Shuangmiao Fm
Type Locality and Naming
Lu-Zong (Lujiang-Zhongyang) volcanic basin. The name of the Shuangmiao Formation was given by the No 317 Geological Team (1969) in Shuangmiao of the Lujiang County, Anhui. The type locality is in Shuangmiao of the Lujiang County, represented by the Wangjialing section in Zhuanqiao (31º02', 117º24').
Synonym: Shuangmiao Gr; [Longmenyuan Fm / Longmenyaun Gr, and the slightly younger Zhuanqiao Fm / Zhuangqiao Gr are also here below this Shuangmiao Gr, and seem to have been merged with it in the schematic regional Cretaceous column?]
Lithology and Thickness
The Shuangmiao Formation is dominated by grey, greyish purple, multiple colored tuff breccia, trachybasalt, breccia-bearing trachybasalt, and tuffaceous sandstone. A layer of mudstone occurs at the bottom, and base conglomerate locally exists. It is 612 to 1098 m thick.
Relationships and Distribution
Lower contact
Next older regional unit is the mid-Jurassic sandstone of the Luoling Fm.
Upper contact
It disconformably underlies the Fushan Fm.
Regional extent
Lu-Zong (Lujiang-Zhongyang) volcanic basin. The formation occurs in Lujiang, Congrong, Fanchang and Huaining areas. "The Lu-Zong (Lujiang-Zongyang) basin is one of the most important volcanic basins in the middle and lower reaches of the Yangtze River area, China. It comprises four shoshonitic volcanic units, which are, in an ascending order, the Longmenyuan, Zhuanqiao, Shuangmiao and Fushan Groups. The LA-ICP MS U-Pb zircon ages [as of 2008] of the four units are: 134.8±1.8 Ma for the Longmenyuan Gr, 134.1±1.6 Ma for the Zhuanqiao Gr, 130.5±0.8 Ma for the Shuangmiao Gr, and 127.1±1.2 Ma for the Fushan Gr. The results indicate that all volcanic rocks in the Lu-Zong basin were formed in the Early Cretaceous from about 135 Ma to 127 Ma, lasting 8–10 Myr. There were no Jurassic volcanic activities in all the volcanic basins including the Lu-Zong basin in the middle and lower reaches of the Yangtze River area." (Zhou, T., Fan, Y., Yuan, F. et al. Geochronology of the volcanic rocks in the Lu-Zong basin and its significance. Sci. China Ser. D-Earth Sci. 51, 1470–1482 (2008). https://doi.org/10.1007/s11430-008-0111-7)
GeoJSON
Fossils
The formation yields Plant fossils Cladophlebis cf. browniana, Ptilophyllum boreale, Branchyphyllum cf. obesum, Padozamites lanceolatus, Elatocladus sp., Brachyphyllum sp.; Spore and pollen Classopollis annulatus; gastropods Probaicalia gerassimovi, P. cf. vitimensis; Bivalves Nakamuranaia chingshanensis, N. subrotunda; ostracods Cypridea (Cypridea), Darwinula sarytirmensis; Conchostracans Orthestheria, Nemestheria.
Age
Depositional setting
Additional Information