Variation of soil DELTA delta~(13)C values in Xifeng loess-paleosol sequence and its paleoenvi-ronmental implication

摘要

The carbon isotopic compositions of soil organic matter (SOM) and total carbonate (TC) in Xifeng loess-paleosol sequence have been studied. The delta~(13)C_(SOM) values vary from -23.8 per thousand to -20.2 per thousand, which are higher in interglacial than in glacial stages. Contrary to delta~(13)C_(SOM) values, the delta~(13)C_(Tc) values vary from -8.5 per thousand to -3.6 per thousand and are lower in interglacial than in glacial stages. The differences (DELTA delta~(13)) between the delta~(13)C_(SOM) and delta~(13)C_(TC) values vary from 14.1 per thousand to 19.4 per thousand. Our results from the Xifeng loess-paleosol sequence indicate that the DELTA delta~(13) values represent the ratio of primary carbonate (PC) to secondary carbonate (SC). The DELTA delta~(13) values were high in the loess stages, and the maximal PC-to-SC ratio can reach 6:4. But in the paleosol stages, the DELTA delta~(13) values were low, with a small proportion of PC. The DELTA delta~(13) values in loess-paleosol sequence also indicate the contributions of the dust to the loess sediment in the Chinese Loess Plateau because the dust contains the PC.