Zhongdai Fm

The base of the formation marked by purple red and purple gray conglomerate and sandy conglomerate is distinguished from the Yongkang Gr marked by light purple acid crystal and lithic tuff, showing an unconformable contact with the latter. However, in West Zhejiang, the underlying unit below a disconformity is the Jiangde Gr (Hengshan Fm).

The top is bounded by the appearance of coffee-colored silty mudstone of the Jinhua Fm, showing a gradational relationship with the latter.

The formation is mainly distributed in the Jinqu basin and then in the Shengxian and Pujiang basins and in the Sian-Jiaxing area where the lithological characteristics are the same as those in the Jinqu basin. But in the Jinqu and Shengxian basins, the lower part of the formation is often intercalated with small amounts of intermediate and basic lava and intermediate acid pyroclastic rocks consisting of sediment tuff, vitric tuff and black amygdaloidal basalt lenses. In the Jinqu basin, the thickness of the formation is controlled by the Xiazhang fault; the lower member of the formation in the southern part of the fault is 500-700 m and is 89-300 m on the northern side of the fault. The upper member of the formation is 600-800 m thick to the west of Longyou, and 340-460 m in the Lanxi-Longyou area.