The University of Southampton
University of Southampton Institutional Repository

Mobility of authigenic rhenium, silver, and selenium during postdepositional oxidation in marine sediments

Mobility of authigenic rhenium, silver, and selenium during postdepositional oxidation in marine sediments
Mobility of authigenic rhenium, silver, and selenium during postdepositional oxidation in marine sediments
Sedimentary records of redox-sensitive trace elements hold significant potential as indicators of paleoceanographic environmental conditions. Records of Re can reveal the intensity of past reducing conditions in sediments at the time of deposition, whereas records of Ag may record the magnitude of past diatom fluxes to the seafloor. Confidence in paleoenvironmental reconstruction from records of either metal, however, requires it to have experienced negligible redistribution since deposition. This study examines diagenetic rearrangements of Re and Ag that occur in response to exposure to bottom-water O2 in environments of low sedimentation rate, including Madeira Abyssal Plain turbidites and eastern Mediterranean basin sapropels. Authigenic Re was remobilized quantitatively by oxidation but poorly retained by the underlying sediments. All records are consistent with previous work demonstrating that only a limited reimmobilization of Re occurs preferentially in Corg-rich, reducing sediments. Silver was also mobilized quantitatively by oxidation, but it was subsequently immobilized more efficiently in all cases as sharp peaks immediately into anoxic conditions below active oxidation fronts, and these peaks remain immobile in anoxic conditions during long-term burial. Comparison of Ag, S, and Se records from various cores suggests that Ag is likely to have been immobilized as a selenide, a mechanism previously proposed for Hg in similar situations (Mercone et al., 1999). Coexisting narrow peaks of Ag and Hg with Se offer a means of assessing whether oxidative burndown has ever occurred at the top of Corg- and sulfide-rich sedimentary units. Although these results suggest that caution must be used when inferring paleoenvironmental information from records of Ag and Re in cores with low sediment accumulation rates (<5 cm ka-1), they should not affect the promise that authigenic Ag and Re records hold for paleoenvironmental reconstruction in sediments with higher accumulation rates and where anoxic conditions have been maintained continuously.
SEDIMENTS, TRACE ELEMENTS, PALAEOCEANOGRAPHY, PALAEOENVIRONMENTS
0016-7037
265-273
Crusius, J.
48ef8abd-6638-4058-ab45-51f408f1ef0c
Thomson, J.
3395054f-e507-4841-9758-a06ed37f7d6b
Crusius, J.
48ef8abd-6638-4058-ab45-51f408f1ef0c
Thomson, J.
3395054f-e507-4841-9758-a06ed37f7d6b

Crusius, J. and Thomson, J. (2003) Mobility of authigenic rhenium, silver, and selenium during postdepositional oxidation in marine sediments. Geochimica et Cosmochimica Acta, 67 (2), 265-273. (doi:10.1016/S0016-7037(02)01075-X).

Record type: Article

Abstract

Sedimentary records of redox-sensitive trace elements hold significant potential as indicators of paleoceanographic environmental conditions. Records of Re can reveal the intensity of past reducing conditions in sediments at the time of deposition, whereas records of Ag may record the magnitude of past diatom fluxes to the seafloor. Confidence in paleoenvironmental reconstruction from records of either metal, however, requires it to have experienced negligible redistribution since deposition. This study examines diagenetic rearrangements of Re and Ag that occur in response to exposure to bottom-water O2 in environments of low sedimentation rate, including Madeira Abyssal Plain turbidites and eastern Mediterranean basin sapropels. Authigenic Re was remobilized quantitatively by oxidation but poorly retained by the underlying sediments. All records are consistent with previous work demonstrating that only a limited reimmobilization of Re occurs preferentially in Corg-rich, reducing sediments. Silver was also mobilized quantitatively by oxidation, but it was subsequently immobilized more efficiently in all cases as sharp peaks immediately into anoxic conditions below active oxidation fronts, and these peaks remain immobile in anoxic conditions during long-term burial. Comparison of Ag, S, and Se records from various cores suggests that Ag is likely to have been immobilized as a selenide, a mechanism previously proposed for Hg in similar situations (Mercone et al., 1999). Coexisting narrow peaks of Ag and Hg with Se offer a means of assessing whether oxidative burndown has ever occurred at the top of Corg- and sulfide-rich sedimentary units. Although these results suggest that caution must be used when inferring paleoenvironmental information from records of Ag and Re in cores with low sediment accumulation rates (<5 cm ka-1), they should not affect the promise that authigenic Ag and Re records hold for paleoenvironmental reconstruction in sediments with higher accumulation rates and where anoxic conditions have been maintained continuously.

Full text not available from this repository.

More information

Published date: 2003
Keywords: SEDIMENTS, TRACE ELEMENTS, PALAEOCEANOGRAPHY, PALAEOENVIRONMENTS

Identifiers

Local EPrints ID: 2112
URI: https://eprints.soton.ac.uk/id/eprint/2112
ISSN: 0016-7037
PURE UUID: 071c3c12-8e9e-46c1-a2ff-646af44b9ff5

Catalogue record

Date deposited: 11 May 2004
Last modified: 17 Jul 2017 17:16

Export record

Altmetrics

Contributors

Author: J. Crusius
Author: J. Thomson

University divisions

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of https://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×