Wudangshan Gr

Hubei northwest. The Wudangshan Gr was named by Li He and Zhu Sen (Chu, S) in 1930. The naming locality is the Wudang Mts. area, northwestern Hubei. The reference section is a composite type, merging the Huanglongdong section (for the lower unit) along Baihe River, Shaanxi Province, and the section along Xiejia River (for the upper unit), Fangxian County, Hubei Province.

Synonym: （武当山群）

It is composed of medium- to low-grade metamorphosed rocks that includes sericite quartz schist, albite schist, actinolite schist, chlorite quartz schist, leptite, quartzite, metamorphosed feldspar quartz sandstone, meta-siltstone, crystalline limestone, marble, carbonaceous schist, and apatite rock. It is subdivided into two informal formation-level units: a Lower volcanic unit and an Upper metasedimentary unit. Lower unit of metamorphosed volcanic rocks, which temporally are assigned as the lower unit, have their typical exposure around Baihe River, Shaanxi. Its lower part is composed of crystal-clast-bearing meta-tuff and albite leucoleptite, mostly altered into medium- low-grade metamorphosed schist, accompanied by minor tuffaceous sandstone and siltstone bands. The middle part is a metamorphosed tuffite sandwiched with tuffaceous sandstone, siltstone and claystone. The upper part is metamorphosed volcanic lava with abundant meta-tuff, tuffaceous sandstone, meta-siltstone, claystone and C-P-Ca-bearing claystone. chert and unstable marble bands or lenses. A meta-tuffaceous conglomerate or pebbly volcanic tuff (commonly called Jiepaiya conglomerate) often occurs at the top. Upper unit of metasediments is mainly composed of interbedded thick-bedded massive metamorphosed feldspar-quartz sandstone, siltstone and muddy sandstone, sandwiched with carbonaceous P-bearing banded claystone and siltstone. The contact surface between the volcanic and the metasedimentary units proceeds along a ductile-shear surface (detachment); and it is difficult to see a clear unconformable contact boundary. The Wudangshan Group has quite different thickness in different places. The maximum exposed thickness is up to 8600 m in the Wudongshan region.

The metasedimentary formation of the group has rich microplants: Leiominuscula, Margominuscula, Quadratimopha, Lopominuscula. Trematosphaerid Lignum, Macroptycha, Nucellosphaeridium, Archaeodiscina, Synsphaeridium, Taeniatum, Protonucellosphaera, Asperatophosphera etc.

Besides the Wudang Mountain area, the same stratigraphic sequence at Dahong Mt., Suixian County, Yunxi County were repeatedly investigated, and the opinions on the sequence and names of the group in that location are quite different. As a result, there are different names for the same group (for which the stratigraphic positions are roughly equivalent to each other), such as Yunxi Gr, Suixian Gr, Yunyang Gr, Hongan Gr, Yingshan Gr, Lianyun Gr, Dagushi Gr, Jingshan Gr and Dalangshan Gr. However, as to its isotopic chronological age, the metamorphosed volcanic formation is dated at 1935±71 Ma and 1967±3 Ma respectively, and the metasedimentary rock is dated at 1090-1252 Ma, according to Tianjin Institute of Geology and Mineral Resources and Northwest Hubei Geological Party of Hubei Bureau. So, it is reasonably to attribute it to Paleoproterozoic and Mesoproterozoic eras.