COMPARISONS OF MINERALOGICAL PROPERTIES BETWEEN TEPHRA-DERIVED SPODOSOLS FROM ALASKA AND NONTEPHRA-DERIVED SPODOSOLS FROM NEW-ENGLAND

This study was conducted to make total comparisons of the mineralogical properties of tephra- and nontephra-derived Spodosols and to indicate a significant background for recognizing tephra-derived Spodosols. For this purpose, seven pedons (all the pedons have at least an albic horizon) were selected from the tephra-derived Spodosols in southcentral Alaska and seven pedons (only one pedon of these has an albic horizon) from the nontephra-derived Spodosols in New England. They were examined in detail by selective chemical dissolution, x-ray diffraction, infrared absorption, and electron microscopic methods to characterize noncrystalline and paracrystalline minerals. It was found that the tephra- and nontephra-derived Spodosols have many similarities in mineralogical properties that can be explained by the recent fulvate-carbonic acid theory on podzolization. The albic horizons and horizons overlying the spodic horizons showed the absence of allophane and imogolite, the presence of a small amount of Al/Fe humus complexes, the predominance of expansible 2:1 layer silicates among crystalline clay minerals, and the presence of pedogenic opal appearing as very thin disks and ellipsoids. By contrast, the spodic horizons exhibited plenty of allophane, imogolite, and Al/Fe humus complexes; the predominance of chloritized 2:1 layer silicates among crystalline clay minerals; and an abundance of ferrihydrite in Fe minerals excepting a few spodic subhorizons containing goethite. We consider that these mineralogical properties afford a significant background for recognizing tephra-derived Spodosols.