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Dakui Formation

Dakui Fm

Period: 
Ordovician

Age Interval: 
Early Ordovician, (64)


Province: 
Hainan

Type Locality and Naming

The type section is the core taken from the hole near Village Dakui in the northern segment of prospecting line No. VI of Damao phosphate deposit in Sanya, Hainan. The Dakui Fm in derived from the Dakui Gr proposed by Guangdong Party of Regional Geological Survey in 1964. Ge Meiyu et al. (1983) renamed the Dakui Gr the Dakui Fm.

Synonym: (大葵组）


Lithology and Thickness

In the type area, the Dakui Fm is divided into two parts. Lower part is composed of light gray, bluish gray inequigranular quartz sandstone. Upper part is represented by gray to dark gray thick-bedded limestone.


Lithology Pattern: 
Sandy limestone


Relationships and Distribution

Lower contact

Disconformably overlies the Damao Fm of middle Cambrian

Upper contact

Conformably overlain by the Yahua Fm

Regional extent


GeoJSON

null

Fossils

It bears minor pebbles and clasts of brachiopod and micropaleoplants such as Leiominuscula sp., Archaeodiscina sp.in the lower part, and yields conodont Pariostodus parallelus, Serratognathus bilobatus, Scolopodus cf. rex, S. cf. rex huolianzhaiensis, Oepikodus cf. ommunis, cf. Scolopodus eburnus and Acontidus? linxiensis in the upper part.


Age 

Early Ordovician. Central-South Compiling Group for Regional Stratigraphic Scale (1974) published the Dakui Gr, and suggested a Late Cambrian age for it. Ni Shizhao et al. (1992) inferred a Late Cambrian to Arenig age for it, on the basis of the study of conodont from its upper part. Zeng et al. (1992) suggested a Late Tremadocian to Middle Arenig age. However, no conodont has been found from its middle and lower parts, and an approximately Tremadocian age is inferred for these two parts and a possible Late Cambrian age for the base.

Age Span: 

    Beginning stage: 
Tremadocian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
486.85

    Ending stage: 
Dapingian

    Fraction up in the ending stage: 
0.5

    Ending date (Ma):  
470.34

Depositional setting


Depositional pattern:  


Additional Information


Compiler:  

Jianpo Wang and Xiaofeng Wang