Thursday, April 5, 2012
Southwest Dating Methods
Dykeman, Douglas D., Ronald H. Towner, and James K. Feathers. 2002 Correspondence in Tree-Ring and Thermoluminescence Dating: A Protohistoric Navajo Pilot Study. American Antiquity 67(1):145-164.
A common theme in analyses of dating techniques is the determination of a particular technique in a region at a time as accurate or inaccurate. The most apparent way of doing this is by using several techniques to date a single artifact in combination with seriation. This article is one such attempt, showing the degree to which tree-ring and thermoluminescense show similar results.
The major reason this article was written was to help alleviate the difficulty of finding accurate but rare tree-ring datable artifacts to help date surrounding strata. Precise dates are important, especially in relatively recent sites. The authors try to show the degree to which thermoluminescense dating methods are similar in accuracy to tree-ring dating methods. Since there is only one possible date for the output of thermoluminescense (unlike such problems as the ‘old wood’ problem in radiocarbon dating), it is a good method for getting the ‘true’ date of an artifact. The authors found a 40% correlation rate between thermoluminescense dates and tree ring dates from the same layer. Although I would not make a claim of this being good, the authors do make such a claim. They also say that with further thermoluminescense research, this number can be brought up much higher. In addition, doing similar studies on a much wider array of sites can help to alleviate some of these differences even further. This study has obvious significance, as it applies to a wide area during a medium span of time.
Eighmy, Jeffrey L., and Jerry B. Howard. 1991 Direct Dating of Prehistoric Canal Sediments Using Archaeomagnetism. American Antiquity 56(1):88-102.
One of the most complex and striking questions regarding the early prehistory of the Southwest is the emergence and dispersal of agriculture. Because of the dry environment present in the Southwest, canals were a common and necessary way to grow these plants. It is therefore a reasonable expansion that dating the earliest canals should give a rough estimation of some of the earliest agriculture. This line of thinking obviously breaks down when one considers that it is far more difficult to find a hole than an artifact, river erosion and the fact that early agriculture likely was concentrated around rivers, and that there is only a very small percentage of land that has been examined thoroughly in the Southwest. Still, knowing the dates of the earliest canals that are known of can be a useful thing to know, as can be the pictures of population growth that examining canal patterns across regions can show.
Dating canals can be extremely tricky, as they seldom contain obviously datable material. Archaeomagnetism, however, has proven to be a good method for dating these canals, at least where they have remained relatively undisturbed. Although individual results may go awry, the results can also be compared to a much larger master database that helps to ensure the results. Although it was not the goal of the authors to date the earliest or trace development patterns, the authors show that archaeomagnetism is a good method for determining the dates in which the canals were dug to within one hundred years.