试论永康群时代及区域地层对比

Age of the Yongkang Group and Regional Stratigraphic Correlation

浙江白垩系上部的永康群,传统习惯根据馆头组所产古生物化石将其时代定为早白垩世中晚期。但馆头组火山岩同位素年龄在113～103Ma间,几个盆地全部古地磁样品均显示正向极性。特别是最近在永康盆地朝川组中发现蜂窝蛋科(Faveoloolithidae)恐龙蛋化石,而这一蜂窝蛋科化石在金衢盆地衢江群兰溪组、天台盆地天台群两头塘组中均有产出,而且永康群与衢江群和天台群的古地磁极性和同位素年龄基本一致。表明永康群与天台群、衢江群一样,时代为早白垩世晚期至晚白垩世。它们之间不存在上下关系,而是同期异相堆积。

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.