Ramped pyrolysis radiocarbon dating: First application to Bronze and Iron Age plaster from the Eastern Mediterranean (ca. 1500-800 BCE)

Radiocarbon dating of mortar has long been an intriguing yet challenging field of research. The key issue involves distinguishing archaeologically meaningful carbon, which reflects the original setting of the mortar, from various types of contaminant carbon. Recent applications of the ramped pyrolysis method, which allows for the separation of carbonates based on their thermal decomposition behaviour, have shown significant potential to overcome this issue. However, so far this technique has only been applied to more recent historical material, generally sampled from favourable above-ground contexts. Its application to much older challenging buried contexts has until now remained untested, though it is vital to unlocking the full impact of the method. In this study, we apply the ramped pyrolysis radiocarbon dating method to samples from recently excavated Bronze and Iron Age contexts.
Excellent agreement was found between radiocarbon dates on lowest temperature (∼620-670 °C) fractions of fine powders of mortar (<38 μm, 38-75 μm) and expected ages for Iron Age (950-800 BCE) plasters. However, application to the lime lumps, which have previously proved successful in above-ground samples, produced promising yet systematically older ages than expected, highlighting the persistence of some complications. Overall, our findings demonstrate that ramped pyrolysis can produce accurate results on archaeological material from excavated contexts when combined with FTIR screening, and careful sample selection. We suggest future refinements to improve the reliability of mortar radiocarbon dating for these types of samples. Eventually, this approach may allow for absolute chronologies to be obtained on archaeological contexts that lack datable organic materials.