Dashuang Fm

The Dashuang Formation lies unconformably on the underlying Maonong Fm (middle Jurassic) or obviously unconformably overlaps the older strata. It lies unconformably over the Jinning granite.

It top is bounded conformably by the occurrence of gray rhyolitic crystal vitric ignimbrite of the overlying Gaowu Fm.

The formation occurs in the form of two almost parallel striped zones in the southeast part of Zhejiang. In the northern striped zone (from Quxian to Shaoxing), the Dashuang Formation varies considerably in thickness, about 2000 m thick in Ruoyang of Jinhua and Houzhai of Yiwu, decreasing towards both the southwest and northeast ends, only 238 m thick in Baozhulong of Quxian, 740 m in Tueshan of Shaoxing. It varies considerably in lithology, which is dominated by intermediate lava in Houzhai of Yiwu and in Sizhai of Zhuji and changes in facies to moderately acidic and acidic volcanic rocks toward southwest and northeast. In the southern zone (from Longquan to Xinchang), the formation varies in thickness to a certain extent and thickens from southwest to northeast, about 804 m thick near Longquanjiao, 1141.3-3746.2 m north of Longquan, and more than 1300 m in the central part of the zone. In the lower part of the formation, sedimentary rocks are not persistent, where intermediate volcanic rocks are predominant, while acidic volcanic rocks are dominant in the upper part.