Paishuichi Fm

The type section of the Paishuichi Formation, measured from Pingkou to Yanxi (old site) along Zijiang River by Wang and Bian (1949), no longer exits as it was submerged by a reservoir after a dam was built downstream on the Zijiang River. A new section, the Nanshichong section measured by Jin Yuqing in 1964, was proposed as representative section of the formation by Zhang (1997). The section is located at Nanshichong Village in Songmutang Township, Taojiang County, Yiyang City, central Hunan Province, 28 km southwest the seat of Taojiang County (112°06’E, 28°11’N). The formation was named by Wang and Bian (1949). The name is derived from Paishuichi (spelled Baishuixi in Hanyu Pinyin), a tributary of the Zijiang River in Baishui Village, Gulou County, Anhua County, Yiyang City, central Hunan Province. Originally it was called Paishuichi Banded Slate (Baishuixi Banded Slate) by Wang and Bian (1949), which was renamed Paishuichi Formation in a 1964 manuscript by Jin Yuqin from the South-Center Institute of Geology and was published by Hunan Bureau of Geology and Mineral Resources (1988). This formation spans the Cambrian-Ordovician boundary.

Synonym: （白水溪组）; Baishuixi Fm

The Paishuichi Formation consists of blue, dark gray laminated mudstone, calcareous slaty shale intercalated with lenticular and thin-bedded limestone (locally silty).. The auxiliary section is divided into 5 lithological beds, from bottom up: 1, grey and dark grey, thin-bedded muddy shale bearing limestone lenses (23.5 m thick); 2, grey and dark grey calcareous shale with lower part bearing limestone lenses (27.0 m); 3, grey, silty shale (1.4 m); 4, grey and dark grey shale bearing barite (14.5 m); 5, grey and bluish grey platy shale, with alternations of greyish white and grayish black bands (64.6 m). In the type section, the formation is 131 m thick. In the type area, the Baishuixi Fm is 120-240 m thick.

In auxiliary section, the lowest bed, the Bed 1, of the Paishuichi Formation yields trilobites Charchaqia norini, Hedinaspis sp., and Lotagnostus hedini; the Bed 2 yields brachiopod Obolus sp., and the Bed 3 yields crustacean Caryocaris sp. In other sections, the formation yields additional trilobites Charchagia sp., Geragnostus sp., Hedinaspis cf. shengi，Lotagnostus americanus, Triarthus sp., T. tetragonalis, and Westergaardites sp.; graptolites Dictyonema flabelliforme sociale，D. flabeliforme regulare，D. tuojiangense and Staurograptus diffissus; bivalve Modiolopsis sp. and small inarticulate brachiopods.