Apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite
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 car...
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ftanucanberra:oai:digitalcollections.anu.edu.au:1885/24087 2023-05-15T13:38:43+02:00 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 2015-12-07T22:40:57Z http://hdl.handle.net/1885/24087 unknown Blackwell Publishing Ltd 0956-540X http://hdl.handle.net/1885/24087 Geophysical Journal International Keywords: diagenesis greigite magnetic reversal paleomagnetism remagnetization siderite oceanic regions Ross Sea Southern Ocean World Antarctica Diagenesis Iron carbonate Iron sulphide Journal article 2015 ftanucanberra 2015-12-21T23:20:14Z 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 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. Article in Journal/Newspaper Antarc* Antarctica Ross Sea Southern Ocean Australian National University: ANU Digital Collections Ross Sea Southern Ocean |
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Open Polar |
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Australian National University: ANU Digital Collections |
op_collection_id |
ftanucanberra |
language |
unknown |
topic |
Keywords: diagenesis greigite magnetic reversal paleomagnetism remagnetization siderite oceanic regions Ross Sea Southern Ocean World Antarctica Diagenesis Iron carbonate Iron sulphide |
spellingShingle |
Keywords: diagenesis greigite magnetic reversal paleomagnetism remagnetization siderite oceanic regions Ross Sea Southern Ocean World Antarctica Diagenesis Iron carbonate Iron sulphide Sagnotti, Leonardo Roberts, Andrew Weaver, Richard Verosub, Kenneth Florindo, Fabio Pike, Christopher Clayton, Trevor Wilson, Gary Apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite |
topic_facet |
Keywords: diagenesis greigite magnetic reversal paleomagnetism remagnetization siderite oceanic regions Ross Sea Southern Ocean World Antarctica Diagenesis Iron carbonate Iron sulphide |
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 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. |
format |
Article in Journal/Newspaper |
author |
Sagnotti, Leonardo Roberts, Andrew Weaver, Richard Verosub, Kenneth Florindo, Fabio Pike, Christopher Clayton, Trevor Wilson, Gary |
author_facet |
Sagnotti, Leonardo Roberts, Andrew Weaver, Richard Verosub, Kenneth Florindo, Fabio Pike, Christopher Clayton, Trevor Wilson, Gary |
author_sort |
Sagnotti, Leonardo |
title |
Apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite |
title_short |
Apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite |
title_full |
Apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite |
title_fullStr |
Apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite |
title_full_unstemmed |
Apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite |
title_sort |
apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite |
publisher |
Blackwell Publishing Ltd |
publishDate |
2015 |
url |
http://hdl.handle.net/1885/24087 |
geographic |
Ross Sea Southern Ocean |
geographic_facet |
Ross Sea Southern Ocean |
genre |
Antarc* Antarctica Ross Sea Southern Ocean |
genre_facet |
Antarc* Antarctica Ross Sea Southern Ocean |
op_source |
Geophysical Journal International |
op_relation |
0956-540X http://hdl.handle.net/1885/24087 |
_version_ |
1766110402254471168 |