青藏高原东北缘北联池剖面清水营组孢粉组合特征及地质意义

青藏高原隆升是新生代最重要的地质事件之一，对邻区乃至全球的气候变化都产生了深远的影响，已有学者研究认为该期隆升与气候冷暖变化之间具有较好的耦合关系。北联池剖面在区域构造位置上隶属于青藏高原东北缘弧形构造带后缘六盘山以西，古近系清水营组主要为一套紫红色泥岩夹薄层石膏层为主的浅湖相沉积，蕴含了丰富的古环境和古气候信息。文章系统研究了剖面的孢粉组合特征，共鉴定出孢粉类型60属65种及若干未定种，其孢粉组合特征中被子植物花粉占绝对优势，裸子植物花粉和蕨类植物孢子含量很少。结合现有区域孢粉的研究成果，综合分析认为清水营组沉积的地质时代属于中晚渐新世—中新世早期。孢粉植物群以桦木科、胡桃科和榆科等落叶阔叶植物为主，组合中还出现了数量不多但种类繁多的热带—亚热带植物的花粉，而典型干旱的灌木和草本植物分子含量少，总体上反映了暖温带较温和湿润的古环境古气候背景。孢粉组合中几乎不见耐寒山地针叶植物花粉的出现，说明该时期区域气候环境尚未发生由暖转冷的重大变化，青藏高原向东北方向的隆升扩展尚未影响到六盘山地区。研究成果为约束青藏高原东北缘清水营组的沉积时代以及青藏高原隆升过程对区域古生态古气候的影响提供新的证据。

Characteristics and geological significance of the palynological assemblages of the Qingshuiying Formation in the Beilianchi section,northeastern margin of the Tibetan Plateau

The uplift of the Tibetan Plateau is one of the most important geological events in the Cenozoic era, which has had a far-reaching impact on climate change in neighboring regions and even the world. Scholars have already considered that the uplift of this period has a good coupling with the warm and cold climate changes. The Beilianchi section is west of Liupan Mountain, the back edge of the arcuate tectonic belt on the northeast margin of the Tibetan Plateau. The Paleocene Qingshuiying Formation is mainly a set of shallow lacustrine deposits dominated by purple-red mudstone with thin gypsum layers containing rich paleoenvironmental and paleoclimatic information. The article systematically studied the palynological assemblage of the Beilianchi section and identified 60 genera and 65 species of sporopollen types as well as several undetermined species. The assemblage is characterized by dominant angiosperm pollen grains and rare gymnosperm pollen and fern spores. Based on the existing research results of regional sporopollen, the geologic age of the Qingshuiying Formation is believed to be the middle-late Oligocene–early Miocene. The sporopollen flora is dominated by deciduous broad-leaved plants such as Betulaceae, Juglandaceae, and Ulmaceae, and pollens from a few but diverse tropical-subtropical plants also occur in the assemblage. In contrast, the pollen content of typical arid shrubs and herbaceous plants is small, generally reflecting the warm-temperate zone's milder and wetter paleoenvironmental and paleoclimatic background. The absence of pollen from cold-tolerant mountain conifers in the palynological assemblage indicates that the regional climatic environment had not yet changed from warm to cold during this period and that the uplift and expansion of the Tibetan Plateau to the northeast had not yet affected the Liupanshan area. The results of this study provide new evidence to constrain the depositional age of the Qingshuiying Formation on the northeastern margin of the Tibetan Plateau and the impact of the uplift process of the Tibetan Plateau on the paleoecology and paleoclimate of the region.