【摘要】 通过毛乌素沙地现代风成沙的粒度与泊江海子剖面沉积物粒度特征对比分析,确定了剖面中4个层位(290—210cm、190—160cm、153.5—123.5cm、50—40cm)基本属于风成砂沉积,并且这些风成砂中间夹杂着三次湖相沉积,结合14C年代测定,我们认为此区域在4 000—5 000a BP存在以下沉积(气候)旋回:至(4 958±84)aBP,沉积风成砂,反映该时期风沙活动强烈,气候干燥,冬季风强盛;(4 958±84)a BP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;(4 958±84)—(4 793±74)a BP,沉积风成砂,反映了湖泊的退缩和沙漠的扩展;(4 793±74)—(4 536±70)a BP,湖相沉积物,反映了流域降水量的增多;(4 536±70)—(4 085±67)a BP沉积风成砂后,(4 085±67)a BP前后又出现了短暂的湖相沉积,之后又是风成砂沙沉积。更多还原

【Abstract】 With a view to attain desertification(eolian activity) information from Mu Us desert,a climatically sensitive region,we have studied the particle size distributions for five modern desert sand samples in Mu Us desert and 30 section samples in the front of low terrace of PJHZ lake.Our results indicate that sample grain size characteristics at depth of 290-210 cm,190-160 cm,153.5-123.5 cm,50-40 cm at PJHZ section are significantly similar with the modern desert sand,which suggested sediments at these depths are paleodesert sand(eolian sediments).Moreover,we have observed there were 3 layers of lacustrine sediments embedding in the PJHZ section during our field investigation.Based on radiocarbon dating,the grain size analysis indicated a sediment sequence ranging from 4 00014C a BP to 5 000 14C a BP as following: before(4 958±84)14C a BP,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 lacustrine sediments implying a brief episode of retreating desert and enlarging lake;eolian sedimentation was occurring between(4 958±84) and(4 793±74)14C a BP,which suggested that the desert expanded again;the period between(4 793±74) and(4 536±70)14C a BP was characterized by a lacustrine sedimentation with a main composition of clay and silt,indicating the catchment of PoJiangHaiZi experienced a significant increase in rainfall;After eolian sedimentation with a thickness of 50 cm between(4 536±70) and(4 085±67)14C a BP,a short period of lacustrine sedimentation occurred during(4 085±67)14C a BP,which followed by an eolian sand layer.更多还原