Dalongkou Fm
Type Locality and Naming
East-central Yunnan. The Dalongkou Fm was named by Huang Yi in 1940. The type section is at Sanyuangong-Dalongkou Villages, Yi-men County, Yunnan Province. The reference section is in Xiaojiazu-Zanlahei, Eshan County, Yunnan Province. It is the upper formation (6/7) of the Kunyang Gr.
Synonym: （大龙口组）
Lithology and Thickness
The formation is dominated by grey-black and dark-grey limestone intercalated with sericite slate, silty-sericite slate and muddy limestone, locally containing chert lumps in lower part. The upper part consists of greyish medium- to thick-bedded algal-clastic limestone, sandwiched with thick-bedded to massive algal limestone and stromatolite-reef limestone. The top is composed of yellow-thin-bedded marl. It is about 2183 m thick in Zanlahei, Eshan, 1695 m in area southwest of Shiping to Yuanjiang and 650 m at Dongchuan-Tangdan.
[Figure: The Dalongkou Fm of the Kunyang Gr in Yimen area, Yunnan Province]
Relationships and Distribution
Lower contact
It is in conformable contact with the underlying Fulianpeng Fm, but where the Fulianpeng Fm is absent, the formation overlaps directly the next older Heishantou Fm.
Upper contact
It has a conformable contact with Meidang Fm.
Regional extent
East-central Yunnan. It spreads mainly in Yimen, Es-ban, Shiping, Yuanjiang and Dongchuan-Tangdan, area.
GeoJSON
Fossils
The limestone yields stromatolite and oncolite. The slate yields microplants. The stromatolites occurring in upper part are mainly Baicalia baicalica, Conophyton cyclindricum, C. baculum, Jurusania alicia, Oshania yunnanense, Minjaria f.，The microplants yielded in upper part are mainly: Asperatop sophosphaera, Leiominuscula, Microconcentrica, Nucellosphaeridium etc.
Age
Depositional setting
Additional Information
The Alayi Fm, upper part of Hekou Fm and Yinachang Fm are equivalent to the Dalongkou Fm.