西天山那拉提东拉尔墩达坂一带石炭系岩石地层单位重新厘定

Division of the Carboniferous Lithostratigraphic Units in Laerdun Daban Area to the East of Nalat, Western Tianshan

西天山那拉提东拉尔墩达坂一带广泛出露石炭纪巨厚火山-沉积建造,最初前人将其划归"大哈拉军山组",后又出现了地层划分与命名上的"同物异名"等问题。经调查认为其自上而下由3部分构成:上部碱性裂谷双峰式火山岩,锆石U-Pb年龄为(301.3±3.8)Ma和(302.5±3.9)Ma,时代为晚石炭世;中部浅海相碎屑岩及碳酸盐岩,含丰富的生物化石Caninophyllum、Kansuella、Athyris等,时代为早石炭世晚期;下部钙碱性岛弧火山熔岩及同质火山碎屑岩,时代为早石炭世早期。这3部分地层间均以角度不整合接触。据地层划分理论和中国地层指南,并与区域地层对比,将其依次重新厘定为早石炭世大哈拉军山组、早石炭世阿克沙克组和晚石炭世伊什基里克组。

A series of Carboniferous volcano-sedimentary formations have been widely exposed in Laerdun Daban area to the east of Nalat,western Tianshan.The predecessors have roughly divided it into the＂Dahalajunshan Formation＂,then the＂Synonym＂phenomenon appeared in stratigraphic division and nomenclature.The investigation now confirms that the＂Dahalajunshan Formation＂could be divided into three parts from top to bottom：The upper alkaline rift bimodal volcanic rock, the zircon U-Pb age of（301.3±3.8） Ma and（302.5±3.9） Ma（Later Carboniferous）;The central shallow Marine pyroclastic rocks and carbonate rocks,including rich biological fossils Caninophyllum,Kansuella,Athyris,etc.（Later stage of Early Carboniferous）;The calc-alkaline island arc volcanic lava and its homogeneous volcanic clastic rocks are early in the lower part（Early stage of Early Carboniferous）. Their contact relationship is angular unconformity. According to stratigraphic division theory and China stratigraphic guide, and contrasting with regional strata,it was redefined：The Early Carboniferous Dahalajunshan Formation, the Early Carboniferous Akeshake Formation and the Later Carboniferous Yishijilike Formation.