Yaoshuiquan Fm
Type Locality and Naming
The type section is at Yaoshuiquan on the southern slope of Laji Hill, Qinghai. The Yaoshuiquan Gr was named by Qinghai Party of Regional Geological Survey in 1960-1962, and was published by Qinghai Compiling Group for Regional Stratigraphic Scale (1980). In 1975, No.2 Qinghai Party of Regional Geological Survey drew the base of the Yaoshuiquan Gr (= Yaoshuiquan Fm) at the unconformity, a suggestion followed by Qinghai Bureau of Geology and Mineral Resources (1991).
Synonym: (药水泉组）
Lithology and Thickness
The formation divided into two parts. Lower part is composed of clastic rock intercalated with volcanic rock, with crystalline limestone at the base. Upper part is dominated by volcanic rock. In the type area, the Yaoshuiquan Formation recorded an incomplete thickness of 880.6 m. The Yaoshuiquan Formation exhibits a vertical rhythm of conglomerate-sandstone, with volcanic rock in the middle part. The composition of the conglomerate changes from complex to simple upward. Horizontally, from west to east, volcanic rock increases, indicating an increasing volcanic activity eastward.
Relationships and Distribution
Lower contact
It rests unconformably on the Chapu Gr
Upper contact
Upper boundary is covered.
Regional extent
With a persistent lithology, the Yaoshuiquan Fm is widespread. At Houwu Hill in Yongjing County, Gansu, the Yaoshuiquan Gr is 7017 m thick, and the lower part yields graptolite Orthograptus truncatus and trilobite Lonchodomas sp. Eastward to Wusu Hill, the Yaoshuishan Gr (= Yaoshuiquan Fm) is composed dominantly of volcanic rock, volcaniclastic rock, lava intercalated with minor phyllite, chert and crystalline limestone, which was previously named the Wusushan Gr (Gansu Compiling Group for Regional Stratigraphic Scale, 1980). At Liujiajing in the western part, the Yaoshuiquan Gr is 4429 m thick. At Baolonggou, Xizhou, in the east part, it is 389 m thick, and is dominated by andesitic breccia, crystalline limestone and meta-siltstone.
GeoJSON
Fossils
The limestone at the base yields brachiopods Strophomena sp., Rafinesquina sp. and Dalmanella sp. At Houwu Hill in Yongjing County, Gansu, the lower part of the Yaoshuiquan Gr yields graptolite Orthograptus truncatus and trilobite Lonchodomas sp.
Age
Depositional setting
Additional Information