Baqi Fm
Type Locality and Naming
The type section is located near Baqi village, northwest of Dale in Xiangzhou County, Guangxi Zhuang Autonomous Region. Its type section is located at Ma’an Hill, Zhongping village (24°4′55.4″N—109°56′15″E) of Xiangzhou County. It was named by Bai Shunliang et al. in 1979.
[Figure - Geographic position of the type locality of Baqi Formation.]
Lithology and Thickness
Siliceous limestone. The Baqi Fm is mainly marked by a large number of thin-bedded siliceous rocks; and is divided into three lithologic members. Lower member, 13.2 m thick, is mainly composed of thin-bedded (ca. 20 cm) pellet limestone, micritic limestone, intercalated with thin-bedded tentaculite-bearing micritic limestone. Middle member, 23.9 m thick, is characterized by tentaculite-bearing limestone with cherty interbeds. Upper member, 8.27 m thick, consists of bioclastic limestone and calcirudite. It contains abundant tentaculites, conodonts and a few brachiopods.
In the Ma’anshan section of Zhongping, this formation is 45.37 m in thickness, but in the naming section (near Baqi Village) the thickness is only 21.7 m. The distance between the two sections is only 8 km but their thicknesses are quite different from each other.
[Figure showing the columnar section of Baqi Formation (left) and the outcrop of limestone intercalated with chert beds (right).]
[Figure Overview of Baqi Formation in the Ma’anshan Hill.]
Relationships and Distribution
Lower contact
The base of the formation is distinguished by the appearance of the thin-bedded tentaculites-bearing marl from the underlying limestone of the Donggangling Fm (Tungkangling Fm).
Upper contact
It is has a conformable contact with the overlying thick-bedded limestone of Guilin Fm.
Regional extent
The Baqi Fm is comparatively extensively distributed. In addition to Xiangzhou and Luzhai in central Guangxi, it can also be observed at Hechi and Huanjiang in northwest Guangxi and at xing’an, Lingchuan, Yongfu, Yangshuo and Guilin of northern Guangxi. It also extends into Hunan Province (Shetianqiao and Jiahe)
GeoJSON
Fossils
Tentaculites: Abundant tentaculite fossils including Tentaculitida, Homoctenida and Dacryoconarida are identified in the Baqi Formation including two assemblages. The first Nowakia tenella – Viriatellina xiangzhouensis Ass. Zone occurs in the upper part of Lower Member, characterized by the concurrent occurrence of Nowakia tenella, N. hetera Wang, N. parotomari Mu et Ruan, Viriatellina xiangzhouensis Wang, V. debilisa Wang and V. cf. amoricana Lardeux. The second Homoctenus aciformis Ass. Zone is marked by the first appearance of Homoctenus and an abundance of the thin-shelled Paradenticulite group, which is concentrated in the lower part of the Middle Member. Associated elements are Unioconus macarus Wang, Milticonus cf. schimanskii Ljaschenko, ? Polycylindrites bouceki Wang and the species of Costulatostyliolina, Styliolina and Striatostyliolina. Brachiopods Leiorhyncus assemblage with a few Stringocephalus sp. have been found in the Formation.
[Figure- Tentaculite Homoctenus aciformis Wang from the Baqi Formation.]
Age
Depositional setting
Its sedimentary environment is considered to be deep-water slope facies to basin facies.
Additional Information