藏北申扎一带下奥陶统拉塞组的发现及意义

吉林省地质调查院在进行1：25万《多巴区幅》区域地质调查时，在西藏北部申扎县一带首次发现一套富含北方珠角石动物群Armenoceras sp.,Wutinoceras sp.,Discoactinoceras multiplerum Kobayashi,Adaomsoceras sp.,Sactoceras sp.,Ordosoceras sp.,Oncoceratida,Ormoceratidae,? Curtoceras sp.,Ormoceras sp.,Liulinoceras sp.,Deiroceras cf.globsom Zholt et Shen及腕足类、牙形刺、苔藓虫、海百合茎等化石的海相碳酸盐岩地层。该地层的岩石组合特征及生物群面貌与区内已知的地层存在明显的差异，其地质时代也明显早于区内已知的其它古生代地层，故建立下奥陶统拉塞组。

The discovery and significance of the Lower Ordovician Lhasai Formation in the Xainza region, northern Xizang

The marine carbonate rocks were discovered for the first time in the Xainza region during the regional geological surveying of the 1:250000 Toiba Sheet in Xizang. These strata contain abundant Boreal Actinoceras faunal fossils such as Armenoceras sp., Wutinoceras sp., Discoactinoceras multiplexum Kobayashi, Adaomsoceras sp., Sactoceras sp., Ordosoceras sp., Oncoceratida, Ormoceratidae,?Curtoceras sp., Ormoceras sp., Liulinoceras sp., Deiroceras cf. globsom Zholt et Shen, brachiopods, conodonts, bryozoans and crinoids. The characteristics of lithologic associations and faunas found here appear to be in conflict with the existing strata in the study area, and the geological ages of the strata are obviously earlier than the other Palaeozoic strata in this area. This is why the Lower Ordovician Lhasai Formation is suggested for the Xainza region, northern Xizang.