Reduction in Marine Primary Productivity in the Early Cambrian Nanhua Basin, South China

Chengsheng Jin; Zihu Zhang; Meng Cheng; Guochang Wang; Huajin Chang; Zhengqi Cao; Tao Zhang

doi:10.1021/acsomega.3c09161

Reduction in Marine Primary Productivity in the Early Cambrian Nanhua Basin, South China

ACS Omega. 2024 Apr 25;9(18):19892-19903. doi: 10.1021/acsomega.3c09161. eCollection 2024 May 7.

Authors

Chengsheng Jin¹, Zihu Zhang², Meng Cheng², Guochang Wang³, Huajin Chang¹, Zhengqi Cao¹, Tao Zhang¹

Affiliations

¹ College of Resource Environment and Tourism, Hubei University of Arts and Science, Xiangyang 441053, China.
² State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation & Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059, China.
³ Yunnan Key Laboratory for Palaeobiology, Institute of Palaeontology, Yunnan University, Kunming, Yunnan 650091, China.

Abstract

The Cambrian explosion is represented by a rapid diversification of early animals in which the role of marine primary productivity remains obscure. In this study, we analyzed multiple geochemical data, including TOC, major, and trace elements, in the basinal Yuanjia section, South China. Covariations among TOC, P/Al, Cu_EF, and Ni_EF suggest that they could be taken as effective marine productivity proxies in the early Cambrian Nanhua Basin. The similarities of Cd_EF and Cd/Mo in the Nanhua Basin and modern upwelling settings suggest that they might be effective to track upwelling, where Cd and Mo were mainly controlled by plankton biomass and redox conditions, respectively. Our results indicate that Co_EF and Co × Mn were invalid in evaluating upwelling because of the significant effects of water-column redox conditions on Co enrichments in the Nanhua Basin. The decreased TOC, P/Al, Cu_EF, and Ni_EF reflect a long-term decline in marine productivity from late age 2 to age 3. In comparison with the published results in the outer shelf (Jinsha, TZS drill core, YJK drill core, and GDM-1 well) and slope areas (TX-1 well), the fall in marine productivity might be common in the early Cambrian Nanhua Basin. Our results exhibit that the reduced marine productivity was accompanied by weakened upwelling, quiet hydrothermal activities, and enhanced local terrestrial fluxes, indicating that variations in marine productivity might be mainly driven by the development of upwelling in the early Cambrian Nanhua Basin. Comparison of marine productivity with fossil records suggests that food availability was sufficient to sustain the Cambrian explosion in the Nanhua Basin. We infer that marine productivity might indirectly stimulate early animal evolution through its significant impact on water-column oxygen levels in the early Cambrian Nanhua Basin.