Age Assignment of the Lycoptera ‐ bearing Bed

Abstract

Abstract In the Yanliao area, the occurrence of the Nestoria ‐ Keratestheria fauna and the Eoparacypris‐ Luanpingella ‐ Darwinula assemblage in the Dabeigou Formation s.s., a Rb‐Sr isochron age of 145.2 Ma for the Baiqi Formation and a complete stratigraphie sequence—all this proves that the Lycoptera‐ bearing bed overlies the Upper Jurassic. The Jehol fauna comprises the primitive Trigonioidids fauna, Eosestheria fauna, Lycoptera fauna et al., and their own laws of evolution expound that they belong to Cretaceous faunas. The associations of Eosestheria with Yanjiestheria, Lycoptera with Eosestheria, and Kuntulunia with Yanjiestheria as well as the occurrence of early angiosperms and sporo ‐ pollen in the Fuxin Formation and its equivalents also demonstrate that the Lycoptera‐ bearing bed should be assigned to the Cretaceous. The confirmation of the existence of Aucellina in the Jixi Group and the correlation of Trigonioidids and Cypridids with those in the equivalent strata of Japan and Western Europe have also been verified by corresponding marine strata. According to the magnetostratigraphic data from Zhejiang and Songliao, it has been preliminarily ascertained that M0 between the mixed polarity zone in the lower part and the normal polarity zone in the middle part of the Cretaceous is located in the upper member of the Huangjian Formation of the Jiande Group and the top member of the Denglouku Formation of the same group, and the isotopic age data of the Jehol and Jiande Groups show that the approximate geologic age of the Lycoptera bed is 135‐122 M a. These prove that the Lycoptera bed should be assigned to the Cretaceous.