Technique and process
A conceptual model for the enhancement of magnetic susceptibility in soils

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Abstract

Mineral magnetic properties of soils can be strongly influenced by soil-forming factors. Understanding how climate influences magnetic transformations in soils may offer insight into paleoclimate and the pedologic history of landscapes. Based on our experience with soils in California and Hawaii, we have developed a conceptual model of the pathways that can lead to enhancement of the magnetic susceptibility in soils. We base our model on three sources of iron in soils: magnetite, maghemite, and other iron-bearing minerals. We find that preferential accumulation, transformation (diagenesis), lessivage, neoformation (authigenesis), and solubilization are the main processes that convert the primary lithogenic minerals inherited from soil parent material to the secondary pedogenic minerals found in the solum. Biosynthesis is included in the model but does not appear to be an important process in aerobic soil environments. Our model shows that a major process in the enhancement of eluvial and illuvial horizons is neoformation of secondary magnetite and maghemite resulting from precipitation of iron from the soil solution. The processes and products in the model are independent of whether the parent material is transported (alluvium or loess) or residuum. For the soils that we have studied, the rates of susceptibility enhancement are shown to be dependent on climate and parent material.

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