Archaeological Chronology Development and the Old Wood Problem on the Northern Colorado Plateau

University Of Arizona, Tucson AZ

Investigators

Abstract

With the support of the National Science Foundation, Dr. Ronald H. Towner, colleagues and students will examine the 'old wood' problem in radiocarbon dating of archaeological sites in western Colorado and eastern Utah. The old wood problem is the tendency for radiocarbon (14C) determinations from wood charcoal to be significantly older than the contexts in which the charcoal is found. Five factors can make firewood dates significantly earlier than their archaeological or modern contexts: 1) the tendency of people to use dead wood for fuel; 2) a dead tree or dead branch may have died long before its wood was used for fuel; 3) weathering, decay, or insect activity after tree death can remove many exterior rings and increase the gap between the date of the deadwood remnant and the time of its use; 4) removal of additional exterior rings by burning can further expand the gap; and 5) dating rings from the inner part of the wood's ring series widens the gap still further. Operating singly or together, these processes can produce a gap between date and wood use that exceeds the uncertainty range of radiocarbon dates and thereby seriously overestimate the age of the site involved. This proposed project uses both radiocarbon and tree-ring dating to examine the impacts of 'old wood' procurement on interpretations of the prehistoric and historical period occupations of western Colorado and eastern Utah. Previous research indicates that the magnitude of the old wood problem varies spatially, environmentally, and perhaps culturally. By collecting abundant samples in three areas along an environmental gradient, the project will assess the impacts of different environments on the age and availability of fuelwood resources. The construction of local multi-species multi-century tree-ring chronologies will be particularly important for dating of Fremont, Gateway Tradition, and Ute sites in western Colorado and eastern Utah, and may be critical in understanding Fremont/Ute relationships and Ute ethnogenesis. This proposed project will help us develop wood use models for the three groups and provide interpretive guidelines for dating the sites. Thus, the intellectual merit of the project is to test environmental variability of radiocarbon dates, create new tree-ring chronologies for the area, develop new models of cultural wood use practices, and evaluate technological change as a factor in radiocarbon dating of sites in these areas. This project will have broader impacts beyond the Fremont, Gateway Tradition, and Ute archaeology in western Colorado and Eastern Utah. It will make important contributions toward the understanding of radiocarbon dating and wood use practices in arid and semi-arid environments worldwide. The project will also contribute toward graduate and undergraduate student training and development. It may also contribute to calibration other chronometric techniques, such as archaeomagnetism and thermoluminescence dating, and to refining ceramic seriation studies of prehistoric Fremont and protohistoric and early historic Ute pottery types. It will refine models of wood use that may have implications for understanding the impacts of technological change on the exploitation of timber resources.