中文摘要：

利用气相色谱-质谱联用仪（GC—MS）对连续取样的洛川黄土剖面弱古土壤层（L1SS1）和相邻黄土层（L1LL1，L1LL2）的分子化石进行了检测，获得正构烷烃、正烷基-2-酮和酰胺等种类众多、丰度较高的分子化石。W草／植=nC31／（nC27＋nC29＋nC31），W木／檀=（nC27＋nC29）／（nC27＋nC29＋nC31）和W木／草=（nC27＋nC29）／nC31记录了草本与植被、木本与植被、木本与草本比例变化规律的古植被信息。检测样品的CPI值为5．60—11．50，地质作用影响较小；通过磁化率、粒度和分子化石指标的相关性分析，认为磁化率、粒度记录了环境变化及主要气候事件（相关系数达-0．81）；而分子化石能较好地反映古植被变化。当气候环境由干冷向温湿变化、水热配置条件改善时，植被变化响应较迅速；当环境恶化、转向干冷时，响应较弱或滞后，这种现象可能是由于植被生态系统稳定性造成的结果。整个研究剖面段样品以nC31为主峰的高碳数优势，分子化石表明末次冰期间冰段洛川地区（黄土高原）发育草本植被而没有出现以森林为主的植被。

英文摘要：

Using GC-MS, biomarkers from the weakly developed paleosol （L1SS1 ） and loess layers （ L1 LL1 and L1 LL2 ） in the Luochuan loess section were measured continuously. All samples are rich in n-alkanes and other biomarkers. The indices, such as Wg/v = nC31/（nC27 ＋ nC29 ＋ nC31 ）, Ww/v = （nC27 ＋ nC29 ）/（nC27 ＋ nC29 ＋ nC31 ）, and Ww/g = （nC27 ＋ nC29 ）/nC31 not only record the ratios between grass and total vegetation, trees and total vegetation, and trees and grass, but also indicate the vegetation change history. The CPI of all the tested paleosol （ L1 SS1 ） samples change between 5.60 and 11.50, and much larger than 1, which indicate that the influences unrelated to the climate during the soil formation are neglectable. Based on relative relationship analyses between magnetic susceptibility, grain size, and biomarker indices, it proved that magnetic susceptibility and grain size generally, the relativity reaches as high as - 0.8 1, recorded environmental change and climatic events, while biomarkers are related to paleovegetation changes. Results indicate that vegetation change is more sensitive to the improvement rather than deterioration of the climate, i. e., when the climate changes from cold-dry to warm-humid, vegetation changes quickly; but when the climate changes from warm-humid to cold-dry, the vegetation change is in a relatively slow pattern. This phenomenon might be attributed to the stability of the vegetation system itself. Biomarkers of all samples analyzed are characterized by a high carbon number majority of C31, indicating that grass predominated the vegetation during the interstade of the Last Glaciation in Luochuan area and there was no forest developed during that period.