The basement of the Ningwu volcanic basin consists of, frombottom to top, the Lower–Middle Triassic Qinglong Group, theUpper Triassic Huangmaqing Formation, the Lower–Middle Jurassic Xiangshan Group, and the Upper Jurassic Xihengshan Formation (Ningwu Research Group, 1978). The Qinglong Group is >500 mthick and contains limestones and intercalated calcareous shales, dolomitic limestones, and lagoonal gypsum and anhydrite layers. The gypsum and anhydrite layers are well exposed in the uppermost Qinglong Group and are <90 m thick in the Ningwu area. The Upper Triassic marine and continental Huangmaqing Formation is 500–800 m thick, consists of calcareous siltstones, siltyshales, and shales, with local intercalations of thinly layered limestones and coal seams. Overlying the Huangmaqing Formation is the 1500 m-thick continental Lower–Middle Jurassic Xiangshan Group, which contains grayish–white quartz sandstone, feldspathic sandstones and locally intercalated siltstone and shale in the lower part (1000 m-thick), and reddish-purple and grayishwhite medium-grained feldspathic quartz sandstone, fine-grained sandstone, marlstone in the upper part (500 m thick).
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