Luoyachushan Fm
Type Locality and Naming
The type section is at Luoyachushan in Subei County (95°45′E, 41°29′N), Gansu. The reference section is in Xiaohuli Hill and Fandi Hill in Erjin Qi, Inner Mongolia (Inner Mongolia Bureau of Geology and Mineral Resources, 1991).
The Formation was divided into two lithological formations whose type sections are on northwest and east of Shajing respectively. In 1991, Inner Mongolia Bureau of Geology and Mineral Resources considered the Xiaohulishan and Fandishan sections as the reference sections of the upper and middle-lower lithological formations. Coeval with the lower part of Huaniushan Gr.
Synonym: (罗雅楚山组）
Lithology and Thickness
The formation is divided into two lithological formations. Lower formation is dominated by medium-grained feldspar-quartz sandstone, fine-grained sandstone and siltstone intercalated with carbonaceous and sandy shale, phyllite, pebbly coarse-grained quart-feldspar sandstone. Upper formation is represented by carbonaceous chert, siliceous slate, silty slate and medium-grained quartzose sandstone intercalated with sandy limestone and calcareous sandstone lenses. In the type area, the Formation is 735 m thick.
Relationships and Distribution
Lower contact
The Formation rests unconformably on the Middle Proterozoic (westernmost Inner Mongolia; column Ordov 14); or overlies the Xishuangyingshan Fm of late Cambrian.
Upper contact
It is disconformably overlain by the pebbly sandstone and dacite intercalated with andesitic basalt at the base of the Xilinkebo Fm (Beishan; column Ordov 13), or by the Xianshuihu Fm (westernmost Inner Mongolia; column Ordov 14).
Regional extent
The upper lithological formation is mainly seen in Toudiaoquan (656 m thick) west of Shajing, westernmost Louchuya Hill (642 m thick) and Baiyun Hill (1634 m thick). The lower lithological formation is exposed in Caohulehade (1899 m thick) and Xichangjing on Yueya Hill (1320 m thick). The Xiaohulishan Fm on Xiaohuli Hill in Erjin Qi, Inner Mongolia is equivalent to the Shajing Gr (Gansu Bureau of Geology and Mineral Resources, 1980).
GeoJSON
Fossils
The middle-upper lithological formation yields the Llanvirn graptolites. The siliceous slate in its upper part of the lower formation yields graptolites Didymograptus, Phyllograptus and Trigonograptus. The upper formation yields graptolites Tetragraptus cf. quadribrachiatus, Amplexograptus, Climacograptus aff. forticaudatus and additional brachiopods Semielliptotheca, Plectambonites in Baiyun Hill.
Age
Depositional setting
Additional Information