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Assessment and integration of bulk and component‐specific methods for identifying mineral magnetic assemblages in environmental magnetism

Assessment and integration of bulk and component‐specific methods for identifying mineral magnetic assemblages in environmental magnetism
Assessment and integration of bulk and component‐specific methods for identifying mineral magnetic assemblages in environmental magnetism
Magnetic parameters are used extensively to interpret magnetic mineral assemblage variations in environmental studies. Conventional room temperature measurements of bulk magnetic parameters, like the anhysteretic remanent magnetization (ARM) and the ratio of the susceptibility of ARM to magnetic susceptibility (χ), can reflect, respectively, magnetic mineral concentration and/or particle size variations in sediments, although they are not necessarily well suited for identifying magnetic components within individual magnetic mineral assemblages. More advanced techniques, such as first‐order reversal curve (FORC) diagrams and low‐temperature (LT) magnetic measurements, can enable detailed discrimination of magnetic assemblages. Here, we integrate conventional bulk magnetic measurements alongside FORC diagrams, LT measurements, and X‐ray fluorescence core‐scan data, transmission electron microscope observations, and principal component analysis of FORC diagrams to identify and quantify magnetic mineral assemblages in eastern Mediterranean sediments. The studied sediments were selected because they contain complexly varying mixtures of detrital, biogenic, and diagenetically altered magnetic mineral assemblages that were deposited under varying oxic (organic‐poor marls) to anoxic (organic‐rich sapropels) conditions. Conventional bulk magnetic parameters provide continuous records of environmental magnetic variations, while more time‐consuming LT and FORC measurements on selected samples provide direct ground‐truthing of mineral magnetic assemblages that enables calculation of magnetization contributions of different end members. Thus, a combination of conventional bulk parameters and advanced magnetic techniques can provide detailed records from which the meaning of environmental magnetic signals can be unlocked.
2169-9313
Qian, Yao
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Roberts, Andrew P.
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Liu, Yan
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Hu, Pengxiang
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Zhao, Xiang
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Heslop, David
f32aae36-7f51-40e1-bf7d-54a561369a8d
Grant, Katharine M.
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Rohling, Eelco J.
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Hennekam, Rick
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Li, Jinhua
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Qian, Yao
ebae36a5-f3a5-461c-8570-c50bc38d2203
Roberts, Andrew P.
bfc571f6-9c7a-4cc5-8df9-2c41ef5ac2a1
Liu, Yan
3d2550f3-df3b-46fd-a49e-511f7abe6424
Hu, Pengxiang
71cac3cf-6094-4ef1-a9ba-3e0a551a5559
Zhao, Xiang
99ee573a-4607-40b5-a473-2046d623a2e0
Heslop, David
f32aae36-7f51-40e1-bf7d-54a561369a8d
Grant, Katharine M.
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Rohling, Eelco J.
a2a27ef2-fcce-4c71-907b-e692b5ecc685
Hennekam, Rick
b666d561-4ddd-4212-8275-51ae65c15704
Li, Jinhua
5cc7001a-39ff-4445-8cfb-9d00451dfcef

Qian, Yao, Roberts, Andrew P., Liu, Yan, Hu, Pengxiang, Zhao, Xiang, Heslop, David, Grant, Katharine M., Rohling, Eelco J., Hennekam, Rick and Li, Jinhua (2020) Assessment and integration of bulk and component‐specific methods for identifying mineral magnetic assemblages in environmental magnetism. Journal of Geophysical Research: Solid Earth, 125 (8), [e2019JB019024]. (doi:10.1029/2019JB019024).

Record type: Article

Abstract

Magnetic parameters are used extensively to interpret magnetic mineral assemblage variations in environmental studies. Conventional room temperature measurements of bulk magnetic parameters, like the anhysteretic remanent magnetization (ARM) and the ratio of the susceptibility of ARM to magnetic susceptibility (χ), can reflect, respectively, magnetic mineral concentration and/or particle size variations in sediments, although they are not necessarily well suited for identifying magnetic components within individual magnetic mineral assemblages. More advanced techniques, such as first‐order reversal curve (FORC) diagrams and low‐temperature (LT) magnetic measurements, can enable detailed discrimination of magnetic assemblages. Here, we integrate conventional bulk magnetic measurements alongside FORC diagrams, LT measurements, and X‐ray fluorescence core‐scan data, transmission electron microscope observations, and principal component analysis of FORC diagrams to identify and quantify magnetic mineral assemblages in eastern Mediterranean sediments. The studied sediments were selected because they contain complexly varying mixtures of detrital, biogenic, and diagenetically altered magnetic mineral assemblages that were deposited under varying oxic (organic‐poor marls) to anoxic (organic‐rich sapropels) conditions. Conventional bulk magnetic parameters provide continuous records of environmental magnetic variations, while more time‐consuming LT and FORC measurements on selected samples provide direct ground‐truthing of mineral magnetic assemblages that enables calculation of magnetization contributions of different end members. Thus, a combination of conventional bulk parameters and advanced magnetic techniques can provide detailed records from which the meaning of environmental magnetic signals can be unlocked.

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2019JB019024 - Version of Record
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Accepted/In Press date: 28 July 2020
Published date: 13 August 2020

Identifiers

Local EPrints ID: 445134
URI: http://eprints.soton.ac.uk/id/eprint/445134
ISSN: 2169-9313
PURE UUID: 7bd44be2-2f12-4600-b7e3-06ecf419b8df
ORCID for Eelco J. Rohling: ORCID iD orcid.org/0000-0001-5349-2158

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Date deposited: 23 Nov 2020 17:30
Last modified: 26 Nov 2021 05:39

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Contributors

Author: Yao Qian
Author: Andrew P. Roberts
Author: Yan Liu
Author: Pengxiang Hu
Author: Xiang Zhao
Author: David Heslop
Author: Katharine M. Grant
Author: Rick Hennekam
Author: Jinhua Li

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