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Reductive diagenesis,magnetite dissolution, greigite growth and paleomagnetic smoothing in marine sediments: A new view

Rowan, Christopher J; Roberts, Andrew; Broadbent, Thomas

Description

In many anoxic sedimentary environments, the onset of sulfate reduction, and pyritization of detrital iron-bearing minerals, leads to a precipitous decline in magnetic mineral concentration during early diagenesis. The usefulness of the surviving paleomagnetic record in such environments is usually argued to depend on how much of the primary detrital magnetic assemblage survives diagenetic dissolution. Detailed rock magnetic and electron microscope analyses of rapidly deposited (~ 7 cm/kyr)...[Show more]

dc.contributor.authorRowan, Christopher J
dc.contributor.authorRoberts, Andrew
dc.contributor.authorBroadbent, Thomas
dc.date.accessioned2015-12-10T21:56:07Z
dc.identifier.issn0012-821X
dc.identifier.urihttp://hdl.handle.net/1885/39275
dc.description.abstractIn many anoxic sedimentary environments, the onset of sulfate reduction, and pyritization of detrital iron-bearing minerals, leads to a precipitous decline in magnetic mineral concentration during early diagenesis. The usefulness of the surviving paleomagnetic record in such environments is usually argued to depend on how much of the primary detrital magnetic assemblage survives diagenetic dissolution. Detailed rock magnetic and electron microscope analyses of rapidly deposited (~ 7 cm/kyr) latest Pleistocene-Holocene sediments from the continental margins of Oman (22°22.4′N, 60°08.0′E) and northern California (38°24.8′N, 123°58.2′W) demonstrate that pyritization during early diagenesis also leads to the progressive down-core growth of the ferrimagnetic iron sulfide greigite. Greigite growth begins with nucleation of large concentrations of superparamagnetic (SP) nanoparticles at the inferred position of the sulfate-methane transition, which can explain the apparently paradoxical suggestion that diagenetically reduced sediments contain enhanced concentrations of SP particles. Looping of hysteresis parameters on a "Day" plot records the dissolution of single domain (SD) (titano-)magnetite and the formation of SP greigite, which then slowly and progressively grows through its SD blocking volume and acquires a stable paleomagnetic signal. This looping trend is also evident in data from several published records (Oregon margin, Korea Strait, Japan Sea, Niger Fan, Argentine margin, and the Ontong-Java Plateau), indicating that these processes may be widespread in reducing environments. Our observations have profound implications for paleomagnetic records from sulfate-reducing environments. The paleomagnetic signal recorded by greigite is offset from the age of the surrounding sediments by 10's of kyr, and ongoing growth of greigite at depth results in smoothing of the recorded signal over intervals of 10's to 100's of kyr. We therefore expect the presence of greigite to compromise paleomagnetic records in a wide range of settings that have undergone reductive diagenesis.
dc.publisherElsevier
dc.sourceEarth and Planetary Science Letters
dc.subjectKeywords: A stables; California; Continental margins; Diagenetic; Early diagenesises; Electron microscope analysis; greigite; Holocene sediments; Iron sulfides; Japan seas; Magnetic minerals; Marine sediments; Paleomagnetic records; Paleomagnetic signals; Pleistoce greigite; hysteresis; magnetite dissolution; sediment diagenesis; sulfate reduction; superparamagnetism
dc.titleReductive diagenesis,magnetite dissolution, greigite growth and paleomagnetic smoothing in marine sediments: A new view
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume277
dc.date.issued2009
local.identifier.absfor040406 - Magnetism and Palaeomagnetism
local.identifier.ariespublicationU4353633xPUB174
local.type.statusPublished Version
local.contributor.affiliationRowan, Christopher J, University of Southampton
local.contributor.affiliationRoberts, Andrew, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationBroadbent, Thomas, University of Southampton
local.description.embargo2037-12-31
local.bibliographicCitation.issue1-2
local.bibliographicCitation.startpage223
local.bibliographicCitation.lastpage235
local.identifier.doi10.1016/J.epsl.2008.10.016
dc.date.updated2016-02-24T11:05:41Z
local.identifier.scopusID2-s2.0-57749121221
local.identifier.thomsonID000262812100025
CollectionsANU Research Publications

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