Luoyukou Fm
Type Locality and Naming
West Henan. The name Luoyukou Formation came from the Luoyukou Bed (near Luoyukou Village, Ruyang County) named by Han Yingshan et al. in 1952. The typical section is situated in Cuizhuang of Hongjian in Ruyang County and the reference section is in Jiunudong of Xiatang Town in Lushan County, Henan Province. Uppermost formation in Luoyu Gr.
Synonym: （洛峪口组）
Lithology and Thickness
The Luoyukou Fm is composed of purple red to greenish gray shale, dolomite and stromatolite-bearing dolomite. Lower part, dominated by organic shale and red purple shale, is quite similar to the Cuizhuang Fm in lithological characteristic, Upper part, dominated by red purple dolomite bearing abundant stromatolites and algae, is considered to be littoral to neritic facies, with a complete sedimentary rhythm composed of sandstone to shale then to dolomite. The thickness is up to 180 m in Ruyang.
Relationships and Distribution
Lower contact
The basal part composed of carbonaceous shale rests conformably on the underlying Sanjiaotang Fm.
Upper contact
The upper part composed of purple red and light gray thin-bedded pelitic dolomite is overlain disconformably by the Huanglianduo Fm (upper Neoproterozoic)
Regional extent
West Henan. It is mainly distributed south of the line from Xin'an County to Sanmenxia City with a variable thickness of 7 to 282 m; northward it is lacking. From north to south, the thickness of the Luoyukou Formation increases. It is relative stable laterally in lithological character, but changeable in thickness from 50 to 180 m; for example it is up to 180 m in Ruyang, but less than 58 m in Mianchi, 53 m in Yiyang, up to 166 m in Lushan, about 114 m in Wugang. In Mianchi area on the north, there is only about 7 m exposed, as greenish gray shale of the basal part; going southward, the upper dolomite part with microlitic and micritic textures appears, which is 169 m thick. In general it is thicker around Lushan and Ruyang, but is thinning both to the northwest and southeast direction, even absent in Yexian and Fangcheng owing to erosion.
GeoJSON
Fossils
The thick-bedded dolomite yields stromatolites Jacutophyton f., Luoyukouella luoyukouensis, algae: Multisiphonia hemicirculis, Parasolenopora liaoningensis. The shale contains mainly microplants Trachysphaeridium cultum, T. planum, T. aff. laminaritum, T. rude, Stictosphaeridium sp., Orygmatosphaeridium sp.
Age
Depositional setting
Additional Information
Upper part is considered to be littoral to neritic facies