DENDROCHRONOLOGY AND WIGGLE-MATCH DATING IN NORTHWESTERN MESOAMERICA

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1 DENDROCHRONOLOGY AND WIGGLE-MATCH DATING IN NORTHWESTERN MESOAMERICA Paula Turkon This collaborative project between Ithaca College Department of Environmental Studies and the Tree-Ring Laboratory at Cornell University represents, to our knowledge, the only current attempt to apply dendrochronological analysis to archaeological wood in Mesoamerica. Integrated with 14C dating (so-called dendro-14c-wiggle-matching), it should provide a near high-resolution chronological framework, focused initially on Epi-Classic sites in northwest Mexico. Though the project is still in its initial stages, preliminary methodological advances suggest that it will help fill a conspicuous gap in our understanding of the pace, timing, and directionality of cultural influences within prehispanic northwestern Mesoamerica, and, by extension, with the north and the central and western Mesoamerican cultural cores. This project is a first step to a longer-term goal to use tree-ring variability to address prehispanic climate change in Mesoamerica. The project is initially focused on existing collections of wood and charcoal in the northwest region, with particular emphasis around the sites of La Quemada, Zacatecas, Alta Vista, Chalchihuites, and El Coporo, Guanajuato (Figure 1). Though occupation ranges vary, all of these regions show significant occupational development during the Epi-Classic period, approximately A.D To dispel the belief that there aren t enough analyzable samples in this region, our first objective was to assemble samples with the highest potential for dendrochronological analysis-that is samples that have more than 50 measurable rings. To date, we have assembled a collection of more than 100 segments of wood from eight collections and are conducting excavations to recover known columns at La Quemada and El Coporo (see Figure 2 for examples). Our second objective is to discover the segments of time the sites represent within the Epi-Classic period. We have used segments of tree-rings in samples from different sites for dendro-14c wiggle-matching to anchor the samples in time. The wiggle-matching fits 14C dates from several specific tree-ring segments (typically of ten tree-rings), with a known number of rings in between the segments, against the 14C calibration curve datasets (Figure 3a). For LAQ31, the result, as seen in Figure 3b, greatly narrows the standard radiocarbon error ranges that usually result from dates analyzed in isolation, and instead achieves a 95.4% probability range of just 56 calendar years and a most likely 68.2% probability range of just 25 calendar years placing the last extant tree-ring of sample LAQ31 at AD Finally, we are initiating the development of floating prehispanic tree-ring sequences. Our team has successfully measured the rings from over 70 segments representing 21 trees with more than 50 rings, and crossdated sequences within sites (Figure 4). The success of this project so far gives preliminary indications that we will be able to establish the calendar dates between sites in the Malpaso valley, and between the Malpaso Valley and Chalchihuites, which will also establish the chronology of development in the region during the Epi-Classic period. Paula Turkon, Ithaca College, pturkon@ithaca.edu Sturt Manning, Cornell University Carol B. Griggs, Cornell University Keywords: dendrochronology, Epi-Classic Mesoamerica, Malpaso Valley and Chalchuites, Zacatecas, Ocampo, Guanajuato Permanent URI: Bounding coordinates (decimal degrees): West: 21.7 North: East: South: Citation Example: Paula Turkon (2015) Dendrochronology and Wiggle-Match Dating in Northwestern Mesoamerica. SAA Current Research 257, accessed (current date) Current Research Online No: 257:1

2 Figure 1. Map of Northwest Mesoamerica showing regions in the study area. Current Research Online No: 257:2

3 Figure 2. Examples of archaeological wood with dendrochronological potential and the represented species from Northwestern Mesoamerican sites in the Malpaso Valley and Chalchihuites. Current Research Online No: 257:3

4 Figure 3a. Location of C14 Wiggle-Match samples form LAQ-31 (from La Quemada) on the tree-ring curve. Current Research Online No: 257:4

5 Figure 3b. LAQ-31 Wiggle Match demonstrates how multiple 14C dates plotted on the calibration curve can narrow the error range. Current Research Online No: 257:5

6 Figure 4. Correlations of tree ring widths from La Quemada samples. Current Research Online No: 257:6 Powered by TCPDF (