9:00 AM - 9:15 AM
[BCG10-01] Revision of the earliest Cambrian SSF stratigraphy: Litho- and SSF stratigraphy of the Xiaolantian section in the Chengjiang area, Yunnan, South China
Keywords:Cambrian, SSF, Yunnan
SSFs were obtained from 20 horizons in the Zhongyicun Mb (except Unit 4) and 1 from the Dahai Mb from the study section. Three distinct SSF assemblages (Assemblage A to C) were recognized; Assemblage A from the lowermost part of Unit 1, with Acanthocassis orthacanthus, Protohertzina anabarica, and Protohertzina unguliformis. Assemblage B from the upper part of Unit 1 to Unit 5, with Ocururanus finial, Yunnanopleura biformis, Helcionella sp.. Assemblage C from Unit 5, mainly with Archaeospira sp., and Obtusoconus sp., Conopoconus sp.. Two genera Conotheca and Siphogonuchites commonly occur from Units 1 to 5 and also from Dahai Mb. The Hongjiachong section, next to the Xiaolantian section in the same area, have also these three assemblages (Assemblage A to C in the Xiaolantian section).
The present results show that Zhongyicun Mb can be subdivided into three SSF assemblage zones (A to C). This interval was previously divided into two. Assemblage A of this study mostly corresponds to the 1st assemblage by Steiner et al. (2007), whereas B and C to the 2nd assemblage. This study confirmed that the first appearance of Assemblage B was detected in much lower horizon than previous believed. This suggests that SSF diversification has started almost at the beginning of the Cambrian, much earlier than previous believed.