Redating of the To’aga site (Ofu Island, Manu'a) and a revised chronology for the Lapita to Polynesian Plainware transition in Tonga and Samoa

Abstract

Radiocarbon dating Pacific archaeological sites is fraught with difficulties. Often situated in coastal beach ridges or sand dunes, sites exhibit horizontal and vertical disturbances, while datable materials such as wood charcoal are typically highly degraded, or derived from old trees or drift wood and bone collagen rarely survives in the tropical conditions. Shell, therefore, is the most logical material for dating Pacific sites since it is resistant to alteration, can be sampled to ensure only the last few seasons of growth are represented and is often closely tied to human economic activities. However, shell radiocarbon (14C) dating has been plagued by interpretive problems largely due to our limited knowledge of the 14C cycle in near shore marine and estuarine environments. Consequently, shell dates are typically ignored in regional chronometric evaluations and often avoided for dating altogether. Recent advances in our understanding of the source of shell 14C content as well as the development of the first South Pacific Gyre model of changing marine 14C over time, combined with Bayesian statistical modelling, have now provided us with insight into the value of these shell radiocarbon dates, enabling a revision of the age of the Toaga site on Ofu Island, an early occupation site associated with the initial Polynesian Plainware period in Samoa, the earliest use of which is now dated to between 2782 and 2667 cal BP.