Quaternary Secondary Chemical Deposition in France

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Abstract
Quaternary gravels of two very distinct types of ferruginization occur: a red or brown type in the B horizon of the soil is continuous and of normal pedologic origin; the other is deeper (to 8 m), lighter in color, essentially discontinuous, in bands or nests (especially at greater depths), and located along or across the strata. The irregular distribution of the latter type precludes origin by vertical percolation or by water-table fluctuations. It is well explained by the hypothesis of soil freezing: the soil solution freezes, ice crystallizes, and the remaining solution is concentrated at certain points and finally precipitates its dissolved matter. The intervention of freezing can contribute to the explanation also of homogenous Quaternary or older sands that contain remarkable iron staining in alternating light and dark horizontal bands or in ice-wedge fillings. It also explains the concentration of MnO2 in Quaternary gravels in strongly localized bands or nests, less common than iron oxide. Certain deposits of secondary carbonate, especially in the form of needles, networks, or crusts, occur under stones or in their interstices. Finally, thin siliceous crusts occur in Antarctica and Siberia. In all these cases, evaporation and biochemical processes are important; freezing has co-operated with them to concentrate the solutions and bring about the deposition.

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