新疆西准噶尔白碱滩一带成吉思汗山组的建立及地质意义

The Definition of Chengjisihanshan Formation and Its Significances in Baijiantan Region,West Junggar,Xinjiang

新疆西准噶尔白碱滩一带出露一套正常层序的火山-沉积地层。在1∶50000区域地质填图的基础上,通过实测1∶5000地质剖面,查明该套地层下部岩性为含砾砂岩、砂岩、凝灰质砂岩、粉砂岩和凝灰质粉砂岩;上部为玄武岩和硅质岩互层,局部见薄层砂岩,出露厚度大于570m,剥蚀未见顶。呈角度不整合超覆于早石炭世包古图组和希贝库拉斯组之上,生物化石资料和火山岩锆石U-Pb同位素定年确定形成时代下限为晚石炭世莫斯科期。展布于达尔布特河北—萨尔托海一带,露头上易于识别,岩石组合以及生物化石与哈拉阿拉特山一带上石炭统哈拉阿拉特组明显有别。根据《中国地层指南》关于"组"的定义及新建要求,指定白碱滩一带成吉思汗山剖面为层型,厘定为成吉思汗山组。

There exists a normal succession of volcanic-sedimentary strata in Baijiantan region, West Junggar. Based on the 1 ： 50000 regional geological survey and measured 1 ： 5000 section, the rock assemblage is found consisted of gravel sandstone, sandstone, tuffaceous sandstone, siltstone and tuffaceous siltstone in the lower part. Interbeds of basalt and siliceous rock coupled with local flagstone constitute the upper part, which is more than 570 m thick and shows angular unconformity overlapping the Early Carboniferous Baogutu Formation and Xibeikulasi Formation. The fossil and volcanite zircon U-Pb isotope dating indicates that this formation occurred in a period later than Late Carboniferous Moscovain. It is distributed from north of Da＇erbu＇te river to Sa＇ertuohai and can be easily recognized on the outcroo. The rock and fossil assemblages are different from the Upper Carboniferous Hala＇alate Formation. According to the definition and establishment requirements about ＂formation＂ in Stratigraphic Guide of China, the Chengjisihanshan section in Baijiantan region is assigned as stratotype and defined as Chengjisihanshan Formation.