Yaomoshan Fm
Type Locality and Naming
The type section is near the mountain pass of Kulong Mountain southwest of Yumen City, Gansu. The reference section is at Shimenzi south of Yumen City (Zhao, 1979). At Luanshidui in Lenglongling, the strata of the Yaomoshan Fm were previously named the Luanshi Limestone (Qilian Party of Geology, Chinese Academy of Sciences, 1975). In Gulang of Gansu, the strata of the Yaomoshan Fm were previously named the Gulang Limestone (Li Shuxun, 1948) or Gulang Fm (Zhao Fengyou, 1978). The Yaomoshan System had previously been referred to as the Cambrian-Ordovician underlying the Silurian near the mountain pass of Kulong Mountain. In 1957, Yin Zanxun renamed it the Yaomoshan Series, and included it in the middle part of the Ordovician. In 1958, Qilianshan Party of Geology, Chinese Academy of Sciences, in turn renamed it the Yaomoshan Limestone. Mu Enzhi (1959) suggested that the graptolite fauna from the lower part of the Yaomoshan Limestone can be correlated with the Nemagraptus gracilis assemblage to Climacograptus peltifer assemblage, and renamed the Yaomoshan Limestone the Yaomoshan Fm in 1964.
Synonym: (妖魔山组）
Lithology and Thickness
The formation is composed of thin- to thick-bedded limestone of shallow-marine setting, with conglomerate and calcirudite at the base. In the type area, the Yaomoshan Fm is 572 m thick.
Relationships and Distribution
Lower contact
It rests disconformably on the Zhongpu Gr (1979, Zhao Fengyou). In Gulang of Gansu, the strata of the Yaomoshan Fm that were previously named the Gulang Limestone or Gulang Fm rests unconformably on the Chelungou Gr.
Upper contact
It is conformably overlain by the black shale at the base of the Nanshimenzi Fm
Regional extent
With a persistent lithology, the Yaomoshan Fm is widespread in Qilian Mountain, i.e. Yumen (572 m thick), Tuza Hill in Changma (461 m thick), Mulong and Suyouhe (799 m thick) on the northern slope of Qilian crest, Yushigou to Dalang (540 m thick) on the southern bank of Heihe River, Gulangxia (85 m thick) and Tiegui Hill (192 m thick) in Gulang County of Gansu and Koumenzi in Daliang (100 m thick) and Luanshidui in Lenglongling (600 m thick), Menyuan of Qinghai.
In Gulang of Gansu, the strata of the Yaomoshan Fm was previously named the Gulang Limestone (Li Shuxun, 1948) or Gulang Fm (Zhao Fengyou, 1978), and is composed dominantly of thick-bedded argillaceous limestone, limestone, dolomitic limestone, and with coarse quart sandstone in the lower part and sandy conglomerate at the base. In 1979, Zhao Fengyou discussed in detail the age of the Yaomoshan Fm, and suggested that the Yaomoshan Fm is equivalent to the Gulang Fm.
GeoJSON
Fossils
Coral Amsassiae chaetetoides zone has been established in the Yaomoshan Fm. In Gulang of Gansu, the strata of the Yaomoshan Fm that was previously named the Gulang Limestone or Gulang Fm yields coral Amsassia cf. chaetetoidea, cephalopods and brachiopods.
Age
Depositional setting
Shallow-marine setting
Additional Information