The base of Cambrian Series 3: the global significance of key oryctocephalid trilobite ranges in the Kaili Formation of South China

Abstract

The stratigraphic ranges of two oryctocephalid trilobites, Ovatoryctocara granulata Chernysheva, 1962, and Oryctocephalus indicus (Reed, 1910), provide important data for the establishment of the base of a newly proposed subdivision of the Cambrian System, namely Cambrian Series 3. Until now, first appearance data (FAD) of both of these taxa have been considered candidates for such a base, the former allowing reliable correlations within all Cambrian faunal realms, the latter mainly within the Redlichiid and Olenellid realms. However, a recent restudy of the Chinese variants of O. indicus has highlighted a significant link with a similar form, previously assigned as a variant of Oryctocephalus reticulatus (Lermontova, 1940) in the paradoxidid Siberian Kounamkites Zone. This indicates that the Kaili Formation of South China is currently the prime succession for defining the base of Cambrian Series 3, because the FAD of O. granulata and the FAD of O. indicus have been identified in well exposed and studied sections. If the former is the preferred choice, it would correspond closely to the traditional Lower-Middle Cambrian Boundary of Cambria (Wales), whereas the latter would virtually correspond to the Lower-Middle Cambrian Boundary as recognised in Laurentia and Eastern Gondwana-Australasia.