Moding Fm
Type Locality and Naming
The type section is located at Liujing railway station of Hengxian County, Guangxi. (see Mintang Fm). It was named by Guangxi Team of Regional Geological Survey in 1982. The upper part of the Moding Formation was cut off by a strike fault between Moding Fm and its overlying Najiao Fm in the type section. Therefore, the Wuxiangling section in the Nanning suburb is used for a reference. Unfortunately, this section is not protected owing to large-scale constructions.
[Figure Simplified geological map of Liujing area showing the location of type sections of some lithostratigraphic units (red lines) A-Nagaoling Fm, B-Yukiang Fm, C-Moding Fm, D-Najiao Fm, E-Mintang Fm and Gubi Fm.]
Lithology and Thickness
Chert. It is characterized by the yellow brown thin-bedded siliceous rocks intercalated with medium- to fine-grained crystalline dolomite at base. Several red-brown banded tuffs and cherts 1-2 cm thick, are intercalated within siliceous rocks. Partially it contains lenses of low metamorphic siltstone and fine-grained sandstone. The thickness is 54.9 m.
Relationships and Distribution
Lower contact
In the reference section of Wuxiangling, the Moding Fm is conformable in contact to the underlying Yukiang Fm (Yujiang Fm) with a bed of 40 cm thick dolomite at the base.
Upper contact
The top of the formation is a fault contact with the overlying Najiao Fm; but conformable with the Tanhe Fm in the reference section. The Tanhe Fm, less than 70 m thick, established in Nanning area is also characterized by the siliceous rocks but contains dacryoconarids belonging to Eifelian stage. The similar lithology and fossils with Moding Fm make it difficult to separate the two formations.
Regional extent
It is restrictively distributed in the Nanning area of Guangxi.
GeoJSON
Fossils
Ammonoids: Anetoceras spp., Erbenoceras sp., Mimagoniatites sp. Dacryoconarids: Nowakia barrandei, N. elegans; and Brachiopods Rostrospirifer spp..
Age
Depositional setting
It is interpreted as a basin facies environment.
Additional Information