Lazigou Fm
Type Locality and Naming
The type section is located at Lubagou, 8 km northwest of Luoda in Têwo County, Gansu Province. It was named by Sun Guangyi in 1980, and Hou Hongfei, Wang Shitao et al quoted it formally in 1988.
Lithology and Thickness
Slate. It is dominated by gray phyllitic calcareous sericite slate and calcareous slate, intercalated with purplish-gray thin- to medium-bedded silty marl and dark-gray thin- to medium-bedded micrite. The thickness is more than 597.7 m.
Relationships and Distribution
Lower contact
At the bottom there is a fault contact with the Bailongjiang Group of the Silurian; although regionally the next older formation is the Shangpugonggou Fm
Upper contact
Conformably overlain by the Lubagou Fm.
Regional extent
GeoJSON
Fossils
There are abundant tentaculites and minor brachiopods in marls. Five range zones and two subzones of tentaculites can be successively distinguished in this formation: Nowakia (N.) zlichovensis zone; N. (N.) praecursor zone; Viriatellina pseudogeinitziana zone; N. (N.) cancellata zone; N. (Sulcatonowakia) sulcata cf. antiqua subzone and the N. (S.) sulcata sulcata subzone.
Age
Depositional setting
Additional Information
The former lower member of the overlying Lubagou Fm shares the same lithology with the Lazigou Fm, and is, therefore, now included as the upper part of this Lazigou Fm; the N. (S.) sulcata sulcata subzone in this portion therefore extends it into early Middle Devonian in age.