CHEMICAL CHARACTERISATION OF SURFACE ORGANIC RESIDUES ON ARCHAEOLOGICAL POTTERY: INVESTIGATING VESSEL USE, PALAEODIET, AND THE ACCURACY OF 14C-DATES

考古陶器中保存着两大类有机残留物，即：内表面可见的沉积物和器壁内吸收的残留物。这两个类别都代表了在容器中加工的有机天然材料的残留物，最常见的出现在被广泛归类为“烹饪”锅的容器上，尽管容器可能被用于涉及加热有机材料的广泛活动。对这类残留物感兴趣的一个主要领域是利用其生物分子和稳定的同位素组成进行调查的可能性：容器的使用、在容器中加工的商品的性质、饮食成分和农业活动。被吸收的残留物比表面残留物得到了更广泛的化学分析和应用，越来越多的动植物产品得到承认，重大的考古问题也得到了解决。被吸收的残留物的吸引力在于它们出现的频率很高，例如，平均约50%的英国烹饪锅含有与容器使用寿命有关的大量有机残留物。相比之下，表面残基的研究要少得多，主要是因为它们相对稀有。在进行了化学研究的地方，碳水化合物和蛋白质等不同类别的化合物被认为是表面残留物，而被吸收的残留物主要是脂类。到目前为止，对表面残留物的研究仅限于少数船只，而对吸收残留物的若干调查表明，对更大数量的数百艘船只进行化学分析，以揭示人类活动随时间和跨地理区域的变化具有价值。表面残留物的一个非常重要的应用是它们在加速器质谱仪(AMS)的放射性碳测年中的应用。表面有机残留物特别适合于这一目的，因为它们可能来自单一的‘烹饪’事件，因此具有‘年轻’的年龄。认识到这一点，英国遗产(EH)已经资助了对&gt；250残基的14C测年，这些残基已经包括在统计(贝叶斯)模型中，以及来自其他来源的日期。这种模型表明，与其他类型的样品相比，这种残基更有可能产生异常年龄。大约15%的样品年龄不能在放射性碳实验室之间重现，与年代学模型中包括的其他信息的一致性很差。似乎在导致这些异常的一些过期残留物中存在污染。由于年代残留物的化学成分尚不清楚，这些异常现象目前无法解释。此外，对血管使用和过去饮食的更广泛解释的机会也错失了。EH测年方案为系统研究考古陶瓷中碳质表面残留物的有机化学提供了一个独特且迅速演变的样本集。在这个项目中，我们的目标是将表面残留物的化学和放射性碳分析结合起来：加强对来自英国的14C测年残留物的船只使用和饮食的解释，并为从部分此类残留物获得的异常14C定年数据提供可靠的解释(S)。该项目的具体目标将是：确定残留物的化学成分，并通过化学分析和稳定同位素分析确定其来源，以便为确定最适合进行14C测年的残留物确定化学标准，包括确定可能产生异常年龄的残留物的标记化合物。该项目将为学生提供一系列新的微观分析方法方面的培训，目的是获得分子水平的化学和稳定的同位素信息，用于在考古学的这一关键方面对有机残留物进行自动多变量数据处理。

Two major classes of organic residue are recognised preserved in archaeological pottery vessels, namely: visible deposits on the interior surface, and absorbed residues within the vessel wall. Both classes represent the remains of organic natural materials processed in vessels and occur most commonly on vessels broadly classified as 'cooking' pots, although vessels would have been used for a wide range of activities involving the heating of organic materials. A major area of interest in such residues comes from the potential to use their biomolecular and stable isotope compositions to investigate: the use of vessels, the nature of commodities processed in vessels, dietary components and agricultural activities. Absorbed residues have been much more widely chemically analysed and applied than surface residues, with an increasing range of plant and animal products being recognised and significant archaeological questions addressed. The attraction of absorbed residues is their high frequency of occurrence, e.g. on average ca. 50% of 'British 'cooking' pots contain significant concentrations of organic residues relating to the lifetime of use of vessels. In contrast, surface residues have been much less studied, mainly because of their relative rarity. Where chemical investigations have been undertaken different classes of compound, e.g. carbohydrates and proteins, are seen to dominate surface residues, compared to absorbed residues, which are dominated by lipids. Up to now studies of surface residues have been limited to small numbers of vessels, whereas several investigations of absorbed residues have demonstrated the value of chemically analysing much larger numbers, several hundred vessels, to reveal changes in human activity through time and across geographical regions. One very significant application of surface residues has been their use in radiocarbon dating by accelerator mass spectrometry (AMS). Surface organic residues are particularly suitable for this purpose as they probably derive from a single 'cooking' event and thus have 'young' ages. Recognising this English Heritage (EH) has funded 14C-dating on >250 residues, which have been included in statistical (Bayesian) models, together with dates from other sources. This modelling suggests that such residues are more likely to produce anomalous ages than other sample types. Around 15% of samples ages are not reproducible between radiocarbon laboratories and have very poor agreement with the other information included in the chronological models. It seems there is contamination in some of the dated residues that cause these anomalies. As the chemical compositions of the dated residues is unknown, these anomalies are currently unexplained. Moreover, the opportunity for wider interpretations of vessel use and past diet are missed. The EH dating programme provides a unique and rapidly evolving sample set for undertaking systematic investigations of the organic chemistry of carbonaceous surface residues from archaeological ceramics. In this project we aim to bring together chemical and radiocarbon analyses of surface residues to: enhance interpretations of vessels use and diet from 14C-dated residues from Britain, and provide a robust explanation(s) for the anomalous 14C-dates obtained from a proportion of such residues. The specific aims of the project will be to: determine the chemical composition of the residues and assign their origins by chemical and stable isotopic analysis, in order to pinpoint chemical criteria for identifying the most suitable residues for 14C-dating, including the identification of marker compounds for residues likely to produce anomalous ages. The project will provide the student with training in a range of novel micro-analytical methods aimed at deriving molecular level chemical and stable isotope information for automated multivariate data treatment for organic residue classification in this key aspect of archaeology.