Developing 230Th/U Dating of Coral Artifacts for High-Precision Cultural Chronologies in Eastern Polynesia

研究人员希望了解从小型创始人群体到复杂的人口众多的社会的崛起克里思以及伴随的环境变化的速度。 对岛屿生态系统上产生的波利尼西亚文化序列进行考古研究非常适合于这种调查。 随着时间的推移，波利尼西亚社会的规模和等级复杂性不断增加。 这种发展伴随着环境的变化，包括对本地植物群和动物群、景观和海洋资源的深刻改变。然而，尽管经过近70年的研究，最初定居的时间以及随后的文化和环境变化的克里思仍然非常不确定。在目前的项目中，W。夏普和P.基尔希以及他们的合作者M.艾伦和G. Molle将进一步开发一种新的方法来测定波利尼西亚文化序列。 测年方面的预期改进将首次为这些波利尼西亚社会的文化和环境变化速度提供清晰的画面。在关键的东波利尼西亚群岛确定更准确的日期，也将有助于解决长期以来关于波利尼西亚人跨太平洋大迁徙时间的争论。发展精确测定珊瑚文物年代的能力将有助于太平洋考古学家为大洋洲其他地方的人类占领和人类与生态系统的相互作用建立精确的年表。 波利尼西亚考古学家传统上几乎完全依赖放射性碳测年（即，14 C测年），为岛屿的殖民化和随后的岛屿文化和环境演变提供定量的时间框架。 尽管放射性碳测年技术多年来取得了显着进步，但放射性碳测年法在应用于过去1000年（东波利尼西亚文化发展的时间框架）时存在严重的固有局限性。 另一种在波利尼西亚的应用中已经证明相当成功的年代测定技术是珊瑚的238 U-234 U-230 Th年代测定，在此称为230 Th珊瑚年代测定。 该技术基于珊瑚中天然存在的铀的衰变，并且可以容易地获得精确度为1-2%的可靠的230 Th珊瑚年龄。 例如，对于500岁的珊瑚，这意味着日期的不确定性只有5到10年。 在目前的项目中，夏普，基尔希和他们的合作者将应用230 Th珊瑚测年法来测量波利尼西亚人用鹿角珊瑚或其他珊瑚制成的珊瑚研磨器，这些珊瑚研磨器是用贝壳制成的鱼钩。 这样的珊瑚研磨器在波利尼西亚考古序列中很常见，并且已经被证明非常适合230 Th测年。 总而言之，该项目将为东波利尼西亚关键群岛的文化序列提供前所未有的准确性和精确性，从而大大促进我们对波利尼西亚史前史的理解。

Researchers wish to understand the tempo of the rise of complex, populous societies from small founder groups and the pace of accompanying environmental change. Archaeological study of Polynesian cultural sequences created on island ecosystems is well suited to such investigations. Beginning with small bands of pioneering settlers, the first humans on the landscape of each newly discovered island, Polynesian societies of increasing size and hierarchical complexity developed over time. This development was accompanied by environmental changes including profound modifications to native flora and fauna, landscapes, and marine resources. However, the timing of initial settlement and the tempo of ensuing cultural and environmental change remain highly uncertain despite nearly 70 years of research. In the current project, Drs. W. Sharp and P. Kirch and their collaborators Drs. M. Allen and G. Molle will further develop a novel approach to dating Polynesian cultural sequences. The expected improvements in dating will, for the first time, provide a clear picture of the speed of cultural and environmental change in these Polynesian societies. Better dates in key Eastern Polynesian archipelagoes will also help resolve a longstanding debate over the timing of the extraordinary trans-Pacific dispersal of the Polynesians. Developing the capability to precisely date coral artifacts will help Pacific archaeologists erect refined chronologies for human occupation and human-ecosystem interaction elsewhere in Oceania. Polynesian archaeologists have traditionally depended almost solely upon radiocarbon dating (i.e., 14C dating) to provide a quantitative temporal framework for colonization of islands and subsequent evolution of island cultures and environments. Despite significant improvements in the radiocarbon technique through the years, radiocarbon dating has severe inherent limitations when applied to the past ~1000 years, the time frame of cultural development in eastern Polynesia. An alternative dating technique that has already demonstated considerable success in applications in Polynesia is 238U-234U-230Th dating of corals, herein referred to as 230Th coral dating. The technique is based on decay of naturally occurring uranium in corals, and reliable 230Th coral ages with precisions of 1-2% are readily attainable. For example, for 500-year old corals this translates into dates with uncertainties of only five to ten years. In the current project, Sharp, Kirch and their collaborators will apply 230Th coral dating to coral abraders made from pieces of Acropora or other corals used by Polynesians to shape fish hooks made from shell. Such coral abraders are common in Polynesian archaeological sequences and have been shown to be highly suitable for 230Th dating. In sum, the project will provide chronologies for cultural sequences in key archipelagoes of Eastern Polynesia of unprecedented accuracy and precision, thereby substantively advancing our understanding of Polynesian prehistory.