Dawan Fm

The type section is at Village Dawan in Fenxiang 16 km northwest of Yichang City, Hubei. The Dawan Fm is derived from the Dawan Bed proposed by Zhang Wentang et al. in 1957.

In 1956, Zhang Wentang et al. suggested that the Chi's (1940) “Meitan Shale" in Fenxiang, Yichang, is not shale but actually nodular limestone intercalated with minor shale, and replaced it with the Dawan Bed. In 1957, Wang Yu and Mu Enzhi heightened the upper boundary of the Dawan Bed, and included the purple limestone in the middle part and the shale intercalated with nodular limestone in the upper part of the Chi's (1940) “Meitan Shale" in the Dawan Bed. In 1962, Zhang Wentang renamed the Dawan Bed the Dawan Fm.

Synonym: (大湾组）

Reference Section:

The reference section is at Huanghuachang 5 km northwest of Yichang City, Hubei (Zeng Qingluan et al., 1983). The reference section is 63 m thick.

In the type area, the Dawan Fm is divided into three members. Lower member is characterized by grayish green nodular limestone intercalated with shale, with a limestone bearing glauconite at the base. Middle member is represented by purple and local green nodular limestone. Upper member is dominated by grayish green shale intercalated with thin-bedded or nodular limestone.

The Dawan Fm yields abundant fossils. The lower member contains the graptolite of the Didymograptus deflexus assemblage and Azygograptus suecicus assemblage; the upper member contains the graptolites of the Glyptograptus? sinodentatus assemblage and Undulograptus austrodentatus assemblage; the middle member contains the cephalopods of the Protocycloceras deprati assemblage. In this formation, a complete conodont sequence has been established, and is divided into five zones as following, in ascending order, Oepikodus evae zone, Baltoniodus triangularis zone, Paroistodus originalis zone, Microzarkodina parva zone and Amorphognathus variabilis zone.