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

Abstract

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.

Keywords

• palynological assemblage
• paleoenvironment
• paleoclimate
• qingshuiying formation
• beilianchi section
• northeastern margin of the tibetan plateau