Late Carboniferous-Early Permian brachiopod fauna of Gondwanic affinity in Xainza County,northern Tibet,China:Revisited

The brachiopods faunas in the middle and upper parts of the Yunzhug Formation and the Angjie Formation in the Deri′angma-Xiala section in the Xainza area, northern Tibet, may be correlated with those in Gondwana and peri-Gondwana areas in China and abroad but show their unique aspects. They may be divided into four assemblage zones (A. Z.), i.e.: the Reedoconcha xizangensis-Spinomartinia xainzaensis A. Z., Cimmeriella mucronata-Reedoconcha excellens A.Z. and Trigonotreta magnifica-Bandoproductus intermedia A. Z. in the middle and upper parts of the Yunzhug Formation and the Aulosteges ingens-Punctocyrtella nagmargensis A. Z. in the Angjie Formation. According to the present study of the ages of brachiopods in the Gondwana and peri-Gondwana provinces and Cathaysia-Tethys province, the brachiopod assemblage zone in the middle of the Yunzhug Formation is Late Carboniferous Bashkirian in age, the two brachiopod assemblage zones in the upper part are Early Permian early Sakmarian and late Sakmarian in age, and the age of the brachiopod assemblage zone in the Angjie Formation is Early Permian Artinskian.