Ningqiang Fm

It was named by Yu Changming et al in the middle—late sixties of the 20th century (Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, 1974). The type section is at Dazhuba, about 30 km southwest of the Ningqiang County seat in southern Shaanxi Province.

Synonym: (宁强组) . Grabau (1924) named the Silurian strata exposed in Ningqiang of Guangyuan City the “Chaotien” Fm, the “Huangpayi” Fm and the “Chienshui” Limestone. The “Chaotien” Fm was named near Chaotianzhen Township, probably indicating the Silurian strata exposed from north of Chaotianzhen Township to Qinfengxia with the main stratohorizons just of the Ningqiang Fm. The “Huangpayi” Fm was named at Huangbayi of Ningqiang and probably comprised the Wangjiawuan Fm and the Ningqiang Fm exposed at north and south of Huangbayi. The “Chienshui” Limestone probably represented the Silurian from Xuanhe to Zhongzipu of Guangyuan City in north Sichuan Province and should also belong to the Ningqiang Fm (Chen Xu et al, 1991). The above-mentioned stratigraphic names, which have long been unused and, hence, already forgotten, should be better abolished.

The formation, 148 m in total thickness, consists of purplish red, bluish gray argillaceous limestone, bluish gray shale intercalated with thin-bedded knotty limestone, bioclastic limestone and hermatobiolithic limestone.

The Yangpowuan member, about 1200 m in thickness, is dominated by green gray, yellow gray shale, silty shale, pelite intercalated with thin-bedded knotty limestone, organic limestone or limestone lenses. It yields graptolites Monograptus spiralis excentricus; brachiopod Nalivkinia cf. magna, Salopinella minuta, Spinochonetes notata, Mesopholidostrophia minor, Atrypoidea lentiformis, Atrypopsis rongxiensis; trilobite Kosovopeltis, Coronaspis, Encrinuroides, Kailia, Astroproetus; bivalves Nuculites, Deceptrix, Palaeoneilo; anthozoa Favosites, Donacophyllum, Tabularia; cephalopod Eridites, Sichuanoceras, Kionoceras, etc.；conodonts Ambalodus galerus, Pterospathodus celloni, P. pennatus, Apsidognathus tuberculatus and chitinozoa Angochitina longicollis, Ancyrochitina brevicollis, Conochitina sp., etc. According to the above-listed fauna, the Yangpowuan member is middle Telychian of Llandovery epoch in age and equivalent to the upper part of the griestoniensis zone.

The lower part of the Shengxuanyi member corresponds to the Ningqiang Fm proposed by Yu Changming, Chen Xu et al. The member is most well developed on the slope from Zhongzi to Fujiawuan, Guangyuan in northern Sichuan Province. It is characterized by yellow green plus purplish red shale, pelite intercalated with several suites of dark gray limestone；purplish red hermatobiolithic limestone often occurs at its base. The member is disconformably overlain by the Devonian(?) sandstone. It bears fossils dominated by shelly fossils including: brachiopods Salopinella minuta, Atrypoidea lentiformis, Atrypopsis rongxiensis, Gotatrypa lauta, Quangyuania ovalis, Pentlandina sinensis, Epitomyonia sp., Striispirifer hsiehi, Nikiforovaena flabillum, Howellella sp., etc.；trilobites Coronaspis, Coronocephalus, Encrinuroides, Kailia, Rongxiella, Astroproetus, etc.; ostracod Eurychitina, Bairdiocypris; cephalopods Sichuanoceras, Protobactrites, Actinodochmioceras, Protokionoceras, Parahelenites, etc.; bivalves Deceptrix, Modiomorpha, Leptodesma; gastropod; bryozoa; chitinozoa Angochitina longicollis; conodonts Ambalodus galerus, Ozarkodina adiutricis, Pterospathodus celloni, Apsidognathus tuberculatus, etc.; graptolites Stomatograptus grandis, S. sinensis, etc.