Tangjiawan Fm
Type Locality and Naming
The type section is located near the Tangjiawan village of southwest Guilin City, about 200 m to north of Wanfu road (G721), which is from Guilin Downtown to Lingui Region (25° 13' 05"N; 110° 15' 05"E,). It was named by Wu Yi et al. in 1992.
[Figure - Topographical map of the southern suburb of Guilin City, Guangxi showing the type localities of the Tangjiawan Fm (A), Guilin Fm (B), Dongcun Fm (C) and Etoucun Fm (D).]
Lithology and Thickness
Dolomitic limestone. The Tangjiawan Formation is characterized by the well-developed carbonate rocks, which display various microfacies, and is well-exposed along the east flank of Huangcun-Maxi anticline, dip eastward with dip angular at 20-30 degrees. The carbonate rocks consist mainly of gray, dark-gray to grayish-black medium- to thick-bedded re-crystalline dolomitic bioclastic and detrital limestone; the medium- to fine recrystalline sparry dolomite and micrite bioclastic limestone. Sedimentary structures such as leopard porphyritic, stromatolithic, birds-eye, and geopetal can be observed. Large globular and semiglobular stromatoporoids built biostroms with a thickness up to 5 m, partly with framwork structure. The dendroid stromatoporoids (Amphiporas) are mainly distributed in the medium-thin bedded grainstone of upper part of the formation associated with rugose corals and few brachiopods. Generally, small cycle sequences are developed, in which the breccia limestone formed the basal part of a cycle, followed by globular stromatoporoid limestone with bioturbation and dendroid stromatoporoid limestone, and the laminated fenestral limestone is at the top of a cycle. The Tangjiawan Fm has a total thickness of about 227 m.
[Figure: column section of the upper Tangjiawan Fm in the type locality showing the main lithofacies (after Yu et al., 1991).]
Relationships and Distribution
Lower contact
The lower part with a bed of 0.8 m thick hematic bioclastic micrite limestone at the base rests conformably on the siliciclastics of the Xindu Fm.
Upper contact
It is overlain by the dark-gray laminated limestone of the Guilin Fm.
Regional extent
This formation is widely distributed in Huanjiang, Luocheng, Rong’an, Quanzhou, Guilin, Lingchuan, Lingui, Yangshuo, Yongfu of North Guangxi, in Fuchuan, Hezhou, Zhongshan of Northeast Guangxi, and also in Mashan, Du’an, Jingxi of southwest Guangxi.
GeoJSON
Fossils
It contains abundant Stromatoporoids Astromastoma sp., Actinostroma clathratum, Stromatopora laminosa, Amphipora sp. and Corals Pseudomicrolasma fongi, Sunophyllum typicum, Stringophyllum sp., Pachypora wangi,Thamnopora raritabulata, Caliapora battersbyi, and a few Brachiopods Stringocephalus sp., Gypidula sp., Emanuella sp..
Age
Depositional setting
It is interpreted as an open to semi-restricted platform with reef environment.
Additional Information