| Title: |
The Origin of Magnetofossil Coercivity Components: Constraints From Coupled Experimental Observations and Micromagnetic Calculations. |
| Authors: |
Xue, Pengfei1 (AUTHOR) pengfeixue@tongji.edu.cn, Chang, Liao2,3 (AUTHOR) liao.chang@pku.edu.cn, Pei, Zhaowen2 (AUTHOR), Harrison, Richard J.4 (AUTHOR) |
| Source: |
Journal of Geophysical Research. Solid Earth. Oct2024, Vol. 129 Issue 10, p1-23. 23p. |
| Subject Terms: |
*MAGNETITE crystals, *MAGNETIC measurements, *PARTICLE size distribution, *MAGNETIC properties, *MAGNETOTACTIC bacteria, *MAGNETITE |
| Abstract: |
Biogenic magnetite crystals produced by magnetotactic bacteria (MTB) and associated magnetofossils in sediments are characterized by variable morphologies, grain sizes, and chain structures. Magnetofossils are widely used in paleomagnetic and paleoenvironmental studies, but the complex magnetofossil shapes and particle arrangements significantly affect magnetic properties, hampering their magnetic detection and proxy interpretation. Here we perform coupled experimental and micromagnetic modeling analyses of typical magnetofossil‐rich sediments, where the effects of magnetofossil crystal forms and microstructures on magnetic properties can be quantitatively separated. Since the in situ magnetofossil chain structures in sediments remain poorly known, we compare results from magnetic measurements and micromagnetic simulations based on realistic magnetofossil shapes and grain size distributions. Our results suggest that bullet‐shaped magnetofossils certainly contribute to the biogenic hard (BH) coercivity component with a minor contribution from elongated prismatic particles, and collapsed equidimensional grains to the biogenic soft (BS) component. Micromagnetic simulations with different collapse models of bullet‐shaped magnetofossils produce variable FORC (first‐order reversal curve) central‐ridge contributions with similar coercivity distributions. Sensitivity test suggests that samples containing different forms of magnetofossils can produce the BH coercivity component if the proportion of the bullet‐shaped particles is more than ∼2%. Magnetofossil assemblages with a higher proportion of bullet‐shaped particles have higher coercivities, squareness ratios, and larger BH contents. Our data shed new light on understanding the origin of magnetofossil coercivity components and the in situ magnetofossil microstructures in sediments, which is widely useful for interpreting magnetofossil proxy signals in geological records. Plain Language Summary: Magnetotactic bacteria (MTB) that produce magnetic nanoparticles are widespread in sediments and water columns. Magnetofossils preserved in sediments after MTB death record ancient biological, geological, and environmental processes on Earth. The diversity of magnetofossil shapes and crystal arrangements significantly affects the magnetic properties of natural samples, making it difficult to interpret ancient environmental conditions. Here we carry out coupled magnetic analyses and numerical modeling to investigate the link between magnetic properties and magnetofossil configurations. Our analyses suggest that bullet‐shaped magnetofossils contribute to the most stable magnetic signals in sediments and that magnetofossils are arranged in highly collapsed arrangements rather than straight chains. Additionally, different combinations of magnetofossil morphologies significantly affect the magnetic properties of magnetofossil‐bearing samples. This study makes major contributions to the interpretation of magnetofossil proxy signals in paleomagnetic and paleoclimatic records. Key Points: Coupled experimental data and simulated results reveal the linkage between bullet‐shaped magnetite crystal and biogenic hard componentDifferent collapse models of bullet magnetofossils produce variable FORC central‐ridge contributions with similar coercivity distributionsSensitivity test suggests that more than ∼2% bullet‐shaped magnetofossils can produce a biogenic hard component [ABSTRACT FROM AUTHOR] |
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