Yijun Fm

The base of the formation is in disconformable contact with the underlying Middle Jurassic Zhiluo Fm or disconformable on the Late Jurassic Fenfenghe Fm or the Anding Fm

The top is in conformable contact with the overlying Luohe Fm.

The present formation is mainly distributed on the southern and western margins of the Shaanxi-Gansu-Ningxia Ordos basin and in Huangling, Yijun, Xunyi, Binxian and Ganyang of Shaanxi. It becomes finer in lithology from the margin to the center of the basin, and thickens from northeast to southwest, generally from 20 to 65 m, up to 302 m in the Fenfanghe area, lying unconformably on the Zhiluo Fm or the Fenfanghe Fm. In Lingwu and Yanchi of east Ningxia, it is built up by purple red and brown red conglomerate and sandy conglomerate with grit and small amounts of mudstone. Generally it tends to become finer in grain size and decrease in thickness from north to south and from west to east, 41 m thick at minimum and 886.8 m at maximum. It lies disconformably on the Anding Fm.