Late Paleocene radiolarian fauna from Tibet and its geological implications

A diverse, abundant, and well-preserved radiolarian fauna in Jiazhu, Zhongba County of Tibet, in the western sector of Yarlung Zangbo Suture Zone, is assigned to a late Paleocene radiolarian zone, the Buryella pentadica interval zone, spanning 59–56.5 Ma. Regionally, a late Paleocene basalt block in the bathyal–abyssal siliceous mudstone and graywacke yielded an age of 59.1 Ma (zircon SHRIMP U–Pb). The late Paleocene radiolarian fauna, the tectonic attribution of the radiolarian cherts and the basalt block indicate that oceanic crust persisted in the Zhongba area until the late Paleocene and the initial collision between the Indian and Eurasian plates post-dates the late Paleocene. It is inferred that the Neo-Tethys transformed into a remnant oceanic basin in the late Paleocene, at the terminal stage of the oceanic crust subduction, and the closure of the remnant oceanic basin in the studied region took place after the late Paleocene. In contrast to the previous investigations, we suggest that there was a remnant oceanic basin to the west of the Saga area and a foreland basin to the east of Saga in southern Tibet during the late Paleocene. We argue that the closure of the Neo-Tethys progressed from east to west.