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.
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
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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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13 August 2020
Qian, Yao
ebae36a5-f3a5-461c-8570-c50bc38d2203
Roberts, Andrew P.
bfc571f6-9c7a-4cc5-8df9-2c41ef5ac2a1
Liu, Yan
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Hu, Pengxiang
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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
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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).
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.
Text
2019JB019024
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Accepted/In Press date: 28 July 2020
Published date: 13 August 2020
Additional Information:
Funding Information:
This work was supported financially by the Australian Research Council (grants DP160100805 and DE190100042) and the National Natural Science Foundation of China (grants 41920104009 and 41890843). Yao Qian is supported by the China Scholarship Council for her study at ANU. TEM experiments were performed at the Electron Microscope Laboratory, IGG-CAS (Beijing, China), with the kind assistance of TEM engineers Mrs. Lixin Gu and Tang Xu.
Publisher Copyright:
©2020. American Geophysical Union. All Rights Reserved.
Identifiers
Local EPrints ID: 445134
URI: http://eprints.soton.ac.uk/id/eprint/445134
ISSN: 2169-9313
PURE UUID: 7bd44be2-2f12-4600-b7e3-06ecf419b8df
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Date deposited: 23 Nov 2020 17:30
Last modified: 17 Mar 2024 06:07
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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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