Age of the Yongkang Group and Regional Stratigraphic Correlation

Abstract： According to the fossils contained in the Guantou Formation, traditionally the age of the Yongkang Group is assigned to Mid-Late Early Cretaceous. However, the isotopic ages of volcanic rocks of the Guantou Formation are in the range of 113-103 Ma. All the paleomagnetic samples in several basins show normal polarity. Especialy, recently dinosaurian fossil eggs of Faveoloolithidae have been found in the Chaochuan Formation in the Yongkang basin, and the fossil eggs of this family also occur in the Lanxi Formation of the Jujiang Group in the Jinju basin and the Liangtoutang Formation of the Tiantai Group in the Tiantai basin. Furthermore, the paleomagnetic polarity and isotope age of the Yongkang Group are essentially consistent with those of the Tiantai and Jujiang groups. These indicate that like the Tiantai and Jujiang groups, the Yongkang Group is late Early Cretaceous to Late Cretaceous in age, and that there do not exist overlying or underlying relationships between them. They are contemporaneous but heteropic deposits.