Hetang Fm

The type section of Hetang Formation, the Hetang village section, is located at the village (118°37’E, 28°51’ N). The section lies about 8 km southwest of the seat of Jiangshan City, and was measured by Lu et al. (1955). In the type section, the formation is 44.2 m thick. The Hetang Formation was named by Lu et al. (1955). The name is derived from Hetang Village in northeast of Dachen Township, Jiangshan City (county level), Quzhou Prefectural City, Zhejiang Province. Originally the unit was called Hetang Siliceous Shale and Bone Coal by Lu et al. (1955), and was renamed Hetang Formation by Lu et al. (1963).

Synonym: （荷塘组）

The Hetang Formation is mainly a siliceous sequence with carbonaceous siliceous rock, carbonaceous and siliceous mudstone and shale, bone coal and limestone lenses. In the type section, the formation is divided into 3 lithologic beds, from bottom up: 1, light grey, thin-bedded, brecciated collophanite (= phosphate), alternated with fine-grained limestone bearing phosphoric concretion (1.00 m); 2, black, carbonaceous chert, carbonaceous siliceous shale and bone coal with lenses of black, carbonaceous limestone (13.10 m); 3, black, thin-bedded carbonaceous chert, siliceous shale with lenses of black, carbonaceous limestone at the base (30.10 m).

Usually, the formation includes three lithologic members. Basal part is the phosphorite member, having one to three beds of stratified or stratoid phosphorite or phosphoric concretion-bearing chert in a tendency of changing lithotrity northwestward from phosphorite to concretionary phosphorite, or to concretion-bearing chert, or concretionary layer; Middle member refers to bone coal member, consisting of stratified or stratoid black carbonaceous shale interbedded with bone coal in a tendency of increasing layers (one to three layers) and thickness (2 to 40 m) of bone coal and optimizing coal’s quality northwestward; Upper member refers to the member of carbonaceous and siliceous shale, consisting black carbonaceous shale and siliceous shale with lenses of dolomitic limestone or thin-bedded argillaceous, dolomitic limestone in a tendency of increasing thickness (20 to 250 m) northwestward.

In the type section of Hetang Formation, the Bed 1 and Bed 2 yield small shelly fossils Anabarites trisulcatus, Archaeoides sp., Calcihexactina sp., Conotheca sp., Fengeuella zhejiangensis, Hertzina? sp., Hyolithellus sp., Kaiyangites jiangshanensis, Kijacus kijanicus, Liangshanella? sp., Lophochites sp., Protohertzina anbarica, and Siphogonuchites carinatus etc. However, these fossils were regarded to be reworked sclerites by Xue and Zhou (2006). The Bed 3 yields trilobites Hunanocephalus ovalis, Shabaella jiangshanensis and S. fengzuensis. In other localities, the formation yields additional trilobites Estaingia transversus, Hunanocephalus rarus, Hupeidiscus orientalis, Neocobboldia zhejiangensis, N. transversus, Shabaella convesa, Sinolenus hotangensis, and S. brevis.