Coordinated ¹⁴C and ²³⁰Th dating of Kitchen Cave rockshelter, Gambier (Mangareva) Islands, French Polynesia: Comparing ²³⁰Th coral dates with Bayesian model ages

Abstract

Establishing the timing of human colonization of the eastern Pacific and developing cultural chronologies within the island groups of Eastern Polynesia has relied primarily on ¹⁴C dating. Despite advancements in ¹⁴C dating, however, uncertainties introduced during calibration to calendar ages remain large relative to the tempo of human settlement of the eastern Pacific and ensuing Polynesian cultural development. ²³⁰Th dating of coral abraders, a common artifact in Polynesian archaeological sites, can potentially provide more precise ages. We report a high-precision chronology for the Kitchen Cave rockshelter on Kamaka Island in the Mangareva (Gambier) Islands, based on parallel series of 13 ¹⁴C AMS dates on short-lived plant materials and 19 ²³⁰Th dates on Acropora coral abraders and non-utilized Acropora coral branches. The ²³⁰Th coral dating results are highly consistent with ages from ¹⁴C dating, except in two cases where corals younger than expected occupied what are most likely intrusive contexts. Moreover, because the ¹⁴C and ²³⁰Th dating techniques are largely independent, obtaining consistent results via the two techniques increases confidence in the resulting chronology. A reliable ²³⁰Th date of 860 ± 5 CE for a coral from the basal layer of the cultural sequence, whose deposition cannot readily be explained by natural processes, raises the possibility of an early Polynesian visit to Kamaka Island some centuries prior to initiation of permanent occupation in the 11th to 13th centuries. These results confirm that ²³⁰Th dating of Acropora branch coral abraders can be applied to other sites in the Pacific with a high degree of confidence.