The Red Bed Sporo-pollen Assemblages、Geological Age and Ecological Environment from Siwangou-Tandonggou of Yaojie, Gansu

Key words: 
• sporo-pollen of red bed section /
• vegetation variation /
• geological age /
• Eogene

Abstract: This paper includes a systematic analysis and correlation study on the sporo-pollen assemblage, stratigraphic sequence and geochronology of the Siwangou red bed section in Yaojie,Gansu. The following sporo-pollen assemblages may be recongnized in the Siwangou section (in ascending order ):① Pinuspollenites-Inaperturopollenites-Taxodiaceaepollenites-Quercoidites-Lygodioisporites assemblage,which may be assigned to Early Oligocene;② Betu laceoipollenites- Quercoidites-Chenopodipollis -Lygodioisporites assemblage,which belongs to Middle Oligocene. The results of this study show that, the geological age of the red bed section belongs to Eocene-Middle Oligocene; the Eocene sporo-pollen assemblages of Yaojie are approximately similar to those of the east region and the west region of China,which indicate a subtropical broadleaf and deciduous forest, mainly composed of the subtropical and warm temperate taxa, and a burning hot climate; from Late Eocene to Early Oligocene, the vegetation of Yao ne evolved to warm temperate mixed broadleaf and needleaf forests, mainly composed of the warm broadleaf and deciduous plants, presumably associated with warm and humid conditions; the Middle-Oligocene sporo-pollen records of Yaojie reflect comparatively warm and wet climates, which indicate that temperate broadleaf and deciduous forests are mainly constituted by Betulaceoipollenites and Quercoidites. The region correlation analysis shows that since Early Oligocene a trend toward difference of vegetation and climate has been on the increase between east and west region of China. Early Oligocene may be an important age of neotectonic movement in China.