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

Author(s)

Simon V. Hohl, Shao-Yong Jiang, Hai-Zhen Wei, Dao-Hui Pi, Qian Liu, Sebastian Viehmann, Stephan J. G. Galer

Abstract

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 δ¹³C_org

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.

Organisation(s)

Department of Geology

External organisation(s)

China University of Geosciences, Max-Planck-Institut für Chemie (Otto-Hahn-Institut), Nanjing University, Tongji University

Journal

Geochimica et Cosmochimica Acta

Volume

263

Pages

195-214

No. of pages

20

ISSN

0016-7037

DOI

https://doi.org/10.1016/j.gca.2019.07.036

Publication date

2019

Peer reviewed

Yes

Austrian Fields of Science 2012

105105 Geochemistry, 105121 Sedimentology, 105118 Palaeontology

Keywords

ASJC Scopus subject areas

Geochemistry and Petrology

Portal url

https://ucrisportal.univie.ac.at/en/publications/51a3324f-227e-44cb-a9a6-1d8deeee95ae

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