Cation ratio dating

Cation-ratio dating is cerrainlj not yet perfected as a dating technique, but the available data indicate c1earl.v that Harry k critique is seriously jlan,ed.

En un reciente articulo, Harry critica el uso de la ttcnica de datacidn por radios de catidn para calcular la edad de arte-Jactos recolectados en la superficie como parte de un rechazo general de esta ticnica de datacidn.

Cation-ratio dating, a Gillespie 1991, 1994; Cahill 1992; Dorn 1992, technique for inferring the age of subaerial rock 1995; Harrington and Whitney 1995; Francis et al. CO 80309-0233 American Ant~qu~ty.121-1 29 62(1), 1997.

varnish on surfaces in arid environments, includ-[1993: Table 11 summarize criticisms of cationing humanly modified surfaces, is a clear exam-ratio dating and responses to these criticisms) and ple of this. pp Copyr~ght% by the Soc~etyfor Amer~can Archaeology My contribution to this debate focuses on two issues.

Rock varnish coats many surfaces of geomorphic and archaeologic interest in arid lands.

All varnish dating techniques are limited by the time lag between the exposure of a surface to subaerial processes and the onset of varnishing.

Cation-ratio dating of rock varnish is an empirical surface-exposure dating method based on decreases in the cation ratio (Ca K): Ti over time.

Although these changes were attributed to the preferential leaching of Ca and K from varnish, the existence of such leaching has not been demonstrated.

Cation ratios have been used to distinguish relative ages of archaeologic artifacts in southwestern North America and to demonstrate that varnish at the South Stoddard locality, Mojave Desert, did not form in 25 yr.

However, Harry k negative conclusions are difficult to reconcile both with the seemingly successful application of cation-ratio dating as part ofthe Intermountain Pon,er Project (IPP) in Califbrnia, the only other project in which surface artifacts have been cation-ratio dated, as well as with Harr? The present comment details substantial differences in (I) the rigor and sophistication of the research designs applied b?

j Harry and the IPP research and (2) the integrity of the sites on n,hich these two projects worked, and points out important components of Harryi data that are inconsistent with her conclusions.

Developed first in the early 1980s, it that addresses a number of important issues. First, neither Harry nor anyone else involved in the debate has considered the impacts of archaeological research design on attempts to apply cation-ratio dating to archaeological materi- als, despite Harry's fairly explicit critique of research carried out under a far more rigorous and sophisticated research design than hers.

For was quickly applied archaeologically to assess the example, Dorn's (1995) inspection of varnished age of both rock art (Dorn and Whitley 1983; surfaces at the site at which Harry worked (5-KER-Francis et al. Second Harry's claims notwithstanding, it is not at all clear that her results indicate that cation-ratio dating provides inaccurate chronological information. archaeological communit[y]," it has actually been applied only rarely, most often to date petroglyphs. Rigorous critique of the method would therefore seem to require a systematic comparison of the methods and results of these two applications.

In principle, this makes it possible to apply the method to surface-collected artifacts, which virtually never produce sufficient varnish for a radiocarbon date.

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