Abstract:

The fossil Pediastrum was investigated from the Gaoximage section ( 42 57''14'''' N, 115 22''3'''' E, Alt 1 253 m ) in the Hunshandak Sandy Land, Inner Mongolia (Nei Mongol) of China in order to gain a better understanding the changes of palaeovegetation, palaeoenvironment and palaeoclimite since 5 000 aBP when the pollen-spore was studied. The results show that the fossil Pediastrum assemblage can be divided into three periods: Ⅰ. 5 000-3 500 a BP, the fossil Pediastrum occurred rarely. Based on this result it can be surmised that the lake might be fresh water with poor organics.Ⅱ. 3 500-1 500 a BP, the fossil Pediastrum likes volcanic emerged. It probably indicate moist conditions and the grasslands were developed during this time; and Ⅲ. 1 500-200 a BP, the fossil Pediastrum disappeared. It can show that the lake water become salty and shrunk, and the weather could become drier and drier. This result shows that Pediastrum, a kind of facies fossil, happened simultaneously in the pollen-spore assemblage during the second period. Sometimes Pediastrum can reach more than 60 per cent of the total spore pollen assemblage, indicating that Gaoximage lake was not only fresh water with abundant eutrophic materials but also occu-pied a large area during 3 500-1 500 a BP.

Key words: Hunshandak Sandy Land, since 5 000 a BP, fossil Pediastrum