江西沟1号风成剖面地球化学元素特征及古环境意义

Geochemical Element Characteristics and Paleoenvironmental Significance of Aeolian Sediments in JXG1 Section

通过对江西沟风成沉积剖面的地球化学分析,并结合OSL年代、粒度和磁化率数据,探讨了末次冰消期以来青海湖南岸气候的演变。剖面常量元素氧化物含量呈SiO_2〉Al_2O_3〉CaO〉Fe_2O_3〉MgO〉K_2O〉Na_2O变化特征,常量元素氧化物及化学元素综合参数与地层有较好的对应性。不同的环境指标对气候变化的敏感性不同,总体上看,地球化学元素的敏感性高,全新世以来粒度和磁化率的变幅较小,即使在全新世大暖期,其值变化都很小。地球化学元素记录所反映的气候变化过程如下。Ⅰ.末次冰消期~12 ka BP,13.2 ka BP前总体上呈相对温暖状态,可能受B/A暖期的影响,13.2~12 ka BP气候不断向干冷方向发展,寒冷程度不断加剧并在12 ka BP达到最强,可能反映出12 ka BP左右的新仙女木事件;Ⅱ.12~9 ka BP,气候呈波动回升状态,暖湿程度呈增加趋势,表现出温凉的气候变化特征;Ⅲ.9~4.5 ka BP,气候温暖湿润,与全新世大暖期相对应,该阶段水热组合达到最佳,但存在阶段性的变化;Ⅳ.4.5~2 ka BP,气候总体向冷干方向转变,3 ka BP前变化幅度较小,气候较温暖湿润,3~2 ka BP气候凉偏干。

The climatic change since the Last deglaciation period was reconstructed based on the analysis of geochemical characteristics of the aeolian deposits profile in JXG1,southern shore of Qinghai Lake,combined with the OSL chronology,grain size and magnetic susceptibility data. The order of major element oxides content is SiO_2 Al_2O_3 CaO Fe_2O_3 MgO K_2O Na_2O,and major element oxides and the chemical elements integrated parameter have a better correspondence with stratum. Different environmental indicators have different degree of sensitivity to climate change,on the whole,geochemical elements have high sensitivity,the change range of particle size and magnetic susceptibility is smaller since Holocene,the variety of their value is very small even during the Holocene warm period. The climatic change based on the records of geochemical elements indicates that： Ⅰ. During the last deglaciation- 12 ka BP,the climate was relatively warm in general before 13. 2 ka BP,possibly affected by B / A period.The dry and cold climate continuously developed during 13. 2 ~ 12 ka BP and coldness reached the strongest in 12 ka BP,implying the Younger Dryas event around 12 ka BP; Ⅱ. In 12 ~ 9 ka BP： The climate rise with fluctuations and the warm and humid degree present an increasing trend,indicating warm and cool characteristics of climate variation;Ⅲ. In 9 ~ 4. 5 ka BP： The climate was warm and moist,corresponding to the Holocene optimum period,hydrothermal combination achieved the best during this period,but it has phase changes; Ⅳ. In 4. 5 ~ 2 ka BP： The climate turned to the cold and dry direction in general,the variation width is smaller and the climate is relatively warm and humid,the cool and dry climate dominated the region during 3 ~ 2 ka BP.