Youshashan Fm
Type Locality and Naming
Qaidam Basin. The naming section is located on the northern limb of Youshagou of the Youshashan structure at Lenghu Township in the Qaidam basin, Qinghai. Named by Pei Wenzhong, Zhou Mingzhen and Zheng Jiajian in 1959.
Lithology and Thickness
Alternating beds of light brown sandy mudstone and sandstone and gray pebbly sandstone and conglomerate. The lithology varies greatly: the lithology is generally dominated by thick-bedded conglomerate on the basin margins and becomes fine gradually toward the basin center; the formation consists of alternating beds of gray conglomerate and sandstone and brown siltstone and sandy mudstone in the western part of the basin and brownish, brownish gray, grayish green and brown sandy mudstone with sandstone and siltstone in the eastern part. Its outcrop thickness is up to 354–1787 m.
[Figure: Outcrops of the Youshashan Formation. A, the lower sandstones; B, the upper mudstones; C, the large tube-like iron concretions in the Youshashan Formation; D, mammalian fossil (Tsaidamotherium hedini) in the Youshashan Formation.
Relationships and Distribution
Lower contact
It probably has a conformable or locally unconformable contact with the underlying Oligocene-Miocene Ganchaigou Fm.
Upper contact
It probably has a conformable or locally unconformable contact with the overlying Pliocene Shizigou Fm.
Regional extent
Distributed in the Qaidam Basin.
GeoJSON
Fossils
Cervidae: Stephanocemas sp., Lagomeryx tsaidamensis; Perissodactyla: Hipparion sp., Acerorhinus tsaidamensis; Artiodactyla: Tsaidamotherium hedini, Olunbulukia tsaidamensis, Tossunnoria pseudibex Qurliqnoria cheni; Proboscidea: Tetralophodon sp.; Charophytes: Tectochara globula, Charites sadleri, Gastropods: Radix ovata, Hydrobia cf. atureensis; Ostracods: Cyprideis, Ilyocypris, Candoniella;
Age
Depositional setting
Shallow-lake, fluvial and lake-basin deltaic deposits.
Additional Information