Xidong Fm

Its unconformable base marked by tuffaceous breccia and tuff is distinguished from brown red clayey siltstone of the underlying Dapo Fm. Regionally, the next older unit is the Shuangyuan Fm siltstone which overlies the Dapo Fm.

Its unconformable top marked by volcanic rocks is bounded by conglomerate of the overlying Luowen Fm.

The formation is mainly distributed in the Ziliang, Taiping and Wangpu basins of southeast and south Guangxi and in the Guluo and Songbo basins at the juncture between Guangdong and Guangxi. In the Ziliang and Taiping basins, it increases remarkably in the amount of conglomerate and sandstone and decreases in the amount of volcanic rocks, with a thickness of 129-190 m. In the Wangpu basin, it is dominated by volcanic rocks with a number of mudstone, measuring 102 m in thickness. In the Guluo and Songbo basins, the lower part of the formation is represented by stratoid quartz-albite porphyry, locally with unstable tuff breccia, measuring 250 m in thickness. It shows an angular discordance with the underlying Ordovician, Devonian, Cretaceous or Jurassic, and a disconformable contact with the overlying Luowen Fm.