Collaborative Research: Radiocarbon Dating of Mesoamerican Lime Mortars and Plasters

在国家科学基金会的支持下，一个包括来自亚利桑那大学(Greg Hodgins博士和A.J.Vonarx女士)和亚利桑那州立大学(George Cowgill博士、Arleyn Simon博士和Tatsuya Murakami先生)的教职员工和学生组成的跨学科和多机构团队将探索一种方法，根据中美洲纪念性建筑中的砂浆和石膏的放射性碳含量直接测定它们的年代。砂浆和灰泥通过在其结构中加入大气二氧化碳而变硬，从而在施工时固定材料的14C含量，并提供了确定施工事件年代的可能性。对中美洲年表的改进将提供对技术风格、地区差异以及时间变化和连续性的洞察。目前，石灰基建筑材料的放射性碳测年主要是在欧洲和中东地区进行的。然而，考虑到石灰基产品的广泛使用和我们对深思熟虑的石灰石膏技术的日益了解，将该方法应用于中美洲材料是理想的。该团队之前的研究表明，开发方法的最佳策略需要同时测定砂浆或石膏碳酸盐的年龄，以及从中分离出的有机包裹体。该项目将分析从各种考古背景中挑选出来的具有良好有机包裹体含量的材料，以调查该方法的稳健性。该小组将对中美洲的三个地点的材料进行年代测定：墨西哥的El Naranjal、Quintana Roo和危地马拉的Tecalote，位于玛雅低地；以及月亮金字塔，特奥蒂瓦坎，位于墨西哥高地。从前两个地点，将获得含有有机包裹体的砂浆或石膏样本，这些有机包裹体可以与砂浆和石膏碳酸盐进行放射性碳测年。还提供了来自月球金字塔多个建造阶段的石膏样品。其中几个地层与陶瓷层和放射性碳测年层有关。这个跨学科团队在中美洲考古学、文物和材料表征、古代技术研究和放射性碳测年方面拥有专业知识。便利的设施是这项工作的理想之选，包括亚利桑那州立大学的考古研究所和戈德沃特固态科学中心，以及亚利桑那大学的NSF-亚利桑那加速器质谱学实验室和人类学考古实验室。这项研究的更广泛影响是，它将推进AMS放射性碳测年技术在中美洲石灰砂浆和灰泥中的应用，使考古学家能够确定建筑工期。鉴于石灰石膏和砂浆在整个中美洲地区的广泛使用，这种方法具有潜在的广泛应用前景。在NSF-Arizona AMS实验室内开发的砂浆年代测定方法可能会使这种分析能够定期提供给考古界，并将为完善中美洲年代学和解释这一复杂而迷人的地区做出实质性贡献。两名研究生将接受放射性碳样品制备程序方面的培训，并将利用这项研究作为其人类学考古学和考古学博士论文的一部分。本科生将参与样品的成分研究，并为测年做准备。对可制作日期的石膏进行定性和收集将涉及与墨西哥和危地马拉的同事和机构继续合作。这些发现将通过自然科学、考古学和社会科学的报告和出版物在国际上分享。

With National Science Foundation support, an interdisciplinary and multi-institutional team including faculty and students from the University of Arizona (Dr. Greg Hodgins and Ms. A.J. Vonarx) and Arizona State University (Dr. George Cowgill, Dr. Arleyn Simon, and Mr. Tatsuya Murakami) will explore a method for directly dating mortars and plasters within Mesoamerican monumental structures based upon their radiocarbon content. Mortars and plasters harden by the incorporation of atmospheric carbon dioxide into their structure, thus fixing the 14C-content of the material at the time of construction and offering the possibility of dating construction events. Refinement of Mesoamerican chronology will provide insights into technological style, regional variation, and temporal change and continuity. At present, the radiocarbon dating of lime-based construction materials has been carried out predominantly within European and Middle Eastern contexts. Yet, the application of the approach to Mesoamerican materials is ideal, given the widespread use of lime-based products and our growing knowledge of prehispanic lime plaster technology. Previous research by the team indicates that the optimal strategy for method development requires simultaneously dating mortar or plaster carbonates along with organic inclusions isolated from them. The project will analyze materials with well established organic inclusion contents selected from a variety of archaeological contexts to investigate the robustness of the method.The group will date materials from three sites within Mesoamerica: El Naranjal, Quintana Roo, Mexico, and Tecalote, Guatemala, in the Maya Lowlands; and, the Pyramid of the Moon, Teotihuacan, in Highland Mexico. From the first two sites, mortar or plaster samples containing organic inclusions that can be radiocarbon dated in parallel with mortar and plaster carbonates will be obtained. Plaster samples from numerous construction phases of the Pyramid of the Moon are also available. Several have stratigraphic association with both ceramic and radiocarbon dated layers. The interdisciplinary team has expertise in Mesoamerican archaeology, artifact and materials characterization, studies of ancient technology, and radiocarbon dating. Accessible facilities are ideal for this work and include the Archaeological Research Institute and Goldwater Center for Solid State Science at Arizona State University and the NSF-Arizona Accelerator Mass Spectrometry Laboratory and the Department of Anthropology Archaeometry Laboratories at the University of Arizona.The broader impacts of the study are that it will advance the application of AMS radiocarbon dating to lime mortars and plasters in Mesoamerica allowing archaeologists to date construction episodes. This method has potentially broad application given the widespread use of lime plasters and mortars throughout Mesoamerica over long periods of time. The development of mortar dating methods within the NSF-Arizona AMS Laboratory will potentially allow such analyses to be offered to the archaeological community on a regular basis and will make substantive contributions to the refinement of Mesoamerican chronology and interpretation of this complex and fascinating region. Two graduate students will be trained in radiocarbon sample preparation procedures and will utilize this research as part of their doctoral dissertations in anthropological archaeology and archaeological science. Undergraduate students will participate in the compositional study of the samples and their preparation for dating. The characterization and collection of datable plasters will involve continued cooperation with colleagues and institutions in Mexico and Guatemala. These findings will be shared on an international level through presentations and publications in natural science, archaeology, and social science.