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JOURNAL OF QUATERNARY SCIENCE (2004) 19(6) 529–535 Copyright ß 2004 John Wiley & Sons, Ltd. Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jqs.849

Environmental change and cultural response between 8000 and 4000 cal. yr BP in the western Loess Plateau, northwest China CHENGBANG AN,1* ZHAODONG FENG1,2 and LINGYU TANG3 1 Key Laboratory of Western China’s Environmental Systems, MOE, Lanzhou University, Lanzhou 730000, China 2 Department of Earth and Environmental Studies, Montclair State University, Upper Montclair, NJ 07043, USA 3 Nanjing Institute of Geology and Paleontology, CAS, Nanjing 210008, China An, C., Feng, Z. and Tang, L. 2004. Environmental change and cultural response between 8000 and 4000 cal. yr BP in the western Loess Plateau, northwest China. J. Quaternary Sci., Vol. 19 pp. 529–535. ISSN 0267-8179. Received 30 September 2003; Revised 4 March 2004; Accepted 20 March 2004

ABSTRACT: Two ancient swamps in the western Loess Plateau, northwest China record the climate history between 8000 and 4000 cal. yr BP. Grain size, CaCO3, organic matter, mollusc fauna and pollen assemblages show that climate was wet between 8300 and 7400 cal. yr BP, distinctly humid and warm between 7400 and 6700 cal. yr BP, semi-humid from 6700 to 6300 cal. yr BP, and semiarid between 6300 and 4000 cal. yr BP. The temporal and spatial distribution of archaeological sites shows that the prosperity of the neolithic cultures in the western part of the Chinese Loess Plateau did not appear until the climate changed to semi-arid, implying that the semi-arid climate was more favourable than wet and humid climate to neolithic peoples, whose subsistence was based on cereals adapted to arid environments. Copyright ß 2004 John Wiley & Sons, Ltd. KEYWORDS: environmental change; neolithic cultural response; western Loess Plateau.

Introduction Cultural evolution is affected not only by a variety of social factors but also by environmental change (Sableff, 1995; deMenocal, 2001; Weiss and Bradley, 2001; Staubwasser et al., 2003). Excellent examples show that climatic perturbations, especially prolonged drought and cold spells, are associated with societal dislocations. For example, a joint study on climatic and archaeological histories of the Akkadian empire suggests that a sudden climatic shift to more arid conditions caused the rapid collapse of the empire at ca. 4200 cal. yr BP (Weiss et al., 1993; Cullen et al., 2000). It has been suggested that recurrent patterns of drought played an important role in the complex history of the Maya Cultures (Hodell et al., 1995, 2001; Haug et al., 2003). In China, at 4000 yr BP a cold event may have caused the collapse of the neolithic cultures (Wang, 1992; Zhang et al., 1997; Shui, 2001; Wu and Liu, 2001). However, is the role of environmental change in the cultural evolution limited to dry or cold events? What is the effect of wet and warm climatic changes on culture? To address these problems, the relationship between environmental change and cultural evolution during 8000–4000 cal. yr BP in the western part of the Chinese Loess Plateau has been examined. A long-held perspective on the interaction between climate and human history is that warm and wet conditions have facili* Correspondence to: ChengBang An, Environment and Resources College, Lanzhou University, 730000 China. E-mail: [email protected]

tated the evolution of prehistoric cultures in China (Wang, 1992; Wang et al., 1993; Mo et al., 1996). Reliable palaeoecological data, particularly pollen analysis of deposits, are needed to test this hypothesis. Reconstructions of long-term palaeoenvironment are often limited in scope (Steig, 1999). Most reconstructions of prehistoric cultures are based on the excavation and interpretation of individual archaeological sites. Integrative studies of multiple sites, multiple proxy records, and larger areas over longer time periods can dramatically improve these interpretations (Redman, 1999; Mann, 2002). Moreover, a given cultural phenomenon may appear across a broad range of environments, or may be limited to a narrow range of environments and time periods. Reliable palaeoecological studies can help to differentiate these cases. Here we present multiple proxy environmental records and large-area archaeological analyses of prehistoric cultures between 8000–4000 cal. yr BP in the western part of the Chinese Loess Plateau. The earliest known neolithic culture in the western Loess Plateau is the Dadiwan Culture (7800–7350 cal. yr BP), followed by the Yangshao Culture (6800–4900 cal. yr BP), Majiayao Culture (5300–4300 cal. yr BP) and the Qijia Culture (4300–3900 yr BP) (Shui, 2001).

Study area The study area is located in the western Loess Plateau (Fig. 1), where agriculture is strongly subjected to climatic

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and originally developed on the first terrace of a small river (Fig. 1). Samples were collected at 5-cm intervals (the top 50 cm of the section was sampled at 10-cm intervals) for a total of 85 samples. The Dadiwan profile (105  540 53.300 E, 35  0000 47.300 N) is located in a valley approximately 1 km wide. The 5-m profile, exposed by riverine erosion, initially developed on the first terrace of a tributary of the Hulu River (Fig. 1) at an elevation of 1400 m a.s.l.. Today, the mean annual temperature is 8–9  C, and the mean annual rainfall is 450–500 mm. Stratigraphical subdivisions are described in Fig. 2. A total of 250 samples were taken at 2-cm intervals along the profile.

Methods Figure 1 Map showing the study area and sites. Shaded area indicates the geographical extent of the Loess Plateau

and hydrological conditions. Today, the mean annual temperature ranges from 6  C to 10  C and the mean annual precipitation is between 300 and 500 mm with an aridity index between 1.2 and 2.5. This area is hilly with dispersed and sporadic woodlands. The elevation varies from 1400 to 2200 m. This study focuses on the sediment sequences from swamp– wetland in the western part of the Loess Plateau. Most of the swamps developed between 10 000 and 4000 cal. yr BP (An et al., 2003; Feng et al., in press). Two profiles, Sujiawan and Dadiwan, have been studied. The Sujiawan profile (104  310 2200 E, 35  320 2000 N) is located in a broad valley at an elevation of 1700 m a.s.l. Today, the mean annual temperature is 6.2  C and the mean annual precipitation is 425 mm. The naturally exposed profile is 4.5 m thick

Carbonate content was measured using a Bascomb Calcimeter, and organic matter (OM) was measured by the titration method (Singer and Janitzky, 1987). The particle size of bulk samples was measured using a Malvern Mastersizer 2000 laser diffraction particle size analyser. The procedures for fossil pollen analysis involve treating 40 g of sediment with 36% HCl, concentrated hydrofluoric acid (HF), heavy-liquid flotation (twice, using potassium iodide, ideal specific gravity 1.9, and repeated HF treatment if necessary). Exotic marker grains of Lycopodium tablets were added to each sample for the calculation of pollen concentrations (Wang et al., 1995). Charcoal fragments were dated using AMS equipment at the University of Arizona and Beta Analytic, and dates were converted to calendar ages using the computer program CALIB Rev. 4.1.2 (Stuiver et al., 1998) (Table 1). A linear interpolation between dates from the same lithological unit was used to assign ages.

Figure 2 Variations of proxies in Sujiawan section. The shaded area shows the variations discussed in the text during the mid-Holocene. OM, organic matter Table 1 AMS 14C dates of the two sections Section Sujiawan Sujiawan Sujiawan Sujiawan Sujiawan Dadiwan Dadiwan Dadiwan Dadiwan

Depth (m) 0.90 2.95 3.05 3.55 4.10 1.70 1.90 3.56 4.72

Copyright ß 2004 John Wiley & Sons, Ltd.

Laboratory No.

Dating Material

Beta-181611 Beta-181612 AA44885 AA44886 AA44886 AA44889 AA44887 AA43798 AA49110

Charcoal Charcoal Charcoal Charcoal Charcoal Charcoal Charcoal Charcoal Charcoal

14

C age (yr BP)

1930  40 3730  40 3805  45 5881  59 8885  55 4955  44 5441  51 7539  49 11190  450

Cal. age (yr BP) (1 sigma) 1922–1824 4147–3988 4245–4093 6777–6642 10156–9875 5729–5612 6291–6197 8388–8334 13 788–12 860

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Figure 3 Pollen percentage assemblage and pollen concentration of Sujiawan section

Results Sujiawan profile—analysis of environmental proxies The wetland–swamp layer in the Sujiawan section, a grey-blue clayey silt unit (about 1 m thick), was formed approximately between 10 000 and 4000 cal. yr BP. It is characterised by a high concentration of carbonate, up to greater than 70% with an average of 50% (Fig. 2). The content of organic matter is relatively high, ca. 2%. The grain size is finer than other stratigraphical units, as indicated by the low percentage of coarse (>63 mm) and the high percentage of fine (