150 ka B.P.以来萨拉乌苏河流域的CaCO_3旋回

Calcium Carbonate Cycles in Salawusu River Valley since 150 ka B.P.

以米浪沟湾地层剖面作为萨拉乌苏河流域的典型剖面,探讨了150 ka B.P.以来的CaCO3含量分布与气候变化的关系。1)该剖面CaCO3含量及其低-高变化同古风成沙与上覆河湖相或古土壤构成的沉积旋回呈现出明显的对应关系。与米浪沟湾剖面的沉积旋回一样,CaCO3在分布上相应地构成了27个含量高低变化旋回。2)CaCO3在风成沙中含量的分布比较稀散,0.8％～7.18％,平均值2.50％;在河湖相和古土壤中相对富集,2.20％～14.90％。平均值5.74％。从而揭示出其时两者的气候背景是不同的,前者是干旱寒冷气候作用下的风力的侵蚀、搬运与堆积的产物;而后者则与暖湿气候环境下萨拉乌苏河流域地处鄂尔多斯高原和黄土高原之间特殊的低洼地貌位置有关。气候暖湿,河湖沼泽发育、成土成壤作用增强,低洼的集水条件有利于CaCO3的聚集。3)导致米浪沟湾剖面CaCO3的多旋回相对稀散与聚集的根本原因可能是150 ka B.P.以来北半球冰期-间冰期气候波动影响下毛乌素沙漠冬夏季风的多次更迭所致。

This paper discuss the relationship between the calcium carbonate content and climatic change in the Milanggouwan stratigraphical section, being regarded as a prototype section in the Salawusu River valley since 150 ka B.P.1) The calcium carbonate content in the section and its low-high change takes on remarkable corresponding relationship with the sedimentary cycles of palaeo-aeolian sands and its overlying fluvio-lacustrine facies or/ and palaeosols. Same as the sedimentary cycles in the section, the calcium carbonate distibution composes 27 cycles of high and low content values accordingly.2) Calcium carbonate in the aeolian sands of Salawusu River Valley is relatively sparse, 0.8% -7.18%, with an average value of 2.50 % ; whereas relatively gathering in fluvio-lacustrine facies and palaeosols, 2.20% - 14.90%, with an average value of 5.74% . It shows that the two climatic backgrounds then were different. The former was the result of erosion and accumulation under wind force during the cold-arid climate, whereas the latter was related to its particular low-lying physiognomy position between the Ordos Plateau and the Loess Plateau under warm-humid climate background. When the climate is warm-humid, fluvio-lacustrine and swamp facies develop, soil forming action strengthen, and low-lying catchment condition is benefit to calcium carbonate assemble.3) The principal reason of multi-cycle relative migration and gather of calcium carbonate in the Milanggouwan stratigraphical section is the repeatedly mutual alternate between the winter and summer monsoons in the Mu Us Desert, which was influenced by the climate vicissitudes in the northern hemisphere during glacial and interglacial periods since 150 ka B.P.