Tianjiaba Fm

Its base marked by poorly-sorted conglomerate lies unconformably on the phyllite of the Upper Silurian Bailongjiang Gr.

Its top marked by purple red and blue gray siltstone lies conformably under yellow green greatly thick-bedded massive sandstone of the overlying Zhoujiawan Fm.

The present formation occurs in EW direction in the Qinling region at the juncture between Shaanxi and Gansu, and is mostly developed in the Huicheng basin of east Gansu. It varies considerably in lithology from basin to basin. To the west of Luotangba of Chengxian County, the lower part of the formation is dominated by purple red siltstone interbedded with conglomerate, while the upper part purple red siltstone with sandstone and sandy conglomerate. Sedimentary rhythms are developed; there is scouring between rhythmic beds; and oblique beddings in single direction are developed. From Luotangba to Fengxian of Shaanxi through Tanba, it has changed to piedmont-diluvial facies consisting of purple greatly thick-bedded massive conglomerate, with mixed gravels of different sizes, showing poor roundness and no beddings. It is 2364 m thick in Luotangba and decreases to 1070 m eastward and less than 1000 m westward. It lies unconformably on the Silurian and Jurassic strata. In the Langmusi basin of Ludian, it is represented by gray purple -dark purple red and gray red sandy mudstone interbedded with conglomerate, measuring 650 m in thickness. Around Diebunizang it is built up by purple red conglomerate of 78 m thick. In the Xinchengzi basin of Dangchang, it is built up by purple red conglomerate and sandstone interbedded with shale, being 1115 m in thickness. In Fengjiashan of Shangxian of Shaanxi there occur a lot of gray green conglomerate and mudstone.