Application of Luminescence Dating in North American Archaeology

University Of Washington, Seattle WA

Investigators

Abstract

Perhaps the most important task of archaeology is providing a chronology for the material remains that are recovered. Any statements about how and why cultures have changed in the past are predicated on an accurate and precise chronology. Archaeologists have utilized an array of physical methods for determining age, most commonly radiocarbon dating. Luminescence dating, which is widely used in Europe, has seen less use in American Archaeology. The National Science Foundation is supporting research by the University of Washington's Luminescence Dating Laboratory, directed by Dr. James Feathers, in expanding the application of this dating method in American archaeology. This research involves addressing some chronological problems that have not been resolved by other dating methods but which are particularly suitable for luminescence dating. Luminescence can be used to date buried sediments, pottery and burned lithics. Primarily pottery dating, with some lithic dating, is being addressed in this project. Luminescence dates pottery to the last time it was heated, usually when it was made or used. Since the manufacture or use is the event that archaeologists are interested in, luminescence has the principle advantage of providing direct dates for pottery and does not rely, as do other dating methods, on association of the pottery with some other event that is dated. This has some particular advantages for some chronological problems, which are being addressed by this research: 1) Archaeologists are interested in regional settlement dynamics, but small sites, particularly those which contain mainly surface material, are difficult to date and thus place in a settlement chronology. Are these sites the same age or different age than larger sites and what does this mean for how the population was dispersed across the landscape? Undiagnostic pottery sherds are often the only artifacts found at these sites. Luminescence is the only method that can date them. 2) A particularly vexing problem in archaeology is the mixing in one deposit of materials of different age. This confounds interpretations of cultural history and blurs evidence on the tempo of change. By directly dating artifacts (in this case pottery sherds), as luminescence can, one can begin to tease apart the different occupations. 3) Duration of occupation in one location is an important variable for understanding population trends and their impact on environment, economy and political complexity. Determining duration has long been problematic in archaeology. By directly dating a number of pottery sherds, luminescence can provide a measure of duration that is statistically quantifiable. Pottery tends to have a relatively short use-life, and emphasis on sherds that have the most fragile fabrics will minimize problems of artifacts that may last longer than the occupations. 4) Dating pre-ceramic sites can also be difficult. Luminescence is able to date heat-treated stone tools as well as pottery and offers a solution to improving the earliest chronologies in America. These problems are being addressed in this research through work in the Mississippi Valley, the Tennessee Valley, eastern Mississippi, central Alabama, and other localities in the Midwest and Southeast. Research into improving the accuracy and precision of luminescence dating of pottery is also being undertaken.