云南鹤庆盆地2.780~1.802MaB.P.期间的 古植被和古气候*

鹤庆深钻421.7m以下岩芯的孢粉组合揭示2.780~1.802MaB.P.期间鹤庆盆地周围山地植被类型的更替主要是松林和寒温针叶林林带的上下迁移,并且研究区在第四纪之前就已基本具备了目前的主要植物种类及其自然地理轮廓。根据孢粉组合中寒温针叶林主要成分的孢粉含量变化推测研究区周围的山顶气候在2.780~1.802MaB.P.期间依次经历了相对温和偏干→整体相对寒冷潮湿→温和偏干→寒冷较湿→温凉较干→温和偏干→寒冷较湿的7次明显波动;同时结合孢粉组合特征和山顶气候推测盆地周围较低海拔区的气候经历了温暖干旱→整体相对温暖潮湿→温暖干旱→温凉较湿→温和偏干→温暖干旱,但夏季有一定降雨→温凉较湿的7次明显波动。在重建古植被与古气候时,还根据孢粉组合中寒温针叶林的主要成分与喜热成分的孢粉含量变化,探讨了2.780~1.802MaB.P.期间不同时段导致研究区周围山地垂直植被带迁移的主要原因,即区分了构造抬升与气候变化对其影响的可能性。研究认为2.729~2.608MaB.P.期间寒温针叶林面积增加主要是由于山体强烈抬升造成的,此次山体强烈抬升正对应着晚新生代地质时期青藏高原强烈隆升的"青藏运动B幕",而其他时段的寒温针叶林面积增减主要是气候变化引起的。

PALEOEGETATION AND PALEOCLIMATE OF THE HEQING BASIN DURING 2.780~1.802MaB.P.IN YUNNAN PROVINCE, CHINA

The pollen assemblage of the below 421.7m core of the Heqing deep drilling core revealed that vegetational succession in mountains around the Heqing Basin was mainly the change of forest-line between Pinus forest and cold-temperature conifer forest during 2.780~1.802MaB.P. , and primary floristics and physical and geographical outline at present have basically existed before the Quaternary in the studied area.According to the pollen percentage changes of main elements of cold-temperate conifer forest we can speculate that the climate of mountaintop around the studied area ordinally went through seven obvious changes during 2.780~1.802MaB.P.: relatively mild and moderately dry condition→ relatively cold and humid condition as a whole→ mild and moderately dry condition→ cold and moderately humid condition→ cool and moderately dry condition→ mild and moderately dry condition→ cold and moderately humid condition.Combined the pollen assemblage features and the climate of mountaintop implies that the climate of the relatively low altitude regions around the Heqing Basin successionally experienced warm and dry condition→ relatively warm and humid condition as a whole→ warm and dry condition→ cool and moderately humid condition→ mild and moderately dry condition→ warm and dry condition with some rainfall in summer→ mild and moderately humid condition.When reconstructing palaeovegetation and palaeoclimate, we discussed main causes resulting in transferring of vertical vegetational belt in mountains around the studied area at different regimes of the period of 2.780~1.802MaB.P.based on the pollen percentage changes of main elements of cold-temperate conifer forest and thermal elements in the pollen assemblage.This can distinguish influence of tectonic uplift and climatic changes on the transferring of vertical vegetational belt.Results also show that the increasing of cold-temperature conifer forest area during 2.729~2.608MaB.P.was mainly due to strong uplift of mountains, and the strong uplift of mountains justly corresponded to "Episode B of Qinghai-Tibet tectonic movement" of Qinghai-Tibet Plateau strong uplift during the Late Cenozoic geologic period, while the increasing and decreasing of cold-temperature conifer forest areas at other regimes were mainly caused by climatic changes.