新疆准噶尔盆地侏罗系—白垩系生物地层和同位素年龄研究的新进展

研究的侏罗系—白垩系包括侏罗系头屯河组、齐古组、喀拉扎组和白垩系清水河组。清水河组的叶肢介、介形虫和孢粉化石组合研究的新成果表明:其地质时代为早白垩世早期(Berriasian)。齐古组下部的同位素年龄为164.6Ma±1.4Ma。此年龄值与国际地质年表对比,几乎与Callovian的底界年龄(164.7Ma±4.0Ma)相当。依据此年龄值和沉积厚度、沉积速率推算,齐古组的主要时代应为中侏罗世卡洛期(Callovian),其下部跨入巴通期最晚期;喀拉扎组的时代可能为牛津期最早期(early Early Oxfor-dian)。上列事实反映出在侏罗系与白垩系之间几乎缺失全部晚侏罗世的沉积,由此可以推断本区在晚侏罗世曾发生过一次较强烈的构造运动。

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 indicate 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.