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

研究人员希望了解复杂、人口众多的社会从小型创始群体崛起的速度，以及随之而来的环境变化的速度。对岛屿生态系统上创造的波利尼西亚文化序列的考古研究非常适合这种调查。随着时间的推移，波利尼西亚社会的规模越来越大，等级制度越来越复杂，最初的拓荒者是一小群拓荒者，他们是每一个新发现岛屿上的第一批人类。这种发展伴随着环境的变化，包括对本地动植物、景观和海洋资源的深刻改变。然而，尽管经过近70年的研究，最初定居的时间和随后的文化和环境变化的速度仍然高度不确定。在目前的项目中。W.夏普和P. Kirch以及他们的合作者。M. Allen和G. Molle将进一步发展一种新的方法来确定波利尼西亚文化序列的年代。对年代测定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一幅清晰的画面。对关键的东波利尼西亚群岛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规模迁徙时间的争论。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居住和人类生态系统相互作用建立精确的年表。传统上，波利尼西亚考古学家几乎完全依靠放射性碳定年法（即14C定年法）来为岛屿的殖民和岛屿文化和环境的后续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重大进步，但在过去~1000年（东波利尼西亚文化发展的时间框架）的应用中，放射性碳测年具有严重的固有局限性。另一种在波利尼西亚的应用中已经证明相当成功的测年技术是珊瑚的238u - 234u -230测年，这里称为230珊瑚测年。该技术基于珊瑚中天然存在的铀的衰变，并且很容易获得可靠的230年代，精度为1-2%。例如，对于500岁的珊瑚来说，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、Kirch和他们的合作者将使用230种珊瑚，这些珊瑚是由波利尼西亚人使用的Acropora珊瑚碎片或其他珊瑚碎片制成的，这些珊瑚碎片被用来塑造由贝壳制成的鱼钩。这种珊瑚磨损物在波利尼西亚考古序列中很常见，并且已被证明非常适合230年代测定。总而言之，该项目将为东波利尼西亚主要群岛的文化序列提供前所未有的准确性和精确性的年表，从而大大提高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.