青藏高原腹地温泉地区新生代生态环境演化与高原表面隆升过程分析

采自青藏高原腹地温泉地区新生代地层中的孢粉组合资料表明:从古新世到早中新世,古植被由早期的针阔叶混交林-森林草原植被向晚期的疏林草原植被演化,古气候也由亚热带暖湿气候向温凉气候演化;从上新世到早更新世,阔叶树种明显减少,而草本植物显著增多,反映气候开始向干冷方向演化;而中更新世晚期以来,出现稀疏草原植被向荒漠草原植被的演化,最终塑造了现代以藜、蒿为主的荒漠草原植被环境。高原腹地生态环境变化揭示了青藏高原自古新世以来至少经历了3次具有生态环境意义的表面隆升事件:古新世—早渐新世沱沱河组冲积扇砾岩沉积以及孢粉组合分析表明,青藏高原在白垩纪末—古新世初已隆升至1000～1500m,高原地形可能是高原(高山)与盆地相间的地貌格局;早中新世五道梁组植被中亚热带成分的显著增高,可能与高原表面隆升诱发高原季风而导致气候湿润有关,推测高原已隆升至2000～2500m;而中更新世晚期以草本植物为主,反映高原植被已经发生了转型,高原已隆升至3000m以上。

Analysis of the evolution of the Cenozoic ecological environment and process of plateau surface uplift in the Wenquan areain the interior of the Qinghai-Tibet Plateau

The data of sporopollen assemblages collected from Cenozoic strata in the Wenquan area in the interior of the Qinghai-Tibet Plateau indicate that: from the Paleocene to early Miocene,paleovegetation evolved from mixed needleleaf and broadleaf forests-forest grassland vegetation in the early stage to veld vegetation in the late stage and the paleoclimate also evolved from the warm-wet subtropical climate to warm-cool one; from Pliocene to early Pleistocene,broadleaf trees were obviously reduced,while herbaceous plants increased markedly,reflecting that the climate began to evolve towards the dry-cold climate; and since the late part of the middle Pleistocene,the evolution from veld vegetation to desert grassland vegetation appeared,which finally molded an environment of modern desert grassland vegetation represented mainly by Chenopodiaceae and Artemisia. The change of the ecological environment in the interior of the Qinghai-Tibet Plateau reveals that the Qinghai-Tibet Plateau has undergone at least three uplift events with ecological-environmental significance since the Paleocene. Fanglomerate sediments and sporopollen assemblages in the Paleocene-early Oligocene Tuotuo River Formation indicate that: the Qinghai-Tibet Plateau had been uplifted to the altitudes of 1000-1500 m above sea level by the terminal Cretaceous-early Paleocene and the plateau landform might have a framework of alternating high mountains and basins; the noticeable increase in subtropical components in the vegetation of the early Miocene Wudaoliang Formation might be related to the climatic wetness caused by plateau monsoons induced by the plateau surface uplift and it is inferred that the plateau had uplifted to 2000-2500 m above sea level. In the late part of the middle Pleistocene,herbaceous plants predominated,indicating that the type of plateau vegetation had changed and that the plateau has been uplifted to an altitude of more than 3000 m above sea level.