Quantitative interpretation of frequency dependent magnetic susceptibility

Measurements of low-field, frequency dependent susceptibility (FDS) is frequently used in paleomagnetism, geological and environmental studies, as a parameter indicative of the concentration of magnetic minerals in rocks and sediments. We propose a method for quantitative interpretation of FDS spectra applying the Debye decomposition (DD) approach that is a methodology commonly used for complex conductivity data. In the DD, the amplitude and phase spectra are considered a superposition of several Debye spectra, characterized by distinct relaxation times. This procedure yields two frequency independent parameters and a relaxation time distribution (RTD). The methodology is applied to a FDS database from organic rich sediments, where methanogenesis conditions are favorable. The objective of this analysis is to identify and characterize magnetite ultrafine magnetite particles possibly associated with methanogenesis. This paper shows preliminary results of this study. The RTD obtained with the DD elucidates some processes affecting magnetic mineralogy and grain size distribution across a 10m deep section intercepting anthropogenic and geogenic organic sediments.