Xitun Fm

The type section is located at Xishancun Village (103^o42’E, 25 ^o30’N) of Qujing City, Yunnan Province. It was named by Zhang Xinping in 1966, who assigned it as a Formation of Cuifengshan Gr.

[Figure Simplified geological map showing the locations of the type sections of Xishancun Fm (D₁ x), Xitun Fm (D₁ xt,), Guijiatun Fm (D₁ g) and Xujiachong Fm (D₁ xj) of Cuifengshan Gr in the West Hill of Qujing City, Yunnan Province.]

The Formation, about 364.5-417.3 m in thickness, is composed of grayish-green, yellowish green massive clayey siltstones in the lower, and gray, purple-red massive calcareous silty marls in the middle-upper part.

[Figure Outcrop showing the alternation of purple-red, gray-green and grayish marls in the Xitun Formation at Xitun.]

The Formation contains bivalves, ostracods, and fish, including: Fish Yunnanolepis chii, Y. chi, Diabolepis sp., Eugaleaspis changi, Youngolepis praecursor, Nanpanaspis microculus, Thelodus sp.; Flora Uncatoella verticillata-Zosterophyllum Assemblage, Spore Synorisporites verrucastus- Apiculiretusisporites plicata Assemblage and Brachiopoda Lingula sp.

[Figure Outcrop showing the bivalve bed in the Xitun Formation at Shengfeng, Qujing.]

A non-marine lacustrine setting is suggested, and the various colors are interpreted as reaction of dry and wet climate change in a relatively shallow lake basin.