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

Dr. Donna C.来自堪萨斯州立大学的罗珀和来自古研究所的琳达斯科特卡明斯博士将合作进行一项研究，旨在制定一项预处理方案，以纠正AMS放射性碳测年陶瓷残留物的年龄偏移。自世纪中期引入以来，放射性碳测年对考古学家以及生物学家、地质学家和在其他领域进行基础和应用研究的科学家至关重要。该方法在随后的几十年中取得了相当大的进步，使时间表的发展更加准确和精确。 AMS技术能够产生高精度的日期，允许分析小的材料，如单个玉米粒碎片或种子，这些材料寿命短，与它们的背景同时存在，从而产生比以往更高精度的年龄。此外，被认为适用于考古年代测定的有机物质的范围也扩大了。 在烹饪过程中燃烧到陶瓷器皿上的烧焦的食物，通常被称为陶瓷残渣，是现在通常选择用于测年的材料之一，并且越来越多地在北美，欧洲和亚洲使用。 随着其使用量的增加，陶瓷残留物的年龄往往比来自同一背景的其他短寿命材料的年龄更老，因此是不准确的。继续假设这些日期的准确性并将其整合到时间轴中，会在该学科能够产生适度高分辨率时间轴的时候精确地降低年表，并使考古学家能够致力于对历史过程的可行叙述。解决这个问题的两种方法包括确定化学成分作为预测哪些样品可能受到影响的预测因素，以及开发年龄校正因子。事实上，最近关于校正因子的结论是，年龄偏移变化太大，任何单一的地方或区域校正因子都是准确的。 该项目的研究小组提出了第三种方法，其中包括一种预处理方案，以去除和丢弃导致异常日期的化合物。因此，可以从残留物的一部分上获得日期，这些残留物显示出与相关的短寿命物质同期的日期。有限的试验已经产生了令人鼓舞的结果，朝着开发一个陶瓷残留物处理协议的一般用途。将对已知产生准确年龄的残留物和背景材料的AMS日期进行配对，以测试开发方法的有效性。测试将包括从一些残留物中确定多个部分的年代，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的史前晚期个体住宅中抽取，这些住宅的使用寿命为10年至15年。测试和审查方法旨在开发一种能够在世界任何地方获得陶瓷残留物准确日期的预处理方案，因为残留物正在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，涉及化学分离的化合物含有旧的碳或粘附在其他材料，打开大门，该协议的应用程序，以额外的样品，使他们可以产生准确和一致的放射性碳日期。

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.