A CONCEPTUAL-MODEL FOR THE ENHANCEMENT OF MAGNETIC-SUSCEPTIBILITY IN SOILS

Mineral magnetic properties of soils can be strongly influenced by soi l-forming factors. Understanding how climate influences magnetic trans formations in soils may offer insight into paleoclimate and the pedolo gic history of landscapes. Based on our experience with soils in Calif ornia 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, maghe mite, and other iron-bearing minerals. We find that preferential accum ulation, transformation (diagenesis), lessivage, neoformation (authige nesis), and solubilization are the main processes that convert the pri mary lithogenic minerals inherited from soil parent material to the se condary pedogenic minerals found in the solum. Biosynthesis is include d in the model hut does not appear to be an important process in aerob ic soil environments. Our model shows that a major process in the enha ncement 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 susceptibil ity enhancement are shown to be dependent on climate and parent materi al. Copyright (C) 1996 INQUA/Elsevier Science Ltd