中文摘要：

通过对我国典型干旱区表土分粒级样品的碳酸盐含量及其碳氧同位素的测试，结果显示：我国西北干旱区表土不同粒级样品的碳酸盐含量以及碳氧稳定同位素组成存在较大的差异。随着粒径的减小，碳酸盐含量逐渐升高，氧同位素逐渐偏正，碳同位素逐渐偏负。可以认为细颗粒组分中土壤次生碳酸盐相对比例大，而粗颗粒组分中原生碳酸盐相对占优势。而次生碳酸盐氧同位素可能受蒸发的控制，碳同位素更多的受植被的影响，所以表现出细颗粒组分较粗颗粒组分碳酸盐的氧同位素更偏正，而碳同位素更偏负。因此，干旱区表土细颗粒组分碳酸盐能更好地反映成壤过程中次生碳酸盐形成时期的气候环境信息。

英文摘要：

The widely distributed arid land in northwest China provides a perfect object for investigating the environment change. The surface soil in arid land is an important carrier of the modem environment change process information. In order to further understand the factors affecting the carbon and oxygen isotope composition of surface soil in arid land, this paper studied the surface soil samples in Xinjiang and Gansu Province, a typical arid land in northwest China. These samples were separated into several different grain sizes fractions by sedimentation, floatation and filtration. Their carbonate contents were measured with titration method and their oxygen and carbon isotope composition was online analyzed using MAT -252. The results of the study indicate that there is a good correlation between the carbonate content and the grain size. The carbonate content increases with the grain size decreasing. The results of isotope analysis show that the stable oxygen and carbon isotopes of different grain size samples are distinctly different. As the grain size decreasing, the oxygen isotope increases and the carbon isotope gets more negative. According to the above results, the conclusion can be drawn that the pedogenic carbonate is regnant in fine grain samples; while the primary carbonate predominates in the coarse grain group. The oxygen isotope of pedogenic carbonate may be controlled by the evaporation. The oxygen isotope of pedogenie carbonate mainly depends on the oxygen isotope composition of soil water. Strong evaporation brings isotopic fractionation, and then leads to the enrichment of 180 in soil water. However the carbon isotope of pedogenic carbonate may be affected by vegetation. The soil carbon dioxide is an important contributor of the carbon isotope of pedogenie carbonates. Moreover the soil respiration releases isotopically light carbon dioxide, and then leads to the carbon isotope of soil carbon dioxide more negative. Therefore, the oxygen isotope shows more positive and carbon isotope more negative i