Characteristics of Early Eocene radiolarian assemblages of the Saga area, southern Tibet and their constraint on the closure history of the Tethys

Quantitative analysis of Early Eocene radiolarian assemblages discovered in the sedimentary melange (accretionary prism) of the Saga area, southern Tibet provides new information to constrain the timing of Tethys closure and the initial collision of India and Eurasia. The radiolarian species of Saga include Amphisphaera coronata (Ehrenberg), Buryella hannae Bak & Barwicz-Piskorz, Buryella clinata Foreman, Buryella tetradica Foreman, Calocycloma ampulla (Ehrenberg), Lamptonium fabaeforme constrictum Riedel and Sanfilippo, Lamptonium pennatum Foreman, Lithomespilus coronatus Squinabol and Lamptonium (?) colymbus Foreman. The adequate and reliable correlation of these radiolarians specimens indicates that the assemblage is of Early Eocene in age. The age and depositional environment of these radiolarians testify that deep ocean basins existed between India Plate and Asia Plate during the Early Eocene. The complete closure of Tethys must have taken place at least after the Early Eocene.