Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Abstract
Volume-dependent magnetic susceptibility (κ) is commonly used for paleoenvironmental reconstructions in both terrestrial and marine sedimentary environments where it reflects a mixed signal between primary deposition and secondary diagenesis. In the marine environment, κ is strongly influenced by the abundance of ferrimagnetic minerals regulated by sediment transport processes. Post-depositional alteration by H2S, however, can dissolve titanomagnetite, releasing reactive Fe that promotes pyritization and subsequently decreases κ. Here, we provide a new approach for isolating the detrital signal in κ and identifying intervals of diagenetic alteration of κ driven by organoclastic sulfate reduction (OSR) and the anaerobic oxidation of methane (AOM) in methane-bearing marine sediments offshore India. Using the correlation of a heavy mineral proxy from X-ray fluorescence data (Zr/Rb) and κ in unaltered sediments, we predict the primary detrital κ signal and identify intervals of decreased κ, which correspond to increased total sulfur content. Our approach is a rapid, high-resolution method that can identify overprinted κ resulting from pyritization of titanomagnetite due to H2S production in marine sediments. In addition, total organic carbon, total sulfur, and authigenic carbonate δ13C measurements indicate that both OSR and AOM can drive the observed κ loss, but AOM drives the greatest decreases in κ. Overall, our approach can enhance paleoenvironmental reconstructions and provide insight into paleo-positions of the sulfate-methane transition zone, past enhancements of OSR or paleo-methane seepage, and the role of detrital iron oxide minerals on the marine sediment sulfur sink, with consequences influencing the development of chemosynthetic biological communities at methane seeps.
Department
Open Access Fund; Earth Sciences
Publication Date
9-12-2021
Journal Title
Geochemistry, Geophysics, Geosystems
Publisher
AGU
Digital Object Identifier (DOI)
Document Type
Article
Recommended Citation
Johnson, J. E., Phillips, S. C., Clyde, W. C., Giosan, L., & Torres, M. E., 2021. Isolating detrital and diagenetic signals in magnetic susceptibility records from methane-bearing marine sediments. Geochemistry, Geophysics, Geosystems, 22, e2021GC009867. https://doi.org/10.1029/2021GC009867
Comments
This is an article published by AGU in Geochemistry, Geophysics, Geosystems in 2021, available online: https://doi.org/10.1029/2021GC009867