Yima Fm
Type Locality and Naming
It was named by the No. 104 Coalfield Party of Henan Province as the “Jima Series” in 1960. The naming section is located in the vicinity of the Yima Coal Mine, Xin’an County, Henan Province, with its reference section being situated in the Anyao-Yangshuzhuang area, Jiyuan County.
Synonym: （义马组）
Lithology and Thickness
Lower part is composed mainly of grey siltstones, intercalated with medium-, and fine-grained arkosic quartz-sandstones and thick coal beds. Upper part consists of grey-black claystones, intercalated with siltstones and thin coal beds, with its basal part being composed of sandy conglomerates, with a total thickness of the strata of about 125 m. In the Jiyuan area it is composed largely of grey-green and yellow-green sandy shales, locally of black shale and claystone, with a thickness of 204-248 m.
Relationships and Distribution
Lower contact
Its basal part is in a disconformable contact with the underlying upper Triassic Tanzhuang Fm
Upper contact
Disconformably overlain by the Ma'ao Fm, with no directly overlying strata having been found.
Regional extent
It is distributed essentially in the Anyao and Yangshuzhuang areas of Jiyuan County, as well as the Shengchi and Yima areas of Xin’an County, western Henan.
GeoJSON
Fossils
It yields plant fossils in a amount of 11 genera and 23 species, belonging to a middle-stage assemblage of the Coniopteris-Phoenicopsis flora, with the spore-pollen fossils being represented by the Cyathidites-Cycadopites assemblage, bivalve fossils as represented by Yananoconcha zaoyuanensis and Y. hengshanensis, as well as fish fossils as represented by Holostei indet and Phdidophoriformes indet.
Age
Depositional setting
The formation is interpreted as fluvial-lacustrine and swamp-facies deposits.
Additional Information