Paleogene integrative stratigraphy, biotas and paleogeographical evolution of the Qinghai-Tibetan Plateau and its surrounding regions

The Paleogene is a crucial period when terrestrial and marine ecosystems recovered from major disruptions and gradually approached their modern states. In the Qinghai-Tibetan Plateau and its surrounding regions, the Paleogene also represents a significant phase of tectonic evolution in the Qinghai-Tibetan Plateau-Himalaya orogeny, reorganization of Asian climates, and evolution of biodiversity. Due to limitations in research conditions and understanding, there are still many controversies regarding stratigraphic divisions in the Qinghai-Tibetan Plateau and its surrounding regions In recent years, extensive studies on sedimentary petrology, magnetostratigraphy, and isotope dating have been conducted in the region. Numerous fossils have been discovered and reported, contributing to a more systematic understanding of biostratigraphy. These studies have laid a solid foundation for the comprehensive investigation of the stratigraphy, biotas and paleogeographic evolution of the Qinghai-Tibetan Plateau and its surrounding regions during the Paleogene. In this paper, we integrate recent research on fossils, isotopic dating, magnetostratigraphy, and geochemistry to refine the stratigraphic divisions and correlation framework of different tectonic units in the region, building upon previous studies. Since the Second Tibetan Plateau Scientific Expedition and Research, the knowledge of Paleogene floras has gradually expanded. This paper discusses the biostratigraphic significance of extinct and newly appeared taxa based on the latest dating results of these plant species. The new understanding of fossil species such as the "Eucalyptus" and Arecaceae establishes connections between the Paleogene flora of the Qinghai-Tibetan region and the biotas of Gondwana, specifically Oceania and South America. The evolutionary history of key taxa near the Yarlung Zangbo suture zone indicates that the collision between the Indian and Eurasian plates occurred approximately 65-54 Ma. Paleoelevation reconstructions, based on plant fossils, suggest that the Hengduan Mountain had already formed their current topographic pattern prior to the Early Oligocene. The warm and humid lowlands adjacent to the main suture zones in the Paleogene Qinghai-Tibetan Plateau served as the primary pathway for biota exchanges. The relatively low elevation of the Himalaya during the Paleogene did not effectively block the moisture from the Indian Ocean.