Abstract
Marine and lacustrine sediments represent an important source of global paleomagnetic data. Although it is usually assumed that detrital iron oxides record most of the magnetic signal in sediments, iron sulfides-which form during bacterial sulfate reduction-can also represent a significant source of sedimentary magnetism. Knowing how sulfate reduction impacts sedimentary magnetism is critical to the interpretation of paleomagnetic records. Here, we show that three distinct types of magnetic particles can be produced by bacterial sulfate reduction, each of which impacts the bulk sediment magnetism in a distinct way. We combined magnetic force microscopy and electron probe microanalysis to image magnetic mineral extracts from Dead Sea sediments from a glacial period and an interglacial period. In sediments from the dry interglacial period, during which bacterial sulfate reduction was suppressed, we found greigite framboids (Fe3S4) with strong intergrain magnetic interactions. Contrastingly, in sediments from the wet glacial period, which experienced extensive sulfate reduction, pyrite (FeS2) is the dominant sulfide phase. Highresolution magnetic imaging of glacial pyrite reveals that greigite is present as single-domain particles within the pyrite. We also found that as titanomagnetite grains undergo bacterially mediated alteration to form pyrite, the original magnetic grains become divided into smaller regions, which potentially facilitates acquisition of secondary magnetization by the reorganization of these magnetic domains. Our results provide a previously undocumented mechanism by which bacterially mediated alteration can overwrite primary detrital magnetic records.
| Original language | American English |
|---|---|
| Pages (from-to) | 291-294 |
| Number of pages | 4 |
| Journal | Geology |
| Volume | 46 |
| Issue number | 4 |
| DOIs | |
| State | Published - 1 Apr 2018 |
Bibliographical note
Funding Information:We thank Ran Issachar for making the first-order reversal curve measurements during a visiting fellowship to the Institute of Rock Magnetism, University of Minnesota (Minneapolis, Minnesota, USA), and to Mike Jackson for assistance. We thank Moshe Eliyahu for assistance with the magnetic force microscopy and Omri Dvir for assistance with the electron probe microanalysis. We thank Andrew Roberts for a helpful and insightful review that significantly improved the paper, and we thank an anonymous reviewer. This study was supported by Israel Science Foundation grant 1364/15 and German-Israeli Foundation (GIF) Young Scientists program grant I-2398–301.8/2015 to Shaar, and the Dead Sea Deep Drill Center of Excellence (COE) of the Israel Science Foundation (grants 1736/11 and 1436/14 to Stein).
Funding Information:
We thank Ran Issachar for making the first-order reversal curve measurements during a visiting fellowship to the Institute of Rock Magnetism, University of Minnesota (Minneapolis, Minnesota, USA), and to Mike Jackson for assistance. We thank Moshe Eliyahu for assistance with the magnetic force microscopy and Omri Dvir for assistance with the electron probe microanalysis. We thank Andrew Roberts for a helpful and insightful review that significantly improved the paper, and we thank an anonymous reviewer. This study was supported by Israel Science Foundation grant 1364/15 and German-Israeli Foundation (GIF) Young Scientists program grant I-2398-301.8/2015 to Shaar, and the Dead Sea Deep Drill Center of Excellence (COE) of the Israel Science Foundation (grants 1736/11 and 1436/14 to Stein). We dedicate this paper to the memory of the late Hagai Ron, who initiated the magnetic research of the lacustrine formations of the Dead Sea and made pioneering efforts in understanding the magnetic properties of the unique mineral assemblage that is formed in the lakes.
Publisher Copyright:
© 2018 Geological Society of America.
