末次冰期MIS 2阶段沙漠-黄土过渡带萨拉乌苏河流域环境演变记录

对毛乌素沙漠南缘米浪沟湾地层（位于沙漠-黄土过渡带萨拉乌苏河流域）沉积物粒度、总有机碳（TOC）、碳酸盐碳氧同位素组成以及有机分子化合物正构烷烃进行了分析。结果表明:MIS 2阶段（6.0~16.5 m、11~30 ka BP）主要以湖沼相（砂质粉砂）—古土壤（泥质粉砂）—河流相（粉砂质砂）组成；总有机碳在湖沼相和古土壤沉积物中较高，而在河流相沉积物中较低；在23~29 ka BP期间，正构烷烃主要以C₂₇、C₂₉、C₃₁为主，指示了稀疏森林草原特征；在17~19 ka BP期间，沉积物中正构烷烃虽然仍以C₂₇、C₂₉、C₃₁为主，但明显低碳数和中等碳数正构烷烃含量增加，指示了森林草原和较长时间淡水湖泊环境；19~23 ka BP期间为该地区末次盛冰期，干冷状态下风沙活动强烈；全新世中期2.3 ka BP左右至8.0 ka BP左右主要以指示菌藻源的C₁₄~C₁₈为主峰碳，为荒漠草原和分散湖泊或水洼环境；MIS 2阶段主要以西风环流水汽输入为主，全新世期间则由夏季风带来降雨；处于季风边缘的沙漠 黄土过渡带，极端干冷环境下冬季风盛行，风沙活动增强，凉湿气候条件有利于植被的繁盛；较高的温度下，尽管绝对降雨量有所增加，但干燥度增加更明显时，生态环境仍然面临恶化的可能。

Paleoenvironmental Change at Desert-loess Transitional Zone in Salawusu River Valley During MIS 2 Stage of Last Glacial Period

Temperature decreases all the world, and summer monsoon in China retreats towards south with winter monsoon strengthened in the last glacial period. Under this palaeoclimatic background, the aeolian activity is intensified in the northern China, and sea-level declines in South China Sea, and lake shrinks. Oppositely, there are several obvious limnetic facies and river facies strata in Salawusu river valley along the desert-loess transition zone in the southern part of Mu Us Desert, which is at the boundary of modern monsoon. Grain size, total organic carbon (TOC), carbon and oxygen isotopic compositions and organic biomarker n-alkane (m/z is 85) of sediment at Milanggouwan section since MIS 2 stage (6.0-16.5 m, 11-30 ka BP) were analyzed. The results show that the sediment in limnetic facies is made up of the sandy silt, and the mean is 4.5 Φ or so; the sediment in the paleosol strata is made up of muddy silt, and the mean is more than 5 Φ; the sediment in the river facies is made up of silty sand, and the mean is about 3 Φ; total organic carbon is 0.1%-1.0% with the average of more than 0.5% in the limnetic and paleosol facies sediments; total organic carbon is lower in the river facies sediments(0.01%-0.10%); there is an incomplete forest steppe during 23-29 ka BP with n-alkane C₂₇, C₂₉, C₃₁ preponderance; forest steppe and fresh water lake with a long residence time during 17-19 ka BP are inferred by the high contents of n-alkane C₂₇, C₂₉, C₃₁, and the contents of n-alkanes with low carbon number and middle carbon number increase; 19-23 ka BP is the last glacial maximum in this area with a strongest aeolian activity under the coldest and driest condition; desert steppe and dispersal lakes and ponds along the river in Middle Holocence from ~2.3 to ~8 ka BP are inferred by the preponderance n-alkane peaks of C₁₄-C₁₈; westerly jet carries water vapor to this area during MIS 2 stage, and summer monsoon carries water vapor to this area during Holocene, but high aridity is not useful for vegetation flourishing; winter monsoon prevails under the dry and cold climate at desert-loess transition zone in the monsoon boundary, and aeolian activity strengthens, and vegetation flourishs under the cool and wet condition; although absolute precipitation increases under the high temperature, if the aridity increases much higher, the ecological environment will be deteriorative possibly much more.