The establishment of the Lower Juras-sic Zhanbeicun Formation in northern Da Hinggan Mountains and its geological significance

The Zhanbeicun area in northern Da Hinggan Mountains develops a suite of volcanic rocks. The rock assemblages of the Zhanbeicun Formation are mainly a suite of light gray-gray rhyolitic pyroclastic rocks, rhyolitic lava, clastic lava with a small amount of volcanic tuff. On the basis of 1:50000 regional geological mapping, the authors found that the lower part of the formation covers Late Triassic monzonitic granite by angular unconformity, and the upper part of the formation is covered by Middle-Later Jurassic Tamulangou Formation by parallel unconformity. The zircon U-Pb isotopic age of Zhanbeicun Formation is about 178~192Ma, sug-gesting Early Jurassic. According to the rule of "formation" establishment in Stratigraphic Guide of China, the Zhanbeicun Formation is chosen as stratotype and established as Zhanbeicun Formation. The establishment of the Lower Jurassic stratigraphic unit has impor-tant geological significance for the study of early Mesozoic volcanic-tectonic magmatic activity in Da Hinggan Mountains and strati-graphic classification and correlation of Mesozoic volcanic rocks.