New advances in the study of Jurassic-Cretaceous biostratigraphy and isotopic ages of the Junggar Basin in Xinjiang and their significance

In this paper the strata studied include the Jurassic Toudunhe Formation,Qigu Formation,Kalazha Formation and the Cretaceous Qingshuihe Formation.Studies of conchostracans,ostracods and spore-pollen assemblages from the Qingshuihe Formation in dicate that the Qingshuihe Formation is early Early Cretaceous(Berriasian) in age.The isotopic age of the tuff from the lower part of the Qigu Formation is 164.6 Ma±1.4 Ma,almost corresponding to 164.7 Ma±4.0 Ma of the Bathonian/Callovian boundary age.Calculation based on the age of 164.6 Ma ±1.4 Ma,deposition thickness and rate of sedimentation shows that the Qigu Formation is mainly Callovian in age,its lower part might have entered the latest stage of Bathonian period,and the Kalazha Formation is early Early Oxfordian in age.These facts show that the Late Jurassic strata were almost wholly absent,suggesting that during the Late Jurassic period there existed a relatively strong tectonic movement in this area.