Description:
Plasma oxidation was used to obtain radiocarbon dates on six different materials from a naturally mummified baby bundle from the Lower Pecos River region of southwest Texas. This bundle was selected because it was thought to represent a single event and would illustrate the accuracy and precision of the plasma oxidation method. Five of the materials were clearly components of the original bundle with 13 dates combined to yield a weighted average of 2135 {+-} 11 B.P. Six dates from a wooden stick of Desert Ash averaged 939 {+-} 14 B.P., indicating that this artifact was not part of the original burial. Plasma oxidation is shown to be a virtually non-destructive alternative to combustion. Because only sub-milligram amounts of material are removed from an artifact over its exposed surface, no visible change in fragile materials has been observed, even under magnification. The method is best applied when natural organic contamination is unlikely and serious consideration of this issue is needed in all cases. If organic contamination is present, it will have to be removed before plasma oxidation to obtain accurate radiocarbon dates.
In the 1970s and 1980s, two significant excavation projects were conducted which contribute substantially to the radiocarbon record of the Lower Pecos: Hinds Cave, excavated by Texas A&M University, and Baker Cave, excavated by the University of Texas at San Antonio. Radiocarbon dates from these projects were applied to a wide range of research problems, including, of course, projectile point chronologies (e.g., Chadderdon 1983), but also including diet breadth studies (e.g., Lord 1984; Brown 1991) and bioarchaeological investigations (e.g., Poinar et al. 2001), as well as to demonstrate the benefits of new radiocarbon measurement methods.
Most of the dates published in recent decades have been used to address narrowly focused research questions. Assays were on objects currently in curation, such as burial items (Steelman et al. 2004, Shafer 2009, Turpin 2012a, peyote effigies (Terry et al. 2006), sandals (Sonderman 2017), and coprolites (Poinar et al. 2001, Sonderman et al. 2019. Numerous other dates have been obtained from earth ovens, burned rock middens, and hearths (e.g., Cliff et al. 2003, Johnson and Johnson 2008, Roberts and Alvarado 2012, Basham 2015, Knapp 2015, and contribute to an ongoing research focus on hot rock cooking.
