西藏羊八井七弄沟泥炭剖面地球化学特征及环境意义

Geochemical characteristics of the peat profile in the Yangbajing basin, Tibetan, China and its paleoenvironmental implications

泥炭沉积物蕴藏着丰富的区域环境演变信息,本文通过分析西藏羊八井七弄沟泥炭剖面特征元素比值(Fe/Mn,Ba/Sr,K_2O/Na_2O)变化特征,结合剖面腐殖化度和汞含量记录的研究结果,发现西藏羊八井泥炭沉积物中特征元素比值可以指示沉积环境的干湿变化.依据元素地球化学记录,西藏羊八井地区的沉积环境划分为9.1～7.6 cal ka BP温度波动上升阶段,沉积环境较湿润;7.6～4.5 cal ka BP温度剧烈波动阶段,沉积环境逐渐干旱;4.5～3.5 cal ka BP温度波动下降阶段,沉积环境变得暖湿.其中共记录4次沉积环境变干,时间分别为5.8、6.1、8.2以及8.8～8.5 cal ka BP左右,与局部乃至全球的气候变化记录存在良好的对应关系.

The peat contains abundant information about climate change.In this study,the ratios of characteristic elements in the Yangbajing basin, Tibetan Plateau, are found to be an good indicator for evaluating the regional sedimentary environment(e.g., the change of wet and dry stages), according to the analytical results of special element rations(Fe/Mn, Ba/Sr, K_2 O/Na_2 O),humification and mercury(Hg) records in the peat cores. The paleoclimate evolution in the Yangbajing basin is classified as three stages as revealed by the elemental geochemical records: Temperature fluctuates and shows an overall increasing trend between 9.1～7.6 cal ka BP. The sedimentary environment is relatively wet during this period. Significant and frequent fluctuation of temperature is observed between 7.6～4.5 cal ka BP. The sedimentary environment tends to be dry; the temperature fluctuats less and shows a decreasing upward trend 4.5～3.5 cal ka BP. The sedimentary environment tends to be warm and wet. A total of four drying events are recorded in the peat profile, which occurs at approximately 5.8, 6.1, 8.2 and 8.8～8.5 cal ka BP, respectively. The four events recorded in the peat core in the Yangbajing basin are consistent with the regional and global climate records.