A Pre-treatment Routine for Correcting Age-Offsets on AMS Radiocarbon Dated Ceramic Residue

堪萨斯州立大学的唐娜·C·罗珀博士和古生物研究所的琳达·斯科特·卡明斯博士将合作进行一项研究，旨在开发一种前处理方案，以校正AMS放射性碳年代陶瓷残留物的年龄偏差。自二十世纪中叶引入以来，放射性碳测年对于考古学家以及在其他领域进行基础和应用研究的生物学家、地质学家和科学家来说一直是至关重要的。在接下来的几十年里，这种方法取得了长足的进步，使得开发出更准确和精确的时间线成为可能。AMS技术能够产生高精度的日期，允许对小材料进行分析，例如单个玉米粒碎片或种子，这些材料的寿命短，与其背景同期，因此得出的年龄比以往任何时候都更准确。此外，被认为适合考古年代测定的有机材料的范围也扩大了。烧焦的食物在烹饪过程中被烧到陶瓷器皿上，通常被称为陶瓷残留物，是现在常用的断代材料之一，在北美、欧洲和亚洲越来越多地使用。随着其使用的增加，陶瓷残留物的年代经常被注意到比来自相同背景的其他短期材料的年代更早，因此不准确。继续假设这些日期的准确性并将它们整合到时间线中，会在该学科能够产生中等高分辨率的时间线的时候精确地退化年代学，并使考古学家能够致力于对历史过程进行可行的叙述。之前解决这个问题的两种方法包括确定化学成分作为哪些样本可能受到影响的预测因素，以及开发年代的修正系数。事实证明，两者都不能令人满意地解决这个问题；事实上，最近关于修正系数的结论是，年龄偏移量对于任何单一的局部或区域修正系数来说都太可变了，不准确。该项目的研究小组提出了第三种方法，其中包括一种前处理方案，以去除和丢弃导致异常日期的化合物。因此，可以获得与相关的短寿命物质同时产生日期的残留物的一小部分的日期。在开发一种通用的陶瓷残留物处理方案方面，有限的试验取得了令人鼓舞的结果。残留物和背景材料上的AMS日期将被配对，以测试开发方法的有效性。测试将包括测定几个残留物中多个组分的年代，包括去除的化合物，以获得有关旧碳含量的信息。样本将从北美大平原史前晚期的个人住宅中提取，这些住宅的使用寿命在十年到十年半之间。测试和审查方法旨在开发一种前处理协议，能够获得世界任何地方陶瓷残留物的准确日期，因为残留物正迅速成为放射性碳测年记录的重要组成部分。此外，这种方法将导致未来的努力，涉及化学分离在其他材料中或附着在其他材料上的含有旧碳的化合物，为将这一协议应用于更多样品打开大门，以便它们可以产生准确和一致的放射性碳测年。

Dr. Donna C. Roper, from Kansas State University, and Dr. Linda Scott Cummings, from PaleoResearch Institute, will collaborate on a study designed to develop a pre-treatment protocol for correcting age-offsets on AMS radiocarbon dated ceramic residue. Since its introduction in the mid-twentieth century, radiocarbon dating has been vital to archaeologists as well as biologists, geologists and scientists conducting basic and applied research in other fields. The method has seen considerable advancement in the ensuing decades, enabling development of evermore accurate and precise timelines. Capable of producing high precision dates, the AMS technique permits assay of small materials, such as individual corn kernel fragments or seeds that are short-lived and contemporaneous with their context, thus yielding ages with higher accuracy than ever before. Also, the range of organic materials believed to be appropriate for archaeological dating is broadened. Charred food burned onto ceramic vessels during cooking, often termed ceramic residue, is one of the materials now commonly selected for dating and increasingly used in North America, Europe, and Asia. As its use increases, ceramic residue ages are often noted to be older than dates on other short-lived material from the same context, and thus are not accurate. Continuing to assume the accuracy of these dates and integrating them into timelines degrades chronologies precisely at the time the discipline is able to produce timelines of moderately high resolution and enable archaeologists to work toward viable narratives of historical process.Two previous approaches to addressing the problem have included determining chemical composition as a predictor of which samples likely are affected, and developing correction factors for ages. Neither is proving capable of satisfactorily addressing the problem; indeed, recent conclusions regarding correction factors are that age offsets are too variable for any single local, or regional correction factor to be accurate. The study team for this project proposes a third approach that includes a pre-treatment protocol to remove and discard compounds responsible for the anomalous dates. As a result, dates may be obtained on a fraction of residue shown to produce dates contemporaneous with associated short-lived materials. Limited trials have produced encouraging results toward developing a ceramic residue treatment protocol for general use. AMS dates on residue and on context materials known to produce accurate ages will be paired to test the efficacy of the developing method. Tests will consist of dating multiple fractions, including removed compounds, from a few residues to obtain information concerning the old carbon content. Samples will be drawn from late prehistoric individual dwellings in the North American Great Plains that had use-lives on the order of a decade to a decade-and-a-half. Testing and vetting methods aims toward development of a pre-treatment protocol capable of obtaining accurate dates on ceramic residue anywhere in the world, as residues are fast becoming a significant part of the radiocarbon dating record. Furthermore, this method will lead to a future effort involving chemical separation of compounds containing old carbon in or adhering to other materials, opening the door to application of this protocol to additional samples so they may produce accurate and concordant radiocarbon dates.