藏南沉错沉积物的粒度特征及其古环境意义

Grain-size Characteristics and Their Paleo-environmental Significance of Chen Co Lake Sediments in Southern Tibet

通过对藏南沉错粒度参数的分析 ,并结合与其它环境代用指标的比较 ,可以将本地区约 1 40 0年来环境变化分为四个阶段 :约 5 93A.D.～ 82 1 A.D.是湖泊水位相对较高而且变化频繁的时期 ,反映了波动较大且比较湿润的气候状况 ;约 82 1 A.D.～ 1 343A.D.是一个较长的气候相对稳定时期 ,粒度指示该阶段湖泊扩张 ,湖面升高 ,反映了湿润的气候状况 ;约 1 343A.D.～ 1 892 A.D.是一个气候波动十分剧烈且频繁的时期 ,其中约 1 60 2 A.D.前后可能出现了一次短时间的流水突然增加 ,而在这前后各有一个浅水阶段 ( 1 343A.D.～ 1 5 1 2 A.D.和 1 670 A.D.～ 1 892 A.D.) ,反映了湖泊补给程度的减弱 ;1 892 A.D.～1 998A.D.是一个相对稳定的时期 ,湖面变化不太明显 ,而 1 892 A.D.前后具有一个明显的补给水动力减弱的变化。粒度参数所反映的湖面波动与环境变化得到了其他环境代用指标较好的支持。

Grain size is one of the useful indices in the lacustrine sedimentary research. By directly indicating the water impetus during the sedimentary period, the grain size of lake sediments indirectly reflects the supplied water volume changes of the lake. Because the lake water volume is greatly influenced by climatic factors, such as precipitation, temperature and induced glacier melting water, the grain size provides more information to elucidate the environmental changes. By the analyses of the grain size parameters and the comparison with other proxies of the Chen Co sediments, four stages of environmental changes since ca. 1400 years ago have been distinguished. 1) Ca. 593～821 A.D. was a high lake level period accompanied by frequent fluctuations. It implies relatively wet climatic conditions with multi time alternative changes. 2) Ca. 821 1343 A.D. was a long and stable wet period, during which the lake enlarged and the lake level rose. 3) Ca. 1343 1892 A.D. was a climatically complex period. The inflow water violently increased around ca. 1602 A.D. while the lake was in the shallow water status in other periods. It suggested that the supplied water of the lake was relatively weak. 4) Ca. 1892 1998 A.D. was another stable period with the light lake level variations. Ca. 1892 A.D. was an obvious borderline for showing the supplied water impetus changes. These environmental changes reflected by the grain size of Chen Co lake sediments were well supported by other proxies and proved by other research results.