tters 244 (2006) 336–348www.elsevier.com/locate/epsl

Earth and Planetary Science Le

Magnetostratigraphic age of the Xiantai Paleolithic sitein the Nihewan Basin and implications for early

human colonization of Northeast Asia

Chenglong Deng a,⁎, Qi Wei b, Rixiang Zhu a, Hongqiang Wang a, Rui Zhang a,Hong Ao a, Liao Chang c, Yongxin Pan a

a Paleomagnetism and Geochronology Laboratory (SKL-LE), Institute of Geology and Geophysics,Chinese Academy of Sciences, Beijing 100029, China

b Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, Chinac School of Ocean and Earth Science, University of Southampton, Southampton SO14 3ZH, UK

Received 16 November 2005; received in revised form 3 February 2006; accepted 3 February 2006Available online 9 March 2006

Editor: V. Courtillot

Abstract

Timing of the early habitation and stone technologies in the Nihewan Basin, North China has provided insights into ourunderstanding of early human adaptability to high northern latitudes in East Asia. Here we contribute to this topic with detailedmagnetostratigraphic investigation, coupled with mineral magnetic measurements and palynological analyses on a lacustrinesequence in this basin, which contains the Xiantai Paleolithic site. Magnetite and hematite were identified as the main carriers forthe characteristic remanent magnetizations. Magnetostratigraphic results show that the Xiantai lacustrine sequence recorded theBrunhes chron, the Jaramillo and the Olduvai subchrons, and successive reverse polarity portions of the intervening Matuyamachron. Stratigraphic correlation in terms of lithology, magnetic susceptibility and magnetic polarity sequences between the Xiantaiand Xiaochangliang sections indicates that the Xiantai artefact layer is readily contemporary with the Xiaochangliang artefact layer,which has been previously estimated to be about 1.36 Ma [R.X. Zhu, K.A. Hoffman, R. Potts, C.L. Deng, Y.X. Pan, B. Guo, C.D.Shi, Z.T. Guo, B.Y. Yuan, Y.M. Hou, W.W. Huang, Earliest presence of humans in northeast Asia, Nature 413 (2001) 413–417.].Early humans of the Xiantai Paleolithic site lived in a steppe paleoenvironment indicated from fossil pollens. Furthermore, thecombined evidence of our magnetostratigraphy and previously published magnetochronology and paleoclimate data documentsthat early humans of North China were able to adjust to an increasing variability of paleoclimates and paleoenvironments over theEarly Pleistocene.© 2006 Elsevier B.V. All rights reserved.

Keywords: magnetostratigraphy; Xiantai Paleolithic site; Nihewan Basin; Early Pleistocene; human evolution

⁎ Corresponding author. Tel.: +86 10 6200 7913; fax: +86 10 62010846.

E-mail addresses: cldeng@mail.igcas.ac.cn (C. Deng),rxzhu@mail.igcas.ac.cn (R. Zhu), wanghq@mail.igcas.ac.cn(H. Wang), ruizhang@mail.igcas.ac.cn (R. Zhang),ah@mail.igcas.ac.cn (H. Ao), changl@soton.ac.uk (L. Chang),yxpan@mail.igcas.ac.cn (Y. Pan).

0012-821X/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.epsl.2006.02.001

1. Introduction

Timing of the early habitation and stone technolo-gies in different regions of the world has been, andcontinues to be, a contentious topic in the study of

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human evolution (see reviews by Zhu et al. [2],Dennell [3], Antón and Swisher [4], Finlayson [5] andDennell and Roebroeks [6]). Especially, the chronologyof East Asian Paleolithic tools is pertinent to earlyhuman occupation in this region and the overallframework of human origin and migration in the OldWorld [1,2,6,7]. The Nihewan Basin, one in a series ofEast Asian Cenozoic basins, offers an excellentopportunity to explore this issue.

Most of the few hominin or Paleolithic sites inChina from the early Pleistocene were found in theNihewan Basin, such as the Majuangou, Xiaochan-gliang, Donggutuo, Banshan, Maliang and Cenjiawansites (Fig. 1). The age of these Paleolithic sites hasbeen controversial for a long time because of theabsence of suitable material for accurate isotopicdating. However, in recent years, considerable prog-ress has been made towards magnetostratigraphicallydating these sites [1,2,7–10]. As a result, this basin

Fig. 1. Schematic map showing the Loess Plateau, Nihewan Basin, and thefrom Zhu et al. [2] and Guo et al. [43]). The Yellow River and Yangtze Rivereast–west trending Qinling Mountains are the traditional dividing line betweeand solid arrows respectively show summer and winter monsoon directions.

has significantly contributed to our understanding ofearly human adaptability to high northern latitudes inEast Asia.

The Xiantai locality (40°13.126′N, 114°39.623′E)is one of the early Paleolithic sites in the NihewanBasin [11]. In this study, we present a detailedmagnetostratigraphic study of the Xiantai sequencebased on mineral magnetism, which contains theXiantai stone artefact layer. In addition, combiningwith published magnetochronologic data of earlyhominin and Paleolithic sites of East Asia and drawingon published marine and terrestrial paleoclimate dataof the this region as well as new palynological resultsof the Xiantai stone artefact layer, we attempted toexplore the insights into early colonization of North-east Asia. Our finding contributes to a better unders-tanding of the chronological framework and envi-ronmental setting of early human occupation at highnorthern latitudes in East Asia.

Paleolithic/hominin sites (triangles) mentioned in this paper (modifiedare the major river systems in north and south China, respectively. Then temperate northern China and subtropical southern China. The dotted

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2. Geological, archeological settings and sampling

2.1. Geological setting and sampling

The Nihewan Basin (Fig. 1), located in the transitionzone between the North China Plain and the InnerMongolian Plateau, is filled with Pliocene to Pleistocenelacustrine and fluvial deposits, which have been namedthe Nihewan Beds [12]. The Nihewan Formation, whichrepresents the type section of the early Pleistocene inNorth China [13], was restricted to the lower portion ofthe Nihewan Beds. Today, this fluvio-lacustrine se-quence, capped by late Pleistocene to Holocene wind-blown deposits, are dissected along a southwest–northeast track by the Sanggan River (Fig. 1c).

Covering an area of ca. 150–200km2, the NihewanBasin provides extensive sedimentary exposures morethan 90m thick. Since the 1920s, the basin has attractedthe attention of geologists and paleontologists because ofits well-developed late Cenozoic strata rich in mamma-lian fossils, known as the Nihewan Fauna. These fossilstraditionally correspond to the Villafranchian fauna inEurope [14,15]. A series of magnetostratigraphical,sedimentological, geochemical, paleontological andpalynological studies have contributed significantly toour understanding of the stratigraphic framework anddepositional systems in the Nihewan Basin (see reviewby Zhu et al. [2]).

The Xiantai section lies in the eastern margin of theNihewanBasin. Here the NihewanBeds have a thicknessof 64.5m, capped by the Holocene soil (0.4m), the lastglacial loess (5.75m) and soil associated with the lastinterglacial (2.3m) and underlain by Jurassic breccia.Block samples oriented by magnetic compass in the fieldwere taken from the depth interval of 11–73m. Total 196block samples were taken at 20–40cm intervals. Cubicspecimens of 20mm×20mm×20mm were obtainedfrom those block samples in the laboratory.

Fig. 2. Examples of stone artefacts excavated from Xiantai: (a) scraper; (b) flastone artefacts.

2.2. Archeological setting

Specifically, the eastern margin of the NihewanBasin, which is located approximately 150km west ofBeijing, has yielded a number of fossil-containing andarcheological localities, including the well knownXiaochangliang [16], Donggutuo [17] and Majuangou[18] and other numerous sites. The Xiantai (also namedDachangliang) Paleolithic locality, about 200m south-west of the Xiaochangliang site, was discovered andexcavated in 2000. The stone artefact layer of this site(7m2 area, 0.58m thick) contains 1 scraper, 4 cores and16 flakes and 12 chunks [11]. In addition, 27 mammalianbone fragments and freshwater bivalve shells wereunearthed from this site. However, the broken nature ofthe fragments hinders an unambiguous identification ofmammalian species [11].

These stone artefacts are made primarily of chert andrarely of volcanic rock and quartz, all obtained from localoutcrops. The only stone tool, a scraper, was crudelymodified by direct hammer percussion and was re-touched on the dorsal surface of a flake [11] (Fig. 2). Theflaking technique was simple hammer percussion [11].

3. Methodology

3.1. Mineral magnetic measurements

In the field, low-field magnetic susceptibility (χ) wasmeasured using a Bartington MS2F magnetic suscepti-bility meter at a 5-cm spacing for depth interval of 8.5–73m. The magnetic susceptibility data obtained in thefieldwere calibrated by using themagnetic susceptibilitiesof paleomagnetic samples measured in the laboratory.

Rock magnetic methods include high-temperaturemagnetic susceptibility (χ–T) and hysteresis measure-ments. χ–T curves were measured on selected samplesusing aKLY-3Kappabridgewith aCS-3 high-temperature

ke; (c) core. Scale bars: 1 cm. See Fig. 6 of Pei [11] for sketches of the

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furnace (Agico Ltd., Brno). Hysteresis parameters, suchas saturation magnetization (Ms), saturation remanence(Mrs), coercivity field (Bc) and the coercivity of remanence(Bcr), were determined using a MicroMag 2900 Alternat-ing Gradient Magnetometer.

3.2. Paleomagnetic measurements

Remanence measurements were made using a 2GEnterprises Model 760-R cryogenic magnetometer in-stalled in amagnetically shielded space (<300nT). Firstly,all the 196 samples were subjected to stepwise thermaldemagnetization by using the MMTD80 Thermal De-magnetizer. Most of them were heated to maximum585°C and some were heated to 680°C, with 12–20 stepsof demagnetization and 10–50°C temperature incre-ments. 147 (75%) samples gave reliable characteristicremanence directions (ChRM). Secondly, 34 samples,which did not give reliable ChRM directions by thermaldemagnetization, were subjected to a 150°C thermaldemagnetization followed by alternating field demagne-tization at peak fields up to 60mTat 2.5–10mT intervals.Only 10 (29%) samples gave reliable ChRM directions.

3.3. Palynological analyses

Three samples (labeled XT-A, XT-B and XT-C) weretaken for pollen and spore analyses, with sample XT-A

Fig. 3. (a–d) High-temperature magnetic susceptibility (χ–T) of selected

20cm above the Xiantai stone artefact layer, sample XT-B within the layer, and sample XT-C 20cm below thelayer. Samples were processed according to standardprocedures (chemical treatment with HCl→HF→KOH→HCl, and heavy-liquid fractionation). Aknown quantity of Lycopodium spores was added toeach sample to calculate pollen concentration [19]. 300pollen grains were counted in each sample. Pollenpercentages were calculated from the sum of pollen andspores.

4. Results

4.1. High-temperature magnetic susceptibility (χ–T)measurements

χ–T curves can provide useful information aboutchanges in magnetic mineral composition duringthermal treatment [20,21]. There are two types ofχ–T curves for the representative samples of thelacustrine sediments from the Xiantai section (Fig. 3).One is characterized by a major drop in magneticsusceptibility at about 585°C, the Curie point ofstoichiometric magnetite, and by the cooling curvesmuch higher than the heating curves after exposure to<585°C (Fig. 3a, b); the other, characterized by amajor drop in magnetic susceptibility at about 610°C,the feature of partially oxidized magnetite, and by the

samples. Solid (dotted) lines represent heating (cooling) curves.

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cooling curves much lower than the heating curvesafter exposure to <610°C (Fig. 3c, d). Thesebehaviors indicate that stoichiometric and partiallyoxidized magnetites are the major contributors to themagnetic susceptibility. All the selected samplesexhibit heating curves with a susceptibility humpnear ∼300°C. The steady increase of susceptibilitybelow ∼300°C may be ascribed to gradual unblock-ing of fine-grained (near the superparamagnetic/single-domain (SP/SD) boundary) ferrimagnetic parti-cles [8,22]. The further drop of magnetic susceptibil-ity between ∼300°C and ∼450°C is interpreted as theconversion of metastable maghemite, which originatesfrom the secondary maghemite grains formed due topedogenesis in the Loess Plateau or the deserts innorthwest China [21], to weakly magnetic hematite[23]. Hematite, which also comes from the hematitegrains formed by chemical weathering in the LoessPlateau region or the deserts in northwest China andserves as another important carrier of the naturalremanence suggested by the progressive demagneti-zation analyses, is not well expressed in the χ–Tcurves because its weak susceptibility is masked bythe much stronger contributions of magnetite andmaghemite.

Fig. 4. (a–d) Hysteresis loops for representative samples after slope correctionfields up to ±1.0T.

4.2. Hysteresis properties

For the four selected samples, two show thehysteresis loops closed above ∼300mT (Fig. 4a, b),and one shows the hysteresis loop closed at above200mT (Fig. 4d), which is consistent with the presenceof a dominant ferrimagnetic phase. One sample showsthe hysteresis loop closed at above 400mT (Fig. 4c),indicating the presence of high-coercivity components,e.g., partially oxidized coarse-grained magnetite oflithogenic origin and/or antiferromagnetic hematite ofeolian origin. The hysteresis ratios (Mrs/Ms vs. Bcr/Bc)[24] indicate that the average magnetic grain size falls inpseudo-single domain range.

4.3. Paleomagnetic results

The intensity of the natural remanent magnetization(NRM) of the samples was usually of the orders of10−2–10−7 A/m. Progressive demagnetization success-fully isolated ChRM components for most of thesamples after removing a viscous component ofmagnetization. Demagnetization results were evaluatedby orthogonal diagrams [25] and the principal compo-nents direction was computed by a “least-squares

for paramagnetic contribution. The hysteresis loops were measured in

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fitting” technique [26]. For most samples, the high-stability ChRM component was separated between250°C and 585°C (e.g., Fig. 5c, d). However, in somesamples, the high-stability ChRM component wasseparated up to 675°C (e.g., Fig. 5a, b) or up to 60mT(not shown). The behaviors indicate that both magnetiteand hematite dominate the remanence carriers in theXiantai lake sediments. The maximum angular devia-tions (MAD) were smaller than 15°, with 83% of thesamples having MAD values smaller than 10° (Fig. 6c).Total 157 (68%) samples gave reliable ChRM direc-

Fig. 5. (a–d) Orthogonal projections of representative progressive thermal demplanes. The numbers refer to the temperatures in °C. NRM is the natural rem

tions. Virtual geomagnetic pole (VGP) latitudes weredetermined from the ChRM vector directions (Fig. 6d).These VGPs were subsequently used to define thesuccession of magnetostratigraphic polarity in thestudied section (Fig. 6e).

Five magnetozones are recognized in the Xiantaisection: three with normal polarity, N1 (11–19.7m),N2 (37.9–40.3m) and N3 (67.8m to the bottom); andtwo with reverse polarity, R1 (19.7–37.9m) and R2(40.3–67.8m). The Xiantai stone artefact layer occurswithin magnetozone R2, which has a midway depth of

agnetization. The solid (open) circles represent the horizontal (vertical)anent magnetization.

Fig. 6. Magnetic polarity stratigraphy of the Xiantai section: (a) declination (Dec.); (b) inclination (Inc.); (c) maximum angular deviation (MAD); (d)virtual geomagnetic pole (VGP) latitude; (e) magnetic polarity zonation.

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57.51m (Fig. 7). In addition, one short interval ofpossible transitional field behavior, labeled e1 in Fig.6e, are recorded within magnetozone R1 at Xiantai(e1: 26.5–28.25m).

4.4. Palynological results

The pollen concentrations are 326, 331, 432 grainsper gram for samples XT-A, XT-B and XT-C,respectively. The sporopollen of sample XT-A includesherbaceous taxa (such as Artemisia, 36.0%; Chenopo-diaceae, 29.0%; Compositae, 11.7%; Gramineae, 5.3%;Urtica, 5.0%; Thalictrum, 1.3%; Ranunculaceae, 0.7%;Solanum, 0.3%), arbor and shrub taxa (such asEuonymus, 8.0%; Pinus, 0.7%; Betula, 0.7%; Populus,0.7%; Ulmus, 0.3%), and fern Selaginella sinensis(0.3%). The sporopollen of sample XT-B includesherbaceous taxa (such as Artemisia, 47.7%; Composi-tae, 33.3%; Chenopodiaceae, 7.0%; Urtica, 6.7%;Umbelliferae, 0.3%; Ranunculaceae, 0.33%; Sedum,

0.3%), arbor and shrub taxa (such as Euonymus, 3.0%;Populus, 0.7%; Pinus, 0.3%), and fern Lycopodium(0.3%). The pollen of sample XT-C includes herbaceoustaxa (such as Compositae, 45.0%; Artemisia, 33.3%;Urtica, 14.0%; Chenopodiaceae, 5.7%; Ranunculaceae,0.3%; Triticum, 0.3%), and arbor and shrub taxa (suchas Euonymus, 1.0%; Securinega, 0.3%).

5. Discussion

5.1. Stratigraphic correlation and age estimation of theXiantai Paleolithic site

The lake margin sediments at Xiantai mainly consistof clay, silts and fine-grained sands. The yellow fine-grained sands have the highest magnetic susceptibilitieswhile the grey and greyish-yellow clay and silts have thelowest (Fig. 7a, b). The Xiantai site is only ∼200msouthwest of the Xiaochangliang site (Fig. 1), which hasbeen well investigated bio-, litho- and magneto-

Fig. 7. Lithostratigraphy, magnetic susceptibility profiles and magnetostratigraphy of the Xiantai (40°13.126′N, 114°39.623 E) (a, b, c) andXiaochangliang (40°13.166′N, 114°39.736′E) (e, f, g) sections. Geomagnetic polarity timescale (GPTS) [29–31] is shown in panel (d). B, Brunhes;K, Kamikatsura; SR, Santa Rosa; M, Matuyama; O, Olduvai. Note that both sections are capped by the same windblown sequence consisting of theHolocene soil, the last glacial loess and the last interglacial soil. Data of the Xiaochangliang section (e, f, g) are after Zhu et al. [1].

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stratigraphically [1,2,27,28]. Thus, close proximity ofthe two sections facilitated precise stratigraphic corre-lation and effectively minimized uncertainty resultingfrom lateral facies variation.

Stratigraphic correlation between sections at Xiantaiand Xiaochangliang has been well constrained bymagnetic susceptibility, lithology, and stratigraphicmarkers. The two sections were found to have almostidentical sequences containing pronounced sedimento-logical marker layers. For example, several fine-grainedsand layers, associated with high values of magneticsusceptibility (layers A-A′, C-C′, D-D′ and F-F′ in Fig.7) are found at the same position within the polarityframework of each section. In addition, a layer of yellowsilts in the Xiantai section could be correlated with thelayer of yellowish-grey clay in the Xiaochangliangsection, both of which contain mollusc fossils (layerE-E′ in Fig. 7). Therefore, except for its bottom part,the Xiantai section can be safely correlated with theXiaochangliang section on lithological, rock-magneticand biostratigraphical grounds.

The stratigraphic correlation has been furtherstrengthened by magnetic polarity sequences of thetwo sections. Based on the lithological, rock-magneticand biostratigraphical correlation mentioned above, themagnetozones determined for the Xiantai section canreadily be correlated to the geomagnetic polaritytimescale (GPTS) [29–31]. Xiantai magnetozones N1and N2 respectively correspond to the Brunhes chronand the Jaramillo subchron; and magnetozones R1 andR2 to the late Matuyama chron separated by theJaramillo subchron (Fig. 7). In addition, a short intervalof possible transitional field behavior, labeled e1 in Figs.6e and 7c, is recorded in the Xiantai section but not in theXiaochangliang section, which may correspond to theKamikatsura or Santa Rosa events (Fig. 7c, d). Both theXiantai and Xiaochangliang artefact layers occur in agreyish-white clay layer within the same magnetozone,which lies below the distinctive mark layer of yellowsands (layer F-F′ in Fig. 7).

The lacustrine sediments of the Xiaochangliangsection was believed to be virtually continuous, andthe only possible sedimentation gap was found betweenthe top of the lacustrine sediments and the bottom of theeolian deposits [1] (Fig. 7g). This is the case for theXiantai section above magnetozone N3 (Fig. 7a,c).Therefore, Xiantai magnetozone N3 can be safelycorrelated to the Olduvai subchron, which is inaccessiblein the Xiaochangliang section. Three sedimentationgaps, namely, two conglomerate layers (68.15–68.45mand 70.1–70.3m) and an erosional hiatus (69.75m)occur within this magnetozone at Xiantai (Fig. 7a, b, c).

However, these sedimentation gaps do not result in anybias to age estimation of the Xiantai artefact layer.Considering all the above-mentioned evidence together,it is reasonable to conclude that the Xiantai artefact layeris readily contemporary with the Xiaochangliang artefactlayer, which has been estimated to be about 1.36Ma [1].

5.2. Paleoenvironment of the Xiantai site

The fossil pollens recovered from the three selectedsamples are dominated by herbaceous vegetation,namely, 89.3% from sample XT-A (20cm above theXiantai artefact layer), 95.7% from sample XT-B (withinthat layer), and 98.7% from sample XT-C (20cm belowthat layer). Only a small amount of arbor and shrub taxaoccurs in those samples. These palynological features areindicative of a steppe paleoenvironment for the sedi-mentary layers within and just below the Xiantai site, andof a desert steppe paleoenvironment for the sedimentarylayer just above the site.

Among the taxa identified from the three selectedsamples, Artemisia and Chenopodiaceae belong toxerophilous plants; and others, mesophilous plants.The pollen percentages for xerophilous and mesophi-lous taxa are respectively 65.0% and 35.0% for sampleXT-A, 54.7% and 45.3% for sample XT-B, and 39.0%and 61.0% for sample XT-C. The dominant occurrenceof xerophilous and mesophilous taxa suggests theXiantai artefact layer and its overlying and underlyingsedimentary layers for continuing dry paleoclimatesassociated with steppe to desert steppe paleoenviron-ments. In addition, the ratio between Artemisia andChenopodiaceae pollen (A/C ratio), which serves as arelative measure of available moisture [19], is used tofurther unravel the paleoenvironment of the Xiantai site.Samples XT-A, XT-B and XT-C show A/C values of1.24, 6.81 and 5.88, respectively. The combinedevidence suggests increasingly drying paleoclimatesfor the periods from sample XT-C, through sample XT-B, to sample XT-A. This is superimposed on the long-term climate fluctuations of North China, which will beaddressed in the following section.

5.3. Early human adaptability to high northernlatitudes in East Asia

Our new magnetochronological finding of theXiantai site further documents unambiguous presenceof early humans in East Asia at a latitude of at least40°N. This magnetostratigraphic age, along withpreviously published ages of the early PleistocenePaleolithic and hominin sites of Majuangou (1.55–

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1.66Ma) [7], Xiaochangliang (1.36Ma) [1], Banshan(1.32Ma) [7], Donggutuo (1.1Ma) [8], Cenjiawan(1.1Ma) [9] and Maliang (0.78Ma) [8] in the NihewanBasin, and Xihoudu (1.27Ma) [2] and Gongwangling(1.15Ma) [32] in the southern Loess Plateau, implies anexpansion and lengthy flourishing of human groupsfrom northern to north-central China during the earlyPleistocene. Especially, those recent developments inthe timing of the early habitation and stone technologiesin the Nihewan Basin has provided significant insights

Fig. 8. A synthetic diagram related all the well-dated Early Pleistocene hominscale (GPTS), and temporal variations of both terrestrial and marine paleoclimδ13C records of ODP site 1143 [36]. (c) Magnetic susceptibility from the Jiaodfor the Jiaodao section was constructed using magnetic susceptibility boundarage model for Chinese loess/paleosol sequences [45]. (d) Changes in sandsequence in the northern Loess Plateau [34]. (e) Changes in the SIRM100

isothermal remanent magnetization, and SIRM100mT represents the residual SIor hominin sites in North China [1,2,7–9,32]. (g) GPTS [29–31].

into early human adaptability to high northern latitudesin East Asia [1,2,7–9].

Up to now, long-term high-resolution paleoclimaterecords directly retrieved from the Nihewan sedimentarysequence are not available. However, a wealth ofinformation on the late Pliocene–Pleistocene climatevariability in East Asia recovered from terrestrial andmarine archives could provide excellent data forexploring early human adaptability to high northernlatitudes in East Asia.

in or Paleolithic sites in North China to the geomagnetic polarity timeatic proxies in East Asia. (a) δ18O records of ODP site 1143 [44]. (b)ao loess/paleosol sequence in the central Loess Plateau. The time scaleies [22] as age controls, and then interpolated by the stacked grain size-grade particle (>63μm%) content from the Jingbian loess/paleosol

mT/SIRM ratio from the Jingbian sequence (SIRM is the saturationRM after 100-mTalternating field demagnetization) [33]. (f) Paleolithic

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During the Plio-Pleistocene period, North China, aswell as the high-latitude East Asia, experienced climateand environmental variability of global and regionalsignificance, which has been well reflected by manystudies by using multiple climate proxy indicators (Fig.8). For example, mineral magnetic studies of Chineseloess–paleosol sequences provide clear evidence oflong-term aridification and cooling of the Asiancontinental interior over the last 2.6Ma (Fig. 8e) [33],which provides general setting for early human evolutionin this area. However, this long-term variability has beenpunctuated by a series of regional environmental shifts,such as stepwise southerly migrations of the Mu Usdesert lying to the north of the Loess Plateau (2.6, 1.2,0.7 and 0.2Ma) (Fig. 8d) [34], C4 plant expansions in theLoess Plateau region (2.9–2.7Ma, 1.3–1.9Ma, 0.6Ma–present) [35], and δ13C maximum events of the SouthChina Sea (δ13Cmax-I, 50–60ka; δ13Cmax-II, 0.47–0.53Ma; δ13Cmax-III, 0.97–1.04Ma; δ13Cmax-IV,1.55–1.65Ma) (Fig. 8b) [36]. These shifts, whichusually mark significant steps in the development ofglacial or interglacial climate, may serve as episodichabitat disturbances, further providing stress for earlyhuman evolution.

Specifically, Early Pleistocene humans of NorthChina (summarized in Fig. 8f, g), met the long-termclimate variability and some of the episodic environ-mental shifts mentioned above (see Fig. 8), similar to thepattern observed in East Africa [37–39]. In addition,during the Early Pleistocene, the early humans broadlyexpanded their geographic range from the NihewanBasin to the southern Loess Plateau (Fig. 1). Apparently,hominins prior to Homo sapiens were also quiteadaptable to environmental change [40]. To sum up,early humans were able to survive in the hostileenvironment of North China, especially of the high-latitude Nihewan Basin during the Early Pleistocene,when that area is characterized by increased variabilityof paleoenvironment and paleoclimate. This findingdemonstrates that the persistence of early humanlineages in the face of wide environmental change wasimportant in hominins even prior to H. sapiens, thusproviding strong support for the variability hypothesisof human evolutionary history [40–42].

6. Conclusions

(1) Magnetostratigraphic results show that the lacus-trine sedimentary sequence bearing the XiantaiPaleolithic site in the Nihewan Basin, North Chinarecorded the Brunhes chron and the Jaramillo andthe Olduvai subchrons, and successive reverse

polarity portions of the intervening Matuyamachron.

(2) Stratigraphic correlation in terms of lithology,magnetic susceptibility and magnetic polaritysequences between the Xiantai and its adjacentXiaochangliang sections indicates that the Xiantaisite is readily contemporary with the Xiaochan-gliang site (1.36Ma [1]). Early humans of theXiantai site lived in a steppe paleoenvironmentindicated from fossil pollens.

(3) The combined evidence of our study and previouslypublished results documents that early humans ofNorth China were able to adjust to an increasingvariability of paleoclimates and paleoenvironmentsover the Early Pleistocene, lending strong supportfor the variability hypothesis of human evolutionaryhistory [40–42].

Acknowledgements

We are grateful to the Editor, Professor VincentCourtillot, and to two anonymous reviewers for theirhelpful comments and suggestions to improve themanuscript. C. Deng gratefully thanks ProfessorRichard Potts for his stimulating instruction. Paleomag-netic and mineral magnetic measurements were made inthe Paleomagnetism and Geochronology Laboratory(SKL-LE), Institute of Geology and Geophysics,Chinese Academy of Sciences. Sporopollens wereidentified by Dr. Shuqin Zhang at Northeast Instituteof Geography and Agricultural Ecology, ChineseAcademy of Sciences. Financial assistance was provid-ed by NSFC grants 40221402 and 40325011, and CASgrant KZCX-3-SW-150. C. Deng acknowledges furtherpartial support from the Royal Society in the form of aBP Amoco Fellowship.

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