Zhoujiawan Fm
Type Locality and Naming
The Zhoujiawan Formation was erected by the Northwest Institute of Geology in 1974. The section for the designation is from Tianjiaba to Caoba of the Kangxian County of Gansu (105°28′E; 33°27′N).
Lithology and Thickness
The Zhoujiawan Formation is represented by mainly purple red, yellow green and gray green variegated mudstone, siltstone with sandstone, sandy conglomerate and conglomerate. It is 1428.3 m thick.
Relationships and Distribution
Lower contact
Its conformable base marked by yellow green greatly thick-bedded massive sandstone is distinguished from the underlying Tianjiaba Fm marked by purple red siltstone
Upper contact
Its conformable top marked by purple red and yellow green siltstone and silty mudstone is distinguished from the Jishan Fm marked by gray black conglomerate.
Regional extent
The present formation occurs in the Qinling area at the juncture between Shaanxi and Gansu and is most developed in the Huicheng basin of east Gansu. It varies considerably both in lithology and thickness. From Liangdang county of Gansu to Fengxian of Shaanxi, it is mainly represented by gray green and yellow green thick-bedded conglomerate, sandstone and clayey siltstone, locally with poor quality coal, measuring 180-851 m in thickness. In the Maoba area of Gansu, the lower part of the formation is built up by intermediate and basic volcanic rocks, up to 3000 m in thickness. In the small intermontane basin in Duoergou of Diebu county of west Gansu, it is built up by purple red and gray green conglomerate, sandstone and mudstone with argillite, measuring more than 520 m in thickness.
GeoJSON
Fossils
The formation yields bivalves Sphaerium selenginesis, S. andersoni, S. jeholense, Nakamuranaiaa chingshanensis; gastropods Viviparus gansuensis, Bithynia kangxianensis, Kangxianensismuornata; ostracods Cypridea sp.; floras Cladophlebis exiliformis, etc.; in the Ganquan area of Wudu county, bivalves Plicatounie naktongensis; gastropods Probaicalia cf. vitimensis and Reptilia; in the Maoba area of Chengxian, floras Brachyohyllum japonicum, Ruffordia goepperti, Onychiopsis psilotoides, etc. It also yields ostracods Cypridea vitimensis, C. sinensis, C. gunsulinensis; bivalves Nakamuranaia elongata, Plicatounia (Plicatounia) naktongensis, P. gansuensis, Ferganoconcha sibirica, F. lingyuanensis, insects, etc.; Charophytes Clypeator jiuvuanensis, Mesochara stipitata, Aclistichara rarispiralis, Flabellocchara irregularis; sporopollen grains represented by the Schizaoisporites- Cicatricosisporites assemblage.
Age
Depositional setting
It belongs to fluvial-lacustrine deposition.
Additional Information