Taosigou Fm
Type Locality and Naming
The type section of Taosigou Formation is the Taosigou section, located at the middle section of Taosi Hill, north of Taosigou Valley, west of Shitangjing, Shizuishan, Ningxia Hui Autonomous Region (106°16’E, 39°13’N). It is the lower portion of the same section shared by the overlying Hulusitai Formation. The section lies about 5 km west of Shitangjing Mining Area, or 4 km northeast of Hulstai Town, and was measured by Stratigraphic Restudy Group of Ningxia Prospecting Institute Geology and Mineral Resources in 1993. In the type section the formation is 70.40 m thick. The Taosigou Formation was named by Shen Yuling in Gu (1996). The name is derived from Taosigou Valley, Shitangjing Mining Area, Dawukou District, Shizuishan City, Ningxia Hui Autonomous Region.
Synonym: （陶思沟组）
Lithology and Thickness
The Taosigou Formation is a clastic sequence with carbonate interbeds. In the type section, the Taosigou Formation is greyish white, light grey, thin-bedded to middle bedded quartzose sandstone, purplish red and yellowish green shale with several interbeds of light grey, grey and dark grey, thin- to thick-bedded or massive dolomite. The top is a layer of dolomite, about 4 m thick. There is a layer of oolitic limestone, about 2 m thick, in lower central part.
Relationships and Distribution
Lower contact
The Taosigou Fm is in conformable contacts with the underlying Wudaotang Fm in the middle section of Helanshan Mountain (between Yinchuan and Dawukou). The lower boundary of the Taosigou Fm is either marked by disconformable plane in the area of northern Helanshan Mountain, or by lithological change from the the algae-bearing limestone at the top of Wudaotang Fm to greyish green shale at the base of Taosigou Fm in the area of middle section of Helanshan Mountain. It is in disconformable contacts with Wangquankou Fm of Pre-Ediacaran System in northern section of Helanshan Mountain (north of Dawukou).
Upper contact
It is in conformable contacts with overlying Hulusitai Fm. The upper boundary of is defined by disappearance of the dolomite at the top of the formation or appearance of the median-bedded sandy limestone at the base of the Hulusitai Fm.
Regional extent
The Taosigou Formation is exposed in the Western Margin Area of North China Region, restricted in the areas of middle and north sections of the Helanshan Mountain, northern Ningxia (Helan and Pingluo counties and Yinchuang and Shizuishan cities) and of adjacent area in southwestern Inner Mongolia (Alxa Left Banner, Wuhai City and Zuozishan Mountain lying north of the Helanshan Mountain). The thickness of the formation decreases northward, varying from 371.4 at Zihuagou in the south middle section of Helanshan Mountain to 28.8 m in the Suyukou area in the north middle section of Helanshan Mountain.
GeoJSON
Fossils
Only trilobite Ptychoparia sp. is reported from the Taosigou Formation (Gu, 1996). In other section, the formation yields additional trilobites Probowmania quadrata, P. sp., and cf. Saimachia sp.
Age
Depositional setting
The formation belongs to open shallow sea and littoral tidal flat setting.
Additional Information