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Oxygen minimum zones in the early Cambrian ocean

R. Guilbaud1,2,

1Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK
2Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK

B.J. Slater2,3,

2Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK
3Department of Earth Sciences, Paleobiology, Uppsala University, 75236 Uppsala, Sweden

S.W. Poulton4,

4School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK

T.H.P. Harvey5,

5Department of Geology, University of Leicester, Leicester LE1 7RH, UK

J.J. Brocks6,

6Research School of Earth Sciences, The Australian National University, ACT 2601, Australia

B.J. Nettersheim6,7,

6Research School of Earth Sciences, The Australian National University, ACT 2601, Australia
7Max Planck Institute for Biogeochemistry, Hans-Knoell-Strasse 10, 07745 Jena, Germany

N.J. Butterfield2

2Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Guilbaud, R., Slater, B.J., Poulton, S.W., Harvey, T.H.P., Brocks, J.J., Nettersheim, B.J., Butterfield, N.J. (2018) Oxygen minimum zones in the early Cambrian ocean. Geochem. Persp. Let. 6, 33–38.

This work was funded by NERC (NE/K005251/1). SWP acknowledges support from a Royal Society Wolfson Research Merit Award.

Geochemical Perspectives Letters v6  |  doi: 10.7185/geochemlet.1806
Received 18 September 2017  |  Accepted 07 February 2018  |  Published 1 March 2018
Copyright © The Authors

Published by the European Association of Geochemistry
under Creative Commons License CC BY 4.0




Figure 1 Core location (red circles) and stratigraphy, modified after Nielsen and Schovsbo (2011)

Nielsen, A.T., Schovsbo, N.H. (2011) The Lower Cambrian of Scandinavia: depositional environment, sequence stratigraphy and palaeogeography. Earth-Science Reviews 107, 207–310.

. Grey and white shadings represent the stratigraphic sequences (e.g., LC2-5). The bars illustrate the analysed core sections (on mudstones and siltstones only); euxinic, ferruginous and oxic depositions are in purple, black and blue, respectively.
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Figure 2 Geochemical data. Inner-, mid-, and outer-shelf environments are indicated by open, red and black symbols, respectively. Grey shadows delimit redox domains and dashed lines represent average shale values. Black arrows are for outpassing data points. Maximum values for U/Al and V/Al are 54 and 434 ppm/wt. %, respectively.
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Figure 3 (a) Distribution of redox ratios (n = 183), binned as a function of their depositional environment. Inner- and outer-shelf environments show significantly more oxic redox populations than corresponding mid-shelves (t test p << 0.05). (b) Example of m/z = 134 partial ion chromatogram revealing the presence of 2,3,6 trimethyl aryl isoprenoids (AI) in mid-shelf facies. High ratios of short- to long-chain AI (AIR) point to strongly varying, intermittent oxygen exposure levels. (c) SCF assemblages from (i) inner-shelf (denticulate metazoan structures), (ii) mid-shelf (protoconodont spines alongside occasional Wiwaxia sclerites) and (iii) outer-shelf environments (priapulid, palaeoscolecid and annelid remains). Scale bars are 100 μm.
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Figure 4 Redox architecture reconstruction, with oxic conditions above and below anoxic settings. Ferruginous conditions dominate in the OMZ, but euxinia develops in zones of increased organic carbon delivery. Metazoan body fossils recovery is shown by the red stars. Evidence for phototrophic GSB (green ovals) in mid-shelf settings corroborates geochemical and palaeontological redox indicators.
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