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Searching for single domain magnetite in the “pseudo-single-domain” sedimentary haystack: Implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations

Searching for single domain magnetite in the “pseudo-single-domain” sedimentary haystack: Implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations
Searching for single domain magnetite in the “pseudo-single-domain” sedimentary haystack: Implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations
Magnetic hysteresis measurements of sediments have resulted in widespread reporting of “pseudo-single-domain”-like magnetic properties. In contrast, the ideal single domain (SD) properties that would be expected to be responsible for high quality paleomagnetic records are rare. Determining whether SD particles are rare or common in sediments requires application of techniques that enable discrimination among different magnetic components in a sediment. We apply a range of such techniques and find that SD particles are much more common than has been reported in the literature and that magnetite magnetofossils (the inorganic remains of magnetotactic bacteria) are widely preserved at depth in a range of sediment types, including biogenic pelagic carbonates, lacustrine and marine clays, and possibly even in glaci-marine sediments. Thus, instead of being rarely preserved in the geological record, we find that magnetofossils are widespread. This observation has important implications for our understanding of how sediments become magnetized and highlights the need to develop a more robust basis for understanding how biogenic magnetite contributes to the magnetization of sediments. Magnetofossils also have grain sizes that are substantially smaller than the 1–15 ?m size range for which there is reasonable empirical support for relative paleointensity studies. The different magnetic response of coexisting fine biogenic and coarser lithogenic particles is likely to complicate relative paleointensity studies. This issue needs much closer attention. Despite the fact that sediments have been subjected to paleomagnetic investigation for over 60 years, much remains to be understood about how they become magnetized.
0148-0227
B08104
Roberts, Andrew P.
4f062491-5408-4edb-8dd1-140c6a42e93f
Chang, Liao
83123f49-dd71-43a9-a0b1-d80777231b44
Heslop, David
f32aae36-7f51-40e1-bf7d-54a561369a8d
Florindo, Fabio
5953170b-79f7-431e-9e08-824a47e0fbd5
Larrasoaña, Juan C.
6bf2e75f-54a1-42b8-96e0-b80d2462de2c
Roberts, Andrew P.
4f062491-5408-4edb-8dd1-140c6a42e93f
Chang, Liao
83123f49-dd71-43a9-a0b1-d80777231b44
Heslop, David
f32aae36-7f51-40e1-bf7d-54a561369a8d
Florindo, Fabio
5953170b-79f7-431e-9e08-824a47e0fbd5
Larrasoaña, Juan C.
6bf2e75f-54a1-42b8-96e0-b80d2462de2c

Roberts, Andrew P., Chang, Liao, Heslop, David, Florindo, Fabio and Larrasoaña, Juan C. (2012) Searching for single domain magnetite in the “pseudo-single-domain” sedimentary haystack: Implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations. Journal of Geophysical Research, 117 (B8), B08104. (doi:10.1029/2012JB009412).

Record type: Article

Abstract

Magnetic hysteresis measurements of sediments have resulted in widespread reporting of “pseudo-single-domain”-like magnetic properties. In contrast, the ideal single domain (SD) properties that would be expected to be responsible for high quality paleomagnetic records are rare. Determining whether SD particles are rare or common in sediments requires application of techniques that enable discrimination among different magnetic components in a sediment. We apply a range of such techniques and find that SD particles are much more common than has been reported in the literature and that magnetite magnetofossils (the inorganic remains of magnetotactic bacteria) are widely preserved at depth in a range of sediment types, including biogenic pelagic carbonates, lacustrine and marine clays, and possibly even in glaci-marine sediments. Thus, instead of being rarely preserved in the geological record, we find that magnetofossils are widespread. This observation has important implications for our understanding of how sediments become magnetized and highlights the need to develop a more robust basis for understanding how biogenic magnetite contributes to the magnetization of sediments. Magnetofossils also have grain sizes that are substantially smaller than the 1–15 ?m size range for which there is reasonable empirical support for relative paleointensity studies. The different magnetic response of coexisting fine biogenic and coarser lithogenic particles is likely to complicate relative paleointensity studies. This issue needs much closer attention. Despite the fact that sediments have been subjected to paleomagnetic investigation for over 60 years, much remains to be understood about how they become magnetized.

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Published date: 2012
Organisations: Geology & Geophysics

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Local EPrints ID: 343365
URI: http://eprints.soton.ac.uk/id/eprint/343365
ISSN: 0148-0227
PURE UUID: 2f930d89-63ac-4262-82c2-6f231558c4d6

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Date deposited: 02 Oct 2012 09:44
Last modified: 14 Mar 2024 12:03

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Contributors

Author: Andrew P. Roberts
Author: Liao Chang
Author: David Heslop
Author: Fabio Florindo
Author: Juan C. Larrasoaña

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