Guotang Fm
Type Locality and Naming
The type section is the Guotang section (117°52’E, 25°59’N). It lies about 1.5 km west of Sanhe Town, the seat of Sandu County, Guizhou, and is measured southwestward along highway from the Sandu Middle School west of the Ironworks by the Southern Guizhou Stratigraphic Team of Chinese Academy of Sciences in 1959. The Guotang Formation was first published by Li and Chen (1962). The name is derived from Duotang Village in the southwest of Sanhe Town, the seat of Sandu Shui Autonomous County, Qiannan Buyi-Miao Autonomous Prefecture, Guizhou Province. The name was originally appeared in a 1959 manuscript by Yang Jingzhi, Qian Yiyuan and colleagues from the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences. Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences (1977) established the Wuliguan Fm overlying the Guotang Fm. Considering the variable lithology of the Wuliguan Fm, Guizhou Bureau of Geology and Mineral Resources (1987) included the Wuliguan Fm in the upper part of the Guotang Fm as a lithologic member.
Synonym: （锅塘组）
Lithology and Thickness
The Guotang Formation is a carbonate sequence of yellow, grayish yellow thin-bedded banded argillaceous limestone, calcareous shale intercalated with micritic calcirudite and minor bioclastic micritic limestone. In the type section the formation is divided into 5 informal lithological members (Dong, 1997). Member 1 consists of grey and dark grey shale interbedded with thin-bedded striped argillaceous limestone (80 m thick); Member 2 consists of grey, thin-bedded micritic limestone intercalated with carbonaceous shale (219 m); Member 3 consists of grey striped limestone with 4 layers of brecciated limestone (112 m); Member 4 consists of grey to dark grey striped limestone or leopard limestone (108 m); Member 5 consists of light red quartzose sandstone intercalated with greyish green sandy shale (only 8 m exposed). In the type section, the top of the formation is not exposed, and the incomplete formation is 522 m thick.
Relationships and Distribution
Lower contact
The Guotang Formation rests conformably on the underlying Yangjiawan Fm. The lower boundary of the formation is marked by the upward disappearance of the carbonaceous shale or marlstone of the Yangjiawan Formation and appearance of massive brecciated limestone at its base of Guotang Fm.
Upper contact
Its upper contact relationship is unknown in type section. Regionally, this stratigraphic unit is confined by the shale at the base of the overlying Tonggao Fm, and a conformable contact between the Guotang Fm and the overlying Tonggao Fm is observed.
Regional extent
The Guotang Formation is exposed in the western part of the Jiangnan Basin Area of South China Region, distributed merely in the Sandu Township, southeastern corner of Guizhou Province. The lithology of the lower part is persistent, and the upper part is of considerably variable laterally. At Sandu high school, the upper part is composed of calcareous siltstone, and calcareous fine-grained sandstone in Datang, bioturbated sandy and calcareous mudstone intercalated with bioclastic limestone lenses in Wuliguan, and changes into fine crystalline dolomite to dolomicrite in Jiaoli and Shuiniuzhai (Guizhou Bureau of Geology and Mineral Resources, 1987).
GeoJSON
Fossils
In the type section, the member 1 of the Guotang Formation yields trilobites Euloma sp., Hedinaspis kueichouensis and Yuepingia sp. and graptolites Dictyonema flabelliforme and D. jugatum sp.; the member 4 yields trilobite Szechuanella sp. and graptolites Callograptus cf. taitzehoensis, and Herrmannograptus uniformis etc. It also yields associated trilobites, cephalopods, brachiopod and Cystoidea.
Age
Depositional setting
Additional Information