Luohandong Fm

The base of the formation, marked by loose arkose and purple red conglomerate, is distinguished from the underlying Huanhe Fm built up by gray green clayey siltstone. They are in conformable contact.

The top, marked by loose sandstone, is separated from blue gray mudstone of the overlying Jingchuan Fm. They are in conformable contact.

The present formation mainly occurs in the southern and northern parts of the Shaanxi-Gansu-Ningxia basin. In Otog Qi, the western part of Otog Qianqi, and the central and western parts of Hanggin Qi, it is mainly represented by tangerine, purple red and gray purple fine sandstone, arkose and mudstone with micro-beddings, up to 350 m thick, and of fluvial and lacustrine deposition. In Longxian, Ganyang, Binxian, Xunyi, Huangling, Ziwuling, Dingbian and Jiyuan of Shaanxi, it is quite persistent in lithology and decreases in the amount of sandstone from north to south and ranges from 106 to 452 m in thickness. Exposed in Huanxian, Zhenyuan, Chongxin and Jingchuan of Gansu, it is dominated by conglomerate with sandstone, and varies considerably in thickness from 141 to 278 m, and increases in grain size from north to southwest. In the “Gujiliang” it overlaps unconformably the Ordovician- Triassic rocks. In Ningxia, it is mainly observed down the boreholes in Yanchi.