干旱盆地古湖相沉积物生物标志物分布特征及环境意义——以柴达木盆地为例

柴达木盆地大面积裸露于地表的古湖相沉积物长期受到物理风化的剥蚀作用,成为风尘堆积的主要物源。而沉积物中的生物标志物在一定条件下会被保存下来,记录了古环境变化。利用气相色谱-质谱联用仪对采自柴达木盆地察尔汗盐湖古湖相沉积物样品进行了分析,结果检测出一系列具有生物源指示意义的生物标志物,主要包括系列正构烷烃、系列正烷基-2-酮、正构脂肪酸/醇/酯、系列支链烷烃、系列烷基酰胺以及若干五环三萜类（非藿烷系列）及甾类化合物。研究发现柴达木盆地察尔汗古湖湖泊沉积物中生物标志物未受强烈的成岩作用及微生物活动的改造,基本保持了原有的分布特征。正构烷烃高碳数系列明显的奇碳优势以及样品中高含量的非藿类五环三萜类生物标志物的检出说明在高原封闭性盐湖中曾经存在着大量高等植物碎屑的输入,指示了沉积时期气候湿润、植被相对繁盛,与柴达木盆地的现代自然地理环境截然不同。

Distribution Characteristics and Environmental Significances of Biomarker in Paleolake Sediments of Arid Basin:A case study in the Qaidam Basin

In Qaidam Basin, a large area of paleolake sediments was exposed to the surface and received strong weathering over time. The weathering products are considered to be a main material source of the aeolian deposits. The biomarker could be well preserved in the sediments in certain circumstances and documented the paleoenvironmental variations. By using the conventional gas chromatography-mass spectrometry (GC-MS) method, the samples collected from the shell bar profile, Qarhan salt lake of Qaidam Basin in northeastern Tibetan Plateau were determined. A series of biomarkers were identified from these lacustrine deposits, mainly including n-alkanes, branch alkanes, n-alkan-2-ones, n-alkanoic acids, alkanol, alkyl amide, ester, triterpenoids and steroids, indicative of various biogenic contributions. The high odd-carbon predominance of n-alkane homologous and the presence of non-hopanoid pentacyclic triterpenoid represent amount of allochthonous terrestrial plant materials were introduced to the lake sediments in Qarhan paleolake, indicating the wet climate and resulted in the plants to flourish in the period in which the lake sediments formed, which is very different with the modern environment in Qaidam Basin.