The Magnetization of Marine Sediments: A Search for Fossil  Biogenic Magnetite
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{'SignBlockName': 'Michael A. Mayhew', 'PO_EMAI': None, 'PO_PHON': None}
In the past two decades, natural remanent magnetization carried         by marine sediments and sedimentary rocks has been used extensively to          monitor the history of the geomagnetic field and to constrain motion of         crustal plates.  But the origin of the magnetic minerals contributing to        observed remanent magnetization is only now being resolved.  Recent work        suggests that crystals of magnetite precipitated by magnetotactic               bacteria and perhaps other magnetotactic microorganisms contribute a            large fraction to magnetization of marine sediments.  Techniques now            exist to extract these particles and identify them with transmission            electron microscopy. Intact 'magnetofossil' chains are found in some            DSDP sediments, and other biogenic magnetites have been extracted from          Early Cambrian limestone. Continued study of bacterial magnetofossils           may contribute to a better understanding of the process of fine-particle        diagenesis as well as direct measurements of rock-magnetic effects of           interparticle interaction. Bacterial magnetofossils may also provide an         independent method of measuring the paleointensity of the geomagnetic           field as recorded by marine sediments, and might also be useful                 indicators of primary magnetic remanence.  Precipitation of magnetite in        bacteria appears to be an oxygen-requiring process, so knowledge of             their distribution in time and space may place constraints on the               history of free oxygen at the Earth's surface.
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[{'Code': '157100', 'Text': 'SCEC'}, {'Code': '157400', 'Text': 'Geophysics'}]
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