Xunjiansi Fm
Type Locality and Naming
Northeast Shaanxi. The Xunjiansi Fm was named by the Qinling Party of Regional Geological Survey, Ministry of Geology in 1959. The naming locality is the Xunjiansi Village, Luonan County, Shaanxi Province. It is the middle formation (3 of 5) of the Guandaokou Gr.
Synonym: （巡检司组）
Lithology and Thickness
The formation is characterized by special development of chert bands. It is a monotonous greyish medium- to thick-bedded, chert-banded (lumps) dolomite. Only in the base lies a relatively stable variegated silty slate, pebbly shale and sand conglomerate. The formation is about 500 m thick.
Relationships and Distribution
Lower contact
The special development of chert bands serves as a division mark from the underlying Longjiayuan Fm. The contact between these two formations is conformable, but disconformable contact is seen locally.
Upper contact
It has a conformable contact with the overlyin gDuguan Fm.
Regional extent
The Xunjiansi Fm is distributed in Luonan County, Shaanxi Province, and in Lushi, Lingbao and Luanchuan counties, Henan Province. It is stable both in lithological character and lithological facies, but variable greatly in thickness; for example, it is about 760-898 m thick around Longxian County; 47 m in Bayuan, Lantian County, Shaanxi Province, 600-700 m in Maping-Shipo, Luonan County, 350-500 m in east of Shipo to Lingbao, Lushi, and 741 m in Jiudinggou, Luanchuan County, Henan Province.
GeoJSON
Fossils
It has some stromatolites and microplants (Leiofusa sp., Taeniatum cf. crassum).
Age
Depositional setting
Additional Information
The upper Baiyugou Fm distributed south of Shimen-Panhe-Machaoying zone was renamed as Xunjiansi Fm by the Party of Regional Geological Survey, Shaanxi Province. Bureau of Geology (1976).