Mid-Pleistocene Environmental Reconstruction Based on Xiashu Loess Deposits in the Yangtze Delta, China

ARTICLE IN PRESS

Quaternary International 135 (2005) 131–137

Mid-Pleistocene environmental reconstruction based on Xiashu loess deposits in the Yangtze Delta, China

Qiang Zhanga,Ã, Cheng Zhub, Tong Jianga, Stefan Beckerc

aNanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, PR China bDepartment of Urban and Resources Sciences, Nanjing University, Nanjing 210093, PR China cDepartment of Geography and Urban Planning, University of Wisconsin-Oshkosh, Oshkosh WI 54901, USA

Available online 30 December 2004

Abstract

A 5.67-m-thick section in loess-like sediments at Xiashu was exposed during archaeological excavation of the Fangniushan Paleolithic site. ESR dating and grain-size analysis suggested that the sediments are wind-blown in origin and were deposited within a period of about 400 kyr. Environmental proxy indicators, including magnetic susceptibility, frequency-dependent magnetism, Kd, median grain size and clay grade percentage show that ﬁve warm and humid climatic periods occurred in the study region in the mid- Pleistocene, namely at 130–90, 192, 195–198, 203–230 and 345–357 ka. These ﬁve periods roughly correspond to the S1, S2, S3, S4 and S5 paleosols in the Chinese Loess Plateau stratigraphy and also to the deep-sea oxygen isotope stages 5, 7, 9, 11, and 13–15. The upper four climatic periods are comparable to the four warm climatic periods recorded in the Laohushan Xiashu loess section. Discovery of stone implements from the sixth and the seventh layers during the archaeological excavation indicates human activities at that time, and the environmental proxies suggest that the environment was suitable for human activities. r 2004 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction sections, especially those that date back to the mid- Pleistocene. Chinese loess-palaeosol proﬁles are now regarded as In this paper, we report the results of a study continental sediments of major importance for the study of a 5.67-m-thick aeolian sediment section exposed of global changes (Liu and An, 1985; An et al., 1991a). during the archaeological excavation of the The magnetic susceptibility signal in these sequences has Fangniushan palaeolithic site (311550N; 1191180E), received notable attention because of its similarity to the 20 m above sea level (a.s.l.) (Fig. 1). Grain-size, deep-sea oxygen isotope record (Steven et al., 1989; magnetic susceptibility, frequency-dependent magnetic Yang, 1991; Zhou et al., 1996). The Xiashu loess in the susceptibility (Xfd) and Kd were measured for the Yangtze Delta region has been studied for about 50 purpose of determining the climatic changes in the years. It is similar in origin to the loess of southern mid-Pleistocene of this region. Based on these data, China (Huang et al., 1988). The source, cause and further studies will be undertaken to investigate the periods of formation of the Xiashu loess have been response of the regional climatic changes to global studied for some time (Huang et al., 1988; Zhang et al., changes. 2000). However, these studies have concentrated on the The vegetation of the study region is characterized by natural sediments, to the neglect of the archaeological mixed deciduous and evergreen forest. Mean annual temperature is 15.5 1C. In summer, the region is dominated by the Subtropical High and the mean 1 ÃCorresponding author. monthly temperature reaches 28.9 C in July. In winter, E-mail address: [email protected] (Q. Zhang). the region is inﬂuenced by the Mongolian High and the

119°E 120°E 121°E 122°E Gaoyou Lake

Huanghai Sea Yangtze River Nanjing City Ning Tangshan site 32°N Jurong City Changdang Lake Fangniushan site Zhen Region East Cheng Lake Huanghai Sea ° 31 N Taihu Lake Dianshan Lake

China Hangzhou Valley Fig. 2. Column section of the Fangniushan paleolithic site, Jurong, the Donghai 0 50 100km 30°N Sea Yangtze Delta.

Fig. 1. Location of the Fangniushan site in the lower Yangtze Delta. one from each of the second, fourth, sixth, and seventh layers. mean temperature is 3.3 1C in January (Jiang, 1991; Yu et al., 2000). The importance of this section lies mainly in the 3. Experimental results following characteristics: (1) It is situated in East China and has a subtropical monsoon climate. It is 3.1. Numerical dating synoptically sensitive because it is located along the transition from subtropical to temperate climatic ESR dating yielded 162732; 192738; 203751 and zones. (2) It contains exceptional information 345769 ka for layers 2, 4, 6 and 7, respectively (Fig. 2). about palaeolithic human activities. Thus, it may help Assuming that 0.73 Ma is the boundary between the to establish the nature of the relationship between middle and upper Pleistocene, the section provides a climatic evolution and human activities in the record of environmental evolution during the mid- mid-Pleistocene. Suchstudies will form an extension Pleistocene. to earlier studies of the relationship between human activities and climatic evolution in the Neolithic 3.2. Grain size (Yu et al., 2000). Four grain-size parameters, MZ (mean grain size), s1 (sorting coefficient), SK1 (skewness), and KG (kurtosis), 2. Materials and methods were determined using conventional methods (Xu et al., 1992). Y1 is a parameter related to the sedimentary The section was divided into seven layers according to environment, determined as Y 1 ¼À3:5688MZ þ 2 the colour of the sedimentary materials (Fig. 2). 3:7016s1 À 2:0766SK1 þ 3:1135KG (Xu et al., 1992). Forty-two samples were taken at intervals of either 10 The maximum value of Y1 is À4.92 (Table 1), indicating or 20 cm from the bottom to the top of the section. that the sediment is wind-blown in origin. ESR dating, Low-frequency magnetic susceptibility was determined field investigation and earlier researchresults ( Huang et in m3/kg using a Bartington magnetic susceptibility al., 1988; Wang and Cao, 1996) support this interpreta- meter (MS2) and probe (MSF). The sensor emitted tion. The mean grain size of the sediments is a 1-Oersted alternating magnetic field and the 2.7–15.4 mm, which is much finer than aeolian sands operating frequency of the probe was 580 Hz and similar to paleosols. Standard deviations s1 are (Thompson and Oldfield, 1986). Particles coarser than between 1.2 and 3.7, a well-sorted to poorly sorted 45 mm were first separated through a gravity screen range, reflecting an important feature of aeolian box (SFY-A), while others were separated using an sediment (Sun et al., 2000). The values of SK1 are optical separator-size analyzer (SKC-2000). ESR À0.57–0.6, indicating a range from negative to positive dating was performed in the Structure Center of China skewness. KG values (0.52–1.79) indicate blunt to peaky Science and Technology University on four samples, kurtosis. The variance in these parameters suggests that ARTICLE IN PRESS Q. Zhang et al. / Quaternary International 135 (2005) 131–137 133

Table 1

Grain-size parameters and the Y1 value of the samples from the Fangnushan Paleolithic site

Sample no. 5% 16% 25% 50% 75% 84% 95% Mz s1 SK1 KG Y1

1 4.9 6.4 6.8 8.4 9.5 9.7 9.9 8.1 1.6 À0.3 0.8 À16.9 2 5.2 6.1 6.4 6.5 9.5 9.7 9.9 7.4 1.6 0.6 0.6 À16.4 3 2.6 6.1 6.5 7.5 8.7 9.1 9.7 7.6 1.8 À0.2 1.3 À10.0 4 5.5 6.2 6.4 6.8 9.3 9.6 9.9 7.5 1.5 0.5 0.6 À17.6 5 4.7 5.4 5.7 6.9 9.4 9.6 9.9 7.3 1.8 0.2 0.6 À12.1 6 5.2 5.8 6.3 8.1 9.3 9.6 9.8 7.8 1.7 À0.3 0.6 À15.4 7 5.9 6.4 6.6 7.5 9.2 9.5 9.8 7.8 1.4 0.3 0.6 À19.3 8 4.4 5.5 6.0 7.7 9.4 9.6 9.9 7.6 1.9 À0.1 0.7 À12.1 9 5.0 5.9 6.3 7.6 9.3 9.6 9.9 7.7 1.7 0.0 0.7 À15.3 10 5.0 5.6 6.0 7.0 9.2 9.5 9.8 7.4 1.7 0.2 0.6 À14.1 11 5.1 5.8 6.2 7.2 9.5 9.6 9.9 7.6 1.7 0.2 0.6 À15.0 12 5.0 5.5 5.8 7.3 8.7 9.3 9.8 7.4 1.7 0.0 0.7 À14.0 13 5.1 5.9 6.3 7.7 7.4 9.6 9.9 7.7 1.6 À0.0 1.8 À12.0 14 4.9 5.5 5.8 7.4 10.0 9.4 9.8 7.4 1.7 À0.0 0.5 À14.0 15 3.6 5.2 5.4 5.8 8.5 9.1 9.8 6.7 1.9 0.5 0.8 À8.8 16 4.6 5.2 5.5 6.5 8.6 9.2 9.8 7.0 1.8 0.3 0.7 À11.8 17 5.9 5.7 7.1 8.5 9.4 9.2 9.9 7.8 1.5 À0.5 0.7 À16.5 18 4.8 5.5 5.9 7.7 9.1 9.4 9.8 7.6 1.8 À0.2 0.7 À13.2 19 5.1 5.4 5.6 6.6 8.6 9.2 9.8 7.1 1.7 0.4 0.6 À13.7 20 4.7 5.3 5.6 7.9 9.5 9.7 9.9 7.6 1.9 À0.2 0.5 À11.8 22 0.0 0.8 5.5 7.7 9.4 9.6 9.9 6.0 3.7 À0.6 1.0 34.0 25 1.8 5.5 5.9 7.9 9.4 9.6 9.9 7.7 2.3 À0.3 1.0 À4.9 26 2.8 5.3 5.6 7.1 9.3 9.6 9.9 7.3 2.1 À0.0 0.8 À6.8 27 2.9 5.2 5.5 7.2 9.0 9.4 9.8 7.2 2.1 À0.1 0.8 À6.9 28 4.9 5.8 6.5 7.7 8.8 9.2 9.8 7.5 1.6 À0.1 0.9 À14.6 29 4.4 5.5 5.9 9.0 9.5 9.7 9.9 8.1 1.9 À0.7 0.6 À12.3 30 4.9 5.4 5.7 7.7 9.4 9.6 9.9 7.6 1.8 À0.1 0.6 À13.0 31 5.1 5.5 5.8 7.7 9.5 9.7 9.9 7.6 1.8 À0.1 0.5 À13.9 32 5.1 5.5 5.8 8.9 9.5 9.7 9.9 8.0 1.8 À0.6 0.5 À14.1 33 5.9 6.6 7.0 8.9 9.5 9.7 9.9 8.4 1.4 À0.5 0.6 À19.7 34 5.2 5.7 6.3 7.6 9.4 9.6 9.9 7.6 1.7 À0.0 0.6 À14.8 35 6.1 6.7 7.1 7.9 9.5 9.7 9.9 8.1 1.3 0.1 0.6 À20.8 36 5.2 5.7 6.2 8.2 9.4 9.6 9.9 7.8 1.7 À0.3 0.6 À15.0 37 5.0 5.5 5.8 8.6 9.5 9.7 9.9 7.9 1.8 À0.5 0.6 À13.5 38 5.3 6.1 7.1 9.2 9.6 9.8 10.0 8.4 1.6 À0.7 0.8 À16.1 39 6.2 6.7 7.1 9.1 9.6 9.7 9.9 8.5 1.3 À0.6 0.6 À20.8 40 6.2 7.1 7.5 8.9 9.5 9.7 9.9 8.5 1.2 À0.4 0.8 À21.8 41 5.1 5.5 5.8 8.0 9.4 9.6 9.9 7.7 1.8 À0.2 0.5 À14.1 42 5.1 5.5 5.7 7.9 9.5 9.7 9.9 7.7 1.8 À0.1 0.5 À13.7

Samples are numbered from top to bottom as indicated in Fig. 2. Grain-size distribution is given in (g). the Xiashu loess has been modified by secondary At the same time, the effect of climatic zonality with processes, especially pedogenesis. The obvious contrast conditions southward warmer and more humid is between the Xiashu loess and the loess of northern reflected in the amount of secondary clay minerals. This China is the evidence for strong pedogenetic modifica- is in line withthegrain-size analyses performed on tion of the Xiashu loess. The origin and the formation Xiangyang section of Xuancheng in Anhui province by processes also appear to have been more complex than Li et al. (1997). those of the loess of northern China. In order to quantify the effects of these differences, 3.3. Magnetic susceptibility grain size data for aeolian sediments from several typical loess sections from northto southacross Chinawere The concentration of magnetic minerals in sediments collected (Table 2, Fig. 3). These results show that the may be reflected by low-field magnetic susceptibility percentage in the coarse sand grade decreases from values (Nawrocki et al., 1996). In some sedimentary north to south, and the percentage of fine sand and clay- rocks, the distribution of magnetic susceptibility (MS) size material increases from north to south, as shown by carriers depends on the climatic conditions in which they Liu and An (1985). These data indicate that the vigor of are deposited. MS has been used as a palaeoclimatic the winter monsoon decreased southward across China. indicator particularly in loess-palaeosol sequences (e.g. ARTICLE IN PRESS 134 Q. Zhang et al. / Quaternary International 135 (2005) 131–137

Table 2 Comparison of grain-size data taken from aeolian sediment in some typical sections from northto southacross China

Loess Grain size (%)

Xifeng loess [1] (Mid-Pleistocene) 40.05 mm 0.05–0.005 mm o0.005 mm 23.72 57.54 18.74

Luochuan loess [2] Upper part of Lishi loess (mid-Pleistocene) 10 63.7 26.3 Lower part of Lishi loess (mid-Pleistocene) 5.3 62.6 31.2 Xiashu loess of Dagang, Zhenjiang [3] 1 layer 0.82 63.58 35.60 2 layers 0.78 65.48 33.74 3 layers 0.65 50.54 48.82 Xiangyang section, Xuancheng, Anhui [4] 6 layers 3.09 43.56 53.35 9 layers 2.06 42 59 Fangniushan section, Jurong, Jiangsu 6.2 43.3 49.5

[1] refers to Working Group of Geology and Hydrology of Liaoning Province (1983); [2] refers to Liu and An (1985); [3] refers to Zheng et al. (1987); [4] refers to Li et al. (1997).

Fig. 3. Location of the loess sections quoted in Table 2.

Heller and Liu, 1986; Maher and Thompson, 1991). The grain size is not only a product of wind transport, but magnetic susceptibility of the Xiashu loess has also been also pedogenesis and chemical weathering following used as an environmental indicator (Li, 1993; Lu et al., sedimentation. These processes allow enhancement of 2000; Zhang et al., 2000). the percentage of finer particles (Derbyshire et al., 1995). The MS record at the Fangniushan site shows three Fig. 4 suggests that, despite the effects of pedogenesis peaks and three troughs (Fig. 4). The most obvious MS and post-depositional chemical weathering on the values are two peaks and one trough. Small fluctuations Xiashu loess, the trend of the median grain size curve also occur within both of these sets of peaks, indicating is in part negatively correlated with MS, although this climatic instability. In recent studies of the loess- relationship is not as clear at Xiashu as it is in the loess- palaeosol sequences of northern China, particle size, palaeosol sequence in northChina. and particularly the median grain size, has been widely Environmental magnetism properties of the loess used as a proxy measure of the vigor of the northwest indicate that, in contrast with MS, the frequency- winter monsoon (An et al., 1991b; Derbyshire et al., dependent susceptibility ððKLF À KHFÞ=KLF 100% ¼ 1995; Porter and An, 1995). At Xiashu, however, this X fd%Þ has unambiguous environmental meaning (Liu indicator must be applied withsome caution because of et al., 1990). Frequency-dependent susceptibility values the evidence of grain size changes induced by strong (Xfd) denote the amount of fine ‘‘viscous’’ ferromagnetic pedogenesis and secondary physical and chemical (magnetite or maghaemite) grains around 0.02 mmin weathering processes. In the conditions at this site, diameter (Thompson and Oldfield, 1986; Li and ARTICLE IN PRESS Q. Zhang et al. / Quaternary International 135 (2005) 131–137 135

Fig. 4. Environmental proxies at the Fangniushan Paleolithic section. Magnetic susceptibility, frequency-dependent magnetic susceptibility (Xfd), median grain size (Md), silt-clay ratios, and percentage of clay content. The shaded zones show the ﬁve warmer and more humid climatic periods. Lithology symbols as in Fig. 4.

Oldfield, 1993). While MS may be a clearer indicator of climatic periods during the period 400–130 ka. These are strongly changing palaeoclimates, frequency-dependent 130–90 ka; 192 ka; 195–198 ka; 203–230 ka and susceptibility is sensitive to temperate climatic fluctua- 345–357 ka, broadly corresponding to the five palaeosol tions, and it can reflect many details not detected by MS layers S1, S2, S3, S4 and S5 (Fig. 5). They also roughly (Liu et al., 1990). This property of the frequency- matchthedeep-sea (Hole V28-239) oxygen isotope dependent susceptibility is revealed in Fig. 3.Asthe stages 5, 7, 9, 11 and 13–15, respectively (Huang et al., curves show, there are several Xfd peaks at depths of 1988). The uppermost four warmer and more around 1.5–2.5 m, indicating warmer and more humid humid climatic periods roughly correspond to the climatic conditions. In comparison, the MS values are uppermost four buried palaeosols in the Laohushan low and the curve is rather unambiguous. The Xfd Xiaoshu section (Fig. 5). Kd values are notably low changes match those in the clay percentages, a finding while the clay content and frequency-dependent MS consistent withtheproduction of finer ‘‘viscous’’ have obvious peaks in the second warm–humid ferromagnetic minerals during pedogenesis. This result climatic period, an interpretation that receives some has also been found in the loess-palaeosol sequences of support from the d18O records of the stalagmite northChina( Liu et al., 1990). On the basis of this in the Tangshan H. Pithecanthropus cave in Nanjing evidence, it is tentatively concluded that the clay content (Wang et al. 1999). In the same period, at 200 ka BP, in the Xiashu loess may be used as an indicator of the typical fauna in the north-east of China was of the climatic changes, although further study will be needed Anping type, withtypical species, Macaca robustus, to test this supposition. Dicerorhinus Kirchborgensis, and Panthera younqi. The Kd value (the ratio of silt content to that of clay, This is also indicative of a warm and humid environ- Kd ¼ (60–8 mm/o5 mm)) is accepted by some workers as ment (You and Yu, 1989). Taken together, the an indicator of formative environments within the loess- evidence of climatic change in the study region is in palaeosol sequences of northChina (e.g. Huang et al., general conformity with the established record of global 1988; Zhang et al., 2000). HighKd values indicate arid climatic changes. and cold environments, and low Kd represent warmer and more humid conditions (Liu and An, 1985; Zhang et al., 2000). There is a negative correlation between the 4. Discussion and conclusions Kd values and clay content, frequency-dependent susceptibility, and MS. These environmental proxy The Xiashu loess has undergone strong pedogenesis indicators, together with ESR dating, combine to that produced an abundant fine grain-size component. indicate at least five relatively warmer and more humid Pedogenic processes distinguish the Xiashu loess from ARTICLE IN PRESS 136 Q. Zhang et al. / Quaternary International 135 (2005) 131–137

Fig. 5. Comparison between the Fangniushan Paleolithic site section, Xiashu section of Laohushan, Nanjing, and Luochuan loess section (after Huang et al., 1988). the typical loess-palaeosol sediment section of north suggests that the Xiashu loess is a consistent indicator of China. global changes and that the climatic changes in the study Grain size analysis suggests that the sediments at region reflect Asian summer monsoon changes. The Xiashu consist of loess. However, the broader range of Ningzhen region lies in the Yangtze Delta, the transi- variation of the grain size parameters suggests that the tional zone from subtropical to temperate climate, Xiashu loess is more complicated in origin. The clay which is largely controlled by different dominant air content in the Xiashu loess serves as a proxy indicator of masses. Suchregions are particularly sensitive to relatively strong pedogenesis and/or chemical weath- climatic changes. The Xiashu aeolian sediments are ering. To a certain degree, it is also an indicator of widespread in the Yangtze Delta, thus providing climatic changes, because the clay content increases in important regional data on past climatic changes. They known periods of warmer and more humid climate. At are worthy of study designed to construct a more the same time, stronger pedogenesis is marked by the complete climate-time sequence, and to help to define greater abundance of finer ‘‘viscous’’ ferromagnetic more precisely the relationship between regional climatic (magnetite or maghaemite) grains (Zhou et al., 1990; evolution and global changes, which includes broader Hus and Han, 1992), which explains the high frequency- influences, such as the uplift of the Qingzang Tibet dependent susceptibility values. However, further study Plateau and variations in the southeast (summer) is needed in order to test the relationship. monsoon. ESR dating, MS, frequency-dependent susceptibility, A number of stone implements, discovered during median grain size, Kd values, and clay percentage reveal archaeological excavation in the sixth and seventh five warmer and more humid climatic periods at 130–90; layers, indicate human activity (about 340–360 ka 192; 195–198; 203–230 and 345–357 ka, generally according to ESR dating). Proxy indicators suchas corresponding to the palaeosol layers OIS 5, 7, 9, 11 those used here indicate that conditions were warm and and 13–15. The periods 130–90; 192; 195–198 and humid at that time and so were suitable for human 203–230 ka correspond to the uppermost four buried occupation. Researchat the H. pithecanthropus cave palaeosols at the Laohushan Xiashu loess section. This (Zhu et al., 1998) has suggested that the region in the ARTICLE IN PRESS Q. Zhang et al. / Quaternary International 135 (2005) 131–137 137 mid-Pleistocene (350 ka) was characterized by decid- Liu, T.S., An, Z.S., 1985. 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