Pedon Zonation of Hydroxy‐interlayered Minerals in Ultic Haplaquods

Abstract

AbstractThe distribution of hydroxy‐interlayered minerals (HIM) was studied in Ultic Haplaquods with respect to horizon and location within the soil matrix. Mineralogy of the clay fraction and of tenacious grain coatings was determined for selected horizons by means of x‐ray diffraction and differential scanning calorimetry. Smectite and kaolinite were the dominant layer silicates in A and E horizons, where sand grains were stripped of coatings and clay occurred as floccules. Hydroxy‐interlayered minerals were the dominant layer silicates in Bh and E′ horizons where grains were coated. Tenacious coatings removed by ultrasound from sands occurring in the Bh and E′ horizons contained more HIM and less quartz than any other portion of the soil matrix. Podzolic stripping of coatings in A and E horizons and transformation of HIM to smectite via interlayer depolymerization could explain the observed HIM depth distribution. Higher HIM concentrations in tenacious coatings in Bh and E′ horizons suggest that the coatings predated podzolization. Hydroxy‐interlayered minerals in Btg1 horizons dispersed in deionized water more readily than did kaolinite, suggesting that differential dispersion in conjunction with a fluctuating water table may be a factor in pedogenic redistribution of clay minerals.