Eocene calcareous nannofossils from southern Tibet: Paleoceanographic implications for the closure of the eastern Tethys Ocean

The India-Asia collision led to the demise of the Tethys Ocean, and the subsequent uplift of the Qinghai-Tibet Plateau had a profound impact on Cenozoic topography, oceanography, and climate. However, collision ages vary depending on collision definition and methodology, with the cessation of marine deposition constraining the minimum/youngest collision age. The Enba and Zhaguo formations of the Qumiba Section (southern Tibet) represent the youngest marine strata in the eastern Tethys Ocean. Previous studies have suggested a middle-late Eocene or early Eocene closure time, however, our nannofossil data indicate an age of 53.67–52.64 Ma (nannofossil zone CNE3, which closely corresponds to Zone NP11). Nannofossil relative abundances can explain the early Eocene tectonic evolution of southern Tibet, with the increasing number of reworked Cretaceous nannofossils over time reflecting the degree of erosion of previously deposited sediments as the plateau uplift progressed. Our data suggest that Cretaceous and Paleocene calcareous nannofossils were an important sediment source to the Qumiba Section.