Distribution and time frame of Nestoria fauna and determination of Late Mesozoic volcanic-sedimentary strata in the Da Hinggan Mountains

In order to improve the regional correlation of the Late Mesozoic volcanic-sedimentary strata in the Da Hinggan Mountains, the authors made reclassification of the strata by using geological mapping at the 1:1 million scale.On the basis of rock associations, stratigraphic relations, and paleontological fossil assemblages combined with the isotopic dating data, the Late Mesozoic volcanic-sedimentary strata containing Nestoria fauna in the Da Hinggan Mountains should respectively belong to the Baiyin'gaolao Formation and Meiletu Formation, thus confirming that the time of Nestoria fauna in the Da Hinggan Mountains region should be from 127.6 Ma to 141 Ma, which is equivalent to the age of Dabeigou Formation(137~133 Ma)in Jibei. Additionally, the Baiyin'gaolao Formation and Meiletu Formation were reclassified, and the ages should be 133~142 Ma and 131~138 Ma respectively.According to the horizon of Nestoria fauna and the isotope dating data, the original acidic volcanic rock strata containing Nestoria fauna of the Manketou'ebo Formation, Murui Formation, Shangkuli Formation and Guanghua Formation were reclassified as the Baiyin'gaolao Formation, meanwhile the original intermediate-acid volcanic rocks containing Nestoria fauna of Ma'nitu Formation were reclassified as the Meiletu Formation.On the basis of stratigraphic relations, the original mapping units were reclassified, which provides important evidence for further study of the volcanic activity in the Da Hinggan Mountains during the Late Mesozoic.