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Apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite

Sagnotti, Leonardo; Roberts, Andrew; Weaver, Richard; Verosub, Kenneth; Florindo, Fabio; Pike, Christopher; Clayton, Trevor; Wilson, Gary

Description

A mixed-polarity zone, representing alternations between remagnetized and non-remagnetized strata, has been documented within the lower few metres of the CRP-1 core (Ross Sea, Antarctica). Detailed rock magnetic investigation of this interval indicates that the normal polarity remagnetization is carried by magnetostatically interacting single-domain particles of a ferri-magnetic iron sulphide mineral, while the reversed-polarity magnetization of non-remagnetized strata is carried by magnetite...[Show more]

dc.contributor.authorSagnotti, Leonardo
dc.contributor.authorRoberts, Andrew
dc.contributor.authorWeaver, Richard
dc.contributor.authorVerosub, Kenneth
dc.contributor.authorFlorindo, Fabio
dc.contributor.authorPike, Christopher
dc.contributor.authorClayton, Trevor
dc.contributor.authorWilson, Gary
dc.date.accessioned2015-12-07T22:40:57Z
dc.identifier.issn0956-540X
dc.identifier.urihttp://hdl.handle.net/1885/24087
dc.description.abstractA mixed-polarity zone, representing alternations between remagnetized and non-remagnetized strata, has been documented within the lower few metres of the CRP-1 core (Ross Sea, Antarctica). Detailed rock magnetic investigation of this interval indicates that the normal polarity remagnetization is carried by magnetostatically interacting single-domain particles of a ferri-magnetic iron sulphide mineral, while the reversed-polarity magnetization of non-remagnetized strata is carried by magnetite with a broad range of grain sizes and negligible magnetostatic interactions. Scanning electron microscope observations of polished sections indicate that the ferrimagnetic iron sulphide mineral is greigite (Fe3 S4). Based on microtextural relationships, it is not possible to determine the relative timing of formation for much of the greigite. However, a significant proportion of the greigite has grown on the surface of authigenic siderite (FeCO3) grains that occur as microconcretions and as cement surrounding detrital matrix grains. In such cases, microtextural relationships indicate that siderite post-dates early diagenetic pyrite and that greigite post-dates the siderite. Siderite usually forms in environments with abundant dissolved iron and carbonate, but without dissolved pore water H2S. This set of geochemical conditions occurs in methanic settings below the sulphate reduction zone (in which early diagenetic pyrite forms). We interpret the observed remagnetization of the lower part of the CRP-1 core as due to a late diagenetic pore water migration event where abundant iron on the surface of siderite grains reacted with fluids containing limited dissolved sulphide, thereby causing precipitation of greigite. The distribution of siderite (and associated greigite) in the lower part of the CRP-1 core is patchy, which accounts for the apparent alternation of polarities. This study is part of a growing catalogue of remagnetizations involving greigite, which suggests that occurrences of greigite should be treated with caution in palaeomagnetic and environmental magnetic studies.
dc.publisherBlackwell Publishing Ltd
dc.sourceGeophysical Journal International
dc.subjectKeywords: diagenesis; greigite; magnetic reversal; paleomagnetism; remagnetization; siderite; oceanic regions; Ross Sea; Southern Ocean; World Antarctica; Diagenesis; Greigite; Iron carbonate; Iron sulphide; Remagnetization; Siderite
dc.titleApparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume160
dc.date.issued2005
local.identifier.absfor040406 - Magnetism and Palaeomagnetism
local.identifier.ariespublicationu4539375xPUB30
local.type.statusPublished Version
local.contributor.affiliationSagnotti, Leonardo, Instituto Nazionale di Geofisica e Vulcanologia
local.contributor.affiliationRoberts, Andrew, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationWeaver, Richard, University of Southampton
local.contributor.affiliationVerosub, Kenneth, University of California
local.contributor.affiliationFlorindo, Fabio, Instituto Nazionale di Geofisica e Vulcanologia
local.contributor.affiliationPike, Christopher, University of California
local.contributor.affiliationClayton, Trevor, University of Southampton
local.contributor.affiliationWilson, Gary, University of Otago
local.description.embargo2037-12-31
local.bibliographicCitation.startpage12p
local.identifier.doi10.1111/j.1365-246X.2005.02485.x
dc.date.updated2015-12-07T10:55:42Z
local.identifier.scopusID2-s2.0-13344285316
CollectionsANU Research Publications

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