Longdonghe Fm
Type Locality and Naming
The type section is lies by the banks of the Longdong River-Xiaomo River, Bi’an, Jinggu County, Yunnan. It was named by Yunnan Party of Regional Geological Survey in 1981, and formally cited in Regional Geology of Yunnan Province in 1990.
Lithology and Thickness
Volcaniclastics and Limestone. Formed by organic limestone and volcanic tuff. The formation can be divided into two members. Lower Member, the lower part is dominated by conglomerate, sandstone and sandy-conglomerate, in which the conglomerate is composed of intermediate-acid volcanic rock and limestone; the upper part consists of limestone, 130 m thick. Upper Member is dominated by intermediate-acid volcanic breccia, ignimbrite (tuff), altered fine-grained tuff and clayey siltstone intercalated with minor radiolarian siliceous rock, 837 m thick. There is some lithologic change in the upper member, with intermediate-basic lava occurring in the lower part, and the middle and upper parts are dominated by quartz-rich albite porphyry volcanics, intercalated with multi-layered radiolarian siliceous rocks.
Relationships and Distribution
Lower contact
Unconformably over the Manxi Fm
Upper contact
Unconformably overlapped by the Xiapotou Fm
Regional extent
Distribution of the formation is relatively narrow, being around the area of Da’aozi of Simao County.
GeoJSON
Fossils
The limestone in the Lower Member yields Fusulinids Triticites, Quasifusulina and Schwagerina as well as Bryozoan Fenestella sp
Age
Depositional setting
It is interpreted as island-arc volcanic siliceous deposits
Additional Information