WEATHERING OF GRANITIC TILLS AND THE GENESIS OF A PODZOL

The bulk chemistry, bulk mineralogy, and clay fraction of a podzolic soil from the Plastic Lake Watershed of central Ontario was examined. The relatively constant Zr/Ti ratio of incremental samples through the soil profile suggests it developed on a homogeneous parent material, thus allowing quantitative documentation of the changes in the chemical constituents. The quantitative data indicate that in the upper zone (Ae horizon) all minerals are subject to significant dissolution and that plagioclase is weathered congruently. The middle zone of the profile differs considerably: most chemical components (including Al) are leached in much lesser proportions than the upper zone, and Fe and Mg are accumulated. Vermiculite, hydroxy-interlayered vermiculite (HIV), and kaolinite dominate the < 2-mu-m fraction of this zone. Bulk compositional and XRD evidence suggests that most, if not all HIV is the first alteration product of mica transformation and that the authigenic production of HIV is a significant process in the middle zone (B horizon). The genesis of this profile is not greatly affected by the chemical translocation of Al, which is currently thought to play critical role in podzol genesis.