黄土中钙结核的碳氧同位素研究(一)氧同位素及其古环境意义

稳定同位素分析已日益广泛用于对古环境的研究，成为一种十分重要的手段。本文从洛川离石黄土古土壤中钙结核的氧同位素组分分析结果，探讨了将钙结核δ^１８Ｏ值转化为古土壤形成时古温度的途径。指出此方法有良好的应用前景，但需要积累大量资料，用统计的方法才能获得可靠的结果。洛川离石黄土中各种古土壤形成时的地表年平均温度都比当地现在的温度要高。发育最好的Ｓ,形成时高出约５℃。用氧同位素组分推算的古温度与其他方法得出的结果可互相比较，但也略有差异。

CARBON AND OXYGEN ISOTOPE COMPOSITIONS OF CARBONATE CONCRETIONS IN LOESS PART 1:OXYGEN ISOTOPE AND PALEOTEMPERATURE

The existence of a direct quantitative relationship between the oxygen isotope composition of soil carbonate and the mean oxygen isotopic composition of local meteoric water and that between the mean oxygen isotopic composition of the meteoric water and the mean annual surface temperature have been demonstrated by several papers published during the last decade. One may be reasonably optimistic about the possibility of carrying out quantitative paleoclimatological and paleoecological studies on the carbonates in the continental deposits of Quaternary age, especially the carbonate concretions in loess. It will be of great importance to study the evolution of climate through time using this technique. However, a most important point has yet to be checked: the real process of the formation of the carbonate concretions in loess.About 75 samples of carbonate concretions related to the paleosols in Lishi Loess (Formation) were collected from Luochuan loess section and measured for their δ^１８O. Oxygen isotopic measurements carried out seem to yield reliable data.The data obtained were transferred to the formation temperature of the paleosols by means of the existing equations. These results confirm the potential of the method and support previous conclusions obtained from the comparison paleosols with their equivalent modern soils even though care must be taken to avoid misinterpretations and inappropriate conclusions.