Chemostratigraphic correlations across the first major trilobite extinction and faunal turnovers between Laurentia and South China

Jih-Pai Lin,Ganqing Jiang,Thomas Wotte,Frederick A Sundberg,Isabel P Montañez

doi:10.1038/s41598-019-53685-2

Abstract

During Cambrian Stage 4 (~514 Ma) the oceans were widely populated with endemic trilobites and three major faunas can be distinguished: olenellids, redlichiids, and paradoxidids. The lower–middle Cambrian boundary in Laurentia was based on the first major trilobite extinction event that is known as the Olenellid Biomere boundary. However, international correlation across this boundary (the Cambrian Series 2–Series 3 boundary) has been a challenge since the formal proposal of a four-series subdivision of the Cambrian System in 2005. Recently, the base of the international Cambrian Series 3 and of Stage 5 has been named as the base of the Miaolingian Series and Wuliuan Stage. This study provides detailed chemostratigraphy coupled with biostratigraphy and sequence stratigraphy across this critical boundary interval based on eight sections in North America and South China. Our results show robust isotopic evidence associated with major faunal turnovers across the Cambrian Series 2–Series 3 boundary in both Laurentia and South China. While the olenellid extinction event in Laurentia and the gradual extinction of redlichiids in South China are linked by an abrupt negative carbonate carbon excursion, the first appearance datum of Oryctocephalus indicus is currently the best horizon to achieve correlation between the two regions.

Highlights

The international correlation of the traditional lower–middle Cambrian boundary has been exceedingly difficult primarily due to apparent diachroniety of the datum species used to define the boundary reflecting the endemic faunas
This study provides detailed chemostratigraphy coupled with biostratigraphy and sequence stratigraphy across this critical boundary interval based on eight sections in North America and South China
This boundary has been marked by the first appearance datum (FAD) of Paradoxides in western Gondwana, Baltica, and Siberia[1,2,3,4,5], the last appearance datum (LAD) of Redlichia in South China[6,7], and the LAD of Olenellus in Laurentia[8,9]

Summary

Introduction

The international correlation of the traditional lower–middle Cambrian boundary has been exceedingly difficult primarily due to apparent diachroniety of the datum species used to define the boundary reflecting the endemic faunas This boundary has been marked by the first appearance datum (FAD) of Paradoxides (and other paradoxidid trilobites) in western Gondwana, Baltica, and Siberia[1,2,3,4,5], the last appearance datum (LAD) of Redlichia (and other redlichiid trilobites) in South China[6,7], and the LAD of Olenellus (and other olenellid trilobites) in Laurentia[8,9]. Our study represents the most comprehensive chemostratigraphy and biostratigraphy across the Cambrian Series 2–Miaolingian boundary interval from Nevada and South China for testing the synchronicity of the olenellid extinction in Laurentia and redlichiid extinction in Gondwana. Sequences III and IV cannot be differentiated in the Split Mountain section

Objectives

Methods

Results

Conclusion