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Redox heterogeneity of subsurface waters in the Mesoproterozoic ocean.

Sperling, E.A. and Rooney, A.D. and Hays, L. and Sergeeva, V.N. and Vorob’eva, N.G. and Sergeeva, N.D. and Pearson, A. and Selby, D. and Johnston, D.T. and Knoll, A.H. (2014) 'Redox heterogeneity of subsurface waters in the Mesoproterozoic ocean.', Geobiology., 12 (5). pp. 373-386.


A substantial body of evidence suggests that subsurface water masses in mid-Proterozoic marine basins were commonly anoxic, either euxinic (sulfidic) or ferruginous (free ferrous iron). To further document redox variations during this interval, a multiproxy geochemical and paleobiological investigation was conducted on the approximately 1000-m-thick Mesoproterozoic (Lower Riphean) Arlan Member of the Kaltasy Formation, central Russia. Iron speciation geochemistry, supported by organic geochemistry, redox-sensitive trace element abundances, and pyrite sulfur isotope values, indicates that basinal calcareous shales of the Arlan Member were deposited beneath an oxygenated water column, and consistent with this interpretation, eukaryotic microfossils are abundant in basinal facies. The Rhenium–Osmium (Re–Os) systematics of the Arlan shales yield depositional ages of 1414 ± 40 and 1427 ± 43 Ma for two horizons near the base of the succession, consistent with previously proposed correlations. The presence of free oxygen in a basinal environment adds an important end member to Proterozoic redox heterogeneity, requiring an explanation in light of previous data from time-equivalent basins. Very low total organic carbon contents in the Arlan Member are perhaps the key—oxic deep waters are more likely (under any level of atmospheric O2) in oligotrophic systems with low export production. Documentation of a full range of redox heterogeneity in subsurface waters and the existence of local redox controls indicate that no single stratigraphic section or basin can adequately capture both the mean redox profile of Proterozoic oceans and its variance at any given point in time.

Item Type:Article
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Publisher statement:This is the accepted version of the following article: Sperling, E. A., Rooney, A. D., Hays, L., Sergeev, V. N., Vorob'eva, N. G., Sergeeva, N. D., Selby, D., Johnston, D. T. and Knoll, A. H. (2014), Redox heterogeneity of subsurface waters in the Mesoproterozoic ocean. Geobiology, 12 (5): 373–386, which has been published in final form at This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.
Date accepted:23 April 2014
Date deposited:12 January 2015
Date of first online publication:29 May 2014
Date first made open access:No date available

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