Description:
Radiocarbon age determinations are presented on three hieroglyphic texts from Naj Tunich cave in Guatemala containing Maya calendar dates. The ages obtained are on average 110-140 years older than the calendar dates. Several possible reasons are discussed for this discrepancy: one that is applicable to all radiocarbon dates on charcoal, one that applies to rock paintings, and one that is specific to the tropics. Possible problems with the ages ascribed to the Maya calendar dates are also discussed. Even with the potential problems that may exist, these dates still fall within 110-140 years of the ascribed calendar dates. Caution is urged in the interpretation of dates on charcoal pigments from rock paintings; consideration of the “old wood” and “old charcoal” factors is important.
These carbonate minerals often consist of dead carbon that no longer contains 14 C due to extreme age and their inclusion would result in an older measured age than the true age of a sample. For example, using plasma oxidation, Armitage et al. (2001) obtained four AMS dates with an average radiocarbon date of 1440 ± 50 14 C years BP on a Mayan charcoal paint sample, whereas a portion of the sample treated only with the usual ABA treatment and combustion gave an age of 11,770 ± 100 14 C years BP. For rock art studies, another consideration is that acid washes conducted during ABA pretreatment may not completely remove carbon-containing oxalate minerals, which are commonly associated with rock surfaces (Hedges et al., 1998; Armitage et al., 2001).
For example, using plasma oxidation, Armitage et al. (2001) obtained four AMS dates with an average radiocarbon date of 1440 ± 50 14 C years BP on a Mayan charcoal paint sample, whereas a portion of the sample treated only with the usual ABA treatment and combustion gave an age of 11,770 ± 100 14 C years BP. For rock art studies, another consideration is that acid washes conducted during ABA pretreatment may not completely remove carbon-containing oxalate minerals, which are commonly associated with rock surfaces (Hedges et al., 1998; Armitage et al., 2001). If not removed, the remaining oxalate would be incorporated into the dated material if combustion is used.
