Luohe Fm

The base of the formation, marked by gravel-bearing sandstone, lies disconformably on the underlying Middle Jurassic Dingan Fm. Regionally, it is conformable on the Yijun Fm of Berriasian.

The top, marked by red and light brown arkose, lies unconformably under the clay bed of the Neogene Gansu Gr. Regionally, it is unconformably overlain by the Huanhe Fm

The present formation occurs in the southern and northern parts of the Shaanxi-Gansu-Ningxia basin, for example, in Uxin Qi and west Otog Qi of Inner Mongolia, and the vast area north of the line linking Yijun, Xunyi, Binxian and Ganyang to the line linking Huangling, Zhidan and Yulin of Shaanxi. It is lithologically monomorphic and persistent and is characterized by the development of large-scale cross-beddings and oblique beddings on the sandstone, which can be used as a marker bed for the stratigraphic correlation within the basin. Generally it tends to decrease in grain size from the margin to the center of the basin and there appear mudstone partings in Wuqi, Zhidan and Qingyang, and tends to increase gradually in thickness from southwest to northeast, from 71 to 390 m. In the Yijun area, it is in conformable contact with the underlying Yijun Formation. It is seen down the boreholes in Zhenyuan of east Gansu and in Yanchi of east Ningxia. It is 243-450 m thick in Zhenyuan and 217-334 m in Yanchi.