DIVISION AND CORRELATION OF THE TRIASSIC STRATA IN DAXINGANLING REGION

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 sporepollen 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.