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。

There are 27 sedimentary cycles that are made up of aeolian facies and fluviolacustrine facies or palaeosol in Milanggouwan section in Salawusu River valley. The contents of Al2O3, TFe, Mn, TiO2, K2O, MgO, CaO and Na2O in the later two are higher than those in the former, and the contents of SiO2 take on converse change. It constitutes 27 element change cycles corresponding with above mentioned sedimentary cycles since 150 ka B.P. Based on the chemical migrating peculiarity of each element and the geomorphological feature of the south east depression of Ordos Plateau where the section stands, it is illustrated that the higher contents of SiO2 and the lower contents of Al2O3, TFe, Mn, TiO, K2O, MgO, CaO and Na2O in aeolian sands are related to cold dry windy predominated climate and to the amount immigration of quart, and the converse distribution situation in fluviolacustrine facies and palaeosol bear relation to this special relative obdurate depression where stable elements Al2O3, TFe, Mn, TiO and unstable elements K2O, MgO, CaO and Na2O can both gather together. The study shows that, in Salawusu River valley, the 27 cycles element change cycles since 150 ka B.P. bears relationship with the repeatedly alternation between winter monsoon and summer monsoon in the Mu Us Desert, influenced by the climate vicissitudes in the northern hemisphere during glacial periods and interglacial periods since 150 ka B.P.

The Milanggouwan stratigraphical section in the Salawusu River Valley takes down 27 alternately evolutionary sediment sequences of the aeolian dune layers with the fluvio-lacustrine facies and palaeosols since 150 ka BP. Based on grain-size analyses of the 86 samples from the section, some views have been put forward: (1) Grain-size accumulative centigrade contents of the aeolian sands in the past 150 ka in Milanggouwan section are mainly characterized by the aeolian palaeo-mobile dune sands, and those of the fluvial facies dominated by very fine sands also contain some quantities of silt and clay. (2) The grain-size general distributional characteristics - Mz (particle diameter) and σ (standard deviation) clearly show that the fluvio-lacustrine facies and palaeosols usually become finer in particles and worse in sorting than the aeolian sands. As regards Sk (bias angle) and Kg (kurtosis) values, the former two increase obviously compared with the latter, displaying positive bias and the latter often proximately symmetrical distributed, only few in negative bias. (3) At vertical direction of the section, the grain-size distributional coarse and fine rhythms vary very pronouncedly with the alternation of sedimentary facies. Mz, σ, Sk, Kg and SC/D (ratio of the sum of silt and clay to sand) of fluvio-lacustrine, palaeosols and aeolian sands separately constitute a commulative between peak and valley values. (4) The values of grain-size parameters lie on their eigenvalues. Taking the eigenvalue Φ50 as a boundary, the Φ75, Φ84 and Φ95 above the eigenvalue have wide flounce range and high sensitivity responding to the sedimentary facies, which may be called "active eigenvalues". In contrast with them, those below the above-cited eigenvalue, i.e., Φ5, Φ16 and Φ25, which have relatively narrow flounce range and low sensitivity, are called "inert eigenvalues".

This paper, with Milanggouwan stratigraphic section as a typical section of the Salawusu River Basin, explores the relation between CaCO 3 content distribution and climate change since 150 ka B. P. and concludes that: 1) The low-high changes of CaCO 3 content in the section has a remarkable corresponding relation with the sedimentary cycles of ancient aeolian sand and overlying fluviolacustrine facies or palaeosols. 2) CaCO 3 distribution in aeolian sand is relatively meagre, ranging from 0.8% – 7.18%, or on an average 2.50 % but relatively enriches in the fluviolacustrine faceis and palaeosols, ranging from 2.20% – 14.9%, or on an average 5.74%. This implies that they have different climatic backgrounds. The former was the product of erosion, transport and deposition by wind under arid and cold climatic conditions, whereas the latter was related to its special low-lying geomorphic position between the Ordos Plateau and Loess Plateau and warm-humid climatic environment. When the climatic became warm and humid, fluviolacustrine and swamp facies developed, soil-forming action strengthened, and low-lying catchment condition was favorable to CaCO 3 accumulation. 3) The basic cause responsible for the multicycle of CaCO 3 migration and accumulation in the Milanggouwan section may be the multiple alterations of winter and summer monsoons over the Mu Us Desert under the influences of climatic fluctuation of glacial and interglacial periods in the Northern Hemisphere since 150ka B.P..

The palaeo-mobile dune sands and fluvio-lacustrine facies with palaeosols in Milanggouwan stratigraphic section of the Salawusu River valley situated at the southeast of the Mu Us Desert experienced abundant remarkable alternative changes of coarse and fine rhythms in grainsize since 150 ka BP, and the grain-size parameters — Mz, σ, Sk, Kg and SC/D also respond to the situation of multi-fluctuational alternations between peak and valley values. Simultaneity the grainsize eigenvalues — ϕ5, ϕ16, ϕ25, ϕ50, ϕ75, ϕ84 and ϕ95 are respondingly manifested as greatly cadent jumpiness. Hereby, the Milanggouwan section can be divided into 27 grain-size coarse and fine sedimentary cycles, which can be regarded as a real and integrated record of climate-geological process of desert vicissitude resulted from the alternative evolvement of the ancient winter and summer monsoons of East Asia since 150 ka BP.