天山东段地区二叠系芦草沟组沉积特征与古环境对比

Comparative study on sedimentary characteristics and palaeoenvironment of the Permian Lucaogou Formation in eastern Tianshan Mountains

天山东段地区二叠系芦草沟组的沉积时代、沉积环境和构造背景存在争议。根据芦草沟组中发现的标准化石桃树园吐鲁番鳕、托姆介介形虫和孢粉化石组合,结合沉积地层中大量碎屑锆石最年轻峰值年龄261 Ma,认为芦草沟组的沉积时代为瓜德鲁普世(中二叠世)而非乌拉尔世(早二叠世)。近年来,在芦草沟组中发现典型海相指示矿物海绿石、海相或海陆交互相托姆介介形虫,加之超高盐度咸化湖盆的证实,认为芦草沟组主体为湖相沉积,但部分沉积时段受到海侵(泛)事件影响。天山东段地区准噶尔盆地、三塘湖盆地、吐哈盆地二叠系芦草沟组具有相似的岩石组合、动物群面貌和构造特征,但不同盆地古盐度、古气候、古氧化还原条件、古水深、初级生产力及热液输入强度等具有差异,分析认为芦草沟组形成于相似的伸展裂谷构造背景,但不同盆地之间沉积特征具有差异、不具备统一的沉积中心,为一系列弥散性裂谷盆地群。

The depositional age,sedimentary environment and tectonic setting of the Permian Lucaogou Formation in eastern Tianshan Mountains are controversial.Based on the standard fossil assemblages of Turfania taoshuyuanensis and Tomiella found in the Lucaogou Formation,the large number of detrital zircons from the sedimentary strata with the youngest peak age of 261 Ma,it is believed that the deposition age of the Lucaogou Formation is Guadalupan(Middle Permian) rather than Uralian(Early Permian).Based on the discovery of typical marine indicator mineral glauconite,the discovery of marine facies or the interactional facies of Tomiella and the confirmation of ultra-high salinity saline lake basin,it is considered that the Lucaogou Formation was mainly lacustrine sediments,but some sedimentary periods were affected by transgression(flooding)events.In eastern Tianshan Mountains,the Permian Lucaogou Formaition of Junggar Basin,Santanghu Basin and Tu-Ha Basins has similar rock assemblages,faunal features and tectonic characteristics,but there are differences in paleo-salinity,paleo-water depth,paleo-climate,paleo-redox conditions and primary productivity among different basins,suggesting that the Lucaogou Formation was deposited in a series of dispersed rift basins,and there is no unified depositional center among different basins.