Succession and global correlation of late Tremadoc graptolite zones from South China

Abstract

The Tremadocian is the first stage of the Ordovician System and is subdivided into two parts in general. The Upper Tremadocian, spanning a temporal interval of ca. 8 Ma, yields graptolite faunas crucial for biostratigraphic division and correlation in high resolution. Relatively complete successions of Upper Tremadoc graptolite zones have been proposed in Scandinavia, and North and South America. In South China, the coeval graptolite strata are widespread in deep water facies, but the successions of graptolite zones recognized so far are quite incomplete and thus very difficult to be correlated with those in other countries. In recent years, we have sampled bed by bed the Nanba section in the Yiyang area, Hunan Province and, below the Tetragraptus approximatus Zone, identified four Upper Tremadoc graptolite zones in descending order: the Hunnegraptus copiosus Zone, the Araneograptus murrayi Zone, the Aorograptus victoriae Zone and the Adelograptus tenellus Zone. To date, the Nanba section is the only section in China that presents a relatively complete and globally comparable succession of Upper Tremadoc graptolite zones. Therefore, this study not only confirms the existence of some Upper Tremadoc graptolite zones that were never found before in China, but also facilitates a highly resolved division and correlation for the Upper Tremadoc graptolite strata in China.