Evidence of magnetite reduction and primary magnetization destruction during early diagenesis in sediments from Maldives Inner Sea

Magnetic experiments have provided insight into the preservation of magnetite in sediments of the Inner Sea of the Maldives during early diagenesis. In this study, we present high-resolution remanence data on the upper 15 meters of the sedimentary record and a detailed magnetic characterization of discrete samples from the top 5.5 meters of the International Ocean Discovery Program (IODP) Site U1471 record. Based on magnetic experiments, it can be concluded that magnetite is rapidly reduced, with a large decrease in natural remanent magnetization (NRM) related to destruction of primary NRM below the upper two meters of the sedimentary record. In thermomagnetic experiments, the appearance of a greigite signal at 3.06 meters below sea floor (mbsf) suggests that current diagenesis could imprint nearly 100 kry of error on the chronology based on magnetostratigraphy. Furthermore, based on X-ray fluorescence data, it can be concluded that magnetite reduction did not affect the Fe record.

Keywords:
IODP exp. 359; Indian Ocean; Magnetostratigraphy; Carbonate platform; Siderite

Authorship

Igor Gustavo da Fonseca Carrasqueira ^** Corresponding author: igor.carrasqueira@usp.br

Conceptualization

Formal Analysis

Investigation

Methodology

Visualization

Writing - Original draft

Writing - Review & editing

Departamento de Oceanografia Física - Instituto Oceanográfico da Universidade de São Paulo (Praça do Oceanográfico, 191 - São Paulo - SP - Brazil - 05.508-120).Universidade de São PauloBrazilSão Paulo, SP, BrazilDepartamento de Oceanografia Física - Instituto Oceanográfico da Universidade de São Paulo (Praça do Oceanográfico, 191 - São Paulo - SP - Brazil - 05.508-120).

https://orcid.org/0000-0001-8887-7218

Luca Lanci

Conceptualization

Methodology

Resources

Supervision

Writing - Review & editing

Department of Pure and Applied Science - University of Urbino(Via S. Chiara, 27 - Urbino - Italy - 61.029).University of UrbinoItalyUrbino, ItalyDepartment of Pure and Applied Science - University of Urbino(Via S. Chiara, 27 - Urbino - Italy - 61.029).

https://orcid.org/0000-0002-3389-6371

Luigi Jovane

Conceptualization

Funding acquisition

Methodology

Project administration

Resources

Supervision

Writing - Review & editing

https://orcid.org/0000-0003-4348-4714

* Corresponding author: igor.carrasqueira@usp.br

Editor:

Rubens Lopes

SCIMAGO INSTITUTIONS RANKINGS

Figures

Figures (8)

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Figure 1
Location of the Maldives Archipelago (yellow rectangle) along the central part of the Chagos-Laccadives Ridge in the Indian Ocean. Site U1471 is located in the deepest part of the Inner Sea, near the outflow of the southern branch of the Kardiva Channel into the Inner Sea (adapted from Betzler et al., 2017aBetzler, C., Eberli, G. P., Alvarez Zarikian, C. A., Alonso-García, M., Bialik, O. M., Blättler, C. L., Guo, J. A., Haffen, S., Horozal, S., Inoue, M., Jovane, L., Kroon, D., Lanci, L., Laya, J. C., Ling Hui Mee, A., Lüdmann, T., Nakakuni, M., Nath, B. N., Niino, K., Petruny, L. M., Pratiwi, S. D., Reijmer, J. J. G., Reolid, J., Slagle, A. L., Sloss, C. R., Su, X., Swart, P. K., Wright, J. D., Yao, Z. & Young, J. R. 2017a. Site U1471. In: Betzler, C., Eberli, G. P., Alvarez Zarikian, C. A. & The Expedition 359 Scientists. Maldives Monsoon and Sea Level. Proceedings of the International Ocean Discovery Program. College Station, TX (International Ocean Discovery Program). DOI: DOI: http://dx.doi.org/10.14379/iodp.proc.359.109.2017
http://dx.doi.org/10.14379/iodp.proc.359... ).

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Figure 2
NRM@30mT intensity from 31 discrete samples compared with BIRM@100mT, BIRM@300mT and IRM@1T obtained at a resolution of 1 cm from U-channels in the upper 15 mbsf. The data show a drop in the remanence values at the top of the record. ARM@90mT data from 40 discrete samples and from U-channels compared with Fe/sum data obtained at a resolution of 1 cm with the XRF scanning method in the upper 15 mbsf. The data show a pattern for Fe/sum, different from the sharp drop in the upper 3 mbsf found for ARM@90mT.

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Figure 3
NRM time series at AF degaussing steps of 0 mT, 30 mT and 90 mT. ARM@90 mT is presented with the number of each sample selected to show the complete degaussing curves.

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Figure 4
ARM@90mT corrected for mass (note that the data are plotted on a logarithmic scale). FORC diagrams measured with a mean time of 4 seconds per point. Dia-paramagnetic corrected hysteresis loop. Day diagram (red dots indicate the current sample) and acquisition of IRM.

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Figure 5
Temperature-dependent magnetic susceptibility corrected for the diamagnetic contribution of the furnace. The heating and cooling curves are plotted in red and blue, respectively.

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Figure 6
ARM@90mT, IRM@1T, S ratio@300mT and Fe/sum data obtained at a resolution of 1 cm from U-channels and half cores in the upper 15 mbsf.

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Figure 7
Comparison between continuous ARM@90mT, IRM@1T and Fe/sum data for the interval between 2 and 4 mbsf. Arrows indicate changes in the mean values between intervals A and B.

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Figure 8
Cross-correlation between the records (A) Fe/sum vs. Si/sum and (B) Fe/sum vs. K/sum. The dashed vertical line shows the point of maximum correlation.

Figure 1 Location of the Maldives Archipelago (yellow rectangle) along the central part of the Chagos-Laccadives Ridge in the Indian Ocean. Site U1471 is located in the deepest part of the Inner Sea, near the outflow of the southern branch of the Kardiva Channel into the Inner Sea (adapted from Betzler et al., 2017aBetzler, C., Eberli, G. P., Alvarez Zarikian, C. A., Alonso-García, M., Bialik, O. M., Blättler, C. L., Guo, J. A., Haffen, S., Horozal, S., Inoue, M., Jovane, L., Kroon, D., Lanci, L., Laya, J. C., Ling Hui Mee, A., Lüdmann, T., Nakakuni, M., Nath, B. N., Niino, K., Petruny, L. M., Pratiwi, S. D., Reijmer, J. J. G., Reolid, J., Slagle, A. L., Sloss, C. R., Su, X., Swart, P. K., Wright, J. D., Yao, Z. & Young, J. R. 2017a. Site U1471. In: Betzler, C., Eberli, G. P., Alvarez Zarikian, C. A. & The Expedition 359 Scientists. Maldives Monsoon and Sea Level. Proceedings of the International Ocean Discovery Program. College Station, TX (International Ocean Discovery Program). DOI: DOI: http://dx.doi.org/10.14379/iodp.proc.359.109.2017
http://dx.doi.org/10.14379/iodp.proc.359... ).

Figure 2 NRM@30mT intensity from 31 discrete samples compared with BIRM@100mT, BIRM@300mT and IRM@1T obtained at a resolution of 1 cm from U-channels in the upper 15 mbsf. The data show a drop in the remanence values at the top of the record. ARM@90mT data from 40 discrete samples and from U-channels compared with Fe/sum data obtained at a resolution of 1 cm with the XRF scanning method in the upper 15 mbsf. The data show a pattern for Fe/sum, different from the sharp drop in the upper 3 mbsf found for ARM@90mT.

Figure 3 NRM time series at AF degaussing steps of 0 mT, 30 mT and 90 mT. ARM@90 mT is presented with the number of each sample selected to show the complete degaussing curves.

Figure 4 ARM@90mT corrected for mass (note that the data are plotted on a logarithmic scale). FORC diagrams measured with a mean time of 4 seconds per point. Dia-paramagnetic corrected hysteresis loop. Day diagram (red dots indicate the current sample) and acquisition of IRM.

Figure 5 Temperature-dependent magnetic susceptibility corrected for the diamagnetic contribution of the furnace. The heating and cooling curves are plotted in red and blue, respectively.

Figure 6 ARM@90mT, IRM@1T, S ratio@300mT and Fe/sum data obtained at a resolution of 1 cm from U-channels and half cores in the upper 15 mbsf.

Figure 7 Comparison between continuous ARM@90mT, IRM@1T and Fe/sum data for the interval between 2 and 4 mbsf. Arrows indicate changes in the mean values between intervals A and B.

Figure 8 Cross-correlation between the records (A) Fe/sum vs. Si/sum and (B) Fe/sum vs. K/sum. The dashed vertical line shows the point of maximum correlation.

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Evidence of magnetite reduction and primary magnetization destruction during early diagenesis in sediments from Maldives Inner Sea

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[1] * Corresponding author: igor.carrasqueira@usp.br