The relationship between carbon and oxygen isotopic composition characteristics of carbonates in loess sediments and paleoclimate

摘要

Based on the carbon and oxygen isotopic compositions of carbonates in loess sediments measured by the methods of stepwise heating and phosphoric acid decomposition from five pieces of samples of paleosol, loess and eolian sand, respectively, the distributive characteristics in different temperature steps and the fractionation mechanisms of carbon and oxygen isotope and their relation to the paleoclimate are discussed. The preliminary results show that, by means of stepwise heating, different carbon and oxygen isotopic compositions are obtained in different temperature steps and carbon and oxygen isotopic compositions of paleosol, loess and eolian sand are in a different distributive pattern in the range of studied temperature steps. The results also show that the δ~(13)C ratios in 700— 800℃ are more sensitive tracers of paleoclimate than those measured by the method of phosphoric acid decomposition. The susceptibility to climatic changes of δ~(18)O ratios analysed by the method of phosphoric acid decomposition is higher than those analysed by the method of stepwise heating, but the δ~(18)O ratios measured by these two methods do not effectively reflect climatic changes.