毛乌素沙地北缘5．8～4．5 cal kaBP的沉积旋回  

Particle size characteristics of deposits from Pojianghaizi Section and their environmental significance

作　　者：隆浩[1] 马海州[1] 王乃昂[2] 李育[2] 

机构地区：[1]中国科学院青海盐湖研究所,青海西宁810008 [2]兰州大学资源环境学院,甘肃兰州730000

出　　处：《兰州大学学报（自然科学版）》2007年第2期1-6,共6页Journal of Lanzhou University(Natural Sciences)

基　　金：国家"973"计划资助项目(2004CB720200).

摘　　要：通过毛乌素沙地现代风成砂与泊江海子剖面沉积物粒度特征对比分析,确定剖面中4个层位(290～210 cm,190～160 cm,153．5～123．5 cm,50～40 cm)基本属于风成砂沉积,这些风成砂中间夹杂着3次湖相沉积,结合年代序列认为此区域在5．8～4．5 cal kaBP存在以下沉积旋回:～5749 cal aBP沉积风成砂,反映该时期风砂活动强烈,气候干燥,冬季风强盛;5 749 cal aBP前后沉积物为灰绿色湖相层,表明这一时期存在短暂的湖面扩展,沙漠退缩;5 749～5370 cal aBP沉积风成砂,反映了湖泊的退缩和沙漠的扩展;5370～4895 cal aBP湖相沉积物,反映了流域降水量的增多;4895～4580 cal aBP沉积风成砂后,4580 cal aBP前后又出现了短暂的湖相沉积,之后又是风砂沉积．With a view to attain information on desertification （eolian activity） from Mu Us Shamo, a climatically sensitive region, we have studied volumetric particle size distributions for five modern desert sand samples and 30 section samples located in Maowusu desert and the front of low terrace of Pojianghaizi Lake, respectively. Our results indicate that samples grain size characteristics at depth of 290-210 cm, 190-160 cm, 153.5-123.5 cm, 50-40 cm at Pojianghaizi Section are significantly similar to those of modern desert sand, suggesting that sediments at these depths are paleodesert sand （eolian sediments）. Moreover, we have observed, during our field investigation, that there were 3 layers of lacustrain sediment embedded in the Pojianghaizi Section. Based on radiocarbon dating, the grain size analysis indicated a sediment sequence ranging from 5.8 cal kaBP to 4.5 cal kaBP as follows： before 5749 calaBP, the overlying eolian sand layer indicated intense eolian activity under a dry and cold climate resulting from the strong winter monsoon, which is followed by a thin layer of lacustrain sedimentation implying a brief episode of retreating desert and enlarging lake; eolian sedimentation was occurring between 5 749 and 5 370 calaBP, which suggested that the desert expanded again; the period between 5 370 and 4 895 cal aBP was characterized by a lacustrain sedimentation with a main composition of clay and silt, indicating that the catchment of Pojianghaizi experienced a significant increase in rainfall. After eolian sedimentation with a thickness of 50 cm between 4 895 and 4 580 cal aBP, a short period of lacustrain sedimentation occurred during 4 580 cal aBP,. which was followed by an eolian sand layer.

关 键 词：泊江海子 粒度 湖相沉积 风砂沉积 

分 类 号：P512.3[天文地球—地质学]