Wudaotang Fm
Type Locality and Naming
The type section of the Wudaotang Formation is the Wudaotang section, located at Mining Area of the Suyukou Phosphorite Mine, Helan, Yinchuan (105°57’E, 38°45’N). It is the upper portion of the same type section with the underlying Suyukou Formation as the lower portion. The section lies 7.5 km northwest of Suyukou or 44 km northwest of seat of Helan County, and was measured in 1975 by No. 2 Geological Team of Ningxia Bureau of Geology. The Wudaotang Formation was named by Zhou and Zheng (1976). The name is derived from Wudaotang, Jinshan Village in Honguang Township, Helan County, Yinchuan City, Ningxia Hui Autonomous Region.
Synonym: (五道淌组) ; Chushatung Fm (see Additional Information)
Lithology and Thickness
The Wudaotang Formation is mainly a carbonate sequence with interbeds of fine clastic rocks. In the type section the formation is 57 m thick and is divided into nine lithologic beds (Bed 5−9), from bottom up: 9, dark grey, thick-bedded, silty calcareous dolomite (22.1 m thick); 8, white, thin-bedded limestone with a few of medium-bedded limestone (23.9 m); 7, light grey, medium-bedded dolomite (1.9 m); 6, thin-bedded-limestone with two of interbeds of purplish red, grey shale, yellowish medium-bedded, calcareous siltstone, and medium-bedded quartzite (4.3 m); 5, grey, medium-bedded limestone (4.8 m). The formation is assigned to semi-enclosed littoral to neritic sedimentation. In the type section the formation is 57 m thick.
Relationships and Distribution
Lower contact
The Wudaotang Fm is in conformable contact with the underlying Suyukou Fm. The lower boundary of the formation is marked by lithologic change from the siltstone of underlying Suyukou Fm to dolomite of Wudaotang Fm
Upper contact
The Wudaotang Fm is in conformable contact with the overlying Hulusitai Fm. The upper boundary by lithologic change from quartzose sandstone at the top of Wudaotang Fm to the green shale at the base of the overlying Hulusitai Fm.
Regional extent
The Wudaotang Formation is in the Yangtze River Area of South China Region, restricted mainly in the middle of the Helanshan Mountain, northern Ningxia (Suyukou and Wudaotang of Helan County) and adjacent Yueshujin of Ordos City, southwestern Inner Mongolia. The formation has sporadic distribution in Tongxin County and Guyuan City, south-central Ningxia, and Pingliang City of northeastern Gansu Province, the formation is not distributed in the northern part of the Helanshan Mountain.
GeoJSON
Fossils
Wudaotang Formation is poorly fossiliferous. Only the Bed 6 yields trilobite Probowmania, and the Bed 9 yields algae Girvanella sp.
Age
Depositional setting
Additional Information
Lithology and Thickness:
The Wudaotang Formation is mainly a carbonate sequence with interbeds of fine clastic rocks. In the type section the formation is 57 m thick and is divided into nine lithologic beds (Bed 5−9), from bottom up: 9, dark grey, thick-bedded, silty calcareous dolomite (22.1 m thick); 8, white, thin-bedded limestone with a few of medium-bedded limestone (23.9 m); 7, light grey, medium-bedded dolomite (1.9 m); 6, thin-bedded-limestone with two of interbeds of purplish red, grey shale, yellowish medium-bedded, calcareous siltstone, and medium-bedded quartzite (4.3 m); 5, grey, medium-bedded limestone (4.8 m). The formation is assigned to semi-enclosed littoral to neritic sedimentation. In the type section the formation is 57 m thick.
Lithology-pattern: Dolomitic limestone
Relationships and Distribution:
Lower contact:
The Wudaotang Fm is in conformable contact with the underlying Suyukou Fm. The lower boundary of the formation is marked by lithologic change from the siltstone of underlying Suyukou Fm to dolomite of Wudaotang Fm
Upper contact:
The Wudaotang Fm is in conformable contact with the overlying Hulusitai Fm. The upper boundary by lithologic change from quartzose sandstone at the top of Wudaotang Fm to the green shale at the base of the overlying Hulusitai Fm.
Regional extent:
The Wudaotang Formation is in the Yangtze River Area of South China Region, restricted mainly in the middle of the Helanshan Mountain, northern Ningxia (Suyukou and Wudaotang of Helan County) and adjacent Yueshujin of Ordos City, southwestern Inner Mongolia. The formation has sporadic distribution in Tongxin County and Guyuan City, south-central Ningxia, and Pingliang City of northeastern Gansu Province, the formation is not distributed in the northern part of the Helanshan Mountain.
GeoJSON:
Fossils:
Wudaotang Formation is poorly fossiliferous. Only the Bed 6 yields trilobite Probowmania, and the Bed 9 yields algae Girvanella sp.
Age:
Late Duyunian (mid-Cambrian).
Age span:
Beginning stage: Cambrian Stage 4
Fraction up in beginning stage: 0.25
Beginning date (Ma):
Ending stage: Cambrian Stage 4
Fraction up in ending stage: 0.85
Ending date (Ma):
Depositional setting:
Depositional-pattern:
Additional Information
The formation is assigned to semi-enclosed littoral to neritic sedimentation. Shen in Gu (1996) regarded the Wudaotang Formation to be synonymous with Chushatung Fm. Lithologically the Chushatung Fm is unlike the Wudaotang Formation by consisting mainly of limestone including crystalline limestone, algal limestone, siliceous limestone and sandy limestone, and some interbeds of dolomite in lower part and dolomitic limestone in upper part. In contrast, the Wudaotang Formation is composed mainly of silty dolomite and limestone, which are alternated commonly with clastic rocks including shale, siltstone and sandstone, and occasionally quartzite. Shen’s viewpoint is not agreed with by Xiang (1981b), Compiling Committee for Chinese Stratigraphic Lexicon et al. (1999) and Yuan et al., (2016), who regarded the Wudaotang Formation as a valid unit, and by this book.