Abstract

Thirty-five radiolarian species, belonging to two assemblages, one from the Changhsingian and the second one from the early Anisian, were recovered from siliceous rocks occurring in Xijirulan orogenic belt, northern Tibet. A new radiolarian species of them, Cryptostephanidium tibetensis, is described. The lower Anisian Eptingium nakasekoi assemblage co-occurs with conodonts belonging to Chiosella timorensis Zone. This fact allows correlation between radiolarian and conodont biozones. The lower Anisian radiolarian assemblage has a high diversity and supports that radiolarian radiation after the end-Permian mass extinction begins in the earliest Anisian. The research on the lithostratigraphic sequence and sedimentology shows that the old land of the Xijirulan orogenic belt, formed by the collision between the Qiangtang and Koh Xil terranes at the latest Early Permian, has disappeared in the early Changhsingian. During the Changhsingian and Triassic, the Xijirulan orogenic belt has become a deep marine basin and was combined with the Bayan Har Basin. This large deep sea basin extended until the end of the Triassic, locally possibly until the Jurassic.

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