Distribution of n-Alkanes as Indicative of Paleovegetation Change in Pleistocene Red Earth in Xuancheng, Anhui
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摘要: 利用气相色谱-质谱联用仪(GC-MS) 在安徽宣城更新世红土中检测出了微量的分子化石,包括正构烷烃、一元正脂肪酸、一元正脂肪醇以及α-正构脂肪酮等.正构烷烃的分布型式表明其来源于低等菌藻类生物和陆生高等植物,其中高碳数正构烷烃主要以C29为主峰,显示流域中的植被类型以木本植物为主; (C27+C29)/(C31+C33) 比值的变化反映出,在以木本植物占优势的背景下,流域中草本植物的相对比例也发生了多次变化.这一比值在本剖面上表现出多阶段的变化,而且这种变化与岩性、粒度变化密切相关,反映出这些参数可能还蕴涵着古气候信息.Abstract: Using GC/MS analysis,a series of molecular fossils,including n-alkanes,n-alkanoic acids,n-alkanols,and n-alkan-2-ones,have been identified from the Pleistocene red earth in Xuancheng,Anhui Province. The n-alkanes are proposed to be of mixed origin,derived from microorganisms and higher plants. The dominance of C29 homologue in the n-alkane distribution in most samples suggests the occurrence of trees in the region studied here. The parameter of (C27+C29)/(C31+C33) n-alkanes,representative of the abundance of grassy plants relative to woody plants,infers a varied grassy density spanning the last 1 Ma. Profiles of this ratio of n-alkanes display a varied trend comparable with the lithology,an indirect inference of paleoclimate which merits further investigation.
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Key words:
- molecular fossil /
- red earth /
- Quaternary /
- paleo-vegetation
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图 1 安徽宣城红土剖面正构烷烃的质量色谱
a.4.8 m处的样品; b.7.8 m处的样品
Fig. 1. GC/MS mass chromatograms of n-alkanes in red earth
图 2 红土正构烷烃(C27+C29)/(C31+C33) 比值的变化曲线(剖面4 m以上的分层及岩性据乔彦松等, 2003)
Fig. 2. (C27+C29)/(C31+C33) of n-alkanes in red earth
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