浙赣边区晚奥陶世地层之新见

New observations on the Upper Ordovician stratigraphy of Zhejiang-Jiangxi border region, E China

浙赣两省交界的三山地区（江山、常山、玉山）晚奥陶世Ａｓｈｇｉｌｌ中期的海相沉积主要包括３种岩相：碳酸盐岩相的三衢山组、碎屑岩相的长坞组以及碳酸盐岩和碎屑岩交互相的下镇组；这３种类型的地层在研究区内的横向分布存在一定规律，即从西南至东北大致为下镇组、三衢山组和长坞组。经详细的生物地层和岩石地层研究，建议取消“大桥灰岩”一名，用“下镇组”代替；整合于三衢山组之上的“文昌组”不宜归为Ａｓｈｇｉｌｌ晚期，仍属Ａｓｈｇｉｌｌ中期的沉积。通过系统的生态地层分析，对研究区内各种岩相地层之间的对比也提出了新的意见。

Late Ordovician (mid-Ashgill) marine deposits in the Zhejiang-Jiangxi border region, Jiangshan-Changshan-Yushan (JCY) area, mainly consist of three lithofacies: carbonate, elastic and carbonates intercalated with elastic rocks. Their distribution shows some regularity from present southwest to northeast, i. e. carbonates intercalated with elastic (Xiazhen Formation) mainly carbonate (Sanqushan Formation) and all elastic (Changwu Formation). On the basis of detailed biostratigraphical studies, the authors suggest that the Xiazhen Formation represents the strata of carbonate rocks intercalated with elastic rocks and Daqiao Limestone, being an informal lithostratigraphical unit, should be. abandoned and replaced by the Xiazhen Formation. The brachiopods (e. g. Antizygospira and Altaethyrella) collected from the Wenchang Formation, which is just underlain by the Sanqushan Formation, are known to occur in the mid-Ashgill strata in Kazakhstan, Altai and Shaanxi. It is suggested, therefore, that the Wenchang Formation is of middle Ashgill, rather than late Ashgill in age. There are no Hirnantian deposits in the JCY area. Based on the ecostratigraphical analysis, some new points on the correlation between the 10sections studied are put forward for the first time.