长江三峡中坝遗址地层中Rb和Sr的分布特征及其古气候演变

长江三峡中坝遗址是我国目前仅有的、世界上也罕见的“通史式”遗址。它不仅蕴藏大量的文化内涵,而且包含极其丰富的自然环境演变信息,是研究三峡地区全新世环境演变的理想剖面。文章对遗址地层中的铷(Rb)、锶(Sr)值进行了测试和分析,结果显示:剖面地层中的Rb含量偏低,而Sr含量偏高,Rb/Sr比值变化较大。Rb/Sr比值已成为区域环境演变研究中较理想的替代指标,根据Rb/Sr比值的环境指示意义发现,长江三峡地区全新世中晚期以来气候环境总体上逐渐趋于恶劣;气候冷暖湿热变化剧烈;寒冷期长于温暖期,并没有明显地向湿热方向发展趋势。与长江下游等东部其他地区相比,长江三峡地区也存在明显不同之处:隋唐暖期不明显,而中世纪暖期表现显著。

THE CHARACTERISTICS OF DISTRIBUTION OF Rb AND Sr AND PALEOCLIMATIC CHANGES IN THE STRATIGRAPHY AT THE SITE OF ZHONGBA OF THE THREE GORGES

A perfect and unique archaeological site is recovered at the Zhongba of the Three Gorges where the legacy of human culture and activities, and the information of environmental changes is recorded completely in a litho stratigraphical sequences since the Late Glacial stage. This is also the best place found to study the environmental changes. Rb and Sr contents in the litho stratigraphical sequences have been tested and the results show a high value of Rb content and low value of Sr content, with a variable Rb/Sr ratio through the profile. The value of Rb/Sr ratio illustrates the natural environmental changes. According to the characteristics of distribution of Rb, Sr and Rb/Sr ratio in the litho stratigraphical sequences at the Site, four distinct periods can be divided(1) Late Neolithic Age(5.1～ 4.3kaB.P.);(2) Late Shaang Dynasty and Xizhou Period (3.4～2.8kaB.P.); (3) The Late Zhan guo Early Qinhan Dynasties(2.4～2.1kaB.P.);and (4) Yuan and Ming Dynasties (0.8～0.7kaB.P.). The high value of Rb/Sr Ratio show that climatic changes were rapid and cold and humid climatic conditions were overwhelming during and after the Neolithic Age. No evidence shows any warm period in the Three Gorges since the Mid Holocene Period. The climatic characteristic in the area is probably related to southeast and southwest monsoon and regional topographic relief. Two warm periods were found separately in Sui Tang Dynasties (1.5～1.1kaB.P.) based on the evidence of Rb/Sr Ratio. Human activities, such as producing salt, were affected by the climatic changes, which might be closely related to the climatic changes in the region of the Three Gorges.