TY - JOUR

T1 - Cd isotopes trace periodic (bio)geochemical metal cycling at the verge of the Cambrian animal evolution

AU - Hohl, Simon V.

AU - Jiang, Shao Yong

AU - Wei, Hai Zhen

AU - Pi, Dao Hui

AU - Liu, Qian

AU - Viehmann, Sebastian

AU - Galer, Stephen J.G.

N1 - Funding information: This research was funded by two young international scientist grants given to S.V. Hohl by the National Science Foundation of China , funding Nos.: 41650110480 and 41750410690 . We want to thank D. Gregory and S. Schuth for helpful discussion on the 2017 South China field workshop as well as Z. Wei, Y. Lin and Y. Zhang for their general help in the field and lab. The collaboration with the research staff from the Max-Planck-Institut für Chemie Mainz, Germany and the Institute for Surficial Geochemistry, Nanjing University, P.R. China are highly appreciated for their help with Cd and C isotope analyses, respectively. Further we would like to thank the associate editors Claudine Stirling and executive editor Jeffrey G. Catalano for handling of this manuscript as well as S. G. John and two anonymous reviewers for their valuable input on an earlier version of this publication. This research was funded by two young international scientist grants given to S.V. Hohl by the National Science Foundation of China, funding Nos.: 41650110480 and 41750410690. We want to thank D. Gregory and S. Schuth for helpful discussion on the 2017 South China field workshop as well as Z. Wei, Y. Lin and Y. Zhang for their general help in the field and lab. The collaboration with the research staff from the Max-Planck-Institut f?r Chemie Mainz, Germany and the Institute for Surficial Geochemistry, Nanjing University, P.R. China are highly appreciated for their help with Cd and C isotope analyses, respectively. Further we would like to thank the associate editors Claudine Stirling and executive editor Jeffrey G. Catalano for handling of this manuscript as well as S. G. John and two anonymous reviewers for their valuable input on an earlier version of this publication. S-Y.J. and S.V.H. planned the research; D-H.P. and S.Y.J. collected samples in the field; Q.L. and H-Z.W. helped with analyses of trace elements, while S.V.H. carried out lab work and Cd isotope analyses. The data were interpreted by S.V.H, S-Y.J. S.V. and S.J.G. and S.V.H. wrote the manuscript with input from the other co-authors.

PY - 2019/10/15

Y1 - 2019/10/15

N2 - Cadmium (Cd) isotopes are an emerging proxy for biological controlled metal and nutrient cycling in the modern oceans, but its potential as a geochemical proxy in ancient environments is still uncertain yet. Sequential leaching experiments of organic matter (OM)-rich shales from the early Cambrian Niutitang Formation (Fm.) were performed in order to understand the cycling of bioessential metals short after the Cambrian animal evolution. Carbonate, OM, sulphide and silicate leachates of OM-rich shales show an overall Cd isotope variation of 6 ε112Cd/110Cd (ε112Cd) units, indicating preferential incorporation of light Cd isotopes in the order sulphide > OM > carbonate > silicate. Carbonate leachates not only show negative correlations of ε112Cd with bulk-rock total organic carbon (TOC) and δ13Corg but also show co-variations with redox-sensitive elements and bioessential metal concentrations, indicating a combined redox and primary productivity evolution of the early Cambrian Nanhua Basin on the Yangtze. Together with increased Cd/Zn ratios and decreasing total organic carbon (TOC) and redox-sensitive elements (RSE) concentrations in the upper Niutitang, this argues for an increase in essential metal availability for primary producers. Coinciding with the transition from a highly unstable ecosystem shortly after the Precambrian/Cambrian boundary to a more habitable environment increased nutrient uptake, oxygen availability and enhanced dissolved organic carbon (DOC) recycling match with the diversification of early metazoan fossil findings at the studied local. Our findings demonstrate that Cd isotopes in combination with trace metals can be used to infer changes in biogeochemical metal cycling in paleoenvironments and further allow establishing Cd isotope systematics as a reliable paleoproductivity proxy in the search for Earth's earliest phototrophic life.

AB - Cadmium (Cd) isotopes are an emerging proxy for biological controlled metal and nutrient cycling in the modern oceans, but its potential as a geochemical proxy in ancient environments is still uncertain yet. Sequential leaching experiments of organic matter (OM)-rich shales from the early Cambrian Niutitang Formation (Fm.) were performed in order to understand the cycling of bioessential metals short after the Cambrian animal evolution. Carbonate, OM, sulphide and silicate leachates of OM-rich shales show an overall Cd isotope variation of 6 ε112Cd/110Cd (ε112Cd) units, indicating preferential incorporation of light Cd isotopes in the order sulphide > OM > carbonate > silicate. Carbonate leachates not only show negative correlations of ε112Cd with bulk-rock total organic carbon (TOC) and δ13Corg but also show co-variations with redox-sensitive elements and bioessential metal concentrations, indicating a combined redox and primary productivity evolution of the early Cambrian Nanhua Basin on the Yangtze. Together with increased Cd/Zn ratios and decreasing total organic carbon (TOC) and redox-sensitive elements (RSE) concentrations in the upper Niutitang, this argues for an increase in essential metal availability for primary producers. Coinciding with the transition from a highly unstable ecosystem shortly after the Precambrian/Cambrian boundary to a more habitable environment increased nutrient uptake, oxygen availability and enhanced dissolved organic carbon (DOC) recycling match with the diversification of early metazoan fossil findings at the studied local. Our findings demonstrate that Cd isotopes in combination with trace metals can be used to infer changes in biogeochemical metal cycling in paleoenvironments and further allow establishing Cd isotope systematics as a reliable paleoproductivity proxy in the search for Earth's earliest phototrophic life.

KW - Biogeochemical metal cycling

KW - Cambrian explosion

KW - Cd isotopes

KW - Paleoproductivity

UR - http://www.scopus.com/inward/record.url?scp=85070806450&partnerID=8YFLogxK

U2 - 10.1016/j.gca.2019.07.036

DO - 10.1016/j.gca.2019.07.036

M3 - Article

AN - SCOPUS:85070806450

VL - 263

SP - 195

EP - 214

JO - Geochimica et cosmochimica acta

JF - Geochimica et cosmochimica acta

SN - 0016-7037

ER -