萨拉乌苏河流域地层沉积时代及其反映的气候变化

Sedimentary Age of Strata in the Salawusu River Basin and Climatic Changing

萨拉乌苏河流域位于我国北方沙漠／黄土过渡带和生态脆弱带，它对全球变化反映非常敏感，是研究全球变化的理想区域。本文根据地质测年、气候地层对比，以及地层中气候代用指标的分析，将萨拉乌苏河流域地层和气候变化划分为：全新统的风成相与湖相沉积（O～11．5kaBP），早、中期气候较暖湿，晚期气候较干旱；上更新统城川组的风成相沉积（11．5～80kaBP），气候干旱寒冷；上更新统萨拉乌苏组的湖相沉积（80～140kaBP），气候温暖较湿润；中更新统上部的河流相与风成相互层（140～190kaBP），气候冷干与温凉半干旱波动；中更新统上郎的冲洪积沉积（190～220kaBP），气候较暖湿等阶段。指出自中更新世晚期以来气候发生频繁波动，无论是暖湿还是冷干阶段，气候都波动频繁，气候变化不稳定性明显。

The Salawusu river basin is situated in the transition zone between desert and loess, and also in a fragile ecotone of northern China. This region is an ideal site for research on the global change due to its high sensitivity to global climate variation. We conducted geological dating for strata in the study region and analyzed the stratigraphic climatic proxies, based on which and according to the climate-stratum comparison method we further divided the strata in the Salawusu river basin into the following sequences： （1） lacustrine and aeolian facies of Holocene dated at 0- 11.5 ka BP, with warm-humid climate in the early and middle phase and arid climate in the late phase; （2） Late Pleistocene aeolian facies of the Chengchuan Group dated at 11.5-80 ka BP, with arid-cold climate; （3） Late Pleistocene lacustrine facies of the Salawusu Group dated at 80-140 ka BP, with warm-humid climate; （4） interbed of fluvial and aeolian facies of Middle Pleistocene dated at 140-190 ka BP, with climate fluctuating between arid-cold and semiarid-warm cool; （5） alluvial facies of Middle Pleistocene dated at 190-220 ka BP, with warm-humid climate. In a word, the climate either in warm-humid phase or in arid-cold phase has been fluctuating frequently since the late Middle Pleistocene, indicating remarkable instability of climatic change.