Yimin Fm
Type Locality and Naming
Hailar Basin. The Yimin Formation was erected by the Section of Geology under the Headquarters of Yimin Coalfields in 1973. The type locality for the designation is in Yimin of the Hailar City of Inner Mongolia. The reference section represents the columnar section along the lines No.3 and No.17 of the Yimin Coalfields about 50 km south of the Hailar City of Inner Mongolia (119°42′E; 48°32′50″N).
Lithology and Thickness
The Yimin Formation is represented by gray white siltstone, sandstone, mudstone, carbonaceous shale with conglomerate and sandy conglomerate, with more than 10 coal beds. The Yimin Formation is 550.9 m thick.
Relationships and Distribution
Lower contact
Its base marked by gray white siltstone is distinguished from grit and gravel-bearing sandstone of the underlying Damoguaihe Fm and shows a disconformable contact with the latter.
Upper contact
Its top is overlain unconformably by the Qingyuangang Fm.
Regional extent
The present formation is distributed in Yimin, Jalainor, the Buir lake, Dayan of Xuguit Qi, Wujiu-Yakeshi, the Miaodu river, Labudalin of Inner Mongolia, and Xigangzi and Sandaogou of the Aihui County of Heilongjiang. It becomes thinner from west to east and is 500 m thick in the Buir lake and Yimin areas, more than 200 m thick in the Xiguit Qi and Miandu river areas; and 247 m thick in Xigangzi and Sandaogou of the Aihui County.
GeoJSON
Fossils
The formation bears floras Coniopteris burejensis, Rufforbidia goepperti, Ginkgo digita; in Jalainor, estheria Estheria sp.; and in Yimin, Chenqi and Jalainor, sporopollen grains represented by the Appendicisporites- Impardecispora- Triporoletes assemblage.
"It yields plant mega- and microfossils, the brackish-water Nyktericysta (Hailaera) hailaerensis dinocyst assemblage, conchostracans, ostracods, and bivalves including Margaritifera tugrigensis. Nyktericysta (Hailaera) hailaerensis is endemic to the Hailaer Basin. Neverthless, Nyktericysta is generally regarded as a Lower Cretaceous indicator, as noted above, and the Albian Pseudoceratium interiorense, present in the underlying Damoguaihe Fm, also occurs in the assemblage. This suggests that the Yimin Formation is Lower Cretaceous, most probably Albian and can be correlated with the Quantou Fm because the dinocysts in these two formations are dominated by Nyktericysta. The upper part of the formation is characterized by the Neozamites - Ginkgo flora assemblage also identified in the upper part of the Fuxin Fm, Wulin Fm, Jilin Fm. The assemblage is correlated with Pseudocycas pecten - Sphenolepis kurriana floristic assemblage identified in the Muling Fm and Dongshan Fm. Therefore, the Yimin Formation is not younger than lower-middle Albian, because the middleeupper Albian interval in northeastern China is characterized by the Pseudofrenelopsis - angiosperms flora assemblage with significant role of angiosperms." [modified quote from Kosenko et al., 2021]
Age
Depositional setting
It belongs to lake bog facies deposition; and fluvial-delta.
Additional Information
Enhanced with Igor N. Kosenko, Jingeng Sha and Boris N. Shurygin (2021). Upper Mesozoic stratigraphy of Sikhote-Alin (Russian Far East) and northeastern China: Non-marine and marine correlations. Part 1: Upper Jurassic-Hauterivian AND 2. Barremian-Aptian. Cretaceous Research, 124: articles 104811 (https://doi.org/10.1016/j.cretres.2021.104811) AND 104812 (https://doi.org/10.1016/j.cretres.2021.104812)