Daxigou Fm
Type Locality and Naming
It was named by Wang Yuelun in 1944. The naming section is located at Daxigou, Agan Township, Lanzhou City, Gansu Province; with its reference section being situated at Dashuitou, Jingyuan County, and the Daoleng Mt of the Sidaogou region, Gansu Province.
Synonym:（大西沟组）
Lithology and Thickness
Composed mainly of grey-green and grey-white breccia, conglomerate, trachyte, pebble-bearing trachyte and grey-green sandstone and siltstone, intercalated with grey-green mudstone, thin coal beds and coal seams, with its basal part representing conglomerate, and its upper part being intercalated with a small amount of purple mudstone; with a thickness of over 380 m.
Relationships and Distribution
Lower contact
Its basal part is in a fault contact with the Tertiary purple conglomerate, or in an unconformable contact with the underlying Proterozoic Erathem. On the Sidaogou section of the Daoleng Mt in Jingyuan County the formation unconformably underlies disconformably the Yaoxian Fm.
Upper contact
Its top part is in a conformable contact with a set of grey-white quartz-conglomerate from the basal part of the overlying Yaojie Fm (Aganzhen Fm). On the Sidaogou section of the Daoleng Mt in Jingyuan County the formation unconformably overlies the Nanyinger Gr (Nanying'er Gr) of the upper Triassic.
Regional extent
The formation is distributed not only in the areas of Agan Township, Dashuitou of Jingyuan County, but also in the areas of Jiutiao Ridge of Wuwei County, Tanshan Ridge of Tianzu County, Yaojie (Tandonggou Fm), Honggu District, Lanzhou City and Tanshangou of Huining County, Gansu Province, as well as in the areas of Daca-Shilang (Riyueshan Formation), Huangyuan County, Qinghai Province. The lithology of the present formation in various places is alike.
GeoJSON
Fossils
It yields plant fossils as represented by Neocalamites carrerei, Cladophlebis cf. koaiana, Cl. williamsoni, Cl. tsaidamensis, Dictyophyllum sp., Raphaelia spp., and Pityophyllum spp., as well as spore-pollen and bivalve fossils. On the Sidaogou section of the Daoleng Mt, the formation yields more abundant plant fossils.
Age
Depositional setting
The formation represents essentially fluvial and lacustrine deposits, intercalated with a small amount of swamp-facies deposits.
Additional Information