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.
