| Abstract: | Prehistoric rock paintings occur worldwide, but until recently, they could not be dated directly. With the advent of radiocarbon dating via accelerator mass spectrometry (AMS) in the late 1970s and early 1980s, which allowed a ten thousand fold reduction in the required sample size, rock art dating became a possibility. Most age determinations of rock paintings have been obtained using pieces of charcoal collected from the ancient paint. Yet, most rock paintings do not incorporate charcoal and can not be dated in this fashion. In 1990, Russ et al. demonstrated the feasibility of using low-pressure, low-temperature oxygen plasma reactions to selectively remove organic matter contained within prehistoric paints by converting the organics to CO2. However, the reactions occurring in the oxygen plasma are sufficiently mild that inorganic carbon sources in the rock substrate, such as CaCO3 and MgCO3, do not decompose. Thus, contamination from these sources is avoided. The resulting CO2 sample is sealed in a glass tube at liquid nitrogen temperature and sent to an AMS facility for radiocarbon dating. The tremendous advantage of our oxygen plasma method is that it is generally applicably to all rock paintings, not just those that contain charcoal. During my doctoral research, I have continued the development and testing of this oxygen plasma technique. In particular, I analyzed samples of known and/or well-constrained ages as tests of the oxygen plasma chemical method. Furthermore, I also used this technique to attempt to resolve significant archaeological controversies regarding the ages of several Utah rock paintings. In addition, I obtained a radiocarbon result for a sample of red paint from Montana which is in excellent agreement with the expected age based on other archaeological evidence. My results provide continued support that this method is capable of providing reliable ages for ancient rock paintings. Still, additional work is required before this technique can be considered routine. |
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