优化US-ESR测年方法及华南早期现代人遗址的年代研究

The cave deposits in the karstic area of southern China yielded abundant human fossils attributed to late Homo sapiens, in association with Paleolithic assemblages and faunal remains. However, accurately dating of human remains from cave deposit is a long-lasting difficulty, mainly due to the complicated stratigraphical relationship and the lack of suitable dating materials. Fossil teeth are very common archaeological findings, and they are often co-existing with human fossils or cultural relics. The coupled U-series and electron spin resonance (US-ESR) dating method is now the most reliable approach for direct dating of fossil teeth. However, with this method, the fossil dental tissue is considered as uniform material. The spatial variations of uranium concentration and U-uptake process are overlooked. In order to optimize the US-ESR dating method, we are planning to analyze the spatial distribution of U-series isotopes in fossil dental tissues with micro-drill sampling and multi-collector inductively coupled plasmas mass spectrometry (MC-ICPMS) techniques. Then we use diffusion-adsorption (D-A) model to diagnose the U-uptake processes, according to the relationship between U concentration and U-series apparent age. The fossil teeth that have relatively homogeneous U concentration and no evidence of U-leaching will be selected for US-ESR dating. The D-A model will be used as quality control in US-ESR dating of fossil teeth, by comparing the reconstructed U-uptake process with the observed spatial distribution of uranium in dental tissue. In this project, the optimized US-ESR dating method will be used to study the recently discovered Middle-Late Pleistocene cave sites in southern China, including Zhirendong, Shuangtandong, Quzaidong, Baxiandong and Gongjishan in Guangxi, Mawokoudong in Guizhou and Yumidong in Chongqing. This project will be able to provide accurate dates for understanding the timing of early modern human settlement of southern China and the evolution process of modern human in East Asia.

我国华南是早期现代人演化与扩散的重要区域，而该地区古人类遗址的年代学研究很薄弱或存在较大争议。动物牙化石常与人类化石共存，可用于铀系与电子自旋共振结合定年法（US-ESR测年法）直接测年。然而，该测年法把牙组织看作均质样品，不考虑其中铀含量分布不均以及铀吸附模式微区差异的现象。本项目拟用微钻取样和多接收电感耦合等离子体质谱分析牙组织中铀的空间分布，并用扩散-吸附模型诊断铀吸附的类型。通过解析铀在牙组织中的空间分布，可以为US-ESR测年筛选出适合样品，还可以检验该方法模拟的铀吸附过程是否与实际的铀空间分布相符合，有助于提高测年结果的可靠性。用此优化的US-ESR测年法，本项目拟研究华南新近发现的多个更新世晚期的早期现代人和考古遗址的年代。本项研究将准确测定早期现代人在多个遗址的出现时间，为重建早期现代人在东亚的演化过程提供时间标尺。

我国华南地区分布多处关键的早期现代人遗址，如通天岩、智人洞、陆那洞和福岩洞等。然而，由于这些遗址都为喀斯特洞穴，其古人类化石的地层年代长期存在争议。铀系法和电子自旋共振法（ESR）可用于直接测定动物化石年代，因此对研究华南早期现代人遗址的地层年代有重要作用。本项目重点发展和优化本实验室的铀系测年技术，并发展铀系与电子自旋共振（ESR）相结合的测年方法。应用铀系和ESR以及其他测年方法，本项目研究了华南的多个中晚更新世的古人类遗址和考古遗址，并取得了重要的年代数据：1）直接测试了通天岩柳江人化石的铀系年代，表明其年代接近2.3万年；2）证实了渠仔洞的动物化石年代混杂的现象，从中发现了年代至少为14万年的一个古人类的牙齿化石；3）测定了智人洞动物群化石的年代接近或大于20万年；4）采用贝叶斯模型，建立了重庆玉米洞~30万年以来的地层年代序列。此外，利用本项目发展的高精度铀系测年技术，本项目直接测定了黑龙江哈尔滨发现的古人类头骨化石的最小年代为14.6万年，为确立该化石的演化地位提供了年代学证据。本项目还利用高精度铀系测年技术，测定了云南沧源岩画的年代为3800–2700年，证实其为该区域新石器晚期的岩画艺术；还将云南丽江虎跳峡万人洞的岩画年代测定为1.36万年至 8.37千年，代表着我国目前已知最为古老的岩画艺术，同时证实了我国境内存在旧石器时代岩画艺术。