Additional Archaeomagnetic Data on the South‐west Usa Master Geomagnetic Pole Curve*

Abstract

Archaeomagnetic dating in the American south-west is progressing rapidly in terms of both method and application. Of particular importance has been the creation of u master curve of geomagnetic direction change ,for the region. However, confirmation, extension and refnement of this curve are always welcome contributions to the technique. So, efforts are under way to accumulate a large body of well-dated virtual geomagnetic pole positions and document these through publication so that the basis for dating samples of unknown age can be evaluated. This article adds 23 new dated pole positions to the list discussed in Eighniy (1991) and reports the results of our experiments with refining the south-west USA master curve, especially the creation of a new south-west master curve, SWCV.595.

The pre-AD 585 extension of the U.S. Southwest archaeomagnetic reference curve

“…A threshold value of 5.0 serves as a compromise between the various studies and facilitates smoothing of the earlier portion of the study dataset, for which the overall data density is relatively low. In addition to the minimum data density threshold, the averaging windows used in this study have a minimum length of 50 years, which is in-line with values used by previous studies (e.g., Hagstrum and Blinman, 2010;LaBelle and Eighmy, 1997;Lengyel, 2004).…”

“…Again, this cut-off is much larger than the 3.0 (Dubois, 2008) or 3.5 (LaBelle and Eighmy, 1997) values utilized in other Southwest archaeomagnetic studies, but it is in-line with larger values used in other recent studies (e.g., Donadini et al, 2009;Hagstrum and Blinman, 2010;Schnepp and Lanos, 2005). It could be argued that a cut-off value is unnecessary, since the data are weighted by their precision (e.g., Lanos et al, 2005;Schnepp et al, 2004); however, samples with a 95 values larger than 10.0 tend to be magnetically unstable and typically are judged to be unreliable for dating or curve construction (e.g., Lengyel et al, 2003).…”

“…In keeping with previous studies in the U.S. Southwest (e.g., Eighmy, 1991;LaBelle and Eighmy, 1997;Lengyel and Eighmy, 2002;Sternberg and McGuire, 1990b), this study used the moving window method developed by Sternberg (1982Sternberg ( , 1989Sternberg and McGuire, 1990a) to fit a smooth temporal curve to the dataset. This approach uses a running average to smooth the archaeomagnetic dataset into a sequential series of mean VGPs that define the regional reference curve.…”

“…Two of the tree-ring dated samples were reported by Cox and Blinman (1999) and are new to the Southwest archaeomagnetic dataset. The remaining 13 tree-ring dated samples are included in the SWCV595/2000 reference curve dataset (Eighmy and LaBelle, 1995) and contribute to the earliest three mean VGPs calculated for those curves (LaBelle and Eighmy, 1997;Lengyel and Eighmy, 2002).…”

“…However, as the scope of archaeological research has shifted to include earlier periods of occupation in this region, the temporal restrictions of the existing archaeomagnetic reference curve have hampered efforts to date these sites. Currently, the most commonly used reference curves for the U.S. Southwest, SWCV595 (LaBelle and Eighmy, 1997) and SWCV2000 (Lengyel and Eighmy, 2002), cover the temporal period between AD 585 and the present. A number of projects in central and southern Arizona, however, have focused on archaeological features and sites that were utilized before AD 585.…”