西藏羊湖地区近1.4万年以来孢粉植物群及古气候研究

Pollen-based Reconstructions of Late Pleistocene and Holocene Vegetation and Climatic Changes of Yang Lake Area, Tibet

通过对西藏羊湖地区ZK1和卡拉苏代牙剖面(IP16)的孢粉分析和总有机碳(TOC)、元素含量分析等,建立了羊湖地区近1.4万年以来的孢粉组合带、重建当时的植被类型及古气候演变序列。结果显示:该时期经历了5次植被类型的更替,即草原型→疏林草原型→草原型→疏林草原型→草原型,与之相对应的气候经历了5次波动(2个半旋回), 即11 220 a.B.P.左右的第一气候旋回:由干旱→半干旱半湿润转化;8 970a.B.P.左右的第二气候旋回,同样由干旱→半干旱半湿润转化,然后进入半个气候旋回,即干旱气候期,推测今后有可能进入半干旱半湿润气候期。

In order to research the late Quaternary palaeoclimate evolution in the Yang Lake area,northern Tibet, we drilled the shallow well and surveyed the profile sections (ZK1 and IP16) in theperiphery of the lake and exposed its river facies sedimentary strata. Abundant sporopollen fossilswere discovered in the 48 samples. According to sporopollen types and contents, from bottom totop, they were divided into five assemblages: (1) Chenopodiaceae high content assemblage. (2)Ephedra-Quercus-Chenopodiaceae-Artemisia assemblage. (3) Ephedra-Chenopodiaceae-Artemi-sia assemblage. (4) Betulaceae-Quercus-Chenopodiaceae assemblage. (5)Ephedra-Chenopodiaceae-Artemisia assemblage. The palaeovegetation reconstructed by a great amount ofpollen records displays five changes: steppe → poor-forest grassland → steppe → poor-forestgrassland → steppe. A synthesis of pollen records, total organic carbon and element content fromZK1 and IP16 showed the history of climate cycle changes during late Pleistocene and Holocene.During 11 220 a.B.P or so, the first climate cycle was characterized by warm and dry climate to semi-dryand semi-humid climate. During 8 970 a.B.P or so, the second climate cycle was characterized by warmand dry climate to semi-dry and semi-humid climate. The last climate cycle is symmetry to the fifthpollen assemblage, was characterized by warm and dry climate. By the climate cycle periodicity, wepresume that the area climate would be semi-dry and semi-humid in the future.