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的、人口众多的社会从小型创始人群体崛起的速度，以及伴随而来的环境变化的速度。考古学研究在岛屿生态系统上创造的波利尼西亚文化序列非常适合这样的调查。从一小群开拓性的定居者开始，在每个新发现的岛屿上的第一批人类，波利尼西亚社会随着时间的推移而发展起来，社会规模越来越大，等级制度越来越复杂。这一发展伴随着环境变化，包括对当地动植物、景观和海洋资源的深刻修改。然而，尽管进行了近70年的研究，最初定居的时间以及随之而来的文化和环境变化的速度仍然非常不确定。在目前的项目中，W.Sharp博士和P.Kirch博士以及他们的合作者M.Allen博士和G.Molle博士将进一步开发一种新的方法来确定波利尼西亚文化序列的年代。约会方面的预期改善将第一次让人们清楚地看到这些波利尼西亚社会的文化和环境变化的速度。在关键的东波利尼西亚群岛更好的日期也将有助于解决关于波利尼西亚人跨越太平洋的非同寻常的扩散时机的长期争论。开发准确测定珊瑚文物年代的能力将有助于太平洋考古学家建立大洋洲其他地方人类占领和人类-生态系统相互作用的精确年表。波利尼西亚考古学家传统上几乎完全依靠放射性碳测年(即14C测年)来为岛屿的殖民和随后的岛屿文化和环境的演变提供一个定量的时间框架。尽管放射性碳技术多年来得到了显著的改进，但放射性碳测年在应用于过去1000年(东波利尼西亚文化发展的时间框架)时具有严重的内在局限性。另一种已在波利尼西亚应用取得相当成功的替代测年技术是238U-234U-230珊瑚测年，这里称为230珊瑚测年。这项技术是基于珊瑚中自然存在的铀的衰变，可靠的230年珊瑚年龄，精度在1-2%是很容易获得的。例如，对于500年的珊瑚来说，这意味着不确定的日期只有5到10年。在目前的项目中，夏普、基尔奇和他们的合作者将对由Acropora碎片或波利尼西亚人用来塑造贝壳鱼钩的其他珊瑚制成的珊瑚研磨器进行第230次珊瑚年代测定。这种珊瑚研磨器在波利尼西亚考古序列中很常见，并已被证明非常适合230年代测定。总而言之，该项目将提供东波利尼西亚主要群岛文化序列的年表，具有前所未有的准确性和精确度，从而大大促进我们对波利尼西亚史前的理解。

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.