The mechanism of argillic horizon formation in arid and semiarid soils has been t:he subject of some controversy among the pedoLogists.Some believe that the illuviation process has the main role whereas the others think that clay formation in situ (e.g.by weathering)is the main factor.With regard to this consideration the micromorphological study of a Xeralphic Haplargid soil in the Goldasht region of Karaj has been carried out in order to evaluate the effect of different factors on argillans formation.
The undisturbed samples from different horizons of the above mentioned soil have been collected by means of Kubiena boxes or as clods. The samples were air dried and impregnated with Methyl—metacrylate resin under vacuum.After polymerization and hardening a thin soil section was prepared.Micromorphological description of soil thin sections were made mainly according to Brewer.
The results of this study showed that clay i:Lluviation is most likely the main process in argillans formation in this soil,and therefore,the clay coatings of the Bt horizon are real cutan rather than the stress one.The asepic plasmic fabric of the Bt horizon is in agreement with this view. The brown rim of the carbonate nodules in the lower )3t horizon is also another evidence of clay illuviation.
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