Yinchupu Fm

No type section was assigned originally. An auxiliary section, the Meiziwang section, was proposed by Yu (1997) as representative section of the Yinchupu Formation. The section is located at Yinzhubu (new site), about 5.5 km northwest of the Fengshui Town, Tonglu County, Hangzhou, Zhejiang Province or about 31 kn northwest of the seat of Tonglu County (119°27’E, 29°56’ N), and was measured by Zhejiang Regional Geological Survey Team in 1993. In the auxiliary section, the formation is 234.90 m thick. The Yinchupu Formation was named by Noda (1915). The name is derived from Yinchupu (spelled Yinzhubu in Hanyu Pinyin), an ancient town by the River Fengshui, which belongs now to the Fengshui Township, Tonglu County, Hangzhou City, Zhejiang Province. The old Yinzhubu Town, then administrated by Fengshui County (now Fengshui Township), does not currently exist because it was submerged by a reservoir. Originally the unit was called Yin-chu-pu Limestone Series by Noda (1915) and was called Yinchufu Series by Zhu and Sun (1924), Yinchu Series by Li (1939), Yin-chu-pu Shale by Lu et al. (1955), Yinchufu Formation by Han (1983) and Yinzhubu Formation by Yu (1997). Liu Jichen and Zhao Yazeng (Y. T. Chao) (1927) had divided the Yinzhubu Series into three parts. Lu Yanhao et al. (1955) included the upper part in the Ningguo Shale (current Ningguo Fm), and named the middle part the Yinzhubu Shale and the lower part the Xiyangshan Shale (spelled Siyangshan Fm in this lexicon). It was renamed Yinchupu Formation by Lu (1963). This formation spans the Cambrian-Ordovician boundary.

Synonym: （印渚埠组）; Yinzhubu Formation

The Yinchupu Fm is a fine clastic sequence of yellowish green shale intercalated with thin-bedded nodular limestone, with common variegated shale at the top and black or dark gray shale at the base. The formation in the auxiliary section is divided into three lithologic beds, from bottom up: 1, bluish grey and yellowish green, medium- to thick-bedded calcareous mudstone (38.7 m thick); 2, yellowish green, medium- to thick-bedded calcareous mudstone with minor interbeds of calcareous nodule-bearing calcareous mudstone (121.6 m); 3, bluish grey and yellowish green, thick-bedded to massive calcareous mudstone bearing rich calcareous nodules (74.6 m).

In the auxiliary section only the Bed 3 yields trilobites Niobella sp. and Symphysurus sp. In other sections, the basal part of the formation, assigned as Hysterolenus Zone (Lu et al., 1984a, b), yields trilobites Acrocephalina sp., Diceratopyge mobergi, Guotangia guotangensis, Hysterolenus asiaticus, Koldinioidia longa, Leiagnostus spp., Micragnostus spp., Euloma (Mioeuloma) subquadratum, Niobella oblonga, Parabolinella ocellata, Plicatolina kindlei, P. xiyangshanensis, Promacropyge carinata, Pseudoperonopsis oblongus, P. orientalis, Rhadinopleura sp., Shumardia changshanensis, Triobagnostus? sp., and Troedssonia wimani; conodonts Cordylodus proavus, Proconodontus muelleri, P. tenuis. Except for Anisograptus? sp., no other graptolite has been found from this trilobite zone. Other Ordovician graptolites in West Zhejiang Province are from younger Staurograptus dichotomus and Dicelepyge sinensis zones (Lu et al., 1984; Lu and Lin, 1984).