中文摘要：

选取位于黄土高原中部西峰和洛川塬面中心地区，分别开挖一个竖井获得L2以来连续黄土-古土壤沉积序列的剖面，并对剖面样品的总有机碳、无机碳酸盐的碳同位素组成进行分析。结果显示黄土-古土壤的有机质碳同位素变化与前人对天然剖面的研究结果一致，同时也注意到黄土-古土壤序列有机碳δ^13Corg与无机碳酸盐δ^13Ccarb有相似的变化趋势，两者在统计学分析意义上均呈显著正相关关系，西峰塬和洛川塬的相关系数分别为r=0．615和r=0．314，α〈0．01，该结果与以往对黄土高原塬面边缘天然露头剖面获得有机碳与总碳酸盐碳同位素呈反相关趋势的结论不一致。对于这种现象的初步解释可能是：（1）来自后期的改造作用：由于黄土沟谷出露的天然剖面多发生在雨水冲刷黄土塬面所切割形成的沟谷两侧，这样天然剖面处于一个开放或半开放的环境，其表层至某一深度受外界水热环境和气体交换影响黄土中的无机碳酸盐；（2）同时黄土-古土壤竖井剖面也可能受土壤CO2分压的影响造成土壤次生碳酸盐的形成而导致同位素变化趋势的复杂性；（3）采样点区域性的差异。结果表明，深入研究不同地区塬面竖井剖面黄土-古土壤碳同位素组成并与相应地区的天然剖面碳同位素组成进行对比，将有助于更准确地理解黄土-古土壤碳同位素所记录的古植被和古气候变化历史。

英文摘要：

Locating in the center of both Xifeng and Luochuan districts on the Chinese Loess Plateau, a continuous loess-paleosol sequence since L2 stage was collected by digging well, and stable carbon isotope compositions were measured in detail including organic matter and inorganic carbonate. The results show the change trend of organic carbon isotope （δ13^Corg） of both sections is consistent with that of the previous results for natural outcrop section. It is also noticed that the change trend of organic carbon isotope （δ^13Corg） is consistent with that of carbonate carbon isotope （δ^13Ccarb） in the loess-paleosol sequences, and δ^13Corg is significantly positive correlation with δ^13Ccarb, with the correlation coefficients of 0. 62 （ α 〈 0. 01） and 0. 314 （ α 〈 0.01）, respectively. This is contrary to the conclusion of carbon isotope compositions from natural outcrop section. The reason of the difference is probably that （1） late reformation： because natural outcrop section mostly occurred on both sides of gully formed from rainfall erosion on the Loess Plateau, the section is in an opening or semi-opening environment which made outside hydrothermal environment and gas exchange influence soil inorganic carbonate from surface to some depth; （2） at the same time, loess-paleosol phreatic section is likely influenced by both upper moisture and fractional pressure of CO2 of soil, and pedogenic carbonate formed, resulting in the complex change tendency of carbon isotope composition; （3） regional difference of sample location. Our study indicates that further research on carbon isotope composition of phreatic section in loess-paleosol sequences of other districts and comparison of corresponding natural outcrops are important to more accurately understand the history of evolution of paleovegetation and palcoclimate recorded in carbon isotope of loess-paleosol sequences.