Greigite Formation Modulated by Turbidites and Bioturbation in Deep-Sea Sediments Offshore Sumatra
Yang, Tao; Dekkers, Mark J.; Zhao, Xixi; Petronotis, Katerina E.; Chou, Yu Min
(2022) Journal of Geophysical Research: Solid Earth, volume 127, issue 11
(Article)
Abstract
Authigenic greigite may form at any time within a sediment during diagenesis. Its formation pathway, timing of formation, and geological preservation potential are key to resolving the fidelity of (paleo-)magnetic signals in greigite-bearing sediments. In the cored sequence of the International Ocean Discovery Program Expedition 362 (Sumatra Subduction Margin), multiple
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organic-rich mudstone horizons have high magnetic susceptibilities. The high-susceptibility horizons occur immediately below the most bioturbated intervals at the top of muddy turbidite beds. Combined mineral magnetic, microscopic, and chemical analyses on both thin sections and magnetic mineral extracts of sediments from a typical interval (∼1,103.80–1,108.80 m below seafloor) reveal the presence of coarse-grained greigite aggregates (particles up to 50–75 μm in size). The greigite formed under nonsteady state conditions caused by the successive turbidites. Organic matter, iron (oxy)(hydr)oxides, Fe2+, and sulfides and/or sulfate were enriched in these intensively bioturbated horizons. This facilitated greigite formation and preservation within a closed diagenetic system created by the ensuing turbidite pulse, where pyritization was arrested due to insufficient sulfate supply relative to Fe (oxy)(hydr)oxide. This may represent a novel greigite formation pathway under conditions modulated by turbidites and bioturbation. Paleomagnetic analyses indicate that the early diagenetic greigite preserves primary (quasi-)syn-sedimentary magnetic records. The extremely high greigite content (0.06–1.30 wt% with an average of 0.50 wt% estimated from their saturation magnetization) implies that the bioturbated turbiditic deposits are an important sink for iron and sulfur. Mineral magnetic methods, thus, may offer a window to better understand the marine Fe–S–C cycle.
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Keywords: bioturbation, greigite, IODP Expedition 362, mineral magnetism, Nicobar Fan, turbidite, Geophysics, Geochemistry and Petrology, Earth and Planetary Sciences (miscellaneous), Space and Planetary Science
ISSN: 2169-9313
Note: Funding Information: Samples and data for this study were provided by the International Ocean Discovery Program (IODP; http://www.iodp.org/access-data-and-samples). We thank the JOIDES Resolution crew and IODP technical team for their contributions during Expedition 362. Dyke Andreasen and Colin Carney of the University of California, Santa Cruz Stable Isotope Laboratory, provided insights into sample preparation and conducted the organic matter analyses. We thank Weiwei Chen and Jie Chen for assistance with paleomagnetic and rock magnetic measurements, Yan Zhang for assistance with low-temperature magnetic measurements, Xiaodong Jiang for assistance with magnetic separation, and Xi Ma for assistance with XRD analysis and data processing, and SEM/EDS observations. We also thank Liao Chang and Qingsong Liu for helpful discussions. Thanks to Andrew Roberts and an anonymous reviewer for their constructive reviews that significantly helped to improve the manuscript, and to Associate Editor Agnes Kontny, and the Editor-in-Chief Isabelle Manighetti for their efficient editorial handling. This work was supported by the National Natural Science Foundation of China Grants 41874105 to TY and 41874076 to XZ. TY acknowledges financial support for expedition participation and postexpedition research from IODP-China. XZ acknowledges support from the U.S. National Science Foundation through Grant EAR-1250444 as well as an USSSP postexpedition grant. KEP acknowledges financial support from the IODP JRSO (NSF Grant OCE-1326927) and a USSSP postexpedition grant. Funding Information: Samples and data for this study were provided by the International Ocean Discovery Program (IODP; http://www.iodp.org/access-data-and-samples ). We thank the crew and IODP technical team for their contributions during Expedition 362. Dyke Andreasen and Colin Carney of the University of California, Santa Cruz Stable Isotope Laboratory, provided insights into sample preparation and conducted the organic matter analyses. We thank Weiwei Chen and Jie Chen for assistance with paleomagnetic and rock magnetic measurements, Yan Zhang for assistance with low‐temperature magnetic measurements, Xiaodong Jiang for assistance with magnetic separation, and Xi Ma for assistance with XRD analysis and data processing, and SEM/EDS observations. We also thank Liao Chang and Qingsong Liu for helpful discussions. Thanks to Andrew Roberts and an anonymous reviewer for their constructive reviews that significantly helped to improve the manuscript, and to Associate Editor Agnes Kontny, and the Editor‐in‐Chief Isabelle Manighetti for their efficient editorial handling. This work was supported by the National Natural Science Foundation of China Grants 41874105 to TY and 41874076 to XZ. TY acknowledges financial support for expedition participation and postexpedition research from IODP‐China. XZ acknowledges support from the U.S. National Science Foundation through Grant EAR‐1250444 as well as an USSSP postexpedition grant. KEP acknowledges financial support from the IODP JRSO (NSF Grant OCE‐1326927) and a USSSP postexpedition grant. JOIDES Resolution Publisher Copyright: © 2022 The Authors.
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