Proposed Stratotype for the Base of the Cambrian Stage 10 at the Lowest Occurrence of Eoconodontus Notchpeakensis (miller) at Wa'ergang, Hunan, China

The taxonomy and distribution of agnostoid trilobite Lotagnostus americanus, which was identified as the marker for the base of Cambrian Stage 10 by the former International Subcommission on Cambrian Stratigraphy (ISCS) about twenty years ago, are considered controversial by some researchers. Easily identified and geographically widespread Eoconodontus notchpeakensis is considered suitable as a primary boundary marker by the reconvened Stage 10 Working Group of ISCS. The lowest occurrence (LO) of E. notchpeakensis is close to a prominent negative excursion in δ13C values, i.e., the HERB/TOCE Event. Then the HERB/TOCE Event has been used as a complementary marker to define the base of Stage 10. Recently, the ISCS voted to accept the LO of E. notchpeakensis as the principal marker for the base of Cambrian Stage 10. The Wa'ergang Section has strong potential as a candidate for defining a GSSP marking the base of Cambrian Stage 10, which is defined by the LO of E. notchpeakensis. This section is exposed along a roadcut in the village of Wa'ergang, Taoyuan, Hunan. It spans the Huaqiao, Shenjiawan and the lower part of the Panjiazui formations, which consist of a thick succession dominated by carbonate rocks deposited in an inferred slope environment. The taxonomy and biostratigraphy of conodonts and trilobites at the Wa'ergang Section have been well studied, and conodont and trilobite zones, from Paibian to Lower Ordovician, have been established. Previous study reveals the LO of E. notchpeakensis, i.e., the base of E. notchpeakensis Zone, to be about 800.3m above the base of the Huaqiao Formation at the Wa'ergang Section. This horizon lies slightly below the top of the Micragnostus chiushuensis trilobite Zone of South China. The HERB/TOCE Event is located in the lowermost part of the E. notchpeakensis Zone and the lower part of the Leiagnostus cf. bexelli-Archaeuloma taoyuanense trilobite Zone at the Wa'ergang Section. The Wa’ergang Section has been extensively collected recently, the samples are being processed, and refined biostratigraphy of conodonts, trilobites and brachiopods will be present soon.