Vegetation and climate of the central and northern Qinghai-Xizang plateau from the Middle Jurassic to the end of the Paleogene inferred from palynology

The collision between India and Eurasia and the subsequent uplift of the Qinghai-Xizang plateau region of the Eurasian continent during the latest Mesozoic and Cenozoic had a significant environmental impact on the region. Understanding the vegetation of both palaeocontinents prior to the collision is crucial for interpreting the evolution of their floras and climatic changes during this period. The composition of the vegetation and climate of the plateau from the Middle Jurassic until the end of the Oligocene are inferred herein from the composition of 14 palynofloras and compared with other regions of China. The palynofloras are similar to those of eastern and northwestern parts of China but bear their own unique features brought about by differing climatic influences. Overall, a warm-hot, arid-semi-arid climate prevailed over the plateau during most of the period from the Middle Jurassic until the end of the Cretaceous. The climate cooled and humidity increased in the Paleogene, and especially during the Oligocene. The long-term climatic change in the Qinghai-Xizang plateau region of the Eurasian continent during the Middle Jurassic-Paleogene that is indicated by the miospore assemblages is broadly comparable to the isotope-based SST (sea-surface temperature) changes that have been identified. It is apparent that climatic changes on a global scale were primarily responsible for controlling the composition and distribution of the vegetation on the plateau; no monsoon features are detectable in the northwestern interior of China. A maximum estimation of 2890 m surface palaeoelevation is inferred for the central and northern plateau during the Oligocene based on vegetation analysis, which is lower than previous estimations based on oxygen isotope and coexistence analyses. The elevation of the southern part of the study area, i.e. the area south of the Gandise Mountains, was low, close to sea-level.