Radiolarian age constraints on Mesotethyan ocean evolution, and their implications for development of the Bangong–Nujiang suture, Tibet

Abstract: Radiolarian discoveries indicate that deep-marine conditions prevailed in central Tibet from the early Middle Jurassic until well into the Early Cretaceous (late Hauterivian–early Aptian; 131–121 Ma) and help to constrain the temporal extent of oceanic conditions along the Bangong–Nujiang suture. These new fossils occur in chert or siliceous mudstone blocks associated with the Lagkor Tso ophiolitic melange. Basin inversion associated with closure of Mesotethys between the Qiangtang and Lhasa terranes was accompanied by melange formation and predated regionally widespread deposition of overlying shallow-marine late Aptian–Albian orbitolinid limestones.