Self-Reversed Magnetization in Sediments Caused by Greigite Alteration

Liao Chang; Zhaowen Pei; Pengfei Xue; Shishun Wang; Zhaoping Wang; Wout Krijgsman; Mark J. Dekkers

doi:10.1029/2023GL103885

Self-Reversed Magnetization in Sediments Caused by Greigite Alteration

Liao Chang^*
, Zhaowen Pei
, Pengfei Xue
, Shishun Wang
, Zhaoping Wang
, Wout Krijgsman
, Mark J. Dekkers

^*Corresponding author for this work

Research output: Contribution to journal › Article › Academic › peer-review

Abstract

Multipolarity remanence in greigite-bearing sediments has long been recognized, but the cause of this anomalous remanence behavior is not well understood. Here, we use electron microscopic and magnetic analyses to investigate the origin of such multipolarity in Miocene greigite-bearing sediments from the Pannonian Basin (Hungary). We find a magnetic softening and partial transformation of iron sulfides to magnetite and pyrrhotite from “single-polarity” to “multi-polarity” samples. The inward alteration of sulfide grains is topotactic and is size-dependent with higher alteration in smaller grains. We propose a multi-phase self-reversal chemical remanent magnetization (CRM) mechanism in altered greigite: the neoformed magnetite/pyrrhotite shell acquires a CRM coupled in the opposite direction to the primary CRM of the greigite core, likely through magnetostatic interactions or interfacial exchange interactions between the closely contacting core and shell. This new greigite self-reversal model can explain the commonly observed antiparallel polarities and has broad geochronological, tectonic and paleoenvironmental implications.

Original language	English
Article number	e2023GL103885
Number of pages	11
Journal	Geophysical Research Letters
Volume	50
Issue number	12
DOIs	https://doi.org/10.1029/2023GL103885
Publication status	Published - 28 Jun 2023

Bibliographical note

Publisher Copyright:
© 2023. The Authors.

Funding

The authors acknowledge Electron Microscopy Laboratory of Peking University for the use of Helios G4 UX FIB and FEI Tecnai F20 TEM, and Jun Xu and Xiumei Ma for technical assistance. We thank Nick Kelder for measuring the thermal demagnetization data, Rong Huang for measuring some of the low‐temperature MPMS data, Andrew Roberts for providing instrumental access to the VSM at the ANU, and Pengxiang Hu and Xiang Zhao for assistance in measurements. We are grateful to editor Monika Korte for efficient handling of this paper, Gillian Turner, and an anonymous reviewer for providing constructive comments. This study was financially supported by the National Natural Science Foundation of China (Grants 41974074, 42061130214, 41722402), and a Royal Society‐Newton Advanced Fellowship (NAF\R1\201096) to L.C. The authors acknowledge Electron Microscopy Laboratory of Peking University for the use of Helios G4 UX FIB and FEI Tecnai F20 TEM, and Jun Xu and Xiumei Ma for technical assistance. We thank Nick Kelder for measuring the thermal demagnetization data, Rong Huang for measuring some of the low-temperature MPMS data, Andrew Roberts for providing instrumental access to the VSM at the ANU, and Pengxiang Hu and Xiang Zhao for assistance in measurements. We are grateful to editor Monika Korte for efficient handling of this paper, Gillian Turner, and an anonymous reviewer for providing constructive comments. This study was financially supported by the National Natural Science Foundation of China (Grants 41974074, 42061130214, 41722402), and a Royal Society-Newton Advanced Fellowship (NAF\R1\201096) to L.C.

Funders	Funder number
Royal Society-Newton
Royal Society‐Newton	NAF\R1\201096
National Natural Science Foundation of China	42061130214, 41974074, 41722402

Keywords

chemical remanent magnetization
greigite
magnetostratigraphy
pyrrhotite
remagnetization
self-reversal

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Geophysical Research Letters - 2023 - Chang - Self‐Reversed Magnetization in Sediments Caused by Greigite AlterationFinal published version, 4.97 MBLicence: CC BY

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title = "Self-Reversed Magnetization in Sediments Caused by Greigite Alteration",

abstract = "Multipolarity remanence in greigite-bearing sediments has long been recognized, but the cause of this anomalous remanence behavior is not well understood. Here, we use electron microscopic and magnetic analyses to investigate the origin of such multipolarity in Miocene greigite-bearing sediments from the Pannonian Basin (Hungary). We find a magnetic softening and partial transformation of iron sulfides to magnetite and pyrrhotite from “single-polarity” to “multi-polarity” samples. The inward alteration of sulfide grains is topotactic and is size-dependent with higher alteration in smaller grains. We propose a multi-phase self-reversal chemical remanent magnetization (CRM) mechanism in altered greigite: the neoformed magnetite/pyrrhotite shell acquires a CRM coupled in the opposite direction to the primary CRM of the greigite core, likely through magnetostatic interactions or interfacial exchange interactions between the closely contacting core and shell. This new greigite self-reversal model can explain the commonly observed antiparallel polarities and has broad geochronological, tectonic and paleoenvironmental implications.",

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author = "Liao Chang and Zhaowen Pei and Pengfei Xue and Shishun Wang and Zhaoping Wang and Wout Krijgsman and Dekkers, \{Mark J.\}",

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doi = "10.1029/2023GL103885",

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AU - Chang, Liao

AU - Pei, Zhaowen

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AU - Wang, Shishun

AU - Wang, Zhaoping

AU - Krijgsman, Wout

AU - Dekkers, Mark J.

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N2 - Multipolarity remanence in greigite-bearing sediments has long been recognized, but the cause of this anomalous remanence behavior is not well understood. Here, we use electron microscopic and magnetic analyses to investigate the origin of such multipolarity in Miocene greigite-bearing sediments from the Pannonian Basin (Hungary). We find a magnetic softening and partial transformation of iron sulfides to magnetite and pyrrhotite from “single-polarity” to “multi-polarity” samples. The inward alteration of sulfide grains is topotactic and is size-dependent with higher alteration in smaller grains. We propose a multi-phase self-reversal chemical remanent magnetization (CRM) mechanism in altered greigite: the neoformed magnetite/pyrrhotite shell acquires a CRM coupled in the opposite direction to the primary CRM of the greigite core, likely through magnetostatic interactions or interfacial exchange interactions between the closely contacting core and shell. This new greigite self-reversal model can explain the commonly observed antiparallel polarities and has broad geochronological, tectonic and paleoenvironmental implications.

AB - Multipolarity remanence in greigite-bearing sediments has long been recognized, but the cause of this anomalous remanence behavior is not well understood. Here, we use electron microscopic and magnetic analyses to investigate the origin of such multipolarity in Miocene greigite-bearing sediments from the Pannonian Basin (Hungary). We find a magnetic softening and partial transformation of iron sulfides to magnetite and pyrrhotite from “single-polarity” to “multi-polarity” samples. The inward alteration of sulfide grains is topotactic and is size-dependent with higher alteration in smaller grains. We propose a multi-phase self-reversal chemical remanent magnetization (CRM) mechanism in altered greigite: the neoformed magnetite/pyrrhotite shell acquires a CRM coupled in the opposite direction to the primary CRM of the greigite core, likely through magnetostatic interactions or interfacial exchange interactions between the closely contacting core and shell. This new greigite self-reversal model can explain the commonly observed antiparallel polarities and has broad geochronological, tectonic and paleoenvironmental implications.

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KW - self-reversal

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DO - 10.1029/2023GL103885

M3 - Article

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Self-Reversed Magnetization in Sediments Caused by Greigite Alteration

Abstract

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Keywords

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