大兴安岭东部地区下白垩统龙江组新认识

对龙江地区龙江组建组剖面进行了岩石地层、生物地层、同位素年代和岩石地球化学等多方面的研究，重新厘定了龙江组的含义.新义龙江组岩石组合由安山岩、英安岩及其火山碎屑岩、流纹质火山碎屑岩和沉积碎屑岩组成；生物化石属于EosestheriaLycoptera-Ephemeropsis trisetalis热河生物群中期生物化石组合，其中叶肢介化石以Eosestheria opima-E.（Dongbeiestheria）guanghuaensis（丰满东方叶肢介-光华东北东方叶肢介）组合为代表；火山岩的岩石地球化学SiO₂含量在59.71%~75.65%之间，具有高Al₂O₃（12.19%~19.39%）和高Na₂O（1.04%~5.24%），较富碱性（Na₂O+K₂O 3.65%~6.25%）的特点，火山岩属于高钾钙碱性岩系列；轻稀土（LREE）富集.全岩激光⁴⁰Ar/³⁹Ar同位素年龄等时线年龄值为125.4±1.8 Ma.

NEW UNDERSTANDING OF THE LOWER CRETACEOUS LONGJIANG FORMATION IN THE EASTERN DAXINGANLING REGION

On the basis of field survey, the stratotype section of Longjiang Formation is researched particularly on the lithostratigraphy, biostratigraphy, isotope chronology and lithogeochemistry. The meaning of Longjiang Formation is redefined. The neologism of Longjiang Formation consists of andesite and dacite with its pyroclastic rocks, rhyolitic pyroclastic rocks and sedimentary clastic rocks. The paleontological fossils belong to Eosestheria-Lycoptera-Ephemeropsis trisetalis fossil assemblage of the Middle Jehol Biota. Among them, Conchostracans are represented by the Eosestheria opima-E. (Dongbeiestheria) guanghuaensis assemblage. The volcanic lithogeochemistry is characterized by SiO₂ contents between 63.88% and 75.65%, high Al₂O₃ (12.19% to 19.39%), high Na₂O (1.04% to 5.24%), rich alkalis (Na₂O+K₂O 3.65% to 6.25%)and strong enrichment in light rare earth elements(LREE). The isotopic age of ⁴⁰Ar/³⁹Ar is 125.4±1.8 Ma.