西北地区晚第四纪沉积地层一元正脂肪酸酰胺分布特征及古气候意义

利用气相色谱质谱联用仪在中国西北地区晚第四纪沉积地层中检测出一类特殊的类脂物分子--一元正脂肪酸酰胺.根据其碳数分布特征及前人的研究成果,认为一元正脂肪酸酰胺来源于各种生物体,产生于生物的某些生理活动过程,而不是来源于石油残余物及各种可能的污染.通过对比3个不同区域相近时期古湖相及黄土沉积地层中的脂肪酸酰胺分布特征,认为柴达木盆地可能不是黄土沉积的主要物源区,而额济纳盆地及邻近区域对黄土堆积有着重要的贡献或具有相同的物源.典型黄土沉积地层中UFAA值(不饱和与饱和脂肪酸酰胺相对含量的比值)与粒度、磁化率等指标具有很好的可对比性,特别是在相对暖湿阶段UFAA值呈现了明显的低值.这一现象表明脂肪酸酰胺在沉积地层中的变化受控于气候变化所导致的成岩作用强度的变化,从而记录了气候变化信息.通过研究,认为生物生理活动过程中所产生的一元正脂肪酸酰胺与构成细胞膜的类脂物分子一样,可记录古气候变化.

Distribution and Characteristics of n-fatty Acid Amides in Late-Quaternary Sediments from Northwestern China and Their Paleoclimatic Significance

A series of analogs of n-fatty acid amide (n-FAA) have been identified in different late Quaternary sedimentary strata from northwest China by using the gas chromatography-mass spectrometry (GC-MS). Based on the carbon distribution as well as the characteristics of n-FAA and previous studies, we suggest that the n-FAA originated from biogenic sources rather than petrolic residues, or any other potential contaminant. By comparing the distribution of n-FAA in different paleo-lakes and loess strata, we propose that Ejina basin is one of the main source areas of Luochuan loess deposits. Alternatively, the relationship of the material source between the Qaidam Basin and Luochuan Loess deposit is low. The ratios of unsaturated to saturated n-FAA (U_FAA) show trends comparable to that of the magnetic susceptibility and grain size variation within the loess, especially the lowest values associated with warm/humid episodes. This phenomenon indicates that the distribution of the n-FAA was influenced by early diagenetic processes, which were controlled by paleoclimatic variations. Our results highlight the variation within n-FAA, which is naturally formed in the physiology of different organisms. n-FAA can also record the paleoclimatic variation, similar to lipids, which originate from the constitutional unit of a cell membrane.