Discovery of Cretaceous radiolarians in“mélanges”in Saiqu,Sa'gya,southern Tibet,and its geological significance

Olistostromic melanges are distributed in the north of the Saiqu area,Sa'gya,southern Tibet.Due to the lack of enough fossil evidence,the age and stratigraphic assignment of the melanges have long been controversial.Abundant Cretaceous radiolarian fossils have been discovered in the melanges and four radiolarian assemblages are recognized:(1)Holocryptocanium aff.barbui-Dictyomitra turris assemblage,(2)Acanthocircus dicrancanthos-Thanarla pulchra assemblage,(3)Thanarla veneta-Pseudodictyomitra pseudo-macrocephala assemblage,and(4)Dictyomitra megnifica-Dictyomitra turritu assemblage.The melange in Saiqu can be correlated with the Zongzhuo Formation in its neighboring areas whether in lithology or in fossil assemblage.Based on that,the“melange”is ascribed to the Late Cretaceous Zongzhuo Formation rather than the Triassic“Xiukang”Group.