达连海沉积物粒度特征及其古环境意义

利用达连海湖心浅井的粒度资料,分析了粒度组成、粒度频率曲线等粒度特征,并探讨了达连海粒度代表的古气候意义。结果表明,达连海沉积物频率曲线主要是正态单峰型,反映流水作用为主要沉积作用。湖心底部降水较多,湖面高,沉积物以细组分占绝对优势,频率曲线显示物源较单一,为深水沉积环境,但后期环境有所变化;中下部降水相对稀少,湖面降低,沉积物以粗组分含量增加,环境可能进一步恶化;中上部湖面上升,细组分含量增加,频率曲线显示物源由复杂变单一,为浅水沉积向深水沉积过渡环境;上部沉积物粗细间隔连续变化,频率曲线显示物源复杂,反映湖区环境进一步恶化,风砂活动频繁。沉积物粒度特征反映了达连海中全新世以来降水、流水和风力作用以及湖面水位高低的变化。达连海5 000多年来的古气候环境演化大致经历了5 600~5 100 cal a BP的湿润、5 100~2 500 cal a BP的干旱、2 500~800 cal a BP的偏湿和800 cal a BP以来的偏干4个阶段。

Grain - size characteristics of Dalianhai lake sediments and its paleaoenvironment significance

Dalianhai lies in the northeast of the Tibet Plateau. That the location of the lake is influ- enced by the East monsoon, Siberian - Mongolian monsoon and the Westerlies enables its deposits record the climatic and environmental change sensitively. The grain - size characteristics of its sediments indicate that the variations of precipitation, hydrodynamics and wind action, and the lake level changes. The grain size characteristics of Dalianhai Lake sedimentary analyzed in this paper, including grain - size distribution and grain - size frequency curves. Based on the analysis of the characteristics of the grain - size frequency curves and grain - size distribution of the lake sediments, two action and two depositions such as fluvial and windy action, low -lake deposition and high -lake deposition are discussed. The results indicate that the fluviation was the main action and source of sediment in Dalianhai Lake. And the Dalianhai Lake had experienced four main environmental evolution stages since Mid -Holocene. It was in wet 5 600 ～5 100 cal a BP, dry in 5 100 ～2 500 cal a BP wet in 2 500～800 cal a BP, and dry again after 800 cal a BP, respectively.