Xiaoqiacuo Fm
Type Locality and Naming
The type section is located in Xiaoqiacuo, upstream of Gema stream, Zaduo County, Qinghai Province. It was named by Ma Fubao, Wang Xiulin and Che Yi in 1984. Its evolution can refer to the Jiezha Gr. Middle formation in Jiezha Gr.
Synonym:
Lithology and Thickness
The formation is dominated by limestone. It can be divided into two parts: Lower member is shelly limestone, dolomitic limestone and dolomite, with a thickness of 463 m. Upper member's lower part is thick-bedded shelly limestone and clotted limestone, and the upper part is clotted cryptocrystalline limestone with a thickness of 972 m. The lithology of this formation is relatively stable, and the thickness varies from place to place, generally above 1000 m.
Relationships and Distribution
Lower contact
The Xiaoqiacuo Fm is conformable in contact to the variegated sandstone and calcareous sandstone of the underlying Yujiang Fm (or Dongmaolong Fm), with the oolitic limestone or dolomite with fine-grained arkose at the base.
Upper contact
Limestone, bioclastic limestone and quartz sandstone in the top of the Xiaoqiacuo Fm is conformable contact to overlying Jiadengda Fm quartz sandstone.
Regional extent
This formation is the central carbonate formation of the former Jianzha group, which is widely distributed in Zhiduo, Zaduo, southern Yushu, Nangqian and the area of Sumang and Niangla to the east of Qinghai.
GeoJSON
Fossils
Fossil in the majority with bivalve, brachiopods, followed by the ammonoids, common a bivalve Halobia ganziensis, H. parplicosa, H. yandongensis, Schafhaeutlia aff. astariformis, S. cf. sphaerioides, Placunopsis sp., Neomegalodon sp., Megalodon sp., etc.; Brachiopoda: Arcosarina foliacea, A. pentagona, Aequspiriferina qinghaiensis, Koninckina gigantea, Oxycolpella elongata, Sanqiaothyris elliptica, Yidunella pentagona, Zeilleria lingulata, Rhaetinopsis sp., Rhaetina sp., etc. The Ammonoid layer can be constructed Protrachyceras victoria layer, which includes Discitropites qinghaiensis, Medaphyllites jarbas, Protrachyceras Victoria, etc.
Age
Depositional setting
It is interpreted as a shallow sea environment.
Additional Information