Experimental Alteration of Fe-Oxyhydroxides to Understand Magnetic Enhancement Processes in Soils
Abstract
The phenomenon of magnetic enhancement in many soil types has been recognized for several years, but the question of whether the enhancement process is primarily driven by microbial activity or abiotic processes is still unresolved. We present results from a series of experiments as part of an on-going interdisciplinary project designed to study the processes responsible for magnetic enhancement during pedogenesis of loess-derived soils. The oxyhydroxides goethite and lepidocrocite were synthesized using wet chemistry methods that yielded particles with uniform nanoscale grain size distributions. This material was then subjected to controlled annealing under either oxidizing or reducing conditions at elevated temperatures (100-300°C). The Fe-rich precursor phases altered to produce various nanoscale Fe-oxides (magnetite, maghemite, hematite). The magnetic properties, microstructure, and grain morphology of the reaction products were examined as a function of heating temperature, atmosphere, and time. We present the results of various sample characterization techniques performed before and after heating including low-temperature magnetic remanence and susceptibility, Mössbauer spectroscopy, high-resolution TEM microscopy, and X-ray diffraction. When compared with results of bio-reduction experiments, our results may help elucidate the relative contributions of biomineralization and abiotic alteration mechanisms to the development of an "enhanced" magnetic signature during pedogenesis. Further work in this area could also lead to assessments of chemical remanence acquisition during alteration and weathering.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMGP41A1093T
- Keywords:
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- 1512 GEOMAGNETISM AND PALEOMAGNETISM / Environmental magnetism;
- 1540 GEOMAGNETISM AND PALEOMAGNETISM / Rock and mineral magnetism;
- 3617 MINERALOGY AND PETROLOGY / Alteration and weathering processes