浙江白垩系上部地层的划分与对比

浙江白垩系上部地层可划分为永康群、天台群和衢江群 ,长期以来 ,认为天台群和衢江群不整合覆于永康群之上。通过对代表性盆地岩石地层层序、古生物、同位素年龄资料的综合分析 ,发现三个群的下部地层 (馆头组、中戴组和天台盆地的塘上组 )为下白垩统 ,上部为上白垩统 ;天台盆地塘上组与仙居盆地小平田组为同物异名的早白垩世晚期火山岩层 ,覆于小平田组之上的“塘上组”是两头塘组的下部层位 ;永康生物群和衢江生物群的主要生物化石时代分别为早白垩世晚期和晚白垩世早期 ,但就两个生物群所涵盖的永康群和衢江群生物化石总体而言 ,其时代均应为早白垩世晚期至晚白垩世早期。永康群、天台群和衢江群是早白垩世晚期至晚白垩世时期的同期异相堆积 ,不存在相互叠覆关系。

SUBDIVISION AND CORRELATION OF THE UPPER BEDS OF THE CRETACEOUS SYSTEM IN ZHEJIANG

The upper beds of the Cretaceous System in Zhejiang were divided into the Yongkang, Tiantai and Qujiang Groups. It has been considered that the Tiantai and Qujiang Groups unconformably overlie the Yongkang Group. Through synthetical analysing to the lithostratigraphic sequences, fossil and isotopic dating in the representative basins, we discover that the lower beds of the three groups (the Guantou, Zhongdai and Tangshang Formations in Tiantai basin) are of Early Cretaceous age, while the upper beds are of Late Cretaceous age. The Tangshang Formation in the Tiantai basin and the Xiaopingtian Formation in the Xianju basin are the synonymous volcanic rocks of late Early Cretaceous age. The Tangshang Formation overlying the Xiaopingtian Formation is the lower part of the Liangtoutang Formation. The age of the dominate fossils from the Yongkang and Qujiang Biotas is respectively late Early Cretaceous and early Late Cretaceous. The fossils of the Yongkang and Qujiang Groups, range in age from late Early Cretaceous to the early Late Cretaceous. The Yongkang, Tiantai and Qujiang Groups are the synchronous heteropic accumulation during the late Early Cretaceous to the Late Cretaceous, and it is impossible for them to over1ap each other.