粘土矿物分析及其指示的气候意义——以毛乌素沙漠滴哨沟湾为例

Climate changes indicated by the clay minerals: a case of the Dishaogouwan section on the southeastern margin of the Mu Us Desert

以毛乌素沙漠东南缘萨拉乌苏河流域滴哨沟湾剖面DGS1层段为代表,对其粘土矿物组成进行分析.结果显示,DGS1层段粘土矿物以石英、钾长石、钠长石、伊利石、蒙脱石、方解石和绿泥石为主,各层位均不含高岭石.各种沉积相矿物组成基本一致,说明该地区的矿物来源基本一致.不同沉积相粘土矿物含量不尽相同,沙丘砂、次生黄土中的石英、长石、伊利石、绿泥石等代表干、寒气候的粘土矿物含量高,湖沼相中的蒙脱石、方解石等代表暖湿气候的粘土矿物含量高,个别湖沼相层位出现了白云石.粘土矿物组分表现出萨拉乌苏河流域全新世气候特征:本地区全新世总体偏冷干,各沉积相缺失高岭石而均存在绿泥石可为证明;本地区全新世气候分为两个主要气候阶段,早期到中期堆积湖沼相为主的时期气候相对温暖湿润;中期以后到现在堆积次生黄土和沙丘砂的阶段气候相对寒冷干燥.

The DGS1 segment of the Dishaogouwan section in the Salawusu River Valley on the southeastern margin of the Mu Us Desert is the typical profile to study climate changes in the past. By the analysis of the composition of clay minerals,the results show that the clay minerals in the DGS1 segment are mainly the quartz,K-feldspar,albite,illite,montmorillonite,calcite and chlorite,without kaolinite in different layers. The mineral composition in different sedimentary facies is nearly the same,which indicates that the mineral sources are basically the same in this region. The contents of clay minerals are different in different sedimentary facies,such as the quartz,feldspar,illite and chlorite that represent cold-dry climate are high in the dune sands and secondary loess,and the montmorillonite and calcite which indicate the warm-humid climate are high in the lacustrine facies,even the dolomite appears in some lacustrine strata. The clay mineral components reveal the climate characteristics in the Salawusu River Valley during the Holocene： the regional climate is overall cold-dry in the Holocene,which is confirmed by the presence of chlorite and absence of kaolinite in each sedimentary facies; and the Holocene climate is divided into two major periods in this region,the climate in the period from the early to the middle is relatively warm and humid with the accumulation of lacustrine facies; the period from the middle till present is relatively cold and dry with the accumulation of dune sands and secondary loess.