大兴安岭地区三叠系划分与对比

DIVISION AND CORRELATION OF THE TRIASSIC STRATA IN DAXINGANLING REGION

厘定后的大兴安岭中南部地区老龙头组以红杂色沉积岩为主,夹或不夹中酸性火山岩层,含早三叠世Calamospora-Lundbladispora-Alisporites和Verrucosisporites-Lundbladispora-Chordasporites孢粉组合,Huanghestheria-Cornia-Palaeolimnadia叶肢介组合以及Darwinula triassiana-D.rotundata介形类组合.大兴安岭中北部地区以安山岩为主的哈达陶勒盖组整合在老龙头组之上,据此将该区下三叠统自下而上分为老龙头组和哈达陶勒盖组.原下侏罗统或上三叠统-下侏罗统东宫组自下而上分为一段和二段,根据一段同位素平均年龄为208.97 Ma(K-Ar法),并被二段(相当于下侏罗统查伊河组)平行不整合覆盖,将第一段单独划为东宫组,时代属于晚三叠世.

In the central-southern part of the Daxinganling region, the redefined Laolongtou Formation is characterized by red-variegated sedimentary rocks, with or without the intercalations of acid-intermediate volcanic rocks, containing the Early Triassic Calamospora-Lundbladispora-Alisporites and Verrucosisporites-Lundbladispora-Chordasporites spore- pollen assemblages, Huanghestheria-Cornia-Palaeolimnadia conchostracan assemblage and Darwinula triassiana-D. rotundata ostracod assemblage. While in the central-northern part, the Hadataolegai Formation is dominated by andesite, which conformably overlies the Laolongtou Formation. Therefore, the Lower Triassic in the region may be arranged （in ascending order） as the Laolongtou Formation and Hadataolegai Formation. The Lower Jurassic or Upper Triassic-Lower Jurassic Donggong Formation in the region was previously divided into the first and second members. Based on the mean isotopic age （208.79 Ma） of the first member and the parallel unconformity with the second member, the authors redefine the Donggong Formation, including only the original first member, assigned to Late Triassic in age.