Paleoenvironment of Late Oligocene in the central Qinghai-Tibet Plateau: Insights from Sporopollen Fossils

The uplift of the Qinghai-Tibet Plateau is considered a major driver of the Cenozoic environmental evolution in Asia. The paleoenvironment reconstruction of the Qinghai-Tibet Plateau provides valuable insights into the study of uplift history and environmental evolution of the plateau. The continuous Cenozoic sediments preserved in the Lunpola Basin, northern Tibet, make it an ideal area for investigating the paleoenvironment of the Qinghai-Tibet Plateau. However, there is still no consensus on the reconstructions of paleoelevation and paleoclimate or on the chronological assignment of their corresponding results. This study focuses on the lacustrine strata of the Dingqinghu Formation in the Lunpola Basin. We combine U-Pb zircon dating with biostratigraphic evidence to place the study section within the Late Oligocene, providing a well-constrained chronological framework. The sporopollen data reveal a paleovegetation landscape consisting of coniferous forest in high-midlands, mixed coniferous and broad-leaved forests in mid-lowlands, and shrubs and herbs distributed within forests. This indicates an obvious vertical vegetation zonation in the Lunpola area. On the basis of sporopollen records, we defined three sporopollen zones and identified a paleoclimatic change characterized by an initial humid phase, a subsequent shift to relatively arid condition, and a final return to a humid climate. The paleoelevation reconstruction carried out on this basis enables us to exclude plateau uplift as a primary driver of the climate change in this period. Furthermore, the observed coupling between the arid trend and contemporaneous global temperature change might suggest that this aridification is linked to the global climate change associated with Antarctic ice-sheet expansion.