Collaborative Research: The Extension of a Dendrochronological Sequence to northern Mexico

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Drs. Paula Turkon, Sturt Manning, and Carol Griggs, along with colleagues from Mexico, will conduct research to provide a high-resolution absolute tree-ring chronology for Northern Mesoamerican archaeological sites using a combination of tree-ring and AMS radiocarbon data. This project extends their preliminary research both geographically and chronologically, with the goal of linking the existing Epiclassic chronology from Northwestern Mesoamerica that ends in the 8th century A.D., to the regionally extensive, calendar-dated chronologies from living and relic trees in the same region. The dendrochronological results will offer dating precision to archaeologists working in these regions for time periods that do not have written sources of chronological data. It will also establish the foundation for climate reconstruction studies that, in the future, will help clarify the long-term relationships between the magnitude of climatic change and human response. In fostering close collaboration between archaeologists, dendrochronologists, graduate, and undergraduate students from multiple institutions throughout Mexico and the United States, this project's mission is to encourage the application of dendroarchaeology [=archaeological dendrochronology], currently not part of archaeological fieldwork or analysis in Mexico. Mesoamerican archaeologists have long acknowledged the need for precise dating methods in order to understand cultural change, particularly in the region north of the core of Mesoamerican culture. Yet despite tremendous success in the development of tree-ring dating of archaeological sites just north in the American Southwest, and the more recent development of long tree-ring chronologies in Mexico that cover the past 1300 years, dendroarchaeology has been virtually absent in Mesoamerica. The first stage of this NSF funded project demonstrated the availability, measurability, and similarities in growth patterns ("crossdatability") of archaeological tree-ring samples in Northwestern Mesoamerica from the 5th to 8th centuries A.D. In this second stage, the researchers will incorporate archaeological samples from Postclassic and historic sites located in a broader geographic region in northern Mesoamerica. Because the new archaeological collections of wood will likewise be from a time period for which there are no well-established master chronologies, the tree-ring sequences produced from the prehispanic sites will be initially anchored in time by "radiocarbon wiggle-matching." This method fits a known relative sequence of radiocarbon dates from specific tree-rings against the radiocarbon calibration curve to achieve a precise fit and thus calendar placement with minimal error. Ultimately, we intend to create a continuous tree-ring record from the present back to the Classic period, using both the archaeological and historic collections, as well as existing calendar-dated chronologies. The resulting data will not only fill a significant gap in our knowledge of the chronology of Northern Mesoamerica, but help address broader questions such as the rate, timing, and directionality of cultural influences with the Mesoamerican cultural core. Since dendroarchaeological methods are cumulative and iterative, the chronologies will gain in length, sample depth, and robustness, and will become increasingly useful to archaeologists working in broader geographic regions and time periods.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.