Gaicha Fm
Type Locality and Naming
It was named by the District Survey Team of Guizhou Geological Bureau in 1976. The named section is located in Gaicha village, about 1 km south of Guiyang Sanqiao. The original "Longtou Formation" represents the deposits dominated by reef (shoal) facies during the middle Ladinian period in Guizhou. In 1987, the Guizhou Bureau of Geology and Mineral Resources revised the meaning of the Longtou Formation to only represent the lower layer of the original "Longtou Formation", and the upper part was called the Gaicha Formation. This lexicon follows it.
Synonym:
Lithology and Thickness
Mainly carbonate rocks. Lower part is gray-green and purple-red shale interbedded with dolomite. Middle part is gray and flesh-red chert interbedded with dolomite, often producing brachiopods. Upper part is gray chert, oolitic chert, dolomitic chert and meso-crustal chert, often with a large number of bivalves "Ostrea" sp.
Relationships and Distribution
Lower contact
The bottom part is a consolidated contact with the underlying Longtou Fm
Upper contact
The top part is a false integration contact with the yellow-green sandstone at the bottom of the overlying Sanqiao Fm
Regional extent
The thickness is 50 to 95 m. To the west of Qingzhen, the bottom shale gradually disappears and is composed of muddy dolomite and tuff; to the north of the line of urnan and Xiuwen, the upper purple layer of the Badong Gr transitions.
GeoJSON
Fossils
Brachiopods and bivalves "Ostrea" sp.
Age
Depositional setting
This group is a carbonate reef (beach) sediment, distributed in the area of Qianzhong, with stable stratification.
Additional Information
In 1976, the district survey team of Guizhou Geological Bureau named the Middle Triassic dolomite dominated strata near Guiyang as Guiyang Fm, which was dated to the Latin period and divided into Lionshan Foot member, Ganyintang member and Changcha member from the bottom up. In 1987, Guizhou Geological and Mining Bureau elevated the Changcha member to a group in view of the significant lithological differences between the section and the underlying strata.