Earliest Use of Birch Bark Tar in Northwest China: Evidence from Organic Residues in Prehistoric Pottery at the Changning Site
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Vegetation History and Archaeobotany https://doi.org/10.1007/s00334-018-0694-7 ORIGINAL ARTICLE Earliest use of birch bark tar in Northwest China: evidence from organic residues in prehistoric pottery at the Changning site Huiyun Rao1 · Qianqian Wang2 · Xiaoyan Ren2 · Zhaoxia Zhang1 · Wanxia Huang3 · Qingxi Yuan3 · Xiaochenyang Jiang1,4 · Yimin Yang4 Received: 7 May 2017 / Accepted: 30 July 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract The analysis of organic residues in pottery can provide abundant information on the lives of ancient people, including the natural resources consumed, the techniques applied, the functions of pottery, and so on. In this paper, a variety of meth- ods, including FT-IR (Fourier transform infrared spectroscopy), GC–MS (gas chromatography-mass spectrometry), SEM (scanning electron microscopy) and SR-μCT (synchrotron radiation micro-computed tomography), have been employed to characterize the carbonized residues from an amphora, unearthed from the Changning site, Qinghai Province, Northwest China. The pottery residues were identified as birch bark tar, so ancient people in China could have used the particular local plant resources, birch bark, to produce tar as early as the Qijia cultural period (c. 4,000–3,500 BP). The birch bark tar could have been used to make composite tools discovered at the Changning site, and the amphora has probably been used for tar production. This, to our knowledge so far, is the earliest evidence for the use of birch bark tar in China. Due to the special geographical location of the Gansu-Qinghai Region, and the transition of subsistence strategy during the Qijia cultural period, the production and utilization of birch bark tar could not rule out the possibility of western influence, which needs further evidence. Keywords Birch bark tar · Pottery function · Carbonized residues · Qijia culture Introduction 1999a; Mottram et al. 1999), dairying (Copley et al. 2003; Evershed et al. 2008; Salque et al. 2013), brewing (Correa- Pottery wares, of different types and functions, are amongst Ascencio et al. 2014) and dyeing (James et al. 2009), have the most common artifacts found at archaeological sites been conducted in pottery vessels, and organic matter pre- across China since the Late Glacial (Kuzmin 2006). A served as carbonized surface residues or absorbed residues variety of processes, such as cooking (Dudd and Evershed in porous ceramic matrices. The characterization of organic residues in pottery can provide valuable information about Communicated by J. Kitagawa. the natural resources consumed or used by ancient people, the techniques applied to prepare all these products and also * Yimin Yang the functions of related pottery. [email protected] Pottery residues have been observed and studied since 1 Key Laboratory of Vertebrate Evolution and Human Origins the end of the 19th century, and research in the area has of Chinese Academy of Sciences, Institute of Vertebrate greatly expanded in recent decades due to improvements in Paleontology and Paleoanthropology, Chinese Academy analytical tools, such as chromatographic and mass spec- of Sciences, Beijing 100044, People’s Republic of China trometric techniques (Evershed et al. 1991; Charters and 2 Qinghai Provincial Institute of Cultural Relics Evershed 1997; Regert et al. 2001; Stott et al. 2003; Hansel and Archaeology, Xining 810007, People’s Republic of China and Evershed 2009; Correa-Ascencio and Evershed 2014). 3 Institute of High Energy Physics, Chinese Academy Fourier transformed infrared spectroscopy (FT-IR) and of Sciences, Beijing 100049, People’s Republic of China mass spectrometric methods [direct inlet electron ionization 4 Department of Archaeology and Anthropology, University mass spectrometry (DI-MS), direct temperature-resolved of Chinese Academy of Sciences, Beijing 100049, mass spectrometry (DT-MS), pyrolysis-mass spectrometry People’s Republic of China Vol.:(0123456789)1 3 Vegetation History and Archaeobotany (Py-MS) etc.] have been employed as preliminary analyses microscopic observations (scanning electron microscopy, of organic residues and could provide the general chemi- SEM, and synchrotron radiation micro-computed tomog- cal information of residues to guide further investigations raphy, SR-μCT), and analytical techniques (FT-IR and (Oudemans and Boon 1991; McGovern et al. 1996; Regert GC–MS). and Rolando 2002; Oudemans et al. 2007; Kaal et al. 2014). Because of their hydrophobicity and thermal resistance, lipids are more likely to be preserved in pottery, and gas Site description chromatography-mass spectrometry (GC–MS) is the most commonly used technique for lipid analysis (Evershed Within the valley of the Huangshui River, the Changn- et al. 1990, 2002; Evershed 2008; Heron et al. 2016). With ing site is situated on the second terrace of the Beichuan the identification of specific biomarkers, a wide range of River, which is approximately 100 km east of Qinghai lipid commodities have been revealed, including animal Lake, Northwest China (Fig. 1). The valley of the Huang- fats (Evershed et al. 2002; Poulain et al. 2016), plant oils shui River has a semi-arid plateau continental climate (Romanus et al. 2007; Dunne et al. 2016), beeswax (Ever- and diverse ecological landscapes, which include desert shed et al. 1997; Heron et al. 2015), epicuticular leaf waxes steppe, steppe, meadow steppe and forest, alpine meadow, (Charters and Evershed 1997; Dunne et al. 2016), birch glaciers, and so on (Wang 2015). Combining fauna with bark tar (Lucquin et al. 2007; Mitkidou et al. 2008), pine pollen data, it can be inferred that the environmental con- resin (Colombini et al. 2005; Jerkovic et al. 2011) and so ditions of the Changning site were similar to today’s tem- on. Recently, gas chromatography-combustion-isotope ratio perate steppe-forest landscape (Li 2012). mass spectrometry (GC-C-IRMS) has also been applied to In 2006, a total area of 3,000 m2 was unearthed, includ- calculate isotope ratios of individual fatty acids in organic ing 15 houses, 150 pits and cellars, and 6 tombs. Vari- residues, and has enabled the differentiation of ruminant ous artifacts were found, such as pottery wares, stone adipose, ruminant dairy fats, non-ruminant adipose, fresh- tools, jade articles, bronze vessels, bone implements and water and marine resources (Evershed et al. 2008; Craig so on. Storage and cooking vessels were the main pot- et al. 2011; Heron et al. 2015; Nieuwenhuyse et al. 2015; tery collections (QPICRA 2006). Besides artifacts, ani- Oras et al. 2017). Immunological methods and proteomic mal bones (sheep, cattle, pig, horse, dog etc.) and plant approaches have been conducted to identify the proteina- remains (Setaria italica—foxtail millet, Panicum mili- ceous residues (Craig and Collins 2000; Wiktorowicz et al. aceum—broomcorn millet, Triticeae tribe etc.) were also 2017). discovered, indicating that both agriculture and animal The Changning site (dated to approximately husbandry have played important roles in the Changning 4,000–3,500 BP; QPICRA 2006) is a large settlement of people’s lives (Li 2012; Li et al. 2013; Wang 2015). As a the Qijia culture in Qinghai Province, Northwest China large settlement of the Qijia culture, the Changning site (QPICRA 2006; Li 2012). A two-handled amphora was developed over a transition period between agriculture and unearthed in a pit at this site, with black charred residues pastoralism, and also within an intermediate period from inside. In this paper, an interdisciplinary methodology has the Neolithic era to the Bronze Age, which is an important been developed to analyse the residues in this amphora, time span for the formation of Chinese civilization (QPI- in order to identify their nature and origins and to reveal CRA 2006; Li 2012). the functions of related pottery. This method comprises Fig. 1 Location of the Changn- ing site, Datong County, Qing- hai Province, Northwest China 1 3 Vegetation History and Archaeobotany Materials and methods Fragments of a two-handled amphora with a red coarse clay body were unearthed from pit H34 at the Changning site. The wall thickness was approximately 1 cm. Figure 2 shows the inner and outer surfaces of two shards S1 and S2 of this amphora. Black residues with a variable thickness were observed on the inner surfaces of these shards (Fig. 2b, d), while black soot traces were detected near the rim on the outer surfaces of the shards (Fig. 2a, c). At the bottom of the amphora, some brown or black charred lumps were found. Fig. 3 The archaeological samples analysed; a the inner surface of The black residues adhering to the inner surface of shard S3 shard S3, where surface residues were sampled (sample label ISR). were scraped with a sterilized blade and collected for further The outer surface residues were also sampled as the control sample (labeled as OSR). Scale bar 4 cm. b The charred lumps (sample label analyses (labelled as ISR) (Fig. 3a), while the outer surface CL), which were sampled from the bottom of the amphora. Scale residues were collected in the same manner as the control bar 1 cm sample (labelled as OSR). Charred lumps were also sampled (labelled as CL) (Fig. 3b). Fresh modern birch bark (Betula platyphylla, plant No. UCAS 20140102, labelled as MB1) Rao et al. (2017).The pottery residue samples and modern was collected as a reference sample from the campus of Uni- birch bark reference sample were further analysed with a versity of Chinese Academy of Sciences. To obtain the mod- 7890A gas chromatograph and a 5975C mass detector in ern charred reference sample (labelled as MB2), the birch 70 eV electron impact mode (GC–MS). The procedure was bark was heated in a muffle furnace at 250 °C for 4 days. modified from procedures used by Regert et al. (2003b), Charred lumps (CL) and inner surface residues (ISR) Mitkidou et al. (2008) and Rao et al. (2017). In brief, CL, were analysed with a Nicolet 6700 (Thermo Scientific) ISR, OSR and MB1 were extracted using chloroform/meth- FT-IR spectrometer.