The nature and origin of nodules in Podzolic soils from Alberta

A common pedological feature in Podzols and Podzolic-like soils in the forest region of Hinton, Alberta is the presence of nodules in the Bf horizons with diameters of 1—20 cm. The nature of these nodules was investigated through physical, chemical, mineralogical and micromorphological examinations. Results showed that the nodule microstructure is mainly bridged-grain type compared to dominantly pellicular type for the soil matrixes. The basic building blocks are (a) coarse components (> 5 μm): quartz, feldspars mainly albite, pseudo sands, sand-sized chlorites and small quantities of anthophyllite, sillimanite, andalusite and lithogenic hematite; (b) fine components (< μm): phyllosilicates (mainly hydroxy interlayered vermiculite, kaolinite, vermiculite, and small amounts of chlorite), quartz and organic matter. Imogolite is present in the very fine clays. The similarity in the mineral suites and the porphyric related distribution pattern between the Bf horizons and the nodules indicate an authigenic origin for the nodules through an eluviation/illuviation process. Fungal hyphae provide a framework for nodule aggregation. In situ XRD determinations revealed that sand-sized Fe concretions are goethite alone or in association with hematite. The omnipresence of quartz in infillings, coatings and opaque coarse components was also evident. Key words: Micromorphology, related distribution pattern, in situ mineral determination