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The carbon isotopic compositions of soil organic matter (SOM) and total carbonate (TC) in Xifeng loess-paleosol sequence have been studied. The δ13CSOM values vary from -23.8‰ to -20.2‰, which are higher in interglacial than in glacial stages. Contrary to δ13CSOM values, the δ13CTC values vary from -8.5‰ to -3.6‰ and are lower in interglacial than in glacial stages. The differences (Δδ13C) between the δ13CS0M and δ13CTC values vary from 14.1‰ to 19.4‰. Our results from the Xifeng loess-paleosol sequence indicate that the Δδ13C values represent the ratio of primary carbonate (PC) to secondary carbonate (SC). The Δδ13C values were high in the loess stages, and the maximal PC-to-SC ratio can reach 6:4. But in the paleosol stages, the Δδ13C values were low, with a small proportion of PC. The Δδ13C 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. [ABSTRACT FROM AUTHOR]