Earth Planets Space, Vol. 58 (No. 10), pp. 1373-1380, 2006
M. J. Orgeira1,2 and R. H. Compagnucci1,3
1Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET, Argentina
2Departamento de Ciencias Geológicas, FCEN, Universidad de Buenos Aires, Argentina
3Departamento de Ciencias de la Atmósfera, FCEN, Universidad de Buenos Aires, Argentina
(Received December 18, 2005; Revised June 4, 2006; Accepted June 6, 2006; Online published November 8, 2006)
A comparison of the index of potential water storage (PWS) with the magnetic properties of soils in Russia and of Argentina and China paleosols suggests the existence of one or two climatic thresholds that affect the formation, preservation or depletion of ferrimagnetic minerals. Soils characterized by a positive PWS are wetted during an important part of the year, creating an appropriate environment that favors the depletion of ferrimagnetic minerals due to mainly reductive dissolution. Such soils are characterized by a depletion of detrital ferrimagnetic minerals, as observed in Argentinean soils and paleosols. On the other hand, a negative PWS prevents highly reducing conditions in the soil, and the detrital ferrimagnetic minerals are preserved. The environmental conditions of these soils allow the formation of (superparamagnetic) pedogenic minerals, together with the preservation of lithogenic minerals. These conditions produce a net magnetic enhancement of the soil, as observed in Russia and China. The second threshold in PWS could be at a positive value. Above this second threshold, the water content of the soil during practically the whole year could allow the formation of (superparamagnetic) pedogenic minerals. This threshold could explain differences in the magnetic enhancement or depletion of Argentina soils characterized by a positive PWS.
Key words: Environmental magnetism, paleoclimate, Late Cenozoic, loess and paleosol sequences.