西峰与段家坡黄土剖面中有机质的特征及古环境信息

对甘肃西峰（X）黄土剖面L1－L6共163个样品进行总有机碳（TOC）和R ock-Eval热解分析，对比分析了西峰和陕西段家坡（D)剖面L5－S5－1层段及其中趋磁细菌的正烷烃与脂肪酸组成，结果显示西峰剖面的TOC与磁化率呈良好的对数关系，两个剖面L5－S5－1层段正烷烃和脂肪酸的分布表明，黄土地区当时古气候偏干冷，黄土高原由西北而东南，古气候呈变暖趋势，西峰剖面从S5－1形成到L5堆积，其古湿度可能有一个突变，即古气候由较湿润突然转变为极干燥，而段家坡地区当时的气候变化则可能较为缓和。

Distribution of Organic Matter in Xifeng and Duanjiapo Loess Sections and the Paleo-environmental Significance

The total organic carbon (TOC) were measured and Rock-Eval pyrogenetion were carried out for 163 loess and paleosol samples collected from Xifeng loess section, Gansu Province Composition of n-alkanes and fatty acid were also analyzed contrastively for L 5-S 5-1 layer samples of both Xifeng and Duanjiapo (Shaanxi Province) sections Good logarithmic relationship was found between TOC and magnetic susceptibility, which shows that TOC can also used as paleoclimatic proxy in loess area It is indicated by the composition of n-alkanes and fatty acid of L 5-S 5-1 layers of both Xifeng and Duanjiapo sections that it was relatively cold and dry in loess areas then, and the climate might became colder and dryer from southeast to northwest along the Loess Plateau A more obvious paleo humidity variation might exist from S 5-1 formation to L 5 accumulation in Xifeng