Current challenges with understanding greigite (Fe3S4) magnetism

Wednesday, 17 December 2014: 3:25 PM
Liao Chang1, Andrew P Roberts2, Michael Winklhofer3, Iuliana Vasiliev4, Mark J Dekkers4 and Wout Krijgsman4, (1)Australian National University, Canberra, ACT, Australia, (2)Australian National University, Canberra, Australia, (3)Ludwig Maximilian University of Munich, Munich, Germany, (4)Utrecht University, Utrecht, Netherlands
Greigite (Fe3S4) is a widespread authigenic magnetic mineral in anoxic sediments, and is also commonly biosynthesized by magnetotactic bacteria in aqueous environments. Despite the importance of greigite in paleomagnetic and environmental magnetic studies, knowledge of its magnetic properties is at a much lower level than for more common rock-forming magnetic minerals. Much recent progress has been made to develop a more complete understanding of the magnetic properties of greigite and the range of grain sizes in which greigite occurs in nature. We present results of new determinations of a range of fundamental magnetic properties of greigite, including the saturation magnetization, the magnetocrystalline anisotropy, and calculated rock magnetic properties. In addition, we provide evidence for the preservation of greigite magnetofossils in ancient sediments, which has important implications for assessing the reliability of paleomagnetic records carried by greigite. Finally, we present an integrated study from a Messinian former Black Sea sedimentary sequence to unravel environmental controls on diagenetic greigite formation, and demonstrates the usefulness of greigite for studying long-term climate variability in anoxic environments.