The palaeoclimatic changes since 13 ka as revealed by sporopollen assemblages in the Yanghu region,northern Xizang

Numerous sporopollen fossils have been taken in recent years from the Holocene sediments in the Yanghu region,northern Xizang. The assemblage zones and sequences of the sporopollen assemblages are established on the basis of the types,contents and ages. The assemblage zones include from the base upwards:(1) Ephedra-Quercus-Chenopodiaceae Artemisia (Zone Ⅰ),(2) Ephedra-Chenopodiaceae Artemisia (Zone Ⅱ),(3) Betulaceae-Quercus-Chenopodiaceae (Zone Ⅲ),and (4) Ephedra-Chenopodiaceae Artemisia (Zone Ⅳ) zones in the ZK₁ borehole section,and (1) Chenopodiaceae (Zone Ⅰ),(2) Betulaceae-Quercus-Chenopodiaceae (Zone Ⅱ),and (3) Ephedra-Chenopodiaceae Artemisia (Zone Ⅲ) zones in the IP₁₆ section. Three cycles of palaeoclimatic changes are also recognized. The palaeoclimatic changes indicated by these cycles are believed to be of important environmental significance.