重庆丰都玉溪剖面的沉积学和气候意义

重庆丰都玉溪剖面AMS14C测年（校正为日历年）配合考古器物断代，证实约8 500～4 800 aBP间该剖面地层基本连续。玉溪剖面下部洪水淤砂—坡积物互层（31～10层）与上部坡积层（9～3层）形成鲜明对比，反映沉积物源和沉积环境曾发生过显著变化。研究认为，Rb、Sr等代用指标曲线的变化特征与剖面沉积结构变化相吻合，揭示了剖面上、下沉积结构的差异主要与不同气候背景有关；剖面下部堆积较厚、持续时间较短及沉积速率较快的洪水淤砂—坡积物互层，是研究区气候不稳定条件下水文异常变化的结果。进一步分析认为，该剖面沉积物的微观隐性代用指标与宏观显性结构的对应性特点还反映，研究区全新世大暖期气候存在阶段性的变化，约8 500～7 200 aBP为大暖期中的气候不稳定阶段；而约7 200～4 800 aBP则体现了大暖期鼎盛阶段暖湿稳定的气候特点，其转折点发生在7 200 aBP前后。

Sedimentological and Climatic Significances of Yuxi Profle in Fengdu, Chongqing

Based upon AMS~(14)C dating (calibrated CY) and inferred dating by archaeological relics, the layers of Yuxi profile in Fengdu, Chongqing can be confirmed a basically sequential deposition during approximately 8 500 ～ 4 800 aBP. There is a sharp contrast between the under-part alternating layers consisting of silt-sand and deluvium (31 ～ 10 layers) and the upper deluvium (9 ～3 layers), which reflects that the sediment sources and environment changed in the past. The research suggests that, the consistency of sedimental structure and curvilinear characteristics of proxy Rb and Sr indicators reveals that the difference of sediment structure of Yuxi profile is mainly related to the different climate backgrounds; the under-part alternating layers which the accumulation is thicker, the persistent peri-od is shorter and the sedimentary rate is higher are the result of abnormal changes of hydrologic phenomena under the background of unstable climate. Further analyzing, we think that the consistency between the sedimentary structure on the macroscopic level and the proxy indicators on the microscopic level of Yuxi profile stratum reflects also that the cli-mate of Megatherma in Holocene existed a obvious phased change in study area, namely approximately 8 500 ～ 7 200 aBP, it was at the stage of unstable climate in Megatherma; and approximately 7 200 ～4 800 aBP, it showed the wet-warm climatic characteristics at the peak of Megatherma, which the turning point occurred in 7 200aBP.