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

Based on the carbon and oxygen isotopic compositions of carbonates in loess sediments meas-ured by the methods of stepwise heating and phosphoric acid decomposition from five pieces of samples ofpaleosol,loess and eolian sand,respectively,the distributive characteristics in different temperature steps andthe fractionation mechanisms of carbon and oxygen isotope and their relation to the paleoclirnate are discussed.The preliminary results show that,by means of stepwise heating,different carbon and oxygen isotopiccompositions are obtained in different temperature steps and carbon and oxygen isotopic compositions ofpaleosol,loess and eolian sand are in a different distributive pattern in the range of studied temperaturesteps.The results also show that the δC ratios in 700-800℃ are more sensitive tracers of paleoclimatethan those measured by the method of phosphoric acid decomposition.The susceptibility to climatic changesof δO ratios analysed by the method of phosphoric acid decomposition is higher than those analysed by themethod of stepwise heating,but the δO ratios measured by these two methods do not effectively reflect cli-matic changes.