Chelungou Gr
Type Locality and Naming
The type section is at Xiaobeigou in Tianzhu County, Gansu. The Chelungou Gr was named by Gansu Team of Regional Geological Survey in 1965, and was published by Zhao Fengyou (1978).
Synonym: (车轮沟群）
Lithology and Thickness
The group is divided into two parts: A Lower part of intermediate acidic volcanic rocks, and an Upper part of clastic rocks. The Lower part is dominated by quartz porphyry, quartz oligophyre, quartz porphyry micritic limestone and tuff, often changing internally into chert. The Upper part is composed dominantly of sericite-quartz chlorite schist, sericite schist bearing tourmaline, two-mica quartz schist and thick-bedded limestone, dacitic tuff intercalated with feldspar-quartz sandstone, pebbly sandstone, hornblende-plagioclase gneiss, with rhyodacite porphyry at the top. In the type area, the Chelungou Gr recorded an incomplete thickness of 3851 m.
Relationships and Distribution
Lower contact
In the type area, the lower boundary of the Chelungou Fm is covered. Regionally, the next older unit is the Heicigou Fm of late-Middle Cambrian.
Upper contact
In the type area, the upper boundary of the Chelungou Fm is covered. At Daogou, it is disconformably overlain by the Tianzhu Fm.
Regional extent
At Gulangxia in Gulang County, the Chelungou Fm, 1332 m thick, is unconformably overlain by the Gulang Fm (present Yaomoshan Fm), and yields cephalopods Lophospira cf. trochiformis, L. cf. gerardi, Liospira sp. and brachiopod in the upper lithological formation. At Dajing, the Chelungou Fm recorded an incomplete thickness of 776 m, and is composed of fine-grained clastic rock, with limestone at the base, and yields brachiopods Parastrophia sp., Chaulistomella sp., Didymelasma sp. and cephalopod Mysterloceras. At Heishan in Jingtai, Alxa Zuoqi Inner Mongolia, it is characterized by 844 m thick sequence of metamorphosed quartz sandstone, chert, slate and siliceous limestone, and yields brachiopod Orthis sp.
GeoJSON
Fossils
From the lower chert-rich strata abundant graptolites such as Paraglossograptus cf. typicalis, Glossograptus cf. hincksii, Isograptus divergens, I. caduceus, I. nanus, Loganograptus gracilis, Didymograptus cf. hemicyclus, Tetragraptus pendens, Cryptograptus sp. Cardiograptus sp. and brachiopods Obolus sp., Orbiculoidea sp. have been found. The limestone in the lower part yields brachiopods Opikina sp., Cyphyomena sp., Plaesiomys sp., Contreta sp. and Sowerbyella sp.
Age
Depositional setting
Additional Information