Strongly magnetic soil developed on a non-magnetic rock basement: A case study from NW Bulgaria

摘要

The enhanced magnetic susceptibility of modern soils is assumed to have several reasons including, e.g., weathering of an iron-rich geological basement, natural fires, bacterial processes and atmospheric deposition of anthropogenic particles. We report on a case where none of the above sources of magnetic enhancement is evident: a modern soil with high magnetic susceptibility over the whole soil profile, developed on nonmagnetic limestones, in an area with no industrial activities. The surface magnetic susceptibility varies from 60 to 110×10−5 SI, while that of the rock basement is nearly zero. Moreover, significant frequency-dependent magnetic susceptibility (> 12%) suggests that superparamagnetic secondary magnetite/maghemite plays an important role. Possible mechanisms, responsible for this magnetic enhancement, are discussed.