also reveal the contribution ofpedogenesis to the magnetic properties, though it is very small.

Moreover, the dry and warm environment during interglacial pe-riod results in thoroughly oxidating conditions in the Yili Basin,which primarily leads to the formation of antiferromagnetic com-ponents during the pedogenic process. This could be seen as thefirst onset of pedogenic enhancement model.

6 C O N C LU S I O N S

Multiparameter rock magnetic investigations on loess deposits in theAsian interior suggest that the predominant ferrimagnetic mineralsin the Talede section are large PSD and MD-like grains of magnetite.Ultrafine magnetite/maghemite of pedogenic origin plays a verylimited role in enhancing the magnetic susceptibility of palaeosols.

Eolian coarse-grained magnetite makes dominant contributionsto the bulk magnetic properties of the Talede loess sediments. Thehigher magnetic susceptibility of loess is attributed to strongerand more frequent wind during the glacial period. Meantime, the

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Figure 10. Correlation between χ fd and χ lf of the Talede loess sediments.

observed enrichment of hematite and ultrafine magnetic grains inpalaeosols, also indicates the first onset of pedogenic enhancement.Therefore, the site could be seen as an end-member of the classicCLP enhancement model.

A C K N OW L E D G M E N T S

We thank the Editor, E. Appel, and two reviewers for their insightfulcomments and suggestions. All the mineral magnetic measurementswere made in the Paleomagnetism and Geochronology Laboratory,Institute of Geology and Geophysics, Chinese Academy of Sci-ences. Financial assistance was provided by the National NaturalScience Foundation of China (Grant no. 40871018) and the Open-ing Foundation of State Key Laboratory of Loess and QuaternaryGeology, Institute of Earth Environment, Chinese Academy of Sci-ences (Grant no. SKLLQG0812).

R E F E R E N C E S

An, Z.S., 2000. The history and variability of the East Asian paleomonsoonclimate, Quat. Sci. Rev., 19(1–5), 171–187.

An, Z.S., Liu, T.S., Lu, Y.C., Porter, S.C., Kukla, G.J., Wu, X.H. & HuaY.M., 1990. The long-term paleomonsoon variation recorded by the loess-paleosol sequence in Central China, Quat. Int., 7–8, 91–95.

An, Z.S., Kukla, G.J., Porter, S.C. & Xiao, J.L., 1991. Magnetic susceptibilityevidence of monsoon variation on the Loess Plateau of central Chinaduring the last 130,000 years, Quat. Res., 36(1), 29–36.

An, Z.S., Kutzbach, J.E., Prell, W.L. & Porter, S.C., 2001. Evolution ofAsian monsoons and phased uplift of the Himalaya-Tibetan Plateau sinceLate Miocene times, Nature, 411, 62–66.

Beget, J. & Hawkins, D., 1989. Influence of orbital parameters on Pleistoceneloess deposition in central Alaska, Nature, 337, 151–153.

Beget, J., Stone, D. & Hawkins, D., 1990. Paleoclimate forcing of magneticsusceptibility variations in Alaskan loess, Geology, 18(1), 40–43.

Bloemendal, J. & Liu, X.M., 2005. Rock magnetism and geo-chemistry of two Plio-Pleistocene Chinese loess–palaeosol se-quences: implications for quantitative palaeoprecipitation reconstruc-tion, Palaeogeogr. Palaeoclimatol. Palaeoecol., 226(1–2), 149–166,doi:10.1016/j.palaeo.2005.05.008.

Chen, T.H., Xu, H.F., Xie, Q.Q., Chen, J., Ji, J.F. & Lu, H.Y., 2005. Char-acteristics and genesis of maghemite in Chinese loess and paleosols:mechanism for magnetic susceptibility enhancement in paleosols, Earthplanet. Sci. Lett., 240(3–4), 790–802.

Chlachula, J., 2003. The Siberian loess recordandits significance for recon-struction of Pleistocene climate changes in north-central Asia, Quat. Sci.Rev., 22(18–19), 1879–1906.

Day, R., Fuller, M. & Schmidt, V.A., 1977. Hysteresis properties of titano-magnetites: grain size and compositional dependence, Phys. Earth planet.Inter., 13, 260–267.

Deng, C.L., 2008. Paleomagnetic and mineral magnetic investigation of theBaicaoyuan loess-paleosol sequence of the western Chinese Loess Plateauover the last glacial-interglacial cycle and its geological implications,Geochem. Geophys. Geosyst., 9, Q04034, doi:10.1029/2007GC001928.

Deng, C.L., Zhu, R.X., Verosub, K.L., Singer, M.J. & Yuan, B.Y., 2000.Paleoclimatic significance of the temperature-dependent susceptibility ofHolocene loess along a NW-SE transect in the Chinese loess plateau,Geophys. Res. Lett., 27(22), 3715–3718.

Deng, C.L., Zhu, R.X., Jackson, M.J., Verosub, K.L. & Singer, M.J., 2001.Variability of the temperature-dependent susceptibility of the Holoceneeolian deposits in the Chinese loess plateau: a pedogenesis indicator,Phys. Chem. Earth Part A, 26(11–12), 873–878.

Deng, C.L., Vidic, N.J., Verosub, K.L., Singer, M.J., Liu, Q.S., Shaw, J.& Zhu, R.X., 2005. Mineral magnetic variation of the Jiaodao Chineseloess/paleosol sequence and its bearing on long-term climatic variability,J. geophys. Res., 110, B03103, doi:10.1029/2004JB003451.

Deng, C.L., Shaw, J., Liu, Q.S., Pan, Y.X. & Zhu, R.X., 2006. Mineralmagnetic variation of the Jingbian loess/paleosol sequence in the north-ern Loess Plateau of China: implications for Quaternary developmentof Asian aridification and cooling, Earth planet. Sci. Lett., 241(1–2),248–259.

Ding, Z.L., Liu, T.S., Rutter, N.W., Yu, Z.W., Zhu, R.X. & Guo, Z.T., 1995.Ice-volume forcing of the East Asia winter monsoon variation in the past800,000 years, Quat. Res., 44(2), 149–158.

Ding, Z.L., Derbyshire, E., Yang, S.L., Yu, Z.W., Xiong, S.F. & Liu, T.S.,2002a. Stacked 2.6-Ma grain size record from the Chinese loess basedon five sections and correlation with the deep-sea δ18O records, Paleo-ceanography, 17(3), 1033, doi:10.1029/2001PA000725.

Ding, Z.L., Ranov, V., Yang, S.L., Finaev, A., Han, J.M. & Wang, G.A.,2002b. The loess record in southern Tajikistan and correlation with Chi-nese loess, Earth planet. Sci. Lett., 200(3–4), 387–400.

Dodonova, E., Shackleton, N., Zhou, L.P., Lomov, S.P. & Finaev, A.F., 1999.Quaternary loess-paleosol stratigraphy of central Asia: geochronology,

C© 2012 The Authors, GJI, 190, 267–277


276 Y. Liu et al.

correlation, and evolution of paleoenvironments, Stratigr. Geol. Corr.,7(6), 581–593.

Dunlop, D.J. & Ozdemir, O., 1997. Rock Magnetism: Fundamentals andFrontiers, Cambridge University Press, New York, NY, 573pp.

Evans, M.E., 1999. Magnetoclimatology: a test of the wind-vigour modelusing the 1980 Mount St. Helens ash, Earth planet. Sci. Lett., 172(3–4),255–259.

Fang, X.M. et al., 1999. Asian summer monsoon instability during thepast 60,000 years: magnetic susceptibility and pedogenic evidence fromthe western Chinese Loess Plateau, Earth planet. Sci. Lett., 168(3–4),219–232.

Fang, X.M., Lu, L.Q., Yang, S.L., Li, J.J., An, Z.S., Jiang, P.A. & Chen,X.L., 2002a. Loess in Kunlun Mountains and its implications on desertdevelopment and Tibetan Plateau uplift in west China, Sci. China SeriesD: Earth Sci., 45(4), 289–299.

Fang, X.M., Shi, Z.T., Yang, S.L., Yan, M.D., Li, J.J. & Jiang, P.A., 2002b.Loess in the Tian Shan and its implications for the development of theGurbantunggut Desert and drying of northern Xinjiang, Chin. Sci. Bull.,47(16), 1381–1387.

Florindo, F., Zhu, R.X., Guo, B., Yue, L.P., Pan, Y.X. & Speranza, F.,1999. Magnetic proxy climate results from the Duanjiapo loess section,southernmost extremity of the Chinese Loess Plateau, J. geophys. Res.,104(B1), 645–659.

Forster, T. & Heller, F., 1994. Paleomagnetism of loess deposits from theTajik depression (Central Asia), Earth planet. Sci. Lett., 128, 501–512.

Forster, T., Heller, F., Evans, M.E. & Havlicek, P., 1996. Loess in the CzechRepublic: magnetic properties and paleoclimate, Stud. Geophys. Geod.,40, 243–261.

Geiss, C.E. & Zanner, C.W., 2007. Sediment magnetic signature of climate inmodern loessic soils from the Great Plains, Quat. Int., 162–163, 97–110,doi:10.1016/j.quaint. 2006.10.035.

Guo, Z.T. et al., 2002. Onset of Asian desertification by 22 Myr ago inferredfrom loess deposits in China, Nature, 416, 159–163.

Han, J.M., Lu, H.Y., Wu, N.Q. & Guo, Z.T., 1996. Magnetic susceptibilityof modern soils in China and climate conditions, Stud. Geophys. Geod.,40, 262–275.

Heil, C.W., Jr., King, J.W., Zarate, M.A. & Schulz, P.H., 2010. Cli-matic interpretation of a 1.9 Ma environmental magnetic recordof loess deposition and soil formation in the central eastern Pam-pas of Buenos Aires, Argentina, Quat. Sci. Rev., 29, 2705–2718,doi:10.1016/j.quascirev.2010.06.024.

Heller, F. & Liu, T.S., 1984. Magnetism of Chinese loess deposits, Geophys.J. R. astr. Soc., 77, 125–141.

Heller, F., Liu, X.M., Liu, T.S. & Xu, T.C., 1991. Magnetic susceptibility ofloess in China, Earth planet. Sci. Lett., 103(1–4), 301–310.

Heller, F., Chen, C.D., Beer, J., Liu, X.M., Liu, T.S., Bronger, A., Suter, M.& Bonani, G., 1993. Quantitative estimates of pedogenic ferromagneticmineral formation in Chinese loess and palaeoclimatic implications, Earthplanet. Sci. Lett., 114, 385–390.

Hovan, S.A., Rea, D.K., Pisias, N.G. & Shackleton, N.G., 1989. A directlink between the China loess and marine δ18O records: aeolian flux to thenorth Pacific, Nature, 340(6231), 296–298.

Kukla, G., Heller, F., Liu, X.M., Xu, T.C., Liu, T.S. & An, Z.S., 1988.Pleistocene climates in China dated by magnetic susceptibility, Geology,16(9), 811–814.

Liu, T.S. & Ding, Z.L., 1998. Chinese loess and the paleomonsoon, Annu.Rev. Earth planet. Sci., 26, 111–145.

Liu, X.M., Rolph, T., Bloemendal, J., Shaw, J. & Liu, T.S., 1995. Quantitativeestimates of paleoprecipitation at Xifeng in the loess plateau of China,Palaeogeogr. Palaeoclimatol. Palaeoecol., 113, 243–248.

Liu, X.M., Hesse, P., Rolph, T. & Beget, J., 1999a. Properties of magneticmineralogy of Alaskan loess: evidence for pedogenesis, Quat. Int., 62,92–102.

Liu, X.M., Hesse, P. & Rolph, T., 1999b. Origin of maghaemite in Chineseloess deposits: aeolian or pedogenic? Phys. Earth planet. Inter., 112,191–201.

Liu, Q.S., Banerjee, S.K., Jackson, M.J., Deng, C.L., Pan, Y.X. & Zhu,R.X., 2004a. New insights into partial oxidation model of magnetites and

thermal alteration of magnetic mineralogy of the Chinese loess in air,Geophys. J. Int., 158(2), 506–514.

Liu, Q.S., Jackson, M.J., Yu, Y., Chen, F., Deng, C. & Zhu,R., 2004b. Grain size distribution of pedogenic magnetic parti-cles in Chinese loess/paleosols, Geophys. Res. Lett., 31, L22603,doi:10.1029/2004GL021090.

Liu, Q.S., Deng, C.L., Yu, Y.J., Torrent, J., Jackson, M.J., Banerjee, S.K.& Zhu, R.X., 2005a. Temperature dependence of magnetic susceptibil-ity in an argon environment: implications for pedogenesis of Chineseloess/palaeosols, Geophys. J. Int., 161(1), 102–112.

Liu, Q.S., Torrent, J., Maher, B.A., Yu, Y.J., Deng, C.L., Zhu, R.X. & Zhao,X.X., 2005b. Quantifying grain size distribution of pedogenic magneticparticles in Chinese loess and its significance for pedogenesis, J. geophys.Res., 110, B11102, doi:10.1029/2005JB003726.

Liu, Q.S., Deng, C.L., Torrent, J. & Zhu, R.X., 2007a. Review of recentdevelopments in mineral magnetism of the Chinese loess, Quat. Sci. Rev.,26(3–4), 368–385.

Liu, X.M., Liu, T.S., Chlachula, J., Xia, D.S., Hesse, P. & Wang, G., 2007b.Two pedogenic models for paleoclimatic records of magnetic susceptibil-ity from Chinese and Siberian loess, Sci. China (D), 50(12), 1–11.

Machalett, B., Oches, E.A., Frechen, M., Zoller, L., Hambach, U.,Mavlyanova, N.G., Markovic, S.B. & Endlicher, W., 2008. Aeolian dustdynamics in central Asia during the Pleistocene: driven by the long-term migration, seasonality, and permanency of the Asiatic polar front,Geochem. Geophys. Geosyst., 9, Q08Q09, doi:10.1029/2007GC001938.

Maher, B.A., Thompson, R. & Zhou, L.P., 1990. Spatial and temporal re-constructions of changes in the Asian palaeomonsoon-a new mineralmagnetic approach, Earth planet. Sci. Lett., 125, 461–471.

Maher, B.A., Mutch, T.J. & Cunningham, D., 2009. Magnetic and geo-chemical characteristics of Gobi Desert surface sediments: implicationsfor provenance of the Chinese Loess Plateau, Geology, 37(3), 279–282.

Matasova, G., Jordanova, N., Zykina, V., Kapicka, A. & Petrovsky, E., 2001.Magnetic study of Late Pleistocene loess /palaeosol sections from Siberia:palaeoenvironmental implications, Geophys. J. Int., 147, 367–380.

Nagata, T., Kobayashi, K. & Fuller, M., 1964. Identification of magnetiteand hematite in rocks by magnetic observation at low temperature, J.geophys. Res., 69, 2111–2120.

Nawrocki, J., Wojcik, A. & Bogucki, A., 1996. The magnetic susceptibilityrecord in the Polish and western Ukrainian loess–palaeosol sequencesconditioned by palaeoclimate, Boreas, 25, 161–169.

Oches, E.A. & Banerjee, S.K., 1996. Rock-magneitc proxies of climatechange from loess-paleosol sediments of the Czech Repubulic, Stud. Geo-phys. Geod., 40, 287–300.

Ozdemir, O., Moskowitz, B.M. & Dunlop, D.J., 1993. The effect of oxidationon the Verwey transition in magnetite, Geophys. Res. Lett., 20, 1671–1674.

Ozdemir, O., Dunlop, D.J. & Berquo, T.S., 2008. Morin transition inhematite: size dependence and thermal hysteresis, Geochem. Geophys.Geosyst., 9, Q10Z01, doi:10.1029/2008GC00211.

Petit, J.R., Mounier, L., Jouzel, J., Korotkevich, Y.S., Kotlyakov, V.I. &Lorius, C., 1990. Paleoclimatological and chronological implications ofthe Vostok core dust record, Nature, 343, 56–58.

Porter, S.C. & An, Z.S., 1995. Correlation between climate events in theNorth Atlantic and China during the last glaciation, Nature, 375, 305–308.

Rea, D.K., Snoeckx, H. & Joseph, L.H., 1998. Late Cenozoic eoliandeposition in the North Pacific: Asian drying, Tibetan up lift, andcooling of the Northern Hemisphere, Paleoceanography, 13(3), 215–224.

Shi, Z.T., 2005. Age of Yili loess in Xijiang and its paleoenvironmen-tal implications, Postdoctoral Report, Chinese Academy of Sciences(unpublished).

Shi, Z.T., Song, Y.G. & An, Z.S., 2006a. Evolution of Gurbantunggut Desertrecorded by Tianshan loess, J. Desert Res., 26(5), 675–679 (in Chinesewith English abstract).

Shi, Z.T., Fang, X.M., Song, Y.G., An, Z.S. & Yang, S.L., 2006b. Loesssediments in the north slope of Tianshan Mountains and its indication ofdesertification since Middle Pleistocene, Mar. Geol. Quat. Geol., 26(3),109–114 (in Chinese with English abstract).

C© 2012 The Authors, GJI, 190, 267–277



Shi, Z.T., Dong, M. & Fang, X.M., 2007. The characteristics of later Pleis-tocene loess-paleosol magnetic susceptibility in Yili Basin, J. LanzhouUniv. (Nat. Sci.), 43(2), 7–10 (in Chinese with English abstract).

Song, Y., Shi, Z., Dong, H., Nie, J.S., Qian, L.B., Chang, H. & Qiang, X.K.,2008. Loess magnetic susceptibility in Central Asia and its paleoclimaticsignificance, Geosci. Remote Sens. Symp., 2, 1227–1230.

Sun, Y.B., Chen, T.H. & Xie, Q.Q., 2009. Substitute indices of summermonsoon in Eolian sediment and its paleoclimatic significance, Geol. J.China Univ., 15(1), 126–134.

Tsatskin, A., Heller, F., Hailwood, E.A., Gendler, T.S., Hus, J., Montgomery,P., Sartori, M. & Virina, E.I., 1998. Pedosedimentary division, rock mag-netism and chronology of the loess palaeosol sequence at RoxolanyUkraine, Palaeogeogr. Palaeoclimatol. Palaeoecol., 143, 111–133.

Verosub, K.L., Fine, P., Singer, M.J. & Tenpas, J., 1993. Pedogenesis and pa-leoclimate: interpretation of the magnetic susceptibility record of Chineseloess-paleosol sequences, Geology, 21(11), 1011–1014.

Westgate, J.A., Stemper, B.A. & Pewe, T.L., 1990. A 3 m.y. record ofPliocene–Pleistocene loess in interior Alaska, Geology, 18, 858–861.

Ye, W., 1999. Characteristics of physical environment and conditions ofLoess formation in Yili area, Xinjiang, Arid Land Geog., 22(3), 9–16 (inChinese with English abstract).

Ye, W., 2000. The mineral characteristics of loess and depositing environ-ment in Yili Area, Xinjiang, Arid Area Res., 17(4), 1–10 (in Chinese withEnglish abstract).

Ye, W., 2001. Study on magnetic susceptibility of loess and paleosol se-quences in westerly region of Xinjiang, J. Desert Res., 21(4), 380–386 (inChinese with English abstract).

Ye, W., Yabuki, S. & Zhao, X.Y., 2005. Comparison of the sedimentaryfeatures of loess between the westerly and monsoon regions in China,Arid Land Geog., 28(6), 789–794 (in Chinese with English abstract).

Zan, J., Fang, X., Yang, S., Nie, J. & Li, X., 2010. A rock magnetic study ofloess from the West Kunlun Mountains, J. geophys. Res., 115, B10101,doi:10.1029/2009JB007184.

Zhu, R.X., Kazansky, A., Matasova, G., Guo, B., Zykina, V., Petrovsky, E.& Jordanova, N., 2000. Rock-magnetic investigation of Siberia loess andits implication, Chin. Sci. Bull., 45(23), 2192–2197.

Zhu, R.X., Shi, C.D., Guo, B., Pan, Y.X., Suchy, V. & Zeman, A., 2001.Magnetic properties and paleoclimatic implications of loess-paleosol se-quences of Czech Republic, Sci. China (D), 44(5), 385–394.

Zhu, R.X., Matasova, G., Kazansky, A., Zykina, V. & Sun, J.M., 2003. Rockmagnetic record of the last glacial–interglacial cycle from the Kurtakloess section, southern Siberia, Geophys. J. Int., 152, 335–343.

C© 2012 The Authors, GJI, 190, 267–277


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