阿拉善高原沙漠地区植物钙质根管的矿物组成特征

在阿拉善高原地区,植物钙质根管的成因及其是否具有一定的环境指示意义,目前尚存在较大争论。分析该区域植物钙质根管的矿物组成,可以为植物钙质根管的成因提供新的证据解释。本文通过近5年的野外考察,先后采集了巴丹吉林沙漠、腾格里沙漠及乌兰布和沙漠腹地33组植物钙质根管和33个地表风积砂样品,通过X衍射的方法,分析了上述样品的矿物组成。结果显示:上述沙漠地区植物钙质根管和地表风积砂中矿物组成以硅酸盐矿物、氧化物和氢氧化物矿物、碳酸盐类矿物为主,没有明显的区域差异。其中碳酸盐类矿物均以方解石为主,较少含有其他盐类矿物,并且植物钙质根管中碳酸盐类矿物百分含量明显高于地表风积砂中碳酸盐类矿物的百分含量。因此,单纯的地下水重结晶作用无法解释本研究区内植物钙质根管中盐类矿物的组成以及碳酸盐类矿物的来源,并且在研究区内现代气候条件不利于植物根系的钙化和钙质根管的形成。植物钙质根管应是地质历史时期的产物,指示了相对湿润的气候条件。

Mineral Composition Characteristics of Calcareous Root Tubes in the Deserts of the Alxa Plateau,NW China

There is debate regarding the formation of calcareous root tubes and their environmental significance in Alxa Plateau. Analyzing the mineral composition of calcareous root tubes could provide new evidence for their formation and their environmental significance. Total of 33 calcareous root tubes and 33 surface aeolian sand samples were collected from the hinterland of the Badain Jaran Desert, the Tengger Desert and the Ulan Buh Desert, then the mineral composition were measured using X-ray diffraction. The results showed that calcareous root tubes contains silicate mineral, mineral oxides and hydroxides mineral, and carbonate mineral. Moreover, calcite is the main carbonate mineral. The mineral compositions were almost identical in different areas. Carbonate mineral percentages of calcareous root tubes is significant higher than aeolian sand. Hence, only groundwater recrystallization cannot explain the mineral composition of calcareous root tubes and the origin of carbonate mineral in this area. In addition, the present climate is not suit for the root calcification and calcareous root tubes formation, and then calcareous root tubes should be formed in the past and could indicate a relatively humid climatic conditions.