Home Multi-Country Search About Admin Login
Cenozoic
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Neoproterozoic
Mesoproterozoic

Search by
Select Region(s) to search
Hold Ctrl (Windows/Linux) or Command (Mac) to select multiple
Sandaogou Formation

Sandaogou Fm


Period: 
Ordovician

Age Interval: 
Darriwilian, (29, 30)


Province: 
Gansu, Ningxia

Type Locality and Naming

The type section is at Sandaogou in Xiamen Township, Pingliang County, Gansu. The Sandaogou Fm was named by Gansu Party of Regional Geological Survey in 1972, and was published by Gansu Compiling Group for Regional Stratigraphic Scale (1980).

Synonym: (三道沟组)


Lithology and Thickness

The formation has a Lower part composed of nodular limestone intercalated with yellowish green calcareous shale, and an Upper part of interbedded thick-bedded limestone, leopard or nodular limestone; of the normal pericontinental sea setting. In the type area, the Sandaogou Fm is about 150 m thick.


Lithology Pattern: 
Clayey limestone


Relationships and Distribution

Lower contact

It rests conformably on the thick-bedded limestone of the Shuiquanling Fm.

Upper contact

The Sandaogou Fm, with a persistent lithology, is disconformably or unconformably overlain by Pingliang Fm or Jinghe Fm. In most of the areas above mentioned, the Sandaogou Fm rests conformably on the underlying strata, but at Baijiatan, Zhenzhuwa to Yagou in Wenshui Township, Longxian, it overlaps on the Upper Cambrian (An et al., 1990).

Regional extent

The Sandaogou Fm, with a persistent lithology, is seen in Huanxian (45.1-200 m thick), Pingliang (150 m thick) of Gansu, Longxian (225-715 m thick) of Shaanxi, in westernmost Ordos. At Xiamaguan in Qinglong Hill, Ningxia, the Sandaogou Fm is dominated by thin-bedded limestone, with shale intercalations in the upper part.


GeoJSON

null

Fossils

The lower part yields trilobite, cephalopod and conodont of Pygodus serrus assemblage; the top yields conodonts of Amorphognathus kielcensis subassemblage of the Pygodus anserinus assemblage. The Sandaogou Fm is equivalent to the lower part of the Didymograptus murchisoni zone. At Xiamaguan in Qinglong Hill, Ningxia, the Sandaogou Fm in the upper part, yields graptolites Pterograptus elegans and Husterograptus teretiusculus. The shale intercalations together with the overlying 44 m thick Pingliang Fm yielding graptolite Husterograptus teretiusculus and consisting of shale and siltstone was previously defined as the Xiamaguan Fm by Huo et al. (1987). At etanggou and Qinjialaozi in Qinglong Hill, its base yields conodont Eoplacognathus suecicus, indicating a base lower than that in the type area.


Age 

Darriwilian. The Sandaogou Fm had previously been thought to be Llanvirn in age, and to be between Early Ordovician Shuiquanling Fm and the Permian. In 1990, An Taixiang et al. studied the graptolite, and defined it to be Late Llanvirn to Early Llandeilo in age.

Age Span: 

    Beginning stage: 
Dapingian

    Fraction up in beginning stage: 
0.6

    Beginning date (Ma): 
470.16

    Ending stage: 
Darriwilian

    Fraction up in the ending stage: 
0.65

    Ending date (Ma):  
462.11

Depositional setting

Normal pericontinental sea setting


Depositional pattern:  


Additional Information


Compiler:  

Jianpo Wang and Xiaofeng Wang