Yahua Fm

The type section is at Damao in Yaxian, Hainan Island. The Yahua Fm is derived from the Yahua Gr proposed based on the drilling data by Guangdong Bureau of Geology and Mineral Resources in 1964. In 1980, He Yangzhi et al. merged the graptolite-bearing black shale in the upper part of the Yahua Fm and the overlying Shatang Fm, and named them the Luoya Shale. Ni Shizhao et al. (1992) reported the section of the Yahua Fm at Luobidong in Sanya. Zeng et al. (1992) further studied the Yahua Fm.

Synonym: (牙花组）

The Yahua Fm is divided into three lithological members. Lower member, 116 m thick, is composed of grayish yellow quartz sandstone intercalated with shale. Middle member, 122-172 m thick, is represented by dark gray, gray thick-bedded limestone, dolomitic limestone intercalated with siltstone and fine-grained sandstone. Upper member, 42 m thick, i.e. He's Luoya Shale, is composed of black calcareous, carbonaceous shale intercalated with crystalline limestone.

The middle member yields conodonts Scolopodus euspinus, S. cf. rex, Drepanoistodus flexilis, Drepanodus cf. planus in the lower part and Glyptoconus cf. cornuformis, Protopenderodus sp. in the upper part, and the upper member yields graptolites Cryptograptus tricornus, Glyptograptus intersitus, Tylograptus globiformis.