西藏札达盆地晚上新世古植被型分析

PALAEOVEGETATION TYPE ANALYSIS OF THE LATE PLIOCENE IN ZANDA BASIN OF TIBET

札达盆地晚上新世生长着以高山荒漠小灌木、草原、亚高山常绿针叶林和中低山常绿针叶林为主的植被。气候显示了从干旱寒冷至温暖湿润的垂向分异 ,总体偏于干、寒 ,属亚热带高山或亚高山类型。当时区内海拔已较高 ,南低北高的地势特征也已形成。古植被重建及现青藏高原的植被调查资料表明 ,当时盆地最低处的海拔可能不会超过 2 5 0 0m ,其周围及北部可能存在海拔 4 0 0 0m的高地或更高的山峰。中、晚上新世迄今 ,该地区隆升的高度可能不会超过 10 0 0m ,其幅度小于喜马拉雅山中部地区。

The palaeovegetation during Late Pliocene in Zanda Basin of southwestern Tibet was mainly made of dwarf half shrub desert, steppe, sub alpine needle leaf forest and montane evergreen needle leaf forest, and possibly mixed with some deciduous broad leaf forest and evergreen broad leaf forest during that time. By comparison with the living environments of modern vegetation types, the climate was inferred as cold, arid or semi arid to semi humid types, which might be a kind of subtropical sub alpine types. During Late Pliocene the lowest elevation in the basin might be a little lower than 2 500 m, and the topographic form was probably similar to that of present status in Zanda, and it was lower in the south and higher in the north. The western plateau might be uplifted around 1 000 m from then on. Compared with about 4 000 m suggested by the central Himalayan area, this value is much smaller.