西藏西部狮泉河地区二叠纪和三叠纪牙形石的发现及其意义

西藏西部阿里狮泉河地区的昂杰组、下拉组和左左组中发现牙形石化石。昂杰组的牙形石组合大致对比于中二叠世空谷期早中期Mesogondolella idahoensis-Vjalovognathus shindyensis组合带。下拉组顶部的牙形石组合大致对比于晚二叠世长兴期晚期Clarkina changxingensis带。左左组中含有早三叠世的Neospathodus sp.和Gladigondolella sp.,左左组和下拉组整合接触,左左组主体时代为三叠纪。狮泉河地区在早二叠世末期就开始由冈瓦纳相碎屑岩沉积转变为特提斯相碳酸盐岩沉积,在晚二叠世长兴期和早三叠世依然维持在海相沉积环境中。冈底斯西部在晚二叠世和三叠纪为古陆的观点有待于重新审视。

Discovery of Permian and Triassic conodonts in the Shiquanhe area, Ngari, western Tibet, China and their significances

Conodonts are discovered in the Angjie, Xiala and Zuozuo formations in the Shiquanhe area, Ngari, western Tibet. The conodont assemblage in the Angjie Formation is roughly correlated to the Middle Permian early-middle Kungurian Mesogondolella idahoensis-Vjalovognathus shindyensis Assemblage Zone, the conodont assemblage at the uppermost part of the Xiala Formation is roughly correlated to the Late Permian late Changxingian Clarkina changxingensis Zone. The Early Triassic conodonts Neospathodus sp. and Gladigondolella sp. are found in the Zuozuo Formation, which conformably overlies the Xiala Formation; therefore the age of the main part of the Zuozuo Formation is Triassic. The transition from the Gondwanic clastic sediments to Tethysian carbonate sediments in the Shiquanhe area started from the terminal Early Permian, and during the Late Permian Changxingian Stage and Early Triassic the Shiquanhe area still remained in a marine environment. So the view that western Gangdise was a land during the Late Permian and Triassic should be reconsidered.