TY - JOUR
T1 - Inverse Magnetic Susceptibility Fabrics in Pelagic Sediment
T2 - Implications for Magnetofossil Abundance and Alignment
AU - Usui, Yoichi
AU - Yamazaki, Toshitsugu
AU - Oka, Toshitaka
AU - Kumagai, Yuho
N1 - Funding Information:
Data are available at Zenodo repository (doi: 10.5281/zenodo.3424949). We thank the Associate Editor Mark Dekkers and two reviewers for careful comments, which greatly improve the manuscript. This study was supported by JSPS KAKENHI Grants JP17H01361 and JP17H04855. Y. U. thanks Aguri Irisawa for assistance in the lab.
Funding Information:
Data are available at Zenodo repository (doi: 10.5281/zenodo.3424949). We thank the Associate Editor Mark Dekkers and two reviewers for careful comments, which greatly improve the manuscript. This study was supported by JSPS KAKENHI Grants JP17H01361 and JP17H04855. Y. U. thanks Aguri Irisawa for assistance in the lab.
Publisher Copyright:
©2019. American Geophysical Union. All Rights Reserved.
PY - 2019/11/1
Y1 - 2019/11/1
N2 - Single-domain magnetite particles exhibit minimum susceptibility along their elongation, resulting in so-called inverse fabric of the anisotropy of magnetic susceptibility (AMS). We report the discovery of inverse AMS fabrics from pelagic clay recovered by a ∼12 m long piston core from the western North Pacific. A previous study identified fossil single-domain magnetite produced by magnetotactic bacteria (magnetofossils) as the dominant ferrimagnetic mineral in the sediment. The inverse AMS fabrics were found in a ∼2 m zone. The ∼6 and ∼4 m of sediment above and below this zone showed normal, horizontal AMS fabrics. Rock magnetic data and ferromagnetic resonance spectroscopy indicated that magnetofossils account for most of the mean susceptibility regardless of normal or inverse AMS. This was explained by the mixing models where the inverse fabric from magnetofossils is nearly balanced by the normal fabrics of terrigenous minerals. The corrected degree of AMS carried by magnetofossils in the sediment was estimated to be ∼1.01, which is comparable to that of typical pelagic sediment at shallow depth. On the other hand, terrigenous minerals in the sediment were estimated to have higher degree of anisotropy, possibly reflecting burial and subsequent erosion of >80 m of sediment, which was also suggested by a subbottom acoustic stratigraphy. This suggests that inverse AMS fabrics due to magnetofossils may be widespread in pelagic clay without strong compaction.
AB - Single-domain magnetite particles exhibit minimum susceptibility along their elongation, resulting in so-called inverse fabric of the anisotropy of magnetic susceptibility (AMS). We report the discovery of inverse AMS fabrics from pelagic clay recovered by a ∼12 m long piston core from the western North Pacific. A previous study identified fossil single-domain magnetite produced by magnetotactic bacteria (magnetofossils) as the dominant ferrimagnetic mineral in the sediment. The inverse AMS fabrics were found in a ∼2 m zone. The ∼6 and ∼4 m of sediment above and below this zone showed normal, horizontal AMS fabrics. Rock magnetic data and ferromagnetic resonance spectroscopy indicated that magnetofossils account for most of the mean susceptibility regardless of normal or inverse AMS. This was explained by the mixing models where the inverse fabric from magnetofossils is nearly balanced by the normal fabrics of terrigenous minerals. The corrected degree of AMS carried by magnetofossils in the sediment was estimated to be ∼1.01, which is comparable to that of typical pelagic sediment at shallow depth. On the other hand, terrigenous minerals in the sediment were estimated to have higher degree of anisotropy, possibly reflecting burial and subsequent erosion of >80 m of sediment, which was also suggested by a subbottom acoustic stratigraphy. This suggests that inverse AMS fabrics due to magnetofossils may be widespread in pelagic clay without strong compaction.
KW - deoformation
KW - environmental magnetism
KW - magnetotactic bacteria
KW - paleomagnetism
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U2 - 10.1029/2019JB018128
DO - 10.1029/2019JB018128
M3 - Article
AN - SCOPUS:85074768054
VL - 124
SP - 10672
EP - 10686
JO - Journal of Geophysical Research: Solid Earth
JF - Journal of Geophysical Research: Solid Earth
SN - 2169-9313
IS - 11
ER -