JishanGansu Fm

Its base marked by gray black conglomerate is distinguished from blue gray and yellow green clayey siltstone of the underlying Zhoujiawan Fm, and lies conformably on the latter.

Its top marked by gray black medium and thick-bedded conglomerate is overlain unconformably by the overlying Quaternary loess.

The present formation occurs in the Qinling Mountain at the juncture of Shaanxi and Gansu, and is especially developed in the Huicheng Basin of east Gansu. To the east of the basin it is generally represented by coal-bearing sediments, and to the west only coal fragments and coal inclusions are observed. It may directly rest on the strata prior to the Jurassic unconformably and is overlain unconformably by the tangerine red beds of the Paleogene Gansu Group. In the area from Liangdang County of Gansu to Fengxian of Shaanxi, the lower part of the formation is represented by gray black and yellow green silty mudstone, siltstone with conglomerate and sandstone, while the upper part gray green and yellow green conglomerate and purple red and gray purple clayey siltstone and siltstone with coal streaks. The Jishan Formation ranges from 473 to 908 m in thickness. In the Qingquan Village -the Guocun Village of Shangxian, it is represented by intermediate volcanic rocks. In Kangxian in the western part of the basin, the lower part of the formation is represented by gray black, yellow green and gray green silty mudstone, siltstone and thick-bedded basal conglomerate, while the upper part yellow green and gray black silty mudstone, mudstone with siltstone, sandstone, conglomerate and coal streaks, with a thickness of more than 334 m.