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Latest Jurassic–earliest Cretaceous radiolarian fauna from the Xialu chert in the Yarlung Zangbo suture zone, southern Tibet: Comparison with coeval western Pacific radiolarian faunas and paleoceanographic implications



Abstract  The Xialu chert radiolarian fauna is latest Jurassic–earliest Cretaceous in age (Pseudodictyomitra carpatica zone) and contains many taxa in common with coeval northern hemisphere middle-latitude (temperate) radiolarian faunas represented by the Torinosu fauna in southwest Japan. Common elements include Eucyrtidiellum pyramis (Aita), Protunuma japonicus Matsuoka & Yao, Sethocapsa pseudouterculus Aita, Sethocapsa (?) subcrassitestata Aita, Archaeodictyomitra minoensis (Mizutani), Stichocapsa praepulchella Hori and Xitus gifuensis (Mizutani). The Xialu fauna is less similar to low-latitude (tropical) assemblages represented by the Mariana fauna. For this reason, the Xialu fauna is regarded as representative of a southern hemisphere middle-latitude (temperate) fauna. A mirror-image bi-temperate provincialism to the equator in radiolarian faunas is reconstructed for the Ceno-Tethys and Pacific Ocean in latest Jurassic–earliest Cretaceous time.