Lopingian Brachiopod Faunas From The Tethys Himalaya And Lhasa Block And Their Paleogeographical Implications

Permian faunas and their affinities in different tectonic entities of Tibet play a critical role in reconstructing their paleogeographic evolutions.Brachiopods are one of the best fossil groups to recognize the paleobiogeographic affinities because they are sensitive to the paleolatitude-related thermal gradient.In this thesis,the brachiopod faunas consist of 14 species belonging to 10 genera and an unidentifiable Orthotetoidea,which are described from the Qubuerga Formation at the Tulong and Kujianla sections in southern Tibet.And another new diverse brachiopod fauna consisting of 17 species of 17 genera and an unidentifiable Orthotetoidea is illustrated from the uppermost part of the Xiala Formation at the Aduogabu section in the central part of the Lhasa Block.Among the brachiopods from southern Tibet,Retimarginifera xizangensis,Costiferina indica,Fusispirifer semiplicatus,Spiriferella sinica,Biplatyconcha grandis and Neospirifer(Quadrospina)tibetensis are all very common species in the equivalents in the Tethys Himalaya region including the Selong Group at the Selong Xishan and Qubu sections in southern Tibet,the Senja Formation in northwest Nepal,the Zewan Formation in Kashmir,and the upper part of the Wargal Formation and the Chhidru Formation in the Salt Range,Pakistan.They are all comparable one another and can be assigned to an age from Wuchiapingian to early Changhsingian.Since the brachiopods from the Qubuerga Formation at Tulong and Kujianla are all composed of typical Gondwanan,bipolar and cosmopolitan elements,it is conclusive that the Tethys Himalaya in the northern margin of the Indian Plate,was still situated in the southern high-latitude region under a cold paleoclimatic condition during the Lopingian.The age of the fauna from the Lhasa Block can be assigned to the Changhsingian(late Lopingian)as indicated by the associated foraminifers Colaniella parva and Reichelina pulchra.Characteristic brachiopods include Spinomarginifera chengyaoyenensis,Haydenella wenganensis,Permophricodothyris sp.and Araxathyris cf.dilatatus.They also generally suggest a Changhsingian age.Palaeobiogeographically,this fauna is uniformly composed of typical Tethyan elements represented by Spinomarginifera and Haydenella,and some cosmopolitan elements,but no typical cold-water taxa with Gondwanan affinity.This is in contrast to the contemporaneous brachiopod faunas from the Tulong and Kujianla sections in the Tethys Himalaya region which are characterized by typical cold-water taxa of Gondwanan affinity.Thus,it is strongly indicative that the Lhasa Block had already drifted into a relatively warm-water regime during the Changhsingian to form a different paleobiogeoraphic province with cold-water Gondwanan Province.Moreover,an analysis of the paleobiogeographic change of brachiopods in the Lhasa Block throughout the entire Permian further suggests that the Lhasa Block probably had rifted away from the northern peri-Gondwanan margin between the latest Cisuralian and middle Guadalupian,that is,the Neotethys Ocean had opened before middle Guadalupian.