Gahai Fm
Type Locality and Naming
The type section is located at Gahai to the northeast of Luqu County (Gansu Province). The reference section is situated at Yiwagou of Diebu County. It was named by Qin Feng et al. in 1976.
Lithology and Thickness
Limestone. It is lithologically divisible into two parts, with the Lower part consisting of grey and light-grey medium-bedded to massive bioclastic micritic limestones; and with the Upper part consisting of grey and dark-grey thick-bedded to massive bioclastic sparitic limestones. The formation does not contain oolite and chert, with the clay content increases upwards. Thickness is 261 m.
Relationships and Distribution
Lower contact
Conformable contact with the underlying oolitic limestone of the Minhe Fm (upper Carboniferous); or the Xiajialing Fm (locally).
Upper contact
Conformable contact with the overlying chert aggregate or bands of the Qixia Fm.
Regional extent
In the Gahai area of Luqu County the formation is composed of light-grey and grey-white massive clastic limestone, which is gradating into medium-, and thick-bedded clastic limestone up to the top part of the formation. In the Buqiala area of Balie County to the west of Langmu Temple the formation is composed of grey and light-grey medium-, and thick-bedded limestone, with a 35-40 m-thick layer of lime conglomerate at the base of the formation. The lithology of the Gahai Fm has been changed a bit in the Meijiachang area of Wenxia County; except for cryptocrystalline limestone, there occur also a lot of grey-white thick-bedded to massive dolomites, intercalated with carbonaceous slate as well. Coeval with the Dongzhakou Fm in this region.
GeoJSON
Fossils
Abundant Fusulinida and Foraminifera.
Age
Depositional setting
It is interpreted as a semi-restricted platform and open-platform facies.
Additional Information