Yangliugang Fm

The type section of Yangliugang Formation is located at west slope of Yangliugang Hill, Dachen, Jiangshan, Zhejiang Province (118°36’E, 28°50’ N). The section lies about 3.5 km northeast of Dachen Village, or about 12 km north of the seat of Jiangshan City, and was measured by Lu et al. (1955). In the type section, the formation is 61.70 m thick. The Yangliugang Formation was named by Lu et al. (1955). The name is derived from Yangliugang Hill in Dachen Township, Jiangshan City, Quzhou Prefectural City, Zhejiang Province. Originally the unit was called Yangliugang Limestone by Lu et al. (1955), and was renamed Yangliugang Formation by Lu et al. (1963).

Synonym: （杨柳岗组）

The Yangliugang Formation is a carbonate sequence, consisting mainly of striped dolomitic limestone, argillaceous limestone with limestone lenses, argillaceous limestone, and carbonaceous siliceous mudstone. In the type section, the formation is divided into 7 lithologic beds, from bottom up: 1, dark grey, thin- to medium-bedded carbonaceous dolomite, alternated with black carbonaceous shale and with a layer of carbonaceous mudstone of 0.4 m thick at base (3.00 m thick); 2, dark grey, thin-bedded fine-grained limestone, alternated thin-bedded micritic limestone (3.30 m); 3, dark grey medium-bedded fine-grained limestone, interbedded with argillaceous limestone and laminated argillaceous limestone (15.50 m); 4, dark grey, medium-bedded, podiform limestone, alternated with thin-bedded limestone (13.6 m); 5, dark grey, thin- to medium-bedded, laminated argillaceous limestone with limestone lenses, alternated with limestone (9.00 m); 6, dark grey, thin- to medium-bedded aphanlitic to micritic limestone, interbedded with bands of argillaceous limestone, and in part with limestone lenses (1.60); 7, dark grey, medium-bedded, laminated, dolomitic argillaceous limestone, in part with limestone lenses (15.70 m). In general, the formation increases carbonaceous, argillaceous, and siliceous content northwestward, whereas calcareous content correspondingly decreases.

The Yangliugang Formation is well fossiliferous with trilobites, especially with agnostoid trilobites. In the type section, each bed, except for Bed 2, yields trilobites, including Clavagnostus sp., Goniagnostus spiniger, Fuchouia oratolimba, Hypagnostus hunanensis, Linguagnostus sp. Lejopyge armata, Ptychagnostus aculeatus, P. atavus, P. sinicus and Yakutiana sp. In other localities, the formation yields additional trilobites, Baojingia dachenensis, Clavagnostus lanceolatus, C. rarus, C. sp., Diplagnostus floralis, D. planicauda, D. zhexiensis, D. sp., Fuchouia chiai, Hypagnostus brevifrons, H. correctus, Lejopyge laevigata, Linguagnostus spinosus, L. transversus, Ovalagnostus bispiniformis, O. changi, O. personatus, Paradamesella nobilis, Peronopsis sp., Phalagnostus carinatus, Pianaspis sinensis, Proceratopyge conifrons, Ptychagnostus gibbus, Tomagnostella jiangshanensis, T. sp., Yakutiana dubia, Y. triangularis, and Y. sp.