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Zhangmu Formation

Zhangmu Fm

Period: 
Devonian

Age Interval: 
D 13-D 21, (new 20), Emsian to Eifelian (Lower to Middle Devonian)


Province: 
Guangxi

Type Locality and Naming

The type section is located along both sides of Nanliujiang channel nearby Beijuntang village, about 3 km east of Zhangmu Town, 35 km southeast of Yulin City. Proposed by Shi W.J. of Guangxi Regional Geological Survey in 1980.

[Figure: Map showing the locations of the Beijuntan Fm, Lianghetang Fm and Zhangmu Fm in the Yulin area of Guangxi]


Lithology and Thickness

Sandy claystone. The Formation is mainly composed of gray-black mudstone and silty mudstone intercalated with thin-bedded siltstone, fine sandstone and several beds of quartz sandstone. The mudstone displays horizontal bedding while the sandstone has small laminae. The exposure of the formation is incomplete and there are occurrences of fault and fold; the thickness is estimated more than hundreds meters.


Lithology Pattern: 
Sandy claystone


Relationships and Distribution

Lower contact

Conformable on the Lianghetang Fm. In the Changwantang Reservoir, 2 km far from type locality it rests on the Silurian strata.

Upper contact

Unclear upper contacts because of cover.

Regional extent

With restricted distribution the formation is only seen in the Yulin area.


GeoJSON

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Fossils


Age 

Fossils of the formation are characterized by the brachiopods and trilobites, the others such as bivalves and corals are rare. The main fossils are: Trilobites: Proetus sp., Gravicalymene cf. maloungkaensis, Phacops sp.; Brachiopods: Orientospirifer cf. wangi, Delthyris sp., Howellella sp., Biconostrophia sp., Cymostrophia sp., Chonetes sp.; Corals: Favosites sp., Tryplasma sp.; Bivalves: Pterochachia sp., Deceptrix sp., Modiomorpha ? sp. The Dacryoconarids have been reported as Nowakia elegans and N. cancellata.

Age Span: 

    Beginning stage: 
Emsian

    Fraction up in beginning stage: 
0.2

    Beginning date (Ma): 
407.27

    Ending stage: 
Eifelian

    Fraction up in the ending stage: 
0.35

    Ending date (Ma):  
391.15

Depositional setting

The dacryoconarids are indicative of deep water basin and the occurrence of large number of benthic fossils suggest a relative shallow shelf margin environment.


Depositional pattern:  


Additional Information


Compiler:  

Hongfei Hou