干旱区生态环境知识资源中心

A series of allochthonous and autochthonous molecular fossils were identified from the Holocene paleosol (S-0), Malan Loess (L-1) and the top Lishi Loess (S-1) in Jiuzhoutai loess profile in Lanzhou through the GC/MS analysis. The allochthonous molecules were transported into the Plateau by the loess grains whilst the autochthonous molecules were related to the input of the local paleo-vegetation and could be used to reconstruct the paleo-vegetation. The distribution of the autochthonous n-alkanes was discriminated from the overlapping allochthonous homologues characterized by the CPI value of unity. The dominance of autochthonous C-31 n-alkane implicates the occurrence of a grassy vegetation over the Loess Plateau since the last interglacier. The warmest period of the Holocene, though dominated by grass, was additionally characterized by the relatively increased abundance Of C-27 n-alkane indicative of woody plants. The desert plants might occur during the last glacier. The molecular fossil record is not contradictory with the recent phytolith data, denying the occurrence of a forest over the Plateau since the last interglacier. These data from the loess molecular stratigraphy indicate the importance of the discrimination of the autochthonous molecules from the allochthonous compounds.