大兴安岭东南部中侏罗统新民组研究新进展

通过野外地质调查、地质剖面测量、钻探岩心编录、古生物化石研究和同位素样品测年分析，并结合对前人资料的综合分析研究，认为：新民组为一套以酸性火山岩、火山碎屑岩为主夹含煤沉积的地层，产有Coniopteris-Phoenicopsis植物群中期组合、Ferganoconcha tomiensis-F.elongata双壳类化石组合和Osmundacidites-Lycopodiumsporites-Piceites孢粉组合，生物群时代为中侏罗世.新民组火山岩锆石U-Pb年龄为161.6 Ma，碎屑岩锆石U-Pb年龄为（175±2）~（2537±20） Ma之间，其中最年轻的碎屑岩锆石U-Pb年龄为175±2 Ma，代表了新民组的沉积下限.上述研究结果可为大兴安岭地区中侏罗世地层的划分对比、建立健全该区的中生代地层格架提供基础资料和科学依据.

PROGRESS ON THE STUDY OF THE MIDDLE JURASSIC XINMIN FORMATION IN SOUTHEASTERN DAXINGANLING MOUNTAINS

By means of field geological investigation, geological section survey, drilling core logging, fossil study and isotopic dating, combined with the comprehensive analysis of previous data, it is concluded that the Xinmin Formation is mainly a set of volcanic rocks and pyroclastic rocks with coal deposits, bearing mid flora of Coniopteris-Phoenicopsis, bivalve fossil assemblage of Ferganoconcha tomiensis-F. elongate and sporopollen assemblage of Osmundacidites-Lycopodiumsporites-Piceites, which belong to Middle Jurassic. The zircon U-Pb age of volcanic rocks is 161.6 Ma; while that of detrital rocks is between 175±2 Ma and 2537±20 Ma. The youngest age of detrital rocks (175±2 Ma) represents the lower deposition limit of Xinmin Formation. The research results would provide essential data and scientific basis for the Middle Jurassic stratigraphic classification and correlation, as well as the establishment and perfection of the Mesozoic stratigraphic framework in Southeastern Daxinganling Mountains.