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A paired sulfate–pyrite δ^(34)S approach to understanding the evolution of the Ediacaran–Cambrian sulfur cycle

Fike, D. A. and Grotzinger, J. P. (2008) A paired sulfate–pyrite δ^(34)S approach to understanding the evolution of the Ediacaran–Cambrian sulfur cycle. Geochimica et Cosmochimica Acta, 72 (11). pp. 2636-2648. ISSN 0016-7037.

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An anomalous enrichment in marine sulfate δ^(34)S_(SO4) is preserved in globally-distributed latest Ediacaran–early Cambrian strata. The proximity of this anomaly to the Ediacaran–Cambrian boundary and the associated evolutionary radiation has invited speculation that the two are causally related. Here we present a high-resolution record of paired sulfate (δ^(34)S_(SO4)) and pyrite (δ^(34)S_(pyr)) from sediments spanning ca. 547–540 million years ago (Ma) from the Ara Group of the Huqf Supergroup, Sultanate of Oman. We observe an increase in δ^(34)S_(SO4) from ∼20‰ to ∼42‰, beginning at ca. 550 Ma and continuing at least through ca. 540 Ma. There is a concomitant increase in δ^(34)S_(pyr) over this interval from ∼ −15‰ to 10‰. This globally correlative enrichment, here termed the Ara anomaly, constitutes a major perturbation to the sulfur cycle. The absolute values of δ^(34)S_(pyr) reported here and in equivalent sections around the world, require the isotopic composition of material entering the ocean (δ^(34)S_(in)) to be significantly more enriched than modern (∼3‰) values, likely in excess of 12‰ during the late Ediacaran–early Cambrian. Against this background of elevated δ^(34)S_(in), the Ara anomaly is explained not by increased fractionation between sulfate and pyrite (Δδ^(34)S), but by an increase in pyrite burial (f_(pyr)), most likely driven by enhanced primary production and sequestration of organic carbon, consistent with earlier reports of elevated organic carbon burial and widespread phosphorite deposition.

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Fike, D. A.0000-0003-2848-0328
Grotzinger, J. P.0000-0001-9324-1257
Additional Information:© 2008 Elsevier Ltd. Received 16 May 2007; accepted in revised form 18 March 2008; available online 10 April 2008. Associate editor: Timothy W. Lyons. This research was supported by Petroleum Development Oman (PDO) and a grant from the Agouron Institute. D.A.F. was additionally supported by an N.S.F Graduate Research Fellowship and the MIT Global Habitability Longevity Award. We thank PDO for access to samples and logistical support, L. Pratt for use of laboratory facilities and discussions, C. Colonero, J. Fong, and S. Studley for laboratory assistance, and A. Bradley, D. Canfield, T. Dimofte, J. Eiler, D. Finkelstein, T. Lyons, A. Maloof, S. Ono, D. Rothman, R. Raiswell, J. Ries, and R. Summons for comments. Helpful reviews by M. Hurtgen, B. Gill, and an anonymous reviewer greatly improved this text.
Funding AgencyGrant Number
Petroleum Development OmanUNSPECIFIED
Agouron InstituteUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Massachusetts Institute of Technology (MIT)UNSPECIFIED
Issue or Number:11
Record Number:CaltechAUTHORS:20130220-145700753
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Official Citation:D.A. Fike, J.P. Grotzinger, A paired sulfate–pyrite δ34S approach to understanding the evolution of the Ediacaran–Cambrian sulfur cycle, Geochimica et Cosmochimica Acta, Volume 72, Issue 11, 1 June 2008, Pages 2636-2648, ISSN 0016-7037, 10.1016/j.gca.2008.03.021. (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37031
Deposited By: Ruth Sustaita
Deposited On:20 Feb 2013 23:36
Last Modified:13 Dec 2019 02:25

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