2000a B.P.来毛乌素地区的沙漠化问题

DESERTIFICATION OF Mu Us REGION SINCE 2000a B.P.

对最近2000aB．P．来毛乌素地区的沙漠化研究表明，现今流沙的分布范围与气候之间“不平衡”，毛乌素沙地并非气候演变的“顶极产物”，而是在特定的自然条件下过度的人类活动使“古沙翻新”的结果，但古沙翻新的形式在不同的地貌位置有所不同。同时，萨拉乌苏组中的古风成砂并非现代流沙的唯一沙源，还有相当一部分来自黑垆土之下的古风成砂。如果未来温室效应继续导致全球变暖，毛乌素沙地不会南侵，有向北退缩的可能。

Located in the north of the Loess Plateau, the Mu Us Desert is a perfect place for study ing the desertification of North China. According to the historic records and field investiga tion, the cause and proeess of desertifieation is well studied. The results show that: (1 ) Although the Mu Us Desert occurred at least as early as in middle Pleistocene and underwent the changes from desert to non-desert or from non-desert to desert for many times, which is disclosed by the aeolian sand-loess-palaeodoil sequence of the region, the present Mu Us Desert is not the result of environmental evolution driven ty the climate change, in other words, the large distribution area of modern aeolian sand can not rnaintain the equilibrium with the present climate condition.(2 ) Since 2000a B. P., human activities have greatly impacted on the environmental change, and both of human and natural factors destroyed the protection layer of the aeolian sand which mainly formed during the last glacial epoch, so the palaeosand dunes activated and the Mu Us Desert formed.(3) If the greenhouse effect causes the advent of future global warming, the rnonsoon cireulation over East Asia will intensify. Therefore, the Mu Us Desert will retreat nouth wards.