Sandaogou Fm
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.
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
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
Depositional setting
Normal pericontinental sea setting
Additional Information